Area Forecast Discussion
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FXAK67 PAJK 042335
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
335 PM AKDT MON MAY 4 2015

.SHORT TERM...LOW PRESSURE SOUTH OF HAIDA GWAII AND HIGH PRESSURE
OVER THE INTERIOR HAS CAUSED A STRONG NORTH PRESSURE GRADIENT AND
NELY GEOSTROPHIC FLOW THROUGH INTERIOR PASSES/OVER THE COASTAL
MOUNTAINS TODAY. DESPITE THE AMPLE SUNSHINE AND HEATING, SEA
BREEZE EFFECTS HAVE NOT BEEN ABLE TO SURPASS THIS SYNOPTIC FLOW IN
MANY PLACES. MODELS DID NOT HANDLE THIS WELL AS MOST WOULD HAVE A
NWLY FLOW THROUGH THE INNER CHANNELS BY NOW. SOME LOCATIONS THAT
NORMALLY HAVE A SOUTH SEA BREEZE DIRECTION HAVE BECOME LIGHT AND
VARIABLE THIS AFTERNOON BUT HAVE NOT ACTUALLY FLIPPED. THE LACK OF
A SEA BREEZE HAS ALLOWED TEMPERATURES TO WARM ABOVE 60F IN MANY
PLACES.

THE LOW WILL CONTINUE MOVING ESE AWAY FROM THE AREA TOMORROW
WHILE THE RIDGE OF HIGH PRESSURE OVER THE WESTERN GULF BUILDS
EAST. THIS WILL FINALLY SHIFT THE WINDS NWLY AND EASE THROUGH THE
DAY. THE WEAKENING PRESSURE GRADIENT OVER THE INNER CHANNELS WILL
ALLOW FOR THE SEA BREEZE TO DEVELOP TOMORROW. THIS WILL KEEP
TEMPERATURES FAIRLY CLOSE TO WHERE THEY ARE TODAY OR EVEN SLIGHTLY
COOLER ALONG THE IMMEDIATE COAST.

CLEAR SKIES WILL ALLOW FOR STRONG RADIATIONAL COOLING AGAIN
TONIGHT. LOCATIONS BLOCKED FROM THE WIND WILL FALL NEAR FREEZING
JUST BEFORE SUNRISE...SIMILAR TO THIS MORNING BUT LIKELY A DEGREE
OR SO WARMER. THE ATMOSPHERE HAS DRIED A LOT TODAY BUT WITH THESE
TEMPERATURES FROST IS STILL LIKELY. FOR THIS REASON HAVE ISSUED A
FROST ADVISORY FOR THE INTERIOR VALLEY LOCATIONS OF
YAKUTAT/HAINES/GUSTAVUS/HOONAH.

MOST CHANGES TODAY WERE FOR LOCAL EFFECTS AS THERE ARE VASTLY
DIFFERENT TEMPERATURE/WIND FORECASTS FOR COASTAL AREAS COMPARED TO
INNER VALLEY LOCATIONS. RECOMMEND USING POINT AND CLICK FOR THESE
MESO/MICROSCALE FEATURES. FORECAST CONFIDENCE ON DRY/MOSTLY SUNNY
WEATHER IS HIGH AND SLIGHTLY LOWER FOR THE FINER DETAILS.

.LONG TERM...THE MID LEVEL RIDGE AXIS OVER THE AK GULF WILL SHIFT
TO THE EAST TRACKING OVER THE PANHANDLE EARLY WEDNESDAY MOVING
INTO BRITISH COLUMBIA BY FRIDAY. MID LEVEL FLOW OFFSHORE FLOW WILL
SWITCH ONSHORE BRINGING IN SOME THIN HIGH CLOUDS AND INCREASED
MOISTURE INTO WEDNESDAY. INNER CHANNEL WINDS WILL HAVE SHIFTED TO
THE SOUTHERN FOR THE NORTHERN LOCATIONS OR HAVE A BRIEF INCREASE
IN THE NORTHERLY ON TUESDAY EVENING THEN DIMINISH AND BECOME
SOUTHERLY BY EARLY WEDNESDAY. A WEAK SHORT WAVE WILL CROSS OVER
THE YUKON WEDNESDAY BUT AS OF NOW THINK THIS WILL BE FAR ENOUGH
NORTH NOT TO IMPACT OUR REGION. LARGE DIURNAL TEMPERATURE RANGE
WITH THE CLEAR SKIES AND RADIATIONAL COOLING OVERNIGHT AND
INCREASED INSOLATION DURING THE DAY,

THE BIG SHIFT FROM THE SUNNY WEATHER WILL BEGIN LATE WEDNESDAY
NIGHT INTO THURSDAY. A FRONT ASSOCIATED WITH A LOW CURRENTLY OVER
THE WESTERN TIP OF THE ALEUTIANS WILL CROSS INTO THE WESTERN GULF
FORMING A WEAK CIRCULATION NEAR KODIAK. THE FRONTAL BOUNDARY
ASSOCIATED WITH THIS LOW WILL TRACK ACROSS THE GULF REACHING THE
PANHANDLE THURSDAY. THIS FIRST WAVE NOT SHOWING MUCH UPPER LEVEL
SUPPORT AND DOES LOOK TO SHEAR APART AS IT MOVES INLAND. THE MAIN
QUESTION IS FRIDAY INTO THE WEEKEND IS WHAT HAPPENS TO THE
ORIGINAL LOW. THE GFS SWINGS THE MAIN SYSTEM INTO THE GULF WHERE
IT RE-INTENSIFIES MOVING ANOTHER FRONTAL BAND OVER THE PANHANDLE
THROUGH SATURDAY AND REMAINS INTACT INTO EARLY NEXT WEEK. WHILE
THE GFS HAS BEEN CONSISTENT WITH THIS SOLUTION THE PAST FEW MODEL
RUNS THINK IT IS OVER DOING TO STRENGTH OF THE LOW. THE GEM/ECMWF
WHILE NOT AS CONSISTENT SEEMED BIT MORE LIKELY WITH A WEAKER LOW.
NEW RUNS DID SHOW A MORE DEVELOPED LOW IN THE GULF ON FRIDAY BUT
THE LOW DOES NOT REMAIN INTACT BEYOND EARLY SATURDAY WITH GRATER
POTENTIAL FOR A RETURN OF CLEAR DRY WEATHER.

MODEL AGREEMENT WAS GOOD EARLY ON. USED A BLEND OF 12Z ECMWF/GEM
TO REFRESH INHERITED GRIDS OUT TO DAY 4. WENT WITH NEW WPC AND THE
ENSEMBLE BLEND THROUGH DAY 8 DUE TO THE MODEL DIFFERENCES. FOR NOW
KEEPING WITH MORE CHANCE WORDING IN THE LATE WEEK FORECAST BUT IF
THE MODEL TREND CONTINUES THE WEEKEND WILL HAVE HIGHER POTENTIAL
FOR RAIN. FORECAST CONFIDENCE IS ABOVE AVERAGE INITIALLY, THEN
DROPS BELOW AVERAGE BY THE END OF THE WEEK.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FROST ADVISORY FROM 1 AM TO 7 AM AKDT TUESDAY FOR AKZ017-019>021.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-022-031.

&&

$$

FERRIN/PRB

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