Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 041151
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
451 AM PDT MON MAY 4 2015

.UPDATE...AVIATION...MARINE...AND FIRE WEATHER DISCUSSIONS
UPDATED.

.AVIATION...FOR THE 04/12Z TAF CYCLE...THE MARINE LAYER IS
MAKING A GOOD PUSH INLAND THIS MORNING, BRINGING MVFR/IFR TO MUCH OF
THE COAST AND THE VALLEYS WEST OF THE COASTAL RANGE. EXPECT THIS
LAYER OF STRATUS, WITH AREAS OF FOG, TO CONTINUE INLAND THROUGH THE
EARLY MORNING, PERHAPS REACHING KRBG BEFORE OR JUST AFTER SUNRISE.
CONDITIONS SHOULD CLEAR TO VFR BY 16-19Z, BUT MVFR WILL LIKELY
RETURN TO COASTAL AREAS BETWEEN 00-03Z AS A WEAK FRONT BEGINS TO
PUSH TOWARDS THE COASTLINE. ELSEWHERE, EXPECT VFR TO PREVAIL. THERE
WILL BE CUMULUS FIELDS AND A SLIGHT CHANCE OF THUNDERSTORMS OVER
NORTHERN CALIFORNIA AND AREAS EAST OF HE CASCADES THIS AFTERNOON,
BUT THUNDERSTORMS WILL BE ISOLATED AT BEST. -BPN

.MARINE...UPDATED 230 AM PDT MONDAY, 4 MAY, 2015...SEAS REMAIN
CHOPPY AS THE LAST OF THE WIND DRIVEN SEAS DIMINISH, BUT CONDITIONS
HAVE FALLEN BELOW THE CRITERIA USED TO ISSUED SMALL CRAFT
ADVISORIES. HAVE THEREFORE CANCELLED THE ADVISORIES, BUT SOME AREAS
MAY STILL EXPERIENCE SOMEWHAT STEEPENED SEAS THROUGH EARLY THIS
MORNING. A WEAK COLD FRONT WILL BRING SOME SHOWERS AND BUILDING WEST
SWELL ON TUESDAY. SEAS WILL SUBSIDE AGAIN ON WEDNESDAY. THEN
MODERATE NORTH WINDS MAY RETURN WEDNESDAY AND THURSDAY AS HIGH
PRESSURE SETS UP OFFSHORE WITH LOW PRESSURE INLAND. WINDS GRADUALLY
LOWER FRIDAY. -BPN/SPILDE

.FIRE WEATHER...UPDATED 445 AM PDT MONDAY, MAY 4, 2015... ISOLATED
THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND EVENING FROM THE
TRINITY ALPS THROUGH EASTERN SISKIYOU COUNTY INTO MODOC COUNTY IN
CALIFORNIA, AND INTO SOUTHEASTERN KLAMATH COUNTY AND THE SOUTHERN
HALF OF LAKE COUNTY IN OREGON. THE BEST CHANCES FOR THUNDERSTORM
DEVELOPMENT WILL OCCUR OVER THE SHASTA HIGHLANDS, MEDICINE LAKE, AND
THE WARNER MOUNTAINS, BUT ANY LOCATIONS DOWNWIND ARE AT RISK FOR
LIGHTNING AS WELL. ALTHOUGH THUNDERSTORMS HAVE FAILED TO DEVELOP
OVER THE WEEKEND, INSTABILITY PARAMETERS APPEAR MORE FAVORABLE
TODAY, ESPECIALLY GIVEN THE APPROACHING MID LEVEL TROUGH AND
FAVORABLE UPPER LEVEL DYNAMICS.  STORMS THAT DO DEVELOP ARE LIKELY
TO BE SINGLE AND MULTI-CELLULAR AND SHOULD MOVE WEST-SOUTHWEST TO
EAST-NORTHEAST AT AROUND 10-15 KNOTS. WITH PRECIPITABLE WATER VALUES
AROUND 0.60" AND THE STORM MOTION MENTIONED, STORMS ARE LIKELY BE A
MIX OF WET AND DRY. DRY LOW LEVELS SUGGEST THAT STORMS COULD PRODUCE
SOME GUSTY AND ERRATIC WINDS IN THE 20 TO 30 KNOTS RANGE.  WITH
CURRENT FUEL CONDITIONS RESULTING IN MODERATE FIRE DANGER, CONCERNS
FOR FIRE STARTS ARE THERE, BUT NOT MAJOR. THIS IS MAINLY DUE TO THE
CURRENT SIGNIFICANT LIVE FUEL COMPONENT. -BTL/BPN

&&

.PREV DISCUSSION... /ISSUED 101 AM PDT MON MAY 4 2015/

DISCUSSION...04/00Z NAM/GFS IN.

MOSTLY CLEAR SKIES PREVAIL ACROSS THE MEDFORD CWA THIS
MORNING...EXCEPT FOR SOME MARINE STRATUS ALONG THE NORTH
COAST...IN THE COQUILLE VALLEY...AROUND BROOKINGS...AND OVER MOST
OF THE MARINE WATERS. THERE IS ALSO BITS OF CONVECTIVE DEBRIS
EAST OF THE CASCADES.

MONDAY WILL BE ANOTHER WARM DAY OVER INLAND AREAS OF THE MEDFORD
CWA...BUT IT WILL BE SEVERAL DEGREES COOLER THAN THE SUNDAY HIGHS
OVER THE WEST SIDE AND NEAR EAST SIDE AS THE MARINE INFLUENCE AND
CLOUD COVER INCREASES OVER THE AREA. HIGHS WILL BE NEAR NORMAL TO
AROUND 5 DEGREES ABOVE NORMAL ALONG THE COAST AND IN THE UMPQUA
BASIN...AND AROUND 10 DEGREES ABOVE NORMAL OVER THE REMAINDER OF
THE WEST SIDE AND NEAR EAST SIDE. OVER LAKE COUNTY AND MODOC
COUNTY...MONDAY HIGHS WILL BE SIMILAR TO THE SUNDAY HIGHS...10 TO
15 DEGREES ABOVE NORMAL.

EAST OF THE CASCADES AND OVER NORTHERN CALIFORNIA...THERE WILL BE
ANOTHER ROUND OF SHOWERS IN ROUGHLY THE SAME AREA AS THE SUNDAY
ACTIVITY...AND MAYBE SOME ISOLATED THUNDERSTORMS AS WELL.

THE TRANSITION TO A COOLER AND SHOWERY PATTERN WILL OCCUR MONDAY
NIGHT INTO TUESDAY AS AN UPPER LEVEL LONG WAVE TROUGH EDGES
ONSHORE. THIS WILL PUSH A COLD FRONT ONSHORE MONDAY NIGHT.
ASSOCIATED PRECIPITATION WILL BE LIGHT AND MOSTLY LIMITED
TO THE WEST SIDE. TUESDAY WILL BE QUITE A BIT COOLER EVERYWHERE
WITH HIGHS DROPPING TO NEAR NORMAL VALUES OVER MOST OF THE
AREA...AND RANGING TO NEAR FIVE DEGREES ABOVE NORMAL OVER LAKE
COUNTY AND NORTHERN CALIFORNIA.

THE TROUGH WILL MOVE THROUGH THE AREA SLOWLY AS SHORT WAVES
DIVING DOWN THE BACK SIDE OF THE TROUGH WILL IMPEDE ITS PROGRESS.
ALL THAT COOL AIR ALOFT AND THE SHORT WAVES WILL SUPPORT ROUNDS OF
SHOWERS TUESDAY NIGHT INTO WEDNESDAY...BUT TIMING THOSE ROUNDS IS
A DIFFICULT FORECAST. TEMPERATURES WILL BE COOLER STILL WITH MANY
AREAS DROPPING SLIGHTLY BELOW NORMAL.

LONG TERM DISCUSSION FROM THE SUNDAY AFTERNOON AFD...THU MAY 7TH
THROUGH MON MAY 11TH...A RATHER SHARP TROUGH OF LOW PRESSURE WITH
AN ASSOCIATED -25C TO -30C 500MB COLD POOL IS EXPECTED TO BE OVER
THE FORECAST AREA THURSDAY. THIS TROUGH WILL ELONGATE AND WOBBLE
SOUTHWARD INTO CALIFORNIA ON FRIDAY, AND THEN WILL MOVE INTO THE
GREAT BASIN ON FRIDAY. THE GFS40 REMAINS SLOWER TO MOVE THE TROUGH
EASTWARD THAN IS THE ECMWF. HAVE LEANED ON THE GFS40 SIDE OF
CONSENSUS DUE TO IT`S BETTER CONSISTENCY IN SLOWING THE LOW`S
PROGRESSION SOUTH AND EASTWARD. IN SHORT, IT WILL BE COOLER WITH
HIGHS MOSTLY IN THE 50S AND 60S. LOWS WILL BE NEAR FREEZING ACROSS
THE EAST SIDE AND IN THE 30S AND 40S ON THE WEST SIDE WITH SOME
FROST POTENTIAL IN THE USUALLY COLDER WESTERN VALLEY SPOTS. WE DO
EXPECT SHOWERS AND A SLIGHT CHANCE OF AFTERNOON AND EVENING
THUNDERSTORMS DURING THIS TIME PERIOD, WITH THE GREATEST CHANCE OF
PRECIPITATION BEING ALONG AND NEAR THE CASCADE CREST THURSDAY
AFTERNOON AND EVENING. SNOW LEVELS WILL BE MOSTLY BETWEEN 5500 AND
7500 FEET. WHILE PRECIPITATION AMOUNTS WILL BE GENERALLY LIGHT, A
QUICK SHOT OF WETTING PRECIPITATION IS POSSIBLE DURING THIS TIME
PERIOD IN ISOLATED TO SCATTERED LOCATIONS. OVER THE LAST 24 HOURS,
BOTH MODELS HAVE TRENDED WETTER FOR THURSDAY, WITH THE GFS40
INDICATING THE POTENTIAL OF SIGNIFICANT PRECIPITATION OVER THE
AREA THURSDAY INTO FRIDAY DUE TO OROGRAPHICS COMBINED WITH LOW
PRESSURE FORCING FOLLOWED BY DEFORMATION ZONE DYNAMICS.

FRIDAY THROUGH SUNDAY THE INITIAL TROUGH IS EXPECTED TO MOVE INTO
THE GREAT BASIN WHILE ANOTHER TROUGH SLIPS ONTO THE WEST COAST SOUTH
OF A STRONG RIDGE OVER SOUTHEASTERN ALASKA AND NORTHWESTERN CANADA.
IT APPEARS THE NET RESULT IS LIKELY TO BE A BIT OF A WARM-UP
FOLLOWED BY ANOTHER OPPORTUNITY FOR SHOWERS AND, POSSIBLY, ISOLATED
THUNDERSTORMS ACROSS THE AREA. WHILE MOISTURE AVAILABLE FOR
PRECIPITATION IS LIKELY TO BE GREATER AS THE EASTERN SIDE OF THIS
TROUGH MOVES INTO THE AREA, DYNAMICS CURRENTLY LOOK RATHER WEAK. IN
SHORT, THE INCREASED CLOUD COVER AND PRECIPITATION DURING THIS
PERIOD IS LIKELY TO SLOW DRYING ACROSS THE AREA. BTL

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

JRS/BPN/MAS/BTL


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