Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 222322

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
622 PM CDT Sat Apr 22 2017

Issued at 622 PM CDT Sat Apr 22 2017

Updated to include 00Z Aviation Discussion below.


.SHORT TERM...(This evening through Sunday)
Issued at 417 PM CDT Sat Apr 22 2017

Expect dry weather to continue through the rest of the weekend.
Meanwhile a band of precipitation will develop across northern MN/WI
but that should be north of our forecast area. The clouds associated
with this precip will keep temepratures cooler north of I-94, but
areas near I-90 should see highs near 70 again on Sunday.

Early afternoon satellite imagery and surface obs showed clear skies
across Minnesota and Wisconsin, but a fairly potent cold front was in
place over the International Border. Over the next 24 hours this
boundary will move southward and a band of frontogenetically forced
precipitation will develop over northern Minnesota and Wisconsin.
Forecast soundings show the best lift around the 700mb level, so
although the surface boundary will reach the northern part of the
forecast area, the omega and precip will be more poleward due to the
slope of the frontal boundary. For that reason, kept the forecast
dry along the Lake Mille Lacs area, but did increase the spread in
temperature between the northern and southern part of the forecast

.LONG TERM...(Sunday night through Saturday)
Issued at 417 PM CDT Sat Apr 22 2017

Run to run model variability continues to be unusually high
throughout the long term. Tuesday was supposed to be one of the
only dry periods next week, now it looks like the wettest.

The system for Monday remains the most consistent feature next
week. Low pressure will track from Wyoming through central MN to
Lake Superior by Monday night. This will lift the front back north
Sunday night with mild and breezy conditions expected area wide
Monday. Much of the forcing and deeper moisture will be near and
north of the low, and likely PoPs are in place for the northern
half of MN. Only a few showers will accompany the cold front
further south.

Attention then quickly turns to a system that has shifted
considerably further north Tuesday. With the comparably weak
preceding system and the boundary that stalls across Iowa, such a
shift seems reasonable. NAM per usual is the most extreme example
spreading 1-2 inches of cold sector rain across much of the CWA.
ECMWF has the same general idea, but with lighter QPF. The GEM is
most suppressed and seems unreasonable, while the GFS is a decent
compromise. Raised PoPs to likely or categorical across
southern/eastern MN and western WI with values tapering off
quickly to nothing north and west of Alexandria. Another issue is
how cold the lower half of the atmosphere will be and whether
snow has any potential to mix in Tuesday night. NAM forecast
soundings point to rain with a deep "warm" layer (+1 to +4C from
3-10 kft) despite near critical surface temps in the low 30s. GFS
cools the column a bit more and does snow accumulation potential
south and east of the metro up through northern WI. With models
not even agreeing where the low will track yet, further
adjustments should be expected.

A big shift has also occurred late week with the large scale
pattern. High pressure is now advertised on all deterministic
models to remain parked over the Great Lakes or nearby for the
rest of the week. Energy is slower to eject northeastward from the
southwest and when it does it seems more suppressed. This will
mean several days with dry and cool conditions, and frosts and
freezes for a few nights. By next weekend, there are still
indications lee cyclogenesis over the central Plains could bring
the next system at the end of or beyond the current forecast


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 622 PM CDT Sat Apr 22 2017

Main forecast issue through the period looks to be wind direction
as the boundary to our north tries to sag south on Sunday while
low pressure begins to move out into the Plains. Wind speeds will
generally be light, so direction shouldn`t be a huge concern, but
speeds will pick up some toward the end of the period as the
gradient tightens a bit ahead of the surface low over the Plains.
Stuck fairly close to the previous forecast in most respects, with
the northern sites being the only ones who should see a lower (but
still VFR) ceiling by late Sunday.

KMSP...Main item of uncertainty is wind direction later tonight
through Sunday. For now, stuck close to the previous forecast and
guidance from the LAMP and GFS, but some adjustments will likely
be needed on Sunday.

Overnight Sunday night...VFR. South wind 10 to 15 kt.
Monday...VFR, MVFR possible late. South wind 15 to 25 kt.
Monday night...MVFR, IFR possible late. Chance of rain. South
wind 10 to 15 kt becoming west.
Tuesday...MVFR, IFR possible. Rain likely. Northwest wind 5 to 15
kt becoming north 10 to 20 kt.
Tuesday night...MVFR, IFR possible. Rain likely early. North wind
10 to 20 kt.
Wednesday...MVFR, mainly early. Chance of rain. North wind 10 to
20 kt.




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