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549
FXUS63 KMPX 220557
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1257 AM CDT Wed May 22 2024

.KEY MESSAGES...

- Severe weather threat quickly diminishing this evening.

- Strong synoptic winds near 50 mph late this afternoon and
  evening in western Minnesota.

- Heavy rainfall is still expected, leading to an increased
  risk for river flooding going into the holiday weekend.

- Active pattern remains in place with several large systems
  bringing additional rain Friday and Memorial Day.

&&

.DISCUSSION...
Issued at 350 PM CDT Tue May 21 2024

TODAY AND TONIGHT...Severe weather is still on track for this
afternoon and evening across much of south central Minnesota
and western Wisconsin. At the surface as of 18z, there are two
low pressure centers; one in far southwest Minnesota and a
second, stronger one near Omaha. The Minnesota low and its
associated warm front have lifted north into central Minnesota
this afternoon and has resulted in the warm sector making it
north of the Twin Cities metro. Previously, there was a lot of
uncertainty regarding how far north this would extend and thus
uncertainty with thunderstorm coverage on the northern and
western edge of this complex system. Further south with the
second, stronger low, a line of severe thunderstorms is
currently pushing into western Iowa. This activity should
continue to move east/northeast at a pretty good clip through
mid afternoon and eventually reach southern Minnesota by around
20z. With the clearing and strong advection of moist unstable
air across south central Minnesota, these storms should be able
to sustain themselves through western Wisconsin this evening.
CAMs and other guidance continue to highlight three main threats
with this event: the risk for all modes of severe weather,
heavy rain and flooding, and very strong synoptic winds on the
backside of the low.

For the severe risk...as mentioned above, all modes of severe
weather are expected this afternoon into this evening with the
highest threat across southern Minnesota and west central Wisconsin.
This is highlighted in the SPC SWODY1 discussion as well as PDS
Tornado Watch 277. Thunderstorm wind gusts in excess of 80 MPH,
isolated very large hail up to 4 inches, and strong (EF2+) tornadoes
are possible. A special 20z MPX sounding will hopefully give us more
insight to the environment, but CAMs and forecast soundings continue
to show very high shear/helicity and moderate MUCAPE values (1000-
1500 J/kg) with higher values 2000 J/kg + in extreme southeastern
Minnesota/Iowa/western Wisconsin. UH tracks have been fairly
consistent in moving across far southeastern Minnesota into western
Wisconsin with a second area further to the northwest across the
Twin Cities metro through 00z.

For the heavy rain/flash flood threat...CAMs are showing impressive
rainfall rates of 1-2"/hour with the storms as they move through.
Per the MPX 12z sounding, PWs were around 1.2" but have likely
increased to near climatological max. The other concern is the
training of storms and recent rainfall across southern Minnesota
over the past few days. This will likely create an elevated flash
flood threat. Additionally, the Twin Cities metro will be
susceptible to flash flooding given the potential for impressive
rainfall rates. This could coincide with the evening rush hour and
will need to be monitored closely.

For the strong wind threat...As the two previously mentioned lows
merge and deepen a little bit more by this evening, 45-50kt synoptic
wind gusts are possible across western Minnesota. A Wind Advisory
remains in effect for this region through 04z. These winds will
diminish below advisory criteria as the low pulls away to the west,
but gusts of 30-35kts are likely across central Minnesota (including
the metro) through 07-08z. Elevated northwesterly winds will remain
in place through Wednesday morning.

WEDNESDAY THROUGH MONDAY...High pressure will briefly settle in
for Wednesday and Thursday as the departing storm system lifts
to the northeast. A few showers will develop in the afternoon
along and north of I-94. Thursday will by dry, with northwest
winds becoming more southerly ahead of the next system that will
bring widespread rain Thursday night into Friday. Convergence
along this boundary is quite impressive, with southerly winds
south of it, and northeast winds on the poleward side. Did
increase precipitation chances toward the higher end of
guidance, as it looks like nearly all locations will see rain.

There will be a brief break in this system, but then another
shortwave trough will move across the region over the second
half of Memorial Day weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
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Issued at 1250 AM CDT Wed May 22 2024

Precipitation is nearly ended for all TAF sites at
initialization, save for a few stray straggling showers at the
WI sites which will last no more than an hour. MVFR ceilings are
still prevalent over eastern MN through western WI to start.
These ceilings will slowly erode to the east through sunrise,
with VFR conditions expected at all sites by late morning. Cloud
decks will gradually lift and coverage will continue to decrease
through the day into tonight, although there is a small chance
of a few wrap-around showers to the north and east of MSP this
afternoon, but nothing that should last long nor be overly
impactful. Breezy W winds will persist through late this
afternoon with speeds generally topping out around 15G25kts,
with a few speeds in western and southern MN close to 20G30kts.
After sunset, speeds will diminish to 10kts or less.

KMSP...No additional precipitation is expected throughout this
duration but ceilings will remain degraded up to around sunrise,
then rise into VFR levels by the tail end of the morning push.
Cloud coverage will continue to diminish through the day while
winds remain breezy from 270-290 direction. Speeds will diminish
from early this evening onward.

/OUTLOOK FOR KMSP/
THU...VFR. Wind W 10 kts.
FRI...VFR/MVFR with -SHRA/TSRA likely. Wind SE 10-15 kts.
SAT...VFR. Wind SE 05-10 kts.
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&&

.HYDROLOGY...
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Issued at 321 PM CDT Mon May 20 2024

Given the setup for widespread heavy rainfall, were certain to
see most rivers in the area end their recent recession and
begin rising once again. Extended probabilistic guidance (HEFS)
shows the potential for decent rises on area rivers should
rainfall exceed 2.5 inches or so over large areas, something
that is in the realm of possibility. The upper Minnesota and
tributaries, as well as the Crow river basin, are probably the
most susceptible to seeing rises to near or above flood stage by
later in the week should this occur. Urban/small
stream/overland flooding is also possible during and shortly
after some of the heavier downpours Tuesday and Tuesday night.

A reminder: The NWS hydrology/river forecast webpage (AHPS) at
water.weather.gov is going to be discontinued next week (May
28th). The new site (NWPS, the National Water Prediction
Service) is located at water.noaa.gov  now is the time to
replace bookmarks and familiarize yourself with how the new site
looks and feels. Resources for learning more are available at
the bottom of this page: https:/www.weather.gov/owp/operations
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&&

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

$$

DISCUSSION...Dye/JRB
AVIATION...JPC
HYDROLOGY...CCS