Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 182317
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
517 PM CST Wed Jan 18 2017

.UPDATE...
Issued at 517 PM CST Wed Jan 18 2017

Updated to include 00Z aviation discussion below.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 300 PM CST Wed Jan 18 2017

A storm system noted on regional satellite imagery across western
Kansas this afternoon will begin to pull ample gulf moisture
northward across the Upper Midwest over the next 24-36 hours.
Temperatures this afternoon has risen into the mid to upper 30s,
with a few lower 40s which is 15 to 20 degrees above normal for the
third week of January. It was also noted that the snow cover across
northeast Iowa and far southwest Minnesota had eroded today which
leads to ample moisture in the boundary layer this afternoon. There
was also still low clouds and fog in far southeast Minnesota where a
strong inversion and the depth of the cloud deck was strong/deep
enough to hold it together. Models have this area of moisture in
southeast Minnesota advecting across western Wisconsin this evening,
which will likely lead to areas of stratus/fog to form.

The amount of low clouds and fog is the main forecast concern
overnight, especially considering the amount of boundary layer
moisture from today`s melting and additional moisture advecting
northward later tonight. The forecast will continue an increase in
cloud cover late tonight, especially north of I-94 where the best
isentropic lift in the 275-285k layer indicated. The other concern
is the depth of the moisture and associated cloud cover Thursday
which may lead to light drizzle by the afternoon. Although the depth
of the moisture remains quite shallow, the strength of the moisture
advection is adequate enough to warrant at least patchy drizzle.
Temperatures overnight will likely only fall to near freezing, with
some upper 20s in west central Minnesota where better terrain
affects area noted.

.LONG TERM...(Thursday night through Wednesday)
Issued at 300 PM CST Wed Jan 18 2017

The long term forecast remained pretty consistent today.  Thursday
night through the weekend and into early next week will feature
temperatures well above normal (about 20 degrees if you average out
the high and low for each day, but mainly thanks to the warm lows).
The normal lows right now are bottoming out and in the single digits
across the local area.  With forecast lows in the 30s in the coming
nights, the departure from normal on the lows will be about 30
degrees above normal.

As an upper low/trough lifts north into our area tomorrow night
dewpoints will rise into the 30s which will be a good setup for fog
and drizzle especially with the melting snow pack.  There will be
some better lift across eastern MN and western WI where primarily
rain will fall, but could see some sleet and freezing rain
overnight. The same holds true through the weekend with likely rain
and drizzle along with fog.  Portions of the forecast area,
primarily central MN, could deal with icing potential overnight this
weekend so did include that in the forecast in those areas.

Over the last several runs of the GFS, a storm for the middle of
next week continues to be advertised.  The 00Z run of the ECMWF
agreed quite well with this scenario, but the 12Z came in with a
much different solution playing out middle of next week.  The big
difference is a much stronger and flatter west to east jet on the
ECMWF which races the parent upper trough straight east from the
four corners region through Tennessee/Kentucky with little impact
here.  The GFS has a more amplified jet pattern which deepens the
trough, with surface cyclogenesis and a northeast trajectory placing
our area in a favorable area for snow.  With such disagreement, kept
pops pretty conservative in the extended forecast.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 517 PM CST Wed Jan 18 2017

There is high confidence that we`ll see flight conditions
deteriorate over the course of the forecast period, but confidence
is much lower in terms of when exactly that will occur with
respect to visibilities and ceilings. Slowed down the arrival of
low ceilings in comparison to earlier forecast, but kept
visibilities similar. Main reason for this is lack of nearby lower
ceilings, with much of what was to our south/southeast having
dissipated this afternoon. In addition, there are significant
differences in the model guidance, with MOS-type guidance being
much more optimistic in comparison to raw gridded model output.
Both are more similar with visibilities than with ceilings, which
is part of why the visibility forecasts weren`t significantly
altered. The warm temperatures and melting that occurred today
should inspire some fog development tonight, but it`s tough to say
how low visibilities will get. The more widespread lower ceilings
may take longer to work into the area, but should they develop
from ground up that could occur sooner. The bottom line is that
things should worsen, but exactly when and to what degree is a
tough call at this point.

KMSP...There is significant uncertainty in when MVFR and lower
conditions will develop, although it appears that lower
visibilities will be an issue prior to any lower ceilings.

/OUTLOOK FOR KMSP/
Thursday overnight through Sunday...MVFR expected, IFR possible.
Occasional light rain/drizzle. Southeast wind less than 10 kt
increasing to 10 to 20 kt late Friday night and Saturday, then
becoming west 5 kt or less Saturday night and Sunday.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

UPDATE...
SHORT TERM...JLT
LONG TERM...SPD
AVIATION...



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