Wildfire in Idaho, August 15 to 16, 2019

Area Forecast Discussion
National Weather Service Pocatello ID
152 PM MDT Thu Aug 15 2019

.DISCUSSION...A short wave pushing through the Northern Rockies
this afternoon and evening will trigger showers and isolated
thunderstorms mainly over the Island Park area to as far south as
Driggs. Further south in the Snake Plain, guidance is showing some
stronger surface winds triggered by the increased mid-level flow
coincident with the short wave. A lake wind advisory is in effect
for American Falls Reservoir through 9 pm this evening. Winds in
the upper valleys may temporarily shift northerly behind the
shortwave. Breezy conditions are expected again tomorrow as a
zonal flow sets up. This puts us in a dry and warm situation
through the weekend. Come Monday, amplification of an upstream
trough will lead to our flow becoming more southwesterly, but
long-term models are giving no hint of any monsoonal moisture
coming our way. Highs next week will be hitting the mid to upper
90s--up to 10 degrees above normal. Hinsberger

&&

.AVIATION...A trough with associated weak cold front continues to
progress across SE Idaho this afternoon. Winds have ranged from 280
in the 10-15 kt range at BYI to 250 in the 10-20 kt range at PIH and
220 in the 15kt range at IDA. Expect winds to increase 5 or so more
knots with locally higher gusts through the afternoon before
gradually diminishing to around 12kt by 03Z, then below 12kt by 06Z
tonight. At KSUN, the typical valley circulation has just been
overwhelmed by the gradient winds, and this has brought cross-runway
winds around 250 degrees to the terminal. Expect these to continue
in the 10-20kt range through around 03Z before the typical down-
valley flow re-develops. VCTS was maintained at KDIJ and KIDA, but
think the odds of seeing VCTS at IDA is very low. Maintained for
forecast continuity, because it can't be completely ruled out. Gusty
outflow winds will be possible as well, mainly at KDIJ, mainly from
23Z-03Z. Otherwise VFR conditions are expected with similar, albeit
slightly weaker winds on Friday. AD

&&

.FIRE WEATHER...A weak cold front continues to sneak eastward across
SE Idaho this afternoon. This is resulting in near critical wind and
min RH, with widespread gusts near 30 mph across 425 and 410 with min
RH expected to drop near 15%. Locally critical min RH and wind
across Desert/Lava portions of 425 and Arco Desert portions of 410
are expected. Given the small areas of these two zones that will
likely see Red Flag Conditions today, and after coordinating with
local Dispatch centers, have opted against a Red Flag for Min RH and
winds. For Friday, winds will be a bit lighter (by a couple of mph),
and min RH will be a bit lower (by 1-3% on average) and this still
results in only small portions of 425 and 410 meeting Red Flag
Criteria, and these are the same small portions as noted above. For
Saturday, breezy westerly flow is maintained, and we're forecasting
a larger area of Min RH below 15% and valley wind gusts around 30
mph, thus a Red Flag Warning may be needed for Saturday afternoon
and evening. Sunday is expected to be similarly breezy/windy and dry
as well.

By Monday, the upper-level flow begins to turn more southwesterly,
and this is expected to result in lower wind speeds across the
region. It is expected to continue to remain dry, however, and
widespread critical minimum RH is forecast. In fact, this trend is
forecast to continue through the week, with any shower or
thunderstorm chances likely not entering the picture until beyond
the end of the forecast period, possibly as early as next weekend.
Temperatures are forecast to remain above seasonable averages
through the period. The forecast can be summed up as warm and breezy
through Sunday, and hot and dry thorugh next week. AD

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory until 9 PM MDT this evening for IDZ054.

&&