Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 250346
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
846 PM MST WED DEC 24 2014

.UPDATE...UPDATE FOR MUCH STRONGER WIND ASSOCIATED WITH FRONT WITH
GUSTS NEAR 50 MPH.  MESSICK

&&

.PREV DISCUSSION... /ISSUED 220 PM MST WED DEC 24 2014/

SHORT TERM...TONIGHT THROUGH FRIDAY. IMPRESSIVE CIRCULATION HAS
MOVED INTO NORTHERN CALIFORNIA PER SAT IMAGERY. SFC LOW NEAR
SOUTHEAST OREGON JUST AHEAD OF BAROCLINIC LEAF SIGNATURE. RADAR AND
AREA WEB CAMS SHOWS LINE OF PRECIP MARCHING STEADILY THROUGH
SOUTHERN IDAHO AHEAD OF FRONT. RAIN/SNOW LINE PRESENTLY JUST NORTH
OF I-84. STEEP SFC DEW PT GRADIENTS MAKES FOR AN INTERESTING
SCENARIO AS PRECIP FALLS AND COOLS LOWER LEVELS TEMPS SHOULD FALL
TO WET BULB TEMPS...RIGHT AROUND FREEZING. THUS EXPECT SNOW TO
PRECEDE COLD FRONT BY A FEW HOURS. OTHER CAVEAT IS STRENGTH OF
DOWNSLOPE WIND IN SOUTHEAST CORNER. SFC LOW OVER SNAKE PLAIN
OVERNIGHT THEN INTO EASTERN WYOMING WITH PASSAGE OF FRONT. HAVE
INCREASED WINDS SLIGHTLY TONIGHT INTO CHRISTMAS DAY. IN
ADDITION...NORTHERLY GRADIENT EXPECTED TO KEEP SNOW ONGOING ACROSS
SOUTHERN HIGHLANDS AND INTERSTATE 84/86 CORRIDOR WELL INTO
CHRISTMAS MORNING AS 500MB LOW CLOSES OVER NORTHERN UTAH. MODEL
SPREAD FOR SNOW STILL IN THE 3-6 INCH RANGE FOR BOTH POCATELLO AND
IDAHO FALLS AND HAVE NUDGED QPF/SNOW AMOUNTS UP SLIGHTLY TO MATCH.
SLIGHTLY HIGHER SNOW AMOUNTS COMBINED WITH MODERATE NORTH WINDS
SHOULD CREATE INCREASED TRAVEL HAZARDS. WITH EXPECTED HOLIDAY
TRAVEL AND ROAD HAZARDS DUE TO SNOW/BLOWING SNOW...HAVE ALREADY
UPGRADED CURRENT ADVISORIES TO WINTER STORM WARNINGS.

BOTH NAM AND GFS KEEP SNOW GOING IN SOUTHERN HIGHLANDS THROUGH
CHRISTMAS AFTERNOON. TIMING OF CURRENT HEADLINES MIGHT BE EXTENDED
TOO LONG FOR NORTHERN ZONES BUT WILL LET FOLLOWING SHIFTS REFINE.
UPPER LOW DROPS SOUTH TO NEAR 4-CORNERS EARLY FRIDAY. HAVE
DRASTICALLY REDUCED POPS CHRISTMAS NIGHT INTO FRIDAY WITH MAIN
DYNAMICS SHIFTING AWAY FROM EAST IDAHO. CANNOT RULE OUT
OROGRAPHIC SHOWERS HIGHER ELEVATIONS IN COLDER AIR MASS.

LONG TERM...FRIDAY NIGHT THROUGH NEXT WEDNESDAY. BOTH THE ECMWF
AND GFS MODELS CONTINUE TO BRING A WET AS WELL AS VERY COLD SYSTEM
THROUGH THE AREA SATURDAY NIGHT INTO SUNDAY. CURRENTLY...EXPECT
TRAVEL IMPACTS ACROSS THE AREA WITH THIS SYSTEM WITH AROUND 2 TO 4
INCHES OF VALLEY SNOW AND 4 TO 8 INCHES OF MOUNTAIN SNOW WITH
LOCALIZED HIGHER AMOUNTS. FURTHERMORE...BLOWING AND DRIFTING SNOW
WILL ADD TO DRIVING HAZARDS. LOOK FOR DRYING CONDITIONS LATER
MONDAY THROUGH WEDNESDAY. TEMPERATURES WILL DROP TO WELL BELOW
NORMAL MONDAY THROUGH WEDNESDAY. EXPECT TUESDAY DAYTIME
TEMPERATURES IN THE VALLEYS IN THE MID TO UPPER TEENS AND IN THE
MOUNTAINS IN THE UPPER SINGLE DIGITS TO LOW TEENS. WYATT

AVIATION...A STOUT PAC TROF WAS OBSERVED MOVING ONSHORE OF THE PAC
COAST THIS AFTERNOON. AHEAD OF THIS TROF...GUSTY SOUTHERLY WINDS
WERE OBSERVED AT PIH AND BYI...OCCASIONALLY OVER 30 KNOTS AT THE
SURFACE. SNOW HAS BEGUN AT SUN...WITH VIS AND CIGS OBSERVED BELOW
AIRFIELD MINIMUMS. EXPECT THESE CONDITIONS TO PERSIST HERE THROUGH
ABOUT 06Z...WITH SNOWFALL ENDING BY AROUND 09Z. EXPECT A RAIN/SNOW
MIX TO DEVELOP AT BYI BY 21Z...CHANGING TO SNOW THIS EVENING.
RAIN/SNOW MIX SHOULD CHANGE OVER TO SNOW AT PIH AROUND 03Z.
LOW-LEVEL DRY AIR MAY ALLOW FOR A QUICKER CHANGEOVER TO SNOW
HOWEVER. ALL SNOW IS EXPECTED AT IDA...WITH SNOW BEGINNING AROUND
SUNSET. A COLD FRONT WILL SWEEP FROM WEST TO EAST ACROSS THE REGION
THIS EVENING...GENERALLY BETWEEN 03 AND 04Z...BRINGING AN ABRUPT
WIND SHIFT TO THE WEST ALONG WITH GUSTS APPROACHING 30 KNOTS...LIKELY
STRONGEST AT BYI. THESE GUSTY WINDS WILL CAUSE BLOWING AND DRIFTING
SNOW. COMBINED WITH FALLING SNOW...MODERATE AT TIMES...EXPECT
SIGNIFICANT REDUCTIONS IN VISIBILITIES TO UNDER 1SM AT TIMES. CIGS
WILL LIKELY LOWER INTO THE LIFR CATEGORY AS WELL. EXPECT LOW-LEVEL
WINDS TO VEER TO A NORTHERLY DIRECTION DURING THE MORNING HOURS OVER
THE SNAKE RIVER PLAIN...ALLOWING FOR UPSLOPE FLOW AND A RESULTING
CONTINUATION OF SNOW ALONG WITH REDUCED VISIBILITIES AND OCCASIONAL
LIFR CIGS THROUGH THE TAF PERIOD...PARTICULARLY AT PIH AND BYI. AD

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 5 PM MST THURSDAY IDZ017-019>024-032.

WINTER STORM WARNING UNTIL 2 PM MST THURSDAY IDZ018-031.

WINTER STORM WARNING UNTIL 5 PM MST THURSDAY IDZ025.

&&

$$







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