Areal Flood Warning 8, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT TUE SEP 17 2012

.ANALYSIS AND UPPER LEVELS...AN IMPRESSIVE UPPER LEVEL TROUGH
ENCOMPASSES THE BERING AND DIGS INTO THE NORTH PACIFIC. TO THE
EAST...A RIDGE STRETCHES ACROSS THE GULF OF ALASKA AND INTO WESTERN
CANADA. AS THESE FEATURES CONTINUE TO AMPLIFY...THE UPPER LEVEL JET
BETWEEN THESE TWO FEATURES WILL INTENSIFY AND HELP TO STREAM TROPICAL
MOISTURE NORTHWARD. A SURFACE LOW WILL DEVELOP BENEATH THE JET THIS
EVENING AND MOVE ONSHORE NEAR KODIAK ISLAND TOMORROW MORNING.  THIS
LOW AND ITS ASSOCIATED JET WILL HELP TO INCREASE THE SURFACE ONSHORE
FLOW AND SUPPORT WIDESPREAD RAIN...AND ALSO HELP TO INCREASE PRESSURE
GRADIENTS AND GAP FLOWS ACROSS THE SOUTHCENTRAL REGION TOMORROW.

.MODEL DISCUSSION...MODELS ARE BEGINNING TO CONVERGE ON THE LOCATION
AND INTENSITY OF A LOW THAT WILL APPROACH SOUTHERN KODIAK ISLAND
WEDNESDAY MORNING. HOWEVER...THE DISAGREEMENT IN CURRENT MODELS IS
ENOUGH THAT THERE IS STILL UNCERTAINTY IN THE TIMING AND INTENSITY OF
GAP WIND FLOW ACROSS THE SOUTHCENTRAL REGION. THE GFS AND ECMWF ARE
IN DECENT AGREEMENT SO A BLEND OF THESE MODELS WAS USED.

.SHORT TERM FORECAST...
.SOUTHCENTRAL ALASKA...A FRONT LINGERING ALONG THE GULF COAST HAS
SUPPORTED STEADY RAIN ACROSS MUCH OF THE REGION TODAY AND GUSTY WINDS
ALONG TURNAGAIN ARM AND HIGHER ELEVATIONS. THESE WINDS ARE EXPECTED
TO BRIEFLY DIMINISH BUT WILL INCREASE IN INTENSITY BY TOMORROW
MORNING AS A LOW PROGRESSES INLAND NEAR KODIAK ISLAND. THERE IS STILL
SOME UNCERTAINTY...BUT MODELS CURRENTLY INDICATE THE PEAK OF THIS
EVENT WILL BE MID MORNING TO EARLY AFTERNOON. THE STRONGEST WINDS
WILL REMAIN ALONG TURNAGAIN ARM AND HIGHER ELEVATIONS...HOWEVER...A
FEW GUSTS MAY REACH THE SOUTH SIDE OF TOWN TOMORROW AFTERNOON INTO
EVENING.

DUE TO THE COPIOUS AMOUNTS OF MOISTURE BEING TRANSPORTED FROM THE
TROPICS TONIGHT INTO TOMORROW...EXPECT HEAVY RAIN TO IMPACT MUCH OF
THE REGION. SINCE SOILS ARE ALREADY SATURATED AND SEVERAL STREAMS ARE
NEAR BANKFULL...LOCAL FLOODING IS POSSIBLE ACROSS THE SOUTHCENTRAL
REGION.

.SOUTHWEST ALASKA...A LOW PRESSURE SYSTEM WILL DEVELOP IN THE NORTH
PACIFIC THIS EVENING AND MOVE INLAND NEAR THE SOUTHERN EDGE OF KODIAK
ISLAND. AS A RESULT...GUSTY WINDS AND RAIN WILL IMPACT THE ALASKA
PENINSULA THIS EVENING AND THEN SPREAD INLAND INTO THE BRISTOL BAY
AND KUSKOKWIM VALLEY REGIONS WEDNESDAY.

.ALEUTIANS/BERING SEA...
GENERALLY WEAK DISTURBANCES ARE IMPACTING THE BERING AND ALEUTIAN
ISLANDS TODAY. AS A RESULT...WINDS HAVE BEEN RATHER LIGHT ACROSS THE
REGION WITH ONLY OCCASIONAL SHOWERS. A MORE WELL DEVELOPED LOW WILL
IMPACT THE WESTERN AND CENTRAL ALEUTIANS BRIEFLY WEDNESDAY AFTERNOON
AND EVENING BEFORE IT DIVES SOUTH.

.LONG TERM FORECAST...
AN ACTIVE AMPLIFIED PATTERN WILL CONTINUE ACROSS THE REGION OVER THE
NEXT WEEK. A STRONG UPPER LEVEL TROUGH WILL DOMINATE THE BERING AND
SUPPORT A SERIES OF LOW PRESSURE SYSTEMS ACROSS THE BERING AND GULF
COAST. HOWEVER...MODELS ARE BEGINNING TO INDICATE A PATTERN CHANGE BY
THE EARLY NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING...101
         FLOOD WARNING...135
         FLOOD WATCH...125 131 145
MARINE...STORM...120 125
         GALE...129 130 132 140 141 150 172 175 176
FIRE WEATHER...NONE

ELN SEP 12