Gale Warning 140, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
630 AM ADT WED APR 16 2008

.SYNOPSIS...

.SHORT RANGE...LATEST SATELLITE IMAGERY SHOWS A COMPLEX DUAL
CIRCULATION LOW IN THE NORTHERN GULF/SOUTHERN YUKON THIS MORNING.
THIS SYSTEM IS SLOWLY PUSHING EASTWARD WITH ONE LOW CENTER NEAR
CAPE SUCKLING AND A SECOND NEAR CARMACKS, YT.  A QUASI-STATIONARY
WARM FRONT IN USHERING STRONG SOUTHWESTERLY FLOW ACROSS THE
EASTERN GULF AND PANHANDLE.  A TIGHT PRESSURE GRADIENT IS
ESPECIALLY EVIDENT IN THE LYNN CANAL AREA WHERE ADVISORY LEVEL
WINDS GUSTS ARE OCCURRING IN HAINES AND SKAGWAY.

AS THE PAIR OF LOWS SLOWLY PUSH EASTWARD AND
WEAKEN...UNSEASONABLE COLD AIR IS EXPECTED TO FILTER IN BEHIND
THE LOW.  THE MAIN FORECAST CONCERN FOR THE SHORT RANGE INVOLVES
THE TIMING OF THIS COLD AIR ADVECTION AND HOW QUICKLY THE LOW
WEAKENS AND SINKS SOUTHWARD ALONG THE PANHANDLE. MODELS WEAKEN
THE LOW TO A TROUGH THROUGH WITH AN AXIS ACROSS THE NORTHERN
PANHANDLE THIS AFTERNOON...THEN START SINKING THE TROUGH
SOUTHWARD OVERNIGHT TONIGHT. HAVE OPTED TO FOLLOW THE 00Z UKMET
FOR THE PACKAGE DUE TO ITS GOOD INTIALIZATION. THE CURRENT
THINKING THAT A RESIDUAL LOW WILL REMAIN IN THE NORTHEASTERN GULF
THROUGH TONIGHT...WHICH THE UKMET HANDLES BETTER THAN THE OTHER
MODELS.

ONCE THE LOW BEGINS TO SINK SOUTHWARD...EXPECT A STRONG NORTHERLY
FLOW RESPONSE IN ITS WAKE.  AS A RESULT...TEMPERATURES WILL
QUICKLY PLUMMET IN THE NORTHERN HALF BEGINNING THIS AFTERNOON AND
CONTINUING TONIGHT.  ADDITIONALLY...THIS SHOULD RESULT IN A
DRYING TREND ACROSS THE NORTH WHICH WILL BE A BIG LIMITING FACTOR
IN PRODUCING SIGNIFICANT SNOWFALL. THE CAVEAT WILL BE WHETHER
THIS COLD ADVECTS QUICKER THAN THE MODELS PREDICT AND BEFORE THE
MOISTURE POOL DRIES UP.  AT BEST HAVE MENTION OF UP TO 2 INCHES
OF SNOWFALL FOR THIS EVENT.

.LONG RANGE...THE TRANSITION TO DRIER CONDITIONS WILL ALREADY
BE UNDERWAY IN THE NRN HALF OF THE PNHDL THU.  THE DRYG WILL
CONT TO SPREAD SE ALONG THE PNHDL AND REACH THE REMAINDER BY
ABT 06Z FRI.  THE MODEL CONSENSUS FOR THE MSLP FIELD IS SMALL
ENOUGH TO CLAIM GOOD CONFIDENCE IN THE TREND FOR THE LOW POPS
AND LACK OF SKY COVER FOR LATE THIS WEEK.  NOTE THE USE OF
SUNNY IN ALL ZONES FOR FRI.  THE ONLY EXCEPTION IS THAT
SOME MORNING FOG SHOULD OCCUR IN WIND SHELTERED LOCATIONS
IN THE SRN HLF, WITH PETERSBURG BEING AN OBSERVATION POINT
THAT TENDS TO VERIFY BEST FOR SUCH EVENTS. SEE ZONE 26.

THE LONG WAVE RIDGE THAT IS THE PRIMARY FEATURE FOR THE DRYING,
AS WELL AS THE LOSS OF CLOUD COVER FOR THE WHOLE DEPTH OF THE
TROPOSPHERE, IS STILL A LOW AMPLITUDE FEATURE IN THE BERING
AND ADJACENT NPAC.  THIS RIDGE ALF WILL DRIFT E AND GAIN
AMPLITUDE THROUGH FRI.  THE GREATEST AMPLITUDE SHOULD BE AT
00Z SAT WHEN IT EXTENDS N FM THE NPAC OVR KODIAK AND BYD BARROW.
THIS RIDGE ALF IS ALSO THE PARENT FEATURE FOR A 1040 MB
HIGH IN CENTRAL YUKON TRRTY LATE THIS WEEK.

MODEL SOLN DOES SPREAD OUT FOR THE RATE THE RIDGE ALF DRIFTS
TOWARD THE PNHDL, BUT THE LONG RANGE PKG LOOKS DRY FOR THE
ENTIRE FCST DOMAIN EARLY NEXT WEEK.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...WIND ADVSRY - 18 AND 19 THRU 6 PM TODAY

MARINE...GALE - 310-52
         SMCR - ELSEWHERE

KJH JT