FXUS65 KPIH 232055
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
200 PM MST WED DEC 23 2009

.SHORT TERM...TONIGHT THROUGH SATURDAY. A RIDGE OF HIGH PRESSURE 
WILL AMPLIFY ALONG THE PAC COAST TONIGHT AND THURSDAY AS A LOW 
PRESSURE SYSTEM DIGS SSE THROUGH ERN MONTANA AND WYOMING. THE 
PASSING LOW WILL HELP TO SUSTAIN A WEAK/DRY UPSLOPE NW FLOW ACROSS 
THE ERN HIGHLANDS TONIGHT AND THURSDAY RESULTING IN OCCASIONAL 
FLURRIES. BY SATURDAY...THE RIDGE EVOLVES INTO A BLOCKY (OMEGA 
BLOCK) PATTERN WHICH WILL CONTINUE TO PROMOTE INVERTED TEMPERATURE 
PROFILES...LIGHT WIND AND DRY CONDITIONS. THE FORECAST PROBLEM OF 
THE DAY REVOLVES AROUND THE EXTENSIVE AREA OF STRATUS CURRENTLY 
ENTRENCHED WITHIN THE SNAKE RIVER PLAIN AND ERN HIGHLANDS...WHEN 
WILL IT DISSIPATE...AND WHAT WILL THE ENSUING IMPACTS BE ON FORECAST 
TEMPERATURES. THE LATEST MODELS STRONGLY SUGGEST THAT THE STRATUS 
WILL HOLD FIRM TONIGHT THROUGH SATURDAY MORNING. THUS WE WILL ADD 
MORE CLOUD COVER TO THE REGION AND WARM NIGHT TIME LOWS UNDER THE 
STRATUS/LOW CLOUDS WITHIN THE SNAKE PLAIN AND ERN HIGHLANDS. HUSTON

.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY. UPPER RIDGE ACROSS 
THE NORTHWEST IS EXPECTED TO SHIFT SLIGHTLY EASTWARD ON SUNDAY AS A 
SYSTEM APPROACHES THE WEST COAST.  MODELS DIFFER SLIGHTLY ON THE 
EVOLUTION OF THIS SYSTEM...BUT IN GENERAL ARE TRENDING TOWARDS 
UNDERCUTTING THE RIDGE WITH THE PACIFIC SYSTEM ON SUNDAY NIGHT. THE 
GFS KEEPS THE CUT OFF LOW FURTHER NORTH THAN THE ECMWF AND AS A 
RESULT...THE NORTHERN PORTION OF THE LOW CLIPS THE SOUTHERN 
HIGHLANDS ON SUNDAY NIGHT. IN THE WAKE OF THIS LOW...PERSISTENT 
NORTHWEST FLOW ENTRENCHES THE AREA THROUGH THE REST OF THE PERIOD.  
THE RESULT IS A MORE MOIST PATTERN...ALBEIT STILL A WEAK ONE.  THE 
ECM IS A BIT MORE PROGRESSIVE IN MOVING OUT THE PACIFIC LOW WITH A 
BRIEF RETURN TO RIDGING FOLLOWED BY WET ZONAL FLOW ON WEDNESDAY. 
&&

.AVIATION...LOW STRATUS AND/OR FOG OVER THE SNAKE PLAIN IS EXPECTED 
TO PERSIST THROUGH THE REST OF THE DAY AND OVERNIGHT. SOME THINNING 
IS POSSIBLE THIS AFTERNOON...BUT A RETURN TO LOW CONDITIONS IS 
EXPECTED BY LATE THIS EVENING. KSUN REMAINS ON THE EDGE OF THE DECK 
AND IS EXPECTED TO REMAIN VFR OVERNIGHT WITH WINDS TURNING MORE 
NORTHERLY...HOWEVER THERE REMAINS A POSSIBILITY THAT THEY WILL 
RETURN TO FOG AND STRATUS IF THE WINDS STAY LIGHT ENOUGH. 
FOG/STRATUS WILL THIN SOMEWHAT THURSDAY AFTERNOON...BUT GENERALLY 
CONDITIONS ARE EXPECTED TO BE SIMILAR TO TODAY.
&&

.AIR STAGNATION...A BLOCKING RIDGE OF HIGH PRESSURE POSITIONED 
ACROSS THE WRN STATES IS EXPECTED TO DOMINATE THE WEATHER PATTERN 
THROUGH SUNDAY. BY MONDAY...PAC SYSTEMS ARE EXPECTED TO BEGIN TO 
UNDER-CUT THE RIDGE AND BY AS EARLY AS TUESDAY THE SURFACE BASED 
INVERSION MAY BREAK ACROSS SE IDAHO. HUSTON
&&

.PIH WATCHES/WARNINGS/ADVISORIES...NONE.
&&

$$