High Wind Watch 11, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1014 PM MST Fri Mar 7 2014

.UPDATE...
Main update this evening is to issue a High Wind Watch for the
Rocky Mountain Front and for northern portions of Toole and
Liberty Counties from late Saturday morning through Sunday
evening. Forecast models bring 50+ kt winds at 700 mb to the Rocky
Mountain Front beginning on Saturday, increasing them to 70+ kt
Saturday night into Sunday morning, then decreasing them through
Sunday evening. A moderate temperature inversion is also forecast
to develop just above ridge top level, which should help focus the
winds down to the surface. Have therefore introduced the
possibility of 70 to 80 mph gusts there. Have also included the
northern portions of Toole and Liberty Counties, as these winds
have a tendency to be brought down to the surface to the lee of
the Sweet Grass Hills. However, it may take a bit longer for these
potentially strong winds to develop there, so am thinking that the
main threat for strong winds will not develop there until Saturday
night and gust potential will mainly be in the 60 to 70 mph range.
Strong wind gusts during these times are possible elsewhere along
the east slopes of the Rockies (including the Cut Bank area), but a
surface trough is expected to develop between the Rocky Mountain
Front and Cut Bank, which tends to hinder winds in the immediate
vicinity of the surface trough axis. Regardless, this situation
will need to be monitored. Also, a pressure gradient favorable for
strong southerly winds will develop across southwest Montana
during this time, so have increased winds in the Norris Hill area.
Again, there is a slight chance that high winds may occur there,
but am not confident enough in the situation to issue a watch
there at this time.

The other minor updates tonight were to decrease cloud cover
overnight across the area and adjust temperatures somewhat. Light
winds and clear skies will allow temperatures to cool
significantly across the plains northeast of a Cut Bank to
Lewistown line, so have lowered lows there to around 10 degrees
above zero. Also, westerly winds will decrease somewhat along the
east slopes of the Rockies early this evening, allowing
temperatures to fall, but they will moderate after midnight as
winds increase once again. This will help limit how far
temperatures will fall, so have generally increased lows 3 to 5
degrees from Cut Bank south through Great Falls into the Helena
area.
Coulston

&&

.AVIATION...
UPDATED 0513Z.
High pressure aloft will continue to build over central Montana
through Saturday. Generally dry conditions are expected, the
exception being isolated snow showers over the mountains. Surface
winds will strengthen and become gusty Saturday afternoon. VFR
conditions will prevail through the next 24 hours.

&&

.HYDROLOGY...
Although flooding conditions have improved slightly, authorities
across southwest and central Montana continue to report areas of
flooding and water running over roadways. However, there are only
isolated closures of smaller roads. Therefore, the Flood Warnings
for Lewis and Clark and northern Gallatin Counties remain in
effect through at least the weekend, as well as Flood Advisories
for the remainder of Gallatin County, as well as Madison,
Jefferson, Broadwater, Fergus, Meagher, and Judith Basin Counties.
With temperatures expected to warm significantly over the weekend,
snowmelt will likely increase across the remainder of north
central and southwest Montana. Therefore, a hydrologic statement
was issued for these areas, addressing the increasing threat for
additional flooding, especially in poor drainage areas, and the
potential for further flood statements.
Coulston

&&

.PREV DISCUSSION...
/ISSUED 251 PM MST Fri Mar 7 2014/

Tonight through Sunday...Though moisture and a few snow showers
will linger in the mountains along the Continental Divide this
evening, drier conditions will persist elsewhere. Temperatures
climbed near to above average for most of the forecast area this
afternoon. A ridge of high pressure will continue to build over
the Northern Rockies tonight and Saturday with temperatures
climbing above seasonal averages with mainly dry conditions.
Overnight lows will also be above freezing for most lower
elevation locations in the plains and valleys. As a result of the
warming temperatures and continued snowmelt, areas of flooding,
especially on small streams and creeks will continue over parts of
central and southwest Montana with the risk for flooding
increasing farther north this weekend. Flood Warnings and
Advisories remain in effect for portions of central and southwest
Montana and will closely monitor conditions and update through the
weekend. If you encounter any water covering the road, turn around
and do not drive through.

As the ridge flattens Saturday night ahead of the next shortwave
trough, a lee- side trough will develop along the Rocky Mountain
Front resulting in increasing westerly downslope winds. These
gusty, westerly winds will continue to increase on Sunday and
spread into the north-central plains. Wind gusts up to 55 mph
with isolated wind gusts up to 60 mph are possible along the
Rocky Mountain Front, but confidence is low in the potential for
widespread high winds so did not issue any high wind highlights.
In addition, as an upper-level Pacific trough pushes into western
Montana on Sunday, moisture and precipitation chances will
increase along the Continental Divide. Thus, have raised pops in
the higher terrain along the Divide. With snow- levels around 7000
feet ahead of this system, a rain/snow mix will be possible at and
below 7000 feet with snow above 7000 feet. Snow levels will lower
as cooler air moves in behind the front on Sunday night.

Sunday night through Friday...Medium range models are in decent
agreement bringing an upper level wave into the Pacific Northwest
Sunday night. This feature continues to move east and reaches the
Northern Rocky Mountain region by Monday night. A surface cold front
will accompany the wave and widespread rain and snow can be
anticipated for Southwest Montana and southern portions of Central
Montana during this period. Residual showers persist across the
region through Tuesday but a dry airmass will move into the forecast
area by Wednesday as another transient ridge builds across the
western states. Temperatures will remain above seasonal average
through mid-week with Tuesday expected to be the coolest and wettest
day. Beyond mid-week, model solutions diverge and have trended the
forecast to remain slightly above average temperatures but cooling
slightly by the end of the week with pops also trending back toward
climatology. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  27  50  37  56 /   0   0   0  10
CTB  27  45  33  51 /   0   0  10  10
HLN  30  49  30  53 /   0   0   0  10
BZN  19  45  27  51 /  10   0   0  10
WEY  11  41  21  43 /  10   0   0  30
DLN  20  45  27  46 /   0   0   0  20
HVR  10  46  31  53 /   0   0  10  10
LWT  25  50  36  54 /  10   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH from Saturday morning through Sunday evening
Liberty...Northern Rocky Mountain Front...Southern Rocky
Mountain Front...Toole.

AREAL FLOOD WARNINGS are in effect for Lewis and Clark, and Gallatin
Counties until Sunday afternoon.

AREAL Flood Advisories are in effect for Gallatin, Madison,
Jefferson, Broadwater, Fergus, Meagher and Judith Basin Counties
until Monday morning.

&&

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