747
FXUS63 KMPX 191719
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1219 PM CDT Sun May 19 2024

.KEY MESSAGES...

- Multiple rounds of showers and thunderstorms are expected beginning
  this evening into Monday morning and Tuesday through Tuesday
  night.

- Increasing likelihood of strong to severe thunderstorms
  Tuesday PM across southern Minnesota and western Wisconsin.
  SPC day 3 SWO brings an Enhanced Risk (3 out of 5) into SE MN.

- Heavy rainfall is likely and totals may exceed 3 inches through
  mid-week. This will likely lead to rises on rivers and their
  tributaries into the holiday weekend.

&&

.DISCUSSION...
Issued at 326 AM CDT Sun May 19 2024

TODAY THROUGH MONDAY NIGHT... Today will be a tale of two halves.
Sunday will start off pleasant with mostly sunny skies and
temperatures climbing into the 70s across the region. The second
half will focus on this evening into tonight as the first of
multiple rounds of rain & thunderstorms will impact the Upper
Mississippi Valley. A few showers or storms will try to fire this
afternoon across western Minnesota but will have to battle plenty of
dry air currently in place. By this evening a strengthening LLJ will
ramp up moisture advection into the area. This will provide a potent
setup similar to what occurred Friday night into Saturday morning.
Better forcing and instability will lead to more widespread nature
of convection that`ll lead to half inch to an inch of QPF by Monday
morning. We`ll see an active wave train with several shortwaves
eject out of the Rockies into the Upper Midwest. We`ll have a brief
period to dry out Monday afternoon and temperatures will be
seasonable in the 70s.

TUESDAY THROUGH WEDNESDAY NIGHT... Our attention turns to the next
event that should be the most impressive wave of the week. It`s not
often we`ll see Summer moisture with Winter synoptic forcing, but
Tuesday`s system will paint a picture of what it would look like.
The sfc low will move from Nebraska into S Minnesota Tuesday
afternoon. This places the most favorable area of lift across the
MPX CWA with the focus over western and central Minnesota. This is
where the cold conveyor belt of northeast flow will wrap into the
SFC low and the TROWAL to produce a prolonged steady moderate rain
event across this region. The TROWAL will provide plenty of moisture
with PWAT values in the 95th percentile per the ECMWF EFI. MSLP is
also in uncharted territory per the EFI, roughly once per decade,
for the MSLP to drop this low.+

Western and Central Minnesota is where we see the highest QPF, with
amounts in ensembles of 2 to 4 inches possible, as mentioned in the
previous discussion. This forecast should not change a whole lot as
this is driven in the cold sector of the system, not the warm
convective portion. However, the convective side of this system
looks increasingly likely to impact southern Minnesota and western
Wisconsin Tuesday afternoon & evening. The SPC day 3 SWO highlights
a rather large enhanced (3/5) risk across portions of the plains
into the Upper Mississippi Valley. It places our I-90 counties in
Enhanced. The Slight risk covers much of the eastern half of our
forecast area or the Twin Cities Metro and points eastward. This
system will have plenty of wind shear with impressive forcing. Less
certain on the instability front. The ECMWF has been consistent in
tracking the low pressure from SW MN to the Twin Cities. It brings
1000 to 1500 j/kg of instability into the region Tuesday Afternoon
that should be plenty to trigger severe weather, but other model
guidance with further east low tracks would bring much less
instability into the area, so for now there is still some
uncertainty and lower confidence. That`s why the greatest risk area
is to the south and east where there is higher confidence of
instability/warmer air mass. This severe chance is also seen in
machine learning outlooks run by CSU. The CSU day 3 suggests that
Tuesday`s severe threat could bring the enhanced area further west,
but again model spread and lower confidence make the current SPC
outlook a great starting point due to that uncertainty. So Tuesday
will be the day to keep an eye on for multiple reasons, slight risk
of excessive rainfall & enhanced/slight risk of severe thunderstorms.
Rain chances persist into Wednesday as this system moves into the
northern Great Lakes. Wednesday will also be the coolest day of the
week with high temperatures in the upper 50s to mid 60s with cloud
cover and northwest flow to blame.

THURSDAY THROUGH SUNDAY... Forecast confidence begins to decrease
beyond mid-week. There are more signals for additional QPF events
among the grand ensemble members, but not as clear of a signal and
much more spread. This active period seems to continue through the
holiday weekend, but confidence on timing of when rain could fall
remains low. Temperatures should be comfortable, in the 60s and 70s,
dependent on precipitation or not. The heavy rainfall from the
Sunday night and Tuesday system will likely lead to rises on the
Upper Minnesota river basin and the Crow River basin. The river
rises should begin as we head into Memorial day weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 1157 AM CDT Sun May 19 2024

Radar returns across central MN are still not making it to the
surface, however returns near the MN/IA border are within the
more moist environment. Isolated to scattered showers will
become more common into this evening before LLJ arrives, causing
more strong forced SHRA/TSRA likely from midnight through the
early morning as the convection moves northeast. Have kept pre-
existing TEMPO TSRA group but have delayed onset time by about 1
hour. Cigs will remain VFR until the heavier precip arrives,
with expected drop to IFR/LIFR left in its wake. Cigs should
slowly improve from west to east during Monday morning. Winds
will be southeasterly around 10 knots (slightly weaker in WI)
into early Monday morning before slowing to at or below 5 knots
and becoming west-northwesterly.

KMSP...Could see some light showers this afternoon but more
sustained showers will arrive late this evening. 06-10Z
continues to look like the best timing of organized SHRA/TSRA.
Post rain stratocumulus will cause cigs to fall to IFR before
improvement to MVFR occurs by late Monday morning, and then VFR
during Monday afternoon.

/OUTLOOK FOR KMSP/
TUE...MVFR or IFR/TSRA likely. Wind SE 10-15G25kts.
WED...MVFR bcmg VFR. Chc -SHRA. Wind W 15G25kts.
THU...VFR. Wind W 10 kts.

&&

.HYDROLOGY...
Issued at 655 AM CDT Sun May 19 2024

A heavy rain event remains on track for Tuesday, with a large
footprint of 1 to 3 inches of rain, with some locations pushing
4 inches. The greatest rainfall totals are expected across
southwest, west central, and central MN. Exactly where and how
much rainfall we see will determine where a threat for river
flooding will exist going into Memorial Day weekend, but given
current rainfall forecasts, flooding during the holiday weekend
may be possible in the Cottonwood, Redwood, Minnesota (upstream
of Mankato), and Crow river basins.

&&

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

&&

$$

DISCUSSION...BPH
AVIATION...CTG
HYDROLOGY...MPG