474
FXAK68 PAFC 211730 CCA
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
930 AM AKDT SAT SEP 21 2019
ANALYSIS AND UPPER LEVELS
CURRENTLY UPPER LEVEL TROUGHING STRETCHES ACROSS MAINLAND ALASKA
WITH A SURFACE LOW CENTERED NEAR PRINCE WILLIAM SOUND. THE
ASSOCIATED FRONTAL SYSTEM EXTENDS OVER MUCH OF SOUTHCENTRAL
WITH A SHORT WAVE TROUGH OVER SOUTHWEST ALASKA AND KODIAK ISLAND
PUSHING EAST. A TRANSIENT UPPER LEVEL RIDGE OVER THE EASTERN
BERING IS PUSHING ONSHORE OVER THE KUSKOKWIM DELTA FOLLOWED BY A
VERTICALLY STACKED LOW IN THE CENTRAL BERING. ANOTHER FRONTAL
SYSTEM IS LOCATED TO THE SOUTHWEST OF THE WESTERN ALEUTIANS.
MODEL DISCUSSION
OVERALL MODELS ARE IN GOOD SYNOPTIC AGREEMENT THROUGH THE SHORT
TERM. SOME DIFFERENCES START BEING INTRODUCED SUNDAY AFTERNOON
THROUGH MONDAY REGARDING THE SPEED AND STRENGTH OF THE LOW THAT
WILL TRACK FROM WEST TO EAST ACROSS THE GULF.
AVIATION
PANC...RAIN WILL PERSIST THROUGH AROUND MIDDAY SATURDAY. WHILE
VISIBILITY MAY BE BRIEFLY REDUCED IN HEAVIER BANDS OF RAIN, EXPECT
VFR CEILING/VIS TO PREVAIL FOR MOST OF THE TIME. DRIER AIR WILL BEGIN
TO FILTER IN SATURDAY AFTERNOON AND EVENING, BRINGING AN END TO
THE RAIN AND ALLOWING CEILINGS TO RISE.
SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)
AREAS OF RAIN AND SHOWERS PERSIST THIS MORNING ACROSS MUCH OF
SOUTHCENTRAL AS THE UPPER LEVEL TROUGH IS SITUATED OVER THE
SUSITNA VALLEY AND SOUTHWARD TO NEAR KODIAK ISLAND. AS THIS TROUGH
PROGRESSES EASTWARD THROUGHOUT THE DAY, RAIN WILL TAPER OFF IN
THE COOK INLET REGION. THE NORTHERN PRINCE WILLIAM SOUND AREA
INTO THE COPPER RIVER BASIN WILL CONTINUE TO SEE SOME RAIN INTO
THE OVERNIGHT HOURS TONIGHT. THE AIR ALOFT IS A BIT COLDER THAN
RECENT SYSTEMS SO FRESH SNOWFALL WILL LIKELY BE SEEN ON SOME OF
THE MOUNTAINS AFTER THIS SYSTEM CLEARS. THE CLEARING TONIGHT IS
STILL EXPECTED ACROSS THE COOK INLET REGION, INCLUDING THE
ANCHORAGE BOWL AND MAT-SU VALLEYS. FOR ANCHORAGE AND NORTHWARD,
THE CLOUDS MAY LINGER WELL INTO THE EVENING WHICH COULD LIMIT THE
EXTENT OF THE AREAS THAT WILL SEE THE FIRST FREEZE OF THE SEASON.
FOG IS ALSO POSSIBLE IN THIS WET ENVIRONMENT WITH CLEARING SKIES.
THE NEXT STORM WILL MOVE INTO THE KODIAK AREA BY SUNDAY AFTERNOON
AND ENCOMPASS THE GULF OF ALASKA AND COASTAL AREAS BY SUNDAY
NIGHT. THIS LOW WILL TRACK ACROSS THE SOUTHERN GULF WHICH WILL
LIMIT THE PRECIPITATION TO MOSTLY COASTAL AREAS.
SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1-3: SAT-MON)
THE Y-K DELTA WILL SEE AN INCREASE IN CLOUD COVER AND RAINFALL AS
A FRONT ASSOCIATED WITH A LOW POSITIONED NEAR ST. MATTHEW ISLAND
MOVES EASTWARD TOWARD THE COAST THIS MORNING. WIDESPREAD SHOWERS
WILL CONTINUE TO MOVE INLAND TOWARDS THE KUSKOKWIM VALLEY THROUGH
THE AFTERNOON. THIS SHOWERY PATTERN WILL STAY AROUND SOUTHWEST
ALASKA LATER TODAY AS A DEFORMATION ZONE DEVELOPS BETWEEN THIS
WEAKENING LOW AND A SECOND, STRONGER LOW ALONG THE CENTRAL
ALEUTIANS ON SUNDAY MORNING. AS THIS NEW FRONTAL SYSTEM MOVES
EASTWARD THROUGH SUNDAY AFTERNOON, THE HEAVIEST RAINFALL WILL BE
MOSTLY CONFINED TO THE AKPEN AND THE SOUTHERN BRISTOL BAY REGION
THROUGH SUNDAY EVENING. A FEW SHOWERS WILL LINGER AROUND THE
REGION THROUGH MONDAY AFTERNOON AS THIS SYSTEM CONTINUES TO
PROGRESS EASTWARD.
SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1-2: SAT-SUN)
GALE FORCE WINDS AND RAINFALL ASSOCIATED WITH A LOW NEAR ST.
MATTHEW ISLAND WILL DIMINISH THROUGH THIS AFTERNOON AS THE LOW
PUSHES INLAND NEAR HOOPER BAY THIS EVENING. AS THIS LOW WEAKENS,
THE FOCUS QUICKLY SHIFTS TOWARDS THE CENTRAL ALEUTIANS THIS
AFTERNOON AS A STRONG LOW IMPACTS THE AREA.
THIS LOW SEEMS TO BE MOVING A BIT FASTER THAN PREVIOUS MODEL
RUNS. AS THE LOW MOVES EASTWARD, IT WILL BRING GALE FORCE WINDS TO
THE EASTERN ALEUTIANS AND BERING BY SUNDAY AFTERNOON, WITH A
BRIEF PERIOD OF STORM FORCE WINDS ON THE BACK SIDE OF THIS LOW
NEAR DUTCH HARBOR TO COLD BAY TOMORROW AFTERNOON THROUGH EVENING.
THIS FEATURE WILL CONTINUE TO STRENGTHEN AS IT MOVES INTO THE GULF
ON MONDAY.
MARINE (DAYS 3 THROUGH 5)
AN OCCLUDED STORM FORCE LOW WILL CONTINUE MOVING EASTWARD INTO THE
GULF MONDAY. BROAD NORTH/NORTHWEST FLOW AT SUB-GALE MAGNITUDE WILL
PREVAIL OVER THE BERING SEA, THOUGH GALES ARE LIKELY TO PERSIST
SOUTH OF THE AKPEN THROUGH MONDAY NIGHT, AS THE BACKSIDE OF THE
PROJECTED LOW WILL BE OVER THE AKPEN/WESTERN GULF. IN THE GULF OF
ALASKA, THERE CONTINUES TO BE UNCERTAINTY REGARDING THE PROGRESSION
OF THE LOW MONDAY. THE LAST SEVERAL RUNS OF THE GFS HAVE SPAWNED
STRONG SECONDARY LOWS IN THE GULF. THOUGH WE'RE NOT BUYING INTO
THESE MESOSCALE FEATURES JUST YET, THERE IS MODERATE CONFIDENCE IN
GALES SOMEWHERE IN THE GULF MONDAY... BUT UNCERTAINTY REMAINS WITH
LOCATION AND DURATION. THE LOW WILL EXIT TO THE EAST TUESDAY INTO
WEDNESDAY AND WINDS OVER THE GULF WILL DIMINISH, THOUGH STRONGER
GAP WINDS WILL LIKELY PERSIST A BIT LONGER OVER THE BARREN
ISLANDS. MEANWHILE, A STRONG LOW WILL APPROACH THE BERING. THIS
WILL LIKELY BRING GALES, IF NOT STORM FORCE WINDS TO THE WESTERN
ALEUTIANS/BERING BY TUESDAY, SPREADING TO THE CENTRAL BERING
WEDNESDAY.
LONG TERM FORECAST (DAYS 3 THROUGH 7)
A RELATIVELY PROGRESSIVE PATTERN WILL CONTINUE AS A LOW TRACKS
EASTWARD INTO THE GULF MONDAY, BRINGING WIDESPREAD PRECIPITATION
TO THE GULF/NORTH GULF COAST MONDAY. MEANWHILE, BROAD NORTHWEST
FLOW WILL PERSIST OVER THE BERING, BRINGING SHOWERS AS COLD AIR
PASSES OVER WARMER WATERS. BRIEF UPPER RIDGING WILL DEVELOP OVER
THE BERING IN THE TUESDAY TO WEDNESDAY TIMEFRAME, AND AS THE GULF
LOW EXITS TO THE EAST, CONDITIONS WILL TREND DRIER. THAT SAID, A
JET STREAK ALONG THE EASTERN EDGE OF THE RIDGE WILL MAINTAIN
CLOUDY CONDITIONS AND SCATTERED SHOWERS OVER THE SOUTHERN MAINLAND
WEDNESDAY.
LOOKING FARTHER WEST, A STRONG LOW WILL APPROACH THE WESTERN
BERING/ALEUTIANS ROUGHLY IN THE WEDNESDAY TO THURSDAY TIMEFRAME.
THIS LOW WILL ORIGINATE FROM TROPICAL STORM TAPAH, WHICH IS
CURRENTLY 300 MILES EAST OF TAIWAN. AS PER USUAL, MODELS ARE
STRUGGLING WITH THE EVOLUTION OF THIS LOW. STRONG WINDS AND A GOOD
SHOT OF RAIN ARE LIKELY OVER THE WESTERN AND CENTRAL ALEUTIANS
THURSDAY INTO FRIDAY. THE WET PATTERN LOOKS TO EXTEND INTO
SOUTHCENTRAL NEXT WEEKEND, BUT IT'S TOO EARLY TO HAVE MUCH
CONFIDENCE IN DETAILS.
AFC WATCHES/WARNINGS/ADVISORIES
PUBLIC...URBAN AND SMALL STREAM FLOOD ADVISORY 101
MARINE...GALE WARNING 130 131 132 150 160 165 170 171 172 173 174
176 180 185 351 352 414.
FIRE WEATHER...NONE.
SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...MM
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