779
FXUS66 KMFR 270513
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
1013 PM PDT SAT APR 26 2025
..UPDATED AVIATION DISCUSSION FOR 06Z TAFS
SHORT TERM
ISOLATED TO SCATTERED THUNDERSTORMS THAT DEVELOPED
EARLIER THIS EVENING/AFTERNOON IN KLAMATH, LAKE AND MODOC COUNTIES
ARE BEGINNING TO DIMINISH. A FEW STRONGER CELLS DEVELOPED IN
NORTHWEST MODOC AND SOUTHERN LAKE COUNTIES. A CELL, SOUTH AND
SOUTHEAST OF NEWELL, DEVELOPED THIS EVENING AND RADAR INDICATED HAIL
UP TO 0.5 INCHES AS WELL AS GUSTY WINDS. THIS CELL IS SHOWING SIGNS
OF WEAKENING AS IT MOVES INTO FAR NORTHWESTERN MODOC. SHOWERS WILL
CONTINUE, MAINLY ACROSS AREAS FROM THE CASCADES EAST AND SISKIYOUS
SOUTHWARD.
THE FORECAST REMAINS ON TRACK FOR TONIGHT INTO SUNDAY. AS THE
UPPER LOW SOUTH OF THE AREA MOVES INLAND TO THE EAST, OVER NEVADA,
LATER TONIGHT INTO SUNDAY, EXPECT SHOWERS TO MAINLY BECOME
LIMITED TO PORTIONS OF EASTERN SISKIYOU, MODOC AND SOUTHERN LAKE
COUNTIES. FOR ADDITIONAL DETAILS, PLEASE SEE THE DISCUSSION
BELOW.
AVIATION...27/06Z TAFS
CLOUD COVER REMAINING IN THE WAKE OF A LOW
PRESSURE SYSTEM IS KEEPING LEVELS GENERALLY AT VFR OR MVFR TONIGHT.
SOME LIGHT SHOWERS CONTINUE AT KLAMATH FALLS, WITH THE LAST SHOWERS
FORECAST TO DRIFT EASTWARD INTO EARLY SUNDAY MORNING. FLIGHT LEVELS
LOOK TO REMAIN BORDERLINE VFR/MVFR INTO EARLY SUNDAY MORNING AS WELL,
WITH GUIDANCE SUGGESTING BRIEF CHANCES OF LOWER VISIBILITIES AT
NORTH BEND.
SOME AMOUNT OF CLOUD COVER LOOKS TO REMAIN ALONG THE OREGON COAST
NORTH OF CAPE BLANCO AS WELL AS INTO THE UMPQUA VALLEY THROUGH THE
TAF PERIOD. OTHER AREAS LOOK TO REMAIN AT VFR FROM SUNDAY MORNING
INTO SUNDAY NIGHT. -TAD
MARINE...UPDATED 800 PM SATURDAY, APRIL 26, 2025
STEEP SEAS IN
ALL WATERS WILL PERSIST INTO SUNDAY MORNING AS CONDITIONS REMAIN
HAZARDOUS TO SMALL CRAFTS. CONDITIONS IMPROVE SOME TONIGHT INTO
SUNDAY AS WINDS EASE, THOUGH STEEP SEAS ARE LIKELY TO PERSIST SOUTH
OF CAPE BLANCO. CONDITIONS CONTINUE TO IMPROVE INTO MONDAY WITH A
THERMAL TROUGH BUILDING MONDAY EVENING INTO TUESDAY. NORTHERLY WINDS
PERSIST INTO MUCH OF NEXT WEEK AS HIGH PRESSURE BUILDS IN THE
REGION.
PREV DISCUSSION
/ISSUED 502 PM PDT SAT APR 26 2025/
DISCUSSION (TODAY THROUGH FRIDAY)...
OVERVIEW:
MAIN WEATHER HAZARDS FOR THIS FORECAST PACKAGE INCLUDE THE THREAT
OF AN ISOLATED THUNDERSTORM THIS AFTERNOON ACROSS THE EASTSIDE,
AS WELL AS AREAS ACROSS NORTHERN CALIFORNIA. NOT EXPECTING SEVERE
THUNDERSTORMS, BUT LIGHTNING WILL REMAIN A THREAT OVER THESE AREAS
THROUGH THIS EVENING. LINGERING SHOWERS TOMORROW WILL END AND
THEREAFTER WE WILL GO DRY UNTIL TUESDAY WITH LOW END CHANCES FOR
SHOWERS. THEN A MUCH BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS
WILL COME FRIDAY, BUT ITS TOO EARLY TO SAY WITH MUCH CONFIDENCE
THE LEVEL OF IMPACTS WE MAY (OR MAY NOT) HAVE LATE NEXT WEEK.
FURTHER DETAILS:
AN UPPER LEVEL (H5) LOW CURRENTLY OFF THE COAST OF CALIFORNIA
WEST OF SAN FRANSISCO WILL SLOWLY MOVE ON SHORE TODAY, AND SHOWERS
WILL FOLLOW SUIT ACROSS OUR FORECAST AREA ON THE POLEWARD SIDE OF
THE LOW. THESE SHOWERS ARE EXPECTED TO SLOWLY MOVE SOUTHWEST AND
SOUTH THROUGH THIS EVENING AND LINGER TOMORROW MORNING BEFORE
DISSIPATING. MUCAPE VALUES TODAY ARE ON THE LOWER END (100-450
J/KG) FOR AREAS MAINLY EAST OF THE CASCADES. CANNOT RULE OUT A
THUNDERSTORM TODAY, BUT WE ARE NOT EXPECTED ANY SEVERE WEATHER,
BUT LIGHTNING WILL BE A THREAT FOR ANYONE WITH OUTDOOR ACTIVES
TODAY. NOT TOO WORRIED ABOUT GUSTY WINDS WITH MOMENTUM TRANSFER
DUE TO WEAK MID-LEVEL WIND SPEEDS. LINGERING SHOWERS TOMORROW WILL
LACK ANY NOTEWORTHY INSTABILITY, SO WE ARE NOT ANTICIPATING ANY
LIGHTNING TOMORROW BEFORE SHOWERS DISSIPATE.
WE WILL TRANSITION TO NORTHERLY FLOW IN THE WAKE OF THE
AFOREMENTIONED LOW AS AN AREA OF HIGH PRESSURE BUILDS OVER THE
PACIFIC. THEN ON TUESDAY WE BRIEFLY GO ZONAL BEFORE A WEAK
EMBEDDED SHORTWAVE TRANSITIONS ACROSS THE FORECAST AREA. WE ARE
LACKING ANY NOTEWORTHY INSTABILITY, SO NOT EXPECTING ANY
THUNDERSTORMS, BUT THERE WILL BE A CHANCE (20-40%) FOR LIGHT
SHOWERS (QPF < 0.10") ACROSS NORTHERN AND EASTERN PARTS OF THE
FORECAST AREA.
THEN A DRY PATTERN WILL DEVELOP UNTIL FRIDAY. A DEEPER NEGATIVELY
TILTED TROUGH IS ANTICIPATED TO DEVELOP WITH THE TROUGH AXIS
EXTENDING DOWN FROM BRITISH COLUMBIA. THE BASE OF THE TROUGH AND
VORTICITY MAXIMUM WILL PASS OVER THE FORECAST AREA. THIS COUPLED
WITH WITH WIDESPREAD AMPLE CAPE (UPWARDS OF 600 J/KG) WILL LIKELY
LEAD TO SHOWERS AND THUNDERSTORMS. BULK SHEAR VALUES AROUND 40-50
KNOTS WOULD ALLOW FOR UPDRAFTS MAINTAINING, SO WE COULD HAVE A
COUPLE STRONG STORMS, BUT ITS TOO EARLY TO SAY WITH MUCH
CONFIDENCE THE COVERAGE OF THESE THUNDERSTORMS. DCAPE VALUES ARE
ON THE LOWER END, AND THIS IS EVIDENT WITH FORECAST SOUNDINGS
INDICATING MOIST LOW LEVELS. IN FACT, EXTENDED RANGE FORECAST
SOUNDINGS SHOW A "TROPICAL" LIKE SOUNDINGS WITH A VERY MOIST
COLUMN. THIS WOULD INHIBIT STRONG DOWNBURST POTENTIAL, SO THE MAIN
THREAT COULD END UP BEING LIGHTNING WITH SMALL HAIL. WILL
CONTINUE TO MONITOR THIS BECAUSE FRIDAY COULD BE IMPACTFUL FROM A
RAIN AND LIGHTNING POINT OF VIEW. PWATS ARE AROUND AN INCH IN SOME
AREAS, SO WE WILL NEED TO ALSO KEEP AN EYE ON HEAVY RAINFALL
CHANCES. EARLY INDICATION SUGGEST THE SYSTEM IS PROGRESSIVE, AND
THE MEAN FLOW COULD RESULT IN FAST MOVING CELLS WHICH WOULD LIMIT
RAINFALL AMOUNTS OVER ONE AREA. STAY TUNED AS WE REFINE THE
DETAILS OVER THE COMING DAYS.
-GUERRERO
MFR WATCHES/WARNINGS/ADVISORIES
OR...CA...NONE.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 AM PDT SUNDAY
FOR PZZ356-376.
SMALL CRAFT ADVISORY UNTIL 5 AM PDT SUNDAY FOR PZZ350-370.
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