Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 251302
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
502 AM AKDT SAT APR 25 2015

.ANALYSIS AND UPPER LEVELS...
THE STACKED AND DECAYING LOW PRESSURE SYSTEM HAS SLID OVER THE END
OF THE ALASKA PENINSULA THIS MORNING AS A RIDGE BUILDS OVER THE
WESTERN BERING SEA...NUDGING THE PREVIOUS SYSTEM TOWARD THE GULF
OF ALASKA. THE MAJORITY OF ACTIVITY WITH THIS WEAKENING SYSTEM IS
WITHIN THE STRONGER CYCLONIC FLOW ON THE NORTHEAST QUADRANT OF THE
SYSTEM...RIGHT OVER THE SOUTHWEST MAINLAND...ALONG WITH A DECAYING
FRONTAL BOUNDARY DRAPED OVER THE CENTRAL GULF. MOST OF THESE
SHOWERS ARE DIURNALLY DRIVEN BUT THERE IS A STRONGER DISTURBANCE
TRACKING ACROSS THE SOUTHWEST THIS MORNING ENHANCING THE ACTIVITY.

&&

.MODEL DISCUSSION...
GUIDANCE CONTINUES TO BE IN GREAT AGREEMENT WITH THE MAIN SYNOPTIC
FEATURES. THE DIFFERENCES THAT HAD BEEN SHOWING UP WITH THE
DEVELOPING SURFACE LOW IN THE NORTHEASTERN PACIFIC ARE NOT AS
GREAT TODAY...SOME SLIGHT POSITIONAL DIFFERENCES WITH THE SURFACE
LOW AS THE AMERICAN MODEL ARE SLIGHTLY TO THE WEST OF THE
EUROPEAN/CANADIAN SOLUTIONS BUT FRONTAL POSITION REMAINS PRETTY
MUCH THE SAME. OVER THE WEEKEND A STRONG UPPER LEVEL DISTURBANCE
WILL RIDE THE JET INTO THE WESTERN BERING BRINGING A FRONT/SURFACE
LOW. GUIDANCE IS IN PRETTY GOOD RELATIVE AGREEMENT WITH THIS
FEATURE.

&&

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

THE SYNOPTIC WEATHER PATTERN WILL BE LARGELY DICTATED BY INTENSIFYING
LOW PRESSURE TODAY APPROACHING THE SOUTHERN GULF BEFORE BECOMING
STATIONARY AND PERSISTING IN PLACE THROUGH THE WEEKEND INTO EARLY
NEXT WEEK.

FOR THE GULF AND GULF COAST INCLUDING KODIAK...THIS WILL MEAN
INCREASING NORTH TO EAST WINDS TO GALE FORCE AS WELL AS PERIODS OF
RAIN OVER THE GULF COASTAL AND OFFSHORE ZONES. FOR INLAND
AREAS...THE MAIN CONCERN AT LEAST THROUGH EARLY SUNDAY WILL BE
WITH THE POTENTIAL FOR CRITICAL FIRE WEATHER CONDITIONS.

MODELS FOR THE THIRD CONSECUTIVE DAY YESTERDAY SIGNIFICANTLY
UNDERESTIMATED THE DEGREE OF DRYING ACROSS ALL OF
SOUTHCENTRAL...WITH CRITICAL HUMIDITY CONDITIONS OBSERVED FROM
ANCHORAGE NORTH THROUGH THE MATANUSKA VALLEY AND SUSITNA
VALLEY...AS WELL AS THROUGH THE COPPER RIVER BASIN (WHERE FUELS
ARE NOT BURNABLE AT THIS TIME). CONDITIONS SHOULD MODERATE
SOMEWHAT ESPECIALLY THIS MORNING AS THICKER MID TO HIGH-LEVEL
CLOUDS SHOULD ALLOW FOR SOMEWHAT HIGHER SURFACE DEWPOINTS ACROSS
THE AREA. HOWEVER...CLEARING WILL OCCUR FROM SOUTH TO NORTH THIS
AFTERNOON AS AN UPPER LEVEL MOVES NORTH TOWARD THE INTERIOR. THIS
SHOULD ALLOW FOR HUMIDITY VALUES TO ONCE AGAIN PLUMMET TO NEAR
CRITICAL THRESHOLDS. FOR THIS REASON...RED FLAG WARNINGS ARE IN
EFFECT FOR LOW HUMIDITY FROM EAST ANCHORAGE NORTH THROUGH THE
MATANUSKA VALLEY INTO THE SOUTHERN SUSITNA VALLEY. VERIFICATION OF
THESE RED FLAG WARNINGS WILL BE HIGHLY CONDITIONAL TO THE EXACT
TIMING OF WHEN THE CLEARING SKIES OCCURS FROM SOUTH TO
NORTH...WITH THE EC AND NAM QUICKER BY A COUPLE OF HOURS OVER THE
GFS.

AS THE LOW BECOMES MORE EXPANSIVE IN THE GULF...THE PRESSURE
PATTERN WILL ALSO CHANGE OVER THE MAINLAND AND RESULT IN AN
INCREASE IN WINDS FROM THE NORTH TO NORTHEAST FROM LATE THIS
EVENING THROUGH SUNDAY MORNING. MODELS CONTINUE TO TREND STRONGER
WITH THESE WINDS...PARTICULARLY OUT OF THE MATANUSKA VALLEY...SO
AT THIS POINT WE CAN NOT COMPLETELY RULE OUT THE POSSIBILITY OF
CRITICAL FIRE WEATHER CONDITIONS OCCURRING DURING PARTS OF THE
OVERNIGHT HOURS TONIGHT IN THE MATANUSKA VALLEY...THOUGH THE
PROBABILITIES WOULD SEEM TO BE RATHER LOW. THIS WILL BEAR CLOSE
WATCHING BY THE DAY SHIFT TODAY. THESE NORTHERLY WINDS COULD ALSO
BRING SOME WIND GUSTS TO NEAR 25 MPH OVER ANCHORAGE AS WELL
OVERNIGHT TONIGHT.

BY SUNDAY AFTERNOON...MOISTURE LEVELS ACROSS NEARLY ALL OF
SOUTHCENTRAL WILL BEGIN IMPROVING AS AN EASTERLY WAVE MOVES WEST
ACROSS THE AREA. BY SUNDAY EVENING WITH SURFACE FRONT
PASSAGE...SOUTHEAST WINDS GENERALLY 10 TO 15 MPH CAN BE EXPECTED
OUT OF TURNAGAIN ARM AND THE KNIK RIVER VALLEY BUT WITH INCREASING
HUMIDITY VALUES AND A CHANCE OF ISOLATED RAIN SHOWERS ALONG THE
CHUGACH AND KENAI MOUNTAIN RANGES FOR SUNDAY NIGHT INTO EARLY
MONDAY.

&&

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

RAIN SHOWERS WILL CONTINUE TO TAPER OFF DURING THE DAY TODAY AS
THE AREA OF LOW PRESSURE THAT HAD BEEN OVER THE EASTERN BERING SEA
CROSSES THE ALASKA PENINSULA EARLY IN THE MORNING AND GETS ABSORBED
BY AN AREA OF LOW PRESSURE DEVELOPING IN THE NORTHERN PACIFIC.
SURFACE WINDS HAVE ALREADY BEGUN TO BACK TO THE NORTH/NORTHEAST
THIS MORNING WHICH WILL HELP USHER IN SOME OF THE DRIER AIR
OBSERVED ACROSS THE INTERIOR OF ALASKA WHILE SETTING UP A DRY
OFFSHORE FLOW PATTERN THROUGH THE WEEKEND. AFTERNOON RELATIVE
HUMIDITY VALUES WILL DROP INTO THE 30 TO 40 PERCENT RANGE FOR MUCH
OF SOUTHWEST ALASKA WITH TEMPERATURES WARMING INTO THE MID 40S TO
MID 50S.

&&

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

AN AREA OF SHOWERS EXTENDING FROM THE PRIBILOF ISLANDS DOWN TO
UNALASKA/DUTCH HARBOR WILL SEE SOME LOCAL ENHANCEMENT FROM SOME
COOLER AIR MOVING ALOFT. THIS WILL HELP STEEPEN THE MID-LEVEL
LAPSE RATES TO HELP SOME CONVECTIVE SHOWERS TO DEVELOP. THE
PRIBILOF ISLANDS WILL LIKELY REMAIN ALL SNOW WHILE UNALASKA WILL
SEE A MIX OF RAIN AND SNOW IN THE MORNING WHICH WILL TRANSITION TO
RAIN IN THE AFTERNOON. SCATTERED SHOWERS WILL BE SEEN ACROSS THE
EASTERN BERING SEA TODAY AS THE LOW DEPARTS THE BERING SEA BUT
WILL TAPER OFF TONIGHT AS THE LOW GETS ABSORBED BY A NEWLY
FORMING LOW IN THE NORTH PACIFIC. ANOTHER AREA OF LOW PRESSURE
WILL DEVELOP OVER THE WESTERN BERING SEA LATE SATURDAY NIGHT/EARLY
SUNDAY MORNING AND WILL BRING SOME GALE FORCE WINDS TO THE WESTERN
ALEUTIANS AND WIDESPREAD RAINFALL ON SUNDAY TO THE WESTERN HALF OF
THE BERING SEA. COLDER AIR FILTERING IN ON THE BACK SIDE OF THE
LOW WILL ALLOW SOME OF THE SHOWERS TO MIX WITH SNOW LATE SUNDAY.

&&

.LONG TERM FORECAST (MONDAY THROUGH FRIDAY)...
GOOD AGREEMENT CONTINUES CONCERNING THE GULF LOW WITH A CONSENSUS
THAT IT WILL REMAIN IN THE SOUTHERN GULF INTO EARLY NEXT WEEK. AN
EASTERLY WAVE RIDING OVER THE NORTHERN EDGE OF THIS LOW ON MONDAY
IS SLIGHTLY STRONGER THAN YESTERDAY. THE NAM IS THE MOST
AGGRESSIVE WITH THIS WAVE AND RESULTING PRECIP INTO THE SOUTHEAST
MAINLAND...BUT IS ALSO MUCH SLOWER WITH THE WESTWARD PROGRESSION
OF THE FEATURE. AS A RESULT PRECIP CHANCES AND CLOUD COVER WERE
INCREASED EARLY NEXT WEEK OVER SOUTHCENTRAL...BUT FURTHER MODEL
TRENDS WILL NEED TO BE MONITORED FOR POSSIBLE THUNDERSTORM CHANCES
(WHICH ARE OFTEN SEEN FROM STRONGER EASTERLY WAVES IN THIS AREA).

OUT WEST THE MODELS ARE COMING INTO BETTER AGREEMENT WITH THE LOW
MOVING ACROSS THE BERING ON MONDAY BUT SOME DIFFERENCES REMAIN
WITH ITS EXACT POSITION. EITHER WAY IT IS EXPECTED TO BE A WEAKER
LOW BRINGING SHOWERS TO THE ALEUTIANS AS IT MOVES THROUGH. BY MID
NEXT WEEK THERE ARE MUCH LARGER DISCREPANCIES BETWEEN THE
GUIDANCE...ESPECIALLY WITH THE REGARDS TO THE LONGEVITY OF RIDGING
OVER THE MAINLAND. AS A RESULT THE ENSEMBLES WERE PREFERRED WHICH
KEEPS LOW PRESSURE IN THE BERING WITH WEAK RIDGING OVER THE
MAINLAND.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 131 132 138 170 172-174 176-178.
FIRE WEATHER...RED FLAG WARNING 101 111 145.

&&

$$

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


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