Roberts, Montana Weather Forecast Discussion

715
FXUS65 KBYZ 081924
AFDBYZ
Area Forecast Discussion
National Weather Service Billings MT
124 PM MDT Mon Sep 8 2025
.KEY MESSAGES...
- Above normal temperatures today through first half of work
  week.
- Repeated late day isolated/scattered showers and storms Tuesday
  through Thursday.
- Good chance of significant precipitation and cooler temps by Friday.
- Persistent periods of wildfire smoke impacts.
&&
.DISCUSSION...
Through Wednesday night...
Main synoptic feature for the short term will be the building of a
ridge of high pressure aloft over the area. Per usual under the
ridge, expect temperatures to be above normal (normal highs this
time of year are in the upper 70s to 80 degrees) peaking Wednesday
in the upper 80s to lower 90s.
What is a bit more unusual is the ridging is going to become
increasingly dirty while its in our area, and this term refers to
increasing moisture, not smoke though smoke will continue to be an
issue this week. Pacific moisture flowing over the ridge today
and tomorrow will moisten the airmass from above bringing a chance
for high based showers and thunderstorms, mainly in the afternoon
and evening hours, but as with today there could be some activity
lingering overnight as well. All of this activity looks very
light in nature with gusty winds (30 to 45 mph) being the main
threat along with occasional lightning.
Tuesday night into Wednesday low level plains moisture
advects into the area on southeast winds adding low level moisture
to the mix, and this is where precipitation chances begin to
increase along with stronger thunderstorm chances as CAPE values
increase too. Overall the best chances for precipitation will be
over the western mountains and foothills. While chances for
precipitation are low over SE Montana due to a mid level inversion
under the ridge, this will be where the highest CAPE values will
exist. As such, not expecting many thunderstorms in this area but
any that do form will have the fuel to become strong into
Wednesday evening.
The near surface winds under the ridge will keep smoke from
dispersing much while the southwest winds aloft will pull in
additional smoke from wildfires in the Great Basin. Latest models
aren`t forecasting choking smoke amounts, but will be dealing with
noticeable smoke for at least several more days. Chambers
Thursday through Monday...
Upper ridge gets shunted eastward as a strong Pacific storms
system moves into the PacNW late Wednesday into Thursday. This
puts our area under increasingly divergent southwest flow aloft as
the trof shifts eastward, bringing cooler air aloft which
increases overall instability, and pushing stronger disturbances
through the region providing forcing for convection over our
area. The result is increasing chances of precipitation across the
area from Thursday through Saturday, along with cooler
temperatures.
While cooler air works into the western portion of the forecast
area on Thursday, southerly winds will keep temperatures warm
central and east with highs still in the mid to upper 80s. Plains
moisture advection and increasing forcing at the surface and aloft
will bring scattered showers and thunderstorms to the western half
of the area with isolated storm for the eastern half. As with
Wednesday, the ingredients for stronger but more isolated storms
will exist over SE Montana and will have to keep a close eye on
this area Thursday afternoon and evening.
The amount of precipitation that falls, particularly in the wetter
Friday-Saturday period, will depend on the track of the upper low.
A track west to east across the northern half of Wyoming is the
most favorable for precipitation across our area while tracks
directly over southern Montana, or further north, become
increasingly dry and windy. The latest cluster analysis of this
system shows two lines of thinking, the majority of the ECMWF
ensembles show a stronger consolidated low that takes a more
southern (favorable precipitation) track, while the GFS ensembles
show a less consolidated system with a more northerly (lower
precipitation potential) track. Canadian ensembles are dispersed
amongst the other two and an even less favorable open wave
solution. The result of the above splits is that the NBM
probabilities for a half an inch or more of precipitation is
currently in the 50 to 70 percent range for Friday through
Saturday, but the spreads at any given point across the forecast
area are large with a reasonable low accumulation (25th
percentile) around a tenth of an inch to a reasonable high (75th
percentile) of over an inch. So, still plenty of uncertainty with
this late week system. If you have outdoor plans please stay tuned
to the forecast for more details through the week.
Upper low opens up and lifts northward on Sunday diminishing
precipitation potential, though not drying things out completely,
through Monday.
High temperatures drop mainly into the 70s on Friday, with
probabilities for highs in the 60s running from 80% west to 50%
east Saturday afternoon. Highs in the 70s will prevail for Sunday
and Monday. Chambers
&&
.AVIATION...
Wildfire smoke aloft may reduce slant range visibility at times.
Isolated showers and thunderstorms, mainly over the mountains,
remain possible into the evening. Scattered showers and
thunderstorms will begin over the west, including near KLVM
Tuesday afternoon. Archer
&&
.PRELIMINARY POINT TEMP/POPS...
Tue     Wed     Thu     Fri     Sat     Sun     Mon
-----------------------------------------------------------
BIL 055/087 058/087 058/084 056/076 056/070 053/074 052/076
    01/H    11/B    33/T    46/T    87/T    53/W    22/W
LVM 047/082 048/082 048/079 045/073 045/066 044/071 044/073
    03/T    33/T    45/T    47/T    76/T    43/T    33/T
HDN 052/088 056/090 056/086 053/078 053/071 049/076 049/078
    00/H    11/H    22/T    45/T    87/T    53/W    22/W
MLS 053/086 060/091 061/088 058/081 057/072 054/075 053/079
    10/U    22/W    21/B    34/T    87/T    63/W    32/W
4BQ 056/084 059/089 062/087 058/081 056/071 052/074 053/078
    00/H    11/B    11/B    24/T    77/T    62/W    21/U
BHK 049/083 054/087 059/089 055/083 054/072 051/073 049/077
    00/H    11/N    21/B    23/T    77/T    63/W    22/W
SHR 050/085 052/088 053/085 050/077 048/070 045/074 046/077
    01/H    21/H    12/T    36/T    87/T    53/W    22/W
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.
&&
$$
weather.gov/billings

NWS BYZ Office Area Forecast Discussion