Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211735
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1135 AM MDT Sat Oct 21 2017

.UPDATE...

Morning update has been published, with only major change being to
upgrade the High Wind Watch to a High Wind Warning for all of the
remaining counties across North Central Montana. In addition to
upgrading, I also added Jefferson and Broadwater Counties to the
High Wind Warning, as northern portions of the counties and
elevations above 6,000ft will likely see wind gusts to 60 mph.
Given this weekend is the opening weekend for deer and elk
hunting (which will lead to above normal foot traffic in wooded
areas), felt it was prudent to add Jefferson and Broadwater
Counties due to the possibility of falling trees (especially
in/near recent burn scars). Early indications this morning suggest
that winds along the Rocky Mountain Front (especially at ridge
tops) may gust upwards of 90 mph, but for now held off mentioning
this in the current hazard for the Rocky Mountain Front zones as
it already contains 85 mph wording. - Moldan

&&

.SYNOPSIS...

Clouds thin today as high pressure moves over the region. Rain and
mountain snow returns tonight through Sunday generally along and
west of the Continental Divide. Potentially damaging winds also
develop overnight, peaking in strength Sunday afternoon.

&&

.AVIATION...
Updated 1735Z.

VFR conditions will prevail for all terminals across North Central
and Southwest Montana through 12z, when-there-after MVFR conditions
may be realized across Southwest Montana due to lowering ceilings
from precipitation. Otherwise, few to scattered mid-level clouds are
expected across the region through the afternoon hours, with
increasing mid-level cloudiness during the evening and overnight
hours as the next disturbance begins to move into the Northern
Rockies. Mountain obscuration is likely across Southwest Montana and
along the Continental Divide this evening and into the morning hours
on Sunday. Westerly winds will be breezy and gusty today and this
evening, but increase in earnest early Sunday morning. LLWS and
mountain wave turbulence is likely over the region, especially
across the North Central and Central Montana terminals of KCTB,
KHVR, KGTF, KLWT, and KHLN. - Moldan

&&

.PREV DISCUSSION...
/ISSUED 400 AM MDT Sat Oct 21 2017/

Tonight through Monday...Cool and breezy conditions prevail today
under clearing skies due to post-wave subsidence. A new surge of
moisture arrives later this evening through Sunday, with rain and
mountain snow developing up to and along the Continental Divide
before spreading further across southwest Montana. Snowfall
amounts of 3-6" are possible over remote areas of the Northern
Rockies, but snow levels actually rise through this event from
around 5 to 8 kft. An unseasonably strong jet stream noses across
North-central MT, resulting in a period of potentially damaging
wind gusts on Sunday afternoon. The strongest winds will be
along the Rocky Mtn Front with gusts into the 70kt range possible.
Across the plains winds 30 to 40kt with gusts into the 50kt range
are possible Sunday afternoon. PN

Monday night through Friday...The main concerns during this
period are a possible wind event for portions of Central Montana
WED, then the potential of sharply colder temps and accumulating
snow WED night/Thursday.

The period starts with an anomalously strong ridge (for this time of
year) building into the western US. Under mostly sunny skies and,
for some, a downsloping SW wind, this should allow temps to warm
into the 60s/70s at lower elevations TUE/WED (although, increasing
clouds may tend to keep it not as mild along the Hi-line by WED).
The breezy/mild conditions may also lead to elevated fire concerns.

Those increasing clouds will signal what is expected to be a potent
shortwave moving over the ridge and crashing into the Northern
Rockies/Northern High Plains late Wednesday/Thursday. This wave
has origins over the Bering Sea and it should be noted that the
models continue to struggle this far out with its track/evolution
and associated impacts. The forecast, then, puts a bit more weight
on the previous forecast to avoid drastic changes one way or the
other. Ahead of the shortwave, another wind event will be
possible, especially portions of Central MT. This is then followed
by a strong cold front. It should be noted that the potential
exists for a fairly drastic temp change from WED to THU in the
wake of the front (possibly a 20-30 degree drop). This system will
also be accompanied by at least some rain/snow, but how much and
how impactful the snow is will very much depend on how quickly the
system moves through. MARTIN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  45  59  45 /   0  10  10  10
CTB  49  41  55  40 /   0  10  20  10
HLN  52  44  59  43 /  10  10  20  20
BZN  51  42  59  42 /  10  10  30  20
WEY  34  31  43  31 /  30  70  60  60
DLN  46  40  56  39 /  10  10  20  20
HVR  54  40  61  40 /  40  30  20  10
LWT  49  40  60  40 /  10  10  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

High Wind Warning from 6 AM to 10 PM MDT Sunday Blaine...
Broadwater...Cascade...Central and Southern Lewis and Clark...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...
Fergus...Hill...Jefferson...Judith Basin...Liberty...Meagher...
Toole.

High Wind Warning from midnight tonight to 10 PM MDT Sunday
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

$$

weather.gov/greatfalls



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