Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 151126

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
526 AM CST Thu Feb 15 2018

.updated for 12z aviation discussion below...

.SHORT TERM...(Today and tonight)
Issued at 308 AM CST Thu Feb 15 2018

The short term concern remains the threat of light snow across
mainly the west and south today into this evening. Water vapor
imagery currently showing several short waves embedded in the
westerly flow ahead of the incoming trough. One exiting the
northern WI with an extension into central South Dakota with the
main trough still to the west. Forcing may be lacking as the main
moisture from the incoming cold front moves through. Various HIRES
solutions were indicating developing over South Dakota mainly
during the afternoon east toward the southern Metro through early
evening. The 06z nam has backed off a little bout we will continue
the likely PoPs into southern third of the area. Any
precipitation should remain light with a dusting to less than an
inch of snow possible. Temperatures will likely fall over the
northwest cwa into the afternoon with perhaps a few degrees
recovery to the southeast before the front/colder air arrives this

This trough/front exits the region this evening and we should see
clearing sky. Northwest winds will increase as the arctic high
moves in with some gusts near 30 mph to the west, Winds should
diminish later tonight with temperatures dropping to the single
digits below zero across most of the area. Wind chills could drop
off to the 20 below to 25 below zero category for a time later
tonight into early Friday...mainly over the northern cwa.

.LONG TERM...(Friday through Wednesday)
Issued at 308 AM CST Thu Feb 15 2018

Friday through Saturday night...The period will commence with
surface high pressure centered over the central CONUS, lagging
behind a long frontal boundary extending from New England to the
ArkLaTex region. Following the surface high, a weaving warm front
extends south over the Rockies from an area of low pressure over
central Alberta province. Aloft, a large upper level low lumbering
over northern Hudson Bay will rotate in place, wobbling slightly,
during the end of the week through the weekend. This will maintain
a broad trough over eastern and central NOAM while a weak ridge
maintains itself over western NOAM. The warm front will slide
eastward Friday through Saturday while the southern periphery of
the upper low flattens out a bit, enough to end the short-term
cold air advection which had returned to the area. But, this will
allow not only enough warming to bring temperatures back to the
freezing mark for Saturday, but also allow enough moisture in
advance of the warm front to work with sufficient isentropic lift
to produce isolated to scattered snow showers over mainly eastern
portions of the WFO MPX coverage area Friday night into Saturday
morning. Otherwise, this portion of the extended is rather benign.
By the time Saturday night arrives, focus turns to a broad trough
moving onshore the Pacific Northwest and southern British Columbia
along with a weak conglomeration of low pressure area over the
CO/WY area in the lee of the Rockies.

Sunday through Wednesday...As alluded to in the previous section,
a large longwave trough will drop into the Pacific Northwest while
a wavy cold front near the international border slowly drops
south. As the trough drops into the western CONUS, this will shift
flow aloft to a more southwesterly configuration, allowing both
Pacific and Deep Southerly moisture to stream well into the
north-central CONUS for late Sunday through early Tuesday. As the
trough deepens, it will aid in cyclogenesis of the weak low
pressure centers into one main low which will drop into southern
Nebraska/northern Kansas, along the northern CONUS cold front.
This surface low will then traverse northeast along the front
Sunday night through Monday night, having plenty of moisture and
upper level support plus cold air advection with which to support
the idea of a potentially significant snowfall event somewhere in
the north-central CONUS. While there is good model agreement in
the broad-scale occurrence of having the event (hence pushing pops
into the 80%-90% range for late Sunday night through Monday),
there are still plenty of details that need to be resolved, such
as timing and amounts. Nevertheless, confidence is growing by the
day of seeing accumulating snow for Washington`s Birthday. Then,
even while the so-called main event winds down Monday night, the
surface front will linger just to the southeast of MN/WI while a
few upper level shortwaves swing through the area Monday night
through Tuesday night. With still a long plume of moisture
potentially available from the southwest along with much colder
air in place as the main system shifts off to the east, snow
showers may well linger from time to time Monday night through
Tuesday night. High pressure, allowing a drying-out period, does
not look to reassert itself until Wednesday and beyond.

Bottom line...all should continue to monitor the latest forecasts
from the NWS Twin Cities office to see how this potential event
may unfold for the upcoming Washington`s Birthday weekend.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 530 AM CST Thu Feb 15 2018

MVFR conditions dropping south with fropa this morning. Perhaps a
period of IFR at KAXN this morning. Expect lower end MVFR cigs
over much of the area with any accumulating snow to the
southwest. Mainly affecting KRWF/KMKT later this afternoon/early
evening. Expect clearing from the northwest late evening and after
08z toward KEAU. SFC winds becoming NW with gusts 25-30kts out
west later this morning/afternoon. Gusts to 20-25kt to the east.
Winds should gradually diminish after 06z Fri.

KMSP...VFR conditions giving way to MVFR cigs and chance of light
snow/flurries into the afternoon. Any accumulation should be
light - trace to maybe a couple tenths of an inch. CLearing
sky/vfr trend after 06z Fri with gusty northwest wind diminishing

Fri night...VFR. Winds SW 5-10 kts,
Sat...VFR. Chc -SN/MVFR in mrng. Winds SW bcmg NW 15G25 kts.
Sun...Confidence increasing in IFR/SN. Winds SE 10-15kts.




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