Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 182005

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
305 PM CDT Wed Oct 18 2017

.SHORT TERM...(This evening through Thursday)
Issued at 245 PM CDT Wed Oct 18 2017

The quiet weather will continue through the short term, with the
only concerns surrounding fire weather.

Cold front continues to make steady progress across MN this
afternoon. Not much of a temperature drop in the MPX area behind the
front (that`s up in North Dakota), but we are seeing a good dewpoint
drop, with several sites seeing dewpoints in the 20s. As a result we
are seeing borderline critical fire conditions with sustained NW
winds up in the ballpark of 20 mph and humidities in the 20-25%
range. Given the borderline nature of both the weather and fuel
conditions, held off on issuing any red flag warnings. Cirrus came
in a bit thicker today than anticipated, which kept temperatures
from getting quite as warm as we had forecast, but airmass is still
plenty warm enough to allow for highs today to be a good 10 to 15
degrees above normal.

Tonight, though we are not expecting the boundary layer to
completely decouple, winds will calm down to around 5 mph or less
and those light winds with the dry air coming in along with clear
skies will allow for efficient radiational cooling, so did go on the
lower side of the guidance envelope for lows tonight.

Also happening tonight, winds will turn back out of the south as a
warm front moves back across the area. We will see 925mb temps warm
to around 15c for Thursday, which will again allow for highs to get
into the low/mid 70s along/south of I-94. We should over achieve
against guidance by a couple of degrees (as we have been doing this
entire fall in patterns like this), so continued to go at the top
end of the model envelop for highs tomorrow.

For fire weather conditions, south winds will be increasing during
the day, with sustained speeds similar to what we are seeing today
expected out in western/central MN once again. The question for
tomorrow is how quickly does the moisture return. The NAM brings it
back pretty fast, and holds humidities up in the 30s, the GFS is
much slower and shows potential for another day with minimum
humidities in the 20-25% range out in western MN. Again, both fuels
and weather conditions look borderline from the red flag
perspective, so will again advertise the elevated fire weather
condition threat for Thursday in the FWF and HWO, but hold off on
any headlines.

.LONG TERM...(Thursday night through Wednesday)
Issued at 245 PM CDT Wed Oct 18 2017

The forecast concerns for the longer term remain temperature
trends and thunder threat for Saturday.

Friday looks to be breezy and warm ahead of the Dakotas cold
front. We may see some increase in high level clouds as well which
may limit significant warming. Tempered highs some with an overall
blend of previous/super and mix down tool. This did continue to
yield highs in the 70s most areas.

Low level flow increases Friday night and we could see some
showers/isold thunder develop later in the night. Timing of the
cold front should bring it through eastern MN by 00Z Sunday. We
will trail pops off from west to east Sunday night. Thunder
threat does develop into Saturday with some forcing along the
front/upper trough and instability increases with the GFS a little
more unstable than the ECMWF. Still should see MUCAPE 500-1000
J/kg lift out ahead of the front with mid level lapse rates around
7. The 00Z GEFS standardized anomaly was indicating PW`s some 2
to 3 standard deviations above normal with the system. This should
give some heavier rains across the eastern cwa. We have QPF of
one quarter to one half inch so far.

The front exits to the east through Saturday night. We left a
small PoP to the east early Sunday but believe we had some model
issues with the GEM developing a closed low over Great Lakes and
affecting model blend PoPs. Both the 12Z GFS and ECMWF are
faster/more progressive with the trough.

After that, an overall cooling trend develops through midweek
with what appears to be the coldest air of the season dropping
into the region as an eastern CONUS trough develops. This should
drop in some colder Canadian air over the Great Lakes. It doesnt
appear to be really below normal however, with overall
temperatures trending closer to seasonal averages. Some small
chances for precipitation into the midweek as well, as a secondary
cold front drops southeast and some possible light QPF affecting
mainly the eastern cwa into midweek.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1255 PM CDT Wed Oct 18 2017

Nothing but a wind forecast this period as a cold front works
through this afternoon, followed by a warm front tonight. The
cold front is coming in an hour or two slower than what the 12z
TAFs had, so only change to the TAFs was to slow the arrival of NW
winds an hour or two, everything else is trending well, including
the return to S/SW winds late tonight as a warm front quickly
swings through.

KMSP...No additional concerns, with high confidence in the TAF.

Fri...VFR. Winds S 10-15G25 kts.
Sat...VFR. TSRA in aftn. Winds S bcmg W 10-15 kts.
Sun...VFR. Winds W 5-10 kts.




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