Gale Warning 584, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
215 PM AKDT SAT SEP 19 2009

.ANALYSIS AND UPPER LEVELS...LONG-WAVE TROUGH REMAINS CENTERED
OVER THE ALASKA REGION WITH A BLOCKING RIDGE JUST UPSTREAM OVER
EASTERN SIBERIA. AN ANCHOR LOW IS LOCATED OVER THE WESTERN ALASKA
PENINSULA ALTHOUGH A STRONG SHORTWAVE IS UNDERCUTTING THE LOW AND
WILL BECOME THE NEW DOMINANT FEATURE IN THE GULF OF ALASKA THROUGH
THE REMAINDER OF THE WEEKEND. ANOTHER WEAKER SHORTWAVE ROTATING
AROUND THE NORTHWESTERN SIDE OF THE UPPER LOW IS BRINGING RAIN TO THE
ALASKA PENINSULA AND EASTERN ALEUTIANS TODAY. WAY OUT WEST IS THE
REMNANTS OF THE TYPHOON CHOI-WAN...NOW LOCATED SOUTHEAST OF THE
KAMCHATKA PENINSULA. DEEP TROPICAL MOISTURE IS EVIDENT ON WATER VAPOR
IMAGERY SPREADING NORTH AND EAST IN ADVANCE OF THE SYSTEM.

.MODEL DISCUSSION...MAJOR PLAYER IN THE MODEL DISCUSSION IS THE
RAPIDLY DEEPENING LOW SOUTH OF THE AKPEN ASSOCIATED WITH THE
AFOREMENTIONED SHORT WAVE. MODELS SEEM TO HAVE A HANDLE ON THE
STRENGTH AND TIMING OF THE LOW AS IT MOVES INTO THE NORTHERN GULF BUT
NOW ARE DIFFERING ON THE POSITION. THE GFS AND UKMET ARE THE FURTHEST
EAST WHILE THE NAM HAS REMAINED CONSISTENT WITH A MORE WESTERN TRACK
TOWARD THE SOUTHEASTERN KENAI PENINSULA. THE ECMWF IS EXACTLY IN THE
MIDDLE OF THE TWO OTHER SOLUTIONS. A BLEND OF THE INHERITED FORECAST
WITH THE NAM IN THE SHORT TERM YIELDED SOMETHING THAT LOOKS VERY
SIMILAR TO THE ECMWF...WITH THE HIGH RESOLUTION OF THE NAM. AFTER
THAT...MAJOR DIFFERENCES ARISE WITH THE HANDLING OF THE TYPHOON
REMNANTS. AT THIS TIME...FEELING FAIRLY CONFIDENT IN THE TRACK EARLY
NEXT WEEK A FEW HUNDRED MILES SOUTH OF THE ALEUTIAN CHAIN. THE
QUESTIONS WITH THE SYSTEM WILL CERTAINLY BE CONCERNING THE STRENGTH
AS COLD AIR IS ADVECTED INTO THE SYSTEM AND THE LOW BOMBS. AT 60
HOURS...THERE IS NOW A 30 MB DIFFERENCE BETWEEN THE NEW AND OLD RUN
OF THE ECMWF. GIVEN THE EXTREME RUN TO RUN INCONSISTENCY...WILL NOT
TOUCH THE INHERITED FORECAST CONCERNING THE LOW AS IT MOVES SOUTH OF
THE CHAIN EARLY NEXT WEEK.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...FAIR WEATHER DOMINATING SOUTHCENTRAL TODAY
AHEAD OF THE DEVELOPING AND APPROACHING LOW NEAR THE AKPEN. THE FIRST
UPPER SHORTWAVE WILL MOVE OVER THE AREA SUNDAY BRINGING MID AND UPPER
LEVEL CLOUDS. FLOW ALONG THE COASTAL SECTIONS WILL BECOME MORE
SOUTHEASTERLY OVERNIGHT...RETURNING THE MOISTURE BY SUNDAY MORNING
FROM CORDOVA DOWN TO KODIAK. WINDS ALONG THE OCCLUSION WILL REACH
MAXIMUM GALE FORCE LATE TONIGHT. THE NORTHEASTERLY COMPONENT OVER THE
WESTERN GULF WILL USHER THESE WINDS INTO KODIAK CITY...WITH GUSTS IN
EXCESS OF 45 MPH LIKELY. THE TRACK OF THE LOW TOWARD PRINCE WILLIAM
SOUND AND THEN NORTHWESTERLY TOWARD THE EASTERN KENAI WILL KEEP THE
STRONGEST WINDS ALONG THE COAST AND EASTERN TURNAGAIN ARM.

THE FORECAST GETS TRICKY AND INTERESTING MONDAY AND MONDAY NIGHT AS
THE LOW MOVES INLAND AND COLD AIR ALOFT BEGINS TO WRAP AROUND AN
UPPER LOW THAT WILL DROP OUT OF THE CHUKCHI SEA. COLD AIR MOVES
INLAND MONDAY NIGHT...DROPPING FREEZING LEVELS TO 2500 FT OR LOWER
WITH PLENTY OF INSTABILITY AND MOISTURE REMAINING. AT THIS TIME...IT
APPEARS THAT SNOW SHOULD FALL ON THE HIGHER PEAKS AND SNOW SHOWERS
COULD REACH SEA LEVEL TUESDAY MORNING. TEMPERATURES AT THE SURFACE
ARE STILL QUITE WARM SO NO ACCUMULATING SNOW IS EXPECTED BUT MODELS
HAVE BEEN CONSISTENTLY SHOWING THIS COLD AIR INTRUSION...LEADING TO
INCREASED CONFIDENCE THAT TERMINATION DUST IS ON ITS WAY EARLY THIS
NEXT WEEK. STAY TUNED.

SOUTHWEST ALASKA...AREAS OF FOG AND STRATUS ARE STILL BURNING OFF
LATE THIS MORNING AND EARLY AFTERNOON. OTHERWISE...MOSTLY SUNNY SKIES
ARE PREVAILING. COLD AIR WILL BEGIN TRANSITIONING SOUTH ACROSS THE
REGION LATE SUNDAY NIGHT ASSOCIATED WITH THE CHUKCHI SEA LOW. COLD
AIR ADVECTION SNOW SHOWERS AND BREEZY NORTHWEST FLOW WILL PREVAIL
THROUGH TUESDAY WHEN TRANSIENT HIGH PRESSURE BUILDS OVER THE REGION
AHEAD OF THE WARM ADVECTION ASSOCIATED WITH THE TROPICAL REMNANTS.

BERING SEA/ALEUTIANS...BROAD NORTHERLY FLOW AND RELATIVELY TRANQUIL
WEATHER WILL PREVAIL BEFORE STORM FORCE WINDS MOVE ACROSS THE WESTERN
ALEUTIANS MONDAY ASSOCIATED WITH THE TROPICAL REMNANTS. MANY
QUESTIONS STILL REMAIN SURROUNDING THE MID WEEK FORECAST BUT CERTAIN
A STRONG FALL STORM WILL IMPACT THE MAJORITY OF THE BERING SEA DURING
THAT TIME FRAME.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 125 130 132 138 140 150.
FIRE WEATHER...NONE.

AB SEP 09