Special Weather Statement, NWS Twin Cities, MN

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1258 AM CDT Sun Jul 26 2020

.UPDATE...
Issued at 1258 AM CDT Sun Jul 26 2020

Updated for aviation discusison below.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 332 PM CDT Sat Jul 25 2020

Extensive cloudiness has held back temps a bit through early
afternoon, but breaks are finally starting to reach eastern
Minnesota and a quick rise to near 90 is still expected during the
next couple hours. Heat indices around 100 are being observed
across western Minnesota.

Scattered showers are redeveloping across southern MN into WI as
instability builds near the MCV that is heading eastward. Aside
from this feature, there is little in the way of forcing for
ascent. Confidence is increasing we will see a continuation of
unorganized scattered showers and thunderstorms through Sunday.
Whether any of this can organize and produce a concentrated area
of heavy rainfall and increased flood risk is still the biggest
question. Some CAMs indicate the potential for isolated areas with
several inches of rain in back-building convection across
southern MN. This seems like a very low probability scenario, but
with pwats in excess of 2 inches instantaneous rain rates will be
quite substantial, if only for a brief time.

Dew points will remain high through most of Sunday, then drop off
rapidly behind the cold front as strong dry air advection works
across the Upper Midwest. Lows in the mid to upper 50s are
probable area wide Sunday night, a marked difference from the last
several nights. Because temperatures are not expected to drop
below the mid 70s again tonight, decided to issue a Heat Advisory
for the metro tonight into late Sunday afternoon following the
expiration of the warning. Admittedly, heat indices will be
marginal on Sunday though unless sun can break through like today.
Something interesting of note... if MSP can stay above 80 through
1 AM, it will be only the 32nd day in the record books a minimum
temp of 80 or warmer was observed.

.LONG TERM...(Monday through Saturday)
Issued at 332 PM CDT Sat Jul 25 2020

At the start of the period, an oblong, closed upper-level low will
be located over south-central Canada. This feature slowly moves east-
southeast (passing just south of the Hudson Bay) and, in doing so,
drags its trailing embedded shortwave through the Northern Plains by
Monday afternoon. While the wave will foster lift, the advection of
colder, drier air gives strong support that no precipitation is
expected Monday. In fact, no precipitation is expected until at
least Thursday as we will remain in northwest flow on the backside
of the aforementioned closed low.

Temperatures this week will slowly but gradually increase. Highs are
forecast to be near 80 Monday afternoon while Monday night's lows
will be around 60. Both should increase rather uniformly until
Thursday where highs and lows are expected to be in the mid-80s and
low-60s, respectively. Should also note that the early part of this
week will have little to no clouds but partly cloudy skies do build
in by Thursday.

More concerning is the very weak upper-level flow forecast over the
north-central US after Thursday. It appears that our area will not
be affected by any well-defined troughs or impulses within the near
future. This causes decreased forecast predictability for
precipitation, which is supported by the NBM only spitting out 20%
PoPs at most over our CWA Thursday evening onward. All forecast
models do try to develop a weak impulse somewhere in the central US
by Thursday evening. But, as of now "somewhere" could either mean
the Southern Plains (GFS and ECMWF) or Midwest (GEM). The good news
is that we cannot stay dry forever. The ECMWF and GEM do provide a
little hope of a passing shortwave and precipitation next weekend.
However, only time will tell if this hope is in vain.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1258 AM CDT Sun Jul 26 2020

Thunderstorms generally along the Minnesota River will persist
tonight, keeping KMKT and KRWF in thunder for much of the night. A
few scattered storms have also been developing in southeast MN and
should make their way to KEAU. Meanwhile, west central and
central MN looks to remain storm free through much of the period.
This leaves the biggest question mark for the area north of the
current storms, including KMSP and KRNH. It may turn out that this
area winds up storm free overnight, but this is uncertain due to
some hints of northward development at times. Have added the
potential for a couple of hours of storms around 12Z for this area
just in case. Some energy aloft arrives late morning from the
southwest, and this could start up another round of storms from
southern MN into western WI. Lastly, some MVFR ceilings in
northwest WI may find their way to eastern MN and west central WI
Sunday morning.

KMSP...It is ratyher uncertain whether storms will affect KMSP
through mid morning, but have included a couple hours of storm
potential 12z-14z in case the southern MN storms expand northward.
Otherwise, nest chance of storms will be midday with arrival of
energy aloft and the incoming cold front. Only other concern
would be potential for MVFR ceiling Sunday morning, but that is
more likely to remain north and east of the metro.

/OUTLOOK FOR KMSP/
Mon...VFR. Wind NW 10-20 kts.
Tue...VFR. Wind NW 5-15 kts.
Wed...VFR. Wind N 5 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Flash Flood Watch until 8 AM CDT this morning for Blue Earth-
     Brown-Dakota-Goodhue-Le Sueur-Nicollet-Rice-Scott-Steele-
     Waseca-Watonwan.

     Heat Advisory until 6 PM CDT this evening for Anoka-Carver-
     Dakota-Hennepin-Ramsey-Scott-Washington.

WI...None.
&&

UPDATE...TDK
SHORT TERM...Borghoff
LONG TERM...CTG
AVIATION...TDK

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