Small Craft Advisory 837, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
536 AM AKDT SAT OCT 24 2015

.ANALYSIS AND UPPER LEVELS...

MAINLAND ALASKA...CURRENTLY A BROAD LOW PRESSURE SYSTEM IS CENTERED
OVER THE EASTERN BERING. EXTENDING FROM THE LOW IS A FRONT
PUSHING NORTHWARD THROUGH THE GULF COLLOCATED WITH A NEGATIVELY-
TILTED UPPER LEVEL SHORTWAVE TROUGH. AHEAD OF THIS FRONT...STRONG
SOUTHERLY FLOW OVER THE GULF IS BRINGING MOISTURE INTO MUCH OF THE
NORTHERN GULF COAST. THE MOISTURE IS BEING UPLIFTED INTO THE KENAI
AND CHUGACH MOUNTAINS BY THE STRONG WINDS. THE FRONT MARKS THE
BACK EDGE OF THE MOISTURE PLUME AS DRIER AIR MOVES IN BEHIND THE
FRONT ON SOUTHWESTERLY WINDS. IN A COMMON PATTERN FOR THE COOK
INLET REGION...THE SOUTHEASTERLY FLOW IS DOWNSLOPING OFF THE LEE
SIDE OF THE CHUGACH AND KENAI MOUNTAINS...CREATING AN AREA WITH NO
PRECIPITATION FROM THE ANCHORAGE BOWL SOUTH ALONG MUCH OF THE
WESTERN KENAI PENINSULA. THE DOWNSLOPING IS WARMING AND DRYING THE
LOWEST LEVELS OF THE ATMOSPHERE. WHERE UPSLOPING RESUMES AGAIN ON
THE EASTERN SLOPES OF THE ALASKA RANGE...THE REFLECTIVITY VALUES
SHOWN ON THE KENAI RADAR PICK RIGHT BACK UP AGAIN. THE 00Z
ANCHORAGE SOUNDING ALSO SHOWS THE EFFECTS OF THE
DOWNSLOPING...WITH A STOUT INVERSION EVIDENT FROM RIGHT OFF THE
SURFACE. WIDESPREAD SCATTERED SHOWER ACTIVITY CLOSER TO THE LOW
PRESSURE CENTER OVER SOUTHWEST ALASKA CONTINUES THIS
MORNING...THOUGH RAINFALL AMOUNTS HAVE BEEN LIGHT.

BERING SEA... THE BROAD SURFACE LOW OVER THE EASTERN BERING LIES
EAST OF AN UPPER LEVEL LOW OVER THE CENTRAL BERING. OVER THE
CENTRAL ALEUTIANS...A SHORTWAVE EXTENDING SOUTH FROM THE UPPER
LEVEL LOW IS MOVING EAST. THE SHORTWAVE IS BUCKLING THE JET. AS IT
PROGRESSES EAST IT WILL BECOME INCREASINGLY ENERGIZED AND
NEGATIVELY-TILTED AS IT TAPS COLDER AIR OVER THE BERING. THIS WILL
RESULT IN RAPID CYCLOGENESIS SOUTH OF THE EASTERN ALEUTIANS GOING
INTO TONIGHT.

&&

.MODEL DISCUSSION...

THE NUMERICAL MODELS CONTINUE TO DEPICT A SIMILAR SYNOPTIC PATTERN
THROUGH MONDAY OF NEXT WEEK...BUT ALSO CONTINUE TO STRUGGLE WITH
THE DEVELOPMENT OF TWO STRONG LOWS...THE FIRST ACROSS THE NORTH
PACIFIC SOUTH OF THE ALASKA PENINSULA...THE OTHER BEING THE
LEFTOVER REMNANTS OF FORMER TYPHOON CHAMPI OVER THE WESTERN
BERING. THE FIRST SYSTEM IN THE NORTH PACIFIC WILL ONLY BE A
GLANCING BLOW TO PARTS OF THE EASTERN ALEUTIANS AND WESTERN ALASKA
PENINSULA...AS WELL AS THE ASSOCIATED COASTAL MARINE WATERS. THE
GFS AND NAM ARE MORE AGGRESSIVE DEVELOPING THIS STRONG STORM FORCE
LOW FARTHER NORTH...BRINGING IN STRONGER GALE TO STORM FORCE WINDS
TO THOSE AREAS. THE ECMWF AND CANADIAN REGIONAL AND GLOBAL MODELS
ARE FARTHER SOUTH. FOR NOW...A MORE NORTHERN SOLUTION WAS FAVORED
GIVEN BOTH THE LATEST MODEL TRENDS AND CURRENT SATELLITE
DATA...WHICH IS HINTING AT THE NORTHERN LOW ALONG THE POLAR JET
BEING MORE DOMINANT. THIS BRINGS STORM FORCE WINDS INTO SOME OF
THE COASTAL WATERS...AND STRONG NORTHERLY WINDS ACROSS PORTIONS OF
THE EASTERN ALEUTIANS AND EASTERLY WINDS OVER THE WESTERN ALASKA
PENINSULA. OVER THE BERING WITH THE REMNANTS OF CHAMPI...THE SREF
AND ECMWF WERE FAVORED...WHICH SUPPORTS A STORM FORCE REMNANT LOW
OVER THE FAR WESTERN BERING AND ALEUTIANS AS CHAMPI RECURVES
NORTHWARD SUNDAY NIGHT INTO EARLY MONDAY. OVER SOUTHCENTRAL...THE
NAM AND CANADIAN REGIONAL WERE FAVORED DUE TO THEIR DEPICTION OF
DOWNSLOPE PRECIPITATION PATTERNS ACROSS INTERIOR LOCATIONS.
FORECAST CONFIDENCE IS MODERATELY HIGH.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

A STRONG FRONT OVER THE NORTHERN GULF MOVES ONSHORE THIS AFTERNOON
AND WEAKENS OVER THE INTERIOR TONIGHT. WIDESPREAD GALES ARE
EXPECTED ALONG THE FRONTAL BOUNDARY WITH A BRIEF PERIOD OF STORMS
ALONG THE NORTH GULF COAST THIS MORNING. STRONG GAP FLOWS ACROSS
TURNAGAIN ARM/PORTAGE VALLEY WILL DIMINISH THIS AFTERNOON WITH
FRONTAL PASSAGE. BRISK SOUTHERLY WINDS ARE EXPECTED ACROSS THE
COPPER RIVER BASIN THIS AFTERNOON INTO THE EVENING HOURS. BRISK
EAST TO NORTHEAST WINDS OVER THE MATANUSKA VALLEY WILL DIMINISH
THIS EVENING. WINDS ACROSS THE SOUTH CENTRAL MAINLAND WILL BECOME
RELATIVELY LIGHT OVERNIGHT AND REMAIN SO THROUGH SUN. RAIN
ASSOCIATED WITH THE FRONT WILL GIVE WAY TO SHOWERS OVERNIGHT WITH
DRYING ON SUN UNDER INCREASING ANTICYCLONIC FLOW ALOFT. THE COAST
THOUGH ON SUN MAY SEE A FEW LINGERING SHOWERS.

ANOTHER FRONT MOVING NORTH INTO THE SOUTHERN GULF SUN NIGHT WILL
BRING ANOTHER ROUND OF RAIN AND WINDS TO THE SOUTHERN GULF AND
KODIAK ISLAND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...SAT AND
SUN)...

THE FRONT HAS MOVED INLAND FROM SOUTHWEST ALASKA WITH
MINIMAL IMPACTS AND LITTLE IF ANY SNOW MIXING IN WITH THE RAIN.
NOW WE WILL WATCH A WEAK LOW SPINNING THROUGH THE EASTERN BERING
TODAY CONTINUE TO PUSH RAIN SHOWERS ONSHORE AND BRINGING SOME
GUSTY WINDS TO THE BRISTOL BAY COAST. THIS LOW WILL TRACK NORTH
ALONG THE COAST THROUGH THE DAY. THEN ALL OF THE ENERGY IN THE
AREA WILL GO INTO A RAPIDLY DEEPENING LOW 350 NM SOUTH OF COLD BAY
BY SUNDAY MORNING. THIS WILL RESULT IN SOME RIDGING STARTING TO
BUILD OVER THE MAINLAND AND CONTINUED WARM SOUTHEAST FLOW. WHILE
THE RIDGE WILL BRING SOME DRYING WITH IT...IT SHOULD ALSO LEAD TO
FAIRLY WIDESPREAD FOG SUNDAY MORNING...SOME OF WHICH COULD BE
DENSE IN SPOTS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...SAT AND
SUN)...

THIS IS WHERE THE FOCUS WILL BE OVER THE NEXT 24-48 HRS AS
TWO FAIRLY STRONG LOWS WILL TAKE SHAPE. THE FIRST WILL BE A
DEEPENING SYSTEM IN THE NORTH PACIFIC. SUBTROPICAL MOISTURE PUSHING
NORTH-NORTHEAST WILL BE MET BY A FINGER OF THE POLAR JET THIS
MORNING. THIS WILL RESULT IN IMPRESSIVE PHASING AND CAUSE THE
CENTRAL PRESSURE TO DROP SOMEWHERE IN THE RANGE OF 30 TO 40 MB
RANGE OVER THE NEXT 24 HOURS. MODELS CONTINUE TO STRUGGLE WITH
THE EXACT DETAILS OF THIS FEATURE (SEE MODEL DISCUSSION) BUT THEY
ARE COMING INTO BETTER AGREEMENT NOW THAT SOME OF THE STRONGER
GALE FORCE WINDS WILL CREEP NORTH OF THE EASTERN ALEUTIANS AND
ALASKA PENINSULA. THE STRONGEST WINDS AND HEAVIEST RAIN WILL
REMAIN SOUTH OF THE AREA. THE SYSTEM WILL SLOWLY MEANDER INTO THE
GULF BY MON...SO EXPECT GUSTY WINDS TO CONTINUE THROUGH THE AK
PENINSULA THROUGH SUN.

FURTHER WEST...VIGOROUS COLD AIR ALOFT CONTINUES TO PRODUCE
OCCASIONAL LIGHTNING STRIKES BETWEEN SHEMYA AND ADAK. THESE SHOULD
TRACK EAST AND DISSIPATE BY TONIGHT. BUT SOME OF THAT COLD AIR
WILL REMAIN AND WILL CAUSE ANOTHER STRONG SYSTEM TO DEVELOP OUT
THERE MON MORNING. AGAIN...SUBTROPICAL MOISTURE WILL BE PARTLY
RESPONSIBLE FOR THIS SURFACE LOW'S DEVELOPMENT. EXACTLY WHERE THE
CIRCULATION CENTER TRACKS IS STILL UP FOR DEBATE. HOWEVER...IT
DOES APPEAR TO BE A STRONG...TIGHT CIRCULATION WITH AT LEAST
STORM FORCE WINDS. WE WILL CONTINUE TO WATCH THE TRENDS TODAY TO
SEE IF A HIGH WIND WATCH IS IN ORDER.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

BY MONDAY MORNING THE LARGE RATHER DEEP VERTICALLY STACKED LOW
WILL BE LOCATED WELL SOUTH OF THE WESTERN GULF...GRADUALLY
FILLING AS IT DRIFTS EAST THROUGH TUESDAY. THE ASSOCIATED FRONTAL
SYSTEM WILL LIFT NORTH THROUGH THE SOUTHERN GULF ON MONDAY
BRINGING EAST TO SOUTHEASTERLY GALES WITH IT. THE FRONT WILL
WEAKEN AS IT LIFTS SLOWLY NORTH ACROSS KODIAK ISLAND MONDAY NIGHT
TO STALL AROUND THE SOUTHERN KENAI TUESDAY. NORTHERLY OFFSHORE FLOW
AND AN UPPER LEVEL RIDGE INLAND SHOULD KEEP PRECIPITATION MAINLY
CONFINED TO THE COASTAL AREAS. AN ACTIVE NORTH PACIFIC JET STREAM
WILL SPIN ADDITIONAL...PROGRESSIVELY STRENGTHENING FRONTAL
SYSTEMS INTO THE GULF OF ALASKA THROUGH THE END OF THE WEEK
BRINGING WINDY CONDITIONS AND SPREADING PRECIPITATION FURTHER
INLAND.

FURTHER WEST A STRONG FRONTAL SYSTEM WILL CROSS THE WESTERN
ALEUTIANS MONDAY BRINGING WIDESPREAD GALES AND AN AREA OF STORM
FORCE WINDS WITH IT. AS THIS DEEP LOW AND THE DEEP LOW SOUTH OF
THE GULF WEAKEN THEY WILL PHASE INTO A VERY LONG WEST TO EAST
UPPER LEVEL TROUGH RUNNING ALL THE WAY FROM 160E TO 130W. SMALLER
SCALE CIRCULATIONS SPINNING AROUND IN THE BROADER TROUGH WILL KEEP
CONDITIONS UNSETTLED WITH AT LEAST SCATTERED SHOWER COVERAGE
ACROSS THE ALEUTIANS...ALASKA PENINSULA AND MUCH OF THE BERING AND
SOUTHWEST ALASKA THROUGH MIDWEEK. ON THURSDAY A TRANSIENT RIDGE
ALOFT WILL MOVE OVER THE WESTERN ALEUTIANS THEN PROGRESS EAST
BRINGING A BRIEF DRIER BREAK WITH IT BEFORE THE NEXT FRONTAL
SYSTEM SWEEPS FROM WEST TO EAST ACROSS THE ALEUTIANS AND BERING
FRIDAY AND SATURDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 119 172.
         GALE WARNING 125 129 150 155 170 171 174 178.

&&

SYNOPSIS AND MODEL DISCUSSION...JW/JA
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...JR