268
FXUS63 KMPX 130519
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1219 AM CDT Sat Jul 13 2024

.KEY MESSAGES...

- Hot and humid this weekend with the potential for several
  conditional chances for strong to severe thunderstorms
  Saturday through Monday.

- Slight Risk (2 of 5) of Severe Weather Saturday. All hazards will
  be possible if thunderstorms develop, best chance along and
  north of I-94.

- Cooler, drier pattern after Monday.

&&

.DISCUSSION...
Issued at 222 PM CDT Fri Jul 12 2024

Rest of Today... Diurnal cumulus clouds this afternoon forming
below an upper level inversion. With this inversion in place
thunderstorm activity should be capped this afternoon and
evening. Continued southerly flow will advect warmer and more
moist air into the Upper Midwest tonight. Subtle curvature aloft
could produce enough lift for some thunderstorm late tonight.

Saturday... Continued from the Rest of Today discussion CAMs
continue to show a line of storms forming Saturday morning. The
best chances will be to north of I-94. But some solutions like
the 12Z HRRR and NAM Nest have taken this farther south.
Continued advection will bring us our hottest day of the year,
especially over western Minnesota where heat index values will
be over 100. Widespread heat index values above 90 expected and
over 95 in the Twin Cities metro. Little recovery from heat
stress expected overnight with lows only in the lower to mid
70s. This will be especially pronounced in the core Twin Cities
where the urban heat island will help keep overnight
temperatures elevated, which is why the Heat Advisory extends
overnight into Sunday. As mentioned in the previous discussion
the environment will be favorable for thunderstorms. Above
normal precipitable water will allow for high rain rates, but
flow should be fast enough to avoid much of a flooding risk. On
the severe side CAPE is very high with multiple CAM soundings
showing values in excess of 3000 J/kg and some as high as 5000
J/kg. The question is when CI will occur. Forcing suggests later
in the day and surface cooling could cause issues with surface
based convection. The timing in most CAMs also suggests more of
an evening timing after peak surface heating. The boundary layer
up into around 850 mb thanks to the WAA will take longer to
cool such that a cap could form. Shear is sufficient for strong
to severe storms. Mid level lapse rates will support upward
motion, but low level lapse rates will depend on the time of
day. As the surface cools it will make the low level lapse more
complicated. SPC continues to have a slight risk (2 of 5) with
all severe hazards possible. Summary of this day, hot and humid
with both early day and late day thunderstorm chances (better
severe chances with the late round).

Sunday... The heat will shift south and east on Sunday with
lower, but still hot temperatures over western Minnesota. With
temperatures remaining hot in the morning there will be little
recovery from heat stress. A shortwave on Sunday will give
another chance for thunderstorms and with the warmth still
around plenty of instability. This will be another day to watch
out for, but this forecast is dependent on how Saturday plays
out. This could be just as hot if not hotter than Saturday for
the Twin Cities depending on where and when storms occur. Also
how worked over the atmosphere gets on Saturday will be key for
storm chances on Sunday. Ensembles highlight variable storm chances
for Sunday and we might not have high confidence until Saturday
afternoon on which direction the forecast goes. Regardless it
will be a hot day with another chance for thunderstorms. It is
just how hot and will storms form that are the questions.

Monday... The peak of the heat will be past us on Monday, but it
will still be hot but likely sub-advisory heat. This looks to
be the best synoptic setup of the next three days based on the
jet streak and 500 mb shortwave. Just less instability and a
shear setup more dependent on speed shear. Once again this day
will be dependent on the weekend days before and how the
atmosphere evolves.

Tuesday through Thursday... On the back side of Monday`s wave
cooler and drier move into the Upper Midwest. Highs will be in
the mid 70s to lower 80s, which after a weekend of 90s will be
quite a cool down.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1152 PM CDT Fri Jul 12 2024

Thunderstorms over eastern ND should continue south-southeast,
eventually reaching western MN early this morning. As such, have
given TEMPOs to AXN and RWF for the increased likelihood of
convection. MVFR visibilities are possible during any storms.
Forecast confidence remains low regarding if more storms form to
the east of the current activity. Have added PROB30s to our
other terminals east of AXN and RWF Saturday morning into the
early afternoon for the possibility of additional lines of
convection developing and tracking through the area. A multi-
hour break in the activity looks likely before another possible
round of storms develop across central MN late Saturday
afternoon and move east-southeast. Outside of storms,
conditions will be VFR while south-southeast winds will turn
more southerly during the daytime hours, increasing to near 10
knots.

KMSP...Have kept PROB30s for the possibility of -TSRA Saturday
morning through the early afternoon and again Saturday evening.

/OUTLOOK FOR KMSP/
SUN...VFR, chc -TSRA/MVFR. Wind S 5-10 kts.
MON...VFR, chc -TSRA/MVFR. Wind NW 5-10 kts.
TUE...VFR, Wind NW 5-15 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Heat Advisory from 1 PM to 8 PM CDT Saturday for Brown-
     Chippewa-Lac Qui Parle-Redwood-Renville-Stevens-Swift-
     Watonwan-Yellow Medicine.
     Heat Advisory from 2 PM Saturday to 8 PM CDT Sunday for Anoka-
     Carver-Dakota-Hennepin-Ramsey-Scott-Washington.
WI...None.

&&

$$

DISCUSSION...NDC
AVIATION...CTG