Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 141025 AAA

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
525 AM CDT Mon Aug 14 2017

.SHORT TERM...(Today and tonight)
Issued at 400 AM CDT Mon Aug 14 2017

A band of showers in advance of a slowly eastward propagating MCV
over the metro will continue for the next few hours. Isolated
shower development may continue through much of the day to the
west of this feature, not unlike what is happening currently over
western MN. Cyclonic flow with the 500 mb trough axis overhead
will keep clouds in place through much of the day, although some
clearing is possible this afternoon from west central to south
central MN with the trough beginning to lift out of those areas
late. Highs today will remain several degrees below normal thanks
to the clouds.

The mid level trough will quickly be replaced by a ridge axis
tonight while a surface high builds southeastward into the Upper
Great Lakes region. With some clearing expected and winds
decoupling, fog is looking like a good proposition particularly as
crossover temperatures exceed 5 degrees. Although unlikely, the
only concern will be whether 10 kt winds aloft help keep the high
RH in the boundary layer more in the form of stratus. This would
be more likely if stratus from today remains in place after

.LONG TERM...(Tuesday through Sunday)
Issued at 400 AM CDT Mon Aug 14 2017

Tuesday and Wednesday... All signals continue to point to the
Tuesday through Wednesday period as one of plenty of rain,
potentially heavy at times. The period will start out dry as a
small area of high pressure departs to the Great Lakes and a ridge
axis sits atop the region at daybreak Tuesday. Meanwhile, a
longwave trough over the Rockies will continue to dig to the Four
Corners region as well as support several shortwave trough
disturbances within the flow. Several weak low pressure centers
over the lee of the Rockies will steadily become more organized
during the day on Tuesday while the longwave trough taps into the
southern subtropical jet. This will shunt plenty of deep moisture
into the Upper Mississippi River Valley region, such that PWATs
increase to nearly 2 inches for much of the time late Tuesday
through Wednesday morning. Chances for precipitation ramp up
Tuesday evening from west to east, reaching categorical level
overnight Tuesday into Wednesday morning. Currently have pops up
to 80% but would not be surprised to see these values increase
given the consistency of the models for this scenario. What looks
to aid precipitation generation even more is a pivoting shortwave
trough and a developing compact cutoff low aloft over the area
offset from a compact surface low also over the area Wednesday
morning, with both low centers moving northeast through Minnesota
towards Lake Superior. These features may well contribute to heavy
rain over portions of the area, possibly with rates exceeding
1"/hr. The surface low with its trailing cold front will shift off
into the Great Lakes Wednesday evening, allowing precipitation
coverage and intensity to wind down. Though there may well be a
convective nature to a small portion of the precipitation, the
bulk of it will be dynamically-driven. Severe potential is non-
zero but given relatively weak lapse rates and fairly short
duration of any appreciable insolation to further destabilize the
atmosphere, chances for any severe storms is quite low.

Thursday through Sunday...High pressure will generally prevail for
the end of the week through the weekend but a shortwave trough
axis arriving from western Canada will drop through the region
during the day on Friday in conjunction with another surge of low-
mid level moisture. The lack of surface features will help
mitigate thunderstorm development so will only look for isolated
thunderstorms coverage Friday afternoon through Friday night.
Another weak disturbance, albeit much weaker, looks to drop
through the region on Sunday, possibly spawning isolated showers
but will again be of little consequence. Temperatures will run
close to normal values with little day-to-day variance due to the
lack of any airmass change, even with the frontal passage earlier
in the week.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 525 AM CDT Mon Aug 14 2017

Cigs are deteriorating to IFR across western MN which should work
eastward during the next few hours this morning before gradually
lifting into the afternoon. Scattered showers will persist across
eastern MN/western WI through at least the morning hours. Clearing
skies and light winds tonight will bring a good fog/low stratus
set up with IFR or lower conditions likely again overnight at most
TAF locations.

KMSP...Bouts of IFR cigs are likely this morning before improving
conditions this afternoon. There is a risk for fog tonight, but
believe the worst conditions will be in outlying areas.

Tue...VFR. MVFR/IFR possible late with SHRA/TSRA. Wind E-SE at
5-10 kts.
Wed...Likely MVFR/TSRA. Wind S-SE at 5-10 kts.
Thu...VFR. Wind N-NW 5-10 kts.




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