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000
FXUS63 KLOT 130156
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
856 PM CDT TUE MAY 12 2009
.DISCUSSION...
856 PM CDT
MINOR UPDATE TO GRIDS/FORECAST TO BRING IN PRECIP A LITTLE FASTER
ACROSS WESTERN IL COUNTIES LATE THIS EVENING...AND TO INCREASE
CLOUD COVER ALL AREAS.
ANALYSIS OF 00Z RAOB DATA...ALONG WITH PROFILER AND WATER VAPOR...
INDICATES MID LEVEL SHORT WAVE TROUGH CURRENTLY PROPAGATING
EASTWARD ACROSS IOWA AND MISSOURI. LARGE AREA OF RAIN AND EMBEDDED
THUNDERSTORMS ACROSS EASTERN IOWA PER REGIONAL MOSAIC OF
88DS...ABOUT TO CROSS RIVER INTO IL. TIMING OF OF LEADING EDGE OF
REFLECTIVITY INDICATES RAIN WILL LIKELY MOVE INTO WESTERN IL
COUNTIES OF CWA SHORTLY...THUS HAVE INCREASED POPS ACROSS THESE
AREAS FOR LATE EVENING HOURS. CG LIGHTNING NETWORK HAS DEPICTED
DECREASING AMOUNT OF LIGHTNING WITH THIS PRECIP LAST COUPLE OF
HOURS...WITH SPC RUC MESOANALYSIS DATA INDICATING RATHER POOR MID
LEVEL LAPSE RATES OF AROUND 5.5 DEG/KM IN 700-500 MB LAYER THUS
WILL LIKELY ONLY SEE ISOLATED/EMBEDDED THUNDER EARLY ON. SHORT
TERM PROGS CONTINUE TO DEPICT 40-50 KNOT LOW LEVEL JET VEERING
INTO IL LATER TONIGHT...09-12Z PERIOD...WITH RELATIVELY STRONG
MOISTURE CONVERGENCE AROUND 850 MB LEVEL INDICATING BETTER FORCING
FOR MORE WIDESPREAD THUNDER DURING PRE-DAWN HOURS OF WEDNESDAY
MORNING. ANY SEVERE POTENTIAL FOR EARLY WEDNESDAY EXPECTED TO BE
IN FORM OF ELEVATED STORMS WITH HAIL.
LITTLE AVAILABLE IN TERMS OF NEW GUIDANCE FOR CONVECTIVE TRENDS
WEDNESDAY SO NO CHANGES BEYOND THE OVERNIGHT FOR NOW.
RATZER
&&
.PREV DISCUSSION...
250 PM CDT
WATER VAPOR IMAGERY EARLY THIS AFTERNOON SHOWS A POWERFUL
SHORTWAVE CURRENTLY CHARGING EASTWARD ACROSS THE NORTHERN ROCKIES.
STRONG MID/UPPER LEVEL HEIGHT FALLS ALREADY TAKING PLACE AT 12Z
THIS MORNING ACROSS THE NORTHERN HIGH PLAINS...WITH THE CONTINUED
EASTWARD PROGRESSION OF THESE HEIGHT FALLS LIKELY HELPING SUSTAIN
THE 40-45KT SOUTHERLY LOW LEVEL JET EVIDENT IN THE REGIONAL
PROFILER NETWORK ACROSS THE CENTRAL AND SOUTHERN PLAINS. SURFACE
OBS AND GOES SOUNDER PRECIPITABLE WATER IMAGERY SHOW THAT LOW
LEVEL MOISTURE IS RESPONDING NICELY TO THE SOUTHERLY FLOW WITH 60F
DEWPOINTS MAKING IT INTO SOUTHERN KANSAS...WITH IN THE UPPER 60S
TO LOWER 70S LURKING OVER EASTERN TEXAS. AS UPPER TROUGH AND
ASSOCIATED HEIGHT FALLS CONTINUE TO PROGRESS EASTWARD LOOK FOR THE
LOW LEVEL JET TO BEGIN DEVELOPING EASTWARD INTO THE MID
MISSISSIPPI VALLEY TONIGHT.
STRONG MOISTURE FLUX CONVERGENCE ALONG THE LEADING EDGE OF THIS
SURGE IN DEEPER MOISTURE IS ALREADY RESULTING IN/MAINTAINING A N-S
AXIS OF SHOWERS AND THUNDERSTORMS OVER THE EASTERN PLAINS. THIS
CONVECTION WILL LIKELY CONTINUE PROGRESSING SLOWLY EASTWARD
THROUGH THE NIGHT AND EVENTUALLY INTO OUR CWA AFTER MIDNIGHT.
GIVEN STRONG LOW LEVEL JET AND STEEP MID LEVEL LAPSE RATES
ADVECTING EASTWARD POTENTIAL DOES EXIST SOME HAIL WITH THE MORE
INTENSE THUNDERSTORMS LATE TONIGHT...THOUGH WOULD LARGELY EXPECT
ANY HAIL THAT DOES OCCUR TO BE SUB-SEVERE (LESS THAN 1"). GIVEN
THE LESS THAN EXPEDIENT MOTION...ALSO COULD SEE SOME LOCALLY HEAVY
RAINFALL TOTALS LATE TONIGHT INTO WEDNESDAY MORNING. FLASH FLOOD
GUIDANCE HAS RECOVERED SOME AFTER THE WEEK OR SO OF DRIER WX SO
NOT PLANNING TO HOIST ANY HEADLINES.
THE SHORTWAVE OVER WESTERN/CENTRAL NEBRASKA WHICH IS HELPING
FOCUS/MAXIMIZE CONVECTION SHOULD CONTINUE EASTWARD TONIGHT AND
EXTRAPOLATION AND MODEL GUIDANCE BOTH SUGGESTING IT SHOULD CLEAR
AREA DURING THE MORNING HOURS WEDNESDAY. WEAK SUBSIDENCE IN THE
WAKE OF THIS WAVE WOULD SEEM TO FAVOR A BREAK IN THE CONVECTION
LATE WED MORNING INTO WEDNESDAY AFTERNOON...THOUGH THE WRF-NAM
WOULD SUGGEST CONSIDERABLE CONVECTION BREAKING OUT IN WARM AIR
ADVECTION REGIME LIMITING ANY BUILD UP IN INSTABILITY. GFS AND
WRF-ARW WOULD FAVOR A SCENARIO WITH A BREAK IN PRECIP...WITH GFS
SHOWING AN ELEVATED MIXED LAYER ORIGINATING FROM THE ROCKIES
ADVECTING EASTWARD WITH STEEPENING MID LEVEL LAPSE RATES.
OBVIOUSLY CONFIDENCE WILL ALWAYS BE LOW WHEN TRYING TO PREDICT
EVENTUAL EVOLUTION OF CONVECTION AND ITS RESULTS...HOWEVER
CURRENT THINKING IS A SCENARIO MORE LIKE THE GFS/WRF-ARW WOULD
SEEM MORE LIKELY THAN CONTINUED CONVECTION THROUGH THE DAY.
SHOULD WE GET THE ANTICIPATED BREAK IN CONVECTION AS
ADVERTISED...THEN THE STEEPENING MID LEVEL LAPSE RATES OVER TOP AN
INCREASING THETA-E RICH BOUNDARY LAYER SHOULD ALLOW FOR POTENTIAL
INSTABILITY TO BUILD DURING THE AFTERNOON. MODIFYING FORECAST
SOUNDINGS FROM THE GFS FOR SFC T/TD OF 72/65 WOULD STILL YIELD
CAPE VALUES IN EXCESS OF 2000 J/KG. GIVEN THE ANTICIPATED STRONG
DEEP AND LOW LEVEL SHEAR PROFILES IN ADVANCE OF THE SHARPENING
UPPER TROUGH...COUPLED INSTABILITY OF THAT MAGNITUDE...CERTAINLY
POINTS TO AT LEAST SOME POTENTIAL FOR A RATHER SIGNIFICANT THREAT
FOR SEVERE THUNDERSTORMS WEDNESDAY AFTERNOON AND EVENING.
OBVIOUSLY STORM MODE QUESTIONS EXIST...HOWEVER FORECAST HODOGRAPHS
SUGGEST THAT MEAN STORM MOTION WILL BE FASTER THAN MOTION OF COLD
FRONT ALLOWING STORMS THE OPPORTUNITY TO PROPAGATE OFF THE
ORIGINATING BOUNDARY. LINEAR NATURE OF FORCING ALONG THE COLD
FRONT AND MID-UPPER LEVEL SHEAR VECTORS ORIENTED NEARLY PARALLEL
TO THE BOUNDARY BOTH POINT TO A RATHER EXPEDIENT TRANSITION TO
LINEAR STORM MODE. IF STORMS DO REMAIN DISCRETE...POTENTIAL FOR
TORNADIC SUPERCELLS WOULD BE RATHER HIGH...THOUGH WITH SEVERAL
FACTORS POINTING TO A MORE LINEAR STORM MODE THREAT WOULD PROBABLY
BE MORE DAMAGING STRAIGHT LINE WIND WITH POTENTIAL FOR SHORT LIVED
TORNADOES EMBEDDED WITHIN ANY BOWING SEGMENTS.
AT THIS DISTANCE...IT APPEARS AS THOUGH CONVECTIVE INITIATION
WOULD OCCUR OVER EASTERN IOWA INTO SW WI DURING THE MID
AFTERNOON...WITH STORMS MOVING INTO OUR WESTERN CWA BY LATE
AFTERNOON OR EARLY EVENING THEN MOVING QUICKLY EAST ACROSS THE
AREA. MOST SIGNIFICANT SEVERE POTENTIAL WILL LIKELY BE INTO THE
EARLY EVENING WITH CHANCES OF SEVERE WEATHER SLOWLY DECREASING AS
STORMS MOVE EAST ACROSS THE CWA...PLACING THE MOST SUBSTANTIAL
SEVERE THREAT OVER OUR WESTERN CWA.
IT IS IMPORTANT TO NOTE...THAT THE SCENARIO DESCRIBED ABOVE IS
JUST ONE POSSIBILITY. IT WOULD TAKE VERY LITTLE DEVIATION IN
FORECAST CONDITIONS TO DRAMATICALLY ALTER THAT FORECAST...SO
DEFINITELY STAY TUNED FOR LATEST THINKING.
COLD FRONT SHOULD BLAST SOUTH OF THE CWA BY MIDNIGHT TOMORROW
NIGHT WITH DRIER AIRMASS FILTERING INTO THE AREA IN ITS WAKE AND
SHOWERS AND THUNDERSTORMS ENDING. FRONT NOT PROGGED TO MAKE IT ALL
THAT FAR SOUTH BEFORE BEGINNING TO STALL OUT DURING THE DAY
THURSDAY AS ANOTHER SHORTWAVE INDUCES THE NEXT ROUND OF HEIGHT
FALLS OVER THE NORTHERN PLAINS. AS THIS SHORT WAVE MOVES EASTWARD
EXPECT FRONT TO LIFT BACK NORTHWARD AS A WARM FRONT THURSDAY NIGHT
AND ARRIVING IN OUR NECK OF THE WOODS BY FRIDAY INTO FRIDAY NIGHT.
SLOWER MOVING FRONT ORIENTED MORE PARALLEL WITH MEAN FLOW COULD
OPEN UP THE DOOR TO THE POTENTIAL OF A MORE SIGNIFICANT RAIN
EVENT FRIDAY INTO FRIDAY NIGHT. SOME SEVERE POTENTIAL COULD EXIST
DURING THIS TIME PERIOD AS WELL...BUT THAT WILL BE HEAVILY
DEPENDENT ON EVENTUAL CONVECTIVE EVOLUTION WHICH IS TOO FAR OUT TO
REALLY LOOK AT.
SHOT OF COOLER AND DRIER WEATHER THEN SLATED TO ARRIVE JUST IN
TIME FOR THE WEEKEND WITH WINDS OFF THE LAKE KEEPING LAKESIDE
LOCATIONS CHILLIER. NEXT NORTHERN STREAM SHORTWAVE PROGGED TO
ARRIVE BY TUESDAY WITH ASSOCIATED THREAT OF SHOWERS/THUNDERSTORMS
AT THAT TIME.
IZZI
&&
.AVIATION...
641 PM CDT
0000 UTC TAFS...MAIN PROBLEM AREAS FOR THE AREA TERMINALS ARE
GOING TO BE COMING IN TWO WAVES OVER THE NEXT DAY WITH THE FIRST
WAVE COMING THROUGH OVERNIGHT INTO WEDNESDAY MORNING.
OVER THE NEXT 6 HOURS...SHOULDN`T SEE MUCH CHANGE TO THE CURRENT
CONDITIONS WITH JUST THE GUSTS SHUTTING OFF FROM THE SOUTHEASTERLY
WINDS BUT SUSTAINED WINDS SHOULD REMAIN UP AROUND 12-14KTS WITH A
GOOD PRESSURE GRADIENT IN PLACE. UPPER LEVEL CLOUD DECK WILL
GRADUALLY LOWER TO AROUND 10KFT AS THE FIRST WAVE OF RAIN AND
EMBEDDED THUNDERSTORMS ENTER THE REGION. MAY BE SLIGHTLY TOO SLOW
WITH THE TIMING OF THE ARRIVAL OF THE RAIN BUT HAVE ADJUSTED TO
DUE TO DRIER AIR CURRENTLY IN PLACE ACROSS THE REGION.
CONDITIONS WILL DETERIORATE WITH THIS RAINFALL AS VIS/CIGS DROP
OUT AHEAD OF THE SFC/LOW LEVEL WARM FRONT WITH CONDITIONS LIKELY
DROPPING TO MVFR AND EVENTUALLY IFR AROUND DAYBREAK TOMORROW.
AS THIS WARM FRONT LIFTS THROUGH THE REGION LATER IN THE
MORNING...CONDITIONS WILL IMPROVE BACK UP TO VFR THROUGH THE
AFTERNOON UNTIL THE SECOND WAVE OF SHOWERS AND STORMS TAKE AIM AT
THE REGION. SOME OF THESE STORMS WILL HAVE THE POTENTIAL OF
PRODUCING STRONG WINDS AND TIMING WILL HAVE TO BE ADJUSTED AS THE
CONDITIONS UNFOLD TOMORROW.
EXPECT VFR CONDITIONS THROUGH TONIGHT WITH DETERIORATING CIGS/VIS
OVERNIGHT DOWN TO MVFR/IFR. CONDITIONS WILL THEN IMPROVE LATE IN
THE MORNING AND AFTERNOON BUT THEN DROP BACK DOWN TO MVFR OR WORSE
IN THE STRONGER THUNDERSTORMS.
HALBACH
&&
.MARINE...
253 PM CDT
SOUTH SOUTHEAST WINDS WILL STRENGTHEN TONIGHT AS THE RIDGE OF HIGH
PRESSURE ACROSS THE GREAT LAKES CONTINUES TO TRACK OFF TO THE EAST.
GUSTS WILL INCREASE INTO THE 25 TO 30 KNOT RANGE LATER THIS EVENING
AND INTO EARLY WEDNESDAY MORNING AS SFC PRESSURE GRADIENT CONTINUES TO
STRENGTHEN AS A RESULT OF EASTWARD PROGRESSION/DEEPENING OF SURFACE
LOW PRESSURE ACROSS THE NORTHERN PLAINS. GUSTY SOUTH SOUTHEAST WINDS
WILL CONTINUE TOMORROW AND THEN VEER MORE SOUTH SOUTHWEST BY
WEDNESDAY EVENING AS A WARM FRONT ASSOCIATED WITH THIS SYSTEM LIFTS
NORTHWARD. WINDS WILL THEN SHIFT TO THE WEST WEDNESDAY NIGHT AS THE
COLD FRONT TRACKS THROUGH. DUE TO STRENGTH OF LOW LEVEL
INVERSION...HAVE HELD OFF ON GALE MENTION AT THIS TIME ALTHOUGH
CANNOT COMPLETELY RULE OUT GUSTS APPROACHING GALES...ESPECIALLY BY
LATE WEDNESDAY AFTERNOON/EARLY WEDNESDAY EVENING. WIND SPEEDS WILL
COME DOWN THROUGH THE DAY ON THURSDAY AS A RIDGE OF HIGH PRESSURE
BEGINS TO BUILD BACK IN. WINDS WILL BECOME SOUTH AGAIN FOR FRIDAY AS
THE RIDGE MOVES OFF TO THE EAST. IN TERMS OF THE NEARSHORE...CURRENT
SMALL CRAFT ADVISORY HEADLINES FROM 12Z WED TO 12Z THU LOOKS
REASONABLE ALTHOUGH MAY CONSIDER NUDGING UP THE BEGINNING TIME OF
THE ADVISORY TONIGHT.
MARSILI
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...7 AM WEDNESDAY TO 7 AM THURSDAY.
&&
$$
