FXUS63 KSGF 031132
AFDSGF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPRINGFIELD MO
532 AM CST THU DEC 3 2009

...UPDATE TO AVIATION...

.DISCUSSION...

QUIET AND SEASONABLY COLDER WEATHER WAS OCCURRING ATTM IN THE WAKE
OF THE FAST MOVING (AND NON-EVENTFUL FOR US) UPPER LOW THAT MOVED
THROUGH THE MID MS VLY LATE YESTERDAY. THE MAIN FORECAST CONCERNS
WILL BE TEMPERATURES OVER THE NEXT FEW DAYS...THEN PRECIPITATION
CHANCES AND TYPE INTO THE EXTENDED PERIODS. 

LARGE RIDGE ALONG THE WEST COAST/WESTERN CANADA IS ALLOWING COLD
AIR TO SPILL INTO THE CENTRAL CONUS. LOW LEVEL COLD AIR ADVECTION
WILL CONTINUE OVER THE REGION TODAY. UPSTREAM RAOBS SHOW 850MB
TEMPERATURES IN THE -12 TO -14 DEG C RANGE OVER THE DAKOTAS...AND
THAT COLD AIR MASS WILL MOVE INTO EASTERN KS/MO TODAY THROUGH FRI AS
A SHORTWAVE PINWHEELS ESE THROUGH THE MIDWEST OVER THE NEXT COUPLE
OF DAYS. A VERY DRY AIR MASS WITH DEW POINTS POTENTIALLY FALLING
INTO THE SINGLE DIGITS (DEG F) COULD ALLOW NIGHTTIME TEMPERATURES
TO FALL WELL DOWN INTO THE TEENS TONIGHT INTO FRI MORNING. WHILE
CONDITIONS WILL NOT BE PERFECTLY IDEAL FOR RADIATIONAL COOLING
TONIGHT WITH AT LEAST SOME MIXING...AND POSSIBLY MID LEVEL CLOUD
COVER AT TIMES...I STILL DID SIDE WITH THE MUCH COLDER NAM MOS
GUIDANCE VERSUS GFS MOS. 

A WEAK SOUTH FLOW BECOMES ESTABLISHED AT THE SFC FRI NIGHT...BUT
TEMPERATURES MAY INITIALLY PLUNGE FRI EVENING BEFORE STABILIZING AS
INCREASED MIXING OCCURS. A LOW AMPLITUDE UPPER RIDGE MOVES QUICKLY
THROUGH THE REGION SAT WITH A BRIEF MODEST WARM UP...ESPECIALLY
OVER WESTERN CWFA COUNTIES.

AN INCREASINGLY DIFFICULT FORECAST COMMENCES SUNDAY. 500MB
HEIGHT FALLS OVER THE CNTRL/SOUTHERN ROCKIES AND RESULTANT SFC LOW
PRESSURE OVER THE HIGH PLAINS WILL ALLOW INCREASING LOW LEVEL
SOUTHERLY FLOW AND ISENTROPIC ASCENT TO INCREASE OVER THE REGION.
INITIALLY...WE WILL BE ON THE EDGE OF THE VERY DRY AIR MASS NOW
ESTABLISHING ITSELF OVER THE REGION...BUT MODIFIED (AND INITIALLY
SHALLOW) GULF MOISTURE WILL STREAM INTO THE REGION SUNDAY.
TEMPERATURES WILL BE TRICKY DEPENDING ON HOW QUICKLY CLOUDS BECOME
ESTABLISHED. BY THIS TIME...THE TIMING OF SYNOPTIC SCALE FEATURES
BECOMES MORE PROBLEMATIC DUE TO THE FAST ZONAL FLOW OVER THE
SOUTHERN CONUS. LOOKS LIKE WE WILL SEE A QUICK FROPA SUNDAY NIGHT
(USING THE FASTER GFS AND GEM VERSUS THE SLOWER ECMWF FOR THIS
TIMING). HAVE ADDED SOME SMALL POPS LATE SUNDAY/SUNDAY EVENING.
PRECIP TYPE WILL BE TRICKY SUNDAY EVENING WITH 850MB/925MB
TEMPERATURES HOVERING NEAR OR BELOW FREEZING. HOWEVER...SHALLOWNESS
OF THE MOIST LAYER MAY NOT ALLOW DENDRITIC PROCESSES EITHER. FOR
NOW...JUST BROAD BRUSHED RAIN OR SNOW. IN ANY CASE...THE QPF WILL
LIKELY BE QUITE LIGHT GIVEN THE LACK OF DEEP MOISTURE.

MONDAY SHOULD BE QUIET AND COLD AS A SFC RIDGE BRIEFLY NOSES ITS
WAY SOUTH INTO THE AREA. BOTH THE ECMWF AND GFS BRING A SOMEWHAT
MORE AMPLIFIED SHORTWAVE FROM THE ROCKIES INTO THE PLAINS ON TUE.
LOW LEVEL THERMAL PROFILES FOR BOTH MODELS ARE SIMILAR WITH 850MB
TEMPERATURES NEAR OR JUST BELOW FREEZING. ONLY COSMETIC CHANGE
MADE TO THE FORECAST FOR TUE WAS TO ADD SNOW TO THE ALREADY GOING
RAIN CHANCES (NOW RAIN AND/OR SNOW). TIMING ANYTHING OUT THIS FAR
WITH THIS PATTERN WILL BE DIFFICULT...BUT THE TUE-TUE NIGHT PERIOD
WILL NEED TO BE WATCHED FOR FORECAST TRENDS IN THE COMING DAYS.
DSA

&&

.AVIATION...

FOR THE 12Z TAFS...VFR CONDITIONS WILL PREVAIL THROUGH THE
FORECAST PERIOD AS HIGH PRESSURE BUILDS INTO THE REGION BEHIND A
COLD FRONT AND IN THE WAKE OF THE DEPARTING UPPER LEVEL LOW. COLD
AND DRY AIR WILL BUILD INTO THE OZARKS TODAY RESULTING IN VERY FEW
CLOUDS AND GOOD VISIBILITIES FOR FLYING. 

HATCH

&&

.SGF WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&

$$