Small Craft Advisory 357, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
443 AM AKDT FRI APR 24 2015

.ANALYSIS AND UPPER LEVELS...
THE MAJOR FEATURE IS A BROAD SPRAWLING STACKED SYSTEM THAT
ENCOMPASSES THE MAJORITY OF THE BERING SEA WITH CYCLONIC FLOW AT
ALL LEVELS SPREADING SOUTH OF THE ALEUTIAN CHAIN AND ENCROACHING
ON THE SOUTHWEST/SOUTHCENTRAL MAINLAND. THIS SYSTEM USED UP MOST
OF ITS BAROCLINITY LONG AGO BUT IS STILL BRINGING SHOTS OF LIFT AS
A NUMBER OF VORTICITY MAXIMA ROTATE AROUND THE LARGE SCALE
CIRCULATION. THE JET STREAM REMAINS WELL SOUTH OF THE CHAIN WHILE
RIDGING ALOFT BEGINS TO PUSH THE INCUMBENT SYSTEM OFF TO THE
EAST/SOUTHEAST. FROM A SENSIBLE WEATHER STANDPOINT...WIDESPREAD
SHOWERS OVER MUCH OF THE BERING SEA AND SOUTHWEST MAINLAND ALONG
WITH MOSTLY CLOUDY CONDITIONS. FURTHER TO THE EAST...MOSTLY QUIET
WEATHER OVER THE SOUTHCENTRAL WHICH IS ON THE PERIPHERY OF THE
CYCLONIC FLOW. MIDDLE TO HIGH LEVEL CLOUDS ARE STREAMING OVERHEAD
FROM THE WESTERN SYSTEM WHILE TEMPERATURES ARE SITTING SEASONABLY.

&&

.MODEL DISCUSSION...
GUIDANCE CONTINUES TO BE IN EXCELLENT AGREEMENT WITH THE MAIN
SYNOPTIC FEATURES FOR THE NEXT COUPLE DAYS. DIFFERENCES DO SHOW UP
IN PLACEMENT OF THE SURFACE SYSTEM AS THE UPPER LOW PRESSURE
SLIDES INTO THE GULF AND SPAWNS A NEW SURFACE LOW....BUT GUIDANCE
IS IN THE SAME GENERAL POSITION AND STRENGTH AS WELL AS FRONTAL
PLACEMENT. FORECAST CONFIDENCE IS HIGH FOR THIS PACKAGE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (TODAY THROUGH SATURDAY)...

MAIN AREA OF CONCERN TODAY IS WITH THE POTENTIAL FOR CRITICAL FIRE
WEATHER CONDITIONS THIS AFTERNOON INTO EARLY EVENING...PRIMARILY
IN THE MATANUSKA VALLEY. OBSERVED MINIMUM RELATIVE HUMIDITIES HAVE
REACHED LEVELS WELL BELOW WHAT HAS BEEN FORECASTED THE LAST COUPLE
OF DAYS...PRIMARILY IN THE COPPER RIVER BASIN...MATANUSKA
VALLEY...AND FROM EAST ANCHORAGE NORTHWARD. IN ADDITION...MODELS
CONTINUE TO DEPICT A VERY DRY LAYER THE ATMOSPHERE DEVELOPING OVER
THE CHUGACH RANGE SINCE YESTERDAY. THIS...COMBINED WITH INCREASED
MIXING EXPECTED THIS AFTERNOON AS WEAK SURFACE RIDGING BUILDS
ALONG THE COAST AND A THERMAL TROUGH DEVELOPS TO THE NORTH...WILL
CAUSE WINDS OUT OF THE KNIK RIVER VALLEY TO INCREASE TO GUSTS NEAR
25 MPH. THIS INCREASED MIXING WILL MOST LIKELY ALLOW THE EXTREMELY
DRY LAYER A FEW THOUSAND FEET ABOVE THE SURFACE TO REACH THE
SURFACE...RESULTING IN RED FLAG CONDITIONS. WHILE THERE IS
MODERATE CONFIDENCE THAT CRITICAL FIRE WEATHER CONDITIONS WILL
OCCUR IN THE MATANUSKA VALLEY...THERE IS LOWER CONFIDENCE THAT
THESE CONDITIONS MAY ALSO EXTEND A BIT WEST INTO THE SOUTHERN
SUSITNA VALLEY (NEAR WILLOW) MAINLY ALONG THE PARKS HIGHWAY AS
WELL AS TO THE SOUTH ACROSS NORTHERN ANCHORAGE...INCLUDING THE
EAGLE RIVER AND EKLUTNA RIVER VALLEYS. HAVE OPTED TO GO WITH THE
RED FLAG WARNING FOR THE ENTIRE MATANUSKA VALLEY ZONE...WITH THE
CONCERN FOR LOW HUMIDITY VALUES POSSIBLY REACHING THE CRITICAL 15
PERCENT THRESHOLD IN THE FIRE WEATHER ZONE FORECASTS FOR THE
SUSITNA VALLEY AND FROM EAST ANCHORAGE NORTHWARD.

THE REASON FOR LOW TO MODERATE CONFIDENCE IN REACHING CRITICAL
FIRE WEATHER CONDITIONS MAINLY CONCERN THE DEGREE OF HIGH LEVEL
CLOUD COVER JUST TO THE SOUTH AND WEST...AND HOW MUCH IT EXTENDS
OVER THE THREATENED AREA.

OTHERWISE...GENERALLY BENIGN AND PLEASANT CONDITIONS
CHARACTERIZED BY MID/HIGH LEVEL CLOUDINESS AND NEAR TO SLIGHTLY
ABOVE NORMAL TEMPERATURES WILL CONTINUE TO PREVAIL ACROSS
SOUTHCENTRAL AK THROUGH THE FIRST PART OF THE WEEKEND AS THE MOST
ACTIVE WEATHER REMAINS CONFINED TO THE FAR SOUTHERN GULF. A
STALLED FRONT OVER THE WESTERN GULF WILL CONTINUE TO BRING
OCCASIONAL LIGHT RAIN TO KODIAK ISLAND AND SOUTHERN PORTIONS OF
THE KENAI PENINSULA AS IT GRADUALLY WEAKENS INTO SATURDAY. MODEST
GAP WINDS WILL DEVELOP THROUGH TURNAGAIN ARM AND THE MATANUSKA
VALLEY ON FRIDAY AS A SURFACE RIDGE BUILDS ALONG THE NORTH GULF
COAST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TODAY THROUGH SATURDAY)...

THE AREA OF LOW PRESSURE SITUATED NEAR THE PRIBILOF ISLANDS WILL
CONTINUE TO PUSH SOUTH AND EAST THROUGHOUT THE DAY. WHAT LITTLE
REMAINS OF A FRONT THAT WAS OBSERVED LAST NIGHT HAS SINCE
DISSIPATED...WITH LARGE SCALE LIFT NOW BEING THE MAIN CULPRIT
BEHIND SHOWER ACTIVITY EXPECTED THROUGH THE WEEKEND. THE SHOWERS
WILL PREDOMINANTLY BE RAIN...WITH SOME SNOW MIXING IN OVERNIGHT
ALONG THE KUSKOKWIM DELTA COAST AND HIGHER ELEVATIONS. AS THE LOW
SLIDES SOUTH OF THE ALASKA PENINSULA ON SATURDAY...THE
SOUTHEASTERLY WINDS WILL SHIFT TOWARD THE NORTH AND A DRYING TREND
WILL BE OBSERVED. THIS SHOULD ALSO ALLOW TEMPERATURES TO GRADUALLY
WARM THROUGH THE WEEKEND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TODAY THROUGH SATURDAY)...

THE MAJORITY OF THE SHOWER ACTIVITY WILL BE CONFINED TO THE
EASTERN BERING SEA AHEAD OF THE AREA OF LOW PRESSURE OVER THE
PRIBILOF ISLANDS. COLD AIR FILTERING ACROSS THE BERING SEA WILL
CREATE STEEP MID-LEVEL LAPSE RATES CONDUCIVE TO SHOWER ACTIVITY
ACROSS THE WESTERN ALEUTIANS THIS MORNING AND GRADUALLY SHIFT
EASTWARD OVER THE WEEKEND. HIGH PRESSURE WILL BEGIN TO BUILD
ACROSS THE WESTERN BERING SEA LATE THIS AFTERNOON...WHICH SHOULD
HELP SUPPRESS SHOWER ACTIVITY FOR THE TIME BEING. AN AREA OF LOW
PRESSURE WILL THEN DEVELOP OVER THE WESTERN BERING SEA SATURDAY
NIGHT...WHICH WILL LEAD TO ANOTHER ROUND OF PRECIPITATION AND WIND
ACROSS THE WESTERN ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THERE IS GOOD AGREEMENT FROM THE MODELS THAT THE GULF LOW THIS
WEEKEND WILL REMAIN WELL SOUTH OF THE MAINLAND INTO EARLY NEXT
WEEK. THIS WILL BRING MOSTLY CLEAR SKIES TO MUCH OF THE
SOUTHCENTRAL FOR THE LATER HALF OF THE WEEKEND AND POSSIBLY SOME
OF THE WARMEST TEMPERATURES OF THE SEASON. ALONG THE NORTH GULF
COAST AND KODIAK ISLAND LIGHT SHOWERS ARE EXPECTED FROM THE LOW.
BY MID WEEK RIDGING FROM THE WEST WILL PUSH THE LOW OFF TO THE
SOUTHEAST.

THERE IS MUCH LESS AGREEMENT OUT WEST WITH THE NEXT LOW MOVING
THROUGH THE BERING SUNDAY AND MONDAY. THE OPERATIONAL RUNS LACK
CONSISTENCY WITH THE PLACEMENT OF THE LOW SO THE ENSEMBLES WHERE
USED FOR A MORE GENERALIZED LOCATION. REGARDLESS OF THE EXACT
TRACK THE LOW WILL BRING RAIN TO THE ALEUTIANS INTO EARLY NEXT
WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 170 172 173-178.
FIRE WEATHER...RED FLAG WARNING 111.

&&

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