Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 192108
AFDIWX

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

.SYNOPSIS...
ISSUED AT 458 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 TOMORROW. SCATTERED SHOWERS AND
THUNDERSTORMS MAY MOVE INTO THE SOUTHERN GREAT LAKES TOMORROW
MORNING...BUT THE COVERAGE OF SHOWERS AND THUNDERSTORMS IS
EXPECTED TO INCREASE LATER TOMORROW AFTERNOON INTO TOMORROW 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 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 145 PM EDT FRI SEP 19 2014

VFR CONDITIONS ARE EXPECTED THROUGH THE BULK OF THIS FORECAST
PERIOD. LARGE LOW LEVEL ANTICYCLONE ACROSS EASTERN CONUS WILL
CONTINUE TO BE THE PRIMARY FEATURE CONTROLLING WEATHER ACROSS
NORTHERN INDIANA THROUGH TONIGHT. SOUTHEAST WINDS ON THE WESTERN
PERIPHERY OF THIS HIGH PRESSURE WILL CONTINUE THROUGH THE
PERIOD...VEERING MORE SOUTHERLY TONIGHT AS NEXT TROUGH OF LOW
PRESSURE TRACKS INTO THE UPPER MIDWEST. STRONG LOW LEVEL THETAE
ADVECTION PRECEDING COLD FRONT IN ASSOCIATION WITH NEXT MID/UPPER
LEVEL SYSTEM WILL WORK ACROSS NORTHERN INDIANA SATURDAY MORNING.
SOME SHOWERS MAY DEVELOP IN ASSOCIATION WITH THIS STRONG LOW LEVEL
THETAE ADVECTION...BUT GREATER CHANCES OF SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO HOLD OFF UNTIL AFTER 18Z AS
MID/UPPER LEVEL TROUGH AXIS APPROACHES WESTERN GREAT LAKES REGION.


&&

.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...MARSILI


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