Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 210850
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
450 AM EDT THU AUG 21 2014

.SYNOPSIS...
ISSUED AT 152 AM EDT THU AUG 21 2014

PERIODIC SHOWERS AND THUNDERSTORMS ARE POSSIBLE INTO FRIDAY AS A
WARM FRONT SLOWLY MOVES NORTH INTO THE AREA. HEAT AND HUMIDITY
WILL RETURN BY FRIDAY AS THIS FRONT MOVES NORTH. HIGHS TODAY WILL
BE IN THE LOWER TO MID 80S. LOWS THE NEXT SEVERAL NIGHTS WILL BE
AROUND 70. HIGHS THIS WEEKEND WILL BE AROUND 90 DEGREES.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 449 AM EDT THU AUG 21 2014

UPPER LEVEL JET DYNAMICS COMBINED WITH THE LEADING EDGE OF THETA E
CONVERGENCE WAS HELPING TO TRIGGER ISOLATED STORMS AND AN AREA OF
SHOWERS NORTH OF THE FRONT. THE STORMS WERE HIGH BASED EARLY THIS
MORNING...BUT SHOULD BECOME MORE SURFACE BASED AS THE FRONT MOVES
NORTH AND AS THE ATMOSPHERE DESTABILIZES WITH DAYTIME HEATING LATER
TODAY. THETA E FLUX WILL INCREASE TONIGHT...WITH A BETTER CHANCE FOR
SHOWERS AND STORMS AS AN UPPER LEVEL DISTURBANCE TOPS THE UPSTREAM
RIDGE AND MOVES INTO THE WESTERN GREAT LAKES REGION. THE 12KM NAM
APPEARED TO HAVE A REASONABLE HANDLE ON THE TIMING OF THIS UPSTREAM
SYSTEM AND THE TRACK OVER THE UPPER LEVEL RIDGE...SO HAVE LIKELY
THUNDERSTORM CHANCES LATER TONIGHT. SEVERE STORMS ARE POSSIBLE GIVEN
LOW LEVEL SHEAR TOPPING OUT AT 30 TO 40 M/S. HAVE RAISED HIGHS
TODAY. THE NAM/MET HAS RAISED HIGHS TODAY 5 DEGREES AT SBN AND
APPEARS ON TRACK...COMING MORE IN LINE WITH THE GFS/MAV. 850 MB
TEMPS WILL BE BETWEEN 18C AND 19C TODAY...AND SOME SUN TODAY SHOULD
ALLOW HIGHS TO RISE TO BETWEEN 82F AND 86F.

&&

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 449 AM EDT THU AUG 21 2014

MAIN CONCERN THIS PERIOD IS POTENTIAL FOR EXCESSIVE HEAT AS STRONG
UPR LEVEL RIDGE BUILDS INTO THE AREA RESULTING IN HEAT INDICES IN
THE 90S EACH AFTN. ALTHOUGH THESE READINGS ARE A BIT BLO OUR
ADVISORY CRITERIA... IMPACTS MAY BE GREATER THAN USUAL DUE EXPECTED
RATHER LONG DURATION OF THE HEAT WAVE... AND DIFFICULTY FOR PEOPLE
TO BECOME ACCLIMATED TO THE HEAT GIVEN ABNORMALLY COOL TEMPS THUS
FAR THIS SUMMER.

CONVECTION AT NOSE OF A WK WLY LLJ MAY BE ONGOING IN OUR AREA AT
THE  THE START OF THE PERIOD FRIDAY MORNING. WK LOW LEVEL WAA
PATTERN AND STNRY SFC BOUNDARY DRAPED ACROSS NERN PORTION OF THE CWA
EXPECTED FRI WHICH MAY PROVIDE FOCUS FOR REDEVELOPMENT IN THE AFTN
AS AIRMASS DESTABILIZES. THIS BOUNDARY EXPECTED TO REMAIN OVER THE
AREA FRI NGT WITH NOSE OF WSWLY LLJ OVER THE MID MS VALLEY PROVIDING
FORCING FOR CONVECTION UPSTREAM OVERNIGHT WHICH COULD BE SUSTAINED
INTO OUR AREA GIVEN LINGERING WK/MODERATE ELEVATED INSTABILITY.
RATHER STRONG NWLY FLOW ALOFT ON EAST SIDE OF MS VALLEY RIDGE WILL
PROVIDE DECENT DEEP LAYER SHEAR FRI/FRI NGT...ESPECIALLY OVER ERN
PORTIONS OF THE CWA WHICH ALSO COULD AID IN CONVECTIVE PERSISTENCE
AS WELL AS SUPPORT A FEW STRONG/SVR STORMS AROUND PEAK HEATING FRI
AFTN/EVE. DOUBT CONVECTION WILL BE SUFFICIENTLY WIDESPREAD OR LAST
LONG ENOUGH TO HOLD TEMPS DOWN SIGNIFICANTLY FRIDAY. GIVEN H85 TEMPS
PROGGED IN THE 19-20C RANGE STAYED CLOSE TO PREVIOUS FCST WITH HIGHS
RANGING FROM THE M80S NE TO AROUND 90 SW. DWPTS SHOULD ALSO BE
RISING TO THE L-M70S WHICH WILL RESULT IN AFTN HEAT INDICES ABOUT
5-10F HIGHER THAN TEMPS. LIGHT WINDS FRI NGT SHOULD ALLOW FOR SOME
RADIATIONAL COOLING SO EXPECT MINS TO BE IN THE U60S NE AND L70S SW.

SIMILAR CONDITIONS EXPECTED SATURDAY. UPR RIDGE AXIS SHOULD MOVE
SLIGHTLY EAST INTO OUR AREA AS STRONG TROF MOVES ACROSS THE NRN
ROCKIES. E-W ORIENTED SURFACE BOUNDARY WILL LIKELY REMAIN OVER THE
AREA PROVIDING SOME FOCUS FOR CONVECTION AS AIRMASS DESTABILIZES
DURING THE DAY. WK LOW LEVEL GRADIENT WINDS AND VERY MOIST AIRMASS
OVER THE AREA SHOULD AGAIN LIMIT HEATING BUT EXPECT SUFFICIENT
MIXING TO ALLOW FOR HIGHS CLOSE TO FRIDAYS READINGS AS SUGGESTED BY
MAV MOS TEMPS.

STNRY SFC BOUNDARY SHOULD LIFT NORTH OF OUR CWA SAT NGT-SUNDAY AS
SFC LOW DEEPENS OVER THE NRN PLAINS. THIS SHOULD RESULT IN MAINLY
DRY CONDITIONS BY SUNDAY WITH TEMPS CONTG TO SLOWLY WARM. NRN PLAINS
LOW EXPECTED TO LIFT NE-E INTO ONTARIO MONDAY AND TO QUEBEC TUE WITH
TRAILING WK CDFNT DROPPING SOUTH INTO OUR AREA BY THAT TIME. SOME
SUPPRESSION OF UPR RIDGE PER ECMWF SOLUTION SEEMS APPROPRIATE AS
SHRTWV BREAKS OVER THE TOP ACROSS THE UPR GRTLKS...  SO WKNG CAPPING
INVERSION/CHC TSTMS... AND SLIGHTLY LOWER TEMPS FCST BY TUE. MEDIUM
RANGE MODELS DIFFERING SOLUTIONS WRT PERSISTENCE OF UPR RIDGE TUE
AMPLIFIES DIFFERENCES BY WED WITH ECMWF SUGGESTING RIDGING BUILDING
BACK INTO THE REGION WHILE GFS FCSTG STRONG SHRTWV APPROACHING.
GIVEN LARGE DIFFERENCES STAYED CLOSE TO PREVIOUS FCST WHICH WAS FOR
CONTD SLOW COOLING TREND AND A LOW CHC OF TSTMS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 152 AM EDT THU AUG 21 2014

UPPER LEVEL JET DYNAMICS WERE HELPING TO TRIGGER ISOLATED STORMS
AND AN EXPANDING AREA OF SHOWERS WELL NORTH OF THE FRONT. STORMS
WERE HIGH BASED...WITH BASES NEAR 100K. HAVE KEPT THE BULK OF THE
TIMING OF THE STORMS IN THE ONGOING TAFS...BUT HAVE RAISED CIGS
EARLY IN THE PERIOD GIVEN THESE HIGH BASES. STORMS LATER TODAY
SHOULD BECOME MORE SURFACE BASED AS THE FRONT MOVES NORTH AND AS
THE ATMOSPHERE DESTABILIZES WITH DAYTIME HEATING. THETA E FLUX
INCREASES TONIGHT...WITH A BETTER CHANCE FOR SHOWERS AND STORMS.
FOR NOW...PLACED VCTS IN THE LAST 6 HOURS OF THE TAF. MAY HAVE TO
ADD A TEMPO GROUP AS MORE PRECISE TIMING BECOMES MORE EVIDENT.


&&

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

$$

SYNOPSIS...SKIPPER
SHORT TERM...SKIPPER
LONG TERM...JT
AVIATION...SKIPPER


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