Area Forecast Discussion
Issued by NWS Medford, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KMFR 050549
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
1049 PM PDT TUE AUG 4 2015

.UPDATE...JUST MADE A VERY QUICK UPDATE TO ADJUST POPS AND
THUNDERSTORM COVERAGE TO CURRENT TRENDS. HAD TO PULL ISOLATED
THUNDER BACK ONTO THE WEST SIDE TO ACCOUNT FOR SOME CONVECTION
THAT JUST POPPED UP OVER MT. ASHLAND. THIS SEEMS TO BE ASSOCIATED
WITH SOME DEFORMATION STRETCHED FROM WEST TO EAST ACROSS THE AREA.
DON`T THINK WE`LL SEE MUCH MORE THAN THIS, BUT OBVIOUSLY WE`LL
HAVE TO KEEP ANY EYE ON IT TONIGHT AS THINGS ARE SOMEWHAT
VOLATILE. THUNDERSTORM COVERAGE IS DEFINITELY INCREASING EAST OF
THE CASCADES, PRETTY MUCH EXACTLY WHERE THE MODELS HAD IT, SO THE
REMAINING RED FLAG WARNINGS LOOK ON TRACK. -WRIGHT

&&

.AVIATION...FOR THE 05/06Z TAF CYCLE...SHOWERS AND THUNDERSTORMS
ARE DIMINISHING ACROSS WESTERN SISKIYOU COUNTY, BUT THEY ARE
DEVELOPING EAST OF THE CASCADES, WHICH WAS EXPECTED. GUSTY,
ERRATIC WINDS, LIGHTNING, AND BRIEF DOWNPOURS WILL BE POSSIBLE
WITH THESE STORMS, INCLUDING AT KLMT FOR THE NEXT FEW HOURS AT
LEAST. STRATUS HAS YET TO MOVE INTO NORTH BEND, BUT ALL
INDICATIONS ARE THAT IT WILL EVENTUALLY. SMOKE HAS DISSIPATED IN
THE ROGUE VALLEY, INCLUDING KMFR, BUT STREAMLINE ANALYSIS SUGGEST
IT MAY COME BACK OVERNIGHT AS LIGHT WINDS BECOME MORE NORTHERLY.
IT SHOULD ALSO INCREASE AGAIN TOMORROW AS DIURNAL WINDS DRIVE IT
IN. THIS DEPENDS ON WHAT HAPPENS WITH THE FIRE, OF COURSE, BUT
FORECAST WINDS SUPPORT A RETURN OF SMOKE. -WRIGHT

&&

.PREV DISCUSSION... /ISSUED 915 PM PDT TUE AUG 4 2015/

DISCUSSION...THE IMMEDIATE FOCUS IS ON THE CONVECTIVE FORECAST.
AN EVENING UPDATE TO THE FORECAST IS NOT NECESSARY. DURING THE
PAST COUPLE OF HOURS, A VERY STRONG COMPLEX OF THUNDERSTORMS
DEVELOPED OVER WESTERN SISKIYOU COUNTY NORTH OF THE SCOTT VALLEY
EXTENDING TO ROUTE 3 BETWEEN FT JONES AND YREKA. THIS COMPLEX HAS
WEAKENED DURING THE PAST HALF HOUR...LIKELY WITH SOME AID FROM THE
END OF DAY-TIME HEATING. BUT, ADDITIONAL ISOLATED TO SCATTERED
THUNDERSTORMS ARE EXPECTED OVERNIGHT UNTIL AROUND 5 AM IN SISKIYOU
COUNTY AND ACROSS MOST OF THE EAST SIDE AS AN UPPER LEVEL TROUGH
NORTH OF THE SAN FRANCISCO BAY CONTINUES MOVING NORTHEASTWARD. THE
INFLUENCE OF THIS TROUGH (WITH THE LIKELY FOCUS FOR OVERNIGHT
THUNDERSTORM DEVELOPMENT) IS SEEN BY THE WEAK RADAR RETURNS IN THE
CURRENT SCAN OVER FAR EASTERN SISKIYOU, MODOC, AND THE SOUTHERN
PORTIONS OF KLAMATH AND LAKE COUNTIES.

THE AIR MASS OVER OUR AREA WILL STABILIZE ON WEDNESDAY AS THE
TROUGH EXITS TO THE EAST AND A MORE MARITIME INFLUENCED AIR MASS
WITH WESTERLY MID-LEVEL FLOW BRINGS COOLER TEMPERATURES FOR ONE
DAY. ANOTHER TROUGH WILL MOVE TO THE CENTRAL CALIFORNIA COAST ON
THURSDAY AND SEND INLAND HIGH TEMPERATURES BACK UP TO THE
NEIGHBORHOOD OF THE READINGS EXPERIENCED THIS AFTERNOON. THIS
TROUGH IS NOT EXPECTED TO FOLLOW EXACTLY THE SAME TRACK AS
TONIGHT`S TROUGH BUT THE 18Z GFS AND 00Z NAM MODELS AGREE ON
INCREASED INSTABILITY AND LITTLE DAY-TO-DAY CHANGE IN HIGHS ON
FRIDAY WITH ISOLATED TO SCATTERED THUNDERSTORMS DURING THE AFTERNOON
AND EVENING FROM THE MT SHASTA REGION ACROSS THE EAST SIDE.

MARINE...UPDATED 230 PM PDT TUESDAY 4 AUGUST 2015...HIGH PRESSURE
WILL BUILD OFFSHORE AND A THERMAL TROUGH WILL DEVELOP ALONG THE
COAST THEN STRENGTHEN INTO THURSDAY. NORTH WINDS AND SEAS WILL
BUILD TONIGHT/WEDNESDAY AND REMAIN MODERATE THROUGH THURSDAY
MORNING. THEN WINDS WILL STRENGTHEN FURTHER THURSDAY AFTERNOON AND
EVENING...POSSIBLY REACHING GALE FORCE OVER THE SOUTHERN OUTER
WATERS. A GALE/HAZARDOUS SEAS WATCH HAS BEEN ISSUED FOR THIS TIME
FRAME FOR AN AREA BEYOND 10 NM AND MAINLY SOUTH OF GOLD BEACH. THE
THERMAL TROUGH WILL WEAKEN FRIDAY INTO SATURDAY. NORTH WINDS AND
SEAS WILL EASE AT THAT TIME. SPILDE

PREV DISCUSSION... /ISSUED 500 PM PDT TUE AUG 4 2015/

SHORT TERM...TODAY AND TONIGHT, A SHORTWAVE MOVING UP FROM THE
SOUTHWEST WILL ALLOW ISOLATED TO SCATTERED THUNDERSTORMS TO
DEVELOP OVER EASTERN AND SOUTHERN PORTIONS OF THE AREA. THIS WILL
MAINLY AFFECT NORTHERN CALIFORNIA AND AREAS EAST OF THE CASCADES.
MODELS CONTINUE TO INDICATE THE BEST CHANCE FOR THUNDERSTORMS IS
OVER WESTERN SISKIYOU COUNTY AND EAST OF THE CASCADES, ESPECIALLY
NEAR SUMMER RIM.

THIS DISTURBANCE WILL SHIFT EAST ON WEDNESDAY AND EXPECT MAINLY
DRY AND WARM CONDITIONS OVER THE AREA. A SURFACE THERMAL TROUGH
WILL DEVELOP ALONG THE COAST WEDNESDAY NIGHT INTO THURSDAY. THIS
WILL BRING BREEZY OFFSHORE FLOW TO THE COASTAL RIDGES WITH A
CHETCO EFFECT BRINGING WARM TEMPERATURES TO THE BROOKINGS AREA.
LATE THURSDAY, EXPECT AN UPPER LOW TO SHIFT INTO THE COAST OF
CENTRAL CALFIORNIA THEN MOVE INLAND THURSDAY NIGHT. AS THIS
FEATURE MOVES INLAND EXPECT SOUTHERLY MOISTURE TO MOVE INTO
SOUTHEAST PORTIONS OF THE AREA WITH A SLIGHT CHANCE OF
THUNDERSTORMS BY FRIDAY MORNING OVER NORTHERN CALIFORNIA ZONES. AS
THE UPPER LEVEL TROUGH SHIRTS NORTHEASTWARD INTO NORTHEAST
CALIFORNIA AND NORTHWEST NEVADA, THE CHANCE FOR THUNDERSTORMS WILL
INCREASE FRIDAY AFTERNOON AND EVENING, MAINLY OVER NORTHERN
CALIFORNIA AND FROM THE CASCADES EAST IN SOUTHERN OREGON.

AREAS OF SMOKE WILL CONTINUE TO AFFECT AREAS FROM THE CASCADES
WEST AT LEAST THROUGH THUS WEEKEND AS DAYTIME NORTH TO NORTHWEST
FLOW PREVAILS. OFFSHORE FLOW ON THURSDAY MAY BRING LESS SMOKE TO
THE CASCADES BUT INCREASED SMOKE TO THE CURRY COAST.

LONG TERM...SATURDAY THROUGH EARLY NEXT WEEK...MODELS ARE SHOWING
AN UPPER LOW WILL GRADUALLY MOVES DOWN THE COAST OF BRITISH
COLUMBIA AND BECOMES CENTERED OFF THE COAST OF WASHINGTON SUNDAY
NIGHT INTO MONDAY. AHEAD OF THIS FEATURE, LINGERING MOISTURE AND
INSTABILITY WILL BRING A SLIGHT CHANCE OF THUNDERSTORMS FROM THE
CASCADES EAST AND OVER NORTHERN CALIFORNIA ON SATURDAY. THEN ON
SUNDAY WITH THE LOW SHIFTING FURTHER SOUTH AND A RIDGE
STRENGTHENING INLAND, EXPECT A SLIGHT CHANCE OF THUNDERSTORMS OVER
CENTRAL AND EASTERN PORTIONS OF THE AREA, WITH BEST CHANCES FROM
THE WESTERN CASCADE FOOTHILLS IN OREGON EAST INTO THE CASCADES AND
NORTHERN KLAMATH COUNTY. SOUTH TO SOUTHWEST 700 MB WINDS INCREASE
ON SUNDAY AND MAY SEE SOME GUSTY WINDS DEVELOP OVER THE HIGHER
TERRAIN ESPECIALLY IN THE CASCADES. MODELS ARE SHOWING BETTER
AGREEMENT WITH THE UPPER TROUGH SHIFTING INLAND ON MONDAY INTO
TUESDAY WITH A SLIGHT CHANCE OF SHOWERS OR THUNDERSTORMS POSSIBLE
IN CENTRAL AND EASTERN PORTIONS OF THE AREA.

THE SOUTHERN PORTION OF THE TROUGH MAY CUTOFF AND BRING A CUTOFF
LOW TO NORTHERN CALIFORNIA AROUND WEDNESDAY. HOWEVER, CONFIDENCE
IS LOW IN THE DETAILS FOR WEDNESDAY GIVEN THE VARIABILITY IN MODEL
ENSEMBLE FORECASTS ON WHETHER A CUTOFF LOW WILL DEVELOP AND WHERE
IT MAY BE POSITIONED. /CC

FIRE WEATHER...UPDATED 200 PM PDT TUESDAY 4 AUGUST 2015... MODELS
HAVE TRENDED TOWARDS A MORE CONVECTIVELY ACTIVE AFTERNOON AND
EVENING TODAY. WHILE THE BULK OF MODEL SOLUTIONS SHOW A SWATH OF
INSTABILITY ACROSS NORTHERN CALIFORNIA AND FROM THE CASCADES EAST IN
OREGON, THERE IS QUITE A DIFFERENCE IN THE PRECIPITATION OUTLOOK.
HOWEVER, THE HIGHER RESOLUTION NAM AND HRRR PRECIPITATION FIELDS ARE
DEPICTING AN AREA OF SCATTERED THUNDERSTORMS DEVELOPING OVER WESTERN
SISKIYOU COUNTY LATE THIS AFTERNOON, AND ANOTHER AREA OVER LAKE AND
KLAMATH COUNTIES LATE THIS AFTERNOON AND EVENING. THIS APPEARS TO BE
THE RESULT OF A CONVERGENCE OF SEVERAL FACTORS, INCLUDING A WEAK
SURFACE BOUNDARY, THE PASSAGE OF THE UPPER LEVEL TROUGH AND
ASSOCIATED VORTICITY, AND SOME JET SUPPORT ALOFT. THESE FACTORS,
WHILE EXISTING ONLY A SHORT TIME OVER SISKIYOU COUNTY, MAY LAST WELL
INTO THE NIGHT FARTHER EAST, AND THEREFORE NOCTURNAL STORMS ARE NOT
OUT OF THE QUESTION EAST OF THE CASCADES.

DESPITE HIGH LEVELS OF UNCERTAINTY, HAVE OPTED TO ERR ON THE SIDE OF
CAUTION, ESPECIALLY GIVEN THE CURRENT STATUS OF FIREFIGHTING
RESOURCES, AND ISSUED A RED FLAG WARNING FOR THE ABOVE AREAS. SOME
STORMS MAY BEGIN DRY, BUT SHOULD TREND WETTER AS THE EVENING
PROGRESSES. UNTIL THEN, GUSTY WINDS ARE OF PRIMARY CONCERN. OVERALL,
LIGHTING HAS THE POTENTIAL TO PRODUCE NUMEROUS STARTS, ESPECIALLY
GIVEN THE IGNITION RATE OVER THE PAST SEVERAL DAYS.

THUNDERSTORMS SHOULD COME TO AN END BY WEDNESDAY MORNING, AND NO
OTHER CONVECTION IS EXPECTED UNTIL THE WEEKEND. UNTIL THEN,
TEMPERATURES AND HUMIDITIES SHOULD REMAIN STEADY, ALTHOUGH THERE MAY
BE PERIODS OF MODERATE OVERNIGHT RECOVERIES ACROSS RIDGELINES AT
VARYING TIMES THROUGH THE WEEK AND THIS WEEKEND. GUSTY WINDS MAY
ALSO BE AN ISSUE THIS WEEKEND WITH THE PASSAGE OF A POTENTIALLY
STRONG UPPER LEVEL TROUGH. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...RED FLAG WARNING UNTIL 5 AM PDT WEDNESDAY FOR ORZ624-625.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT THIS EVENING FOR
     PZZ350-370.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
     EVENING FOR PZZ350-370.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT WEDNESDAY FOR
     PZZ356.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT
     WEDNESDAY FOR PZZ356.
     GALE WATCH FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT FOR
     PZZ376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 AM PDT THURSDAY FOR
     PZZ376.
     HAZARDOUS SEAS WATCH FROM THURSDAY MORNING THROUGH LATE THURSDAY
     NIGHT FOR PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 AM PDT THURSDAY
     FOR PZZ376.

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.