Area Forecast Discussion
Issued by NWS Medford, OR

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170
FXUS66 KMFR 221601
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
900 AM PDT FRI MAY 22 2015

.DISCUSSION...MORNING UPDATE.

SOME RESIDUAL SHOWERS AROUND THE UPPER LOW CENTERED OVER SOUTHERN
CALIFORNIA ARE AFFECTING THE CWA THIS MORNING. SHOWERS ARE MOVING
NORTH TO SOUTH OVER THE CASCADES AND SPREADING INTO WEST SIDE
VALLEYS, SO BUMPED UP POPS IN AREAS FOR THIS MORNING. STEARING FLOW
IS MOSTLY NORTHERLY, THUS HIGHEST ACCUMULATIONS WILL BE IN THE
CASCADES AND CASCADE FOOTHILLS.

THIS AFTERNOON...MODELS SHOW INSTABILITY MAINLY OVER THE EAST SIDE
AND SISKIYOUS, WITH NORTHERLY STEARING FLOW. UPDATED FORECAST TO
KEEP ANY THUNDERSTORMS OUT OF THE WEST SIDE. -MSC/SBN

PREVIOUS DISCUSSION...22/00Z NAM/GFS IN.

SHOWERS ARE NOW WANING OVER THE MEDFORD CWA. THERE IS STILL SOME
SIGNIFICANT PRECIPITATION BEING REPORTED...ESPECIALLY OVER MODOC
COUNTY. THERE IS MORE TO COME OVER THE NEXT SEVERAL DAYS...BUT
COVERAGE WILL BE LESS AND THE FOCUS WILL BE EAST OF THE CASCADES.

THE LARGE SCALE PATTERN SHOWS A BLOCKY PATTERN OVER THIS PART OF
THE HEMISPHERE FOR THE NEXT TEN DAYS...BUT THE EVOLUTION OF THE
BLOCK WILL BRING VARIABLE WEATHER TO THE AREA. IT WON`T BE ONE OF
THOSE "WARM AND DRY FOR TWO WEEKS" SCENARIOS.

CURRENTLY THERE IS A DEVELOPING OMEGA BLOCK WITH A HIGH SETTING UP
ALONG THE ALASKA/CANADA BOUNDARY AND A DEVELOPING EASTERN ANCHOR
LOW ALONG THE CALIFORNIA COAST. THIS PATTERN WILL PERSIST INTO
THE WEEKEND BUT THE EASTERN ANCHOR LOW WILL WEAKEN AND MOVE
NORTHEAST INTO UTAH FRIDAY NIGHT...THEN INTO COLORADO SUNDAY.

AS THIS PATTERN EVOLVES...THE RIDGE PORTION OF THE OMEGA BLOCK
WILL BUILD INTO THE WEST COAST. THIS WILL PUSH THE MOST FAVORED
AREA FOR SHOWERS AND THUNDERSTORMS TO THE EAST. INCREASINGLY
STABLE CONDITIONS WILL ALSO MAKE FOR LESS COVERAGE AND LOWER
INTENSITIES.

ON FRIDAY MORNING...THE LOW WILL BE OVER SOUTHERN NEVADA AND FLOW
ALOFT WILL BECOME NORTHERLY. AN ONSHORE MARINE PUSH ON THE WEST
SIDE WILL PUT THE KABOSH ON SHOWER ACTIVITY THERE LATER THIS
AFTERNOON AND THIS EVENING...AND THE MAIN AXIS OF INSTABILITY
WILL SHIFT TO THE EAST SIDE WITH THE BEST CHANCE OF THUNDERSTORMS
OVER LAKE AND MODOC COUNTIES.

THE EASTERLY PROGRESSION WILL CONTINUE SATURDAY WITH LOWER CHANCES
OF SHOWERS DUE TO THE RIDGE BUILDING IN FROM THE WEST. ONCE AGAIN
ANY ACTIVITY THAT DOES DEVELOP WILL BE OVER LAKE AND MODOC
COUNTIES. THE NAM SHOWS A SHORT WAVE DROPPING SOUTH INTO THE AREA
SATURDAY...BUT THE TRAJECTORY OF THIS LOW EMBEDDED IN NORTHERLY
FLOW INDICATES IT WON`T HAVE MUCH MOISTURE TO WORK WITH. IT WILL
ALSO BE SOUTH OF THE CWA DURING MAXIMUM SOLAR HEATING...SO NVA
ALOFT WILL HELP SUPPRESS SHOWER ACTIVITY. THE STRONGEST EFFECT OF
THIS WAVE WILL LIKELY BE AN ONSHORE MARINE PUSH SATURDAY AFTERNOON
AND EVENING.

SUNDAY LOOKS TO BE MORE UNSTABLE AS A WEAK LOW MOVING THROUGH THE
BLOCK BRINGS A SLIGHTLY COOLER AIR MASS ALOFT FOR A MORE
CONVECTIVE ENVIRONMENT. STILL DOESN`T LOOK IMPRESSIVE...BUT AREAS
FROM THE CASCADES EAST MAY SEE SOME ISOLATED THUNDERSTORM
ACTIVITY.

THE LONG TERM DISCUSSION FOLLOWS...BUT THE LATEST MODEL RUNS NOW
SHOW SIGNIFICANT DIFFERENCES...BOTH BETWEEN MODELS AND RUN-TO-
RUN DIFFERENCES WITHIN THE SAME MODEL. THE GFS KEEPS A CONVECTIVE
ENVIRONMENT OVER THE AREA MONDAY WHILE THE EC BUILDS IN A RIDGE
FROM THE WEST...MAKING FOR MORE STABLE AND DRIER CONDITIONS EXCEPT
FOR THE FAR EAST SIDE. IN LIGHT OF ALL THIS...CONFIDENCE IN THE
EXTENDED FORECAST REMAINS LOW.

LONG TERM DISCUSSION FROM THE THURSDAY AFTERNOON AFD...MONDAY
THROUGH FRIDAY. MODELS BEGIN IN FAIRLY GOOD AGREEMENT THROUGH MOST
OF THE EXTENDED FORECAST PERIOD. MONDAY IS SHOWING THE BEST
AGREEMENT WITH MODELS WITH AN UPPER TROUGH PATTERN OVER THE WEST
COAST AND A CLOSED UPPER LOW OVER WA. THIS WILL INCREASE THE
MOISTURE FEED INTO THE REGION. FROM THERE THE GFS AND THE ECMWF
VARY WITH THE GFS INDICATING A CLOSED UPPER LOW OVER WA BY
WEDNESDAY AFTERNOON WITH THE ECMWF INDICATING A WEAK RIDGE
BUILDING IN FROM THE WEST. THIS IS THE FIRST APPEARANCE OF THE
UPPER LOW WITH THE GFS HOWEVER...AND WITH THE ENSEMBLE PLOTS ALSO
INDICATING THAT THE ECMWF RIDGING IS ALSO AN OUTLIER HAVE BROAD-
BRUSHED SLIGHT CHANCE THUNDERSTORMS OVER PORTIONS OF THE EAST SIDE
THROUGH THE REMAINDER OF THE EXTENDED. -SVEN

&&

.AVIATION...FOR THE 22/06Z TAF CYCLE...FROM THE CASCADES WEST,  MVFR
CIGS WILL CONTINUE THROUGH FRIDAY MORNING WITH GRADUAL CLEARING LATE
IN THE MORNING. THE UMPQUA BASIN COULD SEE MVFR CIGS LINGER INTO THE
AFTERNOON. ISOLATED IFR CIGS MAY ALSO DEVELOP IN THE KRBG AREA EARLY
THIS MORNING. EAST OF THE CASCADES EXPECT VFR WITH AREAS OF MVFR AND
LOCAL IFR CIGS THROUGH EARLY THIS MORNING. EXPECT KLMT TO REMAIN VFR
BUT THERE IS A POTENTIAL FOR MVFR/IFR TO DEVELOP EARLY THIS MORNING.
CONFIDENCE IS LOW FOR THIS TO OCCUR AT THIS TIME. ALONG THE COAST
EXPECT A MIX OF IFR/LIFR...LIFTING TO MVFR IN THE AFTERNOON. /FB

&&

.MARINE...UPDATED 830 PM PDT THURSDAY 21 MAY 2015..HIGH PRESSURE
OFFSHORE AND LOW PRESSURE INLAND WILL CONTINUE NORTHERLY WINDS
INTO NEXT WEEK. FRESH NORTHWEST SWELL WILL RESULT IN STEEP CHOPPY
SEAS OVERNIGHT. NORTH WINDS WILL BEGIN TO TREND HIGHER FRIDAY
AFTERNOON WITH THE POTENTIAL FOR SMALL CRAFT ADVISORY SOUTH OF
CAPE BLANCO FROM FRIDAY INTO MONDAY. MODELS ARE TRENDING HIGHER ON
WINDS FOR THIS WEEKEND AND MONDAY WITH CONFIDENCE INCREASING IN
SMALL CRAFT CONDITIONS SOUTH OF CAPE BLANCO. THESE CONDITIONS MAY
EXTEND NORTH OF CAPE BLANCO AS WELL. NORTH WINDS ARE EXPECTED TO
DIMINISH MONDAY NIGHT INTO WEDNESDAY. EXPECT A MIX OF WEST SWELL
WITH SHORT PERIOD NORTHWEST SWELL AS WELL AS SOUTHERLY SWELL INTO
MID NEXT WEEK. /FB

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS
        UNTIL 3 AM PDT FRIDAY FOR PZZ350-356-370-376.

$$

FB/JRS/DJW/SBN/MSC



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