Monday, November 25, 2013

Big Chill Spreads Across Lower 48 States

It has been cold the past few days, but it was last week when the stage was set for an early appearance of winter weather across the country.  A broad upper level trough was located over the western U.S., and a surge of Arctic air was moving into the northern Rockies. On Thursday the trough became stronger, and by Friday a strong upper level low became disconnected from the westerlies (a "cutoff" low) while the northern portion of the trough continued east, driving cold air as far south as Texas and as far east as the Appalachians.

500 millibar analysis for last Wednesday though Friday
Surface weather map for Friday, November 22.
The surface low associated with the cutoff along with strong high pressure dropping south from Canada was responsible for high winds and heavy snow in the western U.S. from the coast to the Rockies and from Arizona to Idaho. Wind gusts reached 80 mph and resulted in power outages throughout the region.

A reinforcing surge of Arctic air pushed through the central U.S. on Saturday, and by Sunday morning the leading edge of the cold air mass had pushed well into the Gulf of Mexico and halfway through Florida.

Surface weather map for Sunday, November 24.
Meanwhile, the upper low continued to spin over the southwestern U.S. producing snow across the Four Corners region and in Texas. Freezing rain developed from New Mexico eastward across Oklahoma turning roads into skating rinks.

Snowfall for the 48 hours ending at 7:00 a.m. local time Monday, November 25.
In the eastern U.S. cold air flowing across the relatively warm waters of the Great Lakes produced snow from Ohio through New York.

As of this morning snow cover was extensive across Canada and the central Rockies.


How cold has it been? In the central two-thirds of the country temperatures the last week have been well below normal. Over the weekend minimum temperatures dropped into the single digits and teens as far south as the Ohio River and below freezing from central Texas eastward through central Mississippi and Alabama.


Minimum temperatures for 7:00 a.m. EST Sunday, November 24.

1 comment:

Ric Werme said...

Sunday was the coldest afternoon near Concord NH in my 11 years of weather data. From my report to a news station:

I went looking to see how many cold November days I have in my records like today. I started with a small subset, days with highs below 30 since 2010. There weren't any. There was one day below freezing. Even the whole list is short:

mysql> select dt, hi_temp, hi_temp_time, lo_temp from daily where dt like '%%%%-11-%%' and hi_temp < 32.0;
+------------+---------+--------------+---------+
| dt | hi_temp | hi_temp_time | lo_temp |
+------------+---------+--------------+---------+
| 2005-11-24 | 31.8 | 14:40:00 | 16.1 |
| 2005-11-25 | 31.9 | 14:10:00 | 12.1 |
| 2005-11-26 | 28.4 | 14:30:00 | 9.0 |
| 2007-11-24 | 31.8 | 13:10:00 | 18.4 |
| 2008-11-19 | 30.4 | 11:00:00 | 18.8 |
| 2008-11-20 | 30.1 | 12:50:00 | 18.8 |
| 2008-11-21 | 30.3 | 12:40:00 | 18.8 |
| 2008-11-22 | 25.4 | 12:40:00 | 19.2 |
| 2008-11-23 | 30.1 | 13:00:00 | 14.1 |
| 2012-11-30 | 30.7 | 00:00:00 | 21.0 |
+------------+---------+--------------+---------+
10 rows in set, 1 warning (0.00 sec)

Data start in 2003.

The afternoon high on Sunday was 23.8, last 11-30 was a few degrees warmer. The 24 hour high for both days was near midnight.

We also had very strong winds. The morning dog walk was shorter than usual!