1:10 PM | More on the incredible cold winter weather including the latest on the Great Lakes record ice cover extent and some dazzling winter phenomena

[Ice caves at "Apostle Islands National Lakeshore" in northern Wisconsin (Lake Superior); photo taken by Brian Peterson, Minneapolis Star Tribune, via Associated Press]

Discussion

The incredible winter cold and the Great Lakes This winter has brought some incredible cold to much of the eastern two-thirds of the nation, but nowhere has it been more persistent than in the Upper Midwest/Great Lakes region of the country. As a result, the Great Lakes have now reached a record ice cover extent for this late in the season at 90.5% (as of 3/2). The all-time record for ice cover on the Great Lakes is 95% set back in February 1979 (records date back to 1973). That all-time record is certainly within reach as brutal cold air continues to dominate the scene in the eastern two-thirds of the country which will very likely contribute to additional icing on the Great Lakes. In fact, the average 2-meter temperature this morning at 8AM (ET) across the continental U.S. was 19.9°F which may very well be the coldest reading ever this late in the season (source WeatherBell Analytics using NCEP RTMA 2.5 km analysis data).

Currently, Lake Ontario has the least ice cover of the five lakes at 38.2%, but that is more than three times its normal, and it has increased dramatically in recent days. Ontario has a reputation for never freezing as it quite deep so it retains heat longer than the other four lakes. Also, the Niagara River feeds water into Lake Ontario from Lake Erie, providing agitation which keeps the water's surface from freezing. Here are the latest ice cover percentages for all five lakes: Erie 95.4%, Superior 95.0%, Huron 94.5%, Michigan 90.1% and Ontario at 38.2%.

Dazzling winter weather phenomena One of the positive by-products of this bitter cold winter has been the fact that the extensive ice cover has allowed hikers to visit “ice caves” accessible by foot for the first times in many years. For example, tens of thousands of people in northern Wisconsin have taken advantage of this year’s deep freeze to hike across Lake Superior to visit the caves at the western end of the “Apostle Islands National Lakeshore” (see above). These caves were carved out of sandstone by the waves from Lake Superior, the largest by volume and surface area of all five Great Lakes. In addition, an amazing picture from near Mackinac Island, Michigan shows this "frozen" wave on Lake Huron (below).

Philly's chance at history Locally, the Philadelphia region has a chance to make some history late tonight with respect to the bitter cold Arctic air that is currently gripping the region. The record low for tomorrow’s date at Philly Int’l Airport is 7°F and the all-time low temperature for the month of March is 4°F – both within the realm of possibility. Many suburban locations to the north and west of the city will drop down to near 0 degrees by early tomorrow, but milder air will return by the end of the week with highs rebounding to the 40’s.

3:00 PM | The outlook for March - continued cold and snowy

Discussion

Overview It looks like our colder-than-normal weather pattern of recent months in the Mid-Atlantic region will continue on average right through the month of March. One signal that suggests cold weather will indeed continue in March in the eastern U.S. comes from a tropical disturbance known as the Madden Julian Oscillation (MJO). In addition, support for a colder-than-normal month of March comes from a NOAA seasonal climate forecast model called the Coupled Forecast System version 2 (CFSv2).

Background information on the Madden Julian Oscillation (MJO) The MJO is a tropical disturbance that propagates eastward around the global tropics with a cycle on the order of 30-60 days. It is a large-scale coupling between atmospheric circulation and tropical deep convection. The MJO has wide ranging impacts on the patterns of tropical and extratropical precipitation, atmospheric circulation, and surface temperature around the global tropics and subtropics. Furthermore, the MJO influences both precipitation and surface temperature patterns across the US. Specifically, one significant impact of the MJO over the U.S. during the northern hemisphere winter is an increase in the frequency and intensity of cold air outbreaks across the eastern US.

MJO Phases Research has found that the location of the MJO, or phase, is linked with certain temperature and precipitation patterns around the world. The MJO phase diagram illustrates the progression of the MJO index through different phases, which generally coincide with locations along the equator around the globe. When the index is within the center circle, the MJO is considered weak, meaning it is difficult to discern. Outside of this circle, the index is stronger and will usually move in a counter-clockwise direction as the MJO moves from west to east. The very latest European model MJO index forecast (below) propagates the MJO from phase 8 in early March to phases 1, 2 and 3. All of these particular phases of the MJO (i.e., 8, 1, 2 and 3) typically result in a colder-than-normal temperature pattern for the eastern US (see “temperature composites” figure centered on February-March-April).

CFSv2 The latest monthly forecast from NOAA’s Coupled Forecast Model (v2) strongly suggests the colder-than-normal weather pattern of recent months will continue (see below) throughout the eastern two-thirds of the nation. This model is updated on a daily basis and it has done a very good job in its temperature forecasts when reasonably close to event time as we are now with March only a few days away. As has been the case throughout the winter months, the core of the coldest air “relative to normal” will likely be centered from the Northern Plains to the Upper Midwest according to the model forecast, but an incredibly large area across much of Canada and the U.S. will be below-normal for the month of March.

How about snow As far as snow is concerned, the combination of the expected colder-than-normal temperatures along with a newly activated southern branch of the jet stream (e.g., California storms) will quite likely produce above-normal snowfall for the Mid-Atlantic region during the month of March. Philadelphia has actually had 3 straight months (December, January and February) featuring monthly snowfall totals in the top ten for the given month using records dating all the way back to the 1880’s. The 3 consecutive months of top ten monthly snowfall amounts has not happened in Philly since January-February-March of 1978. There has never been a winter with 4 consecutive months ending up in the top ten for that given month so if it happens in March - certainly a possibility given the overall pattern - it would be a first for Philadelphia. As far as seasonal totals are concerned, Philly is in 3rd place on their all-time list some 20 inches shy of the seasonal record set in the winter of 2009-2010 with 58.4 inches so far this season - this record of 78.7" is also within reach given the current overall pattern.

11:00 AM | The California Drought and the Role of the Pacific Ocean

Discussion

Overview Solar and oceanic cycles are the most important drivers of all weather and climate on our planet and the most important ocean of all is the Pacific. This large body of water covers about a third of the planet’s surface and is bigger than all of the Earth’s land masses combined. Both the Pacific and Atlantic Oceans go through sea surface temperature phases that are characterized as cool (negative) and warm (positive). While there are other important factors that contribute to drought conditions in the western U.S. (e.g., hours of sunshine, humidity levels), the given temperature phase of the Pacific Ocean has historically been found to be a major factor in precipitation trends just as it has contributed greatly to global temperature trends. Indeed, the on-going California drought appears to be a natural consequence of the current cool phase of the Pacific Ocean which typically produces an overall dry weather pattern in the western U.S. and, if history is any guide, it is likely to persist for years to come.

Pacific Decadal Oscillation (PDO) The Pacific Decadal Oscillation (PDO) is a climate index based upon long-term patterns of variation in sea surface temperature of the north Pacific. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of about 20°N. During a warm (positive) phase, the west Pacific becomes cool and part of the eastern ocean warms; during a cool (negative) phase, the opposite occurs. These phases result from the direction of winter winds in the northern Pacific: winter winds blowing chiefly from the southwest result in warmer conditions in the northern California Current (CC); conversely, when winds blow primarily from the north, upwelling occurs both in the open ocean and at the coast, leading to cooler conditions in the northern CC.

The PDO temperature phase in the north Pacific tends to have an impact on the shorter-term sea surface temperature cycles of the tropical Pacific in the equatorial region. Specifically, warm phases of the PDO are generally associated with stronger and more numerous El Nino (warmer-than-normal) events in the tropical Pacific and weaker and fewer La Nina (colder-than-normal) episodes. During cold phases of the PDO, La Nina tends to dominate El Nino in the tropical Pacific. In the past several years, during the current cool phase of the PDO, La Nina conditions have indeed dominated the scene in the tropical Pacific region.

Warm and cool phases of the PDO can persist for decades, usually about 20 to 30 years. A warm phase occurred from 1925 to 1946, a cool phase from 1947 to 1976, and then another warm phase from 1977 to 1998. Currently, the Pacific Ocean is in a cool PDO phase that began around the turn of the century and the recent years of 2008 and 2012 actually exhibited the most negative PDO index values since the 1950’s [PDO Index plot below].

PDO Index plot: Time series of shifts in sign of the Pacific Decadal Oscillation (PDO), 1925 to present. Values are averaged over the months of May through September. Red bars indicate positive (warm) years; blue bars negative (cool) years. Note that 2008 and 2012 were the most negative values recorded since 1956.

The PDO and precipitation anomalies and trends Precipitation anomaly charts are shown below for the U.S. with primarily wetter-than-normal conditions seen on a nationwide basis during the warm PDO phase between 1977 and 1998 (top) and generally drier-than-normal conditions experienced during the cold PDO phase that lasted from 1947 to 1976 (bottom). Note the significant dry weather pattern seen across California during the last cold PDO phase with precipitation nearly two inches below the long term average in much of the state.

Precipitation trends in the southwestern U.S. have been shown to have direct correlation to PDO phases in the Pacific Ocean. The plot below displays the PDO index (red) versus the annual precipitation amounts in the southwestern U.S. (blue) all the way back to the year 1900 [source WSI Energy Weather]. In general, when the PDO was in a warm phase, the annual precipitation amounts in the southwestern U.S. tended to climb and in times of a cold PDO phase they typically dropped. This is supporting evidence that the on-going California drought is likely to continue on average as long as the Pacific Ocean’s cool PDO phase persists.

[credit to WSI Energy Weather]

11:15 AM | *Cold is getting old, but it just won't fold*

Discussion

While we are entering a noticeably milder stretch of weather in the Mid-Atlantic region for the second half of this week, there are signs for a return to a very cold weather pattern across the central and eastern U.S. by the middle and latter parts of next week. In fact, upcoming changes to the upper level atmosphere in the northern hemisphere resemble the overall pattern seen during the “polar vortex” cold air outbreak experienced earlier this winter.

The polar vortex is an area of cold low pressure that typically circulates and strengthens around the Arctic region in the wintertime and then weakens in the summer. During winter, pieces of the polar vortex can break off and be sent southward with the jet stream to either the Europe/Asia side of the North Pole or to North America. Meteorologists try to track the positioning of the polar vortex as a way of predicting Arctic air outbreaks that potentially could drop southward into the mid-latitudes. Computer forecast models can show the position of the polar vortex through their forecasts of heights of different atmospheric pressure levels. Last night’s European computer model 10-day forecast of the 500 millibar height field (~18,000 feet up in the atmosphere) clearly shows yet another example of the polar vortex being distributed to mid-latitudes – in this case to both sides of the pole (see forecast map above). This particular upper-level scenario is forecasted to occur in 10 days and it will likely be accompanied by much colder-than-normal air in the central and eastern US.

Not to be outdone, the main U.S. (NOAA) forecast model called the Global Forecast System (GFS) confirms this idea of future cold as it also has a very cold-looking overall weather pattern in the 7-10 time period that coincides with the European model forecast. Last night’s GFS Ensemble 500 millibar forecast map (below) for the 7-10 day time period features a deep trough of low pressure in the northeastern part of the U.S. (blue) and a strong ridge of high pressure (red/orange) extending northward along the west coast of the U.S. and Canada. The combination of the trough in the east and the ridge in the west will likely force numerous Arctic air masses to drop southward from central Canada into the central and eastern U.S. as we close out February and begin the new month of March – just as it did earlier this winter. In addition, the high pressure ridging that virtually surrounds the eastern trough is indicative of a “blocking” pattern in the upper atmosphere that promises to keep the cold air in place for awhile in the central and eastern U.S well into the month of March.

One final note...this winter has had a habit of generating snow at the front-end of a warm-up (e.g., this morning) and at the back-end of a warm-up (e.g. the snowstorm on the day after Super Bowl Sunday). If this pattern holds true, look out for possible significant snow in the early or middle part of next week as we transition back to a much colder-than-normal weather pattern.

[map courtesy Penn State eWALL]

10:20 AM | Two large and active sunspot regions rotating out of the "line of fire"

[Image from Saturday, February 8th]

Discussion

The sun continues to go through a relatively weak solar maximum phase during solar cycle 24; however, in recent days there were two active and large sunspot regions (AR1967 and AR1968) which were being closely monitored for possible major eruptions. Fortunately, these two sunspot regions have now crossed much of the visible side of the sun without producing a single X-class solar flare (most severe type). The latest image of the sun (above) shows these two sunspot regions just about to move onto the back side of the sun and completely out of the “line of fire” with respect to the Earth. NOAA forecasters are still estimating chances of an M-class solar flare at about 60% from these regions and X-class flares at about 20%, but these chances are diminishing and any eruption at this time would likely produce only a glancing blow to the Earth’s upper atmosphere. A minor coronal mass ejection did hit the Earth’s magnetic field on Friday, February 7th, producing northern lights across much of the high latitudes.

12:15 PM | February Outlook: stormy and still cold for the Mid-Atlantic region with above-normal snowfall

Discussion

A look back at January January has featured well below-normal temperatures in the Mid-Atlantic region along with above-normal snowfall in most areas; especially, north of the PA/MD border. Specifically, temperatures through Tuesday, January 28th were 4.2 degrees below-normal at Philly Intl Airport, 3.4 below-normal in Central Park, New York City, and 3.2 degrees below-normal at Reagan National Airport in Washington, DC. Snow-wise it has been a banner month in much of the Mid-Atlantic region north of the PA/MD border. Philadelphia, for example, has received 24.9 inches of snow which ranks as the 4th snowiest January since 1872. Central Park, NY is also well above-normal for January with 18.9 inches of snow accumulation.

A look ahead to February February looks like it’ll be a stormy and colder-than-normal month for the Mid-Atlantic region, but temperature departures from normal will likely not be as significant as they were in January. Snowfall should be above-normal for February as an active and stormy pattern will likely produce multiple snow threats in the region beginning as early as next week – the first full week of the new month. The core of the coldest air in terms of temperature departures from normal has been centered over the Upper Midwest/Great Lakes and that pattern should continue in February. As a consequence, the December-February time period could very well end up being in the “top ten coldest” for places like Chicago, Illinois by the time February is over.

Upper level differences and an "atmospheric battle zone" One difference in the overall upper level pattern in February will likely be the re-establishment of the southeastern ridge of high pressure that was largely absent in January. This will probably result in warmer-than-normal temperatures in the Southeast US for the month and, given the expected continuing cold air across the northern US, it should set up quite an “atmospheric battle zone” with a large temperature gradient across the south-central US and an active southern branch of the jet stream. This "battle zone" between the increasingly warm air in the Southeast US and the lingering cold across the northern tier of states should fuel some pretty strong storms during the month and lead to above-normal snowfall in the Mid-Atlantic region. An important aspect of the increasingly strong southeastern upper level ridge is that it will tend to "open the door" for Gulf of Mexico moisture to flow into the Mid-Atlantic region from the southwest.

NOAA temperature anomaly forecast map for February Finally, one of NOAA’s longer-range computer forecast models (Climate Forecast System) is predicting a cold month for much of the nation (above) where “blues” represent below-normal temperature regions and “red/oranges” warmer-than-normal areas. This model has had a pretty good track record when close to event time and its forecast map represents quite well my thinking for the month of February with respect to nationwide temperature anomalies.

10:00 AM | ***Siberian connection to next week's cold as this incredible long-lasting frigid pattern continues into early February***

[GFS forecast of 2-meter temperature anomalies; courtesy WeatherBEll Analytics]

[GFS forecast of 2-meter temperature anomalies; courtesy WeatherBEll Analytics]

Discussion

Overview In my many years of weather forecasting, I have seldom seen an overall pattern with the type of sustained bitter cold that will likely be experienced in much of the eastern half of the nation this week right into February. To find such brutal cold one has to go back to January 1994 or January 1985 and for sustained cold perhaps to the winters of the middle 1970's (76-77, 77-78). The current air mass in the eastern US rivals the “polar vortex” cold air outbreak of earlier this month, but that was a rather short-lived, albeit very painful, period compared to what we’ll likely experience from today into early February. It is certainly time to take notice when the main US computer forecast model (GFS) predicts temperatures anomalies of 30 to 50 degrees below normal - in back-to-back weeks - during the climatologically coldest time of the year [purple regions of the GFS 2-meter temperature anomaly forecast maps; courtesy WeatherBell Analytics at weatherbell.com]. Heating systems will be sorely tested during this period and, needless to say, the bills will be as high as they have been in a long time.

Next couple of days Tuesday's Mid-Atlantic snowstorm ushered in the first Arctic air mass that began this long-lasting cold weather pattern. Temperatures bottomed out around zero in many of the suburbs of the big cities during the past couple of nights and will no doubt drop to the low single digits late tonight with a fresh influx of Arctic air. Flirting with the 0 degree mark in the I-95 suburban locations for three nights in a row is indeed a rarity in this part of the country. It is not just the Mid-Atlantic region that is in the deep freeze. Temperatures dropped to the freezing mark in many parts of Florida and there is a winter storm warning for the southeastern coastal region of Texas as Houston and Galveston may receive some frozen precipitation in the near term.

Siberian connection to next week's cold Yet another Arctic air outbreak is destined to move into the Mid-Atlantic region on Sunday and then, after a less harsh Monday, an absolute brutal air mass will invade the central and eastern US on Tuesday and Wednesday. That particular Arctic blast has its origins in Siberia and it promises to feature some incredible cold (more details below in the video discussion). Siberian air masses are often quite noteworthy as they have in the past produced some record-breaking cold in this part of the world. Siberia is an extensive land mass and air masses that spend some time in that region this time of year can get amazingly cold as there is no nearby water body to help modify its temperatures. The “cross polar” air mass that is expected to arrive in the eastern US on Tuesday and Wednesday may not be the last as the overall weather pattern could certainly bring another into the US.

Snow threats As far as snow is concerned, with these multiple Arctic air outbreaks there will be numerous snow threats. Snow showers are possible late Thursday in the I-95 corridor before the arrival of the next Arctic blast, but this should not amount to much in terms of accumulations. The next Arctic front on Saturday will contain more moisture and there can be a couple inches of snow as a result in the I-95 corridor before more frigid air moves in for Sunday. Yet another Arctic front will approach the Mid-Atlantic region on Sunday night and Monday and there is the potential for a storm to form along the frontal boundary zone. In fact, the upper air pattern for this frontal system resembles somewhat the pattern associated with Tuesday's snowstorm as there is an impressive short wave of energy rounding the base of a long wave trough. No matter if a storm does actually materialize on Monday near the Mid-Atlantic coast, there will no doubt be some painfully cold air invading the central and eastern US on Tuesday and Wednesday with the arrival of the "Siberian" air mass. Temperatures next week could drop to 25 degrees below zero in Chicago, near zero around the big cities along the I-95 corridor, and a deep freeze is likely way down in the Deep South.

Video

httpv://youtu.be/Ev_17fNbjWo

12:15 PM | **The polar vortex will once again get distributed to the mid-latitudes**

Discussion

The polar vortex is an area of cold low pressure that typically circulates and strengthens around the Arctic region in the wintertime and then weakens in the summer. During winter, pieces of the polar vortex can break off and be sent southward with the jet stream to either the Europe/Asia side of the North Pole or to North America. Meteorologists try to track the positioning of the polar vortex as a way of predicting Arctic air outbreaks that potentially could drop southward into the mid-latitudes. Computer forecast models can show the position of the polar vortex through their forecasts of heights of different atmospheric pressure levels. Last night’s European computer model 10-day forecast of the 500 millibar height field (~18,000 feet up in the atmosphere) clearly shows another rather typical example of the polar vortex being distributed to mid-latitudes – in this case to both sides of the pole (see forecast map). This particular upper-level setup is forecasted to occur in 10 days and it will continue the bitter cold weather pattern that begins early next week in the central and eastern US. One major Arctic air outbreak arrives in the Mid-Atlantic region this coming Tuesday and, given the expectation for the polar vortex to be distributed southward by later this month, another major Arctic air outbreak can be anticipated here in the mid-latitudes as we close out the month of January. This upcoming deep freeze will rival the outbreak earlier this month with sub-zero readings in many areas across the central and eastern US and it will last for a considerably longer period of time.

9:30 AM | A downward trend in global temperature anomalies and the role of the Pacific Ocean

Discussion

Overview Solar and oceanic cycles are the most important drivers of all weather and climate on our planet and the most important ocean of all is the Pacific. This large body of water covers about a third of the planet’s surface and is bigger than all of the Earth’s land masses combined. Both the Pacific and Atlantic Oceans go through sea surface temperature phases that are characterized as cool (negative) and warm (positive). While there are other important factors that impact global temperatures (e.g., solar cycles, volcanic eruptions), the given temperature phase of the Pacific Ocean has historically been found to be a major factor in global temperature anomaly trends. Indeed, the Pacific Ocean seemingly flipped into a long-term cool phase during the previous decade and global temperature anomalies have generally been trending downward since that period of time.

Pacific Decadal Oscillation (PDO) The Pacific Decadal Oscillation (PDO) is a climate index based upon long-term patterns of variation in sea surface temperature of the north Pacific. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of about 20°N. During a warm (positive) phase, the west Pacific becomes cool and part of the eastern ocean warms; during a cool (negative) phase, the opposite occurs. These phases result from the direction of winter winds in the northern Pacific: winter winds blowing chiefly from the southwest result in warmer conditions in the northern California Current (CC); conversely, when winds blow primarily from the north, upwelling occurs both in the open ocean and at the coast, leading to cooler conditions in the northern CC.

The PDO temperature phase in the north Pacific tends to have an impact on the shorter-term sea surface temperature cycles of the tropical Pacific in the equatorial region. Specifically, warm phases of the PDO are generally associated with stronger and more numerous El Nino (warmer-than-normal) events in the tropical Pacific and weaker and fewer La Nina (colder-than-normal) episodes. During cold phases of the PDO, La Nina tends to dominate El Nino in the tropical Pacific. In the past several years, during the current cool phase of the PDO, La Nina conditions have indeed dominated the scene in the tropical Pacific region.

Warm and cool phases of the PDO can persist for decades, usually about 20 to 30 years. A warm phase occurred from 1925 to 1946, a cool phase from 1947 to 1976, and then another warm phase from 1977 to 1998 [PDO Index plot below]. Global temperature anomalies have tended to track these phases quite well with, for example, the very warm decade of the 1930’s having occurred during a warm phase, the colder-than-normal period of the 1950’s, 1960’s and first part of the 1970’s corresponding with a cool phase, and the warmer-than-normal decades of the 1980’s and 1990’s having occurred during a warm phase of the PDO. While the PDO trend has been somewhat jagged after the turn of the 21st century, it now appears that it slipped into a long-term cool (negative) phase during the middle part of last decade and that same sea surface temperature pattern continues today.

PDO Index Plot courtesy NOAA: Time series of shifts in sign of the Pacific Decadal Oscillation (PDO), 1925 to present. Values are averaged over the months of May through September. Red bars indicate warm (positive) years; blue bars cool (negative) years. Note that 2008 and 2012 were the most negative PDO Index values recorded since 1956. For more info: http://www.nwfsc.noaa.gov/research/divisions/fe/estuarine/oeip/ca-pdo.cfm

A downward trend in global temperature anomalies Global temperature anomalies have tended to trend downward, albeit in a jagged fashion, since around the time of the latest flip in the PDO from a warm-to-cool phase. The 2-meter global temperature anomaly plot (below) produced by WeatherBELL Analytics utilizes data from NOAA/NCEP’s Climate Forecast System (CFS). This dataset is an appropriate choice for historical global temperature comparisons and it is described in detail below.

[2-meter global temperature anomaly plot since 2005; courtesy WeatherBELL Analytics at weatherbell.com]

NOAA/NCEP Climate Forecast System “reanalysis” NOAA/NCEP’s Climate Forecast System is a model representing the global interaction between the oceans, land and atmosphere. This model offers hourly data with a horizontal resolution down to one-half degree (about 56km) on a global basis for a number of weather parameters. The CFS model uses the latest scientific approaches for taking-in, or assimilating, observations from many data sources: surface observations, upper air balloon observations, aircraft observations, and satellite observations. This approach has advantages over using “thermometer-based” surface data alone as that type of data is more limited in spatial resolution and often requires “adjustments” in order to reduce or eliminate the known problem of the “urban heat island” effect which impacts many official weather stations around the world. Indeed, the NOAA/NCEP “reanalysis” effort has produced a uniform, continuous, and best-estimate record of the state of the ocean-atmosphere for use in climate monitoring and diagnostics. The NOAA/NCEP method keeps the model’s software constant and runs the model retrospectively from 1979 (beginning of the satellite observation record-keeping era) to the present. [For more info on the NOAA/NCEP CFSR data: http://www.ncdc.noaa.gov/data-access/model-data/model-datasets/climate-forecast-system-reanalysis-and-reforecast-cfsrr].

11:45 AM | January looks to be colder than normal in the central/eastern US - perhaps even significantly - thanks in part to a stratospheric warming event

Discussion

There are reasons to believe that January will be a colder-than-normal month in the eastern and central US - perhaps even much colder-than-normal and the coldest in many years - and part of the reason for this outlook is a stratospheric warming event that is now underway over the northern latitudes. In addition to the stratospheric warming event that is forecasted to continue by the GFS computer forecast model (5-day polar stratospheric temperature forecast map shown above), supporting evidence for a colder-than-normal January comes from the very latest NOAA/NCEP Coupled Forecast System model temperature anomaly forecast for January which is significantly colder-than-normal in the central and eastern US.

The phenomenon of stratospheric warming was first discovered in 1952 and there have been about 30 events registered since then or about one every two winters. Research suggests that stratospheric warming events are a consequence of the interaction between the North Atlantic, the troposphere and the stratosphere, and there tends to be an increased number with a warm North Atlantic Ocean as currently exists. During the winter months in the lower polar stratosphere, temperatures on average are below minus 70 degrees Celsius. The cold temperatures are combined with strong westerly winds that form the southern boundary of the stratospheric polar vortex. The polar vortex plays a major role in determining how much Arctic air spills southward toward the mid-latitudes. This dominant structure is sometimes disrupted in some winters or even reversed. Under these circumstances, the temperatures in the lower stratosphere can rise by more than 50 degrees in just a few days. This sets off a reversal in the west-to-east winds and the partial or even complete collapse of the polar vortex.

In response to the stratospheric warming at the high latitudes, the troposphere in turn cools down dramatically and this cold air displacement is then transported from the tropospheric high latitudes to the tropospheric middle latitudes. The entire process from the initial warming of the stratospheric at high latitudes to the cooling in the troposphere at middle latitudes can take weeks to unfold and ultimately can lead to numerous Arctic air outbreaks in the central and eastern US. An in-depth video discussion on the stratospheric warming phenomenon can be found at http://thesiweather.com/meteorology-101/. A detailed video on the current situation is available (below). We’ll continue to monitor all of this in the days and weeks to come here at "thesiweather.com".

Video

httpv://youtu.be/RchIBfSIhmU