NWS Forecast Discussion

FXUS63 KMPX 222326

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
626 PM CDT Tue Sep 22 2020

Issued at 617 PM CDT Tue Sep 22 2020

Updated to include 00z aviation discussion below.


.SHORT TERM...(This evening through Wednesday night)
Issued at 339 PM CDT Tue Sep 22 2020

Another gorgeous evening is on tap with clear skies, light winds,
and mild temperatures on this Fall Equinox. Wednesday will feature
highs in the low 80s with mostly sunny skies and light southerly
winds into the afternoon. A shortwave trough passing through the
Upper Midwest will increase the chance of a few thunderstorms
Wednesday evening/night. There has been little changes to the
forecast with the recent guidance bringing an MLCAPE axis of 1000
to 2000 J/Kg into central Minnesota Wednesday PM. Effective bulk
shear of 40 to 50 kts and steep mid-level lapse rates (7.0-8.0
C/km)indicate a few of these storms could be severe with large
hail and a damaging winds. Instability quickly decreases after
sunset and capping becomes an issue. For now the best chance for
severe weather is across DLH`s CWA in northeast MN and northwest
WI, but a few could impact our northern counties. Showers could
linger into Thursday AM.

.LONG TERM...(Thursday through Tuesday)
Issued at 339 PM CDT Tue Sep 22 2020

For those who are enjoying the "summer-like" weather this week...
perhaps skip the long term discussion today.

With that out of the way Thursday will be slightly cooler behind
this system, but skies will begin to scatter leaving behind partly
sunny skies in the afternoon. Models continue to bring strong 850
mb WAA into MN Thursday night. 850 mb temperatures warm to near
20C over southern MN supporting highs in the lower to mid 80s on
Friday afternoon. A frontal boundary will develop ahead of the
longwave trough over the PAC NW Friday night. This boundary will
pass through the Upper Midwest Saturday ushering in cooler air and
a better chance of more widespread rain. Some of the 12z forecast
models have trended drier with the frontal passage, After
collaboration with neighboring offices we agreed to a decrease in
the PoPS on Saturday afternoon.

A pattern change is becoming apparent early next week as broad
troughing develops with strong northwesterly flow aloft. Both GFS
and ECMWF ensembles depict a deep upper-level troughing favored
over the eastern CONUS. This will support colder than average
temperatures into early October. With that in mind please enjoy
the last few "summer-like" days on tap this week.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 617 PM CDT Tue Sep 22 2020

Solid VFR conditions are expected through this 23/00z TAF
duration. The only exception is potentially some ground fog around
the sunrise hour at terminals where winds go near calm, with the
usual suspects being STC and both WI TAF sites. Light winds
through the overnight hours into late Wednesday morning will
increase to around 10kt for Wednesday afternoon. Some mid-level
clouds may creep into the area near the end of this TAF period and
into the evening hours with some isolated -SHRA/-TSRA possible
after 24/00z, mainly for the TAF sites along and north of
Interstate 94. Will address this potential more in the 23/06z TAF

KMSP...No additional concerns at this time.

Thu...Mainly VFR. Chc MVFR/-SHRA in the morning. Wind E 5 kts.
Fri...VFR. Wind S to SW 10-15 kts.
Sat...Mainly VFR. Chc MVFR/TSRA. Wind W 5-10 kts.





NWS MPX Office Area Forecast Discussion

Script by Ken True @Saratoga-Weather.org