AREA FORECAST DISCUSSION
NWS CHICAGO IL
AFDCHI 305 AM CST TUE JAN 4 2000
MAIN FORECAST CONCERNS REVOLVE AROUND ENDING OF LGT SNOW/FLURRIES
TODAY AND WINDS AND TEMPS. 07Z SFC ANLSYS PLACES 994 MB SFC LOW IN
THUMB OF MICHIGAN...WITH WRAPAROUND PCPN EXTDNG BACK ACROSS ERN WI
AND INTO NRN IL. PCPN ALL SNOW NOW...WITH 08Z ORD ACARS SOUNDING
SHOWING WHOLE COLUMN NOW WELL BLO FREEZING. IR IMGRY SHOWS COLDER
CLOUD TOPS NOW MOVG WELL NE OF THE AREA. 88D REFLECTIVITY SHOWS SOME
WEAK RETURNS EXITING NE IL...WITH UPSTREAM SFC OBS INDICATING -SN
WITH VSBYS IN THE 7 TO 10SM RANGE. ACCUMULATIONS FROM LAST EVENING
RANGE FROM AROUND 4 INCHES VCNTY RFD TO AROUND AN INCH NORTH SIDE OF
CHICAGO...WITH ONLY A FEW TENTHS HERE AT THE OFFICE. WL DROP WINTER
WX ADVISORY FOR N CNTRL IL...AS ACCUMULATION IS OVER.
MODELS SIMILAR OVERALL IN HANDLING PROGRESSIVE PATTERN NEXT FEW
DAYS. ETA SEEMS TO HAVE BEST HANDLE ON CURENT MOISTURE FIELDS...AND
WILL FOLLOW. COUPLE OF S/WV TROFS PASSING THROUGH MEAN TROF OVR
CNTRL US. FIRST ELONGATED VORT LIFTING OUT ASSOCIATED WITH SFC
LOW...AND SECOND DROPPING INTO TROF OVR PLAINS. ANY SIG LGT SNOW
SHOULD BE ABOUT OVR NOW...BUT WITH UPR TROF OVERHEAD AND SECONDARY
VORT SWINGING THRU WL KEEP CLOUDS AND SOME FLURRIES IN THE FCST
TODAY.
AS FOR WINDS...MODEL SOUNDINGS AND UPSTREAM SFC OBS SUPPORT 15 TO 25
WITH A FEW HIGHER GUSTS. THIS TO KEEP LO LVL CAA GOING THRU THE
DAY...AND SHOULD KEEP TEMPS FROM RISING MUCH IF ANY. WL WORD TEMPS
TODAY AS NEARLY STEADY FROM CURRENT READINGS. UPR AND SFC RIDGING BUILDS
IN TONIGHT AND WED...WHICH SHOULD ALLOW GOOD RADIATIONAL COOLING
ESPCLY OVR SNOW COVER IN NW/NC IL. WL UNDERCUT GUIDANCE TONIGHT
THERE. OTHERWISE FAN/FWC IN GENERAL AGREEMENT AND WL FOLLOW.
NEXT SYSTEM APPROACHES WED...WITH GOOD H85 THERMAL ADVECTION. SFC
LOW PASSES WELL TO OUR NORTH WITH BEST MOISTURE ACROSS WI. WL CONT
CURRENT FCST OF FLURRIES WED NGT AS COLD FNT PASSES THRU LATE.
.CHI...GALE WRNG LAKE MICHIGAN TDY.
RATZER