Small Craft Advisory 379, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
140 PM AKDT TUE APR 30 2013

.ANALYSIS AND UPPER LEVELS...
A COLD UPPER LEVEL TROUGH REMAINS ENTRENCHED OVER MAINLAND
ALASKA...KEEPING TEMPERATURES BELOW NORMAL. A STRONG SHORTWAVE TROUGH
IS MOVING THROUGH SOUTHWEST ALASKA AND IN TO SOUTHCENTRAL. LIFT
ASSOCIATED WITH THIS FEATURE IS PRODUCING WIDESPREAD CLOUDINESS
ACROSS VIRTUALLY ALL OF THE SOUTHERN MAINLAND...WITH STEADY LIGHT
SNOW FALLING PRIMARILY ACROSS THE SUSITNA VALLEY AND TALKEETNA
MOUNTAINS. MEANWHILE...A WEAK INVERTED TROUGH IS HELPING TO PRODUCE
SCATTERED SNOW SHOWERS ACROSS THE WESTERN GULF AND LOWER COOK INLET.
OUT WEST...A COMPLEX AND SLOW-MOVING LOW PRESSURE CENTER SOUTH OF THE
ALEUTIANS HAS AN ASSOCIATED FRONT THAT IS GRADUALLY PROGRESSING
NORTHWARD OVER THE EASTERN ALEUTIANS AND ALASKA PENINSULA. MOST OF
THIS PRECIP IS FALLING AS A COLD RAIN WITH TEMPERATURES IN THE 30S.

.MODEL DISCUSSION...
MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT THAT A SHORTWAVE TROUGH
CURRENTLY NEAR THE NORTON PENINSULA WILL MOVE SOUTHWARD OVERNIGHT AND
HELP THE LONGWAVE TROUGH DIG SOUTHWESTWARD TOWARD BRISTOL BAY. THIS
WILL SWITCH DEEP-LAYER FLOW ACROSS THE SOUTHERN MAINLAND TO A VERY
MOIST SOUTHWESTERLY DIRECTION THROUGH THE END OF THE WEEK. AS THIS
HAPPENS...A PIECE OF ENERGY FROM THE COMPLEX NORTH PACIFIC LOW WILL
BREAK OFF AND MOVE UP INTO THE NORTHWEST GULF ON WEDNESDAY. THERE ARE
A FEW MODEL DISCREPANCIES WITH THE TRACK AND LONGEVITY OF THE ACTUAL
CIRCULATION...BUT MODELS SEEM TO BE CONVERGING ON A SOLUTION WHERE
THE LOW WEAKENS AND DRIFTS WESTWARD TOWARD THE KENAI PENINSULA. THIS
SETS THE STAGE FOR ANOTHER LOW ON FRIDAY TO MOVE INTO THE REGION WITH
MORE ATMOSPHERIC MOISTURE. THE TRACK OF THIS 2ND LOW IS MUCH LOWER
CONFIDENCE...AS THE 12Z EC CONTINUES TO DEEPEN THE MAINLAND TROUGH
THROUGH THURSDAY AND NOW DEVELOPS A CLOSED LOW OVER THE EASTERN
BERING BY THURSDAY EVENING. MEANWHILE...THE AMERICAN MODELS (NAM/GFS)
WEAKEN THE TROUGH AND BEGIN TO MOVE THE TROUGH (AND ACCOMPANYING COLD
AIR) BACK TO THE NORTH. THE STRENGTH AND POSITION OF THE UPPER LEVEL
FEATURES WILL DICTATE HOW FAR NORTH AND WEST THE NEXT SURFACE LOW AND
ASSOCIATED PRECIP WILL PROGRESS...AS WELL AS WHETHER IT FALLS AS RAIN
OR SNOW OVER THE POPULATED PARTS OF SOUTHCENTRAL. AT THIS
POINT...WITH NO OTHER MODELS EVEN SHOWING A TREND TOWARD THE EC
SOLUTION...THE AFTERNOON FORECAST WILL STICK FAIRLY CLOSE TO THE
INHERITED FORECAST WHICH IS MORE IN LINE WITH THE NAM/GFS/GEM
SOLUTION.

.SHORT TERM FORECAST...
SOUTHCENTRAL...AS SHORTWAVE TROUGH MOVES OFF TO THE EAST THIS EVENING
WILL SEE A DECREASE IN CLOUDS AND SNOWFALL ACROSS THE AREA. RAIN WILL
MOVE INTO KODIAK BY MORNING AS A STRETCHED-OUT FRONTAL BAND AND WEAK
ASSOCIATED LOW PRESSURE CIRCULATION MOVE INTO THE GULF. THIS WEAK LOW
WILL MOVE INTO THE NORTHWEST GULF BY WEDNESDAY AFTERNOON AND CONTINUE
TO WEAKEN. STEADY RAIN AND SNOW WILL MOVE INTO PARTS OF PRINCE
WILLIAM SOUND AND THE NORTH GULF COAST BY TOMORROW AFTERNOON BEFORE
DIMINISHING IN THE EVENING. THE NEXT CHANCE OF SIGNIFICANT
PRECIPITATION ACROSS THE REGION WILL COME ON THURSDAY NIGHT AND
FRIDAY AS A 2ND LOW BRINGS ABUNDANT MOISTURE INTO THE AREA. AT THIS
POINT IT LOOKS LIKE THE RAIN/SNOW LINE WILL PROBABLY SET UP FROM THE
NORTHERN KENAI PENINSULA TO THE MATANUSKA VALLEY...WITH THE COAST
GETTING RAIN AND THE SUSITNA VALLEY GETTING SNOW. AS MENTIONED
ABOVE...THE EXACT TRACK OF THE SURFACE LOW IS STILL VERY MUCH IN
DOUBT AT THIS TIME...AND WILL MAKE ALL THE DIFFERENCE FOR THE
PRECIPITATION TYPE THAT WILL BE OBSERVED IN AND AROUND ANCHORAGE AND
THE MATANUSKA VALLEY FOR THE START OF THE WEEKEND.

SOUTHWEST...INCREASING OFFSHORE FLOW WILL KEEP MOST OF THE AREA BELOW
NORMAL FOR TEMPERATURES AND MOSTLY DRY THROUGH THE END OF THE WEEK.
WIDESPREAD DIURNAL CUMULUS CLOUDS HAVE DEVELOPED THIS AFTERNOON IN
CLEARING BEHIND THE SHORTWAVE OVER SOUTHCENTRAL...ESPECIALLY
IMPRESSIVE CONSIDERING SURFACE TEMPERATURES ARE STILL IN THE LOW TO
MID 30S IN MOST LOCATIONS. THE NEXT CHANCE FOR WIDESPREAD RAIN/SNOW
WILL BE AT THE START OF THE WEEKEND AS MOISTURE SURGES NORTH AND
WEST...DEPENDING ON THE EXACT TRACK OF THE SURFACE LOW MOVING UP
TOWARD COOK INLET.

BERING SEA AND ALEUTIANS...RAIN...MIXED WITH SNOW...WILL PERSIST OVER
THE EASTERN HALF OF THE ALEUTIANS THROUGH WEDNESDAY MORNING. FOR THE
SECOND HALF OF THE WEEK...HIGH PRESSURE WILL AGAIN SPREAD ACROSS THE
REGION FROM THE NORTH. WITH A LOW-LEVEL INVERSION
STRENGTHENING...WIDESPREAD MARINE STRATUS AND POSSIBLY FOG WILL
PROBABLY EXPAND IN COVERAGE HEADING INTO THE WEEKEND.

.LONG TERM FORECAST...
AGREEMENT AMONG THE LONG RANGE MODELS DROPS OFF DRAMATICALLY BY EARLY
NEXT WEEK. THE EC IS SUGGESTING A MUCH MORE PROGRESSIVE WEATHER
PATTERN WITH MODERATE TEMPERATURES AND MOSTLY DRY CONDITIONS...WHILE
THE GFS KEEPS A COLD LONGWAVE TROUGH ENTRENCHED OVER THE EASTERN
BERING AND MOIST SOUTHWEST FLOW ACROSS THE MAINLAND. CONFIDENCE IS
VERY LOW IN THE DETAILS AT THIS POINT...BUT THE GENERAL THEME OF
BELOW NORMAL TEMPERATURES IS LIKELY TO CONTINUE THROUGH NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 170 172 179 414
         HEAVY FREEZING SPRAY 160 180
FIRE WEATHER...NONE

AMD APR 13