Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 200013
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
813 PM EDT FRI SEP 19 2014

.SYNOPSIS...
ISSUED AT 758 PM EDT FRI SEP 19 2014

HIGH PRESSURE CURRENTLY OVER THE AREA WILL CONTINUE TO MOVE
EASTWARD THROUGH TONIGHT AND THEN EXPECT AN UPPER LEVEL
DISTURBANCE TO MOVE THROUGH SATURDAY. SCATTERED SHOWERS AND
THUNDERSTORMS MAY MOVE INTO THE SOUTHERN GREAT LAKES BY
MORNING...BUT THE COVERAGE OF SHOWERS AND THUNDERSTORMS IS
EXPECTED TO INCREASE LATER IN THE AFTERNOON AND EVENING. LOW
TEMPERATURES TONIGHT WILL BE IN THE LOWER TO MIDDLE 50S. HIGH
TEMPERATURES TOMORROW WILL BE IN THE UPPER 70S TO LOWER 80S.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 353 PM EDT FRI SEP 19 2014

CONVECTIVE POTENTIAL ON SATURDAY/SATURDAY NIGHT WILL CONTINUE TO
BE THE PRIMARY FOCUS OF THE SHORT TERM.

IN THE MEANTIME...BROAD LOW AMPLITUDE UPPER LEVEL RIDGING WILL
QUICKLY TRANSLATE EASTWARD ACROSS THE GREAT LAKES/OHIO VALLEY
THIS MORNING WITH CONTINUED SLOW EASTWARD MIGRATION OF LOW LEVEL
ANTICYCLONE NORTHEAST CONUS/SOUTHEAST CANADA. A 50-60 KNOT LLJ IS
EXPECTED TO TAKE SHAPE TONIGHT...WITH STRONGEST LOW LEVEL MOIST
TRANSPORT TAKING SHAPE FROM MID MS RIVER VALLEY NORTHEASTWARD
INTO THE WESTERN GREAT LAKES REGION LATER TONIGHT. CONVECTION MAY
DEVELOP IN ASSOCIATION WITH STRENGTHENING LLJ AND WEAK UPPER
PERTURBATIONS ENTERING WESTERN GREAT LAKES OVERNIGHT. HAVE KEPT
FORECAST AREA DRY OVERNIGHT...ALTHOUGH A VERY LOW END CHANCE OF A
SHOWER MAY EXIST ACROSS THE FAR NORTHWEST TOWARD DAYBREAK AS
STRONGER LOW/MID LEVEL THETAE ADVECTION PROGRESSES INTO THE AREA.
OTHERWISE FOR TONIGHT...MID AND HIGH LEVEL CLOUDS WILL BE ON THE
INCREASE PARTICULARLY DURING THE OVERNIGHT HOURS WHICH COMBINED
WITH STRENGTHENING LOW LEVEL WAA WILL PROVIDE MILDER MINS FROM
THE MID TO UPPER 50S...TO THE LOWER 50S OR AROUND 50 EAST.

STILL PLENTY OF UNCERTAINTY REMAINING IN REGARDS TO
CONVECTIVE/SEVERE RISK FOR SATURDAY. CONVECTION MAY BE ONGOING
EARLY SATURDAY MORNING ACROSS THE WESTERN GREAT LAKES IN
ASSOCIATION WITH AFOREMENTIONED LLJ FORCING. WHILE PROPAGATION
VECTORS WOULD TEND TO KEEP THIS ACTIVITY NORTH OF LOCAL
AREA...SOME ADDITIONAL DEVELOPMENT ALONG RESIDUAL OUTFLOW
BOUNDARIES COULD ALLOW FOR A FEW SHOWERS/ISOLATED STORMS TO WORK
INTO FAR NORTHWEST PORTIONS OF THE AREA AFTER DAYBREAK...BUT
CONFIDENCE IN THIS SCENARIO IS LOW. NEXT UPSTREAM MID LEVEL
TROUGH WILL APPROACH THE GREAT LAKES LATE SATURDAY MORNING
ALLOWING FOR AXIS OF STRONG LOW LEVEL MOISTURE CONVERGENCE TO
SHIFT ACROSS APPROXIMATELY NORTHERN HALF OF THE AREA. AS PREVIOUS
DISCUSSION MENTIONED...AVAILABLE INSTABILITY DURING THE DAY
SATURDAY WILL BE HIGHLY SENSITIVE TO NEAR SFC/SFC
TEMPERATURES...AND GIVEN THE ABOVE INCREASE IN FORCING...SOME
POSSIBILITY EXISTS FOR THIS INSTABILITY TO BE TEMPERED. WHILE
MOISTURE TRANSPORT WILL BE STRONG PRECEDING THE FRONT...NAM MAY
BE A BIT AGGRESSIVE WITH SFC DEW POINTS...AND THUS A BIT ON THE
AGGRESSIVE SIDE WITH INSTABILITY PROGS. NEVERTHELESS..GIVEN
STEEPISH MID LEVEL LAPSE RATES...SURFACE BASED CAPES ON THE ORDER
OF 750-1500 J/KG AT LEAST APPEAR TO BE A POSSIBILITY DEPENDING ON
EXTENT OF CLOUD COVER. DEEP LAYER SHEAR AND 0-3 KM SHEAR VECTORS
SHOULD STEADILY STRENGTHEN DURING THE DAY AS BELT OF STRONGER
MID/UPPER LEVEL WESTERLIES PROGRESSES THROUGH BASE OF THE MID
LEVEL TROUGH. GIVEN LOW/MODERATE INSTABILITY AND HIGH SHEAR
ENVIRONMENT...CANNOT RULE OUT AT LEAST AN ISOLD SEVERE THREAT
(MAINLY ISOLD DAMAGING WIND GUSTS) DEPENDING ON HOW INSTABILITY
EVOLVES GIVEN STRENGTHENING BACKGROUND WIND FIELD AND
UNIDIRECTIONAL NATURE TO FLOW. WINDOW OF SEVERE POTENTIAL SHOULD
BE SOMEWHAT LIMITED...WITH PRELIMINARY INDICATIONS IN THE 21Z-03Z
TIMEFRAME.

A PUNCH OF DRIER MID LEVEL AIR TO ADVECT INTO THE AREA
OVERNIGHT...BUT SECONDARY AXIS OF PREFRONTAL LOW LEVEL MOISTURE
POOLING SHOULD KEEP ENOUGH ELEVATED INSTABILITY IN PLACE FOR
CONTINUED SCATTERED SHOWER/THUNDERSTORMS DURING THE OVERNIGHT
HOURS AS NEXT UPSTREAM UPPER LEVEL TROUGH APPROACHES. SLIGHTLY
MORE DELAYED FROPA EARLY SUNDAY MORNING AND ABUNDANT CLOUD COVER
WILL PROVIDE MILDER MINS IN THE LOWER AND MID 60S.

&&

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 353 PM EDT FRI SEP 19 2014

LONG TERM PERIOD BEGINS SUNDAY MORNING WITH DRY SLOT BEHIND COLD
FRONT INITIALLY OVER THE AREA. MOST PCPN ASSOCIATED WITH FRONTAL
BOUNDARY SHOULD BE EXITING THE AREA BY 12Z. MODEL SOUNDINGS
INDICATE POST FRONTAL INVERSION WITH TRAPPED LOW LEVEL MOISTURE
SUGGESTING LINGERING CLOUD COVER INTO EARLY AFTERNOON. WE HAVE
BEEN DISCUSSING THE POSSIBILITY OF SHOWERS WITH SECONDARY SHORT
WAVE FOR SEVERAL DAYS. LATEST MODEL GUIDANCE SHOWING A RATHER
STRONG PV ANOMALY NOW DROPPING INTO THE AREA BY MID DAY WITH
STRONG DPVA WITHIN THIS SHORT WAVE TROUGH. DEEPER MOISTURE IS
CERTAINLY SCOURED AS THIS FEATURE NEARS BUT CONCERN LIES WITH
TRAPPED LOW LEVEL MOISTURE AND ANY WEAK LAKE CONTRIBUTION
PROVIDING ENOUGH MOISTURE WITH LARGE SCALE LIFT TO PRODUCE SOME
LIGHT SHOWERS. SOUNDINGS ALSO INDICATE A BIT OF ELEVATED
INSTABILITY IN WAKE OF MAIN COLD FRONT. HAVE THEREFORE ADDED SOME
LOW CHANCE POPS BACK TO FORECAST SUNDAY...ESPECIALLY NORTH AND
EAST WHERE STRONGER INFLUENCE OF PV ANOMALY SEEMS TO BE FOCUSED
WITH AGREEMENT AMONG THE MODELS. PASSAGE OF THIS FEATURE SHOULD
THEN LEAD TO CLEARING SKIES AND COOLER TEMPERATURES SUNDAY NIGHT.

MODELS HAVE CONTINUED TO TREND WARMER POST FRONTAL WITH MODIFIED
AIRMASS AND DEEPER TROUGH AXIS TO OUR EAST MONDAY. SURFACE HIGH
PRESSURE WILL SETTLE IN MONDAY AND CONTINUE THROUGH THE END OF
THE WEEK WITH A MODERATING TEMPERATURE TREND. EXPECT TEMPS
SIMILAR TO LAST FEW DAYS WITH LOWS IN THE LOWER 40S AND HIGHS IN
THE 60S TO BEGIN THE WEEK BUT WARMING TO LOWS IN THE 50S AND
HIGHS IN THE 70S BY MID TO LATE WEEK. DRY CONDITIONS TO EXIST
WITH RIDGING ALOFT BECOMING ANCHORED RIGHT OVER THE AREA THROUGH
THE WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 809 PM EDT FRI SEP 19 2014

VFR MET CONDITIONS TO DOMINATE THROUGH THE FORECAST PERIOD.
SHARPENING UPSTREAM TROF TO BRING INCREASE IN DEEP LAYER SHEAR TO
REGION SAT AFTERNOON. CONCERN CONTINUES TO REVOLVE AROUND DEGREE
OF INSTABILITY AS ANTICIPATED EARLY MORNING DECAY OF UPSTREAM
CONVECTION MAY INHIBIT SFC HEATING. FOR NOW WILL INTRODUCE AS
VCTS LATE IN FORECAST PERIOD AT KSBN WITH KFWA CONCVECTION FREE
DUE TO BOTH LATER TIMING AND PREVALENT HEIGHT FALL CENTROID TRACK
REMAINING WELL NORTH /NERN WI MIDDAY INTO LAKE HURON SAT
EVENING/.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 5 PM EDT
     SATURDAY FOR LMZ043-046.

&&

$$

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


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