428
FXUS65 KBYZ 170143
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
743 PM MDT Thu May 16 2024

.UPDATE...
Spotty weak convection continues to impact our region this
evening, in response to a weak shortwave and limited instability.
A cell recently developed on the east side of the Snowies and is
approaching NW Rosebud County, but there is no lightning yet.
Mesoanalysis shows lifted indices only around zero. In fact,
there has been very little lightning in our forecast area since
convection developed in the mid afternoon. That said, low level
lapse rates remain steep and any strong-ish cell could produce
enhanced surface wind gusts (to ~40 mph) over the next couple
hours. Activity will diminish through the remainder of the
evening. Overnight weather will be quiet with low temps generally
mid 40s to mid 50s. Forecast is in good shape. JKL

&&

.DISCUSSION...

Tonight through Friday night...

A few showers were moving into the NW zones this afternoon on
radar imagery. Temperatures were in the 60s and 70s, well on their
way to the forecast highs, and winds were gusting into the 20s in
many areas due to deep mixing and strong WNW flow aloft. Surface
CAPES were 500-1000 J/kg this afternoon with Bulk Effective Shear
around 40 kt this afternoon and evening. PWAT`s will be .5-.8
inches. There was not a lot of lift into tonight, but any
perturbation will create showers and thunderstorms. PoPs will be
low, 20-30%, mainly E of KBIL after 00Z and will decrease rapidly
after 06Z Friday. Given the above, any storms will have the
potential for gusty winds and small hail, and the HREF did show a
few weak helicity tracks over the area.

Friday into Friday night will be windy and unsettled as a
cyclonically curved jet moves through the area with good
divergence. Strong shortwave trough will accompany the jet, as
well as a cold front with strong 700 mb frontogenesis. Highest
MUCAPES will be around 500 J/kg with Bulk Effective Shear around
40 kt E of KBIL. PWAT`s will be .5-.9 inches. Combination of the
above will bring high chances (60-90%) of showers and
thunderstorms to the area in the afternoon, with slightly lower
PoPs in the evening. Highest PoPs will be around KBIL into Rosebud
County in the afternoon. PoPs quickly decrease overnight. HREF
showed more helicity tracks Fri. afternoon than there will be
today and the tracks were stronger. So strong storms, with gusty
winds and hail, along with heavy rainfall are possible Fri.
afternoon and evening, mainly E of KBIL.

The other issue will be how windy it gets, especially W of KBIL.
Soundings supported Advisory level winds in KLVM, so have issued
Wind Advisory from 18Z Fri.-06Z Saturday for them. Strong pressure
rises will cross the forecast area in the afternoon and evening
behind the cold front. Soundings and cross-sections showed good
mixing down of at least 45 kt winds, and signatures for mountain
waves in areas from Judith Gap to K6S0. Noted the WSUP viewer
trended higher with probabilities of wind gusts of at least 48 kt
compared to yesterday. Given this dynamic system, have also
issued a High Wind Watch from 18Z Fri.-06Z Sat. for the Judith Gap
to K6S0 areas, including Melville. The mountain wave possibility
looked the best during the late afternoon through the evening. It
will be cooler on Fri., except near 80 in the SE ahead of the cold
front. Snow amounts will be light over the mountains through the
period. Arthur

Saturday through Thursday...

As cyclonic flow moves east and westerly flow moves in, the region
can expect mild and breezy conditions for Saturday. The remainder
of the period looks to remain unsettled with multiple rounds of
disturbances providing increased chances of precipitation.
There does seem to be a lack of any good push of moisture into
the area as PWATs actually fall below normal for much of the
period. Into Sunday, ensembles have a shortwave trough moving
into the west, bringing precip chances of around 30-60% in lower
elevations with a 60-80% chance in the mountains. Chances for a
quarter inch of rain Sunday and Monday look to be best (40-60%)
for Billings down to Sheridan, WY and west, with places east at a
20-30% chance. Brief ridging will build in for Tuesday with only
small chances for precip. Ensembles and clusters then depict
lowering heights moving into western MT sometime late Wednesday
into Thursday with timing currently differing amongst models.

High temperatures will be in the 60s and low 70s through the
period. TS

&&

.AVIATION...

Scattered showers and isolated thunderstorms can be expected this
afternoon with brief MVFR conditions possible under a thunderstorm.
Wind gusts of up to 40-45 kts are possible at KLVM, K1KM, and
K6S0 Friday afternoon into the early evening. Scattered showers
and thunderstorms will begin to develop around 18Z Friday around
KBIL and spread east into the evening. MVFR/IFR conditions are
possible under any thunderstorms producing heavy rain. TS

&&

.PRELIMINARY POINT TEMP/POPS...

    Fri     Sat     Sun     Mon     Tue     Wed     Thu
-----------------------------------------------------------
BIL 051/072 042/066 043/062 041/063 041/067 044/067 045/058
    28/T    50/U    16/T    45/T    12/R    13/T    46/T
LVM 046/067 036/066 042/058 035/059 036/064 042/063 040/055
    16/T    20/N    17/T    45/T    12/R    25/T    57/T
HDN 048/075 040/068 040/066 040/063 040/068 042/070 043/062
    29/T    70/U    14/R    44/T    22/R    13/R    45/T
MLS 050/074 042/066 042/067 042/063 040/066 043/067 044/060
    27/T    50/U    12/R    32/T    11/B    12/R    34/R
4BQ 050/080 042/066 042/070 041/062 040/065 042/070 045/063
    25/T    50/U    01/B    32/R    22/R    12/R    23/R
BHK 048/078 039/065 039/070 039/062 038/062 039/066 040/060
    26/T    50/N    11/B    32/R    12/R    12/R    33/R
SHR 048/081 036/066 040/068 036/059 035/064 039/070 041/064
    25/T    60/U    03/T    44/T    23/R    22/T    35/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Watch in effect from Friday afternoon through
      Friday evening FOR ZONES 63-141-172-228.
     Wind Advisory in effect from noon Friday to midnight MDT
      Friday night FOR ZONE 65.
WY...None.

&&

$$
weather.gov/billings