Area Forecast Discussion
Issued by NWS Twin Cities, MN

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549
FXUS63 KMPX 240926
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
426 AM CDT SAT SEP 24 2016

.SHORT TERM...(Today and tonight)
Issued at 420 AM CDT Sat Sep 24 2016

A very amplified long wave trough is evident across the western
United States with an Upper Ridge centered across the mid section
of the nation. This has led to a very deep, and tropical
moisture plume surging northward across Texas and into the
Northern Plains early this morning. This very anomalous moisture
plume will move across the Upper Midwest later today and lead to
high rainfall rates once thunderstorms develop.

Recent flooding and the continued runoff from swollen creeks and
rivers, will be aggravated from any additional rainfall. Although
it would be wise to issue a part of southern Minnesota in a
flash flood watch due to this conditions, models depict a more
rapid movement of the areal coverage of the precipitation later
today/tonight. This may limit the overall rainfall amounts and be
more localized on anything more than an inch or two. Therefore, am
not issuing a watch at this time, but morning forecasters need to
pay attention on areal coverage once thunderstorms develop this
afternoon. Some of the ensembles are not depicting high rainfall
amounts either, and more of an isolated high total, other than
widespread amounts that we had earlier this week. Severe weather
parameters also are limited due to the lack of sunshine today.
However, wind shear values and lapse rates indicate the potential
of a few large hail stones and gusty winds in the far western and
southwestern part of MPX CWA.

Timing of the rainfall remains close to previous forecast with
western Minnesota having development between 18-21z, with eastern
Minnesota expecting the activity after 00z. Due to the amplified
long wave trough and boundary layer winds nearly parallel to the
mean upper winds, precipitation may linger in eastern Minnesota
and western Wisconsin longer. This is also something to think
about in terms of flooding if rainfall last longer than expected.

.LONG TERM...(Sunday through Friday)
Issued at 420 AM CDT Sat Sep 24 2016

Sunday and Monday...The period will commence with a potent cold
front nearly aligned along the MN/WI border while a cutoff upper
level low straddles the ND international border. A narrow dry slot
will follow the cold front for the first part of Sunday but then
the upper low will open up and expand, allowing for stratus
development with scattered rain showers over mainly northern and
central portions of MN and WI. The upper low will strengthen and
drop back into the Great Lakes region Sunday night into Monday,
keeping the low clouds and scattered showers in place for mainly
northern and eastern parts of the WFO MPX coverage area through
Monday morning. The upper low will then steadily rotate eastward
during the day Monday, allowing for gradual clearing late day
Monday and Monday night. The post-frontal airmass and associated
cloud cover will make for noticeably cooler temperatures Sunday
into Monday. Highs will range from 60-70 degrees on Sunday then
fall further on Monday, only hitting the upper 50s to lower 60s.

Tuesday through Friday...Deep ridging at the surface and aloft
will be the main story for much of the upcoming week behind the
departing aforementioned low pressure system. Gradually increasing
500mb heights along with mainly clear skies will allow for a slow
warming trend as the week progresses. Highs will climb back to
near 70 degrees by the latter half of the week with no
precipitation expected until possibly Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1045 PM CDT Fri Sep 23 2016

Downward ceiling trend to IFR/LIFR overnight at all of the TAF
sites still looks good with many locations in the MN River Valley
already under 010. Ceilings will be slow to rise on Saturday as
a warm front along the IA/MN border lifts slowly north. A cold
front will move into the eastern Dakotas late Saturday afternoon
with TSRA developing ahead of the front in western MN and
spreading eastward during the evening and overnight hours. The
storms will contain torrential downpours.

KMSP...Ceilings will be dropping below 010 by 09z and likely stay
there through mid morning (16z). Indicated improvement to low VFR
ceilings during the afternoon. This may be too aggressive as not
all ceiling guidance is indicating this but with the tightening
pressure gradient and increased mixing ceilings should rise to
035. TSRA will likely pass across the Twin Cities a few hours
either side of midnight with a tempo group indicated.

/OUTLOOK FOR KMSP/
Sun...MVFR/-SHRA early, bcmg VFR. Wind W 10g20kts.
Mon...Chc MVFR/-SHRA. Wind WNW 10g15kts.
Tue...Chc MVFR early then VFR. Wind NW 5-10kts.

&&

.MPX Watches/Warnings/Advisories...
WI...None.
MN...None.
&&

$$

SHORT TERM...JLT
LONG TERM...JPC
AVIATION...RAH



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