Area Forecast Discussion
Issued by NWS Twin Cities, MN

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643
FXUS63 KMPX 212013
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
313 PM CDT THU JUL 21 2016

.SHORT TERM...(This evening through Friday)
Issued at 310 PM CDT Thu Jul 21 2016

Early morning convection that caused significant wind damage
across west central Wisconsin during the pre dawn hours, had
moved rapidly into the Midwest region this afternoon. The residual
outflow boundary and weak front across parts of central Minnesota,
and into west central Wisconsin that was associated with the
earlier convection, continued to develop scattered showers and
thunderstorms along it through the morning, and into the early
afternoon. Surface base CAPEs above 5000 j/kg and weakening cap
allowed for a few strong storms to develop near Red Wing around 2
pm. Other storms were non-severe continued to develop in this
weakening cap regime.

Although models have not been helpful today with the ongoing
activity, there remains enough confidence to include isolated
thunderstorms along the weakening front as it sags southward into
northern Iowa this evening. Based on the instability and wind
shear values, some severe storms are still possible through the
early evening, however, any storms that develop will be isolated.
There still remains some uncertainty with chances of precipitation
overnight, and especially Friday afternoon as the aforementioned
front will washout in northern Iowa Friday morning, before
returning northward Friday night as a warm front. There is also a
weak short wave evident across the central Rockies which may help
to initiate more thunderstorms Friday as it interacts with the
washout front. Will continue to have low percentages along the
Iowa border overnight, but kept chances out of the forecast on
Friday. This needs to be watched for possibly increasing chances
Friday.

As for the heat warning continuing in far southern Minnesota,
including the Twin Cities; due to the lack of cooler air aloft
behind the weak front today, there is still a good likelihood of
heat indices rising above 100 degrees Friday afternoon, especially
along the Iowa border, northwest into west central Minnesota.
This is based on dew points returning into the low to mid 70s,
with high temperatures similar to this afternoon in the upper 80s
to mid 90s.

.LONG TERM...(Friday night through Thursday)
Issued at 245 PM CDT Thu Jul 21 2016

The long term concerns are timing of next convective event and
severe weather/flood threat associated.

It appears the front will begin to return north as a warm front
late friday night across the dakotas. Timing of upper trough has
slowed a bit...perhaps by 6 hours or so...so this may leave much
of Friday evening dry. Will continue to bring in chance pops over
the wet late in the night as waa/destabilization increases.

This trough and associated front drives east Saturday and Saturday
night. Will continue the likely pop trend Saturday afternoon and
Saturday night. Some threat of ongoing convection early Saturday
which may limit destabilization some...but severe weather threat
does remain for this period...as deep layer shear and instability
remains quite strong. Also...PW`s increase to around 2 inches
along/ahead of the front and any organized convection should
produce torrential rains. Will have to monitor this
trend...although limiting factor will be overall progressive
movement of the front.

Drier air moves in following this front through Monday night with
the next convective threat arriving Tuesday through Wednesday as
the fast zonal upper air pattern continues across the northern
states. Temperatures are expected to remain warmer than normal
through the period as well.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1210 PM CDT Thu Jul 21 2016

Main aviation concern this afternoon is isolated thunderstorm
development along a weak front sagging southward across southern
Minnesota and west central Wisconsin. There was an area of
showers and thunderstorms across central Minnesota and into west
central Wisconsin early this afternoon, but has weakened
considerably and will likely weaken this afternoon before more
develop toward 22-24z. However, there remains the weak front
which will likely cause a spotty storms to develop as early as
18-21z, especially across far southern Minnesota, and portions of
west central Wisconsin where instability is highest. Will adjust
tafs based on current radar trends. However, the best scenario is
to use VCTS. Later this evening, the weak front should be far
enough south to limit any thunderstorm activity in MPX forecast
area. Winds will become north-northeast by late afternoon/evening,
with a more east- southeast flow developing Friday morning.

KMSP...

Not much to add with isolated thunderstorms possible after 18z.
Any thunderstorms that develop should be brief with visibility
lowering to IFR at times in the heavier showers.

/OUTLOOK FOR KMSP/

Fri...VFR. Chc -TSRA late. Wind E-SE 5 kt.
Sat...VFR. Chc -TSRA late. Wind S-SE 5-10 kt.
Sun...VFR. Winds NW 10-15 kt.


&&

.MPX Watches/Warnings/Advisories...
WI...Excessive Heat Warning until 7 PM CDT Friday for WIZ024-026.

     Excessive Heat Warning until 10 PM CDT this evening for
     WIZ014>016-023-025-027-028.

MN...Excessive Heat Warning until 7 PM CDT Friday for MNZ054-056-
     060>070-073>078-082>085-091>093.

     Excessive Heat Warning until 10 PM CDT this evening for
     MNZ041>045-047>053-055-057>059.

&&

$$

SHORT TERM...JLT
LONG TERM...DWE
AVIATION...JLT



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