386
FXUS65 KBYZ 171930
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
130 PM MDT Wed Jul 17 2024

.DISCUSSION...

Through Thursday Night...

Satellite imagery shows a ridge axis over central MT and an
upstream weak low over western WA/OR. As expected, we are
beginning to see convection develop over the mountains with
lightning noted south of Cooke City and Sheridan as of 1pm. There
is nothing yet over the Crazies or Snowies, but as the ridge axis
migrates to the east and the air mass moistens a bit more this
should begin to happen over the next few hours (especially given
upslope SE winds from the surface to 700mb). Overall, convection
between now and about 10pm will be weak but may produce erratic
surface winds to about 40 mph. Greatest potential is near the
mountains/foothills but some activity may spread eastward to
include Roundup & Billings this evening. High res models have been
fairly consistent in this regard.

Late tonight and Thursday morning will be dry, then by afternoon
we begin to see the effects of the approaching Pacific low. The
low will crest the ridge and not induce height falls, and flow
aloft will remain quite weak, but the ascent along with a bit
moister air mass (pwats ~0.90") will result in a much greater
potential (30-50% probability) for thunderstorms tomorrow
afternoon and evening across the region. HREF shows only a modest
signal for convective winds, but forecast soundings are somewhat
indicative of wet microbursts and so gusty outflow winds will need
to be watched. Wind shear will be too low and mid levels too warm
for a risk of anything but wind and localized downpours. As the
PV anomaly tracks from north central thru southeast MT, the chance
of showers & thunderstorms will persist over our east thru
tomorrow night.

Regarding fire weather, the increased lightning activity on
Thursday may be problematic given our drying fuels, but the storms
will be wet and there is a reasonable expectation of localized
wetting rains...including during the nighttime hours in southeast
MT.

Temps of course will remain warmer than normal. Look for highs
Thursday in the 90s most places but a few notorious hot spots
could touch 100F as 700mb temps rise to near +14C.

JKL

Friday through Wednesday...

Upper ridge axis will be over W. MT on Friday, while NW flow
brings shortwave energy SSE through the eastern part of the
forecast area. In addition...other shortwaves will move through
the remainder of the area, while monsoonal moisture continues over
the region. PWAT`s will be just over an inch in the far E. Thus
there is a 20% chance of showers and thunderstorms in the morning
from KMLS E and SE. Chances for showers and thunderstorms will
increase from Rosebud County E in the afternoon with highest
chances on the MT/Dakotas border at 40 to 50%. Southern mountains
will have 30-40% PoPs and there will be slight chances (20%) over
KSHR and over areas near the western mountains. Low PoPs linger in
the evening over the SW mountains and far SE MT. The best chances
for 0.25 inches or higher of rainfall through Fri. evening will be
E and SE of KMLS in the teens to around 20%.

Region will be under upper ridging Saturday through Tuesday with
continued monsoonal moisture over the area. Expect 20-30% chances
for showers and thunderstorms over the SW mountains and the NE
Bighorns for the weekend each afternoon. Low afternoon/evening
chances continue over the SW mountains through Tuesday. Models
showed a trough approaching the area from the W on Wednesday with
low PoPs over the western mountains spreading into adjacent areas
including KLVM, K6S0 and Judith Gap. Mean 700 mb temp was 16 degs
C which could cap lower elevation convection, but this was way out
in time in the forecast period, so will continue to watch model
trends.

As for temperatures, highs will be in the upper 80s to low/mid 90s
Fri. through Monday, then in the 90s on Tuesday and in the 90s to
around 100 on Wednesday. There was a 30-50% chance of reaching 100
degrees in the river valleys on Wed. and this area included KBIL,
KMLS and KSHR. KMLS will be close to record temps if this scenario
plays out. Arthur

&&

.AVIATION...

VFR conditions will prevail over the next 24 hours, though slant
range visibility will be reduced at times due to the numerous
wildfires over the western U.S. Isold/Sct thunderstorms expected
mainly over and near mountains thru 04Z this evening.
Thunderstorms have a 10-20% chance of impacting KLVM-KSHR, and a
<10% chance at KBIL. Storms have the potential to produce briefly
erratic surface winds. There is a greater risk of thunderstorms
(plus erratic surface winds and local MVFR) Thursday afternoon &
evening, and all TAF sites may be impacted. JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    Thu     Fri     Sat     Sun     Mon     Tue     Wed
-----------------------------------------------------------
BIL 063/097 064/094 065/093 063/091 062/093 063/095 064/099
    22/T    41/U    11/U    01/U    00/U    00/U    01/U
LVM 056/094 054/094 057/093 055/091 055/091 054/095 057/097
    23/T    22/T    11/U    01/U    01/U    01/U    12/T
HDN 060/099 062/095 062/093 060/092 059/093 059/097 060/100
    22/T    41/U    11/U    11/U    00/U    00/U    00/U
MLS 064/096 068/091 063/090 064/089 064/090 064/094 066/097
    00/U    43/T    11/U    11/U    00/U    00/U    00/U
4BQ 063/097 066/092 063/089 061/087 061/090 063/094 064/097
    00/U    33/T    10/U    01/U    00/U    00/U    00/U
BHK 060/094 063/088 060/087 058/086 059/088 059/092 060/094
    00/U    44/T    11/U    11/U    10/U    00/U    00/U
SHR 056/098 059/093 057/090 056/087 055/090 056/093 058/095
    22/T    22/T    11/U    11/U    01/U    00/U    01/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
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