Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1048 PM CDT Thursday Sep 3 2015
Short term...(this evening through friday)
issued at 411 PM CDT Thursday Sep 3 2015
A couple forecast topics to discuss in the short term period. For
one...could we see a repeat of the foggy morning we had today? Yes
it is possible again early tomorrow morning with a similar
setup...and very high dew points this afternoon with most locations
exceeding 70 degrees. However...there should be a little more wind
tonight which should help inhibit the density of any fog that does
form. There could certainly be a few dense fog patches
tonight...but at this time we don't expect it to be like last
night/early this morning. Still...soundings indicate saturation by
early tomorrow morning with a strong temperature inversion and
hydrolapse increasing with height.
Tomorrow will be another hot and humid day with heat indices in the
90s and with dew points around 70 making it feel very muggy
outside...similar to today. Lastly...a shortwave will race
northeast from the southwestern Continental U.S....fed but the subtropical
jet...and reach the Dakotas tomorrow morning. Introduced slight
chance probability of precipitation into western Minnesota late tomorrow afternoon as this feature
could produce some shower and thunderstorm activity. Winds will
remain from the southeast through the period as a trough of low pressure
lingers to our west...and deepens tomorrow.
Long term...(friday night through thursday)
issued at 411 PM CDT Thursday Sep 3 2015
Heat and humidity will peak this weekend with a pattern
change/more zonal flow arriving for next week. The threat for
showers and thunderstorms will increase across western/central
Minnesota Friday night as a sub-tropical vorticity rides northeast
across the central/northern plains. Another chance will arrive
Saturday night...ahead of an incoming cold front. The cold front
is set to move across the forecast area Sunday and Sunday night with high
chance to likely probability of precipitation in place. Overall...the most significant
rains look to be northwest of the Twin Cities Saturday
night/early Sunday and then east and south of the Twin Cities
Sunday afternoon and evening. The precipitable water forecasts from the GFS
indicate near record values along and ahead of the cold front
(1.75 to 2.00 inches). Training thunderstorms would have the
capability for producing significant amounts of rainfall as was
witnesses in portions of west central WI Wednesday afternoon.
Hence...although there some threat for severe weather along and
ahead of the front...the concern today is more with the heavy rain
The warmest day in the longer term will likely be Saturday with
middle 80s to lower 90s. This combined with dew points in the
lower 70s results in heat indices pushing into the middle 90s.
Little relief will occur Saturday night with lows in the Twin
Cities near 75. Hence...heat headlines may be needed for portions
of the Twin Cities as we fine tune the weekend forecast. Certainly
those out and about Saturday should take extra precautions due to
the heat and humidity.
Temperatures will be on a downward trend next week with highs in
the upper 70s on Monday dropping to around 70 for Wednesday and
Thursday. 12z long term solutions pointed to lesser chances for
precipitation from Tuesday through Thursday versus the 00z runs.
Confidence on the drier forecast was higher to the west and south
of the Twin Cities. Collaboration with our neighbors in these
areas resulted in a dry forecast with small chance probability of precipitation remaining
to the north and east.
Fog and low stratus clouds are still a concern late tonight. The
air mass hasnt changed and there is still a very humid lower
atmosphere. There wasnt any new rain today and winds will be a
little stronger tonight. This might mean less fog and more
stratus. Are latest thinking is that a band of clouds with
400-1000ft ceilings will develop from northern Iowa and stretch north-northwest
toward west central Minnesota. These clouds are then expected to expand
and drift northeast with time. We think there is a better chance
for visible restriction in Wisconsin given slightly lighter winds and
the climatology of fog at krnh and Keau.
Not a slam dunk by any means...but low clouds could once again be
a problem come tomorrow morning. We think a band of clouds will
first form to the west of the metropolitan and then drift in near the
start of the morning rush. By the 09z taf update...we hope the
clouds will be showing their hand at that point. If were lucky the
development will be minimal and the Airport will not see prolonged
impacts. At this point...its Worth bring in IFR ceilings. Theres
enough evidence even with the uncertainty.
/Outlook for kmsp/
Sat...VFR with MVFR and rain showers/thunderstorms and rain possible late. Wind S at 10g20kt.
Sun...VFR with MVFR/IFR thunderstorms and rain possible. Wind S at 15g20kt.
Monday...VFR. Winds northwest at 10kts.