Small Craft Advisory 305, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
601 AM AKDT TUE MAY 8 2012

.SHORT TERM...A WEAK LOW IN THE SOUTHEASTERN GULF CONTINUES TO
TRACK TO THE EAST BUT IS EXPECTED TO TURN NORTHEAST LATER THIS
MORNING AND WEAKEN AS IT CROSSES THE COAST NORTH OF CAPE
EDGECUMBE WEDNESDAY MORNING. THE LOW IS EXHIBITING MULTIPLE WRAPS
OF CONVECTIVE CLOUD COVER. CLOUD TOP TEMPS AND SURROUNDING CLOUD
FEATURES IN SATELLITE IMAGERY INDICATE THE MID LEVEL AIRMASS IS
VERY COLD.

 ANOTHER SMALLER AND WEAKER CIRCULATION HAS ALSO BEEN EVIDENT IN
SATELLITE IMAGERY OVERNIGHT. THIS FEATURE APPEARS TO HAVE MADE
LANDFALL VICINITY CAPE EDGECUMBE AROUND 5 AM THIS MORNING. RADAR
IMAGERY SHOWING MULTIPLE SPIRAL RAIN BANDS. THIS FEATURE WAS
NEVER RESOLVED BY MODELS AND, IN CONJUNCTION WITH A LOW THAT
TRACKED INLAND AND REFORMED OVER SOUTHERN YUKON OVERNIGHT, WAS
RESPONSIBLE FOR SHARPENING THE SURFACE RIDGE AND PRESSURE
GRADIENT OVER THE PANHANDLE OVERNIGHT. GUSTY CONDITIONS WORKED
THEIR WAY UP THE PANHANDLE LAST NIGHT AND WERE CONCENTRATED OVER
LOCATIONS CLOSEST TO THE COAST MOUNTAINS. BRIEF PERIOD OF STRONG
WINDS IN AND AROUND JUNEAU OVERNIGHT WAS FOLLOWED BY GALE FORCE
WINDS OVER NORTHERN LYNN CANAL AND THEN STRONG WINDS OVER SKAGWAY
AND GUSTS TO 35 MPH IN AND AROUND HAINES. STRONG WINDS AND GUSTY
CONDITIONS WILL RELAX FROM SOUTH TO NORTH THROUGH THE DAY.

 CONVECTION FROM THESE TWO LOWS WILL KEEP SHOWER ACTIVITY GOING
ACROSS SOUTHEAST ALASKA THROUGH THE DAY AND INTO THE EVENING. AM
EXPECTING TO SEE SHOWERS BEGINNING TO DIMINISH OVERNIGHT TUESDAY
NIGHT. COLD MID LEVEL AIR MADE IT TO THE SURFACE ALONG THE OUTER
COAST AND MIXED PRECIP WAS FOLLOWED BY A BRIEF PERIOD OF STRAIGHT
SNOW IN YAKUTAT OVERNIGHT. BELIEVE THIS AIR WILL MAKE IT INLAND
FAR ENOUGH TONIGHT TO GET THE SNOW LEVEL DOWN TO NEAR SEA LEVEL
IN SKAGWAY AND HAINES OVERNIGHT TONIGHT. HAVE A MENTION OF RAIN
SHOWERS POSSIBLY MIXING WITH SNOW IN JUNEAU AND HYDER FOR
TONIGHT. NO ACCUMULATION NEAR SEA LEVEL IS EXPECTED.

 USED A BLEND OF GFS AND NAM FOR UPDATES TO PRESSURE AND WIND.
BLENDED GFS AND GEM FOR POP AND QPF. TEMPERATURES ADJUSTED WITH A
COMBINATION OF BIAS CORRECT MOS, ECMWF, AND GFS. NET RESULT WAS A
SLIGHT DECREASE IN DAYTIME HIGHS AND A 2 TO 4 DEGREE INCREASE IN
OVERNIGHT LOWS. FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...SOUTHEAST ALASKA WILL REMAIN ON THE WET SIDE THROUGH
THE REST OF THE WEEK AND INTO THE WEEKEND. A UPPER LEVEL LOW WILL
SET UP JUST SOUTH OF THE AK PENN WITH A RIDGE OVER SE AK. THIS
WILL KEEP THE FORECAST AREA ABOVE AVERAGE IN PRECIP WITH A DEEP
SW FLOW. TEMPS WILL BE BELOW AVERAGE THROUGH THE WEEK WITH CLOUDY
SKIES AND COLD AIR FOR THIS TIME OF YEAR A LOFT. HEAVY PRECIP WILL
DEVELOP OVER THE NE GULF THURSDAY AS A FRONT STALLS AND MULTIPLE
WAVE ROLL UP ALONG THE FRONT THROUGH FRIDAY AND SAT. RAIN FALL
AMOUNTS WILL RANGE FROM 3 TO 5 INCHES FROM PAYA TO PAGS. WILL NEED
KEEP AN EYE ON RIVER LEVELS THROUGH THE END OF THE WEEK WITH
INCREASE SNOW MELT AND RUNOFF FROM HEAVY PRECIP. USED A BLEND OF
THE EC WITH SOME GFS THROUGH DAY 5 AS THEY SEEM TO BE IN GOOD
AGREEMENT ALONG WITH IN LINE THE ENSEMBLE THINKING.

AT THE START OF THE LONG TERM PERIOD A UPPER TROF CURRENTLY OVER
THE EASTERN GULF WILL DRIFT OVER THE FORECAST AREA TO KEEP SHOWERS
LIKELY OVER MOST OF THE AREA WED. THE WINDS WILL BE INCREASING FROM
THE SOUTH AS A SURFACE RIDGE OF HIGH PRESSURE SHARPENS OVER THE
FORECAST AREA AS A FRONT ASSOCIATED WITH A LOW WEST OF KODIAK ISLAND
DRIFTS INTO THE EASTERN GULF. THIS RIDGE WILL PRODUCE SMALL CRAFT
WINDS OVER LYNN CANAL WITH 20KT OVER THE REST OF THE MARINE
WATERS. LAND AREAS WILL SEE SOME GUSTY WINDS WITH THE STRONGEST
NEAR PAGY TO 35/40MPH.

THE WARM FRONT WILL BE OVER THE NE GULF BY WEDNESDAY NIGHT WITH A WAVE
DEVELOPING ALONG THE FRONT OVER THE NORTH PACIFIC. THIS WAVE WILL
PULL BACK TOWARDS KODIAK BUT WILL INCREASE THE WINDS OVER THE
NORTHERN GULF TO GALES AND SMALL CRAFTS OVER THE SE GULF. PRECIP RATES
WILL INCREASE THROUGH THURSDAY AFTERNOON/NIGHT AS ANOTHER SLUG OF
MOISTURE SLAMS INTO THE NE GULF COAST. RAIN WILL BE HEAVY AT TIMES
OVER THIS AREA THROUGH LATE FRIDAY NIGHT WITH AREAS SEEING 3-5
INCHES WITH A DEEP SW FLOW OVER THE GULF AND EXTENDED ALL THE WAY
INTO THE NORTH PACIFIC. THE REST OF THE FORECAST AREA WILL SEE CAT
PRECIP BUT NOT AS MUCH IN AMOUNTS THROUGH SAT AND THE SOUTHERN
AREAS MAY SEE IT DRY OUT SOME WITH MOST OF THE UPPER LEVEL SUPPORT
OVER THE NORTHERN AREAS. THE WINDS OVER THE EASTER GULF WILL
REMAIN TO RANGE FROM 30 TO 40 KT FROM THURSDAY THROUGH EARLY SAT
MORNING AS THE FRONT FINALLY DRIFTS EAST OF THE AREA.

THERE MAY BE A BREAK IN THE PRECIP INTO EARLY NEXT WEEK BUT ATTM
IT IS STILL TO HARD TO TELL WITH THE SPREAD IN THE ENSEMBLES.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 7 AM AKDT THIS MORNING FOR AKZ018.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ013-033-036-041.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ042-043-051.

&&

FRITSCH/ABJ