Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 251154

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
654 AM CDT SUN SEP 25 2016

Issued at 640 AM CDT Sun Sep 25 2016

Updated to include 12z aviation discussion below.


.SHORT TERM...(Today and tonight)
Issued at 326 AM CDT Sun Sep 25 2016

Today and tonight...Surface analysis this morning shows a north-
south cold front along nearly the entire western MN/Dakotas
border with a slight warm sector holding strong in far SW MN.
The main surface low feature associated with these fronts is in
far southern Manitoba province. Aloft, deep southerly flow
continues to stream plenty of moisture into the area in advance
of a deep cutoff low over western North Dakota and this low is
maintained within a longwave trough emanating from north-central
Canada. Coverage thus far early this morning is not entirely
impressive but a pocket of low-level jetting, evidenced by a
small disturbance showing up on WV satellite imagery, is punching
north through eastern Nebraska and western Iowa. Better coverage
of precipitation is associated with the feature aloft but as the
overall pattern presses east, so will the better coverage of
precipitation. As such, aside from possibly an isolated pocket or
two of heavy rain, am not expecting much better coverage of
precipitation within the WFO MPX coverage area than currently
ongoing so am opting to discontinue the Flash Flood Watch prior
to 12z this morning. There is also quite the lack of instability
along with unimpressive lapse rates so am not looking for
anything in the way of strong thunderstorms. Even lightning is few
and far between with this activity. As this precipitation
moves east, a deep dry slot is still indicated on multiple
models immediately behind the cold front but in advance of the
upper level low. This will allow for some brief clearing, or at
least a rise in clouds to higher levels. As the upper level low
rotates northeast toward southeast Manitoba province, the trough
axis will open up and expand southward. The cooler core aloft
combined with trapped moisture within the base of the trough will
spark scattered rain showers moving in from the west and
northwest later this afternoon and evening. The showers will
linger over northern and eastern portions of the coverage area
through daybreak with low clouds also holding strong over much of
the area this evening through overnight tonight. Post-front,
temperatures today will be noticeably cooler and remain as such
through tonight. Highs today will only hit the 60-70 degree range,
which is some 15 degrees cooler than readings recorded over
western and southern Minnesota yesterday. Lows early Monday
morning will drop to the 45-50 degree range.

.LONG TERM...(Monday through Saturday)
Issued at 326 AM CDT Sun Sep 25 2016

Forecast concerns in the extended period deal with the evolution of
an Upper Low forecast to develop and intensify over the Great Lakes
early next week, and slowly drift southward.

Last week`s upper air pattern had been more progressive with a
fast southwest flow aloft and a very potent long wave trough
along the west coast. This long wave trough has progressed eastward
over the Rockies and into the plains, providing ample moisture to
the Upper Midwest overnight. Things will dramatically change over
the next two days as models continue to forecast an Upper Low
forming over the Great Lakes. This will lead to much cooler
conditions as the flow becomes northwest-north across the Upper

As an Upper Ridge forms north of this Upper Low, a blocking type
pattern will develop, leading to slow changes in the weather
department, especially over the Great Lakes. The GFS had been more
persistent in previous runs of this Upper Low development, and now
the latest EC/GEM have come more in line with this scenario.
Therefore, confidence has increased for this cooler pattern with
instability showers rotating around this Upper Low as it drifts to
the south next week and weakens. An Upper Ridge will slow begin to
build south and west across the Rockies by late in the week. This
ridge will build over the Upper Midwest next weekend. Therefore,
temperatures will slowly begin to modify with above normal
temperatures once again by next weekend. I don`t see any
widespread or organized precipitation pattern once todays system
moves off to the east-southeast.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 640 AM CDT Sun Sep 25 2016

Tricky start to the 25/12z TAFs are there is the combination of
progressively-moving light rain and a combination of IFR and MVFR
conditions. The bulk of the problems is tied to the movement of a
cold front currently in western MN. KRWF and KAXN have already
seen the wind shift to westerly with partial clearing so the front
is making progress. It looks to move through all sites by early
afternoon which will result in all sites briefly becoming VFR
post-front. However, a deep upper level low will follow the front
into the Great Lakes area, where residual deep moisture will be
available for MVFR ceilings and possibly some drizzle/mist or some
light showers. This second lighter round of precip will continue
for much of the night for central MN into western WI. When winds
become westerly, they will likely increase to the 15-20G25-30kt

KMSP...MSP starting out straddling the MVFR/IFR line but has
recently risen out of IFR so will likely start with low-end MVFR
which will then become VFR in short order...followed not too
longer after by a return to MVFR with the descending upper level
low from southern Manitoba. Not expecting much in the way of
precip to reach as far south as KMSP so have opted to keep things
dry this afternoon and evening. However, precipitation cannot be
ruled out altogether so that may be a change needed later
depending on the evolution of the upper low. If anything, a
potential precipitation window for -shra looks to be 18z-02z. This
would then be followed by VFR for tonight into Monday morning.

Tue...Chc MVFR early then VFR. Wind NW 10-15 kts.
Wed...VFR. Wind N 5 kts.
Thu...VFR. Wind light and variable.


.MPX Watches/Warnings/Advisories...
WI...Flash Flood Watch until 10 AM CDT this morning for WIZ023>028.

MN...Flash Flood Watch until 10 AM CDT this morning for MNZ063-070-

     Flash Flood Watch until 7 AM CDT this morning for MNZ076-077-



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