Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210016

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
716 PM CDT Tue Mar 20 2018

.UPDATE...For 00z Aviation discussion below


.SHORT TERM...(This evening through Wednesday)
Issued at 315 PM CDT Tue Mar 20 2018

Two short wave were evident across the Northern Plains, and Upper
Midwest this afternoon in the latest water vapor imagery. Forcing
associated with these short waves, and ample moisture, led to
occasional light snow. However, wind energy was weak, leading to
weak convergence and very subtle lift. Therefore, any snow,
combined with stronger solar insolation, kept snowfall amounts
very light. Snowfall amounts after sunrise today were kept below
one inch, and mainly in areas along the Minnesota River Valley
where slightly stronger energy was noted with the short wave in
Iowa. The main change overnight was to add some light freezing
drizzle in western Minnesota due to weak lift and the lack of
cloud ice seeding. A stronger wave was evident across northern
Montana this afternoon which may allow for a more concentrated
area of light freezing drizzle or light snow Wednesday morning in
central Minnesota. The latest HRRR has some weak returns noted in
central Minnesota after 12z Wednesday. However, even if some light
precipitation develops, it shouldn`t have much of an impact due
the very light duration/amounts expected.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 325 PM CDT Tue Mar 20 2018

The main concern for the upcoming weekend storm is whether the
current model trends have the right idea of moving the main storm
system further to the south, and cutting off any significant
precipitation over Minnesota, and western Wisconsin.

Over the past 24 hours, models have trended drier and cooler for
this upcoming weekend storm. Confidence has increased that most of
the precipitation Friday night, and into early Saturday morning
will be in the form of snow. A mixture of rain or snow is possible
Friday, but with a drier east/southeast flow initially, the
precipitation could be delayed. Plus, the higher March sun angle
will also play a role of precipitation type Friday afternoon once
precipitation starts in western Minnesota. Eventually the
combination of strong isentropic lift along a strengthening
thermal boundary will lead to widespread precipitation across
western Minnesota by Friday afternoon, it will slowly move
east/southeast, but the persistent drier easterly flow will limit
the forward progression to the east. This may be one of those
weather systems that have a very sharp precipitation gradient from
west to east. Overall, there remains high confidence that
precipitation will form and overspread Minnesota Friday
afternoon/evening. There is lower confidence on how far
east/northeast the precipitation develops. Therefore, west central
Wisconsin could be in the zone where only a light dusting of snow
occurs, vs a much heavier wet snow develops in central and east
central Minnesota.

This system is also fairly fast which leads to less likely of
flooding problems. However, the mean flow becomes more southwest
next week, and this is a very unsettled pattern for the Upper
Midwest. It is also a warmer pattern which is more prone to liquid
precipitation vs. frozen this time of year. Either way, a much
wetter pattern is likely next week.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 716 PM CDT Tue Mar 20 2018

Snow will linger through the first few hours of the TAF period over
central & south central MN, gradually ending during the mid to
late evening hours. MVFR conditions will prevail into Wednesday,
with IFR possible at times overnight at western sites (KAXN and
KRWF). Improvement will be slow on Wednesday, with MN sites likely
to endure MVFR conditions through much of the day. Southeast winds
gradually become southerly on Wednesday, but speeds will be light
(generally around or below 5 knots).

Snow lingers until about 03Z, with borderline MVFR cigs/vsbys
persisting into Wednesday.

THU...VFR. Wind E_NE 5 kts.
FRI...VFR early becoming MFVR with -RA/-SN. Wind ESE 10G15 kts.
SAT...MVFR with Chc -RA/-SN. Wind ESE 10G15 kts.




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