Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 181045

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

Issued at 540 AM CDT Sun Mar 18 2018

Updated to include 12z aviation discussion below.


.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 12Z TAFS through 12Z Monday morning)
Issued at 540 AM CDT Sun Mar 18 2018

Solid swath of clouds has been slowly pushing eastward through
western MN this morning with MVFR ceilings evident in SW MN. These
clouds will continue pushing east through the day today in
conjunction with the low pressure center in the Central Plains.
Still some uncertainty with the timing of the MVFR ceilings,
especially in eastern MN, but confidence growing that MVFR
ceilings will be realized at all MN TAF sites by early afternoon
then into WI tonight. No precipitation is expected through 12z at
all TAF sites but chances for -RASN gradually increase during the
day tomorrow. Light/variable winds through this evening then
northeast 5-10kt overnight into tomorrow.

KMSP...Have advertised MVFR ceilings starting at 18z although it
is possible the onset of MVFR at MSP could be later by a couple to
several hours due to initial dry air in place over eastern MN.
Will monitor and amend as needed.

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




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