Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 212355
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
555 PM MDT THU JUL 21 2016

Updated Aviation Section

.DISCUSSION...

Tonight through Saturday...Water vapor shows a long fetch of dry air
moving towards Montana and the air mass will remain mostly stable
and dry through the night. The weak ridging over the zones will come
to an end as a low pressure trof over the West Coast approaches the
Rockies Friday. The associated cold front will cross the Rockies and
move into Cut Bank during the late Friday afternoon. The early
evening hours will see frontal passage at Havre, Great Falls, and
Helena. Dynamics associated with the trof will at first be directed
towards the north and models develop weak lift across the Hi-Line
tonight and early Friday, then rather strong lift by Friday
afternoon across most of the region. Moisture will be limited,
however, and most central and southwest zones will remain dry. Low
level winds will strengthen late Friday afternoon and evening ahead
of the trof and remain brisk after frontal passage into Saturday
morning. Stable conditions will once again be in place across the
region Saturday and temperatures will drop back to near normals
behind the front. Zelzer

Saturday night through Thursday...The large upper level ridge over
the central US at this time will weaken some and retrograde over the
weekend and into next week. Locally, this will lead to a zonal flow
aloft across the Pac NW. Within this zonal flow, several weak
shortwaves will likely move through the forecast area, each with at
least a low end chance of showers and storms. At this time, though,
it is too early to determine exact details regarding the timing and
coverage of storms with each s/w. Regarding the strength of the
storms, the potential of a few stronger storms exists next week,
especially Wednesday and Thursday, as both days show the best
combination of shear and instability.

Given the upper level ridge should stay suppressed across the Desert
SW through the middle of next week, temps locally will be warm, but
not quite as warm as would be expected if the ridge were more
amplified over the western US.

The models have come into better agreement late next week,
suggesting the zonal flow may eventually turn more northwesterly as
a weak upper level trough moves SE out of Canada and into the
northern Rockies. If this pans out, this may bring a brief period of
slightly cooler temperatures and a somewhat better chance of
showers/storms by late next week. Martin

&&

.AVIATION...
Updated 2355z.
Dry and stable conditions will continue overnight, though a weak
disturbance aloft may bring isolated showers to the area along the
international boundary after 08z. Gusty southwest winds will
decrease after 02z. VFR conditions prevail.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  91  55  81 /  10  20  20  10
CTB  52  85  53  78 /  40  40  40  10
HLN  61  92  58  83 /  10  20  20   0
BZN  55  92  50  83 /  10  10  10  10
WEY  52  81  42  72 /  10  10  10   0
DLN  55  89  49  81 /  10  10  10   0
HVR  57  93  57  81 /  30  40  40  20
LWT  59  91  54  79 /  10  20  30  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
&&

$$

weather.gov/greatfalls



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