FXUS63 KEAX 102329
AFDEAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
529 PM CST THU DEC 10 2009

...UPDATED AVIATION DISCUSSION...

.DISCUSSION...
/245 PM CST THU DEC 10 2009/
SHORT TERM (TONIGHT THROUGH SUNDAY)...

PRIMARY FORECAST CHALLENGE FOR THE NEXT 48 HOURS WILL BE 
TEMPERATURES...WHICH WILL BE HIGHLY CONTINGENT UPON ALIGNMENT AND 
EROSION OF THE DEEPER SNOW PACK ACROSS THE CWA. TIGHT GRADIENT CAN 
ALREADY BE SEEN TODAY...WHERE HIGHS HAVE PUSHED NEAR FREEZING OVER 
THE SRN CWA...WHILE LANGUISHING IN THE TEENS OVER THE DEEPER SNOW. 
NUMERICAL GUIDANCE APPEARS SLIGHTLY LESS BIASED THAN YESTERDAY...AND 
HAVE ONLY PUSHED TEMPS AT THE LOWEST PACKAGE OVER THE SNOW COVER FOR 
THE NEXT 24 HOURS...AND KEPT AROUND A GUIDANCE AVERAGE ELSEWHERE. 
BIGGEST PROBLEM IS ANTICIPATING THE EFFECTIVE EDGE OF THE SNOW 
INFLUENCE...AS 1) SLY WINDS WILL BE ADVECTING OFF WARMER BARE 
GROUND...EFFECTIVELY DAMPENING OR NEGATING THE SNOW INFLUENCE SOME 
DISTANCE AWAY FROM THE TRUE EDGE OF THE SNOW COVER...AND 2) DEPTH OF 
SNOW WILL BE QUITE VARIABLE ALONG THE SRN FRINGES OF THE PACK 
WHEREAS TRACE OR PATCHY COVER WILL HAVE MINIMAL INFLUENCE VERSUS A 
SOLID 1 INCH ACCUMULATION. UNDOUBTEDLY...ADJUSTMENTS WILL BE 
NECESSARY TO PINPOINT THE STRONGEST TEMPERATURE GRADIENT BEYOND 
FRIDAY AFTERNOON.

WEEKEND FORECAST BECOMES COMPLICATED BY A SURGE OF ELEVATED (H8-H9 
LAYER) HIGHER THETA-E AIR FROM THE WRN GULF COAST (IN ASSOCIATION 
WITH A FEW FAST MOVING PROGRESSIVE SHORTWAVES) OVER THE REMNANTS OF 
THE SNOW COVER. FIRST CONCERN IS THE POSSIBILITY OF DENSE ADVECTION 
FOG...WITH AT LEAST MID/UPPER 20 DEWPOINT SFC AIRMASS ADVECTING 
NORTH. TOO FAR IN THE FUTURE AND ENOUGH UNCERTAINTY TO REALLY 
INCLUDE A STRONGER MENTION YET...BUT CERTAINLY SOMETHING WORTH 
WATCHING. BIGGER CONCERN IS FOR DRIZZLE/SPRINKLE CHANCES LATER 
SATURDAY AFTERNOON THROUGH SATURDAY NIGHT (THEN AGAIN ON SUNDAY 
NIGHT). CERTAINLY NOT A BIG QPF PRODUCER...BUT GIVEN THE NOCTURNAL 
TIMING AND POSSIBLE DETRIMENTAL COOLING INFLUENCE OF THE REMAINING 
SNOW COVER...SFC TEMPERATURES MAY STAND BELOW FREEZING CREATING A 
VERY LIGHT ICING EVENT. SEE LITTLE IN MODEL FORECASTS IN TIME AND 
SPACE SUGGESTING SIGNIFICANT SATURATION OR UVV WITHIN THE ICE 
CRYSTAL GROWTH LAYER...SO FEEL SNOWFALL POTENTIAL IS LOW (MAYBE SOME 
SNOW GRAINS WOULD ACCOMPANY DRIZZLE/SPRINKLE MIX). AGAIN...SFC TEMPS 
AND SNOW COVER EXTENT AND INFLUENCE ARE OF UTMOST IMPORTANCE TO THIS 
FORECAST. KEPT TEMPERATURES CONSERVATIVELY NEAR A GUIDANCE AVERAGE 
OVER THE WEEKEND...THOUGH MANY MODEL PARAMETERS ARGUE FOR EVEN 
WARMER READINGS...AND MAY NEED TO BOOST TEMPS A COUPLE CATEGORIES IF 
FUTURE TRENDS CONTINUE IN THIS DIRECTION (EFFECTIVELY ALLEVIATING 
MUCH OF THE MINOR ICING CONCERN).

21

DAYS 5-7 (MONDAY THROUGH WEDNESDAY)

FOR THE START OF THE WORK WEEK...UPPER AIR FLOW WILL BECOME 
MORE MERIDIONAL AS AN UPPER LEVEL TROUGH STARTS TO DIG INTO THE 
NORTHERN PLAINS. MODELS ARE PICKING UP ON A WEAK AREA OF SFC LOW 
PRESSURE TRACKING FROM THE PACIFIC NORTHWEST INTO THE GREAT PLAINS 
BY MONDAY. MODELS SUGGEST THIS LOW PRESSURE REGION WILL GET SUCKED 
INTO THE INFLUENCE OF THE UPPER LEVEL SYSTEM ON MONDAY...WHICH COULD 
LEAD TO PRECIP OVER THE REGION. HOWEVER...DISCREPANCIES STILL EXIST 
BETWEEN THE GFS/ECMWF MODELS REGARDING THE POSITIONING OF THIS AREA 
OF SFC LOW PRESSURE OVER THE NORTHERN PLAINS. ECMWF SHOWS THE LOW 
PRESSURE BEING SITUATED JUST EAST OF THE CWA MONDAY...TYING INTO THE 
MOISTURE SUPPLY OF BOTH THE UPPER LEVEL SYSTEM OVER CANADA AND THE 
GULF OF MEXICO...AND THUS SUGGESTING THE CHANCE OF PRECIP OVER MUCH 
OF THE CWA. GFS ON THE OTHER HAND...POSITIONS THE SFC LOW FURTHER 
NORTH COMPARED TO THE ECMWF. IT ALSO SHOWS LESS MOISTURE INFLUENCE 
FROM THE GULF OF MEXICO. AS A RESULT...GFS KEEPING A MAJORITY OF THE 
CWA DRY FOR MUCH OF MONDAY. DUE TO THESE DIFFERENCES...CONTINUE TO 
KEEP POPS AT SLIGHT CHANCE UNTIL A BETTER CONSENSUS IS SEEN AMONGST 
THE MODELS. 

THE UPPER LEVEL TROUGH WILL BEGIN TO SHIFT TOWARD THE NORTHEAST BY 
TUESDAY...AND WILL BE REPLACED BY AN UPPER LEVEL RIDGE OVER MUCH OF 
THE WESTERN HALF OF THE U.S. SFC HIGH PRESSURE OVER THE REGION WILL 
KEEP TEMPS UNSEASONABLY COOL AND CONDITIONS DRY THROUGH MID WEEK. 

ACH

&&

.AVIATION...

FOR THE 00Z TAFS...VFR CONDITIONS WILL CONTINUE WITH LIGHT SOUTHWEST 
WINDS BACKING TO THE SOUTH TOMORROW. SOME HIGH LEVEL CLOUDINESS OVER 
SOUTHERN KS MAY MIGRATE NORTHWARD TONIGHT.

MJ

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.

&&

$$