MAJOR STORM BRINGS IT ALL
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THE KITCHEN SINK
A pair of storm systems will bring the kitchen sink and all it can handle to the Midwest starting Thursday night. If you like variety, depending on your location, you may see everything from snow, sleet, heavy rain, strong winds, and thunderstorms, all in the window of a day or two. March Madness is not confined to the basketball court, as we all will see in the days ahead.
REFINING THE CLIPPER AND ITS IMPACTS
The first system, which is yet to show its hand in the form of a clipper, arrives late Thursday night and Friday. Models for days have been struggling to pinpoint the track of the disturbance and a band of snow that is likely to develop to its north. The EURO, (and to their credit the 10k GEM and HRRR), have consistently placed strong deeply sloped frontogenesis near the HWY 20 corridor. You can see this in a number of ways. First, note the 700mb vorticity (forcing) in that general area in red.
Also focus on the 700mb speed max greater than 50kts providing lift along HWY 20 from Iowa through Illinois.
The rain snow thermocline of 0 C. is also positioned south of the same general area early Friday morning. This all points to potent lift and banding in the dendritic snow producing zone. Wherever this sets up, snow rates of an inch or two of wet snow per hour is likely in a very focused west to east zone, probably close to HWY 20.
Another critical factor the EURO has been dialed in on is the amount of dry air available to produce efficient evaporative cooling near and north of HWY 30. At the time precipitation blossoms, surface temperatures may be near or a degree or two above freezing, but dew points are shown in the mid 20s. Earlier Wednesday, I saw some dew points in Iowa as low as -15 degrees.
As precipitation arrives it hits the dry air, initiating the process of saturation which takes heat and energy and cools the full column to 32 or less, allowing snowflakes to form aloft and reach the ground. It seems now that at least a mix of snow, sleet, or rain could fall as far south as I-80. North of HWY 30, the EURO sees mainly snow, especially as you reach HWY 20. Advisory level amounts of 3–6 inches are quite possible in the far north if the further south trends of the EURO and 10K GEM are correct. I expect the NWS to issue winter weather advisories for the area north of HWY 30. These may border on warnings near HWY 20. Not my call.
Something to watch is mesoscale banding, which could even include thundersnow. 24 hours out the EURO shows a narrow intense swath of snow along HWY 20 with localized 10 inch amounts. This may wobble around a bit the next 24 hours, or even fade significantly. However, this has been a shown consistently to some degree for days on the EURO. To me, it looks like a 4-8 inch band is a real possibility from HWY 20 south to about HWY 30. (Maybe a couple amounts locally higher)? Travel could get very messy in this area Friday morning. I'm out on a limb here, but that's what I'm seeing.
Having pointed all this out, the U.S. models are still holding to a track further north, although they have inched further south. It would be ideal to have this all aligned in one general area, but that rarely seems to happen around here. At any rate, this discrepancy leads to lower confidence than I would like. On the other hand, the EURO and 10k GEM have been staunch and more in line with what makes sense with my thinking. If I have to regroup tomorrow I still have time but for now, they are leading the charge. Here's what models are suggesting for snow totals. Again, these are not official forecasts, just raw model data which forecasts are derived from. I will lead with the more southern based accumulations, which I think have the best chance of verifying. The totals may be a bit high, but I certainly prefer the positioning.
The EURO
The 10K GEM
The HRRR
Here is the more northerly solutions of the U.S. based guidance, which I do not prefer but have at least made a significant shift south.
The GFS
The 3K NAM
The 12K NAM
As I write this, the official NWS model is way north and not in line with my thinking. We shall see.
Before any issues develop Thursday night, the day should be relatively quiet. Clouds will be on the increase though as warm advection kicks in ahead of the advancing clipper. That should keep temperatures well below normal, in the mid 30s north to the mid 40s south. Behind the system, lingering snow cover in the north and cold air advection area wide will combine to produce a raw spring day with highs in the low to mid 30s in all but the far south.
NEXT STORM UP...
The next system to impact the region is on a much larger scale. Its energy comes out of a deepening west coast trough that sweeps into the Plains over the weekend and into Canada Tuesday. Fortunately, the strength of the system will be such that the storm takes on a negative tilt and plows nearly straight north. That easily keeps us in the warm sector for the majority of its precipitation. Therefore, snow, of which there will be plenty, stays just to the NW. Watch the upper level evolution below.
While we start chilly Saturday, warmer air reaches the region Sunday and is here in full force Monday. Showers and storms do not make it into the area until late Sunday, more likely Sunday night and Monday, when deep moisture arrives on the subtropical jet. You can see it in play Monday on this surface depiction.
There is a strong cold front set to surge into the region Monday evening, but heating looks somewhat limited, with highs in the 50s. While that may still get us enough instability for thunderstorms, they should remain below severe limits unless we can tap greater warmth. Ample moisture is likely to bring welcome spring rains. The EURO shows this for rain totals.
Very significant wet snow falls over the upper Midwest.
Much colder, windy, and drier weather returns for next Tuesday. That's what I got. Roll weather...TS
