Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 301126

Area Forecast Discussion
National Weather Service Great Falls MT
525 AM MDT TUE AUG 30 2016


Today through Thursday Evening...Broad high pressure ridge currently
extends from the Four Corners area north through MT and into west
central Canada.  With the ridge axis over eastern MT and little
change expected in the ridge`s position or strength over the next 48
hrs, the central and southwest counties will remain under south to
southwest flow aloft.  That translates to mostly dry conditions with
temperatures running about 15 degrees above normal (highs in the low
to mid 90s today and mid and upper 90s tomorrow. Other than the
weakening band of showers and weak thunderstorms moving through
Fergus/Hill/Blaine counties this morning, our forecast area will see
little if any precipitation today. Slightly better chance of
thunderstorms Wed aftn/eve as plume of monsoonal moisture moves
north through ID/WY and into our area. However, rainfall amounts
look to be light (generally less than 0.1 inch) with these storms.
Outflow winds gusting into the 35-45 mph range will be possible with
any storms as model soundings indicate favorable inverted-V
temp/dewpoint profiles that will enhance downdraft cooling and
outflow windspeeds. Drier conditions return for Thurs as the the
monsoonal moisture drifts toward south central and eastern MT.  Part
of the plume may still cover locations along/south of a line from
Helena to Lewistown, so have kept mention of thunder there on Thurs.

Thursday Night through Tuesday...Temperatures trend cooler than
seasonal averages throughout the Labor Day weekend. The transition
begins early Friday morning as the upstream longwave trough begins
to move into the Pacific Northwest. A surface cold front will advance
through the region on Friday, producing scattered showers or
thunderstorms and gusty northwest winds. Although confidence is high
regarding the pattern change for cooler temperatures, the
precipitation forecast remains low confidence amid diverging model
solutions. Once the initial system pulls away on Saturday, a series
of weaker waves will progress through a broad western CONUS trough.
With no clear consensus among the guidance, the forecast is informed
by climatology and a general model blend to maintain slight chances
for showers and afternoon thunderstorms throughout the period.
Backcountry travelers should be aware that snow levels over the
Northern Rockies may drop low enough to allow light snowfall on the
highest peaks through the holiday weekend. PN



VFR conditions prevail. Weak trough that brought -SHRA and a few
short-lived -TSRA through central MT overnight is now east of KHVR,
taking the remaining -SHRA along with it. High pressure ridge
remains parked over central/eastern MT, with spotty pockets of
moisture moving through southwest flow aloft to give SCT/BKN mid-
level clouds today.  Additional moisture arriving late aftn may
spark a few -TSRA near KBZN, so have continued mention of thunder
there, but no convective activity expected at other local TAF sites.


Stationary high pressure ridge will bring unseasonably warm
temperatures across the central MT fire districts through the
midweek period. Minimum humidities will drop into the teens each
aftn from today through Thurs, further drying out fuels, but
surface winds are forecast to remain at/below 15 mph each day, so
fire weather headlines are not anticipated at this time. A few
lightning starts and/or holdovers will be possible from isolated
to scattered thunderstorms (mix of wet/dry types) on Wed aftn/eve
as monsoonal moisture arrives. This moisture will also help
increase overnight humidity recoveries from the 40-50 percent
values this morning to the 50-70 percent range early Wed and Thurs
morning. Waranauskas


GTF  92  57  94  57 /   0  10  10  30
CTB  88  53  89  53 /   0  10  10  30
HLN  91  57  91  57 /   0   0  20  20
BZN  91  51  92  54 /  20  20  20  20
WEY  81  45  79  46 /  10  10  10  20
DLN  89  51  87  53 /  10  10  20  20
HVR  92  58  96  59 /  20  10  10  30
LWT  89  59  94  59 /  10   0  10  20



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