Blizzard and Heavy Snow in Alaska, January 10 to 13, 2010

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
633 AM AKST SUN JAN 10 2010

.SHORT TERM...A 956 MB LOW IN THE SOUTH CENTRAL GULF THIS MORNING
CONTINUES TO TRACK NW. SATELLITE IMAGERY SHOWS AN EXTENSIVE CLOUD
SHIELD THAT COVER THE ENTIRE NORTHERN AND EASTERN GULF AS WELL AS
ALL OF THE PANHANDLE MODEL THICKNESS VALUES AS WELL AS SURFACE
OBSERVATIONS INDICATE THAT THE SURFACE FRONT IS AS FAR NORTH AS
CAPE DECISION AS OF EARLY THIS MORNING. VAD WIND PROFILE INDICATES
THAT THE FRONTAL BOUNDARY IS ABOUT 16K FEET AS OF 5 AM. ADVISORY
LEVEL GUSTS BEING REPORTED IN ZONES 27 AND 28 SO FAR WITH PERIODS
OF HEAVY RAIN AT KETCHIKAN. WILL SEE WINDS AND RAIN INCREASE
THROUGHOUT THE DAY FROM SOUTH TO NORTH AS THE FRONT CONTINUES TO
TRACK UP THE PANHANDLE. HIGH PRESSURE OVER CANADA WILL INTERACT
WITH THE FRONT LATER TODAY AND PRODUCE SOME VERY STRONG OUTFLOW
WINDS. ADVISORY LEVEL WINDS IN HAINES AND SKAGWAY COVERED BY
WINTER WEATHER WARNINGS AND ADVISORY RESPECTIVELY. MORE ON THE
SNOW FOR THOSE ZONES NEXT PARAGRAPH. PRESSURE GRADIENT IS
EXPECTED TO GENERATE STRONGEST OUTFLOW WINDS IN ZONES 17 EAST OF
YAKUTAT. HAVE GUSTS TO 55 MPH IN THAT ZONE FOR TONIGHT BUT HIGHER
ELEVATIONS WELL INLAND COULD SEE SIGNIFICANTLY HIGHER NUMBERS.
HELD OFF ON ISSUING AN ADVISORY FOR ZONE 25 AS ADVISORY LEVEL
WINDS AND GUSTS ARE EXPECTED TO BE OUT OF INTERIOR PASSES IN
UNPOPULATED AREAS. ONE AREA OF CONCERN IS THE TAKU INLET FOR BOTH
WINDS AND SNOW...SO WILL HAVE TO WATCH THAT LOCATION CLOSELY
TODAY.

RAIN TODAY AND TONIGHT FOR MOST PLACES EXCEPT FOR THE NORTHERN
INNER CHANNELS. MAIN CHALLENGE FOR THIS FORECAST ISSUANCE DEALS
WITH THE STRENGTH OF THE ARCTIC PUSH FROM THE NORTH/NORTHEAST
TODAY AND TONIGHT AND WHERE THE RAIN-SNOW LINE WILL BE. HOW MUCH
COLD AIR SPILLS OVER FROM CANADA INTO THE PANHANDLE THROUGH TAKU
INLET...WHITE PASS...AND THE CHILKAT RIVER VALLEY AND HOW SOON
WILL DETERMINE WHETHER OR NOT THIS TURNS INTO A MAJOR SNOW EVENT
FOR THE NORTHERN PANHANDLE BEFORE FRONTAL PRECIP EXITS THE
FORECAST AREA. IN CONJUNCTION WITH THE LONG TERM FORECASTER...HAVE
ISSUED A WINTER STORM WATCH FOR ZONES 20...21...AND 25 VICE A
WINTER WEATHER ADVISORY/WARNING AT THIS TIME DUE TO FORECAST
UNCERTAINTY. ZONES 18 AND 19 CURRENTLY COVERED WITH EXISTING
WINTER WEATHER STATEMENTS...BUT IF COLD AIR PENETRATES STRONGER
THAN FORECAST...WILL HAVE TO EXTEND/UPGRADE THESE TWO STATEMENTS.

FREEZING RAIN NOT OUT OF THE QUESTION EITHER AND HAVE PUT SOME
INTO THE YAKUTAT TAF...WHERE IT IS CONSIDERED TO BE MOST LIKELY
BUT DID NOT GO SO FAR AS TO ISSUE A FREEZING RAIN ADVISORY FOR
THAT ZONE.

.&&

.LONG TERM...THE FORECAST LONGWAVE PATTERN ALOFT...WITH A SLOWLY
FILLING LOW IN THE GULF AND A RIDGE ALONG THE NORTH AMERICAN WEST
COAST...DOES NOT DEVELOP A SIGNIFICANT SPREAD IN ENSEMBLE SOLUTIONS
UNTIL THE LATER PART OF THE WEEK. HOWEVER THE BIGGEST FORECAST
CHALLENGE IS EARLIER AND ON A SMALLER SCALE WITH LARGE MODEL
DIFFERENCES ON THE EXTENT OF LOW LEVEL COLD AIR SPREADING INTO THE
NORTHERN PANHANDLE EARLY IN THE WEEK. WITH PLENTY OF MOISTURE AND
WARM OVERRUNNING THROUGH MONDAY THE POSITION OF THE ARCTIC FRONT
WILL BE CRITICAL IN LOCATING AN AREA OF HEAVY SNOWFALL. MODELS
VARIED BUT THE GFS WAS A GOOD COMPROMISE BETWEEN FORECAST EXTREMES
FOR THE MIDDLE PERIODS. FEW CHANGES WERE MADE BEYOND THAT SINCE
CONFIDENCE WAS LOW.

INTENSE ARCTIC OUTFLOW IS EXPECTED TO PUSH THE ARCTIC FRONT
SOUTHWARD TO JUNEAU BY MONDAY NIGHT BUT BECAUSE OF THE SHALLOW
NATURE OF THE COLD AIR AND LOW CONFIDENCE IN THE TIMING AND
LOCATION OF THE FRONT...A WINTER STORM WATCH WAS ISSUED FOR THE
NORTH CENTRAL ZONES THAT INCLUDE JUNEAU...GUSTAVUS...AND HOONAH.
WARMER AIR GRADUALLY ERODES THE ARCTIC AIR BRINGING MIXED
PRECIPITATION TO THE NORTH CENTRAL ZONES BY THE MIDDLE OF THE
WEEK. SOUTH OF THE ARCTIC FRONT PRECIPITATION WILL BE PRIMARILY
RAIN WITH HEAVY AMOUNTS AT TIMES.

NORTH TO NORTHEAST GALES SHOULD CONTINUE OVER THE NORTHERN THIRD
OF THE PANHANDLE UNTIL TUESDAY WHEN THE OUTFLOW BEGINS TO
DIMINISH. ELSEWHERE SMALL CRAFT SOUTH TO SOUTHEAST WINDS WILL
PREVAIL.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY UNTIL 3 PM AKST THIS AFTERNOON FOR AKZ023-028.
 WINTER STORM WATCH FROM LATE TONIGHT THROUGH MONDAY AFTERNOON FOR
AKZ020-021-025.
 WIND ADVISORY FROM 9 AM THIS MORNING TO 6 AM AKST MONDAY FOR
AKZ017-022.
 WINTER STORM WARNING UNTIL 9 PM AKST THIS EVENING FOR
AKZ019.
 WINTER WEATHER ADVISORY UNTIL 9 PM AKST THIS EVENING FOR
AKZ018.
 MARINE...GALE WARNING FOR PKZ011>013-021-022-031-033-036-042-043-051-052.
 SMALL CRAFT ADVISORY FOR PKZ032-034-035-041.

&&

FRITSCH/CFD