342 
FXUS63 KBIS 272001
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
201 PM CST Wed Nov 27 2019

.UPDATE...
Issued at 150 PM CST Wed Nov 27 2019

Little change in the short term forecast.  

UPDATE Issued at 943 AM CST Wed Nov 27 2019

Decreased the clouds a bit across the central where satellite
shows clearing. Skies remain cloudy west and east. Otherwise
current forecast looks ok. 

UPDATE Issued at 637 AM CST Wed Nov 27 2019

No major changes are needed for this update. Minor adjustments
include aligning sky cover with current trends and increasing 
winds over the James River Valley this morning based on current
observations.

&&

.SHORT TERM...(Today and tonight)
Issued at 429 AM CST Wed Nov 27 2019

Early this morning, diffluent/cyclonic flow aloft has allowed some 
isolated flurries to develop in the James River Valley. These will 
not be impactful and are expected to end around sunrise. Otherwise, 
expect some clearing skies today as upper level ridging and surface 
high pressure build across the area. Expect highs from the mid 20s 
north to lower 30s south. Tonight, we will see southerly return flow 
commence, with a low level jet setting up over the western Dakotas. 
Should remain quiet other than becoming a bit breezy over southwest 
North Dakota.

.LONG TERM...(Thursday through Tuesday)
Issued at 429 AM CST Wed Nov 27 2019

A strong winter storm will impact the region this weekend. A Winter 
Storm Watch has been issued for all of western and central North 
Dakota Friday night through Saturday night.

On Thanksgiving morning, a large, elongated upper level low is 
forecast to be located near the Pacific coast, placing the Northern 
Plains under broad anticyclonic flow. Southerly return flow will be 
present over the area through the day. This warm air advection/ 
isentropic lift regime will eventually lead to the production of 
precipitation, but it will take awhile for the column to saturate. 
Models are becoming less bullish on QPF, but the strong forcing 
signal is hard to ignore. Still think many locations will see light 
precipitation Thanksgiving night through Friday afternoon, though it 
may not be as widespread as previously thought. 

Types will be a concern with this initial round of light 
precipitation. There is growing model consensus that there will be a 
loss of ice production aloft, especially by Friday morning. 
Meanwhile, the return flow will be advecting moisture into the area, 
and soundings/RH fields show saturation in the lowest 1 km with 
temperatures generally warmer than -10 C. Therefore, now expecting 
the majority of this light precipitation to fall as light freezing 
rain, as surface temperatures remain below freezing. A few 
hundredths to near one tenth of an inch of ice accumulation is 
possible. We may need some sort of headline for this hazard, but 
will just continue to mention in the Hazardous Weather Outlook and 
other messaging outlets for now.

By Friday evening, surface cyclogenesis is forecast in northeast 
Colorado. The surface low is forecast to track north and east Friday 
night through Saturday, reaching the SD/NE/IA/MN border intersection 
area by Saturday evening. Multiple ingredients will be in place to 
produce heavy snow over at least the southern half of North Dakota 
during this time (strong jet dynamics/DGZ omega/frontogenesis/ 
slantwise convection potential). The heavier snow is expected to 
move in from the south Friday evening, spreading north through the 
night. There is still uncertainty in how far north the heaviest snow 
will extend, but it appears likely that the I-94 corridor and points 
south will receive at least 8 inches of snow, potentially greater 
than one foot.

Winds will increase in response to the strong pressure gradient. 
Model consensus for momentum transfer potential is around 35 to 45 
kts. Given the expected intensity of this system, these gusts seem a 
little low, although the low may already be entering an occlusion 
phase at that time. Hopefully the higher resolution guidance will 
add some clarity once their forecast range gets out that far. Even 
with only 40 mph gusts, this would still be enough to cause at least 
near-blizzard conditions in areas of falling snow. Due to the 
expected heavy wet nature of the snow, think that snow on the ground 
will have a hard time blowing around.

The deterministic GFS continues to be a significant outlier in both 
its kinematic and thermodynamic fields. What stands out the most is 
the amount of warm air that is being catapulted into southern North 
Dakota Friday night-Saturday morning. For several consecutive runs, 
the GFS has warmed surface temperatures enough above freezing to 
produce moderate to heavy rain across southern North Dakota. Think 
the cause of this anomalous warm air might be that the deterministic 
GFS is also the only model that currently produces a bomb cyclone. 
This would produce a stronger wind field and therefore, bring much 
warmer air around the cyclone. We have kept this scenario out of our 
forecast and messaging for now, but feel it should not be completely 
discounted. We should have a better idea on this potential once more 
high-resolution model guidance output reaches into Saturday.

At this point, confidence is high enough to issue a Winter Storm 
Watch for all of western and central North Dakota Friday night 
through Saturday night. It is especially important to get this 
message out now given the high volume of travel for the holiday 
weekend.

Snow is forecast to end from northwest to southeast Saturday night 
into Sunday morning, with winds also diminishing in the same 
fashion. Dry weather and near normal temperatures are favored early 
next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 150 PM CST Wed Nov 27 2019

Widespread MVFR conditions conditions expected to continue through
Thursday morning. Brief periods of VFR possible, but only
temperaty KXWA-KDIK.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Friday evening through late Saturday 
night for NDZ018>023-025-031>037-040>048-050-051.

Winter Storm Watch from late Friday night through late Saturday 
night for NDZ001>005-009>013-017.

&&

$$

UPDATE...WAA
SHORT TERM...Hollan
LONG TERM...Hollan
AVIATION...WAA