Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
134 PM CDT Monday Sep 22 2014
Short term...(today and tonight)
issued at 417 am CDT Monday Sep 22 2014
Today-tonight...surface analysis shows the center of a large area of
surface high pressure over the middle Mississippi River valley with nearly
meridional flow aloft...helping enhance cold air advection this morning. Colder air
over residual moisture with clear skies and calm winds is helping
promote some patchy fog development...but any fog will burn off
shortly after daybreak. Surface high pressure atop the region
underneath incoming ridging aloft from The Rockies will spell lots
of sunshine with slightly warmer temperatures today due to increasing 500 mb
heights. Surface high pressure is expected to shift off to the east during the
day today while the ridge aloft moves ovhd through tonight. Return southerly
flow on the backside of the high means low temperatures Tuesday morning will not
be as cool as what is experienced this morning. However...there will
be a slight increases in clouds tonight...mainly over southwestern Minnesota...in
response to a shortwave trough aloft over The Rockies. In eastern
portions of the County warning forecast area...where the center of high pressure will still
have some influence...winds will go calm again with the coolest
temperatures in the County warning forecast area so patchy fog looks to again develop over
western WI westward to the Minnesota state line. No precipitation is expected in the
Long term...(tuesday through sunday)
issued at 417 am CDT Monday Sep 22 2014
Sensible weather highlights for the extended period revolve around
upper level ridging bringing warm and dry conditions through the
end of the week. The only exception is late Tuesday into Wednesday
when a weakening upper level wave will move across the upper
Midwest and spread clouds over MN/WI. Aside from the high
confidence in clouds...a few light rain showers are possible as
well...especially across the western County Warning Area. The low level dry air
and lack of elevated instability will keep most locations
dry...but continued with small chances for showers. Temperatures
will continue to run 10 to 15 degrees above the seasonal average
for late September.
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 110 PM CDT Monday Sep 22 2014
For the first 6 hours...expecting westerly to southwesterly winds
to persist Arkansas about 5-10 knots across most of the area. Negative
cumulus rule correctly assessed cumulus development main east of the
Minnesota/Wisconsin border...with few cumulus spreading slightly west
into eastern Minnesota. Did add a tempo for MVFR ceilings at Eau
Claire for the this afternoon given thickening cumulus deck there.
Winds will slacken near sunset and remain generally light and
variable overnight...especially across western WI as the surface
high and ridge axis slide east of the Chicago area tonight.
Inserted fog into the taf for rnh and eau for overnight into
tomorrow morning. Crossover temperatures in the middle to upper 40s in
western WI indicate saturation should occur tonight and given
clear skies and very light wind...redevelopment of fog appears
likely. Left fog out of stc because winds may be able to cause
just enough mixing to prevent saturation.
Kmsp...a few cumulus will develop this afternoon but otherwise clear
skies expected until late tomorrow. Its much more difficult to
saturate in the metropolitan so left fog out of taf for tomorrow
morning...but there should be some fog in nearby river valleys. West
to west-southwest winds will turn to southerly by 00-01z and remain southerly
through Tuesday. Middle/high clouds start to show up near the end of
the taf ahead of an approaching upper level shortwave trough.
/Outlook for kmsp/
Wednesday...VFR...but MVFR ceilings possible overnight. Winds south-southeast 12-15 kts.
Thursday...VFR. Winds S 5-10 kts.
Friday...VFR. Winds south-southeast 5-10 kts.