National Weather Service Raw Text Product

493 
FXUS63 KBIS 241820
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1220 PM CST Thu Dec 24 2020

.UPDATE...
Issued at 1215 PM CST Thu Dec 24 2020

Low clouds are starting to show signs of drying up with breaks
forming as the dewpoint depression increases now that we are into
the afternoon and that warm front is progressing out of western
and into central North Dakota. Will gradually end the flurries 
this afternoon as well. Mid level warm advection clouds will 
continue into tonight before decreasing.

Wind chill advisory expired at noon.

UPDATE Issued at 943 AM CST Thu Dec 24 2020

Flurries are more numerous than earlier expected and radars show
pockets of light snow moving through with the low clouds. Will
update accordingly.

UPDATE Issued at 835 AM CST Thu Dec 24 2020

Have expanded the snow flurry and fog areas based on current
satellite and radar, and have extended their life out a few more
hours this morning. A solid band of low clouds extended through 
central North Dakota oriented north to south. It was progressive 
to the south with the northern end, along the Saskatchewan and 
Manitoba border, showing signs of erosion from both sides. As that
band continues moving south would expect it to start decreasing 
in areal coverage and snow flurries diminishing as holes develop 
in the clouds, but not as soon as earlier expected. This afternoon
should have at least some sunshine everywhere in the forecast 
area.

UPDATE Issued at 559 AM CST Thu Dec 24 2020

Low clouds across central North Dakota have shown little signs of
movement or dissipation this morning. The most recent run of the
RAP has trended toward holding on to these clouds at least through
the morning, which seems reasonable. Meanwhile, mid level clouds
are streaming over western North Dakota. There is a narrow ribbon
of clear skies between the low and mid clouds where temperatures
are much colder than surrounding areas and fog has developed. This
extends roughly from around Tioga and Stanley to Glen Ullin.

The Wind Chill Advisory remains in effect. Several locations are
reporting wind chills from around 25 to 30 below zero this hour.

&&

.SHORT TERM...(Today and tonight)
Issued at 251 AM CST Thu Dec 24 2020

North Dakota sits between a Pacific Coast ridge and a trough digging 
into the Upper Midwest early this morning. Broad surface high 
pressure is located over Manitoba, with ridging extending south into 
eastern North Dakota. A stationary front is analyzed generally along 
the Highway 83 corridor. A band of low level clouds generating 
scattered flurries has been maintained along this baroclinic zone 
through the night. Guidance suggests that the baroclinic forcing 
will begin to diffuse mid to late morning. To the east of the 
stationary front, a cold Arctic air mass has brought early morning 
temperatures well below zero, with wind chills around 25 below. A 
Wind Chill Advisory remains in effect through the morning from the 
Turtle Mountains down through the James River Valley.

Not much change is expected in flow aloft today. At the surface, the 
Manitoba high is forecast to slide into the Red River Valley, while 
the stationary front begins to transition to an eastward 
progressing warm front in response to height rises over the High 
Plains. Enough atmospheric moisture may be present across 
northern North Dakota to produce some flurries along the warm 
front Tuesday afternoon, with forcing assisted by isentropic 
ascent. The RAP is more bullish on sufficient low level moisture 
than other guidance. The presence of the front will create a stark
temperature contrast across western and central North Dakota 
today, with highs ranging from the lower teens east to upper 30s 
southwest.

The warm front will continue to track east across the state tonight, 
with flow aloft becoming more northwesterly as the Pacific ridge 
begins to translate over the Rockies. Lows tonight will be rather 
mild in western North Dakota, but closer to average farther east. 
No weather issues for Santa and his reindeer.

.LONG TERM...(Friday through Wednesday)
Issued at 251 AM CST Thu Dec 24 2020

Upper level ridging is forecast to continue over the Rockies 
Christmas Day, but it will be shunted by a progressive shortwave 
moving from the Northwest Territories of Canada into Ontario. Mild 
temperatures are expected for southwest and south central North 
Dakota, with highs in the upper 30s to mid 40s. Farther north, cold 
air advection should commence by peak diurnal heating, keeping highs 
there closer to the freezing mark.

The upper ridge will begin to flatten out by the time it reaches the 
Northern Plains on Saturday as a series of shortwaves begins to 
cross the Pacific Northwest. Broad surface ridging should maintain 
dry weather on Saturday, but will allow cooler air to seep into the 
region.

Chances for snow will begin to increase Saturday night into Sunday 
as the series of shortwaves approaches the Northern Plains. There is 
very strong ensemble consensus for measurable QPF across southwest 
North Dakota, with slightly lower but still relatively high 
probabilities to the north and east. However, the lack of 
frontogenesis and support from an upper level jet should keep 
accumulations light. The cooling trend will continue, with highs 
falling below normal for most areas.

Surface high pressure is forecast to build over the Northern Plains 
Sunday night into Monday, which could allow overnight lows to fall 
below zero for much of the state. There is then decent model 
consensus that a Colorado Low will develop on Tuesday and track from 
the Central Plains to the Great Lakes. Southern and eastern parts of 
our forecast area may get clipped by this system, but great 
uncertainty remains. The ECMWF ensemble shows around a 35 percent 
chance of 24-hour QPF exceeding one tenth of an inch across the 
southern James River Valley through Wednesday, while the same 
threshold probability in the GEFS is closer to 25 percent. The key 
takeaway from the current set of ensemble data though is that there 
has been a distinctive shift to the north and west for QPF 
probabilities associated with this system over the past two model
cycles.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday)
Issued at 1215 PM CST Thu Dec 24 2020

MVFR ceilings and snow flurries through central north Dakota
(orientation north to south) were showing signs of drying
evidenced by breaks developing in the ceiling. This as the surface
dewpoint depression increases. A warm front was passing through
western toward the central part of the state. Otherwise, VFR 
conditions are expected with a sct-bkn mid cloud level deck.
Low level wind shear is forecast to develop across parts of the
forecast area tonight.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...JPM
SHORT TERM...Hollan
LONG TERM...Hollan
AVIATION...JPM