Small Craft Advisory 38, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
428 PM AKST TUE JAN 13 2015

.ANALYSIS AND UPPER LEVELS...
THE PHRASE RINSE AND REPEAT IS BEING UTTERED TO DESCRIBE THIS VERY
PERSISTENT PATTERN. THE DETAILS OF THE UPPER LEVEL FLOW UNDERGO
SOME FLUCTUATIONS BUT THE MEAN POSITION OF THE LONG-WAVES REMAINS
THE SAME. TAKING A LOOK AT THE LARGE SCALE FLOW THIS MORNING...A
CLOSED HIGH OVER THE NORTHERN BERING SEA CONTINUES TO RETROGRADE
WESTWARD TOWARD SIBERIA ALLOWING THE WARMER AIR MASS WHICH HAS
BEEN SITTING OVER THE SOUTHERN MAINLAND TO PROGRESS TOWARD THE
INTERIOR. A STRONG BLOCKING RIDGE REMAINS CENTERED ALONG THE WEST
COAST OF NORTH AMERICA. UPSTREAM OF THESE RIDGES IS A MERRY-GO-ROUND
OF LOWS...WITH SYSTEMS DEVELOPING ALONG A ROBUST SUBTROPICAL JET
OVER THE NORTH PACIFIC...TRACKING NORTHWARD TOWARD THE GULF OF
ALASKA AND ALASKA PENINSULA...THEN WEAKENING AS THEY TRACK BACK
WESTWARD ACROSS THE BERING SEA. AS EACH STORM PASSES THROUGH THE
AIR MASS OVER THE SOUTHERN MAINLAND WARMS A LITTLE MORE. THIS HAS
DIMINISHED THE THREAT OF FREEZING RAIN...BUT NOT COMPLETELY
ELIMINATED IT AS SOME INTERIOR LOCATIONS REMAIN BELOW FREEZING AT
THE SURFACE.

AS FAR AS SPECIFIC SYSTEMS AFFECTING THE AREA THIS MORNING...ONE
LOW IS WEAKENING AS IT HEADS WESTWARD ACROSS THE BERING SEA. A
WEAKER LOW ALONG THE ALASKA PENINSULA IS DISSIPATING AS UPPER
LEVEL LOW OPENS INTO A TROUGH AND HEAD NORTHWARD. AN ASSOCIATED
WARM OCCLUSION IS TRACKING INLAND ACROSS THE SOUTHERN MAINLAND...
WITH THE BULK OF PRECIP FALLING ALONG THE GULF COAST. INLAND
AREAS ARE MOSTLY DRY THANKS DOWNSLOPE FLOW.

THERE ARE A COUPLE OF DEEP LOWS OVER THE NORTH PACIFIC. THE FOCUS
IS ON THE FARTHEST EAST ONE WHICH IS INTENSIFYING IN THE LEFT EXIT
REGION OF THE SUBTROPICAL JET AND IS POISED TO TRACK UP THE WEST
SIDE OF THE UPPER RIDGE TOWARD THE GULF AND KODIAK ISLAND. THE
OTHER LOW IS ALSO BEGINNING TO CURVE NORTHWARD TOWARD THE EASTERN
ALEUTIANS...BUT THE DOWNSTREAM LOW WILL LIMIT THE NORTHWARD
PROGRESSION OF THIS LOW WITH LESS OVERALL IMPACT ON THE FORECAST
AREA.

&&

.MODEL DISCUSSION...
NUMERICAL GUIDANCE HAS A GOOD HANDLE ON THE LARGE SCALE PATTERN.
MINOR DIFFERENCES DO DEVELOP LATE WEDNESDAY AND WEDNESDAY NIGHT
WITH LOW POSITIONS ALONG AND SOUTH OF THE ALASKA PENINSULA AND
EASTERN ALEUTIANS..BUT THESE DIFFERENCES DON NOT HAVE A HUGE
IMPACT ON THE RESULTANT SENSIBLE WEATHER. THE 12Z GFS SOLUTION HAS
BEEN DISCARDED AS AN OUTLIER WITH NOTABLY FASTER PROGRESSION OF
THE UPPER LEVEL SHORT-WAVE ACROSS THE GULF AND SOUTHERN MAINLAND
AND A FARTHER NORTH CONSOLIDATED LOW CENTER ALONG THE ALASKA
PENINSULA. THE REST OF THE GUIDANCE IS GROUPED CLOSER TOGETHER
WITH NO REAL PREFERENCE FOR ANY INDIVIDUAL MODEL. FORECAST
CONFIDENCE IS GENERALLY ABOVE AVERAGE...WITH MARGINALLY LOWER
CONFIDENCE IN THE IMMEDIATE VICINITY OF THE WEAKENING SURFACE LOWS
WEDNESDAY NIGHT AND THURSDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (TONIGHT THROUGH THURSDAY)...

PRECIPITATION ASSOCIATED WITH A POTENT WARM FRONT HAS NOW SHIFTED
NORTH OF ANCHORAGE INTO THE NORTHERN SUSITNA VALLEY AND EXTENDS
EASTWARD ACROSS THE COPPER RIVER BASIN. THIS HAS BROUGHT AN END
TO PRECIPITATION CHANCES TO THE ANCHORAGE AREA AND MUCH OF THE
KENAI PENINSULA AS CROSS BARRIER FLOW IS NOW MUCH TOO STRONG (30+
KNOTS) TO SUPPORT ANY LINGERING SHOWER ACTIVITY IN THE VICINITY OF
THE FRONT TO MAKE IT ACROSS THE MOUNTAINS. UPSLOPE RAIN SHOWER
ACTIVITY WILL CONTINUE ALONG THE NORTHERN GULF COAST THROUGH
TONIGHT WITH ONSHORE FLOW CONTINUING IN THE WAKE OF THE WARM FRONT.

ATTENTION THEN TURNS TO AN AREA OF LOW PRESSURE NEAR 42N 147W THAT
IS EXPECTED TO MOVE RAPIDLY NORTHWARD OVER THE NEXT 24 HOURS
WHILE INTENSIFYING. THIS WILL BRING YET ANOTHER SURGE OF WARMER
AIR TO SOUTHCENTRAL ALASKA AND ALSO INCREASE PRECIPITATION
CHANCES. FREEZING RAIN IS A BIT LESS LIKELY WITH THIS EVENT THAN
WITH THE PREVIOUS TWO SYSTEMS AS THE AIR MASS OVER THE ALASKA
MAINLAND HAS STEADILY MODIFIED WITH THE PREVIOUS SURGES OF WARM
AIR. AT THIS TIME...IT ALSO LOOKS LIKE THE STRONGEST CORE OF WINDS
WILL BE JUST ABOVE MOUNTAIN TOP LEVEL (5K TO 7K FT)...WHICH SHOULD
ALLOW SOME SPILL OVER ACROSS THE KENAI AND CHUGACH MOUNTAINS.
OVERNIGHT LOW TEMPERATURES ARE EXPECTED TO REMAIN ABOVE FREEZING
OR JUST BELOW FREEZING FOR MUCH OF SOUTHCENTRAL ALASKA...SO AS
MENTIONED EARLIER...THE CHANCE OF FREEZING RAIN IS NOT AS GREAT.
THE ABNORMALLY HIGH TEMPERATURES WILL CONTINUE THROUGH AT LEAST THE
END OF THE WEEK DUE TO STEADY WARM AIR ADVECTION FROM THE NORTHERN
PACIFIC.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE MAIN SHORT TERM CONCERN FOR SOUTHWEST ALASKA IS THE SHORTWAVE
TROUGH LIFTING NORTH OVER THE AREA TONIGHT THROUGH WEDNESDAY
MORNING. THE TROUGH AND ASSOCIATED VORTICITY MAX WILL LIFT INTO
THE BRISTOL BAY AREA AROUND 6 PM THIS EVENING THEN CONTINUE NORTH
UP OVER THE KUSKOKWIM VALLEY BETWEEN 8 PM AND MIDNIGHT. GIVEN THE
GOOD LIFT ASSOCIATED WITH THIS FEATURE THINK THE HIGHER QPF
AMOUNTS THE HIGH RES MODELS ARE SHOWING SEEM QUITE REASONABLE.
WITH THE BULK OF THIS PRECIPITATION FALLING OVER 152 WHERE VALLEY
TEMPERATURES REMAIN IN THE LOW 20S...A COUPLE TENTHS OF AN INCH
OF FREEZING RAIN ARE LIKELY TONIGHT THROUGH WEDNESDAY MORNING.
ALSO THINK A COUPLE INCHES OF SNOW ARE NOT OUT OF THE QUESTION IN
THE MOUNTAINS.

FOR ZONE 155...THE KUSKOKWIM DELTA PRECIPITATION AMOUNTS WILL BE
LIGHTER BUT ALSO THERE WILL ALSO BE THE POTENTIAL FOR FREEZING
RAIN. WITH THE INITIAL UPPER TROUGH TONIGHT MOST ALL WILL BE
FOCUSED TO THE EAST WITH AROUND A TENTH OF AN INCH OVER KALSKAG
TAPERING TO TRACE TO COUPLE HUNDREDTHS OVER BETHEL. WITH A
SECONDARY FEATURE LIFTING NORTH EARLY WEDNESDAY MORNING...STARTING
AROUND 4 TO 6 AM IN THE SOUTHERN PORTIONS OF THE ZONE AND
CONTINUING NORTH THROUGH MID TO LATE MORNING. THE PRECIPITATION
WILL BE SPREAD MORE BROADLY OVER ZONE 155 AND WILL ALSO CONTINUE
IN 152 WITH UP TO AN ADDITIONAL TENTH OF AN INCH OF FREEZING RAIN
POSSIBLE. IN THE BRISTOL BAY AREA...ABOVE FREEZING TEMPERATURES IN
THE UPPER 30S TO LOW 40S WILL CONTINUE WITH BREEZY EAST TO
NORTHEAST WIND KEEPING RAIN THE PREDOMINANT PRECIPITATION TYPE
FOR THAT AREA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
UNSEASONABLY QUIET WEATHER WILL CONTINUE FOR MUCH OF THE ALEUTIAN
CHAIN IN THE SHORT TERM. THE NEXT LOW PRESSURE SYSTEM MOVING UP
FROM THE SOUTH AROUND 170W TONIGHT AND WEDNESDAY ONLY MAKES TO TO
AROUND 50N BEFORE THE DEEPENING LOW SWINGING INTO THE WESTERN GULF
STARTS STEALING ITS ENERGY. THE RESULTS WILL BE ONLY A SMALL AREA
OF GALES BRIEFLY REACHING THE EASTERN ALEUTIANS WEDNESDAY AS IT
WEAKENS AND SMALL CRAFT CONDITIONS PREVAILING MOST ELSEWHERE. THE
EXCEPTION TO THIS WILL BE AREAS ALONG THE ALASKA PENINSULA FURTHER
EAST AND BRISTOL WHERE THE WESTERN GULF LOW WILL INCREASE WINDS TO
GALES AS IT ROTATES THROUGH.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
VARIOUS LOWS WILL MOVE THROUGH THE BERING FOR THE NEXT COUPLE OF
DAYS KEEPING THE LONGWAVE PATTERN SIMILAR WITH TROUGHING OVER THE
BERING AND RIDGING SET UP OVER WESTERN CANADA. THIS WILL KEEP
WARM SOUTHERLY FLOW MOVING OVER MAINLAND ALASKA KEEPING A MIX OF
RAIN AND SNOW FOR THE SOUTHCENTRAL AND SOUTHWEST.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FREEZING RAIN ADVISORIES 152 AND 155.
MARINE...STORMS 130 131.
GALES 119 120 132 136 137 138 150 155 160 165 172 185.
FIRE WEATHER...NONE.

&&

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