FXUS63 KLOT 242104
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
304 PM CST THU DEC 24 2009
.DISCUSSION...
...NEAR TERM (THIS AFTERNOON THROUGH FRIDAY MORNING)...
206 PM CST
EARLY PRECIP TYPE CONCERNS...AND HEAVY RAIN POTENTIAL OVERNIGHT
ARE FOCUS FOR NEAR TERM FORECAST.
TEMPERATURES ACROSS ILLINOIS COUNTIES CAME ABOVE FREEZING RIGHT ON
SCHEDULE AROUND NOON TODAY...BUT DEEPER DEW POINT DEPRESSIONS AND
ASSOCIATED EVAPORATIVE COOLING KEPT TEMPS A DEGREE OR TWO COLDER
OVER NW INDIANA...RESULTING IN A CONTINUED FREEZING RAIN THREAT.
TEMPS HAVE FINALLY COME ABOVE FREEZING ACROSS THE ENTIRE AREA...WITH
FOCUS TURNING TO HEAVY RAIN AND FLOODING POTENTIAL FROM THIS
AFTERNOON THROUGH THE OVERNIGHT HOURS.
UPPER AIR AND WATER VAPOR ANALYSIS INDICATES VERY VIGOROUS STORM
SYSTEM WRAPPING UP NEAR THE TX/OK STATE LINE...WITH RAPID
CYCLOGENESIS TAKING PLACE OVER CENTRAL ARKANSAS. VERY MOIST AIR MASS
ALREADY BEING FUNNELED NORTH OVER THE CWA AT THIS HOUR...AND AS THIS
SURFACE LOW STRENGTHENS AND LIFTS NORTH UP THE MISSISSIPPI VALLEY
THIS EVENING...MOISTURE ADVECTION NORTH FROM THE GULF OF MEXICO WILL
ONLY INCREASE AS THE NIGHT GOES ON. 295K ISENTROPIC ANALYSIS
INDICATES GOOD SET UP FOR HEAVY RAIN THIS EVENING...WITH 175
OR SO MILLIBAR RISE IN THE 295K SURFACE FROM SOUTH TO NORTH OVER THE
CWA...AND A STOUT 55-60 KT WIND HELPING WITH IMPRESSIVE MOISTURE
FLUX VALUES. LOOKS LIKE HEAVIEST RAIN WILL LIKELY OCCUR BETWEEN
ABOUT 03Z TONIGHT AND 12Z TOMORROW MORNING...WITH AT LEAST SOME
INDICATION FROM GUIDANCE THAT BEST LIFT WILL BE OVER WESTERN AND
SOUTHWESTERN HALF OR SO OF THE FORECAST AREA. EXACT QPF VALUES
ALWAYS VERY TRICKY...BUT NUMERICAL GUIDANCE SEEMS TO BE IN GENERAL
AGREEMENT OF BETWEEN 1 AND 2 INCHES OF RAIN ACROSS MUCH OF THE AREA
BY MORNING...AND CERTAINLY THE POTENTIAL FOR A FEW LOCALLY HIGHER
AMOUNTS. WITH SNOW/ICE PACK OF 1 TO 2 INCHES NEAR I-80...TO 7-9
INCHES NEAR THE WISCONSIN STATE LINE...HEAVY RAIN ALONG WITH THIS
SNOW/ICE MELTING CERTAINLY RAISES SOME HYDROLOGIC RED FLAGS. FLOOD
WATCH CONTINUES FOR THE ENTIRE CWA...WITH FLOOD WARNINGS FOR SEVERAL
POINTS ALONG AREA RIVERS. ALONG WITH RIVER FLOODING...THERE COULD
CERTAINLY BE FLOODING OF LOW LYING AND OTHER FLOOD PRONE AREAS LATER
TONIGHT. RIGHT NOW...APPEARS THAT 1/3/6 HOUR QPF VALUES WILL STAY
BELOW LATEST FLASH FLOOD GUIDANCE...BUT THAT BEING SAID...CERTAINLY
CAN'T RULE OUT A FEW AREAS OF PRETTY SWIFT RUNOFF WITH COMBINATION
OF RAIN...RAPIDLY MELTING SNOW...AND FROZEN GROUND.
TEMPERATURES THROUGH THE PERIOD GENERALLY EXPECTED TO STAY NEARLY
STEADY THROUGH THE EVENING AND OVERNIGHT HOURS IN THE MID 30S.
BOXELL
MID RANGE...FRI DAYTIME THRU SUN
303 PM CDT
FORECAST FOR CHRISTMAS DAY THRU HOLIDAY WEEKEND DOMINATED BY
CONTINUED PROCESS OF MERGING UPPER LOWS...CURRENTLY OVER SOUTHERN
PLAINS AND NORTHERN HIGH PLAINS...OVER THE HEART OF THE CONUS BY
FRI AFTERNOON. SYSTEM TO BE PRETTY MUCH VERTICALLY STACKED WITH
LOW LEVEL COLD AIR WRAPPED ALL THE WAY BACK AROUND TO THE N AND NW
SIDES OF THE LOW BY THEN WITH LOW LEVEL THERMAL FORCING NIL. STILL
MID LEVEL UVV FRI MOVING OVER THE FA DURING FRI NIGHT BUT ALSO MID
LEVEL DRY AIR WRAPPING INTO SYSTEM SO EXPECT OFF AND ON FLURRIES
FROM REMNANT LOW LEVEL MOISTURE AND CYCLONIC FLOW MOISTURE WITH
ONLY A CHANCE OF SNOW SHOWERS. LITTLE CHANGE TO THIS SCENARIO AS
THE UPPER LOW TO ONLY VERY SLOWLY DRIFT/MEANDER GENERALLY ENE TO
OVER SE WI BY SUN MORNING SO CLOUDS...FLURRIES AND THREAT OF SNOW
SHOWERS TO PERSIST TIL SUN NIGHT WHEN SYSTEM TRANSITIONS TO AN
OPEN WAVE AS IT MOVES FURTHER E ACROSS THE GRTLKS AND MIDWEST.
STRONG LOW LEVEL CAA WRAPS FROM THE SW AND S OVER THE FA ON SAT SO
TEMPS TO BE FALLING IN THE AFTERNOON. COLD AIR REMAINS OVER THE
REGION SAT AND SUN KEEPING MAX TEMPS IN TH LOWER AND MID 20S WITH
LOWS IN THE TEENS.
TRS
LONG TERM...MON THRU THU
1052 AM CST
AS USUAL AT LONGER RANGES MODELS SHOWING DIFFERENCES IN STRENGTH
AND TIMING OF UPPER FEATURES BUT DO AGREE ON GENERAL TREND OF
OVERALL FLOW PATTERN EVOLUTION.
TROF EXTENDING FROM UPPER LOW OVER NORTHERN HUDSON BAY SE ACROSS
THE LOWER LAKES AND NORTHEASTERN U.S. MON MORNING TO CONTINUE TO
ROTATE TO OVER THE LOWER ST. LAWRENCE VALLEY AND CANADIAN
MARITIMES DURING BY TUE MORNING. COLD DRY ANTICYCLONIC LOW LEVEL
FLOW TO KEEP AREA PCPN FREE EXCEPT POSSIBLY FOR LAKE EFFECT -SHSN
CATCHING THE FAR EASTERN PORTION OF THE FA IN IND ON MON.
MEAN FLOW DOWNSTREAM OVR THE REGION TO BACK IN RESPONSE TO UPPER
TROUGHING MOVING FROM THE ROCKIES E OVER THE PLAINS LATER MON
NIGHT AND TUE. NOT MUCH AGREEMENT BETWEEN MODELS ON ANYTHING
BELOW GENERAL LARGE SCALE PATTERN AT THIS POINT BUT INITIALLY
SHOULD RESULT IN DROPPING POPS TO BELOW EVEN SLIGHT CHANCE VALUES.
BACKING ALSO POINTS TO SOME MODERATION IN TEMPS DURING THIS TIME.
MEAN UPPER TROF TO PASS OVER FA WED-WED NIGHT. MOISTURE LIMITED
WITH NW FLOW SYSTEMS SO ONLY LOW END POPS ASSIGNED AT THIS TIME
AS TROF APPROACHES AND PASSES BY...AND HELD ONTO INTO THU AS
CYCLONIC MID-UPPER FLOW REMAINS OVER THE REGION WITH MORE THAN
LIKELY AN EMBEDDED MINOR SHORT WAVE OR TWO PASSING THRU TO KEEP
LOW THREAT OF -SHSN GOING.
VEERING OF FLOW WITH TROF PASSAGE RETURNS REGION TO LOW LEVEL CAA
FOR THU.
TRS
&&
.AVIATION...
1800 UTC TAFS...WHILE THE THREAT OF FREEZING/FROZEN PRECIPITATION
APPEARS TO BE OVER AT THE TERMINALS ANTICIPATE GRADUALLY
DETERIORATING CONDITIONS THROUGH TONIGHT AS POWERFUL STORM SYSTEM
LIFTS NORTH FROM THE GULF COAST REGION INTO THE MID MISSISSIPPI
VALLEY REGION.
CIGS...VFR CIGS LIKELY TO BUILD DOWN TO MVFR THIS AFTERNOON AND
DOWN FURTHER TO IFR BY LATE AFTERNOON OR EARLY EVENING. AS MORE
MOISTURE LADEN AIR FROM THE GULF WRAPS NORTH INTO THE AREA
OVERNIGHT CIGS MAY WELL BUILD DOWN TO LIFR OR EVEN VLIFR AT TIMES.
SHOULD SEE AN IMPROVEMENT TO AT LEAST MVFR CIGS FOLLOWING PASSAGE
OF OCCLUDED/COLD FRONT LATER FRIDAY MORNING WITH CIGS CONTINUING A
SLOW IMPROVEMENT FRIDAY AFTERNOON AS COLDER AIR MASS BUILDS IN.
VSBYS...SIMILAR TO CIGS EXPECT VSBY TO FALL TO MVFR THIS
AFTERNOON...AND PROBABLY CONTINUE TO FALL TO IFR THIS EVENING IN
RAIN AND FOG. INTENSITY OF THE RAIN WILL LEAD TO VARYING VSBYS
TONIGHT BUT GENERALLY ANTICIPATING IFR OR LOWER THROUGH MOST OF
THE NIGHT.
WINDS...EAST WINDS WILL STEADILY INCREASE TODAY AND BECOME
INCREASINGLY GUSTY AS DEEPENING LOW PRESSURE LIFTS NORTHWARD.
ACARS SOUNDINGS FROM ORD/MDW ALREADY SHOWING 40-45KT WINDS JUST OFF
THE DECK WITH STRONG INVERSION LIKELY SUPPORTING THE THREAT OF
LLWS TODAY. STRONG PRESSURE FALLS IN ADVANCE OF THE LOW SHOULD
RESULT IN INCREASINGLY STRONG GUSTY SURFACE WINDS TONIGHT WITH A
LESSENING RISK OF LLWS OVERNIGHT AS SURFACE WINDS INCREASE TO
20-35 KT.
IZZI
&&
.MARINE...
205 PM CST
NO BIG CHANGES FROM PREVIOUS FORECASTS...STILL EXPECT DEEPENING
LOW TO TRACK FROM THE ARKLATEX REGION NORTH INTO EASTERN IOWA BY
MIDDAY FRIDAY. TIGHTENING PRESSURE GRADIENT AND STRONG PRESSURE
FALLS WEST OF THE LAKE SHOULD SUPPORT GALE FORCE WINDS TONIGHT
INTO FRIDAY. AS WARM AIR ADVECTION DRAWS MILDER AIR NORTHWARD
COULD ACTUALLY SEE BOUNDARY LAYER STABILIZE A BIT OVER THE LAKE
LATE TONIGHT INTO FRIDAY MORNING...WHICH SHOULD PREVENT WINDS FROM
REACHING STORM FORCE THOUGH IT MAY BE CLOSE OVER SOUTHERN PORTIONS
OF THE LAKE. OCCLUDED LOW SHOULD BEGIN TO FILL OVER THE WEEKEND AS
IT MEANDERS SLOWLY EASTWARD WITH THREAT OF GALES SUBSIDING LATER
FRIDAY AFTERNOON AND EVENING. LOW CURRENTLY EXPECTED TO WOBBLE
EAST OF THE LAKE BY LATE SUN INTO MONDAY WITH WINDS BECOMING
NORTHWESTERLY...THOUGH NOT EXPECTING GALES AT THIS TIME WITH THE
NORTHWEST WIND EVENT.
IZZI
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FLOOD WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-
ILZ032-ILZ033-ILZ039 UNTIL 6 AM FRIDAY.
IN...FLOOD WATCH...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 6 AM
FRIDAY.
ICE STORM WARNING...INZ001-INZ002-INZ010-INZ011 UNTIL 3 PM
THURSDAY.
LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
LMZ874-LMZ876-LMZ878 UNTIL 6 PM FRIDAY.
GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
LMZ868 UNTIL 9 PM FRIDAY.
&&
$$
