339
FXUS63 KIWX 130820
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
420 AM EDT TUE AUG 13 2013
.SYNOPSIS...
ISSUED AT 140 AM EDT TUE AUG 13 2013
LARGE CANADIAN HIGH PRESSURE SYSTEM...BUILDING IN BEHIND EXITING
COLD FRONT...WILL BRING COOL AND DRY CONDITIONS FOR THE REST OF THE
WEEK.
&&
.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 420 AM EDT TUE AUG 13 2013
INITIAL SURFACE COLD FRONT AND ATTENDANT LINE OF THUNDERSTORMS
CLEARED OUR CWA AND DISSIPATED SEVERAL HOURS AGO. THERE IS HOWEVER A
SECONDARY COLD FRONT...ASSOCIATED WITH A SHARP VORT MAX CURRENTLY
PINWHEELING ACROSS THE CENTRAL GREAT LAKES...THAT WILL CROSS OUR
AREA DURING THE MORNING HOURS. NO ADDITIONAL PRECIP IS EXPECTED BUT
THIS COLD FRONT WILL MARK THE ARRIVAL OF MUCH COOLER AND DRIER
CANADIAN AIRMASS. STRONG CAA WILL SEND 850MB TEMPS CRASHING WELL
INTO THE SINGLE DIGITS TODAY. 00Z GFS HAS 850MB TEMPS DROPPING TO 5C
IN SOUTHERN LOWER MICHIGAN...WHICH IS ROUGHLY 2SD BELOW NORMAL BASED
ON KDTX UPPER AIR CLIMATOLOGY...AND MAY NOT BE FAR OFF BASED ON
UPSTREAM CANADIAN SOUNDINGS. THERMAL PROFILES WONT BE QUITE THAT
COLD FOR OUR CWA...AND IT WILL TAKE MOST OF THE DAY FOR THE COLDEST
AIR TO FULLY INFILTRATE OUR SOUTHEASTERN ZONES...BUT WILL STILL BE A
FAIRLY COOL DAY. MIXING DOWN 6-8C 850MB TEMPS YIELDS UPPER 60S TO
LOW 70S AT BEST. AUGUST SUN ANGLE IS STILL FAIRLY HIGH BUT COLD
850MB TEMPS AND SOME RESIDUAL BOUNDARY LAYER MOISTURE WILL PROBABLY
LEAD TO A DECENT AFTERNOON CU/STRATOCU DECK. COULD EVEN BE A STRAY
SPRINKLE IN OUR NORTHEAST GIVEN PASSING VORT MAX AND MIDLEVEL COLD
POOL BUT FORECAST SOUNDINGS SHOW A VERY STRONG SUBSIDENCE INVERSION
AND EXCEPTIONALLY DRY MIDLEVELS SO WILL LEAVE POPS AT OR BELOW 10
PERCENT. GIVEN COLD AIRMASS...EXPECTED CLOUDS...AND COOLER MOS
GUIDANCE...HAVE CUT FORECASTED HIGHS A BIT WITH UPPER 60S/LOW 70S
EXPECTED. VERY CHILLY NIGHT IN STORE FOR THE AREA TONIGHT. THERMAL
TROUGH WILL BE DIRECTLY OVERHEAD WITH LIGHT NORTHERLY WINDS
PROMOTING EFFECTIVE BOUNDARY LAYER DECOUPLING. ONLY POTENTIAL
LIMITING FACTOR WILL BE POSSIBLE CLOUD COVER SEEN IN BOTH THE GFS
AND NAM RH FIELDS/BUFR SOUNDINGS ACROSS THE WEST. THIS INCREASED
SATURATION SEEMS TO BE THE RESULT OF ANOTHER WEAK PASSING SHORTWAVE
WITH SOME LAKE INDUCED INSTABILITY/MOISTURE FLUX FROM LAKES SUPERIOR
AND MICHIGAN. 850MB TEMP DIFFERENTIALS ARE GOOD BUT SUBSIDENCE
INVERSION AND DRY AIR ENTRAINMENT SHOULD PREVENT ANY LAKE EFFECT
RAIN SHOWERS FROM DEVELOPING. THIS LAKE INDUCED STRATOCU WOULD
HOWEVER KEEP A BIT OF A FLOOR ON OVERNIGHT LOWS IN THE WEST WITH
VALUES LIKELY HOLDING AROUND 50F. STILL EXPECT INTERIOR SECTIONS TO
DROP INTO THE MID TO UPPER 40S THOUGH WITH A FEW ISOLATED LOW 40S
POSSIBLE IF IDEAL CLEAR SKIES AND CALM WINDS MATERIALIZE.
&&
.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 420 AM EDT TUE AUG 13 2013
LITTLE SUBSTANTIVE CHANGE IN TRANQUIL LONG TERM FORECAST PERIOD.
GREAT CONSENSUS WITH RESPECT TO STRENGTHENING SURFACE HIGH CENTROID
ACROSS NORTHEASTERN WISCONSIN BY F36 TO ASSERT STAIDNESS OF THERMAL
TROF WED/WED NIGHT. IDEAL RADIATIONAL COOLING EFFECTS TO PRESENT
EXTREMELY STEEP EARLY AM SURFACE INVERSION AS WELL AS PERVASIVE
SUBSIDENCE INVERSION BASED NEAR 850MB ANTICIPATED WED AM THROUGH FRI
AM...TO RETARD THERMAL MODERATION. UNSEASONABLE NATURE OF COLD/DRY
AIR EXEMPLIFIED BY SIGNIFICANTLY GREATER THAN M2SD 8H TEMPERATURES
WITH PWAT NEAR M2SD/APPROX 10TH PERCENTILE. AGAIN SLIGHTEST OF NUDGE
DOWNWARD IN TEMPS WED/WED NIGHT PER ABOVE AND IN LINE WITH CONTINUED
COOLER TREND OF RECENT MEX/ENSEMBLE MOS GUIDANCE. BLEED FROM BLEND
NOTED AGAIN ALONG LAKESHORE...AND HAVE SQUELCHED EXCEPT FOR WED WITH
AMBIENT NORTHERLY COMPONENT FLOW. OTHERWISE LAKE/LAND DIFFERENTIALS
DO NOT FAVOR LAKE BREEZE COMPONENT BENEATH SURFACE RIDGE SPRAWLING
E-W THROUGH SOUTHERN GREAT LAKES BY THIS WEEKEND. GREATER LIKELIHOOD
OF NOCTURNAL DOWNSLOPE/LAND BREEZE/COLD AIR DRAINAGE WIND AND HAVE
SHARPLY LOWERED MINIMUMS ALONG LAKE/LAND INTERFACE. GRADUAL MOISTURE
RETURN AND BREAKDOWN OF UPSTREAM RIDGE/REEMERGENCE OF WESTERN GREAT
LAKES/MID MISSISSIPPI VALLEY TROF...POSSIBLY CUTTING OFF NEAR MOUTH
OF OHIO RIVER BY 12 UTC SUN. GIVEN A BIT GREATER LONGEVITY NOW SEEN
TO WESTERN FLANK OF RIDGE HAVE SQUELCHED SHRA/TSRA MENTION THROUGH
SUNDAY. THEREAFTER...CONTINUED MINOR CHANCE POPS WITH LESSER CHC
FOCUS FOR TSRA ACROSS SOUTHERN/SOUTHEAST CWA. RETROGRESSION OF
ATLANTIC SUBTROPICAL RIDGE SHOULD AID IN EASTWARD EXODUS THROUGH
SOUTHERN OHIO BY DY8...CONTINGENT ON LACK OF SIGNIFICANT
CARIBBEAN/TROPICAL DEVELOPMENT THAT COULD SLOW SYSTEM ADVANCE.
&&
.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 140 AM EDT TUE AUG 13 2013
COLD FRONT HAS CLEARED THE AREA WITH ALL SHOWERS AND THUNDERSTORMS
HAVING DISSIPATED OR SHIFTED EASTWARD. QUICK SHOT OF CAA BEHIND
THIS FRONT HAS INTERACTED WITH WET SOIL CONDITIONS TO PRODUCE SOME
PATCHY FOG ACROSS THE AREA. ANY SIGNIFICANT REDUCTIONS TO
VISIBILITY SHOULD REMAIN BRIEF GIVEN APPROACH OF SECONDARY COLD
FRONT AND STEADY NORTHWEST WINDS BUT PERIODS OF MVFR BR WILL BE
POSSIBLE THROUGH SUNRISE. CAA WILL LIKELY PROMOTE A HEALTHY
CU/STRATOCU DECK THIS AFTERNOON BUT CEILINGS ARE EXPECTED TO
REMAIN IN VFR CATEGORY. GUSTY NORTHWEST WINDS WILL ALSO BE
POSSIBLE BEHIND EXITING FRONT THIS AFTERNOON.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...BEACH HAZARDS STATEMENT THROUGH LATE TONIGHT FOR INZ003.
MI...BEACH HAZARDS STATEMENT THROUGH LATE TONIGHT FOR MIZ077.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 5 AM EDT WEDNESDAY FOR LMZ043-046.
&&
$$
SYNOPSIS...AGD
SHORT TERM...AGD
LONG TERM...MURPHY
AVIATION...AGD
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