Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 210014
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
814 PM EDT SAT SEP 20 2014

.SYNOPSIS...
ISSUED AT 745 PM EDT SAT SEP 20 2014

AN UPPER LEVEL DISTURBANCE AND COLD FRONTAL BOUNDARY PRODUCED
SHOWERS AND THUNDERSTORMS SATURDAY EVENING. THE COVERAGE AND
INTENSITY WILL DIMINISH OVERNIGHT. ANOTHER UPPER LEVEL DISTURBANCE
WILL BRING ANOTHER CHANCE OF SHOWERS ON SUNDAY...WITH EVEN AN
ISOLATED THUNDERSTORM NEAR THE MICHIGAN...OHIO AND INDIANA BORDER
REGION. THEN CONDITIONS WILL DRY OUT SUNDAY NIGHT AS A RIDGE OF
HIGH PRESSURE BUILDS INTO THE AREA THROUGH THE EARLY PARTS OF NEXT
WEEK. LOW TONIGHT WILL DROP INTO THE LOWER 60S AND HIGHS ON SUNDAY
WILL BE COOLER...IN THE MID 60S TO LOWER 70S.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 428 PM EDT SAT SEP 20 2014

MAIN FORECAST CONCERN WILL BE SEVERE WEATHER POTENTIAL THIS
EVENING.

A STRONG UPPER VORT MAX TRACKING ACROSS NORTHWEST ILLINOIS AT
THIS TIME WILL BE THE PRIMARY SYNOPTIC FEATURE OF INTEREST THIS
EVENING. THIS SHORT WAVE HAS AN IMPRESSIVE WATER VAPOR
PRESENTATION...WITH A VERY SHARP UPPER LEVEL MOISTURE
DISCONTINUITY. MOST VIGOROUS CONVECTION AT THE PRESENT TIME HAS
DEVELOPED ACROSS NORTHEAST ILLINOIS AND ABOUT TO ENTER FAR WEST
CENTRAL PORTIONS OF IWX FORECAST AREA. DEEP LAYER SHEAR WILL
CONTINUE TO STRENGTHEN THROUGH THE REMAINDER OF THE
AFTERNOON/EARLY EVENING...WITH 0-3KM SHEAR VALUES ALSO INCREASING
INTO THE 35 TO 40 KNOT RANGE. THIS SHOULD HELP TO SUSTAIN WIND
THREAT INTO WESTERN PORTIONS OF THE AREA AND BALANCE COLD POOL
STRENGTH. STORMS SHOULD EVENTUALLY BEGIN TO OUTRUN MOST
PRONOUNCED INSTABILITY AXIS ACROSS NORTHEAST ILLINOIS/NORTHWEST
INDIANA WHERE 100 HPA MLCAPES ON THE ORDER OF 750-1500 J/KG ARE
EXPECTED. THIS MAY TEND TO DIMINISH STORM INTENSITY ACROSS
EASTERN HALF OR EASTERN THIRD OF THE AREA LATER THIS EVENING.
WHILE DAMAGING WIND IS THE MAIN THREAT...A FEW INSTANCES OF LARGE
HAIL WILL BE POSSIBLE WITH THE STRONGER CORES.

WHILE STRONGEST STORMS MAY TEND TO DIMINISH ACROSS EASTERN
PORTIONS OF THE AREA LATER THIS EVENING...PASSAGE OF PRIMARY
UPPER VORT MAX ACROSS NORTHWEST ILLINOIS LATER TONIGHT WILL BE
ACCOMPANIED BY SECONDARY LOW LEVEL MOISTURE POOLING AXIS.
INSTABILITY SHOULD BE SOMEWHAT TEMPERED WITH LOSS OF DEEPER SFC
BASED INSTABILITY BY THIS TIME HOWEVER...BUT ENOUGH ELEVATED
INSTABILITY SHOULD PERSIST TO MAINTAIN AT LEAST CHANCE TSRA POPS
LATE THIS EVENING INTO THE EARLY PORTION OF THE OVERNIGHT.

NOT MUCH CHANGE TO FORECAST FOR SUNDAY...WITH ANOTHER STRONG
UPPER VORT MAX DIVING INTO THE SOUTHERN GREAT LAKES. A TROWAL-
LIKE FEATURE WILL ALSO BE WRAPPING ACROSS NORTHERN PORTIONS OF
THE AREA AND HAVE KEPT SPIRIT OF PREVIOUS FORECAST WITH HIGHEST
POPS ACROSS THE NORTH...AND HAVE JUST ADDED SOME TEMPORAL
RESOLUTION TO CAPTURE BEST FORCING LATE MORNING/EARLY
AFTERNOON...AND AS DRY SLOT SHIFTS SOUTH OF THE AREA. SOME ISO
THUNDER IS A POSSIBILITY...ESPECIALLY ACROSS THE NORTHEAST IN
ASSOCIATION WITH WEAK TROWAL.

&&

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 428 PM EDT SAT SEP 20 2014

A VERY QUIET LONG TERM PERIOD WITH HIGH PRESSURE BECOMING
ENTRENCHED ACROSS THE REGION FOR THE ENTIRE PERIOD. MONDAY WILL
BEGIN ON THE COOL SIDE WITH SOME GUIDANCE AND MIXING TOOLS
SUGGESTING HIGH TEMPS NOT GETTING OUT OF THE 50S. WITH FULL SUN
EXPECTED THINK WE WILL SEE SUPERADIABATIC LAPSE RATES NEAR
SURFACE AIDED BY STILL WARM GROUND OF LATE SUMMER. HAVE USED
SUPERBLEND TO COME UP WITH LOWER 60S NORTH AND MIDDLE 60S SOUTH.
REMAINDER OF THE PERIOD TO SEE A SLOW WARMING TREND WITH HIGHS
EACH DAY A FEW DEGREES WARMER WITH MODERATING AIR AND RISING
HEIGHTS. HIGHS SHOULD RETURN TO THE LOWER 70S BY MID WEEK AND
MIDDLE 70S BY THE END. WITH SUBSIDENCE AND HIGH PRESSURE DIRECTLY
OVERHEAD SHOULD SEE SKIES REMAINING MOSTLY CLEAR THROUGH THE
WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 745 PM EDT SAT SEP 20 2014

GROWING CONCERN FOR FUELING/ALTERNATE CONDITIONS DEVELOPING NEAR
DAYBREAK. AMID HIGHLY PERTURBED AND MOIST NEAR BOUNDARY LAYER
REGION WILL LEAD TO LOW STRATUS PRODUCTION AS POST FRONTAL
WESTERLY FLOW INCREASES. LIFTING BASES INTO LOW END VFR CIGS BY
LATE MORNING AS T/TD DEPRESSION INCREASE WITH SIGNIFICANT NEAR
SURFACE DRY AIR ADVECTION. LOW POINT CHANCES FOR SHRA MIDDAY INTO
SUNDAY AFTERNOON WITH BASE OF MID TROPOSPHERIC TROF SETTLING INTO
MI THUMB THROUGH NRN INDIANA...AND WILL FORGO MENTION ATTM.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LMZ043-046.

     SMALL CRAFT ADVISORY FROM 8 AM SUNDAY TO 11 AM EDT MONDAY FOR
     LMZ043-046.

&&

$$

SYNOPSIS...MURPHY
SHORT TERM...MARSILI
LONG TERM...LASHLEY
AVIATION...MURPHY


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