Small Craft Advisory 593, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT WED AUG 7 2013

.ANALYSIS AND UPPER LEVELS...
THE DOMINANT FEATURE ON WATER VAPOR SATELLITE THIS MORNING IS A LARGE
ELONGATED UPPER LEVEL LOW PRESSURE CENTERED OVER THE ALASKA
PENINSULA. A CLOSED UPPER HIGH ALOFT SITS OVER THE CANADIAN ARCTIC.
THE SQUEEZED HEIGHT GRADIENT BETWEEN THE TWO FEATURES SUPPORTS A 100
KT JET STREAK OVER KODIAK ISLAND THROUGH THE SEWARD PENINSULA WHICH
IS PROMOTING THE DEVELOPMENT OF OROGRAPHICALLY INDUCED CIRRUS CLOUDS
OFF OF THE ALASKA RANGE. BOTH THE UPPER LOW AND SURFACE LOW PRESSURE
ARE IN THE PROCESS OF FILLING WITH THE DRIFTING NORTHWARD WITH THE
STRONGER JET STREAK DOWNSTREAM OF THE SYSTEM. LARGE SCALE ASCENT
AHEAD OF THE TROUGH AIDED BY THE RIGHT ENTRANCE REGION OF THE JET
STREAK AND A WEAK FRONTAL BOUNDARY ARE BRINGING RAIN TO THE GULF WITH
PERSISTENT ONSHORE FLOW OVER THE EASTERN KENAI PENINSULA. DEEP
EAST/SOUTHEASTERLY FLOW OVER MUCH OF THE SOUTHCENTRAL MAINLAND IS
PROMOTING DOWN-SLOPE DRYING OVER THE WESTERN KENAI PENINSULA. WEAKER
SOUTHEASTERLIES OVER THE ANCHORAGE BOWL ARE ALLOWING STEADY RAIN TO
MAKE IT OVER THE CHUGACH.

.MODEL DISCUSSION...
GUIDANCE IS SYNOPTICALLY IN THE SAME BALLPARK WITH THE EVOLUTION OF
THE UPCOMING PATTERN. A SHORTWAVE OVER THE WESTERN BERING SEA
DROPPING INTO THE LONG-WAVE TROUGH LOOKS TO BECOME THE NEW UPPER LOW
CENTER AS THE CURRENT UPPER LOW OVER THE ALASKA PENINSULA DRIFTS INTO
THE NORTHERN GULF WITH AN ACCOMPANYING FRONT. THERE ARE SOME PRETTY
BIG DIFFERENCES PERTAINING TO HOW THE NORTH GULF LOW LIFTS NORTHWARD.
GUIDANCE RIGHT NOW SITS IN TWO CAMPS...THE FIRST LIFTING THE AKPEN
UPPER LOW/TROUGH NORTH/NORTHEAST OVER THE SOUTHCENTRAL AS THE SYSTEM
STAYS UNDER THE INFLUENCE OF THE STRONGER BERING SEA CENTER. THIS
SOLUTION IS FAVORED BY THE ECMWF/NAM/UKMET. THE SECOND SOLUTION KEEPS
THE GULF UPPER LOW FURTHER EAST...NOT LIFTED INTO THE MAINLAND...NOT
AS MUCH INFLUENCED BY THE BERING SEA SYSTEM AND IS EMBODIED BY THE
GFS. THE GEM GLOBAL/REGIONAL AND LOCAL WRF SUPPORT A HYBRID BETWEEN
THE TWO SOLUTIONS. THE SENSIBLE WEATHER IMPACTS BETWEEN THE TWO
SOLUTIONS WILL ENTAIL THE PRECIPITATION ASSOCIATED WITH THE FRONTAL
PUSH INLAND AND STRENGTH/TIMING OF THE TURNAGAIN ARM WIND.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...THE FRONTAL BOUNDARY SHOULD STAY MAINLY IN
PLACE TODAY WITH ONLY SLIGHT NORTHWARD MOVEMENT. STEADY RAIN WILL
CONTINUE TO AFFECT THE EASTERN KENAI PENINSULA AND SOUTHWESTERN
SUSITNA VALLEY. PERIODS OF LIGHT RAIN CAN BE EXPECTED FOR THE
ANCHORAGE BOWL THIS MORNING ALONG WITH THE MATANUSKA VALLEY. THE
WESTERN KENAI PENINSULA WILL CONTINUE TO STAY MOSTLY DRY IN
DOWN-SLOPE WINDS. THE FRONT WILL PUSH OVER THE NORTH GULF COAST
OVERNIGHT INTO THURSDAY MORNING SPREADING RAIN NORTHWARD. EMBEDDED
WAVES IN THE FLOW WILL PERIODICALLY BRING RAIN TO THE ANCHORAGE AREA
ALONG WITH THE TROUGH PASSAGE ON THURSDAY. THE TURNAGAIN ARM/HIGHER
ELEVATION WIND WILL CONTINUE TO STAY IN THE 20 TO 35 MPH RANGE AS THE
PRESSURE GRADIENT ALONG THE MOUNTAINS STAYS IN PLACE. THE ACTIVE
PATTERN WILL CONTINUE THROUGH THE REST OF THE WEEK AS ANOTHER
TROUGH/FRONT APPROACH THE SOUTHCENTRAL ON FRIDAY.

SOUTHWEST ALASKA...AN ACTIVE PATTERN CONTINUES FOR THE SOUTHWEST. THE
STACKED LOW PRESSURE WILL PUSH NORTHWARD. THE BULK OF THE
PRECIPITATION WILL SPREAD OVER THE BRISTOL BAY AND KUSKOKWIM DELTA
AREAS TODAY WHILE THE KUSKOKWIM VALLEY WILL REMAIN MOSTLY DRY. THE
SECOND UPPER LOW IN THE BERING WILL PUSH INLAND THURSDAY AND FRIDAY
BRINGING ANOTHER ROUND OF RAIN.

BERING SEA AND ALEUTIANS...A SHORTWAVE TROUGH DROPPING DOWN THE
WESTERN BERING WILL REINFORCE THE CURRENT UPPER LOW OVER THE AREA
BRINGING RAIN TO THE ALEUTIANS TODAY. RAIN WILL BECOME MORE SHOWERY
AND SPORADIC OVERNIGHT TONIGHT AND CONTINUE THROUGH FRIDAY...MAINLY
FOR THE EASTERN BERING SEA.

.LONG TERM FORECAST...
THE SEASONABLE FALL PATTERN LOOKS TO CONTINUE FOR THE EXTENDED
PERIOD. AN UPPER LOW WILL BE PRESENT IN THE BERING SEA SENDING
PERIODIC WAVES AND FRONTS TOWARD THE MAINLAND MUCH LIKE THE CURRENT
PATTERN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...NONE
FIRE WEATHER...NONE

MTL AUG 13