000 FXUS63 KILX 181552 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 1045 AM CDT WED APR 18 2007 .DISCUSSION... UPDATED THE FORECAST FOR MORE SUNSHINE LATE THIS MORNING...THEN INCREASING CLOUDS THIS AFTERNOON...ESPECIALLY NE AREAS WHERE SMALL CHANCES OF SHOWERS. BUMPED UP HIGHS A FEW DEGREES IN SE IL INTO THE LOWER 60S WITH UPPER 50S OVER CENTRAL IL. NNE BREEZES 10 TO 20 MPH AND GUSTS IN THE 20S TO ADD A CHILL TO THE AIR. A MUCH COOLER DAY THAN YESTERDAY AFTERNOON TEMPS IN THE 70S. 15Z/10 AM SURFACE MAP SHOWS 1007 MB LOW PRESSURE OVER SOUTHERN INDIANA NORTH OF LOUISVILLE WITH ITS COLD FRONT SOUTH OF IL OVER NW PARTS OF KY/TN. ITS CLOUDS HAVE SHIFTED JUST SE OF LAWRENCEVILLE BUT MORE LOW STRATOCUMULUS CLOUDS OVER THE GREAT LAKES INCLUDING NORTHERN IL CIRCULATING AROUND 546 DM 500 MB CUTOFF LOW DEEPENING SOUTHWARD FROM SOUTHERN LAKE MI TO THE NORTHERN IL/IN BORDER. NNE WINDS 9 TO 17 MPH AND GUSTS OF 17 TO 24 MPH USHERED IN MUCH COOLER AIR DESPITE AMPLE SUNSHINE THIS MORNING. TEMPS IN THE UPPER 40S TO MID 50S. RUC AND WRF TAKE STRONG CUTOFF LOW AND ASSOCIATED SHORT WAVE SOUTH ALONG THE IL/IN BORDER THIS AFTERNOON/EVENING KEEPING ITS QPF EAST OF IL OVER INDIANA. BUT THINK CLOSE ENOUGH TO KEEP 20/30 CHANCE OF SHOWERS FROM BLOOMINGTON TO EFFINGHAM EAST. HIGHER LOW LEVEL RH IN NE IL SPREADS SW INTO CENTRAL IL THIS AFTERNOON WHERE SKIES BECOME MOSTLY CLOUDY FROM I-74 NE...WHILE SUNNY SKIES BECOME PARTLY SUNNY SW DURING THIS AFTERNOON. HIGHS IN THE LOWER 60S IN SE IL AND FROM SPRINGFIELD SW WITH UPPER 50S NE AREAS. SO A BIT BELOW NORMAL HIGHS IN THE MID 60S CENTRAL IL AND UPPER 60S SE IL. BREEZY NNE WINDS 10 TO 20 MPH WITHS GUSTS IN THE 20S AND STRONGEST AROUND CHAMPAIGN. && .PREV DISCUSSION... MAIN FORECAST CONCERNS IN THE SHORT TERM INVOLVE CLOUD COVER AND TEMPERATURES TODAY... AS WELL AS LOW CHANCE POPS ACROSS THE EAST. SHORT-TERM...TODAY THROUGH FRIDAY... SHORTWAVE TROUGH IS DROPPING SOUTHWARD FROM THE GREAT LAKES THIS MORNING... AND IS EXPECTED TO INTERACT AND EVENTUALLY PHASE WITH WITH AN UPPER LOW MOVING ACROSS THE OHIO VALLEY TODAY. DYNAMICS WITH THE GREAT LAKES SHORTWAVE ARE ACTUALLY PRETTY DECENT. NAM GUIDANCE FROM A FEW DAYS AGO TURNED OUT TO BE THE BETTER MODEL... AS NORTHERN WAVE IS RATHER SHARPLY AMPLIFIED... AND THE OLD SOUTHWESTERN CUTOFF HAS MANAGED TO TRAVEL FAIRLY FAR EASTWARD AND NORTHWARD INTO THE RIDGING ACROSS THE MIDWEST. 00Z ILX AND DVN SOUNDINGS... AND NAM/RUC/GFS FORECAST SOUNDINGS THROUGH 18Z... INDICATE A DESPERATE LACK OF MOISTURE BOTH AT THE SFC AND ALOFT THROUGHOUT OUR AREA. COOLER/MOISTER AIR COMES IN LATER THIS AFTERNOON... BUT IT IS BEHIND THE SHORTWAVE... AND COMES IN AFTER THE STRONGEST DYNAMICS FOR LIFT/VORTICITY ADVECTION HAS ALREADY PASSED THROUGH. STILL... EXPECT WIDESPREAD CLOUD COVER TO DEVELOP ACROSS THE EASTERN HALF OF THE CWA THIS AFTERNOON... ESPECIALLY AS THE COLD POOL ALOFT MOVES INTO THE PICTURE. HIGH CLOUDS FROM THE SOUTHERN SYSTEM THAT MOVED IN YESTERDAY AFTERNOON ARE BEGINNING TO PUSH SOUTHWARD... AIDED BY PUSH OF DRIER/SUBSIDENT AIR AHEAD OF THE NORTHERN SHORTWAVE. SO DO NOT EXPECT HIGH CLOUD COVER TO PLAY MUCH OF A ROLE IN SFC HEATING AND SUBSEQUENT STEEPENING OF LAPSE RATES ACROSS THE EAST. NE TO NNE LOW LEVEL FLOW WILL CONTINUE TO FLOW ACROSS THE GREAT LAKES... INTO THE AREA. AS EXPECTED... THE COLD FRONT THAT MOVED THROUGH YESTERDAY ENDED UP BECOMING ENHANCED BY THE LAKE... BUT THE LACK OF UPPER DYNAMICS AND BONE DRY ATMOSPHERE PREVENTED ANY ISOLATED PRECIP FROM DEVELOPING. FLOW OFF THE LAKE WILL CONTINUE TO PROMOTE COOLER TEMPS AND PROBABLY LOWER CEILINGS THIS AFTERNOON IN THE NORTHEASTERN CWA. MODELS INDICATE THAT CLOUD COVER THAT DOES DEVELOP MAY TEND TO STICK AROUND TONIGHT AND EVEN INTO THURSDAY AS SHALLOW MOIST LAYER BECOMES TRAPPED UNDER STRENGTHENING SUBSIDENCE INVERSION BEHIND OUR SHORTWAVE. LOW LEVEL FLOW WILL CONTINUE TO BE NORTHEASTERLY... AND IT NORMALLY TAKES A GOOD WIND SHIFT IN THE LOW LEVELS TO SCOUR OUT SHALLOW CLOUD LAYERS... AND THIS PROBABLY WILL NOT ARRIVE UNTIL THURSDAY AFTERNOON. LONG-TERM...SATURDAY THROUGH TUESDAY... UPPER RIDGING WILL BUILD BACK IN ACROSS THE REGION FRIDAY... BRINGING WITH IT A RETURN TO NORMAL AND ABOVE NORMAL TEMPS. BIG QUESTION CONTINUES TO BE THE TIMING OF THE BREAKDOWN OF THE OMEGA BLOCK/HIGH PRESSURE RIDGE ACROSS THE CENTRAL CONUS. WATER VAPOR IMAGERY THIS MORNING SHOWS DEEP TROUGHING JUST OFF THE WEST COAST... AND A MULTITUDE OF UPSTREAM SYSTEMS OVER THE NORTH PACIFIC. THE LONG PROMISED PATTERN SHIFT LOOKS LIKELY TO OCCUR... THE EXACT TIMING KEEPS LOOKING A LITTLE SLOWER. INITIAL SHORTWAVE WILL TAKE THE FIRST CRACK AT THE RIDGE FRIDAY... BUT WILL REMAIN WELL TO OUR WEST AND NORTH. SECOND WAVE WAS EXPECTED TO MOVE ACROSS THE PLAINS AND INTO THE MIDWEST LATE SUNDAY. HOWEVER... THE ECMWF/UKMET/CMC GEM/GFS ENSEMBLES HAVE KEPT TRENDING A LITTLE SLOWER... AND LITTLE FARTHER NORTH AND WEST WITH THIS SECOND WAVE WITH EACH SUCCESSIVE RUN... WHILE TRYING TO MAINTAIN AND BOLSTER RIDGING ACROSS THE EASTERN THIRD OF THE NATION. THE OP GFS CONTINUES TO BE FARTHER EAST AND WEAKER WITH THE RIDGE... BUT IT IS TRENDING SLOWER AS WELL... AND USUALLY PLAYS CATCH-UP WHEN OTHER GUIDANCE IS SO STRONGLY IN FAVOR OF A DIFFERING SOLUTION. THUS... EFFECTS OF THIS SYSTEM MAY HOLD OFF UNTIL LATE SUNDAY... WITH THE BULK OF THE DYNAMICS... AND BEST POTENTIAL FOR SEVERE WX POSSIBLY PASSING OFF JUST TO OUR WEST. STILL TOO EARLY TO CALL SUCH DETAILS THIS FAR OUT. HAVE CARVED SUNDAY POPS FARTHER WEST... WITH SOME COLLABORATIVE COMPROMISES... AND REDUCED THE EASTWARD EXTENT OF 40 POPS ON SUNDAY NIGHT... WITH 30 POPS EAST OF I-55. LONGER RANGE GUIDANCE SUGGESTS THAT OVERALL PATTERN CHANGE... WILL CONTINUE TO DELIVER PERIODIC DISTURBANCES TO THE CENTRAL CONUS... WITH EACH ONE PROGRESSING FARTHER SOUTH AND EAST. AFTER THE SUNDAY/MONDAY WAVE... THE NEXT WAVE LOOKS TO APPROACH THE MIDWEST AROUND THURSDAY. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ HUETTL/HARDIMAN