Winter Storm in Wyoming, April 16 to 18, 2025

Area Forecast Discussion
National Weather Service Billings MT
338 PM MDT Wed Apr 16 2025

.KEY MESSAGES...

- A weather system will bring cool, wet and windy conditions into
  Friday. During this time, heavy snow is expected over the
  mountains and foothills with wet snow/slush accumulations likely
  at lower elevations.

- Impacts to travel, outdoor recreation, and young livestock are
  possible late today through Friday.

- After brief drying into Saturday, more cool and unsettled
  weather is anticipated Sunday through Tuesday.

&&

.DISCUSSION...
Through Thursday Night...

Challenging forecast due to broken up frontogenesis and model QPF
differences with the upcoming system. GFS and ECMWF were in good
agreement aloft in showing a positively tilted trough with two low
centers...one rotating through S Central Canada and the other
dropping S through ID tonight. The trough will affect the area
through the period.

Surface cold front was through Judith Gap at 21Z and moving S.
Models had the right idea with showers developing ahead of the
front in area of weak frontogenesis. These showers with possible
thunderstorms will increase in coverage and spread E through the
rest of the afternoon. Thunder was supported as soundings were
inverted-v with steep lapse rates, and mesoanalysis showed
surface CAPES of 500-1000 J/kg over the far SW part of the
forecast area. Included low thunder chances from KBIL-KSHR W into
early evening. Winds were gusty this afternoon over the W and N
with the front coming into the area, accompanied by a tight
pressure gradient. Models agreed on gusty winds continuing tonight
through Thursday. Strong 700 mb frontogenesis was progged to be W
to E across the central part of the area at 00Z on the GFS. This
forcing then splits overnight with the strongest areas over the
far E and SW. ECMWF has frontogenesis in segments at 00Z with a
better band at 06Z. Both models shift this forcing quickly S
during Thursday. QPF amounts and placement among the models
differed considerably starting at 00z tonight and continuing
through most of the period.

NBM/Forecast QPF reflected a model blend, and total QPF was
similar to the previously forecasted QPF. PWATS will be above
average tonight at 0.5 inches. Snow ratios were a blend of NBM and
WPC and were a bit higher than previous ratios. A couple of other
differences were noted in the latest models, including a more
northerly surface flow into Thursday and a period of decent
dendritic growth on the GFS for KBIL tonight. End result was, have
added Paradise Valley and S. Carbon to the Advisories and went
with Warnings for KLVM, N. Sweet Grass, N. Stillwater and N.
Carbon Counties. Still looking for highest accumulations in higher
elevations. Areas of blowing snow will be a hazard with the tight
pressure gradient. Hazard ending times remain constant with KBIL
ending at midnight Thursday night, Red Lodge ending Fri. morning,
and southernmost areas ending at 18Z Friday. The KBIL area may
need a Warning if the dendritic growth pans out and this will be
something to watch for later shifts. Stay tuned to the forecast.
Arthur

Friday through Wednesday...

Friday morning will feature most of the precip exiting with there
being some lingering snow near Sheridan. There is a chance that
some light showers quickly pass through the eastern 1/3 of the CWA
Friday afternoon as a weak vort max on the backside of the main
trough pushes through. There still is some uncertainty regarding
the timing and intensity of this precip, however, it will be
negligible in the grand scheme of the full event.

The signal for brief ridging on Saturday persists and will bring
temperatures back to average for all locations. For Billings
itself this means temps near 60F. This ridge will also bring us
the only clear day for the next week so get out and enjoy it if
you can.

As Sunday rolls around the next trough begins to enter the region.
This is when a lot more uncertainty begins. The NBM seems to want
to rush precipitation into the area Sunday morning and have it
stick around through Tuesday. The long range models, however, want
to slow down the trough over the PNW and eject a small amount of
energy into MT sunday which could being some mountain snow and
some scattered showers at lower elevations. The ECMWF and GFS are
in even less agreement in the most recent runs compared to the
previous deterministic solutions. The GFS has the trough digging
more than the ECMWF does during the day Monday providing far more
lift which could aid in the showers and rainfall totals.

The main concern with this system will be the potential rain on
snow flooding that could occur in the foothills. The storm over
the next few days is forecast to drop a decent amount of snow,
especially in the foothills. Temps do warm on Saturday in
association with the mostly clear skies which will hopefully melt
all the low elevation snow before this next system moves in.
Regardless, a prolonged period of wet conditions is expected to
start next week. WMR

&&

.AVIATION...

21z Discussion...

Convective showers are rapidly filling in across south central MT.
Any one of these showers could have a decently strong downdraft
with them. These showers will continue through 06z.

Aside from isolated MVFR conditions, VFR should prevail for the
remainder of the daytime hours. As a cold front moves through the
area expect a wind shift at all sites, but most notable at KBIL &
KSHR. Winds will be out of the NE (010-030) sustained up to 20kts
with gusts reaching 30kts at KBIL.

Precipitation will also fill in across the region from west to
east starting at KLVM and KBIL around 21z. These should be rain
showers with a slight chance (25%) of seeing a couple lightning
strikes between 21z-03z. A transition to heavy wet snow will start
at KLVM around 03z and spread east to KBIl around 06z and KSHR by
09z. While KMLS and sites eastward will see precipitation,
impacts will be less than the other sites. Snow will stick around
through the rest of the TAF period. Expect widespread IFR
conditions after this transition to snow for the remainder of the
period. Periods of LIFR are certainly a possibility for most
locations as well.

Mountains will be obscured after 21z.
WMR
&&

.PRELIMINARY POINT TEMP/POPS...

    Thu     Fri     Sat     Sun     Mon     Tue     Wed
-----------------------------------------------------------
BIL 029/040 026/044 026/057 038/060 038/058 036/056 034/060
    +9/S    42/J    00/U    14/W    67/W    43/W    23/W
LVM 026/037 019/042 023/056 037/055 034/053 030/052 031/057
    +9/S    41/B    00/U    25/T    67/W    43/W    23/W
HDN 028/041 026/046 023/059 033/061 036/058 035/057 033/062
    +9/O    43/J    00/U    14/W    67/W    54/W    23/W
MLS 032/045 028/046 025/058 034/060 036/058 036/054 032/060
    95/O    12/J    00/U    02/W    34/W    43/W    22/W
4BQ 030/039 029/044 025/055 033/059 038/058 036/054 033/059
    98/O    43/J    00/U    02/W    25/W    43/W    22/W
BHK 028/044 025/044 023/056 030/060 034/058 033/053 029/057
    95/O    13/J    20/U    01/U    24/W    43/W    22/W
SHR 027/037 024/041 017/053 027/056 031/056 030/053 028/058
    ++/S    85/J    00/U    03/W    46/W    54/W    23/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory in effect from midnight tonight to
      midnight MDT Thursday night FOR ZONES 29-30-57-58-173-235.
     Winter Storm Warning in effect until midnight MDT Thursday
      night FOR ZONES 34-65-141-170-172.
     Winter Weather Advisory in effect until midnight MDT Thursday
      night FOR ZONES 40-42-63-64-139-228.
     Winter Storm Warning in effect until 9 AM MDT Friday FOR
      ZONES 56-66.
     Winter Storm Warning in effect until noon MDT Friday FOR
      ZONES 67-68.
     Winter Storm Warning in effect from midnight tonight to noon
      MDT Friday FOR ZONES 138-169-171.
WY...Winter Storm Warning in effect from midnight tonight to noon
      MDT Friday FOR ZONES 198-199.

&&

weather.gov/billings