Extreme Cold in Illinois, January 24, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
329 PM CST WED JAN 23 2008

.SYNOPSIS...
SLOW MOVING AXIS OF LIGHT SNOW WAS ACROSS CWA ROUGHLY BETWEEN
HIGHWAY 34 AND HIGHWAY 30 CORRIDOR AT 21Z. HEAVIEST SNOW SO FAR HAS
BEEN IN 1 TO 1.5 INCH RANGE ALONG HIGHWAY 30 IN EASTERN IA. THIS
SNOW WAS ASSOCIATED WITH A LOW PRESSURE CLIPPER SYSTEM ANALYZED OVER
SE IA AT 18Z. AXIS OF PRESSURE FALLS NEAR STL AND MUCH LARGER AXIS
OF RISES...5 MB/3 HRS OVER SE SD...INDICATE SYSTEM SHOULD
CONTINUE TO PROGRESS SE. ARCTIC AIRMASS WILL FOLLOW TONIGHT INTO
THU...WITH BITTER COLD WIND CHILL INDEX AS PRESSURE GRADIENT
BETWEEN SURFACE HIGH OVER DAKOTAS AND DEPARTING LOW BRING PERIOD
OF 15 TO 25 MPH WINDS OVERNIGHT.

&&

.SHORT TERM...TONIGHT AND THURSDAY...
BITTER COLD TEMPERATURES AND WIND CHILLS ARE MAIN ISSUES IN SHORT
TERM. WILL WALK CURRENT SNOW AXIS SE OUT OF AREA THIS EVENING WITH
CURRENT SNOWFALL RATES AND VISIBILITIES SUPPORTING HALF TO 1 INCH
AMOUNTS OVER FAR SE IA INTO W CENTRAL IL THIS EVENING.
THEN...NW WINDS WILL INCREASE TO 15 TO 20 MPH RANGE WITH FEW
HIGHER GUSTS IN E CENTRAL IA THIS EVENING PULLING DOWN AS SUB ZERO
AIRMASS CURRENTLY OVER MN. HAVE MOVED UP START TIME FOR WIND CHILL
ADVISORY IN EASTERN IA AND ALSO EXPANDED S AND SE OVER REMAINDER
OF CWA FOR WIND CHILLS DIPPING INTO 15 TO 20 BELOW RANGE AFTER
MIDNIGHT. WINDS SHOULD DIMINISH SIGNIFICANTLY THU MORNING AS HIGH
PRESSURE RIDGE BUILDS EAST INTO CENTRAL IA. WINDS SHOULD DROP
BELOW 5 KTS AT MOST SITES AND HAVE ADJUSTED EXPIRATION TIME OF
ADVISORY A COUPLE HOURS EARLIER TO 16Z THU. BASED ON FRESH SNOW COVER
AND ADVECTION OF AIRMASS OUT OF ND AND MN WHERE LOWS WERE -15 TO
-20...WILL KEEP TONIGHTS MINS IN RANGE OF -10 TO -15 NORTH AND
ABOUT 5 TO 10 BELOW SOUTH. ON THU...HIGH PRESSURE OVERHEAD WILL
LIMIT MIXING AND ACCOUNTING FOR NO MORE THAN 15 TO 20 DEGREE
RISE...TEMPERATURES WILL STRUGGLE INTO SINGLE DIGITS NORTH AND
LOWER TEENS ACROSS THE SOUTH. ..SHEETS..

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY...
WILL BE CONCISE DUE TO TRYING TO CATCHUP FROM SOFTWARE UPGRADE THIS
MORNING...IMPACTING EQUIPMENT OPERATIONS TODAY.  PREFER BLEND OF
UKMET WITH INPUTS FROM HI-RES ECMWF AND GFS.

COLD THURSDAY NIGHT WITH BELOW ZERO READINGS WITH MINS MOST AREAS
LATE EVENING AND EARLY OVERNIGHT.  SOME RISING MINS POSSIBLE WEST
SECTIONS FOR LATER SHIFTS TO CONSIDER. FAVORABLE EAST 1/2 MIN TEMPS
STILL A CATEGORY TOO MILD. FRIDAY INTO SATURDAY...LIGHT SNOW TO
ENVELOP AREA WITH WIDESPREAD SNOW AMOUNTS OF 1 TO 2 INCHES SUGGESTED
PER FORCING.  UPPED POPS AND LATER SHIFTS TO CONSIDER RAISING TO
LIKELY. SUNDAY INTO MONDAY...MAJOR WARMUP AS TEMPERATURES TO RISE
WITH MAX AND MIN TEMPS BASED ON STRONG LOW LEVEL JET AND WARMING
STILL 5-10 PLUS DEGREES TOO COOL.  KEPT MIX OF RAIN AND SOME FREEZING
RAIN INITIALLY FOR MONDAY BUT LIKELY JUST RAIN DUE TO STRONG WARM AIR
ADVECTION. STRONG FRONT TO PASS TUESDAY WITH PHASING ISSUES UNCLEAR
DUE TO COMPLEX PHASING OF UPPER ENERGY. THIS SHOULD BE CLARIFIED NEXT
24 HOURS.  SOME POTENTIAL FOR A WINTER STORM MID TO LATE NEXT WEEK.
..NICHOLS..

&&

.AVIATION...
A LARGE AREA OF LIGHT SNOW ASSOCIATED WITH A FAST MOVING LOW
PRESSURE SYSTEM MOVING OUT OF SE IA THIS AFTERNOON WILL EXIT THE
REGION THIS EVENING. MVFR CONDITIONS ACROSS DBQ..CID AND MLI WILL
IMPROVE TO VFR THIS EVENING WITH SNOW ENDING. NW WINDS INCREASING
TO 15 TO 25 KTS WILL USHER IN ARCTIC AIRMASS AND AREAS OF BLOWING
AND DRIFTING SNOW. OVERALL...MOST SITES WILL HAVE VFR CONDITIONS
BY MIDNIGHT. WINDS WILL DIMINISH TO LESS THAN 10 KTS TOWARD
SUNRISE THU WITH SKIES BECOMING CLEAR FROM NW TO SE OVERNIGHT.
..SHEETS..

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...WIND CHILL ADVISORY FROM 10 PM THIS EVENING TO 10 AM CST
     THURSDAY FOR BENTON-BUCHANAN-CEDAR-DELAWARE-DUBUQUE-IOWA-
     JACKSON-JOHNSON-JONES-KEOKUK-LINN-WASHINGTON.

     WIND CHILL ADVISORY FROM 2 AM TO 10 AM CST THURSDAY FOR CLINTON-
     DES MOINES-HENRY IA-JEFFERSON-LEE-LOUISA-MUSCATINE-SCOTT-
     VAN BUREN.

IL...WIND CHILL ADVISORY FROM 10 PM THIS EVENING TO 10 AM CST
     THURSDAY FOR JO DAVIESS.

     WIND CHILL ADVISORY FROM 2 AM TO 10 AM CST THURSDAY FOR BUREAU-
     CARROLL-HANCOCK-HENDERSON-HENRY IL-MCDONOUGH-MERCER-PUTNAM-
     ROCK ISLAND-STEPHENSON-WARREN-WHITESIDE.

MO...WIND CHILL ADVISORY FROM 2 AM TO 10 AM CST THURSDAY FOR CLARK-
     SCOTLAND.

&&

SHEETS/NICHOLS

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
508 AM CST WED JAN 23 2008

ADDED A HIGHWAY NUMBER TO WIND CHILL DISCUSSION TONIGHT

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-241115-
BUCHANAN-DELAWARE-DUBUQUE-BENTON-LINN-JONES-JACKSON-IOWA-JOHNSON-
CEDAR-CLINTON-MUSCATINE-SCOTT-KEOKUK-WASHINGTON-LOUISA-JEFFERSON-
HENRY IA-DES MOINES-VAN BUREN-LEE-JO DAVIESS-STEPHENSON-CARROLL-
WHITESIDE-ROCK ISLAND-HENRY IL-BUREAU-PUTNAM-MERCER-HENDERSON-
WARREN-HANCOCK-MCDONOUGH-SCOTLAND-CLARK-
508 AM CST WED JAN 23 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
ILLINOIS...NORTHWEST ILLINOIS...WEST CENTRAL ILLINOIS...EAST
CENTRAL IOWA...NORTHEAST IOWA...SOUTHEAST IOWA AND NORTHEAST
MISSOURI.

.DAY ONE...TODAY AND TONIGHT

A CLIPPER SYSTEM WILL BRING SNOW TO MUCH OF THE OUTLOOK AREA TODAY
INTO EARLY THIS EVENING. SNOW ACCUMULATIONS WILL GENERALLY AVERAGE
AROUND AN INCH...WITH LOCALLY HIGHER ACCUMULATIONS AROUND 2 INCHES
POSSIBLE IN A FEW LOCATIONS BETWEEN HIGHWAY 20 AND HIGHWAY 34.
GUSTY NORTH TO NORTHWEST WINDS DEVELOPING THIS AFTERNOON AND
CONTINUING THROUGH THIS EVENING MAY CAUSE AREAS OF BLOWING AND
DRIFTING SNOW AND POOR VISIBILITIES. ARCTIC AIR WILL SURGE INTO
THE AREA ON THE BRISK NORTHWEST WINDS. TEMPERATURES FALLING INTO
THE SINGLE DIGITS TO TEENS BELOW ZERO...COMBINED WITH GUSTY
NORTHWEST WINDS...WILL CAUSE WIND CHILL READINGS TO FALL TO 20 TO
30 BELOW ZERO TONIGHT. AREAS NORTH OF HIGHWAY 34 ARE MOST AT RISK
FOR DANGEROUS WIND CHILL READINGS WHERE A WIND CHILL ADVISORY IS
IN EFFECT FROM MIDNIGHT TONIGHT THROUGH THURSDAY MORNING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY...

ARCTIC AIR WILL REMAIN IN PLACE THURSDAY...WITH DANGEROUSLY COLD WIND
CHILLS OF 20 TO 30 BELOW ZERO LINGERING IN THE MORNING NORTH OF
HIGHWAY 34. HIGH TEMPERATURES ON THURSDAY THROUGHOUT THE OUTLOOK AREA
WILL BE IN THE SINGLE DIGITS TO LOWER TEENS.

AN ACTIVE WEATHER PATTERN WILL CONTINUE OVER THE MIDWEST THROUGH THE
WEEKEND.  A STORM SYSTEM WILL BRING A CHANCE OF SNOW FRIDAY AND
FRIDAY NIGHT.  ANOTHER STORM SYSTEM IS EXPECTED SUNDAY NIGHT INTO
MONDAY...BRINGING YET ANOTHER CHANCE OF RAIN OR SNOW.  IT IS TOO
EARLY TO DETERMINE THE EXACT TIMING...INTENSITY...OR IMPACT OF EITHER
OF THESE SYSTEMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY OR TONIGHT...BUT SPOTTERS
ARE ENCOURAGED TO CONTACT THE NATIONAL WEATHER SERVICE WITH SNOW
MEASUREMENTS TODAY.

DB