AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
356 PM EDT SAT MAY 25 2013
.SYNOPSIS...
ISSUED AT 1040 AM EDT SAT MAY 25 2013
HIGH PRESSURE OVER THE GREAT LAKES AND OHIO VALLEY WILL MOVE
SLOWLY EAST THIS WEEKEND. MORE WIDESPREAD SHOWER AND
THUNDERSTORM ACTIVITY IS EXPECTED TO REMAIN WEST OF THE AREA.
HOWEVER...A FEW SHOWERS FORMING NEAR A WARM FRONT MOVING SLOWLY
NORTH THROUGH THE PLAINS MAY MAKE IT AS FAR EAST AS INDIANA BEFORE
DISSIPATING TODAY AND TONIGHT. BETTER CHANCES FOR RAINFALL WILL
ARRIVE SUNDAY NIGHT INTO MONDAY.
&&
.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 350 PM EDT SAT MAY 25 2013
LATEST SYNOPTIC PATTERN SHOWS BROAD UPPER LEVEL RIDGING ACROSS THE
CENTRAL CONUS WITH SFC HIGH PRESSURE ANCHORED OVER JAMES BAY SOUTH
THROUGH THE GREAT LAKES REGION. NAM ISENTROPIC ANALYSIS SHOWS DECENT
LIFT ALONG THE APEX OF THE CONUS RIDGE...WITH 850MB Theta-e VALUES
OF 320K SURGING NORTHEAST THROUGH IOWA AND MISSOURI INTO EASTERN
ILLINOIS. LATEST RADAR IMAGERY SHOWING ONGOING PRECIPITATION AT THE
PERIPHERY OF THIS LIFT...AIDED BY WEAK DISTURBANCES ADVECTING
DOWNSTREAM THE NORTHWEST FLOW. MAIN FORECAST CHALLENGE FOR THIS
AFTERNOON THROUGH TONIGHT WILL BE PRECIPITATION CHANCES ACROSS
SOUTHWESTERN AREAS AS A STRONGER DISTURBANCE EJECTS TOWARD THE AREA.
POTENT S/W ACROSS EASTERN IOWA WILL ADVECT TOWARD THE AREA INTO THE
OVERNIGHT HOURS. LATEST MODEL RUNS TRACK THIS WAVE ACROSS THE FAR
SOUTHWEST AFTER 00Z. MAIN FORECAST CHALLENGE IS THE EXTENT OF
PRECIPITATION WITH THIS DISTURBANCE GIVEN MANY MITIGATING FACTORS.
FIRST...ISENTROPIC ASCENT AND Theta-e SURGE WILL LAG BEHIND THE
WAVE...NOT ADVECTING INTO THE AREA UNTIL LATER ON SUNDAY.
ALSO...BOUNDARY LAYER EXTREMELY DRY ACROSS THE AREA...WITH ANY
SEMBLANCE OF SURFACE MOISTURE SOUTHEAST INTO MISSOURI. SFC HIGH AND
DRY NORTHERLY FLOW...WITH DEWPOINTS IN THE UPPER 30S TO MID 40S THIS
AFTERNOON ACROSS THE AREA SHOULD INHIBIT PRECIPITATION REACHING THE
GROUND. THEREFORE KEPT MAINLY SLIGHT CHANCE TO VERY LOW CHANCE POPS
AND LITTLE TO NO QPF IN THE REST OF THE AFTERNOON THROUGH TONIGHT.
NO MAJOR CHANGES TO LOWS OVERNIGHT...AS EXPECTED CLOUD COVER SHOULD
KEEP LOWS ABOVE LATEST GUIDANCE/MOS VALUES.
SIMILAR FORECAST CHALLENGES ON SUNDAY...AS ANOTHER SHORTWAVE
CURRENTLY ACROSS NE WY/SE MT ADVECTS TOWARD THE REGION. AS STATED
BEFORE...NAM 320K Theta-e PUSHES INTO THE FAR SOUTHWEST CWA BY
TOMORROW AFTERNOON. MODELS DOING A POOR JOB HANDLING EVOLUTION AND
TRACK OF THIS WAVE. SETTLED ON A SREF/ECMWF COMPROMISE FOR GENERAL
TRACK OF WAVE. LIMITED POPS TO SOUTHWEST AREAS...AND KEPT MAX POPS
IN THE 40 PERCENT RANGE THROUGH 18Z...50 PERCENT IN THE AFTERNOON.
INTRODUCED SLIGHT CHANCE OF THUNDERSTORMS ACROSS FAR SOUTHWEST AREAS
TOMORROW AFTERNOON...AS NEGATIVE 850MB SHOWALTER VALUES CLIP THE FAR
SW CWA. LOWERED TEMPS A TOUCH...MAINLY ACROSS SOUTHWEST AREAS WHERE
CLOUD COVER AND POSSIBLE PRECIP SHOULD PERSIST THROUGH THE DAY.
&&
.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 350 PM EDT SAT MAY 25 2013
OVERALL NO SIGNIFICANT CHANGES MADE TO THE PREVIOUS FORECAST.
STABLE/BLOCKING WAVE PATTERN WHICH HAS CHARACTERIZED EASTERN CONUS
WILL BEGIN TO BREAK DOWN THE LATTER PARTS OF THIS WEEKEND AS
NEGATIVE UPPER HEIGHT ANOMALY ACROSS NEW ENGLAND PHASES WITH EASTERN
CANADIAN UPPER TROUGH. THIS WILL RESULT IN MORE PROGRESSION OF
CENTRAL CONUS RIDGING WHICH WILL ALLOW ZONE OF LOW/MID LEVEL THETAE
ADVECTION TO SHIFT ACROSS THE SOUTHERN GREAT LAKES AND OHIO RIVER
VALLEY. WHILE DETAILS IN TIMING AND PLACEMENT HAVE VARIED FROM TO
RUN TO RUN WITH SMALLER SCALE CONVECTIVELY ENHANCED VORTS WORKING
THROUGH THIS DEAMPLIFYING UPPER RIDGE...GUIDANCE HAS BEEN FAIRLY
CONSISTENT IN HIGHLIGHTING MORE PRONOUNCED SHORT WAVE/CONVECTIVE
VORT MAX PROGRESSING THROUGH THE RIDGE INTO THE LOCAL AREA FOR THE
SUNDAY NIGHT TIMEFRAME. THIS SHORT WAVE WILL BE ASSOCIATED WITH WEST
TO EAST ADVANCING LOW/MID LEVEL POSITIVE THETAE ADVECTION WITH SOME
WEAK ELEVATED INSTABILITY DEVELOPING ACROSS ACROSS SOUTHWEST HALF OF
FORECAST AREA SUNDAY NIGHT. THUNDER PROBS STILL REMAIN QUITE LOW
GIVEN WEAK AND ELEVATED NATURE TO INSTABILITY AND ONLY CHANGE TO
PREVIOUS FORECAST WAS TO SHARPEN THE POP GRADIENT FROM SOUTHWEST TO
NORTHEAST WITH AREAS ACROSS FAR NORTHEAST HANGING ONTO FAIRLY DRY
LOW LEVEL AIR MASS THROUGH MUCH OF SUNDAY NIGHT.
SHORT WAVE SHOULD DAMPEN AS IT TRACKS EAST ACROSS GREAT LAKES
MONDAY...BUT WEAK TO MODERATE LOW LEVEL FGEN RESPONSE AND INCREASING
LOW LEVEL MOISTURE/LOWER BASED INSTABILITY SHOULD COMBINE WITH THIS
MID/UPPER FORCING FOR SCATTERED TO NUMEROUS SHOWERS WITH SOME
EMBEDDED THUNDER MONDAY. PREVIOUS FORECAST SEEMS TO HAVE THIS TREND
WELL IN HAND WITH MAIN ITEM OF LOWER CONFIDENCE IN HOW WIDESPREAD
PRECIP WILL BE ACROSS FAR NORTHEAST SECTIONS WHERE HAVE MAINTAINED
CHANCE MENTION.
TREND TO SUMMERLIKE CONDITIONS STILL APPEARS TO BE ON TRACK FOR
TUESDAY-FRIDAY WITH LOCAL AREA GETTING MORE FIRMLY ENTRENCHED IN
WARM SECTOR BY MID WEEK. SOUTH/SOUTHWEST LOW LEVEL FLOW WILL PROVIDE
SOME CHALLENGE FOR LAKE MICHIGAN SHORELINE TEMPERATURES...AND MAY
EVENTUALLY NEED TO ADJUST SOUTHWEST LOWER MICHIGAN LAKESHORE TEMPS
UP FOR THIS PERIOD. OTHERWISE...HAVE MAINTAINED LOWER TO MID 80S
THROUGH MUCH OF THE PERIOD. HAVE ALSO KEPT LOW CHANCE TSRA FOR
TUESDAY MAINLY ACROSS THE NORTH WHERE CAPPING MAY BE WEAKER
INITIALLY...AND GIVEN PREFERENCE TO EC/GEM ON A BIT MORE AMPLITUDE
WITH NEXT WAVE LIFTING INTO GREAT LAKES IN SOUTHWEST UPPER FLOW.
PROSPECTS FOR ANY ADDITIONAL PRECIP CHANCES LIKELY TO BE DELAYED
UNTIL NEXT WEEKEND WHEN LARGE SCALE WESTERN CONUS TROUGH LIFTS INTO
THE UPPER MIDWEST AND DAMPENS UPPER RIDGE.
&&
.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 110 PM EDT SAT MAY 25 2013
VFR CONDITIONS EXPECTED THROUGH THE FORECAST PERIOD WITH HIGH
PRESSURE ANCHORED OVER THE GREAT LAKES REGION. MID/HIGH CLOUD
COVER WILL INCREASE AT TERMINALS EARLY THIS AFTERNOON DUE TO
UPSTREAM CONVECTION...WHICH SHOULD STAY WELL SOUTHWEST OF THE
TERMINALS THROUGH THE PERIOD. NORTHERLY FLOW WILL VEER EASTERLY BY
03Z SUNDAY.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SYNOPSIS...FISHER
SHORT TERM...NG
LONG TERM...MARSILI
AVIATION...NG
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