Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 210308
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
908 PM MDT FRI MAY 20 2016

.UPDATE...Another active evening in place for east Idaho. Multiple
storms surged north mainly east of I-15 this evening with a lone
cell strengthening to severe producing multiple reports of 1"
hail. Convection has weakened considerably and decreased in
coverage. NAM and RAP appear to have best handle on precip
compared to past few hours and show continual weakening through
about 09z. RAP then shows a resurgence of weak convection along
western edge of central mountains 09z-12z. 18Z GFS leaves weak
convection going overnight. Given dynamics of deep low and amount
of moisture in place along with lingering surface boundaries left
over from convection today, it is extremely difficult to go with
dry forecast rest of tonight. Have made a few minor adjustments to
current forecast for tonight mainly to trend with current
observations and radar imagery. DMH


&&

.PREV DISCUSSION... /issued 202 PM MDT FRI MAY 20 2016/

SHORT TERM...Low pressure system over Northern California
is expected to move E-NE tonight, eventually lifting through Idaho
late Saturday. The strong surface winds that were anticipated in
Cassia County this afternoon are developing further to the south;
the wind advisory may be cancelled yet this afternoon. Another lobe
of energy swings around the center of circulation and into Idaho
late Saturday morning. Models favor by afternoon placing more of the
stronger thunderstorm support into Montana. Current forecast favors
scattered to numerous showers in the mountains with isolated
thunderstorms. For the Snake Plain, more isolated showers and a
slight chance of a thunderstorm. Saturday night showers diminish,
then another disturbance embedded in the broad low pressure trough
will cross southeast Idaho for a showery day. The pattern looks
unsettled through Monday and beyond. rs

LONG TERM...Monday night through Friday night. Both the GFS and
ECMWF models are in good agreement with the upper level trough
dominating the Pacific Northwest through Thursday. Then on
Friday...the ECMWF model has more zonal flow while the GFS model
continues to show an upper level trough over the area. This will
result in afternoon scattered showers with isolated evening showers
and afternoon isolated thunderstorms through Thursday...with
coverage slightly decreasing on Friday. Temperatures start the week
5 to 8 degrees below normal and rise slightly through the week to
near normal by Friday. TW

AVIATION...Current round of light rain showers to exit Sun Valley
and Burley sites with by 21z with  additional light showers expected
at Sun Valley later this evening. It is possible this activity would
also impact Burley. No additional activity forecast at Idaho Falls
or Pocatello. Ceilings will occasionally be MVFR at Sun Valley,
improving when the showers exit the region. What is difficult to
forecast today is the shifting winds both regarding the timing of
the direction change out of the south or southwest and to what speed
they should get to. The official forecast has delayed the expected
increase by at least 3 hours. Without still seeing a substantial
shift from winds out of the south it is very possible this will be
delayed further past the forecast time of 21z at PIH, IDA and BYI.
Amended forecasts are very possible if these winds do not come to
fruition. NP/TW

&&

.PIH Watches/Warnings/Advisories...
None.
&&

$$



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