Scientific Forecaster Discussion
fxus63 kfgf 070741
Area forecast discussion
National Weather Service Grand Forks ND
141 am CST Sat Dec 7 2019
issued at 130 am CST Sat Dec 7 2019
Still seeing indications of freezing drizzle mainly within the Red
River Valley North of Highway 200, and perhaps into portions of
northwest Minnesota. Reissued the Special Weather Statement for freezing drizzle leading
to some slick spots until 4 am, although confidence is not too
high on when cessation will occur. Used lowest level relative humidity fields and
what looks to perhaps be a very subtle vortex in microwave imagery
between 850-700 mb. Patchy fog still looks likely this morning,
mainly before 10 am.
Around sunrise, focus turns to an area of low level warm air advection ahead of a
subtle mid level shortwave that may lead to a period of wintry
mix moving west to east through the morning, again mainly north
of Highway 200. Freezing rain, sleet, and snow are all possible
leading to the chance for a light glazing of ice or a dusting of
snow/sleet. The forecast update reflects this increased chance
for wintry mix this morning. Still unsure of impacts as wintry
precip could be steady, however forcing looks to be progressive
and should not linger over a particular location for more than 1-2
hours. However, this may lead to travel issues given the chance
for light icing.
Update issued at 856 PM CST Fri Dec 6 2019
Added in some freezing drizzle based on reports and saturation
profiles. Chances for the freezing drizzle continue for the next
few hours before the saturation profiles start to look more like
fog than freezing drizzle. Also fog will be present in eastern
North Dakota and northwest Minnesota tonight into Saturday
morning. Some patchy dense fog could occur.
Update issued at 540 PM CST Fri Dec 6 2019
Some light snow showers continue to be possible across northwest
Minnesota this evening. Any accumulation that occurs will be under
an inch with only minimal travel impacts. With the lack of snow
being reported so far the upper end of totals looks less likely.
Short term...(this evening through Saturday night)
issued at 258 PM CST Fri Dec 6 2019
The two potential impacts this period include light snow tonight
and possibly freezing drizzle Saturday night.
Currently, a 1030 mb high exists over Omaha with low pressure to
the north, giving US southerly winds across the northern plains.
An upper level wave will move east-southeast from southern mb across
far northeast ND and northern Minnesota late this afternoon/tonight. This
wave, along with some mid level warm air advection, will help
produce a band of snow from around Hallock/Pembina east-southeast to Beltrami
County. A half inch to an inch of snow will be possible with this
feature, with models in fair agreement that some snow will exist.
However, confidence is lower on the fringes, say in Langdon, Grand
Forks and Park Rapids where only a 20-30% chance exists. Will
continue with only 60% chance in the main band right now as there
are still plenty of ensemble members that have a trace to nothing
in this area. The upper bound appears to be about 1.5". So, there
could be brief travel impacts around the late afternoon/evening
commute in this area due to reduced visibility and light
accumulations. Any snow should be done in our area by
midnight...but could could followed by patchy fog given the
After tonight, an upper wave rotates around a northern Canada
upper low bringing a surface trough of low pressure from Hudson
Bay southwest through the northern plains on Saturday night. So,
after a warm Saturday with highs around 30, temperatures start to
drop with the trough and the associated cold front. Then, there
may be a period of freezing drizzle followed by light snow in the
north late Saturday night. Models produce some quantitative precipitation forecast with the cold
air advection in the low layers...but without the ice crystals
aloft as temps will be around -5c with likely no relative humidity/clouds aloft.
Have continued with the previous shifts mention of a chance of freezing
drizzle for now.
Long term...(sunday through friday)
issued at 258 PM CST Fri Dec 6 2019
The long term period will encompass a chance for light snowfall
Sunday into Monday followed by the coldest Arctic air of the season.
Very cold wind chills, possibly approaching -30, will be the main
impact other than multiple days possibly remaining below 0.
Sunday and Monday
For Sunday, the main story will be a surface low progressing to the
east from northern Wyoming/southern Montana that will bring chances
for wintry precipitation. With the current track expected to be
across the Central Plains, the main area of focus for accumulations
still looks to be along and south of I-94. Light mixed precipitation
possible everywhere preceding the low with the pre-system 500mb
shortwave. For amounts, areas of west central Minnesota and near the
South Dakota/North Dakota border look to have the highest chance for
light accumulations/impacts. The gefs and Canadian ensembles suggest
quantitative precipitation forecast totals in the 0.10" to 0.20" inch range, which would result in
snow accumulations of near the 1 to 2 inch range. Deterministic
American, Canadian, and European solutions key on to higher quantitative precipitation forecast
values near 0.25" inches or more, which would result in snow
accumulations of 3 inches or more in this area. There still is
uncertainty for exact totals Sunday into midday Monday, but
agreement continues for the highest accumulations to be south of the
Fargo-Moorhead area. Behind the frontal passage on Monday, highs
look to reach only into the single digits to near 0 with the worst
of the cold following.
Tuesday through Friday
The focus towards the end of the period turns to an Arctic air
outbreak that could result in multiple days below 0 with lows in the
double digits below 0 area-wide. This bitter cold comes with an
Arctic high that keeps northerly to northwesterly winds, which could
drop wind chills to near -30 in many areas.
Global ensemble and deterministic model guidance point to 850mb
temperatures in the -25 to -30 celsius range. Deterministic model
guidance suggests temperatures similar to these at the 925mb level.
The main factors that will contribute to the depth of this cold that
mixes down to the surface, especially at night, are
Ensemble and deterministic models still point to 850mb temperatures
below -20 celsius with persistent 20 to 40 knot northerly to
northwesterly winds in the 850mb to 925mb levels. Depending on the
efficiency of mixing in the boundary layer, some of these higher
winds could partially mix down to the surface. Initial indications
are for winds to be near 10 knots towards the end of the period,
which would increase likelihood of wind chills below -20 at the
surface. The GFS is the worst case scenario with boundary layer
winds of 15 to 20 knots. Increased winds would moderate temperatures
slightly but could still drop wind chills well below -30.
There is still a lot of uncertainty for the wind speeds, efficiency
of boundary layer mixing, and coldness of the air mass, but very
cold temperatures and frigid wind chills are certainly possible for
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1149 PM CST Fri Dec 6 2019
Widespread IFR and MVFR ceilings with pockets of LIFR ceilings.
There are pockets of light treeing drizzle across far northeast
ND and northwest Minnesota that have impacted kgfk and ktvf this evening,
however how much longer this will be a threat is tough to say and
I limited mention to the early taf period. Fog has developed
across western ND and is spreading east and this could overspread
eastern ND and northwest Minnesota by 12z before lifting 18z, and bring
drops to LIFR vis (best chance at kdvl but not confident enough to
prevail at this time). South winds 5-10kt should shift to the
southwest ahead of the next approaching system that could bring
light wintry precip Saturday-Saturday night. Cold front should
arrive Saturday night with winds shifting back to the northwest.