Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 212354

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
654 PM CDT Mon May 21 2018

Issued at 634 PM CDT Mon May 21 2018

Updated to include 00z aviation discussion below.


.SHORT TERM...(This evening through Tuesday)
Issued at 246 PM CDT Mon May 21 2018

The secondary trough will continue moving through the area this
afternoon and tonight, with plentiful low level moisture and
modest lift persisting but lifting north of the area later this
evening. Scattered showers will continue slowly lifting north, and
QPF values will be very insignificant, generally less than a tenth
of an inch.

With the increased low level moisture and winds becoming quite
light tonight, expect fog to develop overnight. Western MN will be
the most susceptible to potentially dense fog, especially in the
wake of the showery activity that moved through today.

The trough will slowly depart to our east tomorrow as gradual
clearing is anticipated to ensue late in the day. Highs tomorrow
should rebound into the mid to upper 70s.

.LONG TERM...(Tuesday night through Monday)
Issued at 246 PM CDT Mon May 21 2018

The main concerns in the long term period are the rain amounts for
Wednesday through Thursday night and the chance for severe weather
Thursday/Thursday night. Split upper level flow does present a
problem for shear parameters, but instability and moisture will be
ample Thursday/Thursday night.

By tomorrow night, the next shortwave will be quickly approaching
from the southwest with showers and thunderstorms expected to
spread into southwestern MN overnight into Wednesday morning. An
increasing LLJ will provide ample low level moisture convergence
and lead to enhanced lift, tapping into some modest instability.
Precipitable water values will increase to about 1.5", maybe
slightly higher.

The latest guidance for Thursday holds off convective initiation
across western MN to Thursday night as the shortwave arrives from
the west, steepening the lapse rates quickly as mid/upper levels
cool. MUCAPE values around 3000 J/kg will be ample to produce
strong to severe thunderstorms, but shear parameters are weak,
particularly in a deep column, which limit supercell potential.
More than likely, multicell clusters are possible and cold pool
development could lead to forward propagating clusters. Some
severe hail could be possible with that amount of CAPE, but with
the lack of shear, don`t expect widespread severe weather at this
time. Continue to monitor for the latest updates.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 634 PM CDT Mon May 21 2018

Main issue will be fog developing after midnight through daybreak.
Winds going light/variable to calm while a warmer and more moist
airmass arrives will spell fog development over much of the area
during the early morning hours. Many sites are already dealing
with MVFR ceilings and the sites that aren`t currently, will be in
short order this evening. Decoupling with moisture pooling in the
lower levels will allow for low stratus and fog development,
likely into the IFR range, during the pre-dawn hours and lasting
through sunrise. Gradual improvement is expected as winds pick up
out of the southeast by late Tuesday morning.

KMSP...Ceilings likely to drop below 1700ft before midnight and
remain as such through late Tuesday morning. IFR conditions likely
through the morning push due to fog and low ceilings. Conditions
will improve to VFR by midday with no problems expected in the
afternoon and evening.

WED...Mainly VFR. Chance SHRA/TSRA with MVFR. Wind SE 5-10 kts.
THU...Mainly VFR. Chance SHRA/TSRA late. Wind S 10 kts.
FRI...Mainly VFR. Chance SHRA/TSRA late. Wind SW 5-10 kts.




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