-- Discussion containing changed information from previous version are highlighted. --
465
FXUS65 KTFX 191722
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1122 AM MDT Wed Jun 19 2024

...Updated Aviation Section...


.SYNOPSIS...

Unsettled conditions are expected through the remainder of the
work week across the Northern Rockies, with high temperatures
slightly below to near normal. Warmer and drier condtions are
then expected over the weekend, with Sunday being the warmest day
of the upcoming week.

&&

.UPDATE...

Fog has mostly dissipated across the plains of North-central and
Central Montana. As a result the Dense Fog Advisory for those
areas has been cancelled. For areas where there still is fog, it
will dissipate in the next hour or so. High temperatures, hourly
temperatures, dewpoint temperatures, and relative humidity values
were all increased this morning to better reflect current
observations and trends. Minor tweaks were made to the PoP, Sky,
and Wind grids to better reflect current observations and trends.
The rest of the forecast is on track. This afternoon and evening
there will be isolated showers and thunderstorms primarily across
North-central and Central Montana. -IG

&&

.AVIATION...
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19/18Z TAF Period

VFR conditions will prevail across all terminals during this TAF
period. Across all terminals excluding the KEKS, KBZN, and KWYS
terminals there is a 20 - 40% chance for an isolated thunderstorm or
rain shower Wednesday afternoon and evening. Due to the isolated
nature, low probability, and low confidence in the timing of the
rain showers and thunderstorms there is not a mention of rain
showers or thunderstorms in any of those TAFs, but they will be
monitored for amendments. Outside of these showers and thunderstorms
which could lower ceilings and produce erratic wind gusts there will
be few to scattered high-level clouds with light and variable winds
for those terminals during this TAF period. There will be light and
variable winds with few high-level clouds at the KWYS, KEKS, and
KBZN terminals during this TAF period. There is a low chance of fog
at the North-central and Central Montana terminals (KCTB, KHVR,
KGTF, and KLWT) early to mid-morning on Thursday especially if any
of those terminals receive rain Wednesday afternoon or evening. -IG

Refer to weather.gov/zlc for more detailed regional aviation weather
and hazard information.
-- End Changed Discussion --

&&

.PREV DISCUSSION...
/ISSUED 545 AM MDT Wed Jun 19 2024/

This morning...primary forecast concern through the morning hours
across Southwest through North Central Montana will be reduced
visibilities due to fog, with some areas potentially seeing dense
fog. NBM probabilities for visibility of one mile or less through
the morning hours at all locations are at least 10-20%, with a 40-
60% chance across the entirety of the Golden Triangle (Great Falls,
to Havre, to Cut Bank, to Great Falls). Within the Golden Triangle
HREF probabilities for a quarter of a mile or less peak at between
20-50%. Given recent precipitation across this area (i.e. Golden
Triangle) combined with clearing skies and light winds through the
morning hours, a Dense Fog Advisory has been issued through 16z this
morning to cover the potential for significant reductions in
visibility. Fog will gradually dissipate beyond 16z this morning
with increasing solar insolation.

This afternoon through Friday night...unsettled conditions are
expected to persist through the end of the work week across the
Northern Rockies as moist southwest flow aloft, steep afternoon
lapse rates, and shortwaves rippling through the overall flow help
to support daily chances for showers and thunderstorms. This will be
especially true on Friday, when one of the "stronger" shortwaves
traverses over North Central and Central Montana, providing the best
opportunity for scattered to numerous showers and thunderstorms. NBM
probabilities for a 0.25" or more of precipitation on Wednesday and
Thursday are less than 10% across all areas, but on Friday climb to
as high as 30-60% along and north of the Montana Hwy 200 corridor
and east of the I-15 corridor. High temperatures through the
remainder of the work week will continue to run below to near
normal, with highs ranging from the 60s today to the upper 60s to
upper 70s on Thursday and Friday.

Saturday through Sunday...ensemble clusters favor transient ridging
moving over the Northern Rockies over the weekend, which will look
to bring drier and warmer conditions to all of Southwest through
North Central Montana. Leading mode of uncertainty throughout this
timeframe is the amplitude of the ridge as it moves overhead, which
will ultimately determine how warm temperatures rise. Regardless of
the ultimate high temperature on either day, highs rising some 5-10
degrees and 10-20 degrees above average on Saturday and Sunday
respectively can be anticipated.

Monday through next Wednesday...multi-model ensemble supports general
southwesterly flow aloft over the Northern Rockies, with the leading
mode of uncertainty being the position and/or timing of the ridge
axis over the Western CONUS, especially on Tuesday and Wednesday.
Deterministic NBM guidance is currently favoring a drier and warmer
solution as the ridge remains further west and more over the
Northern Rockies; however, should the ridge placement be further
east then a "slightly cooler" and "wetter" solution would then be
favored. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  68  38  74  48 /  20  20  20  20
CTB  66  35  72  44 /  40  20  20  20
HLN  73  43  80  52 /  30  20  20  20
BZN  70  37  76  46 /   0   0  20  10
WYS  64  31  71  40 /   0   0  20  10
DLN  68  35  73  45 /   0   0  10  10
HVR  71  41  76  50 /  20  20  20  30
LWT  66  38  71  46 /  40  20  40  40

&&

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

$$

http://www.weather.gov/greatfalls