768
FXUS63 KMPX 181805
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
105 PM CDT Sat May 18 2024

.KEY MESSAGES...

- Low RH values and breezy west winds will result in elevated
  fire weather conditions in western MN today.

- Another round of showers and thunderstorms, some possibly
  severe, in central WI this afternoon and evening may clip Eau
  Claire, Chippewa, and Rusk counties.

- An active pattern set to begin Sunday night. Multiple chances
  for rain, possibly heavy, and thunderstorms over the next
  week. Greatest risk for heavy rain will be on Tuesday.

&&

.DISCUSSION...
Issued at 253 AM CDT Sat May 18 2024

Meso analysis this morning shows a 50+ kt LLJ screaming from
northeast Nebraska up into western MN. Isentropic upglide within
this LLJ was enough to kick off yet another area of convection
overnight, this on the nose of a tongue of warmer than +8C air at
h7. We`ll likely continue to see weak storms pop up through the
morning as this plume of moisture and forcing works across western
WI. Farther west, a combined outflow boundary and cold front was
just about to move into the northwest reaches of the MPX coverage
area at 2am. The airmass out ahead of this front is incredibly warm,
with locations in west central MN still in the mid 70s at 2am. There
will be two concerns with this front. Ahead of the front, we`ll see
instability build during the day, with mlCAPE peaking in the 1000-
2000 j/kg range. As the previous discussion mentioned, it`s a
question of when/where do storms fire along the front today.
Overnight, the HREF showed storms initiating around 22z, likely just
east of the MPX CWA. Still, that initiation looks to happen close
enough to our far eastern CWA to warrant the marginal risk the Day 1
convective outlook the SPC has for eastern Rusk/Chip/Eau Claire
counties. The other hazard with this front will come in its
wake. A dry and deeply mixed environment will move into western
MN this afternoon. Though highs today will be 15-20 degrees
cooler than what we saw on Friday, the airmass will be
considerably drier, with RHs dipping into the upper teens
possible with west winds gusting to around 30mph leading to
elevated fire weather conditions, likely our last such day of
the Spring fire season.

As has been noted the past few discussions, this weekend will begin
another stretch of busy weather, with ample opportunities for rain,
the most significant of which looks to come Tuesday.

First up will be Sunday afternoon into night. The cold front coming
through today will make it about as far south as the MO/IA border
before another LLJ surge sends it back north across Iowa as a warm
front on Sunday. We`ll see the nose of said LLJ move across southern
MN into central WI Sunday night, with another 0.5" to 1" of rain
expected from south central into east central MN and western WI.
We`ll be well north of the better instability, with our activity
remaining elevated, so the severe threat will be low once again.

We get a break Monday afternoon and evening and then another system
will head our direction out of the central Plains Monday night. This
will bring a deepening sub-1000 mb mature surface low along a
roughly Omaha to Duluth line. The cold conveyer belt and
frontogenesis to the west of the low looks to be a rather efficient
rainfall producer, with a large footprint of 2-4 inches of rain over
a 12-18 hour window expected west of the low track (in the winter,
this would be the zone of highest snowfall amounts). Given the
currently expected track of the low, this looks most likely from
western through central MN. To the east of the low, a severe threat
will likely develop. Although the best instability looks remain down
in northeast Iowa, anywhere as far west as the surface low could see
a severe threat develop, which for us would mean something to keep
an eye on for areas in/around southeast MN. From the flooding
perspective, this looks to be more of a potential issue for river
flooding as we head toward Memorial Day weekend as opposed to an
excessive rain/flash flood risk as the rain is falling. See the
hydrology section for more info on the potential flood threat.

After the Tuesday system, model agreement starts to deteriorate.
However, from the middle of next week into Memorial Day weekend, we
will maintain lower h5 heights across southern Canada, with numerous
shortwaves rotating around the trough across the northern CONUS. It
looks like we`ll have wrap around moisture from the Tuesday system
continue into Wednesday, a break from the wet weather on Thursday,
with the next potential for rain coming either Friday or Saturday
given current timing differences. Looking at the EPS mean h5
pattern, this active pattern does look to start shifting until after
Memorial Day.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 105 PM CDT Sat May 18 2024

The front at 18Z extended from far east central MN to south
central MN with a healthy field of cumulus to its east, and some
showers, especially in Wisconsin. In the wake of the front, west
to northwest winds were often gusting around 25 knots and this
should continue into early evening. A few thunderstorms will
develop this afternoon to the east of KEAU, but KEAU could see a
brief showers. Not enough of a chance to mention, though.

After that, a surface high will track across Iowa tonight with
winds shifting from the west to south overnight. The next wave
of incoming mid/high clouds will arrive Sunday morning in
western MN and spread into Wisconsin during the afternoon.

KMSP...The main concern will be northwest winds gusting to 25-30
knots this afternoon in the wake of the front. Any showers this
afternoon should be well east of the airfield.

/OUTLOOK FOR
KMSP/ SUN...VFR. MVFR/SHRA likely late. Wind SE 10-15kts.
MON...MVFR/-TSRA thru mrng. VFR chc SHRA aftn. Wind SE 5-10kts.
TUE...MVFR/-TSRA likely. Wind NE 10-15 kts.

&&

.HYDROLOGY...
Issued at 253 AM CDT Sat May 18 2024

The heavy rain event for Tuesday currently highlights the
potential for a large footprint of 1 to 3 inches of rain, with
some locations pushing 4 inches to hit much of the upper MN
River Basin. Gauges at Montevideo, Granite Falls, and Morton are
still at or near minor flood stage and if the kind of rainfall
amounts we are currently seeing were to fall in the upper MN
basin, then renewed flooding along the Minnesota River upstream
of Mankato will be possible as we head into Memorial Day
weekend.

&&

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

&&

$$

DISCUSSION...MPG
AVIATION...TDK
HYDROLOGY...MPG