Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 220428

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1128 PM CDT Thu Sep 21 2017

Issued at 1117 PM CDT Thu Sep 21 2017

Updated to include 06z aviation discussion below.


.SHORT TERM...(This evening through Friday)
Issued at 355 PM CDT Thu Sep 21 2017

A surface warm front will continue to lift north across the area
tonight. Surface dewpoints have already moderated into the upper
60s over southern MN this afternoon. As low level moisture
advection increases this afternoon, hi-res models continue to
indicate the potential for isolated showers to pop up this eve.
The more concentrated activity looks to develop around/after 05z
over central/northern MN/WI as the low level jet strengthens.
Anticipate most of this activity to stay north of the Interstate
94 corridor.

Tomorrow expect the nocturnal activity to wane as the CAP builds
in the warm sector. The primary forecast concentration
transitions to how warm we will get, with near-record temperatures
in the forecast. Progged Bufkit soundings indicate we will mix to
between 875-900mb, which would yield highs mostly in the upper 80s
to lower 90s. Given the elevated dewpoints in the lower 70s, heat
indices along and south of I-94 moderate into the 95 to 100
degree range. Given the breezy southerly winds, the true impact
may be abated slightly, but Wet Bulb Globe temperatures still look
to rise into the lower 80s across the metro area. While this is
somewhat borderline for a typical heat advisory day, we do meet
advisory criteria for much of the metro, and given heat
acclimatization has been non-existent given the cool August we
had, issued an advisory for the TC metro for tomorrow afternoon.

.LONG TERM...(Friday night through Thursday)
Issued at 300 PM CDT Thu Sep 21 2017

The longer term concerns remain timing/evolution of the western
conus trough and movement of the surface front.

The front will slowly move into western Minnesota overnight. Day2
outlook continue to paint slight risk of severe thunderstorms in
the vicinity of the front. We should be capped until the front
moves into the area. Models trend a weak surface low traveling
across eastern South Dakota into northwest Minnesota during the
night and this should help move the front east into Minnesota.
Severe weather parameters continue to favor large hail and
damaging winds, with a small tornado threat along and north of the
path the surface low.

We trimmed the eastern extent of the PoP forecast with some leeway
given the small eastward progression of the front on the 12z
ECMWF. Still looks like it should mainly affect the western and
central portion of the area through the day Sunday. This will
leave the eastern cwa in the heat and humidity, but shouldn`t be
as extreme as Friday afternoon. The thunder threat will continue
with the frontal boundary through at least Monday with the slow
passage of the upper trough and surface front into Tuesday. Heavy
rainfall remains a threat as well, with the NAEFS anomalous PW`s
showing around 3 standard deviations through the weekend.

The front exits the east Tuesday followed by cooler and drier
conditions through at least midweek.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1117 PM CDT Thu Sep 21 2017

Convection is now breaking out over central and northern MN in
response to a northward punching warm front and a lingering cold
front near the border with the Dakotas. Can expect scattered
coverage around KAXN with diminishing coverage dropping south to
the I-94 corridor with no precipitation expected south of I-94.
Window for precip is generally 06z-12z so only partly cloudy skies
are expected for much of the day on Friday (along with the very
warm temperatures). The other issue will be strong nocturnal
jetting both overnight tonight and again tomorrow night into
Saturday morning. Directional component plus the speeds around 50
knots will create LLWS conditions.

KMSP...LLWS conditions expected through the morning push on Friday
with SE surface winds and SW winds up to 2 kft at around 50 knots.
Mixing after daybreak will blend those winds aloft down to the
surface, creating breezy southerly winds all day. Chances are
quite low for overnight convection so have opted to run with a dry
TAF this cycle but will monitor radar and amend as needed. LLWS
conditions are again expected tomorrow night.

Sat...Mainly VFR. Slight chance MVFR/TSRA. Winds SSW 5-10 kts.
Sun...Mainly VFR. Slight chance MVFR/TSRA. Winds SW 5-10 kts.
Mon...MVFR/TSRA. Winds S 5-10 kts.


MN...Heat Advisory from 1 PM to 7 PM CDT Friday for MNZ060>063-



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