Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 290103
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
603 PM PDT FRI AUG 28 2015

UPDATED AVIATION AND MARINE SECTIONS AND HEADLINES

.AVIATION...FOR THE 29/00Z TAF CYCLE...SMOKE CONTINUES TO PRODUCE
MVFR VISIBILITIES IN AREAS MOSTLY NORTH OF THE ACTIVE WILDFIRES THIS
AFTERNOON. OTHERWISE, CONDITIONS ARE AND WILL MOSTLY REMAIN VFR INTO
THE EVENING. AN UNSEASONABLY STRONG LOW PRESSURE SYSTEM WILL MOVE
NORTHWARD TOWARD AND THEN ALONG THE COAST OVERNIGHT INTO SATURDAY
MORNING. THE MAIN AVIATION IMPACT WILL BE STRONG WINDS ALONG THE
COAST, MOUNTAINS, AND EAST SIDE LATE TONIGHT AND SATURDAY MORNING
WITH BREEZY WINDS ELSEWHERE. PRIOR TO THE ONSET OF THE STRONGER
SURFACE WINDS LOW LEVEL WIND SHEAR IS EXPECTED, ESPECIALLY ALONG THE
COAST AND INTO THE UMPQUA BASIN. THE FRONT WILL ALSO BRING RAIN AND
MVFR VIS/CIGS TO WEST SIDE LOCATIONS AS IT PASSES THROUGH SATURDAY
MORNING. THE MOST IMPACTING CONDITIONS AT EACH LOCATION FOR WIND
SHEAR, WIND, AND RAINFALL IS LIKELY TO LAST ONLY 3 TO 6 HOURS,
GREATEST ALONG AND NEAR THE COAST, AS THIS WEATHER SYSTEM IS A FAST
MOVER. BTL

&&

.MARINE...UPDATED 330 PM PDT FRIDAY 28 AUGUST 2015... NUMERICAL
MODELS HAVE TRENDED FROM WHAT LOOKED LIKE A VERY WET LOW PRESSURE
SYSTEM CROSSING THE AREA 3 DAYS AGO TO WHAT NOW LOOKS AS IF IT WILL
BE A VERY WINDY SOUTH WIND PRODUCING SYSTEM FOR THIS TIME OF THE
YEAR. IN FACT, STANDARDIZED ANOMALY INFORMATION FROM BOTH THE NAEFS
AND THE GEFS INDICATE THAT SUCH A STORM HAS NOT OCCURRED IN THE
CLIMATOLOGY OF AT LEAST THE LAST 30 YEARS. SINCE WE DON`T GET THIS
SORT OF WEATHER SYSTEM IN AUGUST, TYPICALLY, IT SHOULD BE NOTED
THAT, IF THIS WAS WINTER, THIS STORM SYSTEM WOULD BE ONLY BE
SLIGHTLY MORE INTENSE THAN TYPICAL STORMS. THAT SAID, CALM
CONDITIONS THIS AFTERNOON WILL RAPIDLY DETERIORATE LATE TONIGHT
THROUGH SATURDAY MORNING AS LOW PRESSURE RAPIDLY DEEPENS AS IT MOVES
INSIDE OF 130 WEST LONGITUDE NEAR 42 NORTH LATITUDE AND THEN MOVES
NORTHEASTWARD TOWARD THE PACIFIC NORTHWEST COAST. THE FAVORED NAM12
PUSHES THE LOW PRESSURE CENTER TO ABOUT 65 NAUTICAL MILES WEST OF
FLORENCE BEFORE IT MAKES LANDFALL ON THE WASHINGTON COAST. OTHER
MODELS KEEP THE LOW FARTHER OFFSHORE WITH IT MAKING LANDFALL ON OR
VERY NEAR VANCOUVER ISLAND. SOUTH WINDS ARE EXPECTED TO REACH GALE
FORCE AFTER MIDNIGHT THROUGH SATURDAY MORNING...WITH SOME STORM
FORCE WINDS LIKELY, NORTH AND DOWNWIND OF CAPE BLANCO IN THE AREA
WHERE COASTAL JET STREAMS OFTEN FORM UNDER THIS KIND OF WEATHER
SYSTEM. SOUTH SEAS WILL REACH WARNING CONDITIONS FOR MOST OF THE
AREA WITH THE EXPECTED WINDS...WITH SEAS LIKELY PEAKING IN THE 14 TO
18 FOOT RANGE FROM GOLD BEACH NORTHWARD. SOUTH WINDS AND ELEVATED
SEAS WILL BEGIN TO SUBSIDE SATURDAY AFTERNOON AND EVENING. SHOWERS
AND LIGHTER WINDS ARE EXPECTED SUNDAY. BTL

&&

.FIRE WEATHER...UPDATED 215 PM PDT FRIDAY 28 AUGUST 2015...GUSTY
SOUTHWEST WINDS AND DRY CONDITIONS WILL CONTINUE OVER THE SHASTA
VALLEY AND EAST SIDE INTO THIS EVENING, BUT CONDITIONS ARE EXPECTED
TO STAY BELOW WARNING CRITERIA DUE TO SLIGHTLY INCREASED HUMIDITIES.
HUMIDITIES ARE ALREADY MUCH HIGHER WEST OF THE CASCADES AND WILL
CONTINUE TO INCREASE AS A FRONTAL SYSTEM APPROACHES.

LATER TONIGHT, STRONG SURFACE LOW PRESSURE WILL TRACK NORTH ALONG
THE FRONT AS IT APPROACHES THE COAST AND BRING STRONG WINDS TO THE
COAST, MOUNTAINS, AND EAST SIDE, WITH BREEZY CONDITIONS ELSEWHERE.
RAIN WILL MOVE ONSHORE SATURDAY MORNING AND BRING A WETTING RAIN TO
MUCH OF THE WEST SIDE. AMOUNTS WILL BE MUCH LIGHTER ON THE EAST
SIDE SATURDAY.

WHILE WE WILL GET RAIN OVER MANY OF OUR ONGOING FIRES, THERE ARE
SPECIFIC CONCERNS ABOUT THIS STORM WITH RESPECT TO THOSE FIRES AND
THE PERSONNEL MANNING THEM. THERE IS THE POTENTIAL FOR MODERATE TO
HEAVY RAIN OVER ALL FIRE AREAS FROM THE CASCADES WEST. THIS IS
EXPECTED TO BE A GENTLE SOAKING RAIN RATHER THAN CONVECTIVE, HIGH
INTENSITY RAIN, SO BURN SCAR FLOODING AND DEBRIS FLOWS ARE NOT A
HUGE CONCERN. BUT IT IS SOMETHING TO THINK ABOUT. ALSO, SNAGS,
BURNED TREES, AND OTHER MATERIAL THAT HAVE BEEN WEAKENED OVER THE
SUMMER HAVE THE POTENTIAL TO COME DOWN FROM WIND, THE ADDED WEIGHT
OF RAINFALL, OR A COMBINATION OF BOTH. FIREFIGHTERS SHOULD REMAIN
VERY AWARE OF THEIR SURROUNDINGS THIS WEEKEND, ESPECIALLY ON OR
AROUND EXISTING FIRES AND BURN SCARS.

A SECONDARY FRONT MAY BRING A LITTLE ADDITIONAL RAIN TO WEST SIDE
LOCATIONS ON SUNDAY, OTHERWISE, CONDITIONS WILL IMPROVE. GENERAL
TROUGHINESS WILL REMAIN OVER THE PACNW THROUGH THE UPCOMING WEEK, SO
COOLER AND MORE HUMID THAN NORMAL WEATHER IS EXPECTED. RAIN WILL BE
POSSIBLE AGAIN MID WEEK AS ANOTHER FRONT MOVES THROUGH. -WRIGHT

&&

.DISCUSSION... /ISSUED 259 PM PDT FRI AUG 28 2015/
LOOKING AT THE FORECAST, IT WOULD APPEAR WE HAVE JUMPED AHEAD A
COUPLE OF MONTHS. IN REALITY, WHAT WE ARE GOING TO EXPERIENCE IS A
LATE FALL TO WINTER TYPE WIND AND RAIN STORM, DURING WHAT WOULD
NORMALLY BE THE THICK OF FIRE SEASON. ACROSS THE BOARD, MODEL
SOLUTIONS ARE DEPICTING A SYSTEM THAT DEFIES ANYTHING SEEN IN LATE
AUGUST SINCE AT LEAST 1979, IF NOT LONGER. IN SHORT, EXPECT
WETTING RAINS OVER THE CASCADES AND ALL POINTS WEST, AND GUSTY
WINDS ALONG THE COAST, THE HIGHER TERRAIN, AND ACROSS THE EAST
SIDE.

THE LOW RESPONSIBLE FOR THIS EVENT IS CURRENTLY OFFSHORE, SHOWING A
RATHER IMPRESSIVE BAROCLINIC LEAF, OR RATHER, A VERY UNSEASONABLY
IMPRESSIVE CLOUD FEATURE. THE ASSOCIATED UPPER LEVEL TROUGH IS
DIGGING SOUTH AND WILL CONTINUE TO ROTATE TO A NEGATIVE TILT. THIS
FEATURE IS KNOWN TO PRODUCE RAPIDLY DEEPENING SURFACE LOWS, AND THIS
ONE IS NO EXCEPTION. WITH PRESSURES AT THE CENTER CURRENTLY SITTING
AT AROUND 1007 MILLIBARS, MODELS ARE SUGGESTING THE PRESSURE COULD
DROP TO AS LOW AS 992 MILLIBARS BY 5 AM TOMORROW MORNING. THIS WILL
BE MORE THAN ENOUGH TO PRODUCE STORM FORCE WINDS OFFSHORE AND ALONG
THE IMMEDIATE COAST, PARTICULARLY AT THE HEADLANDS AND CAPES. FLOWS
ACROSS THE MOUNTAINS AND EAST SIDE WILL ALSO BRING STRONG WINDS DOWN
TO THE SURFACE THERE. HAVE ISSUED WIND WARNINGS/ADVISORIES FOR THE
COAST AND EAST SIDE, AS WELL AS THE SHASTA VALLEY, AND ALSO A HIGH
SURF ADVISORY FOR THE COAST NORTH OF HUMBUG MOUNTAIN. SOME AREAS
WITHIN THE WARNINGS/ADVISORIES MAY NOT QUITE REACH CRITERIA, BUT
GIVEN THE HIGH LEVEL OF RECREATION THIS TIME OF YEAR, INCLUDING
FISHING, TOURISM, AND CAMPING, AS WELL AS THE BEGINNING OF SOME
HUNTING SEASONS THIS WEEKEND, HAVE ISSUED FOR THESE AREAS ANYWAY DUE
TO THE POTENTIAL FOR NUMEROUS AND EXTENSIVE IMPACTS. ALSO OF NOTE,
WITH DROUGHT STRESSED TREES AND LEAVES REMAINING ON VEGETATION,
WINDS WILL HAVE EXTRA POTENTIAL TO DOWN OR DAMAGE TREES. TRAVEL,
UTILITIES, AND CAMPERS SHOULD BE ON EXTRA ALERT.

IN TERMS OF RAINFALL, THIS STORM SYSTEM WOULD NOT NORMALLY CAUSE US
TO BAT AN EYE, ASSUMING IT WAS LATE IN THE FALL OR IN THE WINTER.
INSTEAD, WE ARE EXPECTING WETTING RAINS FOR ALL AREAS ALONG AND WEST
OF THE CASCADES, AND HERE IT IS LATE AUGUST. THE FIRST ROUND OF RAIN
WILL ACCOMPANY THE FRONTAL PASSAGE LATE TONIGHT AND TOMORROW,
FOLLOWED BY SHOWERS ASSOCIATED WITH THE UPPER LEVEL TROUGH LATE
TOMORROW THROUGH SUNDAY. ALL TOLD, UP TO AN INCH OF RAIN WOULD NOT
BE OUT OF THE QUESTION ALONG THE COAST, WHILE IN THE COASTAL RANGES
IN FAR SOUTHWEST OREGON, AN INCH AND A HALF OR MORE IS POSSIBLE.
INLAND, THE WEST SIDE VALLEYS CAN EXPECT BETWEEN A TENTH AND A
QUARTER INCH, WHILE THE MOUNTAINS COULD REACH UP TO THREE QUARTERS.
OVERALL, A SIGNIFICANT RAIN EVENT FOR FIRE SEASON, AND ONE THAT
COULD ALSO QUENCH AREA WILDFIRES AND CLEAN THE AREA OF OUR
PERSISTENT SMOKE. WHILE IT IS MUCH TO EARLY TO SAY THIS IS A FIRE
SEASON ENDING EVENT, PENDING A POSSIBLE RETURN TO HEAT AND DRYNESS
IN SEPTEMBER, IT MAY VERY WELL BE THE BEGINNING OF THE END.

BEYOND THIS WEEKEND, THE PACIFIC NORTHWEST WILL REMAIN IN A COOLER
AND WETTER REGIME. MODELS HAVE PLACED A SERIES OF TROUGHS OVERHEAD
FOR THE NEXT WEEK AT LEAST, AND EACH ONE WILL HAVE THE POTENTIAL TO
BRING RAIN AND WIND, ALTHOUGH AT THIS TIME, NONE LOOK ANYWHERE NEAR
AS SIGNIFICANT AS THE FIRST. GENERALLY SPEAKING, EXPECT HIGH
TEMPERATURES TO REMAIN AROUND 10 DEGREES BELOW NORMAL THROUGH NEXT
WEEK, WITH AN INTERMITTENT CHANCE OF RAIN AND SHOWERS. WITH THE
COOLER TEMPERATURES AND PRECIPITATION IN THE FORECAST, DO NOT BE
SURPRISED IF THE PEAK OF MT SHASTA DISPLAYS A HINT OF NEW WHITE
COVERAGE SOMETIME THIS NEXT WEEK.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WARNING FROM 2 AM TO 2 PM PDT SATURDAY FOR ORZ021-022.
     HIGH SURF ADVISORY FROM 5 AM TO 5 PM PDT SATURDAY FOR
     ORZ021-022.
     HIGH WIND WARNING FROM 2 AM TO 5 PM PDT SATURDAY FOR ORZ030-031.
     WIND ADVISORY FROM 2 AM TO 5 PM PDT SATURDAY FOR ORZ029.

CA...HIGH WIND WARNING FROM 2 AM TO 5 PM PDT SATURDAY FOR CAZ085.
     WIND ADVISORY UNTIL 11 PM PDT THIS EVENING FOR CAZ081.

PACIFIC COASTAL WATERS...
- HAZARDOUS SEAS WARNING FROM 5 AM TO 11 PM PDT SATURDAY FOR
  PZZ350-356-370-376.
- STORM WARNING FROM 2 AM TO NOON PDT SATURDAY FOR PZZ350-370.
- GALE WARNING FROM 2 AM TO 2 PM PDT SATURDAY FOR PZZ350-356-370-376.
- SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 11 PM THIS EVENING
  TO 5 AM PDT SATURDAY FOR PZZ350-356-370-376.
- SMALL CRAFT ADVISORY FOR WINDS FROM 2 AM TO 5 PM PDT SATURDAY
  FOR PZZ356-376.

$$

BTL/BPN/TRW


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