Small Craft Advisory 245, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
105 PM ADT MON MAR 12 2007

.DISCUSSION...

UPPER AIR...HIGHLY AMPLIFIED PATTERN WITH RIDGE IN THE BERING AND
TROUGH IN THE GULF WITH A (ESTIMATED 75 MPH) JET EXTENDING FROM
EASTERN RUSSIA SOUTHEASTWARD ACROSS THE EASTERN BERING AND SOUTHWEST
ALASKA. A DEEP CLOSED LOW OVER NORTHERN ALASKA IS DROPPING SOUTHWARD
ACROSS THE STATE BRINGING ANOTHER ROUND OF ARCTIC AIR WITH IT. THIS
LOW WILL DROP INTO THE GULF BY MID WEEK. THE BERING RIDGE BEGINS
TO RETROGRADE WESTWARD MID WEEK AND ALTHOUGH MODEL SOLUTIONS ARE
INCONSISTENT BEYOND THIS POINT...ALL SIGNS POINT TO A GRADUAL SHIFT
IN PATTERN BY NEXT WEEKEND WITH THE SUBTROPICAL JET MOVING NORTHWARD
AND DRIVING STORMS CLOSER TO THE ALEUTIANS. IN ANY CASE...LOOKS LIKE
THIS WILL BE THE LAST BIG ARCTIC PUSH FOR THE TIME BEING...AND
POSSIBLY FOR THE WINTER. PATTERN WILL BECOME LESS AMPLIFIED BY NEXT
WEEKEND ALLOWING FOR MODERATION OF TEMPS.

SURFACE...AT THE SURFACE THERE IS A FAIRLY DIFFUSE SURFACE LOW OVER
THE NORTHERN GULF WITH SCATTERED SHOWERS SPINNING AROUND IT. HIGH
PRESSURE IS PROVIDING CALM CONDITIONS ACROSS THE CENTRAL BERING.
THERE ARE STILL SOME GUSTY WINDS ALONG THE EASTERN BERING AND
AKPENN...BUT THESE WILL CONTINUE TO DIMINISH FROM WEST TO EAST
TONIGHT AS THE HIGH BUILDS SOUTH AND EAST A BIT. THE BEST COLD
ADVECTION HAS SHIFTED TO SOUTHWEST ALASKA AND THE NORTHERN AKPENN.
SATELLITE IMAGERY SHOWS CLOUD STREETS ON THE EAST SIDE OF THE AKPENN
SOUTH OF KODIAK ISLAND AS WELL AS FROM SOUTHERN COOK INLET THROUGH
THE BARREN ISLANDS. AS THE UPPER LOW DROPS TO SOUTHCENTRAL TONIGHT
COLDER AIR WILL BEGIN TO FILTER THROUGH THE ALASKA RANGE. COLD
ADVECTION ACROSS THE SOUTHERN MAINLAND WILL PEAK TUESDAY AND TUESDAY
NIGHT WITH -30 DEGREE 850 MB ISOTHERM DROPPING DOWN TO NEAR
ANCHORAGE. THE BEST UPPER SUPPORT WILL BE WEST OF THE UPPER
LOW...BASICALLY FROM ABOUT 150W AND WESTWARD. EXPECT MAX GALES
ALONG MUCH OF THE WESTERN GULF WITH STORM FORCE GUSTS THROUGH BAYS
AND PASSES. A WIND CHILL ADVISORY WILL BE ISSUED FOR THE SUSITNA
VALLEY AND STRONG WIND HEADLINES WILL BE INCLUDED FOR MOST ZONES.
AT THIS POINT IT DOES NOT LOOK LIKE HIGH WIND THRESHOLD WILL BE MET

ANYWHERE. HOWEVER...THE MAT VALLEY BEARS WATCHING. COLD AIR INITIALLY
COMES FROM THE NORTHWEST...BUT ON TUESDAY AND TUESDAY NIGHT WIND
SHIFTS TO NORTH TO NORTHEAST...A MORE FAVORABLE DIRECTION FRO HIGH
WINDS AS AIR PLUMMETS OFF THE TALKEETNA MOUNTAINS AND CHANNELS
THROUGH TAHNETA PASS FROM THE COPPER BASIN TO THE MAT VALLEY. THE
SURFACE PRESSURE GRADIENT BETWEEN GLENNALLEN AND PALMER DOES NOT LOOK
LIKE IT GETS VERY TIGHT AND UPPER SUPPORT IS QUESTIONABLE...SO 60 TO
65 MPH SHOULD SUFFICE FOR NOW. THE OTHER AREA OF CONCERN IS SOUTHEAST
PRINCE WILLIAM SOUND (CORDOVA). THE MODELS DEPICT A WEAK SHORTWAVE
AHEAD OF THE UPPER LOW DIGGING AS IT MOVES INTO PRINCE WILLIAM SOUND
TONIGHT INTO TUESDAY. WITH LOW LEVEL MOISTURE ROTATING INTO THAT AREA
THIS MAY RESULT IN SIGNIFICANT SNOWFALL. ADD TO THAT COLD ADVECTION
WINDS BEGINNING TUESDAY AFTERNOON AND THERE IS THE POTENTIAL FOR
BLIZZARD CONDITIONS. THEREFORE...WILL ISSUE A BLIZZARD WATCH FOR
TUESDAY AFTERNOON THROUGH TUESDAY EVENING. COLD ADVECTION WILL EASE
OFF WEDNESDAY BUT A TIGHT PRESSURE GRADIENT WILL MAINTAIN STRONG
WINDS THROUGH WEDNESDAY NIGHT WITH IMPROVING CONDITIONS THURSDAY
AND FRIDAY.

MODEL DISCUSSION...MODELS ALL SHOW SAME BASIC SOLUTION...BUT THE KEY
TO THE FORECAST IS IN THE DETAILS. THE LOCATION AND ORIENTATION OF
THE UPPER LOW AS IT DROPS ACROSS SOUTHCENTRAL IS DEPICTED A LITTLE
DIFFERENTLY BY EACH MODEL. THE GFS IS THE FARTHEST EAST...THE NAM IS
THE FARTHEST WEST...AND THE UKMET AND ECMWF ARE SOMEWHERE IN BETWEEN.
THE POSITION OF THIS LOW AND THE TROUGH AXIS WILL DETERMINE WHETHER
STRONG WINDS ALOFT MAKE IT INTO THE MAT VALLEY...ANCHORAGE...WESTERN
KENAI. IF NOT...NORTHERLIES WILL BECOME PRETTY SHALLOW WHILE ALOFT
WINDS WILL VEER TO THE EAST...THIS USUALLY KEEPS THE STRONGEST WINDS
RIGHT ALONG THE INLET. WILL TAKE THE MIDDLE GROUND FOR NOW AND LOOK
TO THE NEXT MODEL RUN TO FINE TUNE THE FORECAST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES...120 121 129 130 132 138 150 176.
         HEAVY FREEZING SPRAY...120 121 125 129 130 132 138 141
                                150 155 165.
FIRE WEATHER...NONE.

SEB MAR 07