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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
408 PM CDT Thursday Aug 21 2014

Short term...(this evening through friday)
issued at 340 PM CDT Thursday Aug 21 2014

Surface analysis shows a low pressure center nearly atop the Twin Cities
metropolitan...with a cold front extending southwestward to near krwf and a warm front
extending southeastward to near krgk. Low clouds remained steadfast over
much of the weather forecast office mpx County warning forecast area for much of the day...aside from the warm
sector of this system which allowed southern Minnesota to have plenty of sun
and also see temperatures rise to the middle 80s to around 90 degrees. Hence
why the heat advisory has been adjusted to just account for a handful
of counties in southern Minnesota through the rest of the afternoon hours. In
addition...this warm sectoring is the focus area for potential
isolated strong/severe thunderstorms due to nearly no capping...MUCAPES over
3000 j/kg /and plenty of other severe indices indicating the same/
and lift provided by the front along with several outflow
boundaries depicted on kmpx radar. North of this system...areas caught
under the cloud cover have had temperatures holding in the 70s
along with dewpoints in the upper 60s to lower 70s. Out in western
Minnesota...winds have shifted to northwesterly and some partial clearing has
allowed temperatures so rise to the low-middle 80s but still with dewpoints
in the low-middle 70s. Overall...a quite the muggy day. With regard
to probability of precipitation...have kept the highest probability of precipitation out in western WI to far eastern
Minnesota...but overall probability of precipitation are not any higher than the chance category.
Going into the evening hours...once the cold front swings through... that
will help stabilize the atmos and bring in slightly cooler temperatures
but will not mitigate the moist atmos. Given the clearing skies
and calming winds...this setup will be pretty ideal for widespread
fog...and fairly thick fog at that. Crossover temperatures look to easily
be reached so have maintained widespread fog down to 1/2sm in
gridded and text products. Am expecting the entire County warning forecast area to be
susceptible...including the Twin Cities metropolitan...though the metropolitan
is likely not to be as affected as outlying areas. Any fog will be
slow to dissipate after daybreak in Friday morning...but with the system
of today exiting to the east and another surface front lingering in the
Dakotas...Minnesota and WI will be in a rather stable environment for Friday
such that no precipitation is expected for the weather forecast office mpx County warning forecast area. Will look
for less of a temperature spread from north to S tmrw...with highs from the
upper 70s to middle 80s. Dewpoints will also be lower...translating to
heat index values hitting the upper 80s to around 90.

Long term...(friday night through thursday)
issued at 340 PM CDT Thursday Aug 21 2014

Long term models have come into better agreement with overall
development/movement of the western Continental U.S. Trough during the
period.

Return flow ahead next developing short wave will begin to affect
mainly the far southwest County Warning Area later Friday night. Fog may become an
issue elsewhere...especially the northeast County Warning Area...with light winds
and only marginal cloud cover. The wave lifts northeast Saturday
into Saturday night with high perceptible water values along with
decent forcing. We should see good shot of heavier quantitative precipitation forecast over the
western and central County Warning Area during this period. Will continue to limit
the highest probability of precipitation to the west.

The surface front remains mainly to the west of the state through
Saturday night. The upper trough moves a bit more east into Sunday
as the upper low and surface low pivots some into southern
Canada. Heat returns ahead of the front...mainly east...with
higher dewpoints. Will have to monitor for cloud cover again...but
better southerly flow in the wake of the Saturday night short wave
should be able clear some. The cold front will move east later
Sunday through Sunday night. Have increased probability of precipitation to the east into
Sunday night as the front moves through. Cooler and drier air will
move in for Monday but the main western Continental U.S. Trough doesnt move
east until Wednesday. Another heavy bout of rain possible Tuesday
over the south and spreading east Tuesday night into Wednesday.

&&

Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 131 PM CDT Thursday Aug 21 2014

With an area of low pressure prognosticated to slide across southern Minnesota
into southern WI through this evening...aside from some clearing over
southern Minnesota...much of the area will remain caught under low MVFR
to IFR ceilings. Very little precipitation to speak of...although
short-term models call for scattered showers and isolated thunderstorms to
develop over eastern Minnesota into western WI this afternoon into evening. The WI
sites may well be susceptible to flight condition reduction but am
not looking for such in Minnesota. After some partial clearing this
evening...cooler temperatures over a highly moist airmass looks to be
very conducive to fog development overnight through daybreak Friday
morning. Have brought down ceilings and visibilities at all sites to IFR-and-
lower overnight as confidence is rather high such conditions will
be seen. There may be some differences in the timing compared to
what is currently advertised...but generally 08z-14z will be the
best timeframe to see the degraded conditions.

Kmsp...MVFR-to-VFR conds expected through this afternoon...with possibly a
few stray -shra as the low pressure center moves through. Winds then
diminish late and conds drop into MVFR in the 06z-08z range...
followed by IFR conds from early morning through daybreak before conds
improve late tmrw morning into tmrw afternoon.

/Outlook for kmsp/
Sat...MVFR with IFR/+tsra possible. Winds east at 10g15 kts.
Sun...VFR with MVFR/thunderstorms and rain possible. Winds northwest 10 kts.
Monday...VFR. Winds variable 5 kts.

&&

Mpx watches/warnings/advisories...
Minnesota...heat advisory until 8 PM CDT this evening for mnz076-077-082>085-
091>093.

WI...none.
&&

$$

Short term...jpc
long term...dwe
aviation...jpc

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