:: Autumnal Conflict
Taking a break from the prognostications for the last week has proven to be a good idea, as post holiday weather has been cool and drab for Lakeville. As I write, however, sunshine is once again breaking through and will slowly warm the local area, as the mid-upper low pressure system finally slides down to Indiana today and out of the Upper Midwest. As we focus on the end of the week forecast models, the models have (as expected) general concurrence in the short term, and some diverging conclusions for the long term.
In the short term, solid agreement on a high pressure ridge building in through the next 24-48 hours. We can expect clearing skies, and warming temps, much more to a seasonable level over this period. Moving into late Thursday, both the GFS and NAM prog a surface low developing in the Powder River basin of WY, as the high pressure ridge gets stalled west of the Appalaichains. Both models -- but especially the NAM -- paint a strong gradient on the back side of the ridge Thursday night as a result of the blocking. Should this contribute to an even deeper southerly flow, temps could ride up in the low levels a bit. Moisture transport may bring cloudiness, however, and this could inhibit any highs beyond the 76-80 degree mark for Thurs into Friday.
As the weekend approaches, the models start to diverge a bit on the timing of another deepening trough off the Pac-NW. This feature is progged by the long-term GFS solution to race off the lee-side of the Rockies Saturday. Preceeding it, both the NAM and GFS paint the WY low to spin off a vort max that moves from Dakota into SW MN by late Friday. That vorticity could join forces with a coupled jet structure to give rise to moderate convection potentials Friday PM, but until local moisture content can be assured, timing for development (if any) is a crap shoot.
GFS has moisture plume riding up the strong-gradient low level jet from the Gulf of Mexico through the 00Z Saturday period in advance of the longwave/surface front, and widens vorticity potentials from the Couteu to the MS River. P-wat values on the current GFS for this timeframe run to 4cm, and lifting indicies jutting above a -2 over western MN. NAM dewpoint plots for the timeframe climb to 65F+ values, but push through the area faster than GFS, indicating main divergence in model construction of the system.
For now, the forecast will be somewhat conservative...but if things "heat up" later in the week, we could see a wet and stormy weekend. If not, we will have a repeat of last weekend, especially if the jet structure does not couple up (and, by the way, GFS hints at this for Sunday-Monday).
TUESDAY...Clearing skies, High 74. Low 52. North wind 5-10mph
WEDNESDAY...Sunny and warmer, High 76. Low 60. North wind 5mph.
THURSDAY...AM fog burns off, Partly Cloudy and 82. Winds turning SE 5-10.
FRIDAY through SUNDAY...Partly to mostly cloudy. Highs of 82 Friday, cooling off Saturday to mid-low 70's. Chance of precip all three days.