123
FXUS65 KBYZ 042044
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
244 PM MDT Sat May 4 2024

.DISCUSSION...

This afternoon through Sunday night...

Main short term impact will be gusty to locally strong southerly
winds over the eastern half of the forecast area on Sunday,
continuing into Sunday night. These gusty winds combined with
temperatures in the 80s and low Relative Humidity values will
bring an elevated grass fire danger Sunday afternoon for areas
east of Billings into the western Dakotas. The strongest wind
gusts may arrive Sunday night over SE Montana, just ahead of a
cold frontal passage, with probabilities for gusts over 45 mph
peaking late evening at 35 to 45% along the eastern state line.

Ridging over the area this afternoon will keep skies sunny and
temperatures pleasant for this time of year, mainly in the 60s.
Mostly clear skies on tap for tonight with temperatures 5 to 10
degrees warmer than this morning as southerly winds begin to
increase across the forecast area ahead of an approaching storm
system.

As mentioned above Sunday will be a transition day with a cold
front and well organized storm system poised to move into the area
by late in the day. Ahead of the late day cold front, winds will
increase out of the south pulling in warmer air and boosting
temperatures into the 70 to 85 degree range for most areas. The
warmest temperatures will be over the Bighorn and Tongue river
valleys where probability for highs over 80 degrees are well above
60 percent (78% Miles City). Winds will be gusty at times in the
35 to 45 mph range, likely strongest from eastern Sheridan county
north into southern Rosebud and Powder River county during the
afternoon, shifting to the rest of SE Montana into the evening as
the approaching cold front compresses the flow. At this time do
not anticipate needing a Red Flag Warning as the southerly flow
will also be bringing increased low level moisture with it.
Combined with increased greening up of grasses across the area the
threat just doesn`t quite rise to the level of needing a warning.
May issue a rangeland fire danger statement tonight, and will
continue messaging through other formats for the need to be
careful not to start a wildfire tomorrow.

Along and behind the cold front will see precipitation chances
increase along and behind the cold front. There looks to be good
moisture associated with this system, but downslope winds kick in
quickly tomorrow night as the front moves through, limiting
precipitation chances and amounts from what they could be. Overall
precipitation trends for tomorrow afternoon and night have trended
lower due to this downslope wind effect. Freezing levels drop from
around 9500 feet Sunday afternoon to around 5500 feet over the
western mountains and foothills by Monday morning. Current
forecast shows 2 to 4 inches of snow Sunday night, mainly on
west/south facing slopes, for the Beartooth/Absaroka and Crazy
mountains. Chambers

Monday through Friday...

Deterministic models have come into better agreement with the
500mb low track on this mornings model runs. The system is
currently forecast to come across the forecast area Monday morning
as an open trof, developing a closed low by the afternoon over
east central Wyoming and then pivot northward into NW SD by Monday
evening. After that the low drifts northward into W ND through
Tuesday, and back into E MT Tuesday night. Additional upper
energy pushes in from the northwest Wednesday, phasing with the
upper low and kicking it quickly eastward on Thursday. General
trofing and northwest flow persists over the area Thursday into
Friday keeping conditions unsettled to end the week.

There are a couple of things that could keep precipitation from
being as heavy as is currently advertised over our neck of the
woods. First, with the system coming through as an open trof we
negate the normal wrapped up storm system easterly winds in the
low to mid levels, and instead go straight to downslope
west/northwest winds that persist through the event. While there
is good dynamics aloft to force precipitation, upslope and
isentropic ascent will be missing for most of the area, especially
central and west. The dynamics will also quickly traverse the area
and set up mainly east of the area near the core of the upper low
limiting residence time over our area. The downslope winds are
being advertised as strong as the storm system sets up shop to our
east and deepens, it will pull winds downhill toward it with
models suggesting gusts in the 40 to 70 mph range Monday and
Tuesday (strongest Tuesday). Winds this strong will disrupt upward
motion and make precipitation production difficult, especiall
over the eastern half of the forecast area. Another issue is that
the NBM has a time lag for precipitation, and while models have
trended lower with precipitation chances on the 12z run due to the
above factors, it will take some time for the NBM precipitation
accumulations to catch up with the current model trend.

All of the above is to say that this system is very dynamic and
strong but still evolving in the computer models, so take the
precipitation totals as having significant uncertainty still.
There is still the potential for some heavy precipitation Monday
into Tuesday in a band somewhere east of Billings (possibly way
east) but the models are showing this potential in various areas.
As such, WPC has a slight risk for excessive rainfall over SE
Montana in a broad swath. Expect this potential to tighten up and
may exit the area completely over the next 36 hours as model
consensus improves further.

Snow levels drop from 9500 feet to 5500 feet by Monday morning and
generally hangs out around that elevation through the week. As
currently advertised not expecting lower elevation snowfall. For
the mountains the wind field supports significant snow mainly
falling on west to south facing aspects through Tuesday. Beyond
that winds should turn more northerly bringing a better chance
for north facing slopes to get in on the snow Wednesday and
Thursday. Posted a Winter Storm Watch for the northern Bighorn
mountains (Monday thru Tuesday morning) to match up with RIW`s
watch. As mentioned above forcing for snow in the Bighorns will be
mainly on west facing slopes, but enough slop over into the
Burgess Junction area to get close to a foot with the latest model
run. Additionally, wind gusts in the 35 to 50 mph range will
produce near whiteout conditions at times Monday into Tuesday.
Totals for the Beartooth/Absaroka/Crazy mountains look less
impressive at this time so decided to go without a watch for these
mountain locations for now. However, given the wind speeds
forecast may need a highlite with subsequent forecasts if the
combination of snow and blowing snow warrants it.

Strong winds Monday and Tuesday will be the main impactful weather
for most areas early in the week, with the band of heavier rain
somewhere east of Billings being a secondary issue. Will likely
need a High Wind Warning for portions, possibly a large portion of
the area for Tuesday, and maybe in some areas on Monday as well,
with models advertising gusts well above 60 mph in many areas.

Winds look to die down some on Wednesday, though still gusty, as
the secondary energy arrives and begins to move the core of the
upper low east. This period is when more widespread wrap around
precipitation may be maximized for many lower elevation locations,
and upslope snow really gets established. The current forecast is
showing over a foot of snow Wed-Thu for the western mountains, and
close to 2 feet possible in the Bighorns. So, this is a tail of
two significant periods with this storm system, Strong winds
Mon/Tue with localized heavy rain somewhere east of Billings, and
more widespread precipitation with heavy mountain snow Wed/Thu.
One thing looks certain, its going to be a tough week for outdoor
activities until probably next weekend. Chambers

&&

.AVIATION...

Winds are still expected to increase this afternoon for a brief
period at all terminals. Otherwise, dry and near-clear sky
conditions will persist through Sunday morning. Expected rain
showers to move across all terminals late Sunday morning and
through the afternoon. Vertz

&&

.PRELIMINARY POINT TEMP/POPS...

    Sun     Mon     Tue     Wed     Thu     Fri     Sat
-----------------------------------------------------------
BIL 038/074 045/056 042/054 040/049 040/056 042/064 041/071
    02/R    55/R    43/R    57/R    86/R    33/R    11/U
LVM 041/066 040/051 035/047 035/047 036/051 037/059 036/068
    06/T    65/R    33/O    57/O    66/R    22/R    11/U
HDN 037/079 044/057 041/055 039/049 039/057 041/064 038/072
    01/B    46/R    64/R    69/R    98/R    43/R    11/U
MLS 039/082 049/059 039/051 038/051 041/060 042/064 041/070
    01/N    49/T    77/R    78/R    77/R    32/R    11/U
4BQ 041/081 047/058 039/052 037/047 039/056 041/061 040/069
    01/N    49/T    75/R    67/R    86/T    43/R    11/U
BHK 036/075 047/062 036/050 036/051 038/058 038/062 038/067
    00/N    69/T    77/R    67/R    76/R    32/R    11/U
SHR 036/078 041/055 037/056 036/048 036/050 037/060 036/067
    01/N    48/R    43/R    47/R    87/R    54/R    11/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...Winter Storm Watch in effect from Monday morning through
      Tuesday morning FOR ZONE 198.

&&

$$
weather.gov/billings