Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 170401
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
901 PM PDT WED APR 16 2014

.DISCUSSION...AN UPDATE TO THE FORECAST IS NOT NECESSARY THIS
EVENING. THE 00Z NAM DATA HAS ARRIVED AND THE 00Z GFS IS JUST NOW
BEGINNING TO STREAM IN. A CHANGE IN OUR WEATHER IS IMMINENT WITH THE
IR IMAGERY SHOWING THE COLDER CLOUD TOPS ASSOCIATED WITH A COLD
FRONT OFFSHORE, ALONG 130W LONGITUDE. THE LOWER LEVELS OF THE
ATMOSPHERE WILL MOISTEN UP AHEAD OF THE FRONT WITH A CHANCE OF
LIGHT RAIN AT THE COAST LATE TONIGHT BEFORE RAIN DEVELOPS IN
EARNEST AFTER 5 AM PDT. THE PREVIOUS DISCUSSION, WHICH IS INCLUDED
BELOW, DESCRIBES THE ANTICIPATED SCENARIO QUITE WELL. THE SNOW
LEVEL IS EXPECTED TO FALL FROM AROUND 9000 FEET TO 6500 FEET
DURING THE DAY BUT LINGERING SHOWERS AND SNOW SHOWERS ARE EXPECTED
THURSDAY NIGHT WITH A DUSTING OF SNOW POSSIBLE AS LOW AS THE 5000
FOOT ELEVATION. WITH A WESTERLY FLOW, QPF WILL BE HIGHEST ON THE
WEST SIDE OF THE CASCADES.

CONDITIONS WILL IMPROVE UNDER WEAK HIGH PRESSURE FRIDAY INTO
EARLY SATURDAY THEN ANOTHER FRONT WITH STRONGER WIND BUT LESS
MOISTURE IS EXPECTED TO AFFECT THE AREA...MAINLY IN THE AFTERNOON
AND EVENING. FOR SATURDAY NIGHT AND SUNDAY AT THE COAST, IT IS
TOO EARLY TO HAVE CONFIDENCE IN THE SWELL FORECAST. BUT DUE
ATTENTION WILL BE PAID TO THE FUTURE MODEL RUNS AS THE 18Z GFS AND
WAVEWATCH SUPPORTED A FORECAST OF WEST TO NORTHWEST SEAS AT HIGH
SURF ADVISORY LEVELS. OTHERWISE, CONDITIONS ACROSS SOUTHERN OREGON
AND NORTHERN CALIFORNIA LOOK TO IMPROVE ON SUNDAY WITH A BREAK
BEFORE THE NEXT COLD FRONT APPROACHES ON MONDAY.

&&

.AVIATION...BASED ON 17/00Z TAF CYCLE...FROM THE CASCADES WEST...VFR
CONDITIONS WILL PREVAIL INITIALLY. AREAS OF MVFR CIGS/VSBYS IN RAIN
AND DRIZZLE WILL DEVELOP AT THE COAST OVERNIGHT AND CONTINUE THURSDAY
MORNING. THE RAIN WILL SPREAD INLAND TO THE CASCADES DURING THE
DAY THURSDAY WITH HIGHER TERRAIN BECOMING OBSCURED. THE LOWER
CONDITIONS WILL CONTINUE INTO THURSDAY EVENING AS RAIN TRANSITIONS TO
SHOWERS. EAST OF THE CASCADES...VFR CONDITIONS WILL PREVAIL INTO
THURSDAY MORNING. LOCAL MVFR CIGS AND RAIN WILL DEVELOP LATE
THURSDAY AFTERNOON INTO THURSDAY EVENING WITH AREAS OF HIGHER
TERRAIN BECOMING OBSCURED. THE LOWER CONDITIONS WILL CONTINUE
THROUGH THURSDAY NIGHT.

&&

.MARINE...IT IS TOO EARLY TO HAVE CONFIDENCE ON THE DETAILS BUT THE
FOCUS IS ON THE POTENTIAL FOR HEAVY WEST TO NORTHWEST SWELL
SATURDAY NIGHT INTO SUNDAY.

GUSTY NORTH WINDS AND STEEP SEAS SOUTH OF GOLD BEACH HAVE
DIMINISHED THIS EVENING. WINDS WILL BACK TO SOUTHERLY ON THURSDAY
MORNING AHEAD OF A COLD FRONT THAT WILL MOVE THROUGH THE WATERS
WITH RAIN. RAIN WILL CHANGE TO SHOWERS LATE THURSDAY MORNING AND
CONTINUE INTO THURSDAY EVENING. HIGH PRESSURE WILL BRIEFLY BUILD
FRIDAY INTO FRIDAY NIGHT WITH DIMINISHING SEAS. A STRONGER FRONT
WILL MOVE THROUGH SATURDAY WITH THE POTENTIAL FOR SMALL CRAFT
ADVISORY LEVEL WINDS AND SEAS. THE WAVEWATCH MODEL INDICATES A
RAPIDLY RISING HEAVY WESTERLY SWELL OF 15 TO 17 FEET WILL DEVELOP
LATE SATURDAY NIGHT INTO SUNDAY...THEN SUBSIDE BUT REMAIN HIGH
THROUGH MONDAY NIGHT. ANOTHER FRONT WILL MOVE THROUGH THE AREA
LATE SUNDAY NIGHT OR EARLY MONDAY.

&&

.PREV DISCUSSION... /ISSUED 259 PM PDT WED APR 16 2014/

DISCUSSION...DRY CONDITIONS WILL CONTINUE INTO TONIGHT WITH
SCATTERED HIGH AND MID LEVEL CLOUDS MOVING THROUGH. THE EXCEPTION
WILL BE IN PARTS OF COOS AND WESTERN DOUGLAS COUNTY WHERE MARINE
CLOUDS ARE INCREASING. PREVIOUS FORECAST HAD A MENTION OF PATCHY
DRIZZLE FOR THE NORTH COAST TONIGHT AS THE MARINE LAYER THICKENS.
NOT CONFIDENT THIS WILL HAPPEN, BUT SINCE IT`S A SLIGHT CHANCE,
WE`LL LEAVE IT IN.

AN UPPER TROUGH NEAR 44N/149W IS HEADING OUR WAY AND WILL MOVE INTO
THE FORECAST AREA THURSDAY. AHEAD OF IT WILL BE A COLD FRONT WHICH
WILL REACH THE COAST AROUND MID MORNING THURSDAY, THEN PUSH INLAND
THURSDAY AFTERNOON. AT THIS POINT, WERE NOT EXPECTING A LOT OF
PRECIPITATION WITH THE HIGHEST AMOUNTS ALONG THE CASCADES FROM
CRATER LAKE NORTH. 0.10-0.20 OF AN INCH IS POSSIBLE ALONG THE
CASCADES FROM CRATER LAKE NORTH, MOST OF WHICH SHOULD BE IN THE
AFTERNOON AND EARLY EVENING. SNOW LEVELS WILL COME DOWN SOME, BUT
THE AIR MASS BEHIND THE FRONT IS NOT THAT COLD, SO SNOWFALL
ACCUMULATIONS AROUND CRATER LAKE WILL BE MINOR IF ANYTHING. THE
MODELS STILL HINT AT WEAK INSTABILITY IN SOUTHEAST LAKE AND EASTERN
MODOC COUNTY THURSDAY AFTERNOON, SO KEPT IN THE SLIGHT CHANCE
MENTION OF THUNDERSTORMS. ALSO LOWERED TEMPERATURES DOWN A BIT WEST
OF THE CASCADES DUE TO THICKER CLOUD COVER AND PRECIPITATION.

THE ABOVE MENTIONED UPPER TROUGH SWINGS THROUGH THE REGION THURSDAY
NIGHT. I EXPECT SHOWERS TO CONTINUE INTO THE EVENING, THEN DECREASE
DURING THE OVERNIGHT HOURS AS THE TROF AXIS SHIFTS EAST, BUT A
WESTERLY FLOW WILL BE IN IT`S WAKE AND EXPECT SHOWERS TO LINGER IN
AREAS OF STRONGER OROGRAPHIC LIFT, LIKE THE CASCADES. DRY WEATHER
RETURNS FRIDAY WITH WEAK RIDGING BUILDING BACK INTO THE AREA. COULD
NOT RULE OUT A FEW LEFTOVER SHOWERS ALONG THE NORTHERN CASCADES
EARLY FRIDAY, BUT THAT`S IT. TEMPERATURES FRIDAY SHOULD REBOUND AND
END UP IN THE UPPER 60S TO LOWER 70S FOR WESTSIDE VALLEYS.

MODELS SHOW ANOTHER FRONT APPROACHING THE FORECAST AREA SATURDAY.
THE NAM IS SLOWER AND WEAKER COMPARED TO THE GFS/EC AND GEM AND GUT
FEELING IS THAT THIS MAY BE CORRECT. AT THIS TIME, WENT WITH A BLEND
BETWEEN THE NAM AND THE OTHER SOLUTIONS, BUT WOULD NOT BE SURPRISED
IF THE OTHER MODELS TREND WEAKER AND DRIER WITH SATURDAY`S FRONT.
-PETRUCELLI

EXTENDED DISCUSSION...FROM SUNDAY MORNING ONWARD. SUNDAY MORNING
STARTS IN A SLIGHTLY SW OF ZONAL FLOW PATTERN. AND A FRONT WELL OFF
SHORE AT AROUND 130W. THE JET ASSOCIATED WITH THIS FRONT IS AROUND
120KT...ALIGNED FROM THE SW WITH THE NOSE OF THE JET AT SEATTLE. THE
CORE OF THE JET MOVES DOWN OVER SW OREGON BY MONDAY MORNING AND
SWEEPS THROUGH THE REGION BRING THE DAY. HOWEVER... THE ANTECEDENT
FLOW AHEAD OF THIS FRONT IS FROM THE NW OFF THE COOLER WATERS AND
LIMITS THE MOISTURE FEED IN AHEAD OF THE FRONT...RESULTING IN JUST
LIGHT TO MODERATE PRECIP AMOUNTS. BOTH THE GFS AND ECMWF ARE IN GOOD
AGREEMENT ON FORMING A CLOSED LOW PAST 130W OFF VANCOUVER ISLAND.
TUESDAY MORNING...AND SWING THE LOW DOWN TO THE OREGON COAST BEFORE
OPENING TO AN UPPER LEVEL TROUGH. THIS WITH THE ONSHORE FLOW WILL
KEEP A SHOWERY PATTERN THROUGH THURSDAY.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

DW/JRS






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