Scientific Forecaster Discussion
fxus63 kmpx 231957
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
257 PM CDT Tue may 23 2017
Short term...(this evening through wednesday)
issued at 250 PM CDT Tue may 23 2017
Scattered showers/isolated thunderstorms were noted this afternoon
near the core of the upper low centered near La Crosse, WI. This
storm system was broad and encompass most of the upper
Midwest/Great Lakes region. The best moisture advection associated
with the upper low was in southeast Minnesota this afternoon and
this is where the best concentration of showers had occurred.
This area of showers will continue to move south/southeast as the
main storm system drifts southward. Although the showers will
likely end this evening, cyclonic flow will likely keep the cloud
cover through most of Wednesday before slowly dissipating as winds
become more east/southeast during the afternoon. The best area of
receiving more sunshine than clouds will occur in west central
Minnesota where winds will shift to the southeast first.
Long term...(wednesday night through tuesday)
issued at 245 PM CDT Tue may 23 2017
The main topics of discussion in the long term are the frontal
passage likely Thursday night into early Friday morning, and the
longwave trough likely to linger in the region for most of the
Holiday weekend, which will lead to repeat opportunities for showers.
Wednesday night through Thursday will be partly cloudy and
seasonable for temperatures with a high pressure ridge at the
surface and the axis of the upper ridge pushing in. By this point,
the main focus of our forecast is the closed upper low/large trough
over southern Saskatchewan.
That low pressure system will move just a little eastward on
Thursday, and our attention will first be on the southward trailing
cold front. The GFS is quite fast with slamming the cold front
through our area from west to east, reaching Eau Claire by 15z
Friday. However, the ec/NAM/Gem all are 12 or more hours slower so
Friday includes chances for showers and isolated thunderstorms if
that fropa is on the slower side. Either way, any thunder would be
garden variety and do not expect much in the way of appreciable quantitative precipitation forecast
along this front, which could move through dry for many.
From Saturday through Memorial Day it looks as if we will be under
the large upper trough from the aforementioned slow moving system.
We'll likely be looking at temperatures slightly below normal with
repeated chances for diurnally driven showers to develop and
northwest winds lasting through this period. The exact placement of
the low is still in question with the ec being farther north than
the GFS, but either way under large scale cyclonic flow and lapse
rates during the day should support a chance for showers to develop
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1210 PM CDT Tue may 23 2017
VFR, with a brief period of MVFR or IFR is likely this afternoon
as several waves of showers move across central/southern
Minnesota, and west central Wisconsin. Typically, this time of day
cigs begin to rise. But, with ample boundary layer moisture and
several weak waves of energy generating showers, cigs will likely
hold between 3k to 4k. A very brief period of IFR vsby is
possible in south central Minnesota due to a more concentrated
area of showers slowly moving southward. A persistent
north/northeast surface wind will continue as the mean surface low
tracks from southwest Wisconsin, southeast into the Ohio Valley.
MVFR cigs likely will redevelop across northern Wisconsin this
evening, and move southwest across Wisconsin, and the southern
half of Minnesota overnight.
No other changes to aforementioned discussion as mainly VFR
conditions will prevail this afternoon. Only a brief period of
MVFR cigs is possible along with scattered showers thru 02z. MVFR
cigs redevelop after 9z. Northeast wind will prevail thru the taf
period, but remain under 10 kts.
/Outlook for kmsp/
Thu...VFR. Wind southeast 5-10 kts.
Fri...VFR. Chc MVFR/-shra. Wind SW 5-10 kts.
Sat...VFR. Wind west 5-10 kts.