WINTER STORM COMES OUT SWINGING..
Hi everyone, as you know, TSwails.com is a no-pay site; we exist on what I call voluntary subscriptions or personal donations. Every year I ask those of you who find value in the site to make the financial donation you feel is worthy. Your contribution, whatever you can swing, supports the content, infrastructure, and operational costs of TSwails.com. To read more about my story and make a donation, CLICK HERE Thanks, it's a pleasure to serve you!
WINTER COMES OUT SWINGING
A potent mid-winter storm is in the process of pounding the region with heavy rain that in some places ends with heavy snow. By the time the system departs, precipitation over an inch is possible in many areas. In fact, the GFS shows the odds of an inch or more falling at 80 to as much as 99 percent from the area near and west of the Mississippi.
Odds that high of an inch or more of precipitation in early February are rare indeed. The moisture feed northward out of the Gulf of Mexico has to be extreme. In this unusual case, it's being powered by an 850 mb jet streak (roughly a mile up) that's roaring at 78 knots (90 mph) early Thursday.
That results in PWATS, precipitible water vapor avialable for precipitation that's shown at 1.5 inches near the SE tip of Iowa. That's high even by mid-summer standards.
This graphic measures the water vapor at 425 percent higher than normal.
That's over 6 standard deviations above normal, very rightous!
Throw in this tight closed low over Missouri at 500mb, and you have the energy and lift to wring the moisture out in the form of heavy precipitation.
With all that in mind, it's no wonder this will be a generous precipitation producer across my area. Here's what models are advertising for precipitation totals through the event.
The GFS
The EURO
The Canadian hi-res HRDPS
The national model blend
The Weather Prediction Center QPF outlook.
I took the average of 7 different models of projected rainfall for the Quad Cities Thursday and came up with a total of 1.47 inches. If that happens to verify, it would be more rain in a day than typically falls in the entire month of February at the NWS office on Davenport, which is 1.44 inches. Crazy!
SO WHAT ABOUT SNOW?
One trend I've noticed tonight is that the high-res convective allowing models (CAMS) have continued to shift the track and heavy precipitation band ever so slightly to the southeast. The deterministic runs of the GFS and EURO have too but not to the degree of the CAMS. That trend is important as it would bring heavier snows to and beyond the Mississippi. It could also decrease totals in the NW which earlier looked to be a lock for the heaviest amounts.
Currently the NWS has has all the warnings and advisories posted for the area NW of a line from roughly Washington, Iowa to Galena, Illinois. If this new trend ends up verifying the NWS will need to push the adviories further to the southeast including places like the Quad Cities, Clinton, Muscatine, and Freeport. Alterations could be made to the warnings in the NW as well. This is all being contemplated at the NWS office right now and any changes will be out by Thursday morning
The other challenging aspect of this storm is the transition to snow. The process does not appear to take place until the 850 low passes south of any given location that recieves snow. Notice at 6:00am (with the 850 circulation SW of the area), the 0 isotherm ( the freezing line necessary for snow) runs from north of Dubuque to about Cedar Rapids. That implies the air aloft to the east is still warm enough to produce mainly rain over the majority of my area.
By 9:00am the 850 circulation is approaching Peoria and the freezing line has quickly advanced east of the Mississippi with dynamic cooling taking place in earnest. What I'm saying is the transition from rain to snow should take place around 7:00am west and 10:00am in the east. At that time, snow should commence falling at a good clip in the primary band. As the storm travels northeast, the snow advances with it departing all areas by late in the afternoon. There should be a good 6-8 hour window where accumulations occur.