Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 221809
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
109 PM CDT Fri Sep 22 2017

.UPDATE...For 18z Aviation discussion below

&&

.SHORT TERM...(Today and tonight)
Issued at 400 AM CDT Fri Sep 22 2017

As of 3AM this morning, the warm front had lifted to the I-94
corridor from Alexandria toward St Cloud, with a mostly capped
environment in the warm sector.  However, accas was fairly
widespread across the state of Iowa and quickly advancing northward.
So, convection is trying across that region and a few cells have
overcome the cap but remain very isolated.

In the vicinity and north of the front though, more widespread
thunderstorms continue to develop early this morning. Expect storms
to move east through central MN through the mid morning hours.  The
warm front will lift north of the forecast area today, with a cap in
place through the day.  850mb temps will soar to near +25C by this
afternoon and southerly flow will bring winds of 15-20 with gusts to
30 MPH as the surface low works through the eastern Dakotas through
northern Minnesota tonight.  Still expect highs in the upper 80s and
low 90s with dewpoints in the low 70s to make for apparent
temperatures in the upper 90s to about 100 degrees this afternoon.
Wet bulb globe temperatures look to reach the lower 80s this
afternoon across most of southern Minnesota and west central
Wisconsin.

The cold front will remain mainly to our west through the evening,
but will begin to encroach on western MN overnight.  With this
boundary comes our next chance of thunderstorm activity.  Due to the
SW to NE orientation of the front, the highest pops overnight are
across much of northern MN extending to the SW encompassing much of
western MN.  Expect eastern MN and western WI to remain dry
overnight with that front reaching western MN by 12Z.

.LONG TERM...(Saturday through Thursday)
Issued at 400 AM CDT Fri Sep 22 2017

Saturday/Saturday night will be wet across the northwestern 1/4 of
MPX forecast area. As with previous discussions, the abnormally
high PWAT values combined with a nearly stationary front, and several
rounds of thunderstorms, will lead to the potential of flooding.
Later shifts may need to see if a Flood Watch needs to be issued
in portions of west central/central Minnesota. Currently WPC has a
slight risk of excessive rainfall on Saturday/Sunday for portions
of west central/southwest and central Minnesota.

After Saturday night,

Although models /EC, GFS, GEM/ are similar in the evolution of the
break down of the upper ridge across the Great Lakes, and mean
trough over the western 1/4 of the CONUS by Sunday night, there
remains a few differences past Sunday.

First, how much energy is left in the Rockies once the mean trough
out west de-amplifies, and one of the short waves move across the
Northern Plains, Upper Midwest by Tuesday? Both the GFS/EC hold more
energy across the southern Rockies compared to the GEM. The GEM
keeps a more progressive long wave trough moving across the Northern
Plains/Upper Midwest by midweek. Although this is similar to the GFS
by late in the week, both these models have a more significant short
wave diving southeast across the Midwest compared to the EC. This
will have considerable differences in the weather next week on which
model is correct. The best approach is to continue a more ensemble
mean which leads to a less amplified short wave diving across the
Midwest. Plus, an upper ridge begins to build back across the
northern Rockies, leading to milder conditions late next week, and
into the first week of October. In simple terms, the abnormally warm
weather will turn more seasonable by early next week, along with a
round or two of showers and thunderstorms, especially late
Monday/Tuesday as the mean short wave ejects across the Upper
Midwest. Drier and more seasonable temperatures will return by
Wednesday/Thursday, with questionable conditions by Friday, and into
next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 110 PM CDT Fri Sep 22 2017

We should be shower & thunderstorm-free through this eve now that
the nocturnally-driven activity has ended and the low/mid level
temperatures are building. Sct-bkn mid level clouds will be
around through most of the period. South/southeast winds will
become gusty this afternoon, then lose the gustiness this eve with
low level wind shear becoming a concern into the overnight hours
(for KSTC/KMSP/KRNH/KEAU). The cold front will be entering western
MN at 06z tonight. Showers and thunderstorms may develop along the
front late tonight into the early morning hours. Have maintained a
PROB30 at KAXN, but confidence/potential is too low to include at
other sites at this point. MVFR level cigs behind the front will
also be possible on Saturday, primarily at KAXN/KSTC during this
TAF period.

KMSP...
VFR expected through tomorrow morning with the potential for low-
end VFR clouds by 18z Saturday. Low level wind shear tonight is
the only other concern, with TS/SHRA activity expected to stay to
the west through Saturday afternoon.

/OUTLOOK FOR KMSP/
Sun...Mainly VFR. Slight chance MVFR/TSRA. Winds SW 5-10 kts.
Mon...MVFR/TSRA. Winds S 5-10 kts.
Tue...Chc MVFR/TSRA early. Winds NW 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Heat Advisory until 7 PM CDT this evening for WIZ023>026-028.

MN...Heat Advisory until 7 PM CDT this evening for MNZ054-056>070-
     073>078-082>085-091>093.

&&

$$


SHORT TERM...SPD
LONG TERM...JLT
AVIATION...LS


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