Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 031837
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
1135 AM PDT SUN MAY 3 2015

.DISCUSSION...THERE ARE STILL LINGERING LOW CLOUDS IN THE COQUILLE
RIVER VALLEYS AS WELL AS ALONG THE SOUTHERN CURRY COUNTY COAST UP
TO JUST SOUTH OF GOLD BEACH. OTHERWISE SKY IS CLEAR ACROSS THE
REST OF THE FORECAST AREA. THE LATEST MODELS CONTINUE TO SHOW
AREAS OF INSTABILITY IN A SIMILAR LOCATION AS YESTERDAY...WHICH IS
ALONG THE LINE FROM MOUNT SHASTA NORTHEASTWARD INTO SE KLAMATH
COUNTY AND SOUTHERN LAKE COUNTY. THERE WERE A FEW LIGHTING
STRIKES YESTERDAY JUST SOUTH AND SOUTHEAST OF MODOC COUNTY. GIVEN
THAT INSTABILITY AREA IS QUITE SIMILAR...WE HAVE EXPANDED THE
SLIGHT CHANCE POTENTIAL INTO SOUTHERN AND SOUTHEASTERN MODOC
COUNTY FOR THIS EVENING...COVERAGE WILL AGAIN BE ISOLATED. /FB

&&

.FIRE WEATHER...UPDATED 1130 AM PDT SUNDAY, MAY 3, 2015... ISOLATED
THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND EVENING FROM THE
NORTHEASTERN TRINITY ALPS EASTWARD TO MAINLY THE NORTH AND WEST SIDE
OF MOUNT SHASTA AND THE GOOSENEST AREA...AND FROM THE MODOC PLATEAU
INTO CENTRAL LAKE COUNTY...AS WELL AS POSSIBLY IN SOUTHEASTERN MODOC
COUNTIES. MOISTURE, INSTABILITY, AND A TROUGH AT 500MB ARE ALL
NOTABLY MORE FAVORABLE FOR DEVELOPMENT THAN THEY WERE YESTERDAY.
STORMS THAT DEVELOP ARE LIKELY TO BE SINGLE AND MULTI-CELLULAR AND
SHOULD MOVE WEST-SOUTHWEST TO EAST-NORTHEAST AT AROUND 10-15 KNOTS.
WITH PRECIPITABLE WATER VALUES AROUND 0.60" AND THE STORM MOTION
MENTIONED, STORMS ARE LIKELY BE A MIX OF WET AND DRY. DRY LOW LEVELS
SUGGEST THAT STORMS COULD PRODUCE SOME GUSTY AND ERRATIC WINDS IN
THE 20 TO 30 KNOTS RANGE.  WITH CURRENT FUEL CONDITIONS RESULTING IN
MODERATE FIRE DANGER, CONCERNS FOR FIRE STARTS ARE THERE, BUT NOT
MAJOR. THIS IS MAINLY DUE TO THE CURRENT SIGNIFICANT LIVE FUEL
COMPONENT. WE EXPECT ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS IN A
SIMILAR AREA WITH PARAMETERS NEARLY IDENTICAL TO SUNDAY`S ON MONDAY,
THOUGH SHIFTED SOUTHWARD A BIT DUE TO MORE OF A DUE WEST TO EAST
FLOW AND STORM MOTION. BTL/BPN

&&

.AVIATION...FOR THE 03/18Z TAF CYCLE...EXPECT VFR TO PREVAIL FOR
MOST OF THE AREA TODAY. THE EXCEPTIONS WILL BE LIFR TO IFR STRATUS
AND FOG AND PARTIAL TERRAIN OBSCURATION FROM BROOKINGS AND THE
NEARBY COASTAL MOUNTAINS SOUTHWARD ALONG THE CURRY COAST, AS WELL AS
POSSIBLE MVFR TO LOCAL IFR VISIBILITIES AND PARTIAL TERRAIN
OBSCURATIONS FROM PRECIPITATION IN ANY SHOWER AND THUNDERSTORMS THAT
DEVELOP ACROSS NORTHERN CALIFORNIA AND SOUTHEASTERN OREGON THIS
AFTERNOON AND EVENING. GUSTY NORTH WINDS WILL RETURN TO THE COAST
THIS AFTERNOON THROUGH MID-EVENING, BUT WILL NOT BE AS STRONG AS THE
PREVIOUS TWO DAYS. IFR CEILINGS AND VISIBILITIES ARE LIKELY TO
RETURN TO THE COAST THIS EVENING, SPREADING INLAND INTO THE UMPQUA
BASIN AND POSSIBLY NORTHWESTERN JOSEPHINE COUNTY MONDAY MORNING AS
THE MARINE LAYER DEEPENS AND FLOW BECOMES MORE ONSHORE. BTL

&&

.MARINE...UPDATED 900 AM PDT SUNDAY, 3 MAY, 2015... MODERATE AND
GUSTY NORTH WINDS AND STEEP TO VERY STEEP SEAS WILL SLOWLY DIMINISH
THROUGH TODAY INTO MONDAY MORNING. A WEAK COLD FRONT WILL BRING SOME
SHOWERS AND BUILDING WEST SWELL ON TUESDAY. SEAS WILL EASE
WEDNESDAY...BUT MODERATE NORTH WINDS ARE LIKELY TO RETURN LATE
WEDNESDAY THROUGH THURSDAY AS LOW PRESSURE INLAND INTERACTS WITH
HIGH PRESSURE CENTERED WELL OFFSHORE. BTL

&&

.PREV DISCUSSION... /ISSUED 1257 AM PDT SUN MAY 3 2015/

DISCUSSION...03/00Z NAM/GFS IN.

MOSTLY CLEAR SKIES PREVAIL ACROSS THE MEDFORD CWA THIS
MORNING...EXCEPT FOR SOME MARINE STRATUS AROUND CAPE BLANCO...
BROOKINGS...THE COQUILLE VALLEY...AND THE OUTER MARINE WATERS.
THERE IS ALSO BITS OF CONVECTIVE DEBRIS EAST OF THE CASCADES.

UPPER LEVEL FLOW WILL REMAIN ROUGHLY ZONAL OVER THE AREA THROUGH
SUNDAY WITH EMBEDDED SHORT WAVES MOVING ONSHORE WELL TO THE NORTH
OF THE CWA...AND A WEAK BAGGY TROUGH OFF TO THE SOUTHWEST.

MOSTLY DRY AND WARM WEATHER WILL PERSIST THROUGH SUNDAY. SUNDAY
HIGHS WILL BE SIMILAR TO THE SATURDAY HIGHS...AROUND 10 DEGREES
ABOVE NORMAL IN THE UMPQUA BASIN AND 10 TO 15 DEGREES ABOVE
NORMAL OVER THE REST OF THE CWA.

SOME SHOWERS DEVELOPED OVER MODOC COUNTY SATURDAY AFTERNOON AND
EVENING...INDICATING THAT SUFFICIENT MOISTURE HAS FILTERED INTO
THE AREA. UPPER LEVEL SUPPORT FOR SHOWERS REMAINS MARGINAL...BUT
IT WILL BE SLIGHTLY BETTER SUNDAY WITH A WEAK ELONGATED SHORT WAVE
OVER THE AREA.

THE 03/00Z MODEL SOLUTIONS ARE FORECASTING INCREASED LIFTED
INDICES AS COMPARED TO WHAT OCCURRED SATURDAY AFTERNOON. OVERALL
THE THUNDERSTORM FORECAST FOR SUNDAY MATCHES UP WELL WITH ALL THE
INPUTS...SO WILL LET THAT FORECAST RIDE FOR THE MOST PART.

THE PATTERN STARTS TO CHANGE MONDAY AS A DIGGING OFFSHORE LONG
WAVE TROUGH WILL BRING INCREASING SOUTHWEST FLOW TO THE AREA.
MONDAY HIGHS WILL BE SEVERAL DEGREES COOLER OVER THE WEST SIDE AND
NEAR EAST SIDE AS THE MARINE INFLUENCE AND CLOUD COVER INCREASES
OVER THE AREA. OVER LAKE COUNTY AND MODOC COUNTY...MONDAY HIGHS
WILL BE SIMILAR TO THE SUNDAY HIGHS. EAST OF THE CASCADES AND OVER
NORTHERN CALIFORNIA...THERE WILL BE ANOTHER ROUND OF ISOLATED
THUNDERSTORMS IN ROUGHLY THE SAME AREA AS THE SUNDAY ACTIVITY.

THE TRANSITION TO A COOLER AND SHOWERY PATTERN WILL OCCUR MONDAY
NIGHT INTO TUESDAY AS AN UPPER LEVEL LONG WAVE TROUGH EDGES
ONSHORE. THIS WILL PUSH A COLD FRONT ONSHORE MONDAY NIGHT INTO
TUESDAY. ASSOCIATED PRECIPITATION WILL BE LIGHT AND MOSTLY LIMITED
TO THE WEST SIDE. TUESDAY WILL BE QUITE A BIT COOLER EVERYWHERE
WITH HIGHS DROPPING TO NEAR NORMAL VALUES OVER MOST OF THE
AREA...AND RANGING TO NEAR FIVE DEGREES ABOVE NORMAL OVER LAKE
COUNTY AND NORTHERN CALIFORNIA.

THE TROUGH WILL MOVE THROUGH THE AREA SLOWLY AS SHORT WAVES
DIVING DOWN THE BACK SIDE OF THE TROUGH WILL IMPEDE ITS PROGRESS.
ALL THAT COOL AIR ALOFT AND THE SHORT WAVES WILL SUPPORT ROUNDS OF
SHOWERS TUESDAY NIGHT INTO WEDNESDAY...BUT TIMING THOSE ROUNDS IS
A DIFFICULT FORECAST THIS FAR OUT. TEMPERATURES WILL BE COOLER
STILL WITH MANY AREAS DROPPING SLIGHTLY BELOW NORMAL.

LONG TERM DISCUSSION FROM THE SATURDAY AFTERNOON AFD...WED MAY
6TH THROUGH SUN MAY 10TH. A TROUGH OF LOW PRESSURE WITH AN
ASSOCIATED -25C TO -30C 500MB COLD POOL IS EXPECTED TO ELONGATE
AND WOBBLE SOUTHWARD FROM WASHINGTON TO CALIFORNIA, INLAND FROM
THE COAST, WEDNESDAY THROUGH THURSDAY. THE EXACT LOCATION OF THIS
TROUGH AND HOW IT IS STACKED VERTICALLY WHEN IT MOVES THROUGH WILL
ALL INFLUENCE PRECIPITATION POTENTIAL AND RESULTANT SENSIBLE
WEATHER FROM THIS WEATHER SYSTEM. IN SHORT, IT WILL BE COOLER WITH
HIGHS MOSTLY IN THE 50S AND 60S. LOWS WILL BE NEAR FREEZING ACROSS
THE EAST SIDE AND IN THE 30S AND 40S ON THE WEST SIDE WITH SOME
FROST POTENTIAL IN THE USUALLY COLDER WESTERN VALLEY SPOTS. WE DO
EXPECT SHOWERS AND A SLIGHT CHANCE OF AFTERNOON AND EVENING
THUNDERSTORMS DURING THIS TIME PERIOD, WITH THE GREATEST CHANCE OF
PRECIPITATION BEING ALONG AND NEAR THE CASCADE CREST. SNOW LEVELS
WILL BE MOSTLY BETWEEN 5000 AND 7000 FEET. WHILE PRECIPITATION
AMOUNTS WILL BE GENERALLY LIGHT, A QUICK SHOT OF WETTING
PRECIPITATION IS POSSIBLE DURING THIS TIME PERIOD IN ISOLATED TO
SCATTERED LOCATIONS.

FRIDAY THROUGH SUNDAY THE INITIAL TROUGH IS EXPECTED TO MOVE INTO
THE GREAT BASIN WHILE ANOTHER TROUGH SLIPS ONTO THE WEST COAST SOUTH
OF A STRONG RIDGE OVER SOUTHEASTERN ALASKA. WHILE DETAILS ARE VERY
MUCH IN QUESTION AS TO HOW AND WHEN THIS PATTERN TRANSITION WILL
OCCUR, IT APPEARS THE NET RESULT IS LIKELY TO BE A BIT OF A WARM-UP
FOLLOWED BY ANOTHER OPPORTUNITY FOR SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS THE AREA.

ALTOGETHER, WE EXPECT THE COOLER CONDITIONS AND SHOWERS TO SLOW
DRYING ACROSS THE AREA. HOWEVER, PERIODS OF WINDY CONDITIONS AND
LOWER DEWPOINTS ARE LIKELY TO COUNTERACT MOISTURE SAVING EFFECTS IN
MANY AREAS. THE LOWER DEWPOINTS ALSO RAISE CONCERN FOR SOME
SEASONABLE FROST AND FREEZE POSSIBILITIES DURING THIS TIME PERIOD IN
SOME WEST SIDE AREAS. BTL

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...
- SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT THIS EVENING FOR
  PZZ350-356-370-376.
- SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 AM PDT MONDAY
  FOR PZZ356-376.
- SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 8 PM PDT THIS
  EVENING FOR PZZ350-370.
- HAZARDOUS SEAS WARNING UNTIL 8 PM PDT THIS EVENING FOR PZZ376.

$$

FJB/BTL



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