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000
FXUS65 KTFX 162059
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
259 PM MDT Sun Jun 16 2013

.DISCUSSION...

Tonight through Tuesday night...Central Montana will be underneath a
high pressure ridge tonight and Monday. A low pressure system over
the Eastern Pacific will be approaching the West Coast Monday and
the effects of this system should start to affect the Northern
Rockies by late afternoon. The airmass will still be rather dry and
most convection will likely begin over the mountains and move
northeast. Neither CAPE nor shear is particularly strong, however,
together some severe thunderstorms are possible. South to southeast
low-level flow will strengthen Monday night and should help moisten
lower layers across the central and northern zones...dewpoints
should be rising late Monday night through Tuesday. The upper level
low pressure center to the west will move over the West Coast late
Tuesday. Moist, unsettled southwest flow ahead of this system will
move over western and central Montana. Instability will increase
during the afternoon with CAPE values in excess of 4000 forecasted
across the central zones. Convective temperatures will be rather
high to the east and convection will generally begin to the west
over the Rockies. A cold front will move through the Rockies by
late afternoon and add some lift to the airmass. This front will
bring increased shear into a very unstable environment as it moves
east during the evening. This will be a wet system with periods of
heavy rain and large hail lasting well into the evening.

Wednesday through Sunday...The medium range will be
influenced by southwest flow aloft as a closed upper low will
push into the Pacific Northwest and move slowly north and east
across southern Canada through the period. Southwest flow aloft
ahead of the low on Wednesday will pull moisture across the
eastern and northern portion of the county warning area resulting
in widespread afternoon thunderstorms. CAPE values Wednesday
afternoon approach 4000 J/kg across the eastern Hi-Line,
resulting in the possibility of strong thunderstorms. Scattered
showers and thunderstorms will continue through the week though
models indicate available moisture will slowly decreases allowing
for areal coverage and intensity of these storms will diminish as
the weekend approaches. By Sunday, the upper low moves to western
Saskatchewan and convective activity becomes isolated over the
area. Temperatures will be generally near to slightly below
seasonal averages.

&&

.AVIATION...
Updated 1800Z.
High pressure will continue to provide dry and warm conditions.
The airmass will destabilize somewhat after 18z with isolated
showers and thunderstorms possible mainly near Southwest Montana
mountains. Winds will remain light. VFR conditions prevail with MVFR
conditions possible in the vicinity of showers and thunderstorms.

&&

.HYDROLOGY...
A point flood warning remains in effect for the Big Sandy Creek
near Havre. A few showers and thunderstorms are possible Monday
and Tuesday of this week, but they should not impact the river
level there significantly. The level should very gradually
decrease through the early part of the week, but it is expected to
remain above flood stage.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  44  80  52  85 /   0  10  30  30
CTB  43  79  49  82 /  20  20  30  40
HLN  48  82  52  86 /  10  20  30  50
BZN  42  81  46  86 /  10  20  20  40
WEY  36  75  39  78 /  20  20  20  30
DLN  45  81  48  84 /  20  20  30  40
HVR  46  81  53  88 /   0  10  10  10
LWT  45  76  50  83 /  20  10  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flood warning continues for Big Sandy Creek near Havre until
further notice.

&&

$$


weather.gov/greatfalls