Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 161601
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
901 AM PDT TUE SEP 16 2014

.DISCUSSION...THE GOING FORECAST LOOKS ON TRACK AND NO UPDATES
WILL BE NECESSARY FOR THIS MORNING. TODAY WILL BE A TRANSITION DAY
WHERE WE ARE IN THE WAKE OF THE PREVIOUS SYSTEM THAT BROUGHT ABOUT
30-40 LIGHTNING STRIKES TO MODOC AND LAKE COUNTIES YESTERDAY.
TEMPERATURES WILL BE ABOUT 5 TO 10 DEGREES COOLER TODAY COMPARED
TO MONDAY AND WINDS WILL GET BREEZY AGAIN IN THE SHASTA VALLEY AND
OVER THE EAST SIDE. TODAY`S FOCUS FOR THE AFTERNOON PACKAGE WILL
BE PRECIPITATION POTENTIAL AND WINDS FOR NEXT SYSTEM DUE IN
TOMORROW/THURSDAY. SEE THE PREVIOUS FORECAST DISCUSSION FOR MORE
DETAILS ON THIS. -MND

&&

.AVIATION...BASED ON THE 16/12Z TAF CYCLE...ALONG THE COAST...PATCHY
IFR CIGS/VSBYS WILL CLEAR TO VFR BY MID-MORNING. VFR CONDITIONS WILL
THEN PREVAIL THROUGH TUESDAY NIGHT.  INLAND...VFR CONDITIONS WILL
PREVAIL THROUGH TUESDAY NIGHT...EXCEPT FOR AREAS OF MVFR VSBYS IN
SMOKE FROM WILDFIRES...MOSTLY OVER SISKIYOU COUNTY AND JOSEPHINE
COUNTY. JRS

&&

.MARINE...UPDATED 900 AM PDT TUESDAY...IT WILL BE ANOTHER QUIET
WEATHER DAY TODAY WITH LONGER PERIOD SWELL REMAINING DOMINANT. LOW
PRESSURE APPROACHING FROM THE SOUTHWEST WILL BRING RAIN WEDNESDAY
INTO THURSDAY AND SOUTH WINDS MAY BECOME GUSTY...AT TIMES. SEAS
WILL GRADUALLY BUILD THROUGH THURSDAY. A DEVELOPING THERMAL TROUGH
WILL LEAD TO INCREASING NORTH WINDS FRIDAY THROUGH THE WEEKEND.
-BTL

&&

.PREV DISCUSSION... /ISSUED 320 AM PDT TUE SEP 16 2014/

DISCUSSION...LATEST SATELLITE IMAGERY SHOWS A BAND OF HIGH AND MID
LEVEL CLOUDS LIFTING TO THE NORTH AND OUT OF THE AREA. THESE
CLOUDS ARE THE LAST VISUAL CUE TO THE SHORT WAVE TROUGH THAT
TRACKED OVER THE REGION LAST NIGHT. THE COMBINED ENERGY OF THIS
LITTLE TROUGH AND THE MUCH BIGGER ONE BEHIND IT, HAS MANAGED TO
BUMP TO THE EAST THE LARGE UPPER LEVEL RIDGE THAT HAD BEEN IN
PLACE OVER THE WEST COAST FOR ALMOST A WEEK. THE RESULT WILL BE
COOLER TEMPERATURES TODAY, WITH DAYTIME HIGHS MUCH CLOSER, BUT
STILL SLIGHTLY ABOVE, NORMAL FOR THIS TIME OF YEAR. MODELS ARE IN
GOOD AGREEMENT CONCERNING THE PATTERN OVER THE NEXT WEEK, ALTHOUGH
THERE ARE SOME DIFFERENCES IN TIMING IN THE LONG TERM.

WITH THE RIDGE MOVING TO THE EAST AND A VIGOROUS TROUGH APPROACHING
FROM THE WEST, THE MAIN BELT OF WESTERLIES WILL LIE DIRECTLY
OVERHEAD TODAY. AS MENTIONED PREVIOUSLY, THIS WILL LEAD TO COOLER
AND MORE SEASONABLE TEMPS, BUT IT WILL ALSO BRING GUSTY WINDS INTO
THE REGION, PARTICULARLY ALONG AND EAST OF THE CASCADES, AND IN THE
SHASTA VALLEY. FIRE INTERESTS WILL NEED TO PAY CLOSE ATTENTION TO
THIS SCENARIO, AS AFTERNOON MIXING WILL LIKELY BRING THE STRONGER
WINDS ALOFT DOWN TO THE SURFACE, THEREBY REACHING SPEEDS THAT COULD
REACH CRITICAL VALUES, ESPECIALLY IN REGARDS TO ONGOING FIRES.
OTHERWISE, EXPECT CLOUDS TO STEADILY INCREASE THROUGH THE LATTER
HALF OF THE DAY AS THE TROUGH AND ASSOCIATED FRONT APPROACH THE
REGION.

THE UPCOMING SYSTEM ON WEDNESDAY WILL BE THE FIRST OF ITS KIND THIS
SEASON, AND MODEL SOLUTIONS ARE TRENDING WETTER WITH THE PAST
SEVERAL RUNS. HAVE THEREFORE KEPT THE CHANCES FOR PRECIPITATION
WIDESPREAD, WITH AREAS ALONG THE COAST LIKELY TO SEE A GOOD WETTING
RAIN THROUGH THURSDAY. BUT A MAJOR CONSIDERATION SHOULD BE GIVEN TO
THE MOISTURE THIS SYSTEM WILL BRING. COMPARED TO THE PAST SEVERAL
MONTHS, THE MOISTURE FLOW IS IMPRESSIVE, HOWEVER, IN TERMS OF WHAT
WE WOULD EXPECT TO SEE DURING THE WET SEASON, IT IS NOT SO
IMPRESSIVE. ALSO, THIS IS THE FIRST SUCH SYSTEM OF THE SEASON, AND
THERE IS A LOT OF DRY AIR AND TERRAIN TO CONTEND WITH. FOR THESE
REASONS, HAVE KEPT PRECIPITATION AMOUNTS ON THE LOW SIDE. ALSO, WHEN
THE TROUGH AXIS SWINGS OVERHEAD THURSDAY AFTERNOON, THE COLDER AIR
ALOFT IS LIKELY TO RESULT IN SOME DEVELOPING INSTABILITY ALONG AND
EAST OF THE CASCADES. HAVE KEPT THE SLIGHT CHANCE OF THUNDER IN
THESE AREAS FROM THE PREVIOUS FORECAST.

THE TROUGH WILL EXIT TO THE EAST THURSDAY INTO FRIDAY, BUT THE
SOUTHERN PORTION OF THE TROUGH IS EXPECTED TO SEPARATE FROM THE MAIN
WAVE, CUT OFF, AND TAKE UP RESIDENCE OVER SOUTHERN CALIFORNIA, WHERE
IT WILL BIDE ITS TIME UNTIL EARLY NEXT WEEK. MEANWHILE, RIDGING WILL
RETURN TO SOUTHERN OREGON AND NORTHERN CALIFORNIA, ALONG WITH THE
THERMAL TROUGH, WHICH NOT ONLY WILL BRING WARMER TEMPERATURES
BACK TO THE AREA BEGINNING FRIDAY, BUT WILL ALSO BRING A RETURN OF
THE OFFSHORE WINDS THAT HAVE BEEN RATHER COMMON OVER THE PAST
SEVERAL WEEKS.

BY MONDAY, WE WILL BE LOOKING AT ANOTHER POSSIBLE TROUGH APPROACHING
FROM THE PACIFIC, BUT MODELS HAVE BEEN INCONSISTENT IN TIMING AND
STRENGTH, SO THERE REMAINS A GOOD DEAL OF UNCERTAINTY REGARDING ITS
EVOLUTION AND PROGRESSION. GIVEN THIS LATEST MODEL CYCLE, IT APPEARS
THAT THINGS MAY PROGRESS IN A SIMILAR MATTER TO THIS WEEK, WITH THE
CUT OFF LOW OVER SOUTHERN CALIFORNIA MOVING BACK NORTH AHEAD OF THE
MAIN TROUGH, THEN THE REST OF THE ACTION FOLLOWING 24 TO 36 HOURS
LATER. GIVEN THE LOW CONFIDENCE, HAVE ONLY INTRODUCED A SLIGHT CHANCE
OF PRECIPITATION TO THE COAST BY MIDWEEK, BUT MAINTAINED ABOVE
NORMAL TEMPERATURES THROUGHOUT THE REMAINDER OF THE FORECAST TERM.
OVERALL, IT APPEARS THAT THERE WILL BE ONE, PERHAPS EVEN TWO, GOOD
CHANCES FOR MUCH NEEDED RAIN OVER THE NEXT WEEK.  -BPN

&&

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

CA...FIRE WEATHER WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY
     EVENING FOR CAZ284-285.

PACIFIC COASTAL WATERS...NONE.

$$

MND/BPN/JRS






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