Area Forecast Discussion
Issued by NWS Northern Indiana

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911
FXUS63 KIWX 170735
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
335 AM EDT SUN MAY 17 2015

.SYNOPSIS...
ISSUED AT 142 AM EDT SUN MAY 17 2015

CHANCES OF SHOWERS AND THUNDERSTORMS WILL INCREASE AGAIN THIS
AFTERNOON INTO THIS EVENING AS AN UPPER LEVEL STORM SYSTEM BEGINS
TO LIFT OUT OF THE CENTRAL PLAINS. WARM CONDITIONS CAN BE EXPECTED
TODAY IN ADVANCE OF THE COOL FRONT WITH THIS SYSTEM...WITH SHOWERS
AND THUNDERSTORMS BECOME MORE LIKELY BY THIS EVENING. SHOWERS AND
STORMS WILL TAPER OFF LATE TONIGHT...BUT A SLOW MOVING COLD FRONT
MAY PROVIDE A FOCUS FOR MORE SCATTERED SHOWERS AND THUNDERSTORMS
ON MONDAY. HIGH TEMPERATURES THIS AFTERNOON WILL REACH AROUND
80...WITH LOW TEMPERATURES TONIGHT ONLY DROPPING INTO THE MID TO
UPPER 60S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 331 AM EDT SUN MAY 17 2015

PRIMARY FORECAST CONCERN WILL CONTINUE TO BE CONVECTIVE
CHANCES...ESPECIALLY FROM LATER THIS AFTERNOON INTO THIS EVENING.

TEMPORARY LULL IN PRECIP CHANCES EARLY THIS MORNING AS WEAK UPPER
LEVEL SHORT WAVE CONTINUES TO EXIT THE AREA ACROSS NORTHERN OHIO
WHILE OVERALL RISING MID LEVEL HEIGHT TENDENCIES CONTINUE. STRATUS
SHOULD CONTINUE TO EXPAND THROUGH THE EARLY MORNING HOURS BEFORE
ERODING TOWARD MIDDAY WHICH SHOULD ALLOW FOR A SLIGHTLY DELAYED
DIURNAL TEMP BOOST INTO LATER THIS MORNING. OTHERWISE FOR
TODAY...LEAD SHORT WAVE KICKING OUT OF THE CENTRAL PLAINS MAY GET
SOME CONVECTIVE ENHANCEMENT FROM DECAYING MCS/SQUALL LINE ACROSS THE
CENTRAL PLAINS/CORN BELT THIS MORNING AS IT APPROACHES THE WESTERN
GREAT LAKES LATER THIS AFTERNOON. INCREASING UPPER DIFFLUENCE AHEAD
OF PARENT UPPER TROUGH AND THE POSSIBILITY OF CONVECTIVELY ENHANCED
VORTICES SHOULD LEND TO PREFRONTAL TROUGH TYPE FEATURE TO REACH
WESTERN PORTIONS OF THE AREA LATE THIS AFTERNOON. NAM MAY BE A BIT
OVERDONE WITH THE EXTENT OF MOISTURE POOLING ALONG THIS PREFRONTAL
TROUGH. NONETHELESS...THIS PREFRONTAL TROUGH FEATURE WILL LIKELY BE
A FOCUSING MECHANISM FOR AT LEAST SCATTERED CONVECTION LATE THIS
AFTERNOON/EARLY THIS EVENING WITH TEMPERED NON-NAM GUIDANCE
SUGGESTING 1500-2500 MLCAPES ACROSS THE AREA. MOST FAVORED AREA
OF FORCING STILL APPEARS TO BE ACROSS NORTHWEST HALF OF THE
FORECAST AREA GIVEN RESPECTABLE AMPLITUDE TO MID LEVEL RIDGING IN
ADVANCE OF THIS SYSTEM. HAVE TENDED TO FAVOR THE SLIGHTLY FASTER
ENVELOPE OF GUIDANCE FOR CONVECTIVE CHANCES ACROSS WESTERN HALF
THIS AFTERNOON GIVEN THE POSSIBLE UPSTREAM INFLUENCES FROM
DECAYING MCS THIS MORNING.

THIS AMPLIFIED NATURE TO THE FLOW WILL ALSO CREATE A SHARP WEST TO
EAST DEEP LAYER SHEAR MAGNITUDE GRADIENT FROM THE MID/UPPER MS
VALLEY INTO THE SOUTHERN GREAT LAKES. THE BEST COMBINATION OF
SHEAR/INSTABILITY FOR LOCAL AREA STILL APPEARS TO BE ACROSS FAR
WESTERN LOCATIONS WHERE MOISTURE POOLING WILL BE MAXIMIZED ALONG
WITH THE PROXIMITY TO THE EASTERN PERIPHERY OF STRONGER MID/UPPER
FLOW. AS PREVIOUS DISCUSSION MENTIONED...MID LEVEL LAPSE RATES
LIKELY TO BE ON THE MARGINAL SIDE...SO ANY SEVERE THREAT WILL DEPEND
HEAVILY ON THE MAGNITUDE OF MOISTURE POOLING/SURFACE BASED
INSTABILITY WITH THE PREFRONTAL TROUGH TO POSSIBLY PARTIALLY MAKE UP
FOR MID LEVEL LAPSE RATES. OVERALL SEVERE THREAT STILL APPEARS TO BE
ON THE LOW SIDE GIVEN THE CONDITIONAL NATURE OF THE INSTABILITY
MAGNITUDES AND SOMEWHAT MARGINAL SHEAR PROFILES...BUT CANNOT
COMPLETELY RULE OUT AN ISOLATED STRONG OR SEVERE STORM LATER THIS
AFTERNOON/EVENING ESPECIALLY ACROSS PORTIONS OF NORTH CENTRAL
INDIANA/SOUTHWEST LOWER MICHIGAN.

EXITING LEAD SHORT WAVE ACROSS SRN LOWER MICHIGAN TONIGHT AND
EASTWARD ADVECTION OF MID LEVEL DRY SLOT SHOULD BEGIN TO DIMINISH
SHOWER/STORM CHANCES FROM WEST TO EAST AFTER 03Z OR 06Z. NOT MUCH
CHANGE MADE TO PREVIOUS LIKELY POPS ACROSS WESTERN TWO THIRDS OF THE
AREA THIS EVENING....ALTHOUGH CONFIDENCE IN CONVECTIVE COVERAGE MAY
BE A BIT LOWER ACROSS SOUTH CENTRAL LOCATIONS MORE DIVORCED FROM
STRONGER MID/UPPER LEVEL FORCING. ANOTHER MILD NIGHT IS IN STORE
WITH LOWS GENERALLY IN THE MID TO UPPER 60S.

&&

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 331 AM EDT SUN MAY 17 2015

ONE LAST (RELATIVELY) ACTIVE DAY ON MONDAY BEFORE VERY TRANQUIL
WEATHER PATTERN SETS UP FOR THE REST OF THE WEEK. CONFIDENCE IN ANY
MEANINGFUL PRECIP ALONG AND AHEAD OF COLD FRONTAL PASSAGE ON MONDAY
IS LOW. MAIN THETA-E RIDGE IS SHUNTED EASTWARD BY MONDAY MORNING
WITH VEERED AND WEAKENING LOW LEVEL FLOW. LITTLE TO NO SUPPORT FOR
ASCENT ALOFT EITHER. UPPER JET AXIS WILL BE ALMOST DIRECTLY OVERHEAD
WITH RIGHT ENTRANCE DYNAMICS FOCUSED TO OUR SOUTHEAST. MAIN AREA OF
CVA IS ALSO DISPLACED TO OUR NORTHWEST...LEAVING LITTLE MORE THAN
SOME VERY BROAD/WEAK CONVERGENCE ALONG SURFACE COLD FRONT TO SERVE
AS IMPETUS FOR CONVECTION. LATEST NAM12 SUGGESTS SBCAPE VALUES
CLIMBING TO AROUND 2500 J/KG MONDAY AFTERNOON BUT THIS SEEMS VASTLY
OVERDONE. RAW NAM GUIDANCE INDICATES SURFACE DEWPOINTS IN THE UPPER
60S TO NEAR 70F BUT MUCH PREFER LOWER 60S SEEN IN RAW GFS AND MOS
GUIDANCE. THIS GENERATES 500-1000 J/KG OF 0-1KM MLCAPE...ENOUGH TO
SUPPORT A FEW ISO/SCT THUNDERSTORMS BUT LACK OF WELL-DEFINED FORCING
AND DEEP LAYER MOISTURE PRECLUDE ANYTHING MORE THAN CHANCE
POPS...WITH THE HIGHEST VALUES IN OUR SOUTHEAST COUNTIES. 0-6KM
SHEAR VALUES DO INCREASE TO AROUND 30 KTS BUT LACK OF GOOD
MOISTURE...INSTABILITY...AND FORCING SUGGEST A LOW RISK FOR SEVERE
WEATHER.

STORY THEREAFTER BECOMES ONE OF COOL...DRY...AND TRANQUIL WEATHER
THROUGH THE END OF THE WEEK. HIGHLY CONFLUENT FLOW OVER THE GREAT
LAKES WITH STRONG RIDGE OVER WESTERN CANADA AND PERSISTENT TROUGHING
OVER QUEBEC WILL MAINTAIN COOL HIGH PRESSURE THROUGH THE REST OF THE
PERIOD. INCREASINGLY SHEARED WAVE WILL TRY TO BRING SOME LIGHT RAIN
TO OUR SOUTHWEST COUNTIES ON WEDNESDAY BUT WEAK FORCING IN A VERY
DRY AND STABLE ENVIRONMENT SUGGEST LITTLE MORE THAN SOME INCREASED
CLOUDS. EXPECT TEMPS ROUGHLY 10 DEGREES BELOW NORMAL TUES-THURS WITH
SOME SLOW MODERATION INTO NEXT WEEKEND. COULD ACTUALLY BE SOME
POTENTIAL FOR FROST IN OUR NORTHERN COUNTIES TUESDAY NIGHT IF SOME
OF THE CURRENT RAW GUIDANCE VERIFIES. STEADY GRADIENT WIND AND
POTENTIAL FOR SOME INCREASING CLOUDS WARRANT A CAUTIOUS APPROACH FOR
NOW BUT DID LOWER MIN TEMPS BY SEVERAL DEGREES. DEFINITELY SOMETHING
TO WATCH OVER THE NEXT FEW DAYS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 137 AM EDT SUN MAY 17 2015

ABUNDANT LOW LEVEL MOISTURE AND WEAK DIURNAL COOLING WILL CONTINUE
TO ALLOW FOR STRATUS REDEVELOPMENT TONIGHT. HAVE SLIGHTLY DELAYED
TIMING OF MVFR CIGS TO 08Z BASED ON CURRENT TRENDS...BUT HAVE
MAINTAINED TEMPO IFR CONDITIONS IN THE 09Z-12Z TIMEFRAME.
IMPROVEMENT TO HIGHER END MVFR OR VFR IS EXPECTED BY AROUND MIDDAY SUNDAY.
PRECIP CHANCES WILL REMAIN LOW THROUGH SUNDAY MORNING...WITH
INCREASING CHANCES FROM WEST TO EAST FROM MID AFTERNOON-EARLY
EVENING. A PREFRONTAL TROUGH AND POOLED LOW LEVEL MOISTURE SHOULD
ACT AS A FOCUSING CORRIDOR FOR AT LEAST SCATTERED CONVECTION IN
ASSOCIATION WITH FAIRLY WEAK LEAD SHORT WAVE. DID ADD SHOWERS/VCTS
MENTION AT KSBN BY AROUND 00Z...BUT WILL HOLD OFF ON MENTION AT
KFWA WITH A BIT LESSER CONFIDENCE AS LEAD SHORT WAVE LIFTS
NORTHEAST ACROSS LOWER MICHIGAN. LIGHT SOUTH WINDS THROUGH THE
PREDAWN HOURS WILL BECOME SOMEWHAT GUSTY INTO THE 15 TO 20 KNOT
RANGE DURING THE DAY SUNDAY.

&&

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

$$

SYNOPSIS...MARSILI
SHORT TERM...MARSILI
LONG TERM...AGD
AVIATION...MARSILI


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