Area Forecast Discussion
Issued by NWS Twin Cities, MN

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941
FXUS63 KMPX 190333
AFDMPX

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

.UPDATE...
Issued at 933 PM CST Wed Jan 18 2017

Updated to include 06Z 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 06Z TAFS through 06Z Thursday night)
Issued at 933 PM CST Wed Jan 18 2017

Thoughts remain similar as with the 00Z issuances. Satellite
imagery shows two areas of lower ceilings and visibilities, one
over far southeast MN and southern WI, lifting north, and a second
area over southern IA lifting north. It`s still unclear if we`ll
see any additional areas of low cloud develop, with most of the
guidance suggesting it will not occur, so we`ll mainly be
advecting the current areas into our area overnight and Thursday.
However, some areas of reduced visibility are likely to develop,
and could lead to ceilings toward 12Z as well. Kept things fairly
close to previous forecast given the overall uncertainty.

KMSP...Continue to have fairly low confidence on exactly when
we`ll see lower ceilings and to what degree visibilities will
decrease overnight. Banking on area of low clouds to the southeast
staying east of the area, and the second area of low clouds over
IA doesn`t look like it would get into the area until around 17Z.

/OUTLOOK FOR KMSP/
Friday 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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