Area Forecast Discussion
Issued by NWS Twin Cities, MN

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799
FXUS63 KMPX 231851
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1251 PM CST Thu Feb 23 2017

.UPDATE...
Issued at 1234 PM CST Thu Feb 23 2017

Updated to include 18Z aviation discussion below.

&&

.SHORT TERM...(Today)
Issued at 400 AM CST Thu Feb 23 2017

Satellite imagery this morning and short term weather models
continued to depict the much drier air advecting southward across
Minnesota. The drier air will have a major impact on the timing of
the precipitation this afternoon which will be limited to far
southern Minnesota where the depth of the moisture will be more
apparent. Temepratures will be much cooler than yesterday, but
still above normal with readings in the 30s, to lower 40s.

.LONG TERM...(Tonight through Wednesday)
Issued at 400 AM CST Thu Feb 23 2017

We`ll start with the highlights for the Friday winter storm.  We
updated the forecast to reflect a blend of the 00z runs of the
GFS/ECMWF along with the WPC QPF guidance. The result of this was
a nearly 50% reduction in the snowfall forecast from Marshall
through much of the Twin Cities metro to Rice Lake, WI and points
north. The heaviest snow in the form of 12-15" with amounts up to
18" not unreasonable is still in the forecast, but is now forecast
along and south of a Fairmont to Eau Claire line with a much
tighter gradient in place to the northwest of where the heaviest
snow band is expected. These adjustments to the snowfall forecast,
along with increased confidence on where the heaviest snow will
fall resulted in upgrades to a blizzard warning in south central
MN, with a winter storm warning to the northeast into Chippewa
county in WI, with a buffer of watches left in place around the
warnings. We also trimmed the northwest tier of counties out of
the watch.

Main change seen with the guidance overnight was an overall
convergence toward what the ECMWF has been showing the past few
days. The NAM and several of the hi-res models lie northwest of
the preferred GFS/ECMWF blend, but even these models have been
trending southeast toward the preferred blend with each successive
run. The current forecast has fairly robust agreement within the
GEFS as well and we have fairly high confidence in the current
forecast, at least for where the heaviest band of snow will fall
(Fairmont up toward Eau Claire). There is less confidence
northwest of the main band, though the gradient in the end may end
up being even tighter than what we currently have. This gradient
makes county based warnings somewhat difficult, which is displayed
best by Washington county, where we currently have about 9 inches
forecast down by Cottage Grove and Afton, with totals closer to 3
inches up by Forest Lake.

Models continue to show a weak upper wave moving across the area
Sunday, with low pops in for that. In addition, our temperatures
after Friday will be strongly tied to our expected change in snow
cover and did move high temperature forecasts Saturday through
Monday toward the ECMWF, which shows considerably warmer
temperatures across western and central MN, where bare ground
is expected to be maintained.

Next potential system of significance comes Tuesday/Wednesday.
The Canadian continues to look unreasonably strong with this
system, the GFS continues to struggle to get anything of
significance going, while the ECMWF continues to have another
decent little precip event for us. Given the spread, we only have
chance pops at best. This looks to be a warmer system as well,
with a rain/snow mix expected.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1234 PM CST Thu Feb 23 2017

Potent winter storm still on track to impact 4 of the 6 WFO MPX
TAF sites (KAXN-KSTC look to remain out of the crosshairs as the
models are still putting SE MN in the crosshairs for heaviest snow
with a sharp dropoff going NW). MVFR to IFR conditions will
develop overnight with some periods of heavy snow over southern MN
into parts of western WI. Winds will also kick up overnight and
remain elevated through tomorrow with speeds increasing to
15-20G30kt for much of the coverage area. These speeds may well
created BLSN concerns for RWF-MSP and potentially the WI TAF
sites. Slow improvement will take place late tomorrow afternoon
through tomorrow evening (mainly past the end time of the 24/18z
TAFs).

KMSP...Timing/durations of IFR look to be less, mainly confined to
around the Friday morning push through midday Friday. Some
ceilings around that time could also drop into IFR levels which
would be lower than currently advertised. The strong winds may
well create visibility issues due to blowing/drifting for much of
the day.

/OUTLOOK FOR KMSP/
Sat...VFR. Wind NW 10-15 kts becoming W.
Sun...VFR. Chc MVFR/-SN. Wind SW-W 5-10 kts.
Mon...VFR becoming MVFR. Chance afternoon -RASN. Wind S 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Warning from 9 PM this evening to 6 AM CST Saturday
     for WIZ015-016-023>028.

     Winter Weather Advisory from 9 PM this evening to 6 AM CST
     Saturday for WIZ014.

MN...Winter Storm Warning from 9 PM this evening to 6 AM CST Saturday
     for MNZ063-069-070.

     Winter Weather Advisory from 9 PM this evening to 6 AM CST
     Saturday for MNZ060-062-065>068-073.

     Blizzard Warning from 9 PM this evening to 6 AM CST Saturday for
     MNZ074>078-082>085-091>093.

&&

$$

UPDATE...JPC
SHORT TERM...JLT
LONG TERM...MPG
AVIATION...JPC



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