Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 052158 CCA
AFDMFR

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE MEDFORD OR
258 PM PDT TUE MAY 5 2015

.SHORT-TERM...TEMPERATURES ARE RUNNING 5 TO 10 DEGREES LOWER THAN
YESTERDAY...COURTESY OF A MOSTLY DRY...COOL UPPER TROUGH SWINGING
IN FROM THE NORTHWEST. PRECIPITATION WITH THIS TROUGH TONIGHT WILL
BE LIMITED TO MAINLY THE UMQPUA BASIN AND COAST NORTH OF CAPE
BLANCO. FAVORABLE DYNAMICS AND MOISTURE ARE STILL WELL TO THE
NORTH...AND SHOULD KEEP MOST OF THE CWA DRY. TOMORROW INSTABILITY
INCREASES AND ENERGY FROM THE UPPER LOW ARRIVES...BRINGING AN
INCREASED CHANCE FOR SHOWERS...AND THUNDERSTORMS ALONG AND EAST OF
THE CASCADES. 850MB COMPUTED LIFTED INDEX VALUES OF ZERO OR JUST
BELOW ZERO ARE NOT IMPRESSIVE...NOR ARE THE MEAGER CAPE VALUES SO
THUS THE SLIGHT CHANCE OF THUNDERSTORMS...BUT THERE SHOULD BE
ENOUGH DYNAMICS TO KICK OFF A FEW THUNDERSTORMS. ADDITIONALLY...A
BREEZY DAY IS EXPECTED ACROSS THE FORECAST AREA.

BY THURSDAY THE UPPER LOW IS IN CALIFORNIA...WITH SOME DEFORMATION-
TYPE DYNAMICS FAVORING SHOWERS AND POSSIBLY A THUNDERSTORM OVER
NORTHEAST CALIFORNIA. BREEZY CONDITIONS ARE EXPECTED AGAIN
ESPECIALLY EAST OF THE CASCADES WHERE IT WILL BE DOWNRIGHT GUSTY.
TEMPERATURES WILL BE COOL AGAIN WITH WHAT WILL BE THE THIRD DAY IN A
ROW OF BELOW NORMAL TEMPERATURES. WHEN EXAMINING THE POTENTIAL FOR
FROST/FREEZE IMPACTS ACROSS THE FORECAST AREA...WE EXPECT
TEMPERATURES TO REMAIN ABOVE THE IMPACT THRESHOLDS. THIS IS
PARTIALLY DUE TO MOISTURE ARRIVING IN THE LOW LEVELS OVERNIGHT WHICH
SHOULD HOLD TEMPERATURES UP. THIS SHOULD BE THE CASE AGAIN WEDNESDAY
NIGHT INTO THURSDAY MORNING. THAT SAID...GROWERS SHOULD BE AWARE
THAT TEMPERATURES WILL BE BELOW NORMAL THE NEXT FEW NIGHTS AND WE
ARE NOT OUT THE WOODS YET IN TERMS OF FROST/FREEZE POTENTIAL THIS
SPRING.

TEMPERATURES WILL RISE BY 5 TO 10 DEGREES ON FRIDAY AS THE UPPER LOW
MOVES OVER LAS VEGAS AND THE AIR MASS WARMS TO NEAR NORMAL VALUES
FOR THIS TIME OF YEAR. NO PRECIPITATION IS EXPECTED ON FRIDAY.


.LONG TERM...SATURDAY THROUGH TUESDAY NIGHT. THE MOST NOTABLE
CHANGES TO THE LONG TERM WERE TO INCREASE HIGH TEMPERATURES FORECAST
FOR SATURDAY AND TO NUDGE THE PROBABILITY OF PRECIPITATION HIGHER
FOR SUNDAY THROUGH TUESDAY NIGHT.

THE 12Z GFS AND ECMWF MODELS ARE IN VERY GOOD AGREEMENT AT THE
BEGINNING OF THE PERIOD WITH A HIGH PRESSURE RIDGE EXPECTED TO BUILD
INLAND ON SATURDAY AND RESULT IN MOSTLY SUNNY TO SUNNY SKIES.

BY SATURDAY EVENING, HIGH CLOUDS WILL BEGIN TO ARRIVE AS THE FIRST
SIGN OF A CHANGE IN THE PATTERN. CLOUDS WILL INCREASE SATURDAY NIGHT
AHEAD OF A BROAD UPPER LEVEL TROUGH. THE ECMWF IS SLIGHTLY
STRONGER/COLDER WITH THE TROUGH BUT THE GFS SOLUTION IS MUCH MORE
MOIST AND ITS INDICATED TRACK IS MUCH FARTHER TO THE SOUTH. THERE IS
SUFFICIENT MODEL SIMILARITY TO HAVE NUDGED UP THE PROBABILITY OF
PRECIPITATION AND LOWER TEMPERATURES AND INCREASE DEW POINTS. BUT,
THE ECMWF SOLUTION RESEMBLES THE TROUGH CURRENTLY MOVING INTO OUR
AREA AND DOES NOT GENERATE MUCH QPF WITH A PATTERN OF COOL
TEMPERATURES AND BREEZY NORTHERLY WINDS. THE ECMWF PRECIPITATION
AMOUNTS DURING ALL OF THE LONG TERM WOULD BE GENERALLY LESS THAN A
TENTH OF AN INCH. THE GFS SOLUTION WOULD BE NOTICEABLY
WETTER...ESPECIALLY SUNDAY NIGHT INTO MONDAY. BOTH MODELS DO NOT
BRING IN ANY PRECIPITATION UNTIL SUNDAY AFTERNOON AT THE EARLIEST.
UNCERTAINTY IS HIGH AND A STRAIGHT BLEND WAS UTILIZED AS THE GFS
SOLUTION HAS BEEN MORE CONSISTENT FROM RUN TO RUN OVER THE PAST
COUPLE OF DAYS, BUT THE ECMWF SOLUTION IS MORE IN HARMONY WITH THE
CHARACTERISTICS OF THE LAST FEW TROUGHS TO IMPACT OUR AREA.
/DW

&&

.MARINE...UPDATED 200 PM PDT TUESDAY 5 MAY 2015...OFFSHORE HIGH
PRESSURE WILL PERSIST INTO THIS WEEKEND. A THERMAL TROUGH NEAR THE
COAST WILL STRENGTHEN THROUGH FRIDAY AFTERNOON...THEN WEAKEN THIS
WEEKEND. OVERALL THIS IS A FAIRLY TYPICAL SUMMER PATTERN WITH
WINDS AND WAVES PEAKING IN THE AFTERNOON AND EVENING. THE THERMAL
TROUGH WILL BE THE DRIVING FACTOR FOR MARINE CONDITIONS INTO THE
WEEKEND. A WEAK FRONT WILL MOVE ONSHORE SUNDAY.

&&

.AVIATION...FOR THE 05/18Z TAF CYCLE...SKIES ARE VFR WITH
SCATTERED CLOUD COVER AS AN UPPER LEVEL TROUGH MOVES INLAND. AN
ISOLATED SHOWER OR TWO IS POSSIBLE AND SKIES WILL MAINLY REMAIN
VFR OVER THE NEXT 24 HOURS. BUT, MODERATE NORTHERLY LOW LEVEL
WINDS WILL BE GUSTY AND AREAS OF MVFR CIGS WITH HIGHER TERRAIN
OBSCURATION WILL RETURN TO THE WEST SIDE LATE THIS EVENING INTO
WEDNESDAY MORNING. /DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS FROM 5 PM WEDNESDAY TO 11 PM PDT
     FRIDAY FOR PZZ356-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT FRIDAY
     FOR PZZ350-356-370-376.

$$

NSK/DW/DW



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