662 
FXUS63 KMPX 132301 AAA
AFDMPX

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
601 PM CDT Mon Sep 13 2021

.SHORT TERM...(This evening through Tuesday night)
Issued at 221 PM CDT Mon Sep 13 2021

The key messages in the short term is the near certainty of rainfall 
for most locations across the region. There is a potential for a few 
severe thunderstorms and locally heavy rainfall. The heaviest rain 
will fall across central Minnesota into northern Wisconsin, where  1 
to 2 inches are likely, with locally 2 inches or greater possible. 
The strongest storms should be across southern Minnesota near I-90, 
with the some gusty winds, hail, and a brief tornado or two 
possible. 

Today and Tonight - Early afternoon satellite/radar imagery together 
with 500mb heights and winds showed an area of showers and 
thunderstorms across the eastern Dakotas and far western Minnesota. 
These were located downstream of a shortwave trough that was 
centered over the Dakotas. A surface trough was located along the 
Mid-Missouri River Valley, with a warm front extending eastward 
across northern Iowa. Over the next 12 hours, this warm front will 
lift northward as the surface low strengthens and moves towards 
northern Wisconsin. The complex of showers and thunderstorms should 
intensify as it too moves eastward across the region. HiRes models 
are in good agreement with precipitation across central Minnesota 
into west central Wisconsin, so have increased the chances for rain 
to near 100 percent in these areas. 

The severe threat is contingent on the amount of instability that 
can develop. Moist mid-level lapse rates and fairly widespread cloud 
cover along the warm front should limit the severe weather potential 
to only a few isolated storms. However the deep layer and even low 
layer shear profiles would support rotating storms. Overall the 
threat is summed up nicely by the latest SPC outlook. The heavy 
rain threat is arguably of more concern, but the progressive nature 
of this system will also keep the flood potential to a minimum, as 
indicated by the WPC Marginal Risk of excessive rain. HiRes models 
are in fairly good agreement with localized areas of 2 to as much as 
4 inches of rain possible, with the highest probability being 
northwest of the Twin Cities. This could results in some quick rises 
on small streams and ponding of water in urban and poor drainage 
areas. The heaviest rain should exit the region by midnight.

Tuesday and Tuesday night - High pressure will build in behind this 
departing system and bring an end to the precipitation. Forecast 
soundings show the potential for clouds through mid-afternoon, so 
did decrease Tuesday's highs toward the lower end of guidance. On 
Tuesday night lows will fall into the mid to upper 40s for most 
locations.

.LONG TERM...(Wednesday through Monday)
Issued at 221 PM CDT Mon Sep 13 2021

We pick up the long term period on Wednesday morning around sunrise 
with high pressure holding over the Great Lakes, allowing for 
overall pleasant conditions Wednesday afternoon with low to mid 70s 
temperatures and mostly sunny skies. As this high pressure moves 
into the eastern Great Lakes, a cold front forming from a 
strengthening upper level low in central Canada will begin to slide 
south towards the area with chances for showers and thunderstorms 
increasing throughout the day on Thursday. A strong 850mb jet ahead 
of the cold front will allow warm and moist air to flow into the 
region, with humid conditions by the afternoon as temperatures reach 
the upper 70s to low 80s with dew points near 70. Our chance for 
showers will continue to increase later in the day and especially 
early Friday morning as the upper level low moves eastwards and the 
cold front begins stall over the area, with the nocturnal 925-850mb 
jet continuing to force showers and potential thunderstorms over the 
area. The GFS has fallen more in line with the ECMWF and bring 
showers to much of our coverage area including southern MN and 
western WI, with instability increasing to around 1000-1500 J/KG 
within model forecast soundings coupled with the moderate to strong 
shear present due to the strength of the low level jet. 

By midday Friday, the upper level low should track far enough 
eastwards that the front becomes occluded and rapidly loses its 
strength, with the low level jet also weakening such that chances 
for showers diminish significantly. Ensemble forecasts continue to 
push for what very well may be our last hot summer-like day on 
Sunday as the low level jet restrengthens with an upper level ridge 
building over central NA, which should also keep us dry aside from 
any surface based activity. High temperatures in the NBM continue to 
fluctuate between low to mid 80s, however this is close to the 25th 
percentile in the GEFS which would suggest a run at 90 is possible 
or even likely with the 50th percentile at 91 degrees Sunday 
afternoon. The period rounds out with a strengthening trough over 
the central Rockies which looks to reintroduce plenty of forcing via 
further 925-850mb jet activity, however the spread and strength of 
any precipitation is large unknown due to amount of time until then 
as well as a somewhat active pattern beforehand.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 601 PM CDT Mon Sep 13 2021

MVFR cigs across southern MN will spread north early this evening,
while showers become more widespread. Thunderstorm development could
occur this evening as well, most numerous across southern MN. Cigs
will deteriorate to IFR levels overnight, then lift and scatter later
Tuesday morning.

KMSP...On and off light showers are possible through 02Z, then
heftier showers and a few thunderstorms should arrive for the rest 
of the evening. Cigs nearing IFR levels overnight expected to improve
mid to late morning Tuesday.

/OUTLOOK FOR KMSP/
Wed...VFR. Wind S 5-10 kts. 
Thu...VFR with MVFR/-SHRA possible late. Wind SSW 10-15 kts. 
Fri...MVFR with -SHRA possible. Wind NW at 10 kts. 

&&

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

$$

SHORT TERM...JRB
LONG TERM...TDH
AVIATION...Borghoff