Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 220333

Area Forecast Discussion
National Weather Service Great Falls MT
933 PM MDT Mon Aug 21 2017


Upper level ridge contiues to build into the Northern Rockies
this evening with some high level moisture/cloud-cover spilling
over the ridge axis and tracking SE across central MT. Surface
high pressure extending from the Canadian Prairies south across
eastern MT and ND will maintain generally light surface winds
through tonight and this combined with a dry airmass will allow
for good cooling overnight. Hoenisch



Upper level ridging will build into the Northern Rockies through
Wednesday, which will bring warm and dry conditions to all of
North Central and Southwest Montana. The warmest day for the
month of August thus far could occur on Wednesday, with high
temperatures reaching into the low to upper 90s.


Updated 2327Z.

VFR conditions are expected at most, if not all, terminals through
Tuesday as an upper level ridge builds in. The only exception may be
KHLN/KEKS/KBZN where wildfire smoke may cause reductions in VIS at
times, possibly as low as MVFR. For now, confidence in reduced VIS
is highest at KBZN and I kept FU/smoke in the TAF there through
tonight. MARTIN



Fire weather concerns heighten as this week progresses with
increasingly hot and dry conditions though Wednesday as an upper
level ridge of high pressure builds over the Northern Rockies. As
temperatures rise to well above seasonal averages Wednesday,
afternoon, humidity will lower to the low teens with potentially
some single digit humidity readings Wednesday afternoon. In
addition, overnight humidity recovery at mid-slopes to ridgetops
will become increasingly poor each night through Wednesday night.
An upper level trough of low pressure moving into British Columbia
Thursday will bring an increasing flow aloft from the SW and
potential for thunderstorms, followed by a likely cold front
passage late Thursday and cooler but continued dry and
potentially windy conditions Thursday night into Friday. This
situation will be monitored closely over the next several days
with possible impacts from the critically hot and dry conditions
mid-week, followed by the potential for new lightning ignitions
Thursday and gusty winds Friday. Hoenisch


/ISSUED 527 PM MDT Mon Aug 21 2017/

Tonight through Wednesday...H500 ridging will build into the
Northern Rockies and Northern High Plains throughout the period.
High temperatures are expected to warm significantly over this
period, as 1000-500mb thickness values climb to around
575-580dam. At this time the warmest day appears to be on
Wednesday, however, high temperatures on Tuesday will still be
some 5 to 10 degrees above normal. For the day on Wednesday,
temperatures are currently expected to rise into the mid to upper
90s across North Central Montana, with the mid-80s to near 90
degrees across Southwest Montana. This would make Wednesday the
warmest day of the month thus far. Very dry conditions are also
expected through Wednesday, with poor relative humidity recovery
during the overnight hours, especially at midslope locations.
Afternoon relative humidity values are expected to easily fall
below critical values on Tuesday and Wednesday, with values
possibly falling below 10 percent at some locations on Wednesday.
While critical relative humidity values are expected on Tuesday
and Wednesday, winds do appear to be light at around 5 to 10 mph.
- Moldan

Wednesday Night through Monday...Period begins with an upper-
level trough digging southward and eastward from British Columbia
Wednesday night into Thursday. In addition, a Pacific cold front
accompanying this trough should sweep eastward over the CWA on
Thursday. Isolated to scattered showers and thunderstorms are
expected, especially Thursday afternoon and evening, when some
storms may be strong. The aforementioned upper trough looks to
continue digging over our region through Friday morning.
Thereafter, the trough should begin lifting northeastward Friday
afternoon as high pressure aloft builds-in from the south and
west. Accordingly, the potential and coverage of showers and
thunderstorms should dwindle on Friday. Drier weather is then
expected during the upcoming weekend and next week Monday as the
aforementioned high pressure ridge aloft continues building over
the area. Sightly above- normal temperatures on Thursday (e.g.
highs in the mid to upper 80`s for most) will be followed by a
cooler day on Friday, when the CWA will reside in a post-frontal
environment. On Friday, readings are expected to be several
degrees below-normal (e.g. highs generally in the mid 70`s to
near 80 degrees). Temperatures are then expected to rebound to
near or slightly above-normal this weekend through Monday of next
week.  Jaszka


GTF  50  91  54  94 /   0   0   0   0
CTB  46  89  50  91 /   0   0   0   0
HLN  51  91  55  90 /   0   0   0  10
BZN  44  90  48  89 /   0   0   0  10
WEY  36  79  40  77 /   0   0   0  20
DLN  45  88  50  86 /   0   0   0  10
HVR  49  92  51  94 /   0   0   0   0
LWT  48  87  52  90 /   0   0   0   0



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