Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 222001
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
401 PM EDT WED APR 22 2015

.SYNOPSIS...
ISSUED AT 401 PM EDT WED APR 22 2015

A WEAK UPPER LEVEL DISTURBANCE WILL TRACK ACROSS THE SOUTHERN
GREAT LAKES REGION TONIGHT. THIS DISTURBANCE MAY BRING SOME
SCATTERED SPRINKLES OR FLURRIES THIS EVENING...WITH DIMINISHING
CLOUDS EXPECTED OVERNIGHT. THE COMBINATION OF DECREASING CLOUDS
AND LIGHTER WINDS WILL RESULT IN TEMPERATURES DROPPING TO AT OR
BELOW FREEZING EARLY THURSDAY MORNING. PARTLY CLOUDY CONDITIONS
ARE EXPECTED ON THURSDAY AS A RIDGE OF HIGH PRESSURE BEGINS TO
APPROACH FROM THE WEST. HIGHS ON THURSDAY WILL RANGE FROM THE MID
40S ACROSS SOUTHEAST LOWER MICHIGAN TO THE LOWER 50S ACROSS WEST
CENTRAL INDIANA.

&&

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 401 PM EDT WED APR 22 2015

THE MAIN SHORT TERM FORECAST CHALLENGE WILL CONTINUE TO BE TEMP
TRENDS...AND POTENTIAL OF TEMPS DIPPING TO AT OR BELOW FREEZING
TONIGHT.

CYCLONIC FLOW CONTINUES ACROSS THE REGION THIS AFTERNOON AS A SERIES
OF SMALL SCALE DISTURBANCES ROTATE THROUGH BROAD NEGATIVE UPPER
HEIGHT ANOMALY CENTERED ACROSS SOUTHEAST ONTARIO. THE FIRST OF THE
DISTURBANCES WHICH BROUGHT PERIODS OF SNOW SHOWERS EARLIER TODAY HAS
SHIFTED OFF TO THE EAST...BUT NEXT UPSTREAM VORT MAX ALREADY APPEARS
TO BE MAKING ITS WAY ACROSS SOUTHERN WISCONSIN/NORTHERN ILLINOIS
THIS AFTERNOON. THE COMBINATION OF THIS FORCING AND A POSSIBLE VERY
WEAK DOWNSTREAM LOW LEVEL FGEN RESPONSE MAY STILL YIELD A FEW
SPRINKLES OR FLURRIES EARLY THIS EVENING. HOWEVER...ADVECTION OF
SLIGHTLY DRIER LOW LEVEL AIR AND LOW LEVEL MIXING SHOULD LIMIT THIS
POTENTIAL.

ATTENTION FOR THIS EVENING WILL SHIFT TO SKY COVER TRENDS AND
ASSOCIATED IMPACTS ON TEMPS. MORE CONVECTIVE NATURE TO CLOUDS PER
VISIBLE SATELLITE IMAGERY THIS AFTERNOON ACROSS SOUTH/SOUTHWEST
PORTIONS OF AREA WOULD SUGGEST A LIKELY DIMINISHMENT IN SKY COVER
ACROSS THESE LOCATIONS WITH SUNSET...WITH THE EXPECTATION THAT
STRATOCU WILL PERSIST LONGER ACROSS THE NORTH IN CLOSER PROXIMITY TO
AFOREMENTIONED UPSTREAM FORCING. PREVIOUS GRIDS ALREADY HAD THIS
TREND CAPTURED WELL AND ONLY MINOR CHANGE WAS TO SLIGHTLY DELAY
TIMING OF DIMINISHING CLOUD COVER. WHILE WINDS WILL DIMINISH WITH
LOSS OF STEEPER LOW LEVEL LAPSE RATES EARLY THIS EVENING...MODEST
GRADIENT SHOULD PROMOTE 5 TO 10 MPH WINDS THROUGH THE NIGHT.
REGARDLESS...DIMINISHING SKY COVER TREND OVERNIGHT AND MAGNITUDE OF
AIR MASS ACROSS THE REGION SHOULD PROMOTE TEMPS DROPPING TO NEAR THE
FREEZING MARK FOR MINS...AND POSSIBLY INTO THE UPPER 20S TO AROUND
30 ACROSS THE FAR NORTHEAST DEPENDING ON STRATOCU TRENDS EARLY
THURSDAY MORNING. WILL GO AHEAD AND ISSUE A FREEZE WARNING FOR
TONIGHT FOR ALL OF THE FORECAST AREA FROM 06Z-13Z.

PATTERN TO BECOME SOMEWHAT MORE PROGRESSIVE ON THURSDAY...WITH
GREATEST AFTERNOON STRATOCU COVERAGE EXPECTED ACROSS EASTERN
LOCATIONS AS UPPER RIDGING BEGINS TO WORK ACROSS CENTRAL CONUS.
DIURNAL MIXING SHOULD SUPPORT LESSER AFTERNOON GUSTS INTO THE 15 TO
20 MPH RANGE WITH HIGHS EXPECTED TO RANGE FROM THE MID 40S NORTHEAST
TO THE LOWER 50S SOUTHWEST. IT IS POSSIBLE IF THICKER LOW CLOUDS DO
MATERIALIZE ACROSS THE NORTHEAST/EAST...MAY NEED TO NUDGE TEMPS DOWN
A BIT FOR THURSDAY AFTERNOON.

&&

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 401 PM EDT WED APR 22 2015

IMPRESSIVE NEGATIVE HEIGHT ANOMALY OVER THE NORTHERN LAKES WILL
EDGE EAST INTO NEW ENGLAND/CANADIAN MARITIMES BY LATE THIS
WEEK...AND REMAIN IN PLACE THROUGH EARLY NEXT WEEK THANKS TO STRONG
NORTH ATLANTIC BLOCKING. THIS WILL KEEP THE LOCAL AREA IN
COOL/MAINLY DRY NW FLOW THROUGH THE PERIOD...ALTHOUGH A LITTLE
MILDER AND LESS WINDY WHEN COMPARED TO THE LAST FEW DAYS/TOMORROW AS
HEIGHT FIELD REBOUNDS WITH DEEPER/MOIST CYCLONIC FLOW SHIFTING MORE
TOWARD THE EASTERN LAKES. THE ONE EXCEPTION WILL LIKELY BE LATER
FRIDAY NIGHT INTO SATURDAY AS MODELS OVERALL ON BOARD WITH SOUTHERN
STREAM SHORTWAVE AND ATTENDANT SFC REFLECTION SHEARING EAST THROUGH
THE OH VALLEY. INITIAL SHOT OF ELEVATED THETA-E ADV/ISENTROPIC
ASCENT LIKELY LIFTS INTO AT LEAST SOUTHERN PORTIONS OF THE FA LATER
FRIDAY NIGHT-SATURDAY MORNING...WITH RAIN CHANCES CONTINUING INTO
THE AFTERNOON/EVENING WITHIN PIVOTING DEFORMATION. NOT AS CONFIDENT
ACROSS NORTHERN ZONES WHERE POPS WERE HELD IN THE LOW/MID CHC RANGE
GIVEN SE SHEARING OF WAVE INTO LINGERING AREA OF MID LVL
CONFLUENCE/SUBSIDENCE ACROSS THE GREAT LAKES.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 141 PM EDT WED APR 22 2015

LOW LEVEL FLOW SHOULD CONTINUE TO SUBSIDE THIS AFTERNOON...BUT
DEEPER DIURNAL MIXING SHOULD KEEP WEST GUSTS INTO THE 20 TO 25
KNOT RANGE THROUGH THE AFTERNOON. LOSS OF MIXING TONIGHT SHOULD
RESULT IN WEST-NORTHWEST WINDS OF 5 TO 10 KNOTS THROUGH THE
NIGHT...WITH LINGERING VFR STRATOCU EXPECTED ACROSS FAR NORTHERN
INDIANA. SCT-BKN VFR STRATOCU EXPECTED ONCE AGAIN ON
THURSDAY. DIURNAL MIXING SHOULD PROMOTE WIND GUSTS OF AROUND 15
KNOTS OR SLIGHTLY GREATER FOR THE DAY WEDNESDAY.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...FREEZE WARNING FROM 2 AM EDT /1 AM CDT/ TO 9 AM EDT /8 AM CDT/
     THURSDAY FOR INZ003>009-012>018-020-022>027-032>034.

MI...FREEZE WARNING FROM 2 AM TO 9 AM EDT THURSDAY FOR MIZ077>081.

OH...FREEZE WARNING FROM 2 AM TO 9 AM EDT THURSDAY FOR OHZ001-002-004-
     005-015-016-024-025.

LM...NONE.
&&

$$

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


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