THE WHIP COMES DOWN...
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THE WHIP COMES DOWN
A very energetic period of weather is set to commence here in the Midwest as a clipper and what appears to be a major spring storm converge on the region back to back. Right out of the gate, there are issues with precipitation placement, type, and even amounts. My area (especially my northern counties) seems to be near the fringe of the freezing precipitation, which could lead to snow there. Otherwise, rain will be the dominate threat, with even a period or two where thunderstorms are possible. The big picture is clear and highly unsettled, it's the details that make parts of the forecast tough to handle and very much low confidence.
THE CLIPPER
Wednesday a wind driven cold front plowed through the central U.S. promoting NW winds that in spots reached 40 mph. The front barely kicked up any clouds but did tap into a cold dry air mass that is producing wind chills in the teens to near 20 Wednesday morning after highs Tuesday in the 60s!
As the cold air deepens aloft, 850 temperatures are expected to reach -10 to -11 C. in my northern counties Wednesday afternoon. That's a very cold, dense, dry air mass that has dew points below zero Wednesday. Even with the strong March sun, highs Wednesday remain around 37 north to 44 south. These dew points reflect the dryness off the air Thursday evening.
The depth of the cold dry low levels will play heavily in how much evaporative cooling can take place for snow production when the clipper arrives later Thursday night. Models are split in two camps but unified that my southern counties avoid accumulating snow. However, the EURO, the 10K GEM, and HRRR nail the northern two tiers of my counties with a decent band of snow, Stout frontogenetic forcing generates banding that could result in localized but excessive snow totals greater than 6 inches (even more on some models).
The U.S. based models such as the 3k NAM and GFS allow the deep cold air mass to retreat further to the north Thursday night. That allows the clipper a more northerly track which dumps the heavy snow well north of HWY 20 missing my northern counties altogether.
Both camps have been consistent with placement in recent runs. However, The EURO has been rock solid with its solution for days. It and the HRRR and 10K GEM also appear to be handling the depth of the cold air and ensuing thermal profiles better. That would account for more evaporative cooling further south, allowing the snow band to get into my northern counties. I also think the late night timing plays into a colder scenario as well. For these reasons, I am leaning towards a snowier solution north of HWY 30 that has advisory level snow and travel impacts early Friday.
I can honestly say that I could well be wrong and will have to shift gears at the last minute. Something I really hate to do. It's obvious, though, something has to give, and maybe it's a move to a middle ground solution. Needless to say, my confidence is not high, but for now my money is on the EURO. With that, let's take a look at what models are suggesting for snow total. Keep in mind, these are not official forecasts, just raw model guidance that forecasts are made from. The snowiest southern solution models first.
The EURO
The 10K GEM
Now the further north based U.S. model solutions.
The GFS
The 3k NAM
The SREF ensemble means at 10:1 ratio
Here is the NBM (National Blend of Models) Sort of a compromise solution on the low end.
This is what the NWS model is currently showing
Below you can see the rain snow line on the EURO Friday morning near HWY 30. The GFS is further north. I will also mention if the further south depiction of the EURO verifies, mixed snow, rain, and sleet could fall at times as far south as I-80.
Well, that was a deep dive into the clipper, which is not even the main event. Let's continue?
MASSIVE SPRING STORM TO CLOSE OUT THE WEEKEND
Due to uncertainties with similar issues such as thermal parameters, precipitation type, duration, track, and amounts, there are still plenty of unknowns with the second larger system. It may be that how the first system performs may even impact how the second evolves. For that reason, there's no sense getting cute beyond the basics. Here goes.
First and foremost, major discrepancies begin immediately with the start of precipitation Sunday. The GFS has a significantly colder air mass in place, and many places are shown starting as snow Sunday morning. As the system lifts NE warm air advection continues in earnest, changing the snow to rain in the south by afternoon and in the evening over the north. By then, several inches of snow is shown to accumulate, especially north of I-80.
With time, the GFS takes the primary surface low and its associated warm front right through my area Sunday night. This places my area in the warm sector, where showers and storms may fall on snow that the GFS showed occurring earlier in the day. Monday could see highs reach the low 60s in the south if indeed the storm goes through central Iowa. Monday evening rain and storms end as the progressive GFS lifts the system out. Personally, I think the GFS is out to lunch from the git go, and I highly doubt it's aggressively cold start with snow Sunday.
The EURO is not nearly as progressive with the mean trough and storm center. It keeps much of Sunday dry and eliminates any snow threat with much warmer air aloft. In fact, the slower progression and deepening of the storm would hold much of the rain off until late Monday or Tuesday. I have not seen the full run of the EURO, but if it intensifies as it appears it could, the storm may take on a negative tilt and head through western Iowa on a slower pace. That could make Tuesday a very warm, muggy day. Depending on timing, a severe threat could develop ahead of the surface low. These are all factors that are still unknown but highly plausible.
Even with two drastically different solutions, both the GFS and EURO signal a wet period ahead. Here are the precipitation forecasts for Wednesday through next Tuesday.
The EURO
The GFS
The Weather Prediction Center
If you think winter is over, (and it may well be soon), that's not the case over the upper Midwest. Look at these forecast snow totals in the EURO and GFS. Woo doggie!
The EURO
The GFS
Clearly we have some challenges ahead and some wild weather on the table. Just the way I like it. We'll see where things stand later today. Roll weather....TS
