Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 240852

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
352 AM CDT Thu Aug 24 2017

.SHORT TERM...(Today and tonight)
Issued at 352 AM CDT Thu Aug 24 2017

Water vapor imagery shows a broad trough dominating the eastern half
of the CONUS, along with a narrow corridor of faint shortwave energy
over the area on the western periphery of the aforementioned trough.
These spokes of weak forcing will rotate over the area today. This
will most likely mean the continuance of spotty light showers
over the area today, particularly south central MN.

Tonight we expect precipitation to become more organized as
southerly/return flow develops locally as the mid/upper trough
shifts farther east and a surface trough enters the High Plains. By
06z Friday, we see decent 925-850mb moisture convergence/transport
nosing into west central MN, and expanding across central MN by
daybreak Friday. Negative best Lifted Indices and MUCapes sufficient
for thunder start inching toward western MN on Friday, so
thunderstorms will become more of a concern.

Cloud cover today will hold temperatures around 5-10 degrees below
normal, with highs remaining in the low/mid 70s.

.LONG TERM...(Friday through Wednesday)
Issued at 352 AM CDT Thu Aug 24 2017

Moisture will continue increasing Friday area wide thanks to a
persistent 25-35 kt LLJ. Scattered showers (and a few
thunderstorms) will be most numerous across Minnesota where the
better LLJ forcing and deeper moisture will reside. By Friday
night, the LLJ from eastern Nebraska, eastern South Dakota, into
southwestern MN will strengthen to 35-45 kt and pwats will
maximize to between 1.5-1.75 inches. This should facilitate the
development of widespread showers and several embedded thunderstorms
capable of heavy rainfall across western MN overnight.

The system will advance eastward Saturday and focus the heavy
rain threat from southwest MN to east central MN and northwest
WI. Better instability with MUCAPE of 1000-1500 J/kg and the high
pwats will allow storms to continually develop ahead of the
surface low/cold front. 00Z GFS and NAM QPF seemed too meager
given this set up, so leaned more toward the Canadian and ECMWF.
The 06Z NAM coming in is indeed heavier, but is also a quick
outlier. Focus will shift to WI Saturday night with a continued
heavy rain threat.

The cold front will clear the CWA by late Saturday night with
cyclonic flow lingering through Tuesday. Some surface based
instability could spark scattered showers/isolated storms Sunday
afternoon, and possibly again Monday afternoon.

Ridging will try to bring warmer temperatures eastward for later
next week, but that could be short-lived with a strong cold front
for the start of the Labor Day weekend.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1031 PM CDT Wed Aug 23 2017

VFR conditions expected throughout this TAF set. Clouds will
increase aloft through the rest of this evening then will look
for ceilings to lower into the mid-levels during the early morning
hours. A few showers are expected mainly from KSTC-KMSP eastward
but nothing that should bring conditions lower than VFR. Showers
will shift off to the southeast shortly after daybreak then
partial clearing is expected through midday tomorrow.

KMSP...VFR expected throughout. Main window for showers looks to
be in the 06z-10z timeframe and only intermittent at best with
minimal impacts expected.

Fri...Mainly VFR. Chance MVFR/-TSRA. Wind SE 5-10 kts.
Sat...Mainly VFR. Chance MVFR/-TSRA. Wind SE 5-10 kts.
Sun...Mainly VFR. Chance MVFR/-TSRA. Wind SW 5 kts becoming NW.




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