AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
857 PM CDT FRI MAY 24 2013
.DISCUSSION...
ISSUED 852 PM CDT FRI MAY 24 2013
THE LARGE CANADIAN HIGH PRESSURE SYSTEM THAT HAS BROUGHT US THE
CHILLY WEATHER OF THE PAST 24 TO 36 HOURS WAS EDGING SLOWLY OFF
TO OUR EAST EARLY THIS EVENING. MEANWHILE...AN UPPER LEVEL
DISTURBANCE TOPPING THE CENTRAL PLAINS RIDGE HAS BROUGHT AN AREA
OF SHOWERS AND THUNDERSTORMS INTO PARTS OF NORTHERN AND CENTRAL
IOWA...WHICH CONTINUES TO MARCH SLOWLY EAST.
00Z ILX SOUNDING SHOWING QUITE A BIT OF DRY AIR IN PLACE THANKS
TO THE HIGH TO OUR NORTHEAST. NAM-WRF FORECAST SOUNDINGS SHOWING
THAT THIS DRY AIR WILL BE STUBBORN TO DEPART FROM OUR AREA AHEAD
OF THE APPROACHING WAVE LATE TONIGHT INTO SATURDAY MORNING. WE
CURRENTLY HAVE LOW CHANCE POPS ACRS THE WEST FOR LATE TONIGHT AND
THAT LOOKS REASONABLE AT THIS TIME...WHILE POINTS FURTHER EAST
WILL BE HARD PRESSED TO SEE MUCH MORE THAN SOME MID LEVEL CLOUDS
SATURDAY MORNING. UNFORTUNATELY...WITH THE NORTHEASTERN U.S. TROF
VERY SLOW TO MOVE AWAY AND THE RIDGE TO OUR WEST GETTING FLATTENED
BY THE LOW AMPLITUDE SHORTWAVES ON A DAILY BASIS...IT APPEARS THE
THREAT FOR OCCASIONAL SHOWERS AND THUNDERSTORMS WILL BE WITH US
THRU THE HOLIDAY WEEKEND.
OTHER THAN THE USUAL ADJUSTMENTS TO THE HOURLY TEMPS IN THE GRIDS
THIS EVENING...NO SIGNIFICANT CHANGES WERE NEEDED THAT WOULD WARRANT
A ZONE UPDATE.
SMITH
&&
.AVIATION...
ISSUED 600 PM CDT FRI MAY 24 2013
VFR CONDITIONS ARE EXPECTED TO HOLD INTO SATURDAY. HIGH AND MID
LEVEL CLOUDS WILL BE ON THE INCREASE LATER TONIGHT AS A BAND OF
SHOWERS AND THUNDERSTORMS PUSHES ACRS NORTH AND NE IOWA. MODELS
WERE HINTING AT THE IDEA THAT WHAT IS LEFT OF THE SHOWER AREA
TO OUR NORTHWEST MAY BEGIN TO AFFECT AT LEAST THE WESTERN TAF
SITES TOMORROW MORNING. LATEST HI-RES SOUNDING DATA OFF THE
NAM MODEL SUGGESTS OTHER THAN SOME LIGHT SHOWERS...THE LOW
LEVELS OF THE ATMOSPHERE WILL BE VERY SLOW TO MOISTEN TO SUPPORT
MUCH MORE THAN VCSH IN THE TAFS AT THIS TIME. FURTHER EAST...AT
KBMI AND KCMI...IT MAY BE REAL TOUGH TO GET RAIN INTO THOSE AREAS
BEFORE AFTERNOON...IF THEN...BASED ON THE SOUNDINGS. THE CONTINUED
MOISTENING OF THE LOWER LEVELS LATER TOMORROW MAY BRING SOME LOWER
VFR CIGS TO KPIA AND KSPI...BUT THAT'S ABOUT AS FAR EAST AS WE
WANT TO GO THIS FCST PERIOD. SFC WINDS WILL BE LIGHT EASTERLY
TONIGHT AND EAST TO SOUTHEAST ON SATURDAY AT 8 TO 13 KTS.
SMITH
&&
.PREV DISCUSSION...
ISSUED 245 PM CDT FRI MAY 24 2013
HIGH PRESSURE REMAINS IN CONTROL THROUGH THE DAY AS THE SKIES
CLEAR AND TEMPERATURES BEGIN TO WARM INTO THE MID 60S. HIGH
PRESSURE RIDGE TO SLIDE SLOWLY EASTWARD...WITH A SOUTHERLY
COMPONENT RETURNING TO THE SFC WINDS IN CENTRAL ILLINOIS. ISSUES
FOR THE HOLIDAY WEEKEND FORECAST BEGIN IMMEDIATELY...WITH PRECIP
ON APPROACH TONIGHT IN THE OVERNIGHT...AND CONTINUING THROUGH
MONDAY NIGHT. ECMWF A LITTLE QUICKER BEFORE 12Z...WITH THE GFS/NAM
HOLDING OFF A BIT UNTIL LATER TOMORROW MORNING...THOUGH THE
REMAINING DIFFERENCES ARE RATHER FEW. IN THE MEDIUM RANGE FORECAST
AND THE EXTENDED...THE ECMWF STARTING TO LOOK MORE LIKE YESTERDAYS
GFS WITH A BREAKDOWN OF THE EASTERN SIDE OF THE 500 MB
RIDGE...PUTTING THE MIDWEST IN SWRLY FLOW...ALBEIT VERY
LIGHT...FOR THE REGION IN THE MIDDLE OF THE NEXT WORK WEEK.
SHORT TERM...TONIGHT THROUGH TOMORROW...
WAVE THAT WILL BE MOVING INTO THE FA AFTER MIDNIGHT/TOMORROW
MORNING ALREADY GETTING GOING IN THE NRN MISSOURI RIVER VALLEY.
TIMING OF PRECIP INTO THE FA A BIT OF A CONFLICT WITH THE NAM AND
THE GFS WAITING TIL AFTER 12Z...AND THE ECMWF A BIT QUICKER. AM
MORE INCLINED TO SIDE WITH THE NAM...BUT ENOUGH OF A DIFFERENCE TO
WARRANT A CHANCE MENTION IN THE NW BEFORE DAWN. TOMORROW EXPECTED
TO BE SHOWERS AND TS THAT MAY BE MORE OFF AND ON...WITH MORE
BREAKS IN THE RAIN SAT NIGHT. CHANCES WILL INCREASE AS THE DAY
PROGRESSES...WITH SUNDAY AND MONDAY EXPECTED TO BE THE WETTEST.
LONG TERM...SUNDAY THROUGH THURSDAY...
AS THE HEAT BUILDS UNDER THE MIDLEVEL RIDGE...A DEVELOPING FRONTAL
BOUNDARY STARTS TO SET UP TO THE SW. THIS BOUNDARY WILL PROVIDE A
FOCUS FOR THE WAVES TOPPING THE 500 RIDGE...SETTING OFF WAVES OF
PRECIP. LOCATION OF THE FRONTAL BOUNDARY STILL A BIT
CONFLICTED...BUT GFS/ECMWF BOTH IN RATHER DECENT AGREEMENT ON THE
SERIES OF DISTURBANCES DIVING INTO THE REGION. PRECIP CHANCES
DWINDLING TUES NIGHT AS EASTERN EDGE OF UPPER RIDGE BREAKS DOWN
AND WESTERN TROF DIGS IN...AMPLIFYING THE WAVE PATTERN OVER THE
CONUS AND LEAVING THE UPPER MIDWEST IN SWRLY FLOW...AND MUCH OF IL
IN WEAK FLOW...IF ANY...UNDER THE BUILDING RIDGE. VERY WARM
MIDLEVELS AND THE GUIDANCE BEING PULLED DOWN A BIT. HAVE BOOSTED
TEMPS TO COMPENSATE...STILL MAY NOT BE ENOUGH. RETURNING POPS ON
THURS NIGHT/FRI STILL VERY MUCH IN DEBATE AS THE GFS AND ECMWF
DIVERGE QUITE A BIT WITH THE PROGRESSION OF THE WAVE PATTERN AT
DAY 7/8.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
