791
FXUS63 KIWX 181949
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
349 PM EDT WED SEP 18 2019
SYNOPSIS
ISSUED AT 348 PM EDT WED SEP 18 2019
DRY AND WARM CONDITIONS WILL PERSIST INTO FRIDAY. CLOUDS WILL
BEGIN TO INCREASE ON SATURDAY, WITH SHOWERS AND THUNDERSTORMS
BECOMING LIKELY SATURDAY NIGHT THROUGH SUNDAY NIGHT. SOME LOCALLY
HEAVY RAINFALL IS POSSIBLE DURING THIS PERIOD. LOW TEMPERATURES
TONIGHT WILL DROP INTO THE MID AND UPPER 50S. HIGH TEMPERATURES ON
THURSDAY WILL REACH INTO THE LOW TO MID 80S.
SHORT TERM
(THIS EVENING THROUGH THURSDAY)
ISSUED AT 348 PM EDT WED SEP 18 2019
QUIET WEATHER TO CONTINUE IN THE SHORT TERM AS UPPER LEVEL RIDGING
ACROSS CENTRAL CONUS CONTINUES TO DOMINATE.
SEVERAL WEAK SHORT WAVES CONTINUE TO TOP THE UPPER RIDGE THIS
AFTERNOON, WITH DEEPER MOISTURE AND ONGOING CONVECTION LIMITED TO
CORN BELT. UPPER LEVEL WAVE PATTERN WILL NOT CHANGE SIGNIFICANTLY
OVER THE NEXT FEW DAYS WITH AFOREMENTIONED UPPER WAVES DOING VERY
LITTLE TO DAMPEN THE AMPLITUDE OF THE UPPER LEVEL RIDGE. DRY LOW
LEVELS SHOULD FAVOR ANOTHER NIGHT OF LARGE DIURNAL SWINGS AND LOW
TEMPERATURES BACK INTO THE MID-UPPER 50S.
FOR THURSDAY, NEXT WEAKER UPPER LEVEL SHORT WAVE ACROSS THE
CENTRAL ROCKIES WILL TOP THE RIDGE AND REACH THE WESTERN GREAT
LAKES REGION THURSDAY NIGHT. GUIDANCE CONTINUES TO INDICATE WEAK
WARM FRONTAL-LIKE FEATURE LIFTING NORTHWARD THURSDAY AFTERNOON
INTO THURSDAY EVENING MARKING THE BEGINNING OF A PERIOD OF
INCREASING LOW LEVEL MOISTURE TRANSPORT. STILL EXPECTING MOSTLY
SUNNY SKIES FOR THURSDAY GIVEN EXPECTATION OF CAPPING TO HOLD,
WITH JUST POSSIBLE INCREASING DIURNAL CU ACROSS THE SOUTH WHERE
BETTER DEW POINT RECOVERY IS EXPECTED ASSOCIATED WITH THE WARM
FRONT/WEAK SFC TROUGH FEATURE. DESPITE RELATIVELY SHALLOW MIXING
LIMITED TO AROUND 900 MB, MUCH ABOVE NORMAL TEMPERATURES ARE
EXPECTED THURSDAY GIVEN LOW LEVEL THERMAL PROGS AND GOOD
INSOLATION.
LONG TERM
(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 348 PM EDT WED SEP 18 2019
FOR THURSDAY NIGHT AND BEYOND FOCUS WILL SHIFT TO THE WEST AS
LONGWAVE EASTERN PACIFIC UPPER TROUGH BECOMES THE EVENTUAL MAIN
WEATHER PRODUCER BY LATER IN THE WEEKEND. INITIAL WEST-EAST
ORIENTED POOLED MOISTURE AXIS WILL LIFT NORTHWARD ACROSS GREAT
LAKES SATURDAY, WITH RENEWED STRONGER LOW LEVEL MOISTURE TRANSPORT
LIKELY HOLDING OFF FROM WEST TO EAST LATE SATURDAY AFTERNOON INTO
SATURDAY NIGHT. THIS MOISTURE TRANSPORT WILL BE ENHANCED BY
STRONGER SOUTHWESTERLY LOW LEVEL FLOW AND NORTHWARD ADVECTION OF
TROPICAL AIR MASS FROM THE LOWER MS VALLEY/GULF OF MEXICO REGION.
GUIDANCE CONTINUES TO INDICATE PWATS INCREASING INTO THE 1.75 TO 2
INCH RANGE LATER SATURDAY NIGHT AND WARM CLOUD DEPTHS RISING TO
AROUND 12K FEET. WITH LEAD SHORT WAVE KICKING NORTHEAST ACROSS THE
UPPER MS VALLEY AND THE ABOVE FACTORS, CONCERN EXISTS FOR SOME
LOCALLY HEAVY RAINFALL SATURDAY NIGHT INTO SUNDAY.
MAIN ITEM OF UNCERTAINTY IN THIS FORECAST DEALS WITH PHASING ISSUES
OF UPSTREAM FORCING, AND HOW QUICKLY LEAD SHORT WAVE PHASES WITH
ANOTHER NEGATIVE UPPER HEIGHT ANOMALY DROPPING ACROSS SOUTH
CENTRAL CANADA. IF BETTER PHASING CAN OCCUR AND SLOWER EVOLUTION
OF FORCING OCCURS, HEAVY RAIN THREAT WOULD EXTEND INTO LATE SUNDAY
OR SUNDAY NIGHT. BY LATER SUNDAY EXPECTING ANOMALOUS MOISTURE
AXIS TO START TO GET PINCHED OFF FROM LOWER LATITUDE CONNECTION AS
LARGE SCALE UPPER TROUGH WORKS ACROSS THE GREAT LAKES AND FLOW
STARTS TO BECOME MORE PARALLEL TO THE ASSOCIATED COLD FRONT. STILL
EARLY TO TALK ABOUT SEVERE POTENTIAL, AND STILL SOME QUESTION AS
TO HOW MUCH INSTABILITY CAN BE REALIZED GIVEN LIKELY MOIST
ADIABATIC MID LEVEL LAPSE RATES. IF SLOWER EVOLUTION IS REALIZED,
PERHAPS SOME LOW END SEVERE THREAT CANNOT BE RULED OUT SUNDAY
GIVEN INCREASING SHEAR PROFILES, BUT HYDRO AND RAIN AMOUNTS WILL
LIKELY BE THE MAIN CONCERN WITH THIS SYSTEM. ANTECEDENT CONDITIONS
ARE QUITE DRY ACROSS MOST AREAS, WHICH COULD LIMIT OVERALL FLOOD
THREAT. WILL NEED TO WATCH THIS PERIOD OVER THE NEXT FEW DAYS
HOWEVER, GIVEN SUCH ANOMALOUS MOISTURE ADVECTING INTO THE REGION.
FRONT SHOULD SLOW OR STALL JUST SOUTH OF THE AREA FOR EARLY NEXT
WEEK WHICH COULD MAKE REGION SUSCEPTIBLE TO SOME ADDITIONAL
CHANCES OF RAIN BY THE TUE-WED PERIOD WITH TEMPERATURES CLOSER TO
SEASONAL NORMS.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 119 PM EDT WED SEP 18 2019
HIGH PRESSURE OVER THE REGION WILL RESULT IN VFR CONDITIONS AND
LIGHT ESE WINDS FOR THE DURATION OF THE 18Z TAF CYCLE.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
SYNOPSIS...MARSILI
SHORT TERM...MARSILI
LONG TERM...MARSILI
AVIATION...MF
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