Heat Advisory 2, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
904 AM PDT WED JUN 24 2015

.DISCUSSION...THE KEY HIGH-IMPACT COMPONENTS TO THE FORECAST ARE
THE UPCOMING RECORD HEAT AND THUNDERSTORM POTENTIAL...AND OUR
DISCUSSIONS AND MESSAGING WILL FOCUS ON THESE. RECORD HIGH
TEMPERATURES ARE LIKELY IN MANY LOCATIONS ON FRIDAY...AND
POTENTIALLY ON SATURDAY TOO. MODELS HAVE TRENDED A BIT HIGHER
COLLECTIVELY WITH THE FRIDAY AND SATURDAY HEAT...SO PLEASE PREPARE
FOR AT LEAST A TWO-DAY EXTREME HEAT SITUATION. SEE READY.GOV/HEAT
WEBSITE FOR TIPS TO PREPARE FOR AND COPE WITH THE HIGH DAYTIME AND
RELATIVELY WARM OVERNIGHT LOW TEMPERATURES.

IN TERMS OF THUNDERSTORMS...CHANCES INCREASE FOR STORMS FRIDAY
NIGHT INTO SUNDAY...GRADUALLY TRANSITIONING FROM NORTHERN
CALIFORNIA INTO THE WEST SIDE AND MOVING TO THE EAST SIDE ON
SUNDAY...AND TRENDING FROM DRY STORMS FRIDAY NIGHT INTO EARLY
SATURDAY TO WETTER STORMS LATER SATURDAY INTO SUNDAY. WE WILL BE
FOCUSING ON THUNDERSTORM CHANCES AND SPECIFIC LOCATIONS
TODAY...AND THEIR IMPACT ON FIRE WEATHER CONCERNS AND POTENTIAL
PRODUCTS. PLEASE SEE THE PREVIOUS DISCUSSION BELOW FOR MORE
DETAILS ON THE HEAT...THUNDERSTORMS...AND LIGHTNING EFFECTS IN THE
CONTEXT OF FIRE WEATHER IN THE FIRE WEATHER DISCUSSION BELOW.

&&

.AVIATION...FOR THE 24/12Z TAF CYCLE...ALONG THE COAST...AREAS OF
IFR CIGS WILL CLEAR TO VFR BY WEDNESDAY AFTERNOON...THEN THE LOWER
CONDITIONS WILL RETURN TO THE COAST NORTH OF CAPE BLANCO WEDNESDAY
NIGHT. THE SOUTH COAST WILL REMAIN VFR WEDNESDAY NIGHT. OVER THE
REMAINDER OF THE AREA...VFR CONDITIONS WILL PREVAIL THROUGH
WEDNESDAY NIGHT.

&&

.MARINE...UPDATED 200 AM PDT WEDNESDAY 24 JUNE 2015...HIGH PRESSURE
OFFSHORE WILL PREVAIL THROUGH THIS WEEKEND. A THERMAL TROUGH NEAR
THE COAST WILL STRENGTHEN INTO FRIDAY...THEN WEAKEN THROUGH THE
WEEKEND. NORTH WINDS WILL GRADUALLY INCREASE THROUGH THURSDAY
EVENING...PEAKING AROUND GALE FORCE SOUTH OF CAPE BLANCO...AND THEN
PERSISTING THROUGH FRIDAY. SEAS WILL START OFF SLIGHT...BUT WILL
BECOME STEEP AND WIND WAVE DOMINATED THURSDAY MORNING SOUTH OF CAPE
BLANCO...AND THEN STEEP TO VERY STEEP THURSDAY AFTERNOON THROUGH
FRIDAY. WINDS WILL DIMINISH AND SEAS SUBSIDE THROUGH THE WEEKEND.

&&

.FIRE WEATHER...UPDATED 200 AM PDT WEDNESDAY 24 JUNE 2015...AN
UPPER RIDGE WILL GRADUALLY BUILD INTO THE WEEKEND...AND RISING
HEIGHTS WILL BRING RISING TEMPERATURES. A THERMAL TROUGH WILL
DEVELOP ALONG THE COAST WEDNESDAY NIGHT...INDUCING LOW LEVEL
OFFSHORE FLOW. FORECAST WIND SPEEDS AND HUMIDITIES COME CLOSE TO
BUT DO NOT QUITE MEET THE RED FLAG CRITERIA OVER THE COASTAL
RANGES...SO WILL CONTINUE TO HEADLINE THE CONDITIONS.

BY FRIDAY...LAPSE RATES WILL BE QUITE STEEP AND COULD TIP THE HAINES
INDEX TO 6 AT BOTH MID AND HIGH LEVEL HAINES FOR MUCH OF SW OREGON,
SOUTHERN KLAMATH AND LAKE COUNTIES, ALONG WITH NORTHERN CALIFORNIA
ZONES.

LOW PRESSURE MOVING UP THE COAST WILL TURN WINDS TO SOUTHERLY ON THE
WEST SIDE OF THE RIDGE BRINGING MONSOONAL MOISTURE NORTHWARD. THIS
WILL SET THE STAGE FOR THUNDERSTORMS AS EARLY AS FRIDAY AFTERNOON...
BUT MORE LIKELY OVER THE WEEKEND INTO EARLY NEXT WEEK. THE HEAT IS
CERTAIN, ESPECIALLY FRIDAY AND SATURDAY, WHEREAS CLOUD COVER ON
SUNDAY COULD BRING HIGHS DOWN A FEW DEGREES. WHILE WE CAN'T YET SAY
SPECIFICALLY WHERE THUNDERSTORMS WILL OCCUR, CONFIDENCE IS HIGH THAT
THUNDERSTORMS WILL OCCUR OVER OUR AREA BY THE TIME THE WEEKEND IS
OVER.

STORMS WILL BE POSSIBLE AT ALL LOCATIONS (EVEN AT THE COAST) AND
NOCTURNAL STORMS ARE ALSO POSSIBLE EACH NIGHT FROM FRIDAY NIGHT INTO
NEXT WEEK. PRECIPITABLE WATER WILL BE WELL ABOVE NORMAL...THUS
STORMS THAT OCCUR DURING THE DAY MAY BE WET. HOWEVER...STORMS THAT
OCCUR AT NIGHT IN THE SUMMER AROUND HERE TEND TO BE ON THE DRY
SIDE...SO DRY LIGHTNING (LAL 6) IS CERTAINLY POSSIBLE. WE WILL BE
SEEING CRITICAL FIRE WEATHER CONDITIONS LATER THIS WEEK INTO AT
LEAST EARLY NEXT WEEK OVER MUCH OF OUR AREA.

THE RIDGE IS FORECAST TO REMAIN OVER CALIFORNIA AND PAC NW ALL OF
NEXT WEEK. HIGH TEMPERATURES IN THE ROGUE VALLEY COULD HOVER
AROUND 100 ALL OF NEXT WEEK.

&&

.PREV DISCUSSION... /ISSUED 424 AM PDT WED JUN 24 2015/

DISCUSSION...SOUTHERN OREGON AND NORTHERN CALIFORNIA WILL HAVE
AN UNUSUALLY LONG PERIOD OF HOT WEATHER FROM THURSDAY INTO NEXT
WEEK WITH A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS FROM FRIDAY
INTO NEXT WEEK. THERE IS VERY GOOD TO EXCELLENT MODEL AGREEMENT
REGARDING THE FORECAST THROUGH SUNDAY THEN CONTINUED AGREEMENT
THAT AT LEAST THE CHARACTER OF OUR WEATHER WILL REMAIN RELATIVELY
UNCHANGED INTO THE MIDDLE OF NEXT WEEK.

IN FACT, SOME MAY CONSIDER IT HOT TODAY WITH READINGS EXPECTED TO
BE A FEW DEGREES HIGHER THAN ON TUESDAY. HEATING TODAY WILL BE
HINDERED TO A SMALL EXTENT BY HIGH CLOUDS THAT WILL BE MOST
NUMEROUS ALONG THE NORTHERN FRINGE OF OUR AREA AS THEY STREAM INTO
THE PACIFIC NORTHWEST. THEY ARE ASSOCIATED WITH A LOW PRESSURE
TROUGH THAT IS MOVING INTO BRITISH COLUMBIA. MEANTIME, OUR AREA
WILL BE BETWEEN THAT TROUGH AND STRONG RIDGING THAT EXTENDS FROM
THE DESERT SOUTHWEST INTO THE GREAT BASIN.

THE RIDGE WILL EXPAND TO THE NORTHWEST INTO OUR AREA ON THURSDAY
WITH SIGNIFICANT WARMING OF SEVERAL DEGREES AND SUNNY SKIES. THE
HIGH TEMPERATURES ON THURSDAY WILL BE SIMILAR TO THOSE DURING THE
3-DAY HEAT WAVE EARLIER THIS MONTH...JUNE 7TH TO 9TH. IN THIS
EPISODE, UNUSUALLY HOT WEATHER WILL CONTINUE THROUGH EARLY NEXT
WEEK AND THERE IS A CHANCE THAT IT WILL PERSIST FOR ALL OF NEXT
WEEK. THE HOTTEST TEMPERATURES WILL OCCUR ON FRIDAY AND SATURDAY
WITH OVERNIGHT LOW TEMPERATURES ALSO TO BE FAR ABOVE NORMAL AS THE
RIDGE BUILDS NORTHWARD. THE HEAT WILL BE EXTREME ON FRIDAY AND
SATURDAY WITH ALL OF OUR STATISTICAL GUIDANCE DURING THE PAST FEW
MODEL RUNS NARROWING IN ON A FORECAST PEAK OF 106 TO 108 DEGREES
AT MEDFORD ON FRIDAY AND 96 TO 99 AT KLAMATH FALLS WITH NEGLIGIBLY
LOWER READINGS BY A DEGREE OR TWO TO FOLLOW ON SATURDAY. THE
FORECAST CONTINUES AT THE HIGH END OF THE NARROW RANGE OF MODEL
GUIDANCE AS HISTORICALLY IT IS MORE OFTEN TOO WEAK RATHER THAN TOO
STRONG WITH SUMMER HEAT WAVES.

WHILE THE RIDGE BUILDS LATE THIS WEEK, LOW PRESSURE WILL PERSIST
OFFSHORE FROM SOUTHERN CALIFORNIA. THIS WILL PRODUCE A SOUTHERLY
FLOW ALOFT WHICH WILL SEND INCREASING AMOUNTS OF MOISTURE INTO OUR
AREA. THE AIR MASS WILL BE TOO DRY FOR THUNDERSTORMS TO DEVELOP ON
THURSDAY THEN ISOLATED THUNDERSTORMS WILL MOSTLY POP UP OVER THE
HIGHER TERRAIN...ESPECIALLY OVER THE CASCADES LATE IN THE DAY
FRIDAY INTO FRIDAY EVENING. THE INCREASED MOISTURE ALONG WITH
EMBEDDED SHORTWAVE DISTURBANCES OF UNCERTAIN TIMING WILL INCREASE
THE PROBABILITY OF THUNDERSTORMS FRIDAY NIGHT INTO EARLY NEXT
WEEK.

THE RIDGE AXIS IS EXPECTED TO SHIFT EASTWARD ON SUNDAY WHILE THE
OFFSHORE TROUGH MOVES NORTH. THIS WILL ALLOW SEVERAL DEGREES OF
COOLING, BUT IT WILL STILL BE QUITE HOT. THE WEAKENED OFFSHORE
TROUGH IS EXPECTED TO SHIFT INLAND SUNDAY NIGHT OR MONDAY AND WILL
LIKELY CAUSE A TEMPORARY DECREASE IN THUNDERSTORM ACTIVITY ALONG
WITH SHIFTING THE FOCUS OF CONVECTION TO THE EAST SIDE.

THEREAFTER, IT IS INCREASINGLY UNCERTAIN TO WHAT EXTENT THE RIDGE
WILL REBUILD INTO OUR AREA AND ALSO WHERE THUNDERSTORM DEVELOPMENT
WILL BE FAVORED. THE GFS MAINTAINS A HOTTER AND MORE CONVECTIVELY
ACTIVE PATTERN THROUGH THE WEEK THAN THE ECMWF. THE GFS PATTERN
NEXT WEEK MORE CLOSELY RESEMBLES WHAT WILL TRANSPIRE LATE THIS
WEEK WHILE THE ECMWF HAS MORE INFLUENCE FROM A PACIFIC NORTHWEST
TROUGH. THE TAIL END OF THE FORECAST LEANS TOWARD PERSISTENCE.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...GALE WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY AFTERNOON FOR
     PZZ376.
     SMALL CRAFT ADVISORY FOR WINDS FROM 5 AM TO 2 PM PDT THURSDAY
     FOR PZZ376.
     HAZARDOUS SEAS WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
     AFTERNOON FOR PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 5 AM TO 2 PM PDT
     THURSDAY FOR PZZ376.

NSK/DW/JRS