Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 252322
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
622 PM CDT Mon Sep 25 2017

.UPDATE...
Issued at 622 PM CDT Mon Sep 25 2017

Updated to include 00Z aviation discussion below.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 315 PM CDT Mon Sep 25 2017

Surface analysis this afternoon indicates a surface low at the
southern tip of Hudson Bay with a trailing cold front extending SW
through Lake Superior into far southeastern Minnesota and continuing
into northeastern Nebraska. Extensive high pressure then takes up
much of central Canada into the Northern Plains. Aloft, A deep
western CONUS trough lingers over the Rockies with a ridge from the
Great Lakes south through the central Gulf of Mexico. There had been
little impetus for the front to shift off to the east over the past
couple days but the upper level trough is expected to lift out which
is helping shove the front to the east. The front is still within a
slot of deeper moisture and instability, hence the breaking out of
thunderstorms over the Wisconsin portion of the WFO MPX coverage
area this afternoon. However, the deepening of the trough aloft and
strengthening of the northern stream jet will allow for more
widespread showers to develop this evening through much of the
overnight hours for much of the coverage area. A cutoff low within
the trough will spin out of the Plains to the Minnesota/Canada
border by midday tomorrow, keeping rain in place for much of the
time along with low overcast. Rainfall amounts are not expected to
be excessively high but from central Minnesota eastward, areas can
expect close to a half inch of rainfall accumulation. As high
pressure makes inroads to the area by late day tomorrow, skies will
start to clear out and drier air will move into the region. The
other main story will be the end of the abnormally warm
temperatures. While inner west-central Wisconsin enjoyed
temperatures into the lower 80s today, with the remainder of the
coverage area having highs in the mid 50s to mid 60s, highs on
Tuesday will range from the mid 50s in western MN to the mid 60s in
western WI. Lows tonight will fall to the upper 40s to lower 60s.

.LONG TERM...(Tuesday night through Monday)
Issued at 315 PM CDT Mon Sep 25 2017

Canadian high pressure will build across the region setting the
stage for seasonably cool and dry weather this week. An upper
level wave will move across the Upper Midwest and bring slightly
warmer temperatures along with a chance of rain late this weekend
and early next week.

Early afternoon water vapor imagery together with GFS 500mb
heights and winds identified a high amplitude longwave trough over
the Rocky Mountains. Over the next few days, this trough will
eventually form a cut off low as a shortwave slides down the west
coast. Meanwhile northwest flow will develop over the Upper
Midwest with large scale subsidence resulting in surface high
pressure for the middle of the week lasting through much of next
week.

Eventually this surface high will shift eastward and the upper
level low will lift northeast bringing ascent across the region
late Sunday into Monday. The ejection of this wave will be driven
by a strong jet that will crash onshore the Pacific Northwest, so
should see the best chance for widespread rain Sunday night into
Monday, especially across northern and western Minnesota.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 622 PM CDT Mon Sep 25 2017

Frontal boundary currently located near or just east of the
forecast area will move very little overnight, with occasional
showers riding northeast along the baroclinic zone in the wake of
the front. A surface wave will develop along the front late
tonight and Tuesday morning, which will then lift northeast toward
Lake Superior by Tuesday afternoon. This will help to produce
better cold air advection and subsidence across our area, which
will work to end any lingering precipitation and raise ceilings,
with scattering out of the lower clouds probably not occurring
until Tuesday night. Until then, we`ll have widespread IFR and
low-MVFR conditions across the area.

KMSP...Main uncertainties are the timing of the arrival and
departure of IFR conditions, and the possibility of brief LIFR
conditions early Tuesday morning. Stayed fairly close to the
previous forecast, and kept things in the IFR range for now.
Timing of arrival/departure of the worst conditions could vary by
several hours from forecast, so amendments may be needed.

/OUTLOOK FOR KMSP/
Tuesday overnight...VFR. Northwest wind less than 10 kt.
Wednesday...VFR. Northwest wind less than 10 kt.
Wednesday night...VFR. Variable wind less than 5 kt.
Thursday...VFR. Northwest wind 5 to 15 kt.
Thursday night...VFR. North wind around 10 kt.
Friday...VFR. North wind 10 kt or less.

&&

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

$$

UPDATE...
SHORT TERM...JPC
LONG TERM...JRB
AVIATION...



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