Area Forecast Discussion
Issued by NWS Great Falls, MT

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS65 KTFX 201742

Area Forecast Discussion
National Weather Service Great Falls MT
1040 AM MST Fri Jan 20 2017

Aviation Section Updated


Mostly minor changes for the morning update. Clouds are beginning to
decrease and radar/SFC obs show very little, if any, precip around
the area at this time. For this reason, I lowered the chance of snow
for most of the area through the remainder of today. The exception
is far SW MT where low clouds and light snow will remain possible
through this afternoon. In that area, though, still only looking
about about an inch or so through today. Another change was to up
temps across our NE counties where model guidance appears to be too
low. In this area (ie. Havre to Lewistown), temps warmed well into
the 40s and even some low 50s yesterday. Given there isn`t much of
an airmass change expected today, temperatures in that area probably
won`t be much lower than yesterday. I made a similar change to some
of the SW valleys as well. Last change was to add patchy freezing
fog to the Helena Valley, but it appears the fog is already
beginning to diminish. Martin


Updated 1740Z.

Clouds are continuing to slowly push east/decrease this morning
across much of the area. The exception is far SW MT where low
clouds/mtn obscurations will likely linger through the day. For now,
I am not expecting any precip at any terminal through 18Z/SAT. The
main concern this morning and again tonight is fog development with
light winds and high pressure overhead at the SFC. For this morning,
the main concern is KHLN where webcams and the ob, itself, show fog
struggling to completely mix out. Thinking conditions there will
gradually improve by 20Z today, but we`ll keep a close eye on
trends. For tonight, I kept a mention of VCFG at the terminals that
appear to have the best chance for fog development. If confidence in
fog increases, later forecasts will likely need to add lower
CIGS/VIS. Martin


/ISSUED 439 AM MST Fri Jan 20 2017/

Today through Sunday...Weak flow to bring clouds and scattered
low impact snow through the short term. A cut off upper low
across the Dakotas...and an encroaching upper low off the Pacific
NW has left us in between systems this morning. Large deformation
zone bringing clouds and a few isolated to scattered rain and
snow showers to the south and east. With weak flow aloft...and no
major weather maker...clouds and scattered precip could linger
through this morning to the mentioned areas. Precip then ends
across the east this afternoon...but could linger across the south
into tonight. Little snow accumulations are expected. Those not
in the precip will still see partly cloudy and slightly cooler
conditions today. Weak flow and mainly dry conditions are then
expected for tonight...with some light snow possible in the south.
Friday will see a slow transition to southwest
flow...however...mainly dry conditions are still expected...except
for scattered showers across sw MT. Saturday we see the Pac NW low
fall apart and send weak waves of energy over a ridge to our south.
This may result in more widely scattered snow and possibly some rain
showers for the region. This ridge then builds northward by
Sunday...bringing mainly dry conditions except across the southwest
where moist southwest flow continues to linger. With no advection of
an airmass change...temperatures will be cooling to near normal for
the short term...with highs in the 20s and 30s...and lows in the
teens to 20s. Anglin

Sunday night through Friday...Medium range models are in reasonable
agreement through most of next week. Period starts with a longwave
upper level trough progressing inland across the western US early in
the week followed by a building upper ridge from the middle through
later portions of next week. Upper level jet and main shortwave
energy associated with the upper trough early next week moves by well
to the south of the region, however some weak shortwave energy does
lift NE across the area on Monday ahead of the trough axis, followed
by additional weak energy embedded within northerly flow behind the
trough axis Monday night through Tuesday night. Best chance for a
period of widespread precipitation will be with the energy ejecting
NE across the region on Monday with southern portions of the
forecast area having the best shot at some light snow accumulations.
Light snow showers will linger Tuesday and Tuesday night in the
northerly flow following the trough axis with drier conditions
moving in Wednesday through the remainder of next week. Temperatures
will cool to near or slightly below seasonal averages for the first
half of next week under the upper level trough. Temperatures
gradually moderate/warm late next week. Upper level ridge with
surface high pressure over the interior western US late next week
may lead to the redevelopment of strong temperature inversions in
the valleys of SW MT, resulting in slower warming and possible
redevelopment of air quality issues in some SW valley areas.


GTF  40  18  33  20 /  10   0  10  20
CTB  39  16  34  18 /  10   0   0  20
HLN  36  10  25  11 /  20   0  20  20
BZN  32   7  26   8 /  20   0  20  20
WEY  26   2  23   7 /  30  20  20  30
DLN  34  13  31  13 /  10  10  20  20
HVR  39  19  32  18 /  10   0   0  10
LWT  42  17  33  19 /  30  10   0  10



$$ is the U.S. government's official web portal to all federal, state and local government web resources and services.