Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 250442
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1030 PM MDT Sun Aug 24 2014

AVIATION SECTION UPDATED

.UPDATE...
No significant changes to the forecast as the upper level low and
associated rain shield continues to move off to the East. Have
tweaked pops mainly over Blaine and Fergus counties as some
lingering showers continue to remain over the area...elsewhere
isolated showers are still moving across the region...however
widespread additional accumulations are not expected. Have added
the wording of patchy fog across the area due to some clearing
behind the main cloud shield...not expecting widespread conditions
at this time...however low level moisture and cool temps should
allow for some fog formation. Suk


&&

.AVIATION...
UPDATED 0430Z.
Current radar imagery showing some lingering -SHRA vcnty
KGTF/KHVR/KLWT but these should continue to slowly taper off through
the overnight hours. A new area of showers associated with a weak
disturbance moving thru central Idaho has reached far southwest MT
and will continue to lift northeastward toward KBZN/KHLN, leading to
some VCSH at those terminals by 10Z. Primary terminals should remain
VFR tonight, except KLWT where rain will dissipate last, so MVFR
ceilings will persist there for a few more hours.

Still concerned about possible fog development tonight/early Mon
morning vcnty KCTB/KGTF/KHLN/KBZN.  Given the saturated near-surface
conditions, a brief break in cloud cover for an hour or so may be
sufficient for dense fog to develop. Have kept mention of fog and
low clouds out of 06Z TAFs, except for KCTB.  Forecast models have
been consistent in showing current widespread mid-level ceilings
only slowly eroding and additional clouds coming in with the weather
system moving thru Idaho should help limit cooling and thus, fog
development.  Confidence is only moderate at best on fog potential,
and overnight TAF amendments may be needed to include MVFR/IFR
conditions from fog.
Waranauskas

&&

.HYDROLOGY...
UPDATED 0945z.
Rainfall amounts of 1 to 5 inches have been reported over the last
24 hours across much of north-central Montana. Flooding has been
reported over portions of Judith Basin and Fergus county and an
urban and small stream flood advisory will continue through Monday
afternoon. Many streams and creeks elsewhere across north-central
Montana are rising to near bankfull. Even though precipitation will
gradually diminish, water levels will continue to rise and flooding
on small streams/creeks remains a threat. No flooding of main stem
rivers is expected.

Lesser rainfall amounts of 0.50 to 1 inch have been reported along
the Rocky Mountain Front and southwest Montana. Water levels in
streams have come up slightly but should remain well below flood
stage. MLV

&&

.PREV DISCUSSION...
/ISSUED 540 PM MDT Sun Aug 24 2014/
Satellite imagery this afternoon shows a well developed mature
cyclone along the NE MT/ND border with deep moisture and warm/cold
conveyor belt features wrapping around the low into north central
MT. The upper low will track slowly NE across NW ND tonight and
continue on into Canada on Monday. A secondary shortwave is
currently dropping into the Pacific NW, and this feature will
continue to dig south, closing off over the Great Basin Monday and
Tuesday. Steady rain over eastern portions of N-Central MT will
gradually diminish to scattered showers later this evening as the
upper low pulls away from the region. Elsewhere, showers will
decrease in coverage this evening but low clouds will likely
continue through most of tonight. Fog is a possibility in any
location tonight that sees breaks in the cloud-cover. Heights rise
through the next several days behind the departing low but broad
troughing remains over the Northern Rockies. This will allow for
warming and drying through Tuesday though weak instability and
lingering moisture will produce at least a slight chance of
afternoon showers and thunderstorms each day with better chances
over SW MT in closer proximity to the upper low over the Great
Basin. Hoenisch

Tuesday night through Sunday...A high pressure ridge will be over
the Pacific Northwest Tuesday night and heights aloft will be rising
over Central Montana. The air mass will trend warmer and generally
remain dry through Friday. A disturbance will be moving through
British Columbia Wednesday and develop low surface pressure over
Alberta. This will tighten the surface pressure gradient across the
Northern Rockies and adjacent plains. Breezy conditions will develop
but nothing extreme. The high pressure ridge over Montana will move
east of the zones as a low pressure trof approaches the West Coast
Friday night. Southwest flow ahead of this system will bring
moisture into the southwest zones and, along with the decreasing
heights aloft, some weak instability along with a slight chance of
thunderstorms. Convection will mainly be over the southwest zones.
The trof will be over the West Coast late Saturday afternoon and
move into the Pacific Northwest Saturday night. Current timing has
an associated cold front moving across the Northern Rockies and
through Cut Bank by early Sunday morning, and central portions of
the CWA during the afternoon, including Great Falls. This front
should be moving into the southwest zones by evening. Cooler
temperatures and moist conditions behind the front should bring
areas of precipitation to Central Montana through Sunday night.
Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  66  46  77 /  30  10  10   0
CTB  42  66  43  77 /  10  10  10   0
HLN  44  70  48  79 /  10  10  20  10
BZN  39  68  42  74 /  10  20  20  20
WEY  35  61  36  66 /  20  40  30  30
DLN  42  65  44  72 /  30  30  30  10
HVR  44  67  43  78 /  60  10   0   0
LWT  41  63  44  74 /  60  20  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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