Heavy Snow in Idaho, February 19 to 20, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
341 AM MST SAT FEB 19 2011

.SHORT TERM...
WATER VAPOR IMAGERY IS SHOWING A DEEP TROUGH SITUATED ALONG THE
WEST COAST. A COUPLE OF SIGNIFICANT SHORTWAVES ARE ROTATING
THROUGH THE TROUGH WITH ONE CURRENTLY MOVING NORTHEAST ACROSS THE
CENTRAL SIERRA NEVADA POISED TO REACH THE FORECAST AREA LATE
TODAY AND TONIGHT. MODELS ARE IN FAIR AGREEMENT WITH THIS SYSTEM
AND A GOOD FEED OF MOISTURE IS EVIDENT ON SATELLITE. SOME LIGHT
RETURNS SHOWING UP ON RADAR OVER THE CENTRAL MOUNTAINS BUT SUSPECT
VERY LITTLE ACCUMULATION AT THIS POINT.

PRECIPITATION WILL GRADUALLY OVERSPREAD THE AREA FROM THE
SOUTH TODAY WITH THE CENTRAL MOUNTAINS BEING THE MAIN AREA FOR
SIGNIFICANT SNOWFALL LATE TODAY AND TONIGHT. LARGE SCALE FORCING
AND A SOUTHERLY OROGRAPHIC COMPONENT WILL DOMINATE TODAY. WINTER
STORM WARNING REMAINS IN EFFECT FOR THE SAWTOOTH MOUNTAINS AND BIG
AND LITTLE WOOD RIVER REGION WITH 8-12 INCHES ABOVE 7000 FEET
LOOKING REASONABLE FOR MUCH OF THE AREA. SOUTH WINDS 20-30 MPH
WITH HIGHER GUSTS ACROSS THE HIGH ELEVATIONS AHEAD OF THE SYSTEM
TODAY. AS THE MID LEVEL LOW MOVES OVER THE AREA TONIGHT WINDS
WILL BE WEAKER AND VARY IN DIRECTION WHILE THE UPPER JET SHIFTS
EAST OF THE AREA. THIS WILL MAKE THE PRECIPITATION A LITTLE HARDER
TO NAIL DOWN LATE TONIGHT. THE EASTERN HIGHLANDS BECOME THE FOCUS
SUNDAY AND SUNDAY NIGHT AS THE FLOW SWINGS AROUND TO WEST-
NORTHWEST AND COLDER ARE SPREADS INTO THE AREA. EXPECT SOME
SIGNIFICANT SNOWFALL ACROSS THE EASTERN HIGHLANDS BEFORE ITS ALL
SAID AND DONE AND WE MAY NEED TO HOIST AN ADVISORY FOR THIS AREA.

AS FOR THE SNAKE PLAIN...NAM SOUNDINGS INDICATE A SHALLOW WARM
LAYER NEAR THE SURFACE WITH TEMPERATURES FROM POCATELLO TO BURLEY
CLIMBING TO AROUND 40 EARLY THIS AFTERNOON. WE MAY SEE SOME RAIN
OR RAIN AND SNOW SHOWERS MIXED THIS AFTERNOON IN THESE AREAS
BEFORE TURNING TO ALL SNOW BY THIS EVENING. GENERALLY 1-3 INCHES
OF SNOW EXPECTED FOR THE SNAKE PLAIN TONIGHT THROUGH SUNDAY. LOW
POPS REMAIN IN THE FORECAST ON MONDAY AS A WEAK WAVE IS PROGGED TO
MOVE ACROSS THE AREA IN COLD WEST FLOW. TAL

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY. BOTH GFS AND ECMWF IN
FAIR AGREEMENT MON NIGHT INTO WED. BOTH SHOWING A STRONG NORTHERN
STREAM UPPER TROF SAGGING SOUTHWARD OUT OF SW CANADA INTO THE PAC
NW/NRN ROCKIES. THIS WILL RAISE THE CHANCES FOR PRECIP TUE INTO
WED...ALONG WITH BRINGING IN COLDER TEMPS. BY THU...THE MODELS
DEPART. BOTH DEVELOP A SHARP UPPER TROF IN THE NRN STREAM OVER THE
EASTERN PAC...BUT THE GFS IS FAR MORE PROGRESSIVE...MOVING THE TROF
INTO NRN CA BY LATE THU. THE ECMWF HANGS IT BACK NEAR VANCOUVER
ISLAND. IN EITHER CASE...PRECIP IS WARRANTED INTO SAT...BUT THE
COVERAGE AND AMTS WOULD VARY CONSIDERABLY DEPENDING ON WHICH
SOLUTION PLAYS OUT. WILL LEAVE POPS NEAR CLIMO VALUES UNTIL
SOLUTIONS BEGIN TO COME TOGETHER...IF THAT HAPPENS. HEDGES

&&

.AVIATION...VFR CONDITIONS EXPECTED TO CONTINUE INTO THE EARLY
AFTN...BUT AS A NEW STORM SYSTEM MOVES IN FROM THE SW...CONDITIONS
WILL BEGIN TO DETERIORATE AT KBYI AND KSUN BY MID AFTN AS PRECIP
SPREADS ACROSS THE AREA. KSUN WILL LIKELY DROP TO IFR CONDITIONS BY
MID AFTN...WHILE KBYI WILL SEE PREDOMINANTLY MVFR. THE PRECIP WILL
SPREAD TO KPIH AND KIDA BY LATE AFTN...WITH MVFR CONDITIONS
DOMINATING. PRECIP SHOULD BE RAIN ACROSS THE SNAKE RIVER PLAIN...AND
SNOW IN THE CEN MTNS. ALL PRECIP SHOULD CHANGE TO SNOW TONIGHT.
HEDGES

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM 11 AM THIS MORNING TO 5 PM MST SUNDAY
ABOVE 7000 FEET FOR THE IDZ018-031.

&&