Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 180923

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

.SHORT TERM...(Today and tonight)
Issued at 345 AM CDT Sun Mar 18 2018

Surface analysis early this morning shows broad high pressure
extending from the Dakotas southeast through the Upper-Mid
Mississippi River Valley through the Ohio River Valley regions. A
weak cold front is draped on the northern fringes of this area of
high pressure, from southern Alberta province through the Great
Lakes. Over the lee of the Rockies, another low pressure center is
gathering strength in eastern CO along a N-S oriented stationary
front from WY through the TX/OK panhandles. Aloft, a deep ridge axis
from MN to LA is slowly showing signs of breaking down while a
digging longwave trough is starting to break out of the western
CONUS. Both the central ridge and western trough will gradually
break down over the next 24 hours, allowing a cutoff low to develop
over the Four Corners region, offset from the developing surface
low. Both features will shift east in tandem through the next 24
hours, similar to the previous system a few days ago which took a
similar track and took on similar features. The ridge atop the Upper
Midwest will not be quite as strong, which will mean that the
northern extent of this incoming low pressure system will have
better reach into MN by daybreak Monday morning. The stacked low is
expected to shift east over KS/OK today through tonight, nearly
reaching the MO border by daybreak Monday morning. With the upper
ridge breaking down and plenty of Pacific moisture being dragged
into the region with this low, clouds will be on the increase from
the west today through tonight with a small chance of some light
snow reaching far western MN before daybreak Monday morning.
Otherwise, the area looks to remain dry through this short-term
period with the larger precipitation issues arising in the longer-
term portion of the forecast. In advance of this system, another
mild day is expected today with highs reaching the lower 40s in
western MN and upper 40s from far eastern MN through western WI.
Lows tonight will similarly run mild, especially with the increased
cloud coverage. Min temps Monday morning will range from the mid 20s
to around 30s.

.LONG TERM...(Monday through Saturday)
Issued at 345 AM CDT Sun Mar 18 2018

The long term concerns remain movement of the Monday/Tuesday
trough and QPF/snow being generated. Focus then turns to late in
the week into next weekend with movement of the next western CONUS

Upper flow is somewhat split with most of the energy driven south
of the region. There does appear enough moisture and forcing with
the northern stream trough to generate snow into western MN
during the west during the day. Movement and forcing works its way
across the MN portion of the cwa Monday night and Tuesday. THe
better QPF rides south along the MN River valley as the 85H
circulation moves along that region. QPF with the GFS seems a bit
overdone considering the forcing is rather weak and snow
potential limited do to the relatively elevated DGZ until during
the day Tuesday to the east. We went with more of a consensus QPF
for now, which gave generally around 0.10 to 0.25 inches over
much of the MN portion of the cwa with the higher amounts to the
southwest. Snow totals range around one inch over eastern MN and 1
to near 3 inches to the west.

This system exits the area Tuesday night. There may be some
lingering flurries into Tuesday night but overall model trends
have weakened the trough as it moves through. Wednesday looks to
remain mostly cloudy as well. There may be some flurries that
work across the southern cwa as well but model trends have
weakened/flattened the incoming short wave into Wednesday.
Temperatures will cool to the 30s for Tuesday and Wednesday.

Heights build ahead of the next trough which is forecast to lift
northeast into the area later Thursday night to the southwest and
over most of the cwa Friday into early Saturday. Both the GFS and
ECMWF draw in decent moisture from the west and total QPF from
0.75 to around 1 inch liquid is dropped over much of the area by
Saturday night. Some of this will likely be some wet snow,
especially across the southwest into Friday and then to the
northeast cwa Friday night into Saturday. The 120hr CIPS analog
is generating a mean QPF of around one half inch and a good 2 to 4
inch mean snow accumulation across the cwa for that period.
Timing still an issue with the overall movement of the trough so
we pretty much kept the blended guidance PoPs for now. We did
trend them down into Saturday with more of a GFS solution with the
next extension of the western trough lifting into the region
Sunday. Temperatures should cool back into the upper 30s to lower
40s by Saturday and even cooler into Sunday as the trough moves
through. Definitely something to monitor.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1029 PM CDT Sat Mar 17 2018

Only concern are clouds encroaching from the west. We have a very
dry airmass in place, so continued to slow play the arrival of
MVFR cigs, especially going into eastern MN and WI, where we have
kept cigs VFR. Continued to lean toward the more optimistic
LAV/LAMP for cigs, though we could certainly see MVFR cigs make it
as far east as MSP by the afternoon. Virtually no wind expected
on Sunday, but we will slowly establish northeast winds again
Sunday night.

KMSP...Still a lot of uncertainty with when we will see MVFR cigs,
with it still looking like it could be as early as 17z Sunday or
as late as 12z Monday. Given how dry our initial airmass is, have
continued to favor the VFR route until we have higher confidence
in how far east the MVFR cigs will be able to make it.

MON...MVFR cigs likely. Wind NE 10 kts.
TUE...MVFR cigs likely. Chc -SN. Wind E 5 kts.
WED...Mainly VFR. MVFR cigs possible. Wind E 5 kts.




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