Areal Flood Warning 5, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT SUN SEP 16 2012

.ANALYSIS AND UPPER LEVELS...
IMPRESSIVE EXTRA TROPICAL CYCLONE NOW LOOKS TO BE FULLY MATURED OVER
BRISTOL BAY THIS MORNING WITH THE CENTRAL PRESSURE OF THE SURFACE LOW
SITTING AROUND 972 MB. RAIN SHIELD ASSOCIATED WITH THE LOW SPRAWLS
FROM THE KUSKOKWIM DELTA THROUGH THE NORTHEASTERN GULF COAST. WINDS
ASSOCIATED WITH THE LOW HAVE BEEN TRICKIER THAN A NORMAL GULF COAST
RIDGE/TURNAGAIN ARM SETUP. WITH THE SURFACE LOW TRACKING FARTHER WEST
MORE OF A DOWN COOK INLET GRADIENT EXISTS KEEPING THE WINDS OUT OF
MOST OF THE ANCHORAGE BOWL. TURNAGAIN ARM AND HIGHER ELEVATIONS ARE
STILL SEEING WARNING LEVEL WINDS BUT WILL BE DIFFICULT TO VERIFY
GIVEN MCHUGH CREEK...BIRD POINT...AND GLEN ALPS ARE ALL OUT OF
COMMISSION. A 91 MPH GUST REPORT DID COME FORM GLEN ALPS SHORTLY
BEFORE MIDNIGHT AND THE TURNAGAIN ARM WINDS CAN BE INFERRED FROM
GUSTS TO 77 MPH AT PARADISE VALLEY AND GUSTS TO 62 MPH AT PORTAGE
WHERE WINDS ARE GENERALLY NOT AS STRONG AS THE BIRD POINT/BELUGA
POINT REGION. NORTHWESTERLY WINDS ON THE BACKSIDE OF THE SYSTEM ARE
STRONGER THAN INITIALLY PROGGED...ESPECIALLY THROUGH CHANNELED
TERRAIN WITH FALSE PASS NEARING WARNING LEVEL.

.MODEL DISCUSSION...
GUIDANCE IN DECENT AGREEMENT WITH QUICKLY MOVING THE SURFACE LOW
INLAND TODAY AS WELL AS THE OCCLUSION PASSING ANCHORAGE IN THE LATE
MORNING/EARLY AFTERNOON TIME FRAME. FURTHER WEST...SOME SMALL
DISCREPANCIES ARISE WITH A LOW MOVING INTO THE WESTERN ALEUTIANS FROM
KAMCHATKA AND THE EVOLUTION OF A TRIPLE POINT LOW ASSOCIATED WITH THE
SYSTEM AS IT WORKS INTO BRISTOL BAY MONDAY AND TUESDAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...WIDESPREAD RAIN CONTINUES THIS MORNING AS THE
STRONG LOW PRESSURE WRAPS UP. CURRENTLY THIS MORNING THE HIGHEST
WINDS REMAIN CONFINED TO TURNAGAIN ARM AND HIGHER ELEVATIONS BUT WILL
SPREAD TO THE REMAINDER OF THE ANCHORAGE BOWL AS THE FRONT PASSES
LATE THIS MORNING USHERING IN SOUTHEAST WINDS IN THE 30 TO 45 MPH
RANGE. WINDS WILL DIMINISH OVERNIGHT SUNDAY INTO MONDAY. THE STEADY
RAIN WILL CONTINUE TODAY AND BEGIN TO WANE DURING THE OVERNIGHT HOURS
MONDAY INTO TUESDAY. HEAVY PRECIPITATION ALONG THE NORTHERN GULF
COAST HAS PROMPTED FLOOD WARNINGS FOR WESTERN AND SOUTHEASTERN PRINCE
WILLIAM SOUND AS WELL AS FLOOD ADVISORIES FOR NORTHEASTERN PRINCE
WILLIAM SOUND AND ANCHORAGE BOWL.

SOUTHWEST ALASKA...THE WIDESPREAD RAIN ASSOCIATED WITH THE OCCLUSION
IS PUSHING NORTHEASTWARD OVER THE KUSKOKWIM DELTA. A SHOWERY REGIME
BEHIND THE FRONT IS TAKING HOLD ALONG WITH BLUSTERY SOUTHEASTERLY
WINDS. THESE CONDITIONS WILL GENERALLY REMAIN AS THE SURFACE LOW
MOVES TOWARD THE COAST...THOUGH RAIN WILL FILL BACK INTO THE BRISTOL
BAY REGION AS THE UPPER TROUGH/SURFACE LOW PUSH INTO THE INTERIOR
LATER THIS AFTERNOON. ON THE BACKSIDE OF THE SYSTEM GUSTY WESTERLY
WINDS WILL REMAIN AFTER PRECIPITATION TAPERS OFF IN MOST LOCATIONS.

BERING SEA AND ALEUTIANS...AS THE LARGE STORM ENCOMPASSES THE EASTERN
BERING AND BRISTOL BAY STRONG NORTHERLY WINDS FROM THE PRIBILOF
ISLANDS EAST THROUGH THE DAY TODAY...THE NEXT FRONT IS ALREADY
AFFECTING THE WESTERN AND CENTRAL ALEUTIANS. LATE TONIGHT THAT
LOW/FRONTAL BOUNDARY WILL ELONGATE RIGHT OVER THE CHAIN AND SPAWN A
TRIPLE POINT LOW BRINGING A MORE SHOWERY REGIME EARLY THIS WEEK.

.LONG TERM FORECAST...
THE HIGHLY AMPLIFIED WET PATTERN LOOKS TO CONTINUE FOR THE EXTENDED
PERIOD. THE LONGWAVE TROUGH OVER THE BERING IS GOING TO PERSIST
THROUGH THE COMING WEEK INTO NEXT WEEK AS WELL AS THE STOUT
NORTHEASTERN PACIFIC RIDGE KEEPING THE SOUTHERN MAINLAND UNDER A
SOUTHERLY FLOW ALOFT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 101 125 135 181
         FLOOD WARNING 125 135
MARINE...HURRICANE FORCE WIND WARNING 120
         STORM 125 138 140 160 165 170 180
         GALE 121 129 130 132 141 150 155 171 176 179 185
FIRE WEATHER...NONE

MTL SEP 12