Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 061550
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
850 AM PDT WED MAY 6 2015

.DISCUSSION...BELOW NORMAL TEMPERATURES ARE BEING OBSERVED THIS
MORNING...COURTESY OF A COOL UPPER TROUGH MOVING OVER THE REGION.
SHOWERS ARE EXPECTED THIS AFTERNOON PRIMARILY ALONG AND EAST OF
THE CASCADES. THE LATEST HOURLY HRRR MODEL ALSO SHOWS SHOWERS
MOVING INTO THE UMPQUA BASIN THIS AFTERNOON. WE HAVE INCREASED
PRECIPITATION CHANCES IN THE UMPQUA BASIN AND IN NORTHERN LAKE AND
KLAMATH COUNTIES BASED ON THIS LATEST GUIDANCE. ADDITIONALLY...ENOUGH
INSTABILITY EXISTS TO GENERATE A FEW THUNDERSTORMS THIS AFTERNOON.

BREEZY TO WINDY CONDITIONS ARE EXPECTED THE NEXT FEW DAYS AS A
NORTH TO SOUTH PRESSURE GRADIENT COMBINES WITH MODERATE NORTHERLY
700MB WINDS.

LASTLY...WE`LL BE EXAMINING THE POTENTIAL FOR FROST CONDITIONS
TONIGHT. THIS MORNING...LOW TEMPERATURES GENERALLY REMAINED ABOVE
CRITICAL VALUES THANKS TO SOME CLOUD COVER AND SOME LOW LEVEL
MOISTURE. TONIGHT WE ARE AGAIN EXPECTING LOW CLOUDS OVER MOST
SOUTHERN OREGON VALLEYS...THOUGH SOME NORTHERN CALIFORNIA
LOCATIONS COULD SEE FREEZING TEMPERATURES. WE`LL ADDRESS THIS IN
THE AFTERNOON FORECAST PACKAGE.

PLEASE SEE THE PREVIOUS DISCUSSION BELOW FOR DETAILS ON THE
UPCOMING WARMER AND DRIER WEATHER THIS WEEKEND.

&&

.AVIATION...FOR THE 06/12Z TAF CYCLE...VFR CONDITIONS WILL PREVAIL
FOR THE NEXT 24 HOURS...EXCEPT FOR TEMPORARY MVFR CIGS IN SHOWERS
ALONG THE COAST AND IN THE UMPQUA BASIN WITH SOME HIGHER TERRAIN
OCCASIONALLY BECOMING OBSCURED. GUSTY WINDS ARE EXPECTED LATE THIS
MORNING INTO THE AFTERNOON FOR ALL TERMINALS. ISOLATED THUNDERSTORMS
ARE ALSO POSSIBLE ALONG AND EAST OF THE CASCADES THIS AFTERNOON AND
EVENING. -PETRUCELLI


&&

.MARINE...UPDATED 200 AM PDT WEDNESDAY 6 MAY 2015...OFFSHORE HIGH
PRESSURE WILL PERSIST INTO THIS WEEKEND. A THERMAL TROUGH NEAR THE
COAST WILL STRENGTHEN THROUGH FRIDAY AFTERNOON...THEN WEAKEN THIS
WEEKEND. MODERATE NORTH WINDS AND STEEP WIND DRIVEN SEAS ARE
EXPECTED TODAY AND CONTINUE THROUGH FRIDAY AFTERNOON. FOR NOW WINDS
AND SEAS ARE EXPECTED TO REMAIN SMALL CRAFT, BUT THE MODELS HINT
THAT WINDS COULD BRIEFLY REACH GALES OVER A SMALL PORTION OF THE
SOUTHERN OUTER WATERS THURSDAY AFTERNOON AND EVENING. -PETRUCELLI


&&

.PREV DISCUSSION... /ISSUED 218 AM PDT WED MAY 6 2015/

DISCUSSION...AN UPPER LOW CENTERED OVER WESTERN WASHINGTON THIS
MORNING HAS MADE LESS PROGRESS IN OUR DIRECTION THAN EXPECTED, BUT
NEVERTHELESS, IT CONTINUES TO MEANDER TO THE SOUTH. LATEST
GUIDANCE IS IN GOOD AGREEMENT AND SHOWS THE LOW OVER NORTH-CENTRAL
OREGON THIS AFTERNOON AND THEN IT MOVES INTO NORTHERN CALIFORNIA
BY TOMORROW. THIS SYSTEM HAS VERY LITTLE MOISTURE TO WORK WITH, SO
IT ISN`T EXPECTED TO DO MUCH OVER OUR AREA, BUT IT WILL BRING
CLOUDS AND A FEW SHOWERS FROM NORTH TO SOUTH LATER TODAY WITH A
SLIGHT CHANCE FOR THUNDERSTORMS FROM THE CASCADE CREST EASTWARD.
TEMPERATURES WILL BE COOLER THAN NORMAL FOR A CHANGE TODAY.

SHOWERS SHOULD DIMINISH TONIGHT AS DAYTIME HEATING WANES, THEN
THEY WILL REDEVELOP TOMORROW, PRIMARILY OVER SISKIYOU AND MODOC
COUNTIES IN CALIFORNIA. THE ONE THING THAT MAY BE A MINOR IMPACT
TOMORROW IS WIND ON THE EAST SIDE. THE LOW WILL BE VERTICALLY
STACKED, AND AS IT PULLS TO THE SOUTH, STRONG GUSTY NORTHEAST
WINDS WILL MIX DOWN OVER EASTERN KLAMATH, LAKE, AND MODOC
COUNTIES IN THE AFTERNOON. WHILE FORECAST WIND SPEEDS FALL SHORT
OF ADVISORY LEVEL, WINDS MAY GUST TO 40 MPH IN THE AFTERNOON AND
EARLY EVENING.

AS THE LOW DEPARTS TO THE SOUTH AND EAST ON FRIDAY, A RIDGE OF
HIGH PRESSURE BEGINS BUILDING OVER THE PACNW WHICH WILL MOVE OVER
US DURING THE WEEKEND. THIS WILL BRING US MOSTLY SUNNY AND DRY
WEATHER WITH TEMPERATURES RISING TO WELL ABOVE NORMAL AGAIN FRIDAY
THROUGH THE WEEKEND. THE PATTERN BRIEFLY TAKES ON THE LOOK OF AN
OMEGA BLOCK OVER THE WEEKEND, BUT THEN THE RIDGE GETS PINCHED OFF
AND MOVES NORTH EARLY NEXT WEEK WHICH ALLOWS LOW PRESSURE TO MOVE
OVER US FROM THE WEST. WHILE THERE ARE DIFFERENCES IN THE POSITION
OF THE VARIOUS FEATURES EARLY NEXT WEEK, THE GFS AND ECMWF AGREE
ON THE BASIC EVOLUTION OF THE PATTERN. IF THIS HAPPENS, WE SHOULD
SEE COOLER, SHOWERY WEATHER EARLY TO MID NEXT WEEK. -WRIGHT

FIRE WEATHER...UPDATED 2 AM PDT WEDNESDAY, MAY 6, 2015...AN UPPER
LOW WILL MOVE SOUTH OVER THE AREA TODAY WITH A COOL POOL ALOFT AT
500 MB WITH TEMPERATURES BETWEEN -27 AND -29 C MOVING OVERHEAD AT
THE TIME OF MAX HEATING RESULTING IN INCREASING MID LEVEL LAPSE
RATES. THE MODELS SUGGEST THERE MAY BE ENOUGH INSTABILITY TO WARRANT
A SLIGHT CHANCE OF THUNDERSTORMS FROM THE CASCADES EAST THIS
AFTERNOON AND EVENING. THE MODELS PUTS THE GREATEST INSTABILITY
ALONG THE CASCADES THIS 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. THE UPPER LOW WILL
MOVE SOUTH INTO NORTHERN CAL ON THURSDAY WITH THE BEST CHANCE FOR
ISOLATED STORMS CONFINED TO MODOC COUNTY. HOWEVER THE MODELS SHOW
700 MB WINDS INCREASING BETWEEN 30-40 KTS FROM THE NORTH TO
NORTHEAST DURING THE DAY THURSDAY AND THIS ALONG WITH WEAK
INSTABILITY AND TIGHT SURFACE GRADIENT COULD RESULT IN SOME OF THOSE
STRONGER WINDS MIXING DOWN AT THE SURFACE ALONG AND EAST OF THE
CASCADES. THIS COULD RESULT IN MODERATE RECOVERIES LATE TONIGHT
ALONG THE MID SLOPES AND RIDGES, BUT MIN RELATIVE HUMIDITIES
THURSDAY AFTERNOON SHOULD BE HIGHER COMPARED TO TODAY WHICH IS A
GOOD THING. -PETRUCELLI

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS FROM 5 PM THIS AFTERNOON TO 11 PM
     PDT FRIDAY FOR PZZ356-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT FRIDAY
     FOR PZZ350-356-370-376.

$$

NSK/TRW/MAP


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