Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 160435
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
924 PM PDT MON SEP 15 2014

.DISCUSSION...SHOWERS HAVE MOVED OUT OF THE REGION AND TOMORROW
STILL LOOKS TO BE A WINDY DAY AHEAD OF THE FRONT THAT MOVES IN
WEDNESDAY. CURRENT FORECAST LOOKS ON TRACK AND WILL NOT UPDATE THIS
EVENING. SVEN

PREVIOUS DISCUSSION...A HIGH PRESSURE RIDGE IS PUSHING EAST OF
OREGON AND CALIFORNIA WHILE A TROUGH MOVES NORTH OVER THE OREGON
OFFSHORE WATERS. AS A RESULT, GUSTY SOUTHERLY WINDS HAVE DEVELOPED
IN THE SHASTA VALLEY WITH PEAK GUSTS TO 40 MPH AND ACROSS THE EAST
SIDE WITH PEAK GUSTS TO 30 MPH. WIND SPEEDS WILL BEGIN TO DIMINISH
AROUND 8 PM. THERE IS ALSO SCATTERED COVERAGE OF CUMULUS CLOUDS
PRIMARILY EAST OF THE CASCADES. THE AREA FROM MODOC AND LAKE
COUNTIES INTO HARNEY COUNTY HAS THE HIGHEST PROBABILITY OF AN
ISOLATED THUNDERSTORM DEVELOPING LATE THIS AFTERNOON INTO THIS
EVENING. BUT, WEAK INSTABILITY WILL BE PRESENT OVER MUCH OF THE AREA
WITH A SLIGHT CHANCE OF A THUNDERSTORM. ANY STORMS WILL MOVE QUICKLY
TO THE NORTH AT 20 TO 25 MPH AND PRODUCE VERY LITTLE OR NO RAINFALL.

THE AIR MASS OVER OUR AREA WILL STABILIZE LATE THIS EVENING WITH
SHORTWAVE RIDGING OFFSHORE TO EXTEND INTO OREGON ON TUESDAY. THIS
CHANGE IN THE PATTERN WILL START A COOLING TREND AND RESULT IN
BREEZY AFTERNOON SHASTA VALLEY AND EAST SIDE WINDS. WIND SPEEDS
WILL NOT BE AS STRONG AS THEY ARE THIS AFTERNOON, WITH WIND GUSTS
OF 25 TO 30 MPH.

THE COOLING WILL BE MORE NOTICEABLE ON WEDNESDAY WITH AN INCREASE
IN CLOUDS IN THE MORNING AHEAD OF A COLD FRONT DURING THE
AFTERNOON AND EVENING. THIS FRONT WILL BRING A SLIGHT CHANCE TO
CHANCE OF SHOWERS...MAINLY FROM THE CASCADES WESTWARD WITH THE
HIGHEST PROBABILITY AT THE COAST AND OVER THE HIGHER TERRAIN WEST
OF INTERSTATE 5. WEAK INSTABILITY INDICATED IN THE 12Z GFS AND
SREF ALSO SUPPORTS CONTINUING THE MENTION OF A SLIGHT CHANCE OF
AFTERNOON AND EVENING THUNDERSTORMS FOR EASTERN DOUGLAS COUNTY TO
THE VICINITY OF CRATER LAKE.  ANOTHER RESULT OF THE FRONT WILL BE
AN INCREASE IN SOUTHERLY WINDS, STRONGEST OVER THE HIGHER TERRAIN,
IN THE SHASTA VALLEY, AND ACROSS THE EAST SIDE.

A BROAD UPPER LEVEL TROUGH WILL FOLLOW LATE WEDNESDAY NIGHT INTO
THURSDAY WITH ADDITIONAL COOLING AND AN INCREASE IN MOISTURE AT
THE LOWER AND MID LEVELS OF THE ATMOSPHERE. THE RESULT WILL BE A
SLIGHT CHANCE TO CHANCE OF SHOWERS ACROSS A WIDER SWATH OF THE
AREA, INCLUDING THE EAST SIDE. ALL-IN-ALL THE PRECIPITATION
AMOUNTS BETWEEN WEDNESDAY AFTERNOON AND THURSDAY EVENING ARE
EXPECTED TO BE MEAGER WITH FEW AREAS RECEIVING MORE THAN A TENTH
OF AN INCH AND MANY INLAND AREAS RECEIVING ONLY A SMATTERING OF
VIRGA AND SPRINKLES.

A STRONG MARINE PUSH WILL FOLLOW LATE THURSDAY NIGHT WITH LOW
CLOUDS SPREADING FROM THE COAST INTO THE UMPQUA BASIN BEFORE
GRADUALLY DISSIPATING DURING FRIDAY. OTHERWISE, THERE WILL BE A
SUBSTANTIAL DECREASE IN CLOUD COVER AND A FEW DEGREES OF WARMING
ABOVE THE READINGS OF THURSDAY AS A HIGH PRESSURE RIDGE CENTERED
OFFSHORE FROM NORTHERN CALIFORNIA NUDGES INTO THE PACIFIC NORTHWEST.

LAST NIGHT`S SUITE OF MODEL DATA WAS IN DISAGREEMENT ON THE
FORECAST FOR THE WEEKEND AND EARLY NEXT WEEK. THE 12Z ECMWF AND
12Z GFS EACH TRENDED TOWARD THE OTHER AND HAVE ALLOWED CONFIDENCE
IN THE EXTENDED FORECAST TO INCREASE TO A MODERATE LEVEL.
THE MAIN SOURCE OF DISAGREEMENT WAS ON THE TRACK OF THE BROAD
UPPER LOW THAT WILL BE OVER OUR AREA ON THURSDAY THEN TRACK
SOUTHEAST INTO NEVADA ON FRIDAY. THE GFS HAD BEEN VERY PROGRESSIVE
AND INDICATED MODERATE TO STRONG RIDGING FOR THE WEST COAST, WHILE
THE ECMWF RETROGRADED AND CUT OFF THE LOW OVER CENTRAL CALIFORNIA
WITH THE POTENTIAL FOR A SUBSTANTIAL INCREASE IN MOISTURE AND
INSTABILITY. THE NEW, FAVORED SOLUTION RETROGRADES THE LOW FARTHER
TO THE SOUTH IN THE VICINITY OF SAN DIEGO. THIS WOULD KEEP THE
MOISTURE AND INSTABILITY OVER ARIZONA, SOUTHERN NEVADA, AND UTAH
AND ALLOW RIDGING TO BUILD ACROSS OUR AREA FOR A WARMING AND
DRYING TREND DURING THE WEEKEND THAT MAY CONTINUE INTO MONDAY.


&&

.AVIATION...BASED ON THE 15/18Z TAF CYCLE...
AT THE COAST- LOCALLY PERSISTENT STRATUS AND FOG WITH IFR CIGS AND
VIS ARE HUGGING THE COAST AND WILL PERSIST INTO THE AFTERNOON WITH A
BRIEF BREAK POSSIBLE AROUND 21Z BEFORE RETURNING LATE THIS AFTERNOON
AND EARLY THIS EVENING AND PERSISTING THROUGH THE NIGHT. CIG/VIS
PROBABLY WON`T BE AS LOW AT THE AIR FIELDS TONIGHT DUE TO SOME
COOLING AT THE TOP OF THE MARINE LAYER. AREAS OF MOSTLY VFR SMOKE
WILL AFFECT MUCH OF WESTERN SISKIYOU COUNTY AND NORTH INTO JACKSON
AND JOSEPHINE COUNTIES. SMOKE IS LIKELY TO BE MORE SUBSTANTIAL- IN
THE MVFR TO IFR RANGE- NEAR THE FIRE POINT SOURCES NEAR HAPPY CAMP
AND ONION MOUNTAIN. ELSEWHERE, VFR CONDITIONS ARE EXPECTED TO
CONTINUE. A LOW OFFSHORE WILL BRING A SLIGHT CHANCE OF THUNDERSTORMS
THIS AFTERNOON AND EVENING, MAINLY ACROSS MODOC, LAKE, AND
SOUTHEASTERN KLAMATH COUNTIES. ANY THUNDERSTORMS ARE EXPECTED TO BE
FAST MOVING FROM SOUTH TO NORTH AROUND 20-30 MPH WITH GUSTY WINDS IN
AND NEAR THEM. BTL

&&

.MARINE...UPDATED 300 PM PDT MON 15 SEP 2014...
A WEAK LOW JUST OFFSHORE WILL MOVE NORTHWARD AND AWAY FROM THE
FORECAST AREA TODAY AND TONIGHT. THEN ANOTHER LOW WILL APPROACH THE
WATERS FROM THE SOUTHWEST ON TUESDAY AND WEDNESDAY. SOUTH WINDS WILL
PEAK LATE TODAY INTO TUESDAY AFTERNOON WITH THE FIRST LOW...WITH
SOUTH TO SOUTHEAST WINDS CONTINUING TUESDAY THROUGH THURSDAY. AFTER A
SLIGHT DECREASE IN WIND SPEEDS WEDNESDAY MORNING...SOUTH WINDS
WILL PEAK AGAIN WEDNESDAY AFTERNOON WITH THE SECOND LOW. SEAS
WILL GRADUALLY INCREASE THIS AFTERNOON THROUGH WEDNESDAY AND THEN
REMAIN AROUND 7 FEET WEDNESDAY INTO WEDNESDAY NIGHT. WINDS
AND SEAS WILL LOWER THURSDAY AS HIGH PRESSURE BUILDS
OFFSHORE. NORTHERLY WINDS MAY RISE TO SMALL CRAFT ADVISORY LEVELS
FRIDAY AFTERNOON AND EVENING WITH STEEP SEAS
POSSIBLE AS WELL.  SK/BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...
CA...FIRE WEATHER WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY
     EVENING FOR CAZ284-285.

PACIFIC COASTAL WATERS...NONE.

$$

DW/MND/BTL









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