Area Forecast Discussion
Issued by NWS Twin Cities, MN
FXUS63 KMPX 260027 AAA
Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
727 PM CDT TUE OCT 25 2016
.SHORT TERM...(This evening through Wednesday)
Issued at 315 PM CDT Tue Oct 25 2016
Early afternoon water vapor imagery together with GFS 500mb heights
and winds showed a longwave trough over New England, with a subtle
low-amplitude shortwave over the western Dakotas. Over the next 24
hours this subtle shortwave will strengthen as the aforementioned
longwave trough retards its progression eastward. Ageostrohpic
divergence in response to the upper level curvature will lead to
rising air which will cause a surface low to track across Iowa. A
broad area of H850 Fgen will develop north of the surface low, and
this focused area of ascent will lead to 1 to 2 inches of rain across
southeast MN and west central WI overnight. At this point is
appears the that the heaviest rain will fall east of Redwood
Falls, south of Lakeville MN, and north of I-90. HiRes models show
convection developing after 00Z, so lifted the chances for thunder
a bit north up to the southern Metro.
Looking ahead, forecast soundings maintain the boundary layer
moisture along with weak omega, so continued with pops Wednesday
morning as there will likely be some lingering light rain and
drizzle. No sunshine is expected for Wednesday, and high temps will
only warm a couple of degrees into the mid 40s.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 325 PM CDT Tue Oct 25 2016
The longer term concerns remain the development of the western
coast trough and ridging ahead of the western CONUS energy with
warming over the area early in period...followed by overall timing
issues of fronts into the weekend.
Models continue to show strong trough over the west coast this
week...with embedded short wave energy ejected eastward affecting
our region. The next wave moves in on Friday...with decent WAA
pattern ahead of the associated surface front. This should provide
some lower 70s to the southwest with fropa...and dependent on
overall opaqueness of cloud cover. Clouds should be increase as
the front arrives...but moisture remains limited with this
system...and better forcing north and rather post frontal. We
warmed SUPERBLEND guidance a few degrees...closer to MOSGUIDE...
with 850mb temps progged in the upper teens.
The models diverge into the remainder of the period with the 12z
ECMWF a bit more amplified with the next short wave for Saturday.
The GFS is currently more progressive with the wave...but both a
pointing to a more post frontal rain shower risk with the system.
We expanded the coverage area of small pops for about the northern
two thirds of the CWA. Another wave approaches the area around
Halloween...but this will be dependent on timing of the west
coast energy. We will retain the small chance pops for this
period for now.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 727 PM CDT Tue Oct 25 2016
VFR conditions will deteriorate as rain continues to develop this
evening and all locations will be IFR by late tonight. Pushed back
the timing of deteriorating conditions by a few hours. Slow
improvement expected Wed afternoon. Best chance of heavy rain and
thunderstorms (some possibly strong with hail) will remain across
southern MN this evening and south of the TAF locations.
KMSP...VFR will transition to MVFR about 03Z, then IFR around
10Z. Storms should remain south but periods of heavy rain are
possible by late evening.
/OUTLOOK FOR KMSP/
Thu...VFR with MVFR Cig possible. Wind VRB 5 kt.
Fri...VFR. Wind S 5-15 kt.
Sat...VFR with MVFR/-Shra possible. Wind N at 10g25 kt.