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01/23/08 FCST (Winter WX): IA/MN/SD/ND

A fast-moving clipper-type system will bring a period of light snow beginning mid-morning and winding down to flurries by late afternoon. The snow will be followed by a reinforcing shot of cold air with falling temperatures in the afternoon along with increasing northwesterly winds which will result in blowing snow. Snowfall totals will be less then two inches in most areas. Below are forecasts for specific locations in east central IA followed by a discussion.

Cedar Rapids:
Light snow will start at 9:30 AM and end at 7 PM. Total accumulation: 0.9 inches (Eastern IA Airport). Further north, along the northern Linn County border, a snowfall total of 1.4 inches can be expected.

Iowa City:
Light snow will start at 10:45 AM and end by 8 PM. Total accumulation: 0.4 inches.

Marengo:
Light snow will start at 9:15 AM and end at 6 PM. Total accumulation: 0.8 inches.

Synopsis:
The WV loop clearly shows the upstream disturbance diving S into MT where 60m H5 12hr height falls are concentrated. Associated with this S/WV are radar returns over the Dakotas where saturation of the H8-H7 column has commenced. SFC low-pressure was situated in WRN ND where light snow has been reported. Further E, the high-pressure ridge has moved E of the Mississippi valley.

Discussion:
The last of a succession of arctic cold fronts will sweep through the area Wednesday morning. A short duration of kinematic forcing accompanied by RH from the SFC through 600mb will provide a period of light snow as a SFC low tracks SE. The column will saturate top-down during the morning hours as an area of QG forcing coincident with H7-H8 frontogenesis overspreads the area. Moisture and ULVL support will be limited, and QPF will be limited to 0.01-0.02 inches in most areas N of I-80, with a 50-mile wide band of 0.06 inch QPF note between US-20 and US-30 in ERN IA. Snow to liquid ratios will be high, ranging from 15:1 to nearly 20:1 with temperatures between -17C and -27C in the snow growth region. The NAM appears to have the best handle on the track and timing of the low as it tracks it into SERN IA by 18Z while slowly weakening it. The NAM has initialized the low 2 mb too weak. Latest model trends have pushed the axis of precipitation further N while increasing QPF totals.

- bill
9:00 PM CST, 01/22/08
 
Looking like another interesting little clipper tomorrow. It will be fast-moving and very moisture starved, but with the upper support associated with it should "squeeze" out all the moisture it can scrounge up. Most areas will probably only get a good inch or two out of it, but most of that will fall within a few hours time.

I think the biggest story with this system will be the brief ramp-up of the winds that'll create considerable blowing and drifting of the pre-existing snowpack, and it's associated shot of bitter arctic air tomorrow night...
 
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