Area Forecast Discussion
Issued by NWS Grand Forks, ND

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FXUS63 KFGF 210341

Area Forecast Discussion
National Weather Service Grand Forks ND
941 PM CST Mon Feb 20 2017

Issued at 941 PM CST Mon Feb 20 2017

Still waiting to see when and where potential dense fog may
develop. Most hi-res and MOS guidance continues to support the
development of fog tonight as winds become light within an
environment of high low level moisture. This scenario makes sense,
although coverage and how dense remain questions. Also, mid-cloud
moving in from the west may limit fog potential. Give the mid-
cloud, went higher coverage east of the valley. Most areas will be
near or slightly below freezing, potentially adding to the impacts
(icy roads?). Lots of uncertainty still.


.SHORT TERM...(This evening through Tuesday)
Issued at 311 PM CST Mon Feb 20 2017

Precip winding down and additional fog formation tonight will be
the main headaches for the period.

The main upper trough continues to lift quickly through the Plains
states, with the surface trough axis currently moving into our MN
counties. The central CWA has seen some break in the rain with dry
slotting but there is still some rain to the west with the mid
level deformation band. The RAP and to a lesser extent HRRR have a
decent handle on rain trends, taking the trailing edge of the
precip into MN in the next 2 to 3 hours with the rest of the rain
exiting the far eastern counties by 03Z. At this point think an
additional 1 to 2 tenths of an inch of rain are possible in spots
but not everywhere.

Clouds have already cleared out of western ND and the clearing
line will begin to move into the western counties in the next few
hours. The center of the surface ridge will pass by to our south
so winds will not go completely light, staying from the west and
then southwest later tonight. In addition, a weak shortwave
approaching through the near zonal flow will bring some additional
cloud cover later tonight to the northern counties. That shortwave
could bring some precip clipping our far northwest later tonight
but not expecting much of anything south of the international
border. With recent rain and melted snow, there will be plenty of
moisture and the west winds bring slight drying but not a lot.
The SREF probabilities of visibility less than a mile are very
high tonight, and many of the CAM models break out fog. Will keep
a fog mention in some areas going but will stay vague on density.
Followed along with the blend of guidance and have fog
redeveloping overnight and moving eastward, but will have to watch
visibilities closely.

As for temperatures, some drier dewpoints moving in will help
readings overnight fall into the mid 20s to mid 30s. Southwest
winds become westerly again tomorrow and fog should burn off by
mid morning. Cold air advection will hold off until Tuesday
evening, so the abnormally warm highs will continue for Tuesday.
Have highs ranging from the upper 30s north to upper 50s in the
far south, with some records again on the chopping block.

.LONG TERM...(Tuesday night through Monday)
Issued at 311 PM CST Mon Feb 20 2017

Temperatures begin to drop Tuesday night from northwest to southeast
as cold air moves in behind the cold front. The general pattern
aloft remains zonal Wednesday, keeping us from plummeting all the
way to seasonal normals until Friday and continuing to bring in
relatively moist air. Several upper level shortwave disturbances
move through Tuesday night through Wednesday night bring
precipitation chances to much of the area. At this time, a general
model consensus indicates scattered light snow showers along and
north of Highway 2 Tuesday night and into early Wednesday. As a dry
layer aloft gradually becomes saturated, precipitation will likely
begin as snow in the north and rain in the south. Colder air moving
in from the north will gradually transition precipitation to a
wintry mix and snow Wednesday afternoon from north to south.
However, the models differ significantly in the
locations/types/amounts of precipitation with temperatures around
the freezing mark in the central valley during the day. Some banding
is indicated by a few models along and south of Interstate 94, but
an overall temperature blend indicates that these heavier amounts
would fall as mainly as rain Wednesday afternoon, if they did occur.
The models do agree that precipitation chances will be out of
eastern North Dakota by Wednesday night and would be entirely out of
northwest Minnesota by Thursday morning.

On Thursday and Friday, the models have been coming into agreement
for the last few runs and generally indicate a Colorado Low system
bringing heavy snow across the Central Plains. Fortunately, this
system keeps us generally in dry northerly flow and is expected to
bring less than an inch of snow across the far southern Red River
Valley and adjacent portions of west central Minnesota. Temperatures
Thursday will still remain slightly above normal.

On Friday through Monday, we will return to near normal temperatures
with highs in the lower 20s to middle 30s and lows in the single
digits to middle teens. The forecast for the weekend looks mostly
dry but cannot completely rule out some flurries over the weekend as
a shortwave disturbance or two pass overhead. Looking into early
next week, several models indicate a disturbance will bring
precipitation chances Monday into Monday night, but there is low
confidence in precipitation type, location, and amounts at this time.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 648 PM CST Mon Feb 20 2017

As the main weather system moves out most locations can expect a
brief period of vfr conditions this evening. Devils Lake has
already developed dense fog, and anticipate most locations to
develop at least MVFR conditions tonight, with dense fog (LIFR)
possible. Still uncertain with duration of any possible LIFR




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