727
FXUS66 KMFR 242154
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
254 PM PDT MON SEP 24 2018
DISCUSSION
ALREADY DRY AIR ACROSS THE FORECAST AREA THIS AFTERNOON IS
BECOMING DRIER, AND WILL CONTINUE TO DO SO THROUGH WEDNESDAY AS
GENERALLY SUBSIDING EASTERLY WINDS CONTINUE ACROSS THE FORECAST
AREA. THIS DRY AIR WILL SUPPORT LARGE DIURNAL TEMPERATURE RANGES
IN AREAS SHELTERED FROM THE EAST WINDS, WHILE AREAS IN THE EAST
WINDS WILL EXPERIENCE CONTINUING WARM CONDITIONS. IT'S CURRENTLY
82 DEGREES IN BROOKINGS AS OF THE 2PM PDT OBSERVATION.
TEMPERATURES THERE ARE EXPECTED TO TOP OUT IN THE MID 80S TODAY,
AND THE UPPER 80S TOMORROW AS THE EASTERLY WINDS KNOWN AS THE
CHETCO EFFECT CONTINUES.
INLAND LOCATIONS ARE ALSO INDICATING LOW HUMIDITIES THIS
AFTERNOON, WHICH IS ALLOWING TEMPERATURES TO CLIMB RAPIDLY.
TEMPERATURE RANGES FOR VALLEY LOCATIONS THIS WEEK, THROUGH
FRIDAY, ARE LIKELY TO BE ON THE ORDER OF 40 TO AS MUCH AS 60
DEGREES BETWEEN HIGHS AND LOWS. THE LARGER END OF THE RANGE WILL
BE ACROSS LOWER ELEVATION LOCATIONS EAST OF THE CASCADES.
SPECIFICALLY, FOR MEDFORD, WHILE OVERNIGHT LOWS WILL THROUGH
FRIDAY ARE EXPECTED TO BE 5 TO 10 DEGREES ABOVE THE 1981-2010
NORMALS, DAYTIME HIGHS ARE EXPECTED TO BE 15 TO 20 DEGREES ABOVE
NORMAL. CURRENTLY, THE WARMEST DAY IS EXPECTED TO BE THURSDAY,
WITH A HIGH OF 96F. WHILE SUCH TEMPERATURES ARE WELL ABOVE NORMAL
FOR THIS TIME OF THE YEAR, NOW RECORDS ARE EXPECTED TO BE BROKEN.
THE EAST WIND PATTERN BRINGING THE DRYING CONTINENTAL AIR MASS TO
THE AREA THIS WEEK IS EXPECTED TO GRADUALLY WEAKEN, SUCH THAT
WINDS WILL BE MORE DIURNALLY DRIVEN IN THE AFTERNOON AND EVENING
HOURS DURING THE LATTER HALF OF THE WEEK. HOWEVER, IT IS LIKELY TO
TAKE UNTIL FRIDAY FOR US TO SEE EVEN SOME SLIGHT COOLING AND
MOISTENING OF THE AIR MASS EVEN FROM THE CASCADES WESTWARD AS THE
WARM DRY AIR OF THE THERMAL TROUGH HOVERS OVER THE AREA.
NUMERICAL MODELS CONTINUE TO BE CONSISTENT IN INDICATING THAT THE
UPPER LOW THAT HAS BEEN PART OF THE CURRENT REX, OR HIGH OVER LOW,
BLOCK IN THE EASTERN PACIFIC TO PUSH TOWARD THE NORTHERN
CALIFORNIA COAST FRIDAY, AND THEN OVER THE FORECAST AREA SATURDAY.
AS THEY OFTEN DO WITH UPPER LEVEL LOWS, EACH MODEL AND MODEL RUN
HAS INDICATED A SLIGHTLY DIFFERENT POSITION FOR THE LOW MOVING
THROUGH, AS WELL AS DIFFERENCES IN TIMING. HOWEVER, FOR AT LEAST A
FEW DAYS NOW (SINCE ABOUT WEDNESDAY) THERE HAS BEEN GENERAL
AGREEMENT AMONG THE MODELS IN SHOWING THIS LOW EJECTING EASTWARD.
IN SUMMARY, THE LATEST MODEL GUIDANCE SHOWS THE POTENTIAL OF SOME
SHOWERS AND THUNDERSTORMS DEVELOPING SATURDAY AFTERNOON AND
EVENING. INSTABILITY IS NOT TREMENDOUS, BUT DOES LOOK TO BE ENOUGH
TO GENERATE SOME RAINFALL. THUS SOME SLIGHT CHANCES TO CHANCES OF
SHOWERS HAVE BEEN ADDED TO THE FORECAST FOR SATURDAY AFTERNOON AND
EVENING. A SLIGHT CHANCE OF THUNDERSTORMS FOR THE AFTERNOON AND
EVENING HOURS HAS BEEN ADDED FOR THE NORTHERN CASCADES FROM ABOUT
CRATER LAKE NATIONAL PARK NORTHWARD DUE TO REASONABLE MODEL
AGREEMENT ON NECESSARY DYNAMICS THERE, AS WELL AS THAT BEING A
CLIMATOLOGICALLY FAVORED AREA FOR SUCH ACTIVITY IN THIS PATTERN.
AS WINDS BECOME MORE WESTERLY LATER THIS WEEK, WE EXPECT ANOTHER
ROUND OF SMOKE TO PUSH EASTWARD ACROSS THE AREA FROM THE KLONDIKE
AND NATCHES FIRES INTO THE ILLINOIS, APPLEGATE, AND ROGUE
VALLEYS. THE TIME OF MOST CONCERN IS FROM THURSDAY EVENING
THROUGH SATURDAY EVENING. THUS, THIS EXPECTATION HAS BEEN ADDED TO
THE FORECAST.
THE MODELS THEN DIVERGE FOR SUNDAY INTO EARLY NEXT WEEK. THE ECMWF
BRINGS IN WHAT LOOKS TO BE A SEASON ENDING RAINFALL EVENT, WHILE
THE GFS HAS TRENDED DRIER. ALL IN ALL, GIVEN THE WIDE SPREAD IN
THE MODELS AND GREAT UNCERTAINTY IN THE FORECAST, THE OFFICIAL
FORECAST IS A CONSENSUS BLEND OF THE GUIDANCE, INDICATING SLIGHT
CHANCES TO CHANCES OF RAIN ACROSS THE FORECAST AREA EARLY NEXT
WEEK. THE WEATHER PREDICTION CENTER AND CLIMATE PREDICTION CENTER
HAVE SOME HELPFUL DISCUSSIONS PROVIDING MORE INFORMATION ON WHAT
IS DRIVING THE MODEL DIFFERENCES IN THE EXTENDED PORTION OF THE
FORECAST. -LUTZ
AVIATION...FOR THE 24/18Z TAFS
VFR WILL PREVAIL ACROSS THE AREA
THIS AFTERNOON AND EVENING WITH GUSTY NORTH WINDS UP TO 30KT ALONG
THE COAST AND SOME BREEZY NNE WINDS DUE TO OFFSHORE FLOW OVER SW
OREGON AND NW CALIFORNIA, INCLUDING THE COASTAL MOUNTAINS. WINDS
EASE FOR ALL BUT THE COASTAL MOUNTAINS TONIGHT, AND WITH A VERY DRY
AIR MASS IN PLACE, IT WILL REMAIN VFR. COASTAL RIVER VALLEY FOG
(COQUILLE/UMPQUA) WILL BE PATCHY AT BEST. -SPILDE
MARINE...UPDATED 230 AM PDT MONDAY 24 SEPTEMBER 2018
THE THERMAL
TROUGH WILL STRENGTHEN TODAY AS INLAND CONDITIONS WARM, AND ANOTHER
ROUND OF GALES AND HAZARDOUS SEAS ARE EXPECTED THIS AFTERNOON AND
EVENING. THE THERMAL TROUGH WILL GRADUALLY WEAKEN STARTING TUESDAY
AND WINDS WILL EASE SOME, BUT REMAIN HAZARDOUS TO SMALL CRAFT
THROUGH MID-WEEK. SEAS WILL REMAIN STEEP AND HAZARDOUS FROM FRESH
SWELL THROUGH AT LEAST TUESDAY NIGHT, GRADUALLY SUBSIDING
BELOW SMALL CRAFT ADVISORY LEVELS BEYOND WEDNESDAY NIGHT.
LATE WEEK AND INTO THE WEEKEND, MODELS ARE SHOWING A CHANGE IN THE
PATTERN WITH AN AREA OF LOW PRESSURE APPROACHING FROM THE SOUTHWEST,
AND DISRUPTING THE THERMAL TROUGH SETUP. CONFIDENCE IS LOW IN THE
DETAILS AT THIS POINT IN THE FORECAST, BUT THERE IS THE POTENTIAL
FOR A SHIFT TO STRONGER SOUTH WINDS BY THE WEEKEND. /BR-Y
FIRE WEATHER...UPDATED 150 PM PDT MONDAY, 23 SEPTEMBER 2018
LOW RELATIVE HUMIDITIES AND NORTHEAST TO EAST WINDS GUSTING UP TO 35
MPH ARE EXPECTED OVER THE COASTAL MOUNTAINS THROUGH TUESDAY MORNING.
THE 06Z NAM12 925MB AND 850 MB WINDS INDICATED THE STRONGEST
WINDS TO OCCUR THIS MORNING, AND SLIGHTLY WEAKER WINDS, BUT
POORER HUMIDITY RECOVERY, FOR TUESDAY MORNING. WITH THE THERMAL
TROUGH GRADIENT TIGHTENING FARTHER EASTWARD THE NEXT TWO NIGHTS,
GUSTY WINDS WILL ALSO SHIFT TO BE OVER THE CASCADES. WITH THE VERY
LOW HUMIDITIES THIS AREA LOOKS STRONGLY POSSIBLE TO REACH WARNING
CRITERIA, AND HAVE ISSUED A WATCH FOR TOMORROW NIGHT INTO
WEDNESDAY MORNING IN THIS AREA.
OTHERWISE, DIURNAL TEMPERATURE RANGES WILL BE WIDE IN VALLEYS WITH
HOT AND DRY CONDITIONS THROUGH FRIDAY AND OVERNIGHT INVERSIONS IN
PLACE. THE STUBBORN BLOCKING PATTERN IS FORECAST TO FINALLY BREAK
DOWN FRIDAY NIGHT WITH A CLOSED UPPER LOW SWINGING IN CLOSE TO THE
COAST SATURDAY. THIS WOULD BRING HIGHER HUMIDITY AND COOLER
TEMPERATURES FOR THE WEEKEND INTO EARLY NEXT WEEK. THE STRENGTH AND
TRACK OF THE LOW ARE VERY MUCH IN QUESTION, WITH THE HIGHEST
UNCERTAINTY REGARDING THE PROBABILITY OF RAIN/SHOWERS AND ANY RISK
OF THUNDERSTORMS. THERE IS GENERAL MODEL AGREEMENT THAT THE
PROBABILITY WILL ONLY BE IN THE SLIGHT CHANCE TO CHANCE CATEGORY
THROUGH THE WEEKEND. THERE IS HIGHER UNCERTAINTY BEYOND THE WEEKEND,
WHICH INCLUDES SOME POSSIBILITY OF A MORE WIDESPREAD RAIN EVENT.
-SVEN
MFR WATCHES/WARNINGS/ADVISORIES
OR...RED FLAG WARNING UNTIL 11 AM PDT TUESDAY FOR ORZ619-620.
RED FLAG WARNING UNTIL 11 AM PDT TUESDAY FOR ORZ618.
FIRE WEATHER WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY
MORNING FOR ORZ617-621>623.
CA...RED FLAG WARNING UNTIL 11 AM PDT TUESDAY FOR CAZ280.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 5 AM PDT WEDNESDAY FOR
PZZ350-356-370-376.
GALE WARNING UNTIL 5 AM PDT TUESDAY FOR PZZ356-376.
HAZARDOUS SEAS WARNING FROM 5 AM TUESDAY TO 5 AM PDT WEDNESDAY
FOR PZZ370-376.
BTL/MAS/SBN
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