Area Forecast Discussion
Issued by NWS Twin Cities, MN

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KMPX 242003

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
303 PM CDT Sun Sep 24 2017

.SHORT TERM...(This evening through Monday)
Issued at 304 PM CDT Sun Sep 24 2017

Widely scattered showers and isolated thunderstorms will continue
to pop up this afternoon ahead of the cold front over the eastern
Dakotas, where boundary layer heating has resulted in 3-hour
MLCAPE increases of 100-200 J/kg over western Minnesota. This
activity will be possible through sunset. A few stronger storms
cannot be ruled out during this time with a damaging wind threat
given 40-50 knot 850-500 mb flow. Overall, however, the severe
potential is low. The concern for large hail is lower given
relatively poor mid level lapse rates.

After sunset the concentration turns to the main area of post-
frontal precipitation that will advance eastward across the area
overnight and Monday. Have included 70-80 percent precip chances
as the front meanders across the area. This event should provide a
good soaking given precipitable water values are forecast to
increase to around 1.75 inches by 12z Monday, coming close to
setting a record high precipitable water value for the date.

With the bulk of the area socked in with clouds and precip behind
the front on Monday, most areas will see highs in the 50s and 60s,
with the exception of Wisconsin where 70s will be common.

.LONG TERM...(Monday night through Sunday)
Issued at 304 PM CDT Sun Sep 24 2017

Things continue to look similar to how they`ve looked the past
several days. In the big picture, the western upper trough will lift
northeast and work its way across our area through midweek. Ridging
will re-build across the west during that time, with northwest flow
setting up over our area for the second half of the week. The
western ridge will then flatten as it shifts east toward our area
over the upcoming weekend. The numerical guidance is in fairly good
agreement on this overall scenario, with no notable differences
until the tail end of the period.

The frontal boundary will continue to push east tomorrow night
through Tuesday, eventually taking lingering precipitation with it
and out of the eastern portion of the area by Tuesday evening. This
timing could be slightly delayed if the surface wave which develops
along the front on Tuesday winds up stronger than currently
indicated. High pressure will build in from the west and provide
cool and dry weather Tuesday night through Wednesday night. But, a
cold front will drop in from the north on Thursday, with an
accompanying chance for showers. A stronger surface high will build
southeast from Canada behind this front, with seasonably cool and
dry weather Thursday night through Saturday evening. The details are
a bit muddy after that, but the GFS and ECMWF both suggest another
frontal boundary and associated shortwave trough will move toward
the area on Sunday, bringing another chance for precipitation.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1243 PM CDT Sun Sep 24 2017

Expect showers and isolated thunderstorms to gradually spread
eastward across the area this evening and overnight. Have included
VCSH mentions a bit farther east of the main activity for this
afternoon given the potential for isolated showers to spawn in
the somewhat unstable airmass ahead of the front/cloud cover.
Otherwise, the most concentrated and widespread precipitation
looks to expand eastward across central/southern MN after 05z,
reaching WI around/after 12z Monday. Low clouds will also
lower/thicken overnight, with most of MN sites experiencing MVFR
conditions through at least Monday morning.

Could see a few showers in the area as early as 00z, but the main
area of showers looks to hold off until after 06z. Thunder threat will
be fleeting/isolated. MVFR cigs/vsbys look to build in after
daybreak Monday, and persist through most of the day.


Mon night...MVFR likely with Likely SHRA and slgt chc TS. Winds NW
5 kts.
Tue...Chc MVFR/TSRA early. Winds NW 5-10 kts.
Wed...VFR. Winds WNW 5-10 kts.
Thu...VFR. Winds W 5 kts.




AVIATION...LS is the U.S. government's official web portal to all federal, state and local government web resources and services.