PDXAFDMFR (05/14/13 0106)


FXUS66 KMFR 140810
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
110 AM PDT TUE MAY 14 2013

.DISCUSSION...14/00Z NAM/GFS IN.

A COLD FRONT IS NOW MOVING OUT OF THE CWA. IT DIDN'T BRING MUCH IN
THE WAY OF PRECIPITATION...ONLY SEVERAL HUNDREDTHS OF AN INCH ALONG
THE COAST...IN THE COAST RANGE...AND THE UMPQUA BASIN. IT DID
BRING SIGNIFICANT WINDS TO THE RIDGES AND EAST SIDE THOUGH...AND
THOSE WINDS ARE DIMINISHING NOW. 

COOLER AIR HAS MOVED IN BEHIND THE FRONT...AND INLAND HIGH
TEMPERATURES TUESDAY AND WEDNESDAY WILL ONLY BE 0-10 DEGREES ABOVE
NORMAL INSTEAD OF 10-20 DEGREES ABOVE NORMAL. NO MORE
PRECIPITATION IS EXPECTED THROUGH WEDNESDAY MORNING.

A WEAK UPPER TROUGH WILL APPROACH THE COAST WEDNESDAY...AND IT
WILL PUSH ANOTHER FRONT ONSHORE WEDNESDAY AFTERNOON AND EVENING.
IN TERMS OF PRECIPITATION...THIS ONE LOOKS TO BE SIMILAR TO THE
ONE THAT JUST MOVED THROUGH THE AREA WITH LIGHT PRECIPITATION
MOSTLY FALLING ALONG THE COAST...COAST RANGE...AND IN THE UMPQUA
BASIN. INLAND TEMPERATURES WILL COOL OFF SOME MORE...WITH THE
THURSDAY AND FRIDAY HIGHS NEAR OR BELOW SEASONAL NORMALS.

ON THURSDAY THERE WILL BE A LONG WAVE TROUGH OVER THE PACIFIC
NORTHWEST AND SHORT WAVES ROUNDING THE BOTTOM OF THE TROUGH WILL
MOVE THROUGH NORTHERN CALIFORNIA DURING AFTERNOON/EVENING SURFACE
HEATING. EXPECT PLENTY OF SHOWER ACTIVITY THURSDAY...AND MOST 
LOCATIONS WILL GET MORE PRECIPITATION FROM THE SHOWERS THAN THEY
WILL WITH THE WEDNESDAY SURFACE FRONT.

THUNDERSTORMS DON'T LOOK LIKE THEY WILL DEVELOP AT LEAST THROUGH
THURSDAY NIGHT. ON WEDNESDAY AFTERNOON AND EVENING...THE MODELS
INDICATE THAT THE UPPER LEVEL SUPPORT FOR CONVECTION...IN THE FORM
OF SHORT WAVES...WILL REMAIN SOUTH AND EAST OF THE MEDFORD CWA. ON
THURSDAY...THE UPPER LEVEL SUPPORT IS BETTER WITH SOME WEAK SHORT
WAVES ROUNDING THE LONG WAVE TROUGH OVER NORTHERN CALIFORNIA...BUT
MODEL LIFTED INDICES INDICATE THAT DEEP CONVECTION IS NOT LIKELY.
COOL SURFACE TEMPERATURES WILL INHIBIT DEVELOPMENT.

LONG TERM DISCUSSION FROM THE MONDAY AFTERNOON AFD...FRIDAY
THROUGH MONDAY...MODEL CONSISTENCY REMAINS QUITE HIGH THROUGH
THE PERIOD AND THUS CONFIDENCE IS HIGH AS WELL. A TROUGH WILL
SWING THROUGH OUR AREA ON FRIDAY. THE INSTABILITY ASSOCIATED WITH
THE COLD POOL ALOFT WILL LEAD TO CONSIDERABLE SHOWER ACTIVITY
AREA-WIDE AND POSSIBLY EVEN SOME THUNDER ON THE EAST SIDE. I
RAISED POPS FOR FRIDAY AND INTRODUCED A THUNDERSTORM CHANCE. THE
FLOW THEN BECOMES ZONAL INTO THE WEST COAST FOR NEXT WEEKEND.
WHILE THERE WILL LIKELY BE IMPULSES WITHIN THE FLOW THAT INCREASE
SHOWER ACTIVITY FROM TIME TO TIME, I GENERALLY KEPT POPS LOW AND
CONFINED TO THE WEST SIDE.

AT THE SAME TIME, A TROUGH IS LIKELY TO COME THROUGH ALASKA AND 
DEVELOP INTO A POTENTIALLY LARGE CUTOFF LOW OVER THE NORTHEAST 
PACIFIC. THIS LOW THEN TAKES UP A POSITION OFF THE PACNW EARLY NEXT 
WEEK. FOR SUCH AN ANOMALOUSLY DEEP LOW, THERE IS REMARKABLY LITTLE 
SPREAD AMONGST THE MODELS, SO IT'S REASONABLE TO ASSUME THAT THERE 
WILL BE SOME SORT OF TROUGH IN THAT AREA NEXT WEEK. OF COURSE, THE 
DETAILS WILL CHANGE OVER TIME, BUT WE SHOULD BE IN SW FLOW ALOFT BY 
MONDAY AS THE RIDGE UPSTREAM OF THE LOW BUILDS. HAVE INCREASED 
TEMPERATURES AND DECREASED POPS FOR MONDAY AS A RESULT. IF THIS PANS 
OUT, WE MAY ALSO SEE SOME THUNDERSTORM ACTIVITY NEXT WEEK FOLLOWED 
BY A COOL, WET PERIOD AS THE LOW COMES IN. THIS ALL REMAINS TO BE 
SEEN, OF COURSE, BUT IT IS SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...BASED ON THE 14/06Z TAF CYCLE.

HIGH PRESSURE IS BUILDING INTO THE AREA FROM THE SOUTHWEST TONIGHT. 
HIGH SURFACE RELATIVE HUMIDITY IN THE UMPQUA BASIN AND ALONG THE 
COAST WILL LIKELY RESULT IN IFR TO MVFR AT TIMES TONIGHT THROUGH MID 
MORNING ON TUESDAY. HOWEVER, DUE TO THE DEVELOPING OFFSHORE 
COMPONENT OF THE FLOW, CONFIDENCE IN THE EXTENT, LEVEL, AND DURATION 
OF THESE CEILINGS IS ONLY MODERATE. OTHERWISE VFR CONDITIONS ARE 
EXPECTED OVER THE NEXT 24 HOURS. IT WILL BE A BIT BREEZY TUESDAY 
AFTERNOON AND EVENING, BUT NOT NEARLY AS BREEZY AS IT WAS ON SUNDAY 
AFTERNOON. BTL 

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.



15/15/18