Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 261959

Area Forecast Discussion
National Weather Service Pocatello ID
159 PM MDT THU MAY 26 2016

.SHORT TERM...Tonight through Sunday afternoon. Latest satellite
imagery shows a disturbance approaching the Idaho Central
Mountains, an isolated thunderstorm cell has already developed
near Fairfield. Thunderstorm activity will increase from Sun
Valley and Stanley this afternoon, through Idaho Falls and Island
Park this evening. Outflow gust potential is a little higher than
the past couple of days, may see local gusts up to 40-45 mph. Fore
the South Central Highlands, models were on the dry side, but
radar indicates some convective cells in that area. Steering winds
do favor movement towards Utah and further drying of the air this
afternoon, but decided to keep isolated thunderstorms in the
forecast for now. As for the low pressure disturbance dropping
south from British Columbia on Friday, models continue to favor a
more eastward turn across the north half of the state. The surface
cold front marches across Montana, the tail end of the cold front
trails into the Arco Desert by noon and almost stalls for most of
the day as it runs nearly parallel to the upper level flow. Winds
in the Snake Plain are expected to be below advisory level, but a
Lake Wind Advisory for American Falls has been issued.
Increasingly dry air in westerly winds continues Saturday,
afternoon thunderstorms will be very spotty near the Montana
border. Sunday, another quick wave could set off convection in the
afternoon hours, but latest models runs are trending drier with
time. RS

.LONG TERM...Sun night through next Thu night. 500mb long wave
pattern continues to show during this period troughing in the
eastern Pacific with the longwave ridge parked over the Great
Plains. For the last 36 hours of the period, the trough retrogrades
farther into the Pacific. This keeps the forecast area in prolonged
southwesterly flow. So no real cold outbreaks expected, but surges
of moisture through this mean flow will continue to bring a threat
of precipitation early. The retreat to the west of the trough should
allow a warming and drying at that time. It is just a matter of
timing for the heavier rainfall events. The main event is still
consistently forecasted for Memorial Day, including a potential
breezy/windy (but not advisory level) event. However, the GFS has
backed off on the amount of precipitation while the ECMWF has
remained more consistent in that department. Have continued to
compromise between the two operational solutions.


.AVIATION...Stability indices (CAPE and Lifted) indicate -TSRA
greatest risk at KSUN and KIDA, much less at KPIH, and near zero for
KBYI. KSUN may still get to marginal VFR, but threat seems fairly
remote. Have timed showers there to coincide with HRRR forecasts of
heaviest precipitation period. Occasional CIGs this afternoon, but
are staying mainly 5000 ft AGL or higher. Gusty wind has best chance
at KBYI and KIDA with a period of subsidence this afternoon to help
the surfacing of some wind. Main problem at KSUN will be the
variable wind during the showers that are expected this afternoon.


.PIH Watches/Warnings/Advisories...
Lake Wind Advisory from 11 AM to 8 PM MDT Friday for IDZ021.


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