Area Forecast Discussion
Issued by NWS Pocatello, ID

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000
FXUS65 KPIH 221017
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
317 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH WED NIGHT. WILL ALLOW WINTER STORM
WARNINGS TO CONTINUE THROUGH TO THEIR EXPIRATION TIME...THEN ONLY
LIGHT SNOWFALL EXPECTED TODAY AT MOST HIGH ELEVATIONS. CLEARING
SHOULD DEVELOP DURING THE EVENING AND HIGH PRESSURE WILL CONTINUE
THE CLEAR SKIES AND COLDER OVERNIGHT LOWS THROUGH TUE/TUE
NIGHT/WED. ON WED NIGHT...ALSO KNOWN AS CHRISTMAS EVE...A PACIFIC
STORM IS MOVING IN TO BRING A MESSY LOW ELEVATION RAIN/SNOW AND
HIGH ELEVATION SNOW EVENT THAT CONTINUES INTO THE MEDIUM RANGE
FORECAST.

BUT THE MAIN FORECAST CONCERN CONTINUES TO BE THE WIND. LOCAL WIND STUDY
INDICATES A RE-DEVELOPMENT OF ADVISORY LEVEL CONDITIONS IN THE
EASTERN MAGIC VALLEY AND LOWER SNAKE RIVER PLAIN. 40KT WINDS AT
700MB, 80-PLUS KNOT WIND AT 500MB, AND 150-PLUS KNOT WIND AT 250MB
ARE THE MAIN SUPPORTERS. THE MSLP GRADIENT DOES NOT STRENGTHEN
UNTIL THE AFTERNOON...BUT IT GETS AT LEAST IN THE STRONG CATEGORY FOR
THAT PERIOD. THE OTHER CONTRIBUTING FACTOR WILL BE STRONG COLD
ADVECTION DURING THE AFTERNOOON. ONLY CONCERN IS THE NORTHWEST
AIRFLOW FOR A DIRECTION AND THE STABLE CONDITIONS. HAVE INCLUDED
SOUTH CENTRAL HIGHLANDS AS WELL. MESSICK

.LONG TERM....LONG TERM...THURSDAY (CHRISTMAS DAY) THROUGH NEXT MONDAY. THE
GFS/ECMWF SHOWED MODEST AGREEMENT ON THE MAIN THEMES IMPACTING THE
LONG TERM THIS MORNING ALTHOUGH THERE WERE SOME STRIKING VARIATIONS
ON TIMING AND TRACK. THE MODELS AGREED THAT A FAIRLY SIGNIFICANT PAC
TROUGH WOULD SWEEP INTO THE REGION SOMETIME WEDNESDAY NIGHT/THURSDAY
AND EXIT TO THE EAST FRIDAY MORNING. THE GFS WAS A BIT SLOWER WITH
THE PROGRESSION HERE AND THE MAIN FORECAST ADJUSTMENT WAS TO BEGIN
TO RAMP UP THE PROBABILITY OF PRECIPITATION CHRISTMAS DAY. THE
CHANCES OF SEEING SNOW IN THE SNAKE RIVER PLAIN ARE LOOKING BETTER
ALTHOUGH SNOW LEVELS START OUT FAIRLY WARM AHEAD OF THE ADVANCING
TROUGH AND THEN DROP TO VALLEY FLOORS AS THE PRECIPITATION BEGINS TO
PLAY OUT THURSDAY AFTERNOON/EVE. BY SATURDAY...THE MODELS WERE
SHOWING THE NEXT PAC STORM SYSTEM ADVANCING INTO THE REGION. THIS
TIME...THE GFS SHOWED A MORE PROGRESSIVE/FASTER SOLUTION WITH THE
THROUGH SWEEPING INTO THE NRN ROCKIES BY SATURDAY AFTERNOON WHEREAS
THE ECMWF PLACED THE TROUGH ALONG THE COAST. GIVEN THE SPREAD IN
TIMING AND TRACK ON THIS PARTICULAR FEATURE...HAVE ONLY NUDGED THE
CHANCES OF PRECIPITATION HIGHER UNTIL THE MODELS COME INTO BETTER
AGREEMENT. HUSTON

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 11 AM THIS MORNING TO 9 PM MST THIS EVENING
IDZ017-021-022.

WINTER STORM WARNING UNTIL 5 AM MST EARLY THIS MORNING ABOVE
6000 FEET FOR THE IDZ031-032.

WINTER STORM WARNING UNTIL 5 AM MST EARLY THIS MORNING ABOVE
7500 FEET FOR THE IDZ019-025.

WINTER STORM WARNING UNTIL 5 AM MST EARLY THIS MORNING IDZ018.

&&

$$







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