Gale Warning 174, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
1100 AM ADT SAT APR 14 2007

.SYNOPSIS...
.SHORT RANGE...TWO WEAK SURFACE LOW CIRCULATIONS...ONE NEAR THE
QUEEN CHARLOTTES AND ONE OVER THE NORTHWEST GULF...WILL WEAKEN
INTO A TROUGH TODAY. THIS SURFACE TROUGH AND AN UPPER LEVEL
TROUGH WILL THEN MOVE ACROSS THE PANHANDLE THROUGH EARLY TONIGHT
KEEPING SKIES MOSTLY CLOUDY WITH SCATTERED TO LIKELY POPS FOR
RAIN SHOWERS. SOUTH TO SOUTHEAST WINDS WILL STILL REMAIN LIGHT
AND BELOW SMALL CRAFT THROUGH EARLY TONIGHT.

A VERY DEEP LOW PRESSURE SYSTEM IN THE 960S CENTERED NEAR 49N
168W AT 18Z WILL WEAKEN INTO THE 980S THROUGH SUN AFTERNOON AS IT
MOVES EAST ALONG 49N TO 150W. THE GFS AND UKMET ARE INITIALIZING
THE BEST WITH THIS SYSTEM THIS MORNING AND WILL BE USED IN THE
GRIDS. THE MAIN FEATURES FROM THIS SYSTEM THAT WILL AFFECT THE
FORECAST AREA WILL BE A SECONDARY LOW THAT DEVELOPS ALONG THE
FRONT OVER THE NORTHWEST GULF TONIGHT AND DEEPENS INTO THE MID
980S ON SUN. THE OCCLUDED FRONT WILL MOVE INTO THE EASTERN GULF
SUN MORNING...THEN ACROSS THE PANHANDLE THROUGH EARLY SUN
EVENING.

PRECIPITATION FROM THE FRONT WILL SPREAD INTO THE PANHANDLE EARLY
SUN...THEN CHANGE TO SHOWERS BEHIND IT FROM WEST TO EAST LATE
AFTERNOON INTO EARLY SUN EVENING. RELATIVELY WARMER AIR IN PLACE
WITH MORE WARM AIR SPREADING NORTH AHEAD OF THE FRONT WILL
ALLOW THE PRECIP TO BE MAINLY RAIN OVER MOST OF THE PANHANDLE.
THE TRICKIEST AREA WILL BE ZONES 18 AND 19 OVER THE NORTHEAST
PANHANDLE. SLIGHTLY COOLER AIR GETS PULLED IN SUN MORNING AND MAY
ALLOW THE PRECIP TO START OUT AS SNOW OVER THE HIGHER ELEVATIONS
AND BRIEFLY MIX WITH SNOW AT SEA LEVEL. BELIEVE THE AIRMASS WILL
WARM UP QUICK ENOUGH WITH AN EAST TO SOUTHEAST FLOW IN ZONE 18 TO
CHANGE ALL AREAS TO RAIN INTO THE AFTERNOON WHEN THE HEAVIEST
PRECIP ARRIVES. SNOW LEVEL SHOULD RISE TO AROUND 2000 FT OVER THE
KLONDIKE HIGHWAY THROUGH THE AFTERNOON WITH ELEVATIONS ABOVE
CONTINUING TO SNOW THROUGHOUT THE DAY. QPF AMOUNTS IN THAT REGION
SUPPORT SNOW TOTALS BELOW ADVISORY CRITERIA BUT WILL WAIT FOR THE
18Z RUN TO MAKE A FINAL DECISION ON WHETHER A SNOW ADVISORY WILL
BE NEEDED FOR THE HIGHER ELEVATIONS.

WINDS AHEAD OF THIS SYSTEM WILL INCREASE TO GALES OVER THE
OUTSIDE WATERS...STORMS IN PKZ052...FOR SUN MORNING THEN DROP TO
15 TO 25 KT BEHIND THE FRONT IN THE AFTERNOON. SMALL CRAFTS WILL
DEVELOP ON THE INSIDE WATERS WITH GALES POSSIBLE IN CROSS
SOUND...SOUTHERN CHATHAM...SUMNER...AND CLARENCE. LYNN CANAL WILL
REMAIN BELOW SMALL CRAFT. WIND ADVISORY GUSTS AHEAD OF THE FRONT
ARE HIGHLY LIKELY OVER ZONES 23 27 28 AND 29 OVER THE SOUTHWEST
PANHANDLE...SO WILL ISSUE ADVISORIES FOR THEM WITH THE 4 PM
PACKAGE. WIND ADVISORY GUSTS ARE POSSIBLE IN 26...MAINLY IN
WRANGELL...BUT WILL REVIEW 18Z RUN BEFORE DECIDING ON THAT.

.LONG RANGE...GOOD AGREEMENT BETWEEN ENSEMBLE MEAN AND
OPERATIONAL GFS AT 500 MB THROUGH 17/18Z. OPERATIONAL RUN THEN
GOES WITH A DEEPER SOLUTION FOR THE NEXT UPPER LEVEL SYSTEM
UPSTREAM FROM THE AJK CWA...A CLOSED LOW OVER EXTREME EASTERN
SIBERIA AND A TROUGH EXTENDING SOUTH THROUGH THE CENTRAL
ALEUTIANS. OPERATIONAL GFS STAMPS A LOW IN THE BASE OF THIS
TROUGH AS EARLY AS 17/12Z AND CARRIES THIS FORWARD TO 19/18Z
BEFORE COMING MORE INTO LINE WITH THE ENSEMBLE MEAN. A SIMILAR
DISPARITY OCCURS OVER THE SAME LOCATION ON 20/12Z WHICH GETS
CARRIED INTO OUR CWA. UKMET AND GFS IN GOOD AGREEMENT ON TIMING
AND LOCATION OF UPPER LEVEL FEATURES. NAM IS RUNNING FASTER AND
DEEPER WITH THE UPPER LEVEL TROUGH/LOW ENTERING THE WESTERN GULF
ON 18 APRIL.

AT THE SURFACE...DIFFERENCES BETWEEN GFS AND UKMET ARE LESS
PRONOUNCED THAT IN THE PREVIOUS MODEL RUN. UKMET IS STILL DEEPER
AND FASTER THAN GFS THROUGH 19/12Z. CP DIFFERENCES BEYOND THAT
POINT DIMINISH GREATLY. HOWEVER...THE UKMET POSITION OVER THE
CENTRAL GULF AS OPPOSED TO THE GFS LOCATION JUST SE OF KODIAK HAS
LARGER IMPLICATIONS ON THE PRESSURE GRADIENT AND FRONTAL LOCATION
OVER THE PANHANDLE. BIGGEST DIFFERENCE BETWEEN MODELS AFTER THIS
TAU IS WHERE THE LOW WILL GO. THE 14/00Z RUN OF BOTH ECMWF AND
GFS190 MOVE THIS LOW FROM NEAR KODIAK TO WEST OF THE WASHINGTON
COASTLINE BETWEEN 13/00Z AND 14/00Z. DURING THIS SAME
TIME...UKMET TRACKS THE SYSTEM TO THE NORTHEAST GULF WHILE THE
14/12Z GFS40 DRIFTS IT NW BACK TOWARDS KODIAK. THERE IS GOOD
CONSISTENCY FROM RUN TO RUN IN GFS40 AND THE AGREEMENT BETWEEN
GFS40 AND UKMET OVER THE DISPOSITION OF THE LOW IN THE NORTHERN
GULF THROUGH 20/00Z. ALSO BELIEVE PREVIOUS FORECAST THOUGHTS ON
BAROCLINIC WAVES SLOWING WHOLE SYSTEM DOWN TO BE WELL FOUNDED.
WILL THEREFORE USE GFS40 AS PRIMARY GUIDANCE FOR TODAY.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...NONE

MARINE...SCA 22 36 41-43 51-52
TAR/FCF