961
FXUS65 KTFX 031120
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
420 AM MDT Fri May 3 2024

UPDATED AVIATION SECTION

.SYNOPSIS...

One more cool and showery day is expected today before milder
temperatures move in for the weekend. Another cool and wet Pacific
weather system impacts North-central and Southwest Montana Sunday
through at least mid next week, with the most significant
precipitation and coolest temperatures expected Monday through
Wednesday.

&&

.DISCUSSION...

The latest satellite and meso-analysis shows abundant cloud cover
within a northwesterly flow aloft. Light snow showers have been
ongoing all night, mostly over the northerly upslope areas
adjacent to the Little Belt, Highwood, and Snowy Mountains. This
shower activity will more or less persist through this
afternoon with the continued northwesterly flow, though
accumulation amounts will generally be negligible. Transient
ridging builds in tonight for clearing skies with temperatures
bottoming out in the 20s for most locations. Patchy fog
development can be expected in spots, but shouldn`t be a
widespread problem. With one more day of ridging aloft, Saturday
should be the driest day over next week while temperatures climb
to near of slightly above average.

Deep southerly flow aloft develops over Southwest MT Saturday
night ahead of a closed low moving onto the Pacific NW coast. This
system will trek eastward into S ID on Sunday, placing the
Northern Rockies on the ascent side of the system for northward
expansion of shower and isolated thunderstorm activity, though
temperatures will remain near average for one more day. H700 flow
slows down by Sunday afternoon and MU CAPE looks to be around 100
to 300 J/kg (highest southwest MT), so not expecting anything
beyond general thunderstorm risks at this time.

Ensembles remain in decent agreement with the aforementioned
closed low swinging NE into E MT and slowing down some Monday
through early Thursday. Although, there are differences on the
precise path of the low, most favor cool, wet, and windy periods
during this timeframe. According to the NAEFS Standardized
Anomaly, H700 temperatures are forecast to be around -8C for much
of this event, which would support mountain accumulating snow, but
mostly rain at lower elevations. Current probabilistic forecasts
for rainfall highlight the eastern portions of North-central MT
with the highest chances (50 to 70%) for 1 inch of rainfall during
the 72 hr period ending next Thursday at 6 am, with nearly all
locations in the CWA standing at least a 50% for a quarter inch of
rainfall for the same time period. The one drier exception looks
to be southwestern valleys from Dillon to the Three Forks area.

As mentioned earlier, thermodynamic profiles should confine
accumulating snow to mountain areas, with the Little Belts and the
Madison/Gallatin ranges seeing 60% + chances for 8 inches of snow
or more Monday through Thursday, with most of it falling Tuesday
night into Wednesday. H700 flow on the backside of this low will
be at or above the 30 to 40 kt range for an extended period,
resulting in gusty to at times strong northwesterly surface winds.
While all days Monday through Wednesday look to be on the windier
side, Tuesday is being singled out by the EC Extreme Forecast
Index and NBM probabilistic forecasts as the windiest day overall,
with many locations seeing 70% + chances for wind gusts above 40
mph.

Drier and milder conditions move in for Thursday and Friday of
next week, though around 50% of the ensembles support weaker
troughing remaining in place for non-zero chances for
precipitation and near average temperatures heading into next
weekend. - RCG

&&

.AVIATION...
520 AM MDT Fri May 3 2024 (03/12Z TAF Period)

North Central (KCTB KHVR) and the plains of Central Montana (KGTF
KLWT): Northerly upslope flow will continue widespread mountain-top
obscuring low VFR/high MVFR ceilings through at least 15Z. However,
lingering light snow along north-facing slopes (mainly east of KGTF
into the KLWT area) will keep conditions there as IFR, obscuring
those mountains. High pressure will start moving into the area from
the west after 15Z, decreasing the snow and allowing broken ceilings
to lift to at least low VFR levels with partial clearing starting
after 18Z. However, weak instability during the afternoon may cause
isolated to scattered light snow showers to form again between 19Z
and 00Z, possibly causing periods of MVFR conditions.

Southwest Montana (KBZN KEKS KWYS): VFR conditions are expected to
continue through at least 04/12Z. Broken ceilings will continue
through at least 18Z, then partial clearing is expected after 18Z.
-Coulston

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  26  63  42 /  30   0   0  10
CTB  49  26  59  37 /  20   0   0  10
HLN  54  31  68  44 /  10   0   0  10
BZN  51  28  66  41 /  10   0   0  10
WYS  46  20  60  36 /   0   0   0  30
DLN  52  30  65  44 /  10   0   0  40
HVR  50  27  63  39 /  40   0   0   0
LWT  42  23  59  37 /  40   0   0  10

&&

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

$$

http://www.weather.gov/greatfalls