Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 140207 AAA
AFDMPX

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
907 PM CDT Fri Apr 13 2018

.UPDATE...
Issued at 907 PM CDT Fri Apr 13 2018

The band of snow between St. Cloud and Alexandria appears to
finally be waning as drier air works southward. Several inches
accumulated in that band in only a few hours. Meanwhile,
widespread showers and thunderstorms across southern MN continue
to lift northeast. Temperatures aloft are above freezing, as
evident in bright-banding and the mostly rain or sleet obs so far.
Radar does indicate this bright-banding starting to erode near
the MN river in east central MN, and this could be the beginning
of a transition to accumulating snow. Hi- res models continue to
be very bullish on QPF for the next several hours before this band
begins to taper off and sink south during the overnight hours.
Some of this could be due to being fooled by the bright-banding
issue. Nonetheless, expecting steady snow from near New Richmond
southwest across the cities and into southwest MN. 3 to 5 inches
are possible in this corridor through 2 AM. Areas to the south
will remain rain/freezing rain or sleet until very late tonight or
Saturday.

Not too much is currently falling across west central MN. Still
expecting snow to fill in tonight or early Saturday morning, so
will leave the Blizzard Warning as is for now but the severe impacts
will be delayed.

Earlier the models had been delaying surging the second round
northward to late Saturday morning or even the afternoon hours.
Recent runs have sped that back up by a few hours. Will continue
to monitor that trend.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 330 PM CDT Fri Apr 13 2018

A very powerful winter storm will bring over a foot of snow to some
locations in Minnesota and Wisconsin. This storm has a lot of
moisture, with strong forcing for ascent with subfreezing
temperatures. What that in mind, it is certainly reasonable that a
few locations in southwest Minnesota will get near 18 inches of
snow. In addition, strong northeast wind will cause blizzard
conditions.

This set up for this cyclone is textbook with a strong low level
temperature gradient, amplified upper level trough, and deep
reservoir of potential vorticity. The heaviest snow will fall where
these three ingredients work together in southwest Minnesota.
Meanwhile, areas in central MN and western WI will see two round of
precipitation which is nicely depicted by the HiRes models. The
first round is tied to the warm air advection and Fgen. As of 3 pm,
this band was starting to take shape along I-94.

There should be a brief break in the precipitation tonight as it
changes to mainly a wintry mix and snow, but then expect another
band of heavy snow to lift up from the south on Saturday. This band
of snow is tied to the positive vorticity advection associated with
the Upper Level shortwave. These lobes of vorticity are difficult to
time, but the HiRes models continue to reflect the message of the
synoptic scale models and have 1-2"/hr snow bands moving through on
Saturday afternoon and evening. Meanwhile a well-defined TROWAL will
keep the highest snowfall amounts tied to this upper level wave.

Forecast models have trended a bit light with winds, and further
south with the precipitation. Tried to reflect this in the forecast,
so have lesser amounts of snow to the north. This centers the
snowband from Redwood Falls through the Twin Cities and Eau Claire.
The 19Z RAP13 and 18Z Nam continue this southern shift, so that will
be the main concern going forward and if the trend continues will
likely see the heavy snow axis shift south.

.LONG TERM...(Saturday night through Friday)
Issued at 330 PM CDT Fri Apr 13 2018

If you`re hoping for a huge warmup during the latter portion of the
forecast period, there isn`t much good news for you. The upper flow
will become fairly progressive, but without any prolonged
significant ridging in our area. So, although temperatures may be a
bit warmer than the past week or two, they still look to remain
below normal. The main weather feature of interest/concern is a
shortwave trough and associated surface low that will move through
the region Tuesday night and Wednesday. The model guidance is
actually in fairly good agreement on the evolution of this feature,
and unfortunately (if you`re looking for Spring) precipitation type
with it looks to partially if not mostly snow. Forcing looks to be
compact and focused with the upper wave, but there will be decent
moisture in place, so the 0.25-0.50" inches of precipitation most of
the guidance suggests seems reasonable. So, could be another
accumulating snow event for portions of the area. Other than that
system, the Monday through Friday time frame will be dry with the
aforementioned below normal temperatures.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 907 PM CDT Fri Apr 13 2018

Showers and thunderstorms across southern MN continue to lift
north and turn to snow north of the MN river. Expecting bands of
heavy snow to develop from along the MN river to MSP and possibly
RNH late this evening before drier air begins to erode the snow
from the north overnight. Could see several inches accumulate
before this occurs, but much will depend on surface temperature.
Otherwise, AXN and STC should be mostly out of the steadier snow
until Saturday afternooon and a mix should turn over to snow at
RWF during the next few hours.

KMSP...A very tricky forecast tonight, but precip has just turned
over to all snow so this may be the beginning of the accumulation
period. Could see inch/hr rates late this evening. The snow
should taper off overnight before starting again Saturday. Timing
may need to be adjusted again for the arrival of snow Saturday,
but will reassess for the 06Z TAF issuance.

/OUTLOOK FOR KMSP/
Sun...IFR/MVFR with lingering snow. Wind N at 15G20 kts.
Mon...VFR. Wind NW 5-10 kts.
Tue...MVFR this -DZ possible. Wind SE at 10 kts.
&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Warning from 1 AM Saturday to 1 AM CDT Sunday for
     WIZ024-026-028.

     Winter Storm Warning until 1 AM CDT Sunday for WIZ014>016.

     Winter Storm Warning until 1 AM CDT Sunday for WIZ023-025-027.

MN...Winter Storm Warning from 1 AM Saturday to 1 AM CDT Sunday for
     MNZ076>078-083>085-092-093.

     Winter Storm Warning until 1 AM CDT Sunday for MNZ049>053-058-
     059-061.

     Winter Weather Advisory from 1 PM Saturday to 7 AM CDT Sunday
     for MNZ043>045.

     Winter Storm Warning until 1 AM CDT Sunday for MNZ060-062-063-
     066>070-075.

     Blizzard Warning until 1 AM CDT Sunday for MNZ047-048-054>057-
     064-065-073.

     Blizzard Warning until 1 AM CDT Sunday for MNZ074-082-091.

&&

$$

UPDATE...BORGHOFF
SHORT TERM...JRB
LONG TERM...
AVIATION...BORGHOFF



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