:: Prelude to a White Christmas?
As recognized in the "Autumnal Review" of the last post, it has not been a "normal" fall and early winter season for Lakeville. That may change with model solutions now starting to settle on a somewhat major shift in the zonal jet stream pattern for late week. Currently, the polar jet is running at around 170kts in the upper levels, racing from the Mexican Pacific coastline, over the Four Corners, across the Great Plains, the Great Lakes and exiting the CONUS over Maine. This places Lakeville directly under the jet max, and all current condition indicators concur...with mostly sunny skies (just high scattered ci in conjunction with the jet core), calm winds at the surface, and a steady temp...after a high yesterday of 36°F and cooling overnight to 17°F, temps have only rebounded to 30°F so far approaching 1900Z and may not get much above yesterday's 36°F.
Change to this pattern has already evolved east of the Sierra Nevadas as the jet had been digging southward along that range over the weekend, and with a kick from the current Aleutian low that has a trough extending south off the CA coast, will spawn an upper level low circulation over the CA desert. Negative tilt resulting from the cyclogenisis will give rise to a corresponding surface low over the Baja.
From this event today, the jet will split into a northern- and southern-branch, with the former acring over AB and SK towards northern MB and ON, then down over Lk Superior towards the confluence of the branches over the OH valley. The southern branch is progged by the GFS to run from the southern tip of Baja to a core max over the TX panhandle through mid-week, as the upper low slowly moves across the Great Basin towards the plains. Lower-level progs show the surface low moving up from NM to KS and NE by Thursday. The GFS progs a turn at the Sioux Empire to move the low directly east and even a little more southeast as it gets affected by the northern branch of the jet...the effect is much like a ping-pong ball moving between two currents.
Unclear at this stage of modeling for the system is moisture content. The upper midwest has seen its fair share of weather makers over the last month, however each has been moisture deficient. GFS paints a typical latent moisture picture enrichening the MS valley pre-arrival of the system to the upper midwest. However, since no frontogenisis is hinted by the models, and due to the "blocking" type setup the split jet presents, no moisture transport feature is evident from the progs. The only chance this weather maker has of contributing significant precip to the upper midwest is its ability to carry moisture from its Pacific-related genesis.
In the 72-hours preceding the manifestation of this pattern over our area, we can expect to remain in a high-pressure dominant situation...southern MN will be comfortably between the two branches of the jet, with light westerly winds, clear skies, and temps above normal in the low 40's. Come Wednesday night, the pattern will shift with the influx of clouds and a windshift to the SW and then SE as the system approaches. Long term outlook has Thursday into Friday looking like our weather days, but still too early to acsertain the extent of significant weather...your Lakeville forecast:
Monday...Fair and cool. High 35 with scattered high clouds, calm winds turning west at 7mph. Low 17 overnight.
Tuesday... Mostly sunny and warmer, High 42. Wind west 5-7mph. Low overnight of 23.
Wednesday...Mostly sunny in AM, turning partly cloudy by sundown. High of 40. Low of 32 overnight, with 30% chance of mixed precip in the early am hours of Thursday.