Area Forecast Discussion
Issued by NWS Pocatello, ID

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000
FXUS65 KPIH 182112
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
212 PM MST THU DEC 18 2014

.SHORT TERM...LOW PRESSURE TROUGH IN THE EASTERN PACIFIC AND QUICK
WESTERLY WINDS KEEP SENDING LITTLE DISTURBANCES THROUGH THIS AREA.
DISTURBANCE JUST TO OUR WEST SHOULD CROSS THIS AREA TONIGHT WITH
LITTLE PRECIPITATION...MOSTLY THE CENTRAL MOUNTAINS NEAR STANLEY
AND THE EASTERN HIGHLANDS FROM MACKS INN TO PALISADES RESERVOIR.
GOOD MORE CLOUDS TONIGHT SHOULD HELP LIMIT FOG
FORMATION...ALTHOUGH SOME PATCHY FOG WILL NEAR RIVERS AND STREAMS
AND FOOTHILLS WHERE CLOUDS MEET TERRAIN. A SECOND AND STRONGER
DISTURBANCE COMES IN FRIDAY...TIMING IS A LITTLE SLOWER FAVORING
FRIDAY AFTERNOON AND NIGHT. SNOW ACCUMULATION IN THE MOUNTAINS OF
1 TO 4 INCHES WITH AN INCH OR LESS IN THE SNAKE PLAIN.

MOIST WESTERLY FLOW OFF THE PACIFIC BEGINS TO SET UP SATURDAY AND
CONTINUE INTO SUNDAY/MONDAY. ON THE ONE HAND...MODELS SUGGEST A
FOOT OR MORE OF SNOW POSSIBLE IN THE CENTRAL MOUNTAINS AND EASTERN
HIGHLANDS. AT THE SAME TIME...WESTERLY WINDS BEGIN TO MODIFY THE
AIR WARMER...RAISING SNOW LEVELS TO 7000-8000 FEET ELEVATION ON
SUNDAY. THE WARM OVER RUNNING AIR COULD BRING A LITTLE FREEZING
RAIN/DRIZZLE TO PLACES LIKE WILLOW CREEK OR GILMORE SUMMIT ON
SUNDAY WHERE VALLEY TEMPERATURES MIGHT YET REMAIN BELOW FREEZING.
THE GFS ALSO TRIES TO BRING IN STRONGER WINDS AT MOUNTAIN TOP ON
SUNDAY. THAT COULD BRING BLOWING SNOW AT SKI RESORT AREAS OR EVEN
SOME UNSTABLE SNOW BUILD UP AREAS. ON THE PLUS SIDE...TRAVEL MAY
NOT BE BAD WITH MORE RAIN THAN SNOW IN THE VALLEYS. RS

.LONG TERM...SUNDAY NIGHT THROUGH CHRISTMAS NIGHT. ACTIVE WEATHER
PATTERN WILL CONTINUE THROUGH MONDAY WITH A SIGNIFICANT AMOUNT OF
MOUNTAIN SNOW. SNOW LEVELS WILL BE GENERALLY 6500 TO 7500 FT MONDAY
MORNING...BUT WILL BE DROPPING MONDAY NIGHT. GFS SHOWS SIGNIFICANT
IVT SIGNIFYING ATMOSPHERIC RIVER PENETRATING THROUGH THE COLUMBIA
RIVER VALLEY INTO THE SNAKE PLAIN SUNDAY NIGHT INTO MONDAY. BY
MONDAY NIGHT...THE MOISTURE TRANSPORT WEAKENS AS A BROAD UPPER RIDGE
BUILDS BRIEFLY INTO THE PAC NW. TOTAL SNOWFALL AMOUNTS FOR THE
DURATION OF THE ATMOSPHERIC RIVER EVENT WILL LIKELY BE VERY LIGHT IN
THE SNAKE PLAIN...UP TO TWO INCHES...BUT WILL BE MUCH HEAVIER IN THE
CENTRAL MOUNTAINS AND THE EASTERN HIGHLANDS. THE SAWTOOTH RANGE AS
WELL AS THE IDAHO WASATCH/CARIBOU HIGHLANDS COULD SEE 18 TO 24
INCHES. FOCUS THEN SHIFTS TO THE UPPER DISTURBANCE THAT WILL MOVE
INTO THE PAC NW FROM THE GULF OF ALASKA ON CHRISTMAS EVE.
OPERATIONAL GFS AND ECMWF HAVE VARIED SOMEWHAT BETWEEN A CUTOFF LOW
DEVELOPING OVER THE EASTERN GREAT BASIN AND A MODEST UPPER TROUGH
EMBEDDED IN THE NORTHWESTERLY FLOW. TOOK A PEEK AT THE PARALLEL GFS
AS WELL...WHICH PRESENTS A DEEPER TROUGH SCENARIO OVER THE GREAT
SALT LAKE AND NEARLY CUTS OFF A LOW CIRCULATION. IT IS A LITTLE
EARLY TO PLACE ANY CONFIDENCE IN EITHER MODEL YET...BUT WILL MONITOR
THE TRENDS THROUGH THE WEEKEND TO SEE IF A CONSENSUS CAN BE MADE ON
A SOLUTION. BOTH GFS AND ECMWF ARE BRINGING COOLER AIR ALONG WITH
THE SYSTEM SO HAVE ADJUSTED MAX/MIN TEMPS ACCORDINGLY.  HINSBERGER

&&

.AVIATION...VFR CONDITIONS EXIST OVER THE SNAKE PLAIN...AND SHOULD
CONTINUE THROUGH THE AFTERNOON. KSUN IS EXPERIENCING 2000 FT
CEILINGS WITH SIGNS OF SOME SNOWFALL APPROACHING FROM THE ENHANCED
IR IMAGERY. A SWITCH TO UP-VALLEY WINDS LATER THIS AFTERNOON MAY
RESULT IN CEILINGS DROPPING BELOW AIRFIELD MINIMUMS. MODELS
SUGGESTING THE SAME...THOUGH NAM MOS FAVORS THE GREATER CHANCE FOR
SOME LIGHT SNOWFALL TODAY.  HINSBERGER

&&

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

&&

$$






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