Area Forecast Discussion
Issued by NWS Twin Cities, MN

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

FXUS63 KMPX 170912

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
412 AM CDT Tue Apr 17 2018

.SHORT TERM...(Today through Wednesday night)
Issued at 405 AM CDT Tue Apr 17 2018

Surface analysis early this morning shows the center of a north-
south oriented swath of high pressure aligned along the
Mississippi River Valley. A potent low pressure system is
developing over eastern WY with a warm front leading the system to
the southeast. Aloft, a ridge axis of high pressure is moving east
through the northern-central Plains while a longwave trough axis
digs south on the windward side of the Rockies.

This trough is expected to pivot as it crosses the Rockies,
staying open yet taking on a negative tilt. The trough itself will
remain open through Wednesday morning then have a closed upper low
form within it during the day Wednesday, allowing it to
temporarily become cut off from the western Canadian trough until
Wednesday night when it then becomes absorbed by the large north
Atlantic trough, helping drag the system away to the east.

In terms of the surface features, the upper trough will help kick
the surface low out of Wyoming today and shift it through Kansas
and northern Missouri tonight into Wednesday morning, then through
the Ohio Valley region Wednesday and Wednesday night. The surface
high pressure will shift off to the east, allowing the influence
of the surface low to take over. Dry conditions are expected today
but clouds will gradually move in from the east. Plenty of deep
Pacific moisture will accompany this surface low, with the
possibility some Gulf moisture may surge well north in advance of
this system early Wednesday morning. In addition, the pivoting
open trough will essentially act as a pathway for a surge of PV
advection late tonight through Wednesday morning, helping enhance
precipitation generation.

Temperatures look to remain colder than normal and a little colder
than guidance, owing to the widespread snow cover across the WFO
MPX coverage area. As the system shifts east and brings a swath of
precipitation into the region, the added lift and dynamics
associated with the features at the surface and aloft will allow
moderate to potentially heavy snow to develop with very little
chance at any icy precipitation. Snow will develop during the
early morning hours Wednesday and persist for much of the day,
with the heaviest closest to the surface low (i.e. around the I-90
corridor). As such, have opted to issue Winter Storm Warnings for
a handful of counties in far southern MN with a Winter Weather
Advisory to the north of the warning, extending nearly into
central MN. Have opted at this point to hold off any headlines
into WI due to some uncertainty at this point. However, confidence
is rather high that 5-8" of snow will be realized in far southern
MN out of this system. The snow will taper off Wednesday evening
such that by the early morning hours Thursday, no additional
accumulations are expected.

In addition, short-term guidance indicates fairly decent mid-level
lapse rates with MUCAPEs again rising to the 1000-1500 j/kg range
(nearly all elevated). Given the high QPF expected out of this
system and the strong dynamics aloft, these instability factors
may aid in producing isolated thunderstorms Wednesday within the
pockets of heavy snow. Have added mention of thunder to far
southern MN.

The saving grace here is that wind speeds will top out in the
15-25 mph range, thus blizzard conditions are not expected. There
may be some areas of blowing/drifting snow, especially in wide
open and unsheltered areas, still making for hazardous travel in
southern MN. In addition, this will again be a high-moisture
content snow.

.LONG TERM...(Thursday through Monday)
Issued at 405 AM CDT Tue Apr 17 2018

The longer term concerns remain temperature trends and the chance
of any significant precipitation.

Following the Wednesday system, cooler but drier air will move
into the region through the remainder of the week. A warming
trend should develop into the weekend and early next week as the
upper flow becomes split. This will take the more significant
storm track south of the area. We may see more clouds and a small
chance of rain or snow over the west Friday night as the main
storm travels south of Minnesota. With a more Pacific west/east
flow developing, temperatures should warm slowly to near normal by
early next week. Overall, temperatures will be modulated by snow
cover and any threat of fog which may result form the more rapid
snow melt.

Model trends also bring a pacific type cold front/trough in the
northern stream by Monday night or next Tuesday. At the moment it
looks warm enough for just rain if it does happen.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1030 PM CDT Mon Apr 16 2018

Continued trend of 00z TAF of favoring the NAM for cloud trends
Tuesday, which is to maintain VFR conditions and not go with an
aggressive expansion of the low clouds as the GFS/LAMP have.
Again, it`s dry N-NW winds tonight combined with subsidence and an
overly moist boundary layer from the GFS that leads us away from
the LAMP for CIGS, though its wind forecast looks pretty good as
we work a ridge axis across MN Tuesday morning and western WI
Tuesday evening.

KMSP...LAMP cigs have been trending more optimistic with time, so
feel more confident in the NAM idea of low clouds remaining out of
MSP until Wednesday morning, when snow will be pushing back in.

Wed...MVFR with IFR/SN possible 14Z-24Z. Wind NE 5-10 kts bcmg NW.
Thu...VFR. Wind NW at 5-10 kts.
Fri...VFR. Wind lgt and vrb.


MN...Winter Storm Warning from 7 AM Wednesday to 1 AM CDT Thursday
     for MNZ084-085-092-093.

     Winter Weather Advisory from 7 AM Wednesday to 1 AM CDT Thursday
     for MNZ065>070-075>078-083.

     Winter Storm Warning from 4 AM to 7 PM CDT Wednesday for MNZ091.

     Winter Weather Advisory from 4 AM to 7 PM CDT Wednesday for



AVIATION...MPG is the U.S. government's official web portal to all federal, state and local government web resources and services.