National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KIWX 031055
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
555 AM EST TUE DEC 3 2013

.SYNOPSIS...
ISSUED AT 400 AM EST TUE DEC 3 2013

LIGHT RAIN WILL BE POSSIBLE TODAY...MAINLY ALONG AND NORTH OF THE
TOLL ROAD...AS A WARM FRONT CONTINUES TO LIFT THROUGH THE AREA.
THIS FRONT WILL ALSO BRING MUCH MILDER CONDITIONS THROUGH
TOMORROW. A COLD FRONT WILL THEN PASS THROUGH THE AREA LATE
WEDNESDAY WITH A CHANCE OF RAIN AND RETURN TO COOLER TEMPERATURES
FOR THE END OF THE WEEK.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 400 AM EST TUE DEC 3 2013

LATEST RADAR/SURFACE OBSERVATIONS SHOW LEADING ARM OF 285-290K
ISENTROPIC ASCENT ASSOCIATED WITH ELEVATED WARM FRONT CURRENTLY
LIFTING ACROSS OUR NORTHEAST COUNTIES. STILL ENOUGH COOL/DRY AIR AT
THE SURFACE TO SUPPORT A LIGHT MIX OF SLEET/SNOW IN THOSE AREAS BUT
WET BULB TEMPS WILL QUICKLY WARM ABOVE FREEZING AROUND SUNRISE AND
EXPECT ANY REMAINING PRECIP TO BE ALL LIQUID IN OUR CWA BY 14Z. WILL
ALSO BE A LULL IN PRECIP AROUND THE SAME TIME THOUGH AS THE MAIN
BAND OF WAA SHIFTS NORTHEAST. POP FORECAST THEREAFTER BECOMES A BIT
CONVOLUTED. MODELS INDICATE ANOTHER SURGE OF WAA/FGEN DEVELOPING
OVER OUR FAR NORTHERN COUNTIES THIS AFTERNOON...AIDED BY EXIT REGION
DYNAMICS OF APPROACHING 250MB JET STREAK. THIS FORCING WILL REMAIN
FOCUSED LARGELY NORTH OF OUR CWA BUT MAY CLIP AREAS ALONG AND NORTH
OF THE TOLL ROAD. THE REST OF THE CWA WILL LIKELY REMAIN DRY BUT
BROAD ISENTROPIC ASCENT AND CONTINUED MOISTURE ADVECTION COULD
GENERATE SOME DRIZZLE OR VERY LIGHT RAIN SHOWERS. LOW CONFIDENCE IN
THIS OCCURRING ANYWHERE SOUTH OF US-30 THOUGH. INHERITED FORECAST
REFLECTS CURRENT THINKING REASONABLY WELL BUT TRIED TO ADD A LITTLE
MORE DETAIL TO THE TEMPORAL AND SPATIAL TRENDS. SIMILAR STORY FOR
THE OVERNIGHT PERIOD. MAIN WARM FRONTAL PRECIP WILL SHIFT NORTH BUT
RESIDUAL WEAK/BROAD ISENTROPIC UPGLIDE MAY SUPPORT SOME VERY LIGHT
PRECIP IN OUR AREA...ESPECIALLY TOWARDS DAYBREAK WEDNESDAY MORNING
AS MAIN TROUGH AND ASSOCIATED SURFACE LOW BEGIN TO APPROACH THE
REGION. PRECIP TYPE WOULD MORE THAN LIKELY BE DRIZZLE IF ANYTHING
WERE TO OCCUR GIVEN PRONOUNCED DRY LAYER AROUND 750MB. WILL
THEREFORE MAINTAIN JUST A SLIGHT CHANCE POP. HIGH TEMP FORECAST
TODAY IS ALSO A DIFFICULT ONE. WAA WILL LEAD TO 925MB TEMPS
APPROACHING 8C BY LATE AFTERNOON. MOST OF THE CWA SHOULD BE ABLE TO
TAP INTO THIS WARMER AIR ALOFT AND CLIMB INTO THE LOW TO MID 50S BUT
NAM BUFR SOUNDINGS INDICATE SOME OF OUR NORTH AND NORTHEAST COUNTIES
MAY STRUGGLE TO MIX OUT STUBBORN INVERSION. SEVERAL GUIDANCE SOURCES
ARE SHOWING A 10-15F DEGREE GRADIENT FROM OUR SOUTHWEST TO OUR
NORTHEAST CWA TODAY. CONFIDENCE IN EXACTLY HOW FAR NORTH WE ARE ABLE
TO MIX IS LOW BUT HAVE ADJUSTED THE FORECAST TO REFLECT A TIGHTER
GRADIENT ACROSS THE CWA. OVERNIGHT LOWS WILL BE DOWNRIGHT BALMY
COMPARED TO SOME OF OUR RECENT NIGHTS. INCREASING SOUTHERLY
FLOW...CONTINUED WARM/MOIST AIR ADVECTION...AND ABUNDANT CLOUD COVER
WILL KEEP OVERNIGHT TEMPS NOT TOO FAR FROM DAYTIME HIGHS...GENERALLY
MID TO UPPER 40S.

&&

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 400 AM EST TUE DEC 3 2013

MODELS HAVE FINALLY BEGUN TO CONVERGE ON AT LEAST REASONABLY SIMILAR
SOLUTIONS FOR ARCTIC FRONTAL PASSAGE AND TIMING OF COLD AIR
ADVECTION ACROSS THE FORECAST AREA. THE TWO MODEL CAMPS HAVE
CONVERGED TOWARD THE SLOWER SOLUTIONS WHICH HAVE BEEN OFFERED BY THE
ECMWF...GEMNH AND UKMET OVER THE LAST SEVERAL RUNS. GFS REMAINS A
PERSISTENT FASTER OUTLIER BUT AT LEAST IT HAS SLOWED TO A REASONABLY
ACCEPTABLE SOLUTION. THUS THE SO CALLED WEATHER CUP APPEARS TO BE
HEADING TO THE NON US MODEL CONTINGENCY FOR THIS PARTICULAR EVENT AS
WE EXPECTED.

WATER VAPOR SHOWS MAIN UPPER LOW OVER ID/MT EARLY THIS MORNING AND
DIGGING SOUTHWARD. THE FRAGMENTED ENERGY WHICH GAVE THE MODELS FITS
IS PROGRESSING EASTWARD ACROSS THE NORTHERN TIER OF STATES AND NOT
NEAR AS STRONG AS THE US MODELS HAD INDICATED. THEREFORE CONFIDENCE
HIGHER IN THE ECMWF/UKMET/GEMNH SOLUTIONS AND TIMING FOR THIS
PACKAGE WHICH MATCHES WELL WITH PREVIOUS GRIDS AND NEIGHBORING
OFFICES.

A 120+ KT MID LEVEL JET WILL ROUND BASE OF WESTERN TROUGH AND MAKE
ITS WAY INTO UPPER GREAT LAKES BY THURSDAY. THIS WILL HELP UPPER LOW
TO FRAGMENT FURTHER WITH SEVERAL PIECES OF ENERGY EJECTING NORTHEAST
THROUGH BROAD LONG WAVE TROUGH. FIRST OF THESE SHORT WAVES TO ALLOW
FOR CYCLOGENESIS ALONG ARCTIC BOUNDARY WED WITH SURFACE LOW
DEEPENING AND MOVING INTO WI WED NIGHT AND TO LAKE SUPERIOR BY THU
MORNING. THIS WILL DRIVE THE INITIAL COLD FRONT THROUGH THE CWA WED
NIGHT WITH WIND SHIFT TO WEST SOUTHWEST INITIALLY. TEMPS TO BEGIN
FALLING WITH THIS INITIAL FRONT WED NIGHT BUT MODELS SHOW DEEPER
COLD WEDGE ARRIVING THURSDAY WITH SECONDARY FRONT. 850MB TEMPS
REALLY BEGIN TO DROP LATER THURSDAY MORNING AND AFTERNOON AS COLD
AIR ADVECTION DEEPENS. THIS WILL LIKELY LEAD TO STEADY EARLY MORNING
TEMPERATURES BEHIND INITIAL FRONT WITH FALLING SFC TEMPS FROM MID TO
LATE MORNING ON. ADJUSTED HOURLY GRIDS TO ACCOUNT FOR THIS
NON-DIURNAL SCENARIO WITH ECMWF SFC TEMPS AS A GUIDE.

WITH BROAD UPPER LEVEL TROUGH THE DYNAMICS AND FORCING WITH THIS
SYSTEM ARE RELATIVELY WEAK CONSIDERING THE THERMAL CONTRAST. MODEL
QPF RATHER LIGHT AS WELL WITH INITIAL BOUNDARY AND THIS LOOKS
REASONABLE. KEPT POPS IN LOW TO MID CHANCE RANGE WITH RAIN
PREDOMINATE TYPE THROUGH WED NIGHT. CHANGEOVER BEGINS ON THURSDAY
BUT MODEL PROFILES SHOWS SHALLOW MOISTURE AND NOT MUCH LIFT SO
EXPECT DRYING IMMEDIATELY BEHIND FRONT WITH A LULL IN PCPN THURSDAY.
NEXT WAVE WILL DEVELOP ALONG FRONT AND RACE NORTHEAST THU NIGHT. BULK
OF PCPN AND STRONGER FORCING LOOKS TO REMAIN SOUTH OF OUR AREA WITH
FAR SOUTHERN CWA ON NORTHERN FRINGES OF DEEPER MOISTURE. THERMAL
PROFILES SUGGEST RAIN AND SNOW EARLY THU EVENING BUT QUICKLY
TRANSITIONING TO SNOW. SOME LIGHT ACCUMULATIONS NOT OUT OF QUESTION
FAR SOUTH.

REMAINDER OF THE PERIOD WILL BE COLD WITH SCATTERED SNOW SHOWERS AT
TIMES. LAKE EFFECT SNOW SHOWERS STILL EXPECTED BUT CP AIR LOOKS VERY
COLD AND DRY WHICH WILL HAMPER ACCUMS. MODELS SHOWING STRONG SURFACE
RIDGING BUT MEDIUM RANGE MODELS RARELY RESOLVE LAKE INDUCED
TROUGHING. CONTINUED WITH BROAD MID CHANCE POPS IN LAKE EFFECT AREAS
FOR NOW. MODELS INDICATING ANOTHER WAVE RIDING NORTHEAST SUNDAY INTO
MONDAY. STAYED WITH ALLBLEND POPS AND TEMPS THESE PERIODS WITH MUCH
UNCERTAINTY ON TRACK AND STRENGTH OF THIS SYSTEM. PROFILES AGREE ON
ALL SNOW FOR THE CWA.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 555 AM EST TUE DEC 3 2013

IFR CONDITIONS WILL CONTINUE THROUGH THE MORNING HOURS AS ELEVATED
WAA HAS CREATED A STRONG LOW LEVEL INVERSION ACROSS THE AREA WITH
PLENTY OF MOISTURE TRAPPED BENEATH IT. HIGH SURFACE DEWPOINTS
RESULTING IN WIDESPREAD BR BUT RELATIVELY STRONG WINDS HAVE
PREVENTED DENSE FOG FORMATION LOCALLY. SOME MARGINAL IMPROVEMENT
EXPECTED LATER TODAY AS WARM FRONT LIFTS NORTH AND THE AREA BEGINS
TO MIX OUT A BIT. NAM FORECAST SOUNDINGS SUGGEST KSBN WILL REMAIN
LOCKED IN IFR STRATUS ALL DAY GIVEN LOW SUN ANGLE AND STRENGTH OF
THE INVERSION. THOUGH POSSIBLE...CURRENT THINKING IS THAT KSBN WILL
EVENTUALLY MIX OUT SOME BY THE AFTERNOON. BOTH TERMINALS SHOULD
RETURN TO HIGH END MVFR BEFORE DROPPING BACK TO IFR AGAIN TONIGHT
IN PERSISTENT WARM/MOIST AIR ADVECTION.

&&

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

$$

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


VISIT US AT WWW.WEATHER.GOV/IWX (ALL LOWER CASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.NORTHERNIN.GOV
WWW.TWITTER.COM/NWSIWX
WWW.YOUTUBE.COM/NWSNORTHERNINDIANA