Flood in Alaska, April 23 to 25, 2012

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
242 PM AKDT MON APR 23 2012

.DISCUSSION...
ALOFT...5170 METER LOW OVER THE EASTERN ALEUTIANS WILL CONTINUE
SOUTHEAST WHILE A WEAK 5320 METER LOW OVER THE NORTHEAST GULF OF
ALASKA WILL WEAKEN TO A TROUGH AND DRIFT NORTHWEST OVER THE
EASTERN ALASKA RANGE TUE AND TUE NIGHT. WEAK LOW NORTH OF LISBURNE
WILL DRIFT NORTH BUT A TROUGH EXTENDING SOUTH WILL DRIFT EAST TO
BARROW 12Z WED. WEAK LOW JUST NORTH OF PRUDHOE BAY WILL DRIFT
SLOWLY NORTH THROUGH WED. MODERATE RIDGE DEVELOPING OVER CHUKCHI
AND NORTH BERING SEA TUE AND PERSISTING THROUGH THU.

SURFACE...991 MB LOW 90 NM NW OF DUTCH HARBOR WILL DRIFT SOUTHEAST
OVER THE WESTERN GULF OF ALASKA. THE ASSOCIATED OCCLUSION FROM
EMMONAK TO ILIAMNA AND FARTHER SOUTHEAST WILL DRIFT NORTH AND
THIS NORTHERN PART OF THE OCCLUSION WILL SLOWLY WEAKEN. 1030 MB
HIGH OVER HIGH ARCTIC WILL DRIFT EAST AND WEAKEN ONLY A LITTLE
THROUGH WEDNESDAY.

MODELS IN FAIRLY CLOSE AGREEMENT IN SHORT TERM. IN MEDIUM RANGE
THE OPERATIONAL ECMWF HAS PULLED BACK ON THE INTENSE LOW MOVING
ALONG THE HIGH ARCTIC NORTH OF RUSSIA TOWARD FAR NW ALASKA...A
WEAKER LOW IS NOW FORECAST AND LOOKS MORE REASONABLE. THE RIDGE
OVER THE BERING AND CHUKCHI SEA IS INDICATED TO BREAK DOWN BY THE
END OF THE WEEK TO MAKE WAY FOR THIS ARCTIC LOW.

NORTH SLOPE...SOME ISOLATED SNOW SHOWERS NEXT 36 HOURS FROM BARROW
EAST WITH THE SEVERAL FEATURES ALOFT MOVING THROUGH. BUT OTHERWISE
LIGHT AND EASTERLY WINDS AS SURFACE HIGH PERSISTS TO THE NORTH.
EXPECT PATCHY TO SCATTERED FOG OVERNIGHT.

WESTERN ALASKA...VERY SPOTTY SNOW SHOWERS TONIGHT NEAR OCCLUSION
LIKE ZONES 214 215 AND MAYBE 212...ALSO WITH UPPER TROUGH MOVING
EAST OVER SOUTHERN CHUKCHI SEA FOR ZONES 207 209 AND 208. BUT
OTHERWISE LOOK DRY THROUGH MOST OF THE WEEK. LIGHT WINDS AS
WELL...GETTING LIGHTER AS HIGH PRESSURE ALOFT BUILDS IN.

CENTRAL AND EASTERN INTERIOR...THE WEAK FLOW ALOFT AND SOMEWHAT
UNSTABLE AIR MASS WILL GIVE RISE TO ISOLATED TO SCATTERED AFTERNOON
AND EVENING SHOWERS MAINLY FROM FAIRBANKS EAST AND SOUTH THROUGH
THE WEEK. WHILE WE STILL HAVE ENOUGH NIGHTTIME COOLING PATCHY
MORNING FOG WILL DEVELOP IN AREAS WHICH GET RAIN SHOWERS THE
PREVIOUS AFTERNOON. THE UPPER TROUGH MOVING NORTHWEST OVER THE
EASTERN ALASKA RANGE WILL HEIGHTEN CONVECTION OVER THE FAR
SOUTHEASTERN AREAS TUE PM AND MAY PRODUCE SOME THUNDERSTORMS OVER
ZONES 223 AND SRN 224...SOMETHING TO WATCH FOR THE TIME BEING.

&&

.FIRE WEATHER...WEAK TO MODERATE INSTABILITY OVER ERN INTERIOR
WILL GIVE SOME DIURNAL SHOWERS OVER THE INTERIOR FROM FAIRBANKS
SOUTHEAST DURING THE AFTERNOON AND EVENINGS. INSTABILITY WILL
ENHANCE A LITTLE MORE TUE AFTERNOON OVER THE SE INTERIOR AS THE
UPPER TROUGH MOVES NORTHWEST OVER THE ERN AK RANGE...SO THERE IS
THE POTENTIAL FOR ISOLATED THUNDERSTORMS SRN 224 AND ERN ZONE 223.
MIN RH VALUES SHOULD BE IN THE 30 TO 40 PERCENT RANGE FOR SOUTHERN
INTERIOR ZONES.

&&

.HYDROLOGY...A FLOOD ADVISORY REMAINS IN EFFECT THROUGH 1100 PM AKDT
TUESDAY FOR THE TANANA RIVER AT SALCHA FROM THE BOONDOX AREA
DOWNSTREAM. PLEASE SEE THE FLOOD ADVISORY AT FAIFLSAFG OR WGAK89
FOR THE LATEST STATEMENT DETAILS.

FROM PREVIOUS DISCUSSION...MOST OF THE LOW ELEVATION SNOW IN THE
FAIRBANKS AREA HAS MELTED OUT...BUT STILL SIGNIFICANT SNOW THAT
HAS RIPENED AT ELEVATION...WITH 17 INCHES AT KEYSTONE RIDGE ON
MURPHY DOME AND 27 INCHES AT MUNSON RIDGE (ELEV 3100 FT) AS OF
SUNDAY. BREAKUP WILL CONTINUE ON THE TANANA FOR ABOUT THE NEXT
7-10 DAYS AND WILL BEGIN IN THE NEXT WEEK OR TWO ON THE UPPER
YUKON.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AKZ222-AKZ223 FLOOD ADVISORY FOR SALCHA AREA.

&&

JL APR 12