Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 222156
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
256 PM PDT MON SEP 22 2014

.DISCUSSION...THE UPPER LOW THAT WILL IMPACT US WITH MODERATE TO
HEAVY RAIN AND GUSTY WINDS IS STARTING TO TAKE SHAPE NEAR 44N/145W.
THIS IS GOING TO BE A SIGNIFICANT EVENT FOR THE FOLLOWING REASONS.
FIRST IT`S RARE THAT A STORM OF THIS MAGNITUDE IMPACTING OUR AREA
THIS TIME OF THE YEAR. SECOND, WERE LOOKING AT OVER 4 STANDARD
DEVIATIONS ABOVE THE STANDARD ANOMALY FOR PWATS TUESDAY NIGHT INTO
WEDNESDAY. EVENTUALLY THIS LOW WILL GET CUTOFF FROM THE MAIN FLOW,
BUT IT`S GOING TO TAP INTO SUBTROPICAL MOISTURE WHICH WILL SET THE
TABLE FOR MODERATE TO HEAVY PRECIPITATION. THE MODELS REMAIN IN
PRETTY GOOD AGREEMENT THAT THE FRONT WILL BE A HEAVY RAIN PRODUCER
WITH PWATS BETWEEN 1.5 AND 1.75 INCHES IMPACTING THE COAST TUESDAY
NIGHT INTO WEDNESDAY MORNING. ALSO THE ORIENTATION OF THE UPPER FLOW
AND FRONT IS ONE THAT WILL HAVE ENHANCED OROGRAPHIC EFFECTS WHICH
WILL WRING OUT ADDITIONAL MOISTURE (LIKE SQUEEZING A SPONGE) WHICH
COULD PRODUCE 2-3 TIMES THE AMOUNT OF RAIN OVER THE SOUTH COAST
RANGE AND MOUNTAINS AS WHAT THE MODELS SHOW FOR QPF AND PWATS. THE
HIGHEST QPF AMOUNTS WILL BE IN THE TYPICAL SOUTHWEST FACING SLOPES
OF THE COASTAL MOUNTAINS WHERE 2-4 INCHES COULD FALL.

THE MAIN QUESTION ON WEDNESDAY WILL BE THE PROGRESSION OF THE FRONT
AS IT MOVES INLAND. THE NAM IS SLOWER THAN THE GFS AND EC AND GIVEN
THE UPPER FLOW IS NEARLY PARALLEL TO THE FRONT, SUSPECT THE FRONT
WILL BE SLOWER TO MOVE. THEREFORE HAVE LEANED TOWARDS THE SLOWER NAM
SOLUTION WITH BULK OF THE PRECIPITATION ALONG AND WEST OF THE
CASCADES. THERE IS A LITTLE MORE UNCERTAINTY WITH RAINFALL AMOUNTS
INLAND. THE MAIN REASON IS THAT WE`LL HAVE A SOUTHERLY FLOW WHICH
WILL HAVE A DOWNSLOPING EFFECT WHICH COULD TYPICALLY BRING LESS
RAINFALL AMOUNTS TO THE ROGUE VALLEY AND TO A LESSER EXTENT THE
UMPQUA BASIN. THE THE GFS AND EC ARE GLOBAL BASED AND WILL NOT
NORMALLY PICK UP ON THESE DETAILS. THEREFORE HAVE KEPT THE HIGHEST
QPF VALUERS ALONG THE MOUNTAINS AND WESTERN SISKIYOU COUNTY. WITH
THAT SAID, THE VALLEYS WILL STILL GET A DECENT AMOUNT OF RAIN WITH
TOTALS BETWEEN 0.30-0.60 OF AN INCH.

KEEP IN MIND THE TIMING AND PROGRESSION OF THE FRONT IS IMPORTANT
BECAUSE OF THE POTENTIAL IMPACT IT COULD HAVE ON THE BURN SCARS FROM
THIS YEARS AND LAST YEARS FIRES. IF THE FRONT IS SLOWER TO MOVE
THROUGH AND MODERATE TO HEAVY PRECIPITATION PERSIST FOR A LONGER
PERIOD OF TIME, WE COULD BE LOOKING AT THE POTENTIAL FOR MUD SLIDES,
ROCK SLIDES AND FLOODING.

THE FRONT WILL SLOWLY MARCH EAST WEDNESDAY NIGHT INTO THURSDAY AND
THE CASCADES AND EAST SIDE WILL GET THE BULK OF THE PRECIPITATION.
HOWEVER MUCH WILL DEPEND ON THE TIMING OF THE FRONT AND HOW MUCH IT
HOLDS UP AS IT MOVES EAST. RIGHT NOW CONFIDENCE IS LOWER ON THE
TIMING.

WINDS ARE GOING TO BE THE NEXT IMPACT. THEY ARE EXPECTED TO BE
STRONGEST ALONG THE COAST, SHASTA VALLEY AND ALONG AND EAST OF THE
CASCADES. THE MODELS SHOW 700MB WINDS AHEAD OF THE UPPER LOW
INCREASING BETWEEN 30-40 KTS TUESDAY MORNING AND IT`S A GOOD BET
SOME OF THIS WILL MIX DOWN NEAR THE SURFACE IN THE SHASTA VALLEY, SO
WOULD NOT BE SURPRISED IF WE SEE PEAK GUST UP TO 40 MPH NEAR WEED
TUESDAY AFTERNOON INTO WEDNESDAY. ALSO GUSTY WINDS ARE LIKELY ALONG
HIGHWAY 31 NEAR SUMMER LAKE. NOT ENOUGH TO WARRANT A WATCH OR
WARNING, BUT GIVEN THAT IT`S BEEN PRETTY QUIET AS OF LATE, THE
PERCEPTION IS THAT IT WILL BE SIGNIFICANT.

IF ALL GOES ACCORDING TO PLAN, THE FRONT WILL PUSH EAST OF THE
CASCADES THURSDAY AND WEAKEN. MEANWHILE A LARGE UPPER TROUGH WILL
WORK IT`S WAY INTO THE AREA WITH MULTIPLE SHORTWAVES MOVING THROUGH
AND COOLER AIR ALOFT MOVING OVERHEAD. THIS WILL RESULT IN SCATTERED
SHOWERS AND BELOW NORMAL TEMPERATURES. WINDS ARE NOT EXPECTED TO BE
AS MUCH OF A CONCERN.

AFTER THURSDAY, THE MODELS BEGIN TO DIVERGE. THE GFS CONTINUES TO
PROGRESS THE UPPER TROUGH FASTER THAN THE EC AND SHOWS A RIDGE AXIS
BUILDING NEAR 140W FRIDAY, SHIFTING TOWARDS 130W SATURDAY. IN
CONTRAST, THE EC IS SLOWER WITH THE PROGRESSION OF THE UPPER TROUGH
AND KEEPS IT OVER THE AREA FRIDAY INTO SATURDAY MORNING, THEN
PUSHING EAST SATURDAY AFTERNOON WITH WEAK RIDGING SATURDAY NIGHT.
ANY RIDGING IS SHORT LIVED AS ANOTHER UPPER TROUGH SWINGS NORTH OF
THE AREA SUNDAY. DUE TO THE LOW CONFIDENCE IN THE EXTENDED, MADE
LITTLE OR NO CHANGES BEYOND THURSDAY. -PETRUCELLI


&&

.AVIATION...BASED ON THE 22/18Z TAF CYCLE...MOST INLAND AREAS WILL
BE VFR THIS AFTERNOON THROUGH TUESDAY MORNING, THOUGH ISOLATED
SHOWERS AND/OR THUNDERSTORMS MAY DEVELOP THROUGH THIS EVENING FROM
THE CASCADES TO NORTHERN KLAMATH/LAKE COUNTIES. SMOKE WILL ALSO
CAUSE LOCALLY REDUCED VISIBILITY AROUND EXISTING WILDFIRES.

AREAS OF MVFR CIGS WILL PERSIST ALONG THE COAST AND WILL BECOME
WIDESPREAD THIS EVENING AS A WEAK FRONT APPROACHES AND MOVES
ONSHORE. THIS FRONT WILL BRING SOME LIGHT RAIN AND PATCHY FOG LATER
TONIGHT INTO TUESDAY MORNING. LITTLE, IF ANY PRECIPITATION WILL MAKE
IT INLAND. A MORE SIGNIFICANT FRONT WILL ARRIVE AT THE COAST TUESDAY
NIGHT WITH GUSTY WINDS DEVELOPING AND THE POTENTIAL FOR HEAVY
RAINFALL AND SIGNIFICANT VIS/CIG REDUCTIONS. RAIN WILL SPREAD INLAND
WEDNESDAY. SPILDE


&&

.MARINE...UPDATED 230 PM PDT MON 22 SEP 2014...SOUTHERLY WINDS WILL
INCREASE LATER TODAY AHEAD OF A COLD FRONT, WHICH WILL BRING PERIODS
OF RAIN, STRONG WINDS, AND HEAVY SEAS TO THE COASTAL WATERS. WINDS
WILL CONTINUE TO INCREASE THROUGH TOMORROW, REACHING GALE STRENGTH
OVER MUCH OF THE AREA BY THE AFTERNOON. GALES ARE EXPECTED TO END
OVERNIGHT, BUT WINDS WILL REMAIN GUSTY THROUGH WEDNESDAY MORNING,
AND SMALL CRAFT ADVISORIES FOR WINDS WILL REMAIN THROUGH THAT TIME.
SEAS WILL GRADUALLY BUILD THROUGH TONIGHT, WITH VERY CHOPPY AND
STEEP SEAS EXPECTED BY TOMORROW AFTERNOON. HAVE ISSUED A HAZARDOUS
SEAS WARNING FOR ALL BUT THE FAR SOUTHERN AND FAR INNER WATERS INTO
WEDNESDAY MORNING. AT THAT TIME, WIND DRIVEN SEAS WILL DIMINISH, BUT
A HEAVY WESTERLY SWELL WILL BUILD INTO THE AREA, KEEPING SMALL CRAFT
ADVISORY CONDITIONS CONTINUING THROUGH AT LEAST THURSDAY. UNSETTLED
WEATHER WILL CONTINUE THROUGH THE REMAINDER OF THE WEEK.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...RED FLAG WARNING FROM 11 AM TUESDAY TO 11 PM PDT WEDNESDAY FOR
     ORZ624-625.

CA...RED FLAG WARNING FROM 11 AM TUESDAY TO 11 PM PDT WEDNESDAY FOR
     CAZ285.
     RED FLAG WARNING FROM 11 AM TO 11 PM PDT TUESDAY FOR CAZ281-284.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS FROM 5 AM TUESDAY TO
     11 AM PDT WEDNESDAY FOR PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING FROM 2 PM TUESDAY TO 8 AM PDT WEDNESDAY
     FOR PZZ350-356-370-376.
     GALE WARNING FROM 2 PM TUESDAY TO 2 AM PDT WEDNESDAY FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 11 PM THIS EVENING
     TO 11 PM PDT THURSDAY FOR PZZ350-356-370-376.

$$





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