Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 252055
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
155 PM MST SUN JAN 25 2015

.SHORT TERM...TONIGHT THROUGH WEDNESDAY. SATELLITE IMAGERY WAS
SHOWING A RIDGE OF HIGH PRESSURE OVER THE WEST WITH A CUT-OFF LOW
POSITIONED ALONG THE BAJA COAST. LOW CLOUDS AND FOG HAVE PLAGUED SE
IDAHO OVER THE LAST FEW DAYS AND I SEE NO REAL GAME-CHANGER IN THIS
REGARD UNTIL THE RIDGE WEAKENS AND SHIFTS EAST LATE TUESDAY
AFTERNOON PER THE MOST RECENT GUIDANCE. AS THE RIDGE WEAKENS AND
SHIFTS EAST...THE LOW OFF THE BAJA COAST WILL LIFT NORTH THROUGH
NEVADA AND ACROSS SE IDAHO TUESDAY NIGHT. THE MAIN FORECAST ISSUE
APPEARS TO BE SNOW LEVELS AS THE UPPER RIDGES GRADUALLY WARM OVER
THE NEXT TWO DAYS WHILE COLD AIR REMAINS TRAPPED IN THE LOWER
VALLEYS. AS THE LOW MOVES OVERHEAD TUESDAY NIGHT...THERE SHOULD
BE ENOUGH MIXING TO WASH OUT THE INVERSIONS THAT HAVE BEEN
SUPPORTING THE LOW CLOUDS...FOG...AND COLD VALLEY TEMPERATURES.
THERE IS A SLIGHT RISK HOWEVER THAT SOME POCKETS OF COLD VALLEY AIR
WILL REMAIN...PARTICULARLY IN THE UPPER VALLEY...WHICH WOULD SUPPORT
THE POSSIBILITY OF FREEZING RAIN SOMETIME TUESDAY NIGHT/WEDNESDAY.
WE WILL CONTINUE TO MONITOR THAT FORECAST ELEMENT AS THE SYSTEM
DRAWS NEAR. HUSTON

.LONG TERM...WEDNESDAY NIGHT THROUGH NEXT SUNDAY NIGHT. AFTER THE
TUE NIGHT/WED STORM...SKIES SHOULD AT LEAST PARTIALLY CLEAR WITH
HIGH PRESSURE MOVING IN FROM THE WEST. FROM ABOUT FRI ONWARD THE
OPERATIONAL ECMWF AND GFS SHOW MUCH DIFFERENT SOLUTIONS. THE ECMWF
SHOWS A SECOND SHORTWAVE MOVING UP FROM THE SOUTH...SIMILAR TO THE
PREVIOUS STORM...BUT ONLY MAKING IT AS FAR AS NORTHERN UTAH BEFORE
IT HEADS EASTWARD. THE UPCOMING WEEKEND ON THE ECMWF INDICATES A
STRONG RIDGE WITH VERY HIGH 500MB HEIGHTS AND WARM AIR MOVING IN.
THE GFS IS FAIRLY MUCH THE OPPOSITE. VERY DRY IN THE BEGINNING...BUT
IN THE LAST 24 TO 36 HOURS OF THE FORECAST A TROUGH MOVES IN FROM
THE WEST. LOTS OF DIFFERENCES MEANS LOW CONFIDENCE FORECAST...EXCEPT
THAT EVEN THE GFS STORM IS NOT VERY POWERFUL...SO DO NOT SEE
ANYTHING HEADLINE-WORTHY DURING THIS PERIOD. BOTH THE ECMWF AND GFS
HAVE LITTLE IN THE WAY OF WIND. THE GFS HAS MUCH WARMER...ABOUT 10
DEG F...THAN NORMAL TEMPERATURES...WHILE THE ECMWF HAS NEAR TO
SLIGHTLY ABOVE NORMAL TEMPERATURES FOR THE EXTENDED FORECAST. THE
ECMWF SOLUTION IS SUPPORTED BY THE LONGWAVE PATTERN...BUT THE UPPER
LEVEL RIDGE DOESNT HAVE MUCH AMPLITUDE SO THE GFS SOLUTION IS NOT
OUT OF THE QUESTION. HAVE CONTINUED DOWNWARD TREND IN POPS AND SKY
COVER. MESSICK
&&

.AVIATION...HIGH PRESSURE RETURNS AFTER THE WEAK WINTER STORM OF
LAST NIGHT. THE MAIN FORECAST PROBLEM IS WHAT WILL THE STRATUS DO.
THE NAM BOUNDARY LAYER MOISTURE INDICATES ENOUGH EASTERLY FLOW TO
KEEP THE NORTH SIDE OF THE SNAKE RIVER PLAIN IN STRATUS WHILE THE
EAST/SOUTH SIDE CLEARS SOMEWHAT. ON THE OTHER HAND...MOS GUIDANCE IS
ALL FOR A RETURN OF THE STRATUS. SO THIS IS A LOW CONFIDENCE
FORECAST FOR THE VALLEY AIRDROMES...ESPECIALLY KIDA AND KPIH. HAVE
LEFT SCATTERED STRATUS IN THE TAFS...BUT BELIEVE THAT THE BOUNDARY
LAYER MOISTURE FORECAST IS BETTER THAN THE STATISTICAL MOS GUIDANCE
FOR THIS SEASON. MUCH MORE ASSURED OF GOOD CONDITIONS AT KBYI AND
KSUN WITH NEARLY BREEZY CONDITIONS AT KBYI KEEPING THE STRATUS AND
FOG BROKEN UP AND NORTHWEST FLOW FOR THE LATE NIGHT AND MORNING
HOURS AT KSUN PUSHING THE FOG BACK DOWN INTO THE SNAKE RIVER PLAIN.
WITH THE BUILDING STRATUS ON THAT SIDE OF THE VALLEY...DO HAVE A
CONCERN THAT KSUN COULD GET THE STRATUS ON MON LATE MORNING OR EARLY
AFTERNOON IF THE SOUTHEAST WINDS KICK IN...AS THEY LIKELY WILL.
MESSICK
&&

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

$$






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