Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 221823

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
123 PM 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 18Z TAFS through 18Z Friday afternoon)
Issued at 123 PM CDT Thu Sep 22 2016

Main question this period is how much influence will dry air from east
winds emanating from a Hudson high influence the area. The hrrr
is the most aggressive with pushing MVFR or lower cigs southwest
of the MN river, with most terminals going vfr late this afternoon
and remaining there through much of the night. SREF probs are
similar as well. Was not quite that aggressive with the TAFs, but
did introduce significant VFR periods to WI terminals who will be
closer to the high and was conservative with keeping IFR
conditions tonight confined to RWF. Also kept TAFs dry, with most
models indicating we`ll see two focused areas of precip through
Friday morning. One down toward northeast IA into southwest WI and
the other way back in the western Dakotas.

KMSP...CIGS are the main issue here. We may see a passing shower
Friday afternoon as the warm front lifts back north, but this TAF
period is looking to bring a much needed 30 hour break from
precip. For CIGs, LAMP maintains an MVFR cig the whole period,
which is plausible, but the SREF and HRRR have MSP going VFR
tonight. Of course we could always head the other direction as
east winds are a favorable direction for getting low CIGs, which
is why we split the difference for now and went with a low MVFR
cigs returning tonight.

Sat...VFR with MVFR/TSRA likely late. Wind SE at 10g15kts.
Sun...VFR. Wind W-SW 10g20kts.
Mon...Chc mvfr/-shra. Wind SW 5-10kts.


.MPX Watches/Warnings/Advisories...


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