Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 061759
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
1059 AM PDT FRI MAY 6 2016

.UPDATE...
AN UPDATE TO THE FORECAST HAS BEEN MADE AND SENT FOR CONDITIONS
THROUGH THIS EVENING. ADJUSTMENTS WERE MADE TO SKY COVERAGE,
PROBABILITY OF PRECIPITATION, PRECIPITATION AMOUNTS, SHOWER AND
THUNDERSTORM COVERAGE, AND LIGHTNING ACTIVITY LEVEL.

&&

.DISCUSSION...
LOW PRESSURE CENTERED OVER CALIFORNIA AND NEVADA THIS MORNING IS
SENDING INVERTED TROUGHS ACROSS THE FORECAST AREA FROM EAST TO
WEST TODAY. PRIMARY FOCUS FOR SHOWER AND THUNDERSTORM ACTIVITY
WILL BE ACROSS MODOC, LAKE, SISKIYOU, AND KLAMATH COUNTIES THIS
AFTERNOON AND EVENING. SOME ACTIVITY IS LIKELY TO REACH TO THE
SOUTHEASTERN PORTION OF THE WEST SIDE LATE THIS AFTERNOON AND,
MORE LIKELY, THIS EVENING FROM ABOUT CRATER LAKE NATIONAL PARK
SOUTHWESTWARD TO THE BEAR CREEK PORTION OF THE ROGUE VALLEY,
OREGON CAVES, AND THE LOWER KLAMATH RIVER VALLEY. FLASH FLOOD
WATCHES REMAIN IN EFFECT FOR PORTIONS OF THE EAST SIDE AND
NORTHERN CALIFORNIA FOR THIS AFTERNOON THROUGH THIS EVENING. BTL

&&

.AVIATION...FOR THE 06/12Z TAF CYCLE...A MIX OF MVFR AND VFR
CONDITIONS WILL CONTINUE THROUGH LATE MORNING. SHOWERS AND
THUNDERSTORMS WILL DEVELOP ACROSS THE EAST SIDE EARLY THIS AFTERNOON
AND THEN MOVE FROM EAST TO WEST ACROSS THE AREA. THE GREATEST THREAT
FOR THUNDERSTORMS IS FROM THE CASCADES/SISKIYOUS EAST, BUT STORMS MAY
ADVANCE AS FAR WEST AS JACKSON/JOSEPHINE COUNTY (INCLUDING KMFR) LATE
THIS AFTERNOON. ANY STORMS WILL BE CAPABLE OF PRODUCING IFR
CIGS/VIS, VERY HEAVY RAIN, SMALL HAIL, AND GUSTY WINDS. SHOWERS AND
STORMS DIMINISH LATE THIS EVENING. -WRIGHT

&&

.MARINE...UPDATED 500 AM PDT FRI 6 MAY 2016...FEW CHANGES WERE MADE
TO THE MARINE FORECAST THIS MORNING. NORTH WINDS WILL INCREASE AGAIN
THIS AFTERNOON AND CONTINUE INTO THE EVENING. THIS TREND OF STRONG
NORTH WINDS/STEEP SEAS IN THE AFTERNOON/EVENINGS AND LULLS AT NIGHT
WILL LIKELY CONTINUE THROUGH THE WEEKEND. A GALE WARNING REMAINS IN
EFFECT THROUGH THIS EVENING OVER THE SOUTHERN WATERS WITH SMALL
CRAFT ADVISORIES ELSEWHERE. MODELS HAVE MAINTAINED THE POTENTIAL FOR
GALES OVER THE WEEKEND AND GALE WATCHES REMAIN IN EFFECT. THESE WILL
LIKELY BE UPGRADED LATER TODAY. -WRIGHT

&&

.PREV DISCUSSION... /ISSUED 339 AM PDT FRI MAY 6 2016/

DISCUSSION...A MOIST AND UNSTABLE AIR MASS CONTINUES OVER MUCH OF
THE FORECAST AREA TODAY...AND WILL HELP GENERATE ANOTHER ROUND OF
SHOWERS AND THUNDERSTORMS...PRIMARILY FOCUSED OVER NORTHERN
CALIFORNIA AND FROM THE CASCADES EASTWARD. THE CUTOFF LOW THAT
DOESN`T QUIT REMAINS OVER SOUTHERN CALIFORNIA...SLOWLY MOVING TO
THE EAST AND FEEDING THE AREA WITH DEEP MOISTURE AND DISTURBANCES
FROM THE SOUTHEAST.

THE INTERSECTION OF DEEP MOISTURE...INSTABILITY...AND FAVORABLE
DYNAMICS WILL BE MOST PROMINENT IN EASTERN
SISKIYOU...MODOC...AND LAKE COUNTIES TODAY. THE WRF ARW AND NMM
SHOW STORMS AND HEAVY RAINFALL FROM MOUNT SHASTA EASTWARD TO
ALTURAS AND NORTHEAST TO LAKEVIEW THIS AFTERNOON AND EVENING AS
SHORTWAVE ENERGY MOVES IN FROM THE EAST PER THE NAM AND SREF MODEL
OUTPUT. THE LATEST HRRR OUTPUT IS SUGGESTING SIMILAR. GIVEN
CURRENT SNOW DEPTH OVER THE WARNER MOUNTAINS OF 62 INCHES PER
DISMAL SWAMP SNOTEL...AND FORECAST SNOW LEVELS OF 9500 FEET...THIS
DEFINITELY PROVIDES THE POTENTIAL FOR RAPID SNOW MELT AND FLASH
FLOODING. A FLASH FLOOD WATCH CONTINUES FOR THE SOUTHERN HALF OF
SISKIYOU COUNTY...MODOC...EXTREME EASTERN KLAMATH...AND MOST OF
LAKE COUNTY. PRECIPITABLE WATER VALUES IN THE TOP 10 PERCENT FOR
THIS TIME OF YEAR ALSO SUPPORT THE FFA AREA. THE WESTERN FRINGES
OF THIS HAZARD AREA ARE LESS LIKELY TO SEE ANY HEAVY RAIN PROBLEMS
BUT HAVE LEFT THE AREA INTACT FROM THE PREVIOUS ISSUANCE GIVEN THE
UNCERTAINTY OF EXACT HEAVY RAIN LOCATIONS...AND WITH LATEST HRRR
OUTPUT LINING UP PRETTY NICELY WITH THE HAZARD AREA.

ADDITIONALLY...THE STORM PREDICTION CENTER HAS MAINTAINED A MARGINAL
RISK FOR SEVERE STORMS OVER MODOC AND SOUTHERN LAKE COUNTIES.
EASTERN SISKIYOU COUNTY ALSO FEATURES A CHANCE FOR SEVERE
THUNDERSTORMS WITH FORECAST MOST UNSTABLE CAPES OF 2000+ J/KG, LI
VALUES -4 TO -6, AND 0-6KM BULK SHEAR VALUES OF 30+KT.  STRONG
WINDS, HAIL, AND HEAVY RAIN ARE ALL A POSSIBILITY TODAY. LATEST
SATELLITE IMAGERY SHOWS THAT THE DAY SHOULD START OUT SUNNY IN MANY
PLACES EAST OF THE CASCADES...WHICH WILL YIELD UNINHIBITED SURFACE
HEATING AND POTENTIALLY MAX OUT THE INSTABILITY THIS AFTERNOON.

INSTABILITY DIMINISHES TONIGHT AND SHOWERS AND THUNDERSTORMS FOLLOW
SUIT. ON SATURDAY A DRYING AIR MASS WEST OF THE CASCADES WILL YIELD
SUNNY AND WARM CONDITIONS WHILE THUNDERSTORMS REMAIN POSSIBLE IN
MODOC COUNTY. TEMPERATURES WILL BE ABOUT 10 DEGREES ABOVE NORMAL
WEST OF THE CASCADES. BY SUNDAY COOL AND DRY NORTHWEST FLOW ALOFT
ELIMINATES THE CHANCE FOR SHOWERS OVER THE VAST MAJORITY OF THE
FORECAST AREA...WHILE A DEEPENING MARINE LAYER COULD BRING DRIZZLE
TO THE COAST.

ON MONDAY A WARM TREND BEGINS THAT WILL LAST INTO THE MIDDLE OF THE
WEEK AT LEAST...WITH TEMPERATURES MONDAY EXPECTED TO BE A FEW
DEGREES ABOVE NORMAL. A PORTION OF THE PREVIOUS LONG-TERM
DISCUSSION FOLLOWS.

TUESDAY THROUGH THURSDAY...AN UPPER RIDGE WILL BUILD OFF THE
COAST TUESDAY WITH A THERMAL TROUGH DEVELOPING AT THE COAST. THE
MODELS DIFFER WITH THE DETAILS AFTER TUESDAY, BUT THE PATTERN
REMAINS FAVORABLE FOR CONTINUED DRY AND WARM CONDITIONS.
-PETRUCELLI

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FLASH FLOOD WATCH THROUGH THIS EVENING FOR ORZ030-031.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
     EVENING FOR ORZ022.

CA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR CAZ080>085.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
     EVENING FOR PZZ350-356-370.
     GALE WARNING UNTIL 11 PM PDT THIS EVENING FOR PZZ356-376.
     GALE WATCH FROM SATURDAY MORNING THROUGH SUNDAY EVENING FOR
     PZZ376.

$$

BTL/NSK/TRW



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