580
FXUS65 KTFX 131711
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1111 AM MDT Tue Aug 13 2024

...Updated Aviation Section...


.SYNOPSIS...
Daily chances for showers and thunderstorms through the forecast
period. On Tuesday afternoon, some storms can become strong to
severe and can produce strong winds, hail, frequent lightning, and
localized areas of heavy downpours. Temperatures cool by a few
degrees after today, and stay consistent through the week

&&

.UPDATE...

Main changes made this morning were to increase POPs a bit,
especially across the plains of North Central Montana, and to add
gusty wind wording to thunderstorms this afternoon. Ludwig

&&

.AVIATION...
13/18Z TAF Period

VFR conditions will prevail during this TAF period for all terminals
except during any thunderstorms that go over and/or near a terminal.
There is a 20 - 40% chance for thunderstorms at the KCTB and KHVR
terminals this afternoon and evening. There is a 60% chance for
showers and thunderstorms at the KHLN, KGTF, KBZN, and KLWT
terminals this afternoon and evening. There will be showers and
thunderstorms at the KEKS and KWYS terminals this afternoon and
evening. The main threats from thunderstorms today will be brief
heavy downpours that will reduce visibility to MVFR levels, strong
to severe wind gusts (at all terminals excluding KCTB), frequent
lightning, and small hail (primarily in Southwestern Montana).
During showers and thunderstorms there will be brief periods of
mountain obscuration. There is a 40% chance for showers and
thunderstorms at all terminals excluding the KCTB and KHVR terminals
Wednesday morning through the end of the TAF period. -IG

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

&&

.PREV DISCUSSION...
/ISSUED 540 AM MDT Tue Aug 13 2024/
Isolated showers linger across the Northern Rocky Mountain Front and
Hi-Line region this morning. An upper level shortwave moving through
starting in the late morning and a cold front passage will develop
scattered to widespread showers with embedded thunderstorms. There
will be enough shear, CAPE, and moisture to produce some strong to
severe storms with strong wind gusts, hail, frequent lightning, and
brief heavy downpours possible. The Storm Prediction Center has put
most areas (besides the northern Rocky Mountain Front) in a Marginal
Risk for severe weather. There`s a 5% for those locations to have
storms produce 58mph gusts or greater, and a 5% for Southwest
Montana storms to produce 1" hail or greater. PWATs up to 1"-1.25"
suggests that localized heavy downpours are possible with the
strongest storms. There`s a 40-70% of locations across the CWA of
receiving 0.25" or greater of rainfall. This is also reflected in
the Weather Prediction Center`s excessive rainfall outlook, with a
5% for areas west of a line from Gallatin County to Teton County for
excessive rain. This can also raise some concern for rapid runoff or
debris flow over burn scars/burned over fire areas, especially the
Horse Gulch burn scar(see Hydrology section). Storm coverage
decreases after sunrise, but there is a slight chance for showers to
linger mainly across North Central Montana overnight into Wednesday
morning.

Model guidance suggests that the weather pattern for daily
precipitation and near normal temperatures stays through the
forecast period. PWATs generally stay around up to an inch daily,
so a few stronger showers and storms can bring heavier rainfall,
and gusty winds. Heading into the weekend, chances of
precipitation decreases slightly as the upper level ridging in
place will help limit storm coverage. However, ensemble models are
still a little uncertain of how long this area of upper level
troughing stays next week, and therefore there`s uncertainty for
when we have a break in the rain chances. -Wilson

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  85  56  80  54 /  60  40  30  10
CTB  83  54  79  53 /  20  20  20  10
HLN  83  55  80  54 /  70  50  30  10
BZN  81  49  77  48 /  70  60  50  10
WYS  69  39  67  36 /  80  70  70  20
DLN  73  46  73  45 /  80  50  50  10
HVR  90  59  85  58 /  20  40  20  20
LWT  85  52  76  51 /  40  70  40  20

&&

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

$$

http://www.weather.gov/greatfalls