Heavy Freezing Spray Warning 85, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST WED FEB 22 2012

.ANALYSIS AND UPPER LEVELS...
A BIT OF A PATTERN CHANGE UNDERWAY WITH THE UPPER LEVELS AS A BROAD
UPPER TROF OVER MAINLAND ALASKA BEGINS TO SHIFT TO THE EAST IN
RESPONSE TO A BUILDING RIDGE OVER THE EASTERN BERING SEA. MULTIPLE
SHORTWAVES EMBEDDED IN THE SOUTHWESTERLY FLOW ALOFT ARE MAKING THE
FORECAST A BIT CHALLENGING AS THE TIMING AND STRENGTH OF THESE
IMPULSES ARE DIFFICULT TO FORECAST.

OVERALL...THE PATTERN IS BECOMING MORE AMPLIFIED AS A RESULT OF A
DEEPENING LOW THAT RECENTLY DEVELOPED OFF THE SOUTHEAST COAST OF
KAMCHATKA PENINSULA. THIS LARGE COMPLEX NORTH PACIFIC LOW HAS AN
IMPRESSIVE FRONTAL BOUNDARY ASSOCIATED WITH IT WHICH IS RAPIDLY
WRAPPING AROUND THE MAIN CENTER.

AT THE SURFACE...MODELS STILL SUGGEST THAT A WEAK AREA OF LOW
PRESSURE IS LINGERING NEAR WESTERN PRINCE WILLIAM SOUND....ALTHOUGH
SATELLITE AND SURFACE OBSERVATIONS ARE NOT AS EVIDENT. THIS LOW
SHOULD BECOME A BIT BETTER ORGANIZED TONIGHT IN RESPONSE TO AN
APPROACHING UPPER LEVEL SHORTWAVE AND ASSOCIATED COLD AIR ADVECTION.
AS A RESULT...SNOW SHOWER ACTIVITY IS INCREASING AROUND SOUTHCENTRAL.
ONSHORE FLOW ACROSS SOUTHWEST ALASKA RESULTING IN WIDESPREAD SNOW
SHOWER ACTIVITY FROM BRISTOL BAY UP TO THE KUSKOKWIM DELTA. HIGH
PRESSURE IS BUILDING OVER THE EASTERN BERING SEA WHILE THE GALE FORCE
FRONT APPROACHES THE WESTERN ALEUTIANS.

.MODEL DISCUSSION...
THE MODELS INITIALIZE WELL ON THE MAIN SYNOPTIC FEATURES COMPARED TO
THE 18Z SATELLITE IMAGERY. THE MINOR DIFFERENCES IN THE SOLUTIONS
CONCERN THE EVOLUTION OF THE UPPER LOW AND AN ASSOCIATED SHORTWAVE
MOVING ACROSS SOUTHCENTRAL ALASKA TONIGHT. THE 12Z AND 18Z NAM SHOW A
MUCH MORE POTENT SHORTWAVE ROTATING AROUND THE BASE OF THE LOW NEAR
BRISTOL BAY AND CROSSING THE ALASKA RANGE TOWARD NORTHERN COOK INLET.
WHILE THE NAM AND GFS ONLY HINT AT ISOLATED TO SCATTERED SNOW SHOWERS
OVER THE REGION...THE THINKING IS THAT SHOWER ACTIVITY MAY BE A BIT
MORE WIDESPREAD IF THIS SHORTWAVE IS AS POTENT AS IT IS BEING
ADVERTISED. WE WILL BE ADJUSTING THE FORECAST TO ACCOUNT FOR THIS
MINOR CHANGE IN THE SHORT TERM.

OTHERWISE THE MODELS HAVE ALTERED THE ORIENTATION OF THE RIDGE AS IT
BECOMES AMPLIFIED THURSDAY AFTERNOON. INSTEAD OF THE SHARP NORTH TO
SOUTH RIDGE AXIS...NOW THE MODELS ARE BENDING THE AXIS BACK TO THE
NORTHWEST AROUND THE NORTH PACIFIC SYSTEM. THIS SLIGHT CHANGE WILL
RESULT IN CLOUDS AND A FEW SNOW SHOWERS LINGERING OVER SOUTHCENTRAL A
BIT LONGER THAN PREVIOUSLY THOUGHT.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
MOSTLY SUNNY SKIES ARE FILLING IN AS AN UPPER WAVE APPROACHES FROM
THE SOUTHWEST. THE SHOWER ACTIVITY IS VERY CONVECTIVE...ALMOST SPRING
LIKE. BELIEVE THAT THE ACTIVITY WILL BECOME MORE WIDESPREAD THIS
EVENING AS THE WAVE APPROACHES...ESPECIALLY IF THE NAM PANS OUT...AND
THEN A GRADUAL CLEARING AGAIN TOWARD MORNING. CLOUDS AND SHOWERS
LINGER THROUGH THURSDAY BEFORE THE RIDGE FINALLY APPROACHES FROM THE
WEST FRIDAY MORNING. MOSTLY CLEAR SKIES WILL PREVAIL BY FRIDAY
AFTERNOON WITH NORMAL TO SLIGHTLY ABOVE NORMAL TEMPERATURES EXPECTED.

THE REMNANTS OF THE BERING SEA LOW APPROACH SOUTHCENTRAL DURING THE
WEEKEND...BRINGING CLOUDS AND THE CHANCE OF PRECIPITATION BACK TO THE
REGION. DO NOT ANTICIPATE ANY WATCHES OR WARNINGS WITH THIS NEXT
SYSTEM AT THIS POINT BUT STILL QUITE A WAYS OUT.

SOUTHWEST...
ONSHORE FLOW WILL DIMINISH TONIGHT...ALLOWING FOR SHOWERS TO FINALLY
DECREASE IN COVERAGE. SKIES WILL CLEAR THROUGH THURSDAY WITH SOME
LOCALIZED FOG LIKELY ACROSS SOUTHWEST ALASKA. THE RIDGE OF HIGH
PRESSURE QUICKLY MOVES EAST OF THE AREA ON FRIDAY WITH THE REMNANTS
OF THE FRONTAL BOUNDARY TO APPROACH THE COAST BY FRIDAY EVENING. THIS
FRONT LOSES A LOT OF ITS ENERGY AS IT APPROACHES THE COAST...SO
COASTAL BLIZZARD CONDITIONS ARE NOT LOOKING AS GOOD AS IT DID WITH
YESTERDAYS FORECAST. STILL SOME SNOW AND LOCALIZED GUSTY WINDS
POSSIBLE AS THE REMNANTS MOVE INLAND FRIDAY NIGHT.

BERING SEA/ALEUTIANS...
THE MOST ACTIVE WEATHER REMAINS OVER THE BERING SEA WHERE THE LARGE
COMPLEX LOW BEGINS WEAKENING TONIGHT. THE ASSOCIATED GALE FORCE FRONT
MARCHES ACROSS THE WESTERN AND CENTRAL ALEUTIANS SPREADING SNOW AND
RAIN WITH IT. TEMPERATURES ARE CURRENTLY BELOW FREEZING BUT BELIEVE
THE SOUTHERLY WINDS AHEAD OF THE FRONT WILL USHER IN ENOUGH WARM AIR
TO ALLEVIATE THE CHANCE OF BLIZZARD CONDITIONS.

A SECOND AND MUCH STRONGER LOW DEVELOPS IN THE SAME REGION OVER THE
NORTH PACIFIC FRIDAY AND BRINGS STORM FORCE WINDS TO THE WESTERN
ALEUTIANS FRIDAY NIGHT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE...155 165 170 171 172 175 176 179 185 411 412 413 414
FIRE WEATHER...NONE

AB FEB 12