Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 241055
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
555 AM EST TUE FEB 24 2015

.SYNOPSIS...
ISSUED AT 415 AM EST TUE FEB 24 2015

A LOW PRESSURE SYSTEM WILL MOVE THROUGH THE GREAT LAKES TODAY.
THIS WILL BRING PERIODS OF LIGHT SNOW AND STRONG WINDS THAT WILL
LEAD TO BLOWING AND DRIFTING SNOW. HIGHS TODAY WILL BE IN THE
LOWER TO MID 20S. SNOW AND BLOWING SNOW WILL GRADUALLY TAPER OFF
OVERNIGHT WITH TEMPERATURES RETURNING TO AROUND TEN DEGREES.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 415 AM EST TUE FEB 24 2015

LITTLE SUBSTANTIVE CHANGE TO THE CRUX OF THE FORECAST MESSAGE FOR
TODAY. STILL EXPECT LIGHT SNOW...WITH BLOWING AND
DRIFTING...ALONG AND NORTH OF THE TOLL ROAD TO IMPACT THE
AFTERNOON COMMUTE. ARCTIC WAVE RESPONSIBLE FOR THIS INCLEMENT
WEATHER APPEARS NICELY ON MORNING WATER VAPOR...SCREAMING SOUTH
TOWARD THE ARROWHEAD OF MINNESOTA. ACTUALLY TWO SEPARATE PIECES
OF ENERGY RIGHT NOW BUT LEAD WAVE WILL GET ABSORBED BY MORE
DOMINANT VORT MAX CURRENTLY FOLLOWING CLOSE ON ITS HEELS. 300-400
MB WIND SPEEDS ASSOCIATED WITH THIS ANOMALY ARE AROUND 130 KTS
AND 1.5 PVU SURFACE EXTENDS THROUGH THE BULK OF THE TROPOSPHERE.
ANOTHER MENACING ARCTIC WAVE TO BE SURE...BUT THE PROBLEM IS THAT
THIS WAVE AND PARENT JET STREAK ARE SHOWN TO ROTATE THROUGH
MICHIGAN LATER TODAY...KEEPING BEST PV ADVECTION AND LEFT EXIT
FORCING NORTH OF OUR CWA. FURTHERMORE...DEEP LAYER MOISTURE IS
SEVERELY LACKING. BY THE TIME LOWER LEVELS ARE SATURATED THIS
AFTERNOON...WE LOSE THE BETTER MIDLEVEL MOISTURE. LOW TO
MIDLEVELS ARE ALSO HIGHLY STABLE DURING THIS EVENT. STILL DO
EXPECT SOME LIGHT SNOW SHOWERS ACROSS NORTHERN COUNTIES DURING
THE AFTERNOON AND EVENING BUT AMOUNTS LOOK TO BE AN INCH OR LESS.

AS HAS BEEN DISCUSSED...STRONG WINDS AND SUBSEQUENT
BLOWING/DRIFTING WILL BE THE MAIN CAUSE FOR CONCERN AND THE
JUSTIFICATION FOR AN ADVISORY. STRONG GRADIENT ALREADY DEVELOPING
ACROSS OUR NORTHERN COUNTIES AND WILL CONTINUE TO STRENGTHEN
THROUGH THE DAY WITH THE APPROACH OF SURFACE PRESSURE TROUGH. NOT
A TYPICAL HIGH WIND SETUP FOR OUR AREA WITH SOUTHWEST FLOW/WAA
AND RELATIVELY LOW MIXING HEIGHTS. AM A LITTLE HESITANT TO RELY
SOLELY ON GRADIENT FLOW TO GENERATE WIND GUSTS UP TO AND OVER 30
MPH BUT LATEST GUIDANCE STILL SHOWS SUSTAINED WINDS AROUND 20 MPH
WITH MIXING HEIGHTS UP TO 900MB SO WILL NOT DEVIATE FAR FROM
GOING FORECAST. CAA WILL ARRIVE AFTER 00Z AND AM CONCERNED THIS
COULD MAINTAIN SOME GUSTY WINDS INTO THE LATE EVENING AS MIXING
HEIGHTS CLIMB. STEEPENING LOW LEVEL LAPSE RATES AND THETA-E FLUX
FROM THE STILL LARGELY OPEN WATERS OF LAKE MICHIGAN WILL ALSO
PROBABLY MAINTAIN SCT SNOW SHOWERS PAST 00Z. GIVEN THESE
FACTORS...DECIDED TO EXTEND THE END TIME OF THE ADVISORY UNTIL
03Z. GRADIENT RELAXES AND DRY AIR ADVECTION TAKES AN INCREASING
TOLL AFTER MIDNIGHT SO CONDITIONS WILL IMPROVE GREATLY BY
WEDNESDAY MORNING. FINALLY...IT SHOULD BE NOTED THAT CONDITIONS
THIS AFTERNOON AND EVENING WILL NOT BE NEARLY AS BAD AS THE
VALENTINE`S DAY EVENT. NORTHWARD DISPLACEMENT OF BETTER FORCING
AND DELAYED CAA WILL LIMIT BOTH WIND SPEEDS AND NEW SNOW AMOUNTS.
STILL ENOUGH TO CAUSE TRAVEL DISRUPTION AND WORTHY OF AN ADVISORY
BUT NOT NEARLY AS EXTREME.

ONCE AGAIN...WIND CHILL VALUES COMPLICATE HEADLINE DECISIONS.
SNOW AND BLOWING SNOW WILL NOT RAMP UP UNTIL LATE MORNING BUT
WIND CHILL VALUES ARE HOVERING AROUND ADVISORY CRITERIA AT
PRESENT. PREFER TO NOT MUDDLE THE MESSAGE OVER BORDERLINE WIND
CHILL CRITERIA AND WILL JUST LET THE FORECAST SPEAK FOR ITSELF.
WILL MAINTAIN 12Z START TIME AND MENTION MORNING WIND CHILL
CONCERNS IN THE TEXT OF THE WSW. WILL HOWEVER EXPAND WIND CHILL
ADVISORY INTO OUR SOUTHWEST COUNTIES BASED ON LATEST OBS FROM
KGGP...KMCX...AND KOXI.

&&

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 443 AM EST TUE FEB 24 2015

NO SUBSTANTIVE CHNGS WRT LONG TERM FCST PD. POST ARCTIC FRONTAL
LES RESPONSE WED INCREASINGLY HAMPERED WITH DRY AIR
ENTRAINMENT/SHALLOW CBL WITH MIXED LAYER EQL GNRLY LTE 4.5KFT.
FURTHERMORE THERMAL INSTABILITY RATHER MARGINAL RELEGATED TO MID
TEENS ALONG WITH CONTD INCREASING MID LAKE ICE PRODUCTION.
PIECEMEAL ENERGY OVERTOPPING EPAC/WRN COAST RIDGE TO DRIVE WEAK
ALBERTA CLIPPER SYSTEM IN CONSORT ALONG SRN/SERN PERIPHERY OF
ARCTIC RIDGES SWD PLUNGE. CLIPPER TO ADVANCE INTO ECTNL MO BY
LATE WED NIGHT/THU AM. LYRD MOISTURE LIKELY TO STYMIE LONGWAVE
LOSSES AND HAVE CONTD RECENT TREND OF WARMER TEMPS THU AM IN
CONCESSION TO MODEST SYSTEM THAT ALSO NOW APPEARS TO HAVE SUPPORT
WITH EJECTION OF QUICKER EWD EJECTION OF CA/AZ THROUGH SRN STREAM
IMMEDIATELY FOLLOWED BY SHARPENING WITHIN SEMI-PERMANENT HUDSON
BAY VORTEX TO AFFORD 40-70M/12 HR HEIGHT FALLS THROUGHOUT SRN
GRTLKS. ENLARGED AREA OF FLURRIES LATE WED NIGHT OUTSIDE OF NWRN
IN LES REGION...THEN MINOR CHCS/ACCUMS THU AM ESPCLY SRN/SERN CWA
AS SYSTEM MOVES INTO MIDATL. HEREAFTER EXTREME CP AIRMASS TO
INVADE. ANTICIPATE MODEST LES RESPONSE AT BEST GIVEN DEARTH OF
MOISTURE...HOWEVER MIN TEMPS FRI AM WL BE HIGHLY CLOUD COVER
DEPENDENT WITH HIGH BUST POTNL EITHER WAY ACRS FAR NWRN/WRN CWA.
LITTLE CHANGE WRT LATE WEEKEND STORM SYSTEM/PATTERN AS DOMINANT
UPSTREAM RIDGING RETROGRADES TO 140-145W. BOTH BROAD/CONTD
SUPPRESSED HGHTS ACRS ERN TWO THIRDS INTO THE WEEKEND AS WELL AS
ARCTIC AIRMASS REACH INTO DEEP SOUTH THROUGH FRI...COULD ONLY
ANTICIPATE A SUPPRESSED SRLY STORM TRACK WITH RATHER DEEP COLD
AIRMASS TO REMAIN FIRMLY ROOTED FOR PRIMARILY FROZEN PTYPE. STILL
WITH GREAT UNCERTAINTY HESITANT TO MAKE WHOLESALE CHANGES...WITH
SLIGHT TREND TOWARD HIR LKLY POPS FOR SN AND GIVE A LESSER CHC
NOD FOR LIQUID MIX IN SRN CWA/PRIOR MIXED AREA...BUT RELEGATED TO
A LESSER TEMPORAL PD/SUN AFTN FOR NOW UNTIL TREND BECOMES
CLEARER.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 555 AM EST TUE FEB 24 2015

WINDS WILL CONTINUE TO INCREASE THROUGH THE MORNING AS POTENT
MIDLEVEL SHORTWAVE AND ASSOCIATED SURFACE PRESSURE TROUGH APPROACH
THE REGION. BEST FORCING PASSES TO THE NORTH BUT SHOULD STILL SEE
SOME LIGHT SNOW SHOWERS...ESPECIALLY AROUND KSBN. THIS...IN
CONCERT WITH THE PRE-EXISTING SNOWPACK...WILL LEAD TO PERIODS OF
BLOWING SNOW AND POTENTIALLY IFR CONDITIONS AT KSBN LATER TODAY.
WORST CONDITIONS STILL LOOK TO BE IN THE 21-00Z TIMEFRAME. MVFR
CEILINGS EXPECTED OVERNIGHT AS CAA RAMPS UP BUT NOT YET CONFIDENT
THAT CONDITIONS WILL REACH FUEL ALTERNATE CRITERIA.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WIND CHILL ADVISORY UNTIL 10 AM EST /9 AM CST/ THIS MORNING FOR
     INZ008-009-012>018-020-022>027-032>034.

     WINTER WEATHER ADVISORY UNTIL 10 PM EST /9 PM CST/ THIS EVENING
     FOR INZ003>007.

MI...WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR
     MIZ077>081.

OH...WIND CHILL ADVISORY UNTIL 10 AM EST THIS MORNING FOR OHZ002-004-
     005-015-016-024-025.

     WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR OHZ001.

LM...NONE.
&&

$$

SYNOPSIS...AGD
SHORT TERM...AGD
LONG TERM...MURPHY
AVIATION...AGD


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