Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 150936
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
536 AM EDT WED APR 15 2015

.SYNOPSIS...
ISSUED AT 100 AM EDT WED APR 15 2015

HIGH PRESSURE CENTERED OVER THE UPPER LAKES WILL CONTINUE TO
PROVIDE THE AREA WITH DRY EASTERLY WINDS TODAY INTO THIS EVENING.
A WEAK UPPER LEVEL SYSTEM AND SURGE OF MOISTURE WILL BRING SHOWER
CHANCES BACK INTO THE FORECAST LATER TONIGHT INTO THURSDAY. HIGHS
WILL REACH THE 60S BOTH TODAY AND THURSDAY...WITH LOWS TONIGHT
FORECAST TO DROP INTO THE 40S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 328 AM EDT WED APR 15 2015

FAIR WX/SEASONABLE TEMPS WILL REMAIN THE STORY TODAY INTO THIS
EVENING AS THE LOCAL AREA REMAINS UNDER THE INFLUENCE OF DRY/STABLE
LOW LEVEL EASTERLY FLOW (LOCATED ON THE SW FRINGE OF A 1030 MB SFC
HIGH DROPPING SE INTO THE EASTERN LAKES/SE CANADA). MODEST DIURNAL
MIXING AND TIGHTENING PRESSURE GRADIENT BETWEEN THIS AND AN
APPROACHING TROUGH WILL SUPPORT INCREASING WINDS BY LATE
MORNING/AFTN...WITH NOTHING MORE THAN SOME HIGH CLOUDS (LIKELY NOT
AS PERSISTENT/THICK AS YESTERDAY...AT LEAST IN THE AM).

RAIN SHOWER CHANCES INCREASE LATER TONIGHT FROM SW TO NE AS A
WEAK/REMNANT CENTRAL PLAINS UPPER LEVEL TROUGH FINALLY GETS KICKED
NE INTO THE REGION. DEEP LAYERED FORCING WITH THIS FEATURE CONTINUES
TO LOOK WEAK...WHILE LOW-MID LEVEL THETA-E ADVECTION APPEARS
SUBSTANTIAL WITHIN RAMPING/VEERING LOW LEVELS IN ADVANCE OF THE
TROUGH AXIS. MIXED SIGNALS (WEAK FORCING BUT AMPLE MOISTURE) SUGGEST
HOLDING WITH CHC POPS/SCT COVERAGE STILL THE WAY TO GO...BEST
CHANCES IN OUR IN/MI ZONES WHERE HIGHER POPS WERE PLACED.

&&

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 328 AM EDT WED APR 15 2015

PRIMARY FORECAST CHALLENGES CONTINUE TO CENTER ON THURSDAY RAIN
CHANCES AND THEN INCREASING RAIN CHANCES AGAIN MAINLY LATE WEEKEND
AS CUT-OFF UPPER LEVEL TROUGH EVENTUALLY APPROACHES THE REGION.

A WEAK PV ANOMALY...THAT WILL GRADUALLY DAMPEN ACROSS THE GREAT
LAKES REGION ON THURSDAY WILL ONLY SLOWLY MEANDER ACROSS THE AREA
WITH WEAK STEERING FLOW PERSISTING. APPROACH OF THIS PV ANOMALY WILL
ALLOW LOW LEVEL MOISTURE AXIS WITH PWATS AROUND 1 INCH TO PERSIST
INTO THURSDAY. WEAK NATURE OF UPPER FLOW AND GRADUAL DAMPENING OF
THIS DISTURBANCE LENDS SOME LOWER CONFIDENCE AS TO DETAILS REGARDING
TIMING OF MID/UPPER LEVEL TROUGH...BUT CURRENT THINKING IS THAT
PASSAGE OF THIS TROUGH SHOULD END RAIN CHANCES LATE AFTERNOON ACROSS
THE WEST. IT STILL APPEARS AS THOUGH MID LEVEL LAPSE RATES WILL
REMAIN IN THE 6-7 DEG CELSIUS/KM RANGE WITH MOST MODEL DEPICTIONS OF
100-200 J/KG MUCAPE AND FOCUSED PRIMARILY ACROSS THE
SOUTH/SOUTHWEST. DID CONTEMPLATE REMOVING THUNDER MENTION...BUT
DEPENDING ON TIMING OF WEAK UPPER PV ANOMALY...SOME ISOLD THUNDER
POTENTIAL MAY EXIST...ESPECIALLY AT PEAK HEATING. MORE LIMITED
MIXING/THICKER CLOUD COVER ON THURSDAY SHOULD LIMIT HIGH TEMPS CLOSE
TO THAT OF WEDNESDAY...GENERALLY IN THE LOW TO MID 60S ALTHOUGH
PERHAPS SLIGHTLY COOLER NEAR LAKE MICHIGAN WHERE ONSHORE FLOW WILL
BECOME MORE LIKELY IN ASSOCIATION WITH EASTWARD PROGRESSION OF
INVERTED SFC TROUGH. LOW LEVEL MOISTURE AXIS WILL GRADUALLY SHIFT
EAST OF THE AREA THURSDAY NIGHT INTO FRIDAY MORNING...AND HAVE ONLY
MAINTAINED SLIGHT CHANCE SHOWER MENTION ACROSS THE FAR SOUTHEAST
FRIDAY MORNING DUE TO SLOW MOVING NATURE OF WEAK UPPER FORCING.

ON FRIDAY...AN ELONGATED LOW LEVEL RIDGE AXIS WILL SETTLE ACROSS
THE GREAT LAKES/OHIO VALLEY WITH MORE DISTINCTION BETWEEN
SOUTHERN/NORTHERN STREAMS BY THIS TIME AS UPPER LEVEL TROUGH CUTS
OFF ACROSS FOUR CORNERS REGION. PRECIP CHANCES FRIDAY NIGHT-SATURDAY
WILL BE LARGELY DETERMINED BY THE STRENGTH OF NEXT NORTHERN STREAM
TROUGH PROGGED TO TRACK ACROSS THE NORTHERN GREAT LAKES SOME TIME
DURING THIS PERIOD. THIS FEATURE IS STILL WELL OFFSHORE NEAR THE
GULF OF ALASKA THIS MORNING AND THUS CONFIDENCE IS SOMEWHAT LOW HOW
THIS FEATURE WILL EVOLVE DURING THIS PERIOD. NAM REMAINS SOMEWHAT
SHARPER WITH THE MID/UPPER LEVEL TROUGH...AND THUS DOES INDUCE A
BETTER AXIS OF POOLED LOW LEVEL MOISTURE ALONG AND AHEAD OF THE
FRONT FRIDAY NIGHT. NOT QUITE READY TO BUY INTO THIS SOLUTION AS OF
YET WITH CONCERN THAT UPPER RIDGING DOWNSTREAM OF ROCKIES CUT-OFF
TROUGH MAY ALLOW FOR A MORE NORTHWARD TRACK OF THE NORTHERN STREAM
WAVE. THEREFORE...WILL MAINTAIN IDEA OF PREVIOUS FORECAST WITH JUST
SLIGHT CHANCE POPS FRIDAY NIGHT/EARLY SATURDAY. LATEST TRENDS WOULD
SUGGEST BULK OF SATURDAY MAY BE DRY...AND MAY BE ABLE TO EVENTUALLY
REMOVE POPS COMPLETELY AFTER 12Z SATURDAY IN FUTURE FORECASTS.

OVERALL...VERY LITTLE CHANGES NEED TO REMAINDER OF FORECAST AS RAIN
CHANCES SHOULD INCREASE ONCE AGAIN LATER SUNDAY/MONDAY AS CUT-OFF
UPPER TROUGH SLOWLY GETS BETTER PHASED WITH NORTHERN STREAM. FAIRLY
GOOD CONSENSUS IN MEDIUM RANGE MODELS EXISTS...WITH A MORE AMPLIFIED
UPPER TROUGH TAKING SHAPE ON THE HEELS OF THIS SHORT WAVE TOWARD THE
END OF THE PERIOD. THUS...WILL CONTINUE TO HEDGE TOWARD COOLER
CONDITIONS BY THE DAY 6-7 TIMEFRAME WITH PERIODS OF SHOWERY WEATHER
GIVEN LARGE SCALE CYCLONIC FLOW/SEVERAL EMBEDDED SHORT WAVES THROUGH
THE MIDDLE OF NEXT WEEK.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 528 AM EDT WED APR 15 2015

VFR/DRY CONDITIONS ARE EXPECTED TO PERSIST TODAY INTO THIS EVENING
AS SFC HIGH PRESSURE DROPS THROUGH THE GREAT LAKES REGION.
EASTERLY WINDS WILL PICK UP INTO THE LATE MORNING/AFTERNOON AS
BOUNDARY LAYER DEEPENS AND PRESSURE GRADIENT TIGHTENS BETWEEN THE
AFOREMENTIONED SFC HIGH AND A WEAK SFC TROUGH ACROSS THE LOWER MS
VALLEY. CHANCES FOR SHOWERS WILL ENTER THE PICTURE LATER TONIGHT
AS A DECENT SURGE OF MOISTURE OVERSPREADS IN ADVANCE OF A WEAK
TROUGH.

&&

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

$$

SYNOPSIS...STEINWEDEL
SHORT TERM...STEINWEDEL
LONG TERM...MARSILI
AVIATION...STEINWEDEL


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