Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 051538
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
838 AM PDT TUE MAY 5 2015

.DISCUSSION...A VERY DRY AIR MASS IS OVER THE FORECAST AREA...WITH
COOLER TEMPERATURES THAN WE`VE SEEN IN THE PAST 5 DAYS OR SO.
PRECIPITABLE WATER...A MEASURE OF THE ATMOSPHERE`S MOISTURE...IS
IN THE DRIEST 10 PERCENT FOR THIS DAY. THEREFORE...EVEN THOUGH AN
UPPER TROUGH WILL BE MOVING TOWARDS THE AREA...IT WILL BE HARD TO
SQUEEZE OUT MUCH IN THE WAY OF RAINFALL. OUR PRECIPITATION CHANCES
ARE LOW...AND I HAVE LOWERED THEM FURTHER BASED ON THE MOST RECENT
GUIDANCE...AND FOCUSED OVER THE COAST AND UMPQUA BASIN.

GUSTY WINDS WERE OBSERVED MOST PLACES YESTERDAY AFTERNOON...AND WE
WILL GENERALLY BE IN A BREEZY PATTERN THE NEXT SEVERAL DAYS UNDER
NORTHWEST TO NORTHEAST FLOW. TOMORROW STILL FEATURES A SLIGHT
CHANCE OF THUNDERSTORMS ALONG AND EAST OF THE CASCADES AS THE
TROUGH MOVES OVERHEAD AND INSTABILITY INCREASES.

PLEASE SEE THE PREVIOUS DISCUSSION BELOW FOR MORE DETAILS ON THE
TROUGH AND UPCOMING RIDGING AND WARMER CONDITIONS.

&&

.AVIATION...FOR THE 05/12Z TAF CYCLE...A MARINE PUSH WILL BRING IN
BROKEN TO OVERCAST SKIES WEST OF THE CASCADES THIS MORNING. THERE IS
A CHANCE TEMPORARY MVFR CIGS COULD DEVELOP IN THE UMPQUA BASIN WITH
HIGHER TERRAIN BECOMING OBSCURED FOR AN HOUR OR TWO BETWEEN 14-16Z,
BUT CONFIDENCE IS LOW AND FOR NOW KEPT IT OUT OF THE ROSEBURG TAF.
ELSEWHERE VFR CONDITIONS WILL PREVAIL WITH HIGHER TERRAIN OBSCURED IN
THE ROGUE VALLEY BETWEEN 14-16Z. -PETRUCELLI

&&

.MARINE...UPDATED 3 AM PDT TUESDAY, 4 MAY, 2015...MODELS SHOW WINDS
INCREASING ENOUGH TO REACH SMALL CRAFT OVER THE SOUTHERN WATERS LATE
THIS AFTERNOON INTO TONIGHT, THUS HAVE ISSUED A SMALL CRAFT FOR
WINDS. IT`S POSSIBLE WINDS WILL DECREASE OVERNIGHT TONIGHT, BUT
CONFIDENCE IS LOW, SO RAN THE HEADLINE UNTIL 12Z WEDNESDAY. STEEP
SEAS WILL DEVELOP ACROSS THE AREA THIS MORNING...SUBSIDING TONIGHT
OVER THE NORTHERN WATERS, BUT THEY ARE EXPECTED TO PERSIST TONIGHT
FOR THE SOUTHERN OUTER WATERS DUE TO A COMBINATION OF SWELL AND
CHOPPY WIND DRIVEN SEAS. ON WEDNESDAY AND THURSDAY, MODERATE NORTH
WINDS AND AREAS OF STEEP SEAS ARE EXPECTED AS HIGH PRESSURE SETS UP
OFFSHORE WITH LOW PRESSURE INLAND. -PETRUCELLI


&&

.PREV DISCUSSION... /ISSUED 537 AM PDT TUE MAY 5 2015/

FIRE WEATHER...UPDATED 3 AM PDT TUESDAY, MAY 4, 2015...THE THREAT
OF THUNDERSTORMS IS NEXT TO ZERO TODAY. AN UPPER TROUGH WILL DROP
SOUTH INTO THE AREA BRINGING SLIGHT COOLING AT 500 MB. HOWEVER MID
LEVEL MOISTURE IS LACKING AND LI`S ARE WELL IN THE POSITIVE RANGE.
SO WERE EXPECTING NOT MUCH MORE THAN SOME CUMULUS BUILD UPS IN THE
AFTERNOON EAST OF THE CASCADES. ANY SHOWERS TODAY WILL BE MAINLY
WEST OF THE CASCADES, BUT QPF AMOUNTS WILL BE LIGHT, IF ANYTHING AT
ALL. ALSO TEMPERATURES WILL BE COOLER AND MIN RH`S ARE EXPECTED TO
BE HIGHER COMPARED TO YESTERDAY. THE UPPER LOW WILL MOVE SOUTH OVER
THE AREA WEDNESDAY WITH COOLING ALOFT. THE MODELS SUGGEST THERE MAY
BE ENOUGH INSTABILITY TO WARRANT A SLIGHT CHANCE OF THUNDERSTORMS
FROM THE CASCADES EAST WEDNESDAY AFTERNOON AND EVENING. THE MODELS
SUGGEST THE GREATEST INSTABILITY WILL BE ALONG THE CASCADES WEDNESDAY
AFTERNOON AND EVENING, SO IT`S POSSIBLE MOST OF THE ISOLATED STORMS
WILL OCCUR THERE, BUT THERE`S ALSO A BETTER CHANCE FOR THESE STORMS
TO BE RAIN PRODUCERS. -PETRUCELLI

PREV DISCUSSION... /ISSUED 202 AM PDT TUE MAY 5 2015/

DISCUSSION...NO SIGNIFICANT CHANGES WERE MADE TO THE FORECAST
THIS MORNING AS THE MODELS REMAIN IN DECENT AGREEMENT AND THE
FORECAST REMAINS ON TRACK. AN UPPER LOW OFF THE BC/WA COAST THIS
MORNING WILL MOVE SOUTH ACROSS OUR AREA OVER THE NEXT COUPLE OF
DAYS. THIS SYSTEM IS NOT PARTICULARLY WET OR DYNAMIC, BUT IT WILL
BE STRONG ENOUGH TO BRING SOME SHOWERS TO OUR AREA ALONG WITH
COOLER WEATHER. DUE TO A FAIR AMOUNT OF LOW CLOUDINESS AHEAD OF
THE SYSTEM, IT WILL BE FAIRLY STABLE TODAY AS THE LOW APPROACHES.
SO SHOWERS ARE EXPECTED TO BE CONFINED TO NORTH OF THE UMPQUA
DIVIDE, AND LIGHTNING ISN`T EXPECTED.

HOWEVER, AS WE GET INTO TOMORROW AND THE UPPER COLD POOL (500 MB
TEMPS AROUND -30C) ARRIVES, WE COULD SEE SOME LIGHTNING. MODEL
SOUNDINGS SHOW A MID LEVEL CAP WEST OF THE CASCADES, SO THE BEST
CHANCE FOR LIGHTNING WILL BE FROM THE CASCADE CREST EAST. THE LOW
EXITS TO THE SOUTH ON THURSDAY WITH CONDITIONS STABILIZING IN ITS
WAKE. THERE IS STILL A POSSIBILITY OF SHOWERS THURSDAY, BUT
THUNDERSTORM CHANCES WILL BE CONFINED MAINLY TO MODOC COUNTY.

WE WILL DRY OUT AND WARM UP JUST IN TIME FOR THE WEEKEND AS A
RIDGE BUILDS IN OVER THE PACNW. MODELS ARE IN AGREEMENT, SO I
HAVE ADJUSTED POPS DOWN AND TEMPERATURES UP OVER THE WEEKEND.
ANOTHER TROUGH MAY TRY TO BREAK THROUGH THE RIDGE AND BRING
SHOWERY, COOL WEATHER AGAIN EARLY NEXT WEEK. THE MODELS DO NOT
AGREE ON MUCH WITH THIS SYSTEM, WITH THE ECMWF KEEPING THE BULK OF
THE ACTIVITY TO OUR NORTH AND THE GFS DIGGING A TROUGH OFFSHORE.
GIVEN THESE DISCREPANCIES, CHANGES WERE NOT MADE. -WRIGHT

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 5 AM PDT WEDNESDAY
     FOR PZZ356-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 5 PM PDT THIS
     AFTERNOON FOR PZZ350-370.
     SMALL CRAFT ADVISORY FOR WINDS FROM 5 PM THIS AFTERNOON TO 5 AM
     PDT WEDNESDAY FOR PZZ376.

$$

NSK/MAP/MAP


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