Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 251908
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
208 PM CDT Tue Jul 25 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 200 PM CDT Tue Jul 25 2017

Surface analysis this afternoon shows a northward-punching warm
front nosing into southwestern Minnesota then weaving back
westward through SD into WY. A cold front hangs southwestward from
a low pressure center over central Manitoba province. High
pressure remains centered over the central Great Lakes. Aloft, an
upper level low is nearly stacked atop the surface low over
Manitoba while the flow to its south, and over the Upper
Mississippi River Valley, is fairly zonal with the jet stream
nearby. As the afternoon progresses, the warm front is expected to
snap northward to meet up with the cold front to the north,
allowing additional deep moisture from the south (and around the
backside of the departing high) to spread into western and
southern portions of the WFO MPX coverage area. Dewpoints will
surge into the lower to middle 70s for much of the coverage area.
This will enhance an unstable atmosphere to the tune of 3000-4000
j/kg MUCAPEs. With lift being focused to near the cold front and
capping eliminated, convection is expected to break out in western
MN by early this evening and develop rather quickly then spread
east, owing to the jetting aloft. Convection will increase in
intensity and coverage as the evening progresses, eventually
reaching eastern MN into western WI with the potential for
strong/damaging winds and large hail. Discrete cells will be less
likely than clusters/bows of storms, thus making large hail and
damaging winds the main threats but isolated tornadoes at storm
initiation cannot be ruled out completely. In addition, the deep
moisture (PWATs approaching 2 inches) and effective precipitation
generation with the nearby fronts and jetting aloft will allow
storms to have rainfall rates in the 2-4 in/hr range which could
cause localized flooding but progressive storm motions should help
mitigate these concerns. The storms will wind down through the
overnight hours with the cold front progressing through the area
and the upper level low also shifting to the east. There will
likely be a bit of a lull in the action close to sunrise before
showers and a few thunderstorms resume over southern portions of
the coverage area tomorrow late morning into the afternoon. The
severe threat for tomorrow will be much lower, nearly nil save for
a handful of counties in southeastern portions of the coverage
area, so the main concern for tomorrow will be any additional
rainfall on top of what is received tonight. Warm and humid
conditions will still be expected tomorrow, mainly in eastern MN
into western WI, but not quite as high as what is being
experienced today. Will look for lows tonight in the mid 60s to
lower 70s followed by highs tomorrow in the upper 70s to lower
80s.

.LONG TERM...(Wednesday through Monday)
Issued at 358 AM CDT Tue Jul 25 2017

Thunderstorms will be ongoing early Wednesday morning ahead of the
cold front pushing into southern and eastern MN. Models are in
pretty good agreement in organizing an MCS over southwest MN and
driving it southeast into Iowa by afternoon. That will likely be
the main feature nearby for Wednesday. Forcing along the front to
the northeast of this area, particularly from west central WI
northeastward, will weaken overnight tonight, the core of the LLJ
will be shifting to the east, and the decaying upper jet will
leave little to support widespread convection into Wednesday
across Wisconsin. Kept 50-60 PoPs in place for now, but this may
be reduced further in future updates.

Surface high pressure builds in late week and into the weekend.
Mostly clear skies and near or slightly below normal temperatures
can be expected.

A front embedded in the northwest flow will push through Sunday.
It appears moisture will be limited with the expansive high
shutting off the Gulf, so not expecting widespread convective
development.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 200 PM CDT Tue Jul 25 2017

A blend of MVFR ceilings and VFR conditions will persist through
20z-21z then VFR conditions will prevail through roughly 00z.
Going into the evening, thunderstorms will erupt along an
eastward-progressing cold front which will create clusters of
strong thunderstorms which may contain heavy rain (reducing
visibility) along with gusty winds and hail. Have highlighted the
best timing of thunderstorms into each terminal via TEMPO groups.
The bulk of the precipitation will wind down during the pre-dawn
hours but there are growing indications of having post-frontal
MVFR ceilings for much of the late morning into the early
afternoon for eastern MN into western WI before VFR conditions
regain control over the entire region by late tomorrow afternoon.
There may be some lingering showers underneath the upper level low
following the front for tomorrow afternoon but chances are fairly
low.

KMSP...Thunderstorms look to move into the MSP area after 01z with
the main window for thunderstorms over the terminal in the 03z-07z
time period. Rain may be heavy at times, which could easily drop
visibility into the IFR-or-lower range. Will also look for a
period of MVFR ceilings through the morning push before VFR
conditions return by midday. There may be some showers with VFR-
to-MVFR ceilings tomorrow afternoon but confidence is not great in
this idea at this point but still bears watching to see if this
scenario develops.

/OUTLOOK FOR KMSP/
Thu...VFR. Wind NE 5-10 kts.
Fri...VFR. Wind E 5 kts.
Sat...VFR. Wind S 5 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Heat Advisory until 7 PM CDT this evening for MNZ054>057-064-065-
     067-073>075-082.

&&

$$

SHORT TERM...JPC
LONG TERM...BORGHOFF
AVIATION...JPC



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