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000
FXUS66 KMFR 211026
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
326 AM PDT TUE MAY 21 2013

.DISCUSSION...TODAY WILL BE MUCH COOLER...WETTER AND WINDIER COMPARED
TO YESTERDAY. TEMPERATURES TODAY WILL BE BETWEEN 15-20 DEGREES
COOLER ON AVERAGE. CURRENT WATER VAPOR IMAGE SHOWS A STRONG UPPER
LOW CENTERED JUST SOUTH OF THE ALASKA PANHANDLE. AT THE SAME TIME AN
UPPER TROF NEAR 128W AND 44N IS STARTING TO BECOME NEGATIVELY TILTED
WHICH IS IS A GOOD INDICATOR OF A DEVELOPING AND STRENGTHENING
SYSTEM. THE MAIN CONCERNS FOR TODAY WILL BE THE FOLLOWING. GUSTY
WINDS...ESPECIALLY ALONG AND EAST OF THE CASCADES...MODERATE TO
HEAVY PRECIPITATION ALONG THE COAST AND COAST RANGE WITH THE
POTENTIAL FOR SMALL HAIL AND SNOW LEVELS RAPIDLY FALLING DURING THE
DAY WITH ACCUMULATING SNOW POSSIBLE BY EVENING UP TOWARDS DIAMOND
AND CRATER LAKE.

SHOWERS WILL START OT MOVE INTO THE COAST AND COAST RANGE EARLY THIS
MORNING...THEN PUSH INLAND DURING THE DAY. AT THIS TIME EXPECTING
MOST OF THE MODERATE TO HEAVY SHOWERS TO BE MAINLY CONFINED TO ALONG
AND WEST OF THE CASCADES AND IN OREGON. DON`T THINK MUCH WILL MAKE
IT INTO NORTHERN CAL...SO DECIDED TO ADJUST POPS AND QPF AMOUNTS
DOWN. COLD AIR MASS ALOFT WILL MOVE INTO THE NORTHWEST PART OF THE
AREA LATE THIS AFTERNOON WITH 500MB TEMPS BETWEEN -25 AND -30 C
MOVING OVERHEAD. COULD NOT RULE OUT ISOLATED THUNDERSTORMS IN
NORTHERN COOS AND DOUGLAS COUNTIES LATE THIS AFTERNOON INTO EARLY
EVENING.

WINDS ARE GOING TO BE ANOTHER CONCERN...ESPECIALLY ALONG AND EAST OF
THE CASCADES. MODELS SHOW 700MB WINDS BETWEEN 30-40 KTS AND 500MB
WINDS BETWEEN 50-60 KTS. I MENTION 500MB WINDS BECAUSE THERE IS THE
POTENTIAL SOME OF THE STRONGER WINDS ABOVE 700 MB COULD MIX DOWN
NEAR THE SURFACE WITH SOME LOCATIONS REACHING WIND ADVISORY
CRITERIA. THEREFORE HAVE DECIDED TO ISSUE A WIND ADVISORY. THERE IS
A CHANCE FOR GUSTY WINDS TO DEVELOP IN THE ROGUE VALLEY. FOR NOW
HAVE OPTED NOT TO ISSUE AN ADVISORY...BUT THE DAYSHIFT MAY NEED TO
REEVALUATE.

SNOW LEVELS START OUT BETWEEN 6500 AND 7500 FEET...BUT WILL QUICKLY
FALL TO AROUND 4000 FEET BY LATE AFTERNOON. THEREFORE ANYONE
TRAVELING TO OR FROM DIAMOND LAKE OR CRATER LAKE NEED TO BE ON THE
WATCH FOR RAPIDLY CHANGING CONDITIONS FROM MODERATE TO HEAVY RAIN TO
RAIN/WET SNOW MIX TO MODERATE TO HEAVY WET SNOW. GIVEN THE GROUND
AND ROAD TEMPERATURES ARE WARM...THE SNOW WILL MELT AT FIRST...BUT I
EXPECT IT TO ACCUMULATE EARLY THIS EVENING THROUGH TONIGHT. SNOW
LEVELS TONIGHT WILL LOWER TO AROUND 2800 FEET...BUT GIVEN THE
CONVECTIVE NATURE OF THE SHOWERS COULD TEMPORALLY DROP DOWN TO
AROUND 2000 FEET.

THE UPPER LOW WILL MOVE OVERHEAD WEDNESDAY AND REMAIN THERE THROUGH
THURSDAY WITH PLENTY OF COLD AIR ALOFT RESULTING IN INSTABILITY
SHOWERS WITH GUSTY WINDS.  SNOW LEVELS START OUT AROUND 2800 FEET
WEDNESDAY MORNING...THEN INCREASING TO 4000 FEET WEDNESDAY
AFTERNOON. MOST OF THE ACCUMULATING SNOW WEDNESDAY WILL BE IN THE
MORNING AND MOST LIKELY AROUND CRATER AND DIAMOND LAKE AREAS. THERE
IS A CHANCE FOR MINOR ACCUMULATIONS NEAR SISKIYOU SUMMIT AND LAKE OF
THE WOODS WEDNESDAY MORNING...THEN ROADS WILL BE WET FROM LATE
MORNING INTO THE AFTERNOON. THUNDERSTORM CHANCES ARE VERY LOW MAINLY
DUE TO LITTLE BREAKS IN THE CLOUD COVER RESULTING IN LESS
INSTABILITY.

THE UPPER LOW GRADUALLY WEAKENS FRIDAY THROUGH NEXT WEEKEND AND THE
AIR MASS IS NOT EXPECTED TO BE AS COLD. STILL THE CHANCE FOR SHOWERS
EXIST WITH TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL. -PETRUCELLI


&&

.AVIATION...

BASED ON THE 21/06Z TAF CYCLE.

CLOUDS WILL SPREAD INLAND ACROSS THE WEST SIDE THIS MORNING WITH A
MIX OF VFR AND MVFR ALONG WITH HIGHER TERRAIN OBSCURATIONS. MVFR
WILL BE MOST PREVALENT AT THE COAST AND INTO THE UMPQUA BASIN. RAIN
AT THE COAST WILL SPREAD TO THE CASCADES LATER THIS MORNING. VFR
OVER THE EAST SIDE WILL GIVE WAY TO SOME CLOUDS LATER THIS MORNING
INTO THE AFTERNOON ALONG WITH SOME SHOWERS, BUT CIGS SHOULD REMAIN
MOSTLY VFR. GUSTY WINDS WILL DEVELOP IN MANY AREAS THIS AFTERNOON
WITH GUSTS OF 25-30 KT AT KMFR AND 30-35 KT AT KLMT. FREEZING LEVELS
WILL DROP ABRUPTLY TODAY FROM NEAR 10000 FT MSL THIS MORNING TO
AROUND 3000 FT MSL BY WEDNESDAY MORNING. SPILDE

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WIND ADVISORY FROM NOON TODAY TO 8 PM PDT THIS EVENING FOR
     ORZ030-031.

CA...WIND ADVISORY FROM NOON TODAY TO 8 PM PDT THIS EVENING FOR
     CAZ085.
     FREEZE WATCH FROM LATE TONIGHT THROUGH WEDNESDAY MORNING FOR
     CAZ081.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS FROM 11 AM THIS MORNING TO 8 PM
     PDT THIS EVENING FOR PZZ350-356.
     HAZARDOUS SEAS WARNING FROM 11 AM THIS MORNING TO 8 PM PDT
     WEDNESDAY FOR PZZ350-356.
     GALE WARNING UNTIL NOON PDT TODAY FOR PZZ370-376.
     HAZARDOUS SEAS WARNING UNTIL 8 PM PDT WEDNESDAY FOR PZZ370-376.

$$