541
FXUS66 KMFR 272342
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
442 PM PDT SUN APR 27 2025
..UPDATED THE AVIATION SECTION
AVIATION...28/00Z TAFS
CONDITIONS EARLY THIS EVENING ARE MAINLY
VFR, THOUGH WITH PARTIAL OBSCURATION OF THE HIGHER TERRAIN. CLOUD
COVER IS THICKEST IN SOUTHERN LAKE AND EASTERN MODOC COUNTIES WHERE
A FEW LIGHT SHOWERS OR VIRGA WILL LINGER FOR A FEW MORE HOURS THIS
EVENING.
ONSHORE FLOW WILL INCREASE LOW LEVEL CLOUD COVER ALONG THE OREGON
COAST NORTH OF CAPE BLANCO AS WELL AS INTO THE UMPQUA VALLEY TONIGHT
INTO MONDAY MORNING WITH A MIX OF VFR AND MVFR CEILINGS FROM AROUND
04Z INTO 18Z. A DEEP, MOIST BOUNDARY LAYER SHOULD ALLOW PATCHY
CEILINGS TO SPILL INTO THE ROGUE BASIN AS WELL.
OTHERWISE, VFR WILL PERSIST THROUGH MONDAY AFTERNOON WITH HIGH
CLOUDS ARRIVING FROM THE NORTH LATE IN THE DAY. -DW
MARINE...UPDATED 200 PM SUNDAY, APRIL 27, 2025
THE STRONGEST
NORTHERLY WINDS AND STEEPEST SEAS WILL BE FOUND SOUTH OF CAPE BLANCO
AS A WEAK THERMAL TROUGH PERSISTS INTO MONDAY NIGHT.
STABLE UPPER LEVEL CONDITIONS WILL ALLOW FOR MORE IMPROVEMENT IN THE
MIDDLE OF THE WEEK. A STRONG THERMAL TROUGH IS NOT FORECAST, SO
PERIODS OF BELOW ADVISORY SEAS WILL BE POSSIBLE. AN APPROACHING
FRONT MAY BRING STEEP SWELL AND MARINE SHOWERS NEAR THE END OF THE
WEEK. -TAD/HERMANSEN
PREV DISCUSSION
/ISSUED 202 PM PDT SUN APR 27 2025/
DISCUSSION...
OVERVIEW:
EXPECTING SEASONABLE TEMPERATURES AND DRY CONDITIONS UNTIL TUESDAY
WHEN LOW END CHANCES FOR SHOWERS ENTER THE FORECAST. THIS WILL BE
FOLLOWED BY WELL ABOVE NORMAL TEMPERATURES (~10+ DEGREES) BOTH
WEDNESDAY AND THURSDAY. THEN A MUCH BETTER CHANCE FOR SHOWERS AND
THUNDERSTORMS ON FRIDAY. ITS TOO EARLY TO SAY WITH MUCH CONFIDENCE
THE LEVEL OF IMPACTS WE MAY (OR MAY NOT) HAVE LATE NEXT WEEK WITH
REGARDS TO THUNDERSTORMS AND RAINFALL. THAT SAID, CURRENT THINKING
IS AT LEAST LOW-END IMPACTS FOR LIGHTNING AND HEAVY RAINFALL THAT
COULD LEAD TO SOME RIVER RISES AS SPRING SNOWMELT CONTINUES.
FURTHER DETAILS:
AN AREA OF HIGH PRESSURE (H5) CONTINUES TO BUILD IN OVER THE
PACIFIC, AND WE HAVE TRANSITIONED TO A NORTHERLY FLOW PATTERN IN THE
WAKE OF YESTERDAYS LOW PRESSURE SYSTEM. THIS PATTERN WILL KEEP US
DRY WITH SEASONABLE TEMPERATURES THROUGH EARLY NEXT WEEK. BY
TUESDAY, WE WILL TRANSITION TO A MOSTLY ZONAL FLOW, BUT WE WILL HAVE
A WEAK EMBEDDED SHORTWAVE WITHIN THIS FLOW THAT COULD IMPACT THE
FORECAST AREA. THERE HAS BEEN SOME FLUCTUATION IN THE PATH OF THIS
SHORTWAVE OVER THE LAST 24 HOURS WHICH KEEPS CONFIDENCE LOW IN
REGARDS TO SHOWER TIMING/COVERAGE, BUT WE HAVE MAINTAINED A LOW END
CHANCES (~20%-35%) FOR MAINLY NORTHERN AREAS AND AREAS EAST OF THE
CASCADES. QPF REMAINS LOW IN THIS PATTERN, AND AREAS THAT HAPPEN
TO RECEIVE RAINFALL ARE LIKELY NOT EXCEEDING 0.05" OF RAINFALL.
AFTER TUESDAY, WELL ABOVE NORMAL TEMPERATURES ARE FORECAST BOTH
WEDNESDAY AND THURSDAY AS HIGH PRESSURE BUILDS IN OVER THE PACNW. IN
FACT, ON THURSDAY THE HIGH COULD BE CENTERED NEARLY OVER THE
FORECAST AREA, AND TO NO SURPRISE THIS IS THE WARMEST DAY OF THE
FORECAST PERIOD WITH MOST AREAS WELL ABOVE NORMAL. HOWEVER, AT THIS
TIME IT DOES NOT APPEAR ANY RECORDS WILL BE BROKEN WITH MOST AREAS
FALLING ABOUT 10 DEGREES SHY OF RECORDS (OFFICIAL CLIMATE SITES).
ON FRIDAY, A DEEPER NEGATIVELY TILTED TROUGH IS ANTICIPATED TO
DEVELOP WITH THE TROUGH AXIS EXTENDING DOWN THROUGH THE PACNW FROM
BRITISH COLUMBIA. THE BASE OF THE TROUGH AND VORTICITY MAXIMUM WILL
PASS OVER THE FORECAST AREA. THIS COUPLED WITH WITH AMPLE CAPE
(UPWARDS OF 600 J/KG) WILL LIKELY LEAD TO SHOWERS AND ISOLATED
THUNDERSTORMS. HOWEVER, IT SHOULD BE NOTED THAT INSTABILITY HAS
DECREASED IN AREAL COVERAGE, WITH INSTABILITY NOW BEING CONFINED TO
AREAS ALONG AND NEAR THE CASCADE, AND AREAS TO THE EAST OF THE
CASCADES (INCLUDING NORTHERN CALIFORNIA. BULK SHEAR VALUES (ALSO
DECREASED) AROUND 30-40 KNOTS WOULD ALLOW FOR UPDRAFTS TO MAINTAIN,
SO WE COULD HAVE A COUPLE STRONG STORMS; HOWEVER, ITS TOO EARLY TO
SAY WITH MUCH CONFIDENCE THE COVERAGE OF THESE THUNDERSTORMS GIVEN
FLUCTUATIONS IN UPPER LEVEL DYNAMICS. DCAPE VALUES REMAIN 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. WILL CONTINUE TO
MONITOR THIS BECAUSE FRIDAY COULD BE IMPACTFUL FROM A RAIN AND
LIGHTNING POINT OF VIEW, BUT SMALL HAIL CANNOT BE RULED OUT EITHER
AT THIS POINT. PWATS ARE APPROACHING AN INCH IN SOME AREAS, SO WE
WILL NEED TO ALSO KEEP AN EYE ON HEAVY RAINFALL POTENTIAL. 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. WE WILL CONTINUE TO MONITOR FRIDAY FOR IMPACTS AS
THIS REMAINS THE DAY WITH THE HIGHEST POTENTIAL.
-GUERRERO
MFR WATCHES/WARNINGS/ADVISORIES
OR...CA...NONE.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 5 AM PDT TUESDAY
FOR PZZ356-376.
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