FXUS63 KILX 260544
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1144 PM CST WED NOV 25 2009
.DISCUSSION...
ISSUED 827 PM CST WED NOV 25 2009
UPPER LOW SPINNING OVER IOWA WILL TRACK EASTWARD OVERNIGHT...REACHING
THE SOUTHERN GREAT LAKES BY 12Z THU. DRY SLOT ASSOCIATED WITH LOW
IS CURRENTLY PUSHING ACROSS SOUTHEAST ILLINOIS...RESULTING IN A
BRIEF BREAK IN THE CLOUD COVER FOR LOCATIONS SOUTH OF I-70.
ELSEWHERE...OVERCAST CONDITIONS PREVAIL. LATEST RADAR MOSAIC AND
SURFACE OBS REVEAL SCATTERED RAIN SHOWERS INCREASING IN COVERAGE
UPSTREAM ACROSS IOWA/NORTHWEST ILLINOIS. THIS PRECIP WILL ROTATE
E/SE INTO CENTRAL ILLINOIS LATER THIS EVENING INTO THE OVERNIGHT
HOURS. 00Z KILX UPPER AIR SOUNDING SHOWED A 2300FT ABOVE FREEZING
SURFACE LAYER...WHICH IS PROGGED BY 00Z NAM-WRF FORECAST SOUNDINGS
TO DECREASE TO BETWEEN 1500 AND 2000FT AFTER MIDNIGHT. THIS
PARTICULAR THERMAL PROFILE WILL SUPPORT MAINLY LIQUID
PRECIP...WITH A FEW SNOW FLAKES MIXED IN FROM TIME TO TIME. HAVE
UPDATED THE GRIDS TO FEATURE LIKELY RAIN/SNOW SHOWERS ACROSS THE
NORTHERN CWA...SCATTERED RAIN/SNOW SHOWERS CENTRAL...AND ISOLATED
RAIN SHOWERS FAR SOUTHEAST. WHERE SNOW DOES OCCUR OVERNIGHT...NO
ACCUMULATION IS EXPECTED...AS THE PRECIP WILL BE TOO LIGHT AND THE
GROUND TEMP WILL BE TOO WARM.
&&
.AVIATION...
ISSUED 1144 PM CST WED NOV 25 2009
CENTRAL ILLINOIS WILL REMAIN UNDER THE INFLUENCE OF A DEEP
UPPER-LEVEL LOW THROUGH THURSDAY MORNING...RESULTING IN OVERCAST
CONDITIONS AND SCATTERED RAIN/SNOW SHOWERS. 00Z MODELS CONTINUE TO
BRING CEILINGS DOWN TO BELOW 1000FT OVERNIGHT...HOWEVER UPSTREAM
OBS ACROSS IOWA/MINNESOTA DO NOT SUPPORT THIS. BASED ON CURRENT
TRENDS...WILL FOCUS LOWEST CEILINGS DURING THE 09Z TO 16Z TIME
FRAME...AS A SURFACE TROUGH SWINGS THROUGH THE AREA. WILL BRING
CEILINGS DOWN TO 800FT AT BOTH KPIA AND KBMI...BUT WILL MAINTAIN
1500FT AT THE OTHER TERMINALS. WILL ALSO CARRY A PERIOD OF
PREDOMINANT -RASN DURING THAT TIME AS WELL. STRONG SUBSIDENCE ON
THE BACK SIDE OF THE DEPARTING UPPER LOW WILL LEAD TO A RAPID
CLEARING TREND LATE THURSDAY AFTERNOON AND EVENING. BASED ON NAM-WRF
RH PROFILES...HAVE SCATTERED THE CLOUD COVER AT KPIA BY 22Z...THEN
FURTHER EAST AT KCMI BY 00Z. WINDS WILL REMAIN GUSTY FROM THE W/NW
THROUGH THURSDAY AFTERNOON...BEFORE DIMINISHING TO UNDER 10KT AFTER
00Z FRI.
BARNES
&&
.PREV DISCUSSION...
ISSUED 232 PM CST WED NOV 25 2009
SFC LOW MAKING ITS WAY THROUGH THE GREAT LAKES TODAY...POST
FRONTAL TROF IS EXITING ILLINOIS TO THE EAST. YET ANOTHER WAVE OF
PRECIP IS MOVING ACROSS NRN IL THIS AFTERNOON...WITH VERY LIGHT
PRECIP FALLING. CLOUDS ARE THINNING AND MIGHT SEE A GLIMPSE OF
SUNLIGHT BEFORE SUNSET. THO MORE PRECIP IS ANTICIPATED FOR THE
HOLIDAY...POSSIBLY SOME SNOW AND RAIN MIXED...BUT NOTHING IN THE
WAY OF ACCUMULATION IS EXPECTED. BLACK FRIDAY SHOPPERS SHOULD
ALSO BE AWARE THAT BEHIND THE PRECIP IS A PRETTY STOUT SHOT OF
COLD AIR TO MAKE ANY CAMPING OUT FOR SALES A RATHER COLD AND DAMP
ENDEAVOR THURSDAY NIGHT/FRIDAY MORNING.
MODELS ARE STILL A BIT OF A WRECK...DIVERGING CONSIDERABLY AT MON
00Z. ECMWF HAS BEEN STRUGGLING WITH WHAT LOOKS LIKE A SPLIT FLOW
PATTERN SHIFT FOR THE PAST FEW RUNS...DEEPENING A STRANGE TROF
FROM THE DESERT SW TO THE MIDWEST...BUT FIGHTING SPLITTING OFF OF
A LOW IN BOTH THE GREAT LAKES AND THE SW. ALSO...FROM YESTERDAY TO
TODAY...ENSEMBLES WERE PUTTING THE NAO IN A NEGATIVE PHASE.
NEGATIVE VALUES FOR THE NAO POINTS TO A WEAKER ICELANDIC HIGH/LESS
AMPLIFIED FLOW. WITH A LESS AMPLIFIED FLOW...PHASING OF THE TWO
ENERGIES IS LESS LIKELY...AND COULD RESULT IN THE SECONDARY LOW
SPINNING OUT OVER THE SW AS THE OTHER MOVES THRU THE GREAT LAKES.
CERTAINLY...THERE ARE STILL MANY TIMING ISSUES AND OTHER PROBLEMS
TO DEAL WITH...BUT AM FAVORING THE SPLIT FLOW/CUT OFF LOW GFS
SOMEWHAT FOR THIS FORECAST.
SHORT TERM...TONIGHT THROUGH FRIDAY...
WILL KEEP THE LIKELY POPS IN THE NORTH TONIGHT...BUT SLIGHTS IN THE
SE TO HANDLE THE MORE SHOWERY ACTIVITY THAT WILL STILL BE
POSSIBLE. AFTER MIDNIGHT...COULD SEE A MIX OF SNOW/RAIN...BUT
WARMER AIR AT THE SFC SHOULD KEEP THE SNOW FROM ACCUMULATING...AND
2" SOIL TEMPS ARE STILL IN THE MID 40S. THANKSGIVING...THE
SHOWERS CONTINUE ON THE BACKSIDE OF THE LOW AS THE COLD AIR WRAPS
AROUND THE SYSTEM KEEPING THE SHOWERS A SNOW/RAIN MIX. BUT THE
GROUND SHOULD BE WET/WARM ENOUGH TO AVOID ANY SIGNIFICANT
ACCUMULATION. WILL CLEAR UP ENOUGH FOR THU EVENING TO WORK IN
COMBO WITH COLDER AIR TO BRING THE COLDEST TEMPS IN THE FORECAST
FOR THU NIGHT/FRI MORNING.
LONG TERM...SATURDAY THROUGH TUESDAY...
SATURDAY THROUGH SUNDAY SHOULD BE A BIT OF TEMP MODERATING...ESP
SAT AS THE FLOW GETS A MORE SOUTHERLY COMPONENT ON THE BACKSIDE OF
THE DEPARTING RIDGE AXIS. MODELS HAVING A MAJOR TIMING ISSUE WITH
THE NEXT PATTERN SHIFT. GFS IS A BIT MORE ADVANCED...TAKING THE
CHANGE OF A SPLIT FLOW BEFORE THE ECMWF HAS COME AROUND...THOUGH
THE ECMWF HAS BEEN HINTING FOR THE LAST COUPLE OF DAYS. WILL BE
WATCHING CLOSELY...AND KEEPING THE MAJORITY OF PRECIP TO THE SOUTH
PER THE GFS..AND LEAVE OPTIONS OPEN FOR ANOTHER WET END OF
WEEKEND/BEGINNING OF WORK WEEK.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
