Large uncertainty with coming storm

12:55 PM, Tuesday, April 14, 2015

A potent Pacific storm system moved onshore today and will be taking shape as it moves eastward into the Rocky Mountain region. The storm appears to be splitting. Some of our weather model guidance- particularly the reliable GFS model- has the northern part of the split storm becoming dominant and tracking into eastern Wyoming. This would put the heaviest precipitation north and east of Cheyenne, with minor amounts for the Colorado Front Range. However, a few model simulations from the GFS, along with the European and Canadian models, have the southern part of the split storm becoming dominant as it moves very slowly through the four corners region and northern New Mexico from late Wed through early Saturday.  That would put the heaviest precipitation in eastern Colorado and southeastern Wyoming.

This is a notable amount of uncertainty for a storm that is within 36 hours of starting. I’m a bit more inclined to trust the guidance in the wetter direction, but I am certainly not very confident. Whatever the outcome, Wednesday is likely to start mild and then turn cooler late in the day with some showery precipitation (rain in the lower elevations). It is likely to be windy at times both before and after the cold front.

Thursday is when the uncertainty starts to play out. The “minor precipitation” scenario would likely bring some unsettled showery weather Thursday, with drier & milder by Saturday.

The “big precip” scenario would likely see the main event late Thursday into Friday for the Colorado Front Range, maybe earlier in Cheyenne. Temperatures are likely to be marginal for snow below 6000 feet. I should point out that the wettest scenarios suggest multiple inches of liquid equivalent in and along the Front Range, and that would probably be mainly heavy snow in the mountains and possibly heavy wet snow in the lower elevations Thursday night.

I will update tomorrow. The storm will be completely inland so hopefully it will be better resolved by the observing network.

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