Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 200525 CCA

Area Forecast Discussion...Corrected Avn Section Time
National Weather Service Great Falls MT
1050 PM MDT Wed Oct 19 2016

Aviation Section Updated.


Minimal changes made to the forecast. Building ridge of high
pressure causing subsidence across the CWA...clearing out skies.
With clear overnight lows in the 20s and 30s are
expected tonight. Ridge breaks down by Thursday morning...and more
moisture and clouds streams into the region. Kept the CWA dry until
this moisture impacts western portions early Thursday morning...then
spreads widely scattered showers eastward throughout the day. Other
item to note will be the potential for strong winds...mainly
Thursday afternoon and evening. NAM indicating 60 knot winds at 700
mb will be possible. This could provide strong to borderline high
winds across the Rocky Mountain Front and adjacent high plains.
Decided to hold off on High Wind Watches/Warnings for now. Impacts
look to be low...duration of winds confined to just the mentioned
time period...and the event is not quite a slam dunk yet. That
said...those traveling on north-south highways should prepare for
strong cross winds.

This Afternoon through Friday Evening...Last remnants of the
shortwave trof that moved through the forecast area this morning are
steadily exiting our area. Very isolated, light showers will move
through the central and southwest counties through late aftn, then
dissipate quickly around sunset as instability wanes. Weak high
pressure ridge just now entering far western MT will move east of
the Continental Divide tonight, bringing mostly clear skies into
Thurs morning. But the ridge doesn`t hang around very long, with
leading edge of moisture from the next Pacific trof beginning to
spread mid- and high-level cloud cover over us by midday tomorrow.
Much of the precip with this system should remain banked up
along/west of the Rocky Mtn Front. A few short-term forecast models
try to bring an area of showers into the central/Hiline counties
tomorrow aftn, but increasing westerly, downslope winds should
significantly limit development of any widespread rainfall. As for
the winds, models continue to indicate breezy to gusty conditions
along the Rocky Mtn Front and adjacent plains Thurs aftn/eve as the
core of 130-140 mph jet stream winds moves into the western half of
MT. However, the strongest mid-level (700 mb/10,000 ft) winds (60-70
mph at 10,000 ft/700 mb) don`t occur until Thurs night, when very
little vertical mixing will be present to bring those winds down to
the surface. The mid-level winds then gradually dissipate Fri
morning as the Pacific trof heads downstream, leaving a pattern of
dry, westerly flow aloft through Fri evening. Temperatures will
increase a few degrees tomorrow and Fri, with mid/upper 50s expected
Thurs and upper 50s to low 60s on Fri. Waranauskas

Friday Night through Wednesday...The general forecast trend is
still on track for much of this period, but some differences have
developed in the Friday night through Saturday period and for the
Tuesday through Wednesday period. There is agreement in bringing
a weak shortwave trough through the westerly flow aloft Friday
night into Saturday, but the difference is in the timing and
placement of potential showers associated with it. The ECMWF
moves a band of precipitation over the forecast area Friday night
into Saturday morning, with the focus being over Southwest and
Central Montana. The GFS delays it until during the day on
Saturday and keeps it more so across North Central Montana. With
this significant of a discrepancy, will stay with more of a
compromise solution until models come into better agreement. Will
go with a broad brushed chance of precipitation mainly over North
Central and Central Montana. The upper level high pressure ridge
will rebuild over the Rockies/Great Plains for Sunday into Monday
as a deep upper level low pressure trough digs south off the
Pacific coast. Under the resulting southwest flow aloft, a few
showers will likely develop over the mountains, but the plains
will mostly remain dry. After Monday, the forecast models move
shortwave troughs of varying timing and strength over the forecast
area. However, they generally yield a solution similar to that
from Sunday into Monday, of showers mainly over the mountains with
less of a chance over the plains. High temperatures will likely
remain within 5 degrees above and below normal through the period
(mostly upper 40s and 50s), and lows will be a bit warmer than
normal (mostly 30s). Temperatures will likely warm through Monday,
then cool a bit with the shortwave passages Tuesday into
Wednesday. Coulston


Updated 0450Z.

Skies are clearing this evening across North-central and Southwest
MT. Winds will remain generally light overnight, with increasing
high clouds again by early Thursday morning. The western mountains
will be obscured at times on Thursday. Gusty west winds will also
develop over the northern Plains by late Thursday morning. PN


GTF  37  57  43  60 /  10  20  20   0
CTB  32  54  37  54 /  10  20  10  10
HLN  33  59  39  60 /  10  10  20  10
BZN  30  55  38  60 /   0  10  10  10
WEY  24  42  28  51 /  10  10  10  10
DLN  30  54  35  59 /  10  10  10  10
HVR  33  55  39  57 /   0  20  20   0
LWT  33  54  41  59 /   0  20  20  10



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