1:00 PM | *Much colder weather pattern setting up for the eastern two-thirds of the country to close out October*

Discussion

Big changes to cold are coming for much of the eastern two-thirds of the country during the last couple weeks of October. Temperatures have run at well above normal levels so far this month in the Midwest, Appalachians and Northeast, but much of that will be negated over the next couple of weeks; especially, from the Upper Midwest to the Appalachians.

An unfolding weather pattern change will bring about a deep upper level trough of low pressure centered over the Upper Midwest and a strong ridge of high pressure along the US and Canadian west coasts. The combination of these two upper level features will promote a flow of air from north-central Canada right into the northern sections of the US and these cold air masses will gradually spread eastward to the eastern seaboard. Last night’s GFS ensemble 500 millibar height anomaly forecast map (above) for next Thursday, 10/24, shows this upper level pattern with the deep trough represented by the blue and the strong ridge shown in red (map courtesy Penn State e-wall). This pattern will bring progressively colder air masses to the Upper Midwest, Great Lakes and Northeast US and very likely the first snows of the season from the Upper Midwest to the Appalachians over the next couple of weeks. The greatest departure from normal will be across the Upper Midwest and Great Lakes regions where the core of the cold will set up. One final note - no matter who wins the American League Championship Series - Boston or Detroit - it looks like there could be some chilly times during the World Series while playing in the American League city.

[NOAA 6-10 day outlook]

12:30 PM | **Big change to cold for much of the country during the second half of October**

Discussion

Temperatures have run at well above normal levels so far this month for much of the Midwest, Appalachians and Northeast sections of the country, but big changes are coming during the second half of October; especially, from the Midwest to the Appalachians. Mid-Atlantic cities such as Philly (+7.0 degrees), DC (+6.4) and New York (+6.6) have all run at well above normal temperature levels in October and so have the Midwestern locations of Chicago (+7.1), Detroit (+6.8) and Minneapolis (+6.0). While it will be quite hard to negate all of that above-average warmth in the Mid-Atlantic during the second half of the month despite the likelihood of experiencing the coldest air yet this season, dramatically colder-than-normal temperatures in the Midwest could manage to do just that for those locations.

An unfolding weather pattern change will bring about a deep upper level trough of low pressure centered over the Upper Midwest beginning over the upcoming weekend (GFS forecast map below, courtesy NOAA) and this will open the door for cold air intrusions into the country for the latter stages of the month possibly resulting in the first lake-effect snow for the Great Lakes region and the first freeze for many locations. The 500 millibar height anomaly map (above) for this weekend from last night’s GFS ensemble computer forecast model run depicts an overall pattern featuring a deep trough in the Midwest (blue region) and strong ridge of high pressure along the west coast (red region) which combine to drop cold air from central Canada into the Upper Midwestern states [map courtesy Penn State e-wall]. It is not out of the question that snow even reaches as far east as the Appalachians by the end of the month depending on the exact timing of the cold air outbreaks with potential east coast storminess.

Video

httpv://youtu.be/Jkz8IUWv4CE

7:00 AM | Stays warm right into the weekend

6-Day Forecast

Today

Mostly sunny, very warm, highs in the mid 80’s

Tonight

Mostly clear, cool, some patchy fog possible late, lows by morning in the upper 50’s

Thursday

Partly sunny, warm, mid 80's

Thursday Night

Mostly clear, cool, some patchy fog possible late, near 65

Friday

Partly sunny, very warm, more humid, slight chance for a shower or thunderstorm, mid 80’s

Saturday

Mostly sunny, very warm, humid, mid 80’s

Sunday

Partly sunny, very warm, humid, maybe a shower or thunderstorm at night, low-to-mid 80's

Monday

Mostly cloudy, cooler, chance for showers and thunderstorms, upper 70’s

Discussion

High pressure will continue to dominate our weather pattern for the remainder of the week and warmer-than-normal temperatures will continue from today right into the weekend. Today’s high temperatures should easily climb into the mid or upper 80’s and the 80 degree mark is likely to be surpassed on Thursday, Friday and Saturday as well. A cool front will approach the eastern states early next week and increase our chances for some rain and there is a chance that tropical moisture gets involved as a system (vis satellite image below) may brew over the Gulf of Mexico this weekend and then ride up the east coast coincident with the frontal passage.

[Tropical system in the western Caribbean]

7:00 AM | Back to the 80 degree mark and above normal temperatures for the remainder of the week

6-Day Forecast

Today

A mix of sun and clouds, warm, highs near 80 degrees

Tonight

Mostly clear, cool, some patchy fog possible late, lows by morning near 60 degrees

Wednesday

Mostly sunny, warm, mid 80’s

Wednesday Night

Mostly clear, cool, some patchy fog possible late, near 60

Thursday

Mostly sunny, warm, near 80

Friday

Mostly sunny, warm, low 80's

Saturday

Mostly sunny, warm, near 80

Sunday

Partly sunny, warm, chance for showers and thunderstorms, upper 70’s

Discussion

High pressure will continue to dominate our weather pattern for much of the week and warmer-than-normal temperatures are expected from today right into the weekend. The normal high temperature for DCA is now 74 degrees and we’ll get close to 80 today and well into the 80’s on Wednesday along with some sunshine each day. Fog is possible each of the next few late nights and early mornings; especially, in suburban locations. A cool front will approach the eastern states late this weekend and increase our chances for some rain early next week.

Video

httpv://youtu.be/xD7JlG2B70Y

7:00 AM | A nice way to begin the week and then above normal temperatures for the remainder of the week

6-Day Forecast

Today

Mostly sunny skies, pleasant, highs in the mid-to-upper 70’s

Tonight

Partly cloudy, cool, some patchy fog possible late, lows by morning in the mid-to-upper 50’s

Tuesday

Mostly sunny, warm, near 80

Tuesday Night

Mostly clear, mild, some patchy fog possible late, upper 50’s

Wednesday

Mostly sunny, warm, low 80's

Thursday

Mostly sunny, warm, low 80's

Friday

Mostly sunny, warm, low 80's

Saturday

Mostly sunny, warm, maybe a shower or thunderstorm, near 80

Discussion

A weak cool front closing in from the Midwest will dissipate over the area today and high pressure will build back into the region for the next few days. Low pressure developed offshore over the weekend and it will pull away from the Northeast US coastline over the next 24 hours or so with no disruption to our nice weather pattern. Temperatures will start the week relatively close to normal, but will reach well above normal levels in the Tuesday to Friday time period.

Video

httpv://youtu.be/Zc9-wVqCrj8

7:00 AM | Nice pattern lasts right through the weekend and well into next week

6-Day Forecast

Today

Clouds this morning then partial sun this afternoon, pleasant, highs in the low-to-mid 70’s

Tonight

Partly cloudy, chilly, patchy fog possible late, lows by morning in the low 50’s

Saturday

Partly sunny, still comfortable, mid 70’s

Saturday Night

Mostly clear, chilly, near 50

Sunday

Partly sunny, nice, mid-to-upper 70’s

Monday

Partly sunny, pleasant, mid 70’s

Tuesday

Mostly sunny, comfortable, mid-to-upper 70’s

Wednesday

Partly sunny, warm, near 80

Discussion

High pressure remains in control of the weather pattern in the Mid-Atlantic region and it will continue to do so right into the early part of next week. Temperatures will continue to remain at or slightly below normal for this time of year and humidity will stay at very comfortable levels. Low pressure will intensify off the east coast later this weekend, but should stay far enough offshore to prevent any impact in the Mid-Atlantic region during the early part of next week.

Elsewhere, cold air has penetrated into the Rocky Mountain States and significant early season snow will fall today in parts of Wyoming, Utah and Montana. The Atlantic Basin (i.e., Atlantic Ocean, Caribbean Sea and Gulf of Mexico) continues to experience quiet conditions with respect to tropical systems and, much farther away, the sun also remains rather quiet with low solar activity and no actively flaring sunspots.

7:00 AM | Nice fall weather continues through the weekend

6-Day Forecast

Today

More clouds than sun, pleasant, highs in the mid 70’s

Tonight

Partly cloudy, chilly, patchy fog possible late, lows by morning in the low 50’s

Friday

Partly sunny, still comfortable, mid 70’s

Friday Night

Mostly clear, chilly, patchy fog possible late, low 50’s

Saturday

Mostly sunny, cool, low-to-mid 70’s

Sunday

Mostly sunny, cool, low-to-mid 70’s

Monday

Partly sunny, nice, mid 70’s

Tuesday

Partly sunny, pleasant, low-to-mid 70’s

Discussion

High pressure remains in control of the weather pattern and it will continue to do so through the upcoming weekend. Temperatures will hold at or below normal levels for the next several days despite some sunshine in the region on each day. Low pressure will intensify off the east coast this weekend, but it continues to look like it will stay far enough offshore to prevent any problems in the Northeast US. Elsewhere, the tropical scene remains quiet in the Atlantic Basin and also throughout the eastern Pacific.

Video

httpv://youtu.be/aA3pDQJjx7w

7:00 AM | Nice weather pattern continues throughout the Mid-Atlantic region

6-Day Forecast

Today

A mix of clouds and sun, pleasant, highs in the low-to-mid 70’s

Tonight

Mostly clear, cool, lows by morning in the low 50’s

Thursday

More sun than clouds, still comfortable, mid 70’s

Thursday Night

Mostly clear, cool, near 55

Friday

Partly sunny, nice, mid 70’s

Saturday

Mostly sunny, pleasant, low-to-mid 70’s

Sunday

Mainly sunny, nice, low-to-mid 70’s

Monday

Partly sunny, pleasant, mid 70’s

Discussion

During a weather pattern like this, words like "nice" and "pleasant" may be overused, but no one seems to be complaining. High pressure continues to remain in control of the weather throughout the northeastern part of the country and will do so right through the weekend. By the end of the weekend, there is likely to be a storm off the Mid-Atlantic coast, but odds favor that system staying off the coast, but we'll continue to monitor it.

Video

httpv://youtu.be/G85YAbC6zFY

9:00 AM | Global sea ice update and the connection between the Atlantic Ocean and the Arctic

Discussion

The northern hemisphere sea ice areal extent has increased significantly from last year’s record low amount and is above four other recent years (2007, 2008, 2010, 2011), but it remains below normal for this time of year. Meanwhile, the southern hemisphere continues at above normal levels and recent measurements suggest it has reached the highest level in decades. On a global basis, sea ice areal extent is currently relatively close to normal with the northern hemisphere near its low point for the year (winter approaching) and southern hemisphere near its high (summer approaching). Oceanic cycles play a major role in weather and climate and can also have a significant impact on sea ice in the polar regions and we’ll focus in on that in this discussion with respect to the Arctic region.

(Courtesy University of Illinois "cryosphere")

Two distinct trend lines can be seen in the northern hemisphere sea ice areal extent dating back to the beginning of satellite era observations in 1979 and there seems to be a direct connection with an oceanic cycle in the north Atlantic involving sea surface temperatures. The Arctic region north of the Atlantic Ocean is open to the warmer waters from the south because of the way the ocean currents flow. These warmer waters can flow into the Arctic and prevent sea ice from forming in the North Atlantic. The northern Atlantic Ocean sea surface temperatures are tracked by meteorologists through an index called the Atlantic Multidecadal Oscillation (AMO) and the two distinct trend lines for northern hemisphere sea ice areal extent are quite well correlated with a flip in phases of the AMO in the mid 1990’s from negative (colder water) to positive (warmer water). Specifically, the northern hemisphere sea ice areal extent featured a general sideways trend at above normal levels from 1979 to the mid 1990’s and then, following that flip in the AMO, there has been an overall downward trend to the current below normal values. These oceanic cycles can last for two or three decades and I believe that when the northern Atlantic sea surface temperatures flip back to cooler-than-normal values – perhaps 5 or 10 years from now - the northern hemisphere sea ice areal extent will return to normal or above normal levels - much like it was before the mid 1990’s while the AMO was negative.

In addition to “areal extent”, “volume” is an important parameter to monitor with respect to sea ice to determine possible long-term climatic trends, but it is harder to measure. In fact, there are no Arctic-wide or Antarctic-wide measurements of the volume of sea ice, but it can be estimated for the Arctic using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) developed at the University of Washington Applied Physics Laboratory/Polar Science Center. PIOMAS blends satellite-observed sea ice concentrations into model calculations to estimate sea ice thickness and volume and comparisons with submarine, mooring, and satellite observations help to increase the confidence of the model results. In general, the overall trends seen for the modeled sea ice volume in the northern hemisphere seem to correlate pretty well with the observed trends seen for areal extent dating back to the beginning of the satellite era. Namely, similar to sea ice areal extent, the volume features a general sideways trend at above normal levels from 1979 to the middle 1990’s and then a downward trend began at that time when the AMO flipped to a positive phase. We’ll continue to monitor all of this at thesiweather.com over the weeks and months to come as we head into the northern hemisphere winter season.

Video

httpv://youtu.be/VraJH6M08pg

7:00 AM | Nice weather pattern continues in the Mid-Atlantic

6-Day Forecast

Today

Mostly sunny skies, cool, highs in the low 70’s

Tonight

Mostly clear, quite chilly, lows by morning in the upper 40’s

Wednesday

Mostly sunny, pleasant, mid-to-upper 70’s

Wednesday Night

Mostly clear, chilly, near 50

Thursday

Mostly sunny, comfortable, mid-to-upper 70’s

Friday

Mostly sunny, cool, low-to-mid 70’s

Saturday

Mostly sunny, nice, mid 70’s

Sunday

Partly sunny, comfortable, mid-to-upper 70’s

Discussion

High pressure remains in control of the weather in the Mid-Atlantic region and will so for much of the week. After a chilly start to the day, temperatures this afternoon will end up in the low-to-mid 70’s and then add a few degrees on Wednesday with plenty of sunshine each day. Looking ahead, one computer forecast model has the possibility of a storm near the east coast late this weekend and we'll have to monitor that threat as the week progresses. Elsewhere, the tropical scene remains quite quiet in the Atlantic Basin.