Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 252031
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
431 PM EDT MON AUG 25 2014

.SYNOPSIS...
ISSUED AT 416 PM EDT MON AUG 25 2014

A SERIES OF WEAK UPPER LEVEL DISTURBANCES WILL COMBINE WITH A VERY
UNSTABLE AIR MASS TO PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS
THROUGH TUESDAY. VERY WARM CONDITIONS WILL CONTINUE THROUGH
TUESDAY...WITH COOLER CONDITIONS FOR WEDNESDAY AS A COLD FRONT
MOVES THROUGH THE AREA.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 416 PM EDT MON AUG 25 2014

REMNANT OUTFLOW BOUNDARY WORKING INTO VERY UNSTABLE ENVIRONMENT HAS
LED TO RENEWED THUNDERSTORM DEVELOPMENT ACROSS NORTHEAST
ILLINOIS...WHICH HAS NOW SPREAD INTO NORTHWEST INDIANA AND SOUTHWEST
LOWER MICHIGAN. STORMS ALSO APPEARED TO GET SOME SUPPORT FROM BROAD
WAA/ISENTROPIC LIFT ACROSS THE WESTERN GREAT LAKES THIS AFTERNOON.
WHILE DEEP LAYER SHEAR IS RELATIVELY WEAK ACROSS NORTHERN
INDIANA...SMALL SCALE VORT ENHANCED BY UPSTREAM CONVECTION APPEARS
TO HAVE ALLOWED FOR POCKET OF SLIGHTLY ENHANCED EFFECTIVE SHEAR
AROUND 25 KNOTS ACROSS NORTHWEST INDIANA. VERY STRONG
INSTABILITY/PRECIP LOADING WILL CONTINUE TO POSE A THREAT OF LOCALLY
DAMAGING WIND GUSTS OVER NEXT FEW HOURS...PARTICULARLY WEST OF A
STURGIS MI TO WARSAW IN TO MONTICELLO IN LINE. WITH STORMS OUTFLOW
DOMINANT AND WEAK FORCING OUTSIDE OF SMALL SCALE CONVECTIVE
VORT...CURRENT THINKING IS THAT ONGOING CONVECTION MAY TEND TO
DIMINISH IN INTENSITY AFTER 22Z AS IT SHIFTS INTO NORTH
CENTRAL/NORTHEAST INDIANA. CONVECTION ALSO HAS INCREASED ACROSS
NORTHWEST ILLINOIS ALONG DPVA ZONE WITH NEXT UPPER LEVEL VORT. THIS
VORT MAX SHOULD WORK INTO THE WESTERN GREAT LAKES THIS EVENING...SO
WILL HAVE TO MONITOR THESE STORMS OVER THE NEXT SEVERAL HOURS AND
WHETHER SOME UPSCALE GROWTH CAN OCCUR. KINEMATIC ENVIRONMENT MAY
POSE SOME CHALLENGE FOR UPSCALE GROWTH HOWEVER...BUT CERTAINLY
SOMETHING THAT WILL NEED TO BE WATCHED FOR AN ISOLATED SEVERE RISK.

HEAT INDICES ACROSS WEST/SOUTHWEST PORTIONS ARE NOW APPROACHING THE
UPPER 90S TO AROUND 100...ALTHOUGH HIGH CLOUD DEBRIS FROM ONGOING
STORMS SHOULD TEND TO CAP INDICES FROM GETTING MUCH ABOVE ADVISORY
CRITERIA. THUS...WILL ALLOW SPS TO CONTINUE AND HOLD WITH NO
HEADLINES.

AFTER SOME INCREASED EARLY EVENING CHANCES OF STORMS WITH NEXT MID
MS VALLEY VORT...FORECAST CONFIDENCE IS SOMEWHAT LOWER WITH
DIFFICULTY IN PICKING OUT NEXT UPSTREAM FORCING OF SIGNIFICANCE.
SOME REINFORCEMENT OF LOW LEVEL THETAE ADVECTION SHOULD OCCUR LATER
THIS EVENING AS WEST-EAST LOW LEVEL THETAE RIDGE WORKS INTO SOUTHERN
LOWER MICHIGAN/NORTHERN INDIANA. WILL MAINTAIN SOME LOW CHANCE POPS
THROUGH THE OVERNIGHT HOURS.

FOR TUESDAY...PRIMARY UPPER LOW TRACKING ACROSS NORTHERN ONTARIO
WILL ALLOW COLD FRONT TO SLIP INTO THE SOUTHERN GREAT LAKES.
MID/UPPER LEVEL FORCING STILL SOMEWHAT MARGINAL FOR LOCAL
AREA...ALTHOUGH WEAKLY CONVERGENT LOW LEVEL FLOW ASSOCIATED WITH
APPROACHING TROUGH AXIS COMBINED WITH AMPLE INSTABILITY SHOULD YIELD
TO SCATTERED AFTERNOON THUNDER. SIMILAR HEAT INDICES ARE EXPECTED
FOR TUESDAY...ALTHOUGH MAY BE TEMPERED DEPENDING ON EXTENT OF CLOUDS
AND PRECIP. SLIGHTLY COOLER HEAT INDICES ALSO EXPECTED CLOSER TO
LAKE MICHIGAN WHERE WESTERLY FLOW OFF LAKE SHOULD PROVIDE SOME
RELIEF. SEVERE THREAT LOOKS TO BE MINIMAL TOMORROW GIVEN LACK OF
SIGNIFICANT SHEAR...ALTHOUGH SOME LOCALLY HEAVY DOWNPOURS WILL ONCE
AGAIN BE POSSIBLE.

&&

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 416 PM EDT MON AUG 25 2014

TEMPERATURES RETURN TO NEAR NORMAL FOR THE LONG TERM PERIOD WITH
PRECIPITATION CHANCES NEARLY EVERY DAY AS A PESKY FRONTAL SYSTEM
LINGERS NEAR THE AREA.

HIGH PRESSURE WILL BUILD SOUTH FROM WISCONSIN ON WEDNESDAY WHICH
WILL FINALLY SHUNT THE FRONTAL SYSTEM SOUTH OF OUR FORECAST AREA.
THIS WILL NOT PERSIST LONG THOUGH AS A CUTOFF LOW MOVES INTO THE
CENTRAL PLAINS AND BEGINS TO LIFT THE FRONT NORTHWARD AS A WARM
FRONT THURSDAY NIGHT. THIS WILL BRING A RETURN OF STORMY WEATHER
THROUGH LABOR DAY WEEKEND.

SEVERE WEATHER CHANCES WILL REMAIN LOW THROUGH THE PERIOD AS FLOW
REMAINS WEAK THROUGH THE TROPOPAUSE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 200 PM EDT MON AUG 25 2014

AN OUTFLOW BOUNDARY ASSOCIATED WITH OVERNIGHT UPSTREAM CONVECTION
HAS BEEN A TRIGGER MECHANISM FOR SHOWERS AND THUNDERSTORMS ACROSS
NORTHEAST ILLINOIS AND SOUTHERN LOWER MICHIGAN. THIS BOUNDARY
SHOULD CONTINUE TO DROP INTO NORTH CENTRAL INDIANA BY 20Z. A
STRONGLY UNSTABLE ENVIRONMENT EXISTS ACROSS THE AREA...WITH MAIN
NEGATIVE FACTOR TO SOUTHEAST EXPANSION OF THE SHOWERS AND STORMS
IS BACKGROUND WEAK UPPER FORCING AND PRESENCE OF MID/UPPER LEVEL
RIDGING. HAVE CARRIED A VCTS MENTION AT KSBN FROM 20Z-22Z AND WILL
BE MONITORING TRENDS OVER NEXT HOUR OR SO FOR POSSIBLE TSRA
INCLUSION. SOUTH WINDS AT KSBN MAY BECOME NORTHWEST FOR A TIME IN
THE 20Z-22Z TIMEFRAME DUE TO THE PASSAGE OF THE OUTFLOW
BOUNDARY...OR VARIABLE IN NATURE. A SHEARED UPPER VORT MAX FROM
CENTRAL WISCONSIN INTO EASTERN IOWA WILL TRACK INTO NORTHWEST
INDIANA THIS EVENING WITH SOME POSSIBILITY OF ADDITIONAL ISOLATED
THUNDERSTORMS. OTHER THAN PASSAGE OF THIS WEAK WAVE THIS
EVENING...FORCING WILL BE SOMEWHAT WEAK WITH LOW CONFIDENCE IN
TIMING AND WILL KEEP TAFS DRY THROUGH THE END OF THE PERIOD.
CHANCES OF THUNDER MAY INCREASE LATE TONIGHT INTO TUESDAY MORNING
AS LOW LEVEL FRONT BEGINS TO APPROACH THE AREA...BUT CONFIDENCE
REMAINS LOW IN TIMING/COVERAGE.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...MARSILI
SHORT TERM...MARSILI
LONG TERM...BENTLEY
AVIATION...MARSILI


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