[LeArc] Forecast Discussion : MLI@ 3/8/03 4:17:48 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 081026
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
425 AM CST SAT MAR 8 2003

SHORT TERM DISCUSSION...

THE SYNOPTIC PICTURE EARLY THIS MORNING SHOWS A STATIONARY FRONT 
EXTENDING FROM A CENTRAL KANSAS LOW ACROSS NORTHERN MISSOURI INTO 
CENTRAL ILLINOIS...WITH A COLD FRONT ACROSS CENTRAL NEBRASKA INTO 
NORTHERN IOWA. SNOW EXTENDS ACROSS EASTERN SOUTH DAKOTA AND THE 
SOUTHERN HALF OF MINNESOTA...INTO NORTHWEST IOWA...IN RESPONSE TO 
STRONG VV'S AND DIVERGENCE AT THE JET LEVEL DUE TO COUPLING BETWEEN 
TWO 130KT JET STREAKS ACROSS THE NORTHERN TIER OF THE U.S.

THE SHORT-TERM MODELS AGREE ON THE STRONG VV'S AND 300MB DIVERGENCE 
MOVING ACROSS THE FORECAST AREA THIS MORNING...AND EAST OF THE AREA 
BY 19Z.  THE TWO FRONTS COALESCE SOUTH OF THE FORECAST AREA MID TO 
LATE MORNING...AND THE KANSAS LOW MOVES RAPIDLY EAST INTO ILLINOIS. 
THE RESULTING COLD FRONT MOVES RAPIDLY EAST THIS AFTERNOON AS HIGH 
PRESSURE BUILDS IN...CREATING STRONG LATE AFTERNOON AND EARLY 
EVENING WINDS.

THE PRIMARY SHORT TERM CONCERN IS PRECIP AND PRECIP TYPE THIS 
MORNING. COLD AIR TRAPPED AT THE SURFACE...COMBINED WITH WARM 850MB 
TEMPS WILL PRODUCE THE CHANCE OF FREEZING RAIN THIS MORNING INTO 
MIDDAY ALONG AND NORTH OF THE I-80 CORRIDOR...WITH A CHANCE OF SNOW 
OR SLEET FURTHER NORTH TO CID AND DBQ.  QPF WILL BE MINIMAL DUE TO 
VERY LIMITED MOISTURE...WITH THE BEST CHANCE OF MEASURABLE PRECIP 
FROM NORTH OF CID TO DBQ.  ANY SNOW NORTH WOULD BE A DUSTING AT 
BEST.  HOWEVER...A CLOSE EYE WILL BE KEPT ON THE FREEZING RAIN 
POTENTIAL ACROSS CENTRAL AND NORTH CENTRAL PORTIONS OF THE FORECAST 
AREA THIS MORNING.  ALTHOUGH QPF IS VERY LOW IN THESE AREAS...ANY 
FREEZING RAIN WOULD CREATE PROBLEMS.  

MEDIUM TO LONG RANGE...TONIGHT THROUGH FRIDAY...

ARCTIC RIDGE NUDGES SOUTHEAST INTO IA OVERNIGHT WITH FRONT WELL TO 
SOUTH. NW FLOW PATTERN PREVAILS THROUGH MIDWEEK WITH PERIODIC 
SHORTWAVES BRINGING PRECIP CHANCES MAINLY MONDAY AND THURSDAY WITH 
GRADUAL WARMING TREND AS WESTERN RIDGE TRANSLATES EASTWARD TO 
CENTRAL CONUS BY FRIDAY. IN NEAR TERM...TEMPERATURES MAIN CONCERN 
TONIGHT AND SUNDAY. TIGHT H85 TEMPERATURE GRADIENT WILL MAINTAIN 
NORTH TO SOUTH SURFACE TEMPERATURE GRADIENT WITH THINNEST
SNOW COVER OVER FAR SOUTH ALSO CONTRIBUTER. COLDER MAV NUMBERS 
PREFERRED LOOKING AT CURRENT READINGS UPSTREAM INTO COLD AIRMASS. 
ALSO ANTICIPATE ENOUGH HIGH CLOUDS IN FAST NW UPPER FLOW TO 
LIMIT DEGREE OF COOLING. SUNDAY...ARCTIC HIGH CONTINUES TO PUSH 
SOUTHEAST BUT WILL STILL SEE A FAIR AMOUNT OF HIGH CLOUDS. WEAK LOW 
LEVEL COLD ADVECTION...CLOUD COVER...AND SNOW COVER WILL LIMIT 
WARMING AND STAYED CLOSE TO COLDER MAV...EXCEPT IN FAR SOUTH. 

SUNDAY NIGHT...CLOUDS THICKEN AHEAD OF NEXT WAVE. MAV LOOKS TOO COLD 
AND TRENDED ABOUT A CATEGORY ABOVE. GFS AND UKMET FASTER WITH VORT 
IN NW FLOW THAN ETA...BUT ALL LOOK TO BE SLOWER THAN PREVIOUS RUNS 
AND HAVE TAILED BACK ON BEGINNING OF PRECIP CHANCES. ETA ALSO KEEPS 
MAIN ENERGY TO NORTH. WILL CONTINUE WITH SOMEWHAT SIMILAR GFS/UKMET 
WITH BEST CHANCES ACROSS SOUTH. WITH MODEL TENDENCY TO SATURATE 
INITIALLY DRY LOW LEVEL AIRMASS TOO QUICKLY TO PRODUCE PRECIP...HAVE 
SCALED BACK POPS TO ONLY E CENTRAL IA EARLY MONDAY MORNING AND THEN 
CUT TO CHANCE POPS IN NORTH ON MONDAY. THERMAL PROFILES POINT TOWARD 
MAINLY SNOW EVENT AND DO NOT FORESEE ENOUGH MOISTURE FOR SIGNIFICANT 
SNOWFALL. CONDENSATION PRESSURE DEFS ON ISENTROPIC SURFACES REACH 
SATURATION AROUND 12Z AND REMAIN SATURATED UNTIL 18Z. MONDAY 
NIGHT...SURFACE HIGH MOVES SOUTHEAST WITH CLIPPER SYSTEM APPROACHING 
FROM NW. MODELS AGREE WITH SURFACE LOW PASSING TO WELL TO NORTH 
TUESDAY...WITH GFS FARTHEST SOUTH AND ALONE IN BRINGING PRECIP 
CHANCES. SCALED BACK SNOW CHANCES TO NORTH OF I-80. WITH DECENT 
PREFRONTAL SOUTHWEST FLOW...GUIDANCE HIGHS INTO UPPER 30S AND LOWER 
40S NOT UNREASONABLE AND ALREADY HANDLED WELL IN GRIDS. 

KEPT NEXT PRECIP CHANCES ON THURSDAY. GOING TEMPERATURES IN GRIDS 
UNCHANGED WITH HIGHS ACTUALLY ABOVE NORMAL FOR A CHANGE ON FRIDAY.

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

$$
REA/DLS