Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
625 PM CDT Monday Aug 3 2015
Short term...(this evening through tuesday)
issued at 313 PM CDT Monday Aug 3 2015
A pleasant weather pattern will persist across the forecast area through
Tuesday as high pressure from the Dakotas to Iowa moves slowly over
Minnesota and WI. The rather extensive cumulus/SC from Mille Lacs to Red Wing
on eastward this afternoon...in response to the cyclonic flow and
colder air aloft...will dissipate early this evening. This pattern
will shift eastward by tomorrow afternoon with only few-scattered cumulus/SC
across the aforementioned area. Mixing this afternoon has lowered
surface dew points into the middle 40s across west central through
portions of south central Minnesota with upper 40s to lower 50s pretty
much elsewhere. Relative humidity levels this afternoon have
reached the 35 to 45 percent range across much of the Minnesota County Warning Area.
Afternoon humidity levels will lower to about this same range on
Tuesday and extend more into western WI. Lows tonight are
forecast to reach the upper 40s to lower 50s...with the exception
of the Twin Cities where around 60 is indicated. Highs on Tuesday
will be similar to today...with readings about 2 degrees warmer.
Long term...(tuesday night through monday)
issued at 313 PM CDT Monday Aug 3 2015
Would really like to see the medium range guidance come into
better agreement on the forecast details from middle-week Onward...
but that would still be an inaccurate statement. There is
agreement on some aspects of the large scale upper air pattern...
with all solutions indicating the current upper low influencing
our area will shift eastward and the pattern will become somewhat
zonal over northern tier of the Continental U.S. With upper lows over British
Columbia and Quebec. However... there will be a northern shortwave
feature moving through our area and a southern shortwave working
into the Ohio Valley during the Wednesday/Thursday time frame. The
GFS/S 12z run was considerably faster with the northern wave...
but maintains a similar track and precipitation potential for the central
and southern portion of our area... albeit 12 to 24 hours sooner.
The NAM is similar but slower than the GFS... and more compact
with its surface reflection... and holds precipitation closer to the Iowa
border as a result. The European model (ecmwf) focuses things farther north/west...
and is also slower than the GFS... while the Gem is somewhat of a
peacemaker and comprises with all solutions. The ensemble guidance
does little more than indicate there is uncertainty and most
possibilities are plausible. After the midweek system... attention
turns toward the weekend with the next main shortwave feature
prognosticated to move along the US/Canadian border sometime in the
Saturday through late Sunday time frame. Once again... there is
agreement on this general idea... but considerable disagreement on
timing... location... and amplitude. The one period where there is
some better agreement on details is Friday... with most guidance
and the expected pattern suggesting mainly dry across the area.
So... Friday will generally have the lowest probability of precipitation for the Thursday
through Sunday time frame. Otherwise... disagreements on low
confidence still lend themselves toward bracketing a fairly long
period of time with low/middle chance probability of precipitation. At the tail end of the
period... it looks like warmer temperatures and more humid
conditions could work back into the area Monday as upper ridging
builds over the area.
Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 625 PM CDT Monday Aug 3 2015
VFR through the period. Cumulus will be dissipating this evening... and
northwest winds will taper off. Some sections in west central to south
central Minnesota may see variable winds late tonight...but this is more
likely to occur Tuesday when ridge axis begins moving across Minnesota.
West central wisc may have some 10-15 knots gusts from the northwest Tuesday
afternoon...but most of the forecast area will see winds generally
staying below 10 kts.
Kmsp...VFR through the period. Some chance of variable wind
direction late tonight but should generally be northwest. Speeds late
tonight will be 5 knots or less.
/Outlook for kmsp/
Wednesday...VFR. Wind southeast 5-10 kts.
Thursday...mainly VFR. Chance MVFR shra/tsra. Wind southeast 5-10 kts.
Friday...mainly VFR. Chance MVFR shra/tsra. Wind east 5-10 kts.