Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 211145 AAA
AFDMPX

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
645 AM CDT Mon Sep 21 2020

.SHORT TERM...(Today through Tuesday)
Issued at 358 AM CDT Mon Sep 21 2020

A few light showers continue across southern Minnesota and western
Wisconsin early this morning, but they are on a downward trend.
These showers are located on the southern edge of richer mid level
moisture. RAP has analyzed 850 mb Tds ranging from +8 to +11C in a
narrow corridor from southwest MN to northwest WI. The +11C
isodrosotherm over southwest MN will advect northeast during the
next several hours to east central MN. 850 mb wind will back a bit
more southerly after sunrise which will result in increasing
moisture flux in a narrow area from near Willmar to Cambridge on the
northern edge of this moisture tongue. Showers and perhaps a
thunderstorm or two may develop in a narrow line within this zone by
8 or 9 AM. RAP and HRRR have advertised this consistently overnight.
Reintroduced some 30-40 PoPs along this line from mid to late
morning, before the moisture max shifts northeast and activity
diminishes. Another modest moisture max will approach from the
southwest this afternoon. Additional isolated to scattered showers
could develop again across southern and east central MN. Right now
nothing too organized is expected, but it still warrants slight
chance PoPs.

The approach of Hurricane Teddy and broad troughing shifting east
across the Great Lakes will weaken the strong surface high over New
England today and shift the center southwest to the Ohio Valley
tonight. This will bring a reprieve from the strong southerly flow
by Tuesday. 925 mb temps from about +20C today to +22C Tuesday will
bring warmer temperatures to start the week. Guidance is very
tightly clustered with highs around 80 today and lower 80s tomorrow.
In fact, the 10th and 90th percentiles vary by only a degree or
two.

.LONG TERM...(Tuesday night through Sunday)
Issued at 358 AM CDT Mon Sep 21 2020

Weak ridging within the zonal split flow will be located over the
Northern Plains Tuesday night. The upper-level pattern has been
progressive, meaning that features such as ridges or troughs tend to
not get stuck/blocked. Mostly clear skies are forecast Tuesday night
with lows in the mid to upper 50s. Wednesday`s highs will be near
80. Skies are forecast to be mostly sunny but some clouds could
build in later in the day as the weak upper-level ridging flattens
and a shortwave approaches. Regarding the shortwave, the 00z ECMWF
is the southernmost solution, with a well defined shortwave passing
through central MN Wednesday night. In this scenario, central MN
into western WI would see showers and thunderstorms overnight
Wednesday into Thursday. Meanwhile, the 00z GFS, NAM, and GEM favor
a weaker shortwave that travels more through northern MN and WI by
Thursday morning. Thus, the main focus of lift and precipitation
would mostly miss the MPX CWA to the north, except perhaps western
WI. The GFS does try to spin up a separate surface low over southern
MN, allowing for additional precipitation to develop. However, this
appears too optimistic as vertical profiles are relatively dry
across southern MN. Have opted to keep PoPs and QPF confined to
eastern MN and western WI for the time being.

As the aforementioned trough exits the region eastward, the split
flow becomes consolidated into a single stream as a strong 150 knot
southwesterly jetstreak arrives over the Pacific Northwest Wednesday
night. While this feature travels eastward, the low-level
ageostrophic response will develop a strong LLJ advecting very warm
850 mb temperatures of over 20 degrees C into the Northern Plains by
Thursday night. Upper-level ridging will build into south-central
Canada allowing for a dry and warm end to the work week. Thus, after
a relatively cooler Thursday in the 70s temperatures will heat up to
well above normal again on Friday.

Chances for rain are looking increasingly better next weekend as a
longwave trough arrives in the Pacific Northwest Friday. All long-
range forecast models translate the trough eastward; nearing the
Northern Plains by Saturday and producing widespread precipitation
across the region through Sunday. Thus, our first soaking rainfall
in a few weeks could very well be on the horizon. Future model
trends will need to be monitored to narrow down precipitation
timing, location, and amount. Also of note, after next week there is
a hint that the pattern cools off to more "Fall-like" weather.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 645 AM CDT Mon Sep 21 2020

VFR conditions through the period. A few showers could develop
across central MN near STC later this morning, with another couple
across southern MN this afternoon.

KMSP...Some wind shear this morning will ease by 14Z. A few
southerly gusts to 20 kt are possible today.

/OUTLOOK FOR KMSP/
TUE...VFR. Wind S 5-10 kts.
WED...VFR. Wind SW 10G20 kts.
THU...Chc MVFR. Wind S 5 kts.

&&

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

$$

SHORT TERM...Borghoff
LONG TERM...CTG
AVIATION...Borghoff



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