Frost Advisory 29, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
800 PM PDT FRI APR 12 2013

.DISCUSSION...13/00Z NAM IN.

SEVERAL SHORT WAVES EMBEDDED IN NORTHWEST FLOW ALOFT WILL MOVE
THROUGH THE PACIFIC NORTHWEST OVER THE NEXT SEVERAL DAYS. EXPECT
SEVERAL ROUNDS OF MOSTLY LIGHT PRECIPITATION WITH THESE SYSTEMS
ALONG WITH GUSTY WINDS OVER THE RIDGES AND EAST OF THE CASCADES.
NO WARNINGS OR ADVISORIES ARE ANTICIPATED AT THIS TIME...BUT WIND
GUSTS WILL APPROACH ADVISORY CRITERIA EAST OF THE CASCADES SATURDAY.

THE FIRST OF THESE WAVES WILL MOVE ONSHORE TO THE NORTH TONIGHT.
IT WILL PUSH A WEAK SURFACE FRONT ONSHORE THIS EVENING. PRECIPITATION
WILL BE LIGHT AND ALMOST ALL OF IT WILL FALL FROM THE CASCADES
WEST AND SISKIYOUS NORTH. SNOW LEVELS WILL DROP TO AROUND 4500
FEET SATURDAY MORNING. WINDS WILL PICK UP TONIGHT...PEAK AROUND
DAYBREAK SATURDAY...THEN DIMINISH SATURDAY EVENING. POST-FRONTAL
SHOWERS WILL ALSO DIMINISH ABOUT THIS TIME. SATURDAY HIGH
TEMPERATURES INLAND WILL BE AROUND 10-15 DEGREES COOLER THAN
FRIDAY.

THE SECOND WAVE WILL BE WEAKER...BUT IT WILL HAVE A MORE SOUTHERLY
TRAJECTORY...MOVING OVER OREGON SUNDAY MORNING. A THIRD WAVE WILL
FOLLOW CLOSE ON ITS HEELS SUNDAY AFTERNOON. THE ASSOCIATED
PRECIPITATION WILL STILL BE LIGHT...BUT MORE WIDESPREAD. MOST OF
THE MEDFORD CWA WILL SEE SOME SHOWER ACTIVITY WITH THIS
SYSTEM...THOUGH MEASURABLE AMOUNTS WILL BE SPOTTY EAST OF THE
CASCADES. WINDS WILL BE LIGHTER THAN THE FRIDAY NIGHT/SATURDAY
SYSTEM AND WILL GENERALLY NOT BE AN ISSUE. IT WILL REMAIN QUITE
COOL...AND FROST ADVISORIES MAY BE NECESSARY IN SOME AREA SATURDAY
AND SUNDAY NIGHT IF THE SKIES CLEAR ENOUGH.

THE LAST WAVE WILL MOVE THROUGH MONDAY. THIS WILL KEEP THE SHOWER
ACTIVITY GOING INTO MONDAY EVENING...THEN THEY WILL DIMINISH.

LONG TERM DISCUSSION FROM THE FRIDAY AFTERNOON AFD...TUESDAY
MORNING THROUGH FRIDAY. MODEL ENSEMBLE PLOTS ARE IN REMARKABLE
AGREEMENT THROUGH TUESDAY MORNING. ON WEDNESDAY THE ECMWF IS
SHOWING A MORE AMPLIFIED TROUGH EXTENDING TO THE FOUR CORNERS
REGION WITH THE GFS SHOWING A MUCH SHALLOWER TROUGH.
HOWEVER...THEY BOTH ARE IN GOOD AGREEMENT BUILDING AN UPPER LEVEL
RIDGE OF VARYING STRENGTHS OVER THE PACNW. FROM THURSDAY ENSEMBLE
ELEMENTS CONTINUE TO DIVERGE WITH THE ENSEMBLE MEANS MAINTAINING A
BROAD RIDGE WITH THE PACNW IN A NW FLOW PATTERN DOWN THE BACKSIDE.
WITH THE MODEL SPREAD CONFIDENCE IS LOW...ESPECIALLY WITH TIMING
OF ANY SYSTEMS THAT MAY SLIDE DOWN INTO THE AREA. SVEN

&&

.AVIATION...BASED ON THE 13/00Z TAF CYCLE.

VFR CONDITIONS OVER THE REGION THIS EVENING EXCEPT ALONG PARTS OF
THE COAST. A WEAK COLD FRONT IS NOW MOVING INTO THE REGION...BRINGING
A LOWERING CLOUD DECK MOSTLY FROM THE CASCADES WESTWARD...WITH HIGHER
TERRAIN OBSCURED. MVFR CIGS WILL BECOME MORE WIDESPREAD AT THE
COAST AND WILL SPREAD INLAND TO AROUND KRBG LATE TONIGHT. GUSTY
WINDS ARE LIKELY FROM THE CASCADES EAST WITH MODERATE TURBULENCE.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

15/15/15