377
FXUS63 KIWX 201015
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
615 AM EDT THU SEP 20 2018
SYNOPSIS
ISSUED AT 424 AM EDT THU SEP 20 2018
ONE MORE HOT DAY WILL BE IN STORE FOR MANY AREAS AS HIGHS REACH
THE UPPER 80S TO LOWER 90S. A CHANCE FOR A SHOWER OR STORM WILL
EXIST MAINLY ALONG AND NORTH OF THE TOLL ROAD INTO THIS AFTERNOON.
THERE WILL BE A CHANCE OF SHOWERS AND THUNDERSTORMS FRIDAY AFTERNOON.
COOLER TEMPERATURES WILL FILTER IN BEHIND A COLD FRONT WITH HIGHS
ONLY INTO THE 60S ON SATURDAY, THEN MAINLY IN THE 70S NEXT WEEK.
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 424 AM EDT THU SEP 20 2018
LOW CONFIDENCE FORECAST REGARDING IMPACTS OF UPSTREAM CONVECTION
AND PRECIP CHANCES INTO THIS AFTERNOON AS WELL AS TEMPERATURES.
ELEVATED FRONTAL BOUNDARY HAS BEEN ACTIVE FOR SEVERAL HOURS NOW
FROM NE NEBRASKA INTO SOUTHERN WISCONSIN. RECENTLY DEVELOPED
SHOWERS AND STORMS WERE ALSO BEING SEEN ACROSS PORTIONS OF WEST
CENTRAL LOWER MICHIGAN. ACTIVITY SHOULD REMAIN NORTH OF THE AREA
UNTIL POSSIBLY CLOSER TO THE 12Z AS OUTFLOW BOUNDARY PUSHES SOUTH
AND ALLOWS FOR AT LEAST A CHANCE FOR A FEW SHOWERS OR STORMS. HAVE
ATTEMPTED TO CAPTURE THIS AS BEST AS POSSIBLE WITH POPS EXPANDING
SOUTHWARD FOR A PERIOD THIS AFTERNOON AS WARM SECTOR BECOMES
RATHER UNSTABLE WITH MLCAPE 1000-2000 J/KG. BEST SHEAR WILL
RESIDE WELL NORTH OF THE AREA RESULTING IN MORE PULSY STORMS THAT
ARE ABLE TO DEVELOP WITH SPC MARGINAL RISK BEING PUSHED NORTH OF
THE FORECAST AREA.
CLOUD COVER TODAY WILL BE KEY IN DETERMINING FINAL AFTERNOON
HIGHS WITH POTENTIAL FOR LOCATIONS IN THE SOUTHWEST TO GET QUITE
WARM ONCE AGAIN. HIGHER DEWPOINTS MAY LIMIT OVERALL POTENTIAL FOR
MID 90S BUT CAN'T FULLY RULE OUT. KEPT WITH PREVIOUS FORECAST WITH
COOLEST READINGS NORTH AND EAST WHERE CLOUDS MAY LINGER LONGER.
DRY FORECAST THIS EVENING AND MOST, IF NOT ALL OF TONIGHT AS LINE
OF SHOWERS AND THUNDERSTORMS ADVERTISED TO DEVELOP WEST OF US
ALONG THE COLD FRONT AND MOVE EAST. MOST MODELS WEAKEN THIS
CONVECTION AS IT OUTRUNS BEST FORCING BUT LEFT SOME LOW POPS IN
W/NW AREAS TOWARDS MORNING. WINDS WILL INCREASE AS LOW LEVEL JET
RAMPS UP TO OVER 50 KTS AND AT LEAST SOME MIXING OF STRONGER WINDS
OCCURS.
LONG TERM
(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 424 AM EDT THU SEP 20 2018
OUTFLOW BOUNDARY/PRE FRONTAL TROUGH FROM OVERNIGHT CONVECTION WILL
BE THE MAIN FOCUS FOR BEST CONVECTION CHANCES. HI RES MODELS
GENERALLY SPLIT ON EITHER THIS BOUNDARY RE-FIRING IN FAR SE AREAS
OR POSSIBLY REMAINING SOMEWHAT ACTIVE WITH SHOWERS DURING THE
MORNING THAT EVENTUALLY INTENSIFY. INSTABILITY AND INCREASING
SHEAR WARRANT A MARGINAL RISK OF SEVERE FOR AT LEAST SE THIRD IF
NOT A BIT FURTHER NW. SPC DAY 2 OUTLOOK EXPANDED MARGINAL NW INTO
SE 2/3RD OR SO OF THE AREA. MAY BE SOMEWHAT OVERDONE BUT WITH SOME
MODELS HINTING AT STORMS FURTHER NW DUE TO POSSIBLE SLOWER
MOVEMENT OF FRONT CAN'T ARGUE.
PRECIP SHOULD BE CLEAR OF THE AREA BY FRIDAY NIGHT WITH MUCH
COOLER AIR FUNNELING IN. HIGHS IN THE 60S WILL DOMINATE SATURDAY
WITH ONLY SOME MODERATION BACK TOWARDS NORMAL TEMPS INTO MID WEEK
AS STRONGER TROUGH DIGS INTO THE PLAINS AND WORKS EAST WITH
INCREASING CHANCES FOR SHOWERS AND POSSIBLY SOME STORMS STARTING
AS EARLY AS MONDAY AFTERNOON BUT ESPECIALLY TUES AFTERNOON AND
EVENING WHEN TIMING OF ENERGY AND PEAK HEATING ALL COMBINE. COLDER
AIR WILL RETURN AGAIN BEHIND THE FRONT.
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 559 AM EDT THU SEP 20 2018
LOW LEVEL WARM FRONT IS BEGINNING TO LIFT NORTHWARD EARLY THIS
MORNING, WITH SOME WARM ADVECTION INDUCED SHOWERS AND A FEW
EMBEDDED STORMS HAVING DEVELOPED ACROSS SOUTHERN LOWER MICHIGAN.
CYCLOGENESIS ACROSS NORTH CENTRAL US AND DIURNAL NORTHWARD MIXING
OF THIS WARM FRONT WILL CONTINUE TO TAKE BETTER WARM FRONTAL
FORCING NORTH OF TERMINALS THIS MORNING. FOR TODAY, WILL HAVE TO
WATCH EVOLUTION OF WEAK OUTFLOW BOUNDARY ACROSS NORTHERN
ILLINOIS FOR POTENTIAL REDEVELOPMENT LATER TODAY, ALTHOUGH SOME
QUESTION AS TO HOW FAR SOUTHEAST THIS BOUNDARY WILL BE ABLE TO
PROGRESS GIVEN BACKGROUND SYNOPTIC FLOW. SOME INDICATIONS NOTED
IN HRRR/ARW MODEL GUIDANCE OF ISOLATED-SCATTERED SHOWERS/STORMS
REDEVELOPING THIS AFTERNOON ACROSS FAR NORTHERN INDIANA. SOME
SUPPORT FOR THIS IDEA COULD BE VERY WEAK VORT MAX LIFTING THROUGH
UPSTREAM PORTION OF UPPER RIDGE FROM STL VICINITY, POSSIBLE
CONTRIBUTION OF LINGERING SHALLOW WEAK OUTFLOW, AND SOME WEAK
DIFFERENTIAL HEATING FORCING GIVEN MID/HIGH CLOUD SHIELD WORKING
ACROSS THE SOUTHERN GREAT LAKES. STILL NOT QUITE ENOUGH CONFIDENCE
FOR ANY PRECIP MENTION AT TERMINALS WITH 12Z TAFS GIVEN OVERALL
LACK OF SUBSTANTIAL MID/UPPER FORCING, BUT THIS WILL BE MONITORED.
NORTHWARD RETREAT OF WARM FRONT WILL ALLOW FOR MODERATE SOUTH-
SOUTHWEST WINDS IN THE 10-15G20KT KNOT RANGE THIS AFTERNOON. DID
INCLUDE MENTION OF LLWS AFTER 05Z TONIGHT AS NORTHERN INDIANA IS
LOCKED IN WARM SECTOR WITH SOME DECOUPLING AND PRESENCE OF STRONG
LOW LEVEL INVERSION. VFR CONDITIONS SHOULD HOLD THROUGH THIS
PERIOD OUTSIDE OF ANY LOW PROB SHOWER/STORM CHANCES BOTH THIS
AFTERNOON, AND THEN AGAIN TOWARD VERY END OF THE PERIOD AS PRE-
FRONTAL TROUGH APPROACHES.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 11 AM EDT
SATURDAY FOR LMZ043-046.
SYNOPSIS...MURPHY
SHORT TERM...FISHER
LONG TERM...FISHER
AVIATION...MARSILI
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