764
FXUS65 KTFX 122057
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
257 PM MDT Sun May 12 2024

.SYNOPSIS...

Hazy conditions from wildfires in Canada continues to diminish this
evening and tomorrow. Above normal temperatures continue through
tomorrow and scattered showers and a few thunderstorms this evening
and again tomorrow afternoon and evening. Next best chances of
precipitation is Monday night into Tuesday.

&&

.DISCUSSION...

Key Points:

- Haze and smoke from Canadian wildfires diminishes across North
 Central Montana through tonight.

- General thunderstorms and rain showers this evening and again
  tomorrow afternoon and evening with above normal temperatures
  and breezy conditions.

- Next weather system arrives for the area Monday night and
 Tuesday with cooler temperatures Tuesday and a return of near
 normal temperatures for Wednesday.

Rest of today through Monday... Latest visible satellite imagery
continues to show hazy conditions clearing out from west to east
across North Central Montana this afternoon. Haze is forecasted to
continue for parts of Hill and Blaine Counties tonight and clear out
for late tonight into tomorrow morning. Visible satellite also
shows developing cumulus clouds across the higher terrain of
Central Montana and a line from the Canadian Border down to Craig.
A few rain showers and general thunderstorms can develop late
this afternoon and early evening across the Hi-Line and from Great
Falls to Lewistown. Primary concerns with any developed
thunderstorms today are a brief downpour and lightning. Low
temperatures remain in the 40s and 50s, except at some higher
mountain elevations with lows in the 30s. Above normal high
temperatures continue tomorrow with highs in the 70s. Winds
increase tomorrow afternoon across the area gusting between 20 and
30 mph, with locally higher wind gusts across the Rocky Mountain
Front and adjacent Plains area.

There`s going to be two primary locations to watch for tomorrow, one
for the Southwest and one along the Hi-Line. For Southwest Montana,
a weak upper level shortwave moves through bringing unsettled
weather conditions to the surface in the form of rain showers and
thunderstorms. Timing for showers and thunderstorms, is favored to
be between 2 PM and 8 PM. For along the Hi-Line and Canadian Border,
a low pressure system with an associated stationary front to our
north is forecasted to move southeast and meet with a cold front
from Pacific Northwest tomorrow afternoon. Primary shower and
thunderstorm activity start time is between 3 to 5 PM that is likely
(>30%) to continue into the early evening hours. Primary concerns
for any developed thunderstorms tomorrow are lightning, a brief
downpour, gusty erratic winds, and small/pea sized hail. Webb

Tuesday...ensemble clusters all favor a secondary shortwave diving
southeast over the Northern Rockies through Tuesday night, with some
uncertainty in the amplitude of the shortwave as it digs from
Western Montana/Idaho towards the Central Rockies. NBM probabilistic
gives areas along and southeast of a Cut Bank to Lewistown line, and
northeast of a Butte to West Yellowstone line, a 40-80% chance for
24hr (12z Tuesday to 12z Wednesday) precipitation amounts to
exceeding 0.10", with generally between a 20-50% chance for amounts
to exceed 0.25". While this precipitation will be beneficial for
many lower elevations, the rain falling on top an already rotting
snowpack across Central Montana mountains will lead to additional
runoff into area creeks and streams. High temperatures on Tuesday in
wake of Monday`s Pacific front will fall back below normal after
several days of above normal temperatures, with readings in the 60s
across lower elevations.

Wednesday through next Sunday...an active and unsettled pattern is
expected through the remainder of the work week and into the
upcoming weekend as quasi zonal to northwesterly flow develops over
the Northern Rockies through much of the period. While the multi-
model ensemble mean favors this pattern there is still a degree of
uncertainty with respect to the amplitude of the ridge over the
Eastern Pacific and trough over the center of the CONUS/Canada,
especially from Thursday onwards, which will have a big impact on
how warm/cool temperatures end up being across Southwest through
North Central Montana over this timeframe. Daily chances for showers
and thunderstorms will be favored across the entire CWA within this
quasi zonal to northwesterly flow regime; however, daily
precipitation values will largely remain below 0.10" where
precipitation is observed. - Moldan

&&

.AVIATION...
12/18Z TAF Period

VFR conditions continue for Southwest Montana airfields through the
TAF period, with gusty winds developing tomorrow afternoon and
probability of showers increasing after the 13/18z timeframe.

Haze from Canadian wildfires continues to impact KCTB, KHVR, and
KGTF. Visibility improves through 21z for KGTF and KCTB, with KHVR
seeing improvement tomorrow morning based on current surface
observation clearing trends and latest near-surface smoke model
guidances. Haze within the KLWT vicinity has been observed on latest
webcams, but based on clearing trends from visible satellite, should
not impact the airfield. KLWT also has potential to see vicinity
showers this evening, but confidence is not high for impacts to the
airfield so it was not included in the TAF. KHVR has potential (50%)
to see rain showers this evening, but visibility could continue to
be impacted from haze after the showers move through. Webb

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.HYDROLOGY...

The Flood Warning for Clear Creek has been cancelled as water
levels have finally fallen below minor flood stage as of early
this (Sunday) morning. Water levels on Clear Creek will continue
to slowly fall to below action stage through Monday afternoon.

The Flood Watch for the Bears Paw Mountains has also been
cancelled this morning given no recent reports of flooding across
the watch area. With this being said, the Big Sandy Creek gage near
Havre (which is outside of the Bears Paw Mountain zone) was
approaching Action Stage as of this morning. We will continue to
monitor this gage through the remainder of the morning and act
accordingly should water levels rise further through Action Stage
towards Minor Flood Stage. - Moldan

The flood watch continues for the mountain ranges of Central
Montana. No new flood impacts have been reported over the past
12-24 hours. This is good news, as this means the runoff is
coming off slowly or the runoff is soaking into the ground. In
either case, if this trend continues, this flood watch could also
be cancelled early. Brusda/Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  49  75  47  62 /  40  30  40  80
CTB  48  72  46  62 /   0  30  50  60
HLN  51  77  50  67 /   0  30  20  70
BZN  45  74  43  65 /  10  40  40  70
WYS  37  64  35  57 /  10  70  60  70
DLN  45  72  43  64 /   0  40  20  50
HVR  50  77  48  69 /  60  40  50  50
LWT  47  71  45  59 /  30  20  50  80

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Monday morning for Cascade County below
5000ft-Fergus County below 4500ft-Judith Basin County and Judith
Gap-Little Belt and Highwood Mountains-Meagher County Valleys-
Snowy and Judith Mountains-Western and Central Chouteau County.

&&

$$

http://www.weather.gov/greatfalls