Freeze Warning 1, NWS Pocatello, ID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
150 PM MDT SUN MAY 11 2014

.SHORT TERM...TONIGHT THROUGH WEDNESDAY. AN UPPER LOW CONTINUED TO
SHIFT SE OF THE REGION TODAY AS A RIDGE OF HIGH PRESSURE AMPLIFIED
ALONG THE PAC COAST. A WEAK DISTURBANCE EMBEDDED IN THE NW FLOW
ALOFT WAS NOTED DIGGING SE ALONG THE DIVIDE AND WILL PROVIDE THE
NECESSARY LIFT FOR AFTERNOON CONVECTION ALONG THE MONTANA AND
WYOMING DIVIDE REGIONS TODAY AND MONDAY. OTHERWISE DRY CONDITIONS
WILL OVERSPREAD THE REGION MONDAY/TUESDAY AS THE RIDGE MIGRATES INTO
THE COAST. A WEAK DISTURBANCE TOPPING THE RIDGE WILL DIG SE ALONG
THE DIVIDE WEDNESDAY AFTERNOON PROVIDING A SLIGHT CHANCE OF
AFTERNOON SHOWERS NEAR ISLAND PARK. A STRONG NORTHERLY SURFACE
PRESSURE GRADIENT WAS POSITIONED OVER THE REGION TODAY...PRODUCING
STRONG NORTH WINDS THROUGHOUT THE SNAKE RIVER PLAIN. MODELS INDICATE
THAT AS THE GRADIENT WEAKENS TONIGHT AND MONDAY...THE WINDS WILL
BEGIN TO WEAKEN. STILL...A LAKE WIND ADVISORY REMAINS IN EFFECT FOR
AMERICAN FALLS THIS AFTERNOON/EVE AND HAVE ADDED A WIND ADVISORY
THROUGH EARLY EVENING FOR THE UPPER SNAKE PLAIN DUE TO THE
PERSISTENT STRENGTH OF THE WINDS IN THAT REGION. IT ALSO LOOKS AS IF
THE NORTH WINDS WILL BE STRONG ENOUGH AGAIN MONDAY...ALBEIT MUCH
WEAKER THAN TODAY...TO SUPPORT YET ANOTHER LAKE WIND ADVISORY FOR
AMERICAN FALLS. CLEARING SKIES WILL ONCE AGAIN SUPPORT FREEZING
TEMPERATURES TONIGHT AND MONDAY NIGHT. ALTHOUGH THE MODEST NORTH
WINDS EXPECTED TONIGHT SHOULD MODERATE THE POTENTIAL COOLING...THUS
HAVE CONVERTED THE FREEZE WATCH TO A FROST ADVISORY FOR ZONES 20 AND
21 FOR TONIGHT.
LIGHT WINDS AND CLEAR SKIES TUESDAY MORNING SHOULD BE VERY
SUPPORTIVE OF A HARD FREEZE IN THE UPPER VALLEY AND FROST IN THE
LOWER SNAKE RIVER PLAIN AND ERN MAGIC VALLEY. THUS HAVE ISSUED A
WATCH FOR THAT TIME FRAME. HUSTON

.LONG TERM...WED NIGHT THROUGH NEXT SUN NIGHT. 500MB LONG WAVE
INDICATES A SHIFT FROM A WEAK TROUGH TO ZONAL FLOW OCCURRING EARLY
WITH ZONAL FLOW CONTINUING TO THE END. THIS WILL MEAN A SHORT-WAVE
DOMINATED WEATHER PATTERN AND THUS VERY LITTLE CONSISTENCY WITH
PREVIOUS GUIDANCE RUNS AND POTENTIALLY STRONG DIFFERENCES AMONG
MODEL SOLUTIONS.  COMPARED TO YESTERDAY...THE GFS AND ECMWF HAVE
BROUGHT IN MORE MOISTURE AND PRECIPITATION WITH SLIGHTLY COLDER
TEMPERATURES. SO HAVE TRENDED IN THIS DIRECTION. 500MB HEIGHTS ARE
NOT QUITE AS INTENSE AND THE UPPER LEVEL RIDGE IS WEAKER IN
AMPLITUDE. ON SAT NIGHT/SUN...THE GFS IS BRINGING IN A TROUGH...AT
LEAST TO THE NORTHERN END OF THE FORECAST AREA. THE ECMWF PERFORMS
SIMILARLY...SO HAVE BEEFED UP POPS AND CLOUD COVER AND HAVE THE
STRONGEST WINDS DURING THE PERIOD ON THIS DAY. OTHERWISE WINDS ARE
INDICATING GUSTY WINDS OVER THE ARCO DESERT QUITE WELL. MESSICK
&&

.AVIATION...NORTH WIND IN HRRR INDICATES STRONGER WIND LASTING INTO
THE EVENING...SO HAVE DELAYED THE DECREASE UNTIL LATER TONIGHT.
NORTH WIND SHOULD EVEN REACH THE EASTERN MAGIC VALLEY DURING THE
AFTERNOON. OTHERWISE CIG AND VSBY SHOULD BE EXCELLENT VFR WITH A CIG
POSSIBLE IN THE MID-LEVELS WHERE THE NORTH WIND MEANS UPSLOPE
CONDITIONS...AT KBYI AND KPIH. THIS IS DUE TO A SLOWLY DEPARTING LOW
THAT IS TRACKING THROUGH UT AND SOUTHERN WY/NORTHERN CO. MESSICK
&&

.PIH WATCHES/WARNINGS/ADVISORIES...
LAKE WIND ADVISORY UNTIL 9 PM MDT THIS EVENING AND AGAIN MONDAY FROM
9 AM TO 9 PM MDT FOR IDZ021.

WIND ADVISORY UNTIL 9 PM MDT THIS EVENING FOR IDZ020.

FROST ADVISORY LATE TONIGHT THROUGH MONDAY MORNING FOR IDZ020-021.

FREEZE WATCH FROM LATE MONDAY NIGHT THROUGH TUESDAY MORNING
IDZ017-020-021.
&&