High Wind in Montana, March 18 to 19, 2017

Area Forecast Discussion
National Weather Service Great Falls MT
253 PM MDT Sat Mar 18 2017

.DISCUSSION...

Rest of this afternoon through Monday...A developing surface low
over West-Central AB will move east-northeastward this evening
through Sunday, allowing the accompanying Pacific cold front to
sweep eastward across North-Central MT this evening through early
Sunday morning. Farther south, this front looks to stall along the
higher terrain of Southwest MT Sunday morning, where the
resulting stationary front should then persist through Monday.
Still expect the cold frontal passage itself and vertical mixing
within the CAA regime behind the front to result in strong, gusty
downslope winds along the Rocky Mountain Front and western
portions of the Hi-Line this evening into Sunday morning.
Accordingly, a high wind warning has been hoisted for these areas
from 5 PM this evening to 9 AM MDT Sunday.

Hydrological concerns continue for portions of the CWA. Please see
hydrology section below for more details. Upslope precipitation
along the roughly north- south portion of the Continental Divide
should taper-off by early Sunday morning, following the passage of
the aforementioned Pac cold front. Farther east, there is only a
slight chance for a few showers with tonight's frontal passage
across the North- Central MT plains, as downslope winds should
result in an extensive rain shadow. For Southwest Montana, periods
of precipitation are expected, especially Sunday through Monday,
due to the aforementioned stationary front interacting with
sufficient moisture. In addition, a weak and brief thunderstorm or
two cannot be ruled-out over Southwest MT on Monday, when
marginal instability and a weak cap may materialize in the
afternoon. An overall cooling trend in temperatures is expected
during the period.
Jaszka

Monday Night through Saturday...The models remain in fairly good
agreement in the extended period with what will likely be a very
progressive pattern. Within this pattern, several shortwaves are
expected to traverse the area. However, it still looks like the main
storm track will remain south/east of the area. Temperatures look to
be near to above normal for most of the week, then potentially
followed up by a cooling trend by next weekend. This pattern does
not appear to favor any significant wind events at this time with
the main jet stream remaining south/east of the area.

The best chance of seeing a bit more widespread precipitation may
come WED/THU. During this time, the models suggest a SFC low may
track northeast through SE Montana which could favor areas from
Bozeman to Lewistown and points east. Right now, the general
consensus is a weaker system with lighter precip amounts (and mostly
rain at lower elevations). Something to watch in coming days,
though, as a stronger/deeper system could mean heavier precip
amounts, especially in that Bozeman to Lewistown area, with a
greater potential for snow at lower elevations. For the plains of
north-central Montana, this pattern continues to look like a drier
one, but each passing shortwave may bring at least a low chance for
showers. Of note, the models this morning continue to suggest enough
instability for some thunder mid-week, but confidence remains too
low to include in the forecast for now. In the mountains, precip may
be enhanced at times next week with the moist W/SW flow aloft and is
where the highest precip totals are expected.
Martin

&&

.AVIATION...
Updated 1723Z

Southwesterly to westerly flow aloft and VFR should prevail through
the period. A disturbance aloft and associated surface cool front
should sweep E'ward across the area between roughly 00Z and 12Z/Sun.
Scattered showers and periods of mountain obscuration are expected
along the Rocky Mountain Front and SW MT mountains. Some rain
showers may impact the terminals with the frontal passage, but
confidence is low. Gusty southwesterly to westerly surface winds are
expected along and near the Rocky Mountain Front, especially between
00Z and 12Z/Sun. This includes KCTB.
Jaszka

&&

.HYDROLOGY...
253 PM Update.

Flood highlights remain unchanged. Hill/Blaine counties seem to
be most impacted right now, with minor flooding occurring from
snowmelt in southern Canada and the water flowing southward into
the Milk River basin.

Otherwise, the main concern today will be near record highs.
There is the potential for flooding to quickly develop late this
afternoon/early this evening for small streams and creeks that
flow out of the mountains because of the warm temperatures.
However, a Pacific cold front will move through the region late
tonight, slowing down/diminishing the flood threat on Sunday
morning.
Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  37  53  26  45 /  20   0   0  10
CTB  30  45  21  41 /  20   0   0  10
HLN  38  54  31  48 /  20  10  10  20
BZN  41  57  33  50 /  30  20  40  50
WEY  34  44  32  44 /  60  60  40  60
DLN  40  57  33  53 /  20  20  20  40
HVR  36  51  24  46 /  10   0   0   0
LWT  37  48  26  41 /  20  20  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 5 PM MDT Saturday until 9 AM MDT Sunday
Eastern Glacier... Liberty...Northern Rocky Mountain
Front...Southern Rocky Mountain Front...Toole.

Flood advisory until 230 PM MDT Sunday for a portion of
Hill...Blaine counties.

Flood Watch through Sunday morning Judith Basin...Meagher.

Flood Watch through Sunday morning Blaine...Hill.

Flood Watch through Sunday morning Beaverhead.

&&

weather.gov/greatfalls