917
FXUS66 KMFR 221551
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
851 AM PDT TUE OCT 22 2024
DISCUSSION
THE FORECAST REMAINS ON TRACK FOR TODAY. HIGH CLOUDS
ARE MOVING OVER NORTHERN CALIFORNIA AND SOUTHERN OREGON ALONG
UPPER LEVEL ZONAL FLOW. TODAY'S HIGHS WILL BE NEAR SEASONAL
LEVELS, WITH MID 60S WEST OF THE CASCADES AND LOW TO MID 60S TO
THE EAST. AN UPPER LEVEL TROUGH WILL MOVE OVER THE AREA QUICKLY ON
WEDNESDAY, BRINGING SLIGHT SHOWER CHANCES EAST OF THE CASCADES AND
CHANCES FOR FROST OR FREEING CONDITIONS TO WEST SIDE VALLEYS ON
WEDNESDAY NIGHT. -TAD
AVIATION...22/12Z TAFS
VFR CEILINGS DUE TO HIGH CLOUDS ARE THE
PREDOMINANT CONDITION. THEY WILL PERSIST TODAY INTO TONIGHT, AND
ACCOMPANY THE NEXT FRONT ON WEDNESDAY. THE EXCEPTION WILL BE PATCHES
OF COASTAL AND VALLEY LIFR/IFR THIS MORNING, MAINLY FOR THE UMPQUA
VALLEY (INCLUDING ROSEBURG). THE PRESENCE OF THE HIGH CLOUDS WILL
LIMIT FOG DEVELOPMENT, BUT YESTERDAY'S RAIN HAS LEFT PLENTY OF LOW
LEVEL MOISTURE WEST OF THE CASCADES. -DW
MARINE (UPDATED 300 AM)
GUSTY NORTH WINDS AND STEEP WIND DRIVEN
SEAS RETURN SOUTH OF CAPE BLANCO THIS AFTERNOON THROUGH THIS EVENING
AS A THERMAL TROUGH BRIEFLY DEVELOPS. CONDITIONS BRIEFLY IMPROVE
EARLY WEDNESDAY, BEFORE A THERMAL TROUGH RETURNS WITH ANOTHER
EPISODE OF STEEP SEAS SOUTH OF CAPE BLANCO. A SIMILAR SCENARIO IS
LIKELY AGAIN DURING THURSDAY AFTERNOON AND EVENING. A LOW MOVING
NORTH TOWARDS THE GULF OF ALASKA WILL BRING INCREASING SOUTHERLY
WINDS AND BUILDING SEAS FRIDAY INTO THE WEEKEND. STEEP TO VERY STEEP
SEAS AND GALES WILL BE POSSIBLE IN THIS ACTIVE PATTERN. -DW
PREV DISCUSSION
/ISSUED 359 AM PDT TUE OCT 22 2024/
SHORT TERM...TODAY (10/22) THROUGH WEDNESDAY NIGHT
10/23...SATELLITE IMAGERY IS SHOWING A STREAM OF CLOUDS MOVING
ACROSS OREGON AND NORTHERN CALIFORNIA WITH SOME LOWER STRATUS
OCCURRING IN THE VALLEYS BELOW THIS CLOUD DECK. OVERALL, THE AREA
REMAINS UNDER ZONAL (WEST TO EAST) FLOW IN THE MID-LEVELS OF THE
ATMOSPHERE. TODAY WILL BE COOL, DRY, WITH RELATIVELY LIGHT WINDS.
THEN, A WEAK LOW PRESSURE SYSTEM PUSHES ACROSS OREGON BRINGING A A
WAVE OF LIGHT SHOWERS ACROSS THE AREA, ESPECIALLY FOR AREAS EAST
OF THE CASCADES. WETTING RAINFALL IS NOT GENERALLY EXPECTED WITH
THIS SYSTEM, AND OTHER IMPACTS WILL BE RELATIVELY LIGHT. THE MAIN
CONCERN, ACTUALLY WILL BE TEMPERATURES AFTER THE FRONT PASSES.
WEDNESDAY NIGHT TEMPERATURES COULD BE 5 TO 10 DEGREES BELOW
NORMAL--LEADING TO THE POSSIBILITY FOR ADDITIONAL FROST OR
FREEZING CONDITIONS IN SOME OF OUR WEST SIDE VALLEYS. FREEZES WILL
BE POSSIBLE (AROUND 30 TO 50% FOR THE ROGUE AND ILLINOIS VALLEYS)
AND MORE LIKELY IN OUR NORTHERN CALIFORNIA VALLEYS (50 TO 70%). AM
HOLDING OFF ON A FREEZE WATCH FOR NOW, BUT ONE MAY BE NECESSARY
ESPECIALLY IF THE FORECAST CONTINUES TO TREND THE WAY IT IS GOING.
STAY TUNED FOR UPDATES. -SCHAAF
LONG TERM....PREVIOUS LONG TERM ISSUED ON OCT 21 FOR THURSDAY
THROUGH MONDAY, OCT 24-28, 2024...
WITH A CLOSED LOW MEANDERING OUT NEAR 36N AND 140W IN THE
PACIFIC EARLY IN THE PERIOD, THE UPPER RIDGE DOWNSTREAM WILL AMPLIFY
SOME ALONG THE WEST COAST THU/FRI, RESULTING IN ANOTHER PERIOD OF
DRY WEATHER. THURSDAY MORNING WILL START CHILLY WITH ANOTHER
WIDESPREAD FROST IN THE WEST SIDE VALLEYS, AND ESPECIALLY SOUTH OF
THE ROGUE-UMPQUA DIVIDE. EVEN THE UMPQUA BASIN COULD SEE
TEMPERATURES CONDUCIVE TO FROST (<=36F) THIS TIME AROUND THOUGH.
RIGHT NOW, GUIDANCE SHOWS A 1 IN 3 (33%) CHANCE THAT TEMPERATURES
DROP TO 36F OR LOWER AT ROSEBURG WITH ODDS JUMPING TO A 2 IN 3 (67%)
CHANCE AT MEDFORD. FREEZING TEMPERATURES ARE LESS LIKELY IN THESE
AREAS, BUT THERE'S A 1 IN 4 (25%) CHANCE AT MEDFORD. WE MAY REQUIRE
FROST/FREEZE PRODUCTS AGAIN AT SOME POINT IN THE NEXT COUPLE OF
DAYS.
WITH THE UPPER RIDGE BUILDING IN, THURSDAY AFTERNOON WILL TURN OUT
SUNNY AND MILDER WITH TEMPERATURES GETTING BACK TO NEAR NORMAL
LEVELS. SW PORTIONS OF THE FORECAST AREA WILL HAVE SOMEWHAT HIGHER
TEMPS DUE TO OFFSHORE NE WINDS AND A THERMAL TROUGH ALONG THE COAST.
WITH HIGH PRESSURE OVERHEAD THURSDAY NIGHT, WE'LL HAVE ANOTHER
NIGHT OF STRONG RIDGE/VALLEY INVERSIONS. COLD AIR WILL POOL IN THE
VALLEYS ONCE AGAIN AND IT COULD BE JUST AS CHILLY AS WEDNESDAY NIGHT
WITH AREAS OF FROST.
AFTER THE COLD MORNING FRIDAY, THE THERMAL TROUGH WILL SHIFT INLAND
AND THE UPPER RIDGE AXIS WILL MOVE EAST OF THE CASCADES. THE CLOSED
LOW OFFSHORE WILL HAVE OPENED UP INTO A TROUGH BY NOW AND WILL
GRADUALLY MAKE ITS WAY TOWARD THE PACNW COAST. WHILE HIGH AND MID
CLOUDS WILL LIKELY INCREASE IN ADVANCE OF THIS SYSTEM, IT WILL ALSO
PROBABLY BE THE WARMEST DAY OF THE PERIOD. GUIDANCE IS SHOWING
WIDESPREAD HIGH TEMPERATURES IN THE LOW TO MID 70S FOR THE VALLEYS
WEST OF THE CASCADES AND HIGHS LARGELY IN THE MID TO UPPER 60S OVER
THE EAST SIDE.
RAIN CHANCES DON'T REALLY INCREASE UNTIL FRIDAY NIGHT WEST OF THE
CASCADES AHEAD OF A WARM FRONT, WITH HIGHEST POPS 20-60% FROM GRANTS
PASS/ROSEBURG WESTWARD (HIGHEST ALONG THE COAST). WITH THE INCREASE
IN CLOUD COVER, FRIDAY NIGHT WON'T BE AS COLD AS PREVIOUS NIGHTS.
AREAS EAST OF THE CASCADES WILL REMAIN DRY. IT SHOULD BE NOTED THAT
MODELS ARE SHOWING A PRETTY GOOD GRADIENT IN ADVANCE OF THE WARM
FRONT, WHICH MAY RESULT IN SOME BREEZY SOUTH WINDS (30-40 MPH PEAK
GUSTS) ESPECIALLY IN THE SHASTA VALLEY AND EAST OF THE CASCADES)
DURING FRIDAY EVENING. SNOW LEVELS WILL ALSO BE WAY HIGH -- UP
AROUND 8000 FEET. MUCH OF THE SUPPORT ALONG THE WARM FRONT WILL RACE
OFF TO THE NORTHEAST SATURDAY, SO WHAT'S LEFT BEHIND IT WILL BE
MOIST LOW-LEVEL ONSHORE FLOW, WITH THE COLD FRONT POISED TO MOVE
ONSHORE. POPS REMAIN HIGHEST NEAR AND WEST OF THE CASCADES (60-80%
CHANCES), BUT ESPECIALLY AT THE COAST. THE COLD FRONT MOVES INLAND
SATURDAY NIGHT AND WEAKENS.
AN ACTIVE WEATHER PATTERN LIKELY CONTINUES SUNDAY INTO MONDAY AS
ANOTHER PACIFIC UPPER LEVEL DISTURBANCE MOVES THROUGH. THIS WILL
BRING A HIGH PROBABILITY OF PRECIPITATION AREA WIDE (60-90% CHANCE),
BUT WITH THE BEST CHANCE FOR MEANINGFUL (WETTING) PRECIPITATION FROM
THE CASCADES WEST. SNOW LEVELS DURING THE TIME PERIOD FALL TO
NEAR 5000 FEET, SO WE'LL BE LOOKING AT A DECENT CHANCE FOR AT
LEAST SOME ACCUMULATING SNOW IN THE MOUNTAINS. -SPILDE
MFR WATCHES/WARNINGS/ADVISORIES
OR...CA...NONE.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FROM 2 PM THIS
AFTERNOON TO 2 AM PDT WEDNESDAY FOR PZZ356-376.
SMALL CRAFT ADVISORY FROM 2 PM TO 11 PM PDT WEDNESDAY FOR PZZ356-
376.
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