Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 231809
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
109 PM EST FRI JAN 23 2015

.SYNOPSIS...
ISSUED AT 400 AM EST FRI JAN 23 2015

HIGH PRESSURE WILL REMAIN OVER THE REGION TODAY BUT SKIES WILL
REMAIN CLOUDY THIS MORNING BUT A FEW BREAKS IN THE CLOUD COVER
MAY DEVELOP THIS AFTERNOON. HIGH TEMPERATURES TODAY WILL
GENERALLY BE IN THE 30S AND LOWS TONIGHT WILL GENERALLY BE IN THE
20S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 401 AM EST FRI JAN 23 2015

ANOTHER QUIET SHORT TERM PERIOD WITH CLOUDS AND TEMPS THE ONLY
CONCERN. AS WE SUSPECTED LAST NIGHT...CLOUD COVER REMAINED LOCKED
IN ACROSS THE REGION THIS MORNING UNDERNEATH STRONG INVERSION WITH
WEAK FLOW. CLOUD COVER HAS BEEN EXPANDING NORTHEAST OVERNIGHT WITH
WEAK SOUTHWEST FLOW ALOFT. BACK EDGE OF CLOUD SHIELD CURRENTLY
ACROSS IA INTO MO AND THIS HAS BEEN ADVANCING SLOWLY EAST LAST FEW
HOURS. FORECAST SOUNDINGS VARY DEPENDING ON MODEL CHOICE. WRF
MODELS ALONG WITH HRRR AND RUC GENERALLY SHOW LOW LEVEL MOISTURE
AND INVERSION HANGING TOUGH THROUGH TONIGHT BEFORE CLOUD COVER
WITH NEXT SHORT WAVE ARRIVES. OTHER MODELS SHOW MUCH LESS MOISTURE
BY AFTERNOON SUGGESTING THINNING CLOUD COVER WITH BREAKS. THIS IS
ALWAYS A DILEMMA IN MID WINTER WITH WEAK MIXING AND LOW SUN ANGLE
AND SOMETIMES WE SEE THE CLEARING AND OTHER TIMES WE DO NOT. HAVE
INCREASED CLOUD COVER TODAY OVERALL WITH CLOUDY THIS MORNING BUT
DID TRY AND DEVELOP SOME BREAKS THIS AFTERNOON GIVEN SATELLITE
TRENDS AND 00Z SOUNDINGS SHOWING RELATIVELY THIN MOISTURE DEPTH.
THIS WILL IMPACT TEMPS AS OVERCAST SKIES THROUGH THE DAY WILL ONLY
ALLOW FOR A COUPLE DEGREE RISE WHILE BREAKS WOULD LEAD TO A FEW
MORE DEGREES IN WARMING. MET MOS SEVERAL DEGREES COLDER THAT MAV
AND EC GIVEN ITS PESSIMISTIC OUTPUT. HAVE OPTED TO STAY WITH A
CONSENSUS BLEND IN MIDDLE OF GUIDANCE ENVELOPE.

NEXT SHORT WAVE AND WEAK SURFACE BOUNDARY WILL APPROACH LATE
TONIGHT. NOT EXPECTING MUCH WITH THIS SYSTEM OTHER THAN CLOUDS AND A
VERY LOW CHANCE FOR SNOW SHOWERS NEAR BOUNDARY. THIS SHOULD BE
CONFINED TO EXTREME NORTHERN COUNTIES AND BASICALLY LEFT A SLIGHT
CHANCE POP IN FOR COLLABORATION LATE TONIGHT.

&&

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 401 AM EST FRI JAN 23 2015

MUCH OF THE UPCOMING LONG TERM PERIOD WILL BE CHARACTERIZED BY
PERTURBED NORTHWEST FLOW WITH THE MAIN EVENT TO WATCH STILL ON
SUNDAY. FIRST WAVE WILL SWING THROUGH THE REGION SATURDAY MORNING
AND SEND A WEAK CONVERGENT BOUNDARY ACROSS OUR CWA. A SECONDARY
EMBEDDED VORT MAX WILL THEN PASS OVER OUR AREA DURING THE AFTERNOON
AND MAY TOUCH OFF A FEW ISOLATED RAIN/SNOW SHOWERS. SYNOPTIC FORCING
IS CERTAINLY WEAK BUT FORECAST SOUNDINGS SHOW DECENT LOW LEVEL LAPSE
RATES AND PLENTY OF MOISTURE IN THE LOWEST 5 KFT. THIS RAISES SOME
CONCERN FOR FREEZING DRIZZLE BUT FORECAST SOUNDINGS ALSO SHOW AT
LEAST SOME VARYING DEGREE OF SATURATION ABOVE THE -10C LEVEL AND
SHOULD PROVIDE ENOUGH ICE NUCLEI FOR JUST SNOW. MAY EVEN BE RAIN
DURING THE AFTERNOON GIVEN SURFACE TEMPS IN THE MID TO POSSIBLY
UPPER 30S BUT WITH SURFACE DEWPOINTS HOLDING AT OR BELOW
30...SUSPECT IT WILL MAINLY FALL AS SNOW AND THEN MELT QUICKLY ON
CONTACT WITH THE GROUND. THESE WARM GROUND/SURFACE TEMPS ARE ANOTHER
REASON THAT FREEZING DRIZZLE IS NOT MUCH OF A CONCERN. BEST CHANCES
FOR PRECIP WILL BE ACROSS OUR NORTH WHERE THETA-E FLUX FROM THE
LAKES MAY PROVIDE A MARGINAL BOOST TO HYDROMETEOR PRODUCTION.

MUCH MORE ROBUST PV ANOMALY DIVES INTO THE MIDWEST BY SUNDAY...ON
THE CYCLONICALLY SHEARED SIDE OF LARGELY MERIDIONAL 130 KT UPPER
LEVEL JET. AS HAS BEEN THE CASE FOR MUCH OF THIS WINTER...MODELS
STRUGGLE WITH EXACT TRACK OF SURFACE REFLECTION AND 850MB LOW.
FORECAST IS FURTHER COMPLICATED BY SURFACE TEMPERATURES RIGHT
AROUND THE FREEZING MARK. NOTABLE SOUTHERN ADJUSTMENT SEEN IN MOST
OF THE 00Z GUIDANCE. 00Z GFS...GEM...AND ECMWF NOW TRACK THE SURFACE
LOW SOUTH OF OUR CWA WITH THE ECMWF ACTUALLY GOING THROUGH SOUTHERN
INDIANA. 00Z NAM IS NOW THE NORTHERN OUTLIER. TOUGH TO IGNORE THIS
MORE SOUTH/WEST TREND BUT CONFIDENCE IN ANY PARTICULARS REMAINS LOW
WITH PARENT JET ENERGY STILL OVER THE NORTH PACIFIC. DID RAISE POPS
AND QPF AMOUNTS QUITE A BIT IN OUR SOUTHWEST CWA. ALSO TRENDED
COLDER THOUGH STILL THINK SOME RAIN MAY CUT INTO SNOW TOTALS ACROSS
AT LEAST OUR FAR SOUTHWEST. DYNAMICS WITH THIS SYSTEM ARE NOT OVERLY
IMPRESSIVE BUT SHOULD SEE A DECENT SLUG OF 285K ISENTROPIC ASCENT
AND LOW LEVEL DEFORMATION/FGEN JUST NORTH OF THE SURFACE LOW TRACK.
GOOD MOISTURE FEED TOO...WITH LOW LEVEL MIXING RATIOS AROUND 3 G/KG
AND PWATS UP TO A HALF INCH. COUPLE THIS WITH GOOD MIDLEVEL CVA AND
UPPER LEVEL SUPPORT AND MODEL QPF VALUES OF UP TO 0.4 INCHES MAY NOT
BE TOO FAR OFF. SNOW RATIOS WILL BE ON THE LOW SIDE GIVEN WARM
GROUND AND ELEVATED/SHALLOW DGZ BUT NEVERTHELESS...ADVISORY LEVEL
SNOW COULD EASILY BE POSSIBLE FOR MOST OF OUR CWA BASED ON THE
LATEST 00Z NWP GUIDANCE. WILL GO WITH A CONSERVATIVE 2-4 INCHES FOR
NOW AND SEE WHAT THE 12Z RUNS HAVE TO OFFER.

REST OF THE FORECAST LOOKS FAIRLY BENIGN. RETURN TO COLD TEMPS
EXPECTED FOR THE FIRST HALF OF THE WORK WEEK...ESPECIALLY IF WE GET
A FRESH SNOWPACK. SINGLE DIGIT LOWS AND HIGHS AROUND 20F EXPECTED
FOR A LARGE PART OF THE CWA. POTENTIAL FOR ANOTHER WEAK CLIPPER
SYSTEM ON TUESDAY BUT AIRMASS WILL BE VERY DRY AND FORCING WEAK.
PREFER A SILENT TEN POP FOR NOW.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1245 PM EST FRI JAN 23 2015

A WEAK RIDGE OF HIGH PRESSURE WAS NORTH OF THE OHIO RIVER...LIKE
AN INACTIVE COL AREA BETWEEN THE DEVELOPING LOW TO THE SOUTH AND
THE APPROACHING SHORTWAVE TROF AND ASSOCIATED SURFACE TROF TO THE
WEST. AIRCRAFT OBSERVATIONS AND EARLY MORNING REGIONAL SOUNDINGS
SHOWED THE INVERSION DEEPENING FROM NORTHEAST TO SOUTHWEST. GIVEN
THIS INVERSION WITH THE COL AREA IN CLOSE PROXIMITY...THE MODELS
APPEAR TO BE CLEARING SKIES AND IMPROVING CONDITIONS TOO FAST...
ESPECIALLY THE GFS. HAVE GONE MORE PESSIMISTIC WITH IMPROVING
CONDITIONS GIVEN ALL OF THESE FACTORS AS BOTH SBN AND FWA OBS
STILL NEAR 015 OVC. THEREFORE... KEPT MVFR AT BOTH SITES FOR THE
ENTIRE TAF PERIOD AT 17Z. TAFS STILL MAY BE TOO OPTIMISTIC WITH
CEILING IMPROVEMENT TO 020...BUT STILL HOPEFUL OF THIS IMPROVEMENT
GIVEN THE 020 MINIMUM FOR FUEL ALTERNATE.

&&

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

$$

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


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