954
FXUS65 KTFX 161443
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
843 AM MDT Thu May 16 2024

.UPDATE...

Satellite imagery this morning shows a fairly extensive area of
mid-high level clouds across much of the area with an embedded
Chinook arch like feature across western portions of north-central
MT. This is all downstream if an incoming upper level jet and mid
level wave moving into BC this morning with a few light rain
showers also noted beneath the Chinook arch and area of deeper
moisture progressing east across north-central MT. Surface low
pressure emerges in southern AB today within a deepening lee-
side trough, resulting a strengthening surface pressure gradient
across north-central/central MT today. This in combination with
increasing mid level flow ahead of the approaching wave/jet and
afternoon mixing will lead to widespread windy conditions across
the area this afternoon with strongest winds adjacent to the Rocky
Mtn Front. A stream of higher mid-upper level moisture remains
embedded in the westerly flow across the area today, maintaining
some risk for showers or an isolated weak thunderstorm this
afternoon and evening, mainly along the Canadian border in closer
proximity to embedded shortwave energy moving across southern AB.
Hoenisch

&&

.SYNOPSIS...

Strong and gusty winds are expected through Friday as an upper
level disturbance and associated Pacific front approach and
eventually cross the Northern Rockies. Light precipitation can be
expected over this timeframe, with the best chance of seeing
amounts in excess of a tenth of an inch occurring over North
Central Montana. Unsettled and cool conditions are then expected
from the weekend through much of next week, with multiple
additional chances for widespread precipitation.

&&

.AVIATION...
16/12Z TAF Period

Expect VFR conditions across North Central and Southwestern Montana
over the next 24 hours, even as winds increase and upper level cloud
cover increases. Winds will be strongest across the plains,
particularly at KCTB and KGTF during the afternoon hours, and we
will have a few light rain or virga showers around, particularly
around KCTB and KGTF this morning before shifting east to KLWT and
KHVR during the afternoon. Ludwig

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

&&

.PREV DISCUSSION...
/ISSUED 540 AM MDT Thu May 16 2024/
Today through Friday... forecast concern through the period
will be strong and gusty southwest to west winds ahead of and
following an upper level disturbance and associated Pacific front.
Main area of concern through the day today for winds will be from
the Rocky Mountain Front to the Interstate 15 corridor in North
Central Montana, especially along the US Hwy 2 corridor from
Shelby to Marias Pass where the latest NBM probabilities supports
a 60-75% chance for maximum 24hr wind gusts to exceed 48kts
through this evening. Hourly wind gusts in excess of 48kts through
this evening peak at between 20-40% from approximately 17z this
morning through 23z this afternoon. This difference between
maximum 24hr and hourly wind gusts probabilities suggests that any
wind gusts approaching or exceeding high wind criteria would most
likely be a one an done type of scenario. The 24hr maximum
sustained probability for the aforementioned areas ranges from
80-90% for today, with the hourly probabilities once again peaking
between 17-23z at between 30-60%. While High Wind criteria wind
gusts and/or speeds may be realized from late this morning through
the afternoon hours in the Browning and Cut Bank Areas, the
overall frequency (i.e. one or two observations of 58+ mph wind
gusts and/or one hour of sustained winds of 40 mph) of these
values being reached are too low to warrant a High Wind Warning at
this time.

By Friday the upper level disturbance will begin to move over the
Northern Rockies, with a Pacific front sweeping eastward and across
Southwest through North Central Montana from the late morning
through afternoon hours. This Pacific front will bring another
period of strong and gusty winds; however, this time the winds will
be experienced across all of Southwest through North Central
Montana. While NBM probabilities do not support widespread High Wind
criteria wind gusts/speeds, wind gusts in excess of 41kts have a
70+% chance of occurring across most of the CWA outside of a small
portion of central North Central Montana. While several locations
may actually realize High Winds on Friday, I do not currently expect
these location to be concentrated enough in one specific area to
warrant a High Wind Watch as it would be like throwing darts at a
dartboard...blindfolded (i.e. high false alarm rate). None-the-less,
Friday will be windy across the entire CWA and travelers will need
to exercise caution, especially if operation high profile vehicles.
Finally, periods of light precipitation will be possible from today
through Friday, but amounts will largely remain below a 0.1" outside
of the Hi-Line and Glacier National Park Area. The East Glacier Park
zone has the highest probabilities for 0.5" of precipitation through
the timeframe at 10-30%, with 20-60% chance for 2" or more of snow.

Saturday through Sunday...ensemble clusters strongly favor longwave
troughing over the Northern Rockies throughout the weekend, with the
leading mode of uncertainty being the overall amplitude of the
longwave trough, specifically on Sunday. A deeper longwave trough on
Sunday, which is overall favored in 3 of the 4 clusters, would
result in cooler and "wetter" conditions through the weekend across
much of Southwest through North Central Montana. Latest NBM
probabilities for a 0.25" of precipitation from 12z Sunday to 12z
Monday generally range from 20-40% south of the US Hwy 2 corridor
and north of the US Hwy 12 corridor. Additionally, the probability
for snowfall of 2" or more along the Continental Divide and across
the mountains of Central Montana over this timeframe is
approximately 30%, with 48hr probabilities (including Saturday and
Saturday night) ranging from 30-50% for these same areas. High
temperatures on Saturday in wake of Friday`s Pacific front will fall
into the 60s, with Sunday only seeing highs rise into the 50s.

Monday through next Thursday...an unsettled and "cooler" pattern is
favored through the upcoming work week, with the multi-model
ensemble cluster suggesting overall longwave troughing over the
Western CONUS and Western Canada and inconsequential periods of
transient shortwave ridging moving over the Northern Rockies. Some
uncertainty exists with the timing, position, and amplitude of
individual shortwaves troughs rotating through the longwave trough,
but the main message to put forward will be that their exists
multiple chances for precipitation (some of which may fall as
mountain snow) and below normal temperatures through the upcoming
work week. - Moldan

.SYNOPSIS...

Strong and gusty winds are expected through Friday as an upper
level disturbance and associated Pacific front approach and
eventually cross the Northern Rockies. Light precipitation can be
expected over this timeframe, with the best chance of seeing
amounts in excess of a tenth of an inch occurring over North
Central Montana. Unsettled and cool conditions are then expected
from the weekend through much of next week, with multiple
additional chances for widespread precipitation.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  75  54  64  42 /  10  10  40  40
CTB  71  48  56  38 /  10  10  60  50
HLN  79  52  67  40 /   0  20  40  10
BZN  77  45  66  32 /  10  20  60  20
WYS  67  35  63  22 /  10  10  30  10
DLN  75  45  67  31 /   0  10  10   0
HVR  77  52  66  42 /  40  20  60  70
LWT  72  45  60  38 /  20  20  60  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

http://www.weather.gov/greatfalls