High Wind in Montana, March 26 to 27, 2018

Area Forecast Discussion
National Weather Service Great Falls MT
1129 PM MDT Mon Mar 26 2018

UPDATED AVIATION

.UPDATE...
The going forecast appears to be on track, so have kept any
adjustments to a minimum. The main update was to lower
low temperatures about 3 to 5 degrees in the colder valleys of
southwest Montana. Forecast models have not been aggressive
enough with cooling these areas. For example, have lowered the low
at West Yellowstone from around 10 degrees to around 5.
Coulston

&&

.SYNOPSIS...

A nice warm up is underway across the area, which will last well
through the day on Tuesday. Strong winds will impact locations along
the Continental Divide on Tuesday, with breezy conditions expected
further east across the Plains. We will return to a winter pattern
beginning on Wednesday with isolated rain and snow shower chances,
with better, more widespread chances of snow by Thursday and Friday
and lasting into the weekend followed by a significant drop in
temperatures.

&&

.AVIATION...
Updated 0529Z.

Cloud cover will increase during next 24-hours as westerly to
northwesterly flow aloft persists. However, mainly VFR are expected.
A disturbance over/near Central BC at 06Z/Tue will continue moving
SE'ward and should reach the MT/ND border region by 06Z/Wed. Periods
of mountain-obscuring snow showers are expected along the
Continental Divide through the period. In addition, lower elevation
locations may experience scattered rain and/or snow showers around
and especially after 00Z/Wed. The best potential for this activity
exists south of a KHLN to KHVR line. Surface winds are expected to
mainly be out of the southwest to west and gusty, especially along
the North-Central Montana plains. In fact, gusts up to 55 to 70
knots are expected along the Rocky Mountain Front. Accordingly,
mountain wave turbulence and low-level wind shear are a concern.
Jaszka

&&

.HYDROLOGY...
Updated 805 PM MDT 3/26/18.

Areal Flood Advisory continues for Chouteau County. Emergency
manager reports minor flooding impacts. Several roadways have
been reported to have water on them or are impassable.
Additionally, some rivers/creeks are bankful or out of their
banks in low lying areas.

Flood Warning remains in effect for the Missouri River (near
Landusky - LDKM8 - in Fergus County). The river level is still
above flood stage and is falling, but it is falling more slowly
than previously expected. It is now expected to fall below flood
stage some time around noon on Tuesday.
MPJ/Coulston/Jaszka

&&

.PREV DISCUSSION...
/ISSUED 525 PM MDT Mon Mar 26 2018/

Tonight through Wednesday...Feels like spring finally across a
large majority of the area! Temperatures today climbed well into
the upper 40's across the Plains thanks to prominent downsloping
chinook winds. We will see one more slightly milder day tomorrow
with a few lucky (I mean traditionally warmer) locations able to
reach the lower 50's across the Plains. Taking a look at the
synoptic pattern in place, we reside on the upslope side of a
departing shortwave trough to the east, with a prominent west to
northwesterly flow aloft. Along this flow, a weak shortwave
trough and associated strengthening low-level jet will progress
quickly across far southwestern Canada and into the northern
Rockies tonight, bringing the potential for strong winds
beginning tonight along the Divide, and locations east including
all of Glacier County. In these locations, wind gusts will easily
exceed 40-50mph overnight tonight and throughout the day on
Tuesday, with a few higher gusts of 60+ possible. The latest
short-range guidance this afternoon continues to support this
with good confidence/trends throughout the day. Because of this,
the decision was made to upgrade the High Wind Watch to a High
Wind Warning for the same time period of 0300Z TUE thru 0300Z
WED. Worthy to note, this is a broad event with not much of one
pinpointed time of the strongest winds as warning criteria winds
may be possible at any time during the 24 hour period the warning
is in effect. The only evolution appears to be during the daytime
on Tuesday, as some of the better upper-level wind support pulls
east out into the Plains. Combined with the development of a
well- mixed layer by the afternoon hours, it appears that gusty
winds will have no problem transferring down to the surface.
Going to keep the warning at the area with highest confidence
along the Divide, but continue to monitor out in the Plains in
case of any additional highlights tonight and into the day on
Tuesday. Otherwise, we will begin to see a major pattern change
beginning into Wednesday, after the passage of a quick moving
cold front across the area. Temperatures will likely fall back to
afternoon highs struggling to reach the 40's with ample cloud
cover. A few areas of light rain and snow showers will follow as
pulses of energy ride along the fast northwesterly flow aloft.
While it will not rain or snow everywhere, the better chances
will be in any higher terrain locations with some light snow
accumulations possible. KLG

Wednesday Night through Monday...Medium range models continue to
show an active weather regime persisting into at least early next
week. Main player in this scenario will be a deep and strong
upper level low over Hudson Bay with an unsettled northwest to
northerly flow aloft over Montana. This pattern will be further
exacerbated by a strong jet stream interacting with shortwave
energy as occasional disturbances in the flow aloft move through
the region. While conditions should be cool and unsettled for the
Wednesday through Friday time period, models bring a push of very
cold Canadian air into the state the second half of Friday and
continuing into early next week. As a result, it seems that
wintry conditions will return with accumulating snows likely in
the mountains and over the plains. We continue to make
significant adjustments in the medium range to increase PoPs and
lower temperatures, especially for Friday and beyond.
Temperatures may need additional adjustments lower for the
weekend. CC/MPJ

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  30  52  30  42 /   0  30  40  40
CTB  30  45  29  36 /  10  20  40  40
HLN  29  50  35  47 /  10  30  40  30
BZN  23  47  34  46 /  10  30  60  40
WEY   6  36  22  39 /  10  30  50  40
DLN  21  48  31  45 /  10  20  30  30
HVR  25  42  27  34 /  10  30  30  30
LWT  24  48  30  38 /   0  30  50  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 9 PM MDT Tuesday Eastern Glacier...
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

Flood Advisory for snowmelt remains in effect
until 4 PM MDT Wednesday for Chouteau County.

Flood Warning for the Missouri River at Landusky remains in effect
until 5 PM MDT Tuesday.

&&

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