Brisk Wind Advisory 37, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
508 AM AKDT SUN APR 19 2015

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVELS CONTINUE TO DEVELOP
THIS MORNING. OUR CLOSED LOW JUST SOUTH OF THE ALASKA PENINSULA IS
MOVING SLOWLY TOWARD BRISTOL BAY. MEANWHILE...ENERGY IS STARTING
TO SHIFT NORTHWARD ALONG THE WEST COAST AND CONSOLIDATE AS A
PARENT LOW NEAR NUNIVAK ISLAND. ONE FRONT RIDING THE BROAD
CYCLONIC FLOW AROUND THE LOW IS PUSHING UP THE COOK INLET AND
INTO COASTAL SITES. WITH A MID-LEVEL RIDGE BUILDING OVER SOUTHEAST
ALASKA AND PUSHING UP INTO THE NORTH CENTRAL PORTION OF THE
STATE...THIS IS KEEPING THE SOUTHEAST GRADIENT RATHER TIGHT AND
BRINGING PLENTY OF GUSTY WINDS TO THE FAVORED AREAS. ANOTHER FRONT
IS NOT FAR BEHIND ALREADY STARTING TO MOVE FROM KODIAK TOWARD THE
SOUTHERN KENAI PENINSULA. WE ARE STARTING TO SEE SOME ENHANCEMENT
WITH THIS FRONT AS THE LEFT EXIT REGION OF A 100-110 KT JET
SUPPORTS IT FROM 30000 FT. THIS IS SOME OF THE STRONGEST JET
ACTIVITY WE HAVE SEEN MOVE OVER THE MAINLAND IN MONTHS. THE JET IS
CONTINUOUS IN A U-SHAPE ALL THE WAY BACK TO EASTERN RUSSIA. THIS
IS KEEPING ALL OF THE BERING FROM COLD BAY EAST UNDER POTENT
NORTHWEST FLOW. THIS IS MAKING FOR COLD AIR ADVECTION SHOWERS AND
GUSTY WINDS ACROSS THE ALEUTIANS...AND ESPECIALLY ON THE BERING
SIDE.

&&

.MODEL DISCUSSION...MODELS CONTINUE TO BE IN VERY GOOD SYNOPTIC
AGREEMENT. THUS...THE HIGHER RESOLUTION MODELS (NAM/GEM-REGIONAL) WERE
USED TO DEAL WITH CONVECTION OVER THE SOUTHWEST AND MULTIPLE WAVES
MOVING THROUGH SOUTH CENTRAL. THE FEW AREAS WHERE THEY DIFFER ARE
WITH HOW THE ENERGY OVER THE WEST COAST CONSOLIDATES INTO ONE
PARENT LOW AND WITH THE FORMATION OF ANY POLAR-VORTEX "ESQUE"
SYSTEMS TODAY. WITH THE FIRST DIFFERENCE...THE ECMWF CONSOLIDATES
THE ENERGY OVER THE EASTERN BERING INTO ONE UPPER LEVEL LOW RATHER
THAN HAVING MULTIPLE CENTERS BY MONDAY AFTERNOON. THIS WILL LIKELY
NOT IMPACT SENSIBLE WEATHER AT THE SURFACE MUCH OTHER THAN THE EC
MAY BE A BIT STRONGER WITH THE LOW ITSELF WHILE THE OTHER MODELS
MAY PUT SOME OF THAT ENERGY INTO THE MANY WAVES ROTATING THROUGH
THE PATTERN. THE EC WAS GENERALLY PREFERRED WITH THIS FORECAST
PACKAGE FOR ITS CONSISTENCY. IN ADDRESSING THE POLAR-LOW
FEATURES...THE GEM-REGIONAL WAS USED. SATELLITE IS ALREADY
STARTING TO SHOW SOME CYCLONIC DEVELOPMENT WITH COLD AIR COMING
OFF OF EASTERN RUSSIA AND THE ICE-EDGE. THE RESOLUTION OF THE GEM-
REGIONAL WILL BE KEY IN DEPICTING THE TIGHT AREA OF GUSTY WINDS
AND INTENSE SHOWERS.

A LITTLE FURTHER OUT TOWARD THE MIDDLE OF THE WEEK...SOME MORE
SIGNIFICANT MODEL DIFFERENCES DEVELOP. WITH CONTINUED COLD AIR
COMING DOWN THE WEST SIDE OF THE PARENT LOW...SOME MORE
SIGNIFICANT TROUGHING DEVELOPS SOUTH OF THE AKPEN INTO THE NPAC.
ALL THE MODELS SHOW SIGNS OF THIS TROUGH PHASING TO SOME EXTENT
WITH A CLOSED LOW NEAR 35N. THIS TROUGH WOULD THEN INTERACT WITH
THE PARENT LOW DRIFTING TOWARD THE BERING STRAIT AND ALLOW A
DEFORMATION AXIS TO SET-UP OVER THE SOUTHWEST. THE EC WAS
PREFERRED IN HANDLING THIS SCENARIO DUE TO BETTER RUN TO RUN
CONSISTENCY.

&&

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

A STRONG FRONT IN THE NORTHERN GULF WILL MOVE NORTHWARD AND
WEAKEN THROUGH THE DAY. THERE WILL BE RAIN ASSOCIATED WITH THIS
FRONT AND THERE IS ENOUGH DEEP MOISTURE AND LIFTING TO OVERRUN THE
DOWNSLOPE EFFECT.

A COLD FRONT MOVING INTO THE AREA FROM THE SOUTHWEST TONIGHT WILL
BRING ANOTHER ROUND OF PRECIPITATION TONIGHT INTO MONDAY. THE
PRECIPITATION TYPE WILL BE INTERESTING WITH THIS SYSTEM SINCE THIS
FRONT IS COLD ENOUGH THAT ANY PRECIPITATION BEHIND IT WILL BE
SNOW. HOWEVER THE MAJORITY OF THE MOISTURE IS AHEAD OF THE FRONT
AND MOST PRECIPITATION TONIGHT SHOULD BE IN THE FORM OF RAIN AT
LOWER ELEVATIONS AROUND SOUTHCENTRAL. THE POST FRONTAL ENVIRONMENT
ON MONDAY WILL BE CONDUCIVE FOR SNOW SHOWERS DESPITE TEMPERATURES
REACHING INTO THE 40S.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
PRECIPITATION WILL BE ON THE INCREASE TODAY OVER THE SOUTHWEST
MAINLAND AS THE VIGOROUS COLD FRONT APPROACHES THE REGION. THIS
FRONT HAS A DEEP COLD POOL ALOFT WHICH WILL GENERATE CONSIDERABLE
INSTABILITY. EXPECT THE PRECIPITATION TO BEGIN AS MIXED RAIN AND
SNOW SHOWERS. MOST MODELS ARE INDICATING MODEST CAPE VALUES FOR
THIS TIME OF THE YEAR AND LIFTED INDICES NEAR 0 THIS AFTERNOON
OVER THE LOWER KUSKOKWIM VALLEY AND INTERIOR BRISTOL BAY REGION.
EXPECT THE PRECIPITATION TO BEGIN AS MIXED RAIN AND SNOW SHOWERS
WITH ISOLATED THUNDERSTORMS POSSIBLE ESPECIALLY IN ELEVATED
TERRAIN. AS THE CORE OF THE COLD POOL MOVES INLAND OVER BRISTOL
BAY TONIGHT INTO MONDAY THE AREA OF ISOLATED THUNDERSTORM ACTIVITY
WILL EXPAND INTO THE LOWER BRISTOL BAY REGION. WITH THE PUSH OF
COLDER TEMPERATURES...THE PRECIPITATION TYPE SHOULD TURN TO
MOSTLY SNOW. ALONG THE KUSKOKWIM DELTA...NUMEROUS RAIN AND SNOW
SHOWERS WILL CONTINUE THROUGH MONDAY NIGHT WITH LOCAL
ACCUMULATIONS OF 2 TO 3 INCHES.

WINDS WILL REMAIN BRISK ALONG COASTAL AREAS TODAY AS THE COLD
FRONT MOVES THROUGH THE REGION. BY EARLY MONDAY MORNING WINDS
WILL BECOME WESTERLY IN THE WAKE OF THE FRONT WITH WINDS NORTH OF
CAPE NEWENHAM DECREASING THIS AFTERNOON. WINDS WILL REMAIN
STRONGER OVER BRISTOL BAY AND THE LOWER KUSKOKWIM VALLEY BEFORE
DECREASING LATE MONDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE MAIN WEATHER FEATURE FOR THE REGION OVER THE NEXT 48 HOURS
WILL BE THE COLD FRONT MOVING THROUGH THE EASTERN BERING SEA TODAY
AND THE PUSH OF COLD AIR ALOFT. THE COMBINATION OF SEA SURFACE
TEMPERATURES IN THE UPPER 30S AND THE COLD AIR ALOFT WILL CREATE
VERY UNSTABLE CONDITIONS OVER THE SOUTH CENTRAL BERING SEA AND THE
ALASKA PENINSULA TODAY WITH THE POTENTIAL FOR ISOLATED
THUNDERSTORMS. THE BEST AREA FOR ANY THUNDERSTORM DEVELOPMENT WILL
BE IN THE SOUTH-CENTRAL BERING SEA EASTWARD INTO THE COASTAL
WATERS OF THE ALASKA PENINSULA. PRECIPITATION WILL INITIALLY BE A
MIX OF RAIN AND SNOW BEFORE TRANSITIONING TO ALL SNOW LATER
TONIGHT AS THE COLDER AIRMASS ENTERS THE REGION. WINDS OVER THE
EASTERN ALASKA PENINSULA WILL STAY HIGH ENOUGH THIS MORNING FOR
ISOLATED AREAS OF BLOWING SNOW.

FOR THE PRIBILOF ISLANDS...WINDS WILL REMAIN STRONG AND GUSTY
THROUGH THE PERIOD AS THE WEAK POLAR-TYPE LOW MOVES EASTWARD OVER
THE BERING SEA NEAR THE ICE EDGE. CONDITIONS WILL REMAIN UNSTABLE
ENOUGH TO GENERATE SNOW SHOWERS WITH AREAS OF BLOWING SNOW.

&&

.LONG TERM FORECAST (TUESDAY THROUGH SATURDAY)...

AN OVERALL SLOWER AND MORE AMPLIFIED PATTERN IS DEPICTED FOR THE
LATEST MODEL GUIDANCE WITH MULTIPLE AREAS OF LOW PRESSURE ACROSS
ALASKAN WATERS AND THE NORTH PACIFIC. A RIDGE OF HIGH PRESSURE
OVER THE NORTH PACIFIC WILL DEVELOP ACROSS THE GULF OF ALASKA ON
TUESDAY AS AN AREA OF LOW PRESSURE DIVES SOUTH FROM THE ALEUTIAN
ISLANDS INTO THE NORTH PACIFIC. THIS RIDGE WILL BRING A RELATIVELY
BENIGN PERIOD OF WEATHER TO MUCH OF SOUTHCENTRAL WHILE A CUT OFF
LOW CONTINUES A SHOWERY PATTERN ACROSS THE EASTERN HALF OF THE
BERING SEA AND SOUTHWEST ALASKA. AS THE LOW DIVES INTO THE NORTH
PACIFIC AND AMPLIFIES THE LONGWAVE TROUGH...LONGWAVE RIDING BEHIND
THE TROUGH WILL ALSO BECOME MORE AMPLIFIED. THIS WILL SLOW DOWN
THE AREA OF LOW PRESSURE PUSHING OFF THE KAMCHATKA PENINSULA...WITH
IT ENTERING THE BERING SEA LATE TUESDAY. THIS WILL ALSO CAUSE THE
LOW TO TAKE A MORE NORTHERN TRACK THROUGH THE BERING SEA AND BRING
HIGH SEAS AND GALE FORCE WINDS TO THE ALEUTIANS BEFORE MOVING
INTO THE GULF OF ALASKA LATE FRIDAY. MODELS ARE STILL HINTING AT A
BUILDING NORTH AMERICAN PACIFIC RIDGE WHICH COULD BRING MUCH
WARMER TEMPERATURES TO THE STATE. HOWEVER...MODELS CONTINUE TO
STRUGGLE WITH THE STRENGTH AND TIMING OF THE RIDGE SO TEMPERATURES
WERE RAISED A BIT AGAIN BUT NOT TOO HIGH AT THIS TIME.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 125 129 131 150 160 165 170-172 179 180 181 185.
         HEAVY FREEZING SPRAY 179 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RF
LONG TERM...MC