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[Printable]
969
FXUS63 KIWX 210551
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1251 AM EST FRI NOV 21 2014

.SYNOPSIS...
ISSUED AT 359 PM EST THU NOV 20 2014

HIGH PRESSURE WILL BUILD ACROSS THE OHIO VALLEY TONIGHT. CLEARING
SKIES AND DIMINISHING WINDS WILL YIELD CHILLY LOW TEMPERATURES IN
THE TEENS. MOSTLY SUNNY SKIES ARE EXPECTED ON FRIDAY AS HIGH
PRESSURE MOVES OFF TO THE EAST WITH HIGHS IN THE MID TO UPPER 20S.

&&

.UPDATE...
ISSUED AT 501 PM EST THU NOV 20 2014

IN LIGHT OF CONTD SEVERE DRY ENTRAINMENT AND GROWING OBSVD SIG SFC TD
DEPRESSIONS NOTED ACRS SW MI HAVE OPTED TO CANCEL ADVISORY EARLY.
IN FACT MUCH OF REMAINING SHSN HAVE DEVOLVED INTO ISOLD FLURRIES
AND W/WKNG SFC GRADIENT BLOWING SNOW SHLD NOT BE AN ISSUE EITHER
GOING FWD OVERNIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 359 PM EST THU NOV 20 2014

DRY AIR ENTRAINMENT HAS SEVERELY LIMITED OVERALL INTENSITY AND
ORGANIZATION OF LAKE EFFECT BANDS RESULTING IN ONLY SPORADIC
REPORTS OF ACCUMULATIONS ACROSS THE PREVIOUS HEADLINE AREAS. THIS
IS DESPITE STRONG INSTABILITY AND A NORMALLY FAVORABLE FETCH.
COVERAGE OF SNOW SHOWERS HAS INCREASED AND ANYONE FORTUNATE ENOUGH
TO GET UNDER ONE WILL SEE A RAPID DROP IN VISIBILITY FOR A SHORT
PERIOD BUT LITTLE OVER ALL ACCUMULATION. GIVEN ALL THESE FACTORS
WAS CONSIDERING DROPPING ALL HEADLINES. HOWEVER...WITH SNOW
SHOWERS TO CONTINUE AND AREAS OF BLOWING AND DRIFTING TO PERSIST
AT LEAST INTO THE EVENING HOURS WILL OPT TO DOWNGRADE THE WARNING
TO AN ADVISORY AND GO WITH LOCAL 1 TO AT MOST 2 INCH ACCUMS
THROUGH TONIGHT...WHICH MAY EVEN END UP TOO HIGH IF TRENDS
CONTINUE. AWAY FROM THE LAKE...DIURNAL CLOUD COVER WILL DISSIPATE
AND LEAD TO MOSTLY CLEAR SKIES AND ANOTHER COLD NIGHT WITH READING
AWAY FROM ANY CLOUD COVER DROPPING INTO THE MID TEENS.

ON FRIDAY...HIGH PRESSURE WILL DRIFT ACROSS ILLINOIS INTO SOUTHERN
INDIANA ALLOWING WINDS TO FINALLY BECOME MORE SW AND MUCH DRIER AIR
FILTER IN AS WELL AS LOWERING INVERSION HGTS. THIS SHOULD ALLOW FOR
THE DEMISE OF ANY LAKE EFFECT ACTIVITY DURING THE MORNING HOURS.
MUCH QUIETER WEATHER WILL BE IN STORE FOR FRIDAY AFTERNOON AS
SUNSHINE TRIES TO DOMINATE. HOWEVER...MID/UPPER LEVEL CLOUDS WILL
START TO MOVE INTO SW AREAS TOWARDS THE END OF THE PERIOD IN ADVANCE
OF THE NEXT SYSTEM WHICH WILL BRING WARMER TEMPERATURES AND CHANCES
FOR LIQUID PRECIP INTO THE LONG TERM. HIGHS WILL ONLY MANAGE MID TO
MAYBE UPPER 20S.

&&

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 359 PM EST THU NOV 20 2014

FEW CHANGES AND CONTINUED FORECAST FOCUS ON WEEKEND PTYPE/AMOUNTS.
CONTINUED CONCERN THAT EMPHATIC WARMING/DEEPENING THERMAL/WET BULB
PROFILES ALOFT TO PRECEDE BULK OF INITIAL MOISTURE FLUX CONVERGENCE
LATE FRIDAY NIGHT INTO SAT AM...WITH CONTINUED HIGH 950-900 MB LAYER
CONDENSATION PRESSURE DEFICITS TO GNAW AT LEADING EDGE...KEEPING
BULK OF LIQUID HYDROMETEORS MOSTLY ALOFT. CANT RULE OUT MINOR ZR
EVENT AT ONSET...THOUGH HAVE LOCKED DOWN TEMPORAL WINDOW TO
PRIMARILY 09-12 UTC SAT WINDOW PER CONSENSUS ARW/NMM FOR WRN HALF
CWA...AS WARM ADVECTION SURGE PER VEERED STRENGTHENING PROFILES
APPEAR SYN OPTICALLY ASSURED. ATTM ANTICIPATE ICING TO BE SPOTTY AND
BRIEF IN NATURE WITH OVERALL PROBABILITIES MUTED OVER EGREGIOUSLY
WET BLEND. BETTER/RENEWED MOISTURE SURGE WITH WRN TRACKED SYSTEM
LIFTING NNEWD THROUGH MS VLY/WRN GRTLKS ESPCLY SUN/SUN NIGHT.
INCREASINGLY NEGATIVELY TILTED UPPER SUPPORT WITH SLOWING EWD
FRONTAL PROGRESS AS SYSTEM LIFTS FROM NERN TX SUN, AND INTO MID/UPR
OH VLY SUN NIGHT. SLIGHTLY DLAY OF DEEPER POST FRONTAL CAA RESULTING
IN LATER TIMING OF SHIFT TO RASN MIX NOW TO MON AFTN...AND
EVENTUALLY TO ALL SNOW BY MON NIGHT. CYCLONIC LOW LEVEL FLOW WITH
LAGGED LAKE AGGREGATE TROF AND MODERATE THERMAL INSTABILITY
SUPPORT WITH LK/8H DIFFERENTIALS TO UPPER TEENS SUGGEST CONTD HIGH
LES POPS TUE/TUE NIGHT. HEREAFTER GFS LARGELY DISCOUNTED/OUT OF
PHASE WITH GFS WRT LONGWAVE PATTERN. STRONG EPAC RIDGING PER ECMWF
WITH PLAINS TROFFING PORTENDING OF OHIO VALLEY TO SRN PLAINS
FRONTOGENESIS AND POTNL SNOW EVENT WITHIN REALM OF POSSIBILITIES
RAMPING UPWARDS FOR HOLIDAY WEEKEND...AT LEAST SUFFICIENT TO KEEP
EYE ON.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1241 AM EST FRI NOV 21 2014

STRONG SYNOPTIC SCALE SUBSIDENCE AND LOWERING INVERSION HEIGHTS
OVERNIGHT WILL GRADUALLY ALLOW LINGERING SCATTERED LIGHT LAKE
EFFECT SNOW SHOWERS AND FLURRIES TO COME TO AN END. MUCH OF THESE
LINGERING SNOW SHOWERS SHOULD REMAIN NORTH OF KSBN WITH JUST LAKE
EFFECT LOW CLOUD CIGS OF 4-5K FT EXPECTED FOR THE NEXT SEVERAL
HOURS. SFC ANTICYCLONE FROM THE MID/UPPER MS RIVER VALLEY WILL
DROP SOUTHEAST INTO THE OHIO VALLEY LATER THIS MORNING ALLOWING
SOUTHERLY WINDS TO RETURN. VFR CONDITIONS ARE EXPECTED TO PERSIST
THROUGH THE PERIOD. JUST AFTER THIS FORECAST VALID PERIOD...WILL
NEED TO ADDRESS -FZRA POTENTIAL IN THE 09Z-15Z TIMEFRAME DUE TO
STRONG LOW LEVEL WAA AND SHALLOW COLD AIR.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 10 AM EST THIS MORNING FOR LMZ043-046.

&&

$$

UPDATE...T
SYNOPSIS...FISHER
SHORT TERM...FISHER
LONG TERM...MURPHY
AVIATION...MARSILI


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