Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 200309
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
809 PM PDT TUE AUG 19 2014

.DISCUSSION...TEMPERATURES ARE ABOUT 5 DEGREES COOLER THAN 24 HOURS
AGO PER CURRENT OBSERVATIONS. THIS DECREASE IN TEMPERATURES IS
DUE TO A COOL UPPER TROUGH PASSING THROUGH THIS AFTERNOON. THE
TROUGH IS EXITING THE FORECAST AREA TO THE EAST THIS EVENING AND
IS TAKING WITH IT ANY LINGERING INSTABILITY. THEREFORE...THUNDERSTORMS
THAT ARE ONGOING OVER SOUTHEASTERN SISKIYOU COUNTY AND MODOC
COUNTIES WILL DISSIPATE SOON...AND NO THUNDERSTORMS ARE EXPECTED
TONIGHT OR FOR THE NEXT SEVERAL DAYS AT LEAST.

A STRONG MARINE STRATUS PUSH INLAND IS EXPECTED TONIGHT AND THIS
WILL MEAN MORNING LOW CLOUDS FOR MUCH OF SOUTHWEST OREGON WEST OF
THE CASCADES. IT`S ALWAYS A CHALLENGE FORECASTING WHETHER MARINE
STRATUS MAKES IT INTO THE ROGUE VALLEY IN AUGUST...AND THIS IS NO
DIFFERENT. THE CURRENT FORECAST CALLS FOR SOME CLOUDS TO MAKE
THEIR WAY INTO THE VALLEY BY MORNING AND THIS SEEMS REASONABLE
BASED ON THE LATEST RAP13 MODEL OUTPUT...WHICH WE`LL FAVOR OVER
STATISTICAL GUIDANCE IN THIS SITUATION. GIVEN SUCH A STRONG PUSH
EXPECTED...ROSEBURG AND THE UMPQUA BASIN SHOULD REMAIN CLOUDY FOR
MUCH OF THE DAY TOMORROW. BEHIND THE TROUGH AND WITH A GOOD
ONSHORE FLOW...TEMPERATURES WILL TREND COOLER TONIGHT AND A RETURN
TO BELOW NORMAL READINGS IS EXPECTED TOMORROW.

PLEASE SEE THE PREVIOUS DISCUSSION BELOW FOR DETAILS ON A
POTENTIAL WARMING A DRYING TREND OVER THE WEEKEND.


&&

.AVIATION...BASED ON THE 20/00Z TAF CYCLE...IFR CIGS HAVE ALREADY
DEVELOPED AT THE COAST AND STRATUS IS EXPECTED MOVE INLAND WITH MVFR
TO LOCAL IFR CIGS DEVELOPING IN THE UMPQUA BASIN OVERNIGHT. SOME
STRATUS WILL PROBABLY ALSO MAKE IT OVER THE UMPQUA DIVIDE WITH AREAS
OF MVFR CIGS IN THE ILLINOIS AND ROGUE VALLEYS BY DAWN WEDNESDAY.
ALL OF THIS WILL CLEAR BACK TO THE COAST BY MID TO LATE MORNING.
ELSEWHERE, VFR CONDITIONS WILL CONTINUE FOR THE NEXT 24 HOURS.


&&

.MARINE...UPDATED 8 PM PDT TUE 19 AUG 2014...OFFSHORE HIGH
PRESSURE WITH A THERMAL TROUGH INLAND WILL PERSIST THROUGH THE WEEK.
MODERATE NORTH WINDS AND STEEP SEAS WILL PERSIST THROUGH WEDNESDAY
EVENING...EXCEPT FOR AN AREA OF NORTH GALES AND VERY STEEP SEAS
OFFSHORE SOUTH OF CAPE BLANCO THROUGH WEDNESDAY EVENING. FROM
WEDNESDAY NIGHT ON...LIGHT TO MODERATE NORTH WINDS AND SEAS WILL
PERSIST INTO THE WEEKEND.


&&

.FIRE WEATHER...GUSTY WEST TO NORTHWEST WINDS WILL BLANKET THE
FORECAST AREA DURING THE NEXT SEVERAL AFTERNOONS AND
EVENINGS...NEGATIVELY AFFECTING CURRENT FIREFIGHTING EFFORTS.
HOWEVER...A COUPLE WEATHER ELEMENTS THAT MAY LIMIT FIRE BEHAVIOR
ARE INCREASING HUMIDITIES TONIGHT AND TOMORROW...AND INCREASING
STABILITY THE NEXT SEVERAL DAYS WHICH WILL LIMIT A FIRE`S ABILITY
TO BE PLUME-DOMINATED.


&&

.PREV DISCUSSION... /ISSUED 313 PM PDT TUE AUG 19 2014/

.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...OUR WEATHER PATTERN
IS IN THE MIDST OF A NOTICEABLE CHANGE. A LONGWAVE TROUGH IS IN
PLACE FROM THE COAST ACROSS THE COASTAL STATES WHILE THE UPPER
LOW THAT WAS LARGELY RESPONSIBLE FOR YESTERDAY`S THUNDERSTORM
ACTIVITY HAS MOVED TO SOUTHERN CALIFORNIA. IN ITS WAKE THERE IS
SUFFICIENT MOISTURE AND INSTABILITY WITH A WESTERLY FLOW FOR
ISOLATED THUNDERSTORMS THROUGH THIS EVENING EAST OF THE CASCADES.
THE TROUGH WITH COOLER AIR IS ALSO INDUCING BREEZY WEST TO
NORTHWEST WINDS.

THERE WILL BE SHORTWAVE RIDGING AT THE COAST LATE TONIGHT INTO
WEDNESDAY MORNING WITH A DEEPENING MARINE LAYER. THIS WILL RESULT
IN LOW CLOUDS AND FOG...SPREADING INTO THE COASTAL VALLEYS THIS
EVENING AND THEN THE UMPQUA BASIN AND LOCALLY SPILLING OVER THE
UMPQUA DIVIDE INTO JACKSON AND JOSEPHINE COUNTIES LATE
TONIGHT...INCLUDING LIKELY UPSLOPE WIND FORCED STRATUS NEAR
ASHLAND TOWARD SUNRISE. IT IS NOT A BIG SURPRISE, BUT THE MODELS
ARE NOT IN HARMONY REGARDING THE EXTENT OF THE JACKSON AND
JOSEPHINE COUNTY LOW CLOUDS NOR THE EXPECTED CONDITION VERY NEAR
TO AND INCLUDING BROOKINGS WHERE BREEZY NORTHERLY WINDS ARE
EXPECTED TO HAVE A SLIGHT OFFSHORE COMPONENT FOR DOWNSLOPE DRYING.
THE 12Z GFS AND NAM BOUNDARY LAYER HUMIDITY FIELDS EACH INDICATED
THE STRATUS WOULD STAY OUT OF BROOKINGS WHILE THE NAM STATISTICAL
GUIDANCE SUGGESTED THE STRATUS WOULD NOT HAVE CLEARED TODAY AND
WOULD LOWER AND THICKEN AGAIN LATE TONIGHT. THREE THINGS FOR CERTAIN
ARE THAT IT WILL BE COOLER ON WEDNESDAY WITH HIGH TEMPERATURES
RETURNING TO AROUND NORMAL, THE AIR MASS WILL STABILIZE, AND IT WILL BE
BREEZY AGAIN IN THE AFTERNOON AND EVENING WITH THE STRONGEST WINDS
AT THE COAST AND ON THE EAST SIDE.

CONDITIONS ON THURSDAY ARE EXPECTED TO RESEMBLE THOSE OF WEDNESDAY
AS A NORTHWEST FLOW ALOFT CONTINUES OVER THE REGION AS AN UPPER
TROUGH MOVES INTO BRITISH COLUMBIA.

THIS TROUGH WILL SUBSEQUENTLY MOVE SOUTHWARD INTO OREGON ON FRIDAY
WITH ADDITIONAL COOLING AND SLIGHT AFTERNOON AND EVENING
INSTABILITY. NEITHER THE GFS NOR THE NAM MODELS INDICATE MUCH IN
THE WAY OF MID-LEVEL MOISTURE FOR THIS TROUGH TO WORK WITH. THERE
IS ALSO UNCERTAINTY ON WHETHER OUR AREA WILL BE UNDER THE
INFLUENCE OF THE STABLE NORTHERLY FLOW ON THE BACK SIDE OF THE
TROUGH OR UNDER THE TROUGH. THUS, I HAVE LEFT ANY MENTION OF A
POSSIBILITY OF THUNDERSTORMS OUT OF THE FRIDAY FORECAST. IF THE
PICTURE SHOULD CHANGE WITH SUBSEQUENT MODEL RUNS, A PLAUSIBLE WORST
CASE SCENARIO WOULD BE A FEW SLOW MOVING THUNDERSTORMS OVER THE
HIGHER TERRAIN.


.LONG TERM...SATURDAY THROUGH TUESDAY...THE LIKELY CHARACTER OF THE
LONG TERM IS A WARMING AND DRYING TREND WITH A PERSISTENT RIDGE
CENTERED OFFSHORE. THE 12Z ECMWF TRACKS THE RIDGE INTO THE WEST
COAST WHILE THE GFS MAINTAINS THE RIDGE AXIS OFFSHORE. THUS, THE
ECMWF SOLUTION WOULD BRING SUBSTANTIAL WARMING WHILE THE GFS
SOLUTION WOULD HAVE HIGH TEMPERATURES MERELY MAINTAINING A
CONSISTENT FEW TO SEVERAL DEGREES ABOVE NORMAL. I LEANED TOWARD
THE GFS AS THE ECMWF SEEMS TOO PROGRESSIVE. IN BOTH SCENARIOS, THE
LONG TERM WOULD HAVE A STABLE AIR MASS OVER OUR AREA.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT WEDNESDAY FOR
     PZZ356-376.
     HAZARDOUS SEAS WARNING UNTIL 11 PM PDT WEDNESDAY FOR PZZ356-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT
     WEDNESDAY FOR PZZ356-376.
     GALE WARNING UNTIL 11 PM PDT WEDNESDAY FOR PZZ376.

$$

NSK/DW/TRW





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