Area Forecast Discussion
Issued by NWS Great Falls, MT
FXUS65 KTFX 251055
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
454 AM MDT Mon Aug 25 2014
WV imagery at ~0930Z/Monday shows a very large upper-level low
centered over the North Dakota/Manitoba border. The influence from
this weather system will continue to lessen as it moves
northeastward. Increasing cloud top temps within the comma-
head/TROWAL, supports rapid weakening/filling. Thus, conditions
will improve over the next few days with warmer temps, clearing
skies, and mainly dry conditions.
One caveat is a chance for showers/storms over far SW Montana
today as a southerly low to mid-level flow advects moisture into
the region. Upper forcing for ascent was hard to find with only
weak cyclonic vorticity advection noted. However, daytime heating
should lead to some sct showers and isolated t`storms over the
mountains of Beaverhead, Madison, and Gallatin Counties. MUCAPE
will stay below 1 K J/kg.
Tonight...Patchy areas of dense fog may develop near river valleys
and in mountain valleys tonight into Tuesday morning...in response
to clearing skies and near-sfc residual moisture.
Tuesday and Wednesday...Mid-level flow becomes zonal between a
strong jet across central Canada and a cut-off upper-low over the
Four Corners. SREF 1000-500 mb thicknesses rise to ~576 dam by
Wednesday...700 mb temps increase from near 2 C today...up to 8 C
by Wednesday aftn. Deep daytime mixing to above 700 mb coupled
with full solar insolation should produce mid 80s F on Wednesday.
Wednesday night through Monday...A disturbance will move across
British Columbia and Alberta and keep Central Montana under the
influence of a rather flat ridge Wednesday night and Thursday. The
air mass will warm and little effect should come from the
disturbance aloft. Heights aloft will build Thursday night as the
disturbance moves east and an upper level ridge will be over the
Rockies by Friday. This ridge will move east of the zones by
Saturday and allow moisture to move across into the zones. A low
pressure trof will approach the West Coast and, with heights falling
aloft and the increased moisture, the air mass will become a bit
unstable. The trof will move over the Pacific Northwest Saturday
night and keep the air mass over Central Montana unsettled. This
trof will also develop a low pressure low over Alberta and
Saskatchewan, thus tightening the surface pressure gradient across
the Rockies and adjacent plains. Some breezy conditions will
develop. The trof will remain over the region through Monday night
and keep unsettled conditions and a chance of precipitation in the
An upper level low pressure system is slowly moving
east and radar indicates precipitation across the region has ended.
A disturbance will move through the Pacific Northwest today and into
Nevada tonight. This will keep cause a slight chance for
precipitation across Southwest Montana tonight. Local MVFR
conditions are possible near precipitation but elsewhere VFR
conditions will prevail through then next 24 hours.
.PRELIMINARY POINT TEMPS/POPS...
GTF 67 46 77 51 / 10 10 0 0
CTB 69 43 78 50 / 10 10 0 0
HLN 72 48 79 53 / 10 10 0 0
BZN 70 43 75 46 / 20 10 10 0
WEY 64 37 67 39 / 50 50 10 10
DLN 68 46 74 48 / 20 20 10 0
HVR 67 43 78 52 / 10 0 0 0
LWT 64 45 74 53 / 20 10 0 0
URBAN AND SMALL STREAM FLOOD ADVISORY...into this afternoon for
Fergus and Judith Basin Counties.