A BIG WIND DRIVEN CHANGE...
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A WIND DRIVEN CHANGE...
Slowly but surely, a stiff southwest wind brought a spring like air mass into the Midwest Wednesday. By late afternoon highs surged into the 50s across my entire area. Even in Minnesota and Wisconsin where up to two feet of snow was on the ground highs f 35 to 40 were common. The really good stuff was out in the central Plains where highs in the 70s were noted.
The most significant warming took place from my area west where highs were 15-20 degrees warmer than Tuesday.
The warm up was spearheaded by a developing low pressure in Colorado. Note the packing of the isobars ahead of the system. That resulted in gusty south winds which continue to blow early Thursday. As a result, the day gets off to a mild start with temperatures near 40 at daybreak.
By then, moisture return has reached significant levels with water vapor exceeding an inch all the way to I-80 at noon.
That will be the fuel for rain and showers that surge into the south shortly after daybreak and then work there way north into the rest of the region by early afternoon. Here's what the surface map is projected to look like 1:00 PM Thursday afternoon. A surface low is tracking northeast along a cold front extending from SC Iowa into SE Minnesota.
That means we are still on the mild side of the system. With clouds and precipitation around that will hinder readings from getting overly warm but mid 40s to mid 50s should show up from I-80 south. The north won't be as fortunate where low 40s are indicated.
Conditions go downhill rapidly towards evening when the surface wave is projected to be be near Burlington. Winds will have turned to the north bringing sharply colder temperatures into my Iowa counties. Rain has or is changing to snow showers in central Iowa.
At midnight the surface low has progressed north of Chicago and the GFS shows strong north winds over all the area and a narrow fast moving band of light snow progressing out of eastern Iowa into western Illinois.
Models are showing some light accumulations in spots, generally less than an inch. That's a hard call due to how long precipitation continues once the transition to cold and snow occurs. In most areas it should happen quickly leaving little time for accumulation. To me, my counties NW of the Quad Cities would have the best chance of seeing up to an inch of snow but that would probably be confined to a narrow swath. I expect most spots probably don't see much more than a dusting if current trends hold. This is a situation where we'll just have to watch how things unfold Thursday morning and adjust from there...what's known as nowcasting. Here's what models are currently suggesting for accumulations. I'll start with the official NWS forecast.
The odds of an inch or more.
Now to model guidance. These are not forecasts, just raw model output that forecasts are comprised off.
The GFS
The EURO
The Canadian GEM, by far the most bullish for snow and an outlier.
The 3k NAM
Precipitation totals are generally light to moderate, 1/4 to 1/2 inch. Models indicate this.
The EURO
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COLD IS COMING...
Regarding the cold air and wind that arrives with the cold front, that is projected to arrive during early evening in my western counties in Iowa, cross the Mississippi by 8 and be through my southeast counties around 10 PM. Northerly winds driven by strong cold air advection could gust to 40mph. By daybreak St. Patrick's day temperatures should resemble these numbers.
Wind chills will be significant in the range of 2 to 7 degrees.
Readings now look like they will get back into the range of 32 to 38 later in the day. However, a secondary surge of cold air arrives later in the day Friday that sends lows deep into the teens Friday night and holds highs on Saturday in the mid to upper 20s. That's roughly 20 degrees below normal. Fortunately we should be without snow cover or it would be even worse like you see in Minnesota and NW Iowa.
Throughout the period Friday through Saturday mostly cloudy conditions are likely and from time to time a few passing snow showers are expected, especially across the north half of the region. Nothing more than a dusting will come of them.
The sun returns Sunday and with winds relaxing and temperatures back in the low to mid 30s the weekend closes on a much better note than it started. I do expect the moderating trend to continue into Monday and Tuesday when 40s return (perhaps a 50 in the south Tuesday.) Believe it or not those readings are still below normal. Here's the average daily temperature departures for the 5 day period ending next Tuesday.
The next chance for rain arrives the middle of next week. With the pattern featuring a block at higher latitudes, this active cooler than normal pattern should last the remainder of the month. That's not to say there won't be a few warm days in there but it will be hard to sustain it for lengthy periods of time. The reds indicate higher pressure in Canada and the blocking March 26th. Storms should cut underneath that in blue where pressures are lower than average.
That my friends is all I have for you tonight. Here's to a solid day despite the gloomy conditions. Roll weather...TS
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