Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 290450
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1250 AM EDT FRI AUG 29 2014

.SYNOPSIS...
ISSUED AT 1250 AM EDT FRI AUG 29 2014

A WARM FRONT WILL LIFT NORTHEAST INTO THE AREA TODAY INTO THIS
EVENING BRINGING INCREASING CHANCES FOR SHOWERS AND
THUNDERSTORMS...ESPECIALLY LATER THIS AFTERNOON AND EVENING ACROSS
NORTHWEST INDIANA AND SOUTHWEST LOWER MICHIGAN. HIGHS THIS
AFTERNOON WILL REACH THE LOW TO MID 80S. SATURDAY WILL FEATURE
BETTER CHANCES FOR THUNDERSTORMS AND LOCALLY HEAVY RAINFALL AS A
LOW PRESSURE SYSTEM TRACKS INTO THE GREAT LAKES REGION. LOWS
TONIGHT WILL DROP INTO THE UPPER 60S...AND RECOVER INTO THE LOW TO
MID 80S ON SATURDAY.

&&

.UPDATE...
ISSUED AT 707 PM EDT THU AUG 28 2014

CONVECTION HAS DEVELOPED UPSTREAM AND MOVING INTO NORTH CENTRAL
ILLINOIS THIS EVENING ALONG THETA E SURGE AND NOSE OF WEAK 20 KNOT
LOW LEVEL JET WITH WEAK SHORT WAVE. THETA E ADVECTION MOVES THROUGH
THE AREA OVERNIGHT WITH NOSE OF THIS WEAK LLJ FOCUSED ACROSS THE
NORTHWEST ON WESTERN PERIPHERY OF MID LEVEL RIDGE. LOW LEVEL EASTERLY
DRY FLOW TO HELP ERODE SOME OF THIS CONVECTION BUT CONCERN SOME
ELEVATED SHRA/TSRA COULD RIDE WITH THE MOISTURE ADVECTION AND
MAKE IT INTO PARTS OF THE WEST AND NORTHWEST CWA. HAVE ADDED LOW
CHANCE POPS FOR NOW TO A LINE ROUGHLY WEST OF LOGANSPORT TO
COLDWATER AND WILL MONITOR TRENDS NEXT FEW HOURS FOR POSSIBLE
UPTICK IN POPS LATER THIS EVENING.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 331 PM EDT THU AUG 28 2014

SFC RIDGE DRAPED THROUGH THE ERN LAKES THIS AFTN WILL GIVE WAY TO
LOW PRES ADVG NEWD THROUGH THE PLAINS. AT THE SFC OLD FNTL BNDRY
DRAPED THROUGH THE MID MS VALLEY WILL MIX RAPIDLY NWD ON FRI AS
PARENT SW TROUGH LIFTS OUT INTO WRN WI BY EVENING.

12Z MODEL GUIDANCE SIMILAR ALOFT YET GENERALLY SLWR W/DEEMED
ADEQUATE LL MSTR FLUX AND HAVE DAMPENED BOTH POP/WX EXTENT DURING
THE DAY AS MOST FVRBL THETA-E SURGE ALG NOSE OF NWD INTENSIFYING LLJ
DVLPS TWD 00Z. OTRWS TEMPS WILL MODERATE CONSIDERABLY VS THIS AFTN
YET KEPT W/A SPLIT BASED MOS BLEND IN LIGHT OF COPIOUS MID-HIGH CLD
SHIELD UPSTREAM RETARDING A MORE SIG DIURNAL AND SUSPECT THIS MAY BE
THE CASE HERE ON FRI ESP W/SFC TRAJECTORIES REMAINING MORE SELY
THROUGH THE DAY.

&&

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 331 PM EDT THU AUG 28 2014

...MAIN CONCERNS FOR THE LONG TERM ARE HEAVY RAIN THIS WEEKEND
AND THE POTENTIAL FOR SEVERE WEATHER FOR THE START OF THE WORK
WEEK...

QUITE AN ACTIVE START TO THE LONG TERM PERIOD...WITH SEVERAL LOW
PRESSURE SYSTEMS FORECAST TO PASS NEAR THE CWA...

THE FIRST SFC LOW PRESSURE SYSTEM TO IMPACT THE CWA DEVELOPS OVER
WI/MN/IA IN RESPONSE TO SEVERAL PERTURBATIONS DEEPENING THE EXISTING
500MB TROUGH FRIDAY NIGHT. BY SUNDAY MORNING...THE LOW WILL REACH
LAKE HURON AND SOUTHERN ONTARIO...WITH THE UPPER LEVEL TROUGH OVER
LOWER MI. THE PRIMARY FORCING ASSOCIATED WITH THE SHORTWAVE WILL
REMAIN NORTH OF THE AREA...WITH A MAXIMUM IN 850-500MB QVECTOR
CONVERGENCE FOCUSED OVER NORTHERN LOWER MI/EASTERN UPPER MI.
HOWEVER...WITH HIGH PRESSURE CENTERED OVER THE ATLANTIC PUMPING
MOISTURE/WARMER AIR FROM THE GULF INTO THE REGION THE COLD FRONT
ASSOCIATED WITH THE APPROACHING LOW PRESSURE SYSTEM STALLS OVER
ILLINOIS/LOWER MI SATURDAY AFTERNOON AND SAT NIGHT. PWATS OVER THE
CWA INCREASE TO 1.5 TO 2 INCHES AND MOISTURE CONVERGENCE IS
MAXIMIZED DURING THIS TIME FRAME. AS A RESULT...KEPT GOING HIGH POPS
ACROSS MUCH OF THE CWA. STILL FEELING CONFIDENT IN THE POTENTIAL FOR
HEAVY RAIN GIVEN WARM CLOUD LAYER DEPTHS OF 12-14KFT AND ROUGHLY
FRONT PARALLEL FLOW. 0-6 KM SHEAR IS NOT ALL THAT IMPRESSIVE
EITHER...THOUGH IT HAS INCREASED FROM PREVIOUS MODEL RUNS TO ROUGHLY
15 TO 25 KNOTS ACROSS THE CWA. KEPT THUNDER IN FOR SATURDAY
AFTERNOON/SUNDAY GIVEN MUCAPE OF 1000-2000 J/KG. WITH INCREASED
MOISTURE...DEWPOINTS FOR THE WEEKEND CLIMB INTO THE UPPER 60S/LOW
70S. WITH HIGH TEMPERATURES IN THE LOW 80S...IT WILL BE QUITE HUMID.
PRECIPITATION CHANCES DWINDLE SUNDAY/SUNDAY NIGHT FROM NW TO SE AS A
RIDGE ALOFT FILTERS INTO THE AREA FOR A BRIEF TIME.

ATTENTION THEN TURNS TO THE START OF THE WORK WEEK...WHEN A SLIGHTLY
DEEPER AND MORE NEGATIVELY TILTED TROUGH SWINGS INTO THE MN/WI/IA
AREA. WITH HIGH PRESSURE STILL HOLDING FIRMLY OVER THE ATLANTIC AND
THE APPROACHING TROUGH/DEVELOPING SURFACE LOW SITUATED IN THE MID
WEST STATES MOISTURE IS ONCE AGAIN EASILY TRANSPORTED INTO THE GREAT
LAKES. PWATS MONDAY GENERALLY BUMP UP TOWARDS 1.5-1.8 INCHES ACROSS
MUCH OF THE IN/SOUTHERN MI/WESTERN OH REGION. THE PATH OF THE
DEVELOPING SURFACE LOW/UL TROUGH IS IMPACTED BY THE EXITING SURFACE
HIGH/RIDGE HOWEVER...MOVING IT FURTHER NORTH THAN THIS WEEKENDS LOW
TRACK. IT LIFTS NORTHEASTWARD FROM THE WI/MN/IA AREA MONDAY
MORNING...INTO UPPER MI MONDAY AFTERNOON...AND JAMES BAY LATE MONDAY
NIGHT. THIS PUTS THE FORECAST AREA UNDER GENERALLY ZONAL FLOW ALOFT
SUSCEPTIBLE TO SMALL PERTURBATIONS. AT THE SURFACE...WE DEAL WITH
THE PASSAGE OF A COLD FRONT. WHETHER OR NOT SEVERE WEATHER DEVELOPS
IN RESPONSE TO THE PASSING SYSTEM WILL DEPEND ON THE TIMING OF THE
FRONT AND WHETHER OR NOT THE HIGHER INSTABILITY/SHEAR MATERIALIZES.
MODELS DISAGREE SLIGHTLY ON THE TIMING...WITH THE GFS BRINGING THE
FRONT INTO IL/LAKE MI BY 18Z MON. THE ECMWF IS A BIT
SLOWER...BRINGING IT INTO THE SAME AREA BY 00Z TUE. IF THE FRONT
ARRIVES DURING PEAK HEATING...THINK SOME STORMS COULD BECOME SEVERE.
GIVEN ABUNDANT MOISTURE AND MODERATE INSTABILITY OF AROUND 1500-2500
J/KG. THE MODELS HAVE BACKED OFF ON THE HIGHER SHEAR VALUES
FORECASTED YESTERDAY...WITH A MAXIMUM OF 30-35 KNOTS. 0-3 KM SRH
VALUES REACH AROUND 150-170 M2/S2...SO WE WOULD BE LOOKING AT
ORGANIZED MULTICELLS. IF INSTABILITY IS HIGHER THAN FORECAST WHEN
SHEAR IS AT A MAXIMUM AND FRONT IS APPROACHING WOULD NOT BE
SURPRISED TO SEE A FEW SUPERCELLS DEVELOP.

MODELS BEGIN TO DISAGREE MORE SIGNIFICANTLY FOR THE MID-LATTER
PORTIONS OF THE WORK WEEK. WITH HIGH PRESSURE TO THE SOUTHEAST STILL
IN PLACE...THE COLD FRONT RESPONSIBLE FOR BUSY WEATHER MONDAY/MONDAY
NIGHT STALLS OUT. GFS/ECWMF DISAGREE WITH THE LOCATION OF THE
STALLED FRONT...AND HENCE THE PRECIPITATION. THE GFS KEEPS THE FRONT
OVER THE CWA...AND THE ECMWF KEEPS IT FURTHER SOUTH...ONLY BRUSHING
THE SOUTHERN FRINGES OF THE CWA. WILL KEEP SLIGHT CHC/CHC POPS FOR
TUESDAY AND WEDNESDAY NIGHT...WITH WEAK HIGH PRESSURE SLIDING INTO
THE AREA. THURSDAY INTO FRIDAY ANOTHER LOW PRESSURE SYSTEM WILL
DEVELOP OVER THE CENTRAL AND NORTHERN PLAINS...BRINGING ADDITIONAL
CHANCES FOR SHOWERS/TSTORMS TO THE AREA. KEPT CONSENSUS POPS FOR NOW
GIVEN UNCERTAINTY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1250 AM EDT FRI AUG 29 2014

MAINLY VFR THROUGH THE TAF CYCLE. REMNANTS OF A CONVECTIVE COMPLEX
WILL LIKELY BRING SOME HIGH BASED/VFR SHOWERS/SPRINKLES TO KSBN
EARLY THIS MORNING...WITH LOW CHANCES FOR ADDITIONAL SCATTERED
SHOWERS THROUGH MID MORNING AT KSBN TIMIED WITH INITIAL 850 MB
THETA-E PUSH. DRIER LOW LEVEL ENVIRONMENT FARTHER REMOVED FROM
WEAK LLJ SUPPORT SHOULD HELP KEEP KFWA MAINLY DRY THROUGH MID AFTN.
SHORTWAVE OPENING NORTHEAST TOWARD IA/SRN MN WILL ALLOW PRIMARY
SFC WARM FRONT/INSTABILITY GRADIENT TO MIX NORTH INTO NORTHERN
INDIANA LATER THIS AFTERNOON-EVENING. THIS FEATURE WILL BRING
INCREASING CHANCES FOR SHOWERS/STORMS WITH IT...ALTHOUGH
CONFIDENCE/COVERAGE REMAINS TOO LOW FOR ANY POINT MENTION AT THIS
FCST RANGE.

&&

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

$$

UPDATE...LASHLEY
SYNOPSIS...STEINWEDEL
SHORT TERM...T
LONG TERM...MCD
AVIATION...STEINWEDEL


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