Area Forecast Discussion
Issued by NWS Grand Forks, ND

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FXUS63 KFGF 181903
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
103 PM CST Mon Dec 18 2017

.UPDATE...
Issued at 1258 PM CST Mon Dec 18 2017

850 mb warm layer disappears early this aftn and we have seen the
area of mixed precipitation turn to mostly snow. Noticeable too is
the rapid decrease in echo returns and precip intensity. Per NAM
max frontogenesis was over the area btwn Roseau and Thief River
Falls late morning/midday...then it weakens. We are seeing the
precip area though fill in as the main short wave is moving east
along the Canadian border into norht central ND. So overall radars
are showing a pretty light precip event. 850 mb temps cooling
enough with this second wave so that light snow is the predominate
type, though some rain mix is psbl just due to enough warming in
the lowest layers nr the sfc where temps are in the mid 30s. Will
let the advisory run thru 21z and then drop. Threat for isolated
heavier areas of snow accumulation appears to have ended, as the
heavier precip was in the form of rain vs snow and intensity of
precip thru the rest of the day/evening will be light. But will
continue to monitor.

&&

.SHORT TERM...(Today and tonight)
Issued at 354 AM CST Mon Dec 18 2017

An upper level wave will move through the region today. It looks
like showers are starting to move into the northwest. And believe
this may be freezing rain to start with before changing to snow.
Still looking for ground truth up in that part of the forecast
area (north of Devils Lake). May need a Winter Weather Advisory or
Special Weather Statement for FZRA potential depending on coverage.
There will be strong frontogenesis and favorable EPV aloft in the
northern part of the Red River valley this afternoon. Confidence
is growing that a snow band of 3-5" is possible in this area
mainly this afternoon and will be considering a Winter Weather
Advisory for today. The NAM Nest`s last three runs have favored
this as well as the 06Z 12km NAM run. The HRRR has a band of 2-3"
and is further east a bit. Will be continuing to evaluate hourly
model runs and consider Adv in near future. Snow comes to an end
during the evening hours in the Bemidji area...with generally an
inch or less in areas outside of the Cavalier to Karlstad to Carp
area.

.LONG TERM...(Tuesday through Sunday)
Issued at 354 AM CST Mon Dec 18 2017

Tuesday... The first round of colder air will move in as a cold
front moves through.

Wednesday... The most impactful system of the next week will be on
Wednesday with snow expected across eastern North Dakota and
northwest Minnesota. Confidence is high that this event will occur
but there are still differences in ensemble and deterministic model
solutions with regard to timing and location of the snowfall. NAM,
GFS, ECMWF, and CMC models are in generally good agreement with the
upper level pattern and location of the main surface low.
Differences still exists with the precipitation with the CMC on the
low end while the NAM and GFS are on the higher end with the ECMWF
closer to but less than the GFS. With ensembles, GEFS plumes still
provide a range of solutions but the outliers have started to come
more move towards the mean in more recent runs. There is also fairly
good agreement between the GEFS mean and operational GFS for Grand
Forks and Fargo. Another factor is the chance for convective banding
as both GFS and NAM show some stronger frontogenesis at mid levels.

Thursday to Monday... Some of the coldest air so far this season
will move in to eastern North Dakota and northwest Minnesota. On
Christmas Day high temperatures could be 15 to 20 degrees below zero
with highs near zero. Based on CPC outlooks the cold is here to stay
for the remainder of December. West central Minnesota could see some
snow on Thursday but the better chances will be farther to the east
and south closer to the surface low.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1258 PM CST Mon Dec 18 2017

Some of the short range models were a bit generous with low
ceilings this aftn/eve so based on current obs and upstream
conditions kept ceilings in the VFR range with some MVFR cigs at
times.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...Winter Weather Advisory until 3 PM CST this afternoon for MNZ001-
     004>009-013>017.

&&

$$

UPDATE...Riddle
SHORT TERM...Knutsvig
LONG TERM...NC
AVIATION...Riddle


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