Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 241743

Area Forecast Discussion
National Weather Service Great Falls MT
1143 AM MDT Mon Oct 24 2016

Updated Aviation Discussion


Main adjustments were to match up better with surrounding offices.
However, forecast models indicate that a weakly unstable and
diffluent southwest flow aloft may bring an isolated
thunderstorms to far Southwest Montana this afternoon into early
evening, so have added a slight chance of thunderstorms for that
time period. Remainder of forecast appears to be on track.



Overall VFR conditions are expected...with increasing clouds...and a
few VCSH to brief light rain showers possible across the southwest.
Increasing moisture in southwest flow will bring increased cloud
cover to most sites today...although remain above VFR levels. A few
showers are possible across the west and southwest...although
confidence is only placed VCSH in TAFs for now...with a
Tempo in KEKS. Brief MVFR conditions are possible with any shower
that does cross a terminal site. Mountains may also be obscured at
times with any shower activity. Shower activity will diminish
tonight...with lingering VFR SCT to BKN cloud decks possible through
Tuesday morning. Winds will be tame throughout much of the forecast
period. Breezy winds may return Tuesday...however...after the
current forecast period...or after 18z Tuesday. Anglin


/ISSUED 520 AM MDT Mon Oct 24 2016/

Today through Wednesday...An upper level ridge remains in place
over the region today and tonight downstream of a deepening
trough off the west coast. Plenty of moisture is streaming NE
across the Western US in SW flow aloft to keep considerable high
level cloudiness across the forecast area today and tonight. Weak
emebedded shortwave energy and somewhat deeper moisture upstream
in NV will track NE through SE ID and WY later today and tonight,
potentially giving some light showers to far southern portions of
SW MT with little or no precipitation expected elsewhere. Next in
a series of shortwaves ejecting out of the offshore trough will
lift NE across the Pacific NW and Northern Rockies Tuesday, then
across AB and SK Wednesday. This will temporarily flatten the
upper level ridge with some potential for light showers as the
energy moves across the region Tuesday. Breezy west winds are
also likely to develop Tuesday afternoon as a surface trough
associated with the upper level energy shifts east across the
region. Temperatures remain about 5-10 degrees above seasonal
averages through Tuesday with slight cooling on Wednesday.

Wednesday Night through Monday...The extended period begins with
a broad upper level ridge axis centered over the Rocky Mountain
west. Fair and mild weather prevails for Thursday under this
ridge. The ridge axis flattens and shifts east on Thursday as an
Alberta Clipper system skirts along the international border.
Rain showers will be possible over the mountains and the north-
central plains as this system quickly moves through on Thursday
evening. A shortwave ridge amplifies along or just west of the
Continental Divide on Friday. Rain chances increase over
Southwest Montana Friday evening as a moist system is drawn up
through California into the eastern Pacific trough. The 00Z ECMWF
solution presents a rather wet outcome as this wave moves over the
Northern Rockies on Saturday morning. In contrast, the GFS and
ensemble mean solutions weaken the wave while it lifts north into
the Canadian Rockies. A model blend is adequate to support
widespread Chance POPs for this system on Saturday. Snow levels
remain above 8000 feet. The western ridge amplifies once again on
Sunday, followed by another round of Pacific moisture on Monday.
Temperatures remain near to above average through the period. PN


GTF  64  43  63  41 /   0  10  10  10
CTB  56  36  57  36 /   0  10  10   0
HLN  64  40  62  38 /  10  10  20  10
BZN  62  42  62  40 /  20  20  20  20
WEY  49  34  51  33 /  50  50  30  20
DLN  61  39  58  37 /  20  20  20  10
HVR  58  35  62  36 /   0  10  10  10
LWT  66  42  64  39 /  10  10  20  20



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