Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 261953

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
253 PM CDT Tue Sep 26 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 251 PM CDT Tue Sep 26 2017

The short term concern remains clearing trend overnight and possible
fog development to the west.

Water vapor imagery still showing southwest flow over the eastern
portion of the cwa...with the upper low over North Dakota. Some
drier air/subsidence under the exiting trough did bring some breaks
in the clouds to the west, but thicker clouds remain farther west
into the eastern dakotas. Models suggest we should maintain cloud
cover to the east overnight with perhaps some clearing to the west.
There is a pressure gradient over the region, which should relax as
the night progresses. The surface ridge builds into the southwest
by Wednesday morning and this should provide light winds and some
fog development. We did mention some areas of fog to the west,
per trend in the namnest and NSSLwrf. With clouds remaining to the
east and clearing to the west, temperatures should drop close to
the blended guidance.

Any fog/stratus should burn off early Wednesday with sunshine
prevalent during the day. Once again, blended guidance temperatures
looks good.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 251 PM CDT Tue Sep 26 2017

Main concern during the extended is timing a fropa and precip
chances in the Sunday night through Monday night time frame. We did
not make any significant changes to the initialized blended
forecast, as model agreement is pretty strong through Saturday, while
timing differences with the fropa Sunday/Monday lend best to
sticking with a blended approach.

For the rest of the work week, the upper trough working across MN
today will continue heading east into northeast Canada. In it`s
wake, we`ll see trough build into the Great Lakes, while an upper
level ridge works into the western CONUS. This will place us in
northwest flow and a cooler/drier air feed. There is one wave
dropping down on Thursday, but it will be going across the Arrowhead
into central lower Michigan, so it`s precip will go to the east of
the MPX CWA and all it will do is drag a dry cold front across our
area. We`ll see a brief warmup Thursday ahead of the front with
highs sneaking up into the 70s, but cooler air will follow to end
the week.

This weekend, we`ll see another strong jet and associated h5 low
come crashing into the Pac NW. The lead shortwave with this will
track from south to north across the High Plains on Saturday and
though passing to our west, we will see strong temp/theta-e
advection Sat/Sat night move across the area. Though forecast
soundings show rather dry low level, the forcing may be enough to
kick off a few showers Sat/Sat night, but better precip chances will
occur with the cold front. Here, model spread actually increased, as
the GFS and especially ECMWF sped up the timing of the front and
precip, while the Canadian/MPAS are still are much slower. Given the
strength of the quasi-zonal jet coming across the northern Rockies,
the faster solutions of the GFS/ECMWF seem more plausible for this
weekend, which would mean rain more Sunday/Sunday night as opposed
to Sunday night/Monday. Kept thunder out of the forecast for now as
h85-h5 differential theta-e and best LIs are trending positive as
the front works through as we lose instability locally.

Behind this system, models are showing a strong ridge building into
the southern Plains, with our weather taking another trip to well
above normal temperature territory during the first week of October.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1255 PM CDT Tue Sep 26 2017

Mainly mvfr cigs across the region. Latest GOES16 vsbl showing
some drying/breaks developing to the west in the wake of the
upper trough and exiting surface front. Expect cigs to become BKN
most areas through the afternoon with perhaps a lingering
sprinkle/light -shra to the east early. Some clearing into the
west during the evening could spell some stratus/fog development
later tonight and did mention it to the west. Not sure how much
clearing will occur to the far east so left that out for now. Any
fog that does develop should burn off through about 14z-15z Wed
with more sunshine expected. w-nw sfc winds a bit gusty into the
afternoon then becoming light w-nw overnight. Should be lightest
to the southwest as the ridge arrives.

MVFR cigs should become vfr into the evening with the cloud deck
possible remaining from east central MN into eastern WI
overnight. Appears wind swill remain up much of the night and may
preclude widespread fog development. Will have to maintain watch
for this into tonight.


Wed night...VFR. Winds WNW 5 kts.
Thu...VFR. Winds WNW bcmg NW 10 kts.
Fri...VFR. Winds N-NNE 5-10 kts.




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