Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 240345

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1045 PM CDT FRI SEP 23 2016

.SHORT TERM...(This evening through Saturday)
Issued at 408 PM CDT Fri Sep 23 2016

Another day and it`s more of the same for this week with PWATs near
2 inches (exceeding climatological records for the end of
September)and more rain falling from the skies. The band out there
now is a waa band that`s going up on elevated instability gradient
based in the h85 to h7 layer. Though radar may not look all that
impressive, the high PWATs are once again resulting in efficient
rainfall producers, with KMPX dual pol radar estimates showing about
an inch of rain was being produced by the band. Only hi-res models
that have had much of a handle on this are ones that are rapid
update (i.e. the hrrr) and we like the idea of this band continuing
northeast into northern MN and northwest Wisconsin this evening
while also weakening in terms of rainfall intensity. The weakening
is the result of the instability feeding these showers not following
them off to the northeast.

For the rest of tonight, it will be another night of low stratus as
we remain north of the warm front. As for the warm front, it is
quite impressive this afternoon. It just sneaks into SW MN where
Luverne was 86 degrees at 3 pm. At the same time, Pipestone right on
the front was 77, while by the time you got up to Marshall it was
only 65. And to boot, 90s were not all that far away with Yankton,
SD sitting at 91. This warm front will not start lifting north until
Saturday morning and will make it about as far north as the upper MN
River Valley before it starts getting swept up by a cold front that
will be pushing through Saturday night. As we have seen today, this
is a very warm warm sector and if we get any clearing in south
central MN tomorrow, then highs near 90 will be possible. However,
for most it will be another day of extensive cloud cover and little
diurnal temperature range.

For precip, as we saw this morning, there will be potential for
drizzle development here north of the warm front overnight, but once
the band currently over the area moves off to the northeast, no
significant precip arrives until the cold front starts nudging into
western MN late Saturday afternoon. There was a general slowing of
how quickly these storms get here, so did slow down how quickly we
bring back PoPs tomorrow afternoon. There will be plenty of low
level shear to support a severe weather threat, but extensive cloud
cover will greatly hamper atmospheric destabilization. In addition,
capping will be weak tomorrow, so once we develop instability, the
atmosphere will quickly consume it.  Still the top analog for the
NAM forecast on Saturday of October 8, 1997 had a good deal of wind
reports with a line of storms that developed ahead of a cold front,
so the severe risk tomorrow is not negligible.

Of course the one thing we don`t need right now is more rain, but
that`s what is coming. In addition, the NAM/GFS again show PWATs up
around 2 inches ahead of the front, so it`s back to more efficient
rainfall producers and heavy rainfall. Fortunately the progressive
nature of the activity looks to limit the flood threat with a
general model consensus on a fairly widespread 0.5" to 1" out of
this front. However, the NAM shows some streaks where around 2" are
possible and given the hydrologic conditions of much of the area,
even modest amounts such as that could lead to excessive rainfall
issues once again and the slight risk of excessive rainfall from the
WPC is warranted.

.LONG TERM...(Saturday night through Friday)
Issued at 408 PM CDT Fri Sep 23 2016

A long line of showers and thunderstorms stretching from the
Canadian border to the Mexican border will develop Saturday
afternoon and track east along a cold front Saturday night. Good
forcing along the front and very high pwat values near 2 inches
should keep the band intact through the CWA. Raised pops further
from previous forecasts to around 100 over eastern MN and over 80
just about everywhere else.

The severe threat appears marginal with a nearly saturated
atmosphere and poor lapse rates. Still, should expect some gusty
winds with the band of heaviest storms with decent low level
shear. Cannot rule out a weak QLCS tornado as well with good
veering profiles in the lower levels in areas that can achieve
better instability.

The dry slot will push in immediately behind the front with some
clearing skies Sunday morning. The upper low will then push east
across the Upper Mississippi Valley bringing widespread stratus
across the region and scattered showers for the northern halves of
Minnesota and Wisconsin. Depending how long it takes the upper low
to eject northeast, we could see some showers linger into Monday
night. GFS and GEM are the slowest, with the ECMWF the quickest.
Usually the slower solutions win out in these circumstances so
maintained such PoPs north of I-94 through Monday night, but did
reduce them Tuesday and Tuesday night.

Mid to late week looks quite pleasant with surface ridging pushing
east across the eastern two thirds of the nation. A mid level
ridge will build across the central CONUS, very likely keeping
dry weather in place for much of the week. Southeast to south flow
will also bring warmer temperatures.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1045 PM CDT Fri Sep 23 2016

Downward ceiling trend to IFR/LIFR overnight at all of the TAF
sites still looks good with many locations in the MN River Valley
already under 010. Ceilings will be slow to rise on Saturday as a
warm front along the IA/MN border lifts slowly north. A cold front
will move into the eastern Dakotas late Saturday afternoon with
TSRA developing ahead of the front in western MN and spreading
eastward during the evening and overnight hours. The storms will
contain torrential downpours.

KMSP...Ceilings will be dropping below 010 by 09z and likely stay
there through mid morning (16z). Indicated improvement to low VFR
ceilings during the afternoon. This may be too aggressive as not
all ceiling guidance is indicating this but with the tightening
pressure gradient and increased mixing ceilings should rise to
035. TSRA will likely pass across the Twin Cities a few hours
either side of midnight with a tempo group indicated.

Sun...MVFR/-SHRA early, bcmg VFR. Wind W 10g20kts.
Mon...Chc MVFR/-SHRA. Wind WNW 10g15kts.
Tue...Chc MVFR early then VFR. Wind NW 5-10kts.


.MPX Watches/Warnings/Advisories...


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