HAMweather.com Area Forecast Discussion for County Warning Area IWX

Thu, 16 Feb 2012 06:32:28 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1241 AM EST THU FEB 16 2012

.AVIATION... /06Z TAFS/
LARGE AREA OF MAINLY LIGHT RAIN/DRIZZLE AFFECTING BOTH TAF SITES
AS OF 5Z. TRACK OF SFC LOW STILL LOOKS TO BE ACROSS THE HEART OF
THE FORECAST AREA BETWEEN KSBN AND KFWA. INCREASING CONCERNS FOR
FURTHER DETERIORATION AT CONDITIONS AT KSBN AS UPSTREAM OBS SHOWING
CIGS DROPPING TO 200 FT IN MANY SPOTS ACROSS CENTRAL ILLINOIS AND
EVEN INTO WESTERN INDIANA WHERE KVPZ ALREADY DOWN TO 3/4SM AND
200 FT. HAVE ADDED TEMPO GROUP FOR THE TIME BEING TO KSBN TO
ADDRESS CONCERNS FOR LIFR CONDITIONS BUT REMAIN SOMEWHAT
CONSERVATIVE TO ENSURE TRENDS CONTINUE. AT KFWA...VFR CIGS AND
MVFR VSBYS SHOULD PREVAIL MUCH OF THE NIGHT. AS SFC LOW APPROACHES
CIGS SHOULD LOWER FURTHER INTO IFR RANGE. BIT CONCERNED THAT CLOUD
COVER UPSTREAM TO HEAD TOWARDS KFWA NOT AS LOW AND TAFS MAY BE TOO
AGGRESSIVE. HOWEVER...WANTED TO LEAVE PREVIOUS TRENDS IN PLACE FOR
NOW WITH ADDITIONAL RAIN EXPECTED TO MOVE IN AND SLOW LOWERING OF
FLGT CONDITIONS. 

COLD FRONT WILL MOVE THROUGH TOWARDS 12Z AT KSBN (TIMING WAS
BACKED OF IN THIS ISSUANCE) AND A BIT LATER AT KFWA. SKIES STILL
LOOK TO CLEAR MID TO LATE AFTERNOON. 

.PREV DISCUSSION... /ISSUED 616 PM EST WED FEB 15 2012/ 

SHORT TERM...

MAIN FOCUS OF SHORT TERM CONTINUES TO BE ON APPROACHING SHORT WAVE 
FOR TONIGHT AND ASSOCIATED PRECIPITATION. SHORT RANGE MODELS HAVE A 
GOOD HANDLE ON SITUATION AND ALIGN WELL WITH CURRENT SHORT TERM 
GRIDS. 

WATER VAPOR SHOWS COMPACT SHORT WAVE BEGINNING TO LIFT OUT OF 
PANHANDLE REGION THIS AFTERNOON. THIS FEATURE WILL DAMPEN SOME AS IT 
ACCELERATES NORTHEAST TONIGHT. STRONG ISENTROPIC LIFT ALREADY 
DEVELOPING AHEAD OF THIS WAVE ACROSS MO AND IL AND EVEN INTO CENTRAL 
INDIANA THIS AFTERNOON. THIS SHOULD FILL IN AND MOVE INTO OUR 
SOUTHWEST CWA VERY EARLY THIS EVENING AND SPREAD NORTH THROUGH THE 
REMAINDER OF THE EVENING. STRONG LIFT AND GOOD MOISTURE ADVECTION 
WILL PROVIDE FOR A PERIOD OF MODERATE RAINFALL LATE EVENING AND 
OVERNIGHT. GENERAL QUARTER TO HALF INCH QPF EXPECTED BUT GIVEN 
STRENGTH OF MOISTURE ADVECTION AND LIFT BEING GENERATED SOME HALF TO 
THREE QUARTER INCH AMOUNTS NOT OUT OF QUESTION.

PRECIPITATION TYPE STILL LOOKS TO BE IN FORM OF RAIN BASED ON 
THERMAL PROFILES OF MOST SHORT RANGE GUIDANCE. DENDRITIC GROWTH ZONE 
REMAINS HIGH AND SATURATED WITHIN STRONG LIFT BUT TEMPERATURES IN THE 
SURFACE TO 900MB LAYER REMAIN VERY WARM IN THE 3C TO 5C RANGE. TOP 
DOWN METHODOLOGY HAS SHOWN THIS IS WARM ENOUGH TO PRODUCE LIQUID. 
SURFACE TEMPS EXPECTED TO REMAIN ABOVE FREEZING IN THE MID 30S SO NO 
FREEZING RAIN ANTICIPATED. WITH STRONG LIFT AND DYNAMICAL COOLING 
PROCESSES STILL CANNOT RULE OUT PERIODS OF WET SNOWFLAKES MAKING IT 
THROUGH THE WARM LAYER IN THE NORTHWEST BUT CURRENTLY NOT EXPECTING 
PCPN TO BECOME ALL SNOW UNLESS MODEL FORECAST SOUNDINGS ARE TOO 
WARM. NO SIGNS OF THIS SO WILL CONTINUE WITH ALL RAIN OVERNIGHT.

COLD FRONT SLIDES THROUGH AREA THURSDAY MORNING IN WAKE OF SURFACE 
WAVE. PRECIPITATION LOOKS TO END BY THE TIME IT BECOMES COLD ENOUGH 
FOR CHANGEOVER TO SNOW. WILL ALLOW A SNOW OR RAIN MENTION TO 
CONTINUE GIVEN COOLING PROFILES AND POSSIBILITY OF SOME LINGERING 
MOISTURE. AGAIN...NO ACCUMULATION EXPECTED. MODELS INDICATING DRYING 
DURING THE DAY WITH CLEARING SKIES POSSIBLE IN AFTERNOON. HAVE 
CONTINUED TO BE OPTIMISTIC WITH SKY GRIDS FOR THIS CLEARING AND THUS 
A SLIGHT BUMP IN TEMPS POSSIBLE IN AFTERNOON WITH SOME SUN. THIS 
CLEARING MAY POSE A PROBLEM FOR THURSDAY NIGHT WITH EITHER FOG OR
STRATUS DEVELOPMENT AS WINDS BECOME LIGHT. THIS WILL BE WATCHED AS
SATURATED GROUND AND LIGHT WINDS WILL PROVIDE FAVORABLE
CONDITIONS.
  
LONG TERM...
FRIDAY THROUGH WEDNESDAY...
WEAK AND MOISTURE STARVED NORTHERN STREAM SYSTEM TO MOVE ACROSS THE 
SOUTHERN GREAT LAKES FRIDAY NIGHT. LATEST MODEL CONSENSUS HAS SFC 
LOW TRACKING ACROSS SOUTH CENTRAL LOWER MICHIGAN ALONG WITH BEST 
FOCUS FOR MOISTURE AND LIFT. WITH REASONABLE PROXIMITY TO NORTHERN 
CWA WILL INCLUDE A SMALL CHANCE FOR LIGHT SNOW ACROSS MICHIGAN 
COUNTIES AFTER MIDNIGHT FRIDAY WITH THIS SYSTEM. POTENTIAL FOR LAKE 
EFFECT SNOW SHOWERS BEHIND THIS SYSTEM DESPITE MARGINAL 850MB TEMPS 
WILL STILL HAVE 6-7KFT INVERSION HEIGHTS AND A FAIRLY UNIFORM NW 
FLOW IN THE CLOUD BEARING LAYER. LINGERING LES INTO SATURDAY NIGHT 
BEFORE SFC RIDGING BUILDS INTO THE REGION BRINGING A COUPLE DAYS OF 
DRY WEATHER. UPPER LEVEL RIDGING ALONG WITH RETURN FLOW ON BACK SIDE 
OF SFC HIGH WILL BRING WARMING TREND BEGINNING OF NEXT WEEK AS HIGHS 
EXPECTED BACK INTO THE 40S BY TUESDAY. WAA AND APPROACH OF WARM 
FRONT WILL BRING NEXT CHANCE OF PRECIP INTO THE AREA MON NITE AND 
CONTINUE FOR THE REMAINDER OF THE EXTENDED PERIOD. PRECIP TYPE DOES 
COME INTO QUESTION BOTH MONDAY AND TUESDAY NIGHT AS TEMPS DROP DOWN 
NEAR FREEZING...WITH MONDAY BEING THE COOLER OF THE TWO EXPECT 
MAINLY SNOW IN NORTH HALF WITH ALL RAIN EXPECTED SOUTHERN HALF BY 
TUESDAY NIGHT.

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.