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ONE DOWN, ONE TO GO...

PILING ON. HEAVY WET SNOW RETURNS FOR SOME

LATE SEASON CLIPPER DELIVERS...

A late season clipper delivered up to 8 inches of snow to parts of the region Thursday night and Friday morning. Wind was never a factor, but snowfall rates up to 2 inches per hour allowed the snow to stack-up in a short amount of time. The greatest accumulations were focused on a 40-mile wideband that extended from HWY 30 to HWY 20. Very intense frontogenic forcing occurred in this region, allowing rapid accumulations.


Some 8 to 9 inch totals were reported around Rockford up to Milwaukee.


One of the unique aspects of the event was the intense mesoscale banding that took place. Notice the reds and oranges in the narrow swath from Cedar Rapids to Iowa City, where snow rates of 1–2 inches per hour were noted. Bright banding is also occurring. Bright banding is the result of the higher reflectivities associated with snow that is melting as it is falling aloft. Ice is a better absorber of radar radiation compared to liquid water. Because of this, snow will show a lower reflectivity on radar when it has the same moisture content as a rain event. When the snow is melting however, a film of water forms on the outside of the snowflake. Since snowflakes can be fairly large, (and these were), when there is a film of water on the snowflake it has the same reflectivity as a giant raindrop or small wet hail. That is a hot looking radar at 9:08 am.


The precipitation depiction mode shows some mixing of rain or ice pellets SW of Iowa City and on the north side of the Quad City metro area. Heavy snow was falling in the deepest shades of blue.


The EURO did a far better job of depicting the banding and showing its location relative to the GFS which was consistently too far north until the very end. Even it was not perfect. However, as you can see below, it made a strong attempt to lay out the narrow heavy snow swath where frontogenisis was maximized.


It ended up about 20 miles too far north, but the EURO was all over this event from the git go. I rode it hard, especially with dew points so low. I knew evaporative cooling was going to play a major role in keeping the snow band further south. This was a tough event to forecast, but a fun and challenging one at the same time. I'm pleased with the outcome!


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A DIFFERENT KIND OF STORM COMING

That leads us into a more formidable storm in terms of size. It will produce widespread heavy snow over the Plains and Upper Midwest, with heavy rain, wind, and even severe thunderstorms in parts of the Midwest. Just look at the winter storm watches from Nebraska to the Dakotas, to Minnesota, and NW Wisconsin. Not very springlike.


The energy is yet to spin out of the southwest, delaying any impacts here in the central U.S. other than clouds Saturday.


Precipitation is not expected to return in any big way until late Saturday night or Sunday morning, when the initial wave of warm advection takes a swipe at my northwestern counties. A period of light snow or a rain snow mix should quickly turn over to rain. Little if any snow accumulation is expected in the north, and overall precipitation from this wave looks light. This is well in advance of the primary energy.


Sunday night and Monday, the low level jet pivots east into the Mississippi Valley as the main storm and its associated surface low grinds into WC Iowa. This is the period when the best moisture is situated over the region. However, forcing is not aligned with it and the fast movement of these cells looks to split the heavy precipitation west and east of my region. Rain totals have come down considerably over the past 24–48 hours. Severe weather potential seems minimal, with limited heating and moisture. Here's what the latest data suggests for rain totals and severe weather potential.


The SPC severe weather risk Sunday.



EURO rainfall through Monday

The GFS rainfall through Monday.


As mentioned, this storm due to its track will not bring heavy rains to my area as it seemed destined to several days ago. That is not good news for drought plagued eastern Iowa, but it is good news in that the system's heavy snow will remain just to the northwest. Get a load of these snowfall forecasts.


The GFS

The EURO


Behind the storm, chilly weather will settle in for Tuesday and Wednesday. Beyond that, return flow brings a nice warm-up by the end of the week. The next rain threat shows up next weekend. Have a great weekend and roll weather...TS

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