9:00 AM | NOAA upgrades its main global computer forecast model (GFS) and enhances its computing power

Discussion

Overview Effective 12Z Wednesday, January 14th, 2015, NOAA’s Environmental Modeling Center (EMC) began running an upgraded version of its main computer global forecast model called the Global Forecast System (GFS). The upgraded GFS model has greater horizontal resolution compared to its predecessor version and the higher resolution runs now extend farther out in time. In preparation for the upgraded computer forecast model, NOAA has recently upgraded its computing capability with each of its two supercomputers by more than tripling their capacity. Much of this effort of upgrading the computer forecast model and computing capability was accelerated after Hurricane Sandy struck the Northeast US in 2012 as the main NOAA forecast model produced some inferior results in its prediction of the storm track when compared to its equivalent European counterpart.

Global Forecast System (GFS) The upgraded GFS model now has increased horizontal resolution in the first segment of its forecast package from 27 to 13 km and this higher resolution now extends out to 10 days whereas previously the higher resolution only went out to 7.5 days. The second segment of the GFS forecast package has seen an increase in horizontal resolution from 55 to 35 km which extends out from 10 days to 16 days. Furthermore, the upgraded model has enhanced physics and a better handling of important parameters such as sea surface temperatures, sea ice concentration, and snow depth which are all utilized by the model.

Computing power Modern numerical weather prediction uses the world’s most powerful computers and the associated software includes millions of lines of code. Some of the biggest computers in the world are used for weather and climate simulations. NOAA has upgraded its computing capability with each of its two supercomputers by more than tripling their capacity to at least 0.776 petaflops for a total capacity of 1.552 petaflops (a petaflop is a thousand trillion operations per second). The amount of data collected for operational numerical weather prediction is mind boggling. Petabytes of weather data are streaming to earth from dozens of weather satellites each day. In addition, hundreds of thousands of surface stations, roughly a thousand radiosondes, thousands of ships and buoys, thousands of aircraft, lightning detection networks, and other sensors are reporting each day adding up to hundreds of terabytes of information. All of this data is distributed around the world, quality controlled, and used to provide a physically consistent description of the three-dimensional atmosphere (info here provided courtesy Cliff Mass, University of Washington). Additional computing capacity and forecast model upgrades are scheduled by NOAA during the next few years.

9:00 AM | **Mid-winter update...cold pattern to continue and snow is sure to follow**

[00Z GFS Ensemble forecast map of 500 millibar height anomalies late this month; map courtesy Penn State eWall]

Discussion

Overview The first half of January has been colder-than-normal in much of the Mid-Atlantic region and indications are quite strong that the cold weather pattern will continue around here for the latter part of January and perhaps for much of February as well. In fact, there is reason to believe that the cold - relative to normal - could actually get much worse during the latter part of January and into early February compared to what we've experienced recently. So far this month, temperatures have averaged 3.5°F below normal at Philly International Airport in South Philadelphia, 3.7°F below normal in Central Park, New York, and 5.6°F below normal at Dulles Airport in Virginia. In addition, the colder-than-normal weather this month has extended across much of the eastern two/thirds of the nation and it is entirely possible that the nation as a whole ends up colder than last January which certainly was well below normal and made famous for its “polar vortex cold”. Snow, on the other hand, has been somewhat sporadic in the Mid-Atlantic region so far; however, sea surface temperature anomalies in both the Pacific and Atlantic Oceans - combined with the cold temperature outlook - suggest significant snowfall amounts are still possible as we progress through the second half of the winter season.

Temperatures and the connection to the 500 millibar height anomaly pattern There is reason to believe that a strong ridge will re-form along the west coast of North America as we progress into the latter part of January. Indeed, the forecast map (above) from last night's 00Z GFS Ensemble run for later this month features strong ridging (oranges) along the west coasts of Canada and the US and this type of pattern usually leads to multiple Arctic air mass incursions into the northern US from northern Canada. In fact, this forecast map suggests that the upper-level winds at 500 millibars – which tend to follow the height anomaly lines - could actually bring air from right around the North Pole into the northern US later this month.

Snowfall and the connection to sea surface temperature (SST) anomalies Snow has been rather sporadic so far this winter in the Mid-Atlantic region, but two far apart sea surface temperature patterns suggest significant snow is still on the table for the second half of the winter season. First, the latest SST anomaly map (below) shows some well-above normal sea surface temperatures near the US east coast (reds, oranges, yellows). Historically, this type of pattern with warmer-than-normal water off the US east coast has been linked with above-normal snowfall in the Northeast US during the second half of the winter season. Warmer-than-normal water just off the US east coast in the wintertime tends to help increase the temperature gradient along the coastline, decrease the stability of the lower atmosphere, and, in general, helps to intensify coastal storms.

In addition, the latest SST anomaly pattern in the central Pacific Ocean features an El Nino (warmer-than-normal; yellows, oranges) and this has often been correlated with above-normal snowfall during the latter half of winter seasons in this part of the country. As an example, the El Nino winter of 1982-1983, which featured little snowfall during the first half of winter, produced a blockbuster snowstorm in the Northeast US during February of that particular winter.

[Current sea surface temperature anomaly chart; courtesy NOAA]

1:45 PM | *Deep freeze grips the nation as we close out 2014...brutal cold coming to central and eastern US next week*

[7AM temperature map across the nation with average CONUS temperature of 14.3°F; map and data courtesy Ryan Maue of Weather Bell Analytics at "weatherbell.com"]

Discussion

It is certainly not too unusual to have cold air across parts of the nation at the end of the month of December; however, today’s nationwide deep freeze is indeed quite impressive. First of all, the average temperature this morning across the Lower 48 bottomed out at 14.3°F (at 7am ET). This is the lowest reading during the month of December since December 23, 1998 – some 16 years ago (data and temperature map above courtesy Ryan Maue of Weather Bell Analytics at "weatherbell.com"). In addition, about 85% of the nation was below freezing as of 7am (ET) this morning. The 12-hour 2-meter temperature anomaly forecast map from this morning’s GFS model run shows almost all “blues and purples” across the nation representing all areas predicted to experience below-normal temperatures (forecast map below courtesy “tropicaltidbits.com”). The current deep freeze extends virtually from coast-to-coast with the only exception being the Florida Peninsula where temperatures will remain above-normal (oranges/yellows).

[12Z GFS 2-meter temperature anomaly forecast map for early tonight; map courtesy "tropicaltidbits.com"]

In addition to the widespread cold which has even extended into southern California, a rare snow is occurring today across the Southwest US at such locations as Lake Havasu, Arizona, Las Vegas, Nevada, and the southern California San Bernardino mountains. Today’s cold and snow is being fueled by intense upper-level low pressure over the Desert Southwest and a very strong Arctic high pressure system over the Northern Plains and Rockies.

[Southern California (Temecula) vineyard in the deep freeze this morning]

Looking ahead to next week, after a brief spike in temperatures on Sunday across the east coast, colder air will again make a move from Canada into the northern US anchored by more strong high pressure. This time the cold air outbreak is likely to spare the western US, but by the second half of next week, the central and eastern US could be in the deep freeze once again and this time Florida may not be so lucky. Next week’s outbreak could very well cause a freeze problem way down the Florida Peninsula and places in the Upper Midwest like Chicago, Illinois could experience sub-zero temperatures.

1:00 PM | Global sea ice surges to above-normal levels seen rarely in recent years

[Yellow line represents southern hemisphere sea ice areal extent throughout 2014; courtesy University of Illinois "cryosphere"; NOAA/NCEP]

Discussion

Overall Summary Southern Hemisphere sea ice areal extent continues to run at or near all-time record high levels in the satellite data era (circled area above) for this particular time of year in records going back to 1979. The northern hemisphere sea ice areal extent continues to run at below normal levels; however, it is well above levels seen on this particular date during the past several years. Overall, the global sea ice areal extent has surged into “above-normal” territory (below) that has been seen rarely during the past several years.

[red line represents global sea ice areal extent relative-to-normal (zero line); courtesy University of Illinois "cryosphere"; NOAA/NCEP]

Southern Hemisphere Sea Ice The rather remarkable period of consistently higher-than-normal sea ice areal extent in this part of the world actually began a few years ago. Back in 2011, the southern hemisphere sea ice areal extent was still at below-normal levels, but it has surged in recent years to nearly 1.5 million square kilometers above the 1979-2008 mean (data courtesy University of Illinois "cryosphere" web site with data originating from NOAA/NCEP Snow and Ice Data Center).

Northern Hemisphere Sea Ice The northern hemisphere sea ice areal extent is still below normal (circled area below) relative to all years going back to 1979 although it is well above the lowest point set during 2012 and noticeably above levels seen earlier this year. The northern hemisphere sea ice areal extent is currently about 0.5 million square kilometers below normal using the base period of 1979-2008 for comparison (data courtesy University of Illinois "cryosphere" web site with data originating from NOAA/NCEP Snow and Ice Data Center).

The northern hemisphere sea ice areal extent has generally trended lower since the mid 1990’s reaching primarily below-normal levels after the turn of the century. In the past several years, however, there has been a leveling off of that downward trend in terms of sea ice areal extent at those below-normal levels. In the time period before the mid 1990’s, the sea ice areal extent was generally above-normal dating back to 1979. The directional shift in the sea ice areal extent trendline that developed during the mid 1990’s in the northern hemisphere correlates quite well with a northern Atlantic Ocean sea surface temperature cycle that is tracked by meteorologists through an index called the Atlantic Multidecadal Oscillation (AMO). Indeed, Atlantic Ocean sea surface temperature anomalies play a critical role in the overall northern hemisphere sea ice areal extent. The AMO index flipped in phase during the mid 1990’s from negative (cold) to positive (warm) and the sea ice areal extent trendline changed direction at precisely that point in time. Once the northern Atlantic sea surface temperatures flip back to cooler-than-normal levels – perhaps in the next few years or so - the northern hemisphere sea ice areal extent should return to the normal or above-normal levels seen prior to the mid 1990’s.

[Yellow line represents northern hemisphere sea ice areal extent throughout 2014; courtesy University of Illinois "cryosphere"; NOAA/NCEP]

11:45 AM | An unfolding stratospheric warming event provides supporting evidence for cold weather ahead

[Polar view of current stratospheric (10-millibars) temperature pattern and the 10-day forecast using the GFS model; courtesy NOAA]

Discussion

One of the ways to monitor the potential for Arctic air outbreaks in the northern U.S. is to follow what is happening in the stratosphere over the polar region of the northern hemisphere. Sudden stratospheric warming (SSW) events in the region of the North Pole have been found to set off a chain of events in the atmosphere that ultimately lead to Arctic air outbreaks from northern Canada into the central and eastern U.S. Indeed, there appears to be a significant stratospheric warming event in the offing over the next 10 days or so (above) centered near the North Pole that provides supporting evidence for cold weather conditions ahead in the central and eastern U.S.

During the winter months in the lower polar stratosphere, temperatures are typically lower than minus 70° Celsius (purple area above). 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° in just a few days. This sets off a reversal in the west-to-east winds and the 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.

The plot (below) shows the stratospheric (10-millibar) temperature pattern for 2013 and 2014 in the high latitude region of 90°N to 65°N. Some stratospheric warming events in recent decades have, in fact, been followed by widespread very cold air outbreaks across southern Canada and the US some two to three weeks after the initial upper atmosphere warming. For example, such an event occurred during December 1984 and this led to an extremely cold January 1985 in much of the central and eastern US. Interestingly, last winter season featured a sharp spike in stratospheric temperatures at just about this same time of year (i.e., late December, left circled region below) and the following couple of months were indeed much colder-than-normal in the central and eastern US. This year saw a sharp, but temporary spike in stratospheric temperatures during the latter part of November and perhaps that atmospheric event contributed to the cold and snow of Thanksgiving week in this part of the country.

A detailed video discussion on “Stratospheric Warming” can be found on the “Meteorology 101” page of the weather web site.

[Stratospheric (10-millibars) temperature plot for 2013 and 2014 in high latitude region of 90N to 65N; courtesy NOAA]

11:30 AM | *Buckle up, it could be a wild ride*

Discussion

Overview This work week will be rather uneventful weather-wise with no big storms and nothing more than a warm frontal passage on Tuesday and a cold frontal passage on Wednesday. The upcoming weekend, however, will bring the threat for a coastal storm to the Mid-Atlantic region and there are numerous signs in the atmosphere and oceans around the world that this potential weekend event may be the beginning of an overall pattern change to “stormy and cold” – not only for the remainder of December, but perhaps right into the New Year as well.

500 mb pattern The overall wind flow in the upper part of the atmosphere around 500 millibars (~18,000 feet) during the next couple of days will be rather zonal (west-to-east) in the northeastern US and this will prevent any significant cold air outbreaks from Canada. Over the next 7-10 days, however, there will be a change to the upper-level wind flow with troughiness developing over the Aleutian Islands (blue area on forecast map below) and high pressure ridging forming along the west coast of the US and British Columbia (red area on forecast map below) [an increasingly +PNA and -EPO pattern]. This type of upper level pattern will increase the chances for Arctic air outbreaks to be able to drop from northern Canada into the northern US as we progress through the rest of December and into January.

[00Z GFS-Ensemble 500 mb height anomaly forecast for Christmas Eve (12/24); map courtesy "tropicaltidbits.com"]

High-latitude blocking In addition, upper-level high pressure ridging is likely to develop over eastern Canada, Greenland and the western Atlantic (circled area above) in the next 7-10 days and this generally leads to a “blocking” pattern in the higher-latitudes which often favors colder and stormier weather in the Northeast US. The change to a “blocking” type of pattern can be tracked by the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) indices which - when negative - usually suggest some “blocking” in the atmosphere at higher latitudes is underway. Indeed, the NAO and AO are forecasted to drop sharply in the next 7-10 days or so into negative territory (red, circled areas on forecast maps below).

[North Atlantic Oscillation index and Arctic Oscillation index forecasts; courtesy NOAA]

An active southern jet Elsewhere, the sea surface temperature (SST) anomaly pattern in the Pacific Ocean currently features colder-than-normal water (blue area) to the north of Hawaii and warmer-than-normal water (yellow, orange area) near Hawaii and this combined with the unfolding weak El Nino (circled area) in the central tropical Pacific Ocean will likely generate an active southern jet stream cutting from west-to-east across the Pacific Ocean (indicated by arrow) and right into the southern US. This type of pattern will likely keep multiple storms coming into California over the next several days and these disturbances will tend to move west-to-east across the country riding along the southern jet stream.

[Current sea surface temperature anomalies; courtesy NOAA]

Multiple storm threats There is the potential for storm development this weekend along the east coast from a system that will hit California on Tuesday, then head to Texas by mid-week, and then pull out of the southern states late in the week and make a move to the northeast. Computer forecast models are not in agreement with this potential threat – par for the course when several days out from any potential event – but the changes in the overall weather pattern as described above suggest that the threat is real. The air mass in place ahead of this potential weekend storm will be only marginally cold enough for snow in the Mid-Atlantic region so odds would probably favor rain at the coast and snow in interior higher-elevation locations with the I-95 corridor in the usual precipitation-type "battle zone" area. This storm may be the first of many over the next couple of weeks. A second storm is possible around the middle of next week and then another one a few days after that.

High-latitude “blocking”, a weak and centrally-based El Nino, and an active southern jet were all major factors in the 2014-2015 Vencore Weather Winter Outlook which favored a colder and snowier winter than normal: http://vencoreweather.com/2014-2015-winter-outlook/

Buckle up, it could be a wild ride.

12:30 PM | There is hope for a white Christmas

[12Z GFS-ENS Christmas Day forecast for 500 mb height anomalies with an upper level trough in the eastern US and impressive blocking high pressure in eastern Canada; map courtesy tropicaltidbits.com]

Discussion

There will be a break in the overall weather pattern over the next week or so in the Mid-Atlantic region from the recent “stormy and cold” conditions to generally dry, chilly and rather uneventful. However, looking ahead to Christmas week, it appears as though the overall pattern may return to “stormy and cold” and that type of weather pattern may just continue right into the New Year.

The stalled out significant Northeast US storm that has impacted the region for the past several days is finally relinquishing control of the weather to building high pressure in the Mid-Atlantic and this will lead to a decent weekend and the nicer weather should continue right into next week. In fact, it looks relatively dry for much of next week and temperatures will gradually climb from chilly levels this weekend to slightly above normal by Tuesday afternoon.

[Probabilities for a white Christmas across the US; courtesy NOAA]

Looking ahead to Christmas week, computer forecast models tend to agree on the re-establishment of a deep trough of low pressure in the eastern US and impressive blocking high pressure in eastern Canada and this will allow for more cold air intrusions from Canada into the US and it could lead to storminess near the east coast. The 12Z GFS-Ensemble 500 millibar height anomaly forecast map (above) shows the eastern US upper-level trough of low pressure (blue) for Christmas Day and the blocking high pressure to the north (orange) - all of which indeed raises some hope for a white Christmas in the Mid-Atlantic region. Stay tuned.

Video

httpv://youtu.be/ynxOm-p2i_A

1:00 PM | *Great Lakes snow machine is running at full force...Buffalo with 4 feet of snow and counting...coldest November day across the CONUS since 1976*

[Buffalo snow as of this morning]

[Looking south over Lake Erie with walls of snow headed towards Buffalo]

Discussion

Great Lakes snow machine Talk about a perfect setup…the combination of southwesterly winds in the lower atmosphere, brutal cold Arctic air for mid-November and relatively warm Lake Erie water temperatures is producing incredible snow amounts in areas just to the south of Buffalo with 4 feet on the ground and several more feet possible over the next day or two. This setup is perfect for Buffalo to get pounded with snow as southwest winds in the lower atmosphere allow the air to flow for the longest period of time over the longest possible path across Lake Erie which is oriented southwest-to-northeast. As this air flows over Lake Erie, it picks up tons of moisture and dumps it on southwestern New York. This same type of pattern is occurring downwind of Lake Ontario in upstate New York and several feet of snow is expected just to the south of Watertown, NY as well.

[Surface map showing southwest winds over Lake Erie which is perfect setup for Buffalo; courtesy NOAA]

Historic Arctic blast As a whole this morning, the continental US experienced its coldest average temperature in the month of November since 1976. According to Weather Bell Analytics (weatherbell.com), the average temperature across the CONUS bottomed out earlier today at 19.4°F when more than 85% of the surface area reached or fell below freezing. All 50-states saw at or below freezing temperatures on Tuesday and should again on Wednesday. Numerous cold temperature records are likely to be broken on Wednesday from the Northeast US to the Deep South as this Arctic blast becomes well-entrenched in that part of the country.

[Coldest November day across the nation since 1976; map and data courtesy Weather Bell Analytics]

Looking ahead Milder weather is in sight. It looks like it’ll turn milder on Sunday and Monday; however, that warm up is likely to be accompanied by some more rainfall.

12:00 PM | **Heavy rainfall today and then an historic cold blast with an amazing current nationwide snow cover extent**

[Current snow cover extent in the US is 50.4%; courtesy NOAA]

Discussion

Today's heavy rainfall The evening rush hour up and down the I-95 corridor from DC-to-Philly-to-NYC will likely be quite a mess with heavy rainfall likely through much of the afternoon and early evening hours in many of these locations. All of this rainfall comes ahead of an Arctic blast that’ll arrive in the overnight hours and it will turn out to be an historic cold blast in many areas of the eastern half of the nation over the next couple of days.

Historic Arctic blast In this part of the country, several records are in jeopardy during this upcoming cold snap that will feature the coldest air seen around here since February. What is coming our way? It is currently 12 degrees in Minneapolis, Minnesota with winds gusting to 26 mph - and its only mid-November. The most likely time for record-challenging cold around here is likely to come on Wednesday as temperatures should bottom out in the teens in the overnight hours leading into the early morning. The record low at Philly Airport (PHL), for example, on Wednesday, November 19th is 20 degrees set in 1936 and this one is in jeopardy. Dulles (IAD), VA has a chance to break the record for its coldest low and high temperature on both Tuesday and Wednesday. BWI Airport in Maryland has a good chance to have its coldest November 18 on record (Tuesday), as well as its coldest low and high temperature on November 19 (Wednesday). Amazingly, the high temperature expected tomorrow in DC (maybe only as high as freezing) is 10 degrees colder than the average high temperature in mid-January. State College, PA will be lucky to see their high temperature reach the lower 20's on Tuesday and their record low maximum is 27 degrees set in 1903.

This historic Arctic outbreak will not only affect the Mid-Atlantic region, but will extend from the northern Plains to the Deep South over the next few days. In fact, record lows will be challenged on multiple occasions through midweek from eastern Texas to the Carolinas with lows near freezing along much of the Gulf Coast. Parts of northern Florida may even have their first freeze of the season as lows dip down into the 20s in cities such as Jacksonville and Tallahassee.

Amazing current US snow cover Not surprisingly, the snow cover across the country has expanded significantly during the past 7 days or so. In fact, the current snow cover extent across the nation is around 50.4% which is the most we’ve seen (by a long shot) in the first half of November since 2003, when the National Snow Analysis archive begins. Only the year 2012 comes close to this year’s 50.4 percent coverage — on Nov. 12, 2012, 31.5 percent of the lower 48 was covered in snow. The normal snow cover extent nationwide at Christmas-time is around 33%. By the way, ice is already starting to appear on Lake Superior and it should expand significantly over the next few days. Last winter's relentless cold caused some record ice cover amounts in all five of the Great Lakes.

Looking ahead Milder weather is in sight for the eastern half of the nation. It looks like it’ll turn milder late this weekend and early next week; however, that warm up is likely to be accompanied by some more rainfall.

[Clouds associated with the Arctic front extend from the Gulf of Mexico to New England; courtesy NOAA]

1:00 PM | Superstorm about to impact the Bering Strait and it will have ramifications on our weather

[Depiction of the forecasted wind field associated with this superstorm near Alaska; courtesy earth.nullschool.net]

Discussion

One of the most intense storms ever is about to move over the Bering Sea and it will have an impact on our weather in the eastern US in coming days. The Bering Sea is one of the stormiest parts of our planet, but it has rarely seen a storm like this and there is a chance that it could feature atmospheric pressure not seen this low in many decades in this part of the world.

Computer forecast models have been signaling for days that the remains of Typhoon Nuri will undergo a transition over the next few days into an extratropical storm as it moves away from Japan. As it does, unusually strong upper-levels winds across the North Pacific will help to intensify the system in a dramatic fashion – perhaps from around 970 millibars today to 925 millibars by tomorrow night. In fact, if it bottoms out at 925 millibars tomorrow night then it would tie the record for the lowest pressure ever recorded in the Bering Sea. The current record holder is 925 millibars and was set in October 1977 (in Dutch Harbor, Alaska). Note- as a point of reference, the lowest pressure recorded with Hurricane Sandy was 940 millibars. The storm will bring howling winds of up to 80 mph or so to the Aleutian Island chain and to the western part of the Alaskan mainland. Seas are forecast to build to at least 50 feet in the southwest Aleutians and perhaps even higher than that in the Bering Strait.

As far as possible ramifications on our weather…many times we’ve talked about “teleconnections” here at "VecnoreWeather.com" in which an event on one part of the world has an effect on another part of the world several days later. Indeed, this deep trough of low pressure developing in the Northern Pacific will likely translate downstream into a deep trough across the central and eastern US in coming days. In fact, it appears the reincarnation of Typhoon Nuri and some other atmospheric factors will lead to multiple rounds of Arctic air outbreaks into the Midwest and eastern US during the remainder of the month of November. One such major cold air outbreak is destined to reach the Mid-Atlantic region around Wednesday of next week.