000 FXUS63 KIWX 100929 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 429 AM EST FRI FEB 10 2012 .SHORT TERM.../TODAY THROUGH SATURDAY NIGHT/ ...QUICK BLAST OF ARCTIC AIR ARRIVING LATER TODAY WITH ONE OR MORE CHANCES FOR SNOWFALL... QUIET START TO THE PERIOD ACROSS THE AREA AS MAIN FEATURES OF INTEREST LIE TO THE NORTH IN THE FORM OF A MODIFIED ARCTIC FRONTAL BOUNDARY POISED TO DROP THROUGH THE AREA TODAY AND SOUTHERN STREAM ENERGY MOVING NE TO PHASES WITH NORTHERN SYSTEM. SOME CHANGES REQUIRED TO GRIDS FOR CHANGING MODEL SOLUTIONS WITH HIGHER CHANCES FOR AT LEAST SOME LIGHT ACCUMS ACROSS THE AREA ALONG/AHEAD OF THE FRONT FOLLOWED BY MODIFICATIONS TO LAYOUT OF LAKE EFFECT SNOW TONIGHT INTO EARLY SATURDAY MORNING. TEMPS WILL SLOWLY CLIMB INTO EARLY AFTERNOON AHEAD OF THE FRONT AS SW FLOW CONTINUES TO KEEP TEMP PROFILES FROM CHANGING MUCH. BUFKIT DATA AGREES ON VERY STRONG OMEGA LINING UP WITH AND IMMEDIATELY BEHIND FRONT WITH 90+% RH ALLOWING FOR SNOW TO BREAK OUT ACROSS THE AREA FROM MID AFTERNOON INTO THIS EVENING WITH BEST WINDOW IN THE 21Z-03Z PERIOD. STILL APPEARS TO BE LIGHTER END EVENT WITH ANYWHERE FROM A DUSTING TO MAYBE A FEW INCHES OF SNOW. FACTORS AGAINST HEAVIER SNOW ARE 1) DGZ ABOVE AREA OF STRONGEST LIFT AND DEEPEST MSTR AND 2) SPEED OF FRONTAL BOUNDARY. IF ONE OR BOTH OF THESE FACTORS CHANGE...POTENTIAL FOR HIGHER AMOUNTS WOULD INCREASE. WITH SLOWER ARRIVAL OF FRONT...HIGHS SHOULD STILL BE REACHED BY EARLY TO MID AFTERNOON WITH STEADY OR FALLING TEMPS INTO TONIGHT. GRIDS HAVE BEEN UPDATED TO REFLECT A SLOWER ARRIVAL TO COLD FRONT WITH ALL MODELS AND SFC OBS INDICATING FRONT A BIT BEHIND SCHEDULE. IN ADDITION...POPS HAVE BEEN INCREASED TO A PERIOD OF CAT POPS DURING MOST FAVORABLE TIME FRAME. HEADLINES COULD BE NEEDED FOR FREEZING OF ANY MELTED SNOWFALL ON ROAD SURFACES AND IMPACTS FROM SLICK ROADWAYS THAT CAN BE SEEN IN LIGHT SNOW SITUATIONS. HOWEVER...SINCE EXACT TIMING AND AMOUNTS ARE STILL A BIT QUESTIONABLE WILL GO WITH SPS AND DEFER TO DAY SHIFT FOR ANY HEADLINES. ATTENTION TURNS TO LAKE EFFECT WHICH REMAINS RATHER TROUBLESOME IN TERMS OF PLACEMENT...STRENGTH AND DURATION OF ONE OR MORE POTENTIALLY STRONG BANDS OF SNOW SHOWERS. PAST 2 NAM12 MODEL RUNS HAS BEGAN A SLOW TREND OF SHIFTING HEAVIEST SNOW BAND MORE INTO PORTER AND LAPORTE COUNTIES EXTENDING SOUTH. AS MENTIONED BY DAY SHIFT...WHILE MODERATE TO EXTREME INSTABILITY AND FAVORABLE INVERSION HGTS WOULD LEAD TO STRONG POTENTIAL FOR HEADLINE SNOWFALL AMOUNTS...A LOT OF DRY AIR WILL BE MOVING ACROSS THE AREA AND IF LINEUP OF TRAJECTORY ISN'T PERFECT DOWN THE MAJOR AXIS OF THE LAKE...ENTRAINMENT OF THIS DRIER AIR COULD BRING HIGH ACCUMS TO A SCREECHING HALT. SREF AND LOCAL WRF LEAN MORE IN THIS DIRECTION WITH VERY LIMITED MSTR CAUSING ISSUES WITH DEVELOPMENT. BASED ON NAM TRENDS AND COLLABORATION WITH CHICAGO OFFICE HAVE INCREASED POPS ACROSS FAR WESTERN TIER OF COUNTIES INTO HIGHER END LIKELY LATER TONIGHT DURING MOST FAVORABLE TIME FRAME. WENT AHEAD AND PLACED A INCH OR 2 OF SNOW IN THESE AREAS AS WELL. OUTSIDE OF THE LAKE EFFECT...COLD NIGHT WILL BE IN STORE WITH LOWS INTO THE TEENS. LOCAL WRF SUGGESTING TEMPS COULD FALL INTO SINGLE DIGITS IF SKIES CAN CLEAR OUT AND GIVEN UPSTREAM TEMPS CAN'T ENTIRELY DISMISS. PRECIP WILL QUICKLY WIND DOWN DURING SAT AFTERNOON WITH DRIER CONDITIONS. A PIECE OF ENERGY WILL MOVE THROUGH THE BASE OF THE TROUGH TO BRING A INCREASE IN CLOUDS BUT SHOULD REMAIN DRY AND WITH HIGHS ONLY IN THE LOWER TO MIDDLE 20S AND A COOL NIGHT SATURDAY BACK INTO THE TEENS. && .LONG TERM...SUNDAY THROUGH THURSDAY HIGHLY AMPLIFIED PATTERN TO CONTINUE ON TUESDAY WITH DEEP NORTHWESTERLY FLOW ACROSS THE AREA ALONG WITH CONTINUED MID LEVEL SUBSIDENCE AND A DRY LOW/MID LEVEL AIR MASS IN PLACE. WEAK LOW LEVEL WARM AIR ADVECTION COMBINED WITH THIS LARGE SCALE SUBSIDENCE WILL CONTINUE TO MODERATE THE AIR MASS WITH HIGHS IN THE UPPER 20S TO AROUND 30 POSSIBLE. DID TRY AND HINT AT SOME SLIGHTLY COOLER MAX TEMPS IN THE MID TO UPPER 20S ACROSS THE NORTHWESTERN INLAND AREAS WITH THE POTENTIAL OF MORE SUBSTANTIAL SNOW COVER FROM SATURDAYS LAKE EFFECT SNOW SHOWERS. A RATHER COMPLICATED UPPER LEVEL FLOW SCENARIO TO UNFOLD FOR THE LATE SUNDAY THROUGH TUESDAY PERIOD WITH DIGGING SOUTHERN STREAM TROUGH INDUCING MODEST HEIGHT RISES ACROSS THE CENTRAL PLAINS. AS THIS OCCURS...SHEARED UPPER LEVEL VORT MAX ACROSS THE NORTHERN PLAINS BECOMES DIVORCED FROM MORE PROGRESSIVE FLOW IN SPLIT FLOW TYPE PATTERN ACROSS WESTERN CONUS. EVENTUALLY...THE NEXT EASTERN PACIFIC SHORT WAVE REACHING THE WEST COAST MONDAY NIGHT WILL KICK THIS NORTHERN PLAINS VORT MAX EASTWARD...POSSIBLY PHASING WITH THE INITIAL SOUTHERN STREAM TROUGH. WHILE DIFFERENCES IN DETAILS REGARDING AMPLITUDE/PHASING HAVE BEEN NOTED OVER PAST SEVERAL MODEL RUNS...OVERALL TIMING OF THIS MID/UPPER FORCING AND ISENTROPIC FORCING HAVE BEEN QUITE CONSISTENT FROM RUN TO RUN IN HIGHLIGHTING THE MONDAY NIGHT/TUESDAY PERIOD FOR BETTER PRECIP CHANCES AND HAVE CONTINUED TREND OF INCREASING POPS FOR THIS PERIOD. PRECIP TYPE SHOULD BE MAINLY SNOW WITH NAM/GFS WET BULB TEMPS RIGHT AROUND FREEZING TUESDAY AFTERNOON ACROSS THE SOUTH WHERE HAVE MAINTAINED RAIN/SNOW WORDING. CURRENT INDICATIONS STILL SUGGEST A POTENTIAL OF ONE OR TWO INCHES OF SNOW WITH THIS RATHER DISJOINTED SYSTEM MONDAY NIGHT/TUESDAY POSSIBLY ENDING AS A PERIOD OF PATCHY DRIZZLE/FREEZING DRIZZLE OR FLURRIES TUESDAY NIGHT AS DEEPER MOISTURE PROFILES SHIFT EAST OF THE AREA. NEGATIVE UPPER LEVEL HEIGHT ANOMALY ACROSS WESTERN CONUS FOR MID WEEK SHOULD MAINTAIN TEMPS NEAR NORMAL OR SLIGHTLY ABOVE NORMAL THROUGH MUCH OF THE MID TO LATE WEEK PERIOD WITH STILL A LOW DEGREE OF CONFIDENCE WITH EVOLUTION OF THIS SOUTHERN STREAM TROUGH AND HIGH LEVELS OF UNCERTAINTY ONCE AGAIN WITH POTENTIAL PHASING ISSUES. LATEST 00Z ECMWF ACTUALLY CUTS OFF THIS SOUTHERN STREAM NEGATIVE HEIGHT ANOMALY ACROSS BAJA OF CALIFORNIA THURSDAY WHILE THE GFS REMAINS A BIT MORE PHASED AND MORE PROGRESSIVE TAKING NEXT SHORT WAVE INTO THE SOUTHERN GREAT LAKES THURSDAY. HAVE PUT MORE WEIGHT INTO THE MORE RUN TO RUN CONSISTENT GFS SOLUTION AT THIS TIME WHICH ALSO FALLS INLINE WITH FORECAST CONTINUITY...WHICH IS LIKELY THE COURSE OF LEAST REGRET CONSIDERING THE HIGHER THAN NORMAL UNCERTAINTY FOR DAYS 6/7. THUS...HAVE MAINTAINED CHANCE RAIN/SNOW POPS ON THURSDAY MORE INLINE WITH PREVIOUS FORECAST/00Z GFS...BUT LOWERED POPS A BIT FROM CR ALLBLEND PER COLLABORATION WITH SURROUNDING OFFICES GIVEN THE ABOVE ISSUES. && .AVIATION... INITIAL 6 TO 9 HOUR PERIOD OF TAFS PRETTY STRAIGHT FORWARD LOOKING WITH MODERATE TO HIGH CONFIDENCE IN PERSISTENT AREA OF LOW END VFR CLOUDS TO OVERSPREAD THE AREA AND PERSIST PRIOR TO FROPA THIS AFTERNOON. AS FRONT APPROACHES BY EARLY AFTERNOON INCREASING FORCING AND MSTR WILL ALLOW FOR EXPANDING AREA OF LIGHT SNOW. SEVERAL OF THE MODELS ARE HINTING AT A PERIOD OF ENHANCED SNOWFALL POTENTIAL WITH VSBYS DROPPING BELOW 1 MILE /HINTS AT LOWER THAN 1/2SM AT TIMES/. HAVE OPTED TO ADD A BIT OF DETAIL WITH FROPA TO BRING IN IFR CONDITIONS TO BOTH SITES FOR AT LEAST A FEW HOURS ALONG AND AHEAD OF THE FRONT. WITH LOW TO MODERATE CONFIDENCE IN LOWER CIGS/VSBYS HAVE REMAINED SOMEWHAT CONSERVATIVE WITH LATER FORECASTS LIKELY FINE TUNING TIMING AND INTENSITY. ONLY LIGHT SNOW WILL LINGER WELL BEHIND THE FRONT INTO FRI EVE BUT SHOULD QUICKLY WIND DOWN AND TRANSITION TO LAKE EFFECT SNOW THAT WILL REMAIN WELL WEST OF KSBN FOR THE REMAINDER OF THE PERIOD. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...SMALL CRAFT ADVISORY UNTIL 7 PM EST SUNDAY FOR LMZ043-046. && $$ SHORT TERM...FISHER LONG TERM...MARSILI AVIATION...FISHER