Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Twin Cities/Chanhassen Minnesota
1202 am CDT Tuesday Oct 25 2016
Short term...(this evening through tuesday)
issued at 400 PM CDT Mon Oct 24 2016
Tonight and tomorrow morning are the lull before the storm. There
is an impressive low pressure system off the Pacific northwest
coast that is spreading moisture across the entire western Continental U.S.
And rockies. Ridging has set up across the center of the U.S. And
high pressure has settled overhead in Minnesota/WI today. Tonight, a
shortwave will take shape across Wyoming/Montana and head across the Dakotas
by tomorrow morning. The response at the surface will be a slowly
deepening low that will track across NE/South Dakota throughout the day
tomorrow. High clouds will be on the increase during the morning,
but the deep moisture and widespread rain chances really don't
arrive until late tomorrow afternoon and tomorrow evening. There
could be a couple warm advection bands of showers/light rain as
early as tomorrow morning in western Minnesota, but that rain will come
from high-based clouds and the rain shouldn't be persistent or
heavy in intensity until the surface low approaches after sunset.
Long term...(tuesday night through monday)
issued at 400 PM CDT Mon Oct 24 2016
The longer term concerns remain timing of the upper trough moving
through the area Tuesday night into Wednesday night along with the
quantitative precipitation forecast and thunder threat.
Strong moisture feed ahead of the upper trough along with strong
forcing should be enough to generate at least some isolated thunder
over mainly the southern quarter of the state into Tuesday night.
Most deterministic models drive this east during the night and
across mainly the eastern portion of the cwa into Wednesday morning.
Better moisture feed rides across far southern Minnesota as well. Quantitative precipitation forecast
forecast continues to have a swath of 1 to 1.7 inches of rain over
the southeast half of the region during this period. This currently
looks a pretty reasonable forecast.
Clouds will linger through much of Wednesday...especially to the
east as an inverted trough moves slowly to the east. A few light
showers will linger east of this trough. High temperatures will
struggle to warm through the 40s to around 50.
Drying follows into Thursday as a surface high pressure area moves
through. A southerly wind will redevelop later Thursday and this
will draw limited moisture north as the next short wave move through
on Friday. A small chance of showers will be retained with this
system...mainly to the east. Temperatures are expected to warm out
ahead of the frontal system...with some lower 60s likely over the
southern third of the area.
Models diverge some on handling the next short wave. The GFS
becomes more amplified with ridging over the central Continental U.S. Keeping
the area dry through the weekend. The 12z European model (ecmwf) resolves a flatter
flow...with an embedded short wave moving through the area on
Saturday. For the moment we will follow the GFS...which gives most
of the cwa a dry and breezy Halloween.
Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1202 am CDT Tue Oct 25 2016
VFR conditions through tonight and at least Tuesday morning.
Then, rain will develop across southwestern Minnesota early
afternoon Tuesday, spreading northeast into the evening hours.
MVFR or IFR conditions will follow the onset of the rain.
Kmsp...VFR through Tuesday, then deteriorating conditions early
Tuesday evening. IFR conditions are possible by mid to late
/Outlook for kmsp/
Wed...MVFR/IFR with -ra early. Wind east-northeast 5-10kt.
Thu...VFR. Wind vrb 5kts.
Fri...VFR. Wind S 5-15 kt.