Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 220940
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
440 AM CDT THU SEP 22 2016

.SHORT TERM...(Today and tonight)
Issued at 357 AM CDT Thu Sep 22 2016

Early this morning, thunderstorms were continuing across south
central MN in the vicinity of the stalled surface front. However,
these have weakened significantly as apparent on the instantaneous
rainfall rate product.  These storms will continue festering this
morning but in terms of QPF, we do not expect significant
additional amounts from these cells this morning. The low level
jet will weaken throughout the morning and storms should be able
to sag southward, but will do so slowly.

The front will linger in far southern MN/northern IA through the
day and the main upper level shortwave will push off to the
east. With the front in the area through the day, still have
chances for showers and thunderstorms across far southern MN
through the day. With the widespread 3-6 inches and isolated
amounts of near 10 inches from last night, continued the Flash
Flood Watch for today as this area will continue to be very
sensitive to additional precipitation.

Tonight...continue to advertise chance pops across much of far
southern Minnesota as the front continues to linger in the area.
With the upper wave off to the east, PWATs lower than last night,
and instability not as impressive, not expecting widespread
activity tonight.

.LONG TERM...(Friday through Wednesday)
Issued at 357 AM CDT Thu Sep 22 2016

Friday through Sunday...The aforementioned surface front which is
forecast to slowly move through the area today will sag south
and settle over Nebraska/northern Iowa/northern Illinois from
Friday morning through Saturday morning. Meanwhile, aloft, a
sharp longwave ridge will punch northward from the lower-middle
Mississippi River valley regions into the Dakotas and MN/WI
Friday through Saturday. This combination of features will result
in lesser coverage of precipitation, mainly due to the lack of
upper level support. However, the close proximity of the surface
feature within a continued deeply moist airmass will produce
isolated to scattered showers and thunderstorms Friday and Friday
night. The ridge axis will not linger long over the region as a
large scale cutoff low over the central Rockies will start to
swing northeastward and aid in cyclogenesis of a surface low over
eastern Colorado and western Nebraska. As this upper low swings
north, it will shove the strengthening surface low through the
Dakotas Friday night. As the surface low moves north, so will the
previously stalled front as a warm front. Placing the WFO MPX
coverage area squarely in the warm sector of this developing
system will result in an increase in surface dewpoints and deep
moisture, making for a highly unstable airmass in advance of the
cold front of this developing low pressure system. Deep
southwesterly flow aloft will efficiently tap Baja moisture and
drag it well north into the central CONUS, again bringing PWATs
to unseasonably high levels. Thus, pockets of moderate to heavy
rain cannot be ruled out starting Saturday in western MN then
spreading into the rest of MN Saturday night and on into western
Wisconsin on Sunday. High confidence on the large scale features
allow for PoPs to be pushed into the categorical range.
The evolution of small jet streaks within this system will
likely determine any severe weather potential so with fairly high
model discrepancies this morning, it is difficult to pinpoint
areas of or timing of any severe weather.

Monday through Wednesday...The extended portion of the
forecast becomes highly difficult to determine for early next
week due to high variability not only between current runs of the
GFS and EC but also among several previous runs of each model.
Each model has gone through iterations of having surface high
pressure with ridging then flip-flopped to having strong and deep
low pressure systems over the region so confidence is pretty low
in the extended. That said, have maintained slight-to-low chance
range pops over much of the coverage area throughout the forecast
to account for such uncertainty. As for temperatures, the trend
of a gradual cooling has been maintained but temperatures will
still be generally close to normal for late September.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1047 PM CDT Wed Sep 21 2016

SCT SHRA/TSRA will continue for much of the night across
eastern/southern MN and western WI. MVFR ceilings will deteriorate
to IFR during the overnight hours and continue Thursday morning
before slowly improving back to MVFR for the afternoon/evening.
Visibilities will be highly variable due to the precipitation. SCT
SHRA/TSRA expected to become dominate again late Thursday
afternoon across southern MN with the activity spreading northward
Thursday night. Mainly ENE winds 6-12 knots through the period.

KMSP...SCT SHRA/TSRA will occur through the first 6 hours of the
TAF along with ceilings deteriorating to IFR. Ceilings will be
slow to improve during the day. SHRA/TSRA chances rise again
Thursday evening.

/OUTLOOK FOR KMSP/
Fri...MVFR/SHRA possible. Wind E 5-15kts.
Sat...VFR with MVFR/TSRA likely. Wind SE at 10g15kts.
Sun...VFR. Wind W-SW 10g20kts.

&&

.MPX Watches/Warnings/Advisories...
WI...Flash Flood Watch through this evening for WIZ024-026-028.

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

&&

$$

SHORT TERM...SPD
LONG TERM...JPC
AVIATION...RAH



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