Area Forecast Discussion
Issued by NWS Great Falls, MT
FXUS65 KTFX 281034
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
434 AM MDT Thu Aug 28 2014
Zonal flow has lead to a nice mild night across the region. Temp at
GTF was still at 60 F as of 1000Z/Thursday. WV imagery over the
Gulf of Alaska and E Pacific Ocean shows a vorticity max near 47 N
135 W moving eastward. Upstream of this feature, a large wrapped-up
cyclone and expansive trough, with an impressive cold frontal cloud
band, was making steady progress to the southeast. The first
disturbance will bring sct showers to the area tonight. By Friday
night...the large trough will reach Montana and signal a change to
below normal temps.
Today...Breezy SW winds will develop with gusts over 25 mph at
times. The tail end of an upper jet will brush north-central MT
tonight and a 500 mb vort max will traverse through MT from west to
east. These features should produce some showers into early Friday
morning. In concert with these mid/upper level disturbances, a
low-level cold front, albeit a weak one, will slide through
north-central MT. The NAM has MUCAPE values up to 1 K J/kg pooled
along the boundary. Therefore, there is a chance for thunder too.
Friday...Quiet weather is forecast with the exception of a few
isolated showers/storms over the far Southwest and possibly near the
Little Belt and Snowy Mountains. Highs will still be near 80 F.
Saturday...Models are in agreement with mid and upper dynamics
moving across the N Rockies early Saturday morning into the aftn.
300 mb divergence will overspread the region as a strong jet exit
region dives through Idaho. A defined area of 700 mb frontogenesis
will also pass through during the morning...and linger into the
aftn over the Southwest. Went with a blended QPF approach which
painted 0.10 to 0.20 inch amounts south and east of a HLN-to-LWT
line. Areas that receive heavier showers may accumulate over 0.25
Saturday Night through Thursday...This period begins with scattered
showers behind the cold front lingering mainly over the southwest
counties and over toward Lewistown. Slightly unstable conditions,
coupled with northwest flow aloft and residual moisture will also
produce isolated showers on Sunday along the Rocky Mtn Front and
over the southwest mountain ranges. A weak shortwave trof will move
quickly through our forecast area on Mon, bringing a fair amount of
cloud cover, but GFS and ECMWF models disagree on whether we`ll
actually see precipitation with the trof, so have kept just a slight
chance for showers from around Harlem to Dillon on Mon aftn/eve.
Tuesday and most of Wednesday looking dry at all locations as weak
high pressure ridging tracks through the state. By Wed night, the
next shortwave trof reaches central WA/OR and pushes a sharp cold
front east of the Continental Divide. Widespread showers are
expected along/ahead of the front early Thurs morning and then
additional rainfall develops with the passage of the trof axis Thurs
night. Current model runs are indicating rainfall amounts of a
tenth to one-half inch from the nighttime precipitation.
Temperatures remaining cooler than normal through the period.
Quiet conditions are expected tonight with light and variable winds.
Southwest winds will increase and become breezy by midday Thursday
as a shortwave trough and surface cold front begin to push into the
Northern Rockies. An isolated afternoon/evening thunderstorm is
possible at KHLN and KBZN and have added VCSH to the TAF. The
surface cold front is expected to cross the International Border
between 20z and 00z with showers developing along and behind the
front. Overall, VFR conditions are expected for the next 24 hours.
Though forecast confidence is low, brief periods of MVFR conditions
are possible after 03z on Friday. MLV
.PRELIMINARY POINT TEMPS/POPS...
GTF 85 54 80 54 / 10 20 10 10
CTB 80 50 79 53 / 10 20 10 10
HLN 87 54 83 54 / 0 20 10 20
BZN 85 47 81 49 / 0 30 20 20
WEY 72 39 71 41 / 10 20 20 20
DLN 82 49 80 51 / 0 20 10 20
HVR 85 52 79 55 / 10 20 20 10
LWT 84 53 77 53 / 10 20 20 10