Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 032153
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
253 PM PDT TUE MAY 3 2016

.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...AN UPPER LEVEL
TROUGH IS ALONG 130 WEST THIS AFTERNOON. THE TROUGH WILL SPLIT
AND THE SOUTHERN PIECE OF ENERGY WILL CLOSE OFF AS IT HEADS
SLOWLY EAST TOWARD THE CALIFORNIA COAST OVER THE NEXT 24 HOURS.
THE RESULTANT SOUTH TO SOUTHEAST FLOW ALOFT IS TRANSPORTING
MOIST, WEAKLY UNSTABLE AIR INTO NORTHERN CALIFORNIA AND SOUTHWEST
OREGON ALONG WITH SCATTERED SHOWERS/ISOLATED THUNDERSTORMS. WE`VE
HAD A BROAD, THICK CIRRUS SHIELD OVER US MOST OF THE DAY, WHICH
HAS MOSTLY INHIBITED CONVECTIVE DEVELOPMENT WEST OF THE CASCADES.
HOWEVER, THE DEEPER MOISTURE IS BEING TRANSPORTED INTO THE
SOUTHWEST PART OF THE AREA AND SHOWERS ARE DEVELOPING IN RESPONSE
TO A SUBTLE SHORT WAVE FROM WESTERN SISKIYOU COUNTY NORTHWARD INTO
SOUTHWEST OREGON. THIS WILL PROPAGATE NORTH-NORTHWESTWARD WEST OF
THE CASCADES THIS AFTERNOON/EVENING AND WILL BE ONE FOCUS AREA FOR
SHOWERS. PRECIPITABLE WATER VALUES IN THIS REGION ARE NEARING
1.00INCH, SO SOME SHOWERS MAY PRODUCE MODERATE TO HEAVY RAINFALL.
THERE IS ANOTHER FOCUS AREA FARTHER EAST, FROM MODOC COUNTY NORTH-
NORTHWEST TO WINTER RIM AND NORTHERN KLAMATH/NORTHWEST LAKE
COUNTIES, WHERE SOME SUNSHINE THIS MORNING ALLOWED THE ATMOSPHERE
TO DESTABILIZE. EXPECT SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS THERE THROUGH THIS EVENING. OVERNIGHT INTO EARLY
WEDNESDAY MORNING, EXPECT A DOWNWARD TREND IN SHOWER COVERAGE AS
THE SHORT WAVE LIFTS NORTHWARD AND INSTABILITY WANES.

LATER WEDNESDAY MORNING THROUGH WEDNESDAY EVENING, EXPECT ANOTHER
ROUND OF SHOWERS AS THE LOW CLOSES OFF JUST WEST OF THE SAN
FRANCISCO BAY AREA KEEPING SOUTHWEST OREGON AND NORTHERN
CALIFORNIA IN THE SOUTH FLOW OF MOIST AIR. ISOLATED THUNDERSTORMS
CAN BE EXPECTED JUST ABOUT ANYWHERE FROM THE CASCADES EASTWARD ON
WEDNESDAY, BUT THE BEST LAPSE RATES (>7C/KM) FOR THUNDERSTORMS
WILL BE OVER THE FAR EAST SIDE FROM THE MODOC WARNER MOUNTAINS UP
INTO EASTERN LAKE COUNTY.

THIS PATTERN WILL NOT RESOLVE QUICKLY WITH AN OMEGA BLOCK SET
UP ACROSS THE COUNTRY. ANOTHER CLOSED LOW RESIDING OVER THE
EASTERN U.S. AND STRONG RIDGING OVER THE NATION`S MIDSECTION WILL
PREVENT THE CLOSED LOW OFF THE CALIFORNIA COAST FROM PROGRESSING
EASTWARD...ONLY SLOWLY EDGING INTO THE SOUTHWEST UNITED STATES
LATE THIS WEEK. THIS WILL KEEP SHOWERS AND THUNDERSTORMS IN THE
FORECAST, WITH THE BEST CHANCES FROM THE CASCADES SOUTH AND
EASTWARD THURSDAY THROUGH FRIDAY. SPILDE

.LONG TERM...SATURDAY THROUGH TUESDAY...THE MODELS REMAIN IN FAIRLY
GOOD AGREEMENT WITH THE LARGE CLOSED UPPER LOW THIS WEEKEND. THE
CENTER OF THE LOW STARTS OUT IN THE DESERT SOUTHWEST ON SATURDAY
JUST WEST OF THE FOUR CORNERS, THEN GRADUALLY MOVING INTO NORTHERN
UTAH/COLORADO/SOUTHERN WYOMING SUNDAY. THE MODELS HAVE BACKED OFF ON
THE WESTWARD EXTENT OF THE WRAP-AROUND MOISTURE THIS WEEKEND, THUS
DECIDED TO KEEP THE HIGHEST POPS IN SOUTHWEST LAKE AND MODOC
COUNTIES WITH A FAIRLY HIGH PROBABILITY IN THESE AREAS. IN ADDITION
THE MODELS SUGGEST INSTABILITY WILL BE MARGINAL AT BEST AND HAVE
TRIMMED BACK THE COVERAGE OF ISOLATED THUNDERSTORMS. WOULD NOT BE
SURPRISED IF THERE ARE NO STORMS, BUT NOT CONFIDENT ENOUGH TO REMOVE
THEM COMPLETELY. THE MODELS SHOW THE UPPER RIDGE STARTING TO NUDGE
INTO THE AREA ON SUNDAY AS THE AFOREMENTIONED UPPER LOW MOVES EAST,
WITH DRY CONDITIONS FOR MOST OF THE AREA, EXCEPT FOR THE SOUTHEAST
PORTION OF OUR CWA. THE RIDGE (ALBEIT NOT A STRONG ONE) WILL MOVE
OVER THE AREA NEXT MONDAY AND REMAIN THERE INTO TUESDAY WHICH WILL
RESULT IN A GOOD CHANCE FOR FLAT OUT DRY CONDITIONS. -PETRUCELLI

&&

.AVIATION...FOR THE 03/18Z TAF CYCLE...MVFR CIGS ARE EXPECTED TO
PERSIST ALONG AND AT THE COAST THROUGH THIS EVENING. THERE IS A
CHANCE CIGS COULD BRIEFLY IMPROVE TO VFR AROUND 0Z, BUT CONFIDENCE
IS NOT HIGH, THUS WE`LL LEAVE MVFR CIGS IN THE TAF. INLAND, THE MAIN
CONCERN IS THE POTENTIAL FOR ISOLATED THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING WHICH COULD PRODUCE GUSTY OUTFLOW WINDS.
CONFIDENCE IS LOW TO MODERATE FOR ISOLATED STORMS IN KLAMATH FALLS,
SO WE`LL LEAVE IT IN THE TAF. CONFIDENCE IS LOWER ISOLATED STORMS
WILL DEVELOP AND/OR MOVE OVER ROSEBURG, SO KEPT IT OUT OF THE TAF
FOR NOW. I DID MENTION VCTS FOR MEDFORD, BUT LATER SHIFTS WILL NEED
TO REEVALUATE AND DETERMINE IF VCTS SHOULD BE MAINTAINED. VFR CIGS
ARE EXPECTED TO BE THE PREDOMINATE CONDITION INTO EARLY THIS EVENING
WITH BRIEF MVFR CIGS POSSIBLE WITH PARTIAL TERRAIN OBSCURATION.
-PETRUCELLI

&&

.MARINE...UPDATED 200 AM PDT TUE 3 MAY 2016...A WEAK FRONT WILL
DISSIPATE OFFSHORE TUESDAY NIGHT. A THERMAL TROUGH WILL DEVELOP NEAR
THE COAST WEDNESDAY AND WILL PERSIST INTO THE WEEKEND. THIS WILL
BRING AN EXTENDED PERIOD OF MODERATE TO STRONG NORTH WINDS.
WIDESPREAD SMALL CRAFT CONDITIONS WILL DEVELOP WITH PERIODS OF
HAZARDOUS SEAS OR GALES POSSIBLE...MAINLY IN THE AFTERNOONS SOUTH OF
CAPE BLANCO.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 11 PM PDT FRIDAY FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 11 PM THIS EVENING
     TO 11 PM PDT FRIDAY FOR PZZ350-356.
     GALE WARNING FROM 11 AM WEDNESDAY TO 11 PM PDT FRIDAY FOR
     PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 11 PM THIS EVENING
     TO 11 AM PDT WEDNESDAY FOR PZZ376.

$$

MAS/MAP/DW



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