Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 141829
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
129 PM CDT Sat Apr 14 2018

...HISTORIC BLIZZARD ONGOING...

.Updated for short term and 18Z Aviation discussion.

UPDATE Issued at 111 PM CDT Sat Apr 14 2018

The Blizzard Warning has been expanded eastward through the Twin
Cities metro and into far western WI. Winds have strengthened as
the heavy snow builds in with gusts of 40 to 45 mph common. Solid
blizzard criteria are occurring and are expected to continue for
several hours. Snowfall rates nearing 2 inches per hour have been
reported at MSP. This is an historic storm that will make travel
impossible in open areas this afternoon and tonight. Additional
snowfall will be at least a foot from southwest to east central MN
into portions of west central Wisconsin. This system will rank up
there as one of the most significant winter storms in some time.

&&

.SHORT TERM...(Today and tonight)
Issued at 350 AM CDT Sat Apr 14 2018

Significant winter storm will continue across the area today,
including snowfall rates around and possibly over one inch per
hour for much of the area this afternoon into this evening.

Surface analysis this morning shows the deep occluding low
pressure center near the Kansas City area with a snaking warm
front extending east through MO-IL-IN-OH and its trailing cold
front south over eastern OK/TX. Extensive high pressure centered
over southern Manitoba/Ontario provinces expands south into the
Dakotas, Minnesota and the Great Lakes. Aloft, the deep upper
level low remains offset to the east of the surface low, within a
deep trough digging into TX/NM. A stout Bermuda high pressure dome
remains in place to the east of the trough. Per radar/satellite
imagery, a relative lull has developed over central/eastern
portions of the WFO MPX coverage area, with splotches of light
snow over western and southeastern portions of the coverage area.
Light additional accumulations can be expected in these locations
through daybreak.

As the morning progresses, the surface low will shift east to the
MO/IL border while the upper level trough tightens and pivots to a
more neutral and potentially negative tilt. PVA will heighten in
advance of the trough, particularly on the northern and eastern
peripheries of the upper low within the center of the trough.
There is still plenty of moisture available and with just enough
cold air advection to wipe away any semblance of a low level warm
layer while focusing much of the moisture within the DGZ, there is
plenty of evidence that when the snow resumes late this morning
through this afternoon, it will be heavy and prolonged. With
temperatures remaining below zero throughout the temperature
profile, the threat of freezing rain after daybreak through the
rest of the period will drop to zero, making the only precip type
expected to be snow. Multiple short- term models agree with
having snowfall rates around and potentially over 1 in/hr for much
of the area, specifically from southwest MN through the Twin
Cities into northwestern WI. From daybreak through dusk, it will
not be unreasonable to see snow accumulations between 6-10" for
much of the area. There will be a tight gradient on the northern
side of the snow band while the southern side will have a more
gradual snow gradient. As such, closer to the IA border,
accumulations in the 4-8" will be more realistic while in west-
central MN, accumulations may well only range 1-4".

There is still MUCAPE in the 1000-2000 j/kg range aloft, along
with decent mid-level lapse rates, mainly focused in southern MN.
Thus, there is still potential for a few isolated thunderstorms to
accompany some of the stronger bursts of snow. This aligns well
with the outline of general thunderstorms for southern MN into
southwestern WI on the SWODY1. That said, no severe thunderstorms
are expected.

The other complicating factor will be the tight pressure gradient
on the northern side of the surface low, especially over the open
areas of western through southern MN. Have bumped up wind speeds a
bit and this necessitates expanding the Blizzard Warning eastward
by a tier of counties. To the east of the Blizzard Warning, the
Winter Storm Warning will continue through Sunday afternoon.

The snow and winds will slowly diminish late tonight through
Sunday but additional minor accumulations will still occur during
this period. This snow will will have a high moisture content so
it will be strenuous to remove and also make for slippery road
conditions.

.LONG TERM...(Sunday through Friday)
Issued at 350 AM CDT Sat Apr 14 2018

The main concern in the long term is the winter storm affecting the
area. Then the chance for the next system to affect the area midweek.

Overall, the models have slowed the progression of the closed low
over the area. Isentropic forecast shows lift into the eastern
portion of the CWA through at least 18z Sunday. QPF of a tenth to
quarter of an inch will still give an additional 2 to 4 inches
accumulation into Sunday. We will need extend the warning expiration
until 00z Mon in the east. It does look like accumulation should
taper off Sunday afternoon however.

Following this system, high pressure should bring more sunshine but
it will remain on the cool side through Tuesday. The flow pattern
across the CONUS remains rather amplified with the next western
CONUS trough advancing east into the area Tuesday night into
Wednesday night. The GFS and Canadian pull a little warmer air north
into at least the southeast CWA initially which could generate some
mixed precipitation, but the ECMWF is cooler overall. They all paint
more accumulating snow for the area during this period. Temperatures
continue to trend at least 10 to 15 degrees below normal through the
period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 113 PM CDT Sat Apr 14 2018

LIFR conditions today will gradually improve to IFR/MVFR by
tomorrow. In the mean time expect 1/4 to zero visibility with
northeast winds near 30 kts across southern Minnesota. Conditions
will be slightly better in eastern Wisconsin at KRNH and KEAU. The
heaviest snow should end tonight with a few light snow showers
continuing into Sunday.

KMSP...
The next 6 hours will have the lowest visibility with generally
1/2 to 1/8 during this time. HiRes guidance continues to show some
improvement around 00Z, so should see visbys improve slightly, and
that trend continuing through Sunday morning. Light snow will
linger overnight, so anticipate that we will hold on to IFR/MVFR
conditions through at least 06Z.

/OUTLOOK FOR KMSP/
Mon...VFR. Wind NW 5-10 kts.
Tue...Mainly VFR. MVFR ceilings possible late. Wind E 5-10 kts.
Wed...MVFR conditions likely in -RA/-SN. Wind NE 5-10 kts becoming
NW.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Blizzard Warning until 7 AM CDT Sunday for WIZ023-024.

     Winter Storm Warning until 7 PM CDT Sunday for WIZ014>016-
     025>028.

MN...Blizzard Warning until 7 AM CDT Sunday for MNZ059>063-068>070-
     076>078-084-085-093.

     Winter Storm Warning until 7 PM CDT Sunday for MNZ044-045-
     049>053.

     Winter Weather Advisory until 7 PM CDT Sunday for MNZ043.

     Blizzard Warning until 1 AM CDT Sunday for MNZ047-048-054>058-
     064>067-073>075-082-083-091-092.

&&

$$

UPDATE...BORGHOFF/JRB
SHORT TERM...JPC
LONG TERM...DWE
AVIATION...JRB



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