Area Forecast Discussion
Issued by NWS

Home | 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
000
FXAK67 PAJK 221440
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
540 AM AKST SAT NOV 22 2014

.SHORT TERM...BROAD UPPER LOW IS OBSERVED IN WV IMAGERY THIS
MORNING CENTERED OVER THE SWRN TIP OF THE AK PENINSULA. POLAR JET
RESIDES S OF THIS FEATURE...AND SPREADS EWD INTO ORE/WA. MIDLEVEL
VORT LOBE POSITIONED OVER THE CNTRL GULF IS ADVANCING N AND E
AROUND THE UPPER LOW. A PIECE OF THIS FEATURE WILL SHEAR EWD INTO
SERN AK THIS AFTERNOON/EVENING...LIKELY AIDING IN A MORE ORGANIZED
BAND OF SHOWERS. MIDLEVEL LAPSE RATES ARE STEEP ACROSS THE REGION
GIVEN THE PRESENCE OF H5 TEMPERATURES AROUND -32C. AS A
RESULT...WEAK MUCAPE VALUES ARE WIDESPREAD. THIS POTENTIAL
INSTABILITY COULD SUPPORT AN ISOLATED THUNDERSTORM OVER THE GULF
WATERS AND ADJACENT COAST. HOWEVER...THE COMBINATION OF
RELATIVELY COLD WATER TEMPERATURES /AROUND 9C/...AND WEAK FORCING
FOR ASCENT ASSOCIATED WITH THE PREVIOUSLY MENTIONED UPPER VORT
LOBE MAKES THE OVERALL PROBABILITY TOO LOW TO INCLUDE IN THE SHORT
TERM FORECAST.

THOUGH SURFACE ISOBARS ARE GENERALLY ORIENTED PARALLEL TO N-S
CHANNELS...SOME ENHANCEMENT TO SLY WINDS IS EXPECTED OVER LYNN
CANAL AND STEPHENS PASSAGE THROUGH THIS AFTERNOON/EVENING AS THE
DISTURBANCE OVER THE GULF APPROACHES THE CNTRL PANHANDLE. CURRENT
FORECAST CALLS FOR SLYS TO 20 KT...WITH WEAKENING OCCURRING OVERNIGHT.
ONLY MARINE HAZARD CONTINUES TO BE SMALL CRAFT SEAS OVER THE
OUTSIDE WATERS. SOME BREAKS IN MIDLEVEL CLOUD COVER WILL BE
POSSIBLE OVER THE SRN HALF OF THE PANHANDLE TONIGHT AS PRIMARY
BAND OF SHOWERS PASSES E WITH THE DISSIPATING UPPER WAVE. THIS MAY
YIELD ENHANCED RADIATIONAL COOLING AT THE SURFACE...AND WHEN
COMBINED WITH RECENT RAINFALL...WOULD INCREASE THE PROBABILITY FOR
FOG. HOWEVER...THIS SCENARIO COULD BE OFFSET BY THE STEEP LAPSE
RATE/CONVECTIVE ENVIRONMENT. DESPITE THIS CAVEAT...INCLUDED PATCHY
FOG FROM JUNEAU S TO KETCHIKAN LATE TONIGHT.

.LONG TERM...WHILE THE BROAD UPPER LOW NOTED ABOVE AGES IN PLACE
OVER THE FAR WESTERN GULF, THE RESULTANT ONSHORE FLOW PATTERN
OVER SOUTHEAST ALASKA WILL CONTINUE TO DIRECT SHOWERS OVER THE
PANHANDLE FOR SUNDAY. BUT LOOKING WESTWARD ACROSS THE PACIFIC TWO
OTHER CHARACTERS WILL ALSO IMPACT SOUTHEAST`S WEATHER, ONE
POTENTIALLY SHIFTING US TO A DRIER PATTERN BY MIDWEEK.

THE FIRST IS A SHORT-WAVE CURRENTLY DROPPING SOUTH ACROSS THE
ALEUTIANS INTO THE NORTH PACIFIC AROUND 45 N 175 W. THIS SHORTWAVE
WILL LATCH ON TO A 175 KT SOUTHWESTERLY JET DEVELOPING ACROSS THE
PACIFIC WHICH WILL USHER IT INTO THE SOUTHEASTERN GULF SUNDAY
NIGHT. A BAROCLINIC LOW WILL FORM ALONG THIS WAVE AS IT ARRIVES
SOMEWHERE CLOSE TO PRINCE OF WALES ISLAND/DIXON ENTRANCE LATE
SUNDAY NIGHT/EARLY MONDAY MORNING. THIS IS A NEW FEATURE THAT THE
MODELS HAVE RESOLVED AND MAKES SENSE WITH ITS DEVELOPMENT, GIVEN
ITS POSITION EXITING THE JET ALONG A REGION OF CLOSELY PACKED
ISOTHERMS. THE MAIN UNCERTAINTY IS PATH AND TO SOME DEGREE ITS
STRENGTH. THE ECMWF AT THIS JUNCTURE SEEMS A LITTLE WEAK WITH THE
FEATURE AND FARTHER SOUTH AND EAST THAN THE OTHER SOLUTIONS. AS
THE GEM ADVERTISED A SLIGHTLY STRONGER FEATURE AT 997 MB, WE
PREFERRED THE MIDDLE GROUND OF THE 06Z NAM AND THE 00Z GFS.
DESPITE A LOWER LEVEL JET AT 925 MB OF 40 KT, WE HELD CLARENCE
STRAIT TO 25 KT SINCE THE WARM AIR ADVECTION ASSOCIATED WITH IT
SHOULD MITIGATE MOMENTUM DOWN TO THE SURFACE. IN TURN WE DID
RAISE WIND SPEEDS TO 15 TO 25 MPH FOR ZONE 27, BUT DID NOT INCLUDE
GUSTS AT THIS POINT DUE TO INCREASING STABILITY. THIS FEATURE WILL
DAMPEN CONVECTION ACROSS THE NORTHERN PANHANDLE WITH SOME OFFSHORE
COMPONENT WINDS DEVELOPING, BUT WILL PERHAPS SPREAD SOME HEAVIER
RAINS FOR THE FAR SOUTHERN ZONES LATE SUNDAY NIGHT.

ANOTHER FEATURE JUMPING OFFSHORE FROM THE SIBERIAN COAST WILL REV
UP AS IT TAPS MOISTURE FROM THE PHILIPPINES. THIS DEEPENING LOW
WILL PROP UP THE RIDGE TO ITS EAST ESCORTING THE LOW INTO THE BERING
SEA. AS IT DOES SO, THE FORWARD MOMENTUM WILL PUSH THE FORMER
GULF UPPER LOW, NOW A TROUGH TO THE EAST. AS THE TROUGH PASSES THE
PANHANDLE, SOMETIME AROUND MID-WEEK, A DRYING PERIOD COULD EMERGE
WITH SOME CONTINUING COOLING AS WELL. BUT UNCERTAINTY STILL EXISTS
AS A THIRD PLAYER IN THE FORM OF CUT-OFF LOW TO THE SOUTH COULD
POTENTIALLY SPREAD MOISTURE LATE IN THE WEEK NORTHWARD. SO AT THIS
TIME, KEEPING RAIN LIKELY TO END THE WEEK, ESPECIALLY FOR THE
SOUTHERN PANHANDLE WITH A CHANCE FOR THE NORTH.

1000 TO 850 MB THICKNESSES STILL GREAT ENOUGH TO SEEMINGLY PREVENT
MOST RAIN SHOWERS FROM BEING MIXED WITH SNOW IN THE NEAR TERM. BUT
THEY DO DECREASE SLOWLY THROUGH EARLY NEXT WEEK. HOWEVER, THIS
COOLING IS LIKELY TO BE ACCOMPANIED BY A DIMINISHING TREND IN THE
SHOWERS. THUS WHILE A FEW FLAKES ARE NOT OUT OF THE QUESTION, A
FIRST BIG SHOVEL-DESERVING SNOW DOES NOT APPEAR TO BE IN THE CARDS
LEADING INTO THE BIG HOLIDAY.

USED 00Z GFS/06Z NAM FOR WIND UPDATES SUNDAY NIGHT INTO MONDAY
MORNING. NUDGED TO 00Z GFS FOR TUESDAY/WEDNESDAY TO CONTINUE A
DRYING TREND MID-WEEK. FORECAST CONFIDENCE GOOD THROUGH
MONDAY...INCREASING FOR MID-WEEK BUT STILL NOT GREAT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043-051-052.

&&

$$

GARNER/ADKINS

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU








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