Area Forecast Discussion
Issued by NWS Northern Indiana

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546
FXUS63 KIWX 210543
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
143 AM EDT THU MAY 21 2015

.SYNOPSIS...
ISSUED AT 511 PM EDT WED MAY 20 2015

A WEAKENING UPPER LEVEL DISTURBANCE MAY BRING A PERIOD OF LIGHT
RAIN OR SPRINKLES TO THE AREA THIS EVENING...WITH THE BEST
CHANCES ALONG AND SOUTH OF HIGHWAY 30. LOWS TONIGHT WILL BE IN
THE 40S. EXPECT TEMPERATURES TO WARM GRADUALLY THROUGH THE
WEEKEND...WITH HIGHS EVENTUALLY RISING BACK INTO THE 60S AND 70S.
TEMPERATURES WILL BE A LITTLE COOLER NEAR LAKE MICHIGAN.

&&

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 331 PM EDT WED MAY 20 2015

COOL WX CONTINUES THIS PERIOD WITH MAIN FOCUS ON CHANCES FOR LIGHT
RAIN/SPRINKLES LATE THIS AFTERNOON/EVENING...

AN UPPER LEVEL SHORTWAVE OVER MINNESOTA/IOWA AS OF 19Z WILL
SHEAR/WEAKEN EAST THROUGH THE LOWER GREAT LAKES THIS EVENING INTO
THE EARLY OVERNIGHT. MODEST PV ADVECTION AND UPPER JET SUPPORT WITH
60-70 METER HEIGHT FALLS THROUGH THE LOWER LAKES WILL SUPPORT A
PERIOD OF DECENT MID/UPPER LEVEL ASCENT DURING THIS TIME...WITH
ASSOCIATED CORRIDOR OF SYSTEM RELATIVE ISENTROPIC ASCENT TRANSLATING
THROUGH (20-25 KTS OF CROSS ISOBARIC FLOW AND A 5-6 G/KG TAP ON 300K
SFC). LIMITING FACTOR FOR PCPN WILL BE DRY ENE FEED WITHIN LOWEST
5-7 KFT MAKING IT A DIFFICULT POP FCST (SPRINKLES VERSUS LIGHT
MEASURABLE RAIN). WITH THAT SAID DID OPT TO RAISE POPS THIS
EVENING GIVEN UPSTREAM TRENDS AND LATEST HIRES GUIDANCE...ESPECIALLY
ACROSS WESTERN/SOUTHERN ZONES NEAR INVERTED TROUGH/PWAT RIDGE PIVOT
(AMOUNTS LIGHT/LESS THAN A TENTH OF AN INCH AT BEST).

MODELS ARE IN GOOD AGREEMENT IN DROPPING A SECONDARY PV ANOMALY
WITHIN BROADER TROUGH AXIS THROUGH THE LOCAL AREA TOMORROW.
ASSOCIATED COLD POCKET ALOFT AND STEEPENING LOW LEVEL LAPSE RATES IF
ANY CLEARING OCCURS COULD HELP POP A FEW SPRINKLES ACROSS EASTERN
ZONES BY LATE MORNING/AFTERNOON...ALTHOUGH OPTED TO MAINTAIN A DRY
FCST GIVEN DEARTH OF MOISTURE. OTHERWISE...SUBTLE LATE DAY THERMAL
ADVECTION AND AT LEAST PARTIAL CLEARING (BEST CHANCES NORTHERN
ZONES) IN ADVANCE OF A SFC TROUGH WILL AFFORD A MILDER DAY WHEN
COMPARED TO THE PREVIOUS TWO DAYS.

&&

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 331 PM EDT WED MAY 20 2015

WEAK SHORT WAVE WILL SWING ACROSS THE AREA THURSDAY NIGHT WITH AN
ASSOCIATED WEAK SURFACE FRONT MOVING THROUGH OVERNIGHT. VERY WEAK
LIFT AND SHALLOW MOISTURE SO NOT MUCH IN WAY OF PCPN EXPECTED. DID
INCLUDE A SPRINKLE MENTION WITH A FEW HIRES MODELS SHOWING
POSSIBILITY OF SOME VERY LIGHT PCPN BUT VERY ISOLATED...WEAK AND
BRIEF. JUST CANNOT SUPPORT MEASURABLE CHANCES AT THIS TIME.

HIGH PRESSURE THEN BUILDS IN FOR FRIDAY AND SATURDAY WITH GRADUAL
WARMING TREND AND DRY CONDITIONS. PATTERN BEGINS TO CHANGE FOR
LATTER PART OF WEEKEND INTO NEXT WEEK AS WESTERN CONUS TROUGH MOVES
INTO PLAINS AND SOUTHWEST FLOW DEVELOPS ACROSS THE MIDWEST. PCPN
CHANCES BEGIN TO INCREASE INTO LOW CHANCE CATEGORY LATE SATURDAY
NIGHT WITH INCREASING MOISTURE FLUX BUT ONLY WEAK SHORT WAVES WHICH
WILL LIKELY NOT PRODUCE MUCH THIS FAR EAST. BETTER MOISTURE AND A
LITTLE BETTER FORCING IN THE WEST AND NORTH SUNDAY BUT ESPECIALLY
SUNDAY NIGHT AND MONDAY AS TROUGH GETS CLOSER...HEIGHTS FALL AND
SHORT WAVES LOOK TO BE A LITTLE STRONGER. LOW LEVEL JET SUNDAY NIGHT
ALONG WITH WEAK SURFACE BOUNDARY LIFTING NORTH SUPPORTS THE
INHERITED LOW END LIKELY POPS NORTHWEST. WILL CONTINUE TO DISCUSS
HOW THE MODEL CONVECTIVE TRENDS AND SCHEMES MEANS THUNDERSTORM
ACTIVITY MORE THAN LIKELY TO BE LIMITED IN BOTH SPACE AND TIME
VERSUS MODEL DEPICTION OF MORE WIDESPREAD ALL DAY TYPE PCPN. WILL
NOT REALLY BE ABLE TO NAIL DOWN THIS DETAIL UNTIL 12 TO 24 HOURS OUT
SO HOLIDAY WEEKEND BY NO MEANS A WASHOUT.

TROUGH BEGINS TO LIFT OUT BY TUESDAY INTO WEDNESDAY WITH POSSIBILITY
OF ANOTHER WEAKER SYSTEM ON ITS HEELS FOR WEDNESDAY. GRADUAL
DECREASE IN POPS BUT DID LEAVE LOW CHANCE MENTION IN FOR LATER
PERIODS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 143 AM EDT THU MAY 21 2015

VFR CONDS WITHIN EXTENSIVE POST SW STRATOCU CLD FIELD WILL GRADUALLY
ERODE THROUGH LT MORNING/ERLY AFTN AS MIDLVL SUBSIDENCE RAMPS
APPRECIABLY.

&&

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

$$

SYNOPSIS...MCD
SHORT TERM...STEINWEDEL
LONG TERM...LASHLEY
AVIATION...T


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