Area Forecast Discussion
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FXAK67 PAJK 242346
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
346 PM AKDT THU JUL 24 2014

.SHORT TERM...A SOMEWHAT AIMLESS LONGWAVE CUT-OFF LOW OVER THE
GULF OF ALASKA THAT WAS RESPONSIBLE FOR SOME FRONTAL RAINS THIS
MORNING AND SOME SHOWERS THIS AFTERNOON OVER THE PANHANDLE IS
PRIMED FOR SOME EXCITEMENT TONIGHT AS A SHORTWAVE ENERGY BURSTS
SOUTH ACROSS THE KATMAI. THIS ENERGY WILL DEEPEN THE
TROUGH...FARTHER ENOUGH INTO THE NORTH PACIFIC TO TAP SOME
SUBTROPICAL MOISTURE. THIS WILL BEGIN ROUNDING THE BEND NORTHWARD
INTO THE PANHANDLE STARTING FRIDAY AND CONTINUE INTO THE WEEKEND.
THE SHORTWAVE WILL DEVELOP A SURFACE LOW WEST OF HAIDA GWAII LATE
THURSDAY NIGHT THAT WILL DRIVE A FRONT INTO THE SOUTHERN
PANHANDLE INTO FRIDAY.

FIRST PRECIPITATION...RAIN THAT HAS FALLEN OVER THE AREA HAS BEEN
SPOTTY AND SOMEWHAT INTENSE IN NATURE. I SHOULD ADD THAT THE
ECMWF`S TREATMENT FOR YAKUTAT AS WET TURNED OUT TO BE MORE CORRECT
THAN THE MUCH DRIER GFS AND NAM. THUS THE CONVECTION CALLED FOR
TODAY WORKED OUT FAIRLY WELL. THIS COLD POOL ASSOCIATED WITH THE
LOW OVER THE GULF WILL SUPPORT SHOWERS THROUGH TONIGHT AND WILL
ONLY TRANSITION INTO MORE STEADY RAINS BEGINNING FRIDAY MORNING
FOR THE SOUTHERN PANHANDLE BEFORE EXTENDING AS FAR NORTH AS LYNN
CANAL BY THE AFTERNOON. NAM SOUNDINGS SUGGEST THAT AREAS CLOSEST
TO THE CORE OF THE UPPER LOW MAY STAY A LITTLE MORE UNSTABLE, WITH
A SOUTHERLY 850 JET SPREADING NORTHWARD, IT WAS HARD TO TURN
AGAINST THE CONCEPTUAL PARADIGM OF PRE-FRONTAL STRATIFORM...SO
JUST PAINTED EVERYTHING AS RAIN FOR FRIDAY AFTERNOON SOUTHWEST OF
YAKUTAT.

WINDS...NO BIG WORRIES EXCEPT FOR THE STRENGTH OF THE SOUTHERLIES
RISING IN THE SOUTH FRIDAY MORNING. SMALL CRAFTS FOR SOUTHERN
PASSAGES LOOKED GOOD. DID CONTINUE THE TREND OF BOOSTING WINDS FOR
BLOWHOLES LIKE HYDABURG AND ADDED SOME GUSTY LANGUAGE FOR SOUTHERN
BARANOF. PARTNER ON OUR DESK TODAY NOTICED THE WRF HAD CORRECTLY PREDICTED
THE GUSTINESS IN SITKA TODAY. WRF...WE MISSED YOU DURING YOUR
ABSENCE. ALWAYS A LITTLE SKETCHY ON STRENGTH AND EVEN DIRECTION OF
WINDS WHERE SURFACE GRADIENT RUNS COUNTER TO WINDS ALOFT. KIND OF
TOOK AN AVERAGE OF STRONG SOUTHERLIES AND WEAK NORTHERLIES TO
ARRIVE AT WEAK SOUTHERLIES FOR STEPHENS PASSAGE/NORTHERN CHATHAM.

NO BIG HYDRO ISSUES EXPECTED IN THE SHORT-TERM. BUT AS IN A LOT
OF SITUATIONS THE RAINFALL AMOUNTS HAVE BEEN ON THE HEAVIER SIDE
OF PREDICTION WITH SOME OF THESE SHOWERS. GFS/GEM STILL SEEM A
LITTLE HEAVIER THAN 12Z NAM AND ECMWF. COVERED BASES AND USED A
BLEND OF BOTH.

EMPLOYED NAM/ECMWF FOR PRESS/WINDS. REPLACED NAM WITH SREF AND
ADDED GEM/GFS FOR POP/QPF. FORECAST CONFIDENCE ON GOOD SIDE OF
AVERAGE.

.LONG TERM...UPPER LEVEL LOW/TROUGH WILL REMAIN IN THE GULF OF
ALASKA THROUGH THE FORECAST PERIOD DUE TO A BLOCKED PATTERN. THIS
LOW WILL CONTINUE TO SEND WAVES OF ENERGY OVER THE PANHANDLE AND
MAKE FOR A RATHER WET FORECAST. CHALLENGE WITH THESE SORT OF
SYSTEMS IS TIMING OF THE RAIN...AS THERE WILL BE BREAKS IN
BETWEEN. ALSO EACH MODEL PLACES THE WAVES OF ENERGY (VORT MAXES)
DIFFERENTLY WHICH RESULTS IN LARGER DIFFERENCES AT THE SURFACE.

OPTED TO USE AN ENSEMBLE APPROACH TO THE FORECAST WHICH MADE FOR
ONLY MINOR CHANGES. BIGGEST ADJUSTMENT WAS TO FLIP MANY OF THE
INSIDE WATERS DIRECTIONS TO SOUTHERLY. AS MENTIONED IN THE SHORT
TERM SECTION...FLOW AT ALL LEVELS AROUND THE GULF LOW WILL BE
S-SELY OVER THE PANHANDLE. THE SURFACE PRESSURE GRADIENT IN MANY
CASES WOULD SUGGEST A LIGHT NORTH WIND WHILE THE FLOW ALOFT WOULD
SUPPORT SOUTHERLY. OPTED TO GO FOR THE GEOSTROPHIC SOUTHERLY
FLOW...HOWEVER THERE ARE SOME TIME FRAMES WHERE THE NORTH WINDS
WILL WIN OUT...IE LIKE WHEN THE LOW CENTER IS SLIGHTLY MORE TO
THE SOUTH OR WHEN THERE IS A LIGHT DIURNAL SHIFT TO NORTH IN THE
EARLY MORNING HOURS.

CONTINUED WITH THE SMALLER DIURNAL TEMPERATURE RANGE UNDER THE
CLOUDY/RAINY CONDITIONS WITH LOWS IN THE LOWER 50S AND HIGHS IN
THE UPPER 50S. MOS GUIDANCE WOULD SUGGEST HIGHS IN THE LOWER 60S EACH
DAY...BUT THERE TENDS TO BE A WARM BIAS WITH THE MOS IN THESE
CONDITIONS. FORECAST CONFIDENCE ON WET IS ABOVE AVERAGE...BUT
LOWER ON TIMING OF EACH BAND OF PRECIP MOVING IN/OUT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-033-035-036-041-042.


$$

JWA/FERRIN







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