Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 222020
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
420 PM EDT FRI AUG 22 2014

.SYNOPSIS...
ISSUED AT 404 PM EDT FRI AUG 22 2014

A SERIES OF WEAK UPPER LEVEL DISTURBANCES WILL CONTINUE TO
APPROACH THE REGION TONIGHT INTO SATURDAY PROVIDING A THREAT OF
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS. AN UPPER LEVEL
RIDGE WILL BUILD INTO THE REGION SATURDAY NIGHT INTO SUNDAY
GRADUALLY DIMINISHING THE CHANCE OF THUNDERSTORMS. HOT AND HUMID
CONDITIONS WILL PERSIST THROUGH THE EARLY PARTS OF NEXT WEEK.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 404 PM EDT FRI AUG 22 2014

ADDITIONAL CONVECTIVE CHANCES AND POTENTIAL ADDITIONAL HYDRO IMPACTS
WILL CONTINUE TO BE THE PRIMARY SHORT TERM FOCUS.

EFFECT OF CLOUDS AND PRECIP EARLIER TODAY HAVE LIMITED
DESTABILIZATION SOMEWHAT ACROSS THE AREA...ALTHOUGH LATEST RUC
INITIALIZATIONS DO DEPICT AROUND 1500 J/KG MLCAPE ACROSS SOUTHEAST
PORTIONS OF THE AREA. SOME WEAK SB CIN MAY STILL EXIST...BUT A
COUPLE OF WEAK TRIGGERS ARE EXPECTED TO ROUND UPPER LEVEL RIDGE INTO
THE LOCAL AREA THIS EVENING. THE FIRST OF THESE WAVES IS HIGHLY
SHEARED IN NATURE AND DROPPING SOUTHEAST OUT OF WEST CENTRAL LOWER
MICHIGAN. CU FIELD HAS BECOME A BIT AGITATED ACROSS EASTERN PORTIONS
OF THE AREA THIS AFTERNOON WHERE INSOLATION HAS BEEN A BIT
STRONGER...AND APPROACH OF THIS WEAK VORT MAY BE ENOUGH TO GENERATE
SOME ISOLD/SCT SHOWERS AND THUNDERSTORMS ACROSS NORTHEAST
INDIANA/SOUTH CENTRAL LOWER MICHIGAN/NORTHWEST OHIO. A SECOND VORT
APPEARS TO BE TRACKING OUT OF NORTHERN MISSOURI AND BROAD ISENTROPIC
ASCENT ASSOCIATED WITH THE DAMPENED LOW LEVEL THERMAL RIDGE MAY BE
ENOUGH TO SUPPORT ISOLD/SCT THUNDER ACROSS ESPECIALLY SOUTHWEST
PORTIONS OF THE AREA TONIGHT. IN ADDITION...DEVELOPING WEAK ONSHORE
FLOW COULD SUPPORT ENOUGH LOW LEVEL CONVERGENCE TO GENERATE ISOLD
SHOWERS IN VICINITY OF LAKE BREEZE THIS EVENING.

THE GREATEST CONCERN WILL BE POTENTIAL OF ANY LOCALIZED HEAVIER
SHOWERS AND THUNDERSTORMS ACROSS AREAS WHICH HAVE ALREADY RECEIVED
HEAVY RAINFALL OVER THE PAST 36 HOURS. AMPLIFYING UPSTREAM MID LEVEL
RIDGE HAS ALLOWED FOR SOME SLIGHT SUPPRESSION OF LOW LEVEL THETAE
GRADIENT AND THUS EXPECTATION IS THAT BEST FOCUS FOR ISOLD/SCT
THUNDERSTORMS THROUGH SATURDAY SHOULD BE CONFINED TO SOUTHWEST HALF
OR THIRD OF THE AREA. A SHORT WAVE TROUGH DROPPING ACROSS THE
EASTERN LAKES SHOULD TEND TO ENHANCED LOW LEVEL NORTHERLY FLOW
ACROSS THE GREAT LAKES WHICH SHOULD SETUP A BROAD AND WEAK SYNOPTIC
CONFLUENCE ZONE ACROSS THE AREA. THIS BACKGROUND FLOW COULD BE
ENOUGH TO SUPPORT ISOLD OR SCT SHOWERS/STORMS SATURDAY ACROSS THE
ENTIRE FORECAST AREA DESPITE AMPLIFYING UPPER RIDGE SO HAVE
MAINTAINED SLIGHT CHANCE POPS ACROSS THE EAST. ANOTHER WARM AND
HUMID DAY IN STORE FOR SATURDAY WITH HIGHS IN THE MID 80S...TO
POSSIBLY UPPER 80S ACROSS THE SOUTHWEST. THIS SHOULD KEEP HEAT
INDICES IN 90 TO 95 DEGREE RANGE SATURDAY.

&&

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 404 PM EDT FRI AUG 22 2014

UPPER LEVEL RIDGE AXIS WILL FOLD SOUTHEAST THROUGH THE GREAT LAKES
REGION SUNDAY INTO EARLY NEXT WEEK...WITH SUBTROPICAL HIGH CENTER
(590-591 DM) BUILDING EAST-NORTHEAST INTO THE OHIO VALLEY BY
MONDAY-TUESDAY. THIS WILL RESULT IN A CONTINUATION OF MAINLY
DRY/HOT/HUMID WX. A LARGE EASTERN CANADA LOW LEVEL ANTICYCLONE WILL
EXPAND SOUTHWARD INTO THE NORTHEAST US BY SUNDAY. THIS FEATURE WILL
ALLOW A MORE STABLE AIRMASS TO BRIEFLY ADVECT INTO OUR
EASTERN/CENTRAL ZONES WITHIN WEAK EAST-SOUTHEAST LOW LEVEL
FLOW...WITH NONZERO (10%) CHANCES FOR MAINLY AFTN/EVE CONVECTION
RELEGATED TO OUR SOUTHWESTERN ZONES NEAR A LEFTOVER/DIFFUSE
THETA-E/INSTABILITY GRADIENT. HUMIDITY AND DEGREE OF DIURNAL BL
DESTABILIZATION WILL INCREASE MONDAY INTO TUESDAY AS THE FLOW VEERS
SOUTH-SOUTHWEST. THIS WILL OCCUR IN RESPONSE TO DAMPENING OF THE
GREAT LAKES UPPER RIDGE AS LEAD SHORTWAVE ENERGY EJECTS OUT OF A
WESTERN CONUS UPPER TROUGH INTO SOUTH-CENTRAL CANADA. HARD TO
COMPLETELY RULE OUT ISO AFTN/EVE CONVECTION CONVECTION GIVEN
UNSTABLE AIRMASS...ALTHOUGH WARM PROFILE ALOFT AND LACK OF ANY
OBVIOUS TRIGGER SUPPORTS A MAINLY DRY FCST MONDAY-TUESDAY.
MORE PROGRESSIVE FLOW PATTERN BY MID-LATE WEEK WITH WESTERN CONUS
TROUGH/HEIGHT FALLS PROPAGATING EAST OVER A MOIST/UNSTABLE AIRMASS
WILL RESULT IN INCREASING CHANCES FOR SHOWERS/STORMS ALONG AN
ASSOCIATED CDFNT/PRE-FRONTAL TROUGH BY AROUND WEDNESDAY-THURSDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 150 PM EDT FRI AUG 22 2014

A MID/UPPER LEVEL SHORT WAVE HAS DROPPED SOUTHEAST OF THE AREA
THIS AFTERNOON ALLOWING FOR A LULL IN PRECIP CHANCES. SCATTERED
SHOWERS AND STORMS HAVE BEEN REGENERATING BACK ACROSS WEST CENTRAL
ILLINOIS IN ELEVATED WAA REGIME. WATER VAPOR IMAGERY SUGGESTS
ANOTHER SHORT WAVE ROUNDING THE UPPER LEVEL RIDGE ACROSS SOUTHERN
IOWA WHICH SHOULD EVENTUALLY WORK INTO THE SOUTHERN GREAT LAKES
THIS EVENING. MODERATELY UNSTABLE CONDITIONS WILL DEVELOP THIS
AFTERNOON WITH MAIN QUESTION ON PRECIP CHANCES DEALING WITH
FORCING MECHANISM. RESIDUAL OUTFLOWS FROM MORNING CONVECTION MAY
TEND TO FOCUS LATE AFTERNOON/EVENING THUNDERSTORM CHANCES...ALONG
WITH THE POSSIBILITY OF WEAK CONVERGENT AXIS DOWNWIND OF LAKE
MICHIGAN SERVING AS ANOTHER FOCUS. EXPECTED COVERAGE/CONFIDENCE OF
OCCURRENCE IS TOO LOW TO INCLUDE TS FOR THE 18Z TAFS AT THIS TIME.
HAVE MAINTAINED TREND TO IFR/LIFR CONDITIONS LATE TONIGHT IN FOG
WITH VERY WEAK GRADIENT AND PLENTY OF LOW LEVEL MOISTURE
LINGERING. IF STRATUS/FOG DO MATERIALIZE...THE IFR/LIFR CONDITIONS
SHOULD IMPROVE TO MVFR TOWARD MID MORNING SATURDAY.

&&

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

$$

SYNOPSIS...MARSILI
SHORT TERM...MARSILI
LONG TERM...STEINWEDEL
AVIATION...MARSILI


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