116
FXUS65 KTFX 151118
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
518 AM MDT Sun Sep 15 2024

Updated Aviation Discussion

.SYNOPSIS...

Seasonably mild temperatures and mainly dry conditions continue
through Monday before the next fall weather system brings
increasing chances for showers and thunderstorms late Monday
through Tuesday. Periods of rain and cooler temperatures are
expected Tuesday night into Wednesday.

&&

.DISCUSSION...

A southwest flow aloft maintains seasonably mild temperatures
across the area today with a greater coverage of clouds and a
slight chance for showers near Glacier NP as mid level moisture
and a subtle disturbance move through a baroclinic zone in place
across the Northern Rockies. A few isolated showers and
thunderstorms are also possible late this afternoon end evening
across SW MT as mid level moisture and some instability creep
north in more southerly flow aloft developing downstream of a
deepening upper level trough along the west coast.

A closed mid-level low develops in NV by late Monday within the
larger scale upper trough and models are in reasonably good
agreement with the track of the mid level circulation to the
north and northeast, eventually lifting across central and eastern
MT Tuesday night through Wednesday.

Shower and thunderstorm chances increase across mainly southwest
MT Monday with with deeper moisture and stronger forcing ahead of
the incoming mid-upper low bringing a more widespread coverage of
showers and thunderstorms to the the area by Tuesday afternoon.
There is some uncertainty with the degree of instability and
potential for strong thunderstorms Tuesday, but forcing from the
approaching upper level system and deepening moisture profiles
should support some thunderstorm organization with locally heavy
rain and gusty winds the primary concern as coverage increases
Tuesday afternoon/evening.

The most widespread period of rain/showers is likely to occur
Tuesday night through Wednesday morning as the mid-level
circulation tracks north across central/eastern MT. Probabilities
for 0.50" or greater precipitation amounts (Tues-Wed) are 60% or
higher across most of the forecast area with 50-60% probabilities
for 1.00" or greater amounts across much of the Golden Triangle
portion of North-central MT. There remains a risk for locally
excessive precipitation over sensitive burn scar areas, mainly
Tuesday afternoon and evening. Snow levels still look to fall as
low as around 8000 ft, limiting any measurable snow to mainly the
highest peaks.

Larger scale troughing remains across the western US in the wake
of the exiting low later this week with troughing shifting
eastward next weekend. There is still considerable
spread/uncertainty with features moving through the trough by next
weekend with some potential for a cooler system in NW flow moving
across the area. Hoenisch

&&

.AVIATION...
15/12Z TAF Period

Variable mid to high level cloud-cover streams across the region in
southwest flow aloft today, backing to more southerly tonight. VFR
conditions prevail at all terminals with just a slight (10-20%)
chance for isolated showers over the mountains of SW MT and near
Glacier NP. Northeast to east surface winds increase this afternoon
with a period of breezy winds at some terminals this evening.
Hoenisch

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  72  45  71  49 /  10  10  20  40
CTB  66  43  69  45 /  20  20  20  30
HLN  76  50  74  51 /  10  20  30  60
BZN  81  45  76  46 /  10  20  40  70
WYS  72  37  69  35 /  10  30  70  90
DLN  76  45  74  45 /  10  40  40  80
HVR  76  48  76  52 /   0  10  20  40
LWT  76  44  73  47 /   0  10  10  40

&&

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

$$

http://www.weather.gov/greatfalls