Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1045 PM CDT Sat Jul 30 2016
Short term...(this evening through sunday)
issued at 253 PM CDT Sat Jul 30 2016
While high pressure is still generally prevailing across the area
before departing to the east tonight, a weak surface trough over
far southeast Minnesota into NE Iowa combined with modest convergence evident over
the same region in WV satellite imagery is allowing for isolated
showers/thunderstorms over southeast portions of the coverage area.
Focused mainly along and east of I-35 and along and south of I-94,
in east-central and southeast Minnesota into west-central WI, showers and
storms that have formed are slow-movers with little duration so
aside from some brief heavy downpours, will not look for much
development or coverage through the rest of the daylight hours.
Partial clearing tonight will linger into tomorrow though a
lingering mid-level trough and weak disturbance passing through
the region looks to be enough to spark off additional isolated
showers/storms over southwestern Minnesota during the day tomorrow.
Again, not looking for anything strong/severe but some may well be
slow-movers which could produce brief heavy downpours.
Temperatures will run fairly similar tomorrow as today, possibly
1-3 degrees warmer tomorrow with high pressure exiting and a
stronger backside southerly flow bringing in slightly warmer and
slightly more moist air from the deep south.
Long term...(sunday night through saturday)
issued at 253 PM CDT Sat Jul 30 2016
Things look to be somewhat unsettled across the area for much of
the week, with chances for showers and thunderstorms, although
the most significant precipitation looks like it north and south
of the area. We'll initially see the upper ridge build over the
area into Monday, before a piece of the shortwave trough currently
over British Columbia moves across southern Canada and pushes a
weak front through the region on Tuesday, with northwest upper
flow returning for a time. A more significant upper trough will
track farther south during the Wednesday/Thursday time frame, with
a sub-1000 mb low moving across southern Canada in association
with it. Although the guidance is similar in the overall evolution
of things, there are timing differences in the deterministic and
ensemble solutions. The GFS remains quicker with the front in
comparison to the European model (ecmwf) and Canadian. The GFS would bring the
front across Wednesday night, while the other solutions wait until
Thursday afternoon. The timing could certainly play a role in any
severe weather potential, as we should have decent instability
back in place across the area. However, the better large scale
forcing and deep layer shear looks to be to our north during that
time frame. For now, given the spread in ensemble solutions, can't
go all-in on any particular solution, and keep some pops over the
area into Thursday night.
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1045 PM CDT Sat Jul 30 2016
The concerns for this taf period are the extent of any br/haze late
tonight along with any MVFR or lower ceilings. Lamp probabilities
and thresholds remain consistent this evening on developing MVFR
or lower visibilities in br after 09z at the taf sites. Therefore
left the earlier trend on development in place. However,
probabilities are not that high for MVFR or lower ceilings, which
was the case back at 31/00z, and was the main reason on not adding
widespread ceilings. The only taf really under the gun remains
kstc. For this taf cycle, raised the tempo ceilings at kstc to
bkn020. Thunderstorms and rain chances look less now for late tonight across
western Minnesota so continued with not mentioning anything at krwf.
There is a small threat for rain showers/thunderstorms and rain developing Sunday afternoon
across eastern Minnesota/western WI, very similar to today, but with the
activity mainly isolated, didn't mention anything in the taf at
this time. Light southeast winds overnight increasing to around 10 knots
by late Sunday morning.
Kmsp...only minor tweaks made to the 00z taf for 06z. Otherwise a
small threat does exist for rain showers/thunderstorms and rain for Sunday afternoon but
the chance/coverage is minimal at this point with no mention in
the taf. Winds similar to those described above.
/Outlook for kmsp/
Mon...mainly VFR. Chance MVFR/tsra. Winds southeast 5-10 kt.
Tue...mainly VFR. Chance MVFR/thunderstorms and rain early. Wind light/variable.
Wed...mainly VFR. Chance MVFR/thunderstorms and rain late. Wind southeast 5-10 kt.