Area Forecast Discussion
Issued by NWS Anchorage, AK

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
000
FXAK68 PAFC 240023
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
423 PM AKDT SUN AUG 23 2015

.ANALYSIS AND UPPER LEVELS...
THE MAIN FORECAST CHALLENGE OF THE DAY CONTINUES TO BE STRONG
NORTHWESTERLY WINDS FROM THE ALASKA PENINSULA THROUGH
SOUTHCENTRAL ALASKA. A STRONG PRESSURE GRADIENT BETWEEN A
WEAKENING VERTICALLY STACKED OCCLUDED LOW IN THE NORTHEASTERN GULF
OF ALASKA AND PERSISTENT HIGH PRESSURE OVER THE CENTRAL ALEUTIANS
IS FORCING THE STRONG WINDS THROUGH FAVORED GAPS. ADDITIONAL
SUPPORT FOR THE WINDS IS BEING PROVIDED THROUGH SUBSIDENCE BEHIND
AN UPPER WAVE MOVING THROUGH SOUTHCENTRAL ALASKA. FURTHER
WEST...AN UPPER LEVEL JET STREAK STRETCHES FROM EASTERN RUSSIA
THROUGH TO KODIAK ISLAND. THIS IS TRANSPORTING A STREAM OF
MOISTURE FROM A SUBTROPICAL AIRMASS LOCATED OVER THE FAR WESTERN
BERING SEA SOUTHEASTWARD ACROSS WESTERN ALASKA AND THROUGH TO THE
NORTHERN PACIFIC.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT SYNOPTICALLY THROUGH THE MID TERM.
THE RIDGE OVER THE BERING SEA WILL BUILD EASTWARD OVER THE
MAINLAND TUESDAY BEFORE FLATTENING OUT MIDWEEK AS A STRONG
SUBTROPICAL JET MOVES IN FROM THE BERING SEA. FURTHER UPSTREAM...
MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE TRACK OF A LOW THAT
WILL ELONGATE OVER THE FAR WESTERN BERING SEA MON NIGHT WITH ONLY
MINOR DIFFERENCES IN THE PLACEMENT OF THE CONSOLIDATED LOW CENTER.
THIS ELONGATED LOW WILL RESULT IN AN INCREASED PRESSURE GRADIENT
OVER THE BERING SEA AND WESTERN ALEUTIANS WITH THE IMPACTS OF THE
MODEL DIFFERENCES REMAINING MINIMAL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
OUTFLOW WINDS ARE EXPECTED TO CONTINUE THROUGH EARLY TUESDAY
MORNING AS THE LOW IN THE SOUTHEASTERN GULF OF ALASKA MOVES
SLOWLY SOUTHEASTWARD AND WEAKENS. PRECIPITATION WILL BEGIN TO
TAPER OFF OVER THE REGION OVERNIGHT WITH ONLY ISOLATED SHOWERS
EXPECTED MONDAY OVER THE ALASKA RANGE AND THE WRANGELLS. GALE
FORCE WINDS ALONG THE BARREN ISLANDS AND THE SOUTHERN TIP OF
KODIAK ISLAND WILL DIMINISH OVERNIGHT.

AS THE RIDGE BUILDS NORTHEASTWARD INTO THE NORTHERN GULF OF
ALASKA ON MONDAY...THE FLOW ALOFT OVER SOUTHWEST AND CENTRAL
ALASKA WILL BECOME SOUTHWESTERLY...ALLOWING A SWATH OF TROPICAL
MOISTURE TO MOVE INTO WESTERN AND INTERIOR ALASKA. WHILE MOST
OF THE MOISTURE WILL REMAIN NORTH AND WEST OF SOUTHCENTRAL...A
SHORTWAVE MOVING ALONG THE TOP OF THE RIDGE ON TUESDAY WILL
PRODUCE SCATTERED SHOWERS OVER THE SUSITNA VALLEY AND THE
COPPER RIVER BASIN.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 - 3)...
IMPULSES MOVING AROUND THE BERING HIGH WILL CONTINUE TO BRING
MAINLY SHOWERS THROUGH TUE. AS THE FRONT REARRANGES ITSELF ALONG
THE NORTHERN EDGE OF THE RIDGE...MORE SUBSTANTIAL RAIN WILL SPREAD
INLAND OVER SOUTHWEST AK TUE NIGHT AND WED. THIS WILL BE
ACCOMPANIED BY SLOWLY INCREASING SOUTHWEST WIND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 - 3)...
AS THE BERING RIDGE SLIDES EAST...RAIN AND GALE FORCE WINDS WILL
SPREAD FROM THE WESTERN ALEUTIANS TO THE CENTRAL ALEUTIANS
TONIGHT INTO TUE. AT THAT TIME THE FRONT WILL REORIENT AND STALL
ACROSS THE SOUTHERN BERING THROUGH WED...AS WINDS DIMINISH TO
SMALL CRAFT LEVELS. THE HEAVIEST RAIN THROUGH THIS TIME FRAME WILL
FALL JUST NORTH OF THE CHAIN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE MODELS REMAIN IN FAIR OVERALL AGREEMENT THROUGH MIDWEEK...BUT
CONTINUE TO DIVERGE LATER IN THE WEEK. THEY DIFFER WITH REGARDS TO
THE STRENGTH OF THE BERING SEA RIDGE AND ASSOCIATED ENERGY RIDING
OVER TOP OF IT. THE ECMWF...BEING THE FAVORED SOLUTION...CONTINUES
TO BRING AN UPPER LEVEL TROUGH DIGGING THROUGH THE BERING SEA AND
SOUTHWEST MAINLAND WEDNESDAY NIGHT THROUGH THURSDAY...AND INTO THE
GULF BY THURSDAY NIGHT. ONE TROUGH AFTER ANOTHER WILL DROP OUT OF
EASTERN SIBERIA AND FOLLOW A SIMILAR TRACK THROUGH THE BERING AND
INTO THE SOUTHERN MAINLAND THROUGH EARLY NEXT WEEK...KEEPING MUCH
OF THE SOUTHERN MAINLAND UNDER A WET AND COOLING REGIME FROM
MIDWEEK THROUGH EARLY NEXT WEEK. THE GFS ON THE OTHER HAND KEEPS
A MORE PERSISTENT RIDGE OVER THE NORTH PACIFIC AND BERING WHICH
KEEPS ANY ENERGY EXITING SIBERIA FURTHER NORTH BEFORE DIVING
SOUTHEASTWARD ACROSS MAINLAND ALASKA...AND EVENTUALLY INTO THE
GULF. THE GFS IS ALSO MORE AGGRESSIVE WITH SPINNING UP A STRONGER
SURFACE LOW OVER THE GULF BOTH OVERNIGHT THURSDAY AND SUNDAY
MORNING. THIS PATTERN WOULD BRING SLIGHTLY DRIER CONDITIONS LATER
IN THE WEEK INTO NEXT WEEKEND...ALONG WITH STRONGER NORTHWEST FLOW
AND OUTFLOW GAP WINDS OVER THE AREA IN THIS TIME FRAME.

IN EITHER CASE...RAIN WILL LIKELY AFFECT THE SOUTHERN MAINLAND
SOMETIME MID TO LATE IN THE WEEK...WITH A COOLING TREND SETTING
UP OVER THE BERING AND MAINLAND THURSDAY THROUGH EARLY NEXT WEEK.
FORECAST CONFIDENCE IN THE DETAILS REMAINS LOW DUE TO CONTINUED
LARGE SCALE DIFFERENCES IN THE MODELS.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 130 131 132 150 176 177 178 179 181 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...RD
SOUTHCENTRAL ALASKA...RF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...TP



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.