Wednesday, November 30, 2011

Update on Late Week / Weekend Winter Storm in Rockies / Plains...

As mentioned in a brief post yesterday evening, the latest model trends had shifted to a more Northerly track with respect to the most likely areas to be impacted by the approaching winter storm.  This trend has continued during the day today, with a continued focus on an area from northcentral and northeast New Mexico into southcentral and southeast Colorado, western and northern Kansas, roughly the southeast half of Nebraska and on into the northwest half of Iowa.

Here is the set-up as the situation is unfolding currently...

The latest water vapor satellite image shows an area of disturbed weather taking shape in the middle and upper-atmosphere over the southwest (red circled area on the image below):

This area of developing low pressure is forecast to spin around the southwest for the next 24-48 hours, while ejecting pieces of energy out to the Northeast across the central and southern Rockies.  

Snow will increase across this region tonight and Thursday, with locally heavy accumulation indicated by the yellow and orange shaded areas on the image below valid 6pm CST on Thursday evening (scale in inches on the bottom left side of the image):

As the trough of low pressure digs Southward across the southwest on Thursday and Friday, increasing amounts of energy will spread out to the East across the southern Rockies, resulting in heavier snowfall southward into New Mexico and Arizona, as indicated on the image below, valid 6pm CST on Friday evening:

Snow is forecast to increase in intensity across northeast New Mexico and the adjacent Plains Friday night and early Saturday.  The images below are valid 3am CST and 6am CST on Saturday morning, respectively:

As you can see, locally heavier snows will begin to spread Northeastward into portions of western Kansas, eastern Colorado and southwest Nebraska by dawn on Saturday morning.  By Saturday afternoon, this trend will continue Northeastward into the northwestern half of Iowa, as shown by the forecast images valid at 1pm and 4pm CST, respectively:

Strong and gusty North-Northeast winds of 20-30 mph with gusts over 40 mph will create blowing and drifting snow in some areas of the Plains in association with this system.  Winter Storm Watches and/or Warnings are already in effect for much of the central and southern Rockies, and I would expect to see these issued out Eastward into the Plains by tomorrow.

Meanwhile in the warm sector of the storm system, widespread rains will fall, with 1-2 inches indicated across portions of west-central Texas, and in an even larger area extending from east-central Texas across the mid-Mississippi Valley region.  Most of the rain on the image below will fall during the period Friday through Sunday:

Cold air will spill Southward across the Plains in association with a strong surface cold front, with temperatures forecast to reach 15-20 degrees below normal levels across much of Texas by 1pm CST Sunday:

Once in place, the cold air is likely to remain entrenched across much of the nation, as indicated on the 8-day temperature average (departure from normal) image shown below:

Folks across the indicated areas of the southern and central Rockies into the central and southern Plains should "stay tuned" for later updates as this weather situation continues to unfold...

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