Flash Flood Warning 5, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKDT FRI MAR 27 2009

.MODEL DISCUSSION...

STUCK MOSTLY WITH EXISTING GRIDS THROUGH 48 HOURS GIVEN THE ERUPTIONS
OF MT. REDOUBT THIS EVENING AND THE MONITORING OF THE ASH PLUMES.
AFTER 48 HOURS...USED THE NAM FOR DAY 3 ON THE EAST SIDE.  LONG TERM
GRIDS WERE LEFT MOSTLY AS IS.

.ANALYSIS AND UPPER LEVELS...

PLEASE SEE THE PUBLIC INFORMATION STATEMENT AND LATEST PUBLIC
ADVISORIES AND WARNINGS FOR THE LATEST INFORMATION ABOUT THE
ERUPTIONS OF MT. REDOUBT AND ITS ASSOCIATED PLUMES OF ASH.

LOW PRESSURE REMAINS NEARLY STATIONARY IN THE VICINITY OF THE KENAI
PENINSULA THIS MORNING...WITH AN APPROACHING UPPER SHORTWAVE FROM THE
SOUTH AND WEST HELPING TO INDUCE MOSTLY SNOW SHOWERS WITH A FEW
POCKETS OF RAIN.  THE UPPER SHORTWAVE THAT IS SUPPORTING THE SHOWERY
ACTIVITY IS MOVING NORTHEASTWARD CURRENTLY ACROSS THE AKPEN IN
CYCLONIC FLOW JUST TO THE EAST OF THE NARROW BUT SHARP LONGWAVE
TROUGH OVER NORTHWEST ALASKA TO THE CENTRAL ALEUTIANS.  AT THE BASE
OF THE LONGWAVE TROUGH IS A SHORTWAVE AND ASSOCIATED 1006 MB SURFACE
LOW JUST TO THE NORTH OF THE CENTRAL ALEUTIANS.  ANOTHER UPPER LOW
WITH A MUCH STRONGER 986 MB SURFACE LOW IS MOVING NORTHEASTWARD
TOWARDS THE BASE OF THE LONGWAVE TROUGH.

.SHORT TERM FORECAST...

THE ASH PLUME FROM MT. REDOUBTS ERUPTIONS LATE YESTERDAY EVENING AND
EARLY THIS MORNING IS BEING MONITORED CLOSELY.  FOR RIGHT
NOW...EXPECTING ONLY VERY LIGHT ASHFALL TO A TRACE TO OCCUR IN THE
ANCHORAGE BOWL AND THE MATANUSKA VALLEY...WITH HIGHER AMOUNTS TO AN
EIGHTH OF AN INCH FOR THE NORTHERN KENAI PENINSULA AND IN THE SUSITNA
VALLEY.

THE SHORTWAVE CURRENTLY OVER THE AKPEN THIS MORNING WILL MOVE
NORTHEAST ACROSS SOUTHCENTRAL TODAY...SUPPORTING THE CONTINUATION OF
SHOWERY ACTIVITY ACROSS MOST OF SOUTHCENTRAL.  PRECIPITATION CHANCES
WILL NOT TOTALLY END ACROSS SOUTHCENTRAL UNTIL THE PASSAGE OF A
SECOND SHORTWAVE SATURDAY INTO SATURDAY NIGHT...ENDING FROM WEST TO
EAST.

ATTENTION THEN TURNS TO THE EVOLUTION OF THE NEXT STRONG SYSTEM THAT
WILL BEGIN TO FORM LATER TODAY IN THE NORTH PACIFIC TO THE SOUTH OF
THE ALEUTIANS.  MODEL RUNS TODAY HAVE SWITCHED TO A TRACK THAT WILL
TAKE THIS SYSTEM MORE NORTH THAN YESTERDAYS MODEL RUNS...BRINGING IT
INTO BRISTOL BAY AND THEN INTO SOUTHWEST ALASKA NEAR DILLINGHAM THIS
WEEKEND.  HESITANTLY...THE MORE NORTHERN TRACK SOLUTION IS PREFERRED
AND THUS THE POSSIBILITY OF A MUCH WARMER EVENT SEEMS
POSSIBLE...THOUGH IT WOULD NOT SURPRISE TO SEE THE TRACK MOVE BACK
CLOSER TO BRINGING THE LOW TOWARDS KODIAK AND THE NORTHERN GULF.

REGARDLESS OF THE EVENTUAL TRACK...THIS SYSTEM WILL BRING LOTS OF
PRECIPITATION AND WIND TO THE STATE FOR THE WEEKEND AND INTO THE
FIRST HALF OF THE NEXT WEEK.  THE WARM FRONT MOVING NORTH WITH THIS
SYSTEM INDUCES A STRONG BARRIER JET ON SOME MODELS IN THE NORTHERN
GULF...SO THE POSSIBILITY OF STRONG WINDS TO STORM FORCE BEGINNING
LATE SATURDAY NIGHT INTO SUNDAY CERTAINLY IS WITHIN THE REALM OF
POSSIBILITY.

.LONG TERM FORECAST...

THE NEXT IN THE SERIES OF STRONG LOWS ON THE DOWNSTREAM SIDE OF THE
TROUGH LOOKS TO AFFECT THE REGION RIGHT ON THE HEELS OF THIS
WEEKENDS STORM SYSTEM.  MODELS WILL LIKELY FLUCTUATE BETWEEN A TRACK
NORTH OR SOUTH OF THE AKPEN.  EITHER WAY...CONTINUED UNSETTLED
WEATHER IS LIKELY THROUGH THE MIDDLE OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...ASHFALL ADVISORY...121 145
MARINE...GALE...150 155 160 165 170 172 175 179
         HEAVY FREEZING SPRAY...155 165 179
FIRE WEATHER...NONE.

CC MAR 09

SPECIAL WEATHER STATEMENT...UPDATED
NATIONAL WEATHER SERVICE ANCHORAGE AK
450 AM AKDT FRI MAR 27 2009

AKZ101-111-272000-

...VERY LIGHT ASHFALL POSSIBLE ACROSS THE ANCHORAGE BOWL AND
MATANUSKA VALLEY...

MOUNT REDOUBT HAD A SERIES OF ERUPTIONS BEGINNING AT 1148 PM THURSDAY
NIGHT. LIGHT RAIN AND SNOW SHOWERS ARE CURRENTLY MOVING FROM THE
NORTHERN KENAI PENINSULA TO THE MATANUSKA VALLEY AND THE ANCHORAGE
BOWL. RESIDUAL ASH FROM THE ERUPTIONS MAY FALL AS THE SHOWERS
MOVE OVERHEAD. ASHFALL AMOUNTS ARE EXPECTED TO BE A TRACE
OR LESS.