358
FXUS66 KMFR 162357
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
457 PM PDT WED SEP 16 2026
..UPDATED AVIATION DISCUSSION FOR 00Z TAFS
KEY MESSAGES
* SHOWERS AND THUNDERSTORMS ARE POSSIBLE TODAY AND TOMORROW
AFTERNOON/EVENING WITH THE MAIN THREATS BEING LIGHTNING AND
GUSTY ERRATIC OUTFLOW WINDS (UPWARDS OF 40-45 MPH)
* TEMPERATURES WARM THROUGH THE WEEKEND WITH ABOVE NORMAL
TEMPERATURES EXPECTED
* SIGNAL FOR DRY WEATHER AND SEASONABLE TEMPERATURES CONTINUES
FOR NEXT WEEK
DISCUSSION
SATELLITE IMAGERY SHOWS A VERY DISTINCTIVE AREA OF CYCLONIC
ROTATION OVER THE FORECAST AREA WITH THE CENTER OF THE LOW
CURRENTLY OVER NORTHERN CALIFORNIA. ONCE WE REACH PEAK HEATING,
TEMPERATURES WILL BE VERY CLOSE TO--IF NOT REACHING--CONVECTIVE
TEMPERATURES. WE WILL ALSO HAVE MUCAPE VALUES AROUND 400-800 J/KG
WITH SOME OUTPUTS AROUND 1000 J/KG. THESE ARE VERY HIGH
INSTABILITY VALUES FOR THIS AREA. THESE PARAMETERS COMBINED WITH
STEEP LAPSE RATES 8-9 C/KM WILL LIKELY LEAD TO THUNDERSTORM
DEVELOPMENT THIS AFTERNOON AND CONTINUING THROUGH THE EVENING
HOURS. GIVEN THE POSITION AND ORIENTATION OF THE CUTOFF LOW, THESE
STORMS WILL LIKELY START ALONG/NEAR A LINE FROM WESTERN SISKIYOU
COUNTY NORTHEAST TO CRATER LAKE IN ADDITION TO SOME INITIATION
OVER NORTHERN CALIFORNIA. IN FACT, ALREADY SEEING CUMULUS
DEVELOPING ACROSS THE AREA AS OF 2PM. THESE WILL VERY LIKELY
TRAVEL NORTHWEST INITIALLY AND THEN MORE WESTERLY AS THE AFTERNOON
AND EVENING HOURS PROGRESS. HODOGRAPHS AND THE MEAN FLOW SUGGEST
THESE STORMS MAY ONLY MOVE AROUND 25 MPH BUT SOME INSTANCES WE
COULD SEE THESE MOVING AROUND 35 MPH. PWATS ARE AROUND 0.50"-0.75"
IN A LOT OF CASES/LOCATIONS, BUT WE ARE SEEING SOME AREAS WITH
OUTPUTS CLOSER TO AROUND 0.80"-1.00". GIVEN ALL THAT, A FEW OF
THESE STORMS COULD PRODUCE DECENT RAINFALL AMOUNTS IN A SHORT
AMOUNT OF TIME. FOR EXAMPLE, IT WOULD NOT BE OUT OF THE QUESTION
TO SEE ISOLATED AMOUNTS OF 0.25"-0.50" IN AN 1-1.5 HRS.
ADDITIONALLY, FORECAST SOUNDS ARE DEPICTING AN INVERTED-V PROFILE
WITH DCAPE VALUES UPWARDS AROUND 600 J/KG. WITH EVAPORATIVE
COOLING PROCESS IN THESE DRY LOW LEVELS, WE COULD SEE SOME
ISOLATED GUSTY OUTFLOW WINDS AROUND 40-45MPH. IT GETS A LITTLE
TRICKY WITH TERRAIN, AND IF A STORM HAPPENS TO ALIGN WITH THE
TERRAIN IN A FAVORABLE FASHION WITH THESE OUTFLOWS, WE COULD SEE
LOCALIZED HIGHER GUSTY ERRATIC OUTFLOWS, AND THIS WOULD BE
ESPECIALLY TRUE FOR WESTSIDE AREAS AS THE STORMS MOVE OVER THE
CASCADES. OF COURSE, THE OTHER PROBLEMS IS THE STORMS MAY NOT
MAINTAIN GOING OVER THE CASCADES. ALL THAT SAID, THE MAIN TAKE
AWAY IS IF ANY STORMS MAKE IT OVER TO THE WESTSIDE, WE COULD SEE A
FEW LOCALIZED STRONG OUTFLOW WINDS IN ADDITION TO LIGHTNING.
WESTSIDE AREAS MEAN AREAS WEST OF THE CASCADES IN NORTHERN
CALIFORNIA AND SOUTH/SOUTHWEST OREGON.
THE NEXT BIG QUESTION IS HOW MUCH WILL THUNDERSTORMS THIS
AFTERNOON AND EVENING AFFECT CHANCES FOR TOMORROW. WE WONT SEE
MUCH OF AN AIRMASS CHANGE WITH THE LOW MEANDERING OVERHEAD
TOMORROW, SO MODELS MAY NOT BE HANDLING THURSDAY CONVECTION VERY
WELL. HOWEVER, THERE IS ENOUGH EVIDENCE TO SUGGEST WE WILL SEE
CONTINUED ACTIVITY TOMORROW, BUT THIS WILL LIKELY BE MORE FOR
AREAS ALONG/NEAR THE CASCADES AND EAST VERSUS TODAY'S MORE AREA-
WIDE CHANCES. ADDITIONALLY, COOLER TEMPERATURES ON THE EASTSIDE
COULD LIMIT DESTABILIZATION WHICH MAY LIMIT THE LIGHTNING
POTENTIAL. ADDITIONALLY, MUCAPE VALUES ARE FAR LESS TOMORROW,
ESPECIALLY THROUGH LATE AFTERNOON/EARLY EVENING WHICH FURTHER
LEADS TO LESS LIGHTNING POTENTIAL. THERE IS ALSO VIRTUALLY NO
DCAPE SO THE MAIN THREAT WOULD BE LIGHTNING FOR THURSDAY, BUT EVEN
THAT IS A LOW THREAT AT THIS TIME. IF LIGHTNING DOES OCCUR, THESE
WOULD BE VERY LOW TOP THUNDERSTORMS.
HIGH PRESSURE THEN MOVES IN OVER THE AREA BEHIND THE LOW AS IT
EXITS ON FRIDAY. THIS WILL RESULT IN A RIDGE ALOFT THROUGH THE
WEEKEND AND ABOVE NORMAL TEMPERATURES. SOME WESTSIDE AREAS COULD
POTENTIALLY BE IN THE LOWER 90S FOR A HIGH ON BOTH SATURDAY AND
SUNDAY. A LOW DOES FORM LATE IN THE WEEKEND AS THE RIDGE SLIDES
EAST, BUT THIS LOW IS CURRENTLY PROGGED TO REMAIN SOUTH OF THE
FORECAST AREA WHICH WOULD PUT MOSTLY ZONAL FLOW ALOFT OVER THE
AREA. CURRENT SIGNAL DOES PLACE THE FORECAST AREA IN A DRY PATTERN
WITH SEASONABLE TEMPERATURES THROUGH MUCH OF NEXT WEEK.
-GUERRERO
AVIATION...17/00Z TAFS
VFR LEVELS ARE PRESENT ACROSS NORTHERN
CALIFORNIA AND SOUTHERN OREGON, BUT ACTIVE WEATHER IS PRESENT.
THUNDERSTORMS ARE MOVING TO THE NORTHWEST ACROSS SISKIYOU, MODOC,
LAKE, AND KLAMATH COUNTIES. LIGHTNING STRIKES ARE BRING OBSERVED
WITH THESE STORMS, AND GUSTY WINDS AS WELL AS LOCALLY MODERATE TO
HEAVY RAINFALL WILL BE POSSIBLE. ISOLATED CELLS ARE POPPING UP IN
JACKSON COUNTY AS WELL, BUT HAVE BEEN SHORT-LIVED AND WITHOUT
LIGHTNING. GUSTY WINDS ARE PRESENT AT NORTH BEND. COASTAL WINDS AND
INLAND THUNDERSTORMS SHOULD EASE INTO THE EVENING, ALTHOUGH ISOLATED
SHOWER ACTIVITY MAY CONTINUE INTO THE NIGHT.
MARINE STRATUS IS EXPECTED TO DEVELOP ALONG THE COAST EARLY THURSDAY
MORNING, BRINGING IFR TO LIFR LEVELS. THIS LAYER SHOULD CLEAR LATE
IN THE MORNING. ANOTHER ROUND OF AFTERNOON ACTIVITY IS EXPECTED, BUT
INSTABILITY LOOKS TO BE LESS OF A FACTOR. ISOLATED THUNDERSTORMS ARE
STILL POSSIBLE EAST OF THE CASCADES, WITH WIDESPREAD LIGHT SHOWERS
THAT MAY BRING LOCALLY LOWER FLIGHT LEVELS. -TAD
MARINE
UPDATED 1200 PM PDT WEDNESDAY, SEPTEMBER 16,
2026...GUSTY NORTH WINDS AND STEEP SEAS WILL CONTINUE INTO EARLY
THURSDAY MORNING, BUT CONDITIONS WILL STEADILY IMPROVE BEGINNING
LATE TONIGHT. CONDITIONS EASE BELOW ADVISORY CRITERIA BY THURSDAY
AFTERNOON AND LIKELY PERSIST THROUGH FRIDAY NIGHT. NORTH WINDS
INCREASE AGAIN SATURDAY AND LIKELY PERSIST INTO NEXT WEEK. STEEP,
HAZARDOUS ARE POSSIBLE AGAIN BY SATURDAY NIGHT, ESPECIALLY SOUTH
OF CAPE BLANCO.
/BR-Y
MFR WATCHES/WARNINGS/ADVISORIES
OR...CA...NONE.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 AM PDT
THURSDAY FOR PZZ350-356-370-376.
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