815
FXAK67 PAJK 251347
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
547 AM AKDT SUN AUG 25 2019
SYNOPSIS
LOW PRESSURE IN THE NORTHWEST GULF DISSIPATES AS MORE
LOW PRESSURE DEVELOPS IN THE SOUTHWEST GULF THIS AFTERNOON. THE
LOW IN THE SOUTHWEST GULF THEN TRACKS INTO THE EASTERN GULF
THROUGH TUESDAY EVENING. A FRONT LIFTS ACROSS THE EASTERN GULF
MONDAY AND INTO SOUTHEAST ALASKA MONDAY NIGHT. A RIDGE OF HIGH
PRESSURE OVER THE INNER CHANNELS SHIFTS EAST INTO WESTERN CANADA
SUNDAY NIGHT.
SHORT TERM
NUMEROUS SHOWERS OCCURRED OVER MOST PORTIONS OF
SOUTHEAST ALASKA OVERNIGHT. SOME OF THE SHOWERS PRODUCED HEAVY
RATES OF RAINFALL OVERNIGHT; HOWEVER, ACTUAL 12-HOUR RAINFALL
AMOUNTS, ALTHOUGH NOT INSIGNIFICANT, MAINLY WERE UNDER A HALF
INCH. AN INTENSE SHORT-WAVE YESTERDAY EVENING DEPICTED IN WV
IMAGERY SHOT ACROSS THE NORTHERN GULF SATURDAY AND THE NORTH-
CENTRAL PANHANDLE SATURDAY EVENING. THIS FEATURE CLEARLY ENHANCED
SHOWERS. BUT UPON APPROACHING THE COAST MOUNTAINS, A THUNDERSTORM
ERUPTED IN THE HOLKHAM BAY, TRACY ARM, AND ENDICOTT ARM AREA.
FOLLOWING THE SHORT-WAVE'S CROSSING INTO BC, LIGHTNING ENDED OVER
OUR REGION.
A WEAK RIDGE OF HIGH PRESSURE OVER THE PANHANDLE WILL STRENGTHEN
THROUGH THIS EVENING. OROGRAPHICALLY ENHANCED SHOWERS WILL TEND
TOWARD WEAKENING THROUGH TONIGHT AS THE RIDGE SHARPENS AHEAD OF
A BIG STORM APPROACHING SOUTHEAST ON MONDAY. SO FAR, CONSENSUS IS
ONLY MARGINALLY BETTER, BUT CHANGES WERE MADE WITH THE ECMWF AND
06Z NAM AND CANADIAN THROUGH MONDAY NIGHT TO ELEVATE QPF, AND SOME
POP ADJUSTMENTS WERE MADE TO REFLECT THIS. AS BEST WE CAN TELL
RAIN WILL BEGIN ALONG THE IMMEDIATE COAST EARLY MONDAY MORNING AND
QUICKLY SPREAD INLAND THROUGH THE DAY. AT THIS POINT MOST ALL
POINTS WITHIN THE PANHANDLE LOOK TO RECEIVE 1 TO 2 INCHES MONDAY
AND MONDAY NIGHT. THE ONE EXCEPTION BEING YAKUTAT WHO LOOKS TO
RECEIVE LESS THAN AN INCH. BUT EVEN AS THE WEATHER FRONT PRESSES
NORTHWARD AND HANGS UP ACROSS THE NORTHERN PANHANDLE, A
DEFORMATION BAND LOOKS TO SET UP SOMEWHERE AHEAD OF THE MAIN LOW
CENTER. SHOULD THE DEFORMATION BAND SET UP OVER THE PANHANDLE, THE
NORTH-CENTRAL PANHANDLE FROM SITKA TO JUNEAU MAY SEE HEAVY RAIN
PERSIST WELL INTO MONDAY NIGHT.
WINDS WILL LIKELY BE A FACTOR AS MUCH AS HEAVY RAIN. WE INCREASED
THEM ONCE AGAIN OVER THE OUTER GULF TO AROUND 30 KT. AS GUIDANCE
NARROWS ON THE POSITION OF THE LOW, WE MAY INCREASE THEM FURTHER
TO GALES. SOME WORK WAS ALSO DONE THROUGH THE INNER CHANNELS WITH
HIGHER INCREASES OF EASTERLIES THROUGH CROSS SOUND. STRONG WIND
GUSTS OF 45 MPH OR SO ARE POSSIBLE FROM SITKA SOUTHEAST TO
KETCHIKAN AND ALL POINTS BETWEEN. WHILE ONLY HINTED AT IN THE
FORECAST, WE HOPE TO BETTER DEFINE REGIONS OF STRONG WIND GUSTS
IN THE NEAR FUTURE.
FORECAST CONFIDENCE IS MEDIUM HIGH, WITH SOME DETAILS YET TO
COMPLETELY IRON OUT.
LONG TERM.../TUESDAY THROUGH SUNDAY NIGHT/
AN UPPER LOW WILL
BE MOVING ASHORE NEAR CAPE FAIRWEATHER AT THE START OF THIS LONG
RANGE FORECAST PERIOD. A SHORT WAVE TROUGH WITH A 100KT JET MAX
WILL BE LOCATED OVER THE SOUTHERN PANHANDLE. A MUCH LARGER AND
POSITIVELY TILTED UPPER TROUGH WILL EXTEND FROM THE UPPER LOW WSW
TO THE FAR SOUTHWEST GULF. THIS LARGER TROUGH WILL PINCH OFF AN
UPPER LOW AND BECOME MORE NORTH-SOUTH ORIENTED BY WEDNESDAY
MORNING. THE CAPE FAIRWEATHER LOW WILL HAVE TRACKED WELL TO THE
EAST - TO THE NWT - BY THAT TIME AND THE JET CORE WILL HAVE
SHIFTED NORTH TO THE CENTRAL PANHANDLE AS A BROAD UPPER RIDGE
BUILDS NORTH OVER THE EASTERN GULF AND SOUTHEAST ALASKA.
AT THE SURFACE, THE LOW ASSOCIATED WITH THE UPPER LOW WILL BE
LOCATED WEST OF CROSS SOUND, SOUTH OF YAKUTAT, AND WEAKENING AS IT
MOVES SLOWLY TO THE SOUTHEAST. SHOWERS WILL BE DIMINISHING THROUGH
TUESDAY AND BY WEDNESDAY MORNING ALL OF SOUTHEAST ALASKA SHOULD BE
DRY, IF NOT SUNNY. THE DRY WEATHER SHOULD RELIABLY LAST THROUGH
THURSDAY NIGHT. BY FRIDAY MORNING, WPC AND THE NATIONAL BLEND ARE
TRYING TO BUILD IN PRECIPITATION FROM THE WEST. ECMWF IS PUSHING A
FRONT OVER THE NORTHERN PANHANDLE FROM THE SOUTHWEST AT THAT
TIME, AND THE GFS IS TOTALLY DRY. AS A RESULT, CONFIDENCE IN A DRY
WEEKEND IS BELOW AVERAGE.
MODELS ARE STILL TRYING TO BRING DOWN DAYTIME HIGHS FOR THE SECOND
HALF OF THIS WEEK. WE ARE NOW LOOKING AT HIGHS IN THE SECOND HALF
OF THE WEEK IN THE MID TO UPPER 60S. NOT THE 70S WE WERE
ORIGINALLY EXPECTING, BUT STILL SOLIDLY ABOVE NORMAL FOR THIS TIME
OF THE YEAR.
AVIATION
IF TAF WRITING WERE A VIDEO GAME, THIS WOULD BE LEVEL
FIVE DIFFICULTY, GIVEN SHOWERS AND THEIR INHERENT CEILING AND
VISIBILITY VARIABILITY, POTENTIAL CLEARING, AND FOG FORMATION. OUR
SYNOPTIC SKILL LEVEL CAN ONLY HOPE TO NEGATE THE NOISE OF VOLATILE
CHANGEABILITY AT THE CONVECTIVE MESOSCALE LEVEL. THEREFORE, 12Z
TAFS STROVE TO MAINTAIN MEAN CONDITIONS AND NOT TO GAMBLE ON
EXTREMED OUT THERE. BECAUSE OF ATMOSPHERIC INSTABILITY, WE FEEL
THAT ANY FOG THAT FORMS WILL BE FAIRLY TEMPORARY, AND THAT LOW
STRATUS WILL BE MORE LIKELY TO OCCUR. WE DO EXPECT SOME MODEST
IMPROVEMENTS TO OCCUR INTO THE AFTERNOON, BUT CONFIDENCE IN NOT
GREAT. WE ANTICIPATE A SLIGHT DETERIORATION OVERALL TONIGHT WITH
BOUNDARY LAYER COOLING. WINDS WILL NOT BE FACTOR DURING THIS TAF
PERIOD WITH SHEER FROM THE NEXT STORM LIKELY HOLDING OFF UNTIL
AFTER 12Z MONDAY.
MARINE
CONDITIONS WILL BE BENIGN TODAY AND TONIGHT ACROSS MOST
OF THE AREA (LESS THAN 25 KT WINDS); HOWEVER, A BARRIER JET IN THE
NORTHERN GULF TIPS MARINE ZONE 52 INTO SMALL CRAFT EARLY MONDAY
MORNING. WINDS AND SEAS ONLY GROW INTO TUESDAY. WE LOWERED SEAS
OVER THE NEXT 12 TO 18 HOURS OR SO TO BETTER REFLECT BUOY
INDICATED SEA-STATES.
AJK WATCHES/WARNINGS/ADVISORIES
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ052.
JWA/FRITSCH
VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page