Tuesday, March 12, 2019

Updated Forecasts For Wednesday's Mega-Storm

Warnings
As of 4:06p CDT, here is a rundown of the warnings in effect:
  • Orange, blizzard warning. Includes Denver and Cheyenne.
  • Pink, winter storm warning
  • Hunter green, flash flood watch
  • Browns, high wind warnings
  • Dark blue is a winter storm watch. 
  • Gray is a dense fog advisory
  • Light green is an "areal flood warning" which means they are localized spots of high water 
  • My opinion: there is a very high avalanche risk in the Rockies the next three days
I am, frankly, shocked the NWS in central Nebraska still has a "watch" out but so be it. My forecasts are below. 


Widespread Damaging Winds
Via the ECMWF model, here is a forecast for the peak wind gusts with the weather system regardless of when they occur (scale below). The highest gusts, in some spots 90 mph or stronger, will occur
in Colorado and New Mexico, please see detailed map below.

Colorado and northern New Mexico: Essentially, yellow is peak wind gusts of 50-55 mph and browns are wind gusts of 80 to 90 mph. The scale, in knots, is at the right. In isolated spots, gusts may exceed 90 mph if skies are sunny tomorrow morning (long meteorological story having to due to lapse rates and "mixing" that I won't go into here).

From roughly the counties containing I-70 and points north in Colorado, there will be severe blizzard conditions which will extend into southwest Wyoming and western Nebraska and, perhaps, far NW Kansas.

Blowing dust will likely occur farther south.

Interstates 25, 70, 76 and 80 in this region will likely be closed due to blizzard conditions from roughly Interstate 70 on north. I-25, I-27, and, maybe I-40, US 54 and US 50 will also have to be closed due to high winds.

Farther north, Interstate 90 may be closed across South Dakota.

In addition, there will be power failures in some areas due to these extreme winds. In some cases, the power may be off for days, especially over parts of the blizzard and ice storm area. Prepare accordingly.

Severe Blizzard Conditions
The above map is my interpretation of of most likely snow amounts. This does not include drifting! Drifts will be above 10' in some cases, especially in southeast Wyoming. Travel could be deadly. Don't.

Ice Storm Conditions
See the area where the blizzard warning (orange) becomes a pink winter storm warning (a seemingly lesser condition) in eastern South Dakota. This is because the primary threat is freezing rain rather than snow. For reasons I don't understand, the NWS is not issuing a freezing rain warning or ice storm warning. I believe they should.
Power may be out for days isn this area along with adjacent parts of north central Nebraska.

Airline Travel
I am shocked United, Frontier and Southwest do not seem to have waivers out for tomorrow's flights to/from/through DEN, COS and CYS. Regardless, if you have travel plans, I'd get on the phone to reservations to see if you can take a late flight today rather than deal with the nightmare cancellations, delays and turbulence of tomorrow. With regard to turbulence,
  • Severe turbulence is a well-defined term in aviation. It is rare but it will occur tomorrow and tomorrow evening in the above region and points north. 
  • Drink little before boarding so you so not need to get up.
  • Keep your seatbelt on the entire flight.
  • Eat as little as possible.
  • Unless you react adversely, take air sickness medicine before you depart. 
This will be the last forecast for this storm. I will update on short-term forecasts and conditions tomorrow. 

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