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000
FXUS65 KBYZ 152039
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
239 PM MDT Mon Apr 15 2024

.DISCUSSION...
Today through Tuesday night...

Weak thunderstorms and rain showers have continued across the
northwestern counties of the forecast area today. The strongest
storms produced several lightning strikes this morning. With a low
pressure system moving across the Central and Northern Plains
today, convective activity is expected to increase this afternoon
and evening, with models showing 500-2000 J/kg of CAPE. The
highest amount of instability will be confined to the far
southeast, where there is a small area included in the Storm
Prediction Centers Marginal Risk for severe thunderstorms. Along
with the instability, an upper level low over Wyoming is producing
lots of divergence, as a result an increase in surface level
convergence will provide ample forcing. The main concerns for
these storms is hail and lightning, as well as some strong winds.
There is a decent amount of moisture available across much of the
area tonight as well, with PWATs up to 1 inch in SE MT. Currently,
total rainfall amounts tonight into tomorrow morning range from a
few hundredths to a few tenths from Miles City to Fort Smith and
west. As for locations south and east of this line (including
Sheridan), 0.25-1" of total precipitation is possible, with much
of Powder River and Carter Counties in a 0.5" to 1" range.

Tomorrow, as the upper low departs WY, a diffluent pattern setups
from W-E as a trof digs into the northern Rockies from Canada. As
this trof progresses south and east, cold air and moisture will
surge into the region. Precipitation type will be snow in the
mountains while rain is expected in the foothills and lower
elevations initially. For the foothills, a transition to snow is
expected Tuesday night, as temperatures drop into the 30s. Snow
levels will drop down to ~3000ft by Wednesday morning, allowing
for some potential snowfall in lower elevations including
Billings. Up to an inch of snowfall is possible in Billings,
however with highs in the 60s to low 80s lately, and warm soil
temperatures, accumulations would be hard to see for non-
foothill/mountain locations. As a result, Winter Storm Warning is in
place for the Absaroka/Beartooths, Pryors, and Big Horns
beginning Tuesday evening and ending Thursday afternoon. A Winter
Storm Watch is in place for the Beartooth and Red Lodge Foothills
will also go into effect 9pm MDT Tuesday.

Latest snowfall probabilities can be found at weather.gov/byz

With the departing surface low in the Plains, strong winds will
wrap around it, resulting in breezy to gusty conditions tomorrow.
Wind gusts across much of the area in the 20-40 mph range with
gusts into the 40-50mph in Sheridan County. The strongest winds
will begin to diminish by mid-morning, coming back down into the
30-40 mph range.

High temperatures for Tuesday will be in the 50s to mid 60s.

Matos

Wednesday through Sunday...

Upper level storm system is centered over SC Canada on Wednesday
morning with a trof digging down the backside into W MT/ID during
the day and into Wednesday night. Normally having the low centered
that far north and east would put our part of the world in a
downslope dry and windy quadrant. But, there is some QG forcing
aloft that slides across the southern half of the forecast area
during this period associated with a strong cyclonically oriented
jet stream along the MT/WY line. This jet with just a bit of
curvature will provide the upper support for what is mainly a low
level upslope/isentropic lift type of event. The bulk of the
precipitation will occur along the north facing foothills and into
the mountains.

NBM Probabilities for warning criteria foothills snow (6+
inches):

Red Lodge   75%
Nye         85%
Livingston  25%
Big Timber  15%
Columbus     5%
Harlowton    0%
Sheridan WY  0%
Story WY    80%

Current forecast shows 10 inches from Red Lodge to Nye, with
3 to 4 inches from Columbus to Big Timber and Livingston. Also
have 2 to 4 inches for the Sheridan Foothills along I-90, with 10
for Story.

Given the time of year and ground temperatures, not expecting much
impactful accumulation during the daytime hours, and even in the
higher foothills would expect roads to melt during the afternoon
hours. Thinking the mountains are a high probability (75% greater
than a foot of snowfall) warning, but for the foothills not as
confident in the impacts. The ground temperatures/time of year/and
low level winds being a bit northwesterly (doesn`t favor Red
Lodge upslope) are a concern for warning type impacts, and an
advisory might be good enough. Plan to Upgrade to warnings for the
mountain zones, but will hold off on the foothills and let the
mid shift take another look tonight as the snow holds off until
after midnight Tuesday night.

The heaviest precipitation will taper off Wednesday night as dry
air pushes in from the north dropping PWATs under a quarter of
an inch by Thursday morning. The northerly winds in the lower
levels will continue into Friday before turning east and then
south heading into the weekend. During this northerly wind period
will continue to see upslope enhanced rain/snow showers in the
foothills, with light additional snow accumulations for the
mountains each day. The northerly winds will keep temperatures
cool across the forecast area, with highs staying mainly in the
40s through Saturday. Shortwave ridging builds in for Sunday for a
warmer day with more sun. Chambers

&&

.AVIATION...

VFR conditions will prevail tonight. Scattered showers and
isolated thunderstorms could bring local MVFR conditions at times
through the night tonight, especially over SE Montana. Small hail
is possible with any thunderstorms or heavier showers this
afternoon through tonight, and an isolated severe storm is not out
of the question over Powder River/Carter counties through 06z
tonight with large hail and heavy rain the main threats. Winds
will be northerly and gusty 20 to 35kts for most of the forecast
area, with SE Montana holding on to a gusty southerly wind until
just before sunrise. Wind gusts along the Bighorn mountain
foothills in Wyoming could gust over 40kts at times through
tonight, impacting the KSHR terminal at times through sunrise
Tuesday. Chambers

&&

.PRELIMINARY POINT TEMP/POPS...

    Tue     Wed     Thu     Fri     Sat     Sun     Mon
-----------------------------------------------------------
BIL 047/064 035/044 028/045 025/043 026/049 030/064 038/065
    52/W    76/S    22/S    12/S    11/U    02/R    22/R
LVM 038/059 031/041 021/041 019/039 020/047 030/060 034/062
    34/W    87/S    33/S    21/B    11/U    02/R    22/R
HDN 047/066 036/046 027/047 023/044 023/052 028/067 035/067
    41/B    66/S    22/S    11/B    11/U    01/B    22/R
MLS 046/064 037/046 028/043 022/041 022/048 029/064 038/065
    41/N    11/N    11/N    01/B    00/U    01/U    11/B
4BQ 047/062 037/046 027/045 023/041 023/047 029/066 037/064
    62/W    12/S    11/N    11/B    01/B    01/U    11/B
BHK 042/062 033/046 024/041 019/039 019/045 024/059 033/062
    54/W    01/N    11/N    01/B    01/B    01/U    11/B
SHR 044/062 032/041 022/041 020/041 019/047 025/062 032/062
    51/N    78/S    52/S    22/S    22/S    11/B    21/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch remains in effect from Tuesday evening
      through Thursday morning FOR ZONES 56-66.
     Winter Storm Warning in effect from 6 PM Tuesday to 6 PM MDT
      Thursday FOR ZONES 67-68-171.
     Winter Storm Watch remains in effect from Tuesday evening
      through Thursday afternoon FOR ZONES 67-171.
WY...Winter Storm Warning in effect from 6 PM Tuesday to 6 PM MDT
      Thursday FOR ZONE 198.
     Winter Storm Watch remains in effect from Tuesday evening
      through Thursday afternoon FOR ZONE 198.

&&

$$
weather.gov/billings