[LeArc] Forecast Discussion : MLI@ 2/20/03 2:06:00 PM

[learc@mailman.qth.net]

The following weather message is provided by McDonough County E.S.D.A.


FXUS63 KDVN 202014
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
205 PM CST THU FEB 20 2003

CHALLENGING FORECAST TO SAY THE LEAST...WITH LOTS OF THINGS TO
CONSIDER NEXT FEW DAYS. BIG CHANGES ON THE WAY!

.MODEL INITIALIZATION AND OVERVIEW...
SPLIT FLOW DOMINATES CONUS. VIGOROUS SOUTHERN STREAM WAVE DIGGING THROUGH
SOUTHWEST AZ. HEIGHT FALLS SUGGEST FURTHER DIGGING INTO NORTHERN SECTIONS
OF OLD MEXICO NEXT 12 HRS OR SO...THEN SHIFTING EAST ACROSS 
SOUTHERN TX FRI BEFORE BECOMING NEG TILTED AND EJECTING INTO OHIO VALLEY ON
SAT. DECENT PCPN EVENT EXPECTED FROM SOUTHERN STATES TO THE EAST COAST 
NEXT COUPLE OF DAYS...AS SYSTEM INTERACTS WITH IMPRESSIVE SUBTROPICAL STREAM.
AT SFC...NARROW RIDGE AXIS EXTENDS FROM OHIO VALLEY INTO 
MID MISSISSIPPI VALLEY. ARCTIC FRONT EXTENDS FROM NORTHERN MN TO NEAR THE
ND/SD BORDER. ABERDEEN SD 41 DEGS AT 19Z WHILE JUST 100 MI OR SO NORTH
JAMESTOWN ND IS AT 16 DEGS. OVERALL...THERMAL GRADIENT OF NEARLY 50 DEGS ACROSS
THE DAKOTAS AT 19Z. IMPRESSIVE. VISIBLE SATELLITE PICS SHOW EVER SHRINKING
SNOW COVER FROM NEAR CID TO SOUTH OF MLI TO MQB HAVING SMALL IMPACT
ON TEMPS...WITH READINGS SOME 3 DEGS OR SO WARMER IN BARE GROUND. NEXT SYSTEM
OF INTEREST JUST COMING ASHORE IN WESTERN B.C. NORTH OF VANCOUVER...AND
WILL BE A PLAYER IN OUR WX COME LATE IN THE WEEKEND. AS FOR MODEL INITIALIZATION
ETA 2M TEMPS REMAIN USELESS WITH SNOW COVER FEEDBACK ISSUES.
AT 18Z AVN/GFS WAS UNDERONE BY 5-7 DEGS ON SFC DEWPTS ACROSS THE REGION.
MODELS ALSO HAVING SOME TROUBLE DEPICTING STRATUS PRESENT ACROSS SOUTHERN MO.

...WARMUP FRIDAY THEN WEEKEND PCPN POTENTIAL AND SIGNIFICANT COOL DOWN WITH
NEXT ARCTIC SYSTEM REMAIN MAIN FORECAST ISSUES...

.DIAGNOSIS AND DAYS 1-3...
LOOKS LIKE TYPICAL PATTERN WE/VE SEEN THIS WINTER...WITH SYSTEM NEAR BAJA
OF CA PASSING JUST TO OUR SOUTH ON SAT. JET STRUCTURE SUPPORTS THIS
SCENARIO...THUS TYPICAL SWIPING WITH SOUTH/EAST SECTIONS STANDING BEST CHC
OF PCPN. CRITICAL LLVL TEMPS AND THICKNESS FIELDS SUPPORTS SNOW.
AS SYSTEM LIFTS OUT NEG TILTED ON SAT...H5 TROUGH SHARPENS OVERHEAD AND 
WILL KEEP PCPN CHCS WITH THIS FEATURE. ARCTIC AIR LOOKS LIKE IT WILL BE "OOZING"
RATHER THAN "BLASTING"...AS PROCESS WILL BE GRADUAL DUE TO 
IMPACTS OF SOUTHERN STREAM SYSTEM. COULD SEE SOME SNOW ACCUMS MAINLY E/SE
OF MLI TO FSW LINE. DIFFICULT TO SAY HOW MUCH. CERTAINLY DOESN/T LOOK LIKE
ADVISORY...BUT AN INCH OR TWO POSSIBLE. TIMING OF ARCTIC AIR WILL BE
CRITICAL WITH BIG IMPACT ON SNOW/WATER RATIO/S. BRIEF BREAK IN ACTIVE PATTERN
BEFORE NEXT SYSTEM IN WESTERN CAN DIVES THROUGH ROCKIES AND EJECTS
OUT INTO THE MID MISSISSIPPI VALLEY ON SUN. LOW CONFIDENCE WITH PHASING 
OF SYSTEM AND ARCTIC AIRMASS...THOUGH POTENTIAL EXISTS FOR ADDITIONAL ACCUMS SO
WILL BE KEEPING CLOSE EYE ON THIS ONE. SYSTEM TO BE IMPACTED BY LEAD NEG TILT
SYSTEM ON SAT...SO DIFFICULT TO ASCERTAIN STRENGTH AND MOISTURE 
ATTIM. GFS-AVN ENSEMBLE DOES SUPPORT 12Z UKMET AT 72 HRS (12Z SUN)...WHICH
WOULD SUGGEST SNOW MOST OF THE AREA WITH BEST CHC OF ACCUMS >1 INCH
ACROSS THE SOUTHERN 1/2. TEMPS TO BE SOMEWHAT TRICKY. AS MENTIONED 2M TEMPS
FROM BOTH AVN/GFS AND ETA USELESS WITH FEEDBACK PROBS FROM SNOW FIELD.
FRI SHOULD BE THE LAST MILD DAY FOR SOME TIME. PROBLEM FRI IS MODELS SUGGEST
SLIGHTLY COOLER AIR WITH WINDS BECOMING LIGHT S/SE WITH AIR CIRCULATING
FROM BENEATH SURFACE HIGH IN OHIO VALLEY. ALSO HAVE LITTLE BIT OF CONCERN WITH 
REGARDS TO STRATUS ACROSS SOUTHERN MO NOT BEING HANDLED WELL. 
FLOW (BACKSIDE OF RETREATING HIGH) CONDUCIVE TO SLOSH SOME OF THIS UP 
OUR DIRECTION...THOUGH FLOW WILL BE RELATIVELY WEAK WITH FRONT APPROACHING THUS
NOT CONFIDENT WE/LL SEE MUCH. WEAK FLOW TO ALSO LIMIT MIXING. 
GIVEN THE ABOVE FEEL BEST TO STAY CLOSE TO CURRENT FORECAST WHICH IS GOOD 
BLEND FAVORING WARMER END OF GUIDANCE.  
   
EXTENDED (MON-THU)...ON MON...WITH CYCLONIC FLOW...STEEP LAPSE RATES
FROM SFC-H85 AND COLD POOL WILL CONTINUE WITH CHC SHSN. PRESSURE GRADIENT 
SUGGESTS WINDS OF 15 TO 25 MPH WITH WIND CHILLS 10 TO 20 BELOW ZERO. 
MON NGT/EARLY TUE MORNING LOOKS THE COLDEST WITH CANADIAN HIGH SETTLING 
OVERHEAD WITH NEARLY IDEAL RADIATIONAL COOLING CONDITIONS. THIS COUPLED WITH 
H85 TEMPS OF -20C TO -26C LATE MON SUGGEST PREVIOUS SHIFT/S MINS 
ON TRACK WITH SINGLE DIGITS ABOVE/BELOW ZERO...WITH WILD CARD BEING POSSIBLE 
SNOW COVER IN SOME AREAS. CANADIAN HIGH SLIDES EAST LATE TUE/WED WITH
CHC OF SNOW AND GRADUAL WARMING WITH WARM FRONT. PHASING ISSUES BY THU WITH
VARYING MODEL SOLUTIONS...THUS WILL OPT TO LEAVE DRY FOR NOW. 


.DVN...
IA...NONE.
IL...NONE.
MO...NONE.

$$

M^2