Area Forecast Discussion
Issued by NWS Northern Indiana

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS63 KIWX 200013 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 813 PM EDT FRI SEP 19 2014 .SYNOPSIS... ISSUED AT 758 PM EDT FRI SEP 19 2014 HIGH PRESSURE CURRENTLY OVER THE AREA WILL CONTINUE TO MOVE EASTWARD THROUGH TONIGHT AND THEN EXPECT AN UPPER LEVEL DISTURBANCE TO MOVE THROUGH SATURDAY. SCATTERED SHOWERS AND THUNDERSTORMS MAY MOVE INTO THE SOUTHERN GREAT LAKES BY MORNING...BUT THE COVERAGE OF SHOWERS AND THUNDERSTORMS IS EXPECTED TO INCREASE LATER IN THE AFTERNOON AND EVENING. LOW TEMPERATURES TONIGHT WILL BE IN THE LOWER TO MIDDLE 50S. HIGH TEMPERATURES TOMORROW WILL BE IN THE UPPER 70S TO LOWER 80S. && .SHORT TERM...(THIS EVENING THROUGH SATURDAY) ISSUED AT 353 PM EDT FRI SEP 19 2014 CONVECTIVE POTENTIAL ON SATURDAY/SATURDAY NIGHT WILL CONTINUE TO BE THE PRIMARY FOCUS OF THE SHORT TERM. IN THE MEANTIME...BROAD LOW AMPLITUDE UPPER LEVEL RIDGING WILL QUICKLY TRANSLATE EASTWARD ACROSS THE GREAT LAKES/OHIO VALLEY THIS MORNING WITH CONTINUED SLOW EASTWARD MIGRATION OF LOW LEVEL ANTICYCLONE NORTHEAST CONUS/SOUTHEAST CANADA. A 50-60 KNOT LLJ IS EXPECTED TO TAKE SHAPE TONIGHT...WITH STRONGEST LOW LEVEL MOIST TRANSPORT TAKING SHAPE FROM MID MS RIVER VALLEY NORTHEASTWARD INTO THE WESTERN GREAT LAKES REGION LATER TONIGHT. CONVECTION MAY DEVELOP IN ASSOCIATION WITH STRENGTHENING LLJ AND WEAK UPPER PERTURBATIONS ENTERING WESTERN GREAT LAKES OVERNIGHT. HAVE KEPT FORECAST AREA DRY OVERNIGHT...ALTHOUGH A VERY LOW END CHANCE OF A SHOWER MAY EXIST ACROSS THE FAR NORTHWEST TOWARD DAYBREAK AS STRONGER LOW/MID LEVEL THETAE ADVECTION PROGRESSES INTO THE AREA. OTHERWISE FOR TONIGHT...MID AND HIGH LEVEL CLOUDS WILL BE ON THE INCREASE PARTICULARLY DURING THE OVERNIGHT HOURS WHICH COMBINED WITH STRENGTHENING LOW LEVEL WAA WILL PROVIDE MILDER MINS FROM THE MID TO UPPER 50S...TO THE LOWER 50S OR AROUND 50 EAST. STILL PLENTY OF UNCERTAINTY REMAINING IN REGARDS TO CONVECTIVE/SEVERE RISK FOR SATURDAY. CONVECTION MAY BE ONGOING EARLY SATURDAY MORNING ACROSS THE WESTERN GREAT LAKES IN ASSOCIATION WITH AFOREMENTIONED LLJ FORCING. WHILE PROPAGATION VECTORS WOULD TEND TO KEEP THIS ACTIVITY NORTH OF LOCAL AREA...SOME ADDITIONAL DEVELOPMENT ALONG RESIDUAL OUTFLOW BOUNDARIES COULD ALLOW FOR A FEW SHOWERS/ISOLATED STORMS TO WORK INTO FAR NORTHWEST PORTIONS OF THE AREA AFTER DAYBREAK...BUT CONFIDENCE IN THIS SCENARIO IS LOW. NEXT UPSTREAM MID LEVEL TROUGH WILL APPROACH THE GREAT LAKES LATE SATURDAY MORNING ALLOWING FOR AXIS OF STRONG LOW LEVEL MOISTURE CONVERGENCE TO SHIFT ACROSS APPROXIMATELY NORTHERN HALF OF THE AREA. AS PREVIOUS DISCUSSION MENTIONED...AVAILABLE INSTABILITY DURING THE DAY SATURDAY WILL BE HIGHLY SENSITIVE TO NEAR SFC/SFC TEMPERATURES...AND GIVEN THE ABOVE INCREASE IN FORCING...SOME POSSIBILITY EXISTS FOR THIS INSTABILITY TO BE TEMPERED. WHILE MOISTURE TRANSPORT WILL BE STRONG PRECEDING THE FRONT...NAM MAY BE A BIT AGGRESSIVE WITH SFC DEW POINTS...AND THUS A BIT ON THE AGGRESSIVE SIDE WITH INSTABILITY PROGS. NEVERTHELESS..GIVEN STEEPISH MID LEVEL LAPSE RATES...SURFACE BASED CAPES ON THE ORDER OF 750-1500 J/KG AT LEAST APPEAR TO BE A POSSIBILITY DEPENDING ON EXTENT OF CLOUD COVER. DEEP LAYER SHEAR AND 0-3 KM SHEAR VECTORS SHOULD STEADILY STRENGTHEN DURING THE DAY AS BELT OF STRONGER MID/UPPER LEVEL WESTERLIES PROGRESSES THROUGH BASE OF THE MID LEVEL TROUGH. GIVEN LOW/MODERATE INSTABILITY AND HIGH SHEAR ENVIRONMENT...CANNOT RULE OUT AT LEAST AN ISOLD SEVERE THREAT (MAINLY ISOLD DAMAGING WIND GUSTS) DEPENDING ON HOW INSTABILITY EVOLVES GIVEN STRENGTHENING BACKGROUND WIND FIELD AND UNIDIRECTIONAL NATURE TO FLOW. WINDOW OF SEVERE POTENTIAL SHOULD BE SOMEWHAT LIMITED...WITH PRELIMINARY INDICATIONS IN THE 21Z-03Z TIMEFRAME. A PUNCH OF DRIER MID LEVEL AIR TO ADVECT INTO THE AREA OVERNIGHT...BUT SECONDARY AXIS OF PREFRONTAL LOW LEVEL MOISTURE POOLING SHOULD KEEP ENOUGH ELEVATED INSTABILITY IN PLACE FOR CONTINUED SCATTERED SHOWER/THUNDERSTORMS DURING THE OVERNIGHT HOURS AS NEXT UPSTREAM UPPER LEVEL TROUGH APPROACHES. SLIGHTLY MORE DELAYED FROPA EARLY SUNDAY MORNING AND ABUNDANT CLOUD COVER WILL PROVIDE MILDER MINS IN THE LOWER AND MID 60S. && .LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY) ISSUED AT 353 PM EDT FRI SEP 19 2014 LONG TERM PERIOD BEGINS SUNDAY MORNING WITH DRY SLOT BEHIND COLD FRONT INITIALLY OVER THE AREA. MOST PCPN ASSOCIATED WITH FRONTAL BOUNDARY SHOULD BE EXITING THE AREA BY 12Z. MODEL SOUNDINGS INDICATE POST FRONTAL INVERSION WITH TRAPPED LOW LEVEL MOISTURE SUGGESTING LINGERING CLOUD COVER INTO EARLY AFTERNOON. WE HAVE BEEN DISCUSSING THE POSSIBILITY OF SHOWERS WITH SECONDARY SHORT WAVE FOR SEVERAL DAYS. LATEST MODEL GUIDANCE SHOWING A RATHER STRONG PV ANOMALY NOW DROPPING INTO THE AREA BY MID DAY WITH STRONG DPVA WITHIN THIS SHORT WAVE TROUGH. DEEPER MOISTURE IS CERTAINLY SCOURED AS THIS FEATURE NEARS BUT CONCERN LIES WITH TRAPPED LOW LEVEL MOISTURE AND ANY WEAK LAKE CONTRIBUTION PROVIDING ENOUGH MOISTURE WITH LARGE SCALE LIFT TO PRODUCE SOME LIGHT SHOWERS. SOUNDINGS ALSO INDICATE A BIT OF ELEVATED INSTABILITY IN WAKE OF MAIN COLD FRONT. HAVE THEREFORE ADDED SOME LOW CHANCE POPS BACK TO FORECAST SUNDAY...ESPECIALLY NORTH AND EAST WHERE STRONGER INFLUENCE OF PV ANOMALY SEEMS TO BE FOCUSED WITH AGREEMENT AMONG THE MODELS. PASSAGE OF THIS FEATURE SHOULD THEN LEAD TO CLEARING SKIES AND COOLER TEMPERATURES SUNDAY NIGHT. MODELS HAVE CONTINUED TO TREND WARMER POST FRONTAL WITH MODIFIED AIRMASS AND DEEPER TROUGH AXIS TO OUR EAST MONDAY. SURFACE HIGH PRESSURE WILL SETTLE IN MONDAY AND CONTINUE THROUGH THE END OF THE WEEK WITH A MODERATING TEMPERATURE TREND. EXPECT TEMPS SIMILAR TO LAST FEW DAYS WITH LOWS IN THE LOWER 40S AND HIGHS IN THE 60S TO BEGIN THE WEEK BUT WARMING TO LOWS IN THE 50S AND HIGHS IN THE 70S BY MID TO LATE WEEK. DRY CONDITIONS TO EXIST WITH RIDGING ALOFT BECOMING ANCHORED RIGHT OVER THE AREA THROUGH THE WEEK. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING) ISSUED AT 809 PM EDT FRI SEP 19 2014 VFR MET CONDITIONS TO DOMINATE THROUGH THE FORECAST PERIOD. SHARPENING UPSTREAM TROF TO BRING INCREASE IN DEEP LAYER SHEAR TO REGION SAT AFTERNOON. CONCERN CONTINUES TO REVOLVE AROUND DEGREE OF INSTABILITY AS ANTICIPATED EARLY MORNING DECAY OF UPSTREAM CONVECTION MAY INHIBIT SFC HEATING. FOR NOW WILL INTRODUCE AS VCTS LATE IN FORECAST PERIOD AT KSBN WITH KFWA CONCVECTION FREE DUE TO BOTH LATER TIMING AND PREVALENT HEIGHT FALL CENTROID TRACK REMAINING WELL NORTH /NERN WI MIDDAY INTO LAKE HURON SAT EVENING/. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 5 PM EDT SATURDAY FOR LMZ043-046. && $$ SYNOPSIS...LOTHAMER SHORT TERM...MARSILI LONG TERM...LASHLEY AVIATION...MURPHY 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

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.