Snow Advisory 2, NWS Pocatello, ID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
312 AM MST SUN JAN 20 2008

.SHORT TERM...STRONG LOW PRESSURE SYSTEM DROPPING SOUTHWARD THROUGH
WASHINGTON AND OREGON TODAY. FORECAST WILL BE QUITE DIFFICULT AS
MODELS SHOW SIGNIFICANT VARIATIONS IN WIND FIELD AT 700 MB
COMPLICATING TERRAIN EFFECTS. BOTH MODELS PINCH OFF A LOW PRESSURE
CIRCULATION OFF THE OREGON AND NORTHERN CALIFORNIA COAST. CLOSER
TO HOME NAM DEVELOPS CLOSED 700 MB CIRCULATION AROUND MONIDA PASS
AREA THIS EVENING AND SLOWLY DRIFTS IT TOWARDS WYOMING THROUGH
MONDAY NIGHT WHILE GFS DEVELOPS A CIRCULATION MORE OVER THE
CENTRAL MOUNTAINS AND IS LESS PERSISTENT WITH IT. BOTH MODELS
AGREE ON AXIS OF THE UPPER TROUGH SLIPPING THROUGH SOUTHERN IDAHO
MONDAY NIGHT. A STRONG SURFACE PRESSURE GRADIENT DEVELOPS ALONG
THE UPPER SNAKE HIGHLANDS SUNDAY NIGHT INTO MONDAY MORNING SETTING
UP POTENTIAL FOR EXTREME WIND CHILL TEMPERATURES. HAVE ISSUED A
WATCH FOR THIS AND A REPEAT EVENT MAY DEVELOP TUESDAY MORNING. SNOW
AMOUNTS GENERALLY LOOK TO BE 4 TO 8 INCHES IN THE UPPER SNAKE
HIGHLANDS AND EASTERN HIGHLANDS AND 1 TO 2 INCHES IN THE UPPER
SNAKE RIVER VALLEY. NAM12 POINTS TO SNOW DEVELOPING ALONG THE EDGE
OF COLD AIR ADVANCING OVER THE DIVIDE THIS EVENING WITH FOCUS
BETWEEN DUBOIS AND IDAHO FALLS THROUGH MIDNIGHT. RAISED POPS IN
THAT AREA TONIGHT. GFS DEVELOPS MORE PRECIPITATION OVER THE
SOUTH CENTRAL AND CARIBOU HIGHLANDS THIS AFTERNOON AND TONIGHT.
WATER VAPOR IMAGERY INDICATED A DISTURBANCE IN THE WEST TO
SOUTHWEST FLOW PASSED THROUGH THE ISLAND PARK AREA WHERE .29 INCH
LIQUID PRECIPITATION WAS REPORTED THE LAST 6 HOURS. THAT
DISTURBANCE IS ROTATING INTO MONTANA SO PRECIPITATION OF THAT
INTENSITY PROBABLY WILL NOT CONTINUE. NO HIGHLIGHTS ISSUED FOR
SNOW AT THIS TIME BUT ADJUSTMENTS COULD BE NEEDED AS THINGS
UNFOLD. RS

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...BOTH ECMWF AND GFS
HAVE ID STUCK IN THE COL BETWEEN THE ARCTIC NRN STREAM FLOW EAST
OF THE DIVIDE AND THE UPPER CLOSED LOW OFF THE CA COAST ON WED
MORN. THIS WILL RESULT IN DRY CONDITIONS EXCEPT FOR ISOLD SNOW
SHOWERS IN THE ERN HIGHLANDS CLOSER TO THE NRN STREAM FLOW. BY THU
MORNING...BOTH MODELS PUT THE FCST AREA UNDER SW FLOW...WITH THE
UPPER LOW NEAR THE SF BAY AREA. THIS FLOW MAY BRING LIMITED MSTR
INTO THE SRN HIGHLANDS ...THUS ISOLD SNOW SHOWERS. BOTH MODELS
BRING NRN STREAM ENERGY INTO THE NRN ROCKIES ON FRIDAY...WHILE THE
SRN STREAM SOLUTIONS DIVERGE. IN EITHER CASE...THIS WILL INCREASE
THE CHANCES FOR PRECIP ON FRI/SAT...BUT NOT MUCH ORGANIZATION SEE
AT THIS TIME. WILL KEEP THE POPS ON THE LOW SIDE...AND PRIMARILY
IN THE MTNS UNTIL THE PICURE BECOMES A LITTLE CLEARER. BOTH MODELS
DO AGREE IN BRINGING A DEEP UPPER LOW INTO THE BC COAST ON SUNDAY.
THIS INTENSIFIES THE SW FLOW OVER THE PAC NW IN PREPARATION FOR
WHAT MAY BE AN ACTIVE WX PATTERN. HEDGES

&&

.AVIATION...AS THE MAJOR UPPER LOW MOVES SE THRU THE PAC NW...LIGHT
SNOW IS BEGINNING TO MOVE INTO THE CEN MTNS AND THE ERN MAGIC
VALLEY. THE SNOW WILL REDUCE CIGS/VIS TO MVFR AND OCCASIONALLY IFR.
THE SNOW IS EXPECTED TO SPREAD ACROSS ALL OF ERN ID TODAY...AND
TAPER OFF TO SNOW SHOWERS TONIGHT. MVFR AND OCNL IFR CIG/VIS
CONDITIONS CAN BE EXPECTED TO PREVAIL INTO THE EVENING HOURS. HEDGES

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...BOTH ECMWF AND GFS HAVE
ID STUCK IN THE COL BETWEEN THE ARCTIC NRN STREAM FLOW EAST OF THE
DIVIDE AND THE UPPER CLOSED LOW OFF THE CA COAST ON WED MORN. THIS
WILL RESULT IN DRY CONDITIONS EXCEPT FOR ISOLD SNOW SHOWERS IN THE
ERN HIGHLANDS CLOSER TO THE NRN STREAM FLOW. BY THU MORNING...BOTH
MODELS PUT THE FCST AREA UNDER SW FLOW...WITH THE UPPER LOW NEAR THE
SF BAY AREA. THIS FLOW MAY BRING LIMITED MSTR INTO THE SRN HIGHLANDS
...THUS ISOLD SNOW SHOWERS. BOTH MODELS BRING NRN STREAM ENERGY INTO
THE NRN ROCKIES ON FRIDAY...WHILE THE SRN STREAM SOLUTIONS DIVERGE.
IN EITHER CASE...THIS WILL INCREASE THE CHANCES FOR PRECIP ON
FRI/SAT...BUT NOT MUCH ORGANIZATION SEE AT THIS TIME. WILL KEEP THE
POPS ON THE LOW SIDE...AND PRIMARILY IN THE MTNS UNTIL THE PICURE
BECOMES A LITTLE CLEARER. BOTH MODELS  DO AGREE IN BRINGING A DEEP
UPPER LOW INTO THE BC COAST ON SUNDAY. THIS INTENSIFIES THE SW FLOW
OVER THE PAC NW IN PREPARATION FOR WHAT MAY BE AN ACTIVE WX PATTERN.
HEDGES

&&

.AVIATION...AS THE MAJOR UPPER LOW MOVES SE THRU THE PAC NW...LIGHT
SNOW IS BEGINNING TO MOVE INTO THE CEN MTNS AND THE ERN MAGIC
VALLEY. THE SNOW WILL REDUCE CIGS/VIS TO MVFR AND OCCASIONALLY IFR.
THE SNOW IS EXPECTED TO SPREAD ACROSS ALL OF ERN ID TODAY...AND
TAPER OFF TO SNOW SHOWERS TONIGHT. MVFR AND OCNL IFR CIG/VIS
CONDITIONS CAN BE EXPECTED TO PREVAIL INTO THE EVENING HOURS. HEDGES

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
WIND CHILL WATCH FROM THIS EVENING THROUGH MONDAY MORNING FOR
IDZ019.

&&

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