Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 240929
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
329 AM MDT SUN JUL 24 2016

.DISCUSSION...

Today through Tuesday...Broad ridging aloft will support large-
scale subsidence across the forecast area as visualized in water
vapor satellite imagery. Forecast soundings indicate generally
zero CAPE with convective temperatures above forecast highs.
Hence, have assigned zero POPs and mostly clear skies through
Monday morning. Weak shortwave energy flattens the ridging to a
zonal flow on Monday afternoon. This could produce a few mainly
mountain showers or thunderstorms, but with little rainfall
reaching the ground. A slightly more robust shortwave trough
arrives on Tuesday afternoon and should produce more widespread
showers and thunderstorms. Temperatures gradually warm through the
period. Afternoon relative humidity will continue to drop below 20
percent in many areas, especially the southwest valleys, but winds
remain light enough to reduce fire weather concerns. PN

Tuesday Night through Sunday...Period begins with one day of active
weather (Wed) then gets progressively more quiet heading into the
weekend.  Models have maintained good continuity and reasonable
agreement on a weak shortwave trof tracking through the Northern
Rockies on Wed. Scattered thunderstorms associated with the trof
will develop mainly along and east of line from Glacier NP to Great
Falls to White Sulphur Springs, with more isolated storm coverage in
southwest MT. Biggest question at this point is how much rainfall
can be expected with some of these storms, as precipitable water
values have trended upward in latest model runs.  This is especially
true for the Hiline counties where model soundings now indicate PW
values of 1.00-1.20 inches around Cut Bank and Havre. While
thunderstorms in our region usually only convert a fraction of all
that moisture into rainfall at the surface, the current model
precipitation estimates seem a bit low, with values of only 0.05-
0.15 inch for Wed aftn/eve across the Hiline.  We`ll have to see how
PW and precip totals trend over the next several model runs to get a
better handle on expected rainfall.

After this shortwave heads into the Dakotas Wed night, a minor
secondary shortwave arrives Thurs eve, bringing another round of
isolated storms from the Little Belt Mtns east to Blaine/Fergus
counties.  That may be the last chance for precip for a few days as
the persistent high pressure ridge over the Southwest US amplifies
northward, giving us mostly dry conditions and temperatures
returning to the upper 80s and low 90s through the weekend.
Waranauskas

&&

.AVIATION...
Updated 0520Z.
High pressure brings mostly clear skies and light winds to the
forecast area tonight through Sunday. VFR conditions prevail.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  87  53  90  56 /   0   0  10  10
CTB  83  51  85  53 /   0   0  10  10
HLN  88  60  92  60 /   0   0  10  10
BZN  87  51  91  53 /   0   0  10  10
WEY  76  41  80  44 /   0   0   0   0
DLN  84  52  88  53 /   0   0   0   0
HVR  86  55  90  58 /   0   0   0  10
LWT  84  56  88  58 /   0   0  10  20

&&

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

$$

weather.gov/greatfalls


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