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Forecast from NOAA-NWS for Peotone IL. |
000 FXUS63 KLOT 100533 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 1133 PM CST TUE MAR 9 2010 .DISCUSSION... 331 PM CST A PLETHORA OF POTENTIAL PROBLEMS TO PONDER PROGNOSTICATING THE WEATHER OVER THE NEXT SEVERAL DAYS. ISSUES INCLUDE DENSE FOG POTENTIAL...TEMPS IN WAKE OF WARM FROPA TOMORROW...THUNDERSTORM POTENTIAL AND JUST TO KEEP THINGS INTERESTING POTENTIAL FOR HYDROLOGIC PROBLEMS. FORCING AND SHOWERS ASSOCIATED WITH THE FIRST SPOKE OF VORTICITY WRAPPING AROUND THE MASSIVE ATMOSPHERIC GYRE OVER THE MID-SECTION OF THE NATION SHOULD CLEAR THE CWA BY 00Z. IN WAKE OF SPOKE 1 LOOK FOR MUCH OF TONIGHT TO BE DRY WITH CONCERN TURNING TO POTENTIAL FOR FOG RE-DEVELOPMENT AS NOCTURNAL COOLING ALLOWS BOUNDARY LAYER TO APPROACH SATURATION AGAIN. FOG POTENTIAL APPEARS TO BE GREATEST NEAR THE LAKE AS 40F+ DEWPOINTS ARE ADVECTED OVER THE STILL CHILLY LAKE. AWAY FROM THE LAKE ITS POSSIBLE THERE COULD BE ENOUGH WIND/MIXING TO RESULT IN LOW STRATUS VS FOG...BUT WILL BE A CLOSE CALL AND HAVE INCLUDED FOG IN THE GRIDS CWA-WIDE BUT HIT IT HARDEST NEAR THE LAKE. WILL ALLOW LATER SHIFTS ISSUE ANY HEADLINES AS IS OFTEN THE CASE WITH FOG CONFIDENCE ISNT ALL THAT HIGH. NEXT VORT TO AFFECT THE AREA SHOWS UP NICELY ON WATER VAPOR IMAGERY OVER MISSOURI THIS AFTERNOON AND WILL ARRIVE IN OUR CWA LATER TONIGHT INTO WEDNESDAY MORNING WITH MORE SHOWERS. RELATIVELY WEAK MID LEVEL LAPSE RATES AND ONLY MODEST THETA-E ADVECTION SHOULD RESULT IN MINIMAL DESTABILIZATION AND HAVE OPTED TO PULL MENTION OF THUNDER OUT OF THE GRIDS FOR LATE TONIGHT/WEDNESDAY MORNING. MODELS IN GOOD AGREEMENT ON LIFTING WARM FRONT NORTH ACROSS THE CWA WEDNESDAY AS SURFACE LOW ASSOCIATED WITH THIS SHORTWAVE LIFTS NORTH INTO IOWA WITH STRONG PRESSURE FALLS OVER THE UPPER GREAT LAKES. WOULD EXPECT CEILINGS TO LIFT ABRUPTLY WITH WARM FROPA AND EVEN SOME PARTIAL SUNSHINE BY WEDNESDAY AFTERNOON. HAVE BUMPED UP TEMPS TOMORROW WITH MOST AREAS HAVING A GOOD SHOT AT HITTING 60 WITH SOUTHERN CWA LIKELY CLIMBING WELL INTO THE 60S. BIG EXCEPTION MAY END UP BEING NEAR THE LAKE FROM THE LOOP NORTH TO THE WI LINE WHERE A SOUTHEASTERLY COMPONENT TO THE FLOW WILL LIKELY RESULT IN MUCH COOLER CONDITIONS THERE WITH FOG AND STRATUS LIKELY SLOWER TO CLEAR OUT. FIRST SFC LOW PROGGED TO FILL OVER SOUTHERN MINNESOTA WEDNESDAY NIGHT WITH A NEW SURFACE LOW DEVELOPING OVER THE SOUTHERN PLAINS. THIS WILL RESULT IN WARM FRONTOGENESIS TAKING PLACE SOUTH OF THE CWA WITH A MORE DEFINITIVELY EASTERLY SYNOPTIC FLOW DEVELOPING WED NIGHT RESULTING IN COOLER LAKE AIR SPREADING FARTHER INLAND. ALSO WOULD SUSPECT THAT THERE COULD BE SOME MORE PROBLEMS WITH DENSE FOG AS COOL MARINE LAYER DISPLACES AIRMASS WITH DEWPOINTS IN UPPER 40S/NEAR 50F WEDNESDAY NIGHT INTO THURSDAY MORNING. WARM FRONT THEN PROGGED TO BEGIN MAKING NORTHWARD PROGRESS DURING THE DAY THURSDAY AS POWERFUL SHORTWAVE WITH CLOSED CIRCULATION ESSENTIALLY FUJIWARAS AROUND THE FIRST UPPER LOW. EXPECT WELL DEVELOPED WARM CONVEYOR BELT OF RAIN AND POSSIBLY A THUNDERSTORM OR TWO TO LIFT NORTHWARD ACROSS THE CWA THURSDAY MORNING ENDING FROM THE SOUTH THURSDAY AFTERNOON. THIS WILL LIKELY BE THE PERIOD WITH THE MOST SIGNIFICANT RAINFALL AND MOST LIKELY TO RESULT IN HYDROLOGIC PROBLEMS ON SOME OF THE LARGER RIVERS IN THE CWA. IN THE WAKE OF THIS BATCH OF PRECIPITATION SOME MODELS ARE SUGGESTING THAT A NARROW TONGUE OF SURFACE BASED INSTABILITY WILL DEVELOP AHEAD OF ADVANCING SURFACE FRONT. WRF-NAM HAS TONGUE OF SBCAPES OF 500-1000 J/KG NOSING UP INTO OUR SOUTHERN CWA BY LATE THURS PM WITH SLIGHTLY WEAKER BUT STILL SUFFICIENT SBCAPE PROGGED BY THE WRF-ARW RUN AT WFO LSX. SHOULD THERE BE SOME CLEARING AND THIS INSTABILITY ACTUALLY DEVELOP AS PROGGED THEN THE POTENTIAL WOULD EXIST FOR LOW TOPPED CONVECTION TO DEVELOP ALONG THE FRONT THURS AFTERNOON INTO THURSDAY EVENING. GIVEN EXPECTED LOW TOPPED NATURE OF ANY CONVECTION THAT DOES GET GOING THINK THE SEVERE HAIL/WIND THREAT WILL BE EXTREMELY LOW...HOWEVER A VERY SMALL CONDITIONAL TORNADO THREAT CANNOT BE RULED OUT AT THIS DISTANCE. RELUCTANT TO EVEN MENTION THIS THREAT BUT WITH SWODY3 ALREADY PLACING OUR SOUTHERN CWA IN 5% RISK FIGURE IT WAS WORTHY OF AN AFD PARAGRAPH. LARGE UPPER LOW IS THEN EXPECTED TO WOBBLE SLOWLY EASTWARD WITH SHOWER CHANCES LINGERING INTO AT LEAST THE FIRST PART OF THE WEEKEND. UPPER LOW SHOULD FINALLY DEPART BY EARLY NEXT WEEK WITH MEDIUM RANGE MODELS NOT IN ALL THAT GREAT OF AGREEMENT ON THE EXTENT OF THE COOL DOWN PROGGED TO TAKE PLACE. FOR NOW HAVE STUCK CLOSE TO HPC NUMBERS FOR TEMPS OVER THE WEEKEND INTO EARLY NEXT WEEK WITH SOME MINOR DOWNWARD ADJUSTMENTS NEAR THE LAKE. IZZI && .AVIATION... 0600 UTC TAFS...MAIN FORECAST CHALLENGES ARE WITH CEILINGS AND THE POTENTIAL FOR LOW VISIBILITIES. EXTENSIVE AREA OF CLOUDS CONTINUES TO WRAP AROUND UPPER LEVEL SYSTEM CIRCULATING ACROSS THE CENTRAL PLAINS. LATEST SATELLITE IMAGERY INDICATING THAT WITHIN THIS FLOW...SEVERAL MID LEVEL WAVES CAN BE SEEN PROPAGATING NORTH AROUND THIS SYSTEM. THIS IS HELPING TO PROVIDE SOME SCATTERED LIGHT RAIN ACROSS THE TERMINAL. WHAT HAS NOT DEVELOPED TONIGHT ARE THE LOW CEILINGS AND DENSE FOG...WHICH WAS EARLIER THOUGHT TO HAVE OCCURRED ALREADY. THE AMOUNT OF CLOUD COVER ACROSS THE AREA HAS HELPED KEEP RADIATIONAL FOG DEVELOPMENT DOWN DESPITE INCREASING LOW LEVEL MOISTURE. DO THINK THAT THIS LOW VIS AND LOWER CEILINGS WILL OCCUR...BUT MORE TOWARDS THE MORNING HOURS WITH THE APPROACH OF THE WARM FRONT. AS THIS TIME APPROACHES CEILINGS WILL BE TRENDING FROM THE OBSERVED VFR CEILINGS TO MVFR...THEN LOW END MVFR. WITH GUIDANCE HINTING AT STAYING WITHIN MVFR CONDITIONS...HAV DECIDED TO LEAVE OUT THE IFR CEILINGS. ALSO...HAVE PULLED OUT ANY MENTION OF RAIN BEYOND THE IMMEDIATE TIMEFRAME. LATEST TRENDS WOULD SUGGEST THAT UPPER LEVEL SYSTEM WOULD STAY MORE TO THE WEST WITH THESE MID LEVEL WAVES AND STRONGER FORCING ALSO STAYING TO THE WEST. WITH THAT...BESIDES RFD...HAVE PULLED THE RAIN THINKING THAT IF IT DID HAPPEN IT WOULD NOT BE ANYTHING PREVAILING. WITH WARM FRON LIFTING NORTH ACROSS THE TERMINALS BY LATE MORNING...EAST/SOUTHEAST WINDS WILL CONTINUE TO VEER TO THE SOUTH WITH CONDITIONS ALSO IMPROVING DURING THIS TIME FRAME. RODRIGUEZ && .MARINE... 1139 AM CST A RIDGE OF HIGH PRESSURE EXTENDS FROM LAKE SUPERIOR...SOUTHEAST ACROSS THE LOWER LAKES. THIS RIDGE WILL CONTINUE TO DRIFT SOUTHEASTWARD ACROSS THE MID ATLANTIC STATES TONIGHT...WHILE A LOW PRESSURE OVER SOUTH CENTRAL KANSAS LIFTS NORTHEAST INTO IOWA BY MIDDAY WEDNESDAY...AND SLOWLY WEAKENS. ANOTHER LOW IS THEN FORECAST TO DEVELOP ACROSS OKLAHOMA WEDNESDAY NIGHT WHILE THE IOWA LOW CONTINUES TO DISSIPATE. THIS NEW LOW WILL DEEPEN AS IT MOVES TO NORTHEAST MISSOURI BY LATE THURSDAY. THE LOW WILL THEN DRIFT EASTWARD ACROSS ILLINOIS AND INTO INDIANA ON FRIDAY. THIS SCENARIO WILL MAINTAIN A GENERAL EASTERLY AIR FLOW ACROSS LAKE MICHIGAN THROUGH WEDNESDAY NIGHT. A STRONGER NORTHEASTERLY FLOW IS FORECAST TO DEVELOP LATE FRIDAY INTO SATURDAY AS THE LOW CENTER PASSES SOUTH OF THE GREAT LAKES. MERZLOCK && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ |