Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 292337

Area Forecast Discussion
National Weather Service Great Falls MT
535 PM MDT MON AUG 29 2016



Tonight through Wednesday...A very warm and unstable southwesterly
flow aloft will impact the forecast area through this period. This
is due to an upper level low pressure trough deepening off the
Pacific coast and the upper level high pressure ridge over Montana
amplifying and moving east into the Great Plains. A disturbance in
the flow will likely move isolated thunderstorms from Western and
Southwest Montana to the North Central Montana plains overnight.
Moisture is somewhat lacking with these storms, so gusty winds
will be the main threat with little rainfall. A few storms may
develop again over the western mountains late Tuesday afternoon,
but any that move out onto the plains overnight will be very
spotty at best. The flow aloft may start tapping into some
monsoonal moisture Wednesday afternoon into Wednesday evening,
bringing an increased chance for thunderstorms with a better
potential for showers. However, the warm surface temperatures will
also keep a chance of gusty winds with any storms that develop.
Temperatures will be 10 to 15 degrees above normal during this
period, but better radiational overnight cooling in the southwest
valleys will help lows reach near normal levels there. Smoke from
fires west of the Continental Divide will generally drift just
east of the Divide, but southeast winds will hinder any
significant spread out onto the plains and only keep skies hazy.
Southwest Montana will continue to have limited visibility at
times, as smoke from fires in West Central Montana and Southern
Idaho continues to spread into the area. The very warm
temperatures will also cause very dry conditions (afternoon
humidity in the 10 to 20 percent range), but relatively light
winds will keep the chance for increased fire weather concerns
fairly low.  Coulston

Wednesday Night through Labor Day...After changing the track and
reducing the strength and associated precipitation of the Pacific
upper-level trof that will influence our weather this week,
latest GFS/ECMWF model runs have partially reverted back to
solutions from a few days ago. Namely, the forecast track of the
system now extends well south of the US/Can border and broad
moisture coverage is back in the picture, notably on Fri eve.
Before that though, our region will be under southwest flow aloft
on the eastern flank of the trof. Monsoonal moisture being pulled
northward will bring scattered showers and thunderstorms, mainly
over the southwest counties, on Thurs aftn/eve. After a break in
the showers through Fri morning, more thunderstorms are expected
Fri aftn in conjunction with passage of a sharp cold front. The
tight pressure gradient with the front will also produce gusty
westerly (downslope) winds for a few hours Fri eve. Dry, but cool
conditions return on Sat, but showers are back in the forecast
for Sun as a second shortwave trof drops south from Alberta and
moves quickly across the state. Weak high pressure ridging
arrives for Mon, with mostly dry conditions expected. As for
temperatures, the slight delay of not bringing the Pacific trof
ashore until Fri morning means Thurs will be another very warm
day, with highs in the upper 80s, with a few sites along the
Hiline reaching the low 90s. The sharp frontal passage on Fri
will bring a quick end to the warm temps, as highs on Fri will
only reach the mid 70s, then decrease to the upper 60s for Sat
and Sun. Waranauskas



VFR conditions are expected at least through the day on Tuesday and
light easterly winds will continue east of the Rockies. Scattered to
broken higher clouds will persist in a southwest flow through the
period. However, a weak disturbance will move over North Central
Montana, which may bring a few thunderstorms to the Hi-Line area
(including KCTB and KHVR) between 04Z and 12Z. The main threat from
these storms will be wind gusts up to 40 kt. A storm or two may also
develop as far south as Central Montana (KGTF and KLWT), but
confidence in this happening is much lower.  Coulston


GTF  57  94  58  93 /  20   0  10  10
CTB  50  89  54  88 /  20  10  10  10
HLN  56  94  57  91 /  10  10  10  10
BZN  51  93  52  92 /  10  10  10  10
WEY  36  81  46  79 /  10   0  10  10
DLN  51  90  52  87 /  10  10  10  20
HVR  55  93  59  96 /  20  10  10  10
LWT  56  92  59  93 /  10  10  10  10



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