599
FXUS63 KMPX 232339
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
639 PM CDT Sun Jun 23 2024

.KEY MESSAGES...

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

- Active pattern continues with another round of widespread
  rainfall Thursday afternoon through Friday night.

- 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.

&&

.DISCUSSION...
Issued at 353 PM CDT Sun Jun 23 2024

Isolated thunderstorms have developed across northeast Minnesota and
may track through portions of eastern MN and western WI this
afternoon. These showers miss the majority of us, but the unlucky
few will see brief downpours and a few flashes of lightning.
Elsewhere, temperatures have warmed in the upper 70s and lower 80s
with scattered CU and dry conditions. Northwest winds have produced
a few gusts up to 20 mph and winds will taper off this evening.

For tonight, the forecast remains dry with lows in the 60s for most
of us. Some patchy fog cannot be ruled out in W WI given the recent
stretch of wet weather and light winds forecast tonight. By
daybreak, a warm front will lift through the region with
southeasterly winds ramping up by Monday morning. Some guidance
tracks elevated convection into west central MN that dissipates by
mid-morning. There isn`t enough confidence to reflect this in the
PoPs, but if this does happen it`ll add additional complexity to
Monday`s severe weather setup.

On Monday, a complex conditional (boom or bust) severe weather setup
Monday evening across MN and NW WI. SPC`s mid-day update to the Day
2 severe weather outlook has maintained a Slight Risk (level 2 out
of 5)across most of Minnesota and all of northwest Wisconsin after
collaboration with the SPC. However, there was an addition of sig
wind hatching over central Minnesota & western Wisconsin that I`ll
expand on later. Aloft, a shortwave trough over the Canadian
prairies will trek east during the day. It`ll bring a cold front
through the Dakotas and into Minnesota Monday afternoon. In the warm
sector, warm air advection increases across the Upper Midwest Monday
morning, resulting in a very warm and humid day on tap with highs in
the mid 80s to low 90s out in W MN. Moisture transport will push
surface dewpoint temperatures level moisture to the warm sector res
in the the upper 60s to mid 70s by mid-afternoon. Guidance continues
to advertise an impressive thermodynamic environment in the warm
sector. 12Z HREF develops strong to high-end instability with MLCAPE
values pushing 4000-5000+ J/kg. This high-end instability would
favor a severe risk should thunderstorms develop, but will they?
CAMs offer a few different scenarios for Monday afternoon into
Monday night. Global models offer additional solutions that we can
infer the outcome from. So I`ll do my best to break down the
potential scenarios similarly to what the previous shift did.

Forecast soundings highlight an impressive EML building across much
of south central Minnesota during the daytime, effectively capping
the extreme instability and limiting convection across the MPX CWA.
Looking at the 700hPa layer offers support to this with temperatures
between 14 to 16c by 21Z Monday. The capping is present in all of
the models I`ve looked at so why are we concerned about potential
severe? Let`s dive into the potential outcomes for Monday`s severe
threat below:

1) Scenario #1 is the most likely scenario given the environment in
place, but it doens`t guarantee severe wx in the MPX cwa. In this
scenario, Monday is very quiet across south central Minnesota and
western Wisconsin under the cap. Most of us have to combat the heat
and humidity while instability builds in beneath the cap. Further
northwest, the approach of a cold front in northwest Minnesota will
be the focus for convection during the mid-afternoon/evening hours,
likely developing along the northern edge of the instability axis.
Differences exist in where this axis will setup will could have big
implications for where the convection tracks Monday evening. Once
storms develop over NW MN, they will be able to intensify quickly
into a MCS that would be capable of producing potentially
significant damaging winds as it tracks along the CAPE gradient
across central MN into NW WI. However, if it`s further north, it
would keep the severe storms in FGF/DLHs forecast areas. Regardless
of where storms develop, the track of said complex of storms would
likely move southeast along the CAPE gradient, with an expected
growth along the MCS as the nocturnal low-level jet strengthens into
the evening. This solution would mean a threat for severe weather
would be Monday evening, but the threat would persist well into the
night if the storm complex can maintain it`s cold pool.

2) This is the slightly less favored, but still possible. Some
models maintain elevated convection across the Dakotas into western
Minnesota Monday morning. There is some possibility that convection
makes it into W MN and continue east along the instability axis
lifting north Monday morning. If this were to happen, we could be in
for a round of storms, possibly strong, before they taper out by
late morning. This would impact the location of the warm front and
recovery potential across the area. This would further throw a
wrench into the setup for the remainder of the day and add
additional complexity. This scenario would likely see development
of isolated to scattered elevated thunderstorms on the nose of the
nocturnal LLJ Monday late evening into Tuesday morning across
central and southern MN. These could post a severe hail threat but
little to no wind concern given the stable nocturnal boundary layer.

The continued Slight Risk from the SPC represents some of the
uncertainty expressed above with the overall setup, however given
the extreme instability, steep lapse rates, and adequate shear would
support any convection becoming severe if a convective event may
unfold. The SPC did add an area of sig wind hatching across central
MN and NW WI. This represents the potential for a higher end MCS
solution with damaging winds, but other threats such as large hail
and a few tornadoes will also be in play. It was hinted at in the
SWODY2 update that tonight`s SPC update could begin to ramp up the
severe risk if confidence increases. The pattern does support the
potential for a long-lived MCS wind producer across the region IF
storms can develop and organize before sunset. Finally, storms may
produce heavy rain given the ample moisture forecast to be present,
however the progressive nature of the storm motion should limit the
flash flood threat. Additional rises in area rivers would also delay
crests.

Tuesday and Wednesday offer a break from the active pattern as
high pressure builds in for the middle of the week. Temperatures
remain warm on Tuesday, in the 80s, but we`ll see highs in the
upper 70s on Wednesday. Thursday and Friday, a large system will
move into the Plains on Thursday. Large scale warm advection
sets up on the return flow Thursday afternoon. A low pressure
will move into the Dakotas late Thursday, setting the table for
another round of thunderstorms Thursday night into Friday. This
system may threaten to produce additional rounds of heavy rain
given favorable moisture transport & forcing aloft. The WPC`s
Day 5 Excessive Rainfall Outlook supports this potential with a
Marginal Risk across most of Minnesota and western Wisconsin,
along with a Slight Risk across southern Minnesota/northern
Iowa. Unfortunately, the concern for additional flash flooding
and river flooding remains with us for the foreseeable future.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 639 PM CDT Sun Jun 23 2024

VFR and light winds tonight. Some patchy fog could develop in
WI, but confidence is low in RNH or EAU experiencing it
directly. Winds become south and gusty Monday with storms
possible, primarily north of I-94 Monday night.

KMSP...No significant concerns tonight. Northwest winds will
ease and become light later this evening, then become SSE and
gust 25-30 kts late Monday morning and afternoon. TS potential
Monday evening is too uncertain to include in this TAF set, but
a PROB30 may be considered for the next issuance.

/OUTLOOK FOR KMSP/
TUE...VFR. Wind NW 10-15 kts.
WED...VFR. Wind NW 5-10 kts.
THU...VFR. MVFR/-TSRA likely Thursday night. Wind S 5-10 kts.

&&

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

&&

$$

DISCUSSION...BPH
AVIATION...Borghoff