:: Storm of the Season - a preview
Yes, I know, the absence has been long...but I really had nothing to sink my teeth into, ya know? We had a protracted and severe cold snap as the polar jet moved way into the central plains a couple weeks back, and the polar jet has now receded back to its "normal" home near the Arctic Circle. In its place the subtropical jet has moved up from the mid lats and has ushered in the great peace of zonal flow for the last couple days...bringing a nice fetch of Pac air to warm us to 40's the last couple days...a 60 degree swing since two or so weeks back with temps in the -10's and -20's. A clipper pushed through yesterday cooling things back off for today, which was seasonal at mid-lower 30's. Temp grids are still low and a few inches more of snowpack remaining in South Cent MN has helped keep the air at the surface colder...and primed for the upcoming storm.
So...here it is, "The Preview" of what our local Commercial weather folks are calling the storm of the season. PacNW low scooted over the Cascade range, southeast to lower ID early this AM, and now has settled into the Bitteroot Valley of western MT. As a matter of fact, the 00Z model runs nailed the 06Z position of the 996mb low over Dillon, MT...with good initialization elsewhere, as confirmed by spot on surface as well as RAOB checks. The models are tight...both NAM and GFS very close to each other in addition to their prog checks.
Sfc low is progged to slip east-south-east over Yellowstone Park overnight, and slide down the front range from the Bighorns to the Tetons south to near Denver by mid-afternoon. Drawing strength from subsidence left by the high pressure Chinooks that had winds off the front range yesterday gusting over 60 kts, the low will stabilize as the H50, and eventually H30 upper lows will begin to form up over the Rockies. Ahead of this is a dramatically deveoping LLJ streak from the Gulf of Mex straight up the mid-MS valley states...going to a 70kt jet max at H85 by noon saturday. It is this low level flow that will kick off precip for the Lakeville area tomorrow night.
SE-Southerly flow tomorrow will continue to increase precipitable water values and hum through Saturday. As this moisture runs over our cold air surface stratas, we will see the isentropic precip begin to fall sometime close to sundown tomorrow, mainly as snow. Meanwhile, the system stacks up over KS, and moves out by late Saturday...both NAM and GFS track the low as a stacked system (no more tilt like prev models) and moves to central MO/IA border by 0600 am Sunday. This is when I think we will see the next big precip wave hit the area, and the pressure gradient would suggest some very windy conditions developing with the system along with the revived snowfall.
Models track low over Chicago by 6am monday, and still strong wrap-around dynamics will affect us as we see back-side effects from the storm. Snow should then taper by mid-late Monday. This storm almost seems prolific, as it covers a ton of area very slowly and purposefully. MOS categoricals on the snowfall chances are 4-6" between Friday and Saturday AM, and then 8"+ for late Sat into Sunday, and then another 2-4" from late Sun through Monday. No disagreement between NAM or GFS MOS for these stats either...so I think the following approach is valid: get ready for snow!! My mark on Lakeville storm total (Friday through Monday) is at 16"...a bit on the heavy side for some, but I think this has the markings of a whopper.