507
FXUS63 KMPX 050402
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1102 PM CDT Thu Jul 4 2024

.KEY MESSAGES...

- Thunderstorms and locally heavy rainfall likely today and tonight.

- Numerous chances for showers and a few thunderstorms will
  linger into next week with temperatures remaining below
  normal.

&&

.UPDATE...
Issued at 818 PM CDT Thu Jul 4 2024

We`re all but done with phase one of this system with the
primary WAA band of showers and storms now exiting stage right.
Phase two is associated with the upper low that on water vapor
imagery was centered between Willmar and Olivia at 8pm. Lift
associated with the upper low is helping force the showers we
see near the upper low and that trend will continue through the
night as the upper low slowly moves east. For the metro, despite
the less than ideal weather during the day, any firework shows
still planned to go on this evening should find a window of dry
weather to get those off before showers return for the rest of
the night with the upper low. Severe risk the rest of the night
is gone with the loss of instability. The excessive rain risk
looks minimal as well as rain rates have come down considerably.
Still the showers associated with the upper low are moving slow
and locations that get under these downpours could pick up a
fairly quick half inch of rain before they move on.

&&

.DISCUSSION...
Issued at 159 PM CDT Thu Jul 4 2024

Our first round of rain today is currently located along the I-94
corridor and slowly moving northeast. Rainfall amounts from this
activity has resulted in generally 0.1-0.2" with up to 0.5" within
the very isolated heavier cells. Behind this first round is a brief
clearing, evidenced by the lack of returns on radar and thinning
clouds and small clearings on satellite over southern MN. However,
in our weakly stable environment, it won`t take much for new
convection to develop with a little daytime heating as the mid-level
jet and vorticity maximum moves in from the west. Indeed, scattered
showers and thunderstorms are in the process of developing across
southwestern MN late this morning. This activity will move
northeast, growing in coverage into scattered broken lines of cells,
reaching the Twin Cities around 2-3 PM and western WI later this
afternoon. The best chance of severe weather remains in southern to
southeastern MN along I-90 where enough heating should result in
1500-2000 J/kg of MLCAPE within 35-40 knots of bulk shear. A weak
tornado or two is possible within the surface vorticity rich
environment near the surface low, but the main threat from any
stronger storms will be large hail.

Heavy rain will be possible with any thunderstorms, as PWATs range
from 1.2-1.4" and vertical profiles are very moist. Though, the
transient non-continuous nature of the storms should limit the flash
flooding risk to a large degree. Nevertheless, rounds of storms with
rainfall rates of 1-1.5" per hour over the same area could lead to
localized flash flooding. This will be especially true as we
progress through tonight, as the precip becomes more favored from
south-central MN into northwestern WI. Precip in southeastern MN
should decay with the dissipating instability while precip within
the deformation zone north of the occluding surface low will be
favored as synoptic lift increases. Showers and thunderstorms will
wrap westward around the surface low as it travels east, meaning
that a county wide or two area could see heavier rainfall rates for
a period of 2-4 hours. This could lead to localized areas of 3-4" of
rain while elsewhere from south-central MN to western WI will see
rainfall of 1-2.5" by 12Z Friday. The low pressure system will
slowly move east-northeast out of our area by early Friday afternoon
with lingering, but decaying wraparound precip exiting with it.
However, isolated showers and a thunderstorm may occur across MN
during Friday afternoon underneath the backside of the upper-level
shortwave.

While the aforementioned shortwave will move east into the
Great Lakes Saturday, a broader longwave trough will settle in
over the Northern Plains/Upper Midwest through at least early
next week. This will result in stagnant, mild temperatures
(highs in the mid 70s to lower 80s into Monday). Additional
chances for precipitation will also be possible Saturday through
at least Tuesday as embedded impulses round through the trough.
The heavy rain and severe weather threats don`t appear to be
significant with any of the impulses, but don`t expect a
prolonged break in the wet weather just yet. However, long-range
forecast models do suggest the trough finally exits to our east
during mid-next week. At the same time, a strong upper-level
ridge will move into the western CONUS, with pieces of this
ridge potentially spilling over into the central CONUS the
latter half of next week. This signals a potential warmer,
drier summer pattern occurring eventually for our region (also
supported by the 6-10 and 8-14 Climate Prediction Center
Outlooks) sometime within the next 2 weeks. We just need to get
through a few more days of rain first.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1047 PM CDT Thu Jul 4 2024

We`ve moved off to phase 2 of this system and thats rain
associated with the upper low itself, which at 11pm, water
vapor imagery showed being not far from Litchfield (KLJF).
Rotating around this low as been a broad shield of light to
moderate rain with some embedded downpours. As the low slowly
track ESE through the night, these areas of showers are expected
to follow the upper low. Besides the rain, the expanding
IFR/MVFR obs we`re seeing with obs is supported by moist low
levels in RAP soundings and we expect extensive MVFR/IFR stratus
through the night near the surface low that is slowly taking
shape between MSP & MKT. CIGS will slowly improve through the
morning, with another round of diurnally driven scattered
shra/tsra expected Saturday afternoon. Have included PROB30s to
cover that threat. HREF is most bullish with activity Saturday
happening west of I-35, so kept MSP/EAU/RNH dry after the upper
and surface lows clear the area in the morning.

KMSP...We expect one more round of shra to move through MSP
overnight as the upper low passes nearby. 8z-12z looking to be
the window when -shra is most likely. For Saturday afternoon,
MSP looks to have enough influence in the subsidence region of
the departing upper low to suppress diurnal activity.

/OUTLOOK FOR KMSP/
SAT...Chance PM MVFR/SHRA/TSRA. Wind SW 5-10 kts.
SUN...VFR. Chc aftn SHRA/TSRA. Wind SW 10-20 kts.
MON...VFR. Chc aftn SHRA/TSRA. Wind WNW 5-10 kts.

&&

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

&&

$$

UPDATE...MPG
DISCUSSION...CTG
AVIATION...MPG