Small Craft Advisory 871, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
530 AM AKDT WED OCT 28 2009

.MODEL DISCUSSION...
ALL MODELS CONTINUE TO STRUGGLE WITH THE EVOLUTION OF TROPICAL
SYSTEMS INTO OUR AREA. ALL MODELS SEEMED TO INITIALIZE PRETTY WELL IN
THE UPPER LEVELS BUT HAVE SOME DISCREPANCIES AT THE SURFACE...AND THE
TRUE SURFACE CIRCULATIONS ARE IMPOSSIBLE TO PICK UP WITH MINIMAL
GROUND TRUTH OBSERVATIONS OVER THE OCEAN AND BECAUSE THE CIRCULATIONS
ARE UNDER AN EXTENSIVE CLOUD SHIELD. THESE PROBLEMS AT THE SURFACE
QUICKLY EVOLVE INTO LARGER ISSUES BEYOND BY THURSDAY AS A LARGE LOW
SLAMS INTO SOUTHEAST. THE ECMWF HAS BEEN SURPRISINGLY STABLE OVER THE
LAST TWO RUNS...WHILE THE GFS HAS SLOWED THE STORM DOWN AND WEAKENED
IT. THE ENSEMBLE SPREAD IN THE GFS IS RATHER LARGE EVEN BY TOMORROW
NIGHT. WITH THE PROBLEMS OF THE GLOBAL MODELS OVER OUR AREA
TONIGHT...THE FORECAST REMAINED MOSTLY UNCHANGED AT THE SYNOPTIC
LEVEL WITH ONLY LOCAL ADJUSTMENTS.

.ANALYSIS AND UPPER LEVELS...
SATELLITE DERIVED PERCENT OF NORMAL PRECIPITABLE WATER SHOWS THAT THE
LARGE LOW PRESSURE COMPLEX IN THE NORTH PACIFIC IS PACKING AN
ENORMOUS AMOUNT OF WATER...OVER 200 PERCENT ABOVE NORMAL. THE
SAME CAN BE SAID FOR THE REMNANTS OF LUPIT OUT WEST AS IT MOVES INTO
THE WESTERN BERING. AN UPPER LEVEL TROUGH STRETCHES ALONG THE ALASKA
RANGE. AN UPPER LEVEL RIDGE OVER THE CENTRAL BERING/ALEUTIANS IS
SLOWLY MOVING EAST. AN UPPER LEVEL JET IS DRAPED ACROSS THE GULF AND
WILL HELP TO PUSH THE LOW COMPLEX TOWARDS PORT ALEXANDER.

.SHORT TERM FORECAST...
OUT EAST...LARGE SNOWFLAKES FELL ACROSS THE ANCHORAGE BOWL LAST
NIGHT. ALL OF THE SNOW TENDED TO MELT ON CONTACT WITH THE GROUND AT
THE LOWER ELEVATIONS WHILE STICKING AT HIGHER ELEVATIONS. THE ON AND
OFF SNOW SHOWERS WILL OCCASIONALLY BE MIXED WITH RAIN
TODAY...ESPECIALLY AS THE TEMPERATURES SLOWLY RISE INTO THE AFTERNOON
BUT WILL CUT OFF LATER TODAY AS THE OVERRUNNING PROCESSES BEGIN TO
SHUT OFF AND THE FLOW THROUGH H50 MOVES TO THAT OF MORE OF A
NORTHEASTERLY COMPONENT. ALONG THE GULF COAST AND THROUGHOUT PRINCE
WILLIAM SOUND...WINDS ARE EXPECTED TO PICK UP BEYOND 45 MPH LATER
TONIGHT AND LAST THROUGH THE END OF THE WEEK. THIS IS IN RESPONSE TO
A STRONG PRESSURE GRADIENT FORMED BETWEEN HIGH PRESSURE THAT IS
BUILDING IN THE INTERIOR AND A STRONG AREA OF LOW PRESSURE MOVING
THROUGH THE GULF AND INTO SOUTHEAST. TEMPERATURES WILL CONTINUE TO
TREND DOWN...AND TOWARDS THE END OF THE WEEK WHEN THE SKIES CLEAR
OUT...RADIATIONAL COOLING COULD ALLOW FOR SOME RATHER COOL
NIGHTS...THAT HAVE NOT BEEN SEEN IN THE AREA SINCE MARCH.

OUT WEST...A LARGE RIDGE OVER THE BERING WILL CONTINUE TO BLOCK THE
PROGRESSION OF STORMS FROM THE WEST THROUGH THE WEEKEND. ANY STORM
THAT ADVANCES FROM THE WESTERN PACIFIC WILL SLAM AGAINST THE RIDGE
AND SLIDE NORTH BEFORE WEAKENING. STORM FORCE WINDS ARE PRESENTLY
BEING SEEN ACROSS THE FAR WESTERN CHAIN AND WILL ULTIMATELY CONTINUE
THROUGH THE NEXT DAY AS THE REMNANTS OF LUPIT MOVE CLOSER TO THE
CHAIN AND IT CONTINUES TO WEAKEN. RAIN WILL GENERALLY BE SEEN FROM
DUTCH WEST IN RESPONSE TO THESE SYSTEMS. AREAS IN AND AROUND DUTCH
THROUGH THE AKPEN ARE FEELING THE EFFECTS OF THE RIDGE OVERHEAD...
THAT BEING LIGHT WINDS AND THE TYPICAL MARINE STRATUS / FOG LAYER. ON
THE MAINLAND...LIGHT OFFSHORE FLOW IS GENERALLY KEEPING THE FOG AND
LOW CLOUDS AWAY...WITH THE EXCEPTION OF THE KUSKOKWIM DELTA. THE ONLY
SNOW SHOWERS EXPECTED ON THE MAINLAND ARE ALSO IN THE KUSKOKWIM DELTA
WITH A WEAK SHORTWAVE DIVING OVER THE RIDGE TO THE WEST. WEAK ECHOES
ARE NOTED ON RADAR THIS MORNING ALONG SOME OF THE ROLLING HILLS TO
THE NORTH. ACTIVITY SHOULD REMAIN MINIMAL AND ONLY THROUGH THE EARLY
AFTERNOON.

.LONG TERM FORECAST...
VARIABILITY AND INCONSISTENCY CONTINUES TO PLAGUE THE LONG RANGE
FORECAST. THE OVERNIGHT PACKAGE KEPT THE PICTURE STATUS QUO WITH THAT
OF THE FORECAST FROM LAST NIGHT. OUT EAST THE RIDGE SHIFTS ACROSS THE
ALASKA RANGE AND ANOTHER LOW PRESSURE SYSTEM WILL WORK INTO THE
EASTERN GULF. OUT WEST ANOTHER LOW COMPLEX WILL WORK IN BEHIND THE
THE RIDGE AS IT MOVES EAST. AS THE LONG RANGE GETS CLOSER TO THE
SHORT TERM...BETTER MODEL CONSENSUS WILL AID IN IRONING OUT ALL OF
THE DETAILS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM...175 176 411
          GALE...121 185 352 412 413
FIRE WEATHER...NONE

SHEA OCT 09