Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201138
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
638 AM CDT TUE SEP 20 2016

.UPDATE...For 12z Aviation discussion below

&&

.SHORT TERM...(Today and tonight)
Issued at 400 AM CDT Tue Sep 20 2016

An area of showers with a few embedded thunderstorms is spreading
eastward across the Dakotas this morning. This activity correlates
well with the 700-600mb 2-D frontogenesis off of the RAP13 solution,
which is forecast to expand across central and northern Minnesota
throughout the morning hours. Have included 30-40 percent precip
chances from west into central Minnesota. A fair amount of mid level
clouds will be present again today, but we should still see a mild
day with highs in the lower 70s to lower 80s.

Tonight marks the beginning of a very wet period for the forecast
area. A warm front lifts into southern Minnesota tonight as moisture
returns on a 25-35 knot low level jet. There is a small threat for
large hail given decently steep lapse rates, but the primary focus
will be on the potential for heavy rainfall and flooding given the
possibility of training storms and the precipitable water increase
to around 1.75 inches over the southern third of Minnesota into west
central Wisconsin.

.LONG TERM...(Wednesday through Monday)
Issued at  400 AM CDT Tue Sep 20 2016

Heavy rainfall and possible flooding remain the primary weather
threats Wednesday through Thursday. Wednesday and Wednesday night
still look to be the higher risk periods with that continued
Moderate Risk of excessive rainfall. Coverage area also looks to be
in the vicinity of the warm front/stationary frontal boundary across
southern MN into WI.

By 12Z Wednesday morning, the surface low will be across central
Nebraska with the warm frontal boundary extending northeast through
the Sioux Falls area and east from there through the southern third
of Minnesota and into western Wisconsin.  The LLJ still doesn`t look
impressive, but is strong enough to get thunderstorms along the
front.  PWATs starting out around 1.6 inches will increase to near
1.9 inches as the tropical moisture from Paine races northeast into
the Upper Midwest.  Thunderstorms could train along the front and
lead to flash-flooding, but there is still uncertainty in exactly
where the front becomes stationary.  The hi-res ARW and NMM, as well
as the NAM-NEST indicated a farther north progression of the front
during the day on Wednesday with thunderstorm activity from central
MN through northwest WI.  Not buying into that quite yet, but the
point is, the exact placement of this front is not yet known for
Wednesday night. So, continue to hold off on issuing any sort of
Watch product until confidence is higher in amounts and location. At
this time, we still expect that front across far southern MN into
western WI.  This agrees with the WPC Moderate risk of excessive
rainfall.

Meanwhile a highly amplified trough/deep upper level low will be
slowly advancing east across the western CONUS. Late Thursday
through much of Friday looks to be our best chance of a lull in
widespread precipitation, but still carrying low POPs as scattered
shower and thunderstorm development will remain possible. The
approaching system will bring two opportunities of more rain. Late
Friday through early Saturday will see the warm front with this
system bring chances for showers and thunderstorms, with more
widespread thunderstorms likely Saturday night through much of
Sunday. There are timing differences with the GFS being more
progressive than the EC in kicking that system out and drying
things out early next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 638 AM CDT Tue Sep 20 2016

Mid level clouds will spread into the area from the west this
morning and gradually lower and thicken through the period. An
area of showers over the eastern Dakotas at TAF onset (12z) will
likely push toward KAXN and KSTC. Associated conditions should be
VFR however. Higher and more widespread precipitation chances
arrive tonight as a warm front lifts into southern Minnesota. Most
of the precip looks to stay south of the TAF sites this period,
with the exception of KMSP which may have showers and even
thunderstorms around by 06z Wednesday. Calm to light southerly
winds gradually back to east/northeast tonight.

KMSP...
Light rain showers entering west central MN at the start of the
TAF period are expected to stay mainly north of KMSP. Higher
chances arrive toward daybreak Wednesday, when cigs also degrade
to mvfr.

/OUTLOOK FOR KMSP/
Wed...MVFR. IFR psbl with SHRA/TS. Wind SE 10-15kts.
Thu...MVFR. IFR likely with SHRA/TS. Wind SE 10-20 kts.
Friday...MVFR possible. Wind E 5-15kts.

&&

.MPX Watches/Warnings/Advisories...
WI...None.
MN...None.
&&

$$

SHORT TERM...LS
LONG TERM...SPD
AVIATION...LS



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