Office: BOI
FXUS65 KBOI 201537
AFDBOI
Area Forecast Discussion
National Weather Service Boise ID
937 AM MDT Mon Aug 20 2018
.DISCUSSION...Showers and storm continue across the southeast and
northwest corners of our CWA. The activity in the southeast will
push off to the east and out of the area around noon, while the
activity in the northwest is expected to move east and intensify
this afternoon. SPC has far eastern Valley County in the
"marginal" category for severe storms today. The main threats
will be winds near 60 mph and possibly hail to 1 inch. Brief heavy
rain is likely with these storms. Northwest winds will be
moderate from Baker County into the Treasure and Magic Valleys
this afternoon into this evening. Smoke was becoming worse behind
a cold front that was slowly working its way through the CWA, with
visibilities down as low as 2 1/2 miles at Nampa at this time. It
is expected to stay bad through the day and into the night over
most of the area. A small update was done earlier this morning to
account for current location of showers/storms.
&&
.AVIATION...MVFR to IFR conditions in wildfire smoke. Isolated to
scattered showers and thunderstorms north of KBNO-KSNT today, and
SE of KMUO this morning. Surface winds: generally north-
northwest 10-20kt with afternoon gusts to 30kt near KBOI-KMUO.
Winds aloft near 10 KFT MSL: generally north-northwest 10-20kt,
except southwest 15- 25kt near KTWF-KJER this morning.
&&
.PREV DISCUSSION...
SHORT TERM...Today through Tuesday...An upper low was supporting
scattered showers and isolated thunderstorms in northeast Oregon
and in the West Central Mountains early this morning. The
activity is expected to continue and expand eastward with an
increase in coverage through the afternoon. The bulk of the
convection will occur near the center of the low, which includes
the Boise Mountains and West Central Mountains. Some of the storms
may be strong, capable of producing hail, heavy rain, and strong
winds. A cold front accompanying the low will move southeastward
across the area today. Breezy northwest winds will develop this
afternoon behind the front. The upper low will weaken tonight and
Tuesday, but will hang over the area resulting in a slight chance
of showers and afternoon thunderstorms, mainly near the Nevada
border and across the northern high terrain. The breezy northwest
winds today will diminish late this evening with lighter winds
expected on Tuesday. Temperatures will trend cooler - toward
normal on Tuesday.
LONG TERM...Tuesday night through Monday...The upper level
trough is slowly pushing out to start the period leaving lingering
showers and thunderstorm threats to the area for Wednesday. A
mild, zonal pattern sets up for the start of the weekend ahead of
our next weather system. Models have been in fairly good agreement
the past two days with the next trough digging well south Sunday
and associated precipitation making its way into SE Oregon by
early Monday morning. Both the ECMWF and GFS have a fairly well
defined precipitation band pushing through our CWA with this
system which, if it holds together, will bring much needed/wanted
precipitation to the valleys. However, with this system comes more
instability and afternoon thunderstorm threats. Temperature
forecasts for Monday are indicating almost 10 degrees below normal
on some models.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Red Flag Warning until 8 PM MDT this evening IDZ420-424-426.
Red Flag Warning until 9 PM MDT this evening IDZ401>403-421.
OR...None.
&&
$$
www.weather.gov/Boise
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DISCUSSION...SP
AVIATION.....KA
PREV SHORT TERM...BW
PREV LONG TERM....JC
Office: PIH
FXUS65 KPIH 200931
AFDPIH
Area Forecast Discussion
National Weather Service Pocatello ID
331 AM MDT Mon Aug 20 2018
.SHORT TERM...Today through Wednesday
Active weather is expected today as a strong low pressure system
brings showers and thunderstorms back to the area. Ongoing
convection in eastern Oregon will slide into central Idaho this
morning along a focused mid-level frontal boundary. Activity will
blossom under strong warming and increasing westerly flow setting
up divergence in the upper-levels. While showers and
thunderstorms are possible across most locations, the focus will
reside along the aforementioned frontal boundary in the central
mountains. The latest HRRR and RAP depict strong outflow
propagation from this convection, which seems prudent given the
punch of dry air progged at 500mb and DCAPE values into the
~1500J/kg ballpark. Will keep gusty thunderstorm wind mention in
the forecast for the area roughly outlined by the coinciding
Marginal risk from SPC.
Elsewhere, isolated strong thunderstorms are possible, but
coverage will be lower. Steep lapse rates this afternoon could
allow mixing to near 600mb in the lower Snake Plain, leading to
dry and gusty conditions. This brings added fire concerns to this
area. Refer to the Fire Weather discussion below for more
information.
Tuesday and Wednesday we'll remain under the influence of the
slow moving upper low, so daily shower and thunderstorm chances
exist. The limiting factor, however, looks to be an increasingly
drying air mass from which to tap. Will keep PoPs rather low
through this time, but we'll need to monitor upstream monsoonal
moisture availability for the potential of increased coverage,
especially Wednesday. TAX
.LONG TERM...Thursday through Monday
The trend heading into the weekend will be to a drier forecast as
the main upper-low over the area shifts eastward. Pretty strong
model agreement that dry westerly flow will establish over the
PNW. This will keep sky conditions relatively clear and
temperatures near seasonal averages.
The upper-level flow pattern again amplifies early next week as a
low slides into the PNW, poised to become our next organized
disturbance. TAX
&&
.AVIATION...Fairly active day expected today. Thunderstorms will
create periods of lowered vis and possibily CIG heights for a brief
period should any occur on station; otherwise the primary concern
will be wind. Winds will generally be on an increasing trend this
afternoon across each site out of the south or southwest (west for
BYI) with speeds peaking over 50 mph through early this evening.
Higher gusts are possible near/in thunderstorms. Winds are expected
to shift out of the north at SUN this evening then shift at PIH/IDA
and DIJ overnight. NP/TAX
&&
.FIRE WEATHER...An upper low situated to our west will create the
focus for fire weather concerns today. Winds today will initially
start out from the south across the zones 413 and 427 while
northeast winds are noted across 425 and 410 around 15 mph.
Otherwise, various wind directions at less than 10 mph will start
the day across the remaining fire weather zones. As the afternoon
arrives, anticipate increasing wind speeds near 25 with higher gusts
across 427 and 425. As speeds increase and RH values decrease, we
will issue a RED FLAG WARNING starting at noon through 9 pm MDT with
the strongest winds anticipated mid to late afternoon. Wind speeds
will start to shift out of the southwest in the middle of the
afternoon across zones 422, 476 and 475 ahead of a boundary and then
shift northwest or west behind the passage of the boundary this
evening. Expect strong and gusty winds behind the passage as well in
these zones, upwards of 35 mph and gusts to 60 mph. In light of
these gusty winds, combined with scattered thunderstorms in these
same areas, a RED FLAG WARNING will remain in effect today starting
at noon and continue through 9 pm MDT. A mix of wet and dry
thunderstorms is forecast, with the best chances for wetting rains
this afternoon and the potential for 0.15" or higher with wet
storms. Across 410 and 411, wind directions are expected to shift
out of the north this afternoon and increase to speeds upwards of 35
mph late this evening, particularly near Dubois, Mud Lake and
Spencer. Speeds will decrease but remain elevated around 15 mph
across 410 and 411 overnight from the north and northeast; however a
caveat to this will be the Dubois and Spencer area where strong
winds near 25 mph are forecast to persist overnight. QPF amounts in
these areas are not expected to amount to much; at less than 0.10".
Winds in Zone 413 generally are forecast out of the east this
evening with the boundary approaching with speeds near 15 mph,
decreasing overnight.
Tomorrows forecast becomes less confident resulting from uncertainty
in the progression of the upper low. It is forecast to essentially
park itself to our west through Wednesday. Bouts of moisture
incoming from the southwest will lead to continued chances for
showers and thunderstorms; but their favored locations are a bit
uncertain for Tuesday and Wednesday. Forecast models have still be
ping-ponging in their solutions. NP/TAX
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 9 PM MDT this evening for
IDZ422-425-427-475-476.
&&
$$
