Area Forecast Discussion
Issued by NWS Great Falls, MT
FXUS65 KTFX 261140
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
540 AM MDT Thu Mar 26 2015
UPDATED AVIATION SECTION
...RECORD HIGH TEMPERATURES POSSIBLE FRIDAY...
...STRONG WINDS LIKELY FOR MUCH OF THE AREA SATURDAY...
Today through Saturday...Mid/high cloudiness with scattered
showers over the mountains of western and central Montana will
decrease today and tonight as an upper level ridge of high
pressure moves into the state from the west. A surface trough will
remain in place over central Montana through Friday, continuing
the gusty southwest downslope winds, especially along the Rocky
Mountain Front, where gusts of 40 to 50 mph will be common.
Increasing subsidence with the strengthening high pressure aloft
will pair with the gusty winds to keep temperatures unseasonably
warm. Highs today will mostly be in the mid 50s to mid 60s (10 to
15 degrees above normal), then they will warm into the mid 60s to
mid 70s (20 to 25 degrees above normal, and possibly record
highs). Conditions will change Friday night into Saturday with the
approach and passage of a shortwave trough/Pacific cold front
system. The system will initially bring an increasing chance of
showers to the western mountains Friday night, then to the
remainder of north central and southwest Montana on Saturday.
Temperatures will also cool back down into the mid 50s to mid 60s.
However, the greater impact will be due to increasing winds. Winds
will increase initially along the Rocky Mountain Front and
adjacent plains ahead of the cold front Friday night, then winds
will increase out of the west across the remainder of the area on
Saturday with the passage of the front and the mixing down of 45
to 55 kt winds aloft. Winds will mostly be in the 20 to 30 mph
range on Saturday, with gusts reaching 45 mph over the plains.
However, the pressure gradient with the front will be strongest
along the Rocky Mountain Front and out along the Hi-Line to the
Sweet Grass Hills. Wind gusts there could mostly exceed 60 mph at
times, with gusts over 70 mph possible along the Rocky Mountain
Front. Have therefore issued a High Wind Watch for that area for
late Friday night through early Saturday evening. Will continue to
monitor the situation for possible expansion of the Watch.
Saturday Night through Thursday...Period begins with high pressure
ridging redeveloping over the northern Rockies. Swaths of moisture
crossing through the top of the ridge will bring scattered cloud
cover, but no precipitation is expected from Sun thru Mon night.
Forecast models continue to indicate arrival of a quick-moving
shortwave trof on Tues that will produce areas of light valley
rain/mtn snow on Tue aftn/eve. Lower elevation sites along the
Rocky Mtn Front and parts of the Hi-Line and southwest MT could
see some rain/snow mix or light snow Tues night as colder air
mixes with waning moisture before the system moves off into
eastern MT. Central and Hi-Line counties could also see a period
of strong, gusty winds on Tues with the trof`s passage, resulting
from both mixing of 60 mph winds aloft and a sufficiently tight
surface pressure gradient. Models are in general agreement that
cool, moist northwest flow aloft will persist during the latter
half of the week with another Pacific shortwave trof coming into
the state on Thurs, accompanied by a mix of light rain/snow.
VFR conditions are generally expected across the region through at
least 12Z Friday. A moist northwesterly flow aloft will continue to
bring mid and high level cloudiness to the area through the day
today. Scattered showers in the mountains will decrease throughout
the day, bringing a chance of MVFR ceilings to KHLN and KBZN this
morning. Gusty west winds will also strengthen across the area
today, especially over the plains. Clouds and winds will decrease
after 00Z as high pressure aloft builds into the area.
On Friday, dry conditions (afternoon humidities in the 15 to 25
percent range) with near record high temperatures (mostly mid 60s
to mid 70s) and gusty winds (especially along the Rocky Mountain
Front) will heighten fire weather concerns. However, winds will
likely not be strong enough to warrant a Fire Weather Watch at
this time. The passage of a cold front on Saturday will cause
winds to become quite strong across most of the area (again,
especially along the Rocky Mountain Front), but cooler and more
moist air with a chance for showers will keep humidities above 20
percent. Regardless, both of these periods will continue to be
monitored for potential fire weather highlights.
.PRELIMINARY POINT TEMPS/POPS...
GTF 63 42 74 44 / 0 0 0 0
CTB 62 41 71 45 / 0 0 0 10
HLN 63 41 73 42 / 10 0 0 10
BZN 63 33 72 36 / 10 10 0 0
WEY 50 24 58 29 / 10 10 0 0
DLN 62 38 71 41 / 0 0 0 0
HVR 67 36 75 40 / 10 0 0 0
LWT 61 41 73 44 / 10 10 0 0
HIGH WIND WATCH from late Friday night through Saturday evening
Eastern Glacier...Liberty...Northern Rocky Mountain Front...
Southern Rocky Mountain Front...Toole.