Gale Warning 145, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
1100 AM ADT TUE MAR 20 2007

.SYNOPSIS...
.SHORT RANGE...A MESSY WEATHER SITUATION IS TAKING SHAPE ACROSS
SOUTHEAST ALASKA FOR THE NEXT 24 TO 36 HOURS. LARGE SCALE LOW NOW
APPROACHING THE SOUTHWESTERN GULF OF ALASKA WILL CONTINUE TO
EVOLVE AS IT MOVES EAST-NORTHEASTWARD THROUGH THE NEXT 36 HOURS.
THE MODELS APPEAR TO BE IN PRETTY GOOD AGREEMENT WITH THE
HANDLING OF THIS SYSTEM AT LEAST IN THE SHORT TERM PORTIONS OF
THE FORECAST.

THE FRONTAL BAND ASSOCIATED WITH THIS SYSTEM WILL BEGIN TO
APPROACH THE OUTER COAST LATE TONIGHT. AS THIS HAPPENS...SNOW
WILL BEGIN TO RE-DEVELOP OVER THE SOUTHERN ZONES...AND QUICKLY
SPREAD NORTHWARD. WATER VAPOR IMAGERY INDICATES THERE IS PLENTY
OF MOISTURE AVAILABLE FOR THIS SYSTEM...SO IT APPEARS THERE WILL
BE SIGNIFICANT SNOWFALL AND RAINFALL.

THE MAIN PROBLEM WITH THIS FORECAST WILL BE THE TIMING OF THE
CHANGEOVER FROM SNOW TO RAIN. THE AREAS MOST LIKELY TO SEE THE
EARLY CHANGEOVER WILL BE THE SOUTHWESTERN ZONES AS THEY WILL BE
THE FIRST TO EXPERIENCE FRONTAL PASSAGE. SNOW AMOUNTS IN THESE
AREAS LOOK AS THOUGH THEY WONT MEET ADVISORY OR WARNING
CRITERIA. THE INTERIOR PARTS OF THE CENTRAL PANHANDLE WILL LIKELY
SEE SUFFICIENT SNOW FOR AT LEAST AN ADVISORY WHILE THE NORTHERN
PANHANDLE AND YAKUTAT WILL MOST LIKELY MAKE WARNING AMOUNTS.

THE CHANGE TO RAIN SHOULD COMMENCE AROUND 12Z AND CONTINUE
THROUGH THE MORNING FROM SOUTH TO NORTH. RAIN WILL BE HEAVY AT
TIMES AND MAY CAUSE SOME URBAN FLOODING AS DRAINAGE AREAS ARE
BLOCKED DUE TO THE LARGE AMOUNTS OF SNOW ON THE GROUND. WILL
LIKELY BE SENDING OUT AN URBAN AND SMALL STREAM FLOOD ADVISORY
FOR THOSE AREAS OF SOUTHEAST ALASKA THAT HAVE AT LEAST A FOOT OF
SNOW STILL ON THE GROUND. AT THIS POINT IN TIME...IT DOES NOT
APPEAR THERE WILL BE MORE THAN NUISANCE FLOODING...BUT THIS
MATTER WILL NEED TO BE MONITORED.

THE FINAL PROBLEM WILL BE THE WIND WITH THIS SYSTEM. THE PRESSURE
GRADIENT WILL BEGIN TO TIGHTEN LATE TODAY AND INTO TONIGHT AS THE
LOW CENTER MOVES INTO THE GULF. EXPECT TO SEE ADVISORY WIND GUSTS
TO DEVELOP MID TO LATE EVENING...MAINLY OVER THE OUTER PORTIONS
OF THE AREA. THE WINDS WILL THEN SPREAD INLAND AND WILL AFFECT
THE ENTIRE PANHANDLE. THE WINDS WILL GRADUALLY DIMINISH THROUGH
THE DAY AND EARLY EVENING AS THE SYSTEM FILLS AS IT MOVES INLAND.

.LONG RANGE...
LONG RANGE MODELS MOVE THE NEXT SYSTEM INTO THE GULF OF ALASKA
THU NIGHT BUT WITH DIFFERENCES IN THE SPEED AND TRAGECTORY. THE
GFS ENSEMBLE MEAN IS SLOWER AND DEEPER THAN THE OPERATIONAL GFS
KEEPING A LOW IN THE NORTHEAST GULF WHILE THE OPERATIONAL GFS
MOVES THE LOW QUICKLY INTO NORTHWEST CANADA BY FRI AFTERNOON.
EXPECT A LEADING LOW WILL MOVE ONSHORE FRI BUT LEAVE A RESIDUAL
LOW IN THE GULF OF ALASKA UNTIL A NEW LOW MOVES INTO THE GULF TO
REPLACE IT OVER THE WEEKEND. THERE IS CONSIDERABLE ENSEMBLE
DIVERGENCE IN THE GULF OF ALASKA OVER THE WEEKEND.

WINDS WILL INCREASE AGAIN WED NIGHT AS THE NEXT LOW MOVES INTO
THE GULF. PRECIPITATION WILL BE PRIMARILY RAIN THROUGH THE WEEK
HOWEVER AS THE LOW APPROACHES THE EASTERN GULF INCREASING OUTFLOW
FROM INTERIOR PASSES WILL LIKELY CHANGE THE RAIN TO SNOW IN THE
NORTHERN PANHANDLE THU NIGHT.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...WINTER STORM WATCH AKZ017>022-024>026 SNOW ADVISORY
AKZ029 WIND ADVISORY AKZ017>029
MARINE...GALE WARNING PKZ021>022-033-036-041>043-051>053 SCA
PKZ011>012-031>032-034>035