Gale Warning 389, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 AM ADT SUN APR 23 2006

.DISCUSSION...

.ANALYSIS...WEATHER IS PRETTY QUIET ACROSS THE ANCHORAGE FORECAST
AREA TONIGHT. OLD UPPER LOW CENTER SPINNING SOUTH OF THE AKPENN
GENERATING JUST A FEW SHOWERS IN THE VICINITY. UPPER TROUGH AXIS
EXTENDS NORTHWESTWARD FROM THIS LOW TO A VERY COLD UPPER LOW ALONG
THE NORTHERN SIBERIA COAST. NORTHERLY FLOW HAS SLACKENED ACROSS THE
BERING SEA TO 20 KT OR LESS. THERE IS STILL SOME WEAK COLD ADVECTION
AND A FEW SNOW SHOWERS ALONG WITH LOTS OF STRATUS AND STRATOCUMULUS.
SATELLITE IMAGERY SHOWS CIRRUS APPROACHING THE WESTERN ALEUTIANS.
THIS IS ASSOCIATED WITH AN UPPER LOW WELL TO THE SOUTHWEST OF THE
REGION. RADAR IMAGERY SHOWS SCATTERED SHOWERS ACROSS SOUTHCENTRAL.
THESE ARE DO TO WEAK VORTICITY ADVECTION ON THE EAST SIDE OF THE
UPPER TROUGH AND AN UNSTABLE AIR MASS WITH VERY COLD AIR ALOFT. THE
00Z ANCHORAGE SOUNDING SHOWED A LIFTED INDEX OF 0.8 WITH A 500 MB
TEMP OF -35 DEGREES. THE FOCUS FOR THIS EVENING IS ON THE STATIONARY
FRONT LYING NORTH-SOUTH BETWEEN 140W AND 145W. THERE IS AT LEAST
ONE FRONTAL WAVE DEVELOPING ALONG THIS FRONT AROUND 45N. THIS WILL
BE THE NEXT WEATHER MAKER FOR SOUTHCENTRAL.

.MODEL ANALYSIS...THE GFS IS THE MOST CONSISTENT IN HANDLING OF LOW
DEVELOPING ALONG FRONT. THE NAM AND PARALLELNAM HAVE TRENDED A LOT
CLOSER TO THE SOLUTION OF THE GFS IN TRACKING LOW TO KENAI PENINSULA
AND INLAND ACROSS THE SUSITNA VALLEY. GFS IS STILL A BIT FASTER THAN
THE OTHER MODELS. WITH INFLUENCE OF 90 KT UPPER LEVEL JET PREFER THE
FASTER GFS SOLUTION UNTIL THE LOW REACHES THE KENAI PENINSULA. THE
GFS THEN SHOWS ITS BIAS OF MARCHING STORMS INLAND MUCH TOO FAST. THE
INTERACTION WITH THE TERRAIN WILL SLOW THE LOW DOWN. THEREFORE WILL
USE A MODIFIED GFS SOLUTION. OUT WEST MODELS REMAIN IN GOOD AGREEMENT
IN DROPPING UPPER LOW SOUTHWARD ACROSS THE BERING SEA.

.AER SHORT-TERM FORECASTS...AS THE DEVELOPING LOW MOVES INTO THE GULF
SUNDAY AFTERNOON MOISTURE WILL GRADUALLY SPREAD INTO EASTERN PRINCE
WILLIAM SOUND AND INTO ANCHORAGE AND VICINITY SUNDAY EVENING. THERE
WILL BE ABUNDANT MOISTURE AND WARMER AIR FROM EAST WILL OVERRIDE
COLDER AIR ON WEST SIDE OF KENAI AND CHUGACH MOUNTAINS. PRINCE
WILLIAM SOUND WILL BE MAINLY RAIN. THE QUESTION IS WHAT WILL THE
PRECIP TYPE BE ON THE OTHER SIDE OF THE MOUNTAINS. MODELS INDICATE
1000-850 THICKNESS GREATER THAN 1290 OVER ALL OF SOUTHCENTRAL SUNDAY
NIGHT. HOWEVER WITH IMPRESSIVE OVERRUNNING THINK PRECIP WILL BE
STEADY ENOUGH TO COOL THE LOW LEVELS TO NEAR OR BELOW FREEZING VIA
MELTING. THEREFORE...THINK THE PRECIP WILL START AS RAIN MOST PLACES
ON LEE SIDE OF MOUNTAINS AND SWITCH TO SNOW WITHIN A FEW HOURS. THERE
WILL LIKELY BE A BREAK IN PRECIP ANCHORAGE AND VICINITY AS LOW MOVES
OVERHEAD EARLY MONDAY MORNING. COLD ADVECTION WILL THEN ENSUE UP COOK
INLET MONDAY AFTERNOON. THIS IS WHERE WE HAVE THE MOST POTENTIAL FOR
SNOW ACCUMULATION. BASED ON MODEL QPF LOOKS LIKE WILL SEE 1 TO 4
INCHES FROM THE WESTERN KENAI TO THE SUSITNA VALLEY ON MONDAY. WILL
ISSUE A SPECIAL WEATHER STATEMENT TO HIGHLIGHT THE RETURN OF WINTER
WEATHER TO THE REGION. SPRING SNOWS CAN BE ESPECIALLY DANGEROUS FOR
DRIVERS BECAUSE MANY PEOPLE HAVE REMOVED THERE WINTER TIRES. THERE
IS ALSO A POTENTIAL FOR ADVISORY LEVEL SNOW MONDAY NIGHT IN THE
NORTHERN SUSITNA VALLEY IN SOUTHERLY FLOW AND COLD ADVECTION BEHIND
THE LOW. WILL TAKE A CLOSER LOOK AT THAT WITH THE NEXT MODEL CYCLE.
TUESDAY LOOKS SHOWERY ALONG COAST AS AN UPPER LEVEL SHORT-WAVE
APPROACHES WHILE INLAND AREAS WILL DRY OUT.

ALU SHORT-TERM FORECASTS...LOOK FOR QUIET CONDITIONS UNTIL LOW DROPS
INTO BERING MONDAY AND TRACKS SOUTH OF AKPENN TUESDAY NIGHT. THIS
LOW WILL BRING A WINTER LIKE BLAST OF COLD AIR DOWN FROM SIBERIA
(GFS SHOWS -42 DEGREES AT 500 MB AND -18 DEGREES AT 850 MB OVER THE
BERING TUESDAY. PRECIP TYPE WILL BE ALL SNOW IN TRACK OF THE LOW.
COLD ADVECTION SNOW SHOWERS WILL THEN PREVAIL IN THE WAKE OF THE LOW.
LOOK FOR MAX GALE TO MIN STORMS ON THE WEST SIDE OF THE LOW MONDAY
NIGHT THROUGH TUESDAY NIGHT.

EXTENDED FORECASTS...DO NOT SEE ANY MAJOR PATTERN CHANGES IN THE
EXTENDED TO MOVE US OUT OF THIS COLD PATTERN. WE REMAIN UNDER THE
INFLUENCE OF A VERY COLD UPPER LOW THROUGH NEXT WEEKEND. AT THIS
POINT LOOKS LIKE UPPER LOW WILL DROP TO 50N MID WEEK AND THEN LIFT
NORTHEASTWARD TO SOUTHCENTRAL LATE IN THE WEEK. AFTER A BRIEF BREAK
MID WEEK OVER SOUTHCENTRAL EXPECT DAILY RAIN AND SNOW SHOWERS TO
DEVELOP LATE IN THE WEEK AS COLD AIR ALOFT MOVES ACROSS THE AREA.
OUT WEST NORTHERLY FLOW AND SHOWERS WILL PERSIST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 120 125 130. HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

SEB APR 06