Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 200521

Area Forecast Discussion
National Weather Service Great Falls MT
1120 PM MDT Mon Mar 19 2018

...Aviation Section Updated...


No major changes were necessary in this evenings update package,
as the forecast remains on track. Only impacts for tonight look to
be minor, with snow showers expected to diminish overnight. There
may likely be areas of fog developing later tonight and through
the early morning hours in northern Montana, specifically for
areas along and near the Milk River Valley along the Hi-Line.
However, these areas should improve after sunrise tomorrow with a
nice stretch of calm, sunny and slightly warmer temperatures
ahead! KLG



Dry weather is expected for most through Wednesday. However, snow
showers along the Hi-Line should end this evening, while bands of
light to moderate snow are expected for Southwest Montana,
especially in the mountains, late this afternoon through Tuesday
morning. Near-normal temperatures are forecast for most through the
middle of the week. However, below-normal highs are likely for most
of the Hi-Line.


Updated 0520Z.

VFR conditions are expected at most terminals through the duration
of the 2006/2106 TAF period, with the only exception being the KHVR
terminal. At the KHVR terminal, dense fog reducing visibilities to
LIFR conditions is expected to persist through the remainder of the
overnight hours. A gradual improvement in visibilities and ceilings
is expected then during the mid-morning hours at the KHVR terminal,
with VFR conditions resuming around 16z. Otherwise, breezy
southwesterly winds will be experienced at the KGTF and KCTB
terminals tonight and during the day on Tuesday. - Moldan


/ISSUED 440 PM MDT Mon Mar 19 2018/

Rest of today through Wednesday...Primarily westerly to
northwesterly flow aloft is expected through Wednesday. Within this
flow, one disturbance over North-Central MT this afternoon will exit
to the east by late evening. Accordingly, scattered snow showers
along/near the Hi-Line should diminish by this mid to late evening.
Additional snow accumulations from this activity should generally be
an inch or less. Partial clearing, weak winds, and residual low-
level moisture from recent precipitation should allow patchy fog to
develop along eastern parts of the Hi-Line tonight into Tuesday
morning. Another disturbance will affect Southwest MT this afternoon
through Tuesday morning. During the passage of this disturbance,
frontogenetical forcing for ascent should trigger some localized
bands of steadier snow over Southwest MT. These bands should produce
no more than 1-4 inches of new snow, especially in the mountains.
Due to the expectation of minimal impacts, do not plan to issue a
Winter Weather Advisory for these snow bands. Behind the
disturbances, a high pressure ridge aloft is expected to build over
the region as Tuesday and Wednesday elapse. This will result in dry
weather for many. However, additional weak disturbances will
traverse this ridge from west to east, resulting in the chance for
isolated snow showers over our mountains later Tuesday into
Wednesday. This will particularly be the case for Southwest MT. Near-
normal low temperatures are expected during the period. As for
highs, those will be near-normal for most. However, along the Hi-
Line, highs are expected to be several degrees below-normal due, in
part to a greater snow pack.

Wednesday night through Sunday...Towards the middle of the week, a
large upper level low will slide south off the west coast of North
America, allowing an upper level ridge over the Rockies to amplify.
This ridge will not stick around long, though, as the upper low
gradually works inland by the end of the week. Locally, it is
expected that this evolution will put an end to the moderating
temperatures and drier conditions expected through mid-week,
transitioning to cooler and more unsettled conditions once again.

As the low moves inland, a broad SW flow aloft develops across the
West, potentially allowing an atmospheric river to develop and move
across the Central Rockies. For now, it looks like the best
moisture, then, will stay south of Montana. That said, a potent
shortwave, forecast to move through the area late Thursday into
Friday, may be able to briefly tap into some better moisture. The
models differ on the handling of this wave, but it bears watching as
it has the potential to produce some modest precipitation amounts,
some in the form of rain, which could have hydrology impacts.
Warm air aloft ahead of this wave combined with near/below
freezing surface temps may allow a window of mixed precipitation
to develop across parts of Central Montana Thursday/Thursday
night. There may also be an opportunity for stronger winds along
the Rocky Mountain Front Thursday night/Friday. After this initial
wave passes, a gradual cooling trend is expected which should
lead to primarily a rain or snow scenario by the weekend. For now,
the forecast over the weekend reflects a generally unsettled
pattern as it is too early to get specific regarding the
timing/impacts of each wave embedded within the trough. MARTIN


GTF  25  45  24  49 /  10   0   0   0
CTB  21  42  20  43 /  20  10   0  10
HLN  27  47  25  48 /  10   0  10  10
BZN  23  44  23  48 /  20  10  10  10
WEY  15  33  18  38 /  30  20  30  40
DLN  18  43  21  46 /  30  10  20  20
HVR  16  36  16  36 /  30  10  10  10
LWT  25  42  23  47 /  20   0   0   0



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