556
FXUS65 KTFX 032055
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
255 PM MDT Fri May 3 2024

.SYNOPSIS...

Lingering showers and snow showers will be around through the early
evening ahead of a mild and dry Saturday. Precipitation chances will
return Sunday into much of next week, with potential for an
impactful spring system over the middle of next week.

&&

.DISCUSSION...

Through Saturday... Transient shortwave ridging is beginning to
build in across the Northern Rockies between one upper disturbance
exiting eastward across Southern Canada and another approaching the
Pacific NW. Lingering northwesterly flow aloft will combine with
daytime heating to result in rain and snow showers the remainder of
this afternoon and early evening, primarily across the plains.
Clearing skies and light winds tonight will allow for patchy fog
formation into Saturday morning, but is not expected to pose many
impacts at this time.

Saturday looks to be a pleasant day as the aforementioned ridge
moves overhead, with the only potential blemish being breezy
easterly to southeasterly winds across the plains in the afternoon.
Daytime highs look to rise to near to a touch above average in most
areas. -AM

Saturday night into next week... 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...
1111 AM MDT Fri May 3 2024 (03/18Z TAF Period)

Primary concerns through this TAF period will be for lingering low
clouds and rain/snow showers, primarily across the plains this
afternoon and early evening. Looking ahead toward Saturday, VFR
conditions prevail, with a breezy easterly to southeasterly wind
developing across the plains by late morning. Mountains will be
obscured through the afternoon today across Central and North-
central Montana. -AM

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  26  64  42  63 /  20   0  10  40
CTB  26  60  37  59 /  20   0  10  30
HLN  31  69  44  69 /  10   0  10  60
BZN  25  67  42  65 /  10   0  10  70
WYS  19  60  36  52 /  10   0  30  90
DLN  30  66  43  60 /  10  10  40  70
HVR  25  64  39  71 /  20   0   0  20
LWT  23  59  36  65 /  20   0  10  30

&&

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

$$

http://www.weather.gov/greatfalls