Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
317 PM CDT sun Sep 21 2014
Short term...(this evening through monday)
issued at 317 PM CDT sun Sep 21 2014
Quiet weather this period as departing upper low departs the region
to the east. Afternoon visible satellite imagery shows cumulus field in
the cyclonic flow on the back side of the upper low is quickly
eroding in eastern Minnesota and western WI. A thicker cloud deck across
western Minnesota wont be so quick to diminish...but should dissipate by
this evening as subsidence moves in with the anti cyclonic flow from
the incoming high pressure area currently positioned over the
Dakotas. The ridge axis associated with the high will move over the
area tonight and under clear skies...a decent chance for fog
development exists. The high itself will sink just south of the
forecast area. Any fog will dissipate quickly early tomorrow
morning as winds pick up to 5-10 miles per hour and the temperatures increase
with bright sunshine. Monday will be clear and dry. Slightly
decreased temperatures tonight into the 40s everywhere under light
winds and clear skies.
Long term...(monday night through sunday)
issued at 317 PM CDT sun Sep 21 2014
A rather uneventful and high confidence forecast for the long
term. Two of the biggest forecast challenges were 1. Whether the
upper low ejecting northeast into the Midwest from California
would produce any rain during the middle of the week...and 2.
Whether temperatures later this week would be pleasant or very
Models continue to shear out the energy as it approaches the
region Monday night and Tuesday. In addition...surface ridging is
now shown to extend a bit further west from the Great Lakes which
will lead to more dry air entrainment from the southeast.
Therefore...confined probability of precipitation to western Minnesota Tuesday afternoon
and Tuesday night when the lift is expected to be strongest...with
a dry forecast now for Wednesday and Wednesday night across the
entire County Warning Area as the system opens up and its moisture is diminished.
The strange vorticity prognosticated to dive south around the western ridge late
in the week on the Canadian and GFS for is now gone. Models are in
rather good agreement through the period with an expansion of an
anomalously warm middle level ridge across much of North America...
centered over the upper Midwest/Great Lakes by Friday. Temperatures
are forecast to inch upward each day this week and top out in the
upper 70s to lower 80s /possibly warmer/ by Friday and Saturday
before slowly declining by early the following week as the ridge
begins to break down. The cfs actually hints at the ridge remaining
intact or building a bit further into early October. Regardless...there
are still plenty of good weather days ahead as astronomical autumn
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1249 PM CDT sun Sep 21 2014
Main focus today is cumulus field wrapping around the back side of the
upper low that is moving east across the Great Lakes. Much of
eastern Minnesota and western WI has quickly seen the cumulus field become
scatter and that trend will continue this afternoon. Expect VFR
ceilings for stc and areas east. A thicker cloud deck to the west
continues streaming southward and will continue MVFR ceilings at axn
and rwf for the next few hours. Trimmed back on the wind gusts
given trends have been a bit less windy overall through the day so
far. Winds will remain northwesterly...and the cumulus field will
continue to diminish to clear skies tonight. Clear skies and light
winds from the west to southwest through tomorrow are expected.
Kmsp...VFR ceilings expected through the period. However...will have
to watch the thick cloud deck to the west as the upper low pushes
eastward. Currently anticipating this Dec to scatter out this
afternoon and even if broken ceilings move back in to msp...should be
above 3k feet due to daytime heating.
/Outlook for kmsp/
Tuesday...VFR. Winds S 10 kts.
Wednesday...VFR. Winds S 10-15 kts.
Thursday...VFR. Winds south-southeast 5-10 kts.