Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 191042

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
442 AM CST Thu Jan 19 2017

.SHORT TERM...(Today and tonight)
Issued at 440 AM CST Thu Jan 19 2017

The snow melt of yesterday has made for a rather moist boundary layer
out there this morning and that moist boundary layer is only being
aided by southerly winds. We saw one area of dense fog form across
central MN/western WI to the north of a weak warm front overnight.
There have been widespread visibilities of a quarter mile or less,
hence the dense fog advisory across central MN into NW WI. We went
with a 9am end time for this as the HRRR, which picked up on this
fog pretty good, shows it continuing its slow northward movement
this morning, reaching northern MN and mostly clearing the MPX CWA
by mid morning. Of course as we lose this area of fog, there is
another area of dense fog streaming north across IA right now. We
will be adding a dense fog advisory to areas south of the Cities
this morning for this fog coming out of IA. Will end this advisory
at 15z as well for simplicity, but this region may need to be
extended out in time as it looks to have a bit more staying power.

This fog also signals the arrival of the gloomy weather we have been
harping on the past few days. Even with the clouds though,
temepratures this morning are already in the lower 30s for most
locations and the continued WAA on south winds will send highs today
to similar levels to what we saw yesterday. We will just be
replacing beautiful sunny skies with a gloomy low stratus, fog, and
haze. Main change to the forecast today was to increase sky cover
and remove any drizzle mention, as moisture profiles are not deep
enough to support drizzle/precip generation until tonight.

As for tonight, it will be ugly for the aviation end of the
building. We will likely see more dense fog, ceilings likely under
500 feet, and to add to the fun, we`ll through in drizzle and rain
as well. The precip will come up out of eastern IA and will
primarily impact areas east of I-35, as this is where moisture is
deepest and clouds will likely be mixed phase. West of I-35, mid
levels look to stay dry and clouds will consist of only liquid
droplets, with drizzle generation looking possible all the way to
the SD border. Pops in there now are based on a blend of the CAMs
and are keyed in more on where the rain as opposed the drizzle will
be. The south wind and clouds will keep us mild again and did warm
lows a couple of degrees, with lows currently progged to be in the
30-34 range. Beside being a good 25 degrees above normal, it looks
like it will be warm enough to keep any potential freezing
rain/drizzle impacts to a minimum.

.LONG TERM...(Friday through Wednesday)
Issued at 440 AM CST Thu Jan 19 2017

By Friday the long wave pattern will be transitioning from a
split flow pattern to a more traditional dominate Polar Jet
across the southern CONUS. A west coast trough will slowly slide
east across the Plains and Upper Mississippi River Valley FRI-SAT.
There are two smaller waves embedded in the larger pattern - the
first coming through on Friday and the second quick on its heels
Saturday. These aren`t particularly deep lows, but given the
fairly high atmospheric moisture content over the next few days
with PWATS between 0.45"-0.60" - these two waves could produce
0.25" of precipitation for portions of the area. The forecast
soundings are warm, and we`d be surprised if there was anything
but light rain or drizzle for a vast majority of the area. It`s
possible a little sleet/snow mix in across central/western MN late
Saturday, but most of the area will have a 2000-4000ft freezing
level through Sunday. That would certainly be liquid. The ground
is still frozen, so there could still be slick spots around at
night with temperatures hovering near or just above freezing. The
first two weeks of the month left us well below normal for
temperatures locally, but the past two days alone have nearly
reversed the departure to above normal.

A deep trough moves across the central US during the middle of
next week. The GFS/ECMWF both show the potential for several
inches of snow with a mature cyclone moving through the region. We
will continue to monitor the track of this potential snow maker.


.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.

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.


WI...Dense Fog Advisory until 9 AM CST this morning for WIZ014>016-

MN...Dense Fog Advisory until 9 AM CST this morning for MNZ041>045-



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