High Wind in Montana, April 10 to 11, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1142 AM MDT Thu Apr 10 2014

Updated Aviation Forecast

.UPDATE...
No significant changes to the forecast this morning. Have
continued the Flood Watch through Friday evening due to
temperatures remaining above seasonal values ahead of the cold
front that will move into the area late Friday and Early Saturday.

&&

.AVIATION...
UPDATED 1800Z.
A relatively dry NW flow aloft will continue through Friday
providing manly clear to partly clouds skies and VFR with just a
few periods of broken high cloudiness at times. Gusty westerly
surface winds will continue through this afternoon then diminish
some tonight. Hoenisch

&&

.HYDROLOGY...
A Flood Watch is in effect for all of north-central and southwest
Montana through Friday Evening. Recent warm temperatures have
caused snow melt at the mid to upper elevations of area mountain
ranges. Mountain fed streams and creeks will see rises with areas
of flooding possible. Some of these streams and creeks remain ice-
covered at high elevations, which could lead to the potential for
ice jam flooding. Warm temperatures are forecast to remain through
Friday.

&&

.PREV DISCUSSION...
/ISSUED 538 AM MDT Thu Apr 10 2014/
weather day across central and southwest MT today as region will
be under mostly dry northwest flow pattern aloft. Pockets of
moisture moving through the flow will be sufficient to produce
partly to mostly cloudy skies, especially along the Rocky Mtn
Front where current satellite imagery shows a chinook arch cloud
layer extending from the US/Can border near Glacier NP southward
to Helena. Despite the clouds, no precipitation is expected
through early Fri morning. Next chance for precip comes late Fri
morning into aftn, but will mainly be just scattered showers
confined to the Hiline counties as a weak upper-level trof moves
through southern Alberta/Saskatchewan. High temperatures will
remain about 7 to 10 degrees above normal, reaching the upper 50s
to mid 60s both today and tomorrow. Forecast models still in
relatively good agreement that a stronger, more moist weather
system will arrive on Sat, with initial cold front passage during
the morning/early aftn and a reinforcing shot of colder Canadian
air arriving Sat eve. Temperature forecast is a bit tricky for Sat
as accuracy will depend on the timing of the frontal passage. With
an expected earlier passage over areas from Great Falls northward,
high temps should only reach the mid 30s to low 40s there. Further
south, areas around Helena/Bozeman/Dillon should make it to upper
40s to mid 50s before the front arrives in the aftn. The cooling
temps will combine with widespread moisture to generate periods of
light rain, rain/snow mix, and light snow through Sat eve. Snow
accumulations look to be one inch or less over the valleys and
plains, with 3 to 7 inches in the mtns.
Waranauskas

Saturday night through Thursday...Medium range models are in better
overall agreement than previous days with the overall pattern trend
through the period. As the upper level trough of low pressure
deepens over the northern and central Rockies Saturday night, the
associated energy combined with the northerly upslope flow and
frontogenetic forcing will keep snow over most of western and
southern Montana. Have therefore increased the mention of snow to
reflect this. A few showers will linger across these mountain areas
into the day on Sunday due to the northwesterly flow aloft left in
the wake of the trough passage. An upper level ridge of high
pressure will then move over the Rockies for Sunday night and
Monday, for drier conditions and temperatures a few degrees warmer
than seasonal averages. The forecast models indicate differing
details regarding the weather pattern after Monday, but the overall
trend is that a broad upper level trough of low pressure will
gradually move into the area. Have therefore raised the chances for
precipitation to above seasonal climatology by Tuesday to indicate
an unsettled weather pattern. The models also indicate that a cooler
airmass will move into the area after Tuesday with this trough, so
have kept temperatures about 5 to 10 degrees below normal to reflect
this. There is little indication at this point of either
exceptionally cold conditions or significant precipitation, but the
situation will continue to be monitored for potential changes.
Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  60  36  63  35 /   0   0  10  50
CTB  57  36  59  28 /   0  10  30  60
HLN  62  38  67  38 /   0   0  10  30
BZN  61  33  67  35 /   0   0  10  20
WEY  53  29  56  33 /  10   0  10  10
DLN  60  34  66  36 /   0   0  10  10
HVR  62  35  64  35 /   0   0  20  60
LWT  57  32  61  34 /   0   0  20  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH through Friday evening Beaverhead...Blaine...
Broadwater...Cascade...Central and Southern Lewis and Clark...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...
Fergus...Gallatin...Hill...Jefferson...Judith Basin...Liberty...
Madison...Meagher...Northern Rocky Mountain Front...Southern
Rocky Mountain Front...Toole.

&&

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