Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 050409
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
909 PM PDT SAT JUL 4 2015

.DISCUSSION...UPDATED THUNDERSTORM COVERAGE FOR THIS EVENING TO
INCREASE COVERAGE IN SHASTA VALLEY OF SISKIYOU COUNTY. OTHERWISE
THE THUNDERSTORMS OCCURRED WHERE WE THOUGHT THEY WOULD. ALSO
UPDATED SKY GRIDS FOR TONIGHT.

NEW MODEL RUN SHOWS INSTABILITY AND MOISTURE MAY NOT BE SHIFTING
EAST AS FAST AS WE THINK. NIGHT SHIFT WILL HAVE TO RE-EVALUATE
COVERAGE FOR SUNDAY. /FB

&&

.AVIATION...FOR THE 05/00Z TAF CYCLE...ALONG THE COAST...VFR
CONDITIONS WILL PREVAIL ALONG THE COAST WITH AREAS OF MVFR/IFR CIGS
OFFSHORE. IFR TO LIFR CIGS WILL DEVELOP TONIGHT...AND CLEAR SUNDAY
MORNING. THERE IS A CHANCE OF IFR VIS ALONG THE COAST TONIGHT...BUT
MODEL GUIDANCE INDICATES INVERSION WILL BE TOO HIGH FOR FOG. VFR
CONDITIONS WILL PREVAIL IN WEST SIDE VALLEYS.

SCATTERED THUNDERSTORMS ARE OCCURING IN SOUTHERN AND NORTHEAST
SISKIYOU COUNTY. EXPECT THESE TO PERSIST WITH GRADUAL SOUTHWEST TO
NORTHEAST STEARING. COULD NOT RULE OUT THUNDERSTORMS IN THE VCTY OF
KLMT GIVEN SURFACE TEMPERATURE AND INSTABILITY...BUT DRY MIDLEVELS
MAY PREVENT FORMATION.

AFTERNOON THUNDERSTORMS ON SUNDAY WILL BE MORE
WIDESPREAD...GENERALLY FROM THE CASCADES EAST AND SISKIYOUS SOUTH.

-MSC/JRS


&&

.MARINE...UPDATED 900 PM PDT SATURDAY 4 JULY 2015...A THERMAL
TROUGH NEAR THE COAST HAS WEAKENED...AND WINDS WILL DECREASE AND
BEGIN TURNING ONSHORE OVERNIGHT THROUGH SUNDAY. THE SMALL CRAFT
ADVISORY FOR SEAS WAS CANCELLED...AS OBSERVATIONS INDICATE CURRENT
CONDITIONS ARE SUB-ADVISORY LEVEL...AND GUIDANCE INDICATES SEAS
WILL GRADUALLY SUBSIDE TONIGHT THROUGH SUNDAY. STRATUS WILL
INCREASE OVER MOST OF THE COASTAL WATERS BY SUNDAY...BUT EXPECT
ENOUGH MIXING TO PREVENT FOG. MONDAY...WINDS WILL BACK TO
SOUTHERLY AROUND A LOW OFFSHORE. WINDS WILL TURN NORTH TO
NORTHWESTERLY BY MIDWEEK. WINDS AND SEAS WILL STAY BELOW ADVISORY
CRITERIA THROUGH AT LEAST MIDWEEK...POSSIBLY THROUGH THE END OF
THE WEEK. -MSC


&&

.FIRE WEATHER...UPDATED 830 PM PDT SATURDAY 4 JULY
2015...THUNDERSTORM DEVELOPED FARTHER WEST THAN EXPECTED AND
NUMEROUS LIGHTNING OCCURRED IN THE SHASTA VALLEY OF SISKIYOU
COUNTY. ELSEWHERE THUNDERSTORMS OCCUR ALONG WHERE WE THOUGHT IT
WOULD...FROM MEDICINE LAKE NE INTO THE GERBER AREA OF SOUTHERN
OREGON THEN TO THE HART MOUNTAIN REFUGE. THE STORMS IN SISKIYOU
COUNTY PRODUCED RAIN WITH THE ONES IN THE SHASTA VALLEY PRODUCING
BETWEEN 0.25-0.50 INCH. WE UPDATED THE RED FLAG WARNING TO INCLUDE
ZONE 281 AND IT WOULD BE INTERESTING TO KNOW HOW MANY OF THOSE
STRIKES OCCUREED OUTSIDE THE RAIN CORE. THE FOLLOWING PARAGRAPHS
ARE FROM THE PREVIOUS FORECAST THIS AFTERNOON BUT STILL PERTAIN TO
FUTURE CONDITION. /FB

UPDATED 230 PM PDT SATURDAY 4 JULY 2015...IN TERMS
OF WHAT HAS CHANGED, THERE IS INCREASED CONFIDENCE IN THUNDERSTORMS
THIS EVENING AND TONIGHT THAN IN PREVIOUS CYCLES. MANY OF THE HIGHER
RESOLUTION MODELS TODAY HAVE CONSISTENTLY PRODUCED AN AREA OF
CONVECTION DEVELOPING AROUND 00 UTC THIS EVENING, OR 5 PM PDT,
ROUGHLY CENTERED AROUND AND TO THE SOUTHEAST OF A LINE FROM MEDICINE
LAKE IN NORTHERN CALIFORNIA TO SUMMER LAKE IN SOUTH CENTRAL OREGON.
THE MOISTURE IS PRESENT, AS IS THE INSTABILITY. THE QUESTION REMAINS
AS TO THE NATURE AND TIMING OF AN UPPER LEVEL WAVE WHICH WOULD
PROVIDE THE LIFT NEEDED TO GET STORMS ROLLING. THE LATEST MODELS
TODAY HAVE ALL BEGUN TO PRODUCE SUCH A WAVE LATE THIS AFTERNOON AND
EVENING, OR EARLY TONIGHT, THEN KEEPING THE ENERGY IN THE AREA
THROUGH THE OVERNIGHT HOURS. FOR THIS REASON, SUSPECT THAT NOCTURNAL
STORMS ARE POSSIBLE TONIGHT AS WELL. HOWEVER, ANOTHER FACTOR WILL BE
DRY AIR IN THE MID LEVELS, WHICH WOULD INHIBIT STORM FORMATION AND
STRENGTH. MODEL GUIDANCE SHOWS THIS DRY AIR PUSHING IN FROM THE
WEST, AND THIS WOULD LIKELY BEGIN TO PUSH THE MAIN AREA OF STORMS TO
THE EAST LATE TONIGHT AND TOMORROW. TAKING ALL OF THIS INTO ACCOUNT,
HAVE DECIDED TO UPGRADE TO A RED FLAG WARNING FOR MOST OF THE WATCH
AREA, BUT HAVE CUT OUT SOME OF THE MORE WESTERN LOCATIONS, AS THE
DRY AIR AND A LACK OF UPPER LEVEL SUPPORT SHOULD INHIBIT ANY MORE
THAN ISOLATED DEVELOPMENT THERE. ALL THUNDERSTORMS DURING THIS TIME
SHOULD BE RAIN PRODUCERS. HOWEVER, GIVEN DRY LOW LEVELS, LIGHTNING
OUTSIDE THE MAIN CORES WOULD BE DRY. THERE IS ALSO THE POTENTIAL FOR
GUSTY OUTFLOW WINDS, WHICH COULD HELP NEW STARTS TAKE HOLD.

LOOKING AHEAD TO NEXT WEEK, AN APPROACHING TROUGH FROM THE SOUTHWEST
WILL BE THE PRIMARY THREAT FOR PRODUCING NOT ONLY THUNDERSTORMS, BUT
DEPENDING ON ITS TRACK AND TIMING, COULD ALSO PRODUCE GUSTY WINDS.
THE FORECAST WILL KEEP AFTERNOON AND EVENING THUNDERSTORM CHANCES IN
PLACE, PERHAPS EXPANDED TO THE WESTERN FOOTHILLS OF THE CASCADES AS
WELL, FOR JUST ABOUT EVERY DAY THROUGH THE WEEK, WITH THE BEST
CHANCE FOR MORE WIDESPREAD STORMS POSSIBLE ON TUESDAY. -BPN

&&

.PREV DISCUSSION... /ISSUED 524 PM PDT SAT JUL 4 2015/

DISCUSSION...IT`S ANOTHER HOT DAY TODAY...WITH A CURRENT READING OF
99F AT ROGUE VALLEY INTERNATIONAL AIRPORT. SO...THE HEAT ADVISORY AT
NPWMFR CONTINUES THROUGH THIS EVENING FOR THE
ROGUE...ILLINOIS...KLAMATH RIVER...AND SCOTT VALLEYS. RELIEF FROM
THE HEAT WILL BE VERY SUBTLE...COOLING BY A DEGREE OR SO EACH OF
THE NEXT FEW DAYS AS AN UPPER LOW APPROACHES FROM THE
WEST...COOLING THE AIR MASS AND BRINGING IN SOME ADDITIONAL CLOUD
COVER.

THIS UPPER LOW WILL HELP DICTATE OUR WEATHER PATTERN INTO NEXT WEEK.
WE HAVE BEEN PORING OVER DATA TODAY TO HELP DETERMINE THE
EVOLUTION OF THUNDERSTORM COVERAGE AND TIMING THE NEXT FEW DAYS.
MODEL CONSENSUS SUGGESTS THUNDERSTORMS THIS AFTERNOON WILL BE
FOCUSED OVER NORTHERN CALIFORNIA AND SOUTHERN LAKE AND KLAMATH
COUNTIES...WHERE SUFFICIENT MOISTURE ALOFT INTERSECTS WITH
GREATEST INSTABILITY. LATE TONIGHT...A DISTINCT SHORTWAVE TROUGH
SHOWN ON THE NAM...GFS...SREF...AND ECMWF OUTPUT...NEARS NORTHEAST
CALIFORNIA AND SHOULD HAVE ENOUGH INSTABILITY TO WORK WITH TO
DELIVER ISOLATED THUNDERSTORMS MAINLY IN MODOC AND SOUTHERN LAKE
COUNTIES. TOMORROW...THERE ARE A FEW KEY ELEMENTS TO THUNDERSTORM
POTENTIAL. THE AFOREMENTIONED SHORTWAVE WILL CONTINUE TO TREK
NORTHWARD...CLEARER ON THE NAM12...AND THIS SHOULD CONTINUE TO
FOCUS SCATTERED THUNDERSTORMS OVER THE SOUTHEAST PORTION OF THE
CWA. ADDITIONALLY...DRIER AIR ALOFT WILL MAKES ITS WAY WEST TO
EAST THROUGH THE CWA DURING THE DAY...DIMINISHING THUNDERSTORM
CHANCES DURING ITS TRANSIT. A RED FLAG WARNING AT RFWMFR HAS BEEN
ISSUED FOR THE AREAS MOST LIKELY TO SEE SIGNIFICANT
LIGHTNING IN EASTERN SISKIYOU...MODOC...AND SOUTHERN KLAMATH AND
LAKE COUNTIES...AND YOU CAN READ MORE ABOUT THIS IN THE FIRE
WEATHER DISCUSSION BELOW. ADDITIONALLY...WEST OF THE CASCADES IN
THE SOUTHWEST OREGON VALLEYS THERE ARE IS NOT SUFFICIENT DYNAMICS
OR MOISTURE...AND TOO MUCH STABILITY...TO WARRANT THUNDERSTORM
CHANCES.

MODELS SUGGEST SOMEWHAT OF A DECREASE IN THUNDERSTORM ACTIVITY ON
MONDAY...BUT HAVE KEPT POPS SIMILAR LATE MONDAY BECAUSE DEEP FLOW
BEGINS TO TURN SOUTHERLY AGAIN...SO HAVE A MIX OF SLIGHT CHANCE TO
CHANCE OF THUNDERSTORMS FOCUSED OVER THE SOUTHERN PORTION OF THE
CWA. INTERESTINGLY...CONVECTIVE INHIBITION IN THE ROGUE VALLEY IS
LOWER ON MONDAY THAN PREVIOUS DAYS...BUT WITHOUT A GOOD
TRIGGER...ONLY HAVE ABOUT A 15% CHANCE OF THUNDERSTORMS.

TUESDAY THROUGH WEDNESDAY ARE VERY SIMILAR PATTERNS...WITH STOUT
EAST-SOUTHEASTERLY FLOW ALOFT AND PLENTY OF MOISTURE AND INSTABILITY
FOCUSED OVER THE SOUTHWESTERN PORTION OF THE CWA. HAVE MAINTAINED A
BROAD AREA OF 20-30% CHANCE OF THUNDERSTORMS BOTH DAYS...WITH A
CHANCE OF SHOWERS OVERNIGHT...AS ANY NOCTURNAL THUNDERSTORM
POTENTIAL WILL BE DEPENDENT ON SHORTWAVE ACTIVITY THAT WILL BE
DEFINED IN FUTURE MODEL RUNS. ONE ASPECT OF THE CONVECTION ON
TUESDAY AND WEDNESDAY IS THE HIGH MOISTURE CONTENT. PRECIPITABLE
WATER VALUES OF 1 INCH+ WILL AFFECT SW OREGON AND NW
CALIFORNIA...WHICH ARE ANOMALOUSLY HIGH FOR THIS TIME OF YEAR.
HEAVY RAIN MAY ACCOMPANY SOME OF THESE STORMS.

COOLER TEMPERATURES WILL FINALLY ARRIVE IN EARNEST LATER NEXT WEEK
AS THE OFFSHORE UPPER LOW MOVES INLAND...BRINGING TEMPERATURES TO
THE NEAR-NORMAL RANGE.

AVIATION...FOR THE 05/00Z TAF CYCLE...ALONG THE COAST...VFR
CONDITIONS WILL PREVAIL ALONG THE COAST WITH AREAS OF MVFR/IFR CIGS
OFFSHORE. IFR TO LIFR CIGS WILL DEVELOP TONIGHT...AND CLEAR SUNDAY
MORNING. THERE IS A CHANCE OF IFR VIS ALONG THE COAST TONIGHT...BUT
MODEL GUIDANCE INDICATES INVERSION WILL BE TOO HIGH FOR FOG. VFR
CONDITIONS WILL PREVAIL IN WEST SIDE VALLEYS.

SCATTERED THUNDERSTORMS ARE OCCURRING IN SOUTHERN AND NORTHEAST
SISKIYOU COUNTY. EXPECT THESE TO PERSIST WITH GRADUAL SOUTHWEST TO
NORTHEAST STEARING. COULD NOT RULE OUT THUNDERSTORMS IN THE VCTY OF
KLMT GIVEN SURFACE TEMPERATURE AND INSTABILITY...BUT DRY MIDLEVELS
MAY PREVENT FORMATION.

AFTERNOON THUNDERSTORMS ON SUNDAY WILL BE MORE
WIDESPREAD...GENERALLY FROM THE CASCADES EAST AND SISKIYOUS SOUTH.

-MSC/JRS

MARINE...UPDATED 300 PM PDT SATURDAY 4 JULY 2015...A THERMAL TROUGH
NEAR THE COAST HAS WEAKENED...AND WINDS WILL DECREASE AND BEGIN
TURNING ONSHORE THIS EVENING THROUGH SUNDAY. THE SMALL CRAFT
ADVISORY FOR SEAS WAS CANCELLED...AS OBSERVATIONS INDICATE CURRENT
CONDITIONS ARE SUB-ADVISORY LEVEL...AND GUIDANCE INDICATES SEAS WILL
GRADUALLY SUBSIDE TONIGHT THROUGH SUNDAY. STRATUS WILL INCREASE OVER
MOST OF THE COASTAL WATERS BY SUNDAY...BUT EXPECT ENOUGH MIXING TO
PREVENT FOG. MONDAY...WINDS WILL BACK TO SOUTHERLY AROUND A LOW
OFFSHORE. WINDS WILL TURN NORTH TO NORTHWESTERLY BY MIDWEEK. WINDS
AND SEAS WILL STAY BELOW ADVISORY CRITERIA THROUGH AT LEAST
MIDWEEK...POSSIBLY THROUGH THE END OF THE WEEK. -MSC

FIRE WEATHER...IN TERMS OF WHAT HAS CHANGED, THERE IS INCREASED
CONFIDENCE IN THUNDERSTORMS THIS EVENING AND TONIGHT THAN IN
PREVIOUS CYCLES. MANY OF THE HIGHER RESOLUTION MODELS TODAY HAVE
CONSISTENTLY PRODUCED AN AREA OF CONVECTION DEVELOPING AROUND 00
UTC THIS EVENING, OR 5 PM PDT, ROUGHLY CENTERED AROUND AND TO THE
SOUTHEAST OF A LINE FROM MEDICINE LAKE IN NORTHERN CALIFORNIA TO
SUMMER LAKE IN SOUTH CENTRAL OREGON. THE MOISTURE IS PRESENT, AS
IS THE INSTABILITY. THE QUESTION REMAINS AS TO THE NATURE AND
TIMING OF AN UPPER LEVEL WAVE WHICH WOULD PROVIDE THE LIFT NEEDED
TO GET STORMS ROLLING. THE LATEST MODELS TODAY HAVE ALL BEGUN TO
PRODUCE SUCH A WAVE LATE THIS AFTERNOON AND EVENING, OR EARLY
TONIGHT, THEN KEEPING THE ENERGY IN THE AREA THROUGH THE OVERNIGHT
HOURS. FOR THIS REASON, SUSPECT THAT NOCTURNAL STORMS ARE POSSIBLE
TONIGHT AS WELL. HOWEVER, ANOTHER FACTOR WILL BE DRY AIR IN THE
MID LEVELS, WHICH WOULD INHIBIT STORM FORMATION AND STRENGTH.
MODEL GUIDANCE SHOWS THIS DRY AIR PUSHING IN FROM THE WEST, AND
THIS WOULD LIKELY BEGIN TO PUSH THE MAIN AREA OF STORMS TO THE
EAST LATE TONIGHT AND TOMORROW. TAKING ALL OF THIS INTO ACCOUNT,
HAVE DECIDED TO UPGRADE TO A RED FLAG WARNING FOR MOST OF THE
WATCH AREA, BUT HAVE CUT OUT SOME OF THE MORE WESTERN LOCATIONS,
AS THE DRY AIR AND A LACK OF UPPER LEVEL SUPPORT SHOULD INHIBIT
ANY MORE THAN ISOLATED DEVELOPMENT THERE. ALL THUNDERSTORMS DURING
THIS TIME SHOULD BE RAIN PRODUCERS. HOWEVER, GIVEN DRY LOW LEVELS,
LIGHTNING OUTSIDE THE MAIN CORES WOULD BE DRY. THERE IS ALSO THE
POTENTIAL FOR GUSTY OUTFLOW WINDS, WHICH COULD HELP NEW STARTS
TAKE HOLD.

LOOKING AHEAD TO NEXT WEEK, AN APPROACHING TROUGH FROM THE SOUTHWEST
WILL BE THE PRIMARY THREAT FOR PRODUCING NOT ONLY THUNDERSTORMS, BUT
DEPENDING ON ITS TRACK AND TIMING, COULD ALSO PRODUCE GUSTY WINDS.
THE FORECAST WILL KEEP AFTERNOON AND EVENING THUNDERSTORM CHANCES IN
PLACE, PERHAPS EXPANDED TO THE WESTERN FOOTHILLS OF THE CASCADES AS
WELL, FOR JUST ABOUT EVERY DAY THROUGH THE WEEK, WITH THE BEST
CHANCE FOR MORE WIDESPREAD STORMS POSSIBLE ON TUESDAY. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...RED FLAG WARNING UNTIL 11 PM PDT SUNDAY FOR ORZ624-625.
     HEAT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR ORZ024-026.

CA...RED FLAG WARNING UNTIL 11 PM PDT SUNDAY FOR CAZ285.
     RED FLAG WARNING UNTIL 5 AM PDT SUNDAY FOR CAZ281-284.
     HEAT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR CAZ080-081.

PACIFIC COASTAL WATERS...NONE.

$$

FJB/FJB/MSC


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