Area Forecast Discussion
Issued by NWS Northern Indiana

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KIWX 210956
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
556 AM EDT TUE APR 21 2015

.SYNOPSIS...
ISSUED AT 356 AM EDT TUE APR 21 2015

STRONG WESTERLY WINDS ARE EXPECTED TODAY WITH GUSTS AS HIGH AS 45
MPH. THERE IS ALSO A SLIGHT CHANCE FOR A FEW AFTERNOON RAIN
SHOWERS...MAINLY ALONG AND NORTH OF THE TOLL ROAD. HIGHS TODAY WILL
BE IN THE MID 50S WITH LOWS TONIGHT IN THE MID 30S. COOL AND DRY
CONDITIONS WILL THEN CONTINUE THROUGH THE REST OF THIS WEEK.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 356 AM EDT TUE APR 21 2015

STRONG WINDS WILL BE THE FORECAST MESSAGE OF THE DAY. STILL A
DECENT HEIGHT/PRESSURE GRADIENT IN PLACE BETWEEN LARGELY
BAROTROPIC LOW PRESSURE NEAR JAMES BAY AND ANTICYCLONE ACROSS THE
GULF COAST. HOWEVER...THE REAL KEY FACTOR FOR GUSTY WINDS WILL BE
VERY DEEP BOUNDARY LAYER MIXING. COMBINATION OF DRY AIR ADVECTION
NEAR THE SURFACE...STRONG LATE APRIL SUN...AND VERY COLD
CONDITIONS ALOFT WILL SET THE STAGE FOR MIXING HEIGHTS TO CLIMB TO
AT LEAST 6 KFT WITH SOME MODELS (GFS AND RAP) SUGGESTING BOUNDARY
LAYER DEPTHS WILL APPROACH 9 KFT. WIND SPEEDS AT THOSE LEVELS WILL
BE IN THE 40-50 KT RANGE. NO DOUBT IT WILL BE WINDY BUT THE
QUESTION IS WILL IT REACH ADVISORY CRITERIA (39KTS/45MPH). LACK OF
GOOD ISENTROPIC DESCENT TO FORCE DOWN HIGHER MOMENTUM AIR IS
CONCERNING...AS IS LACK OF ISALLOBARIC COMPONENT. ALWAYS SOME
QUESTION AS TO HOW EFFICIENT TURBULENT MIXING ALONE WILL BE IN
PRODUCING HIGHER GUSTS AT THE SURFACE....ESPECIALLY WHEN MIXING
OVER SUCH A DEEP LAYER...AND NAM (AS WELL AS SOME OTHER HI-RES
MODEL) SOUNDINGS ARE NOT QUITE AS BULLISH. THAT BEING SAID...MOST
MODELS SHOW WIND SPEEDS AROUND 40 KTS AT THE TOP OF THE BOUNDARY
LAYER AND SEVERAL INDICATE MIXING INTO SOME 50 KT WINDS. GIVEN
THIS AND POTENTIAL FOR CONVECTIVE SHOWERS TO ENHANCE DOWNWARD
MOMENTUM TRANSFER (SEE NEXT PARAGRAPH)...FEEL IT IS PRUDENT TO GO
AHEAD AND PULL THE TRIGGER ON A WIND ADVISORY. EVEN IF MORE
IMPRESSIVE GFS AND RAP FORECAST SOUNDINGS/WIND FIELDS DONT
VERIFY...WILL STILL BE CLOSE TO ADVISORY CRITERIA.

500MB TEMPS BELOW -30C WILL SUPPORT A VERY DEEP LAYER OF STEEP LAPSE
RATES DURING THE DAY TODAY. DEGREE OF MOISTURE AVAILABLE IS VERY
MUCH IN QUESTION AND REMAINS A SIGNIFICANT LIMITING FACTOR FOR
PRECIP DEVELOPMENT BUT SHREDS OF VORTICITY ROTATING AROUND LARGE
CLOSED LOW COULD PROVIDE JUST ENOUGH MIDLEVEL CONVERGENCE/SATURATION
TO WARRANT A FEW ISOLATED SPRINKLES/SHOWERS...MAINLY IN OUR NORTHERN
COUNTIES. INHERITED FORECAST OF LOW CHANCE POPS ACROSS THE NORTH
SEEMS REASONABLE. IF ANY SHOWERS DO MANAGE TO DEVELOP...STRONG
NEGATIVE BUOYANCY DUE TO EVAPORATIONAL COOLING WITH "INVERTED V"
SOUNDING COULD HELP MIX DOWN SOME HIGHER GUSTS. COULD ALSO BE SOME
SMALL HAIL GIVEN COLD/DRY AIRMASS BUT VERY MARGINAL CAPE VALUES
SUGGEST ANY SUBSTANTIVE UPDRAFTS WILL BE FEW AND FAR BETWEEN.

SLIGHT CHANCE FOR SOME PRECIP LATE TONIGHT AS A MORE POTENT
SHORTWAVE SWINGS THROUGH THE AREA. MOST MODELS KEEP LOW LEVEL FGEN
RESPONSE JUST TO OUR SOUTH THOUGH AND WILL HOLD WITH A LOW CHANCE
POP. DESPITE VERY COLD AIR ALOFT...TEMPS SHOULD RECOVER INTO THE MID
50S TODAY GIVEN DEEP MIXING. LOWS TONIGHT SHOULD GENERALLY HOLD IN
THE MID 30S WITH STEADY WEST WINDS AND AT LEAST SOME CLOUDS KEEPING
THE THREAT OF FROST LOW.

&&

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 356 AM EDT TUE APR 21 2015

NEG HGT ANOMALIES WILL PERSIST OVR SE CANADA THIS PD IN ASSOCN/W SLW
EWD MEANDER OF DEEP CUTOFF FM THE LAKES THROUGH SE CANADA. THIS
YIELDS A CONTN OF NW FLW ALOFT ACRS THE LAKES/OH VALLEY ALG W/MUCH
BLO NORMAL TEMPS AND DRY WX THIS PD.

HWVR POTENTIAL PITFALL EXISTS IN FRI NIGHT-SAT TIME FRAME W/BOTH
HANDLING/PLACEMENT OF NWWD ORIENTED MID LVL TROUGH AXIS EXTENDING
BACK INTO THE NRN PLAINS AND NEWD EJECTION OF SRN STREAM SW LOCATED
OFF THE SRN CA COAST THIS MORNING. EC ELUCIDATED THIS POSSIBILITY
FIRST LAST NIGHT AND NOW HAS GROWING SPRT FM GEM. THUS FELT IT
PRUDENT TO PLACE SOME CONFIDENCE IN ALLBLEND GUIDANCE FOR THIS
TIME PD.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 556 AM EDT TUE APR 21 2015

DEEP MIXING AND TIGHT GRADIENT IN THE WAKE OF LOW PRESSURE OVER
ONTARIO WILL LEAD TO STRONG WESTERLY WINDS TODAY. WIND SPEEDS AT
THE TOP OF THE BOUNDARY LAYER ARE IN THE 40-50 KT RANGE SO EXPECT
GUSTS UP TO AROUND 40 KTS FROM LATE MORNING THROUGH THE AFTERNOON.
DRY AIR AND DEEP MIXING WILL HOWEVER KEEP CEILINGS ABOVE 5 KFT
THROUGH THE PERIOD. SLIGHT CHANCE OF A SPRINKLE/SHOWER AT KSBN
BUT NO IMPACT EXPECTED.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WIND ADVISORY FROM 11 AM EDT /10 AM CDT/ THIS MORNING TO 8 PM
     EDT /7 PM CDT/ THIS EVENING FOR INZ003>009-012>018-020-
     022>027-032>034.

MI...WIND ADVISORY FROM 11 AM THIS MORNING TO 8 PM EDT THIS EVENING
     FOR MIZ077>081.

OH...WIND ADVISORY FROM 11 AM THIS MORNING TO 8 PM EDT THIS EVENING
     FOR OHZ001-002-004-005-015-016-024-025.

LM...SMALL CRAFT ADVISORY UNTIL 11 AM EDT THIS MORNING FOR LMZ046.

     SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 4 PM EDT
     WEDNESDAY FOR LMZ046.

     GALE WARNING FROM 11 AM THIS MORNING TO 8 PM EDT THIS EVENING
     FOR LMZ046.

     SMALL CRAFT ADVISORY UNTIL 4 PM EDT WEDNESDAY FOR LMZ043.

&&

$$

SYNOPSIS...AGD
SHORT TERM...AGD
LONG TERM...T
AVIATION...AGD


VISIT US AT WWW.WEATHER.GOV/IWX (ALL LOWER CASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSNORTHERNINDIANA
WWW.TWITTER.COM/NWSIWX
WWW.YOUTUBE.COM/NWSNORTHERNINDIANA






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.