Lake Wind Advisory 5, NWS Pocatello, ID

660 
WWUS75 KPIH 162005
NPWPIH

URGENT - WEATHER MESSAGE
National Weather Service Pocatello ID
205 PM MDT Fri Apr 16 2021

IDZ054-170100-
/O.CON.KPIH.LW.Y.0005.000000T0000Z-210417T0100Z/
Lower Snake River Plain-
Including the cities of Pocatello, Blackfoot, American Falls, 
Shelley, and Fort Hall
205 PM MDT Fri Apr 16 2021

...LAKE WIND ADVISORY REMAINS IN EFFECT UNTIL 7 PM MDT THIS
EVENING...

* WHAT...Northeast winds 10 to 15 mph with gusts up to 20 mph 
  expected.

* WHERE...American Falls Reservoir.

* WHEN...Until 7 PM MDT this evening.

* IMPACTS...Strong northeast winds and rough waves will create 
  hazardous conditions for small craft on the reservoir.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Boaters on area lakes should use extra caution since strong winds
and rough waves can overturn small craft.

&&

$$

For more information from the National Weather Service visit
https://weather.gov/pocatello

234 
WWUS75 KPIH 170101
NPWPIH

URGENT - WEATHER MESSAGE
National Weather Service Pocatello ID
701 PM MDT Fri Apr 16 2021

IDZ054-170215-
/O.EXP.KPIH.LW.Y.0005.000000T0000Z-210417T0100Z/
Lower Snake River Plain-
Including the cities of Pocatello, Blackfoot, American Falls, 
Shelley, and Fort Hall
701 PM MDT Fri Apr 16 2021

...LAKE WIND ADVISORY WILL EXPIRE AT 7 PM MDT THIS EVENING...

Winds continue to weaken this evening across American Falls
Reservoir. Locally gusty north winds may occur through sunset
toward the north end of the reservoir. 

$$

For more information from the National Weather Service visit
https://weather.gov/pocatello

Area Forecast Discussion
National Weather Service Pocatello ID
153 PM MDT Thu Apr 15 2021

.SHORT TERM...Tonight through Saturday night. Upper low continues
to spin with circulation center over southwest Wyoming. Moisture
continues to wrap around the low into Eastern Idaho with radar
showing light returns and continued isolated light mixed
precipitation. Models including short term ensembles favor broad
area of light precipitation over the Eastern Magic Valley/Sun
Valley area shifting south toward the southern Sawtooth through
the evening. Have made sure the precipitation chances through the
evening were nudged upward in this area, though snow accumulations
will remain low. Northeast gradient remains in place with marginal
thresholds met for gusty winds over American Falls Reservoir, thus
have left Lake Wind Advisory in place. Expect winds to continue to
decrease through the evening. Some clearing may be possible
overnight, and there is a low confidence, low coverage potential
for pockets of fog across these areas, but not enough to paint
across the grids at this time. Shifting into Friday, models paint
a very weak shortwave wrapping around the low, but any isolated
precipitation from the feature should be limited to the southeast
corner and southern highlands through the day. The remainder of
the short term should be dominated by upper ridge folding into
East Idaho from the north. Clearing skies, light winds and a
warming trend are expected headed into the weekend. DMH

.LONG TERM...SUNDAY THROUGH NEXT THURSDAY...
The main synoptic player in the long-term is a potential shortwave
coming down from the north Mon, with fairly uneventful conditions
outside of that. The 12z suite of deterministic models take the
brunt of this wave to our east across MT/WY, with just a glancing
blow to our CWA. WPC 500mb height cluster analysis agrees...every
ensemble cluster keeps us on the far SW fringes of this system,
almost centered between troughing to the NE and ridging to the W,
with forecast uncertainty (via the EOF) spread pretty evenly between
position/timing uncertainty and amplitude/strength uncertainty (and
the monopole/dipole signatures we look for to evaluate these
uncertainty sources on the EOF are quite weak). No parameter is
lighting up as particularly anomalous on the ECMWF EFI (Extreme
Forecast Index) either (which serves as a nice situational-awareness
glance at what hazards we may need to focus on), and QPF is highly
variable (poor clustering) on GFS/EC meteograms, although below
0.20" for most locations. Thus, for now we will say overall forecast
is low, but high-impact wind or precip appear unlikely, and the odds
currently favor the greatest impacts remaining east of the CWA. High
temps next week will fluctuate a bit but overall should remain in
the 50s to mid 60s, very close to climatological norms for this time
of year. - KSmith

&&

.AVIATION...
Light rain/snow showers are stubbornly holding on across much of SE
Idaho, a bit more widespread and stratiform than most high-res
guidance has been advertising, as our current low pressure system
slowly pushes east into WY/CO. This is allowing fluctuating MVFR
cigs to hold on a bit longer than originally expected at many of the
TAF terminals. The general TREND for the rest of the afternoon/eve
should be for precip to become more isolated/showery, cigs to nudge
back toward VFR, and then things to eventually dry out more
definitively after 04-05z (10-11pm), but in the meantime, the
challenge is chasing where precip upgrades from VCSH (usually via
TEMPO groups) remain necessary. Most of the HREF ensemble members do
generate perhaps a slightly more organized area of rain around 22-
23z (4-5pm) over the cntl Snake Plain and take it SSW potentially
affecting KBYI through 05z (11pm), but frankly confidence is low on
occurrence and exact track (not to mention that things aren't playing
out perfectly today anyway), so prefer to monitor radar trends and
now-cast this, with some potential for a period of -RA to be added
to KBYI with future TAF updates/amendments. A NE down-plain flow is
expected at the Snake Plain terminals tonight, but with sfc speeds
generally 10kts or less. A few isolated showers may redevelop Fri
afternoon as the influence of the low is slow to depart, along with
a diurnal uptick in the NE down-plain flow. - KSmith

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory until 7 PM MDT this evening for IDZ054.

&&