559
FXUS63 KMPX 190402
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1102 PM CDT Wed Jun 18 2025

.KEY MESSAGES...

- Thunderstorm complexes capable of heavy rain, damaging winds,
  and large hail are possible during the overnight hours
  Thursday and Friday. The best chance Friday night will be
  north of I-94.

- Hot and very humid this weekend with heat indices above 100
  degrees. An Extreme Heat Watch is in effect.

- The active weather pattern continues next week with the
  potential for heavy rain.

&&

.DISCUSSION...
Issued at 630 PM CDT Wed Jun 18 2025

The gradual loss of instability this evening along with weak
outflow boundary collisions moving to the southeast of the WFO
MPX coverage area has allowed convection to rapidly diminish and
dissipate. After the remaining isolated showers come to an end
within the next hour or so, no additional precipitation is
expected. The rest of the night will be quiet and dry, with
lows in the upper 50s and lower 60s.

The active pattern continues for Thursday and Friday ahead of
intense heat and humidity for the weekend. West northwest mid
level flow with embedded disturbances will track from the
northern Plains to Great Lakes through Friday night. A warm
front will be set along the I-94 corridor Thursday. The front
will be the main foci for thunderstorm development during the
day, but a strengthening 40-50 kt LLJ should bring development
into the warm sector Thursday night. Moderately steep mid level
lapse rates (6-7 C/km) and 40-50 kts of deep layer shear could
give enough support for a few severe storms capable of large
hail and damaging winds. Otherwise, scattered to numerous
showers and thunderstorms are expected. By Friday morning,
convection should be dissipating with the veering of the
nocturnal LLJ to the east. By afternoon, a redevelopment of the
LLJ should occur and will strengthen markedly to 50-60 kts
Friday night. The nose of the jet will focus across central or
northern MN. In addition, as the hot and humid airmass begins to
work in, 700 mb temperatures could exceed +15C as early as late
Friday afternoon south of I-94 and greater than +17C area wide
by early Saturday morning. This points to significant capping
(+12C at 700 mb is a typical subjective isotherm to determine if
convection is supported or suppressed). With the nose of the
LLJ to the north and unfavorable 700 mb temperatures across the
southern half or two thirds of MN, the better bet is for any
thunderstorm development to remain across northern MN Friday
night. If an intense MCS can develop and track eastward on the
periphery of the ridge, there`s an outside chance it can
penetrate deeper into the more unfavorable area, but chances
remain quite high the southern end of it will remain north of
I-94.

The airmass set for this weekend is quite impressive. The
strength of the ridge across the Ohio Valley will lead to
climatologically extreme heights and temperatures aloft across
parts of the Great Lakes and Upper Midwest. 850 mb temperatures
are expected to reach +25 to +27C with 925 mb temps of +28C to
+31C. This type of airmass could support highs in the mid 90s to
low 100s. In addition, dew points in the mid to upper 70s will
significantly raise the risk of heat illness. Heat indices of
100 to 110 are becoming increasingly likely. Further, gusty
winds Saturday night with dew points remaining in the upper 60s
to lower 70s will keep low temperatures well into the 70s or
even low 80s. An Extreme Heat Watch will be issued shortly for
the whole region Saturday afternoon into Sunday evening. Because
this will be the first hot and humid airmass of the season and
the conditions will be climatologically impressive, this will be
a particularly hazardous event. It should be noted the airmass
will start moving in late Friday and lows Friday night will also
be well into the 70s barring any significant convection. A Heat
Advisory may also be necessary for parts of the area Friday
afternoon through Saturday morning until the watch takes effect.

A cold front will push through Sunday night as a shortwave
breaks down the northwestern portion of the large ridge. The
ridge will keep southwest flow over the Plains and Upper Midwest
and won`t allow the front to stray too far southeast. Continued
moisture advection along the boundary and favorable jet dynamics
will mean repeated rounds of showers and thunderstorms early
next week. There is some uncertainty where the boundary will
stall, but generally southern/eastern MN and WI stand the best
chance at heavy rainfall totals through midweek. If the ridge is
a bit stronger than forecast, then this could shift northwest
some. One thing that seems more certain will be a significant
cool down, especially with post frontal showers and storms next
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1056 PM CDT Wed Jun 18 2025

VFR conditions expected through Thursday afternoon, with chances
for precipitation increasing Thursday evening, thus have added
in PROB30 mention (which may need to be changed to TEMPOs in
later TAF issuances). Have also kept conditions as VFR but there
is a growing likelihood of not only MVFR conditions Thursday
night with the precipitation but also the potential for CB/TS,
so that possibility will also be investigated with later model
runs. Winds will go light/variable overnight then pick up from
the SW during the day Thursday in the 5-10kt range.

KMSP...No issues through sunset Thursday evening, then chances
for rain increase, such that prevailing rainfall is expected
from around midnight onward. CB/TS is a possibility but
timing/placement too early to determine and confidence too low
to pinpoint so have left its mention out at this point.

/OUTLOOK FOR KMSP/
FRI...VFR/MVFR, chc mainly morning IFR/TSRA. Wind S 10-15 kts.
SAT-SUN...VFR and hot. Wind SW 10-20G20-30 kts.
MON...MVFR/RA likely, chc IFR/TSRA. Wind W 10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Extreme Heat Watch from Saturday afternoon through Sunday
     evening for Anoka-Benton-Blue Earth-Brown-Carver-Chippewa-
     Chisago-Dakota-Douglas-Faribault-Freeborn-Goodhue-
     Hennepin-Isanti-Kanabec-Kandiyohi-Lac Qui Parle-Le Sueur-
     Martin-McLeod-Meeker-Mille Lacs-Morrison-Nicollet-Pope-
     Ramsey-Redwood-Renville-Rice-Scott-Sherburne-Sibley-
     Stearns-Steele-Stevens-Swift-Todd-Waseca-Washington-
     Watonwan-Wright-Yellow Medicine.
WI...Extreme Heat Watch from Saturday afternoon through Sunday
     evening for Barron-Chippewa-Dunn-Eau Claire-Pepin-Pierce-
     Polk-Rusk-St. Croix.

&&

$$

DISCUSSION...Borghoff
AVIATION...JPC