Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 251945
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
245 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 night through Tuesday)
Issued at 245 PM CDT Tue Jul 25 2017

Fairly quiet long term period is expected as the upper flow
becomes more amplified, with ridging building to our west and
troughing to our east. Surface high pressure to our northeast will
be a dominate player for most of the period, with very little in
the way of airmass changes expected as highs will consistently top
out around 80, with lows bottoming out around 60.

Our best chance for rain doesn`t even look all that great and it
comes this weekend. Models continue to show a wave dropping across
the upper MS Valley in NW flow this weekend, but it will be
getting increasingly sheared out as it moves across the area. Its
associated cold front will become less defined as it`s parent
upper wave weakens and the combination of weak upper forcing and
weak surface covergence equals fleeting chances for rain. We have
small chances moving into western MN Saturday afternoon that
follow whats left of the boundary across the area through Sunday,
but think even that may overdone. Given the lack of upper forcing
and weak surface convergence, prefer the ECMWF solution for the
weekend, which is dry for the MPX area. The pops we have are
courtesy of the GFS and Canadian, but both of these models look
overdone with their QPF given the lack of upper air and surface
forcing they have.

Next week, the eastern troughing looks to weaken, but the core of
the upper ridge looks to remain over the Rockies. This will keep
us in a mainly dry weather pattern, but the weaker NW flow aloft
will allow temperatures to sneak back up above normal through the
course of the week.

&&

.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...MPG
AVIATION...JPC



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