Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 211615
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1215 PM EDT MON APR 21 2014

.SYNOPSIS...
ISSUED AT 1215 PM EDT MON APR 21 2014

TEMPERATURES WILL CLIMB INTO THE MID TO UPPER 70S THIS AFTERNOON
AHEAD OF A COLD FRONT THAT WILL MOVE ACROSS THE AREA OVERNIGHT.
SHOWERS AND ISOLATED THUNDERSTORMS WILL ARRIVE LATE THIS
AFTERNOON AND CONTINUE INTO THE OVERNIGHT HOURS. COOLER AND DRIER
WEATHER IS EXPECTED FOR TUESDAY AND WEDNESDAY AS HIGH PRESSURE
SETTLES IN...WITH HIGHS IN THE 50S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 345 AM EDT MON APR 21 2014

PAIR OF PV ANOMALIES CURRENTLY TRAVERSING SOUTHERN CANADA...ONE
WITH A WELL DEFINED "SWIRL" ON MORNING WATER VAPOR...WILL BE THE
MAIN ITEMS TO NOTE FOR TODAY`S SHORT TERM FORECAST. THERE ALSO
EXISTS A LOOSELY ORGANIZED MIDLEVEL TROUGH OVER THE SOUTHERN
PLAINS...MUDDLED BY CONVECTIVE ELEMENTS...THAT MAY AID PRECIP
CHANCES SOMEWHAT LATER TODAY AS IT SHEARS NORTHEAST. NORTHERN
STREAM WAVE WILL BE THE MAIN FEATURE TO WATCH THOUGH AS A
STRENGTHENING MID/UPPER LEVEL JET STREAK IS EXPECTED TO CARVE OUT
A DECENT TROUGH OVER THE GREAT LAKES BY LATE TONIGHT DUE TO
AMPLIFYING PATTERN ALOFT OVER MUCH OF THE CONUS. THIS WILL SUPPORT
CYCLOGENESIS OVER THE CENTRAL GREAT LAKES WITH A CORRESPONDING
COLD FRONTAL PASSAGE FOR OUR CWA AROUND MIDNIGHT TONIGHT. BEST
UPPER JET DYNAMICS PASS JUST TO OUR NORTH BUT DECENT MIDLEVEL
HEIGHT FALLS AND CORRESPONDING LOW LEVEL CONVERGENCE SHOULD BE
ABLE TO SUPPORT AT LEAST SCATTERED SHOWERS OVERNIGHT GIVEN
ADEQUATE MOISTURE/INSTABILITY. SOUTHWEST FLOW/THETA-E ADVECTION
FINALLY BEGINS TO INCREASE THIS AFTERNOON AND FORECAST
SOUNDINGS/RH FIELDS SHOW A HEALTHY REGION OF DEEP LAYER MOISTURE
CONVERGENCE RIGHT AHEAD OF THE FRONT. SURFACE BASED INSTABILITY
DOES INCREASE BUT WILL BE VERY LIMITED WITH ONLY A FEW HUNDRED
J/KG GIVEN LARGELY MOIST ADIABATIC LAPSE RATES. THIS WILL LIKELY
AID THE RESPONSE TO OVERALL MODEST SYNOPTIC FORCING BUT COULD ALSO
SUPPORT AN ISOLATED THUNDERSTORM DURING THE EVENING HOURS. DOUBT
PRECIP COVERAGE WILL BE WIDESPREAD ENOUGH TO WARRANT CATEGORICAL
POPS THOUGH AND WILL STICK WITH LIKELY WORDING. ALSO EXPECT PRECIP
TO HOLD OFF FOR MUCH OF THE DAY GIVEN LATE ARRIVAL OF CONVERGENT
BOUNDARY AND SUFFICIENT LOW LEVEL MOISTURE...AN IDEA SUPPORTED BY
LATEST HI-RES GUIDANCE. THIS SHOULD ALLOW FOR ANOTHER DAY AT LEAST
IN THE MID 70S...IF NOT UPPER 70S...GIVEN INCREASING WAA AND MUCH
DEEPER PBL MIXING. NOTE THIS WILL BE IN SPITE OF INCREASING CLOUD
COVER. EXPECT A SHARP GRADIENT IN OVERNIGHT LOWS DEPENDING ON
EXACT TIMING OF COLD FRONT. AIRMASS IMMEDIATELY BEHIND THE FRONT
IS NOT PARTICULARLY COLD BUT STEADY CAA AND NORTHWEST FLOW OFF
LAKE MICHIGAN COULD ALLOW OUR NORTHWEST ZONES TO DROP INTO THE
UPPER 30S/LOWER 40S AROUND 12Z TUESDAY.

&&

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 345 AM EDT MON APR 21 2014

TUESDAY WILL BEGIN THE PERIOD WITH COLD AIR ADVECTION AND A RETURN
TO BELOW NORMAL TEMPERATURES. COLD FRONT WILL BE EAST OF THE AREA
WITH NORTHWEST WINDS IN ITS WAKE. LAKE SHADOW SHOULD SPREAD WELL
INLAND AND KEEP TEMPS ACROSS NW IN AND SW MI IN THE UPPER 40S TO
LOWER 50S AT BEST. REMAINDER OF THE AREA LIKELY TO REBOUND INTO MID
AND UPPER 50S WITH AFTERNOON INSOLATION BUT BREEZY CONDITIONS WILL
MAKE IT FEEL EVEN COOLER. HIGH PRESSURE WILL NOSE IN TUE NIGHT AND
STILL EXPECT A GOOD RADIATIONAL COOLING NIGHT WITH LOWS NEAR OR JUST
BELOW FREEZING AND WIDESPREAD FROST LIKELY.

HIGH SLIDES EAST ON WEDNESDAY WITH RETURN FLOW DEVELOPING WED AFTN
AND NIGHT. MODELS DEVELOPING SOME LIGHT QPF IN WARM AIR ADVECTION AS
LOW LEVEL JET INCREASES WED NIGHT. SOUNDING PROFILES ARE VERY DRY IN
THE LOWER LEVELS AND IT WILL ONCE AGAIN BE DIFFICULT TO SATURATE
LOWER LEVELS. LIKELY SEE VIRGA EVENT WITH SOME POSSIBLE SPRINKLES
OVER THE NW. NOT READY TO INCLUDE THE VERY LOW POPS GIVEN BY
ALLBLEND LOOKING AT THE SIGNIFICANT DEW POINT DEPRESSIONS.

BETTER CHANCE FOR SHOWERS AND A FEW THUNDERSTORMS ARRIVE LATE
THURSDAY AFTERNOON IN WEST AND IN THE EVENING MOST AREAS. MODEL
TIMING DIFFERENT BY A FEW HOURS BUT STILL WORTHY OF LIKELY POPS WITH
GOOD FORCING ALONG OCCLUDED FRONT LIFTING THROUGH THE AREA.

SIGNIFICANT MODEL DIFFERENCES CONTINUE IN WAKE OF THIS BOUNDARY FOR
FRIDAY AND THE UPCOMING WEEKEND WITH SECONDARY COLD FRONT. GFS
CONTINUES TO SHOW MUCH COLDER AIR WRAPPING AROUND A STRONG LOW IN
THE WESTERN LAKES WHILE ECMWF IS NOT AS COLD AND FURTHER NORTH. 00Z
GFS IS VERY COLD AT 850MB FOR THIS WEEKEND WITH TEMPS AROUND -7C TO
-9C SATURDAY OVER OUR AREA WHILE ECMWF IS IN THE +2C TO +7C RANGE.
GIVEN THE DIFFERENCES AND UNCERTAINTY HAVE OPTED FOR THE ALLBLEND
WHICH IS STILL QUITE COOL AND SIMILAR TO MEAN MODEL ENSEMBLES.
FURTHER ADJUSTMENTS WILL OBVIOUSLY BE NECESSARY AS DETERMINISTIC
MODEL SOLUTIONS CONVERGE.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 555 AM EDT MON APR 21 2014

VFR CONDITIONS WILL PERSIST THROUGH THE AFTERNOON. SHORTWAVE
TROUGH WILL THEN DIG OVER THE GREAT LAKES TONIGHT AND SEND A COLD
FRONT THROUGH THE REGION. LOW LEVEL CONVERGENCE IN A MOIST AND WEAKLY
UNSTABLE ENVIRONMENT WILL LEAD TO NUMEROUS SHOWERS AND PERHAPS AN
ISOLATED THUNDERSTORM LATE THIS EVENING. LATEST HI-RES GUIDANCE
STILL SUGGESTS PRECIP HOLDING OFF UNTIL AROUND 00Z FOR KSBN AND
03Z FOR KFWA. BRIEF REDUCTIONS TO MVFR CATEGORY ARE POSSIBLE BUT
IMPROVEMENT EXPECTED BY TUESDAY MORNING AS HIGH PRESSURE AND DRY
AIR PUSH BACK INTO THE REGION.


&&

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

$$

SYNOPSIS...CEO
SHORT TERM...AGD
LONG TERM...LASHLEY
AVIATION...AGD


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