Area Forecast Discussion
Issued by NWS Anchorage, AK

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
000
FXAK68 PAFC 101434
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
534 AM AKST WED FEB 10 2016

.ANALYSIS AND UPPER LEVELS...

A BROAD AND COMPLEX UPPER LEVEL LOW CENTERED NEAR 46N 160W
CONTINUES TO DRIVE THE WEATHER PATTERN FOR MUCH OF THE AREA OF
RESPONSIBILITY...WITH A TRAIN OF DISTURBANCES ROTATING AROUND THE
PRIMARY CENTER OF ACTION. THE MOST NOTABLE CURRENTLY HAS A 969 MB
SURFACE LOW CENTERED NEAR 52N 156W AND ATTENDANT SURFACE FRONT
EXTENDING WELL NORTHEAST OF THE LOW MOVING WEST AND NORTH FROM THE
NORTH PACIFIC AND GULF TOWARD THE EASTERN AND SOUTHERN BERING
REGION. SATELLITE-DERIVED WINDS INDICATE MAINLY SOLID GALES WITH
NORTHEAST WINDS OUT AHEAD OF THE SYSTEM IMPACTING THE SOUTHWEST
GULF...SHELIKOF STRAIT...AND THE SOUTHERN ALASKA PENINSULA COASTAL
WATERS...WITH A SMALL AREA OF LOW-END STORM-FORCE WINDS SOUTHWEST
OF KODIAK ISLAND. ADDITIONALLY...MIDDLETON ISLAND NEXRAD DEPICTS A
LARGE AREA OF STRATIFORM PRECIPITATION MOVING NORTHWEST TOWARD THE
NORTH-CENTRAL AND NORTHWEST GULF COAST.

AS THIS SYSTEM CONTINUES TO GRAZE SOUTHERN ALASKA...THE PRESSURE
GRADIENT HAS INCREASED ALONG THE NORTH GULF COAST. THIS HAS
RESULTED IN INCREASED WINDS THROUGH THE NORTH-SOUTH ORIENTED
GAPS...ESPECIALLY NEAR THOMPSON PASS...WHERE STRONG WINDS ARE
COMBINING WITH 8 INCHES OF TRANSPORTABLE SNOW TO CREATE
SIGNIFICANT VISIBILITY RESTRICTIONS WITH BLOWING SNOW.

BEHIND THIS DISTURBANCE...THE NEXT SYSTEM WITH 977 MB SURFACE LOW
AND ATTENDANT FRONT IS PUSHING NORTH THROUGH THE NORTHEAST PACIFIC
TOWARD THE SOUTHERN GULF OF ALASKA.

&&

.MODEL DISCUSSION...

MODEL AGREEMENT IS GOOD THROUGH THE SHORT TERM WITH THE CURRENT
AND TRAILING SYSTEMS ROTATING AROUND THE NORTH PACIFIC LOW...HOWEVER
MINOR DISCREPANCIES BEGIN TO ARISE BY FRIDAY WITH A THIRD AND
POTENTIALLY FOURTH SYSTEM MOVING TOWARD THE GULF OF ALASKA.
DIFFERENCES ALSO BEGIN TO EMERGE SOUTH OF THE CENTRAL AND EASTERN
ALEUTIANS AT THIS TIME AS A BROAD AND COMPLEX LOW PRESSURE SYSTEM
WITH EMBEDDED ROTATING DISTURBANCES MOVES FROM THE NORTHWEST
PACIFIC TOWARD THIS AREA. THE FORECAST THROUGH THE SHORT-TERM
UTILIZES MAINLY THE HIGH-RES MODELS AND THE GFS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE BROAD AREA OF LOW PRESSURE SOUTH OF THE ALASKA PENINSULA IS
SWINGING A COUPLE FRONTS TOWARDS THE SOUTHCENTRAL FROM THE SOUTH.
THE FIRST IS ALREADY MOVING THROUGH THE NORTH GULF COAST BRINGING
RAIN AND SNOW TO THE AREA. HOWEVER...MUCH OF THE PRECIPITATION
WILL STAY ON THE GULF SIDE OF THE COASTAL RANGES. THE NEXT FRONT
WILL IMPACT THE COAST TONIGHT WITH ONLY A SMALL BREAK BETWEEN THE
TWO SYSTEMS. SOUTHERLY FLOW WILL THEN KEEP RAIN AND SNOW ALONG THE
COAST THROUGH THURSDAY.

A STRONG PRESSURE GRADIENT ALONG THE COAST IS HELPING TO CAUSE
OUTFLOW WINDS THROUGH THE NORTH SOUTH ORIENTED GAPS. THOMPSON
PASS IS ONE OF THOSE GAPS AND WITH WINDS AND TRANSPORTABLE SNOW ON
THE GROUND...BLOWING SNOW IS A CONCERN THROUGH THE PASS. THE
WINDS WILL DIMINISH THROUGHOUT THE DAY AND LESSEN THE CONCERN FOR
BLOWING SNOW IN THE AFTERNOON EVEN AS NEW SNOW FALLS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...WED AND
THU)...GUSTY NORTHEAST WINDS WILL BE THE STORY FOR THE NEXT 24
HOURS. THE MID 970 MB LOW SOUTH OF THE ALASKA PENINSULA IS WORKING
IN TANDEM WITH AN ARCTIC HIGH OVER THE ARCTIC OCEAN TO PRODUCE A
FAIRLY TIGHT GRADIENT ACROSS MUCH OF THE SOUTHWEST. WHILE THE
INLAND AIRMASS IS NOT OVERLY COLD (ESPECIALLY FOR THIS TIME OF
YEAR)...THERE WILL BE ENOUGH THERMAL DIFFERENCE TO CREATE SOME
GUSTS TO NEAR 50 MPH TODAY. PRECIPITATION ASSOCIATED WITH THIS LOW
WILL CONFINED TO THE ALASKA PENINSULA AND EASTERN ALEUTIAN RANGE.

ON THURSDAY...YET ANOTHER LOW WILL MAKE A TREK FROM THE CENTRAL
GULF TOWARD KODIAK ISLAND. THIS LOW WILL TRACK SLIGHTLY FARTHER
NORTH. AS IT PUSHES ANOTHER PULSE OF WARM AIR UP AGAINST THE
CONTINENTAL POLAR AIR INLAND...AN INVERTED TROUGH WILL DEVELOP.
THIS FEATURE WILL SWING FROM THE ALASKA RANGE THROUGH THE YK-
DELTA. IT WILL LIKELY BRING SOME RAIN TO AREAS FURTHER SOUTH...BUT
COULD BRING SOME ACCUMULATING SNOW TO PARTS OF THE KUSKOKWIM
VALLEY AND LOCATIONS EAST. WE WILL BE WATCHING THIS FEATURE AS THE
FORECAST DEVELOPS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...WED AND
THU)...THE LOW THAT WAS SOUTH OF THE CENTRAL ALEUTIANS YESTERDAY
IS BECOMING JUST A REMNANT BOUNDARY ACROSS THE WESTERN BERING. IT
CONTINUES TO PRODUCE SOME LIGHT RAIN AND SNOW SHOWERS.
MEANWHILE...THE LOW NEAR THE AKPEN WILL BE THE DRIVER FOR THE
NEXT DAY OR SO. AS IT SLIPS TOWARD DUTCH HARBOR LATER
TONIGHT...EXPECT PRECIPITATION...MOSTLY IN THE FORM OF RAIN...TO
IMPACT ALL OF THE EASTERN ALEUTIANS. THE HEAVIEST RAIN WILL BE ON
THE PACIFIC SIDE. EAST TO NORTHEAST WINDS WILL ALSO BE ON THE
INCREASE THROUGH THE DAY UNTIL THE LOW STARTS TO FILL LATER
TONIGHT. BROAD SUB-GALE FORCE CYCLONIC FLOW WILL TAKE OVER ON
THURSDAY. ONE WEAK LOW APPROACHES THE WESTERN ALEUTIANS FROM THE
NORTH PACIFIC TOWARD THE END OF THE WEEK...BUT LOOKS TO HAVE
MINIMAL IMPACT.

&&

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

NUMERICAL MODELS CONTINUE TO BE IN GOOD AGREEMENT THROUGH THE
BEGINNING OF NEXT WEEK WITH THE OVERALL PROGRESSION OF THE
LONGWAVE PATTERN OVER THE BERING SEA AND NORTH PACIFIC. THE
AMPLIFIED LONGWAVE TROUGH SITUATED OVER THE BERING SEA AND NORTH
PACIFIC WILL SLOWLY PROPAGATE EASTWARD AND SWITCH FROM A NEGATIVE
TILT TO A POSITIVE TILT AS THE JET ENERGY TRANSITIONS FROM THE
ENTRANCE REGION OF THE TROUGH TO THE EXIT REGION. AS THIS
HAPPENS...SEVERAL UPPER LEVEL DISTURBANCES AND ASSOCIATED SURFACE
FEATURES WILL IMPACT THE GULF OF ALASKA AND SOUTHCENTRAL ALASKA.
SEVERAL FRONTS WILL IMPACT MAINLY THE NORTHERN GULF COAST WHICH
WILL KEEP RAINFALL CHANCES PRETTY HIGH AS RAIN UPSLOPES ALONG THE
MOUNTAINS. WITH NOT A LOT OF UPPER LEVEL SUPPORT THESE FRONT
SHOULD FALL APART ALONG THE COASTAL MOUNTAINS AND LEAVE MUCH OF
INTERIOR SOUTHCENTRAL ON THE DRY SIDE. SOUTHWEST ALASKA AND THE
BERING SEA WILL BE ON THE SHOWERY SIDE WITH NO STRONG FEATURES
EXPECTED UNTIL LATE MONDAY INTO TUESDAY WHEN MODELS START HINTING
AT A DECENT LOW PRESSURE SYSTEM REPLACING THE SLOWLY DEPARTING
UPPER LEVEL TROUGH. THE REASON FOR THE SHOWERY REGIME IS DUE IN
LARGE PART TO THE BROAD CYCLONIC FLOW ASSOCIATED WITH THE LONGWAVE
TROUGH. THE AMPLITUDE OF THE LONGWAVE TROUGH IS SUCH THAT IT IS
PREVENTING ANY LOW PRESSURE SYSTEMS FROM THE NORTH PACIFIC TO BE
ABLE TO RE-CURVE INTO THE BERING SEA. TEMPERATURES LOOKS TO
REMAIN WELL ABOVE NORMAL FOR MUCH OF SOUTHERN ALASKA THROUGH THE
WEEKEND BEFORE SOME COLD AIR ADVECTION IS EXPECTED ON THE BACK
SIDE OF THE UPPER LEVEL TROUGH ON TUESDAY.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLOWING SNOW ADVISORY 131
MARINE...STORM 138
         GALE  119 120 127 130 131 132 139 150 155 160 165
               180 351 352
         HEAVY FREEZING SPRAY 180 181 185

&&

$$

SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...MC


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.