FXUS63 KLOT 092358 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 650 PM CDT SAT MAY 9 2009 .DISCUSSION... 310 PM CDT MAIN FORECAST CONCERNS TODAY INCLUDE ISOLD SHOWER CHANCES THE NEXT COUPLE DAYS...FOLLOWED BY WARM-UP AND CONVECTIVE CHANCES ASSOCIATED WITH NEXT SIGNIFICANT SHORTWAVE ARRIVING BY MID-WEEK SURFACE LOW RESPONSIBLE FOR THIS MORNING'S 40 TO 50 MPH WINDS HAS RAPIDLY MOVED EASTWARD AND THE REMARKABLE GRADIENT HAS RELAXED ENOUGH FOR A LAKE BREEZE TO DEVELOP AND PUSH INLAND THIS AFTERNOON JUST 5 HOURS AFTER NEARLY 50 MPH WNW WINDS. NOW THAT A SURFACE RIDGE HAS BUILT IN AND IS PROGGED TO FESTER ABOUT THE REGION...WOULD EXPECT THE TYPICAL SPRINGTIME AFTERNOON LAKE BREEZES TO FORM THE NEXT COUPLE OF DAYS PROVIDING FOR LAKE COOLING. WHILE LOW...THE RAIN CHANCES THE NEXT COUPLE OF DAYS ARE NOT ZERO. FAIRLY VIGOROUS SHORTWAVE LOCATED OVER THE NORTHERN PLAINS HAS BEEN PRODUCING SOME SHOWERS THIS AFTERNOON. THIS WAVE IS PROGGED TO DE-AMPLIFY AS IT TRACKS INTO THE WESTERN GREAT LAKES REGION SUNDAY...HOWEVER SEVERAL MODELS ARE SPITTING OUT SOME LIGHT QPF. IT IS QUITE TEMPTING TO INTRODUCE SOME LIGHT SHOWER CHANCES INTO THE FORECAST FOR SUNDAY...ESPECIALLY GIVEN SREF POPS NEARING 50 PERCENT...BUT WILL HOLD MY BREATHE AND GO WITH CONTINUITY FOR NOW MAINTAINING A DRY FORECAST. NOTHING ELSE UPSTREAM SHOWING UP ON WATER VAPOR IMAGERY UPSTREAM OF THIS WAVE...THOUGH NORTHWEST FLOWS ARE NOTORIOUSLY TROUBLESOME SO RAIN CHANCES CERTAINLY NOT ZERO HEADING INTO THE START OF THE WORK WEEK. NEXT MORE SIGNIFICANT SHORTWAVE CURRENTLY OVER THE GULF OF ALASKA IS PROGGED TO TRACK ALONG THE U.S./CANADIAN BORDER EMERGING TO THE LEE OF THE ROCKIES TUESDAY NIGHT. STRONG LOW LEVEL JET WILL DEVELOP IN RESPONSE TO THE HEIGHT FALLS IN ADVANCE OF THIS SYSTEM AND DRAW INCREASING RICH THETA-E AIRMASS NORTHWARD IN ADVANCE OF THE SYSTEM. CERTAINLY THERE ARE THE USUAL TRACK/TIMING ISSUES THAT ARE COMMON THIS FAR OUT...BUT OVERALL LOOKS LIKE A PRETTY GOOD SHOT AT THUNDERSTORMS WEDNESDAY. GIVEN THE STRENGTH OF THE SYSTEM IT WILL NEED TO BE WATCHED FOR SEVERE WEATHER POTENTIAL SOMEWHERE IN THE REGION...BUT THERE'S STILL PLENTY OF TIME TO GET WORKED UP ABOUT THAT. DOESN'T APPEAR TO BE ANY SIGNIFICANT SHOT OF COLD AIR TO FOLLOW BEHIND THE MID-WEEK SYSTEM AS UPPER FLOW QUICKLY GOES ZONAL ONLY TO POSSIBLY BE FOLLOWED BY ANOTHER SYSTEM TOWARD NEXT WEEKEND. IZZI && .AVIATION...DISCUSSION REGARDING 00Z TAFS... 650 PM CDT WIND SHIFT ASSD WITH LAKE BREEZE FRONT CONTINUES TO BE A PROBLEM THIS EVENING...ESPECIALLY INVOF ORD. THIS FRONT DEVELOPED AND PUSHED INLAND DESPITE MODEST NWLY GRADIENT FLOW EARLIER THIS AFTERNOON...THEN RETREATED BACK TO THE EAST AND WEAKENED. HOWEVER...AS LARGER SCALE WNWLY FLOW HAS BEGUN TO WEAKEN HEADING INTO THE EVENING HOURS...THIS FRONT HAS ONCE AGAIN BECOME MORE PRONOUNCED AND CONTINUES TO PUSH BACK TO THE W. RADAR PLACES ITS POSITION FROM LAKE/MCHENRY COUNTY LINE...TO JUST W OF ORD...THEN SSEWD TO A POINT ABOUT 14E OF JOT TO 15 NE OF IKK. EXPECT WSWWD MOVMT TO CONTINUE THROUGH 01Z AS LARGER SCALE GRADIENT FLOW RELAXES WITH LOSS OF DAYTIME MIXING. EVENTUALLY WINDS TO GO LGT/VRBL AOB 5 KTS LATER THIS EVENING AS SFC HI PRESSURE BUILDS TOWARD MID MS VLY AND SFC COOLING RESULTS IN DECOUPLING OF WIND FLOW. WINDS TO PICK UP AGAIN FROM NW BY 15Z SUNDAY DUE TO DIURNAL HEATING...BUT ACTUAL PRESSURE GRADIENT WILL BE MUCH WEAKER SO WINDS GENLY EXPECTED TO TOP OUT AROUND 10 KTS. THE FLIPSIDE OF THIS WEAKENING GRADIENT IS THAT WE'LL LIKELY BE DEALING WITH ANOUTHER LAKE BREEZE BY MID AFTN OVR NERN IL/NWRN IN. INSTABILITY CU FIELD OF EARLIER TDY HAS LIFTED AND SCATTERED OUT AND EXPECT SKIES TO BE GENLY CLR BY 02Z. HOWEVER...WILL MAINTAIN VFR CIGS FROM EARLIER FCST...BRINGING MID LVL CLOUDINESS OVR RGN DURG OVERNIGHT/EARLY MORNING HRS. SATLT IMAGERY DOES SHOW SHORT WAVE OVR ERN DAKS ROTATING SSEWD TOWARD UPR MS VLY. SOME HI BASED CONVECTION WITH THIS AERA ATTM...BUT WITH LTL LLVL MOISTURE...EXPECT THESE TO DSIPT QUICKLY WITH SUNSET. NO VIS RESTRICTIONS EXPECTED THRU FCST PERIOD. MERZLOCK && .MARINE... 224 PM...LOW PRESSURE OVER NEW YORK WILL CONTINUE TO QUICKLY LIFT ACROSS NEW ENGLAND TONIGHT. BROAD BUT WEAK HIGH PRESSURE OVER THE NORTHERN AND CENTRAL PLAINS WILL MOVE EAST ACROSS THE LAKES AND THE OHIO VALLEY SUNDAY INTO MONDAY AS IT STRENGTHENS. BY TUESDAY... THIS HIGH WILL EXTEND FROM NEW ENGLAND TO THE SOUTHEAST U.S. AS IT CONTINUES TO SLOWLY MOVE EAST. THIS HIGH WILL ALLOW A LAKE BREEZE TO FORM ACROSS THE IL/IN NEARSHORE SUNDAY AND MONDAY AFTERNOONS. A TROUGH OF LOW PRESSURE WILL DEVELOP OVER THE PLAINS TUESDAY NIGHT INTO WEDNESDAY WITH DEEP LOW PRESSURE MOVING NORTHEAST ACROSS ONTARIO WEDNESDAY INTO WEDNESDAY NIGHT. CMS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS UNTIL 1 AM SUNDAY. && $$