Small Craft Advisory 639, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT SUN SEP 9 2012

.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL AND SURFACE LOW ARE SITUATED OVER THE EASTERN GULF.
SHOWERS AND CLOUDS EAST OF THE CHUGACH/TALKEETNA RANGE THIS MORNING
ASSOCIATED WITH A SHORT WAVE DISTURBANCE MOVING AROUND THE LOW IN THE
GULF. THE GRADIENT COMBINED WITH MODERATE NORTHERLY WINDS ALOFT ARE
CREATING STRONG NORTHWEST/NORTHERLY GAP FLOWS OVER SOUTHCENTRAL. A
RIDGE OVER THE EASTERN BERING/WEST ALASKA COAST COMBINED WITH THE JET
AXIS FROM THE EASTERN BERING ACROSS THE AKPEN STILL CREATING SOME
MODERATE TO STRONG NORTHWEST FLOW AT THE SURFACE ESPECIALLY THROUGH
GAPS AS WELL. ANOTHER UPPER LOW OVER THE WESTERN BERING BEGINNING TO
WRAP UP A LOW PRESSURE SYSTEM. SOME MODERATE SURFACE WINDS AND PRECIP
ACCOMPANYING THIS LOW.

.MODEL DISCUSSION...
MODELS CONTINUE TO BE IN GOOD AGREEMENT THROUGH TUESDAY. ONCE AGAIN
THE NEXT SYSTEM EXPECTED TO COME OUT OF EASTERN RUSSIA
TUESDAY/TUESDAY NIGHT IS THE UNCERTAIN FEATURE.

IN THE FIRST FEW DAYS...THE LOW IN THE GULF TO BECOME MORE OF A BROAD
TROUGH OVER THE EASTERN GULF TONIGHT AND DISSIPATE TOMORROW. IN THE
MEANTIME...THE GRADIENT TO REMAIN SIGNIFICANT THROUGH MUCH OF
TONIGHT. THE LOW IN THE WESTERN BERING WILL DEEPEN A BIT FURTHER AND
MOVE TO THE CENTRAL BERING TOMORROW. THE ASSOCIATED FRONT TO HIT THE
WEST COAST TOMORROW. THE BECOMES A BROAD LOW OVER BRISTOL BAY TUESDAY
AFTERNOON WITH A FRONT MOVING UP THE GULF. A TRIPLE POINT LOW TO
DEVELOP IN THE GULF TUESDAY AFTERNOON/EVENING. THIS WILL INCREASE THE
CHANCES OF A BARRIER JET IN THE EASTERN AND NORTHERN GULF COAST AREAS
INTO WEDNESDAY MORNING. THE UPPER LEVEL SUPPORT LEAVES THE LOW
STRUCTURE OVER BRISTOL BAY AND THE GULF WEDNESDAY. THE LOW IN BRISTOL
BAY WILL DISSIPATE AS THE TRIPLE POINT LOW WEAKENS WEDNESDAY. THE
UPPER LEVELS BECOME AN OPEN WAVE WEDNESDAY EVENING AND THE LOW
WEAKENS FURTHER OVER SOUTHCENTRAL.

THE LOW ENTERING THE WESTERN BERING TUESDAY AFTERNOON IS THE
UNCERTAIN FEATURE. ALL MODELS DIFFER ON THE PHASING OF THE ENERGY
WITH THE LOW. SO...SURFACE DEVELOPMENT IN THE BERING IS IN QUESTION.
WHAT IS NOT IN QUESTION IS THE FACT A LARGE AMPLITUDE TROUGH DEVELOPS
OVER THE BERING LATER THIS WEEK INTO THE WEEKEND WITH A STRONG RIDGE
OVER THE PANHANDLE.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
LOW IN THE EASTERN GULF TO WEAKEN THROUGH THE NIGHT. STILL A DECENT
GRADIENT THROUGH MUCH OF THE NIGHT FOR STRONG WESTERLY/NORTHERLY GAP
FLOWS. FLOW ALOFT TO INCREASE A BIT TONIGHT AND COLD ADVECTION OVER
THE COPPER RIVER BASIN TO MAINTAIN WINDS IN THE PRINCE WILLIAM SOUND
AREA. THIS CONDITION TO WEAKEN LATE TONIGHT INTO TOMORROW MORNING.
AIR MASS CONTINUES TO REMAIN SOMEWHAT UNSTABLE FOR A FEW SHOWERS OVER
THE MOUNTAINS THIS AFTERNOON/EVENING AGAIN. WITH THE NORTHWEST
FLOW...DO NOT EXPECT ANY SHOWERS TO ROLL OVER THE ANCHORAGE BOWL
AGAIN TONIGHT.

ALMOST THE ENTIRE MAT VALLEY AND ANCHORAGE BOWL REACH FREEZING LAST
NIGHT. TONIGHT IS GOING TO BE A BIT COLDER STILL. SO...WE WILL
PROBABLY ISSUE THE FREEZE WARNING AGAIN TONIGHT.

THE FRONT MOVING ACROSS SOUTHWEST ALASKA MONDAY WILL REACH KODIAK BY
MONDAY AFTERNOON. AS THE LOW AND FRONT ROTATE INTO THE GULF
TUESDAY...A BARRIER JET WILL SET UP OVER THE NORTHERN GULF. RAIN WILL
SPREAD TO THE GULF COAST LOCATIONS BY TUESDAY MORNING. SHOWERS WILL
SPREAD OVERNIGHT TUESDAY AS THE FRONT PASSES. THE LOW WILL WEAKEN AND
BROADEN OVER THE AREA WEDNESDAY WITH SHOWERS AND LIGHT WINDS.

SOUTHWEST ALASKA...
JET OVER THE EASTERN BERING STRETCHING OVER THE AKPEN WITH A
WEAKENING PRESSURE GRADIENT. THE WINDS TO DIMINISH OVERNIGHT AS THE
GRADIENT DISAPPEARS. CLOUDS SHOULD REMAIN IN THE AREA AS A FRONT
WORKS TO THE COAST TOMORROW MORNING WITH STRONG WINDS ALONG THE COAST
AND AKPEN. PRECIP SHOULD BE MODERATE WITH THE FRONT AND REMAIN MAINLY
ALONG THE COAST. THE LOW IN THE BERING WRAPS TO BRISTOL BAY TUESDAY
MORNING AS THE FRONT WEAKENS. PRECIP WILL BECOME MORE SHOWERS AND
AFFECT MORE OF THE AREA TUESDAY. WINDS WILL DIMINISH CONSIDERABLY AS
WELL. LIGHT WINDS AND SHOWERS REMAIN THROUGH TUESDAY EVENING AND MUCH
OF WEDNESDAY.

ALEUTIANS/BERING SEA...
A LOW IN THE WESTERN BERING WITH AN ASSOCIATED FRONT IN THE CENTRAL
ALEUTIAN CHAIN. SMALL CRAFT TO MINIMAL GALE FORCE WINDS ASSOCIATED
WITH THE LOW. THE FRONT WILL PUSH TO THE WEST COAST TOMORROW MORNING
WITH SOME JET SUPPORT. GALE FORCE WINDS MAY BE EXPERIENCED ALONG THE
IMMEDIATE COAST. THE LOW WEAKENS AND BECOME MORE BROAD MONDAY NIGHT
INTO TUESDAY WITH SHOWERS REMAINING OVER THE EASTERN BERING. THE NEXT
LOW ENTERS THE WESTERN BERING TUESDAY NIGHT/WEDNESDAY MORNING. THERE
SHOULD BE STRONG WINDS AND A GOOD AREA OF MODERATE PRECIP WITH THIS
FEATURE.

.LONG TERM FORECAST...
THE LOW ENTERING THE WESTERN BERING TUESDAY AFTERNOON IS THE
UNCERTAIN FEATURE. ALL MODELS DIFFER ON THE PHASING OF THE ENERGY
WITH THE LOW. SO...SURFACE DEVELOPMENT IN THE BERING IS IN QUESTION.
WHAT IS NOT IN QUESTION IS THE FACT A LARGE AMPLITUDE TROUGH DEVELOPS
OVER THE BERING LATER THIS WEEK INTO THE WEEKEND WITH A STRONG RIDGE
OVER THE PANHANDLE. THE UNCERTAINTY WILL MEAN NO CERTAIN AREAS OF
STRONG WINDS AND PRECIP. WHAT WE DO KNOW IS A LOW WILL BE IN THE
EASTERN BERING SOMETIME LATE NEXT WEEK WITH WARM EAST AND COLD WEST
OF THE AXIS OF THE TROUGH IN THE EASTERN BERING.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...FREEZE WARNING 101 111
MARINE...GALE 127 170 172 175 180 185
FIRE WEATHER...NONE

JN SEP 12