Frost Advisory 5, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
1200 PM ADT FRI OCT 19 2007

.SYNOPSIS...
.SHORT RANGE...VISIBLE SATELLITE SHOWS TWO WEAK LOW CIRCULATIONS
SPINNING OVER THE NORTHERN GULF THIS MORNING AND WILL CONTINUE TO
BRING CLOUDS AND SCATTERED SHOWERS TO THE NORTHEAST GULF COAST
THROUGH THE AFTERNOON. OTHERWISE...A WEAK HIGH TO THE EAST AND A
LOW TRACKING SOUTH OF THE QUEEN CHARLOTTES HAS ALLOWED ENOUGH
OFFSHORE FLOW TO BRING MAINLY CLEAR SKIES OVER THE PANHANDLE.
AREAS OF FOG OVER THE INNER CHANNELS ARE EVIDENT ON VISIBLE
SATELLITE AND VIA OBS BUT WILL BURN OFF INTO THE EARLY AFTERNOON.
WEAK FLOW OVER THE REGION IS RESULTING IN NO SIGNIFICANT WINDS.

TONIGHT...THE LOW TRACKING SOUTH OF THE QUEEN CHARLOTTES MAY
BRING SOME MID AND HIGH CLOUDS TO THE SOUTHERN THIRD BUT WILL
MOVE OUT OF ZONE 27 AND 28 BY MORNING. THE LOWS OVER THE NORTHERN
GULF WILL CONTINUE TO WEAKEN THROUGH THE NIGHT WITH ISOLATED
SHOWERS DIMINISHING ALONG THE NORTHEAST GULF COAST WITH SOME
BREAKS IN THE CLOUDS DEVELOPING AND AREAS OF FOG POSSIBLE.
OTHERWISE...WEAK OFFSHORE FLOW WILL PERSIST THROUGH MUCH OF THE
NIGHT RESULTING IN MAINLY CLEAR SKIES AND AREAS OF FOG. ONSHORE
FLOW RETURNS TOWARD MORNING ALONG THE CENTRAL COASTAL AREAS AS A
RIDGE BUILDS OVER THE CENTRAL GULF AND A TROUGH HEADS TOWARD THE
NORTHEAST GULF. THIS WILL LIKELY BRING CLOUDS BACK INTO THE
COASTAL AREAS FROM SITKA NORTHWARD.

THE BIGGEST FORECAST PROBLEM FOR TONIGHT WILL BE THE TEMPERATURES
AND FROST/FREEZE POTENTIAL WHERE A HARD FREEZE HAS NOT OCCURRED.
THE POTENTIAL FOR CLOUD COVER OVER THE SOUTHERN THIRD WILL MAKE
THINGS TRICKY. LOOKS LIKE SKIES SHOULD CLEAR OUT IN ZONES 27 AND
28 LATE TONIGHT AS THE LOW CONTINUES EAST AND MAY ALLOW A FEW
HOURS OF RADIATIONAL COOLING TO PRODUCE SOME FROST. ZONE 26 WILL
HAVE MORE TIME TO RADIATE TONIGHT WHERE PETERSBURG MAY REACH
FREEZE CRITERIA WITH WRANGELL AND KAKE COMING CLOSE AS WELL.
FROST ADV POTENTIAL WILL OCCUR IN ZONES 18 19 23 AND 24. FINAL
DECISION WILL BE MADE AFTER EVALUATING 18Z MODEL RUNS.

TOMORROW...A SURFACE AND UPPER TROUGH WILL MOVE INTO THE
NORTHEAST GULF TOMORROW BRINGING CLOUDS AND SHOWERS TO THE
NORTHEAST GULF COAST AND CENTRAL COAST AS FAR SOUTH AS PORT
ALEXANDER. ELSEWHERE...A SOUTHWEST ONSHORE FLOW WILL RETURN EARLY
IN THE MORNING TO THE CENTRAL AND NORTHERN PANHANDLE BRINGING THE
RETURN OF CLOUDS AND ISOLATED SHOWERS. A WEAK RIDGE MOVING INTO
THE SOUTHEAST GULF WILL WEAKEN AWAY IN THE AFTERNOON AND ALLOW
THE CLOUDS TO RETURN TO THE SOUTHERN THIRD IN THE AFTERNOON. FLOW
WILL CONTINUE TO BE WEAK WITH NO SIGNIFICANT WINDS EXPECTED. TAR

.LONG RANGE...THIS MORNING SYNOPTIC SCALE MODEL SOLUTIONS ARE
STILL IN POOR AGREEMENT FOR THE EARLIER PART OF LONG TERM
FORECAST WITH THE POTENTIALLY HAZARDOUS STORM ENTERING THE
CENTRAL OR EASTERN GULF LATE SATURDAY INTO SUNDAY.  HOWEVER...THE
OVERALL MODEL RUN SHOWS A BIT BETTER CONSISTENCY THAN YESTERDAY.
MAJOR DIFFERENCES ARE SHOWN PRIMARILY AT THE LOWER LEVELS BETWEEN
THE GFS/UKMET AND NAM.  BY EARLY NEXT WEEK...MODELS AGREE ON
BUILDING A RIDGE OVER THE AREA FOLLOWED BY ANOTHER PASSAGE OF
TROUGH LEADING TO FURTHER UNCERTAINTY FOR THE LATER PORTIONS OF
THE LONG TERM FORECAST.

MODEL INITIALIZATION IS GOOD SINCE 06Z LAST NIGHT.  YET FOR THE
STORM ENTERING THE EASTERN GULF...STILL HAVE NO PARTICULAR ONE
MODEL IN PREFERENCE.  BY 12Z THIS MORNING...ONE SHIP OBSERVATION
IN THE NORTH PACIFIC SHOWED A HINT OF THE DEVELOPING LOW WEST OF
160W.  THE GFS PICKS THE LOW AS 993 MB WEST OF 160W NEAR 40N
TRACKING NORTHEASTWARD AS IT DEEPENS TO 988 MB BY 06Z TONIGHT.
IT HAS A FAIRLY GOOD CONTINUITY IN INTENSIFYING THE STORM UP TO
SATURDAY AFTERNOON AS IT BECOMES 973 MB AND APPROACHES TO NEAR
50N IN THE CENTRAL GULF BY 00Z.  THEN THE NAM JOINS SOUTH OF THE
GFS POSITION BUT WITH A WEAKER IN STRENGTH...ABOUT 983 MB.
ALTHOUGH MODEL CONSENSUS BETWEEN THE GFS AND UKMET STILL KEEPS
THE STORM WEST OF 140W BY 06Z SUNDAY...IT SEEMS TO MAKE A MORE
FAVORABLE SOLUTION FROM LATE SATURDAY NIGHT INTO EARLY SUNDAY
FORECAST.  THE NAM LOOKS LIKE AN OUTLIER AFTER THIS TIME FRAME.

PREFER TO USE THE GFS AND UKMET GUIDANCES TO EDIT THE INHERITED
GRIDS.  THIS MAY BRING THE LOW CENTER A BIT MORE WEST CLOSER TO
140W WITH A SLIGHTLY SLOWER THAN PREVIOUS FORECAST BUT STRONGER.
BY EARLY SUNDAY MORNING BOTH THE UKMET AND GFS HAVE 967 MB LOW IN
THE CENTRAL GULF JUST WEST OF 140W.  THE GFS GOES TO EVEN
STRONGER AS LOW AS 963 MB BY MIDDAY SUNDAY.  AS FAR AS THIS TIME
OF YEAR IS CONCERNED...THE STRENGTH OF THIS STORM COULD BE EVEN
DEEPER THAN WHAT MODEL CONSENSUS SHOWS.  IN THIS WORST SCENARIO
...SOUTHERLY HURRICANE FORCE WINDS UP TO 64 KTS WOULD BE POSSIBLE
FOR THE OUTSIDE WATERS FROM DIXON ENTRANCE TO CAPE DECISION
SUNDAY MORNING AND STORM FORCE WINDS UP TO 60 KTS POSSIBLE OVER
MOST OF THE OUTSIDE WATERS FROM EARLY SUNDAY MORNING THROUGH LATE
SUNDAY AFTERNOON.  IN ADDITION TO THE STRONG WINDS...LONG PERIOD
SOUTHWEST SWELLS WILL BUILD HIGHER SEAS...GREATER THAN 30 FEET...
OVER THE OUTSIDE WATERS.  MAY NEED TO ISSUE HIGH WIND WARNING FOR
THE COASTAL ZONES FOR SUNDAY AS WELL AS WIND ADVISORY FOR INNER
PASSAGES.  NONETHELESS...THE GFS MAINTAINS THE INTENSITY VERY
MUCH THE SAME THROUGH SUNDAY AFTERNOON AND MOVES TO NEAR
SOUTHWEST OF YAKUTAT...BUT UKMET JUMPS UP TO 973 MB WHILE KEEPING
THE TRACK WEST OF 140W.  THE GFS GUIDANCE MAY MAKE A BETTER STORY
AT THIS POINT.

A WEAK RIDGE OF HIGH PRESSURE WILL REBUILD FROM THE SOUTH OVER
THE SOUTH EASTERN GULF AND BRITISH COLUMBIA LATE MONDAY THROUGH
EARLY TUESDAY.  HOWEVER...A RESIDUAL LOW OVER NORTH CENTRAL GULF
WILL GENERATE A TIGHT PRESSURE GRADIENT ACROSS NORTHERN HALF OF
THE PANHANDLE FOR PERSISTING STRONG SOUTHERLY FLOW.  THE AREA OF
HIGH PRESSURE WILL DRIFT EAST QUICKLY AS THE NEXT LOW ENTERING
INTO THE EASTERN GULF EARLY TUESDAY MORNING.  THIS LOW SEEMS LIKE
TO MOVE DIRECTLY OVER THE CENTRAL PANHANDLE THROUGH TUESDAY
AFTERNOON WITH ANOTHER ROUND OF STRONG NORTHERLY FLOW THROUGH
LATE TUESDAY EVENING.  MODEL OUTPUTS LEAD TO A GREATER
UNCERTAINTY ON THIS SYSTEM BUT WILL LEAN OVER THE GFS GUIDANCE IN
GENERAL THROUGH THE END OF THE LONG TERM FORECAST PERIOD. AHN

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...NONE.
MARINE...SCA DUE TO SEAS PKZ041 PKZ043.