000
FXUS61 KILN 200840
AFDILN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
333 AM EST THU NOV 20 2008
.SYNOPSIS...
MUCH COLDER AIR WILL SPILL INTO THE LOWER GREAT LAKES AND OHIO
VALLEY TODAY AND FRIDAY IN THE WAKE OF AN ALBERTA CLIPPER. SEVERAL
UPPER LEVEL DISTURBANCES WILL CONTRIBUTE TO SCATTERED SNOW SHOWERS
ACROSS THE REGION INTO FRIDAY. HIGH PRESSURE WILL THEN BUILD INTO
THE OHIO VALLEY FOR MUCH OF THE WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
SFC LO OVER SRN ONTARIO WITH COLD FRONT PROGRESSING THRU FAR ERN
PORTIONS OF FCST AREA AT 08Z. SC DECK THAT OVERSPREAD MUCH OF THE
FCST AREA NORTH OF THE OHIO RIVER LATE LAST EVNG HAS REMAINED
RELATIVELY STEADY STATE SINCE WITH SRN FLANK UNABLE TO PROGRESS
ANY FURTHER SOUTH DUE TO PRESENCE OF A WELL DEFINED BAROCLINIC ZONE
RESTING NW-SE FROM ERN ILLINOIS INTO NRN/CNTRL KY. SOME WEAK
DIVERGENCE IN WAKE OF FROPA HAS ALLOWED FOR A BRIEF BREAK IN SC
ALL THE WAY UP INTO CNTRL OH. WITH FRONT NOW THRU MAJORITY OF FCST
AREA... BAROCLINIC ZONE WILL BEGIN TO SHIFT SOUTH WITH SC DECK
EXPANDING SOUTH ALONG WITH IT. SC DECK SHOULD ENCOMPASS MOST IF
NOT ALL OF THE FCST AREA BY 12Z. TEMPS REMAINED IN THE 30S ERLY
THIS MRNG.
LK EFFECT ACTIVITY OFF LK MICHIGAN HAS YET TO REALLY GET ITSELF
GOING THIS MRNG BUT AS LO LVL CAA STRENGTHENS THRU MRNG HOURS AND
SHALLOW BNDRY LYR INSTABILITY BECOMES PREVALENT...EXPECT
INCREASING -SHSN DVLPMNT TO NORTHWEST OF FCST AREA. UPR TROF
RELOADING OVER WRN GRT LKS CURRENTLY AND POISED TO ENVELOP THE
REGION THRU TONIGHT AS SVRL MID LVL S/WVS DIVE SOUTHEAST THRU THE
TROF. EXPECT MAINLY CLOUDY SKIES THIS MRNG OVER FCST AREA WITH
ONLY FEW FLURRIES CONFINED MAINLY ALONG AND NORTH OF I-70. LO LVL
CAA REALLY INTENSIFIES OVER FCST AREA THIS AFTN. WITH MODEL
SOUNDINGS CONTINUING TO SHOW LO LVL LAPSE RATES STEEPENING AND
WEAKLY UNSTABLE BNDRY LYR DVLPG...EXPECT SCT -SHSN TO BECOME
PREVALENT ACRS FCST AREA. GREATEST COVERAGE INITIALLY WILL BE ACRS
NRN 1/2 FCST AREA BUT AS MID LVL VORT ENERGY DIVES INTO FCST AREA
BY LATE AFTN...EXPECT MOST OF THE FCST AREA TO GET INTO THE -SHSN
ACTIVITY. WILL CONTINUE WITH CHC POPS ACRS FCST AREA THIS AFTN.
BEST COVERAGE AND INTENSITY TO -SHSN SHOULD TAKE PLACE THIS EVNG
AND INTO THE OVERNIGHT AS TWO DISTINCT S/WVS WITH EMBEDDED MID LVL
VORT ENERGY LEND WEIGHT TO CONDITIONALLY UNSTABLE BNDRY LYR.
INITIAL S/WV WITH SFC TROF OR SECONDARY COLD FRONT MOVES THRU
REGION BTWN 00-06Z...WITH A SECONDARY S/WV CLOSER TO DAYBREAK FRI.
HAVE INCREASED TO 40-50 POPS FOR MUCH OF THE FCST AREA WITH THE
LEAD S/WV THIS EVNG. 00Z MODELS OFFERING SLIGHT VARIATIONS REGARDING
LO LVL WIND FIELDS...BUT APPEARS SFC WINDS WILL BE FROM 300-320
DEG WITH WINDS VEERING TO MORE OF A 320-340 DIR THRU THE BNDRY
LYR. THIS WOULD FAVOR BEST AND MOST INTENSE -SHSN TO AFFECT AREAS
FROM CVG METRO AND POINTS NORTH/EAST. LOCATIONS THAT MAY END UP
SEEING BEST OPPORTUNITY AT HEAVIER -SHSN WILL BE WEST CNTRL OH
S/SW INTO THE NRN WHITEWATER VLY AS DEEPEST MOISTURE LINES UP WITH
BEST UVV IN THESE AREAS AFT 00Z. ONE POINT OF INTEREST IS THAT NW
LO LVL FLO OVER LK MICHIGAN WILL PROVIDE LESS FETCH FOR THE BANDS
TO WORK WITH AND CONSEQUENTLY MAY KEEP THE HEAVIER -SHSN BANDS
FROM WORKING WELL INTO FCST AREA. A NRLY FLO ENCOMPASSING THE FULL
FETCH (OR CLOSE TO IT) OF LK MICHIGAN BEFORE BACKING TO NW WOULD
PACK MORE OF A PUNCH ACRS FCST AREA. REGARDLESS THOUGH...
COMBINATION OF THE FEATURES LISTED ABV WILL COMBINE TO PROVIDE
GOOD -SHSN COVERAGE FOR MUCH OF THE NIGHT. DO NOT THINK IT WILL BE
OUT OF THE QUESTION FOR SOME MINOR ACCUMS...MAYBE AS MUCH LOCALLY
AS AN INCH OR SO WHERE HEAVIER BANDS SET UP. THE EVOLUTION OF THE
MESOSCALE SETUP AND LO LVL WIND FLO WILL BE CRUCIAL IN DETERMINING
WHERE SPECIFICALLY THIS MAY END UP. AT THIS POINT...ANY LOCATION
NORTH AND EAST OF A RICHMOND-CVG METRO-MAYSVILLE LINE ARE FAIR
GAME FOR MINOR ACCUMS. WITH TEMPS IN THE 20S TONIGHT...SNOW WILL
ALSO HAVE NO TROUBLE STICKING.
TEMPS...TRICKY TEMP FCST FOR TODAY WITH SUBTLE WAA ALONG FRNTL
BNDRY HOLDING CURRENT TEMPS UP IN THE M30S ACRS MUCH OF THE
REGION. WITH THE ONSET OF CAA PRIOR TO DAYBREAK...AM EXPECTING
TEMPS TO FALL BACK A FEW DEG FROM CURRENT READINGS. MAY SEE TEMPS
CLIMB BACK A DEG OR TWO THIS MRNG BUT ARRIVAL OF MORE INTENSE CAA
THIS AFTN SHOULD ALLOW FOR STEADY THEN FALLING TEMPS INTO THE
EVNG. FCST HIGHS WILL ONCE AGAIN BE BELOW MOS GUID. WITH A
REINFORCING SHOT OF COLDER AIR OVERNIGHT...TEMPS WILL HAVE NO
PROBLEM BOTTOMING OUT NEAR 20 DEG.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
SECONDARY S/WV WILL BE TRANSITIONING THRU FCST AREA FRI MRNG AND
SHOULD ALLOW FOR SCT -SHSN TO PERSIST INITIALLY. NW LO LVL WINDS
REMAIN SUFFICIENT FOR SOME LK MICHIGAN ENHANCEMENT AT 12Z...BUT
WEAKEN AND BACK THRU MIDDAY. THIS SHOULD ALLOW FOR A GRADUAL
DECREASE IN -SHSN COVERAGE AND INTENSITY TO JUST SCT FLURRIES ACRS
SW 1/2 FCST AREA BY ERLY AFTN. SCT -SHSN WILL LINGER FOR A GOOD
PART OF THE DAY ACRS NRN FCST AREA BUT EVEN HERE...EXPECT PCPN TO
DIMINISH TO FLURRIES THEN END BY LATE AFTN AS UPR TROF MOVES OFF
TO THE NORTHEAST. SC WILL SLOWLY BREAK UP FROM SW TO NE DURING THE
AFTN WITH SKIES BECMG MSTLY CLR ACRS MUCH OF THE FCST AREA FRI
EVNG AS LARGE SFC HI PRES BUILDS INTO THE OH VLY.
SFC HI WILL REMAIN CONTROLLING WX FEATURE FROM FRI NIGHT THRU
REMAINDER OF EXTENDED AS IT DRIFTS ACRS ERN CONUS. WEAKENING S/WV
MOVING QUICKLY THRU NW FLO WILL MOVE ACRS OH VLY ON SAT. SOME
MINOR TIMING DIFF BTWN VARIOUS MODELS BUT S/WV WILL SPREAD MID/HI
LVL CLOUDS ACRS REGION SAT AFTN/EVNG. BOTH NAM/GFS INDCG NICE SHOT
OF ISENT LIFT AT 290K FOR ABOUT 4-6 HOURS...WHICH MAY END UP
TRANSLATING TO A BRIEF PERIOD OF MSTLY CLDY SKIES LATE ON SAT.
SYSTEM WILL PASS THRU REGION DRY WITH PRESENCE OF SFC HI AND
ABUNDANCE OF DRY AIR THRU THE BNDRY LYR. SKIES WILL BECOME
GENERALLY CLR ONCE AGAIN ON SAT NIGHT.
TEMPS...CONTINUED TO UNDERCUT MOS GUID THRU SHORT TERM PERIOD. 850
TEMPS AT -15 TO -13C ON FRI ALONG WITH A FAIR AMOUNT OF CLOUDS
WILL HOLD TEMPS LIKELY AT THEIR COLDEST DAYTIME READINGS SO FAR
THIS FALL. MOST IF NOT ALL OF THE FCST AREA MAY STRUGGLE TO REACH
THE FREEZING MARK...WITH AREAS ALONG AND NORTH OF I-70 POSSIBLY
STAYING IN THE U20S. LEANED TOWARDS COLDER MET GUID FOR LOWS FRI
NIGHT IN THE M/U TEENS. IF -SHSN OVER NEXT 24-36 HOURS CAN PROVIDE
ANY SORT OF ACCUM...TEMPS WILL NEED TO BE LOWERED. DESPITE DVLPG
LO LVL WAA SAT...PRESENCE OF CLOUDS SHOULD KEEP TEMPS IN THE 30S.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
SFC HIGH PRESSURE WILL BE IN CONTROL TO START SUN BUT HAS SOME
RETURN FLOW...SO THIS SHOULD BE THE WARMEST DAY OF EXTENDED FCST
WITH READINGS IN THE LOW TO MID 40S DEPENDING ON LATITUDE. ERN
SITES MAY BE JUST AS WARM ON MON WITH A COLD FRONT KNOCKING
THROUGH WRN FCST AREA EARLY IN THE DAY. OCCLUDED LOW OVER GTLKS IS
MAKING A SE PROGRESSION TOWARDS THE ATLANTIC AND THERE SHOULD BE
ENOUGH OF A SLY COMPONENT OF THE WIND TO WARM UP CMH AND SCIOTO
VALLEY BEFORE TEMPS TAKE A NOSEDIVE IN THE COLD AIR THAT IS
WRAPPED UP WITH THIS VIGOROUS SYSTEM. NRLY FLOW ON TUES WILL KEEP
HIGHS ON THE COOL SIDE...ABOUT 10-15 DEG BELOW CLIMO WITH LAKE
EFFECT SNOW SHOWERS. HIGH PRESSURE SETTLING OVER THE MIDWEST ON
WED WILL CUT OFF ANY SHOWERY ACTIVITY BUT STILL LIMIT HOW MILD
TEMPS WILL BE ABLE TO RECOVER...EVEN IF SUSPECTED CLOUD COVER FROM
CAA ON THIS DAY IS LACKING.
HIGHEST POPS WILL OCCUR MON WITH FROPA AND LINGER INTO TUES.
MODELERS ARE TAKING A MIDDLE OF THE ROAD APPROACH WITH THE
PLACEMENT OF THE VIGOROUS LOW ON DAYS 6-7 WITH GFS BEING THE CLOSEST
TO THE MIDDLE GROUND BETWEEN CANADIAN AND ECMWF...AND PREV ENSMEAN
FCSTS.
&&
.AVIATION /08Z THURSDAY THROUGH MONDAY/...
A COLD FRONT WAS CURRENTLY CROSSING THE TAF FORECAST REGION AT
AVIATION DISCUSSION ISSUANCE. CAA AND STRATOCUMULUS CLOUD DECK
WILL CONTINUE TO SPREAD SOUTH AND EAST ACRS THE REMAINDER OF THE
REGION. IT APPEARS THAT CIGS WILL STAY IN THE VFR CATEGORY UNTIL
ABOUT 14Z TO 15Z WHEN DIURNAL INSTABILITY WILL ALLOW CIGS TO DROP
INTO THE MVFR CATEGORY. COLD AIR CROSSING THE WARM WATERS OF THE
GREAT LAKES...COMBINED WITH AN APPROACHING UPPER LEVEL WEATHER
DISTURBANCE...WILL RESULT IN SCATTERED SNOW SHOWERS ACRS THE
REGION...MAINLY FROM THIS AFTERNOON INTO TONIGHT. CHANCES FOR
SNOW WILL RANGE IN THE 30 TO 40 PERCENT RANGE...TOO SMALL AT THIS
POINT TO PLACE IN THE TAFS. WILL CONTINUE WITH THE VCSH
DESCRIPTOR. WILL TRY TO ASCERTAIN ANY MESOSCALE FEATURES...SUCH AS
LAKE EFFECT SNOW BAND STREAMERS...IN THE NEXT TAF ISSUANCE WHICH
MAY ALLOW THE INTRODUCTION OF A TEMPO GROUP TO BE INCLUDED AT SOME
TAF SITES. SNOW SHOWERS...WHETHER THEY OCCUR AT THE TAF SITES OR
NOT...WILL BE CAPABLE OF LOWERING VSBYS INTO THE MVFR/IFR
CATEGORY AT TIMES.
OUTLOOK...MVFR CIGS EXPECTED INTO FRIDAY. MVFR CIGS/VSBYS POSSIBLE
DUE TO RAIN AND/OR SNOW SHOWERS MONDAY.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...NONE.
KY...NONE.
IN...NONE.
&&
$$
SYNOPSIS...RYAN
NEAR TERM...RYAN
SHORT TERM...RYAN
LONG TERM...FRANKS
AVIATION...HICKMAN
