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000 FXUS63 KLOT 110322 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 1022 PM CDT SUN MAY 10 2009 .DISCUSSION... 311 PM CDT MAIN FORECAST FOCUS TODAY IS WITH ESCORTING CURRENT SHORTWAVE OUT OF THE AREA THIS EVENING...FOLLOWED BY NEXT...MUCH MORE SIGNIFICANT...WAVE PROGGED TO ARRIVE MIDWEEK. CONSIDERABLE SUNSHINE THIS AFTERNOON HAS ALLOWED HIGHS TO REACH THE CONVECTIVE TEMPS...WITH RECENT ACARS SOUNDINGS FROM ORD AND SPC`S MESOANALYSIS PAGE BOTH SUGGESTING SBCAPES HAVE CLIMBED TO JUST OVER 250 J/KG WITH LITTLE TO NO INHIBITION REMAINING. THIS ALONG WITH WEAK UPPER SUPPORT AND BROAD LOW LEVEL CONVERGENCE HAS BEEN ENOUGH TO ALLOW SCT SHOWERS/ISOLD THUNDERSTORMS TO DEVELOP THIS AFTERNOON. INSTABILITY IS WEAK...HOWEVER STRONG EFFECTIVE DEEP LAYER SHEAR AND LOW FREEZING LEVELS COULD ALLOW FOR A FEW MORE SMALL HAILERS WITH THE STRONGEST UPDRAFTS. LOSS OF DAYTIME HEATING SHOULD TAKE A TOLL ON THE SHOWERS...SO EXPECT ANY RAIN TO END OVER SE CWA BY ABOUT 02Z AT THE LATEST. NEXT CONCERN FOR TONIGHT WILL BE WITH CLOUD COVER. FAIRLY LARGE AREA OF DIURNALLY ENHANCED STRATOCUMULUS COVERS MUCH OF WI AND SE MN THIS AFTERNOON. THIS CLOUDINESS WILL BEGIN DISSIPATING AFTER SUNSET...THOUGH IF LAST NIGHT IS ANY INDICATION OF WHAT IS TO COME TONIGHT THEN SOME STRATOCU COULD LINGER THROUGH THE NIGHT. THE AMOUNT OF CLOUD COVER TONIGHT WILL BE KEY TO POTENTIAL FOR SOME PATCHY FROST TO DEVELOP. CONFIDENCE IN FROST OCCURRING IS LOW GIVEN EXPECTED MARGINAL TEMPS AND POSSIBILITY OF SOME CLOUDINESS...BUT SINCE FROST IS IN THE GRIDS/FORECAST ALREADY COURSE OF LEAST REGRET IS TO PROBABLY RETAIN IT FOR NORTHERN SUBURBS WEST INTO NC IL. QUIET AND SEASONABLE CONDITIONS ARE EXPECTED MONDAY INTO TUESDAY. WHILE LAKE BREEZES ARE LIKELY BOTH DAYS...MOST SIGNIFICANT INLAND PENETRATION WILL LIKELY TAKE PLACE MONDAY SINCE GRADIENT WILL BE LIGHTEST. BY TUESDAY AFTERNOON A MORE SOUTHERLY GRADIENT WILL FAVOR MOST SIGNIFICANT INLAND PENETRATION ALONG THE NORTH SHORE AREAS. OUTSIDE OF THE LAKE COOLING...TEMPS WILL MODERATE MONDAY AND TUESDAY WITH HIGHS NEARING THE 70 DEGREE MARK INLAND BY TUESDAY AFTERNOON. WEATHER WILL TAKE A TURN FOR THE MORE INTERESTING COME TUESDAY NIGHT INTO WEDNESDAY AS THE POWERFUL UPPER LOW OFF THE BRITISH COLUMBIA COAST OPENS UP INTO AN OPEN...ALBEIT SHARP...UPPER TROUGH WHILE TRACKING QUICKLY EASTWARD ACROSS THE NORTHERN TIER OF STATES. MOIST AIRMASS FESTERING ABOUT ALONG THE GULF STATES SHOULD BE DRAWN RAPIDLY NORTHWARD BY 50KT+ LOW LEVEL JET IN ADVANCE OF THIS SYSTEM. WOULD BE ABSURD TO START GETTING BOGGED DOWN IN TALKING ABOUT DETAILS OF A CONVECTIVE EVENT THIS FAR OUT...HAVING SAID THE OVERALL SYNOPTIC SET-UP IS CERTAINLY LOOKING INTERESTING FOR A POTENTIAL SEVERE WEATHER EVENT EITHER HERE OR NEARBY WEDNESDAY AFTERNOON/EVENING. SHOULD SEE A QUICK SHOT OF COOLER/DRIER CONDITIONS THURSDAY AND POSSIBLY INTO FRIDAY...BEFORE NEXT WAVE ARRIVES BY NEXT WEEKEND. MUCH MORE UNCERTAINTY WITH THE DETAILS OF THIS SYSTEM...SO JUST GOING TO RUN WITH CHANCE POPS THROUGH THE WEEKEND. DETAILS WILL UNDOUBTEDLY BECOME CLEARER WITH TIME... IZZI && .AVIATION... 0600 UTC TAFS...GLOB OF SC OVER SRN WI HAS BEEN ERODING SLOWLY ALTHO SOME SWD PROGRESS HAS BEEN EVIDENT VIA SATL PIX. THIS SWD ADVANCE BEING OFFSET BY DISSIPATING NEAR THE WI BORDER. WILL LEAVE MENTION OF 5K SC AT RFD BUT NOT TAKE IT INTO A CEILING. THIS STILL A POSSIBILITY HOWEVER. OTHERWISE...WEST TO EAST STREAMING AC/CI IN UPPER LVL CONVERGENCE ZONE FROM THE CENTRAL PLAINS THROUGH ILLINOIS WILL SLOWLY DROP SOUTH OVERNIGHT AND LEAVE CLEAR SKIES AT TERMINALS BY MORNING. LOOKS LIKE ANTICYCLONIC FLOW PREVAILS UNDER SFC HIGH PRESSURE ON MONDAY. MAY BE A FEW CU NEAR 5K CONSIDERING A CONVECTIVE TEMP OF 60 WHILE FORECASTING HIGHS IN THE LOW TO MID 60S. WITH LIGHT NORTHERLY WIND FIELD ON MONDAY...CAN EXPECT ANOTHER EARLY TO MID AFTN LAKE BREEZE TO KICK IN AND SHIFT WINDS TO THE EAST. AGAIN THESE WILL DROP OFF NEAR SUNSET TO LIGHT AND VARIABLE. HAS BEEN DRYING LAST COUPLE OF DAYS AND SEE NO PROSPECT FOR DENSE FOG FORMATION TONIGHT OR MONDAY NIGHT. BUT SINCE IT WILL BE RADIATING VERY WELL OVERNIGHT...WOULD NOT BE SURPRISED TO SEE SOME MORNING GROUND FOG IN FIELDS THAT LIFT BRIEFLY TO LOWER MORNING VSBY DOWN TO 4 OR 5 MILES. RLB && .MARINE... 210 PM...A WEAK AREA OF LOW PRESSURE OVER SOUTHERN LAKE MICHIGAN THIS AFTERNOON WILL MOVE SOUTHEAST ACROSS NORTHERN INDIANA AND OHIO TONIGHT. A LARGE AREA OF HIGH PRESSURE OVER SOUTHERN CANADA AND THE PLAINS WILL MOVE EAST ACROSS THE LAKES REGION AND THE OHIO VALLEY TONIGHT THROUGH MONDAY NIGHT...REACHING THE ATLANTIC COAST BY WEDNESDAY MORNING. LOW PRESSURE WILL MOVE EAST ACROSS SOUTHERN CANADA TUESDAY NIGHT REACHING JAMES BAY BY THURSDAY MORNING. A TRAILING FRONT/TROUGH OF LOW PRESSURE FROM THIS LOW WILL MOVE EAST ACROSS LAKE MICHIGAN WEDNESDAY EVENING. AHEAD OF THIS FRONT...THE GRADIENT WILL TIGHTEN WITH SOUTHERLY WINDS INCREASING TO 15-25KTS WITH SOME HIGHER GUSTS POSSIBLE. WINDS TURN WESTERLY AND DIMINISH SOME BEHIND THE FRONT. CMS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
