Freezing Rain Advisory 7, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
526 AM AKST TUE JAN 13 2015

.ANALYSIS AND UPPER LEVELS...

THE BLOCKING HIGH OVER ALASKA IS RAPIDLY WEAKENING AND
RETROGRADING INTO THE BERING AS A VIGOROUS NORTH PACIFIC WARM
FRONT TRACKS INLAND ACROSS SOUTHERN MAINLAND ALASKA. THIS IS
VISUALIZED ON WATER VAPOR SATELLITE IMAGERY AS AN ELONGATED
DEFORMATION ZONE AND REGION OF ENHANCED MID AND UPPER LEVEL
MOISTURE VALUES...STRETCHING FROM THE EASTERN BERING INTO THE
YUKON TERRITORY. TWO OTHER WELL DEVELOPED STRONG CYCLONES ARE
FORMING ALONG THE LEFT EXIT OF THE POWERFUL PACIFIC JET NEAR
40N...AND WILL EVENTUALLY MOVE NORTH INTO THE GULF OF ALASKA
THROUGH THURSDAY.

THE AFOREMENTIONED WARM FRONT HAS TRACKED INLAND BASED ON REGIONAL
RADAR IMAGERY...WITH A SWITCH TO SOUTHEAST WINDS ACROSS THE
NORTHERN GULF COAST MARINE WATERS. THE 12Z UPPER AIR RADIOSONDE
FROM ANCHORAGE DEPICTS THE LOW LEVEL SOUTHEAST WINDS...ALSO
INDICATIVE OF FRONTAL PASSAGE ALOFT. GIVEN THE CONTINUED DOWN
INLET PRESSURE GRADIENT...AND LACK OF PRESSURE FALLS INLAND...THE
LOWEST LEVELS OF THE ATMOSPHERE REMAIN DECOUPLED FROM THE
ATMOSPHERE ALOFT...ESPECIALLY ACROSS COLDER BASINS. THIS WARMING
ALOFT HAS RESULTED IN MORE AREAS OF FREEZING RAIN AND RAIN SHOWERS
THIS MORNING. THIS THREAT WILL GENERALLY DIMINISH AS THE FRONT
WEAKENS AND MOVES INLAND TODAY.

THE POWERFUL NORTH PACIFIC JET STREAM WILL REMAIN THE ACTIVE
DRIVER OF SENSIBLE WEATHER ACROSS MAINLAND ALASKA FOR THE
FORESEEABLE FUTURE. THIS WILL KEEP THE GULF OF ALASKA PRONE TO
SUBTROPICAL WARM FRONTS AND CONTINUED WARM ANOMALIES. WINTER IS
NOWHERE IN SIGHT FOR SOUTHERN ALASKA. THE RECORD BREAKING WARM
WINTER MARCHES ON...LIKELY AIDED BY A REINVIGORATED MADDEN JULIAN
OSCILLATION...AND AN ARCTIC TROUGH DIGGING INTO THE CENTRAL
BERING...AS WE HEAD INTO THE LATE WEEK.

&&

.MODEL DISCUSSION...

THE NUMERICAL MODELS ARE IN EXCELLENT AGREEMENT WITH THE LARGE
SCALE PATTERN HEADING DEEP INTO THIS WEEK. AS USUAL...THERE ARE
MORE SUBTLE DIFFERENCES AS EARLY AS 48 HOURS...MAINLY WITH THE
TIMING OF TWO MORE FRONTS MOVING INTO SOUTHERN ALASKA WEDNESDAY
AND WEDNESDAY NIGHT/THURSDAY. THE GFS WAS THE LARGEST OUTLIER ON
TIMING OF THESE FRONTS...SO THE NAM WAS A GOOD MIDDLE GROUND
SOLUTION AS IT FIT CLOSE TO THE ECMWF AND CANADIAN GDPS. THE NAM'S HIGHER
RESOLUTION AND BETTER DEPICTION OF PRECIPITATION FIELDS ACROSS THE
MOUNTAINS/VALLEYS WAS ALSO FAVORED.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

THE STRONG WARM FRONT OVER THE GULF OF ALASKA HAS MOVED ON SHORE
IN SOUTH CENTRAL ALASKA. THERE WAS STRONG DOWNSLOPING WITH THIS
FRONT AND THAT KEPT MOST OF THE LEE SIDE AREAS PRECIPITATION FREE
THROUGH THE NIGHT. THERE IS A LOT OF WARM AIR ALOFT WITH THIS
FRONT WHICH IS BRINGING SOME FREEZING RAIN FROM THE THOMPSON PASS
AREA NORTHWARD OVER PARTS OF THE COPPER RIVER BASIN. AREAS CLOSER
TO VALDEZ ARE ABOVE FREEZING AND THEREFORE PRECIPITATION HAS BEEN
RAIN. OTHER COASTAL AREAS HAVE ALSO BEEN ALMOST ALL RAIN.
A LITTLE BIT COOLER AIR WILL MOVE OVER SOUTHCENTRAL TONIGHT BUT
BY WEDNESDAY NIGHT ANOTHER WARM FRONT WILL MOVE INTO THE REGION
AND BRING THE THREAT FOR FREEZING RAIN BACK TO PARTS OF
SOUTHCENTRAL ALASKA. THIS NEXT FRONT WILL PROBABLY NOT BRING
WIDESPREAD FREEZING RAIN AS TEMPERATURES WILL BE ABOVE FREEZING IN
A LOT OF THE LOCATIONS THAT GET THE RAIN. AS WITH THIS CURRENT
SYSTEM THE ONE COMING IN WEDNESDAY NIGHT WILL MOSTLY DOWNSLOPE
OUT THE PRECIPITATION IN THE LEE OF THE MOUNTAINS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...TUE AND WED)...ENERGY
IS SHIFTING FROM THE LOW SOUTH OF THE ALASKA PENINSULA TO THE LOW
APPROACHING THE PRIBILOF ISLANDS. THE OCCLUDED WARM FRONT
ASSOCIATED WITH THE PRIBILOF LOW IS BEING STRETCHED OUT ACROSS
MUCH OF THE AREA THIS MORNING. THIS FRONT BROUGHT MOSTLY RAIN TO
THE BRISTOL BAY AREA...WHILE THE YK DELTA HAD A WINTRY MIX WITH
SOME VERY LIGHT FREEZING RAIN IN BETHEL AND SNOW ALONG THE COAST.
RADAR CONTINUES TO SHOW SOME LIGHT PRECIPITATION NORTH OF BETHEL
STRETCHING TO THE COAST. BUT PRECIPITATION AND WINDS WILL CONTINUE
TO WIND DOWN AS THE FRONT FALLS APART THIS MORNING.

THE NEXT LOW TO IMPACT THE AREA IS ALREADY VISIBLE ON SATELLITE IN
THE NORTH PACIFIC. THIS LOW WILL TAKE A NORTHERLY TRACK OVER THE
NEXT 24 HOURS AND BRING MORE OF THE SAME TYPE OF WEATHER TO THE
AREA. CONDITIONS WILL ONCE AGAIN BE WARM...WINDY...AND SOMEWHAT
WET ACROSS BRISTOL BAY. PRECIPITATION SHOULD REMAIN RAIN ACROSS
NEARLY THE ENTIRE AREA WITH TEMPERATURES ALREADY ABOVE FREEZING
AND NO SIGN OF COLD AIR MOVING IN BEFORE THIS SYSTEM ARRIVES. AS
PRECIPITATION SPREADS NORTH TOWARDS THE KUSKOKWIM VALLEY AND YK
DELTA LATER WEDNESDAY...THERE WILL BE YET ANOTHER CHANCE FOR
FREEZING PRECIPITATION. AT THIS TIME AMOUNTS LOOK TO BE VERY LIGHT
AS EAST TO SOUTHEAST FLOW SHOULD CREATE A DOWNSLOPING EFFECT OFF
THE MOUNTAINS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...THE LOW
NEAR THE PRIBILOF ISLANDS THIS MORNING WILL CONTINUE TO WORK
TOWARDS THE WESTERN ALEUTIANS THROUGH THE DAY. THIS WILL KEEP A
RELATIVELY TIGHT GRADIENT AND GALE FORCE WINDS OVER THE NORTHERN
PORTION OF THE BERING AS HIGH PRESSURE REMAINS BOTTLED UP OVER THE
CHUKCHI SEA. THE LOW WILL ALSO KEEP RAIN AND SNOW SHOWERS IN THE
FORECAST SPREADING ACROSS THE BERING THROUGH WED. YET ANOTHER LOW
SOMEWHERE NEAR 960 MB IN STRENGTH WILL APPROACH THE CENTRAL
ALEUTIANS FROM THE SOUTH THROUGH THE DAY ON WED. IT WILL BRING
RAIN AND MINIMUM GALE FORCE WINDS TO AREAS FROM THE ALASKA
PENINSULA THROUGH THE CENTRAL ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

AN UPPER LEVEL TROUGH WILL CONSOLIDATE OVER THE EASTERN BERING AND
AKPEN THU AND FRI...AND THEN MERGE WITH A LOW DIVING SOUTH ACROSS
THE BERING STRAIT ON SAT. THIS WILL RESULT IN AN UPPER LOW OVER
THE NORTHERN BERING...WITH A SURFACE LOW SPINNING AROUND THE AKPEN
AND DRIFTING TO KODIAK ISLAND BY SUN. WITH EACH CONSOLIDATION AND
MERGER A SURGE OF WARM AIR WILL MOVE ACROSS THE GULF AND
REPEATEDLY REINFORCE THE UPPER RIDGE OVER THE WEST COAST OF NORTH
AMERICA. AND EACH REINFORCEMENT OF THAT RIDGE WILL BE ASSOCIATED
WITH A FRONT MOVING INLAND ALONG THE NORTH GULF COAST...IN
PARTICULAR ON THU AND AGAIN ON SAT. THESE WILL BE WINDY SYSTEMS
WITH RAIN ALONG THE COAST AND SNOW INLAND.

AT THE SAME TIME...FLOW ALONG THE WESTERN FLANK OF THE BERING LOW WILL
BRING COLD AIR ACROSS THE WESTERN BERING AND ALEUTIANS ON FRI.
THIS AIR WILL SLOWLY SPREAD EAST...BUT BECAUSE OF THE BLOCKING
RIDGE...WILL NOT REACH WESTERN AK UNTIL SUN. THIS MEANS THE
POSSIBILITY OF SHOWERS OF RAIN AND FREEZING RAIN WILL CONTINUE
OVER SOUTHWEST AK INTO THE WEEKEND...WHILE RAIN AND SNOW SHOWERS
ALONG THE ALEUTIANS WILL STEADILY CHANGE OVER TO ALL SNOW SHOWERS
BY THE WEEKEND. THE FORECAST RELIES HEAVILY ON THE WPC ENSEMBLE
SOLUTION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 119-20 130-32 136-38 150 155 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...DS