657
FXUS63 KMPX 241736
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1236 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

- Slight Risk (Level 2/5) of severe thunderstorms this evening.
  Uncertainty remains due to a conditional setup, but if storms
  develop they`d likely have significant severe weather given
  the environment.

- Active pattern continues with another round of widespread
  rainfall Thursday afternoon through Friday night and another
  system for the start of July.

- Local river levels remain on the rise following the recent
  rainfall. River flooding remains a concern, as several sites
  have yet to crest in moderate or major flood stage.

&&

.UPDATE...
Issued at 1236 PM CDT Mon Jun 24 2024

Confidence is increasing on thunderstorm evolution this
afternoon and evening, such that a Flood Watch for the potential
for flash flooding as been issued for portions of eastern MN and
western WI.

17Z SPC mesoanalysis highlights a pronounced instability
gradient from Alexandria to Rochester. It is also along this
line where the H7 +12C isotherm is located, which is generally
the level that convection has trouble developing (capped).
Elevated ACCAS/light showers and a few thunderstorms are ongoing
across western MN, although ceilings are greater than 12kft. As
low pressure treks eastward across South Dakota this afternoon,
very rich Theta-e air will advect northward into western and
southern MN. Mid level lapse rates in excess of 8.5 C/km will
spread over this moisture-rich airmass and result in extreme
instability likely exceeding 5000 J/kg. In addition, the 850 mb
jet will strengthen to 40 kts and impinge on the surface front
near the Mississippi River. Despite marginal H7 temps, it is
believed this front and LLJ will initiate convection late this
afternoon across east central MN. CAMs have trended this way in
big fashion today. The initial cluster will form and propagate
southeast along the instability gradient into far western WI
and southeastern MN. Given extreme instability and favorable
shear, very large hail and destructive winds are possible. SPC
has upgraded this area to a level 3 Enhanced Risk. Following the
initial cluster, additional clusters may redevelop again
upstream with the LLJ orthogonal to the front. The LLJ will
replenish the atmosphere and maintain a healthy pool of
available instability. The renewed cluster(s) will also have the
potential for very large hail and destructive winds. Further,
potential training of these clusters appears likely and multiple
CAMs highlight an increasing likelihood of localized totals
exceeding 3 inches from the Twin Cities metro area, southeast
toward Eau Claire, Rochester, and La Crosse. Given the state of
the ongoing flooding, recent rainfall, and thus low flash flood
guidance values, a Flood Watch is necessary for these areas this
evening. Outflow from previous clusters could displace
subsequent clusters slightly farther southwest, so the watch was
given a wide berth to the southwest to account for this
potential. H7 temps may limit this to some degree, however.

&&

.DISCUSSION...
Issued at 329 AM CDT Mon Jun 24 2024

All eyes are on today and the potential for a high-end severe
weather event across MN/WI. Water vapor imagery shows a series of
shortwaves this morning from Montana up into Saskatchewan. In
response to these features, we`ve seen both a very warm EML and Gulf
moisture getting pulled north up into the Dakotas. Within this
environment, we`ve seen a severe cluster of storms drop out of
Saskatchewan into north central NoDak. These storms have not been
handled well by guidance (including CAMs) and represents the first
bit of uncertainty for this forecast. The CAPE gradient and 850-
300mb thickness pattern would say this cluster of storms will make a
run toward Fargo the rest of the night, with the big question being
how deep into MN does this cluster make it as it encounters an
environment with less instability and increasingly stronger capping
(as h7 temps push to upwards of 14+ C). Given the increasingly
hostile environment for convection, this activity is expected to be
not much more than some disorganized showers (if they`re even still
producing rain) into central MN by late this morning. However, how
this activity modifies our environment in terms of what the northward
extent of the capping h7 thermal ridge and surface warm front end up
being are still uncertain for our potential severe event late in
the day.

For later today/tonight, the warm front is expected to at the very
least clear the upper MN River. Dewpoints behind this warm front
will increase into the mid and possibly even upper 70s, this
combined with air temperatures in the upper 80s to lower 90s sends
forecast heat index values into the 100 to 105 range from Fairmont
and Mankato up along the MN River to the SoDak border, so have
issued a Heat Advisory along the upper MN River Valley for today. h7
temperatures will be increasing to between 14C and 16C. These warm
h7 temps will allow for dry adiabatic mid-level lapse rates to
develop above a surface environment with observations in the ballpark
of 90/75. This combination will create a thermodynamic environment
with extreme instability, with mlCAPE values likely to exceed 5000
j/kg in the warm sector. This instability is the reason for the
"boom" or "bust" messaging we`ve had. If updrafts form in this
environment, they will be strong to violent (boom), but those toasty
h7 temps also mean we have the bust in play given the capping. When
looking at the HREF the non-HRRR members all produce a forward
propagating MCS, but differ on where that develops. The northern
outlier is the Fv3, which keeps its MCS north of the Arrowhead. At
the other end of the spectrum, you have the ARW/NSSL WRFS which
bring the MCS through central MN and western WI (including the Twin
Cities). Given the convective debris we`ll have today, we favor that
more southern solution, with storms developing in west central MN in
the late afternoon, quickly growing upscale and racing southeast
along the CAPE gradient. This is a high end severe environment given
the degree of instability with the curved hodographs and 40-50 kts
of deep layer shear. There`s still enough uncertainty on convective
initiation that the SPC maintained a slight risk, but the hatched
wind area they have is a pretty good indication for where the most
likely region to see a significant wind event evolve resides.

For Tuesday, some instability lingers across southern MN, but the
main surface front by the afternoon will reside from roughly Des
Moines to Milwaukee, so other than some lingering showers in
southern MN Tuesday morning, Tuesday continues to look like a day to
dry out with mostly sunny skies and highs in the low to mid 80s,
very similar to what we just saw on Sunday (minus the isolated
showers in western WI!). Wednesday will be dry as well as high
pressure moves through, but as we`ve seen going back to the second
half of March, dry stretches tend to not last all that long!

The next period of active weather continues to be Thursday through
Friday, with Thursday night/Friday morning looking to be the most
likely window for seeing more showers/storms. If you`re looking for
some good news, models overnight started backing down some on the
heavy rain signal as this system is looking a bit more organized.
The 00z guidance has started trending toward the idea that we see a
double warm front structure develop with this system. One down in
Iowa will have the tropical airmass (and dewpoints in the 70s, with
another up along the international border (with dewpoints in the
60s). We`re kind of stuck between the two, with lesser QPF resulting
for the MPX area (with heavier precip focused to the north and
south). Still, we will have favorable upper diffluence with a LLJ
moving through, so the likely PoPs we have Thursday night are still
warranted, we`ll just hopefully be able to avoid the worst of the
heavy rain with this one.

Behind this system, the last weekend of June looks to be absolutely
spectacular, good news for once if you have any outdoor plans.
However, in a growing theme for this warm season, the nice/dry
weather will be short lived with the ensembles and deterministic
models showing another seasonably strong cyclone impacting the upper
MS Valley in the July 1-2 period, but this looks to be another
opportunity for severe weather and excessive rainfall. When it rains
it pours...

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1230 PM CDT Mon Jun 24 2024

Our main concern continues to revolve around the potential severe
storms with destructive wind gusts to form this evening. Forecast
confidence has increased to include in the 18Z TAFS. Thunderstorm
initiation is now expected after 21Z across central Minnesota before
congealing into a line of severe thunderstorms that will track
southeast. Potential for impacts include STC/MSP/RNH/EAU. Latest
TAFS use the 12z CAMs to support the earlier timing for TS
development. There`s still some uncertainty with where storms
develop, so kept the TS in a TEMPO for STC for now until there`s
better confidence on if/when/where the cap breaks. Storms remain
possible overnight for AXN/RWF/MKT, but chances at these terminals
are low enough to keep the TS mention out until later updates.

KMSP... Increased confidence that thunderstorms will develop over
central MN after 21Z and tracking across the metro this evening.
Opted for prevailing -TSRA between 22z-04z with a TEMPO of +TSRA and
strong wind gusts (hurricane force gusts possible) from 23z to 01z.
There is still variability in timing of TSRA but TSRA now appears
likely for MSP.

/OUTLOOK FOR KMSP/
WED...VFR. Wind NW 5-10 kts.
THU...VFR. MVFR/-TSRA likely overnight. Wind S 5-10 kts.
FRI...VFR. MVFR/-TSRA likely morning. Wind S 10-15 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Flood Watch from 5 PM CDT this afternoon through late tonight
     for Anoka-Carver-Chisago-Dakota-Freeborn-Goodhue-Hennepin-
     Isanti-Le Sueur-Ramsey-Rice-Scott-Sherburne-Steele-Waseca-
     Washington-Wright.
     Heat Advisory until 8 PM CDT this evening for Blue Earth-Brown-
     Chippewa-Faribault-Lac Qui Parle-Martin-Nicollet-Redwood-
     Renville-Watonwan-Yellow Medicine.
WI...Flood Watch from 5 PM CDT this afternoon through late tonight
     for Dunn-Eau Claire-Pepin-Pierce-Polk-St. Croix.

&&

$$

UPDATE...Borghoff
DISCUSSION...MPG
AVIATION...MPG