Area Forecast Discussion
Issued by NWS Northern Indiana

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000 FXUS63 KIWX 282321 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 721 PM EDT THU AUG 28 2014 .SYNOPSIS... ISSUED AT 331 PM EDT THU AUG 28 2014 THERE IS A CHANCE FOR SHOWERS AND THUNDERSTORMS OVERNIGHT ACROSS NORTHWEST INDIANA AND SOUTHWEST LOWER MICHIGAN AS AN UPPER LEVEL DISTURBANCE MOVES THROUGH. A WARM FRONT WILL LIFT NORTH THROUGH THE REGION ON FRIDAY WITH A CHANCES FOR SHOWERS AND THUNDERSTORMS...ESECIALLY BY LATE AFTERNOON. LOW TEMPERATURES TONIGHT WILL RANGE FROM THE UPPER 50S IN NORTHWEST OHIO TO THE MIDDLE 60S ALONG THE OHIO RIVER. HIGH TEMPERATURES ON FRIDAY WILL RANGE FROM THE LOWER 80S IN SOUTHERN MICHIGAN TO THE UPPER 80S NEAR THE OHIO RIVER. && .UPDATE... ISSUED AT 707 PM EDT THU AUG 28 2014 CONVECTION HAS DEVELOPED UPSTREAM AND MOVING INTO NORTH CENTRAL ILLINOIS THIS EVENING ALONG THETA E SURGE AND NOSE OF WEAK 20 KNOT LOW LEVEL JET WITH WEAK SHORT WAVE. THETA E ADVECTION MOVES THROUGH THE AREA OVERNIGHT WITH NOSE OF THIS WEAK LLJ FOCUSED ACROSS THE NORTHWEST ON WESTERN PERIPHERY OF MID LEVEL RIDGE. LOW LEVEL EASTERLY DRY FLOW TO HELP ERODE SOME OF THIS CONVECTION BUT CONCERN SOME ELEVATED SHRA/TSRA COULD RIDE WITH THE MOISTURE ADVECTION AND MAKE IT INTO PARTS OF THE WEST AND NORTHWEST CWA. HAVE ADDED LOW CHANCE POPS FOR NOW TO A LINE ROUGHLY WEST OF LOGANSPORT TO COLDWATER AND WILL MONITOR TRENDS NEXT FEW HOURS FOR POSSIBLE UPTICK IN POPS LATER THIS EVENING. && .SHORT TERM...(THIS EVENING THROUGH FRIDAY) ISSUED AT 331 PM EDT THU AUG 28 2014 SFC RIDGE DRAPED THROUGH THE ERN LAKES THIS AFTN WILL GIVE WAY TO LOW PRES ADVG NEWD THROUGH THE PLAINS. AT THE SFC OLD FNTL BNDRY DRAPED THROUGH THE MID MS VALLEY WILL MIX RAPIDLY NWD ON FRI AS PARENT SW TROUGH LIFTS OUT INTO WRN WI BY EVENING. 12Z MODEL GUIDANCE SIMILAR ALOFT YET GENERALLY SLWR W/DEEMED ADEQUATE LL MSTR FLUX AND HAVE DAMPENED BOTH POP/WX EXTENT DURING THE DAY AS MOST FVRBL THETA-E SURGE ALG NOSE OF NWD INTENSIFYING LLJ DVLPS TWD 00Z. OTRWS TEMPS WILL MODERATE CONSIDERABLY VS THIS AFTN YET KEPT W/A SPLIT BASED MOS BLEND IN LIGHT OF COPIOUS MID-HIGH CLD SHIELD UPSTREAM RETARDING A MORE SIG DIURNAL AND SUSPECT THIS MAY BE THE CASE HERE ON FRI ESP W/SFC TRAJECTORIES REMAINING MORE SELY THROUGH THE DAY. && .LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY) ISSUED AT 331 PM EDT THU AUG 28 2014 ...MAIN CONCERNS FOR THE LONG TERM ARE HEAVY RAIN THIS WEEKEND AND THE POTENTIAL FOR SEVERE WEATHER FOR THE START OF THE WORK WEEK... QUITE AN ACTIVE START TO THE LONG TERM PERIOD...WITH SEVERAL LOW PRESSURE SYSTEMS FORECAST TO PASS NEAR THE CWA... THE FIRST SFC LOW PRESSURE SYSTEM TO IMPACT THE CWA DEVELOPS OVER WI/MN/IA IN RESPONSE TO SEVERAL PERTURBATIONS DEEPENING THE EXISTING 500MB TROUGH FRIDAY NIGHT. BY SUNDAY MORNING...THE LOW WILL REACH LAKE HURON AND SOUTHERN ONTARIO...WITH THE UPPER LEVEL TROUGH OVER LOWER MI. THE PRIMARY FORCING ASSOCIATED WITH THE SHORTWAVE WILL REMAIN NORTH OF THE AREA...WITH A MAXIMUM IN 850-500MB QVECTOR CONVERGENCE FOCUSED OVER NORTHERN LOWER MI/EASTERN UPPER MI. HOWEVER...WITH HIGH PRESSURE CENTERED OVER THE ATLANTIC PUMPING MOISTURE/WARMER AIR FROM THE GULF INTO THE REGION THE COLD FRONT ASSOCIATED WITH THE APPROACHING LOW PRESSURE SYSTEM STALLS OVER ILLINOIS/LOWER MI SATURDAY AFTERNOON AND SAT NIGHT. PWATS OVER THE CWA INCREASE TO 1.5 TO 2 INCHES AND MOISTURE CONVERGENCE IS MAXIMIZED DURING THIS TIME FRAME. AS A RESULT...KEPT GOING HIGH POPS ACROSS MUCH OF THE CWA. STILL FEELING CONFIDENT IN THE POTENTIAL FOR HEAVY RAIN GIVEN WARM CLOUD LAYER DEPTHS OF 12-14KFT AND ROUGHLY FRONT PARALLEL FLOW. 0-6 KM SHEAR IS NOT ALL THAT IMPRESSIVE EITHER...THOUGH IT HAS INCREASED FROM PREVIOUS MODEL RUNS TO ROUGHLY 15 TO 25 KNOTS ACROSS THE CWA. KEPT THUNDER IN FOR SATURDAY AFTERNOON/SUNDAY GIVEN MUCAPE OF 1000-2000 J/KG. WITH INCREASED MOISTURE...DEWPOINTS FOR THE WEEKEND CLIMB INTO THE UPPER 60S/LOW 70S. WITH HIGH TEMPERATURES IN THE LOW 80S...IT WILL BE QUITE HUMID. PRECIPITATION CHANCES DWINDLE SUNDAY/SUNDAY NIGHT FROM NW TO SE AS A RIDGE ALOFT FILTERS INTO THE AREA FOR A BRIEF TIME. ATTENTION THEN TURNS TO THE START OF THE WORK WEEK...WHEN A SLIGHTLY DEEPER AND MORE NEGATIVELY TILTED TROUGH SWINGS INTO THE MN/WI/IA AREA. WITH HIGH PRESSURE STILL HOLDING FIRMLY OVER THE ATLANTIC AND THE APPROACHING TROUGH/DEVELOPING SURFACE LOW SITUATED IN THE MID WEST STATES MOISTURE IS ONCE AGAIN EASILY TRANSPORTED INTO THE GREAT LAKES. PWATS MONDAY GENERALLY BUMP UP TOWARDS 1.5-1.8 INCHES ACROSS MUCH OF THE IN/SOUTHERN MI/WESTERN OH REGION. THE PATH OF THE DEVELOPING SURFACE LOW/UL TROUGH IS IMPACTED BY THE EXITING SURFACE HIGH/RIDGE HOWEVER...MOVING IT FURTHER NORTH THAN THIS WEEKENDS LOW TRACK. IT LIFTS NORTHEASTWARD FROM THE WI/MN/IA AREA MONDAY MORNING...INTO UPPER MI MONDAY AFTERNOON...AND JAMES BAY LATE MONDAY NIGHT. THIS PUTS THE FORECAST AREA UNDER GENERALLY ZONAL FLOW ALOFT SUSCEPTIBLE TO SMALL PERTURBATIONS. AT THE SURFACE...WE DEAL WITH THE PASSAGE OF A COLD FRONT. WHETHER OR NOT SEVERE WEATHER DEVELOPS IN RESPONSE TO THE PASSING SYSTEM WILL DEPEND ON THE TIMING OF THE FRONT AND WHETHER OR NOT THE HIGHER INSTABILITY/SHEAR MATERIALIZES. MODELS DISAGREE SLIGHTLY ON THE TIMING...WITH THE GFS BRINGING THE FRONT INTO IL/LAKE MI BY 18Z MON. THE ECMWF IS A BIT SLOWER...BRINGING IT INTO THE SAME AREA BY 00Z TUE. IF THE FRONT ARRIVES DURING PEAK HEATING...THINK SOME STORMS COULD BECOME SEVERE. GIVEN ABUNDANT MOISTURE AND MODERATE INSTABILITY OF AROUND 1500-2500 J/KG. THE MODELS HAVE BACKED OFF ON THE HIGHER SHEAR VALUES FORECASTED YESTERDAY...WITH A MAXIMUM OF 30-35 KNOTS. 0-3 KM SRH VALUES REACH AROUND 150-170 M2/S2...SO WE WOULD BE LOOKING AT ORGANIZED MULTICELLS. IF INSTABILITY IS HIGHER THAN FORECAST WHEN SHEAR IS AT A MAXIMUM AND FRONT IS APPROACHING WOULD NOT BE SURPRISED TO SEE A FEW SUPERCELLS DEVELOP. MODELS BEGIN TO DISAGREE MORE SIGNIFICANTLY FOR THE MID-LATTER PORTIONS OF THE WORK WEEK. WITH HIGH PRESSURE TO THE SOUTHEAST STILL IN PLACE...THE COLD FRONT RESPONSIBLE FOR BUSY WEATHER MONDAY/MONDAY NIGHT STALLS OUT. GFS/ECWMF DISAGREE WITH THE LOCATION OF THE STALLED FRONT...AND HENCE THE PRECIPITATION. THE GFS KEEPS THE FRONT OVER THE CWA...AND THE ECMWF KEEPS IT FURTHER SOUTH...ONLY BRUSHING THE SOUTHERN FRINGES OF THE CWA. WILL KEEP SLIGHT CHC/CHC POPS FOR TUESDAY AND WEDNESDAY NIGHT...WITH WEAK HIGH PRESSURE SLIDING INTO THE AREA. THURSDAY INTO FRIDAY ANOTHER LOW PRESSURE SYSTEM WILL DEVELOP OVER THE CENTRAL AND NORTHERN PLAINS...BRINGING ADDITIONAL CHANCES FOR SHOWERS/TSTORMS TO THE AREA. KEPT CONSENSUS POPS FOR NOW GIVEN UNCERTAINTY. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING) ISSUED AT 707 PM EDT THU AUG 28 2014 MOISTURE ADVECTION UPSTREAM AND A WEAK UPPER LEVEL DISTURBANCE HAS SPAWNED A SMALL COMPLEX OF SHOWERS AND THUNDERSTORMS NOT HANDLED WELL BY HIRES GUIDANCE. EXTRAPOLATION SUGGEST SOME OF THIS ACTIVITY COULD GET INTO KSBN LATER THIS EVENING BUT IT WILL BE ENCOUNTERING DRIER LOW LEVEL AIR AND LOSS OF ANY CONTRIBUTION FROM DAYTIME HEATING. HOWEVER...WEAK LOW LEVEL JET OF 20KTS IS FOCUSED INTO NW INDIANA AND THIS MAY ALLOW SOME PCPN TO MAKE IT. FOR NOW WILL ADD A VCTS BUT HOLD OFF ON ANY FURTHER RESTRICTIONS FOR A FEW HOURS AS WE MONITOR TRENDS WITH LOSS OF HEATING AND EASTWARD PROGRESSION. KFWA LOOKS TO BE FAR ENOUGH EAST WITHIN DRIER LOW LEVEL AIR SO VFR PLANNED THERE. VFR FRIDAY MORNING WITH INCREASING CHANCES FOR CONVECTION IN AFTERNOON. CONFIDENCE AND COVERAGE TOO LOW FOR ANY POINT MENTION NOW IN THE LATER PORTIONS OF TAF. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ UPDATE...LASHLEY SYNOPSIS...T SHORT TERM...T LONG TERM...MCD AVIATION...LASHLEY VISIT US AT WWW.WEATHER.GOV/IWX (ALL LOWER CASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSNORTHERNINDIANA WWW.TWITTER.COM/NWSIWX WWW.YOUTUBE.COM/NWSNORTHERNINDIANA

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