Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 280618
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
118 AM EST SAT FEB 28 2015

.SYNOPSIS...
ISSUED AT 100 AM EST SAT FEB 28 2015

HIGH PRESSURE WILL DRIFT ACROSS THE AREA TODAY WITH DRY
CONDITIONS...BUT BELOW NORMAL TEMPERATURES. OVERNIGHT
LOWS WILL DROP WELL BELOW ZERO...WITH SOME LOCALLY COLD SPOTS
FALLING TO NEAR 15 BELOW ZERO. THE FIRST OF 2 WINTER SYSTEMS WILL
THEN TAKE AIM ON THE AREA STARTING TONIGHT INTO SUNDAY...BRINGING
ACCUMULATING SNOW TO THE AREA. HIGH SATURDAY WILL REBOUND TO
AROUND 20 DEGREES...BUT STILL CLOSE TO 20 DEGREES BELOW NORMAL.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 332 PM EST FRI FEB 27 2015

SFC HIGH PRESSURE OVER THE AREA WILL MOVE SLOWLY EAST TONIGHT
PROVIDING NEARLY CALM WINDS. ANY LINGERING CU/STRATO-CU SHOULD
DISSIPATE THIS EVE BUT AN INCREASE IN HIGH CLOUDS EXPECTED LATE
TONIGHT AS A WK SHRTWV OVER THE CENTRAL HIGH PLAINS MOVES EAST
INTO THE MIDWEST. COMBINATION OF DRY AIRMASS... LIGHT WINDS...
SNOW COVER... AND AT LEAST SOME PERIODS OF CLEAR SKIES SHOULD
RESULT IN ANOTHER NIGHT OF STRONG RADIATIONAL COOLING ALLOWING
TEMPS TO FALL INTO THE -3 TO -8 RANGE ACROSS THE AREA BY SATURDAY
MORNING (RECORD LOW AT BOTH SBN/FWA FOR 2/28 IS -4). AS HIGH
DEPARTS TO THE EAST ON SATURDAY... WAA WILL COMMENCE. FAIR WX/DRY
AIRMASS WILL PERSIST... BUT BACKING WINDS ALOFT ASSOCIATED WITH
DEEPENING WRN TROF WILL ADVECT MID-HIGH LEVEL MOISTURE NEWD WHICH
SHOULD LEAD TO THICKENING HIGH CLOUDS OVERSPREADING THE AREA IN
THE AFTN. HIGH TEMPS EXPECTED TO BE A LITTLE WARMER THAN TODAY...
IN THE UPPER TEENS/L20S.

&&

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 332 PM EST FRI FEB 27 2015

...FOCUS OF FORECAST ON IMPACTS FROM FIRST OF TWO SIGNIFICANT
WEATHER SYSTEMS TO IMPACT REGION THIS PERIOD...

A WEAK UPPER LEVEL WAVE...AIDED BY LEFT FRONT QUAD OF A 125 KT JET
STREAK...WILL INDUCE MODEST ISENTROPIC LIFT ALLOWING FOR NEAR
SATURATION ACROSS MUCH OF THE FORECAST AREA WITH LIGHT SNOW BREAKING
OUT QUICKLY SATURDAY NIGHT. ACCUMULATIONS SHOULD BE SOMEWHAT LIMITED
RANGING FROM AN INCH OR SO NORTH TO AROUND 2 SOUTHWEST. SOMEWHAT
STRONGER WAVE WILL MOVE IN SUNDAY INTO SUNDAY EVENING...BRINGING
MORE WIDESPREAD SNOW TO THE AREA AS 150+ KT JET STREAK MOVES QUICKLY
ACROSS THE AREA ENHANCING LIFT ACROSS THE REGION. 2 TO 3 G/KG MIXING
RATIOS ADVECT INTO THE AREA WITH HIGHEST IN S/SE LOCATIONS. SOME
NEGATIVES FOR HEAVY SNOW FALL ARE 1) SFC TEMPERATURES IN THE MID-UPR
20S KEEPING SNOW RATIOS LIMITED 2) HIGHEST MSTR AND LIFT LOCATED
BELOW A MUCH HIGHER LEVEL DGZ 3) ISENTROPIC LIFT PLENTIFUL BUT NOT
PERPENDICULAR TO PRESSURE SURFACES...POSSIBLY LIMITING MESOBANDING.
4) LACK OF CLOSED OFF LOW/MID LEVEL FEATURES. NAM/GFS/ECMWF HAVE ALL
COME INTO SOME AGREEMENT WITH QUARTER INCH NORTH TO HALF INCH OR
MORE SOUTH/SE OF QPF WITH GENERAL 3 TO 6 INCH ACCUMULATIONS STILL
LOOKING REASONABLE. 9Z SREF PUSHED THE RAIN/SNOW LINE WELL NORTH
INTO THE FORECAST AREA...REDUCING SNOW AMOUNTS IN THE SOUTH AND
SHIFTING NORTHWARD HIGHEST ACCUMS. INITIAL FRAMES OF 15Z RUN APPEARS
TO BE TRENDING BACK SOUTH WITH THE RAIN/SNOW LINE AGAIN. AT THIS
POINT...PREVIOUS FORECAST STILL ON TRACK IN TERMS OF ACCUMULATION
POTENTIAL. COULD BE ARGUED TO SHIFT NORTHWARD SOMEWHAT BUT WITH
CONCERNS OUTLINED ABOVE BEST OPTION IS TO LEAVE ALONE. DID INCREASE
POPS TO HIGHER CATEGORICAL AND REALIGNED TIMING SATURDAY NIGHT TO
BETTER REFLECT TRENDS. COLLABORATION WITH SURROUNDING OFFICES WAS TO
HOLD OFF ON ANY HEADLINES BUT ADVISORY WILL LIKELY BE NEEDED FOR
MOST IF NOT ALL OF THE AREA...ESPECIALLY ON SUNDAY WHEN THE HEAVIEST
SNOW WILL OCCUR.

REGION WILL GET A BRIEF BREATHER BEFORE WAVE CURRENTLY OVER ALASKA
DROPS SOUTH ALONG THE COAST AND BEGINS TO DEEPEN AS IT
INTERACTS/PHASES WITH ORPHANED CLOSED UPPER LOW OVER SW STATES.
GFS/ECMWF CONTINUE TO VARY ON HANDLING/PHASING OF THESE FEATURES AND
SUBSEQUENT TIMING OF EJECTION TOWARDS THE REGION. GFS REMAINS FASTER
WITH PRECIP MOVING IN AS EARLY AS MONDAY NIGHT WITH ECMWF WAITING
TILL MID DAY TUESDAY. DESPITE THIS...BOTH MODELS DO SHOW MIX
POTENTIAL AT THE ONSET OF THE EVENT AS WARMER AIR ALOFT IS FASTER TO
MOVE...WITH AN INITIALLY SLOW DISPLACEMENT OF COLD SFC DOME OF AIR.
THIS STRUGGLE WILL BE KEY IN DETERMINING HOW FAST ANY
FREEZING/FROZEN PRECIP CHANGES TO ALL RAIN (ASSUMING IT DOES
EVERYWHERE) AND POTENTIAL SNOW/ICE ACCUMULATIONS. PERIOD OF FROZEN
PRECIP AT THE ONSET SHOULD BE QUIET BRIEF AS SOUNDINGS SATURATE AND
DEPTH OF WARM AIR INCREASES. MOST FAVORABLE TIME FRAME STILL LOOKS
TO BE IN THE FIRST 6 TO 9 HOURS OF THE PRECIP ARRIVING...MEANING
LATE MONDAY NIGHT INTO TUES AM PER THE GFS AND TUES AFTERNOON ON THE
ECMWF. GIVEN THE STRENGTH OF THE OVERALL SYSTEM...ECMWF CANNOT BE
DISMISSED AS FULL PHASING OF THE TROUGH AND SW CLOSED LOW WOULD SLOW
THINGS DOWN CONSIDERABLY. SFC LOW TRACK HAS SHIFTED SE SOMEWHAT
COMPARED TO 24 HOURS AGO WITH TRACK NOW SHIFTED TO A CENTRAL
ILLINOIS TO SE MICHIGAN LINE. THIS ALSO SHIFTS HIGHEST QPF FURTHER
SOUTH AND INCREASES POTENTIAL FOR SIGNIFICANT ICING FOR PARTS OF THE
AREA AS COLDER SFC AIR WOULD BE HARDER TO DISLODGE ESPECIALLY NW. NO
CHANGES MADE TO PTYPE FROM WHAT WAS INHERITED FROM OVERNIGHT SHIFT.
HOWEVER...DID INCREASE TO HIGHER END CAT POPS WITH GROWING
CONFIDENCE OF SOMETHING REACHING THE GROUND. SYSTEM WILL NEED TO BE
CLOSELY WATCHED IN THE COMING DAYS WITH TROUGH OF CONCERN YET TO
FORM. IN ADDITION TO PTYPE CONCERNS NOTED ABOVE...RUNOFF FORM ANY
NEW PRECIPITATION AND SNOW MELT COULD CAUSE ISSUES BOTH INLAND AND
OVER RIVER BASINS WITH FROZEN GROUND/RIVERS ACROSS THE AREA. LAST
FROST DEPTH FOR THE OFFICE ON THURSDAY WAS 10 INCHES DEEP.

COLDER AIR WILL FILTER BACK IN ON WEDNESDAY WITH HIGHS OCCURRING
EARLY IN THE DAY AND THEN FALLING TEMPS WITH READINGS ON THURSDAY
ONLY IN THE TEENS. SOME HINTS THAT TEMPS COULD RISE BACK TO NEAR
NORMAL LEVELS AGAIN TOWARDS THE END BUT FOR NOW HAVE STAYED
CONSERVATIVE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1255 AM EST SAT FEB 28 2015

A 1041 MB HIGH PRESSURE WILL DRIFT OVER THE AREA THIS MORNING WITH
CALM OR NEARLY CALM WINDS. LIGHT SNOW IS POSSIBLE BY THE END OF
THE TAF PERIOD AS RETURN FLOW BECOMES ESTABLISHED WITH INCREASING
MOISTURE IN THE LOW LEVELS.


&&

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

$$

SYNOPSIS...SKIPPER
SHORT TERM...JT
LONG TERM...FISHER
AVIATION...SKIPPER


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