Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 151518
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
918 AM MDT Sat Jul 15 2017

.UPDATE...

Satellite shows a weak feature that is producing a few showers
near and along the wyoming border this morning. Updated forecast
to account for showers near the border this morning and into the
afternoon.

Valle

&&

.PREV DISCUSSION... /issued 324 AM MDT Sat Jul 15 2017/

DISCUSSION...Through this weekend. SE Idaho will remain firmly
entrenched beneath the fringes of a strong high pressure system
centered over the Great Basin through today. On Sunday,
developing low pressure will swing through central British
Columbia and Alberta, which will flatten the high pressure ridge
and send a weak cold front across our region. Now for some
details: A weak disturbance is rotating NE across our area this
morning, firing off showers and isolated thunderstorms along the
Montana border. By mid-afternoon, shower and thunderstorm activity
will become more active, particularly across higher terrain areas.
The Sawtooths/Pashimeroi and surrounding Central Mountain region
will see scattered thunderstorm coverage at times, and combined
with critical fuels in the valleys a Red Flag Warning has been
issued for these areas. Can`t rule out shower and thunderstorm
activity across the Snake Plain and Eastern Magic valley, although
the most widespread coverage should remain confined to the
mountains. Any Thunderstorm will be capable of producing strong,
gusty winds. Activity should gradually move eastward and/or
diminish after midnight. For Sunday, a frontal zone will take up
residence across SE Idaho, and this will provide a focus for
additional shower and thunderstorm activity, which is forecast to
develop during the morning and become more numerous by afternoon.
Activity should be mainly confined to areas along and east of the
Snake Plain. After another hot day Saturday, enough cloud cover
and a slight intrusion of cooler air behind the cold front may
prove enough to end the 90 degree stretch at Pocatello. We`re
currently forecasting a high in the upper 80s to near 90. With the
cold front, SW winds may become a bit breezy on Sunday, creating
chop on area bodies of water. This will require monitoring for a
potential Lake Wind Advisory, but will hold off for now as most
(but not all) guidance suggests winds will remain below the
threshold outside of shower and thunderstorm outflow.

Monday through next Saturday. The slight cooldown will be short-
lived as the ridge of high pressure rebounds early in the week,
with SE Idaho expected to once again reside on the northwest
fringes of this circulation. Thus, temperatures will rise a couple
of degrees both Monday and Tuesday, peaking on Wednesday before
Monsoonal moisture once again makes a return into SE Idaho. High
temperatures should be well into the 90s most of the week once
again across the Snake Plain, Eastern Magic Valley and Southern
Highland Valleys. Dry conditions expected Monday and Tuesday with
a chance for isolated showers and thunderstorms focused on the SE
corner of the state through the end of the week. AD/Hedges

AVIATION...Aviation forecast dominated today by broken record syndrome.
Increasing monsoonal moisture, interacting with hot/unstable air,
and using the higher terrain as a primary trigger/lifting mechanism,
will spark isolated t-storms again this afternoon and eve. Will
initiate VCTS at 20Z for KBYI/KSUN/KDIJ due to proximity to the
mntns. Will add KPIH/KIDA an hour or two later as best VCTS
potential across the Snake Plain will wait for outflow boundaries as
a source of lift. Overall coverage may be just a bit greater
compared to yesterday as a disturbance/weak cold front crosses the
region. Once again, greatest threat to aviation will not be MVFR/IFR
conditions, but gusty and erratic outflow winds of 35-55 MPH with
stronger cells. Sun forecast almost identical, except t-storm threat
looks to shift SE, which may keep KSUN dry. -KSmith/Hedges

FIRE WEATHER...An upper ridge to the east of Idaho is resulting in
southwest flow pulling monsoon moisture into the area. Scattered
thunderstorms are expected to develop this afternoon and early
evening across the eastern Magic Valley...southern highlands...and
the central Idaho mountains. These thunderstorms may produce gusty
outflow winds and mainly light rainfall amounts. This has prompted a
Red Flag Warning for 425 and 427...and lower elevations of
422...475...and 476. Mainly isolated thunderstorms expected
elsewhere. Scattered thunderstorm activity shifts eastward on
Sunday...mainly along the Divide and the WY border. Temperatures
fall back a few degrees on Sunday...but rise back up next week.
Afternoon humidity readings run in the mid to upper teens today and
Sunday...but run lower next week. Hedges

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 2 PM this afternoon to 10 PM MDT this
evening for IDZ422-425-427-475.

&&

$$


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