Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 230618
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
218 AM EDT THU APR 23 2015

.SYNOPSIS...
ISSUED AT 218 AM EDT THU APR 22 2015

CLOUDS WILL CONTINUE TO DIMINISH EARLY THIS MORNING IN THE WAKE
OF THE DEPARTURE OF AN UPPER LEVEL DISTURBANCE...SETTING THE STAGE
FOR A FROSTY MORNING. LOOK FOR MOSTLY SUNNY SKIES TODAY AS A
RIDGE OF HIGH PRESSURE BEGINS TO APPROACH FROM THE WEST. HIGHS
TODAY WILL RANGE FROM THE UPPER 40S ACROSS SOUTHEAST LOWER
MICHIGAN TO THE MID 50S INTO WEST CENTRAL INDIANA. ANOTHER FROSTY
NIGHT IS EXPECTED TONIGHT WITH LOWS DROPPING TO AROUND 30 DEGREES.

&&

.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 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 142 AM EDT THU APR 23 2015

(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 825 PM EDT WED APR 22 2015

MUCH DRIER AIR ALONG WITH INCREASING SUBSIDENCE WILL HELP KEEP VFR
CONDITIONS THROUGHOUT THE TAF PERIOD. DAYTIME HEATING WILL ALLOW
MIXING DOWN OF HIGHER MOMENTUM AIR...ALTHOUGH WINDS TODAY SHOULD
NOT BE AS HIGH AS THEY WERE WEDNESDAY. WINDS SHOULD DECOUPLE
TONIGHT AS HIGH PRESSURE MOVE OVER THE AREA ALLOWING WINDS TO
BECOME LIGHT.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...FREEZE WARNING UNTIL 9 AM EDT /8 AM CDT/ THIS MORNING FOR
     INZ003>009-012>018-020-022>027-032>034.

MI...FREEZE WARNING UNTIL 9 AM EDT THIS MORNING FOR MIZ077>081.

OH...FREEZE WARNING UNTIL 9 AM EDT THIS MORNING FOR OHZ001-002-004-
     005-015-016-024-025.

LM...NONE.
&&

$$

SYNOPSIS...MUPRHY/SKIPPER
SHORT TERM...MARSILI
LONG TERM...STEINWEDEL
AVIATION...SKIPPER


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