Wildfire in Idaho, July 2 to 3, 2019

Area Forecast Discussion
National Weather Service Pocatello ID
301 AM MDT Tue Jul 2 2019

.SHORT TERM...Through Friday. A broad low pressure trough remains
off of the PacNW coast at this hour. This trough remains on track
to begin its inland trek by late today -- eventually crossing SE
Idaho on July 4th while simultaneously weakening. This will
maintain a persistent SW flow regime through midweek. As is
typically the case in these SW flow regimes, embedded disturbances
within the flow combine with just enough moisture, instability and
orographic influences to produce the occasional
isolated/scattered shower/thunderstorm activity. The challenge is
accurately depicting the timing and location of any activity, as
the majority of models are suffering from run-to-run and model-to-
model consistency, resulting in a low confidence forecast, mainly
with respect to precipitation timing and placement. One thing we
can say with a decent level of confidence is that as the trough
approaches, precipitation potential will increase across the
Central Mountains and Continental Divide region, and this should
be especially true on Wednesday afternoon/evening. Backing up a
bit, shower and thunderstorm chances today are a bit less, but we
could see some activity in the higher terrain areas just
south/east of the I-15/86 corridors once again.

On July 4th, a surface boundary remains on track to cross the
region, and this will aid in enhancing shower and thunderstorm
activity. Guidance still has yet to converge on a consistent
solution, but there are a couple of trends emerging. One is a more
consistent timing/location of the attendant trough's propagation,
and another trend is a band of precipitation in association with
the frontal passage that should develop Wednesday night along/east
of the I-15/86 corridors extending NE towards the Teton Valley.
This activity is then forecast to exit the region by early
afternoon before isolated showers develop mainly along/near the
WY/MT border areas. More early-morning convection may result in
less precipitation later in the day and vice-versa.

An uptick in winds is expected on Wednesday and Thursday in
association with the trough/surface boundary passage. Winds will
be strongest during the afternoon/early evening hours each day and
strongest across the Arco Desert, with 15-25 mph winds common. For
the sunset hours Thursday, winds may be close to 15 mph for many
areas along/near the Interstate corridor, but should be gradually
decreasing through the evening. Wind trends will be monitored
closely over the next couple of forecast cycles. Temperatures are
forecast to fall back below seasonal averages on Wednesday and
continue below average on the 4th. AD

.LONG TERM...Saturday through next Tuesday. Another area of low
pressure is forecast to take up residence across the PacNW on
Friday and is forecast to slowly track towards our region by early
next week. This is nearly a repeat pattern to the pattern we're in
now, which features the broad SW flow, seasonable temperatures
and embedded disturbances resulting in occasional precipitation
that will be difficult to pin down in terms of location/timing. In
this pattern, the first 90-degree temperatures of the season may
be reached across the southern Snake Plain/eastern Magic Valley
over the weekend. AD

&&

.AVIATION...Weak impulses continue to eject northeast across East
Idaho. There is just enough moisture and with plenty of sunshine
during the day, just enough instability to be able to fire some
convection across the region. Models are inconsistent with
convective production so terminal forecasts will remain a mix of
persistence and short term high-res solutions. Not a lot of
confidence in any particular direction for any of the sites. Outside
of the impact of potential TS, VFR conditions expected with bump in
winds during the afternoon into the 10-15kt range. DMH

&&

.FIRE WEATHER...Upper low remains centered along the PacNW coast,
and is still projected to shift across Idaho later this week. In the
meantime, weak impulses continue to rotate around the low. There is
plenty of daytime instability available for storms to develop. Just
not enough confidence to try to pick out day to day where the best
chances are going to be. Wednesday and Thursday appear to have the
most widespread threat for thunderstorms across the region. Passage
of the upper trough still appears to be Thursday (Independence Day),
along with continued potential for gusty afternoon winds. Frontal
boundary is not as defined so uptick in winds has trended downwards
slightly, along with a weaker cooling trend. DMH

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&