FXUS63 KMPX 192013
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
313 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 312 PM CDT Sun May 19 2024

Radar returns from western to central MN have not been able to reach 
the surface thru this afternoon due to very dry low-level air in 
place (evidenced in MPX's 12Z sounding). Returns near the MN/IA 
border have had more success reaching the surface, as southerly flow 
has begun to advect greater moisture into our region. Isolated to 
scattered showers will become more common as we go thru this evening 
in response to moisture advection and a strengthening LLJ moving in 
from the west. Eventually, clusters of thunderstorms will develop 
near midnight along the nose of the LLJ, likely over south-central 
to southern MN, and move east-northeast thru WI into Monday morning. 
We're not expecting much in terms of severe weather (owing to the 
minimal CAPE and marginal wind shear), but the 12Z HREF LPMM 
forecasts most of southern MN and into western WI receiving at least 
0.5-0.75" of QPF tonight thru Wednesday. There are also several 
embedded streaks of QPF over 1.25" to upwards of potentially 2", 
which seems possible if localized areas can receive repeated rounds 
of storms. Rain should mostly exit to our east by mid-Monday 
morning, while overcast low stratocumulus will be slower to break 
up. But, some larger pockets of clearing should occur by the 
afternoon allowing temperatures to warm into the low to mid 70s.

Most guidance favors keeping us dry through at least the first half 
of Monday night. However, the HRRR, and to extent the GFS, ECMWF, 
and GEM, do try to develop convection and QPF over southern MN 
(mainly along I-90) where there is a reservoir of 1000-2000 
J/kg MUCAPE. This precip would theoretically develop near a 
stationary boundary and in response to an approaching upper-
level trough and jetstreak. While shear again looks marginal, 
likely leading to a more multi-cell storm mode, a severe wind 
gust or hail stone cannot be ruled out. This region has also 
been outlined as a Marginal risk (1 out of 5) in SPC's 1730Z Day
2 Convective Outlook. Tuesday basically looks like a lock for 
widespread, accumulating rainfall from the aforementioned trough
developing a strong, synoptic cyclone as it crosses the 
Rockies. NAEFS and EPS climatological guidance both show the 
surface low becoming abnormally deep and having anomalously high
moisture transport as it travels into the Upper Mississippi 
Valley into Tuesday evening. The first round of showers and 
thunderstorms looks to occur during Tuesday morning/early 
afternoon, moving northeast out of our CWA by mid-afternoon. 
This precip should develop underneath divergent upper-level flow
and within the right-entrance region of a downstream jetstreak.
CAMs show a brief break in the precip occurring before another 
round of showers and thunderstorms develops over IA (close to 
the surface low and frontal boundaries) and moves northeast 
Tuesday afternoon/evening. This round will eventually affect the
entire CWA by Tuesday evening leading to more accumulating 
precipitation. Another focus with this system will be the 
potential for severe weather later Tuesday. With such a strong 
synoptic system forecast, the kinematics will be in place for 
strong to severe thunderstorms within the impending buoyant warm
sector. Current consensus within the guidance places the warm 
sector from southeastern MN into western WI. Indeed, forecast 
severe variables and soundings show strong shear and veering 
wind profiles, especially close to the warm front. Where the 
uncertainty looms is how much daytime heating and thus 
destabilization can occur? Mostly cloudy skies should be 
overhead from the copious amounts of moisture and lift, so 
breaks in the clouds will be necessary to increase CAPE and 
improve low-level lapse rates. If some heating can occur, we 
could have a potentially dangerous severe weather environment to
monitor. SPC has also recognized this possibility and issued an
Enhanced risk for much of the Midwest, including southeast MN 
and southwest WI. A Slight risk extends farther north due to the
uncertainty of the northern extent of the warm sector.

Returning to storm total rainfall with this system through Wednesday 
afternoon, the NBM has a mean of 1.25-2" of QPF for most of the MPX 
CWA. Increasing to the 75th percentile of the ensemble results in 
MPX's area seeing at least 1.75" with localized amounts approaching 
2.5". The 90th percentile is where things get really interesting 
where area-wide amounts generally rise to well over 2.75", showing 
the high precip potential of this system. Would not be surprised to 
see localized streaks of even higher amounts, depending on where 
rainbands set up. This will also have be monitored as flooding could 
become an issue, especially for low-lying and urban areas.

Guidance shows the cyclone pushing off to our east on Wednesday, 
cooling our highs into the 60s and causing precip to taper off. 
However, temperatures should recover towards normal to end the week 
as another shortwave crosses the Rockies by Friday. This shortwave 
looks to bring another good chance of rain to our region during 
Friday, though likely not as significant (in terms of amounts) 
compared to Tuesday. Looking beyond the period, guidance hints a 
couple more chances of precip through the end of May as a continued 
train of shortwaves is favored. But, model differences grow during 
this time leading to decreased forecast certainty.

&&

.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...CTG
AVIATION...CTG
HYDROLOGY...MPG