[LeArc] Forecast Discussion : MLI@ 2/1/03 2:24:54 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 012034
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
230 PM CST SAT FEB 1 2003

VERY FUN AND CHALLENGING FORECAST...WITH LARGE THERMAL GRADIENTS MAKING 
FOR TRICKY TEMP FORECAST...THEN POTENTIAL WINTER STORM EARLY NEXT WEEK. 

SYNOPSIS...12Z UA ANALYSIS INDICATES 120+ KT H3 JET ANTICYCLONICALLY CURVED 
FROM PACIFIC NORTHWEST INTO UPPER MIDWEST. MAIN SHORTWAVE
NOW COMING ASHORE ON WEST COAST...WITH WATER VAPOR AND SATELLITE SHOWING
PLENTY OF MID/HIGH CLOUDS FROM ROCKIES THROUGH THE PLAINS.
H85 ANALYSIS SHOWED STRONG BAROCLINIC ZONE ACROSS STATE OF IA WITH 
OMA AT +12C AND DVN -2C. THERMAL GRADIENT EXTENDS INTO THE NORTHERN PLAINS
AND UPPER MIDWEST. THIS COUPLED WITH RRQ OF UPPER JET AND VORT MAX
GENERATING LIGHT PCPN FROM DAKOTAS INTO SOUTHWEST MN. DMX WSR-88D SHOWS
ECHOES EXPANDING AND INTENSIFYING OVER NORTHERN SECTIONS OF IA. CLOSER TO HOME
LOW CLOUDS ROUGHLY NEAR A LINE FROM CID TO MLI TO GBG. 
DECENT SUNSHINE ACROSS THE SOUTH HAS ALLOWED TEMPS TO SOAR WELL INTO THE
40S TO NEAR 50 DEGS...WHILE LOW CLOUDS HOLDING TEMPS IN M30S 
NORTHEAST. IT/S THIS THERMAL GRADIENT ENHANCING FRONTOGENESIS WHICH WILL
POSE CHALLENGE TO FORECAST IN SHORT TERM.  

NEAR TERM...NONE OF THE MODELS HANDLING ONGOING PCPN IN THE NORTHERN PLAINS
ALL THAT WELL...SO WILL BE LEANING TOWARD RADAR/SATELLITE TRENDS
WITH DOSE OF CONCEPTUAL MODELING...WHICH SUPPORTS SOME CHANCE LIGHT RAIN
OR SPRINKLES NORTHERN 1/3RD OR SO THIS EVE. SATURATION IS OF CONCERN
ALONG WITH HOW FAR SOUTH TO MENTION PCPN. TIME SECTIONS KEEP LOW LEVELS 
SOMEWHAT DRY NORTH SO MAY BE MAINLY SPRINKLES WITH CHANCE OF LIGHT RAIN.
BASED ON LOCATION OF FRONTAL ZONE AND EXTRAPOLATION OF RADAR/SATELLITE
SUGGEST I-80 CORRIDOR WOULD BE ABOUT AS FAR SOUTH AS WOULD NEED TO MENTION 
AND WILL WAIT TIL LAST MINUTE TO MAKE THAT DECISION. NEXT CONCERN IS WITH
POTENTIAL FOR FREEZING RAIN FAR NORTH. DEWPTS WILL CONTINUE INCREASING THIS EVE
SO EXPECT TO SEE NORTHERN LOCATIONS GO ABOVE FREEZING NEXT FEW HOURS...THUS
THREAT APPEARS MINIMAL AND SHORT LIVED AND GIVEN VERY LIGHT INTENSITY OF 
PCPN...SEE NO NEED FOR ANY HIGHLIGHTS. WILL MAKE LAST MINUTE DECISION AS TO 
WHETHER OR NOT TO INCLUDE MENTION IN FAR NORTH. OTHER MAIN CONCERN IS
WITH DENSE FOG POTENTIAL. NOT MUCH THREAT SOUTH OF FRONTAL ZONE...WHICH IS
EXPECTED TO LIE SOUTH OF HIGHWAY 34. MAIN THREAT WILL BE TO THE NORTH
OF FRONT AND WILL WORD FOR DENSE FOG IN ZONES BUT HOLD OFF ON ADVISORY DUE
TO UNCERTAINTIES ON HOW WIDESPREAD AND LOCATION.  

ON SUNDAY...WARM FRONT TO SET UP NEAR OR JUST SOUTH OF INTERSTATE 80 CREATING
LARGE TEMP VARIATION FROM NORTH TO SOUTH OF PROBABLY 25 DEGS OR MORE.
NORTH OF FRONT IT WILL BE NASTY WITH CLOUDS...DRIZZLE...AREAS OF LIGHT RAIN
AND FOG POSSIBLY DENSE. SOUTH OF FRONT WILL BE QUITE NICE WITH SUNSHINE 
AND WARM TEMPS. CHALLENGE OF COURSE WILL BE TO DEPICT THIS SCENARIO
ADEQUATELY IN THE ZONES. CURRENT FORECAST LOOKS TO HAVE REAL GOOD HANDLE.  

MODELS STILL HAVING PHASING ISSUES WITH EARLY WEEK SYSTEM AND THUS HARD
TO FIND GOOD RUN-RUN CONTINUITY...SO CONFIDENCE IS SOMEWHAT LOW 
MAINLY WITH MAGNITUDE OF SYSTEM...AS ADVERTISED PCPN TYPES/CHANGEOVER STILL 
LOOK ON TARGET WITH PREVIOUS FORECAST. INTERESTING THAT 12Z ETA BONE
DRY FOR ENTIRE AREA WITH MINIMAL POPS!! HOW MANY TIMES HAVE WE SEEN THIS...
JUST CRAZY. CONCERNS OF COURSE WITH DOUBLE VORT...SIMILAR TO 
RECENT THU NGT-EARLY FRI EVENT. ONE VORT PASSES ACROSS UPPER MIDWEST WITH
SECOND AND STRONGER VORT EJECTING FROM SOUTHERN PLAINS INTO
MISSISSIPPI VALLEY. THIS MAY LEAD TO HEALTHY PCPN SHIELD TO OUR SOUTH WHICH
COULD ROB MOISTURE FEED THUS CUTTING INTO AMOUNTS...BUT STILL EXPECT
PCPN MOST AREAS WITH PASSAGE OF UPPER TROUGH. FEW OF THE MODELS PUT MORE 
EMPHASIS ON NORTHERN SFC WAVE WHICH TRACKS ACROSS SOUTHEAST IA AND NORTHERN IL
SUN NGT-MON. GFS AND ECMWF DEPICT SECONDARY WAVE TRAVERSING
NORTHEAST ALONG FRONTAL ZONE WHICH THEN DEEPENS NORTHERN SURFACE WAVE 
BY NEARLY 10MB. BELIEVE THIS SCENARIO MORE REASONABLE...AND WELL HANDLED WITH 
CURRENT FORECAST SO WILL STAY THE COURSE AND MAKE FEW CHANGES.  

.EXTENDED (WED-SAT)
UPPER FLOW GENERALLY NORTHWEST SUPPORTIVE OF ARCTIC INTRUSION. SAME CONCERN 
STILL EXISTS WITH HOW MUCH (IF ANY) SNOW WE/LL RECEIVE WHICH WILL HAVE 
IMPACT ON TEMPS. MANY AREAS LIKELY TO HAVE SOME SNOW...AND SO WILL CONTINUE
WITH PREVIOUS IDEA OF THIS OFFSETING FMR/MEX COLD BIAS. THUS...LEANED
TOWARD BLEND OF FMR/MEX GUIDANCE. NEXT CONCERN IS DAILY PCPN CHCS.
AVN/GFS SHOWING DECENT RUN-RUN CONTINUITY WITH FRONTAL SYSTEM WED-EARLY THU
AND WILL CONTINUE WITH CHANCE OF SNOW...WITH LINGERING FLURRIES FRI 
WITH UPPER TROUGH AND COLD CYCLONIC FLOW. TEMPS CERTAINLY THE MAIN CHALLENGE
DURING THE PERIOD AND IF WE RECEIVE MORE SNOW THAN ANTICIPATED THEN I AM
LIKELY TOO OPTIMISTIC. 

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

$$
M^2