FXUS63 KABR 070340
AFDABR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
940 PM CST SUN DEC 6 2009

.UPDATE...
00Z UPPER AIR ANALYSIS AND WV IMAGERY CONTINUES TO DEPICT A WEAK
UPPER LEVEL S/W TRACKING ACROSS NE/IA...RESULTING IN A WEAK PVA
REGIME OVER SD/ND. IR IMAGERY DOES INDEED INDICATE COOLING CLOUD
TOPS OVER SD...ALTHOUGH REGIONAL RADAR MOSAIC CONTINUES TO SHOW
HIGHEST RADAR RETURNS CONFINED OVER FAR SRN AND SERN SD.
EXPECTING OCCNL LIGHT SNOW SHOWERS/FLURRIES TO CONTINUE OVER MUCH
OF THE AREA OVERNIGHT...ALTHOUGH LITTLE OR NO ACCUMULATION
EXPECTED. 

WITH ABUNDANT CLOUD COVER AND A STEADY LIGHT BREEZE...TEMPS HAVE
REMAINED FAIRLY STEADY THIS EVENING...SO AM A BIT WORRIED THAT LOW
TEMPS MAY BE A BIT TOO COLD. HOWEVER...WITH SINGLE DIGITS UPSTREAM
OVER WRN SD/ND...WILL NOT MAKE ANY MAJOR ADJUSTMENTS AT THIS POINT.

NEW AVIATION DISCUSSION BELOW.

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

MAIN ISSUE THIS PERIOD WILL BE SNOWFALL AND POSSIBLE ACCUMULATIONS
FOR MONDAY NIGHT/TUESDAY. FIRST...REGIONAL SNOWFALL TODAY WITH
WEAK SYSTEM HAS BEEN A NONFACTOR. KICR ASOS HAS REPORTED ONLY
INTERMITTENT 1 MILE AND KPHP HAS SEEN MAINLY FLURRIES...SO WILL
KEEP POPS/ACCUMS MINIMAL. THE NEXT SYSTEM APPEARS TO TAKE A
SLIGHTLY FURTHER NORTHWARD TRACK THAN PREVIOUS GUIDANCE. FURTHER
NORTH AWAY FROM THE STRONGER ISOTROPICALLY INDUCED
SNOWFALL...PERSISTENT LOW LEVEL MOISTURE UNDER AN AIRMASS WITH A
THERMAL PROFILE FAVORABLE FOR DENDRITIC GROWTH PRESENTS US WITH
THE PROSPECT FOR ADDITIONAL ACCUMULATIONS DUE TO SEEDER-FEEDER.
TEMPERATURES...VERY LITTLE THERMAL ADVECTION IN THE LOW LEVELS FOR
MUCH OF THE FORECAST PERIOD...SO TEMPERATURE FORECAST DOMINATE BY
CLOUD AND SNOW COVER. WEDNESDAY MORNING NORTHWEST WINDS
PICK UP...AND H85 TEMPERATURES DIVE BACK INTO THE NEGATIVE TEENS.

.LONG TERM...WEDNESDAY THROUGH SATURDAY.

MEDIUM RANGE MODELS AGAIN ARE DOING FAIRLY WELL. THE BIGGEST
CONCERN FOR THIS PERIOD IS HOW MUCH COLD AIR WILL SWEEP INTO THE
REGION AND HOW FAR WEST WILL IT GO. THE PERIOD OPENS WITH THE
LARGE LOW THAT IS THE CONCERN OF THE SHORT TERM MOVING EAST INTO
INDIANA. IT CONTINUES TO LOOK LIKE THIS AREA WILL MISS THE BRUNT
OF THIS SYSTEM BUT BEHIND IT THERE IS A VERY STRONG POLAR VORTEX
IN NORTHERN CANADA WITH H85 TEMPERATURES APPROACHING -30 C. THIS
AREA IS UNDER -20 C H85 TEMPERATURES. WITH A HIGHLY AMPLIFIED H5
UPPER LEVEL RIDGE IN THE GULF OF ALASKA THE SOURCE REGION FOR AIR
AFFECTING THIS AREA WILL BE CONTINENTAL CANADIAN ARCTIC. THIS IS
NOT A PLEASANT SITUATION IN DECEMBER. THERE IS ALSO AN H5 UPPER
LEVEL LOW IN THE NORTH PACIFIC CAUSING A REX TYPE BLOCK ALOFT
KEEPING THINGS FAIRLY STATIONARY. AS THE PERIOD PROGRESSES BY
FRIDAY THE VERY COLD CANADIAN AIR SLIDES SOUTH AND IS SHUNTED
SLIGHTLY EAST OF THE AREA BY WARM PACIFIC AIR THAT IS MOVING
ACROSS THE ROCKIES AS THE PACIFIC LOW MOVES TOWARD THE COAST WITH
A WELL DEVELOPED SURFACE LOW HELPING TO PUSH WARM AIR ONSHORE.
THIS SLIGHT DIFFERENCE IN THE UPPER FLOW WILL BEGIN BRINGING
WARMER AIR ALOFT TO THE REGION. BY SATURDAY H85 TEMPERATURES HAVE
WARMED FROM AROUND -20 C TO AROUND -10 C. THE QUESTION WILL BE HOW
FAR INTO THE AREA WILL THE COLD AIR PUSH. HAVE STAYED PRETTY CLOSE
TO THE GOING GRIDS EXPECTING THE COLDEST AIR TO CROSS JUST THE
NORTHEAST CORNER OF SOUTH DAKOTA. DID NOT VARY GREATLY FROM HPC
STARTING GRIDS ON TEMPERATURE. ALSO KEPT THE ENTIRE PERIOD DRY.

&&

.AVIATION...
A WEAK UPPER LEVEL DISTURBANCE MOVING SOUTH OF THE REGION WILL
CONTINUE TO TRIGGER AREAS OF LIGHT SNOW SHOWERS/FLURRIES. VSBYS
SHOULD REMAIN GENERALLY IN THE 3-6SM RANGE...ALTHOUGH BRIEF IFR
VSBYS POSSIBLE IN HEAVIER SNOWBANDS. LITTLE OR NO SNOW ACCUMULATION
EXPECTED.

CIGS ALSO EXPECTED TO REMAIN PRIMARILY MVFR...EXCEPT
OVER FAR SOUTHERN AND EASTERN SD WHERE IFR CONDITIONS MAY DEVELOP
AROUND OR AFTER 06Z. KATY WOULD BE MOST LIKELY TO SEE THESE LOWER
CIGS IF THEY DEVELOP. PREVAILING WINDS WILL REMAIN N/NWLY
OVERNIGHT AND INTO THE DAY ON MONDAY.

&&

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

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

WEATHER.GOV/ABERDEEN