Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 182328

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
628 PM CDT Sun Mar 18 2018

.SHORT TERM...(This evening through Monday)
Issued at 242 PM CDT Sun Mar 18 2018

A still and cloudy day across the region beneath high pressure. The
lack of sunshine or mechanical mixing kept high temperatures about
10 degrees cooler than yesterday.

Over the next 24 hours a weak upper level short wave will move
across the region and lead to broad ascent across the region. Clouds
should prevail, and deeper saturation should lead to some
precipitation developing across western Minnesota Wednesday
afternoon. Thermal profiles show a mix of rain/snow. Should have
enough ice crystals to limit any potential for freezing rain, so
have continued along the lines of the previous forecasts and removed
it from the forecast. This system will gradually weaken as it heads
toward eastern Minnesota and western Wisconsin Monday night into
Tuesday. Total accumulations will be around 2 inches in western
Minnesota, only a trace in eastern Minnesota and western WI.

.LONG TERM...(Monday night through Sunday)
Issued at 242 PM CDT Sun Mar 18 2018

Aside from the aforementioned light rain/snow on Monday night and
Tuesday, the upper level wave will also push a reinforcing cool
airmass across the Upper Midwest. Meanwhile height rises and warm
air advection over the Rockies will lead to a tight temperature
gradient oriented along the Missouri River Valley.

This temperature gradient will become active Thursday night into
Friday as an upper level wave move onshore the west coast. A
shortwave trough will take on a negative tilt as it moves across the
High Plains. Despite a pronounced deepening surface low pressure
system, there will be very strong frontogenesis which will lead to a
band of heavy precipitation Friday/night into Saturday.

Thermal profiles off the ECMWF are much cooler than the GFS and show
a significant snow storm over the forecast area. Meanwhile the GFS
is warmer, but still produces enough QPF for several inches of snow
to accumulate. Given the high-impact potential for this event, did
increase the temperature spread to have snow mentioned on Saturday.
Details will probably be difficult to pin down with this set up, so
don`t get too hung up on any one model forecast.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 628 PM CDT Sun Mar 18 2018

Main question tonight is as northeast winds become established,
how far west will MVFR and lower cigs retreat. These northeast
winds will be advecting dry air back into the area, so agree with
the trends we are seeing with the guidance in that MVFR cigs will
retract back to the west. The HRRR is most aggressive with this
cig improvement, taking VFR cigs all the way west of even AXN/RWF.
For now trended us that direction, with VFR cigs returning for
all by AXN/RWF. As for when MVFR cigs come back once VFR
conditions return, low confidence here, but will likely not be
until precip moves in, which looks to move in largely after this
TAF period. As for the precip, slowed it`s arrival quite a bit and
only AXN has a threat of snow right at the end of this period.

KMSP...VFR cigs may return earlier than 10z, but once they get
here, they may be here for quite some time, with MVFR or lower
conditions likely not returning until Monday night, closer to when
the snow threat arrives.

TUE...MVFR cigs likely. Chc IFR with -SN. Wind E 5 kts.
WED... MVFR cigs possible. Wind E 5 kts.
THU...VFR. Wind SE 5 kts.




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