Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 311932

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
232 PM CDT Sun May 31 2020

.SHORT TERM...(This evening through Monday night)
Issued at 231 PM CDT Sun May 31 2020

Surface analysis shows the center of high pressure over the Ohio
Valley while a frontal system becomes more organized over the
northern Rockies, associated with a low pressure center over
southern  Alberta province. Aloft, a sharp ridge axis aligned over
the Plains continues to slowly move east.

Being on the backside of high pressure combined with the
approaching ridging aloft is producing widespread clear skies
this afternoon, with only some cloud cover over far southwestern
MN. The upper ridge will gradually flatten out overnight through
Monday, with a more downslope flow with several buckles within the
generally WNW-ESE flow atop MN/WI by Monday evening. In
conjunction with these upper features, the warm front out west
will budge across the Dakotas tonight and move into southwestern
MN by daybreak Monday morning. Still evident in the modest is
strong low-to-mid level jetting of around 50kts with still
relatively colder air aloft. Moisture return will not be overly
impressive with much of the additional moisture progged to be in
the area tomorrow being advected in with the frontal system while
only minor amounts from the south. Nevertheless, isolated to
scattered showers and thunderstorms can be expected to develop
over west-central MN and curve ESE through east- central MN into
western WI. While coverage will not be all that impressive,
conditionally some storms could be strong to severe as lapse
rates, strong shear, and sufficient MUCAPE will be available for
storms to tap. The main hazards look to be large hail and damaging
winds. The timing of storms looks to be from shortly after
daybreak to the early afternoon hours.

Going into the evening hours, the more broader ridge from the
Dakotas to the Deep South will slide east just a bit, putting a
cap in place for the rest of the short-term period. The warm
front will slide across WI and into MI Monday night into Tuesday
morning while the cold front pushes across MN and into
northwestern WI while settling across far southern MN. The warm
sector of this system will make for very warm and humid conditions
Monday into Monday night. After lows tonight in the mid 50s to
mid 60s, highs on Monday will surge to the lower 80s in western WI
to the lower 90s in western MN. The corridor from the Twin Cities
down to Mankato will run in the 86- 89 degree range. With
dewpoints tomorrow in the low-mid 60s, heat index values will run
near 90 to the low 90s for much of the WFO MPX coverage area. Then
nearly no cold air advection Monday night despite a nearly
frontal passage, lows will hold in the mid-to-upper 60s for much
of the area.

.LONG TERM...(Tuesday through Sunday)
Issued at 231 PM CDT Sun May 31 2020

By Tuesday, upper-level ridging will be centered over western
Ontario with the 850 mb thermal ridge shifting through the
Northern Plains. This will allow for another day of very warm
temperatures with forecast highs near 90. Just behind the ridging
is a weak shortwave trough that will bring our next chance for
thunderstorms (some possibly severe) Tuesday afternoon and
evening. Initial storms are forecast to form in eastern South
Dakota and move east with time. Steep mid-level lapse rates
associated with the 850 mb thermal ridge will be located over
South Dakota and southwestern Minnesota contributing to upwards of
3000 J/kg MLCAPE. The nearby jetstreak within the upper-level
shortwave will allow for vertical wind shear values of nearly 50
knots across west-central Minnesota. These variables together will
allow for supercells with damaging hail possible across southwest
Minnesota. Additional storms should form across southern
Minnesota with time however, shear decreases rapidly in this
region where multicell/mixed mode are more favored. Storms are
forecast to merge and grow upscale Tuesday night and hail and
damaging winds will be possible across southern Minnesota.

One major caveat does exist for Tuesday`s setup: Forecast GFS and
NAM low-level moisture values at MPX on Tuesday evening are near
or above the climatological maximum. However, forecast low-level
wind fields do not show an overly strong connection with this
moisture to the Gulf of Mexico. On the other hand, the ECMWF is
more conservative with dewpoints near 70 across southern
Minnesota. Lesser amounts of moisture would affect how much
instability is realized.

After Tuesday, temperatures will cool slightly but we are still
forecast to have highs as much as 10 degrees above normal through
the rest of the period. More zonal upper-level flow will move over
the Northern Plains by mid-week and Wednesday should be quiet and
sunny. However, another chance for thunderstorms for the CWA is
forecast on Thursday/Thursday night as an embedded jetstreak
within the flow will pass thru northern Minnesota. The GFS and
ECMWF differ on convective timing as the ECMWF`s jetstreak arrives
later and more in line with peak diurnal heating. This would
favor greater coverage of storms while the earlier arriving GFS
favors precipitation in west-central Wisconsin Thursday night.

By Friday, the upper-level pattern will undergo a large change as
the cutoff low located west of the Baja Peninsula is forecast to
merge into the northern stream. This system will travel
northeastward from the southwest US and possibly affect our region
by with precipitation by Saturday evening. However, large
differences between the GFS and ECWMF exist on the location and
timing of the precipitation. Thus, forecast confidence is
currently low.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1244 PM CDT Sun May 31 2020

VFR conditions expected through tonight. Clouds will lower to
5kFT-6KFT this afternoon/evening as the next system approaches the
area. Showers with this system look like they will split around
most of the Minnesota terminals and most should stay dry, except
for AXN where the chance of a shower is higher. For RNH and EAU,
there should be showers around in the morning hours. Winds will be
primarily from the S/SSE and gusty for the western terminals, and
lighter in the east. There is a chance for some low level wind
shear overnight in the early morning hours.

KMSP..Showers approaching with the next system look to go well south
of the Metro area so kept the TAF dry.

Tue...VFR with a chance of MVFR/TSRA. Wind WSW 5 kts.
Wed...VFR. Wind NW 5-10 kts.
Thu...VFR with a chance of MVFR/TSRA. Wind NW 5-10 kts.




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