FXUS63 KABR 060111 AAA
AFDABR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ABERDEEN SD
711 PM CST SAT DEC 5 2009

.UPDATE...
NO CHANGES PLANNED TO THE FORECAST AT THIS TIME. FORECAST IS ON
TRACK...WITH LOW LEVEL CAA CONTINUING...ALONG WITH SOME
FLURRIES/OCCASIONAL VERY LIGHT SNOW OUT OVER THE MISSOURI RIVER
VALLEY FORECAST ZONES.

UPDATED AVIATION DISCUSSION BELOW.

&&
.PREV DISCUSSION...
.SHORT TERM...THROUGH TUESDAY AM

MAIN SUITE OF MORNING GUIDANCE INDICATING THAT SHEARED VORT LOBE
HEADED OUT OF ND/MT WILL DISSIPATE IN FAVOR OF A SOUTHERN IDAHO
SHORTWAVE WHICH WILL THEN EJECT ENERGY OUT OF THE ROCKIES AND SOUTH
OF THE CWA. THIS WAVE REMAINS FAIRLY MOISTURE STARVED AND HAS ONLY
BEEN PRODUCING MID/HIGH CLOUDS AND A BAND OF FLURRIES. THIS BAND
WILL WEAKEN OVERNIGHT...IN FAVOR ISENTROPIC FORCING AHEAD OF THE
SOUTHERN IDAHO WAVE. WITH MUCH OF THE CWA ON THE NORTHERN FRINGE
OF THIS SYSTEM...EXPECT MAINLY MID/HIGH CLOUDS AND
FLURRIES...HOWEVER SOUTH OF I90 COULD RECEIVE ENOUGH SNOW TO
MEASURE BASED ON RESIDENCE TIME. EXPECT A BRIEF INTERLUDE BEHIND
THE FIRST SYSTEM BEFORE A SECOND WAVE WILL EJECT SOUTH OF THE CWA
FOR TUESDAY. DURING THIS TIME PERIOD...SURFACE PRESSURE PATTERN
WILL REMAIN AMOEBIC WITH LIGHT WINDS AND NEGLIGIBLE ADVECTION.
WILL SEE A STRONGER ADVECTION TERM AND ISENTROPIC FORCING AHEAD
OF THE TUESDAY SHORTWAVE...ALL WITHIN THE DENDRITIC GROWTH ZONE.
THE TRACK OF THIS SYSTEM FAVORS ACCUMULATING SNOW ALONG AND SOUTH
OF THE I90 CORRIDOR WITH THIS SYSTEM.

.LONG TERM...TUESDAY THROUGH FRIDAY

MEDIUM RANGE MODELS ARE IN PRETTY CLOSE AGREEMENT. THERE ARE
SEVERAL PERIODS OF INTEREST DURING THIS PERIOD. THE FIRST IS THE
EVOLUTION OF THE STORM SYSTEM THAT IS SPOOLING UP AS THE PERIOD
OPENS. AN UPPER LEVEL H5 TROUGH EXTENDS FROM HUDSON BAY TO
NEVADA. THE SURFACE REFLECTION OF THIS SYSTEM IS NEAR THE FOUR
CORNERS AREA OF THE SOUTHWEST UNITED STATES. THIS STARTING
POSITION IS THE NORMAL START OF OUR MAJOR WINTER STORMS THAT CAN
TAP INTO GULF MOISTURE. HOWEVER THIS SYSTEM IS PROGGED TO FOLLOW
THE SOUTHERN STREAM. THE SOUTHERN JET IS VERY STRONG DURING THIS
TIME WITH THE ECMWF SHOWING OVER 150 KT JET ROUNDING THE BASE OF
THE LOW. THE UPPER LEVEL SOUTHERN STREAM THEN CONTINUES BASICALLY
STRAIGHT EAST AND TAKES THE SURFACE LOW ALONG. THIS PERIOD OPENS
IN THE GRIDS WITH CHANCE CATEGORY PROBABILITIES OVER MUCH OF THIS
AREA WITH PROBABILITIES INCREASING TO THE SOUTH. THE PRECIPITATION
WILL MOVE THROUGH THIS AREA BY WEDNESDAY MORNING AND CONTINUE TO
THE SOUTH AND EAST OF HERE. THE NEXT PERIOD OF INTEREST HAPPENS
TOWARD THE END OF THE PERIOD. AS THE STRONG LOW MOVES EAST THIS
AREA ONCE AGAIN COMES UNDER THE NORTHERN STREAM ALOFT. BY THURSDAY
VERY COLD CANADIAN AIR IS ROTATING SOUTH UNDER THE POLAR VORTEX.
THERE IS SOME DIFFERENCE IN THE WAY THE MODELS DEAL WITH THIS COLD
POOL. THE GFS SPREADS IT MUCH FARTHER WEST AND SLIDES IT OVER THIS
REGION. THE ECMWF ROTATES THIS ARE TO THE EAST BEHIND THE BIG
SURFACE SYSTEM. THIS IS IN RESPONSE TO THE NEXT PACIFIC LOW MOVING
ONTO THE WEST COAST. AT THIS POINT TRIED TO HEDGE THE BETS BY
BRINGING COLD AIR ALONG THE EAST SIDE OF THE AREA. THIS WILL
SURELY NEED SOME ADJUSTMENT UP OR DOWN AS SUBSEQUENT MODEL RUNS
CLARIFY THE TRACK OF THE UPPER SYSTEMS.

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL THROUGH EARLY THIS EVENING AT ALL TAF
SITES EXCEPT KMBG...WHERE OCCASIONAL MVFR CIGS AND MVFR/IFR
VISBIES IN LIGHT SNOW MAY BE OBSERVED. DURING THE LATE EVENING AND
OVERNIGHT HOURS...THE LESS THAN IDEAL FLYING WEATHER WILL SHIFT
SOUTH INTO THE KPIR TERMINAL.

THERE IS AN AREA OF MVFR/IFR LOW CIGS DEVELOPING/WORKING DOWN
THROUGH NORTHERN MINNESOTA AND NORTH DAKOTA...AND COULD VERY WELL
BE IMPACTING THE KABR AND KMBG TERMINALS BETWEEN 06Z AND 12Z
SUNDAY MORNING.

THE SYSTEM RESPONSIBLE FOR THE LIGHT SNOW POTENTIAL AT KMBG AND
KPIR TONIGHT WILL EXIT THE REGION BY SUNNDAY MORNING...ALLOWING
MVFR/VFR CONDITIONS TO RETURN BY LATE SUNDAY MORNING. WHETHER OR
NOT ALL THE LOW CLOUDS DEPART WITH THE LOW PRESSURE REMAINS TO
BE SEEN.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
&&

$$
UPDATE...DORN
SHORT TERM...CONNELLY
LONG TERM...KEEFE
AVIATION...DORN

WEATHER.GOV/ABERDEEN