Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 201747
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1247 PM CDT Fri Oct 20 2017

.SHORT TERM...(Today and tonight)
Issued at 356 AM CDT Fri Oct 20 2017

Early morning water vapor imagery together with 500 mb heights and
winds identified an upper level longwave trough across the
western Conus with a downstream ridge over the central United
States. The warm temperatures associated with the upper level
ridge will remain with us 1 more day as breezy southerly flow
brings mid to upper 70s across the region this afternoon.
Increased afternoon highs and winds above guidance.

Over the next 24 hours the aforementioned upper level trough will
move eastward and a very strong jet will round the base of the
trough leading to cyclogenesis across central Canada. This will
advect warm moist boundary layer air across the Upper Midwest
which will lead to clouds and precipitation developing late Friday
night into Saturday. This air mass together with the strong winds
will keep overnight lows near 60s for Saturday morning.

.LONG TERM...(Saturday through Thursday)
Issued at 356 AM CDT Fri Oct 20 2017

It is going to rain on Saturday. There is no doubt about that.
This is a strong synoptic system that has a seasonably high PWAT
values as well as instability. For that reason increased pops to
near 100 percent. Most locations can expect around 0.50 inches,
with some areas picking up around an inch if a thunderstorm or two
moves overhead.

The storm prediction center lifted the slight risk of severe
weather into southeastern Minnesota. There is certainly some shear
and some CAPE, but have a feeling that the strong forcing will
lead to widespread showers and thunderstorms so any CAPE will
quickly be used up and envision many weak sub-severe updrafts as
opposed to a few stronger storms. The highest severe weather
threat is wind, since H850 winds will be around 50 kts and could
cause wind damage if this manages to get transfered to the
surface. All-in-all, cant rule out the severe threat but at this
time feel it is fairly low.

Looking ahead, an active weather pattern with a strong upper level
jet will continue to bring several weather systems across the
Upper Midwest. Expect warmer temps ahead of these waves, with
gradually more significant cool downs behind them. This high
amplitude pattern can change from model run to model run, so did
not stray from the blended guidance beyond this weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1247 PM CDT Fri Oct 20 2017

Our run of VFR conditions and dry weather will come to an end
during the course of this TAF period. For MVFR cigs, favored the
forecast of their return more in line with the slower GFS since they
are just now approaching the I-20 corridor in northeast TX, so
will take a while for that moisture to get here. Do like the
NAMnest idea of a cluster of shra/tsra coming out of Iowa after 9z
tonight as short wave currently in the CO/NM/TX/OK/KS borders
region lifts northeast toward the Twin Cities. SHRA/TSRA chances
look to increase across central MN after 18z Saturday ahead of a
cold front that will be moving across MN.

KMSP...Was conservative with the arrival of MVFR cigs and it is
possible we could see MVFR conditions as early as 11/12z. Also
kept cigs above 017, though depending on how much rain we see in
the morning (and the moistening of the lower atmosphere seen
because of it), we could certainly see cigs below this level by
the afternoon.

/OUTLOOK FOR KMSP/

Sun...VFR. Winds WSW 10G20 kts.
Mon...VFR. Winds W 15G25 kts.
Tue...Chc MVFR. Wind NW at 10G20 kts

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...JRB
LONG TERM...JRB
AVIATION...MPG



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