Area Forecast Discussion
Issued by NWS Twin Cities, MN

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387
FXUS63 KMPX 242109
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
309 PM CST Tue Jan 24 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 305 PM CST Tue Jan 24 2017

Anticipated winter storm remains on track to affect a small
portion of southern Minnesota starting late this afternoon and
continuing into Wednesday. How far north the accumulating snowfall
progresses remains the forecast problem as these type of systems
have a very sharp cutoff from several inches of snow, to only a
few flurries or a light dusting on the northern edge.

The onset of the light snow has slowed considerably from
yesterdays model runs, but still close enough to hold onto the
timing of light snow developing along the Iowa/Minnesota border by
4-5 pm. Regional radar, satellite imagery and short term model
reflectivity simulation, does support light snow moving into
Fairmont, Blue Earth and Albert Lea by 4 to 5 pm. IR/Water Vapor
imagery does show a pronounced upper circulation south of Sioux
Falls, South Dakota which indicates the strong upper forcing
affecting northern Iowa. Surface observations/web cams across
northern Iowa support a small band of moderate to heavy snow
lifting north-northeast. Again, this band of snow will move into
far southern Minnesota before sunset, and expand to the north-
northeast across far southern Minnesota through midnight.

Several of the model reflectivity simulations have a fairly
strong band of snow moving across I-90 during the evening. This is
where snowfall rates will increase to 1 inch per hour after 6 pm.
This simulated stronger band of reflectivity does support the
current winter storm warning across far southern Minnesota where
locally 8 to 12 inches of snow is likely. The heaviest snow bands
will occur this evening as the strong upper level support moves
across this region. Further north, a general light snow event is
expected. The lighter snow further north is based on weaker
forcing and a shorter span of any higher snowfall rates.

Once the stronger forcing moves into Wisconsin late this evening,
a broader area of weak forcing will continue a light snowfall
through Wednesday afternoon, especially along a developing
deformation band on the northwest side of the upper low track. I
would not be surprised to see very little accumulation or just
flurries north of Benson to St. Cloud and Rush City. In the Twin
Cities metro area, Elk River may have a light dusting, where as
southern Dakota county from Lakeville to Hastings may receive 4 to
6 inches by Wednesday afternoon. Due to the precipitation and
cloud cover, very little change in the temperatures are expected
until late Wednesday afternoon as cold air advection increases.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 250 PM CST Tue Jan 24 2017

In general, the extended period will be quiet with no significant
snowfall accumulations, plenty of cloud cover, and high
temperatures closer to seasonable values (lows will still be running
around 10 degrees above normal though).

Thursday and Friday, we`ll be in NW cyclonic flow, Saturday we`ll
see a strong shortwave drop south through the area on the back side
of the eastern trough, with Mon/Tue featuring a vigorous fast
moving wave going across northern MN. Model agreement is high
through Friday, but Saturday, the GFS is stronger and farther west
with that wave, and the system for next week is stronger/farther
south with the GFS and weaker/farther north with the ECMWF.

In terms of any changes made to the blended forecast we initialize
with, we made very few, with the only one of significance being to
increase sky cover as we look to be in a very cloudy regime the next
week.

For Saturday, though not anticipating much in the way of measurable
snow, it does look like it could be one of those days with numerous
light snow showers. GFS soundings show a deep (nearly 800 mb) and
well mixed boundary layer developing, with the top of the boundary
layer getting into the DGZ. This is the type of pattern that gives
you on and off snow showers as horizontal convective rolls become
established. We have a "quiet" forecast at the moment, but we may
need to beef up pop/light snow mention in the coming days.

For the system next week, the ECMWF keeps the precip north of us,
and instead puts us in a strong warm sector, with highs in western
MN progged to get into the 40s on Monday. The GFS brings precip down
to about I-94 and in turn is not as warm as the ECMWF. The GEFS
shows plenty of spread with this system as well, so stuck with
blended guidance for Mon/Tues, which is cooler than the ECMWF with
chances for snow dipping down to about I-94.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1230 PM CST Tue Jan 24 2017

Developing surface cyclone currently observed over far North
Central KS. Cyclone will slowly trek NE into far South Central IA
by 25/06Z. MVFR Cigs will be seen over most TAF sites for
remainder of afternoon, (save RWF). Delayed onset of snowfall
slightly across most airport locations as storm system
progression slowed somewhat with latest guidance. Biggest impact
for snow at this juncture appears to be EAU, RNH and RWF as 50H
Low develops to NW of surface cyclone overnight. Long period of
IFR cigs/Vsbys will develop by late this evening most TAF
locations and continue into around 14Z most locales. MVFR
Cigs/VSBYS will continue from that point to end of TAF period most
sites (minus MSP).

KMSP...

/OUTLOOK FOR KMSP/

KMSP...Delayed start of light snow by one hour compared to
previous guidance. Presence of near IFR cigs to our South prompted
lowering of CIGS a tad faster this aftn, with IFR conditions
developing by mid evening. Anticipate short periods of less then
one mile VSBY between 25/07-14Z time period. Although VFR VSBYs
will develop by late Wed afternoon, MVFR cigs will continue into
Wed evening.

Thursday through Friday...MVFR CIGS likely with a slight chance
of snow Thursday morning. Northwest wind 10 to 20 kt.
Friday night...MVFR possible early. Northwest wind around 10 kt.
Saturday...MVFR possible with a chance of snow. Northwest wind 5
to 10 kt.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 6 PM this evening to 6 PM CST
     Wednesday for WIZ024>028.

MN...Winter Weather Advisory from 6 PM this evening to noon CST
     Wednesday for MNZ064-065-067-069-070-073.

     Winter Storm Warning until 6 PM CST Wednesday for MNZ074-082>085-
     091>093.

     Winter Weather Advisory from 6 PM this evening to 6 PM CST
     Wednesday for MNZ075>078.

&&

$$

SHORT TERM...JLT
LONG TERM...MPG
AVIATION...AJZ



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