NWS Forecast Discussion

816
FXUS63 KMPX 191057
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
557 AM CDT Mon May 19 2025

.KEY MESSAGES...

- Soaking rain arrives today through Tuesday night. Highest
  chances for rain in western into southern MN while lowest
  chances are north of I-94. Severe weather is not expected.

- 2.5" to over 3" of rain is expected for western to southern
  MN today into Wednesday.

- Drier and warmer for the second half of the week.

&&

.DISCUSSION...
Issued at 321 AM CDT Mon May 19 2025

Cloud cover has spread over nearly all of our entire region early
this morning as southerly flow streams in moisture ahead of our next
weather system. Only our far northern WI counties have cooled enough
to where areas of frost are possible. The forecast for our next
system Monday into Wednesday remains mostly on track. Showers and
thunderstorms currently over the Central Plains will continue
lifting north-northeast tonight within the low-level warm conveyor
belt of moisture. The initial surge of precip will reach
southwestern MN near sunrise but should be losing steam as it moves
away from the synoptic lift and instability. Still, CAMs do show a
decaying, weak MCS-like feature moving northeast into southern MN
this morning. Questions remain on how far this feature persists but
did add in 40-60% PoPs that translate northeast through our southern
MN counties.

Additional northward moving showers and thunderstorms should focus
over southwestern and western MN by early this afternoon as a low
pressure center over SD occludes. Precipitation will slowly make its
way east into this evening as it advances ahead of an arching cold
front. However, did try to delay the rain`s arrival for eastern MN
(including MSP) and WI by a few hours. Forecast soundings delay
large-scale vertical saturation until at least after 7 PM tonight
for these regions. During Monday night, the upper-level trough
driving the entire system will become negatively tilted over the
central CONUS as a second jetstreak rounds the base. Large amounts
of synoptic scale lift and a south-southeasterly LLJ of moisture
will focus over the Upper Midwest (with secondary surface
cyclogenesis occurring over IA). The result will be the formation of
a large stratiform shield of rain across the entire southern halves
of MN and WI late Monday night. This feature should remain mostly in
place (besides its long axis pivoting counter-clockwise around the
low to the south) Tuesday into Wednesday; leading to a long-duration
rainfall event. The good news with this event is that MUCAPE will be
very low to zero, meaning we won`t have widespread convectively
enhanced rainfall. But, the Grand Ensemble still produces at least
1.5" of mean QPF into Wednesday south of I-94. Amounts climb over 2"
for western to southern MN with the Twin Cities near the edge of the
probabilistic gradient for this amount. Areas near Mankato and south
to the MN/IA border currently have the best chance at seeing the
most rain. The 50th percentile QPF of the EPS and GEFS both have
over 2.5" in this region. Amounts jump to well over 3" when stepping
up to the 75th percentile! Currently, have 3.0-3.5" of rain forecast
for south-central MN but localized areas could see amounts go even
higher if some convection does manage to occur. Widespread flooding
will likely not be an issue, but don`t be surprised if ponding of
water occurs, especially in low-lying areas.

It should also be mentioned that it will be very breezy Monday
through Tuesday with the strong LLJ and deepening surface lows.
Winds Tuesday morning look to be especially strong, particularly
across southeast MN and western WI where gusts could reach 40 MPH.
The 00Z HREF has mean wind gusts of 45 to even 50 MPH in this
region! Though, this ensemble can be known to over-forecast
winds. Still, this will need to be watched in case a wind
headline is needed for Tuesday morning.

Guidance begins to slightly diverge during Wednesday with regards to
how quickly precipitation dissipates as the low pressure system
slowly exits east into the Ohio Valley. Each deterministic model
keeps a northwest to southeast band of precip draped from the
Dakotas through MN and into WI along what seems to be a trailing
stationary front. This precip should taper off as we get later into
Wednesday but, a few more tenths of an inch of rain may occur if it
holds on longer than expected. The forecast finally quiets down by
Thursday as northwesterly flow brings in drier air. Guidance
suggests this northwest flow to last through the end of this week
with temperatures rebounding towards normal. Currently have mid 60s
and very low PoPs forecast Thursday through Saturday so it should be
a pleasant end to the week. An impulse or two in the upper-level
flow could bring back rain chances near the start of next week, but
forecast certainty is low at this time due to model spread.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 554 AM CDT Mon May 19 2025

We begin VFR with high level CIGS for all but EAU as -SHRA will
spread across all TAF sites from SW to NE, beginning in RWF at
~14z and reaching EAU/RNH by 00-02z. Winds will likewise
increase as the surface low nears with a consistent 060-090
direction increasing to 20G30kts. -TSRA is possible for a 3-4
hour window, however with such a cool airmass it may just end up
being a few rumbles rather than legitimate TS. CIGS are expected
to drop to MVFR as -SHRA increases in intensity, roughly 6-8
hours after it arrives at each individual site.

KMSP...The main change from the 06z TAF was tightening the
window for -TSRA based off the RAP from 00-03z. The confidence
in legitimate TS is low, such that a few rumbles are the main
expectation due to the cooler airmass.

/OUTLOOK FOR KMSP/
WED...MVFR/-SHRA early, then VFR. Wind NE 10-15kts.
THU...VFR. Wind N 10-15kts.
FRI...VFR. Wind NE 5-10kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.

&&

$$

DISCUSSION...CTG
AVIATION...TDH

NWS MPX Office Area Forecast Discussion

Script by Ken True @Saratoga-Weather.org