Scientific Forecaster Discussion
fxus63 kmpx 210409 aac
Area forecast discussion...updated
National Weather Service Twin Cities/Chanhassen Minnesota
1109 PM CDT Tue Aug 20 2019
issued at 946 PM CDT Tue Aug 20 2019
Updated grids to warm overnight temps several degrees. Drier air
has been slow to advect in due to the light winds. Dew points
have fallen into the 50s from the Brainerd lakes region and north,
but remain in the mid to upper 60s, and even some low 70s, across
central and southern Minnesota into WI. The forecast now calls for mid
50s to lower 60s, warmest in the Metro and southeast where the
drier air will be slowest to arrive.
Short term...(this evening through Wednesday night)
issued at 323 PM CDT Tue Aug 20 2019
No significant redevelopment of thunderstorms is expected ahead of
the cold front through this evening, thanks in large part to storms
that tracked across the area this morning. Although Storm Prediction Center meso
analysis shows MLCAPE values have built back up to the 1500-3500
j/kg range ahead of the cold front. Forecast soundings from the rap
and NAM show a strong subsidence inversion in place at h8.
Convergence along the front is weak and there's no discernible upper
wave, so this lack of forcing will allow this cap to hold. You can't
completely rule out a stray shower developing along the front north
of I-94 from central Minnesota into western WI, but it looks unlikely given
the lack of forcing. Already this afternoon on radar on satellite,
we've seen a few attempts at initiating convection along the front
from central Minnesota into The Arrowhead, but nothing has ever been able
to sustain itself and expect this trend to continue.
For tonight through Wednesday night, high pressure centered to the
west of Hudson Bay will be nosing into the upper MS valley. This
will result in some of the best weather you can Cook up in Minnesota during
the Summer. The one thing to watch both Wednesday and Thursday is we
will see very deep mixing and will be tapping into a very dry
airmass as we mix deeper. So afternoon dewpoints and humidities will
likely be lower than what we currently have. During the overnights,
the airmass will be too dry to support any widespread fog. Winds
will help make sure we don't see fog tonight, but Wednesday night,
we'll have light/calm winds, so some valley fog will be possible in
the the valleys along the MS south of the St. Croix and up the
Chippewa valley into WI, other than that, it's windows open weather
for the next couple of days.
Long term...(thursday through tuesday)
issued at 323 PM CDT Tue Aug 20 2019
Pleasant, early Fall-like, weather continues into Friday as
troughing extending south from eastern Canada keeps cool
temperatures aloft over the upper Midwest, and high pressure over
Ontario keeps any systems away from the region. Highs are only
expected to reach into the low to mid 70s Thursday afternoon and
cool, dry NE winds off of Lake Superior will keep dewpoints in the
40s and low 50s. Southeasterly flow picks up on Friday as the high
slides off to the east, with temperatures warming a few degrees and
more humid air working into the area.
Precipitation still looks likely this weekend, but trough and
surface front driving the chance for showers and thunderstorms has
slowed by a day or so as the ridge over eastern North America slows
its progress. Friday evening now looks dry across the area and
precipitation may even hold off through most of Saturday across
eastern Minnesota/western Wisconsin as the front slowly
approaches from the Dakotas. Best chance for precipitation now
looks like it will occur from overnight Saturday into Monday,
although timing differences still exist among the models during
this timeframe. Models have trended stronger with the trough and
linger it longer over the region, as the eastern ridge continues
to stall its progress. Models show some pretty heavy quantitative precipitation forecast amounts
Sunday into Monday as showers and thunderstorms linger over the
area and show precipitable water values approaching 2 inches. Will have to monitor
the heavy rain/flooding potential over the second half of the
weekend. Drier weather looks possible Tuesday after the front
passes, as high pressure briefly moves into the region.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1109 PM CDT Tue Aug 20 2019
VFR conditions and northwest winds 5-10 kts expected through the
period. Clouds will continue to dissipate overnight, with high
clouds returning to southern Minnesota Wednesday. Some patchy fog appears
likely later tonight across southern/eastern Minnesota and western WI.
/Outlook for kmsp/
Thu...VFR. Wind NE 5 kts.
Fri...VFR. Wind southeast 5-10 kts.
Sat...VFR. Chc -tsra/MVFR. Wind southeast 10g20 kts.