494
FXUS65 KTFX 142313
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
515 PM MDT Sun Jul 14 2024

Aviation Section Updated

.SYNOPSIS...
Well above normal temperatures and overall dry conditions will
persist through the week as upper level ridging dominates over the
Northern Rockies. While isolated to scattered thunderstorms are
possible each day through at least the middle of the work week, most
notably in Southwest and North Central Montana, most areas will
remain dry.

&&

.DISCUSSION...
Rest of today through tonight...A surface front will move south from
Alberta late this afternoon and across the plains of North Central
and Central Montana through the the evening hours tonight. This
front will bring a wind shift to the north, in addition to a period
of breezy and gusty winds. As the front advances south, expect
thunderstorms to develop across Southern Alberta initially, with
thunderstorms then propagating to the southeast across portions of
North Central Montana, generally northeast of a Marias Pass, to
Conrad, to Loma, to Hays line. Sufficient shear and instability
northeast of this line will support the potential for a few strong
to severe thunderstorms, with the Storm Prediction Center (SPC)
highlighting at least a Marginal Risk for most of the aforementioned
area. The primary threat with any thunderstorm that does become
severe will be large hail in excess of 1" (~15% chance of occurring)
and/or damaging wind gusts greater than 58 mph (~15% chance of
occurring), with the peak window for severe thunderstorms occurring
between 4-10 PM MDT. Additional thunderstorms are also possible
along and south of a White Sulphur Springs (WSS) to Helena line
given the arrival of monsoonal moisture to portions of the Northern
Rockies, most notably south of the I-90 corridor. For areas south of
the WSS to Helena line, while severe thunderstorms are not expected
through tonight, gusty and erratic winds will be possible with any
thunderstorm given very dry air in the low levels (i.e. inverted-V
soundings). These gusty and erratic winds will be especially
concerning where they occur in proximity to existing fires. - Moldan

Monday through next Sunday...Temperatures cool down by a few degrees
on Monday in the wake of the passing weather system, but many
locations will be breezy with minimum relative humidities dipping
critically low again. Isolated shower thunderstorm activity with
little rainfall relief can also be expected. The latest 3 to 7 day
cluster analysis still favors the upper level ridge amplifying mid-
late week, yielding more hot and dry conditions while lingering
moisture bring daily chances for isolated to scattered showers and
storms. - RCG

&&

.AVIATION...
15/00Z TAF Period

Showers/thunderstorms will affect Southwest MT through this evening,
with the better chance for storms south of a line from Dillon to Big
Sky. A few thunderstorms are possible this evening in the
Havre/Harlem areas. Otherwise, VFR conditions are expected overnight
elsewhere. A few isolated storms could redevelop though towards
Monday evening along the MT/ID border near West Yellowstone and then
also in the Havre/Harlem areas once again. Some distant mountains
will be obscured by smoke/clouds through the period. Brusda

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

&&

.FIRE WEATHER...

Well above normal high temperatures and dry conditions, with minimum
relative humidity values falling into the teens to 20s percent, will
persist through the foreseeable future across all of Southwest
through North Central Montana. Monsoonal moisture, which has made its
way beneath the upper level ridge, will continue to bring daily
chances for isolated to scattered thunderstorms to portions of
Central and Southwest Montana through at least the middle of the
upcoming work week. Given that this monsoonal moisture is mostly
elevated, a mixture of wet and dry thunderstorms can generally be
expected through this timeframe. Very dry air in the low to mid-
levels will allow for the transfer of gusty and erratic winds to the
surface beneath these thunderstorms, especially beneath any
collapsing cores. Further north across North Central Montana, subtle
waves moving over the ridge axis and dropping southeast will help to
support additional chances for thunderstorms. These thunderstorms
will be on the wetter side given PWATs of 1-2 standard deviations
above normal; however, given the continued rapid drying of fuels a
stray lightning strike outside of any precipitation core may lead to
additional fire starts. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  93  56  90 /  10   0   0  10
CTB  51  91  53  89 /  30  20  20  20
HLN  61  97  57  96 /  10   0   0  10
BZN  57  93  52  93 /  20  10  10  10
WYS  51  82  42  83 /  50  40  30  30
DLN  59  88  50  88 /  30  20  10  10
HVR  55  90  56  91 /  30  20  20  20
LWT  54  87  53  86 /  10  20  10  20

&&

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

&&

$$

http://www.weather.gov/greatfalls