Small Craft Advisory 585, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1241 PM AKDT MON AUG 4 2014

.ANALYSIS AND UPPER LEVELS...A DEEP COLD CORE LOW IS WOBBLING NORTHWARD
INTO THE GULF OF ALASKA. A POTENT SHORT-WAVE ROTATING AROUND THE NORTH
SIDE OF THE LOW IS BRINGING WIDESPREAD RAIN TO SOUTHCENTRAL ALASKA.
INSTABILITY UNDER THE UPPER LOW CENTER WAS ENOUGH TO PRODUCE A FEW
THUNDERSTORMS OVER THE GULF LAST NIGHT THROUGH EARLY THIS MORNING.
EXPECT A REPEAT OF THIS ACTIVITY OVER THE NORTHERN GULF AS THE LOW
CENTER CONTINUES NORTHWARD LATER TODAY. MEANWHILE...THUNDERSTORMS
WERE FIRING FOR MUCH OF THE NIGHT ALONG THE THERMAL TROUGH OVER
SOUTHWEST ALASKA AIDED BY UPPER WAVES MOVING OVER TOP OF THE GULF LOW.
LIGHTNING STRIKES HAVE DIMINISHED...BUT EXPECT ACTIVITY TO INCREASE
QUICKLY AS SURFACE HEATING PROGRESSES TODAY. CONDITIONS ARE RELATIVELY
CALM OVER THE BERING AND ALEUTIANS UNDER A LOW AMPLITUDE RIDGE...BUT
A STRONG SUBTROPICAL JET OVER THE NORTHWEST PACIFIC IS POISED TO
DRIVE A TROUGH OVER EAST ASIA INTO THE BERING TAPPING INTO DEEP
TROPICAL MOISTURE OVER THE WEST PACIFIC ALONG THE WAY.

&&

.MODEL DISCUSSION...ALTHOUGH THE GENERAL SYNOPTIC EVOLUTION OF MODELS
IS SIMILAR...SOLUTIONS QUICKLY DIVERGE WITH HANDLING OF MESOSCALE
OR SMALLER FEATURES. MORE SPECIFICALLY...IT IS QUITE THE CHALLENGE
TO TRACK INDIVIDUAL WAVES MOVING AROUND THE GULF LOW...WHICH HELP
DETERMINE WHERE THE SURFACE LOW IS CENTERED. DO PREFER THE HIGHER
RESOLUTION MODELS (NAM/GEM-REG) FOR SUPERIOR HANDLING OF WINDS ALONG
THE NORTHERN GULF AND PRINCE WILLIAM SOUND AREAS. OTHERWISE...WILL
USE THE GENERAL MODEL TRENDS TO AID IN POP/QPF FORECAST.

OUT WEST...MODEL SPREAD GROWS FAIRLY LARGE WITH SPEED OF LOW PRESSURE
SYSTEM ACROSS THE BERING SEA WEDNESDAY AND THURSDAY. WITH INITIAL
JET SUPPORT IT SEEMS FASTER SOLUTION MAKES SENSE...BUT AS SYSTEM
RAPIDLY OCCLUDES AND JET PASSES BY FORWARD PROGRESSION SHOULD SLOW.
FOR NOW WILL STICK CLOSE TO INHERITED FORECAST WHICH IS JUST A BIT
SLOWER THAN THE FASTEST SOLUTION (ECMWF).

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE CURRENT SHORT-WAVE WILL PROVIDE THE MOST
WIDESPREAD RAIN ACROSS SOUTHCENTRAL. AS IT ROTATES SOUTHWARD WEAKER
WAVES WILL FOLLOW IN BEHIND IT...BUT WILL TAKE AN INCREASINGLY
TIGHTER TRACK NEAR THE LOW CENTER. THUS...THE BULK OF RAIN TONIGHT
INTO TUESDAY WILL BE ALONG THE COAST WITH JUST A FEW SHOWERS INLAND.
THUNDERSTORMS WILL REMAIN A THREAT UNDER THE UPPER CENTER...PRIMARILY
OVER THE NORTHERN GULF. WILL KEEP A CLOSE EYE ON CONVECTION FORMING
SOUTH OF CAPE SUCKLING TO SEE IF IT MAKES IT ALL THE WAY INTO PRINCE
WILLIAM SOUND WHERE IMPACTS WOULD BE GREATER (DUE TO A HIGHER NUMBER
OF SMALL RECREATIONAL BOATS THIS TIME OF YEAR). THE GULF LOW WILL
EXIT SOUTHWARD ACROSS THE GULF VERY SLOWLY TUESDAY THROUGH THURSDAY.
IN ITS WAKE WEAK AND CONFUSED FLOW MAKES IT HARD TO LATCH ON TO
ANY PARTICULAR FEATURES. TYPICALLY WITH THIS SORT OF PATTERN WOULD
EXPECT A MIX OF SUN AND CLOUDS ALONG WITH SOME WEAK DIURNAL CONVECTION.
THE BERING SEA SYSTEM WILL APPROACH LATE IN THE WEEK...WITH LOW
FORECAST CONFIDENCE IN TIME OF ARRIVAL.

SOUTHWEST ALASKA...EXPECT PERSISTENT CONDITIONS OVER SOUTHWEST ALASKA
THE NEXT COUPLE DAYS...WITH THERMAL TROUGH CENTERED APPROXIMATELY
ALONG THE KUSKOKWIM MOUNTAINS SOUTHWESTWARD INTO THE KUSKOKWIM
DELTA AND WEAK UPPER WAVES MOVING IN FROM THE EAST. SHOWERS AND
THUNDERSTORMS WILL LARGELY BE FOCUSED ALONG THE THERMAL TROUGH...WITH
STORM MOTION OUT OF THE NORTH SUPPORTING TRAINING OF CELLS OVER
THE SAME GENERAL REGION. HOWEVER...DO EXPECT SOME CONVECTION TO
INITIATE ALONG THE ALASKA RANGE AS SHORT-WAVE CROSSING SOUTHCENTRAL
APPROACHES LATE THIS AFTERNOON INTO EVENING. AS WAS THE CASE LAST
NIGHT...CONTINUED MID-LEVEL FORCING WILL ALLOW CONVECTION TO
LINGER INTO THE OVERNIGHT HOURS. WEDNESDAY LOOKS LIKE A TRANSITION
DAY...WITH FLOW SHIFTING AROUND TO SOUTH AHEAD OF APPROACHING
BERING SYSTEM AND THERMAL TROUGH LIFTING NORTHWARD. STILL EXPECT
SOME CONVECTION...BUT IT WILL LIKELY BE FOCUSED FURTHER NORTH AND
WILL BE MORE WIDELY SCATTERED AS THE ENVIRONMENT GRADUALLY
BECOMES MORE STABLE. FORECAST CONFIDENCE IS LOW FOR TIMING OF THE
BERING LOW...BUT WOULD EXPECT RAIN WILL BE MAKING ITS WAY INTO
BRISTOL BAY AREA WEDNESDAY NIGHT OR THURSDAY.

BERING SEA/ALEUTIANS...WET AND WINDY CONDITIONS WILL SPREAD
EASTWARD ACROSS THE BERING AND ALEUTIANS THE NEXT COUPLE DAYS AS
A SURFACE LOW DEVELOPS OVER THE FAR SOUTHWESTERN BERING AND
TRACKS QUICKLY EASTWARD. VERY WARM AND MOIST AIR ORIGINATING IN
THE WEST PACIFIC WILL CONTRIBUTE TO MODERATE TO HEAVY RAIN ALONG
THE ALEUTIAN CHAIN...SPREADING TO THE ALASKA PENINSULA BY
THURSDAY.

&&

.LONG TERM FORECAST (FRI AUG 8TH - MON AUG 11TH)...

A RATHER ABRUPT SHIFT IN THE LONGWAVE PATTERN WILL BE UNDERWAY
ACROSS THE REGION BEGINNING FRIDAY...WITH A LARGE AND DYNAMIC LOW
ACROSS THE EASTERN BERING...AND A LARGE SUBTROPICAL WARM FRONT
MOVING INTO THE GULF OF ALASKA. THE NORTHERN GULF COAST AND
EASTERN KENAI WILL TAKE THE BRUNT OF PRECIPITATION...WITH MUCH
DRIER CONDITIONS ACROSS MOST INLAND LOCATIONS OWING TO DOWNSLOPE
DRYING IN DEEP SOUTHEASTERLY FLOW ALOFT. CLOUDS...HOWEVER...WILL
BE EXTENSIVE...AND WILL KEEP TEMPERATURES SLIGHTLY BELOW AVERAGE
ACROSS SOUTHERN ALASKA THROUGH THE WEEKEND. NORTHERLY FLOW ACROSS
THE BERING THROUGH SATURDAY WILL KEEP FOG AT BAY...BUT EXTENSIVE
STRATUS WILL REMAIN. A MORE ACTIVE PATTERN WILL PERSIST INTO
MONDAY AS TROPICAL CYCLONES FROM THE TROPICAL PACIFIC INTERACT
WITH THE NORTH PACIFIC JET STREAM.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 120.
FIRE WEATHER...NONE.

&&

SEB AUG 14