Winter Weather in Illinois, December 8, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
337 PM CST WED DEC 7 2005

.SYNOPSIS...
REGIONAL RADAR IMAGERY SHOWS SLOW-MOVING WAVE BRINGING SNOW TO
WESTERN MISSOURI... SOUTHWESTERN IOWA... AND EASTERN NEBRASKA/KANSAS
THIS AFTERNOON.  AFTER A NEAR-RECORD TO RECORD COLD NIGHT LAST
NIGHT... TEMPS HAVE RECOVERED INTO THE SINGLE DIGITS ACROSS THE
CWA... WITH CIRRUS CLOUDS BEGINNING TO ENCROACH THIS AFTERNOON AHEAD
OF THE NEXT SYSTEM.  SUBJECTIVE 12Z UPPER AIR ANALYSIS SHOWS 500MB
LOW CUTTING OFF OVER THE NEB PANHANDLE AND SOUTHWESTERN SD.  500MB
HEIGHT FALLS IN COLORADO INDICATE SYSTEM IS STILL DIGGING SOUTH AS
IT PROGRESSES EASTWARD.  MOISTURE IS POOLING ALONG THE GULF COAST
AND IN TEXAS AT 850MB AND IS FEEDING INTO THE SYSTEM... WITH A SHARP
GRADIENT IN 850MB TEMPS ACROSS THE SOUTHERN PLAINS.

&&

.SHORT TERM...TONIGHT AND TOMORROW...
ALL EYES ARE ON THE NEXT SYSTEM TO IMPACT OUR AREA AS IT MAKES SLOW
PROGRESS INTO MISSOURI.  HAVE ISSUED A SNOW ADVISORY FOR THE
SOUTHEASTERN HALF OF THE CWA FOR 06Z THURSDAY THROUGH 03Z FRIDAY.
MODELS ARE IN GOOD AGREEMENT REGARDING PLACEMENT AND DEPTH OF MOST
FEATURES AND HAVE LEANED ON A GFS/NAM BLEND FOR THE PERIOD.  AS
500MB LOW/VORT MAX APPROACHES THE AREA... INVERTED SURFACE/850MB
TROUGH WILL PASS THROUGH MO/IA/IL JUST AHEAD OF THE LOW... WITH
PRECIP AHEAD OF THE TROUGH AND SHUTTING DOWN QUICKLY BEHIND IT
TOMORROW NIGHT.  500-300MB LAYER Q-VECTOR DIVERGENCE SHOWS VERY
FAVORABLE REGION FOR LIFT PASSING ACROSS SOUTHERN IA AND NORTHERN MO
THROUGH THE DAY TOMORROW... WITH POSITIVE PV ADVECTION AHEAD OF THE
TROUGH AS SEEN ON 320K ISENTROPIC SURFACE AND A DEEP DIP IN THE
TROPOPAUSE... ALL INDICATORS OF VERY FAVORABLE SYNOPTIC ENVIRONMENT
FOR LIFT ENOUGH TO PRODUCE SNOW.  WEAK MID-LEVEL FRONTOGENESIS
SIGNAL IN THE SOUTHERN CWA AHEAD OF THE TROUGH WILL BE ENOUGH TO
PROVIDE FOCUS THERE FOR MORE INTENSE SNOW TOMORROW LATE
MORNING/EARLY AFTERNOON.  BEST LIFT AS INDICATED BY FRONTOGENESIS
(AND SUPPORTED BY OMEGA FIELD) WILL OCCUR IN A LAYER OF -10 TO -14 C
TEMPS... QUITE CLOSE TO THE DENDRITIC LAYER.  CROSS-SECTION OF
THETA-E TEMPS AND SATURATED EPV INDICATE MINIMIZED STABILITY...
ESPECIALLY SOUTH OF I-80.  THUS... THOUGH BEST SUPPORT REMAINS AT
THE SOUTHERN EDGE OR JUST SOUTH OF THE CWA... STILL EXPECT FAIRLY
SIGNIFICANT SNOW TOTALS LASTING 12-18 HOURS IN THE ADVISORY AREA.
12Z ETA/GFS DIFFER ON QPF... WITH GFS NEAR 0.25 INCHES FOR A 24 HOUR
TOTAL IN THE FAR SOUTHERN TIER AND ETA GIVING 0.05-0.1 INCHES MORE.
WITH SNOW RATIOS LIKELY NEAR 18:1... THAT DIFFERENCE WILL MAKE AN
INCH OR TWO DIFFERENCE IN SNOW TOTALS.  GFS HAD A SLIGHTLY BETTER
MOISTURE FIELD INITIALIZATION AND HAVE LEANED TOWARD ITS QPF
AMOUNTS.  DRY AIR IS LOCKED IN NEAR THE SURFACE... AND FORECAST
SOUNDINGS SHOW AREA WILL NEED TO SATURATE TOP-DOWN BEFORE SNOW
BEGINS... THUS EXPECT SNOW TO START NEAR 06Z IN THE SOUTHERNMOST
COUNTIES AND AROUND 09Z CLOSER TO KMLI.  SYSTEM WILL BE PICKED UP BY
UPPER-LEVEL JET AND ACCELERATE AWAY BEGINNING TOMORROW EVENING...
WITH PRECIP ENDING IN WESTERN COUNTIES AS EARLY AS 18Z.

.LONGER TERM...THURSDAY NIGHT THROUGH NEXT WEDNESDAY...
THURSDAY NIGHT IS SOMEWHAT TRICKY...WITH THE SNOW EVENT FROM
TONIGHT AND THURSDAY ENDING.  THE MAIN QUESTION IS IF THERE WILL BE
ANY LINGERING ACCUMULATING SNOWS.  HAVE GONE WITH A BLEND OF THE GFS
AND NAM WITH THE RETREATING SNOW AND CLOUDS...WHICH SHOULD RESULT IN
PERHAPS AN ADDITIONAL INCH OR SO DURING THE EVENING HOURS IN THE FAR
EASTERN COUNTIES.  SNOW SHOULD SHUT DOWN QUICKLY THOUGH...AND BE
COMPLETELY DONE BY 06Z...IF NOT EARLIER.  IN FACT...BECAUSE OF THIS
SHARP CUTOFF TO THE BACK EDGE OF THE ACCUMULATING SNOW...HAVE
DECIDED TO END THE SNOW ADVISORY AS 03Z RATHER THAN DRAGGING IT OUT
TO MIDNIGHT.  COLD AIR ADVECTION BEHIND THIS SYSTEM TO BRING IN LOTS
OF COLD DRY AIR...AND WITH THE FRESH SNOW ON THE GROUND AND THE
NEARLY CLEAR SKIES BY MORNING...ANTICIPATE A VERY COLD NIGHT
THURSDAY NIGHT.  HAVE GONE 5 DEGREES BELOW COLDEST GUIDANCE...AND IT
COULD BE COLDER YET IN THE NORTHWEST PORTIONS OF THE CWA...BUT DIDNT
WANT TO GO TOO HOG WILD IN CASE THE CLOUDS HANG IN A LITTLE LONGER
THAN ANTICIPATED.  FRIDAY AND FRIDAY NIGHT ARE TO BE COLD
AGAIN...THOUGH NOT AS FRIGID AS TODAY...AND BEGIN A MODERATING TREND
THAT SHOULD CONTINUE INTO THE WEEKEND.  THE UPPER LEVEL NORTHWEST
FLOW SHOULD KEEP TEMPERATURES FROM WARMING ANY FURTHER THAN
CLIMATOLOGY...THOUGH LOW LEVEL SOUTHWEST FLOW SHOULD HELP WARM
THINGS TO THAT POINT.  IT ALSO HELPS THAT THE POLAR AIRMASS OVER THE
CWA THIS MORNING GETS SWEPT EAST AND MODIFIES AND BEGINS TO TAP INTO
THE RELATIVE WARMTH OVER THE GULF STATES...JUST AS IT BEGINS TO PUSH
SOME DECENT RETURN FLOW INTO OUR AREA ON SATURDAY.  SATURDAY ANOTHER
SHORTWAVE DROPS ACROSS THE AREA...A NICE ALBERTA CLIPPER TYPE SYSTEM
WHICH MAY BE ABLE TO BRING A COUPLE OF INCHES TO SOME LOCATION IN
THE REGION...THOUGH IT IS TOO SOON TO TELL IF THAT WILL BE WISCONSIN
OR IOWA. SATURDAY NIGHT AND SUNDAY TO BE CLOUDY...WHICH SHOULD KEEP
THE FRESH SHOT OF COLD AIR FROM COOLING THE CWA OFF TOO MUCH AND
HOLD ONTO THE MODERATE...JUST BELOW CLIMATOLOGY NORMALS FOR
TEMPERATURES.

SUNDAY NIGHT THROUGH WEDNESDAY...ANOTHER SHORTWAVE IS DUE TO DROP
INTO THE AREA SUNDAY NIGHT AND MONDAY...AND FOR NOW THINK THAT THE
DYNAMICS ARE ONLY STRONG ENOUGH TO SQUEEZE OUT SOME PRECIPITATION ON
SUNDAY NIGHT...THOUGH MONDAY AND MONDAY NIGHT WILL REMAIN COLD AND
CLOUDY...WITH SOME FLURRIES POSSIBLE MONDAY.  TUESDAY TO BE QUIET
WITH THE CLOUDS CLEARING OUT FROM THE SUNDAY NIGHT/MONDAY
SHORTWAVE...AND THE NEXT BREWING OVER SOUTHERN CANADA.  IT APPEARS
THAT THIS ONE WILL BE DUE THROUGH ON WEDNESDAY.  MODELS ARE HAVING
SOME TROUBLE WITH THESE SHORTWAVES...BOTH IN TIMING AND STRENGTH AND
WITH THE TIME RANGE...HAVE ONLY GONE WITH SLIGHT CHANCES BOTH SUNDAY
NIGHT AND WEDNESDAY.  LATER SHIFTS CAN INCREASE POPS IF THESE WAVES
STILL LOOK GOOD.  TEMPERATURES THROUGH THE PERIOD STILL LOOK ON THE
COLD SIDE...AND HAVE GONE WITH MAX AND MINS BELOW GUIDANCE
THROUGHOUT.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...SNOW ADVISORY FROM MIDNIGHT TONIGHT TO 9 PM CST THURSDAY FOR
     IAZ078-IAZ087-IAZ088-IAZ089-IAZ098-IAZ099.

IL...SNOW ADVISORY FROM MIDNIGHT TONIGHT TO 9 PM CST THURSDAY FOR
     ILZ016-ILZ017-ILZ018-ILZ024-ILZ025-ILZ026-ILZ034-ILZ035.

MO...SNOW ADVISORY FROM MIDNIGHT TONIGHT TO 9 PM CST THURSDAY FOR
     MOZ009-MOZ010.

&&

MAYES/LE

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
510 AM CST WED DEC 7 2005

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-081100-
BENTON IA-BUCHANAN IA-BUREAU IL-CARROLL IL-CEDAR IA-CLARK MO-
CLINTON IA-DELAWARE IA-DES MOINES IA-DUBUQUE IA-HANCOCK IL-
HENDERSON IL-HENRY IA-HENRY IL-IOWA IA-JACKSON IA-JEFFERSON IA-
JO DAVIESS IL-JOHNSON IA-JONES IA-KEOKUK IA-LEE IA-LINN IA-LOUISA IA-
MCDONOUGH IL-MERCER IL-MUSCATINE IA-PUTNAM IL-ROCK ISLAND IL-
SCOTLAND MO-SCOTT IA-STEPHENSON IL-VAN BUREN IA-WARREN IL-
WASHINGTON IA-WHITESIDE IL-
510 AM CST WED DEC 7 2005

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
BITTERLY COLD TEMPERATURES WILL BE OVER THE AREA AGAIN THIS
MORNING. IF YOU WILL BE GOING OUTSIDE EARLY THIS MORNING DRESS
APPROPRIATELY FOR THE COLD TEMPERATURES.  LAYER CLOTHING FOR
MAXIMUM WARMTH AND COVER AS MUCH EXPOSED SKIN AS POSSIBLE TO PROTECT
AGAINST FROSTBITE.

LIGHT SNOW IS EXPECTED TO DEVELOP OVER AREAS SOUTHWEST OF AN
INDEPENDENCE...QUAD CITIES LINE LATE TONIGHT.  BY THURSDAY MORNING
SNOWFALL AMOUNTS SHOULD RANGE FROM JUST OVER AN INCH IN NORTHEAST
MISSOURI TO AROUND A HALF INCH IN EAST CENTRAL IOWA.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

SNOW WILL SPREAD OVER MUCH OF THE AREA ON THURSDAY AS AN UPPER
LEVEL DISTURBANCE PASSES OVERHEAD. LATEST INDICATIONS SUGGEST 3 TO 5
INCHES OF SNOW MAY FALL SOUTHEAST OF A LINE FROM FAIRFIELD IOWA...TO
ALEDO...AND TO PRINCETON ILLINOIS BY THURSDAY EVENING. THERE MAY
EVEN BE SOME LOCALIZED HIGHER AMOUNTS IN THESE AREAS. 2 TO 4 INCHES
OF POWDERY SNOW ACCUMULATION WILL BE POSSIBLE ALONG AN AXIS FROM
SIGOURNEY...THROUGH THE QUAD CITY AREA...AND TO STERLING. LIGHTER
AMOUNTS IN THE 1 TO 3 INCH RANGE MAY OCCUR FROM MARENGO...TO
MAQUOKETA...AND TO FREEPORT. AREAS WEST OF DUBUQUE SUCH AS MANCHESTER
AND INDEPENDENCE MAY ONLY RECEIVE AN INCH OR LESS. AT THIS POINT...
THERE STILL IS SOME UNCERTAINTY OF THE EXACT TRACK OF THE SYSTEM AND
HOW MUCH MOISTURE IT WILL HAVE TO WORK WITH TO PRODUCE SNOW. THUS IT
IS RECOMMENDED TO STAY TUNED FOR FURTHER UPDATES AND POTENTIAL
ADVISORIES OR WARNINGS CONCERNING THIS WINTER STORM SYSTEM.

ALTHOUGH THE WINDS WILL BE ON THE LIGHT SIDE ON THURSDAY LIMITING
THE BLOWING AND DRIFTING SNOW POTENTIAL...AREA ROADS MAY STILL BECOME
SNOW PACKED AND SLIPPERY. THURSDAY TRAVELERS ARE URGED TO PREPARE FOR
POTENTIAL WINTER DRIVING CONDITIONS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED.

DLF/12