362
FXUS63 KMPX 231211
AFDMPX

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

.KEY MESSAGES...

- Slight Risk (Level 2/5) of severe thunderstorms Monday
  evening. Coverage and timing of storms remains in flux, but
  those that do see storms could be in for an intense round of
  convective weather.

- 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 309 AM CDT Sun Jun 23 2024

Early morning satellite imagery reveals the gradual easterly
departure of widespread stratus across southeast Minnesota and
western Wisconsin. Back to the west, a few pockets of stratus remain
but the overall theme will be for skies to clear towards daybreak.
The combination of clearing skies and light winds has resulted in
the development of fog sampled on the latest surface observations
across western central Minnesota. It appears likely that areas of
fog will expand across western Minnesota through daybreak, before
eroding shortly thereafter. The remainder of our Sunday forecast
looks nice! Morning lows in the 50s/low 60s are forecast to climb
into upper 70s/low 80s this afternoon under partly to mostly sunny
skies. The vast majority of locations will run dry today, however we
have included slight chance PoPs for a few showers or an isolated
storm along and north of I-94 in far eastern MN/western WI during
the afternoon to early evening period. This activity is tied to an
upper-level wave moving from northern Minnesota into Wisconsin. The
threat for severe weather is low due to limited instability.

The main forecast concern over the next few days will be the threat
for severe weather Monday into early Tuesday. SPC`s latest Day 2
severe weather outlook has maintained a Slight Risk (level 2 out of
5)across most of Minnesota and all of northwest Wisconsin. A mid-
level shortwave tied to zonal flow aloft is forecast to drift east
across southern Canada Monday. Warm air advection will increase
across the Upper Midwest ahead of this feature, resulting in a much
warmer day with highs in the mid to upper 80s. A few locations may
reach the low 90s in far western MN! Moisture advection across the
warm sector will push dew points into the upper 60s to mid 70s,
setting the stage for a very warm and humid start to the week. Given
the expected thermodynamic environment, guidance is in good
agreement that a strongly unstable airmass will develop, with CAPE
solutions pushing 4000-5000 J/kg. The extreme instability would tend
to mean that storms would pose a severe risk should they develop,
however that is the part of the forecast that contains questions at
this distance. Model soundings indicate a stout EML building across
much of south central Minnesota during the day, likely working as a
strong cap to limit convection. This idea is reinforced by the
expected expansion of 700mb temperatures at or above 12C across
southern/central Minnesota. We`ve narrowed the evolution of Monday`s
threat down into two possible outcomes:

1) We`ll call this the more likely of the two scenarios, which is
captured well in the 00z ECMWF. In this scenario, much of Monday is
very quiet across south central Minnesota and western Wisconsin. The
temperatures and moisture mentioned above will have free reign to
build across the warm sector and a strong cap will be in place. This
is reflected by the northward expansion of 12C+ 700mb temperatures
to varying latitudes across central Minnesota. The approach of a
cold front in northwest Minnesota will be the focus point for
convection during the late afternoon/evening hours, likely
developing along the northern edge of the instability axis.
Differences exist in where this axis will setup, but the general
thinking is that a complex of storms would initiate well to the
north of I-94. Once storms develop, they may intensify quickly into
a bowing MCS that would be capable of producing damaging wind gusts.
The track of said complex of storms would most likely be to the
southeast along the forecast CAPE gradient, with an expected
expansion of storms along the MCS as the low-level jet strengthens
into the late evening. To make a long story short, this solution
would mean a threat for severe weather may not develop until Monday
evening, but the threat would persist well into the night.

2) Scenario #2 is a little bit of a possible "failure mode" to
scenario #1.  Guidance indicates that convection will develop on the
nose of the low-level jet across the Dakotas early Monday morning.
There is at least plausible reason to believe that convection could
dive southeast along the instability axis that will be lifting north
Monday morning. If this were to happen, we could be in for a round
of strong to potentially severe thunderstorms earlier in the day, in
a location that is quite a bit further to the south compared to
scenario #1. In theory, this could work against the northward
progression of the instability and further throw a wrench into the
setup for the remainder of the day.

We`ll continue to lean heavily on the first scenario as it is
represented across the majority of the model guidance and
conceptually seems to make the most sense. The widespread 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 sufficient shear parameters, a fairly intense
convective event may unfold. Damaging winds tend to quickly become
the primary risk when previewing a bowing MCS event, but other
threats such as large hail and a few tornadoes will also be in play.
Finally, thunderstorms will have the potential to produce heavy rain
given the ample moisture forecast to be present, however we are
currently thinking that the progressive nature of the storm motion
may work against a flash flood threat.

The threat for severe weather will depart to the southeast on
Tuesday. High pressure builds for the middle of the work week, with
highs in the upper 70s and sunshine on Wednesday. Of course, it
probably comes as no surprise that more rain is in the forecast by
late week. Large scale warm advection and moisture transport will
setup on Thursday, with the return of widespread rain set to arrive
late Thursday into much of Friday. PWATs are in the 99th percentile
per the NAEFS, indicating an atmosphere supportive of heavy rain.
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.
While the fine details can and will change, the large scale theme
supports further concerns with river flooding for the foreseeable
future.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 650 AM CDT Sun Jun 23 2024

Areas of low clouds and fog were leading to pockets of IFR
conditions, while other sites have clear skies and VFR
conditions. For the rest of today, expect VFR conditions
to become more widespread by the afternoon. A stray afternoon
rain shower is possible, but for now did not include a mention
in the TAFs. Looking ahead, we expect another round of low
stratus and fog again Sunday night into Monday morning.

KMSP...
VFR conditions throughout, but there could be a small window of
low cumulus later this morning. Winds will become more westerly
later today, and eventually southeast by Monday morning.

/OUTLOOK FOR KMSP/
MON...VFR. Chc -TSRA/MVFR after 02Z. Wind SSE 10-15 kts.
TUE...VFR. Wind NW 10-20 kts.
WED...VFR. Wind NW 5-10 kts.

&&

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

&&

$$

DISCUSSION...Strus
AVIATION...JRB