Plains Severe Weather, Northeast Frost/Freeze Tonight

Written by on October 12, 2012 in North and South America, United States of America with 0 Comments

The storm system which has been discussed for days, finally made an impact yesterday bringing a wild day across California and the Desert Southwest with heavy rain as well as gusty winds, hail and even waterspouts. As much as 1-2 inches of rain fell across Las Vegas as well as many areas across the Desert Southwest and these rain produced flooding.

It’s as this unusually strong and far south October storm as it crosses the southern Rockies and reaches the High Plains this afternoon where we will see the thunderstorms that are already forming, turn severe.

Good upper support and cold with WSW mid and upper levels winds, combined with warm, moist southerly surface winds which will create the thermal contrast within the atmosphere and the adequate shear which will turn thunderstorms quickly severe, especially later this afternoon as daytime heating kicks in.

The below graphic shows today’s risk area from the Storm Prediction Center.

Tomorrow will see the biggest threat as the subtropical jet gets forced north as the trough pushes northeast into the central Plains. This forces heat and high dew point north up into the Mid-Mississippi Valley where it comes up against the cold air and the northern branch jet. An area from Dallas, Texas to Madison, Wisc is of concern as this region will be positioned on the right side of the trough where the front right quadrant of subtropical jet will enhance the upward motion, and help surface convergence.

The area of greatest risk however is over Missouri, Iowa and Illinois as these states will find themselves beneath the region where the two jet branches come close to each other and where there’s the greatest temperature contrast between air masses as well as where the greatest lapse rate is.

Below is the SPC risk area for tomorrow.

Northeast Frost & Freeze Tonight

While a lot of focus is upon the severe threat over ther Plains today and tomorrow.. tonight will be a cold one across the Northeast with a high chance of a regional wide frost all the way to the Big Cities with a freeze may also get close too with temperatures expected to fall into the 20s widely. The cold night is thanks to a large high building into the region today from Ontario. The high is being fed with cold air and with a widespread clear sky, this sets the stage for a plant ruining frost and freeze.

How cold will it get?

I believe that while the heart of the big cities from Washington to New York should hold at around 34-36F, the north and west suburbs should hit 32F or below with a chance at seeing 20s. Boston has the biggest chance at seeing freezing within the city. The interior from Maryland to Maine should easily fall into the mid and low 20s and I expect the classic cold spots to dip into the teens.

Here’s the expected lows tonight off the NCEP NAM.

Courtesy of WeatherBELL

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