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000
FXAK67 PAJK 251424
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
624 AM AKDT SAT MAY 25 2013

.SHORT TERM...SCATTERED SHOWERS ARE EXPECTED THIS AFTERNOON FOR
MANY OF THE ZONES NEAR THE COAST MOUNTAIN RANGE. OTHERWISE THE
STABLE CONDITIONS INCLUDING DIURNAL CYCLES OF SEA STRATUS AND FOG
ARE EXPECTED TO BE PREVALENT. SHOWERS DEVELOPING FROM THE EASTERLY
FLOW FEATURES HAVE BELOW AVERAGE CONFIDENCE. THE REMAINDER OF THE
SHORT RANGE FORECAST PACKAGE HAS AVERAGE CONFIDENCE.

A 500H LOW OVER THE SEATTLE VICINITY, AS WELL AS A SECOND LOW OVER
ALBERTA, ARE SUPPORTING SYNOPTIC-SCALE FLOW THAT INCLUDES E FLOW
ACROSS MOST OF B.C. THE GOES IR LOOP SHOWS SEVERAL SMALL- SCALE
VORTICITY FEATURES MOVING FROM OVER CENTRAL B.C. AND OVER THE
PANHANDLE.

A 500H RIDGE EXTENDS WSW FROM OVER GREAT SLAVE LAKE AND OVER THE
CENTRAL PANHANDLE. WE SOMETIMES CALL A RIDGE ALOFT "DIRTY" IF
SHORT WAVES ARE ABLE TO TRAVEL THROUGH IT, EVEN IF THESE WAVES ARE
WEAKENING. IN THE PRESENT CASE, WE HAVE A DIRTY RIDGE THAT IS
WEAKENING THE SHORT WAVES ENOUGH TO LIMIT PRECIPITATION, BUT THE
ISENTROPIC LIFT SHOULD PREVAIL ENOUGH TO GENERATE THE SCATTERED
SHOWERS DISCUSSED ABOVE. THE ISENTROPIC LIFT IS WEAK AND DIFFICULT
TO IDENTIFY S OF SUMNER STRAIT.

THE MODELS POINT TO A SMALL LOW ALOFT ABOUT 300 NM S OF MIDDLETON
ISLAND, AND THE GOES IR SHOWS A LIMITED AREA OF CLOUD MASS
CONSISTENT TO THIS COLD CORE LOW ALOFT. THIS LOW WILL DRIFT N BUT
HAS ALMOST NO ASSOCIATED FEATURES LOWER THAN THE 700H.

A SURFACE RIDGE OF HIGH PRESSURE EXTENDS N FROM THE N PACIFIC
ALONG TO THE VICINITY OF ICY CAPE. THE RIDGE AXIS WILL TILT IN
RESPONSE TO A 995 MB LOW ABOUT 400 NM S OF KODIAK, AND BY 12Z SUN
THE RESULT WILL BE THE RIDGE EXTENDING NW ALONG A LINE FROM
KETCHIKAN TO SITKA AND NW TO PRINCE WILLIAM SOUND.

THE GOES IR ALSO SHOWS THE CLOUD SHIELD ASSOCIATED WITH AN OCCLUDED
SYSTEM WITH A TRIPLE POINT ABOUT 500 NM S OF KODIAK. THE NAM IS
ACCEPTED WITH A SOLUTION OF 25 KT WINDS IN THE SW SECTION OF THE
OFFSHORE ZONE (PKZ310) BY 12Z SUN. THE SYSTEM DISCUSSED IN THIS
PARAGRAPH IS NOT SIGNIFICANT FOR ANY OTHER ZONE IN OUR AREA OF
RESPONSIBILITY THROUGH 12Z SUN. PLEASE NOTE THE LONG RANGE SECTION
FOR FEATURES MOVING TOWARD OUR AREA FROM THE SW.

MODELS: THE CONVECTION FOR THIS AFTERNOON WILL BE ASSOCIATED WITH
ESE FLOW ACROSS THE COAST MOUNTAIN RANGE. ISENTROPIC UPGLIDE IS
INDICATED FOR THE FLOW MOVING PAST THE UPPER LEVELS OF THE COAST
MOUNTAIN RANGE ON THE TWO MODELS THAT HAD BEST INITIALIZATION: THE
NAM AND THE ECMWF.


 .LONG TERM...UPPER HIGH OVER NW CANADA WILL DRIFT WWD INTO SE
INTERIOR AK BY TUE. ELONGATED UPPER LOW WILL DRIFT EWD ACROSS THE
NE PAC THEN STALL OVER THE FAR ERN PART OF THE NE PAC BY TUE
NIGHT. A GENERAL ELY FLOW WILL CONTINUE OVER SE AK THRU MIDWEEK.
MODELS STILL STRUGGLING WITH DETAILS ON SHORTWAVES MOVING WWD THRU
THE AREA...WITH THE MOST CONCERNING SHORTWAVE NOW OVER SRN ALBERTA
PROVINCE. LOOKS LIKE THIS FEATURE WILL DRIFT NW THRU SUN NIGHT
THEN DRIFT WWD ACROSS NRN BC EARLY NEXT WEEK. EVENTUALLY THE UPPER
LOW TO THE SOUTH WILL LIFT NWD THRU THE AREA...LIKELY DURING THE
LATTER HALF OF NEXT WEEK. ENDED UP USING A GFS/NAM BLEND MAINLY
FOR THE WAY THEY HANDLED THE WINDS OVER THE GULF FOR SUN- MON
PERIOD.

FOR SUN INTO MON...SMALL UPPER LOW OVER THE GULF WILL DRIFT NW
ACROSS THE NRN GULF EARLY IN THE PERIOD. THIS FEATURE WILL
INTERACT WITH SOME OF THE MOISTURE BEING ADVECTED IN FROM THE ESE
AND LIKELY CAUSE SOME RAIN OVER THE NE GULF AREA SUN MORNING.
WOULD EXPECT THIS PRECIP TO MOVE OUT SUN AFTERNOON AS UPPER LOW
PULLS AWAY FROM THE AREA AND SHORT WAVE RIDGING MOVES IN. THE
OTHER AREA THAT MIGHT GET SOME PRECIP DURING THIS PERIOD IS THE
FAR SE...WHERE SOME SHORTWAVE ENERGY WILL MOVE ACROSS FROM THE E.
THIS PRECIP LOOKS MORE SHOWERY...AND BY MON AFTERNOON...SOME
MODELS SUGGEST POTENTIAL FOR TSTMS IN THE HYDER AREA. DID NOT PUT
TSTMS IN YET DUE TO MODEL TIMING OF SHORTWAVE FEATURES AND
POSITION OF BEST INSTABILITY AND LOW LEVEL CONVERGENCE CHANGING
WITH EACH MODEL RUN. GFS DID SHOW NEGATIVE SHOWALTER INDEX
VALUES...WHICH WOULD ALLOW CONVECTION MOVING IN FROM THE E TO
SURVIVE LONGER EVEN IF LOWER LEVEL AIRMASS REMAINS ON THE COOL
SIDE.

FOR MON NIGHT INTO MIDWEEK...LOOKS LIKE MORE SHORTWAVE ENERGY
WILL BE MOVING IN FROM THE E DURING THIS TIME. BROUGHT IN MORE
CLOUDS TO MUCH OF THE AREA MON NIGHT AND TUE DUE TO POTENTIAL FOR
MID-LEVEL CLOUDS MOVING IN FROM THE E. ALSO WENT FOR A LARGER AREA
OF CHANCE POPS ESPECIALLY BY LATE TUE NIGHT DUE TO THE UNCERTAINTY
ON EXACT TRACK OF SHORTWAVE FEATURES. BLENDED IN WPC POPS WITH
PREVIOUS FORECAST TO DO THIS.

BETTER CHANCE FOR PRECIP SHOULD ARRIVE FOR THE LATTER HALF OF THE
WEEK AS UPPER LOW LIFTS NWD THRU THE ERN GULF. KEPT IN CHANCE TO
LIKELY POPS FOR MOST OF THE AREA WED NIGHT INTO FRI. ALL IN
ALL...FORECAST CONFIDENCE REMAINS BELOW AVERAGE DUE TO THE UPPER
AIR PATTERN WE ARE IN.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...DENSE FOG ADVISORY UNTIL 8 AM AKDT THIS MORNING FOR AKZ017.
MARINE...NONE.

&&

$$

JBT/RWT