Vencore Weather
17Dec/14Wed

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

Stratospheric_warming
[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.

10mb_temperatures_90Nto65N
[Stratospheric (10-millibars) temperature plot for 2013 and 2014 in high latitude region of 90N to 65N; courtesy NOAA]

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17Dec/14Wed

7:00 AM | Cold frontal passage ushers in colder air for tonight, tomorrow and Friday…weekend system looking rather weak, but still time for that to change

6-Day Forecast

Today

Partly sunny, becoming breezy, cool, highs not far from 50 degrees

Tonight

Partly cloudy, breezy, turning noticeably colder late, lows by morning in the upper 20’s

Thursday

Mostly sunny, breezy, cold, near 40 degrees

Thursday Night

Partly cloudy, cold, upper 20’s

Friday

Mostly sunny, cold, near 40 degrees

Saturday

Becoming mostly cloudy, cold, chance for rain and/or snow late, upper 30’s

Sunday

Mostly cloudy, cold, chance for rain and/or snow, upper 30’s

Monday

Mostly cloudy, cold, still the threat for some rain and/or snow shower activity, upper 30’s

Discussion

A warm front pushed through the region on Tuesday and a cold front has followed closely on its heels. After a relatively mild day today with highs near 50 degrees, colder air will become noticeable tonight and then the next two days will return to colder-than-normal conditions. The weekend will feature low pressure moving from the southern states towards the Mid-Atlantic coastline. The main disturbance involved with this potential Mid-Atlantic storm is just now moving onshore in California. Latest indications are that this system will remain rather weak this weekend and that any potential precipitation event around here would be only of the "light-to-moderate" variety; however, there is still time and reason to believe that this can change. There is some hinting that an inverted trough of low pressure will try to throw additional rain/snow shower activity our way on Monday and then a stronger storm is possible on Christmas Eve (next Wednesday). As of now, odds favor rain from that mid-week storm in the Mid-Atlantic region and then it would likely set up a cold pattern around here for the week between Christmas Day and New Year's Day. Stay tuned...an active pattern setting up with a lot going on over the next 7-10 days.

Video

Filed under: PHL Comments Off
17Dec/14Wed

7:00 AM | Cold front ushers in colder air for tonight, tomorrow and Friday…weekend storm looks rather weak, but still time for that to change

6-Day Forecast

Today

Mostly sunny, becoming quite breezy, cool, highs not far from 50 degrees

Tonight

Partly cloudy, breezy, turning noticeably colder late, lows by morning near 30 degrees

Thursday

Mostly sunny, breezy, cold, low-to-mid 40’s

Thursday Night

Partly cloudy, cold, upper 20’s

Friday

Mostly sunny, cold, low-to-mid 40’s

Saturday

Becoming mostly cloudy, cold, chance for rain and/or snow late, near 40 degrees

Sunday

Mostly cloudy, cold, chance for rain and/or snow early, near 40 degrees

Monday

Mostly cloudy, cold, maybe some rain and/or snow shower activity, near 40 degrees

Discussion

A warm front pushed through the region on Tuesday and a cold front has followed closely on its heels. After a relatively mild day today with highs at or slightly above 50 degrees, colder air will become noticeable tonight and then the next two days will return to colder-than-normal conditions. The weekend will feature low pressure moving from the southern states towards the Mid-Atlantic coastline. The main disturbance involved with this potential Mid-Atlantic storm is just now moving onshore in California. Latest indications are that this system will remain rather weak this weekend and that any potential precipitation event around here would be only of the "light-to-moderate" variety; however, there is still time and reason to believe that this can change. There is some hinting that an inverted trough of low pressure will try to throw additional rain/snow shower activity our way on Monday and then a stronger storm is possible on Christmas Eve (next Wednesday). As of now, odds favor rain from that mid-week storm in the Mid-Atlantic region and then it would likely set up a cold pattern around here for the week between Christmas Day and New Year's Day. Stay tuned...an active pattern setting up with a lot going on over the next 7-10 days.

Video

Filed under: WMA Comments Off
17Dec/14Wed

7:00 AM | Cold front ushers in colder air for tonight, tomorrow and Friday…weekend storm looks rather weak, but still time for that to change

6-Day Forecast

Today

Partly sunny, becoming breezy, cool, highs not far from 50 degrees

Tonight

Partly cloudy, turning noticeably colder, maybe a rain or snow shower, lows by morning in the low-to-mid 30's

Thursday

Partly sunny, breezy, cold, low 40's

Thursday Night

Partly cloudy, cold, near freezing for lows

Friday

Mostly sunny, cold, near 40 degrees

Saturday

Increasing clouds, cold, chance for rain and/or snow at night, near 40 degrees

Sunday

Mostly cloudy, cold, chance for rain and/or snow, near 40 degrees

Monday

Mostly cloudy, cold, maybe some rain and/or snow shower activity, near 40 degrees

Discussion

A warm front pushed through the region on Tuesday and a cold front has followed closely on its heels. After a relatively mild day today with highs near 50 degrees, colder air will become noticeable tonight and then the next two days will return to colder-than-normal conditions. The weekend will feature low pressure moving from the southern states towards the Mid-Atlantic coastline. The main disturbance involved with this potential Mid-Atlantic storm is just now moving onshore in California. Latest indications are that this system will remain rather weak this weekend and that any potential precipitation event around here would be only of the "light-to-moderate" variety; however, there is still time and reason to believe that this can change. There is some hinting that an inverted trough of low pressure will try to throw additional rain/snow shower activity our way on Monday and then a stronger storm is possible on Christmas Eve (next Wednesday). As of now, odds favor rain from that mid-week storm in the Mid-Atlantic region and then it would likely set up a cold pattern around here for the week between Christmas Day and New Year's Day. Stay tuned...an active pattern setting up with a lot going on over the next 7-10 days.

Video

Filed under: NYC Comments Off