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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