Scientific Forecaster Discussion
fxus63 kmpx 260435
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1135 PM CDT Mon Sep 25 2017
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 Continental U.S. 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 weather forecast office 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 Minnesota 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
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 06z tafs through 06z Tuesday night)
issued at 1131 PM CDT Mon Sep 25 2017
Ceilings are a bit squirrelly out there tonight, and generally
are higher than expected so far. They should settle into the
IFR/low MVFR range tonight with some LIFR mixed in and in the
heavier rain areas. Stratus should linger essentially through
Tuesday and into Tuesday night at least.
Kmsp...no change from the main discussion.
/Outlook for kmsp/
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.