993
FXUS65 KBYZ 190836
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
236 AM MDT Sun May 19 2024

.DISCUSSION...

Through Tuesday night...

A couple of disturbances will impact portions of the forecast
area over the next 72 hours. The first is already here and will
impact mainly the western mountains and foothills Today before
lifting northeast of the area tonight. The second better organized
system will take a more southerly track across central Wyoming
and impact western and then southern sections of the forecast
area. This second system has more energy/dynamics associated with
it with the potential to bring more significant precipitation to
the southern mountains and foothills. Heavy snow is a possibility
for the higher elevations of the Beartooth/Absaroka and Bighorn
mountains from Monday through Tuesday.

Today...A broad open trof that has sagged southward over the
PacNW over the past 24 hours will move across W MT this morning
and then lift northeast into NE MT/NW NoDak this evening. Good
QG/Jet forcing will reside over the western third of the forecast
area this morning, diminishing as the trof fills and moves
northeast this afternoon/evening. North to northwest winds will
enhance lift along the north facing slopes of the Beartooth front
today, and increased instability during the day under the
generally trof will aid in shower development. Can`t rule out an
isolated thunderstorm today, with small hail the main threat. The
best chances for precipitation will be west of a Roundup to
Billings to Red Lodge through early afternoon, with precipitation
chances tapering off mid afternoon into the evening as the system
shifts northeast. Snow levels today will be 6200 feet in the Crazy
mountains, 7000 feet in the Beartooth/Absaroka mountains, and
8500 feet in the Bighorn mountains, dropping about 500 feet this
evening as precipitation tapers off. Heaviest snow forecast is for
the Beartooth/Absaroka mountains where 3 to 6 inches of snowfall
is expected through tonight.

Monday-Tuesday...Expect a break in precipitation late Sunday
evening into Monday morning as the first trof pulls away and the
next system organizes and drops through Idaho on its way into
West-Central Wyoming by Monday night. As the system tracks this
way the flow aloft backs to the south and becomes more divergent,
increasing QG forcing over western zones by late morning. This
will increase precipitation chances over the western mountains and
foothills mid to late morning, spreading eastward as the system
intensifies and makes an eastward pivot toward Wyoming. Tuesday
sees the core of the system down around Casper by mid day, then
opening up and shifting northeast into SoDak/NE Tuesday night. An
ideal track for this system to maximize precipitation over our
area is about 100-150 miles further north of the currently
advertised track.

Precipitation...As currently advertised this system should still
bring good precipitation to areas along the MT/WY line. Mon-Tue
Probabilities for over half an inch of rain/melted snow are in the
40-70 percent range south of a
Livingston/Absarokee/Wyola/S.Powder River line. The 50% 0.25 inch
probability line runs from Harlowton/Billings/Lame Deer/just south
of Ekalaka. Upslope winds will enhance precipitation in the
immediate vicinity of the E/N facing slopes area mountains, so
locally heavier amounts around an inch are possible where winds
are favorable.

Snow...Snow levels Monday afternoon will be around 6500 feet in
the Crazy mountains, 7200 feet in the Beartooth/Absaroka
mountains, and 7600 feet in the Bighorn mountains, dropping around
500-1000 feet Monday night into Tuesday morning, then rising
uniformly to around 7200 feet Tuesday afternoon. Probabilities for
a foot+ of snow in the Beartooth and Crazy mountains Mon-Tue
evening are around 25 percent. For the Bighorn mountains the
chances are higher, from around 50 percent along the
Sheridan/Johnson county line, to around 30 percent in the Burgess
Junction area. Current forecast using WPC/NBM QPF and SLR are
coming in a bit higher deterministically than these probabilities
imply with just under a foot for the western mountains (above
8000feet) and up to 14 inches in the Big/Little Goose drainages of
the Bighorn mountains.

Winter highlites...This model run went heavier on precipitation
and snow compared to previous runs due to a more organized
structure and more favorable track. Any shift of the track further
south would diminish precipitation potential significantly, with
a shift north increasing it. Given the current NBM probabilities,
thinking an advisory might be the best option for the Bighorn
mountains. In coordination with WFO Riverton elected to hold off
on a Winter Storm Watch given the lean toward an advisory and let
the Sunday Day shift take a look at another run before committing
to that course of action since the main snow period will be Monday
night into Tuesday. At this time not anticipating any Beartooth
highlites as the Beartooth Highway is still closed, and
probabilities for a foot+ of snow there is ~25 percent. Chambers

Wednesday through Sunday...

By late Wednesday, energy from an incoming trough will bring a
30-50% chance (highest over the west) of precipitation to the
plains west of Forsyth and a 50-70% chance to the mountains and
foothills. Thursday afternoon into evening, the chance for
widespread precip increases further, with a 50-70% chance
(highest over the west) of at least 0.25" of precip over the
plains and a 50-60% chance of at least 0.5" over the mountains
through Friday night. Over the highest peaks, this could
translate to several inches of snow, with a 40% chance of at least
5 inches.

For late Friday into the weekend, there is more uncertainty on the
timing and strength of the next system, although the overall
pattern looks to remain unsettled. Some model solutions bring in
the next trough by Saturday evening while others hold off until
Sunday afternoon. Currently, there is a 30-50% chance (highest
over the west) of precip over the plains and a 50-60% chance over
the mountains and foothills for Saturday and Sunday.

High temperatures will primarily be in the upper 50s over the
west to low 70s over the southeast. Friday is currently expected
to be the coolest day, with highs in the 50s to low 60s. Archer

&&

.AVIATION...

Showers will spread from west to east and become more numerous
today. With this, breezy northwest winds will occur with gusts up
to 25-30 kts. Expect mountain obscurations. Archer


&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Mon     Tue     Wed     Thu     Fri     Sat
-------------------------------------------------------
BIL 060 038/060 043/062 042/069 045/061 042/060 041/066
    6/R 25/T    45/T    13/W    47/T    65/W    34/W
LVM 057 035/056 037/061 037/064 040/054 037/058 037/063
    7/T 27/T    55/T    15/T    69/T    65/T    35/T
HDN 065 038/061 043/063 039/071 045/065 041/060 040/068
    4/R 24/R    45/R    12/W    46/T    75/W    34/W
MLS 068 039/062 043/063 041/069 046/065 043/056 040/066
    3/R 32/R    22/R    11/B    25/T    65/W    33/W
4BQ 070 041/060 044/061 040/069 045/069 044/059 040/066
    2/R 23/R    45/R    21/U    14/T    65/W    33/W
BHK 070 038/061 039/062 038/068 042/067 041/057 037/065
    3/T 32/R    23/R    11/B    14/T    65/W    33/W
SHR 068 036/056 038/055 035/068 040/066 038/056 037/066
    3/T 26/R    78/T    32/T    25/T    65/W    33/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
weather.gov/billings