Wildfire in Idaho, September 15 to 16, 2018

Area Forecast Discussion
National Weather Service Pocatello ID
858 AM MDT Sat Sep 15 2018

.UPDATE...Updated today/tonight for issuance of Wind Advisory for
much of our southeastern zones. Recent hi-res model guidance
agrees with local diagnostic study that wind advisory criteria
will be met for portions of the southern highlands as well as some
of the Snake River Plain. Sustained winds of 25-35 mph are
expected with gusts 40-50 mph possible. This will preclude the
need for a Lake Wind Advisory for American Falls Reservoir, but
hazardous lake conditions are expected for all local lakes in the
Advisory area.
TAX

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.PREV DISCUSSION... /issued 223 AM MDT Sat Sep 15 2018/

DISCUSSION...Active weather today with strong upper-level dynamics
associated with a short wave pushing through the Intermountain West.
A cold front will also drag across southeast Idaho this afternoon
and evening, which will keep winds elevated through the day. Mid-
level wind max of 40 kts across the Southeastern Highlands may
mix to the ridgetops this afternoon. This will be along and behind
the surface cold front. Isolated afternoon and evening thunderstorms
will impact mainly the Central Idaho Mountains as well as the
Spencer/Dubois and Island Park areas later this evening. It will
be drier, and a little less breezy tomorrow while a weaker
shortwave trough moves into northern Idaho. An upper trough will
move in from the west on Wednesday, but models indicate a split in
the shortwave energy as it makes landfall. This will likely
result in dry and breezy conditions across the Snake Plain, with
thunderstorm potential north and south of the forecast area. Model
solutions diverge as we head into Friday with the GFS bringing an
upper trough through Idaho while the ECMWF suggests upper
ridging. Hinsberger

AVIATION...Frontal boundary drives across the region today,
bringing an increase in winds and a threat for thunderstorms most
areas. Best chances KSUN and northeast through central mtns toward
the Divide, but cant rule out thunder at any of the other terminals.
Will likely continue to carry VCTS and just adjust timing to fit
latest high-res model runs. Winds the main threat today with strong
mid-level jet pushing into the southern portion of the region just
ahead of frontal boundary. Sustained winds could approach 20kts
especially KBYI/KPIH late this afternoon, dropping off after 00Z but
remaining gusty through 06Z. DMH

FIRE WEATHER...Critical conditions expected to continue today.
Strongest winds likely across the Southern Sawtooth NF and the
Caribou NF, creeping into the southern portions of the Snake Plain.
Frontal boundary drives across the region mid-late afternoon,
producing wind shift to the west/northwest and remaining gusty
through the evening behind the front. Concern is the 700mb winds
which exceed 50kts just ahead of frontal boundary as it drives
through the eastern highlands this evening. Thunderstorms also add
to the mix today, though the best chances appear to be across the
Central Mtns and the Targhee NF. Cant completely rule out an
isolated storm elsewhere along the frontal boundary, given the very
strong dynamics with this system, but the limiting factor will be
the moisture availability given that the low levels are extremely
dry. Shortwave passage overnight pushes convective threat out of the
region, but Sunday could remain critical or near critical as drier
air mass arrives despite cooler temperatures - humidities look to
lower and locally windy conditions are expected to continue. Thus
fire headlines may remain in place. Next amplified trough to drive
through the region appears to arrive generally Wednesday. DMH

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 9 PM MDT this evening for
IDZ410-413-427.

Wind Advisory from noon today to 9 PM MDT this evening for
IDZ053-054-057>063.

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