Area Forecast Discussion
Issued by NWS Twin Cities, MN

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944
FXUS63 KMPX 232342
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
642 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 00Z TAFS through 00Z Saturday evening)
Issued at 642 PM CDT Fri Sep 23 2016

SHRA and isolated TSRA along and north of I-94 this evening will
continue to trek northeast near 20 knots. Hence, KRNH will see a
couple hours of SHRA while activity diminishes for KSTC and KMSP.
Another rough night with ceilings due to a developing warm front
from SD through IA. This feature will lift slowly northward
tonight and reach into southern MN. Extensive IFR/LIFR ceilings to
continue/develop at the TAF sites this evening and continue
through at least 18z on Saturday across southern MN on over to
KEAU and through the period from the Twin Cities on north into
central MN. A cold front will reach the SD/MN border near 25/00z.
TSRA will likely develop ahead of the front across western MN
late tomorrow afternoon and push eastward toward the Twin Cities
during the evening. For now, inserted VCTS for KRWF and KAXN after
20z. winds tonight will be ESE near 10 knots. It will be a little
stronger in western MN. Winds will pick up to near 15 knots on
Saturday as the pressure gradient tightens across the region ahead
of the front. Gusts near 25 knots are likely across western and
southern MN.

KMSP...The back edge of the SHRA will be just east of the
airfield at the start of the TAF. However, a few renegade SHRA
cannot be ruled out early this evening. Ceilings have lifted to
VFR in the wake of the SHRA and expect this to only last an hour
or two before MVFR ceilings return. Little change to the ceiling
forecast for the overnight hours through early Saturday from the
previous TAF as we head under 010. Current thinking is for
extensive SHRA and embedded TSRA reaching the airfield near the
end of the TAF window (25/06z) and then continuing through
daybreak Sunday before diminishing. This will be addressed in the
next TAF package which will reach through 25/12z.

/OUTLOOK FOR KMSP/
Sun...MVFR/-SHRA/-TSRA 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...
WI...None.
MN...None.
&&

$$

SHORT TERM...MPG
LONG TERM...BORGHOFF
AVIATION...RAH



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