FXUS63 KIWX 231727
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1227 PM EST WED DEC 23 2009
.AVIATION /18Z TAFS/...
BAND OF LIGHT SNOW/SLEET WITH MVFR CONDITIONS WAS LIFTING NORTH
ACROSS NRN INDIANA THIS AFTN. PRECIP MAY END AS A BRIEF PD OF ZR-
AS WAA ALOFT CONTS. AFTER THIS INITIAL BAND OF PRECIP MOVES
THROUGH, CONDITIONS SHOULD IMPROVE TO VFR THROUGH 18Z THU. OCNL
LIGHT PRECIP MAY CONT AT SBN OVERNIGHT AND EARLY THU, BUT ATTM
EXPECT IT WOULD BE VERY LIGHT IF IT OCCURS AT ALL SO LEFT MENTION
OUT OF TAFS.
&&
.UPDATE...
WK LEAD SHRTWV AND WAA RESULTING IN A BAND OF PRECIP MOVG INTO THE
CWA THIS MORNING. SFC OBS AND FCST SOUNDINGS SUGGEST FREEZING RAIN
POTENTIAL ACROSS SWRN PORTION OF CWA... TRANSITIONING MORE TO
FROZEN PRECIP (I.E. SNOW/SLEET NE). THUS, MAIN CHANGE IN UPDATE
WAS TO EXPAND WINTER WX ADVISORY FOR SLEET/ZR MIXTURE EASTWARD
ACROSS OUR SOUTHERN TIER OF COUNTIES THIS AFTN/EVE. IF BAND CONTS
WITH CURRENT PROGRESS MAY BE ABLE TO CANCEL ERN PORTION OF
ADVISORY EARLY THIS EVE. ONLY OTHER CHANGE WAS TO BUMP UP POPS A
BIT NORTH OF THE PRECIP BAND.
&&
PREV DISCUSSION... /ISSUED 524 AM EST WED DEC 23 2009/
SHORT TERM /TODAY THROUGH THURSDAY NIGHT/...
A BUSY MORNING AT THE FORECAST OFFICE AS WELL ADVERTISED LOW
PRESSURE SYSTEM STARTS TO CONGEAL OVER THE SOUTHERN PLAINS AS AN
IMPRESSIVE UPPER LEVEL LOW DIVES INTO THE DESERT SOUTHWEST...
BRINGING WITH IT VICIOUS WINDS AND DUST STORMS OVER THAT REGION.
MODELS ARE IN GOOD AGREEMENT WITH LITTLE SIGNIFICANT CHANGES IN
THE OVERALL THINKING SINCE YESTERDAY. PRIMARY CONCERNS ARE WITH
1-WARM ADVECTIVE PRECIP THAT HAS BLOSSOMED OVER THE MID
MISSISSIPPI VALLEY EARLY THIS MORNING AND WILL IMPACT MY AREA BY
LATE MORNING AFTERNOON AND 2-MORE SIGNIFICANT QPF EVENT LATE
THURSDAY/THURSDAY NIGHT AHEAD OF SURFACE OCCLUSION AND POTENTIAL
FOR SIGNIFICANT ICING.
AFOREMENTIONED AREA OF PRECIPITATION HAS DEVELOPED AT THE NOSE OF
A 30KT SOUTHWESTERLY LET AT H85 SHOWN BY AREA VWPS/PROFILERS. THIS
JET IS LOCATED BELOW A SIGNIFICANT SHORTWAVE ALOFT THAT HAS BEEN
KICKED NORTHEAST BY THE DEEPENING SOUTHWESTERN CONUS TROUGH. THE
QG FORCING ASSOCIATED WITH THIS WAVE ALONG WITH THE POSITIVE H85
THETA E ADVECTION WILL MOVE NORTHEAST...BUT GRADUALLY TURN MORE
NORTHWARD AS THE H85 FLOW BACKS IN RESPONSE TO IMPRESSIVE HEIGHT
FALLS AHEAD OF THE UPSTREAM TROUGH. CAN/T SEE THIS PRECIP MISSING
MY WESTERN ZONES AND HAVE UPPED POPS TO LIKELY HERE AS A RESULT.
THIS IS WELL CAPTURED BY THE 21/03Z SREFS AS WELL AS THE 12KM NAM
AND OUR IN HOUSE 4KM WRF. IN FACT IT IS POSSIBLE THAT THE LIKELIES
MAY NEED FURTHER EAST EXPANDING IF THE BACKING DOES NOT OCCUR SOON
ENOUGH. AS FOR PRECIP TYPE...NAM/SREF/WRF ALL SUGGEST THAT WET
BULB TEMPS WILL RISE ABOVE FREEZING OVER MY FAR SOUTHWEST BY LATE
MORNING...WITH THIS FREEZING LINE EDGING UP ALONG MY WESTERN
BORDER COUNTIES AS THE AFTERNOON PROGRESSES. THIS PROGGED 0C LINE
LINES UP WELL WITH CURRENT LIGHT ZR/PL BEING REPORTED JUST SOUTH
OF MY CWA EARLY THIS MORNING. SURFACE TEMPS REMAIN BELOW FREEZING
AND DON/T SEE THEM MOVING AT ALL GIVEN STIFF EASTERLY LLEVEL FLOW.
THEREFORE WEST OF 31 TODAY...A PERIOD OF ZR/IP IS BECOMING
INCREASINGLY LIKELY. AMOUNT OF ICING WILL BE LIGHT...BUT WILL
LIKELY CAUSE SOME SIGNIFICANT TRAVEL HEADACHES. THEREFORE...HAVE
GONE AHEAD AND ISSUED A WINTER WX ADVISORY FOR AREAS SOUTH AND
WEST OF A LAPORTE TO ROCHESTER LINE. LATER SHIFTS WILL HAVE TO
WATCH THE NEXT ROW OF COUNTIES NORTH AND EAST GIVEN POSSIBLE
EASTWARD PUSH TO PRECIP EDGE...AND SOUTH TO NORTH WARMING ALOFT BY
LATE IN THE DAY.
WEDNESDAY NIGHT...LIGHT ZR WILL LIKELY CONTINUE OVER MY FAR
NORTHWESTERN ZONES...BUT AN OVERALL WANING TREND IN PRECIPITATION
INTENSITY/COVERAGE IS EXPECTED AS THE ABOVE MENTIONED WAVE ALOFT
SHIFTS NORTH OF THE AREA WITH THE FLOW ALOFT CONTINUING TO
BACK...WITH HEIGHTS AT H5 EVEN RISING SLIGHTLY. THE NORTHWARD
STREAM OF MOISTURE WILL CONTINUE TO THE WEST...AND A LITTLE LIGHT
ZR/PL MAY BRUSH MY FAR WEST...BUT EXPECT ANY IMPACTS TO BE
PRIMARILY RESTRICTED TO THE EVENING HOURS.
IF THERE IS ANY MEANINGFUL DIFFERENCE IN THE GUIDANCE SINCE
YESTERDAY...IT IS A SLOWER ARRIVAL OF PRECIPITATION AHEAD OF THE
SURFACE OCCLUSION ON THURSDAY. HAVE TRENDED TOWARDS 21/03 SREF
POPS WHICH SUGGEST AREAS EAST OF 31 MAY REMAIN DRY FOR MUCH OF THE
DAY AS THE FLOW ALOFT CONTINUES TO BACK DEEP LOW PRESSURE CROSSES
FROM SOUTHEASTER OK EARLY IN THE DAY TO SOUTHERN MO BY EVENING.
GIVEN THE CONTINUED ONSLAUGHT OF WARMING ALOFT...EXPECT SURFACE
TEMPS TO EVER-GRUDGINGLY BEGIN TO RISE. SO...WHILE PRECIPITATION
MAY REDEVELOP AS ZR/PL IN THE WEST DURING THE MORNING...A
TRANSITION TO PLAIN RAIN IS LIKELY BY AFTERNOON. EAST OF
31...IMPACTS WILL LIKELY BE FAIRLY MINIMAL THROUGH THURSDAY
EVENING BEFORE HEAVIER PRECIP BEGINS. NEEDLESS TO SAY TEMPS WILL
FALL RIGHT NEAR THE 32F MARK.
COMPLEX SCENARIO THURSDAY NIGHT AS THE SURFACE OCCLUSION NEARS THE
REGION FROM THE SOUTHWEST. MOISTURE TRANSPORT AHEAD OF THIS FRONT
WILL BE IMPRESSIVE WITH A 60-80KT SOUTHEASTERLY JET AT H85 EAST OF
A ROUGHLY 990MB SURFACE LOW CENTERED OVER MO. HAVE NO REASON TO
DOUBT THE STRENGTH OF THIS FLOW GIVEN 00Z OBS AND STORM HISTORY
OVER THE DESERT SOUTHWEST. THIS LLJ WILL TRANSPORT 1 INCH PWAT AIR
OVERHEAD AND SETS THE STAGE FOR A PERIOD OF MODERATE AND
POTENTIALLY HEAVY PRECIP OVERNIGHT. GIVEN THE LOCATION OF THE
SURFACE LOW AND INTENSE 1040 HIGH NORTHEAST OF THE GREAT
LAKES...EXPECT A SOUTHEASTERLY BL FLOW TO CONTINUE...WHICH WILL
NOT LET SFC TEMPS WARM RAPIDLY. THIS SUGGESTS A PERIOD OF LIKELY
ICING...PARTICULARLY OVER NORTHEASTERN AREAS OVERNIGHT.
COMPLICATING FACTOR WILL BE THAT THE STRENGTH OF THE FLOW ALOFT
WILL TRANSPORT COPIOUS AMOUNTS OF WARM AIR ABOVE THE SURFACE WITH
H9 TEMPS INCREASING TO AROUND 5-7C DURING THE EVENING...THEN
WARMER STILL AFTER MIDNIGHT. WHILE WE DO HAVE STRONG HIGH PRESSURE
TO THE NORTH...THE ANTECEDENT AIRMASS IS NOT ALL THAT COLD WITH
THE BEST COLD AIR STILL OVER LOWER MICHIGAN. ALSO THIS COLDER AIR
TO THE NORTH WILL LIKELY NOT PLAY A HUGE ROLE GIVEN THE LLEVEL
SOUTHEASTERLIES. SO...WHILE SOME LLEVEL COLD AIR WILL BE LOCKED IN
PLACE...EXPECT INEFFICIENT FREEZING OF RAIN THAT FALLS GIVEN ITS
WARMTH. SO...AT THIS TIME...HAVE PAINTED A MAXIMUM OF 0.10-0.15
INCHES OF ICE IN THE GRIDS OVER THE FAR NORTHEAST AND GUT FEELING
IS THAT WARNING CRITERIA WILL BE HARD TO COME BY. HOWEVER...WANT
TO LET ANOTHER SHIFT OR TWO REASSESS BEFORE MAKING CHANGES TO THE
CURRENT WATCH. AT THIS TIME...SEE NO REASON TO EXPAND IT...BUT DO
EXPECT THAT WE MAY NEED AN ADVISORY FOR A FEW MORE COUNTIES IN NE
INDIANA AND NW OHIO BEFORE ALL IS SAID AND DONE. QPF AMOUNT WILL
REACH NEAR ONE INCH...AND WHILE SOME PONDING OF WATER SEEMS LIKELY
GIVEN FROZEN GROUND...DON/T EXPECT SIGNIFICANT HYDRO CONCERNS IF
THESE RAINFALL AMOUNTS PAN OUT. TEMPS WILL SLOWLY RISE INTO THE
MID/UPPER 30S OVERNIGHT.
ONE FINAL HAZARD TO MENTION WILL BE THE WINDS WHICH MAY APPROACH
ADVISORY LEVELS THURSDAY NIGHT GIVEN 50 MB PRESSURE GRADIENT FROM
MO TO JAMES BAY. LLEVEL INVERSION SHOULD PRECLUDE MIXING DOWN MUCH
OF THE 50KT FLOW AT H92...BUT 25KT SUSTAINED SURFACE WINDS WITH
GUSTS TO 40KTS IS CERTAINLY PLAUSIBLE.
LONG TERM...
.CHRISTMAS DAY THROUGH TUESDAY...
MOST OF LONG TERM PERIOD WILL BE AFFECTED BY FILLING CLOSED UPPER
LOW THAT WILL HANG AROUND THE GREAT LAKES REGION INTO EARLY NEXT
WEEK. MEDIUM RANGE MODELS IN CONSENSUS ON STRONG CLOSED LOW IN THE
MID MS RIVER VALLEY REGION ON CHRISTMAS DAY SLOW FILLING AND
DRIFTING EAST ACROSS THE GREAT LAKES THIS WEEKEND BEFORE FINALLY
EXITING OUR AREA EARLY NEXT WEEK. DETAILS REMAIN UNCERTAIN WITH
AMOUNT OF MOISTURE AND SHORT WAVES EMBEDDED AROUND THE WEAKENING
LOW. BULK OF THIS FORECAST SHIFT FOCUSES ON FRIDAY INTO SATURDAY
WITH FEW CHANGES BEYOND THAT GIVEN UNCERTAINTY IN DETAILS.
POTENT WINTER STORM WILL BE UNDERWAY TO OUR WEST AT BEGINNING OF
THIS LONG TERM PERIOD ON CHRISTMAS DAY. STRONG WARM AIR ADVECTION
SHOULD HAVE PRECIPITATION AS ALL RAIN OVER OUR ENTIRE FORECAST AREA
AFTER DAYBREAK ON CHRISTMAS MORNING. THICKNESS SCHEMES AND SOUNDINGS
FROM MOST MODEL DATA SUPPORT THIS IDEA. DEEP WARM LAYER EXPECTED
OVER THE AREA CHRISTMAS MORNING WHICH SHOULD KEEP TEMPS ABOVE
FREEZING AND LINGERING RAIN WILL BE WARM DROPLETS VERSUS
SUPERCOOLED. THEREFORE NOT EXPECTING ANY TRAVEL PROBLEMS AT THIS
TIME ON CHRISTMAS MORNING WITHIN OUR FORECAST AREA.
STRONG COLD AIR ADVECTION BEING PROGGED IN MID AND LOWER LEVELS
CHRISTMAS DAY AS SYSTEM OCCLUDES TO OUR WEST AND OCCLUDED FRONT
MOVES FROM SOUTHWEST TO NORTHEAST ACROSS AREA. 850MB TEMPS DROP
DRAMATICALLY FROM MID MORNING INTO EARLY EVENING. SREF AND NAM12
SURFACE TEMPS ARE LAGGING A BIT AND WE SOMETIMES SEE THIS LAG WITH
OCCLUDED SYSTEMS AND COLD AIR ADVECTION FROM THE SOUTHWEST. HAVE
SLOWED THE COOLING ON FRIDAY WITH A SLOWER TIMING BUT STILL HAVE
FALLING TEMPS IN THE AFTERNOON AND ESPECIALLY LATE AFTERNOON AND
EVENING. CONTINUED WITH LIKELY TO CATEGORICAL POPS CHRISTMAS DAY BUT
LATEST TRENDS SUGGEST DRY SLOT TO QUICKLY MOVE IN DURING THE MORNING
AND MORE THAN LIKELY WILL END RAIN DURING THE MORNING. DRY SLOT MAY
BE STRONG ENOUGH TO PROVIDE SUBSIDENCE AND PARTIALLY CLEAR SKIES AND
END ANY CHANCE OF PCPN IN AFTERNOON. FOR NOW WILL KEEP MOSTLY CLOUDY
WITH A CHANCE OF LIGHT SNOW OR RAIN BUT HAVE TRENDED POPS DOWN IN
AFTERNOON. IF DRY SLOT CAN INDEED CLEAR SKIES AND ALLOW FOR SOME
WEAK MIXING...WINDS COULD BE STRONGER WITH NEAR ADVISORY LEVELS AS
925MB TO 850MB WIND FIELD OF 30 TO 40 KNOTS EXPECTED.
BELOW NORMAL TEMPERATURES EXPECTED FOR REMAINDER OF LONG TERM WITH
COLD CORE ALOFT DRIFTING OVER THE AREA. SNOW SHOWER CHANCES TO
CONTINUE...ESPECIALLY NORTH.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
MORNING FOR INZ003>007.
WINTER WEATHER ADVISORY UNTIL 1 AM EST /MIDNIGHT CST/ THURSDAY
FOR INZ003-012-013-015-020-022.
WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR
INZ023>027-032>034.
MI...WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
MORNING FOR MIZ077>081.
OH...NONE.
LM...GALE WATCH FROM THURSDAY MORNING THROUGH FRIDAY AFTERNOON FOR
LMZ043-046.
SMALL CRAFT ADVISORY UNTIL 7 AM EST THURSDAY FOR LMZ043-046.
&&
$$
SHORT TERM...ARNOTT
LONG TERM...LASHLEY
AVIATION...JT
UPDATE...JT
