736
FXUS63 KMPX 210240
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
940 PM CDT Thu Jun 20 2024

.KEY MESSAGES...

- A Flood Watch has been issued for much of the area starting
  Friday and lasting into Saturday. Multiple round of
  thunderstorms will lead to heavy rain and flooding concerns.
  If these thunderstorms track over the same location,
  significant flooding is possible.

- The latest trend shows a southern shift in rain, with the heaviest
  amounts along and north of I-90.

- Going into next week, the weather pattern will become more
  progressive, but not necessarily dry. Additional thunderstorm
  chances will continue at times next week.

&&

.UPDATE...
Issued at 940 PM CDT Thu Jun 20 2024

Light showers continue across southern MN late this evening
with more robust thunderstorm activity along I-90 in eastern
South Dakota. The west-east orientation of the convection along
the interstate is training and resulting in flash flooding. 00Z
models are coming in and none of the guidance is handling the
current activity particularly well. However, as the night
progresses, the best moisture transport will veer from SD toward
MN, allowing the convection to spread eastward. Each model has
a different spatial pattern with convection, but generally the
orientation is ENE from southwest to east central MN. QPF on all
the guidance through mid morning Friday ranges from 1 to 3
inches within this corridor, with local bullseyes in the 4 or 5
inch range. With the already highly favorable antecedent
conditions left from earlier in the week and the potential for
multiple inches in spots as early as tonight, pushed up the
start time of the Flood Watch to 06Z across western MN and 09Z
farther east.

&&

.DISCUSSION...
Issued at 335 PM CDT Thu Jun 20 2024

TODAY THROUGH SATURDAY...Early afternoon radar and satellite imagery
shows scattered convection ongoing across the region, with the most
concentrated area of storms across eastern South Dakota and
southwest Minnesota. These storms were developing along a stationary
boundary, and over the next 48 hours, this boundary will be the
focus for multiple rounds of thunderstorms. By Saturday afternoon,
most locations across southern Minnesota and into west central
Wisconsin will see 2 to 4 inches, with pockets of 5+ inches likely.
As to how high that "plus" is will be whether or not multiple rounds
of storms track over the same location. The latest trends show the
rain shifting slightly to the south, with the highest axis along and
just north of I-94.

As for the meteorology, PWAT values are approaching record values,
with weak southwest flow aloft parallel to the surface boundary.
This will result in continued ascent along the boundary, with storms
tracking across the same location. Forecast soundings show
tropopause values up near 150mb indicating a tropical air mass.
While confidence is high that heavy rain and flooding will occur
across parts of the region, there is still uncertainty on where
exactly this will happen. The overall synoptic forcing is weak,
meaning that there isn`t a strong wave or deepening low pressure
system driving the QPF. Instead it is a stationary boundary with
around 20 to 25 kts of H925 low level jet that continually develops
storms across the region. Some models show this convection further
north along the front, say east/west of the Twin Cities, while now
more models are starting to come in line with a more southern
solution closer to the I-90 corridor. For now, have targeted the
Flash Flood Watch to the south, but can`t completely rule out a
northward expansion.

There is also a slight risk for severe weather on Friday, mainly
near I-90. Storms will be ongoing in the morning, and could
intensify as peak heating warms the southern side of the boundary.
At this point, wind is the primary threat, with a secondary risk of
hail and tornadoes. This slight risk area shifts eastward into
eastern Minnesota and western Wisconsin for Saturday.

SUNDAY THROUGH WEDNESDAY...Eventually the aforementioned boundary
will move east as a shortwave trough drives the low toward the Great
Lakes. A brief area of high pressure will settle in through early
next week, but another chance for thunderstorms returns Monday
night. This will be followed by a couple more dry days on Tuesday
and Wednesday, with the next system arriving sometime later next
week. At this point, locally heavy rain and/or severe weather could
be possible, but details will remain uncertain until we get through
the next couple of days.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 644 PM CDT Thu Jun 20 2024

Widespread showers across southern MN will impact primarily MKT
and RWF during the next few hours. They should then weaken,
before another batch arrives overnight. That round will have
some TS and periods of heavy rain. Conditions will deteriorate
to IFR overnight area wide.

KMSP...A few showers could lift north to MSP this evening,
otherwise two rounds are expected during the next 24 hours. The
first will arrive tonight around 09Z. TS and periods of heavy
rain are likely though mid morning. Then, the second round will
arrive late Friday afternoon or early evening. Conditions will
deteriorate to IFR levels tonight and remain there through the
rest of the period.

/OUTLOOK FOR KMSP/
SAT...TSRA/IFR likely early, bmcg MVFR in aftn. Wind SW 10-15 kts
becoming NW.
SUN...VFR. Wind NW 10-20 kts.
MON...VFR. Chc -TSRA/MVFR. Wind S 10 kts.

&&

.HYDROLOGY...
Issued at 335 PM CDT Thu Jun 20 2024

Main item to pass along is the latest river forecast that were
issued this morning include 48 hours of QPF. This means the
forecast hydrographs on the webpage capture most of they heavy
rain that is expected the next couple of days. As a result,
moderate or major flooding is expected at many of the sites
along the mainstem rivers.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Flood Watch from 4 AM CDT Friday through Saturday afternoon
     for Anoka-Blue Earth-Carver-Dakota-Faribault-Freeborn-
     Goodhue-Hennepin-Le Sueur-McLeod-Nicollet-Ramsey-Rice-
     Scott-Sibley-Steele-Waseca-Washington-Wright.
     Flood Watch from 1 AM CDT Friday through Saturday morning for
     Brown-Martin-Redwood-Renville-Watonwan-Yellow Medicine.
WI...Flood Watch from 4 AM CDT Friday through Saturday afternoon
     for Dunn-Pepin-Pierce-St. Croix.

&&

$$

UPDATE...Borghoff
DISCUSSION...JRB
AVIATION...Borghoff
HYDROLOGY...JRB