Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 042136
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
236 PM PDT WED MAY 4 2016

.SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO CONTINUE ACROSS MUCH OF OUR
FORECAST AREA. RADAR IS INDICATING THAT STORMS ARE ALREADY
BEGINNING TO FIRE EAST OF THE CASCADES. THESE STORMS ARE PRODUCING
FREQUENT CLOUD TO GROUND LIGHTNING, AND A FEW OF THEM ARE ALSO
PRODUCING SMALL HAIL. THIS WILL BE THE TREND FOR THE REMAINDER OF
THE AFTERNOON FOR THE EAST SIDE. MEANWHILE, DESPITE ONLY SEEING
SHOWERS THIS AFTERNOON, THE THUNDERSTORM THREAT ACROSS THE WEST
SIDE WILL CONTINUE THIS EVENING AS A SHORTWAVE LOOKS TO APPROACH
THE WEST SIDE. THIS WILL HELP BREAK THE CURRENT CAP AND ALLOW THE
ATMOSPHERE TO TAP INTO THE CONVECTIVE AVAILABLE POTENTIAL ENERGY
(CAPE) A BIT LATER.

THIS PATTERN OF SHOWERS AND STORMS IS EXPECTED TO CONTINUE THROUGH
THE REST OF THE WEEK DUE TO A LOW PRESSURE SYSTEM THAT IS
DEVELOPING OFF THE CENTRAL AND SOUTHERN CALIFORNIA COAST. THIS LOW
PRESSURE SYSTEM IS BRINGING WRAP AROUND MOISTURE AS WELL AS
SEVERAL SHORT WAVES WITH IT. THE MODELS ARE IN DECENT AGREEMENT
THAT THIS SYSTEM WILL MOVE SLOWLY ACROSS CALIFORNIA OVER THE NEXT
FEW DAYS, BUT THERE IS A BIT OF LOWER CONFIDENCE REGARDING THE
EXACT TRACK AS THE LOW IS EXPECTED TO WOBBLE. THE MAIN CONCERN
FOR THE SHOWERS AND STORMS WILL BE ON FRIDAY AFTERNOON ACROSS THE
EAST SIDE. THE STORM PREDICTION CENTER HAS PLACED PORTIONS OF LAKE
AND MODOC COUNTIES IN A MARGINAL RISK FOR A FEW SEVERE STORMS.
LOOKING AT LIFTED INDICIES AS WELL AS SHEAR AND CAPE VALUES, HAVE
INCREASED THE THUNDERSTORM CHANCES IN THE MARGINAL RISK AREAS.
OTHERWISE, THUNDERSTORMS ARE STILL EXPECTED IN AREAS WEST OF THE
CASCADES AS WELL.

AS THE LOW MOVES AWAY FROM CALIFORNIA INTO THE FOUR CORNERS
STATES ON SATURDAY, PRECIPITATION WILL BEGIN TO DECREASE ACROSS
MOST OF THE AREA. WINDS, HOWEVER, WILL SHIFT TO BECOME MORE
NORTHERLY; AND MODELS ARE INDICATING A PERIOD OF STRONG NORTHERLY
WINDS ACROSS THE EAST SIDE. CONFIDENCE IS TOO LOW AT THIS POINT TO
ISSUE A WIND ADVISORY SINCE THIS IS THE FIRST SET OF MODEL RUNS TO
SHOW THIS PATTERN, AND THIS SORT OF PATTERN WILL HINGE ON THE
TRACK OF THE LOW PRESSURE SYSTEM. -SCHAAF

.LONG TERM...SUNDAY THROUGH WEDNESDAY...THE MODELS REMAIN IN
FAIRLY GOOD AGREEMENT DURING THIS PERIOD. THE LARGE UPPER LOW WILL
MOVE NEAR THE FOUR CORNERS AND WEAK RIDGING WILL START TO BUILD IN
FROM THE SOUTHWEST. THE EC HAS BEEN SHOWING A WEAK FRONT MOVING
INTO THE AREA THE PAST COUPLE OF RUNS AND NOW THE GFS SHOWS THE
SAME. THE MAIN EFFECT FROM THIS WILL BE INCREASING ONSHORE FLOW,
THEREFORE HAVE ADJUSTED MAX TEMPERATURES DOWN BY A FEW DEGREES ON
AVERAGE WEST OF THE CASCADES. KEPT IN THE BEST CHANCE FOR SHOWERS
IN SOUTHEAST MODOC AND LAKE COUNTY, BUT IT`S POSSIBLE NOTHING
HAPPENS THERE. CONFIDENCE IS MODERATE THAT WE`LL REMAIN FLAT OUT
DRY FOR THE FIRST HALF OF NEXT WEEK. AN UPPER TROUGH WILL MOVE
SOUTHEAST INTO EASTERN WASHINGTON, NORTHEAST OREGON AND WESTERN
IDAHO MONDAY THROUGH TUESDAY. AS THIS HAPPENS AN UPPER RIDGE WILL
BUILD OFF THE COAST WITH A THERMAL TROUGH DEVELOPING AT THE COAST.
THE MODELS DIFFER WITH THE DETAILS AFTER TUESDAY, BUT THE PATTERN
IS STILL FAVORABLE FOR DRY CONDITIONS. -PETRUCELLI

&&

.AVIATION...FOR THE 04/18Z TAF CYCLE...ISOLATED THUNDERSTORMS WILL
BE THE MAIN CONCERN TODAY FOR INLAND TAF LOCATIONS WITH SOME
PRODUCING GUSTY AND ERRATIC WINDS. FOR NOW KEPT VCTS IN THE TAF FOR
KLAMATH FALLS. A TOUGH CALL FOR VCTS IN ROSEBURG AND MEDFORD AS
INSTABILITY IS MARGINAL AT BEST. KEPT IT OUT OF THE TAFS FOR NOW,
BUT THIS WILL NEED TO BE MONITORED CLOSELY SO WATCH OUT FOR UPDATES
SHOULD CONDITIONS WARRANT PUTTING THEM IN THE TAFS. CIGS ARE
EXPECTED TO VARY BETWEEN VFR AND MVFR WITH THE BEST CHANCE FOR MVFR
CONDITIONS IN SHOWERS AND ISOLATED THUNDERSTORMS. HIGHER TERRAIN IS
EXPECTED TO BE OBSCURED. AT THE COAST, THE MAIN CONCERN WILL BE
GUSTY NORTH WINDS AND MVFR CIGS ARE EXPECTED TO BE THE PREDOMINATE
CONDITION INTO TONIGHT.

&&

.MARINE...UPDATED 230 PM PDT WED 4 MAY 2016...THERE WAS LITTLE
CHANGE NEEDED FROM THE INHERITED FORECAST. OFFSHORE HIGH PRESSURE
AND INLAND LOW PRESSURE WILL PRODUCE PERSISTENT GUSTY NORTHERLY
WINDS AND STEEP TO VERY STEEP SEAS THROUGH FRIDAY EVENING. THE
STRONGEST WINDS AND HEAVIEST SEAS WILL OCCUR OVER THE OUTER WATERS
SOUTH OF CAPE BLANCO. WINDS ARE STILL EXPECTED TO WEAKEN SLIGHTLY
THIS WEEKEND WITH SPEEDS LIKELY TO BE AT ADVISORY LEVELS INCLUDING
THE HIGH END OF ADVISORY CRITERIA IN THE OUTER WATERS SOUTH OF
CAPE BLANCO. A SLOW IMPROVING TREND IS LIKELY TO CONTINUE EARLY
NEXT WEEK. -DW


&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 PM PDT FRIDAY
FOR PZZ350-356.
 GALE WARNING UNTIL 11 PM PDT FRIDAY FOR PZZ356-376.
HAZARDOUS SEAS WARNING UNTIL 11 PM PDT FRIDAY FOR
    PZZ350-356-370-376.

$$

BMS/MAP/DW


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