Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 241804
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
104 PM 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.

&&

.UPDATE...
ISSUED AT 1254 PM EST TUE FEB 24 2015

NARROW BAND OF LIGHT TO MODERATE SNOWFALL WAS DROPPING RAPIDLY
SE...NOW MOVING THROUGH SW MICHIGAN. VSBYS HAVE DROPPED IN AREAS
BELOW A HALF MILE FROM A COMBINATION OF SNOW AND BLOWING SNOW.
OVERALL THE BAND ISN`T IMPACTING CONDITIONS MORE THAN AN HOUR OR
SO. REGARDLESS OF THE LOCATION OF THIS INITIAL FEATURE...ALL AREAS
HAVE SEEN A UPTICK IN WIND SPEEDS AND GUSTS AS EXPECTED WITH WINDS
OUT OF THE SW NOW SUSTAINED IN THE 10 TO 25 MPH RANGE AND
OCCASIONAL GUSTS TO 35 MPH. THIS WILL CONTINUE THROUGH THE
AFTERNOON WITH BLOWING AND DRIFTING STILL A CONCERN MAINLY IN
RURAL AREAS. WILL NOT EXPAND HEADLINES FOR NOW WITH SPS STILL OUT
TO TRY TO HIGHLIGHT CONCERNS.

FEW BREAKS IN CLOUD COVER ARE NOTED AHEAD OF THE BAND OF SNOW AND
MAY ALSO MATERIALIZE BEHIND IT BUT BY IN LARGE MOSTLY CLOUDY TO
CLOUDY SKIES WILL PREVAIL.

&&

.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 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1254 PM EST TUE FEB 24 2015

TOUGH TAF PERIOD...ESPECIALLY NEXT 6 HOURS...WITH APPROACH OF 2
BANDS OF SNOW SHOWERS TO IMPACT AT LEAST KSBN AND POSSIBLY KFWA.
FIRST BAND WAS JUST NORTH OF KSBN AND DROPPING RAPIDLY SE.
UPSTREAM SITES HAVE SEEN VSBYS DROP TO IFR/LIFR FOR A PERIOD IN
SNOW AND BLOWING SNOW. TIRED TO ADD A BIT MORE TIMING TO THE BAND
IN TEMPO GROUP WITH 3/4SM VSBY FOR A BRIEF PERIOD FOLLOWED BY MVFR
CONDITIONS OUTSIDE IT. WILL NEED TO MONITOR BLOWING SNOW TRENDS
FOR POSSIBLE LOWERING OF FLGT CONDITIONS. AT KFWA...SOUTHERN
EXTENT OF BAND QUESTIONABLE AS IT THE IMPACTS WITH HIGH RES MODELS
SHOWING A WEAKENING TREND BY THE TIME IT REACHES THE AIRPORT. HAVE
WENT MORE CONSERVATIVE FOR NOW. 2ND BAND OF SNOW SHOWERS MORE SCT
IN NATURE ON THE COLD FRONT TO ARRIVE LATE AFTERNOON/EARLY
EVENING. NOT GOING TO MAKE ANY SIG ADJUSTMENTS BEYOND 1ST 6 HOURS
WITH UNCERTAINTY OF IMPACTS RIGHT NOW. GUSTY SW WINDS WILL PERSIST
INTO EARLY EVENING FOR BOTH SITES WITH GUSTS NEAR OR OVER 30 KTS
AT TIMES.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...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...WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR OHZ001.

LM...NONE.
&&

$$

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


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