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FXUS65 KPIH 200858

Area Forecast Discussion
National Weather Service Pocatello ID
258 AM MDT Sun Oct 20 2019

.SHORT TERM...Today through Tuesday. Early morning satellite imagery 
was showing the remains of yesterdays storm sweeping east through 
NRN Wyoming with some residual wrap-around moisture shearing SE 
through the region. Further upstream, a second disturbance was 
visible rotating SE toward the WRN Canadian coast. Numerical models 
show the Wyoming low sweeping rapidly SE into Nebraska by mid-day 
with an increasingly drier NW flow trailing across SE Idaho and 
dwindling upslope snow showers over the CNTRL and NE mountains. The 
second aforementioned disturbance, shears SE into and through the 
NRN Rockies overnight with both the operational GFS and NAM showing 
a fairly decent upslope precipitation signature over the CNTRL, ERN, 
and SE mountains overnight. Not enough accumulation to really 
warrant any highlights but certainly the possibility for 1 to 4 
inches of accumulation especially over the higher terrain. By 
Monday, the ridge positioned off the California coast expands 
slightly NEWRD shunting the storm track a little further north 
resulting in isolated shower activity persisting mainly along the 
Montana and Wyoming divide regions while drier conditions edge into 
the area from the SW. Weak, ill-timed disturbances rotating over the 
ridge Monday night through Tuesday will present a modest threat of 
continuing snow shower activity along the Montana and Wyoming border 
regions through Tuesday afternoon. The flow aloft will remain fairly 
robust throughout the forecast period, enough to support breezy to 
windy conditions at times. A gradual warming trend is anticipated 
today through Tuesday as the ridge expands NE into the region. Huston

.LONG TERM...Tuesday night through next Sunday. A moist ("dirty") NW 
flow continues Tues night, but by Wed we may start to break out of 
the stagnant pattern, so to speak, with 2 wx systems for the rest of 
the week/weekend. The GFS/EC/Canadian are FINALLY showing better 
agreement in a weak, embedded wave brushing across the CWA Wed, 
sharpening into a pronounced trough as it drops SE into WY/CO Wed 
eve. This may result in a bit of an uptick in rain/snow shower 
activity across the Upper Snake Highlands/areas generally east of I-
15 to the WY border mid-AM through eve, and we nudged NBM PoPs 
higher/broadbrushed them out a bit in these areas. That said, QPF 
amounts are projected to remain light (less than 1/10th of an inch) 
at this time with not much wind, so this system appears to be low-
impact. A ridge of high pressure arrives Thurs/Fri with better 
forecast confidence in dry/mostly sunny conditions and slightly 
moderating temps. Models advertise a stronger trough pushing into 
the nrn Rockies Sat/Sun, with gradually increasing chances of 
precip, breezy conditions, and colder temps by Sun.

.AVIATION...Persistent light snow showers will continue this AM at 
KDIJ with predominantly MVFR cigs/vsbys, but this activity should 
diminish with time today, with improvement back to VFR expected by 
afternoon. Elsewhere, today will be dry with continued moderate SW 
winds the main concern for aviation. Speeds should gradually relax a 
bit at KPIH/KBYI compared to what we are seeing pre-dawn this AM. 
Trajectories align well with the major runways, so in general we are 
not expecting major crosswind issues. A weak disturbance will bring 
VCSH snow showers back to all terminals this eve into tonight, with 
KDIJ likely falling back into MVFR cigs. Any vsby reductions will 
largely be governed by occurrence of snow showers at/near a 
terminal. Will monitor guidance for potential upgrades to -SHSN, but 
don't have enough confidence to push beyond VCSH with the 12z TAFs.

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