Area Forecast Discussion
Issued by NWS Fairbanks, AK

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FXAK69 PAFG 032139
AFDAFG

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
139 PM AKDT SUN MAY 3 2015

.DISCUSSION...
NUMERICAL MODELS SIMILAR THROUGH ABOUT 60 HOURS. UPPER LEVEL RIDGE
ORIENTED NORTH SOUTH OVER MAINLAND ALASKA TODAY WITH EMBEDDED
CUTOFF LOW NEAR BRISTOL BAY. LOW WILL PERSIST BEFORE BEING
ABSORBED INTO FRONTOGENESIS OF NEW LARGE NEW UPPER LEVEL LOW
SOUTH OF THE ALEUTIANS ON MONDAY. MEANWHILE UPPER LEVEL RIDGE
DEVELOPS LOBE FROM EAST TO WEST ACROSS THE FORECAST AREA AND INTO
FAR EAST RUSSIA DURING SAME TIME STAMP.

COLD OCCLUSION MOVING EASTWARD ACROSS THE ARCTIC COAST TAPS INTO
WEAK AREA OF FRONTOGENESIS POSITIONED FROM UPPER LEVEL LOW NEAR
BRISTOL BAY. Q VECTORS OF VERTICAL MOTION INDICATE WEAK VERTICAL
MOTION OVER ARCTIC COAST FROM ABOUT PRUDHOE BAY TO ABOUT BARROW
THIS EVENING WITH STRONGER VERTICAL MOTION FOR PORTIONS OF THE
WESTERN INTERIOR SUCH AS THE LOWER KOYUKUK AND MIDDLE YUKON
VALLEYS. BUT FRONTOLYSIS BEGINS TO RAPIDLY BEGIN BY LATE SUN
EVENING OVER THE WESTERN PORTION OF THE AFFECTED AREA. VERTICAL
MOTION SPREADS EAST WHILE THE AREA STABILIZES TO THE WEST.

AFTER CURRENT COLD OCCLUSION TREKS EASTWARD ACROSS THE ARCTIC
COAST BY MON AFTERNOON...ANOTHER INTRUSION INTO THE UPPER LEVEL
RIDGE DOMAIN OCCURS FROM THE WEST WITH A MORE SUBSTANTIAL COLD
OCCLUSION WHICH WILL EXTEND FROM A VERY WEAK SURFACE LOW THAT WILL
DEVELOP NORTH OF PRUDHOE BAY ON MON. THE FRONTOGENESIS DYNAMICS
ASSOCIATED WITH THIS SYNOPTIC FEATURE IS MUCH MORE DRAMATIC THAN
THE PREVIOUS OCCLUSION. THE Q VECTOR ANALYSIS SHOWS A MUCH MORE
ORGANIZED AREA OF VERTICAL LIFT WHICH WOULD BE ATTRIBUTED TO THE
MUCH COLDER AIR UNDERCUTTING THE ALREADY COLD AIR. BUT WHEN
LOOKING AT THE MOISTURE ADVECTION AND CONVERGENCE
PARAMETERS...THESE ARE WEAK GIVEN THE LACK OF AVAILABLE MOISTURE
TO BE ADVECTED IN FROM THIS SOURCE REGION. EXPECT SOME VERY LIGHT
SNOW OR FLURRIES WHILE THE STRATUS WILL LIKELY REMAIN BUT THE FOG
SHOULD THIN OUT A BIT THROUGH TUESDAY.

CONVECTIVE PARAMETERS ARE WEAK AT BEST OVER ALL OF THE FORECAST
AREA. LIFTED INDICES ARE STABLE AND CAPE IS LESS THAN 100 JOULES
FOR THE MOST PART. THE ONLY EXCEPTION IS ON TUESDAY THE MODELS
INDICATE AN AREA OF INSTABILITY IN THE FAR EASTERN INTERIOR
AROUND EAGLE. LIFTED INDICES APPROACH ZERO WHILE CAPE VALUES RISE
TO NEAR 400 JOULES. THIS WILL BE ASSOCIATED WITH AN UPPER LEVEL
SHORT WAVE MOVING EASTWARD ACROSS THE AREA AT THAT TIME. Q VECTOR
ANALYSIS INDICATES AN ASSOCIATED AREA OF MODERATE LIFT AND 500H
FRONTOGENESIS VECTOR ANALYSIS DOES INDICATE A MODERATE AREA OF
CONVERGENCE AT THAT LOCATION. THERE IS A WEAK THERMAL TROF JUST TO
THE SOUTH THAT WILL ALLOW FOR A A SMALL AMOUNT OF INSTABILITY.
THETA E RIDGE IS VERY WEAK BUT THERE IS A RESEMBLANCE OF ONE
THERE AT THIS TIME. THERE IS MORE OF AN INVERTED THETA E RIDGE
FROM NORTHEAST TO SOUTHWEST BUT SINCE THE SOURCE REGION IS FROM A
VERY STABLE AIR MASS.

NUMEROUS UPPER LEVEL SHORT WAVE FEATURES WILL TRAVERSE THE UPPER
LEVEL RIDGE THIS WEEK AND MOVE FROM WEST TO EAST ACROSS NORTHERN
ALASKA ALTHOUGH MOST OF THE IMPACT WILL BE SPARED AN THE WEST
COAST. COOL DRY STABLE AIR MOVING EASTWARD WILL HAVE LITTLE INPUT
FOR PRECIPITATION ON THE WEST COST FROM THE SEWARD PENINSULA
SOUTHWARD. THERE MAY BE SOME OROGRAPHIC EFFECT IN THE BROOKS RANGE
THAT WILL LEAD TO A FEW SHOWERS MON NIGHT AND TUESDAY BUT SHOWERS
SHOULD BE LIGHT IF ANY.

&&

.FIRE WEATHER...AS PREVIOUSLY SUGGESTED...THE AIRMASS DID DRY
SOMEWHAT ON SAT AS RH VALUES REACHED INTO THE 20S AND LOWER 30S
IN MANY AREAS IN THE EASTERN INTERIOR. MOISTURE ADVECTION APPEARS
TO BE NEARLY STABLE. SLIGHTLY MORE MOIST AT THE SURFACE THROUGH
THE CENTRAL INTERIOR BUT SLIGHTLY DRIER FOR THE ALASKA RANGE ZONES
THIS AFTERNOON AND TUESDAY AFTERNOON. AS REASONED...EXPECT AN
INCREASE IN MOISTURE OVER THE EASTERN INTERIOR EAST OF A FAIRBANKS
TO FORT YUKON LINE ON TUESDAY AHEAD OF UPPER LEVEL SHORTWAVE. RH
VALUES SHOULD REMAIN NEARLY STABLE AND ONLY FLUCTUATING SLIGHTLY
UNTIL TUESDAY. EXPECT RH VALUES IN THE 20S AND 30S THROUGH
TUE...SLIGHTLY HIGHER THOUGH ON TUESDAY AFTERNOON IN THE FAR
EASTERN INTERIOR.


&&

.HYDROLOGY...NO SYNOPTIC OR EVEN MESOSCALE FEATURES THAT APPEAR
TO CONTRIBUTE OR CAUSE ANY HYDROLOGY ISSUES AT THIS TIME...EVEN
THOUGH RUNOFF IS LIKELY DUE TO HIGH SOIL SATURATION AND FROZEN
GROUND.


&&

.AFG WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

CF MAY 15


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