Area Forecast Discussion
Issued by NWS Pocatello, ID

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000
FXUS65 KPIH 200212
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
712 PM MST FRI DEC 19 2014

.SHORT TERM...TONIGHT THROUGH MONDAY. A QUICK UPDATE THIS EVENING AS
RAIN HAS TURNED OVER TO SNOW IN THE UPPER VALLEY WITH DECREASING
RADAR RETURNS/PRECIPITATION FROM WEST TO EAST. ADDED A MENTION OF
PATCHY FOG WITH PARTIAL CLEARING LATE TONIGHT. SEE PREVIOUS
DISCUSSION BELOW. HUSTON

A MINOR UPPER TROF WILL MOVE THRU ID TODAY BRINGING LIGHT MTN SNOW
AND VALLEY RAIN THIS AFTN AND EVE. LATE TONIGHT...THE PRECIP WILL
SHIFT MAINLY TO THE EASTERN HIGHLANDS. STRONG WESTERLY FLOW ALOFT
SETS UP ON SATURDAY...WHICH WILL TRANSPORT SUBSTANTIAL PAC MOISTURE
INTO THE NW US. THIS TYPE OF FLOW FAVORS THE MTNS...WITH WESTERN
SLOPES CATCHING THE MOST PRECIP DUE TO UPSLOPE. PRECIP WILL
INTENSIFY OVER THE MTNS DURING THE DAY ON SATURDAY...AND CONTINUE
HEAVY INTO SUNDAY NIGHT. THE CENTRAL MTNS SHOULD SEE THE HEAVIEST
PRECIP. WESTERLY FLOW IS RELATIVELY MILD TEMPWISE...SO SNOW LEVELS
WILL BE ON THE HIGH SIDE. PRECIP WILL BE WIDESPREAD IN THE VALLEYS
BY SAT NIGHT...BUT PRECIP AMOUNTS WILL BE MUCH LIGHTER THAN THE
MTNS. SNOW IS EXPECTED TO ACCUMULATE TO OVER A FOOT ABOVE 7000 FT IN
THE CENTRAL MTNS BY SUN EVE...AND 8 TO 12 INCHES ABOVE 7000 FT IN
THE EASTERN HIGHLANDS. THE UPPER RIDGE OVER THE EASTERN PAC BEGINS
TO BUILD UP SUN NIGHT...WHICH WILL PUSH THE UPPER FLOW OVER THE PAC
NW TO MORE NWRLY. THIS WILL LIMIT THE FLOW OF PAC MOISTURE...AND
REDUCE THE PRECIP ACROSS THE FCST AREA ON MONDAY.

THE STRONGER UPPER LEVEL WINDS SAT NIGHT AND SUNDAY WILL RESULT IN
SIGNIFICANT BLOWING AND DRIFTING SNOW AT THE HIGHER ELEVATIONS
SUCH AS RIDGE TOPS AND HIGHER PASSES. STRONG SURFACE WINDS ARE
EXPECTED ACROSS THE SNAKE RIVER PLAIN/EASTERN MAGIC VALLEY SUN
AFTN AND EVE. HEDGES

.LONG TERM...MONDAY NIGHT THRU FRIDAY. MORE STABLE WEATHER IS HEADED
OUR WAY AS ATMOSPHERIC RIVER MOISTURE DIMINISHES ON ACCOUNT OF A
BUILDING RIDGE INTO THE PAC NW. FAIRLY WEAK POPS OVER HIGHER
ELEVATIONS ON ACCOUNT OF UPSLOPE FLOW. ECMWF HOLDS ON TO MUCH MORE
MOISTURE THAN GFS FOR WEDNESDAY MORNING...BUT ALSO MAINTAINS A
FLATTER RIDGE. GEM/DGEX SOLUTIONS A BIT MORE IN AGREEMENT WITH THE
ECMWF...BUT NOT QUITE AS WIDESPREAD WITH PRECIP. MODELS STILL
PROJECTING UPPER TROUGH TO DROP INTO PAC NW CHRISTMAS EVE AND OVER
THE INTERMOUNTAIN REGION ON CHRISTMAS DAY. GFS/ECMWF HAVE BACKED OFF
ON A CLOSED LOW DEVELOPING TO OUR SOUTH...WHICH WOULD FAVOR A HEAVY
SNOW EVENT...IN FAVOR OF A MODERATE UPPER TROUGH IN THE
NORTHWESTERLY FLOW. THERE WILL BE AN INFLOW OF WARMER AIR AHEAD OF
THIS SYSTEM WHICH COULD RAISE SNOW LEVELS OFF THE VALLEY FLOOR...BUT
SNOW LEVELS FALLING AGAIN WITH THE PASSAGE OF THE SYSTEM. HINSBERGER
&&

.AVIATION...WEATHER SYSTEM MOVING ACROSS IDAHO THIS AFTERNOON WILL
BRING RAIN AND SNOW TO THE TERMINALS. CONDITIONS ARE CURRENTLY
DETERIORATING AT KSUN WITH SNOW BEGINNING JUST RECENTLY. HRRR
SHOWING HEAVIEST PRECIPITATION WILL BE AROUND MID-AFTERNOON FOR KSUN
THOUGH TEMPS MAY WARM ENOUGH TO SEE A CHANGE OVER TO RAIN/SNOW MIX.
THE LOW LEVEL MOISTURE WILL KEEP CEILINGS LOW THROUGH AROUND
MIDNIGHT TONIGHT WHILE THE OTHER TERMINALS IN THE SNAKE PLAIN WILL
LIKELY SEE A MIX OF IFR/MVFR CEILINGS THROUGH THE END OF THE
PERIOD...EVEN AFTER THE UPPER DISTURBANCE HAS PASSED. HINSBERGER
&&

.PIH WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY AFTERNOON THROUGH LATE SUNDAY
NIGHT ABOVE 6000 FEET FOR THE IDZ019-023-025-031-032.

WINTER STORM WATCH FROM SATURDAY AFTERNOON THROUGH LATE SUNDAY NIGHT
IDZ018.
&&

$$









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