FXUS63 KMPX 200055

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
755 PM CDT Mon Aug 19 2019

Issued at 739 PM CDT Mon Aug 19 2019

Updated to include 00z aviation discussion below.


.SHORT TERM...(This evening through Tuesday night)
Issued at 401 PM CDT Mon Aug 19 2019

Quiet start to the forecast period through this evening, but
thunderstorm chances return overnight and through the day tomorrow
as a cold front advances through the region. Southwest flow has
developed this afternoon on the back side of departing high
pressure and ahead of a cold front dropping south across the
international border. This warm advection will bring in much more
humid air through tomorrow morning, with upper 60s dewpoints
already present across southwest Minnesota and low to mid 70s
dewpoints over northeast nebraska expected to eventually make
their way into the region. With 2000-3000 J/kg MUCAPE building in
this increasingly unstable atmosphere, a compact shortwave
skirting just south of the Minnesota/iowa border is expected to
intitiate a thunderstorm complex overnight, and track southeast
through Iowa. There is a chance this complex initiates far enough
north to impact the I-90 corridor, but expect the bulk of this
activity to remain south of the CWA. North of this complex, some
guidance suggests a band of thunderstorms induced by forcing along
the low-level jet forming out ahead of the advancing cold front.
Best chances for these thunderstorms will be across western and
southern Minnesota, with uncertainty on how far east they will
linger into central and eastern Minnesota as forcing will be
waning after sunrise. Can't rule out some isolated damaging wind
gusts or large hail with these thunderstorms given the unstable
atmosphere in place.

Another round of showers and thunderstorms looks possible along
the cold front as it passes from central Minnesota into west-
central Wisconsin late tomorrow morning into the evening. Despite
up to 2000 J/kg MUCAPE present out ahead of this front,
thunderstorm development will be conditional on how widespread
cloud cover will be during the day and on whether any shortwave
energy can pivot this far south from the upper low lover Manitoba.
For now, cloud cover looks to remain fairly stout throughout the
day so have kept PoPs in the chance range to account for this
conditional threat. If thunderstorms are able to initiate along
the front, bulk shear of 30- 40 kts along with the unstable
atmosphere will be sufficient to support at least an isolated
severe weather threat Tuesday afternoon- evening. Damaging wind
gusts and large hail would be the primary hazards.

Temperatures Tuesday will depend on the amount of cloud cover
present during the afternoon, but a muggy day is expected as
dewpoints rise into the upper 60s to low 70s. Highs in the low to
mid 80s are possible if skies clear out, with highs in the 70s/low
80s looking more likely under more cloud cover. Much cooler and
drier air filters in behind the front Tuesday night.

.LONG TERM...(Wednesday through Monday)
Issued at 401 PM CDT Mon Aug 19 2019

Not much has changed with thinking in the long term, with what
will be two of the nicest weather days of the year Wednesday and
Thursday, followed by increasing humidity and chances for
thunderstorms this weekend.

For Wednesday and Thursday a strong h5 low by James Bay with a
building ridge in its wake across central Canada will promote the
development of a surface high over the Canadian Prairies that will
slowly spread across the upper MS Valley Wednesday and Thursday.
This will drop dewpoints down into the 40s and 50s, with highs in
the low to mid 70s and lows in the upper 40s to mid 50s,
absolutely perfect weather to kick off the MN State Fair.

For the end of the week, a strong short wave will move across
southwestern Canada into the Canadian Prairies. This will knock
down the Canadian ridge and will leave behind an upper trough that
will remain across western Canada into the northern CONUS through
the weekend. This first wave will send a cold front into MN Friday
night, but as this upper wave moves toward western Hudson Bay,
we'll see the upper flow become more parallel to the front, which
means once this front arrives, we will be dealing with it bouncing
between eastern MN and the eastern Dakotas until a kicker wave
finally shunts it east of the area Monday or Tuesday next week.
Southerly winds with the front in the area will allow dewpoints to
creep back up, likely back into the mid 60s/low 70s. This
moisture in turn will support the development of an unstable
airmass and the result is the prolong period of PoPs in the
forecast starting Friday afternoon in western MN and lasting
through Monday. Through all of this, the windows where storms look
most likely are Friday night when the front initially arrives.
After that, it will retreat west on Saturday before returning
Sunday, so precip chances really pick up again Sunday into Monday.
Given instability/shear parameters, some severe weather would be
possible with any activity we see, so that will be something to
keep an eye on as we approach the weekend.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 739 PM CDT Mon Aug 19 2019

VFR with mostly clear skies through this evening. RA/TSRA chances
develop overnight at AXN/RWF/RNH and after daybreak at STC/MSP.
Ceilings will begin to lower overnight with MVFR conditions
expected by tomorrow morning at MN terminals and by late morning
at RNH/EAU. IFR ceilings appear possible across western MN where
ceilings will be lower. A thunderstorm complex is expected to
develop over southwest MN and generally progress east along the
I-90 corridor overnight, but confidence is low on how widespread
thunderstorm coverage becomes north of this complex through
tomorrow morning. Best chances for RA/TSRA will be at
AXN/RWF/MKT, but have maintained PROB30 mentions at all MN

KMSP...Ceilings are expected to lower overnight, with MVFR
ceilings expected by mid-morning. Two periods of RA/TSRA appear
possible: late morning/early afternoon and then again tomorrow
evening, but confidence remains low in how widespread coverage
will be at the terminal.

Wed...VFR. Wind NW 5-10 kts.
Thu...VFR. Wind NE 5 kts.
Fri...VFR. Wind SE 5-10 kts.




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