084
FXUS65 KTFX 090914
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
314 AM MDT Sun Jun 9 2024

.SYNOPSIS...

Showers and thunderstorms increase over Southwest Montana this
afternoon before spreading northward into central and north-
central areas later in the evening and the overnight hours. The
stronger storms may contain strong, gusty winds, hail, and heavy
downpours, particularly for southwestern locations. Shower and
thunderstorm activity diminishes Monday with breezy and much drier
conditions expected heading into the mid-week period.

&&

.DISCUSSION...

Lower level north/easterly flow has persisted through the
overnight hours for continued breezy conditions and scattered to
broken clouds, mostly over central and north-central MT. Lower
level cloud cover associated with this set up is expected to
retreat to the northeast as a southwesterly flow aloft begins to
develop ahead of a shortwave currently moving into the Pacific
Northwest. An initial wave of weakening showers and isolated
thunderstorms moving through Central Idaho is already being
tracked on radar and should reach Beaverhead County later this
morning in the form of isolated lighter end showers/virga and
perhaps a lightning strike or two.

Southwesterly flow aloft becomes more established ahead of the
approaching shortwave later today, providing ascent, shear, and
modest instability for afternoon and evening shower and
thunderstorm development. The highest CAPE (500 to 1,000 J/kg)
looks to be for areas south of I90, where gusty winds and hail may
accompany the stronger cells. Precipitable water values will
generally range in the 0.75 to 1 inch mark, so localized heavy
downpours can also be expected. This activity will lift northward
into Central/North- central MT during the evening and the
overnight hours, but the loss of diurnal heating will result in a
more benign brand of showers and general rains. While hi-res
guidance does bring a secondary round of showers and storms to the
southwest late tonight, a more stabilized atmosphere should
preclude the potential for stronger development in a similar
fashion as northern areas. Westerly winds increase and things dry
out on Monday following the passage of the shortwave, but another
weak perturbation does move across the region during the afternoon
hours for additional isolated to scattered showers and
thunderstorms, mostly along the Hi-Line and over and near areas of
higher terrain elsewhere.

Ensembles remain in fairly good agreement with a zonal flow aloft
settling in for the mid-week period. H700 to H500 flow will be on
the stronger side for this time of time of year, mostly between
40 and 50 kts or 2 to 3 standard deviations above climatology
according to the NAEFS (North American Ensemble Forecast System).
Deep layer mixing should encourage breezy to windy conditions,
especially over the plains and the Rocky Mountain Front on
Wednesday. Wind exceedence probabilities suggest that peak wind
gusts will mostly fall between the 35 and 55 mph range except
along the Rocky Mountain Front and adjacent high plains where
gusts up to and exceeding 60 mph will be more common. The primary
impact will be to summer outdoor recreation and travel; however,
afternoon temperatures in the 70s and 80s combined with the said
winds and minimum relative humidity values in the teens and 20s is
expected to accelerate the curing/drying of grassland fuels.
While no fire products are anticipated this time around, this may
set up fire weather concerns in the future.

Uncertainty remains in terms of forecast details for the upcoming
weekend, but ensembles continue to highlight a Pacific trough
exerting an influence over the Northern Rockies. At this time,
there is an expectation for breezy conditions, isolate to
scattered shower and thunderstorm activity, and a slight cool down
for Saturday and Sunday. - RCG

&&

.AVIATION...

09/06z TAF Period

VFR conditions continue through the beginning of the TAF period with
conditions having potential to degrade across Southwest Montana late
Sunday afternoon through the overnight hours Sunday. Thunderstorms
are likely to develop between the 09/20z and 10/06z period for
Southwest Montana airfields, but quickly move through with some
lingering rain showers behind the storms. Primary concerns for any
developed thunderstorm is lightning, gusty winds, small sized hail,
and a brief heavy downpour that can lower visibility. KBZN will need
to be monitored for low forecasted ceilings after the rain showers
move through the airfield tomorrow night into Monday morning.
Scattered rain showers move into Central Montana after the 10/00z
time frame into Monday morning. VFR conditions prevail for KCTB and
KHVR through the TAF period. Webb

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  74  53  77  49 /  10  70  30  10
CTB  69  48  73  47 /  10  60  30   0
HLN  78  55  80  52 /  30  70  30   0
BZN  77  51  77  47 /  40  80  50   0
WYS  75  45  69  39 /  70  70  60   0
DLN  76  51  75  46 /  70  80  20   0
HVR  73  52  75  49 /  10  70  50  10
LWT  73  50  73  47 /  10  70  40  10

&&

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

$$

http://www.weather.gov/greatfalls