Area Forecast Discussion - Southeastern
FXAK67 PAJK 012356
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
356 PM AKDT SAT AUG 1 2015
.SHORT TERM...A WEAK UPPER LEVEL LOW HAS FORMED OVER THE EASTERN
GULF AND WILL DRIFT EAST OVER THE SOUTHERN PANHANDLE THROUGH
SUNDAY AFTERNOON. PLENTLY OF ASCENT VIA STRONG MID LEVEL VORTICITY
WILL KEEP SCATTERED SHOWERS GOING THROUGH THE SHORT TERM FORECAST
PERIOD. NOTABLY, MODELS ARE INDICATING A WELL DEFINED BAND OF WRAP
AROUND SHOWERS IN THE NORTHWEST QUADRANT OF THE UPPER LOW OVER THE
NORTHERN INNER CHANNELS FOR LATER TONIGHT AND LASTING THROUGH
TOMORROW AFTERNOON. HAVE INCREASED POP OVER THE NORTHERN PANHANDLE
IN RESPONSE TO THIS. AT THE SURFACE, WEAK HIGH PRESSURE
DOMINATES THE EASTERN GULF AND A WEAK TO MODERATE SOUTHERLY
PRESSURE GRADIENT IS FORMING OVER THE FAR NORTHERN INNER CHANNELS.
HAVE A MARGINAL, SHORT-LIVED SMALL CRAFT ADVISORY OUT FOR NORTHERN
LYNN CANAL FOR TOMORROW AFTERNOON. ATMOSPHERIC STABILITY IN THE
LOWERS LEVELS WILL KEEP SKIES MOSTLY CLOUDY TO CLOUDS WITH LOW
CEILINGS AND AREAS OF FOG OVERNIGHT. NET EFFECT WILL BE CONVECTION
ABOVE A LOW LEVEL STABLE LAYER MANIFESTING AS PERIODS OF RAIN
THROUGH THE DAY. INSTABILITY PARAMETERS INDICATING THE POSSIBILITY
OF ISOLATED THUNDERSTORM ACTIVITY AND HAVE INCLUDED THIS IN THE
FORECAST FOR TOMORROW, BUT WITH NO NEAR SURFACE TRIGGERS SUCH AS
MECHANICAL LIFTING OR SURFACE BASED THERMAL ASCENT, ANY
THUNDERSTORM ACTIVITY WILL LIKELY HAVE TO ORIGINATE IN CANADA AND
ADVECT TO THE WEST IN THE UPPER LEVEL FLOW TO REACH SOUTHEAST
ALASKA.

NUDGED PREVIOUS PRESSURE AND WIND FORECAST TOWARDS THE 12Z NAM
MODEL RUN. POP AND QPF FROM A BLEND OF NAM, SREF, AND GFS. NO
CHANGES TO TEMPS. OVERALL FORECAST CONFIDENCE IS AVERAGE.
.LONG TERM...MODELS REMAIN IN GENERAL AGREEMENT FOR THE UPPER LOW
OVER THE SOUTHERN PANHANDLE SUNDAY NIGHT SLOWLY DRIFTS
SOUTHEASTWARD TO BRITISH COLUMBIA COAST THROUGH LATE TUESDAY.
EXPECT A SLIGHT CHANCE OF THUNDERSTORMS IN VICINITY OF THE UPPER
LOW MONDAY AFTERNOON INTO EVENING HOURS. A TROUGH OF LOW PRESSURE
FORMS ACROSS THE NORTHERN PANHANDLE SUNDAY NIGHT AND REMAINS
THROUGH THE MID WEEK. HIGH PRESSURE OVER THE SOUTH CENTRAL GULF
EXTENDS THE RIDGE ACROSS THE CENTRAL GULF. THE NAM12 WAS
INITIALIZED BEST AND USED TO REFRESH THE INHERITED FORECAST
THROUGH TUESDAY EVENING. GENERAL OFFSHORE FLOW WILL BRING SOME
BREAKS OF WET PATTERN OVER SOUTHEAST ALASKA WITH POSSIBLE SPORADIC
SHOWERS. THE TROUGH OF LOW PRESSURE OVER THE NORTHERN PANHANDLE
WILL PRODUCE UP TO 20 KNOTS WINDS FOR NORTHERN LYNN CANAL SUNDAY
NIGHT BUT CONTINUE TO DIMINISH BY EARLY NEXT WEEK.

MODEL DIFFERENCES BECOME LARGER BY MID WEEK AND USED THE WPC
ENSEMBLE GUIDANCE FROM WEDNESDAY ONWARD AND MADE A FEW CHANGES FOR
WINDS ACROSS THE OFFSHORE WATERS. A SLIGHT WARMING TREND IS
EXPECTED DURING THE FIRST HALF OF NEXT WEEK FOLLOWED BY A BIT
COOLING TREND TOWARD THE WEEKEND. 

&&
.AVIATION...PRIMARY CONCERN THROUGH THE SHORT RANGE PERIOD WILL BE
LOW CEILINGS AND GROUND FOG OVERNIGHT AND THROUGH THE START OF
AVIATION OPERATIONS SUNDAY MORNING. HAVE INCLUDED FOG IN VARIOUS
TAFS AS A RESULT. FLYING CONDITIONS IN THE LOWERS LEVELS TOMORROW
SHOULD BE SMOOTH, BUT WILL LIKELY BE A BIT MORE BUMPY ABOVE THE
CLOUDS IN A MORE CONVECTIVE AIRMASS. BE ON THE LOOKOUT FOR LARGER
CONVECTIVE BUILDUPS AND POSSIBLE THUNDERSTORMS APPROACHING
THE PANHANDLE FROM THE EAST AS THE DAY GOES BY.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012. 

&&

$$

FRITSCH/AHN

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