Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201941
AFDMPX

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

.UPDATED for 18Z Aviation discussion...
Issued at 1228 PM CDT Tue Sep 20 2016

&&

.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 18Z TAFS through 18Z Wednesday afternoon)
Issued at 228 PM CDT Tue Sep 20 2016

VFR conditions should persist overnight and continue for KAXN and
KSTC. However the rest of the sites will see MVFR/IFR clouds and
rain move in. The best chance for rain tonight will be south and
east of KMSP. Another round of storms is expected late Wednesday
afternoon.

KMSP...
Showers and thunderstorms are possible in the 03 to 06Z timeframe,
but the strongest storms should be south and east of KMSP so did
not include mention in the TAF. Have -shra after 06Z, but could
have lighting as well. At this time the best chance for thunder at
KMSP will be Wednesday late afternoon with widespread storms
possible Wednesday night.

/OUTLOOK FOR KMSP/
Thu...MVFR. IFR likely with SHRA/TS. Wind SE 10-20 kts.
Fri...MVFR possible. Wind E 5-15kts.
Sat...VFR with MVFR/SHRA possible. Wind SE at 10g15kt.

&&

.MPX Watches/Warnings/Advisories...
WI...Flash Flood Watch from 10 PM CDT this evening through Thursday
     evening for WIZ024-026-028.

     Flash Flood Watch from Wednesday afternoon through Thursday
     morning for WIZ014>016-023-025-027.

MN...Flash Flood Watch from 10 PM CDT this evening through Thursday
     evening for MNZ067-069-070-074>078-082>085-091>093.

     Flash Flood Watch from Wednesday afternoon through Thursday
     morning for MNZ051>053-059>063-066-068.

&&

$$

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



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