Area Forecast Discussion
Issued by NWS Great Falls, MT

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS65 KTFX 260930

Area Forecast Discussion
National Weather Service Great Falls MT
330 AM MDT Wed Oct 26 2016


Today through Friday...Area remains beneath anti-cyclonically curved
west/southwest flow aloft as a broad upper level ridge over the
region gradually progresses eastward through late this week as
several shortwave disturbances eject out of the eastern Pacific
trough and over the upper ridge. Weak embedded shortwave energy is
lifting NE across ID/NW MT this morning with an area of light rain
showers primarily expected to affect western portions of central
and N-central this morning as the disturbances moves by. Next
round of energy to lift out of the Pacific trough will move into
the Pacific NW tonight with additional energy following on
Thursday. This energy will flatten the ridge somewhat and also aid
in the development of the lee-side trough/low along the MT/AB
border on Thursday which shifts east across the Canadian Prairies
Thursday night. Development of the surface low and increasing SW
flow aloft will bring increasing winds to the forecast area
Thursday with many locations seeing gusts in the 35-45 mph range
with higher gusts likely along the immediate Rocky Mtn Front. A
Pacific front will also shift east across the region late
Thursday with widespread precipitation primarily confined to the
mtns of western and SW MT with just a few showers possible as the
front progresses east across central MT Thursday evening. A cooler
airmass from Canada moves south behind the low moving east across
the Canadian prairies Friday, shifting winds to the north by
Friday afternoon across much of the forecast area. Shortwave
energy moving through the base of the eastern Pacific trough near
140W this morning will swing into CA and the Great Basin early
Friday, reaching southern ID by Friday afternoon. Models have come
into better agreement on the timing and location of precipitation
in advance of this feature with widespread rain likely to reach as
far north as the I90 corridor by Friday afternoon. Hoenisch

Friday Night through Wednesday...A rather unusual pattern evolves
over the region Friday night and Saturday. While heights rise with
an amplifying ridge over the Canadian Rockies, a shortwave trough
lifts through the Great Basin and cuts under the ridge through
Southwest Montana. Model solutions have reached a general consensus
on this feature, so have raised to categorical POPs Friday night
for the southwest, with only slight-chance for the North-central
plains. Rainfall amounts range from around one-quarter inch in the
southwest valleys to near one inch over the southwest mountains.
Snow levels remain above around 8000 feet, with a few inches of snow
possible on the higher summits and no snow-related impacts on area
roads. This wave clears to the east by Saturday afternoon, with
mostly cloudy but generally dry and mild conditions prevailing
through Sunday. The next weather system crosses Oregon and Idaho
Sunday night, producing periods or rain over our forecast area early
Monday. This is a broad and disorganized system, so will seek to
refine timing and spatial coverage of rainfall with subsequent
forecast updates. Although cooler with seasonal temperatures, the
westerly flow pattern remains relatively mild so do not
anticipate winter weather impacts. Weak ridging, or at least a
confluent flow aloft produces generally drier and mild conditions
Tuesday and Wednesday. PN


.AVIATION...Updated 0445Z.

Moist southwest flow aloft will continue over Central and Southwest
Montana through Wednesday. However, lower levels will remain dry
through. The next disturbance will approach the Rockies late
Wednesday but any precipitation should remain over the mountains.
VFR conditions will prevail through the next 24 hours.


GTF  63  46  68  41 /  40  10   0  20
CTB  56  39  60  36 /  40  10  10  10
HLN  65  41  66  40 /  20  10  10  20
BZN  66  41  68  43 /  20  10   0  10
WEY  54  28  57  35 /  10   0   0  30
DLN  65  38  65  41 /  10  10   0  10
HVR  59  40  65  39 /  10  10  10  20
LWT  65  43  69  41 /  20  10   0  10



$$ is the U.S. government's official web portal to all federal, state and local government web resources and services.