Helena Valley, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

844
FXUS65 KTFX 130507
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1007 PM MST Tue Nov 12 2024

Aviation Section Updated.

.KEY MESSAGES...

- Breezy to windy conditions continue, especially Wednesday and
  Thursday and again on Sunday.

- Another round of light mountain snow is expected Wednesday night
  through early Thursday, mostly impacting the higher terrain of
  the Rocky Mountain Front.

- General unsettled conditions continue through early next week,
  with increasing snow chances expected over portions of Central
  and Southwest Montana late Friday and Saturday.

&&

.UPDATE...

Tonight through tomorrow light snow will continue along the
Northern Rocky Mountain Front. Tomorrow it will be warm and
breezy across North-central, Central, and Southwestern Montana
with light snow along the Idaho Montana border in Southwestern
Montana. For the update, wind speeds and wind gusts across the
area were decreased to better match current observations and
trends. Sky grids were adjusted to better match observations and
current satellite imagery and trends. Minor tweaks were made to
hourly temperatures and overnight low temperatures across the
plains of North-central Montana. The rest of the forecast is on
track. -IG

&&

.DISCUSSION...
/Issued 735 PM MST Tue Nov 12 2024/

 - Meteorological Overview:

Transient ridging aloft moves in tonight into Wednesday for
general mild and dry conditions despite some lingering low
stratus/patchy fog along the ID/WY border and to a lesser degree
along the Continental Divide. Broad troughing then moves onto the
Pacific Northwest coast and brings southwesterly flow aloft for
increased winds by Wednesday afternoon followed by the passage of
a shortwave and a round of mountain snow Wednesday night into
early Thursday. Winds with this system look to mostly remain in
the 30 to 55 mph range. Snowfall also looks to be on the lighter
side and mostly confined to the higher terrain along the Rocky
Mountain Front.

The aforementioned Pacific Northwest trough ejects eastward this
weekend and brings the next chance for accumulating snow late
Friday into Saturday. Despite much of this system`s energy
expected to dive south of our CWA, a majority of deterministic
models highlight a weak low trekking northeast from the Great
Basin into the eastern portion of Montana. H700 temperatures cool
to around -10C on the backside of the low via weak northerly flow.
Model guidance has struggled with this system over the last few
days, but the current meteorological setup is favorable for at
least some accumulating snow over the southwest and the north
facing slopes of the central MT island ranges along the highway
200 corridor.

This system quickly exits the region later on Saturday, leaving
another period of transient ridging through Sunday afternoon.
Primary concern will be the potential for stronger winds from a
tightening surface pressure gradient and potential mountain wave
activity on Sunday. The strongest winds look to occur along the
Rocky Mountain Front and along the highway 200 corridor in Central
MT. Ensembles then generally favor broad troughing moving into
the Northern Rockies late Sunday into early next week for more
mostly mountain snow chances and temperatures cooling slightly
below average. - RCG

 - Forecast Confidence & Scenarios:

Winds :

While the entire forecast period is expected to be on the windier
side, the strongest winds are expected Wednesday and Thursday and
again on Sunday. The winds initially increase along the the Rocky
Mountain Front and the north-south oriented valleys/mountain
peaks of Southwest MT before moving onto the plains on Thursday. A
few locations such as the Madison valley/Norris Hill area and
areas along the Rocky Mountain Front have around a 50% chance for
seeing sustained winds over 40 mph for short periods or gusts over
55 mph.

Sunday will be another notably windy day along the Rocky Mountain
Front and the Central MT highway 200 corridor where a tightening
pressure gradient and or mountain wave activity push the potential
for sustained winds over 40 mph and or gusts over 55 mph to the
50 to 80 percent range.

Snow :

Mountain snow is expected along the higher terrain of the Rocky
Mountain Front as early as Wednesday afternoon and will continue
through early Thursday. There is around a 60% chance for 2 inches
of snow or more at Marias Pass, but only a 30% chance for snowfall
exceeding 4 inches. The higher terrain in and around Glacier
National Park will see amounts greater than 6 inches.

Snow moves into Central and Southwest Montana late Friday into
early Saturday. The north facing slopes of the central island
ranges have over a 60% chance for 2 inches of snow or more, while
there are similar probabilities for amounts in excess of 4 inches
over the Madison/Gallatin ranges.

Confidence is much lower for lower elevation snow, especially for
locations on the northern periphery of the highway 200 corridor
from Great Falls to Lewistown. These areas currently have less
than a 30% chance for 1 inch or snow or more. This chance
increases to around 50% for the Bozeman and Ennis areas.

the unsettled conditions continue into early next week, but there
is little confidence in precipitation other than lighter mountain
snows late Sunday through next Tuesday. - RCG

&&

.AVIATION...
13/06Z TAF Period

VFR conditions are expected to continue at the terminals across
North Central (KCTB, KHVR), Central (KLWT, KGTF, KHLN), and
Southwest (KBZN, KEKS) Montana through at least 14/06Z. However,
an increasingly moist flow aloft shifting more southwesterly will
gradually increase high- and mid-level cloudiness and mountain-
top obscuring mountain precipitation over the area through the
period.

Regarding winds, the increasing flow aloft will cause widespread
mountain wave turbulence. Low level wind shear on the Rocky
Mountain Front will decrease through 12Z, but it will become more
widespread across the area after 21Z. Southerly surface winds
will remain breezy, but will become more gusty after 16Z; most
terminals will gusty up to 30 kt, but more funneled winds through
the Madison River valley will cause gusts to around 40 kt at KEKS.
-Coulston

The KWYS TAF will not be issued until airport operations resume
next spring.

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  31  53  39  53 /   0   0   0   0
CTB  26  50  35  49 /   0   0  10   0
HLN  25  51  32  54 /   0   0  10  10
BZN  19  46  27  51 /   0   0  10  10
WYS  10  32  19  36 /  10  20  50  50
DLN  19  40  23  45 /   0   0  10   0
HVR  27  56  34  57 /   0   0  10  20
LWT  25  51  34  52 /   0   0   0   0

&&

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

$$
http://www.weather.gov/greatfalls