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000
FXUS65 KTFX 190459
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1058 PM MDT Tue Sep 18 2018

UPDATED AVIATION

.UPDATE...

Most of the forecast through tomorrow morning remains valid.
However, freshened POPs given latest radar trends and by blending
the latest short-term models` consensus with our previous
forecast. Weak isentropic lift ahead of an approaching disturbance
from the west will continue to have the potential to trigger
isolated to scattered showers through Wednesday morning. In
addition, upslope flow may trigger or enhance precipitation
somewhat along the northern aspects of our central MT mountains.
Lastly, elevated instability may be sufficient for a brief
thunderstorm or two over eastern portions of north-central MT
through this evening.
- Jaszka

&&

.SYNOPSIS...

A cold front moving through North-central Montana will bring
cooler temperatures on Wednesday, along with low clouds and areas
of fog. Mostly cloudy skies persist on Wednesday, while areas of
light rain develop over Central and Southwest Montana. Rainfall
and high elevation snow spread north and east Wednesday night
through Thursday. Skies clear early Friday, with fair but seasonal
conditions to follow into the weekend.

&&

.AVIATION...
Updated 0458Z.

Southwesterly flow aloft persists over MT for the next 24-hours as
the axis of a Pacific disturbance approaches and reaches the ID
Panhandle to south-central UT by 12Z/Thur. At the surface, a cold
front extends eastward between KHLN/KLWT and KBZN. This front will
continue moving southward before stalling near the southwest MT/ID
border by 12Z/Wed, where this front will move little through
12Z/Thur. North of this front, primarily MVFR to IFR CIGS will
continue to form and expand in areal coverage, resulting in mountain
obscuration. Periods of light rain and patchy fog remain possible
north of the front through Wed morning. Light to occasionally
moderate rain is then expected to become more persistent after
18Z/Wed, especially east of a KHVR-KGTF-KHLN line.
- Jaszka

&&

.PREV DISCUSSION...
/ISSUED 302 PM MDT Tue Sep 18 2018/

Skies are clear over Southwest Montana this afternoon where
relative humidity has dropped below 15 percent. It`s cooler with
scattered low clouds over North-central Montana following a cold
front that has now stalled out over central Montana. Short- term
guidance continues to indicate the cold front will begin moving
further south overnight, moving cooler temperatures with lower
clouds and areas of fog into southwest Montana. High clouds
streaming over the area on a southwest flow aloft reveal the
approaching shortwave trough presently located upstream over
Oregon. This wave will amplify while crossing the forecast area
Wednesday and Thursday. Rain will develop initially over central
Montana while most areas remain overcast with some drizzle on
Wednesday. A change with today`s forecast has been to slow this
system down. Rain is now forecast to begin spreading across the
area from southwest to northeast overnight Wednesday into
Thursday. Rainfall amounts have not changed much from the prior
forecast, expecting around 0.10" along the Rocky Mountain Front to
near or above 0.75" east of a line from Havre to Lewistown. Snow
levels may lower to around 7500 feet by Thursday morning. Skies
begin to clear from west to east late Thursday night, with areas
of frost likely on Friday morning. Fair weather with seasonal
temperatures follow Friday and Saturday.

Sunday through Tuesday....below to near normal temperatures are
expected into next week, as zonal flow shifts back to the
southwest. While it is to early to say with much
confidence/accuracy due to model guidance undoubtedly changing
over the next several days/runs, there does exist the potential
for a fairly significant cool down and precipitation event early
next week.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  50  41  55 /  30  40  60  40
CTB  37  52  39  55 /  30  20  30  60
HLN  46  56  43  60 /  30  40  60  30
BZN  44  59  42  59 /  30  30  50  40
WEY  30  64  32  57 /   0  10  30  30
DLN  39  60  37  60 /  10  50  60  30
HVR  41  56  42  54 /  20  30  70  70
LWT  41  49  40  51 /  40  50  80  80

&&

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

$$

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