000
FXUS63 KIWX 071123
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
623 AM EST WED JAN 7 2009
.AVIATION...
PRECIPITATION HAS CHANGED TO ALL SNOW AT KSBN BUT STILL SOME
OCCASIONAL FREEZING DRIZZLE AT KFWA FOR A FEW HOURS THIS MORNING
BEFORE LAYERS BECOME COMPLETELY SATURATED AND PCPN BECOMES ALL LIGHT
SNOW. MID LEVEL TROUGH TO PASS THROUGH WITH SCATTERED SNOW SHOWERS
DEVELOPING. DIFFICULT VIS FORECAST AND WILL DEPEND ON AMOUNT OF
COVERAGE AND INTENSITY OF THESE SNOW SHOWERS. WILL BE GENERAL MVFR
FOR NOW GIVEN CURRENT OBSERVATIONS AND EXPECTED INCREASE IN
COVERAGE. FLOW OFF OF LAKE MICHIGAN PUTS KSBN ON SOUTHERN PERIPHERY
OF LAKE EFFECT SNOW SHOWERS TONIGHT. HAVE KEPT AN MVFR VIS GROUP
THERE NOW TO COVER THIS POTENTIAL. WINDS WILL ALSO INCREASE TODAY
AND CONTINUE GUSTY INTO TONIGHT WITH SUSTAINED 10 TO 20 KNOTS AND
GUSTS TO AROUND 30 KNOTS POSSIBLE THIS AFTERNOON AND TONIGHT WITH
COLD AIR ADVECTION. BLOWING SNOW ALSO A POSSIBILITY WHERE LOCATIONS
RECEIVE SOME ACCUMULATION TODAY.
&&
.SHORT TERM...
TODAY THROUGH THURSDAY NIGHT...
...ICY ROADS STILL POSSIBLE THIS MORNING...
INTERESTING SHORT TERM FORECAST WITH A MAINLY LIGHT PRECIPITATION
EVENT THAT WILL BE STRETCHED THROUGH MOST OF THIS SHORT TERM PERIOD.
MOST OF FORECAST AREA HAS SEEN FREEZING DRIZZLE OVERNIGHT AS
DENDRITE GROWTH ZONE...DGZ...HAS BEEN ABOVE CLOUD LAYER AND IN
RELATIVELY LOW RH. SATELLITE SHOWS MID AND HIGH CLOUDS INVADING FROM
WEST IN ASSOCIATION WITH MID LEVEL TROUGH THAT WILL MOVE ACROSS THE
AREA TODAY. THESE HIGHER CLOUDS PROVIDING THE NEEDED SEEDING OF
LOWER CLOUDS FOR ICE NUCLEATION TO CHANGE PCPN OVER TO LIGHT SNOW.
SURFACE OBSERVATIONS REFLECT THIS WITH MANY SITES CHANGING OVER FROM
WEST TO EAST AS OF THIS WRITING. WITH SATELLITE TRENDS SHOWING THE
HIGHER CLOUDS ADVANCING EAST...SHOULD JUST BE A FEW HOURS BEFORE
MOST SITES SWITCH OVER TO ALL LIGHT SNOW. WILL LIKELY CARRY A
MENTION OF PATCHY FREEZING DRIZZLE FOR VERY EARLY THIS MORNING BUT
CHANGE TO ALL SNOW NEAR DAYBREAK. GIVEN THE ICY CONDITIONS ON ROADS
AND SIDEWALKS...ESPECIALLY THOSE UNTREATED...AND THE LIGHT SNOW ON
TOP OF THIS GLAZE...HAVE DECIDED TO CONTINUE THE WINTER WEATHER
ADVISORY THROUGH THE MORNING COMMUTE. SEVERAL CALLS FROM OBSERVERS
EARLY THIS MORNING INDICATE SECONDARY ROADS ESPECIALLY ARE STILL ICY
AND HAZARDOUS. SURFACE TEMPERATURES REMAIN IN THE MID TO UPPER 20S
PER ROAD SENSORS AND OBSERVATIONS...AND HAVE SEEN THIS TYPE OF
SITUATION BEFORE WHERE FRICTION FROM TRAFFIC ALSO MELTS THE LIGHT
SNOW ONLY TO SEE IT REFREEZE ON THE GLAZED UNTREATED SURFACES.
MID LEVEL TROUGH AND COLDER AIR MOVING ACROSS THE REGION TODAY
COUPLED WITH CYCLONIC FLOW SHOULD LEAD TO NUMEROUS SNOW SHOWERS BY
LATE MORNING OR EARLY AFTERNOON. FOLLOWING BLEND OF NAM WRF 12KM AND
4KM RUNS ALONG WITH SREF WHICH ALL SHOW LIGHT SNOW ACROSS MUCH OF
THE AREA. HIGHER CHANCES FAR NORTH WHERE SOME LAKE ENHANCEMENT
POSSIBLE AND FAR EAST WHERE A LITTLE BETTER MOISTURE AND AFTERNOON
TROUGH LOCATION WILL PROVIDE ADDITIONAL LIFT. LOOKS LIKE A HIGH POP
LOW QPF EVENT BUT SOME LIGHT SNOW ACCUMULATIONS
POSSIBLE...ESPECIALLY NORTH AND EAST.
ATTENTION SHIFTS TO NORTHWEST FLOW AND MARGINAL LAKE EFFECT TONIGHT
INTO THURSDAY NIGHT. DELTA T VALUES MARGINAL JUST INTO MID TEENS
WITH SOME LOW LEVEL WIND SHEAR EARLY TONIGHT. DEPTH OF MOISTURE AND
LACK OF INVERSION ALONG WITH POSSIBLE FEEDER BAND FROM LAKE SUPERIOR
SHOULD ALLOW FOR LAKE EFFECT SNOW SHOWERS...WITH BEST WINDOW LATE
TONIGHT INTO THURSDAY MORNING AS LOW LEVEL SHEAR DECREASES. LIGHT
ACCUMS EXPECTED BUT STRUNG OUT OVER THESE NEXT 4 PERIODS MAY ALLOW
TOTAL ACCUMS TO PUSH 2 TO 4 INCHES. NO HEADLINES ANTICIPATED GIVEN
THE LONG DURATION AND BORDERLINE AMOUNTS FOR ADVISORY.
USED A BLEND OF LATEST MOS GUIDANCE AND CURRENT GRIDS FOR TEMPS WITH
A NOD TOWARD THE COOLER GRID TEMPS GIVEN COLD AIR ALOFT.
&&
.LONG TERM...
FRIDAY THROUGH TUESDAY
ACTIVE NORTHWEST FLOW WILL ALLOW SEVERAL CLIPPER SYSTEMS TO AFFECT
THE REGION WITH TIMING/TRACK/AND INTENSITY STILL VERY MUCH IN
QUESTION...ESPECIALLY BY LATE IN THE PERIOD. PATTERN TRANSITION TO
ACTIVE NORTHWEST FLOW WILL ALLOW THE REGION TO TAKE A ROLLER COASTER
RIDE IN THE TEMPERATURE DEPARTMENT...WITH TEMPS WARMING TO AT OR
SLIGHTLY ABOVE CLIMO IN THE WAA ZONE AHEAD OF EACH
DISTURBANCE...THEN FALL WELL BELOW CLIMO NORMS POST FRONTAL. THE
BOTTOM IS EXPECTED TO DROP OUT WRT TEMPS BY NEXT WEEK AS STAUNCH
RIDGING IN THE EASTERN PAC AND WESTERN US IS REALIZED...ASSOCIATED
WITH A POSITIVE PNA REGIME. THIS IS IN DIRECT REPONSE TO THE
REINVIGORATION OF THE EAST ASIAN UPPER JET AS IT/S EASTWARD
EXTENSION SUPPORTS PROPAGATION OF THE THE GULF OF ALASKAN UPPER
TROUGH TO THE EAST. END RESULT IS HIGHLY AMPLIFIED FLOW INTO
ALASKA...WITH STAUNCH RIDGING EXPECTED THERE. NORTHWEST FLOW INTO
THE REGION WILL DIRECT POTENT MID LEVEL DISTURBANCES INTO THE LOCAL
AREA...ALLOWING ADVECTION OF THE MODIFIED ARCTIC AIR /IN PLACE IN
THE HIGH LATITUDES/ INTO THE REGION. SFC TEMPS IN PORTIONS OF ALASKA
AND NORTHWEST CANADA HAVE BEEN DIPPING TO -60F...AND THIS RESERVOIR
OF COLD AIR HAS BEEN EXPANDING. ECMWF DOES INDICATE THE POSSIBILITY
OF A SIBERIAN EXPRESS CONNECTION WHICH WOULD FURTHER SUPPORT VERY
COLD AIR INTO THE NORTHERN US.
GFS AND ECMWF DETERMINISTIC SOLUTIONS HAVE BEEN WAVERING ON
TRACK/INTENSITY/AND THERMAL FIELDS RELATED TO THE CLIPPER SYSTEMS
FRIDAY/MONDAY/AND TUESDAY. MEAN ENSEMBLES OF THE NAEFS AND GEFS NOT
MUCH BETTER...WITH SIGNS OF HIGH SPREAD IN SLP AND QPF
FIELDS...ALTHOUGH H85 T FIELDS HAVE BEEN FAIRLY SOLID IN THE LAST
SEVERAL RUNS WRT TO SAT-SUN. FSU GFS ENSEMBLE CONFIDENCE GRAPHICS
HIGHLIGHT THE GROWING UNCERTAINTY WITH INCREASING SLOPE LATE IN THE
PERIOD. FELT THE BEST OPTION WAS TO STICK CLOSER TO ENSEMBLE
MEANS...SHYING AWAY FROM DETERMINISTIC GFS/GEM/ECMWF
RUNS...ADJUSTING CLIMO NUMBERS TO ENSEMBLE TRENDS. DID FEEL CHANCE
POPS BEYOND SUN ARE WARRANTED EVEN THOUGH TIMING AND STORM TRACKS
ARE STILL UNCERTAIN...GIVEN THE PATTERN IN PLACE WITH A 2 DAY
CLIPPER FREQUENCY.
FRI INTO SUN...MODEL TRENDS IN THIS PERIOD ARE FOR A DEEPER SFC LOW
REFLECTION WITH A DESCENT WARM UP FRI NIGHT AHEAD OF THE SFC COLD
FRONT. HAVE LEANED TOWARD THE STRONGER SFC REFLECTION DEPICTED IN
GFS AND NAM PROGS GIVEN TYPICAL INTENSE NATURE OF
NORTHERN STREAM UPPER TROUGH IN A STRONG BAROCLINIC ENV. GIVEN
ANTICIPATED WARM NOSE ALOFT WITH A COLD SFC LAYER IN
PLACE...EXPECTING ANOTHER MIX PRECIP EVENT ESPECIALLY IN THE
NORTH...WITH A PERIOD OF FREEZING RAIN AND/OR SNOW FRI NIGHT.
FREEZING DRIZZLE WOULD ALSO BE EXPECTED GIVEN SFC LOW TRACK NEAR OR
OVER THE FA WITH A PERIOD OF MID LEVEL DRYING OVER LL SATURATION.
HAVE OPTED FOR MIX WORDING...AND TRENDED TOWARD THE FASTER SYSTEM
SPEED OF THE GFS...WHICH IS TYPICAL FOR NW FLOW SFC LOWS. STRONG CAA
COUPLED WITH A TIGHT PRESSURE GRADIENT IN PLACE AND STEEP LL LAPSE
RATES WILL SUPPORT GUSTY WINDS SATURDAY...WITH PERIODS OF LAKE
EFFECT SNOW POSSIBLE IN THE NW. HAVE OPTED TO END PRECIP SLIGHTLY
FASTER SUN GIVEN FAST PROGRESSIVE FLOW IN PLACE...SUPPORTING MID
LEVEL RIDING BY SUN.
SUN NIGHT-TUES...ACTIVE NORTHWEST FLOW CONTINUES WITH 2 CLIPPER
SYSTEMS EXPECTED TO IMPACT THE REGION. ONE SUN NIGHT INTO MON AND A
SECOND SYSTEM THAT IS EXPECTED TO SUPPORT AN ARCTIC INTRUSION GIVEN
H85 TEMPS DOWN TO -20 TO -25C BY TUES. VERY COLD AIR AND STEEP LL
LAPSE RATES WOULD LIKELY SUPPORT LK SNOW SHOWERS. IN
ADDITION...DANGEROUSLY COLD TEMPS BELOW ZERO WOULD BE A POSSIBILITY.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER WEATHER ADVISORY UNTIL 9 AM EST /8 AM CST/ THIS MORNING
FOR INZ003>009-012>018-020-022>027-032>034.
MI...WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR
MIZ077>081.
OH...WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR OHZ001-
002-004-005-015-016-024-025.
LM...SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 7 PM EST
THURSDAY FOR LMZ043-046.
&&
$$
SHORT TERM...LASHLEY
LONG TERM...JC
AVIATION...LASHLEY
