822
FXUS65 KTFX 290605
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1205 AM MDT Tue May 29 2024

...Updated Aviation Section...


.SYNOPSIS...

Showers and thunderstorms continue today with some isolated severe
gusts possible primarily across west Central/North Central, and
Southwestern Montana. By Wednesday afternoon, precipitation spreads
east to eastern Central/North-Central and Southwest Montana. Gusty
winds are possible along the Rocky Mountain Front Wednesday. By
Thursday, precipitation shifts north to North-Central Montana.
Warmer and drier weather returns for Friday and Saturday.

&&

.UPDATE...

Scattered thunderstorms and rain showers continue to move
northeast from Southwest to North Central Montana this evening and
through the overnight hours. Only minor adjustment needed to the
probability of precipitation for the next 4 to 6 hours as the
shower activity continues based on current surface observations
and latest high resolution model guidance. The rest of the
forecast is doing well and on track for tonight into tomorrow.
Webb


&&

.AVIATION...

29/06Z TAF Period

VFR conditions will prevail for the KHLN, KGTF, KCTB, and KHVR
terminals for this TAF period. At the KBZN, KEKS, KWYS, and KLWT
terminals there is a 50% chance for thunderstorms to occur and
reduce visibility to MVFR levels Wednesday afternoon and evening.
Wednesday afternoon at the KBZN, KEKS, KWYS, and KLWT terminals
ceilings will be reduced to MVFR levels. At the KBZN, KEKS, KWYS,
and KLWT terminals there will be rain showers Wednesday afternoon
and evening due to a front moving the area. At the KLWT and KWYS
terminals winds will gust up to 22 kts Wednesday afternoon and
evening. At the KBZN, KEKS, and KWYS terminals there is 20% chance
for showers and thunderstorms during the first 6 hours of this TAF
period. At the KHVR and KGTF terminals for the first 3 hours of this
TAF period there is a 20% chance for thunderstorms. At the KGTF and
KHVR terminals there is 50% chance for rain showers Wednesday
morning. At the KHLN and KCTB terminals for the first three hours of
this TAF period there is a 50% chance for thunderstorms around those
terminals. For the KHLN and KCTB terminals there is 20% chance for
showers and thunderstorms from 3 AM to 6 AM Wednesday morning. At
the KHLN terminal there is a 50% chance for rain showers the rest of
Wednesday morning. During thunderstorms there will be gusty and
erratic winds. At the KGTF and KHVR terminals winds will gust up to
25 kts from the middle of this TAF period through the end. At the
KCTB terminal during the middle of this TAF period through the end
winds will gust up to 38 kts. At the KHLN terminal from the middle
of the TAF period through the end winds will gust up to 29 kts.
There will be mountain obscuration during this TAF period. During
the middle and end of this TAF period there will be mountain wave
turbulence. -IG

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

&&

.PREV DISCUSSION...
/ISSUED 541 PM MDT Tue May 28 2024/

Tonight Through Tomorrow Morning
Current satellite shows cumulus clouds and a few showers popping
up along Southwest MT, the Continental Divide. The upper level
shortwave and a cold front will continue to initiate afternoon
showers and thunderstorms. The Storm Prediction Center has the
Inverness to Bozeman corridor and west in a Marginal Risk for some
isolated severe wind gusts(5%). Mesoscale analysis shows
instability building in (up to 1,000 J/kg of CAPE). This along
with deep inverted V`s vertical profile soundings support an
isolated severe wind gust(58mph) threat. Small hail can also
accompany any stronger storm. Another impact we will watch for is
for higher mountain snowpack run off with heavier precipitation
from thunderstorms along the Continental Divide. Precipitable
water(PWAT) along the higher end amounts from models of 0.7-0.8"
indicate there can be some heavier rainfall with showers/storms.
The Weather Prediction Center has the Continental Divide in a
Marginal Risk for excessive rainfall. Meaning, there`s a 5%-15% of
exceeding flash flood guidance through early Wednesday morning.
However, there`s a 20-40% of the immediate eastern slopes of the
Rocky Mountains receiving a half inch of precipitation. This
should keep runoff impacts limited but something we will continue
to monitor. Storms wind down as the sun sets tonight, but showers
continue to be scattered to widespread along the cold front
through Wednesday morning.

Wednesday
With the upper level trough still in the region and the
cold front propagating east across the CWA, there will be
redevelopment of widespread precipitation Wednesday afternoon. The
bulk of the heavier precipitation will mostly be from southwest
Madison County to Lewistown line and to the southeast. Although
the thunderstorm risk will be lower tomorrow afternoon,
precipitation concerns still linger. The Weather Prediction Center
has a Marginal Risk for excessive rainfall(5-15% of exceeding flash
flood guidance)along that corridor. Probabilities are showing a
10-20% of precipitation amounts exceeding 1" for the
Madison/Gallatin Counties and Big Snowy mountains. Warmer rain
falling on the snowpack can melt snow and increase surface run
off. Since models keep higher end precipitation amount to 1" of
QPF and impacts on rivers don`t look to be widespread, I am
holding off on Hydrology highlights for now. However, we will
continue to monitor the situation. Look in the HYDROLOGY section
for more information. In addition to precipitation on Wednesday,
gusty conditions are possible along the Rocky Mountain Front.
700mb winds between 30-45kts and a pressure gradient force sets up
along the Rocky Mountain Front Wednesday through Thursday
morning. Probabilistic guidance shows most of the gusty winds stay
along the immediate eastern slopes of the Rocky Mountain Front.
Locations along the adjacent plains of the Northern Rocky Front
through Cut Bank have a 40-60% of exceeding 55mph (High Wind
Warning Criteria). Since the threat of winds reaching High Wind
Warning criteria is more isolated, I have hold off of any wind
highlights for now.

Thursday through Friday
As the upper level trough propagates eastwards Thursday, we
transition into northwest flow aloft. An upper level disturbance
tries to clip North Central MT/Central MT mountains on Thursday,
bringing lower end, light precipitation chances. Probabilistic
guidance shows a 20-40% of those locations receiving at least a
tenth of an inch of precipitation. By Friday, dry and warmer
weather moves in, moving temperatures up close to seasonable
averages. -Wilson

Saturday through next Tuesday... On Saturday a weak upper-level
ridge moves over North-central, Central, and Southwestern Montana.
This will warm up temperatures and keep most of North-central and
Central Montana dry with some precipitation chances for Southwestern
Montana. On Sunday cluster analysis shows that an upper-level ridge
remains over North-central, Central, and Southwestern Montana which
will allow temperatures to warm up on Sunday. On Monday cluster
analysis keeps the upper-level ridge over the area. Two of the
clusters have a very strong ridge over North-central, Central, and
Southwestern Montana. This could cause hot temperatures for the
area. This will need to continue to be monitored. Next Tuesday three
clusters (81% of ensemble members) keep the upper-level ridge over
North-central, Central, and Southwestern Montana. The other cluster
(19% of ensemble members) shows an upper-level trough beginning to
move over Montana. This indicates that the weather pattern has the
potential to change for the middle of next week. -IG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  52  65  41  62 /  50  60   0  20
CTB  48  60  38  60 /  80  30  10  20
HLN  52  64  41  63 /  60  50  10  10
BZN  46  59  34  59 /  50  90  50  10
WYS  42  59  30  53 /  40  90  60  10
DLN  46  62  33  60 /  70  80  20   0
HVR  54  67  41  63 /  60  50  10  50
LWT  49  62  36  57 /  20  90  30  20

&&

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

$$

http://www.weather.gov/greatfalls