000
FXUS63 KIWX 172302
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
658 PM EDT SAT MAY 17 2008
.SHORT TERM...
TONIGHT THROUGH SUNDAY NIGHT
DISTURBED UPPER LEVEL FLOW WILL CONTINUE TO SUPPORT THE PROPAGATION
OF NUMEROUS MID LEVEL DISTURBANCES THROUGH THE REGION. CURRENT SAT
AND RADAR ANALYSIS CONFIRMS AN EXITING DISTURBANCE OVER SE
MI...SUPPORTING SCATTERED SHOWERS THERE IN CONJUNCTION WITH A WEAK
SFC TROUGH. FARTHER UPSTREAM...VWP AND MODEL ANALYSIS REVEALS
A POTENT JET STREAK PUSHING INTO THE UPPER MIDWEST. ASSOCIATED LIFT
FROM THIS FEATURE ON THE LEFT EXIT REGION IN COUPLED WITH SHARP MID
LEVEL COOLING IS CONTINUING TO SUPPORT THE DEVELOPMENT OF NUMEROUS
SHRA/TS ACROSS PORTIONS OF MN AND WESTERN WI. THIS SYSTEM WILL DIVE
SE AND AFFECT THE FA TONIGHT. OTHERWISE...TEMPERATURES AS OF 18Z
EXHIBITED A LARGE SPREAD ACROSS THE FA WITH MID 70S SW TO LOWER 50S
NEAR LK MI. IN FACT...THE STABLE LAKE LAYER/DOME IS SO DOMINANT THAT
WINDS WERE GENERALLY LIGHT NORTHWESTERLY WITH 5 KNOTS BEING REPORTED
AT A SHORELINE SITE SOUTH OF BEH. UTILIZED THE SREF/NGM/AND GFS FOR
THE SHORT TERM FORECAST. THE NAM12 SEEMS TO BEING SUFFERING FROM
CONVECTIVE FEEDBACK AS INDICATED BY ITS OVERLY INTENSE SFC-H85 WINDS
PER CONVECTION THIS EVENING. LL PV FIELDS CONFIRM THIS. SURPRISINGLY
THE NGM IS THE PREFERRED MODEL OF CHOICE...AS ITS TIMING AND
SYNOPTIC
FIELDS LOOK WELL PORTRAYED.
TONIGHT...ISOLATED SHOWER ACTIVITY OVER NE ZONES WILL QUICKLY
DIMINISH EARLY THIS EVENING. SYSTEM UPSTREAM WILL QUICKLY ADVANCE
TOWARD THE REGION THIS EVENING. GFS/SREF/AND NGM ALL INDICATE RATHER
IMPRESSIVE QPF NUMBERS GIVEN LITTLE MOISTURE TO WORK
WITH...ESPECIALLY THE NGM WHICH EXHIBITS THE DRIEST COLUMN.
HOWEVER...THE LEFT EXIT REGION OF AN INTENSE JET STREAK IN
CONJUNCTION WITH A POTENT MID LEVEL IMPULSE /WITH OMEGA OF NEARLY 20
MBAR/S AT H7/ WILL SUPPORT RATHER INTENSE LIFT. IN ADDITION...THE
NEARLY 125 KNOT UPPER LEVEL JET WILL MOST LIKELY AID IN THE
INTENSIFICATION OF MOISTURE CONVERGENCE VIA INDUCED LL SOUTHERLY
FLOW...WHICH WILL ALSO LEAD TO INCREASED CONVERGENCE AROUND
H925-H85. HAVE RAISED POPS TO 50 FOR THIS. PROGGED NEGATIVE
SHOWALTER VALUES WITH MID LEVEL COOLING WILL ALSO SUPPORT ISOLATED
THUNDER GIVEN STAUNCH LIFT.
SUNDAY...MID LEVEL CLOUDS WILL CLEAR BY MID MORNING.
HOWEVER...ADVANCING -20 TO -25 C H5 COLD POOL UNDER CYCLONIC FLOW
WITH EMBEDDED SPEED MAXIMA WILL SUPPORT RAPID CU GROWTH BY LATE
MORNING...LENDING TO SCT-BKN CONDITIONS BY AFTERNOON WITH SHOWERS
POSSIBLE SAVE AREAS NEAR LAKE MI...WHERE A LAKE SHADOW IS EXPECTED
ONCE AGAIN...SIMILAR TO CONDITIONS OVER MB AND UPPER MI. CAA BEHIND
THE SFC TROUGH WITH H85 TEMPS PLUNGING TO AROUND 0C...6 TO 7
DEGREES LESS THAN TODAY WILL ALLOW FOR MUCH COOLER CONDITIONS. HAVE
OPTED FOR A MIX TO H85 WHICH PROGS HIGHS IN THE MID 50S. HIGHS MAY
BE OPTIMISTIC IF BKN SKY COVER BECOMES DOMINANT AWAY FROM LAKE MI.
HAVE NOT ADDED SLIGHT THUNDER WORDING WITH LI/S PROGGED NEAR
ZERO...GIVEN QUESTIONS ON INSOLATION.
SUNDAY NIGHT...LOOK FOR CLEARING SKIES THROUGH THE EVENING...WITH
MOSTLY CLEAR SKIES EXPECTED BY MIDNIGHT. FROST MAY BE A CONCERN
GIVEN
DRY AIR ADVECTING INTO THE FA WITH DEWPOINTS FALLING TO THE LOWER
30S AND MOS PROGGING LOWS IN THE MID 30S AT MANY LOCATIONS. HAVE
LEFT FROST OUT OF THE FORECAST FOR NOW GIVEN CONCERNS ON WINDS. HIGH
PRESSURE WILL STILL BE NW OF THE FA THROUGH THE NIGHT SUPPORTING AN
ISSALOBARIC GRADIENT INTO THE FA. SFC PRESSURE GRADIENT STILL LOOKS
TO BE TOO STRONG FOR FULL DECOUPLING AT THIS TIME. WILL LET LATER
SHIFTS MONITOR AND UPDATE AS NECESSARY.
&&
.LONG TERM...
MONDAY THROUGH SATURDAY...A WEAK UPPER LEVEL TROF WILL ROTATE AROUND
THE MAIN UPPER LOW AND MOVE INTO THE WESTERN GREAT LAKES BY
TUESDAY. HAVE ADJUSTED THE RAIN CHANCES SLIGHTLY WITH THIS
SYSTEM...BUT STILL KEPT A CHANCE FOR RAIN MONDAY NIGHT AND TUESDAY.
THE DYNAMICS WITH THIS SYSTEM ARE NOT IMPRESSIVE AND MOISTURE IS
LIMITED...SO EXPECT PRECIPITATION AMOUNTS SHOULD BE RELATIVELY
LIGHT. FOR THE REST OF THE PERIOD...A CANADIAN VORTEX WILL CONTINUE
OVER THE HUDSON BAY REGION. THERE WILL BE A LARGE SURFACE
ANTICYCLONE ASSOCIATED WITH THIS SYSTEM...HELPING TO KEEP THE FLOW
AT THE SURFACE NORTH TO EAST. THE UPPER LEVEL LOW WILL BE PART OF A
LARGE BLOCK IN THE ATMOSPHERE KNOWN AS AN OMEGA BLOCK AS ANOTHER
DEEP UPPER LOW DEVELOPS OVER THE WESTERN CONUS WITH A STRENGTHENING
UPPER RIDGE BETWEEN THEM. THE GFS AND ECMWF HAVE HAD SIGNIFICANT
DIFFICULTY IN HANDLING THIS BLOCKING PATTERN. PREFER THE GFS
HANDLING OF THE PATTERN FOR NEXT WEEK OVER THE ECMWF GIVEN RECENT
MODEL PERFORMANCE...BUT WITH SOME RESERVATIONS. THE ECMWF WAS TOO
ROBUST IN BUILDING THE UPPER RIDGE EAST IN PREVIOUS RUNS WHILE THE
GFS WAS NOT AS EXTREME IN BUILDING THE RIDGE EAST. AT THE SAME
TIME...FOR SOME PREVIOUS RUNS...THE GFS STARTED OUT WITH A COOL
SOLUTION FOR MID WEEK OVER THE WESTERN GREAT LAKES...BUT TRENDED
WARMER. HOWEVER...THE MOST RECENT GFS RUNS HAVE RETURNED BACK TO THE
ORIGINAL COOLER PATTERN FOR THE MIDDLE OF THE UPCOMING WEEK. FOR
THIS PACKAGE...KEPT TEMPERATURES THROUGH THURSDAY BELOW NORMAL AS
CHILLY AIR FROM CANADA SPREADS ACROSS SOUTHEASTERN CANADA INTO THE
FORECAST AREA. KEPT A CHANCE FOR THUNDER THURSDAY AND FRIDAY ONLY
OVER WESTERN AREAS...THEN DRY.
&&
.AVIATION.../00Z TAFS/
SHRTWV OVER LS/MN EXPECTED TO MOVE S-SE AND CROSS NRN INDIANA
09Z-12Z. SHOWERS OVER WI/MN IN ADVANCE OF THE SHRTWV LIKELY TO
PERSIST OVERNIGHT AS WK INSTABILITY DUE TO VERY COLD TEMPS ALOFT
OVERSPREADS THE AREA. ALTHOUGH CIGS WILL LOWER AS SHOWERS MOVE
THROUGH THE AREA... LOW LEVELS EXPECTED TO REMAIN DRY ENOUGH FOR
VFR CONDITIONS TO CONT. SOME DECREASE IN CLOUDINESS MAY OCCUR BEHIND
THIS SHRTWV TOWARD DAYBREAK... HWVR... CU EXPECTED TO FORM RAPIDLY
SUNDAY MORNING WITH DIURNAL SFC HEATING AND VERY COLD AIR ALOFT. NW
WINDS WILL AGAIN STABILIZE AREAS DOWNWIND OF LAKE MICHIGAN ON
SUNDAY... HOWEVER...INSTABILITY MAY BE SUFFICIENT FOR SHOWERS TO
DEVELOP WELL INLAND BY AFTN WHICH COULD AFFECT FWA.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SHORT TERM...CHAMBERLAIN
LONG TERM...SKIPPER
AVIATION...JT
