Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 291117
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
417 AM PDT SUN MAR 29 2015

.DISCUSSION...
HIGH PRESSURE IN THE FORM OF A FLAT RIDGE WILL CONTINUE TO DOMINATE
THE WEATHER THROUGH MONDAY. PERIODS OF HIGH AND MID-LEVEL
CLOUDINESS WILL MOVE THROUGH DURING THIS TIME FRAME AS TWO WEAK
MID-UPPER LEVEL SHORTWAVE TROUGHS MOVE INTO THE RIDGE AND NUDGE
IT EASTWARD.

MONDAY NIGHT THROUGH TUESDAY A MAJOR WEATHER CHANGE IS EXPECTED
ACROSS THE AREA AS TEMPERATURES FALL FROM 10 TO 20 DEGREES ABOVE
NORMAL FOR INLAND LOCATIONS MONDAY AFTERNOON TO 5 TO 10 DEGREES
BELOW NORMAL FOR TUESDAY AFTERNOON. SAID ANOTHER WAY, HIGHS WILL
BE 15 TO 25F COOLER ON TUESDAY AS COMPARED TO MONDAY. THUS, WE`LL
BE GOING FROM LATE SPRING NORMALS TO WHAT`S MORE TYPICAL FOR THIS
TIME OF THE YEAR. SINCE IT`S GENERALLY BEEN SO ANOMALOUSLY WARM
MUCH OF THE LAST MONTH, THIS SIGNIFICANT TEMPERATURE CHANGE IS
LIKELY TO BE A BIT OF SHOCK TO SOME. ALSO, IT DOES APPEAR THAT THE
COOLER NEAR NORMAL TEMPERATURE CONDITIONS WILL GENERALLY CONTINUE
THROUGH NEXT WEEKEND.

MONDAY NIGHT THROUGH TUESDAY EVENING THE COLD FRONT MOVING
THROUGH THE AREA WILL BRING PRECIPITATION IN ADDITION TO THE MAJOR
TEMPERATURE DROP. MOST OF THE PRECIPITATION WILL FALL FROM THE
MARBLE MOUNTAINS, SISKIYOUS, AND OREGON CASCADES WESTWARD UNDER
WEST TO NORTHWEST FLOW. PRECIPITATION AMOUNTS IN THESE AREAS LOOK
MODEST, WITH 0.25" TO 0.75" IN MOST LOCATIONS. SNOW AMOUNTS ARE
LIKELY TO BE 1-3 INCHES ABOVE 5KFT, THOUGH 3 TO 6 INCH AMOUNTS ARE
POSSIBLE ACROSS THE HIGHEST PORTIONS OF THE OREGON CASCADES.

WINDS WITH THIS FRONTAL SYSTEM ARE A CONCERN FOR THOSE ATTEMPTING
TO SUMMIT OR CAMP ON THE PEAKS OF THE CASCADES MONDAY NIGHT
THROUGH TUESDAY. THIS IS DEPICTED IN THE MOUNT SHASTA
RECREATIONAL FORECAST. ADDITIONALLY, THOSE WHO MAY BE PLANNING TO
CONDUCT PRESCRIBED BURNS ACROSS THE HIGHER ELEVATIONS AND EAST
SIDE TUESDAY AFTERNOON SHOULD USE EXTRA CAUTION, ESPECIALLY WHERE
LITTLE OR NO PRECIPITATION IS EXPECTED.

IT WILL REMAIN BREEZY TO WINDY AND COOL ON WEDNESDAY AS A -30C
500MB COLD POOL MOVES THROUGH FROM THE NORTHWEST. MODELS DIFFER ON
THE AMOUNT OF PRECIPITATION EXPECTED WITH THIS. EXPECT THAT THERE
WILL BE SHOWERS, BUT AMOUNTS WILL BE FAIRLY LIGHT. IT WILL BE
NOTABLE, HOWEVER, THAT SNOW LEVELS WILL FALL TO BETWEEN 3500 AND
4500 FEET. WITH THE HIGH LAPSE RATES AND VERY COLD AIR ALOFT,
SUSPECT THAT SHOWERS WILL BE BRIEFLY MODERATE TO HEAVY WHERE THEY
OCCUR AND COULD CONTAIN SMALL HAIL OR GRAUPEL EVEN AT WEST SIDE
VALLEY FLOORS.

GUIDANCE CONTINUES TO LEAN TOWARD A BREAK IN THE PRECIPITATION
THURSDAY THROUGH FRIDAY. THIS WILL INCREASE DIURNAL TEMPERATURE
SPREADS AND YIELD FROST AND FREEZE CONCERNS FOR OUR AGRICULTURAL
AREAS WEST OF THE CASCADES. WIND AND CLOUD COVER IS LIKELY TO
MODERATE CONDITIONS, BUT GROWERS ARE ADVISED TO TAKE NECESSARY
PRECAUTIONS.

NEXT WEEKEND ANOTHER UPPER LEVEL TROUGH WILL BEGIN TO AFFECT THE
AREA. MODELS HAVE DIFFERED AS TO HOW PROGRESSIVE THIS TROUGH WILL
BE. PREVIOUSLY PROGRESSIVE GFS40 GUIDANCE IS NOW SLOWING THE
TROUGH WITH THE NET EFFECT OF A MORE SIGNIFICANT AND MORE SOUTH TO
NORTH ORIENTED FLOW BY EARLY NEXT WEEK. THE EUROPEAN MODEL, ON THE
OTHER HAND, INDICATES FAIRLY WEAK FRONTAL SYSTEMS NEXT WEEKEND
THROUGH EARLY NEXT WEEK UNDER A NORTHWEST FLOW. CONSISTENCY CAUSES
ME TO LEAN TOWARD THE LATTER FOR NOW, BUT THERE`S PLENTY OF TIME
FOR THIS TO CHANGE. BTL

&&

.AVIATION...FOR THE 29/12Z TAF CYCLE...VFR CONDITIONS WILL
PERSIST THROUGH SUNDAY NIGHT...EXCEPT FOR AREAS OF MVFR/IFR CIGS
WHICH WILL DEVELOP ALONG THE COAST SUNDAY NIGHT.

&&

.MARINE...UPDATED 200 AM PDT SUNDAY 29 MAR 2015...HIGH PRESSURE OVER
THE WATERS WILL PERSIST THROUGH MONDAY MORNING. MODERATE WEST SWELL
WILL BUILD SUNDAY MORNING AND SUBSIDE LATE SUNDAY NIGHT. THE WHOLE
AREA WILL SEE SMALL CRAFT ADVISORY SEAS WITH THIS SWELL. SOUTH WINDS
WILL INCREASE MONDAY AFTERNOON AND EVENING AHEAD OF A STRONGER COLD
FRONT...WHICH WILL MOVE ONSHORE MONDAY NIGHT. AT THIS TIME IT LOOKS
LIKE SEAS WILL REACH SMALL CRAFT ADVISORY CRITERIA...BUT THE WINDS
WILL REMAIN JUST BELOW CRITERIA. OFFSHORE HIGH PRESSURE WILL BRIEFLY
REBUILD TUESDAY...THEN WEAK LOW PRESSURE WILL MOVE INTO THE WATERS
TUESDAY NIGHT. OFFSHORE HIGH PRESSURE WILL RETURN WEDNESDAY AND
THURSDAY.

&&

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

CA...NONE.

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

$$

BTL/15



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