FXUS63 KIWX 260915
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
415 AM EST SAT DEC 26 2009
.SHORT TERM...
CONTINUED UNSETTLED WEATHER THROUGH THE SHORT TERM AS HUGE SYSTEM
OVER THE CENTRAL CONUS CONTINUES TO MEANDER AROUND THE UPPER
MISSISSIPPI VALLEY AND SLOWLY MAKE HEADWAY TO THE NORTHEAST ON
SUNDAY. UPPER LOW SITUATED OVER ILL/WIS BORDER WITH COLD WRAPPED SFC
LOW/H85 CENTER WEST OVER SOUTHERN IA TRAILING A LONG OCCLUDED FRONT
THROUGH WISCONSIN/MI/OH. MOISTURE HAS BEGUN TO ROTATE INTO THE AREA
EARLY THIS MORNING BEHIND MID LVL DRY SLOT WITH A THIN CONVECTIVE
BAND OF HEAVIER SNOWFALL MAKING ITS WAY ACROSS THE EASTERN HALF OF
THE CWA DURING THE PRE DAWN HOURS.
UPPER/LOWER CIRCULATION CENTERS WILL WOBBLE AROUND ONE ANOTHER ON
SATURDAY AS COLD WRAPPED SFC LOW WEAKENS TAKING THE SFC-H85 LOW JUST
TO OUR NW WHILE DEEPER MOISTURE ROTATES BACK TO THE CWA. RIPPLES OF
ENERGY CONTAINED IN STRONGLY CYCLONIC FLOW WILL ALOFT WILL WAFT
OVERHEAD SUPPORTING SHSN THROUGH THE WEEKEND...WITH MAIN SHRTWV
ENERGY EVIDENT ON W/V IMAGERY EXTRAPOLATED TO MOVE IN THIS
AFTERNOON. ULTIMATELY...SNOWFALL AMOUNTS MAY DEPEND ON MESOSCALE
FEATURES SUCH AS THIS MORNINGS CONVECTIVE BAND. NAM12 CAUGHT ON TO
THIS FEATURE...THOUGH A BIT SLOW...PER ITS H92/H85 OMEGA/WIND
CONVERGENCE FIELDS AND SPORTS A SIMILAR BUT STRONGER FEATURE MIDDAY
SUNDAY. FOR THIS PACKAGE...WILL CONTINUE WITH POPS GRADUATED FROM NW
TO SE MIRRORING AVAILABLE MOISTURE ALONG WITH POTENTIAL
ACCUMULATIONS GENERALLY RANGING FROM 2 INCHES NW TO AN INCH
SE...WHILE KEEPING A WARY EYE ON FUTURE DEVELOPMENTS.
LAKE RESPONSE SETS UP SUNDAY NIGHT WITH LITTLE CHANGE TO THINKING FROM
PREV SHIFT. WINDS BECOME FAVORABLE WITH SHALLOW WESTERLY FETCH
SUNDAY EVENING VEERING NW OVERNIGHT AS H85 TEMPS SLOWLY FALL WITH
PEAK LAKE INDUCED INSTABILITY SUNDAY AFTERNOON WANING INTO THE
OVERNIGHT. RAISED POPS AFTER 18Z SUN INTO BERRIEN/CASS COUNTIES WITH
FEW OTHER CHANGES.
&&
.LONG TERM.../MONDAY THROUGH FRIDAY/...
LONG TERM PERIOD WILL BEGIN WITH THE EXIT OF POTENT STORM SYSTEM
THAT HAS PLAGUED THE CENTRAL CONUS FOR THE PAST SEVERAL DAYS. LAKE
EFFECT SNOWS WILL LIKELY BE ONGOING ON MONDAY WITH DELTA T VALUES IN
MID TEENS AND WEST TO NORTHWEST FETCH. HOWEVER...SECONDARY SURFACE
TROUGH AXIS AHEAD OF NORTHERN STREAM SHORT WAVE WILL BE MOVING
ACROSS THE AREA ON MONDAY. THIS SHOULD HELP BACK LOW LEVEL WINDS
SHIFTING LAKE SNOW NORTHWARD TEMPORARILY. DELTA T VALUES ALSO
DECREASE AS WEAK WARM AIR ADVECTION OCCURS AHEAD OF THIS WAVE.
BUFKIT INDICATING A DECENT AMOUNT OF LOW LEVEL SHEAR GIVEN THE
VARIABLE FLOW SO THINK THIS WILL HELP KEEP AMOUNTS DOWN. AFTER
PASSAGE OF SHORT WAVE AND SURFACE TROUGH DELTA T VALUES CLIMB BACK
INTO MID AND UPPER TEENS WITH A LITTLE BETTER FETCH AND
UNIDIRECTIONAL FLOW. HOWEVER THE COLDER AIRMASS IS BEING SHOWN BY
MODELS TO BE RATHER DRY WITH MOISTURE CONFINED TO LOWEST 3KFT AND A
LOWERED INVERSION HEIGHT. AGAIN EXPECT SOME LIGHT ACCUMS BUT NOTHING
SIGNIFICANT AT THIS POINT UNLESS DEEPER MOISTURE IS REALIZED. WILL
CONTINUE WITH A COUPLE INCHES TOTAL FOR THIS LAKE EFFECT EVENT WITH
LIKELY OR SCATTERED WORDING.
HIGH PRESSURE SCOOTS QUICKLY ACROSS THE AREA ON TUESDAY. DEVELOPING
SOUTHWEST FLOW TAKES PLACE TUE NIGHT INTO WED AHEAD OF YET ANOTHER
SHORT WAVE. INCREASING MOISTURE AND THETA E ADVECTION SUGGEST A
DECENT CHANCE FOR MORE LIGHT SNOW MAINLY WED NIGHT AND THURSDAY.
AFTER THIS FORECAST BECOMES A BIT MORE INTERESTING. ECMWF DEVELOPS A
STRONG COASTAL LOW FRIDAY INTO SATURDAY AS MID LEVEL ENERGY DIVES
THROUGH THE GREAT LAKES. AS WE HAVE MENTIONED NUMEROUS TIMES IN
THESE DISCUSSIONS...A BIAS EXISTS IN THE MODELS TO TAKE SYSTEMS TOO
FAR EAST IN THESE TYPE OF PATTERNS WHEN DIGGING WAVES TAKE ON A
NEGATIVE TILT. ECMWF SHOWING H7 AND H5 LOWS MOVING OUT OF DEEP SOUTH
THROUGH TENNESSEE VALLEY AND THIS HAS BEEN A GOOD INDICATOR OF
EVENTUAL SURFACE LOW DEVELOPMENT AND MOVEMENT...ASSUMING OVERALL
ECMWF IDEA VERIFIES. THIS WILL HAVE TO BE WATCHED AS MODELS
CURRENTLY KEEP COMMA HEAD MOISTURE AND HEAVIEST PRECIPITATION
SOUTHEAST OF OUR AREA. CURRENT GRIDS ALREADY HAVE A LOW POP IN FOR
LIGHT SNOW WITH UPPER SYSTEM CROSSING THE AREA SO WILL CONTINUE WITH
THIS.
SEASONABLE LATE DECEMBER TEMPS THROUGH THE PERIOD JUST BELOW NORMAL.
POTENTIAL STILL EXISTS FOR A DECENT ARCTIC AIRMASS TO MOVE SOUTH BY
EARLY JANUARY.
&&
.AVIATION...
PERIODIC SNOW SHOWERS AND PERSISTENT MVFR CIGS WILL CONTINUE
OVERNIGHT AS MOISTURE BEGINS TO WORK BACK INTO MID LEVEL DRY SLOT
OVER THE REGION. AN ENHANCED BAND OF SNOW ADVANCING NE THROUGH
CENTRAL INDIANA WILL FOR THE MOST PART PASS BETWEEN TERMINALS HWVR
EXPECTING KFWA TO BE IMPACTED BETWEEN 07Z-10Z. UPSTREAM THIS BAND
BROUGHT LOCALIZED LIFR CONDS TO KHUF AND WHILE THIS IS NOT
ANTICIPATED A SHORT PD OF OPTIMISTIC VSBY/CIG RESTRICTION IS INCLUDED IN
KFWA TAF. INTO SATURDAY...INCREASING MOISTURE AS SFC LOW ADVANCES
INTO NORTHERN ILLINOIS IS EXPECTED TO BRING A PERIOD OF SNOWFALL
DURING THE AFTERNOON HOURS...WHILE SHSN AND GUSTY SSE WINDS
CONTINUE THROUGHOUT THE PERIOD AS MOIST SYSTEM CONTINUES TO LINGER
IN THE AREA.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SHORT TERM...LUD
LONG TERM...LASHLEY
AVIATION...LUD
