WINTER GOES OUT WITH A BANG...

April 17, 2020

For most of Iowa south of I-80 on into northern Missouri and WC Illinois this is one of snowiest mornings (if not the snowiest ever) for so late in the season. A potent storm loaded with spring moisture and rich dynamics has turned the tables on spring.

 

By 9:00 pm. Thursday evening Decatur City in SC Iowa had picked up 12,0" of snow. Nearby Garden Grove had 10". The heavy wet snow was coming down at the rate of 2" per hour. The Storm Prediction Center went so far as to put out a mesoscale discussion for the intense snowfall rates. Fascinating to be seeing this April 16-17th!

HEAVY SNOW DISCUSSION

Areas affected...Southeast Nebraska...southern Iowa... northern Missouri...and far west central Illinois

 

Concerning...Heavy snow Valid 162243Z - 170245Z SUMMARY...A band of heavy snow with snow rates between 1-2 in/hr will likely continue across far southeast NE, southern IA, northern MO, and far west central IL through the evening hours.

 

DISCUSSION...Recent ASOS observations from eastern NE report heavy snow with visibility at or below one mile at times. These reports, in conjunction with snowfall reports from the past few hours of 1-2 inches of snow accumulation, suggest that the snow band in place across east/southeast NE, southern IA, and northern MO continues to produce areas of snow rates between 1-2 in/hour. Recent radar trends show increasing organization of this band, which is largely being driven by strengthening 850-700 mb frontogenesis and strong isentropic ascent over the region ahead of a mid level shortwave trough. Low to mid level cold advection across the central High Plains through the evening hours will hinder rapid eastward translation of the shortwave trough and may act to increase mid level flow via thermal wind responses. As such, the forcing mechanisms of this snow band will likely continue through the evening hours as the feature slowly propagates to the east within the mean flow.

 

Given the strength of the mesoscale forcing for ascent and radar presentation, snowfall rates of 1-2 in/hour should still continue at least for the next several hours. There is some uncertainty regarding the eastward extent of the heavy snowfall potential across southeast IA/west central IL where surface wet bulb temperatures are current at or just above freezing amid relatively high (5-10 F) surface dewpoint depressions. This implies that snowfall rates may be reduced due to low level evaporation prior to full column saturation.

 

Here's what the system looked like Thursday night on the hi-resolution GOES satellite imagery. A beautiful perspective from the top down.

If the models hold the snow should end from west to east across the southern half of my area Friday morning with only minor additional accumulations of an inch...maybe two between 6 and 10:00 am.

 

Later in the afternoon temperatures are likely to reach into the mid and upper 30s which will allow for rapid improvement on any snow covered roads one the snow lets up and crews get to work. The good thing is there will be no school closings which there would have been otherwise in parts of my southern counties due to the virus.

 

Far more positive is the fact that after Friday this cold pattern starts to break down and weekend temperatures will rapidly moderate. If it weren't for existing snow cover Saturday would be around 60 or better across my area. However, some of the warming in my southern counties will go into melting snow which should vanish in a hurry. Highs will actually be warmer in the north thanks to a snow free surface.

 

Sunday a front passes and winds go back to the north putting the warming on hold. It resumes again Monday as we get back into the 60s and by Tuesday we should be close to 70. This whole snow debacle will be nothing more than a bad memory. You can see temperatures are looking a whole lot better in the 6-10 day period!

 

Well, that's it for now. The last snow of the season is soon to be behind us. Hopefully summer doesn't take as long to find us as spring! Roll weather....TS

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© 2019 Terry Swails