Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211236

636 AM MDT Mon Jul 21 2014

Have increased the chances of rain in the area of rain that
extended from western Teton and northern Lewis and Clark counties
through eastern Pondera County and into Toole and Liberty
counties. Also increased sky cover for this morning but decreased
it in the far northwest for late this morning. Finally limited the
threat of thunderstorms for this morning to southwest Montana.


A moist southwest flow aloft will continue over the area today but
some drying could occur in the far north during the day. Unlike the
typical summer scenario of afternoon and evening showers and
thunderstorms..expect scattered showers and isolated thunderstorms
not only during the afternoon and evening but also during the
morning and late night hours as well. There will be a threat of
local MVFR/IFR conditions in heavy rain in the north this morning
and over the south this afternoon. For forecast wind groups other
than VRB ones or winds over 10 knots..confidence is low with
forecast wind directions. Blank


/ISSUED 550 AM MDT Mon Jul 21 2014/
Monday through Wednesday...A dramatic pattern change is beginning to
occur as the weather pattern shifts to a more southwesterly flow
under the influence of a large scale closed low off the Canadian
Pacific Coastal. A few shortwave disturbance being ejected from
this system will move across the area over the next few days along
with moist Pacific flow aloft. This will allow for showers and
thunderstorms to develop and move across the area. While scattered
showers can be expected during peak heating due to diurnal warming
of the surface...additional support from these upper level
intrusions will allow for strong possibly severe storms to occur
along with an increased chance for showers and thunderstorms
through the overnight hours. Every day will likely experience
scattered showers and thunderstorms.
Tuesday will have an enhanced chance for strong and severe
thunderstorms...mainly due to strong potentially damaging winds due
to dry air near the surface. By Wednesday afternoon a greater
dewpoint depression, along with warmer temperatures and steeper
lapse rates should allow for a better chance of strong damaging
winds and a slightly increased chance for a hail threat as well.
Temperatures throughout the period will remain near seasonal
values...but should generally increase with each successive day.
Precipitable water values should remain between three quarters of
an inch to a an inch throughout this time period providing ample
moisture aloft to allow for significant rainfall and potential
hail production dependent on cape amounts through the hail growth
zone. Suk

Wednesday night through Monday...Wednesday evening a weather
disturbance aloft will be moving northeast through the area. This
disturbance is ahead of an upper low that will move into Washington
or far southern B.C. Wednesday night. Although models differ on
details of the precipitation associated with the disturbance have
increased the chances of precipitation especially towards the
Canadian border. Precipitation will come in the form of showers and
thunderstorms and there could be a risk of strong thunderstorms
early in the evening. Thursday afternoon and evening the remnants of
the upper low will swing through the forecast area. Increased low
level downslope could limit the threat of precipitation over the
lower elevations during that time frame. Thursday the flow aloft
should be strong enough for a chance of high winds over Logan Pass
with a small chance elsewhere over the Rocky Mountain Front. Behind
the upper trough a dry airmass will move over the forecast area.
Over the weekend models are on the same page in developing a strong
upper ridge over the western U.S. which could further intensify on
Monday. The upper ridge will result in warming temperatures. It
should also result in no precipitation at least through Sunday.


GTF  81  58  84  61 /  50  30  40  30
CTB  79  51  80  55 /  40  10  50  30
HLN  83  59  88  60 /  60  40  40  40
BZN  82  53  86  52 /  70  50  40  30
WEY  70  40  78  42 /  70  50  30  10
DLN  79  52  82  53 /  70  50  50  30
HVR  83  55  88  59 /  60  10  30  30
LWT  82  57  87  58 /  50  40  40  30



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