Area Forecast Discussion
Issued by NWS Northern Indiana

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000 FXUS63 KIWX 280723 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 323 AM EDT FRI AUG 28 2015 .SYNOPSIS... ISSUED AT 1257 AM EDT FRI AUG 28 2015 HIGH PRESSURE OVERHEAD WILL MOVE EAST THROUGH THE LOWER GREAT LAKES TO THE MID ATLANTIC REGION OVER THE NEXT FEW DAYS. THIS WILL ALLOW TEMPERATURES TO WARM ABOVE NORMAL BY EARLY NEXT WEEK. IN THE MEANTIME...A WEAK UPPER LEVEL SYSTEM WILL BRING A CHANCE FOR SHOWERS AND THUNDERSTORMS THIS WEEKEND. HIGHS TODAY WILL REACH THE MID TO UPPER 70S. && .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 320 AM EDT FRI AUG 28 2015 LIGHT WINDS AND MAINLY CLEAR SKIES ASSOCIATED WITH SFC HIGH PRESSURE CENTERED OVER THE EASTERN LAKES HAS ALLOWED TEMPS TO NEAR XOVER VALUES EARLY THIS MORNING. NOT SEEING ANY BR/FG RESTRICTIONS IN LATEST OBSERVATIONS BUT WOULD NOT BE SURPRISED TO SEE SOME PATCHY FOG (NOT AS WIDESPREAD AS YESTERDAY) BETWEEN 10-13Z GIVEN LINGERING BOUNDARY LAYER MOISTURE. ANY PATCHY FOG SHOULD LIFT OUT TO A SCT STRATO CU DECK BY MID MORNING. WINDS SHIFTING MORE SOUTHERLY BY LATER THIS MORNING/AFTERNOON IN RESPONSE TO EASTWARD SHIFT OF THE ABOVE MENTIONED SFC HIGH WILL SUPPORT A WARMER DAY (YET STILL BELOW NORMAL FOR LATE AUGUST) WITH HIGHS INTO THE MID-UPPER 70S. EXPECT ANOTHER QUIET DAY OTHERWISE WITH INCREASING MID-HIGH LEVEL CLOUDS IN ADVANCE OF A CONVECTIVELY ENHANCED SHORTWAVE (OVER EASTERN NEBRASKA AS OF 07Z) AND ATTENDANT SFC REFLECTION MODELED TO TRACK SLOWLY EAST THROUGH IOWA. ELEVATED THETA-E ADVECTION (WITHIN 20-30 KNOTS OF CROSS ISOBARIC FLOW ON THE 305K SFC) IN ADVANCE OF THIS FEATURE MAY BE ENOUGH TO SPREAD SHOWERS INTO OUR NORTHWESTERN ZONES BY LATER TONIGHT...ALTHOUGH KEPT POPS LOW GIVEN EXPECTATIONS FOR BULK OF PRECIPITATION TO ALIGN WEST- NORTHWEST OF THE IWX CWA ALONG SLOWLY ADVANCING MOISTURE AXIS/ PV ANOMALY. && .LONG TERM...(SATURDAY THROUGH THURSDAY) ISSUED AT 320 AM EDT FRI AUG 28 2015 FOR SATURDAY...A SOMEWHAT DISJOINTED UPPER LEVEL TROUGH WILL BE MAKING ITS WAY THROUGH THE AREA AS NORTHERN STREAM PV ANOMALY ATTEMPTS TO PARTIALLY PHASE WITH PACIFIC SHORT WAVE TRACKING ACROSS THE WESTERN GREAT LAKES REGION. BROAD ISENTROPIC LIFT ASSOCIATED WITH WARM FRONT LIFTING THROUGH THE AREA WILL PRECEDE THIS FORCING ALTHOUGH LOW LEVEL MOISTURE RETURN IS EXPECTED TO BE SOMEWHAT LIMITED AT THE ONSET ON SATURDAY MORNING. TWO DISTINCT POCKETS OF BETTER INSTABILITY MAY DEVELOP SATURDAY AFTERNOON...ONE ACROSS SOUTHEAST PORTIONS OF THE AREA MORE DIVORCED FROM STRONGER MID/UPPER LEVEL FORCING AND ANOTHER AREA IN CLOSER PROXIMITY TO ASSOCIATED SFC TROUGH/LOW LEVEL CONVERGENT AXIS ACROSS NORTHEAST ILLINOIS/EXTREME NORTHWEST INDIANA. LEAD VORT MAX ASSOCIATED WITH PACIFIC WAVE SHOULD TEND TO OUTRUN THIS BETTER LOW LEVEL CONVERGENCE DURING THE DAY SATURDAY...SO SOME QUESTION AS TO EASTWARD EXTENT OF PRECIP COVERAGE. SECONDARY SHORT WAVE ASSOCIATED WITH NORTHERN STREAM SHOULD BE ON THE HEELS OF THIS LEAD WAVE WITH A BETTER CHANCE OF CONVECTIVE DEVELOPMENT ACROSS THE WEST/NORTHWEST SATURDAY AFTERNOON/EARLY EVENING WHERE LOW LEVEL MOISTURE MAY BE MORE EFFECTIVELY POOLED. PREVIOUS POPS SEEM TO CAPTURE CURRENT TRENDS WELL SO NO DRAMATIC CHANGES MADE FOR THIS FORECAST CYCLE WITH HIGH CHANCE POPS NORTHWEST TAPERING TO LOW CHANCE SOUTHEAST ON SATURDAY AFTERNOON. ANY NOTABLE BELTS OF STRONGER DEEP LAYER SHEAR SHOULD BE SHIFTING EAST OF THE AREA BY SATURDAY AFTERNOON IN ASSOCIATION WITH 40 KNOT MID LEVEL SPEED MAX...AND OVERALL LIMITED NATURE TO SURFACE BASED INSTABILITY/MARGINAL MID LEVEL LAPSE RATES SUGGEST LITTLE TO NO SEVERE THREAT AT THIS TIME. MAINTAINED LOW CHANCE POPS INTO THE OVERNIGHT HOURS SATURDAY AS SURFACE TROUGH ENTERS NORTHERN INDIANA...BUT BY THIS TIME MID/UPPER FORCING SHOULD BE ON THE DECLINE AS UPPER VORT MAX BECOMES MORE ATTENUATED. THIS WEAK FORCING WILL PERSIST INTO SUNDAY AND HAVE THUS CONTINUED LOW CHANCE POPS THROUGH EARLY SUNDAY EVENING. DESPITE LOW LEVEL WAA...IMPACTS OF GOOD DEAL CLOUD COVER/PRECIP SHOULD LIMIT HIGH TEMPS FROM UPPER 70S TO LOWER 80S FOR BOTH SATURDAY/SUNDAY. EVENTUAL DECAY OF THIS PV ANOMALY EARLY NEXT WEEK WILL BE FOLLOWED BY BUILDING MID/UPPER LEVEL HEIGHTS SUPPORTIVE OF PREVIOUSLY ADVERTISED WARMING TREND FOR THE TUESDAY/WEDNESDAY TIMEFRAME. WEATHER SHOULD BE RATHER UNEVENTFUL FOR MUCH OF THE UPCOMING WEEK UNDER THE INFLUENCE OF THIS UPPER RIDGING WITH HIGHS GENERALLY IN THE MID TO UPPER 80S AND LOWS IN MID 60S. SOME POSSIBILITY MAY EXIST FOR A FEW WEAK WAVES TO MEANDER THROUGH MEAN UPPER RIDGING IN THE WED/THU TIMEFRAME...BUT OVERALL UNSUPPORTIVE BACKGROUND THERMODYNAMIC ENVIRONMENT SUGGESTS MAINTAINING DRY FORECAST IS MOST PRUDENT AT THIS TIME. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT) ISSUED AT 1257 AM EDT FRI AUG 28 2015 GOOD RADIATIONAL COOLING WILL ALLOW TEMPS TO NEAR XOVER VALUES EARLY THIS MORNING. RESULTING PATCHY FOG MAY IMPACT THE TERMINALS TOWARD DAYBREAK (MAINTAINED MVFR BR TEMPO GROUP BTW 10-12Z). LIGHT/CALM WINDS WILL VEER MORE SOUTHERLY BY LATE MORNING/AFTERNOON AS SFC RIDGE CENTERED OVER THE LOWER/EASTERN LAKES PUSHES EAST. VFR OTHERWISE WITH INCREASING MID-HIGH CLOUDS AS SYSTEM APPROACHES FROM THE WEST (EXCEPTION MAY BE A PERIOD OF MVFR STRATOCU IN THE 13-16Z WINDOW BEFORE MIXING UP/OUT). && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ SYNOPSIS...STEINWEDEL SHORT TERM...STEINWEDEL LONG TERM...MARSILI AVIATION...STEINWEDEL 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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