Wildfire in California, September 15 to 21, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
1151 AM PDT MON SEP 15 2014

.DISCUSSION...THE FORECAST HAS BEEN UPDATED TO CANCEL THE FIRE
WEATHER WATCH FOR THE OREGON CASCADES. THE 12Z NAM AND GFS MODELS
HAVE EACH TRENDED WEAKER WITH CASCADE INSTABILITY. WEAK
INSTABILITY WILL BE PRESENT OVER ALL OF OUR AREA EXCEPT CURRY
COUNTY THIS AFTERNOON AND EVENING AS AN UPPER LOW MOVES NORTH OVER
THE OFFSHORE WATERS. BUT, THE GREATEST INSTABILITY/HIGHEST
PROBABILITY OF THUNDERSTORMS WILL BE OVER EASTERN MODOC AND LAKE
COUNTIES. THIS TROUGH WILL ALSO GENERATE BREEZY SOUTHERLY WINDS IN
THE SHASTA VALLEY AND ACROSS THE EAST SIDE.

A COOLING TREND WILL COMMENCE TONIGHT FOLLOWED BY ANOTHER BREEZY DAY
ON TUESDAY FOR THE SHASTA VALLEY AND EAST SIDE UNDER A STABLE
SHORTWAVE RIDGE. A MORE SUBSTANTIAL CHANGE/MORE NOTICEABLE COOLING
ARRIVES WITH THE NEXT TROUGH WEDNESDAY INTO THURSDAY. A FOCUS FOR
THE AFTERNOON PACKAGE WILL BE ADJUSTING THE PROBABILITY OF
PRECIPITATION TO REFLECT THE LATEST DATA. THE PROBABILITY OF RAIN
WILL BE HIGHEST ALONG THE COAST AND SECONDARILY INTO JOSEPHINE
AND WESTERN SISKIYOU COUNTIES DURING LATE WEDNESDAY AFTERNOON INTO
THE EVENING. THE TROUGH ITSELF WILL MOVE INLAND THURSDAY WITH A
SLIGHT CHANCE TO CHANCE OF LIGHT SHOWERS. SHORTWAVE RIDGING WITH A
DECREASE OF CLOUDS AND SLIGHT WARMING IS EXPECTED FOR FRIDAY.

THERE IS CURRENTLY A HIGH LEVEL UNCERTAINTY REGARDING THE WEEKEND
FORECAST AS THE 12Z GFS CONTINUES TO BE MUCH MORE PROGRESSIVE THAN
THE 00Z ECMWF. THE GFS SOLUTION WOULD BRING WARMER AND DRIER
WEATHER FOR OUR AREA, WHILE THE ECMWF DEVELOPS A CUT-OFF LOW OVER
THE CENTRAL CALIFORNIA COAST WHICH WOULD RESULT IN THUNDERSTORMS
OVER NEVADA AND THE SIERRA NEVADA THAT COULD EXTEND INTO OUR AREA.

&&

.AVIATION...BASED ON THE 15/18Z TAF CYCLE...
AT THE COAST- LOCALLY PERSISTENT STRATUS AND FOG WITH IFR CIGS AND
VIS ARE HUGGING THE COAST AND WILL PERSIST INTO THE AFTERNOON WITH A
BRIEF BREAK POSSIBLE AROUND 21Z BEFORE RETURNING LATE THIS AFTERNOON
AND EARLY THIS EVENING AND PERSISTING THROUGH THE NIGHT. CIG/VIS
PROBABLY WON'T BE AS LOW AT THE AIR FIELDS TONIGHT DUE TO SOME
COOLING AT THE TOP OF THE MARINE LAYER. AREAS OF MOSTLY VFR SMOKE
WILL AFFECT MUCH OF WESTERN SISKIYOU COUNTY AND NORTH INTO JACKSON
AND JOSEPHINE COUNTIES. SMOKE IS LIKELY TO BE MORE SUBSTANTIAL- IN
THE MVFR TO IFR RANGE- NEAR THE FIRE POINT SOURCES NEAR HAPPY CAMP
AND ONION MOUNTAIN. ELSEWHERE, VFR CONDITIONS ARE EXPECTED TO
CONTINUE. A LOW OFFSHORE WILL BRING A SLIGHT CHANCE OF THUNDERSTORMS
THIS AFTERNOON AND EVENING, MAINLY ACROSS MODOC, LAKE, AND
SOUTHEASTERN KLAMATH COUNTIES. ANY THUNDERSTORMS ARE EXPECTED TO BE
FAST MOVING FROM SOUTH TO NORTH AROUND 20-30 MPH WITH GUSTY WINDS IN
AND NEAR THEM. BTL

&&

.MARINE...UPDATED 1150 AM PDT SUN 15 SEP 2014...
A WEAK LOW TO THE SOUTHWEST WILL MOVE NORTHWARD ALONG THE COAST
TODAY AND TONIGHT. THEN ANOTHER LOW WILL APPROACH THE WATERS FROM
THE SOUTHWEST ON TUESDAY AND WEDNESDAY. SOUTH WINDS ARE EXPECTED TO
INCREASE A BIT OVER THE WATERS BEGINNING THIS AFTERNOON AND EVENING.
THE LOW WILL ALSO BRING A SLIGHT CHANCE OF THUNDERSTORMS TO THE
WATERS MAINLY FROM NORTH BEND NORTHWARD. SOUTH TO SOUTHEAST WINDS
WILL CONTINUE TUESDAY THROUGH THURSDAY. ALTHOUGH WINDS ARE EXPECTED
TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS...SEAS WILL GRADUALLY
INCREASE TODAY THROUGH WEDNESDAY DUE TO A MIX OF WIND WAVES AND
MIXED WEST AND SOUTH SWELL. STEEP SEAS REACHING 7 TO 8 FT ARE
POSSIBLE BY WEDNESDAY EVENING...CONTINUING INTO THURSDAY. ON
THURSDAY THE SECOND LOW IS EXPECTED TO GRADUALLY MOVE INLAND...WITH
WINDS LOWERING THURSDAY NIGHT AND BECOMING NORTHERLY AS HIGH
PRESSURE BUILDS OFFSHORE. NORTHERLY WINDS MAY RISE TO SMALL CRAFT
ADVISORY LEVELS FRIDAY AFTERNOON AND EVENING WITH STEEP SEAS
POSSIBLE AS WELL.  BTL/CC

&&

.PREV DISCUSSION... /ISSUED 302 AM PDT MON SEP 15 2014/

DISCUSSION...THE MAIN FOCUS AHEAD IS THE POTENTIAL FOR ISOLATED
THUNDERSTORMS LATE THIS MORNING INTO THIS EVENING. ESPECIALLY GIVEN
THE EXTREME DRY FUELS AND THE POSSIBILITY ANY STORM WILL PRODUCE
LITTLE OR NO PRECIPITATION. CURRENT WATER VAPOR IMAGE SHOWS THE
UPPER TROUGH NEAR 36N/131W STARTING TO BECOME NEGATIVELY TILTED AS
IT MOVES NORTHWEST TOWARDS SOUTHWEST OREGON. THE MODELS HAVE BACKED
OFF SOME ON THE AMOUNT OF INSTABILITY WEST OF THE CASCADES AND SOUTH
OF CRATER LAKE. HOWEVER IT SHOWS MORE INSTABILITY EAST OF THE
CASCADES IN LAKE AND SOUTHEAST KLAMATH COUNTIES. ADDITIONALLY, THERE
IS MORE SHORTWAVE ACTIVITY MOVING INTO THE AREA IN THE AFTERNOON
ALONG WITH UPPER LEVEL DIVERGENCE. MODEL SOUNDINGS CONTINUE TO SHOW
AN INVERTED-V PROFILE, THEREFORE EXPECT MOST, IF NOT ALL ISOLATED
STORMS TO PRODUCE LITTLE OR NO PRECIPITATION. THE PATH OF THE UPPER
TROUGH AND THE FACT IT'S NEGATIVELY TILTED IS A CONCERN FOR ME AND
DESPITE THE FACT THE MODELS HAVE BACKED OFF ON THE AMOUNT OF
INSTABILITY, MADE LITTLE CHANGES TO THE PREVIOUS FORECAST.

THE NEXT CONCERN IS MODERATE WINDS ALONG THE MID SLOPES, RIDGES AND
ALONG AND EAST OF THE CASCADES. THE MODELS CONTINUE TO SHOW 700MB
WINDS BETWEEN 25-35 KTS FROM THE SOUTH THIS MORNING, THEN SHIFTING
SOUTHWEST TONIGHT.

THE EC AND GFS AND GEM HAVE NOW COME INTO BETTER AGREEMENT WITH THE
EVOLUTION AND TIMING OF THE LARGE SCALE UPPER TROUGH IN THE EASTERN
PACIFIC. THE MODELS SHOW THE UPPER TROUGH DEVELOPING NEAR 140W WITH
A SOUTHWEST FLOW ALOFT. SEVERAL PIECES OF ENERGY WILL GET EJECTED
OUT AHEAD OF THE UPPER TROUGH TUESDAY, BUT THEY ARE WEAK AND NOT
MUCH IF ANYTHING WILL HAPPEN. TEMPERATURES WILL BE COOLER TUESDAY
AND RELATIVE HUMIDITIES WILL BE HIGHER, BUT WE'LL CONTINUE TO HAVE
GUSTY SOUTHWEST WINDS EAST OF THE CASCADES WHICH WILL BE A FIRE
WEATHER CONCERN.

THE MAIN UPPER TROUGH APPROACHES THE COAST WEDNESDAY, THEN MOVES
INLAND THURSDAY. THIS WILL BRING AN INCREASING CHANCE OF SHOWERS AND
A SLIGHT CHANCE OF THUNDERSTORMS WEDNESDAY AND THURSDAY.
TEMPERATURES WILL BE COOLER AND WILL END UP BELOW NORMAL BOTH DAYS
WITH PLENTY OF CLOUD COVER, SO THIS COULD LIMIT THE AMOUNT OF
THUNDERSTORMS, BUT STILL FEEL THAT THE EASTSIDE STANDS THE BEST
CHANCE OF GETTING STORMS. GUSTY WINDS WILL CONTINUE MAINLY ALONG AND
EAST OF THE CASCADES, BUT ALSO OVER THE RIDGES IN WESTERN SISKIYOU
COUNTY.

THE EC AND GFS SHOW THE TROUGH SPLITTING WITH A CLOSED LOW
DEVELOPING IN CALIFORNIA FRIDAY, BUT THEY DIFFER WITH THE LOCATION.
THE GFS IS MORE PROGRESSIVE AND MOVES IT INTO SOUTHERN CALIFORNIA
WHILE THE EC IS SLOWER AND FARTHER NORTH. EITHER WAY, AN UPPER RIDGE
WILL NOSE INTO THE AREA BRINGING DRY AND WARMER WEATHER.

OF NOTE, THE EC SUGGEST THE CUTOFF LOW SPINNING IN CENTRAL
CALIFORNIA STARTING TO DRIFT NORTH SATURDAY WITH A MOIST SOUTHEAST
FLOW MOVING INTO NORTHERN CALIFORNIA. ALSO THE EC SHOWS QPF BREAKING
OUT IN NORTHERN CALIFORNIA. IN CONTRAST THE GFS IS MORE PROGRESSIVE
AND MOVES THE LOW INTO ARIZONA. SO IT REMAINS TO BE SEEN IF OR WHEN
THE MODELS WILL COME INTO BETTER AGREEMENT. -PETRUCELLI

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

DW/BTL/MND