Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 271832
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1232 PM CST Mon Feb 27 2017

.UPDATE...
Issued at 1211 PM CST Mon Feb 27 2017

Updated to include 18z aviation discussion below.

&&

.SHORT TERM...(Today and tonight)
Issued at 400 AM CST Mon Feb 27 2017

Frontal boundary that sagged into the area yesterday started
lifting back north as a warm front overnight. Upglide over the
boundary has resulted in cloud cover and light snow developing
north of the boundary, but this snow will quickly lift into
northeast MN early this morning as the warm front continues to
lift north. By the afternoon, this front is progged to get near an
Aberdeen, SD to Hibbing line, which would place the entire MPX
area in southerly winds and the warm sector. As we have seen this
February, south winds plus bare ground results in high
temperatures that often come in at the high end of guidance. As a
result have highs today pushing well into the 40s north of the
snowpack, with some 50s not out of the question out around
Madison. The one limiter for temperatures today is the potential
for ample mid/upper level cloud cover. However, current forecast
is near where majority of bias corrected grids are going, so feel
pretty confident in the warmer highs projected in the snow free
areas.

For tonight, things start getting a little murky. As moisture
advection increases ahead of the frontal boundary, which tonight
will become stationary near the northwest end of the MPX area. At
the same time, a significant surge of theta-e rich air will be
building north out of the mid/lower Missouri River valley within a
coupled upper jet structure. The best forcing with the coupled
upper jet and a 50kt LLJ both look to go across Iowa toward
southern WI. This puts much of the MPX area between main sources
of forcing to the northwest with the surface front and southeast
with the upper forcing and LLJ. This sets us within a zone of mid-
level dry air, which means drizzle. In addition, high dewpoint air
moving over the snowpack will result in a threat for fog over the
snow, though the boundary layer looks to remain mixed, which may
keep us more 1-3 mile vis with 200-500 foot ceilings as opposed to
dense fog.

With the front looking to remain mostly NW of the MPX area, we did
boost lows quite a bit for tonight, with lows currently progged to
remain above freezing tonight for all but the northwest CWA. This
helped to keep p-types pretty simple as well, with snow where temps
are forecast to go below freezing in the northwest with
drizzle/rain everywhere else.

.LONG TERM...(Tuesday through Sunday)
Issued at 400 AM CST Mon Feb 27 2017

The longer term concerns remain initial snow event for
Tuesday/Tuesday night and the overall warming trend into the
weekend.

The 00z deterministic runs continued to show a potential snow
band across portions of our western cwa. The 00z GEFS
probabilities of greater than 2 inches in 12hrs was also pointing
in that direction. We will mention an inch or two accumulation for
now mainly west of a line from near Willmar to Mora. The surface
low track is forecast to move from Colorado this evening...to
near Omaha by 12z Tuesday...and to southwest Wisconsin by Tuesday
evening. Normally...this would be a more favorable snow track a
little farther to the south of the current forecast. Models
guidance suggests better forcing to remain across the west and
northeast into the day Tuesday. Expect light rain/drizzle to be
the main weather p-type over the southeast portion of the area as
warm air remains in place. As the trough pushes east...we should
see mainly snow to the northwest...transitioning to
drizzle/freezing drizzle or light snow before it ends over most
the region through Tuesday night.

Cooler air drops over the area with the northern plains/western
Great Lakes near the baroclinic zone. The northwest flow does
bring down a weak clipper type system in the Wednesday
night/Thursday time frame. The GFS drops a couple inches of snow
with this feature across parts of southern Minnesota. Models
diverge some on the strength of the system so we will keep with
the chance type pops for the event for now.

More zonal flow develops late in the week with an overall warming
trend expected. We will see readings warm back into at least some
lower 50s in the southwest by Saturday. We expect 40s to be
common across the region for the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1211 PM CST Mon Feb 27 2017

Surface front will remain over south-central MN into northern WI,
wobbling north-south over the area through the next 24 hours. This
may cause minor but quick wind shifts from time to time but
overall the winds will generally come from the south today then
back to southeast this evening before shifting to north tomorrow.
Speeds throughout will generally be 10 knots or less. Clouds will
steadily lower this evening through tonight as a weak upper level
shortwave disturbance arrives. Light wintry mix of precipitation
will develop in western-central MN overnight and persist into
tomorrow while eastern MN into western WI receives -DZ/-RA. Flight
conds will likely bottom out into IFR levels by daybreak tomorrow
and remain there through much of the day tomorrow.

KMSP...VFR conditions will prevail into the early morning hours
then conditions deteriorate rather quickly during the pre-dawn
hours with mainly -DZ developing along with BR/FG. Ceilings likely
to drop to IFR levels after daybreak tomorrow with visibilities
mainly in MVFR but IFR visibilities not out of the question.
Conditions slowly improve late tomorrow. Winds will slowly back to
S from SSW this afternoon and continue backing to SE overnight.
Winds then expected to go light/variable through the morning push,
which will contribute to the low stratus/fog development, before
going to NE and N by tomorrow afternoon.

/OUTLOOK FOR KMSP/
WED...MVFR ceilings likely. Winds NW 5-10 kts.
THU...Chc MVFR/-SN. Winds NW 5-10 kts.
FRI...Mainly VFR. Chc MVFR ceilings. Winds S 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

UPDATE...JPC
SHORT TERM...MPG
LONG TERM...DWE
AVIATION...JPC


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