Small Craft Advisory 43, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST SUN JAN 13 2013

.MODEL DISCUSSION...
THE VARIOUS NUMERICAL MODELS ARE NOT IN PARTICULARLY GOOD AGREEMENT.
THIS IS NOT A SURPRISE CONSIDERING THE COMBINATION OF A STRONG JET
AND THE FACT THAT THE FLOW IS FROM THE SOUTH...WHERE THERE ARE FEW
OBSERVATIONS OF ANY TYPE. THE DISAGREEMENT EARLY ON IS FOCUSED ON
THE FORECAST SPEED AND STRENGTH OF THE SURFACE LOW CURRENTLY SOUTH
OF THE ALASKA PENINSULA. THE NAM IS THE FASTEST...AND ALSO THE
FASTEST TO WEAKEN THE LOW. THE GFS IS THE SLOWEST TO WEAKEN THE
SYSTEM...BUT THE SPEED OF MOVEMENT IS FASTER THAN THE ECMWF. BEYOND
DAY TWO THE PATTERN IS MUCH LESS ACTIVE SO MODEL DIFFERENCES DON'T
AFFECT THE FORECAST TOO MUCH...BUT FROM 60 HOURS TO 84 HOURS THE
DIFFERENCES IN THE GULF OF ALASKA ARE FAIRLY LARGE...AND THE ECMWF
WAS PREFERRED DUE TO ITS RECENT BETTER PERFORMANCE AND A SMOOTHER
TRANSITION TO THE EXTENDED FORECAST.

.ANALYSIS AND UPPER LEVELS...
STRONG SOUTHERLY FETCH IS PUSHING INTO SOUTHERN ALASKA FROM THE
SUB-TROPICS. THIS LIES BETWEEN A STRONG RIDGE OF HIGH PRESSURE ALONG
THE WEST COAST OF NORTH AMERICA AND TROUGHS OVER THE NORTHERN BERING
SEA AND THE NORTH PACIFIC. AS A RESULT OF THIS TEMPERATURES ARE VERY
WARM FOR THIS TIME OF YEAR AND MUCH PRECIPITATION IS OCCURRING
(MAINLY AS RAIN IN THE LOWER ELEVATIONS).

A LOW PRESSURE SYSTEM JUST SOUTH OF THE ALASKA PENINSULA IS MOVING
RAPIDLY NORTH IN THE SOUTHERLY FETCH. THE WARM FRONT ASSOCIATED WITH
THIS SYSTEM IS CURRENTLY MOVING INTO SOUTH CENTRAL ALASKA WITH THE
OCCLUDED FRONT STRETCHING FROM JUST SOUTH OF DUTCH HARBOR TO THE
SOUTHERN TIP OF KODIAK ISLAND.

.SHORT TERM FORECAST...
THE WARM FRONT ASSOCIATED WITH THE ALASKA PENINSULA LOW WILL PROVIDE
THE FIRST BURST OF HEAVY PRECIPITATION TO SOUTH CENTRAL ALASKA THIS
EVENING...THEN THE OCCLUDED FRONT WILL PROVIDE ANOTHER BURST LATER
TONIGHT INTO MONDAY MORNING. THIS WILL OCCUR AS THE LOW MOVES
RAPIDLY NORTH. THE SURFACE LOW WILL BE OVER THE EASTERN SEWARD
PENINSULA BY LATE MONDAY MORNING. FAIRLY GUSTY WINDS WILL FOLLOW THE
OCCLUDED FRONT THROUGH THE KENAI PENINSULA AND ANCHORAGE MONDAY
MORNING. COOLER AND DRIER AIR WILL THEN MOVE INTO THE AREA AS THE
MAIN JET STREAM SLIDES EAST INTO THE ALASKA PANHANDLE MONDAY
AFTERNOON.

A PERIOD OF QUIETER WEATHER WILL BE OVER SOUTHERN ALASKA ON TUESDAY
AND WEDNESDAY WITH A FEW WEAK IMPULSES BRINGING PERIODIC CHANCES OF
PRECIPITATION. THIS PRECIPITATION WILL BE IN THE FORM OF SNOW FOR
MOST LOCATIONS.

.LONG TERM FORECAST...
GENERALLY QUIET WEATHER WILL CONTINUE THROUGH ABOUT FRIDAY WITH AN
UPPER LEVEL LOW OVER MAINLAND ALASKA. ON THE WEEKEND IT LOOKS LIKE
THIS LOW WILL MOVE WEST ALLOWING MORE SOUTHERLY FLOW TO BRING ACTIVE
WEATHER BACK TO THE AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER STORM WARNING 145.
         FLOOD WATCH 101 111 121 125 131 135 145.
MARINE...GALE WARNING 120 130 132 136 138 140 150 155 160.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

LUDWIG JAN 13