090 
FXUS63 KBIS 061006
AFDBIS

AREA FORECAST DISCUSSION
National Weather Service Bismarck ND
406 AM CST Sun Nov 6 2022

.SHORT TERM...(Today and Tonight)
Issued at 243 AM CST Sun Nov 6 2022

The main forecast concerns in the short term period will be winds 
today, then winds and snow Monday. 

Currently, surface low pressure was located in southern Manitoba.
Strong westerly gradient winds were located across western and 
central North Dakota as the initial push with the cold front has 
passed through the forecast area. We had a few areas gust to right 
around 50 knots last evening, but winds have dropped off a bit over 
the past few hours. The wrap around moisture has southward through 
northern and central ND. Clear skies still remain in the far 
south. Except for a stray flurry or snow show, precipitation has 
remained north of the border as of 07 UTC. 

For today, we will continue the High Wind Warning. A secondary 
pressure fall-rise couplet associated with the Canadian surface low 
will track along the International border, across northwest ND 
mainly prior to 12 UTC and north central ND 12-18 UTC. There is 
some isallobaric component farther south, but much less than along
and north of the Highway 2 corridor. Although cold advection is 
not overly impressive with this system. This timeframe is also 
when we do get another surge of stronger cold advection behind the
stacked system. Thus we still see the potential for strong winds,
especially over the north half of the CWA and into the northern 
James river Valley, through the morning hours. In addition, we 
still have strong winds of 50 to 55 knots at the top of the mixed 
layer across all of western and central North Dakota. Strong lapse
rates will remain across central and southern portions of the 
forecast area through the day. Although we do not get the strong 
isallobaric component farther south, with the steep lapse rates in
place, the potential remains for these strong winds to work down 
to the surface. We do think that beginning early afternoon in the 
far southwest, the potential for Strong wind gusts will start to 
spread eastward, so it's possible we may be able to cancel western
portions of the HWW early. But until at least early this 
afternoon will stick with the current HWW across western and 
central North Dakota.

Chances for snow remain mostly over the far northern tier
counties, and especially around the Turtle Mountains. Snow amounts
are a half inch or less, except for maybe an inch or two localized
to the Turtle Mountains. With the strong winds in place, as snow
develops south into the state, we could see some areas of reduced
visibilities. Estevan has dropped down to around a mile at times
through night, with even lower visibilities a little farther north
in heavier bands of snow. Have added a mention of reduced
vsbys in snow along the Canadian border. Will need to monitor in
case a heavier band does move into the state later this morning.

Another concern is for fire weather conditions across the far
southwest and south central. The latest temperature guidance
is slightly cooler than yesterday, and therefore minimum
humidities in the far south are right around 30 percent from
eastern Adams and Hettinger counties, east through Grant and 
Sioux counties and into Emmons county. If we would reach fire
weather conditions this afternoon, at this time it looks like the
duration would be no longer than the minimum of 3 hrs needed for a
RFW. With forecast highs in the upper 30s, we will hold off on
issuing fire weather headlines at this time and message near
critical fire weather conditions with the potential for rapid 
fire growth due to the very strong winds. 

After a quick break in the action tonight, attention then shifts 
back to the west, and especially the southwest on Monday as the 
leading impulse rotating through a developing west coast upper 
trough, lifts into the Northern Plains. 

Early Monday morning, surface high pressure is situated across the 
forecast area making for a cold and quiet start to the day. It won't 
stay quiet for long as cyclogenesis in the lee of the Northern and 
Central Rockies has already begun, and a surface low emerges over 
southeast Montana by 00 UTC Tuesday. Therefore, we will see a quick 
return of strong southerly winds spreading across the CWA. It is
possible that we may need wind highlights in the far southwest, 
but it's too early at this time, especially with our current 
headlines in place.

In addition, we also see a quick burst of isentropic ascent 
lifting southwest to northeast through the forecast area during 
the day. This is expected to produce a band of snow with light 
accumulations across a good portion of the forecast area. At this 
time the highest qpf is located across northwest and north central
ND, but does extend southward into the south central. Lightest 
qpf amounts are in the James River Valley and the far southwest. 
Currently, NBM probabilities of an inch of snow are at or above 50
percent over far northwest and over north central ND down through
southern Ward and Mchenry counties. Then taper to 30-40 percent 
from around Watford City southeast to Bismarck, and then back up 
towards Harvey. Probabilities taper southward through the 
southwest and James River Valley. It is possible that we may need 
wind highlights in the far southwest, but it's too early at this 
time, especially with our current headlines in place. 

At this time it looks like a sub-advisory event, but with warm 
surfaces, breezy to windy conditions and a quick burst of some snow, 
travel hazard, including reduced visibilities and slippery roadway 
could make for some hazardous travel at times. The snow looks to 
taper across the far north central early Monday evening, with dry 
conditions through the remainder of the night. The southeast 
Montana surface low tracks into the western Dakotas, making for a 
much warmer night, compared to Sunday night, with lows mainly in 
the 20s. 

.LONG TERM...(Monday through Saturday)
Issued at 243 AM CST Sun Nov 6 2022

Chances for impactful winter weather across the Northern Plains 
during the Wednesday night to Friday timeframe are increasing, 
although there remains considerable uncertainty on how much of 
western and central North Dakota may be impacted.

Strong low level warm air advection will blanket most of the area on 
Tuesday as the area of low pressure responsible for Mondday's snow 
and strong easterly winds lifts into the western Dakotas. It does 
not appear that there will be enough boundary layer saturation to 
support any drizzle or freezing drizzle, but mostly cloudy skies 
could maintain a low level temperature inversion through the day. 
Far western North Dakota is less likely to feel the full affects of 
the warm sector, where highs are only forecast to reach the mid and 
upper 30s. Meanwhile, afternoon temperatures as high as the lower 
50s are possible from south central into southeast North Dakota.

Shortwave energy ejecting from a strong western CONUS trough will 
begin reaching the state Tuesday night into Wednesday, while the 
passage of a surface trough ushers in a much colder air mass. There 
isn't really a strong forcing signal evident in deterministic 
guidance, nor a probabilistic signal in ensemble QPF/snow guidance 
that would suggest any significant winter weather through Wednesday 
afternoon, nor favor one area over the other. Therefore, widespread 
20 to 40 percent chances of precipitation given by the NBM makes 
sense for Wednesday. Forecast thermal and moisture profiles suggest 
mixed precipitation types are possible from south central into 
eastern North Dakota during the day Wednesday, with above freezing 
temperatures aloft and a loss of ice nucleation both in play.

Wednesday night into Friday is when the forecast becomes very 
interesting. There is now growing ensemble consensus that the 
upstream longwave trough approaching the Rockies will induce 
cyclogenesis in eastern Colorado Wednesday night, with a deepening 
low over the Central Plains on Thursday followed by a northeast 
track towards the Great Lakes region Thursday night into Friday. 
Analysis of ensemble MSLP low locations indicates high confidence in 
the formation of a Colorado low (subjectively estimated to be at 
least 75 percent), but still notable spread within each ensemble 
system on placement, and perhaps more so on timing. While some 
clustering of low locations has occurred within each ensemble, there 
is a very distinct northward shift of the ECMWF cluster versus the 
GEFS cluster. All told, probabilities for at least 6 inches of snow 
(using a 10:1 liquid ratio) have greatly increased in all ensemble 
systems, but with large placement disparities. The 00z GEFS places 
24-hr +6" snow probabilities as high as 60 percent from central 
South Dakota to southeast North Dakota, while the 18z ECMWF ensemble 
places those same probability threshold as high as 40 percent from 
southwest to northeast North Dakota. Another ensemble tool that 
provides increasing confidence in a more impactful system is that 
the ECMWF EFI is now depicting the potential for high-end snow 
accumulations, though its placement is likely not dispersive enough.

Some ensemble and deterministic models depict the potential for 
freezing rain or sleet as warmer air aloft gets wrapped around the 
low. Sounding analysis and NBMv4.1 precipitation type probabilities, 
which carries greater membership than the operational NBMv4.0, are 
not that excited about this potential outcome, which if it were to 
verify could be completely outside of our forecast area. Therefore, 
we will not be messaging mixed precipitation types with this storm 
system at this time, though impactful ice accumulations remains a 
reasonable worst-case scenario within the PDF of outcomes. Aside 
from that, temperatures are expected to be cold enough for all snow. 
As is the case with most Colorado lows, winds are likely to be an 
issue, which there is already a signal for in the ECMWF EFI.

To summarize, a Colorado low now appears likely to develop and 
impact parts of the region Wednesday night through Friday. Higher 
probabilities for winter impacts exist across southern and eastern 
North Dakota compared to the north and west, but the probability of 
a Winter Storm at any given point appears no greater than 60 percent 
as of this writing.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
Issued at 243 AM CST Sun Nov 6 2022

A low pressure system will track across southern Canada tonight
through Sunday morning, bringing strong westerly winds. Wind 
gusts exceeding 50 kts at times are likely. Additionally some 
periods of MVFR cigs are also expected, mainly north across KXWA-
KMOT, but could approach KDIK and KBIS in the 12-16 UTC timeframe.
Winds are expected to diminish from west to east Sunday afternoon
and evening. 

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 6 PM CST this evening for NDZ001>003-
009>011-017>021-031>034-040>045.

High Wind Warning until 6 PM CST this evening for NDZ004-005-012-
013-022-023-025-035>037-046>048-050-051.

&&

$$

SHORT TERM...TWH
LONG TERM...Hollan
AVIATION...TWH