Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 211758
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1258 PM EST FRI NOV 21 2014

.SYNOPSIS...
ISSUED AT 1245 PM EST FRI NOV 21 2014

A RIDGE OF HIGH PRESSURE ACROSS THE MID MISSISSIPPI VALLEY WILL
TRACK INTO THE OHIO VALLEY TODAY. SOUTHERLY WINDS WILL INCREASE
INTO SATURDAY...DRAWING IN WARMER AIR INTO THE REGION. RAIN WILL
MOVE INTO THE AREA IN ADVANCE OF A WEAK SYSTEM...STARTING AS A
PERIOD OF LIGHT FREEZING RAIN BEFORE TEMPERATURES QUICKLY RISE
ABOVE FREEZING AFTER SUNRISE. HIGH TEMPERATURES TODAY WILL RANGE
FROM THE LOWER 30S ACROSS NORTHEAST ILLINOIS...TO THE MID 20S
ACROSS SOUTHEAST LOWER MICHIGAN INTO NORTHERN OHIO. LOW
TEMPERATURES TONIGHT WILL RANGE FROM THE MID 20S ACROSS NORTHEAST
ILLINOIS...TO THE UPPER TEENS ACROSS NORTHWEST OHIO AND SOUTHEAST
LOWER MICHIGAN.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY MORNING)
ISSUED AT 358 AM EST FRI NOV 21 2014

QUIET CONDITIONS TO BEGIN THE SHORT TERM FOR TODAY WILL BE FOLLOWED
BY POTENTIAL OF FREEZING RAIN LATE TONIGHT INTO THE EARLY MORNING
HOURS OF SATURDAY.

LAKE EFFECT CLOUDINESS PERSISTS ACROSS EXTREME NORTHERN INDIANA AND
SOUTHERN LOWER MICHIGAN WITH SCATTERED SNOW SHOWERS ONLY LIMITING
VSBYS IN THE 3-6 MILE RANGE. NOT EXPECTING ANY ACCUMULATION THIS
MORNING ALTHOUGH A STRAY TENTH OF AN INCH OR SO WILL BE POSSIBLE
ACROSS SOUTHERN LOWER MICHIGAN THROUGH 12Z. SFC ANTICYCLONE
DROPPING SOUTHEASTWARD OUT OF CENTRAL ILLINOIS WILL ALLOW FOR
BACKING LOW WINDS AND REDUCED FETCH. LAKE INDUCED INSTABILITY ALSO
TO STEADILY DECREASE OVER THE NEXT SEVERAL HOURS AS INVERSION
HEIGHTS CONTINUE TO CRASH UNDER THE INFLUENCE OF RISING MID LEVEL
HEIGHTS AND LARGER SCALE SYNOPTIC SUBSIDENCE. MOSTLY SUNNY
CONDITIONS SHOULD SHAPE UP ACROSS THE AREA FOR THE REMAINDER OF
THE DAY WITH SOUTHERLY LOW LEVEL WINDS DEVELOPING. ARCTIC DOME
WILL BE SOMEWHAT STUBBORN TO SCOUR OUT...AND HAVE NOT MADE MUCH
CHANGE TO PREVIOUS MAX TEMPS FROM AROUND 30 WEST...TO THE MID 20S
EAST.

ATTENTION FOR TONIGHT WILL SHIFT TO UPPER LEVEL TROUGH CURRENTLY
PROGRESSING THROUGH THE ROCKIES EARLY THIS MORNING. VERY STRONG LOW
LEVEL MOISTURE ADVECTION WILL DEVELOP AS VERY DRY AIR MASS SUBJECT
TO HISTORY OF SUBSIDENCE ACROSS THE GREAT LAKES SHIFTS ACROSS THE
MID ATLANTIC STATES. LOW LEVEL MOISTURE TONGUE WILL RAPIDLY LIFT
INTO THE MID MS RVR VALLEY THIS EVENING IN ADVANCE OF APPROACHING
WAVE...AND THEN WEST TO EAST ACROSS THE LOCAL AREA IN THE 06Z-18Z
TIMEFRAME. MID/UPPER FORCING DOES NOT APPEAR TO BE OVERLY IMPRESSIVE
GIVEN BROAD...LOW AMPLITUDE NATURE TO THE ROCKIES UPPER TROUGH BUT
STRONG LOW LEVEL MOISTURE CONVERGENCE/ISENTROPIC LIFT SHOULD SUPPORT
AT LEAST LIGHT PRECIP SPREADING INTO WESTERN PORTIONS OF THE CWA
TOWARD THE 06Z TIMEFRAME. MAIN CONCERN AT THIS TIME IS POTENTIAL
OF SHALLOW SUB FREEZING LAYER TO REMAIN IN PLACE WITH WARM LAYER
ALOFT BECOMING MORE PRONOUNCED AFTER 06Z. A BRIEF PERIOD OF LIGHT
FREEZING RAIN APPEARS TO BE A GOOD POSSIBILITY ALTHOUGH INITIALLY
THE VERY DRY NATURE TO THE LOW LEVEL AIR MASS OFFERS SOME LOWER
CONFIDENCE REGARDING ONSET TIME AND PRECIP AMOUNTS. GIVEN STRONG
MOISTURE TRANSPORT...ISENTROPIC UPGLIDE...AND AT LEAST WEAK
MID/UPPER FORCING HAVE FOLLOWED GUIDANCE TRENDS TO HIGHER POPS FOR
THE LATE TONIGHT/SATURDAY MORNING PERIOD. PERIOD OF GREATEST
FREEZING RAIN POTENTIAL APPEARS TO BE IN THE 09Z-15Z TIMEFRAME
FROM WEST TO EAST ACROSS THE AREA. SOME LIGHT ICE ACCUMULATION IS
POSSIBLE BUT WITH AFOREMENTIONED LOWER CONFIDENCE IN
TIMING/AMOUNTS AND BEING A LATE 2ND PERIOD POTENTIAL EVENT...WILL
LET DAY SHIFT ASSESS NEED FOR HEADLINES FURTHER. PLUME OF
RELATIVELY STEEP 700-500 HPA LAPSE SHOULD ADVECT ACROSS ESPECIALLY
NORTHERN HALF OF THE AREA OVERNIGHT. SO WHILE PRECIP AMOUNTS
SHOULD BE QUITE LIGHT IN WEAKLY FORCED ENVIRONMENT (GENERALLY
LESS THAN TENTH OF AN INCH)...MAY NEED TO KEEP AN EYE ON ANY
WEAKER CONVECTIVE RESPONSE LATE TONIGHT/EARLY SATURDAY FOR ANY
LOCALIZED HIGHER PRECIP AMOUNTS.

PRECIP TO CHANGE OVER TO RAIN SATURDAY MORNING AS WARM/MOISTURE
ADVECTION OVERWHELMS PROFILES FROM WEST TO EAST...WITH EVEN FAR
EASTERN LOCATIONS TO LIQUID PRECIP TYPE BY 14 OR 15Z.

&&

.LONG TERM...(SATURDAY AFTERNOON THROUGH THURSDAY)
ISSUED AT 358 AM EST FRI NOV 21 2014

WET/WARMER THIS WEEKEND/MONDAY WITH A RETURN TO UNSEASONABLY COLD WX
THEREAFTER....

ONGOING ISENTROPIC ASCENT/MOIST ADVECTION ASSOCIATED WITH WEAK
SHORTWAVE ENERGY AND STRENGTHENING MID/UPPER JET WORKING EAST
THROUGH THE GREAT LAKES IN ZONAL FLOW MAY KEEP AREAS OF LIGHT
RAIN/DRIZZLE AROUND INTO SATURDAY AFTN/NIGHT AS SFC WARMS WARM ABOVE
FREEZING. MUCH BETTER CHANCES FOR MORE WIDESPREAD/HEAVIER RAINFALL
ARRIVES SUNDAY AFTN/NIGHT AS SRN STREAM PV ANOMALY (NOW OVER SRN CA)
LIFTS NNE THROUGH THE REGION. EXPECTED NEGATIVE TILT TO WAVE,
PHASING/STRENGTHENING OF UPPER JET ROUNDING BASE OF AN AMPLIFYING
PLAINS LONGWAVE TROUGH, AND GOOD FEED OF MOISTURE/CONVERGENCE WILL
SUPPORT CYCLOGENESIS WITH MODELS AGREEING ON SFC REFLECTION TRACK
NNE THROUGH THE MID MS VALLEY/WESTERN LAKES. AT LEAST THE WESTERLY
TRACK OF SYSTEM WILL ALLOW MUCH WARMER AIR TO OVERSPREAD THE REGION
DURING THIS TIME.

THIS WARMUP WILL BE SHORTLIVED HOWEVER AS THE NEXT DEEP LAYERED
TROUGH CONSOLIDATES INTO THE EASTERN US BRINGING ANOTHER SHOT OF
UNSEASONABLY COLD AIR TO THE LOCAL AREA MONDAY NIGHT AND BEYOND.
TRAILING COLD FRONT THAT WILL USHER IN THIS NEXT COLD BLAST
(ALTHOUGH NOT AS EXTREME AS THIS PAST WEEK) WILL TRANSLATE THROUGH
ON MONDAY WITH FALLING TEMPS EXPECTED LATE MORNING-AFTN. FRONTAL
WAVE/MID LVL FGEN RESPONSE CONTINUES TO SHOW UP IN BULK OF GUIDANCE
HINTING AT THE POTENTIAL FOR ADDITIONAL PCPN (MAINLY RAIN) TO
BLOSSOM/EXPAND NE INTO THE AREA MONDAY. OTHERWISE...CAA/CYCLONIC
FLOW SCT FLURRIES/SNOW SHOWERS CAN EXPECTED WITHIN TROUGH AXIS LATER
MONDAY NIGHT INTO TUESDAY WITH SOME LAKE ENHANCEMENT/ACCUMS POSSIBLE
ACROSS LOWER MI/FAR NRN IN.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1240 PM EST FRI NOV 21 2014

TRANQUIL WEATHER TO START OUT THE TAF PERIOD AS HIGH PRESSURE
DRIFTS ACROSS THE REGION. THE NEXT SYSTEM WILL ADVANCE RAPIDLY
FROM THE SOUTHWEST WITH MOISTURE RAPIDLY INCREASING AFTER 6Z. A
MASSIVE SURGE OF WARM AIR ALOFT WILL ACCOMPANY THIS
SYSTEM...KEEPING ANY PRECIPITATION IN THE LIQUID VS FROZEN FORM.
HOWEVER...SURFACE TEMPERATURES WILL BE NEAR OR JUST BELOW FREEZING
FOR A FEW HOURS AT THE ONSET...WARRANTING A CONTINUATION OF OF
LIGHT FREEZING RAIN MENTION. HAVE KEPT THIS GOING FOR ABOUT A 4
HOUR PERIOD AT EACH SITE BUT THIS MAY BE TOO LONG WITH SEVERAL
HIGH RES MODELS COMING IN WITH SFC TEMPS RAPIDLY CLIMBING ABOVE
FREEZING AROUND 12Z. CIGS WILL DROP RAPIDLY INTO MVFR RANGE AS
PRECIP STARTS AND PERSIST THROUGH THE REST OF THE PERIOD.

OTHER NOTEWORTHY ITEM IS STRONG INVERSION ABOVE THE SURFACE WILL
KEEP A STRONG WIND FIELD FROM MIXING TO THE GROUND AS 2000 FT
SPEEDS LOOK TO BE AROUND 50 KTS LATER TONIGHT INTO AT LEAST
SATURDAY MORNING. HAVE INTRODUCED LOW LEVEL WIND SHEAR INTO BOTH
TAFS.

&&

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

$$

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


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