Record cold for Feb 5?

Record low for Saint Johnsbury is -36 F. It is currently -6 F as of 1 AM. We're not even close.

• Station data at Saint Johnsbury
• Record lows
  

High pressure system and eastern cold surge

The image at right is for 0Z Thursday 05 Feb
2009 (7PM EST Wednesday 04 Feb 2009). A line of high pressure systems over the eastern U.S. dominates the eastern half of the continent. A line of high pressure centers is called a ridge. The circulation around this ridge is clockwise and outward. This means that to the east of the high the winds blow from northwest and push in cold air (blue arrows). To the west of the highs, winds blow from the southeast (red arrows). Note that the cold arctic air is transported all the way to southern Florida behind a cold front. The temperature at Savannah Georgia is approaching freezing (36 F).

The second image shows a forecast valid one day later at 0Z Friday 06 Feb 2009 (7PM EST Thursday 05 Feb 2008). The high pressure centers have moved southeastward to the Florida panhandle. The associated ridge to the north shifts eastward, extending across New York State into Canada, indicating that pressure over Vermont and New England will continue to rise. Cold northwesterly winds will continue through all of Thursday. A low pressure system forms over southern Alberta (an Alberta clipper!).


The third image shows a forecast valid two days later at 0Z Saturday 07 Feb 2009 (7PM EST Friday 06 Feb 2008). The high pressure system has moves souteastward to the coast of northern Florida. As a result, a south or southwesterly wind now dominates much of the eastern part of the U.S., bringing with it warmer air. It appears that this will warm up temperatures over the weekend starting Saturday morning.

The dark black arrow indicates the path of the Alberta Clipper moving into the Dakotas from southern Alberta. The counter clockwise circulation around the low enhances the southerly winds to the east of the system. This low pressure system will bring it with cloud and light precipitation as it moves rapidly across the continent this weekend.

Cold air and high pressure

The trace of weather data from LSC for Wed. Feb 5, 2008 indicates rising pressures and falling temperatures. As of 10:30 PM, the temperature is already -3 F, colder than the overnight low of 2 F the previous morning. The pressure trace shows a rise in pressure to about 1015 mb currently from about 10 mb from 1005 mb at midnite the previous evening. (Note however that the pressure values are low compared to other stations, indicating possible problems with the barometer). In the bottom panel, sustained winds (blue) and gusts (purple) become calmer and calmer as the high pressure moves in.