Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 220219
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
819 PM MDT Thu Mar 21 2024

.UPDATE...

Updated forecast precipitation chances and amounts along with a
slight cooling of temperatures and adjustments to precipitation
type and snow amounts for tonight into tomorrow.

Reason for the adjustments is the recent models poor handling of
the cold air position in the surface to 700mb layer and thus the
handling of the over-running precipitation. Recent models think
the low level frontogenesis is near a Miles City to Ekalaka line,
but its actually from south of Harlowton to Laurel to Alzada based
on surface analysis and radar returns showing where the over-
running precipitation bands are.

This was a problem earlier today as well with the snow around
Billings being depicted well to the northeast in
Musselshell/Rosebud county. The last several HRRR runs are
getting a better handle on things but the NBM is still showing the
precipitation in the wrong location (too far north). So, adjusted
precipitation further south.

Models all drag colder air south across the whole CWA, so this
will happen faster than previous forecast anticipated, and
precipitation type will switch to snow sooner over central and
western zones. Expect a broad band of snow to set up from
Harlowton to Billings to southern Rosebud county late tonight into
tomorrow morning along the 850-700 frontogenesis band. Snow
accumulations will generally be in the 1 inch range by mid to late
morning, but locally 2 or maybe even three inches is possible
where this banding sets up and persists, especially over higher
hilltops. Precipitation accumulations look to be 0.05 to 0.15
through tomorrow morning. Lows tonight will be mainly in the low
to mid 20s, with a bit warmer conditions in the western foothills
closer to 30 degrees.

Expect locally slick road conditions for the Friday morning
commute, along with patchy fog further reducing visibility along
with the light snow. Chambers

&&

.DISCUSSION...

Rest of Today through Friday Night...

The baroclinic zone is beginning its fluctuations across the area.
We had the backdoor cold front pass through this morning and keep
us on the cool side of things. That said,a thermal trough is
providing one last push of snow across the area, briefly reducing
visibilities down to half a mile under it. Behind it is finally
the brief warm-up of today via some surface downsloping and the
sun trying to peak through the clouds. This will help surfaces
melt any lingering snow or ice lingering on them. That said,
instability is increasing over the mountains for this afternoon,
and will result in a small chance for light storm activity and
even thundersnow to occur. Latest hi-res model guidance has
continued to have high confidence in putting snow and rain over
the mountains and adjacent foothills, especially the Beartooths.
That said, this weakly forced system has not been depicted well by
the models over the past 24 hours, so that does lead to a
decrease in confidence in this splattering of rain/snow to occur
through this afternoon.

Another front pushes the baroclinic zone back into the mountains
tonight and more upslope flow and cooler temperatures return for
all of southern MT. An overrunning of mid-level moisture will
occur throughout Friday to bring a 30-60% chance of snow across
the area, but any accumulations will generally stay under an inch.
Temperatures look to hover more on the cool side finally for
Friday and not retreat to the north this time, keeping Friday`s
highs only climbing into the mid to upper 30s. The end of the week
is the start of the change back to cold and snowy conditions. The
false spring is over.

Vertz

Saturday through Wednesday...

.Key Messages...

... Significant winter storm hitting the area Saturday night into
 Sunday.

... Cold temperatures come in behind the snow storm with subzero
 lows possible.

Shortwave ridging will begin to flatten out on Saturday, as a
dynamic low pressure system approaches from the west. This system
will bring colder temperatures and ample moisture into Monday.
Temperatures will be in the upper 30s to upper 40s on Saturday,
before dropping into the upper teens and mid 20s, Sunday and
Monday.

Models are showing a low pressure center setting up in NE Wyoming
Saturday night, with a strong flow at 850mb coming up from the
Gulf of Mexico. These winds will wrap around the low pressure,
becoming north-east oriented, and provide a potentially favorable
period of upslope for the mountains. The extent of these low-
level winds is notable, with models depicting near-blizzard
criteria winds out east, near Baker, for a several hour period
Sunday. With high snow amounts and 30-40 mph winds, traveling
conditions will deteriorate greatly. Initial snow ratios will be
in the low teens, before enough cold air infiltrates the region,
raising them into the upper teens to around 20 to 1. With this
occurring, accumulations will further increase, especially out
east for Fallon County where current forecasts have around 10
inches of snowfall. As for other counties in the north and east,
4-7 inches are currently forecasted, and 1-4 inches elsewhere. As
for the mountains, 6-12 inches are possible. With the higher
amounts, winter highlights may be needed. Precipitation chances
will decrease into Monday, leaving scattered chances across the
area.

Another important aspect of this system will be just how cold
temperatures are going to get. Sunday high temperatures in the
20s, which would be 25-30F below normals, and Monday high temps in
the upper teens and 20s, 30-35F below normal. Overnight lows in
the low 10s and single digits Sunday and Monday night. Areas that
see higher snow accumulations, specifically out east, have
overnight lows in the single digits forecast.

An unsettled pattern continues into the middle of the week,
although temperatures will rise back into the 30s and 40s. Periods
of precipitation are possible once more as a disturbance wafts
through the region Tuesday. Another potential system is shown by
models late Wednesday, however it is too soon too determine what
to make of this right now.

For relevant snow probabilities, go to weather.gov/billings.

Matos


&&

.AVIATION...

A band of snow showers will set up NW of KBIL down through KSHR
around 6Z tonight and slowly move east through the morning.
MVFR/IFR conditions will be possible for these locations and east.
Snow showers will begin to develop over the mountains and
foothills late into the afternoon. Mountain obscurations are
possible. TS

&&

.PRELIMINARY POINT TEMP/POPS...

    Fri     Sat     Sun     Mon     Tue     Wed     Thu
-----------------------------------------------------------
BIL 025/038 026/039 021/025 011/025 010/038 020/047 028/042
    67/S    46/O    +9/S    43/S    12/S    22/R    35/S
LVM 030/046 028/043 023/028 014/032 018/044 026/048 030/042
    22/O    38/O    97/S    32/S    23/S    23/O    56/S
HDN 024/039 024/045 020/027 009/028 006/039 016/050 025/043
    78/S    44/O    +9/S    53/S    11/B    21/B    35/S
MLS 022/031 023/037 019/021 007/017 000/027 008/037 019/036
    54/S    64/S    9+/S    51/E    00/B    00/B    13/S
4BQ 022/036 024/046 021/025 009/022 003/035 014/048 023/045
    33/S    31/B    89/S    51/E    00/B    00/B    13/O
BHK 018/031 016/031 014/023 004/017 905/025 005/036 016/037
    62/S    65/S    9+/S    61/E    00/B    00/B    12/S
SHR 028/044 024/050 021/028 009/027 010/042 021/053 026/046
    43/O    12/R    99/S    42/S    11/B    11/B    25/O

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch in effect from Saturday evening through
      Sunday evening FOR ZONES 31>33-37.
WY...None.

&&

$$
weather.gov/billings


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