Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 220608

Area Forecast Discussion
National Weather Service Great Falls MT
1145 PM MDT THU JUL 21 2016

Aviation Section Updated.

Update forthcoming. Satellite imagery showing an area of mid and
high clouds moving across southwest Montana at this time. Radar
returns also showing up. Likely any precipitation from these clouds
is not reaching the ground. HRRR analysis also indicates some light
precipitation across this area overnight. Have therefore included
an area of low PoPs for the next few hours. Remainder of forecast
looks good.


Updated 0545z.
VFR conditions prevail through mid-day Friday. A weak disturbance
aloft is moving mid-level clouds through central MT tonight. A cold
front will cross through the region late Friday afternoon. Winds
will shift to westerly and become gusty behind the front. Scattered
thunderstorms are probable at KCTB/KHVR/KLWT, producing temporary
MVFR and perhaps even brief IFR conditions if TS move directly over
the terminals. PN


.PREV DISCUSSION...Issued 236 PM MDT THU JUL 21 2016

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


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



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