FXUS63 KIWX 240957
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
457 AM EST THU DEC 24 2009
.SHORT TERM /TODAY THROUGH FRIDAY NIGHT/...
WELL ADVERTISED LOW PRESSURE SYSTEM IS NOW TAKING SHAPE OVER EASTERN
TEXAS WITH SURFACE PRESSURES DROPPING TOWARDS 996 MB SOUTH OF DALLAS
AS OF 06Z. THIS LOW IS BEING DRIVEN BY A POWERFUL SHORTWAVE NOW
PULLING EAST INTO WESTERN TEXAS. DOWNSTREAM BLOCKING IS WELL
ESTABLISHED WITH STRONG CUTOFF OFF THE NEW ENGLAND COAST FORMING A
REX BLOCK OVER THIS REGION NORTHWARD INTO EASTERN CANADA.
FINALLY...ANOTHER...LARGER SHORTWAVE IS DROPPING INTO NORTHEASTERN
MONTANA AS OF THIS WRITING. THIS LATTER WAVE WILL SERVE THE ALL-
IMPORTANT PURPOSE AS KICKER TO THE SOUTHERN WAVE WITH THE TWO
ROTATING AROUND EACH OTHER THROUGH THE SHORT TERM PERIOD.
THUS...BY FRIDAY EVENING...THE SURFACE LOW WILL ONLY BE SLIGHTLY
EAST OF ITS CURRENT POSITION!! THE PRIMARY TREND IN THE GUIDANCE
OVER THE PAST 24 HOURS HAS BEEN FOR THE LOW TO BE A LITTLE DEEPER
AND THE SOUTHERN SHORTWAVE TO MAKE IT A LITTLE FURTHER EAST BEFORE
GETTING CAUGHT BY THE UPSTREAM KICKER. THIS WILL CONTINUE TO SLOW
THE EVENTUAL ARRIVAL OF THE SURFACE OCCLUSION THURSDAY NIGHT.
THE 00Z GFS HAD A GREAT HANDLE ON CONVECTION NOW OVER ARKANSAS
INTO SOUTHERN ILLINOIS OVERNIGHT WITH THE NAM ALSO DOING A
REASONABLE JOB. THIS CONVECTION WILL LIKELY BE THE PRIMARY FOCUS
FOR OUR WEATHER TODAY. THIS PRECIPITATION HAS FORMED AT THE
NORTHERN CUSP OF A 50KT SOUTHERLY LLJ THAT EMANATES FROM THE GULF
WITH RADAR RETURNS CERTAINLY INDICATING THE LLJ COMES WITH AMPLE
MOISTURE. THIS JET WILL RAPIDLY MOVE NORTH TODAY IN RESPONSE TO
THE CONTINUED DEEPENING OF THE LOW THROUGH THE LOWER TROPOSPHERE.
PRECIPITATION HAS ALREADY REACHED THE LONGITUDE OF HIGHWAY 31 AS
OF 9Z AND CONTINUES TO MAKE PROGRESS NORTH AND EAST. GIVEN THESE
TRENDS...AM NOT EXCITED TO SEE THE NAM KEEP ALMOST ALL PRECIP WEST
OF THE CWA THROUGH THE DAY TODAY. THEREFORE HAVE LEANED TOWARDS
THE GFS WITH PRECIP COVERAGE...KEEPING IN MIND MODEL PERFORMANCE
YESTERDAY WHICH DRASTICALLY UNDERESTIMATED THE EASTWARD PROGRESS
OF PRECIP. THEREFORE PLAN LIKELY TO CAT POPS ALONG AND WEST OF
IN-13 FOR THE DAY WITH CHANCES RAPIDLY DIMINISHING TO THE EAST.
AS WELL ENTRENCHED DRY EASTERLY FLOW SHOULD HELP ERODE PRECIP
SOMEWHAT...AND AS THE FLOW ALOFT BECOMES ALMOST DUE
SOUTHERLY...ENDING ANY STEERING FLOW TO THE EAST. AS FOR PTYPE...I
WILL LEAN CLOSER TO THE NAM THERMAL PROFILES GIVEN IT/S USUAL
SUPERIOR PERFORMANCE IN SHALLOW COLD DOME SCENARIOS. IT ALSO HAS A
BETTER HANDLE ON CURRENT OBS WHICH SHOW NO WARMING
OVERNIGHT....AND A SIGNIFICANT LOWERING IN DEWPOINTS.
THEREFORE...ANY CHANGEOVER TO PLAIN RAIN WILL LIKELY WAIT UNTIL
THIS EVENING. WITH TAMDAR FLIGHTS OUT OF IND SUGGESTING WARM NOSE
TEMPS REACHING +7C IN THIS AREA...WITH THIS WARMING GRADUALLY
MOVING NORTH...EXPECT MOSTLY ZR WITH SOME IP POSSIBLE GIVEN THE
DRY BL AIR THAT HAS ADVECTED WEST INTO THE REGION OVERNIGHT. BEST
QPF AMOUNTS WILL LIKELY BE ALONG MY WESTERN BORDER COUNTIES GIVEN
DEEPEST MOISTURE AND BEST H85 THETA E ADVECTION. IN THESE AREAS
COULD SEE 3 TENTHS OF AN INCH LIQUID...WHICH FROM PULASKI COUNTY
NORTH SHOULD MOSTLY ACRETE AS ICING. THEREFORE...HAVE EXPANDED ICE
STORM WARNING SOUTH TO COVER PULASKI. FURTHER SOUTH BL TEMPS MAY
PRECLUDE FULL FREEZING OF ALL THE RAIN THAT FALLS. FURTHER
EAST...QPF AMOUNTS WILL BE LIGHTER GIVEN THE DRY LLEVEL EASTERLY
FLOW AND DEEPER MOISTURE WEST OF THAT AREA. SO...WILL
ISSUE/CONTINUE A WINTER WX ADVISORY FOR AREAS ALONG/WEST OF A
MARION TO LAGRANGE LINE. FURTHER EAST...CONFIDENCE IN PRECIP
ARRIVING TODAY IS NOT HIGH ENOUGH FOR A DAYTIME ADVISORY. TEMPS
WILL PRETTY MUCH BE STUCK IN THE 28-33F RANGE FROM NORTHEAST TO
SOUTHWEST.
TONIGHT LOW PRESSURE MOVES NORTH OVER EASTERN MISSOURI WITH
SURFACE OCCLUSION FINALLY NEARING THE REGION TOWARDS DAYBREAK.
GIVEN A SLOWER OVERALL TREND IN FRONTAL TIMING...WILL MAINTAIN
ONLY LIKELY POPS OVER NORTHEASTERN AREAS IN THE EVENING WITH CAT
SOUTH AND WEST. AFTER MIDNIGHT EVERYONE SHOULD SEE PRECIP AND
GIVEN PWATS NEAR ONE INCH...INCREDIBLE DYNAMIC FORCING AND A
60-80KT H85 JET...EXPECT PRECIP TO BE HEAVY AT TIMES. THE
NORTHEASTERN QUARTER OF THE CWA WILL LIKELY SEE ZR IN THE EVENING
AS PRECIPITATION BEGINS...WITH A GRADUAL CHANGE TO RAIN OVERNIGHT
AS TEMPS NEARING +9C AT H9 OVERWHELM THE COOLING EFFECTS OF THE
LLEVEL EASTERLIES. FOR THESE AREAS...EXPECT THE PRECIP RATES AND
TEMPS ALOFT TO PRECLUDE FULL ACCRUAL OF ALL THE QPF AND FOR THIS
REASON EXPECT 0.25" ICING WILL BE HARD TO COME BUY. THEREFORE HAVE
TRANSITIONED THE WATCH TO AN ADVISORY...WHICH ALSO INCLUDES
ANOTHER ROW OF COUNTIES SOUTH...AND NORTHWEST OHIO.
FINALLY...WILL CONTINUE TO WATCH WINDS THURSDAY NIGHT WITH MOS
PROGS AROUND 25 KTS AND STRENGTH OF THE LLEVEL GRADIENT BETWEEN THE
985 LOW AND 1040 HIGH OVER EASTERN CANADA SUGGESTING A NEAR-
ADVISORY EVENT. WILL NOT ADD A WIND ADV AT THIS TIME GIVEN A
PERSISTENT STRONG LLEVEL INVERSION WHICH WILL HELP PRECLUDE MIXING
OF THE MUCH STRONGER WINDS ALOFT. THIS WILL STILL HAVE TO BE
WATCHED THOUGH. HAVE MENTIONED WINDS IN THE WSW AS THIS WILL
LIKELY DOWN TREE LIMBS/POWER LINES ANYWHERE WHERE ICING OCCURS
THURSDAY/THURSDAY EVENING.
OCCLUSION PASSES THROUGH THE REGION ON CHRISTMAS WITH RAIN
TAPERING TO SHOWERS BY AFTERNOON...AND THEN SLOWLY TRANSITIONING
FROM RAIN TO SNOW LATE IN THE DAY. DRY SLOT DOESN'T APPEAR TO
ARRIVE UNTIL PERHAPS FRIDAY NIGHT...SO THE CLOUDS SHOULD REMAIN
SOCKED IN. HIGHS WILL LIKELY REACH THE UPPER 30S TO AROUND 40 JUST
AHEAD OF THE OCCLUSION...BUT THEN FALL RAPIDLY TOWARDS EVENING.
TOTAL QPF FOR THE EVENT WILL GENERALLY BE 0.75 TO 1.25 INCHES
FROM EAST TO WEST...SO WE COULD SEE SOME LOCALIZED FLOOD
CONCERNS...BUT FOR THE MOST PART...WE SHOULD BE ABLE TO HANDLE
THESE AMOUNTS WITHOUT MUCH MORE THAN SOME MINOR PROBLEMS.
INTENSE UPPER LOW JUST TO OUR WEST FRIDAY NIGHT WITH THE ARRIVING
WESTERN VORT MAX PROVIDING QG FORCING FOR ASCENT ALONG WITH AMPLE
LLEVEL CYCLONIC FLOW. DRY SLOT MAY WORK IN AND LIMIT MOISTURE AND
MAY ALLOW FOR A DRY NIGHT /PARTICULARLY IN THE EAST/...BUT GIVEN THE
COMPLEX INTERACTION BETWEEN THE TWO INTENSE UPPER VORTS...DON/T WANT
TO GET TOO DETAILED ON POPS AND WILL CONTINUE WITH CHC SHSN
MENTION...WITH GREATEST POPS OVER THE FAR NORTHWEST NEAREST THE VERY
LIMITED LAKE MICHIGAN INFLUENCE UNDER SSW FLOW ALOFT. TEMPS WILL
FALL INTO THE LOWER 20S...PERHAPS A LITTLE COOLER IF WE DO BREAK
OUT OF THE CLOUDINESS.
&&
.LONG TERM...
...SATURDAY THROUGH WEDNESDAY...
NO SIGNIFICANT CHANGES NEEDED TO LONG TERM GRIDS. MEDIUM RANGE
MODELS REMAIN IN GOOD AGREEMENT ON SYNOPTIC EVOLUTION WITH
DIFFERENCES IN THEIR DETAILS THROUGH THE PERIOD.
EVENTUAL PHASING OF UPPER LEVEL SOUTHERN STREAM LOW WITH DIGGING
NORTHERN STREAM LOW STILL EXPECTED AND SHOULD BE OCCURRING BY START
OF LONG TERM PERIOD. THE PHASED SYSTEM WILL THEN ONLY SLOWLY MEANDER
ACROSS THE MID MS RIVER VALLEY REGION AND DRIFT EAST INTO WESTERN
GREAT LAKES THROUGH THE WEEKEND. MODELS CONTINUE TO ADVERTISE AN
EASTWARD EJECTION ON MONDAY AS A NORTHERN STREAM SHORT WAVE DIVES
SOUTH FROM CANADA AND BRINGS A REINFORCED SHOT OF ARCTIC AIR MONDAY
NIGHT INTO TUESDAY.
GRIDS HAVE A DECENT HANDLE ON THIS SITUATION SO ONLY SOME MINOR
CHANGES MADE BASED ON LATEST SUITE OF MEDIUM RANGE GUIDANCE.
CONTINUED HIGH CHANCE POPS ON SATURDAY AND SATURDAY NIGHT AS A SLUG
OF MOISTURE AND LIFT MOVE ACROSS THE AREA AHEAD OF UPPER LOW. COULD
SEE ANOTHER EXTENDED PERIOD OF LIGHT SNOW WITH MINOR ACCUMULATIONS
OF A FEW INCHES. NORTHWEST FLOW BEHIND DEPARTING LOW ON MONDAY BUT
LOW LEVEL THERMAL FIELDS WARM AHEAD OF NEXT SHORT WAVE AND COLDER
AIR FOR MONDAY NIGHT AND TUESDAY. CONTINUED LOW CHANCE POPS FOR LAKE
EFFECT THOUGH DELTA T VALUES NOT IMPRESSIVE UNTIL COLDER AIR ARRIVES
MONDAY NIGHT AND TUESDAY. HOWEVER...MODELS INDICATING THIS TO BE A
RATHER DRY POLAR AIRMASS SO AGAIN NOT A GREAT SET UP FOR LAKE
EFFECT.
TEMPS GENERALLY SEASONABLY COOL FOR LATE DECEMBER WITH HIGHS IN THE
20S AND LOWS IN THE TEENS EXPECTED.
&&
.AVIATION /06Z TAFS/...
VFR AT BOTH TERMINALS ATTM AS LIGHT FZRA CONTINUES JUST NORTHWEST
OF SBN WITH FWA IN THE CLEAR. FOR THE OVERNIGHT...COULD SEE
ANOTHER LIGHT BOUT OF FZRA AT SBN FOR THE NEXT FEW HOURS...BUT
OVERALL VFR CONDITIONS SHOULD PERSIST. BAND OF HEAVIER PRECIP WILL
APPROACH THE TERMINALS FROM THE WEST AND SOUTH ON THURSDAY.
EXPECT THAT THIS WILL BEGIN REACHING THE AREA BY AFTERNOON AND
START AS A FZRA/PL MIX BEFORE GOING TO ALL RAIN TOWARDS 00Z.
VSBYS/CIGS WILL ALSO DETERIORATE TO MVFR DURING AND THROUGH THE
EVENING HOURS.
EAST WINDS 15 KTS WILL CONTINUE OVERNIGHT AND THROUGH THE DAY
THURSDAY BEFORE STRENGTHENING TO 18G28KTS THURSDAY NIGHT. LLWS A
CONCERN BY AFTERNOON AT SBN AND EVENING AT FWA AS 2KFT WINDS
INCREASE TO AROUND 50KTS FROM THE SOUTHEAST. THESE ROBUST
WINDS...COUPLED WITH A STRONG LLEVEL INVERSION PORTENDS A CLASSIC
SETUP FOR STRONG LLWS.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
FRIDAY FOR INZ007-009.
ICE STORM WARNING UNTIL 7 PM EST /6 PM CST/ THIS EVENING FOR
INZ003-012-013.
WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 3 AM EST
FRIDAY FOR INZ004>006-008-014-016-017.
WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR INZ015-
020-022>025-032.
MI...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
FRIDAY FOR MIZ080-081.
ICE STORM WARNING UNTIL 7 PM EST THIS EVENING FOR MIZ077.
WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 3 AM EST
FRIDAY FOR MIZ078-079.
OH...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
FRIDAY FOR OHZ001-002-004-005.
LM...GALE WARNING UNTIL 1 PM EST FRIDAY FOR LMZ043-046.
&&
$$
SHORT TERM...ARNOTT
LONG TERM...LASHLEY
AVIATION...ARNOTT
