Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 300859

Area Forecast Discussion
National Weather Service Pocatello ID
259 AM MDT Fri Jul 30 2021

.SHORT TERM...Today through Sunday night. Early morning satellite
imagery continued to show a broad high pressure ridge centered over
the mid-west with a very moist sub-tropical flow rotating through
the desert SW into SRN Idaho. One very clear cyclonic wave was
observed lifting WNW along the SW Texas border with perhaps a second
weaker leading wave shifting into SE Arizona. Further north across
NE Utah there very well may be yet another system trekking north but
obscured by considerable convective debris (we will take that as a
hint). The numerical models continue to cycle the sub-tropical
moisture north into the region today through Sunday while lifting
the Arizona wave north into SRN Nevada today, the Idaho-Oregon-
Nevada triple point Saturday afternoon, and then into NE Oregon by
Sunday morning with enhanced precipitation totals accompanying this
system through the Great Basin. With all that in mind, the obscured
disturbance lifting north through NE Utah this morning will likely
shift NE through SW Wyoming this afternoon triggering enhanced
diurnal convection across the SE mountains while something more akin
to airmass thunderstorm activity fires along a line from Galena
Summit to Gilmore under an upper deformation axis. Early morning
Hires Convective (HRRR) model runs (the last 6 of 9) were actually
showing the potential for Debris Flow triggering rainfall over the
Badger Fire Scar today. As a result, a burn scar Flash Flood Watch
may be forthcoming later this morning. Cloud cover advecting into
the region in advance of the Nevada system will likely inhibit
shower and thunderstorm activity across SE Idaho Saturday morning
but just as a hedge we will keep a chance mention of precipitation
going across the area as the track of that system is still
somewhat fluid. By Saturday afternoon as the wave hits the
aforementioned triple point, we should see scattered convection
firing across the region favoring the Magic Valley and Wood River
Valley regions closer to the passing system which will continue
into the late evening hours as the disturbance lifts north toward
Pendleton. By Sunday, the wave will have lifted north into
Washington and the Panhandle with the CNTRL mountain zones falling
on the periphery of influence. Further south across the Snake
River Plain and SE mountains, the National Blend of Models is
still advertising some fairly elevated precipitation potential
which is not entirely supported by either operational model (GFS
or NAM). My only thought here is that perhaps some trailing energy
perhaps from the Texas wave will translate into the region Sunday
evening (which is partially supported by the GFS) supporting
convection. A lot of moving parts here in the forecast...with the
screaming message being we stand a strong chance of getting wet
across the region either Saturday or Sunday from one or both of
these advancing waves. The second item of concern is the potential
for flash flooding which we will try to hone in on over the
course of the next several forecast cycles. Stay tuned! Huston

.LONG TERM...Monday through Friday.
Expect Monday to be the last day of extensive moisture as last of
monsoonal moisture will bring widespread shower activity as short
wave pushes through Idaho. Expect some drying Tuesday as upper
level ridging slides in with only slight chance of showers and
thunderstorms. Another wave may approach late Wednesday into
Thursday with better chance of showers and thunderstorms again.
Ridging will bring drying again on Friday. Monday likely to be
coolest day with well below normal temperatures possible in clouds
and precipitation. Expect rising temperatures the remainder of
next week with high temperatures back to normal by Friday.


Will be similar conditions today with again a chance for
thunderstorms across all of southeast Idaho. Have vicinity at all
sites this afternoon and evening. Showers and thunderstorms will
continue Saturday and Sunday and will be the main impact for
several days.


.FIRE WEATHER...A very moist sub-tropical flow will continue across
the region through Sunday. A disturbance rotating NE out of Utah
into SW Wyoming today will help to enhance thunderstorm activity
across the SE highlands with the potential for heavy rainfall.
Instability showers (along with heavy rain) will likely form along a
line from Galena Summit to Gilmore. A second disturbance lifting NNW
out of Arizona will hit the Idaho-Oregon-Nevada triple point
Saturday afternoon resulting in enhanced thunderstorm activity
skirting the Magic Valley, Wood River, and Saw Tooth`s Saturday
afternoon and evening. A third disturbance rotating out of SW Texas
should arrive sometime Sunday evening bringing yet another round of
enhanced showers and thunderstorms to the region. At this time the
system looks to rotate through the Boise area but stay tuned, these
things never follow a set playbook. Screaming message in all this,
organized disturbances translating through moist sub-topical
environments can produce very heavy rainfall events. Landmanagers
operating in and around fires or burn scars should be extra
attentive to developments this weekend. It looks like we cycle back
into a drier SW flow/ridge pattern briefly Tuesday followed by a
Pacific trough lifting through the region Thursday. Lots of moving
parts here folks...stay tuned! Huston



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