Flood in Alaska, May 18 to 21, 2012

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
430 AM AKDT FRI MAY 18 2012

.DISCUSSION...
UPPER AIR...A 554 DM RIDGE AT 500 MILLIBARS IS CENTERED OVER THE
NOATAK VALLEY EARLY THIS MORNING.  THE RIDGE WEAKENS TODAY AND
ELONGATES AS IT BEGINS TO RETREAT INTO SOUTHEAST RUSSIA. A STRONG
RIDGE IS EXPECTED TO REMAIN ACROSS THE SEA OF OKHOTSK THROUGH THE
WEEKEND.  A 536 DM LOW ABOUT 100 MILES EAST OF WRANGEL ISLAND DRIFTS
ONLY VERY SLOWLY TO THE EAST THROUGH SAT NIGHT BEFORE RETREATING TO
THE NORTH.  AN UPPER LOW IN THE YUKON IS EXPECTED TO DRIFT INTO THE
NORTHEAST MAINLAND SAT. THE MODELS DIFFER SOME ON THE DEPTH AND
LOCATION OF THE LOW...BUT IT IS EXPECTED TO HAVE MINIMAL
IMPLICATIONS ON THE SENSIBLE WEATHER.

SFC...A BROAD RIDGE COVERS THE AREA FROM THE EASTERN BEAUFORT SEA
INTO THE SOUTHERN CANADIAN ARCHIPELAGO AND INTO NW CANADA.  THE
RIDGE IS EXPECTED TO REMAIN IN TACT THROUGH SUN.  A 1010 MB LOW NEAR
WRANGEL ISLAND EARLY THIS MORNING DRIFTS SLOWLY TO THE
EAST/NORTHEAST AND IS EXPECTED TO A 1006 MB LOW 300 MILES NORTHEAST
OF WRANGEL ISLAND BY 00Z MON.  A 998 MB LOW NEAR UNALASKA REMAINS
QUASI-STATIONARY THROUGH TON AND THEN GETS ABSORBED BY A 989 MB
LOW 300 MILES SOUTH OF COLD BAY SAT. A WEAK THERMAL TROUGH
DEVELOPS TODAY FROM ABOUT MCGRATH-FAIRBANKS-CHICKEN AND BECOMES
STRONGER OVER THE WEEKEND. BY SUNDAY AFTERNOON THE THERMAL TROUGH
WILL STRETCH FROM HOLY CROSS-ALLAKAKET-EAGLE.

INTERIOR...THE AIR MASS HAS WARMED SIGNIFICANTLY OVER THE LAST 48
HOURS WITH THE 850 MB TEMP AT FAIRBANKS RISING FROM -5C AT 12Z WED
TO +3C AT 12Z THIS MORNING. MOST OF THE WARMING IS DONE...BUT A
BIT MORE TODAY WITH AN 850 MB TEMP OF +4-5C EXPECTED BY THIS EVE
ALONG THE THERMAL TROUGH AXIS THAT WILL BE ACROSS THE SOUTHERN
INTERIOR. TEMPS THIS AFTERNOON WILL TOP OUT IN THE MID 60S TO LOW
70S IN MOST INTERIOR VALLEYS. THERE MAYBE JUST ENOUGH INSTABILITY
AND MOISTURE IN THE SOUTHEAST INTERIOR THIS AFTERNOON FOR AN
ISOLATED SHOWER. A BIT MORE CONVECTION OVER THE WEEKEND AS THE THE
THERMAL TROUGH STRENGTHENS...BUT SHOULD STILL REMAIN ISOLATED.
TEMPS TO REMAIN SEVERAL DEGREES ABOVE NORMAL THROUGH THE WEEKEND.
LOW DEW POINTS AND A MAINLY CLEAR SKY WILL ALLOW FOR LARGE DIURNAL
RANGES.

NORTH SLOPE...AREAS OF LIGHT RAIN THIS MORNING ALONG THE WESTERN
AND NORTHERN ARCTIC COAST WILL MOVE OFFSHORE THIS PM. A SLIGHTLY
COOLER AIR MASS WILL MOVE OVER THE ARCTIC COAST FROM BARROW SOUTH
AND WEST TONIGHT AND SATURDAY AS THE UPPER LOW IN THE CHUKCHI SEA
DRIFTS EAST AND THE RIDGE IN THE NOATAK VALLEY WEAKENS. IT SHOULD
AT LEAST PRODUCE ENOUGH COOLING THAT ANY ISOLATED SHOWERS WILL
CHANGE TO SNOW. THE NAM MOS HAS A HIGH OF 47F AT BARROW
TODAY...WHICH IS NOT ONLY A RECORD HIGH FOR MAY 18TH BUT IS ALSO
THE ALL-TIME HIGH FOR THE ENTIRE MONTH OF MAY. GIVEN THE OFFSHORE
FLOW AND POTENTIAL FOR SOME SUNSHINE THIS AFTERNOON IT IS NOT OUT
OF THE QUESTION THAT HIGHS GET INTO THE LOWER 40S. WILL PUT IN A
HEADLINE FOR NEAR RECORD HIGH TEMPS TODAY AT BARROW. BARTER
ISLAND HAS BEEN FOGGY ALL NIGHT WITH VISIBILITY ONE QUARTER MILE
OR LESS AND WILL EXTEND THE DENSE FOG ADVISORY HEADLINE THROUGH
NOON.

WEST COAST...THE UPPER RIDGE IN THE NOATAK VALLEY WEAKENS AND
ELONGATES OUT...BUT STILL REMAINS A DOMINATE FEATURE THROUGH THE
WEEKEND. SOME ENERGY DROPS ALONG THE NORTHEAST RUSSIA COAST AND TO
THE CHUKOTSK PENINSULA SUNDAY. THIS WILL PUSH A SLIGHTLY COOLER
AIR MASS SOUTH TO THE BERING STRAIT SUN-MON. OTHERWISE TEMPS WILL
AVERAGE 5 TO 10 DEGREES ABOVE NORMAL THROUGH THE WEEKEND WITH A
VERY WEAK FLOW REGIME. WEAK ONSHORE FLOW IN SPOTS ALONG THE COAST
WILL LEAD TO PATCHY COASTAL STATUS AND FOG.

MID-RANGE...MODEL SPREAD INCREASES SIGNIFICANTLY HEADING INTO NEXT
WEEK.  THERE IS IN A GENERAL SENSE AGREEMENT THAT A TROUGH SOUTH OF
THE MAINLAND EXPANDS EAST TO THE AK PANHANDLE TOWARD THE MIDDLE OF
NEXT WEEK.  NORTH OF THE TROUGH A WEAK FLOW REGIME IS EXPECTED
ACROSS THE NORTHERN MAINLAND.  A THERMAL TROUGH IS EXPECTED TO LIE
BETWEEN THE AK RANGE AND BROOKS RANGE THAT WILL BE FOCUS FOR MAINLY
DIURNAL CONVECTION.  TEMPS LIKELY TO CONTINUE TO AVERAGE A LITTLE
ABOVE NORMAL MOST AREAS.

&&

.FIRE WEATHER...FAIRLY WIDESPREAD MIN RH'S NEAR OR BELOW 15 PCT
IN ZONES 220-221-222-223-226 YESTERDAY AFTERNOON. MIN RH'S ARE
EXPECTED TO BE NEAR 15 PCT THIS AFTERNOON.

&&

.HYDROLOGY...A FLOOD WATCH IS IN EFFECT THROUGH THIS AFTERNOON FOR THE
YUKON RIVER AT RUSSIAN MISSION AND MARSHALL. MINOR ICE JAM FLOODING
IS POSSIBLE AT RUSSIAN AND MARSHALL...BUT NO HOMES OR BUILDINGS ARE
CURRENTLY THREATENED.

BREAKUP WILL CONTINUE ON THE LOWER YUKON FOR ABOUT THE NEXT
WEEK...AND WITH THE WARMER WEATHER WILL BEGIN ON NW ALASKA RIVERS
OVER THE NEXT WEEK TO 10 DAYS...AND THEN FINALLY THE ARCTIC IN LATE
MAY/EARLY JUNE. STILL SOME TIME TO GO ON THE BUCKLAND RIVER WHERE
PEOPLE ARE STILL DRIVING ACROSS THE ICE AS OF THURSDAY AFTERNOON.
SO FAR IT HAS BEEN A FAIRLY GENTLE BREAK-UP FOR MOST AREAS.

&&

.CLIMATE...THE HIGH YESTERDAY AT BARROW WAS 36F. THIS IS ABOUT 3
WEEKS LATER THAN AVERAGE FOR THE FIRST ABOVE FREEZING TEMP AT
BARROW. YESTERDAY WAS THE FIRST TIME THE HIGH TEMPERATURE CLIMBED
ABOVE FREEZING SINCE OCTOBER 9TH 2011...MAKING A TOTAL OF 220 DAYS
WHERE THE TEMP REMAINED BELOW FREEZING. THIS FALLS SHORT OF THE
ALL-TIME RECORD OF 250 CONSECUTIVE DAYS BELOW FREEZING FROM SEP
23, 1975 TO MAY 30, 1976.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

FLOOD WATCH FOR THE YUKON RIVER AT RUSSIAN MISSION AND MARSHALL
(AKZ215).

&&

CB MAY 12