Area Forecast Discussion
Issued by NWS Twin Cities, MN
FXUS63 KMPX 300921
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
421 AM CDT TUE AUG 30 2016
.SHORT TERM...(Today and tonight)
Issued at 420 AM CDT Tue Aug 30 2016
Showers and a few thunderstorms continue early this morning across
southern MN and portions of west central WI, with the most
concentrated activity in the MN River Valley. A combination of the
ARW, NMM and NSSL WRFs were used as guidance for the precipitation
placement today. They would suggest that the precipitation
diminishes rather significantly by daybreak with only small chances
in the far south through the morning. This coincides well with
deterministic solutions showing the right entrance region of the
upper jet, which has been across central MN and northern WI
overnight, weakening and moving east. In addition, a shortwave from
near the Twin Cities to Sioux Falls will be pushing into southern WI
and northern IA as the morning progresses.
In the mean time, it looks as though the extensive cloud cover over
all but NW portions of the FA may keep dense fog from forming. Still
concerned that central MN could deteriorate quickly just before
daybreak given the 4+ inches of rain that fell Monday evening from
KSTC on northeast through Milaca in addition to the 2 to 4 inches of
rain that fell around Alexandria Monday morning. Winds across this
area are nearly calm with the cold front overhead. The front will
slip south this morning with light northerly winds enveloping the FA.
Cloudiness will be on the decrease with a good amount of sunshine
for the CWA during the afternoon. Bias corrected temperature data
indicates highs around 80 from the Twin Cities to Eau Claire today
with middle to upper 70s elsewhere.
We finally start to dry out tonight with regards to the dew
points as high pressure builds in. Still expect lows near 50
across central MN as well as along highway 8 in WI. Readings in
the lower to middle 50s elsewhere except in the Twin Cities where
upper 50s prevail.
.LONG TERM...(Wednesday through Monday)
Issued at 420 AM CDT Tue Aug 30 2016
In the long term, we will have at least 4 and maybe 5 days to dry
out before we get into another active pattern Saturday night that
lasts through the Tuesday following Labor Day. Tuesday through
Thursday will be some of the best weather days we have seen all
summer with highs in the 70s, low humidity, sunshine and light
winds. The south winds look to get cranking Friday and Saturday,
with rain chances starting to pick up significantly Saturday night.
Through the extended, models do not differ significantly on the large
scale pattern evolution, with an amplified trough/ridge/trough
(western NOAM/central NOAM/eastern NOAM)pattern developing the rest
of the week. This weekend, the pattern shifts east enough where we
get into an active SW flow aloft, with multiple rounds of showers
and thunderstorms expected Saturday night through Tuesday of next
For Tuesday through Friday, dry high pressure will setup shop from
Hudson Bay down through the Great Lakes and all the way into
northeast TX. It will be hard to beat the weather these days with
highs/lows right near normal and dewpoints comfortably in the 50s.
As we get into Friday, the surface high will shift east enough to
allow a tight pressure gradient to move into the upper MS Valley.
Forecast soundings on the GFS still show gusts to around 30 mph
developing Friday in the west, with that type of wind shifting
across the rest of MN for Saturday. In addition, the GFS continues
to slow its eastward progression of precip out of the Plains states
at the end of the week and is now nearly in line with the ECMWF in
bring precip into the MPX area in earnest Saturday night. Pops are
now gone from Friday night and only slight chances are left during
the day Saturday out in western MN, though they are dwindling with
each forecast update.
Saturday night, the upper ridge finally shifts far enough east to
allow moisture to surge back into the upper MS Valley. This moisture
will surge into the area ahead of a cold front associated with a
deep surface cyclone that will be going across far northern Canada.
Being this far south, the front quickly becomes parallel to the
upper flow, which means it stalls out over the upper MS Valley by
Sunday. Where we finally start getting into some model disagreement
is with a significant upper wave that will be riding up along the
front around Labor Day. The GFS is the strongest with the wave, with
a surface low eventually moving across MN on Tuesday while ECMWF
takes a weaker low across WI, also on Tuesday. At either rate, both
the ECMWF and GFS are showing another shot at seeing fairly
widespread QPF amounts between 2 and 4 inches Saturday night through
Tuesday. PWATS increasing to around 2 inches again this weekend will
fuel yet another excessive rainfall threat, while the initial
moisture surge coming through Saturday night/Sunday will have around
40 kts of wind at 850, so a severe threat will likely evolve with
time, especially on Tuesday when the surface low arrives, depending
on where it tracks.
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1219 AM CDT Tue Aug 30 2016
TSRA sinking slowly southward early this morning through the Twin
Cities, KRNH and KEAU. This activity is well ahead of a cold front
that was located over central MN between KAXN and KSTC at
midnight. Two concerns for early this morning, first is that the
convection is back building to the west and may impact KRWF in the
07z to 09z time frame while the TSRA from the Twin Cities on east
continues to sink slowly south and weaken early this morning.
The second concern overnight is the threat for dense fog with
VLIFR conditions. Much of this will depend on how fast clouds
dissipate early this morning, if at all. The site where
confidence is highest is KSTC where over 4 inches of rain fell
this evening. KRWF...KRNH and KEAU may also see these low
conditions if clouds dissipate.
KMSP...+TSRA until 07z then SHRA through 08z with the rain
expected to be over for the rest of the night. A cold front
across central MN will pass the airfield around 12z with north
winds less than 10 knots through the day on Tuesday.
/OUTLOOK FOR KMSP/
WED...VFR. Wind NNE 5 kts.
THU...VFR. Wind E 5 kts.
FRI...VFR. Wind SSE 7-10 kts.