Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 232339
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
639 PM CDT SAT MAY 23 2015

.SHORT TERM...(TONIGHT)
ISSUED AT 255 PM CDT SAT MAY 23 2015

HIGH PRESSURE CENTERED OVER WEST VIRGINIA WILL CONTROL THE WEATHER
ACROSS CENTRAL ILLINOIS TONIGHT...KEEPING RAIN CHANCES LARGELY AT
BAY UNTIL SUNDAY.  19Z/2PM OBSERVATIONS CONTINUE TO SHOW AN EASTERLY
COMPONENT TO THE LOW-LEVEL FLOW AROUND THE HIGH...WHICH IS KEEPING A
DRY AIRMASS IN PLACE.  SURFACE DEWPOINTS ARE MAINLY IN THE 40S THIS
AFTERNOON...AND WILL REMAIN LOW UNTIL WINDS VEER TO THE
SOUTH/SOUTHWEST AND ALLOW A MORE HUMID AIRMASS CURRENTLY POISED
UPSTREAM ACROSS MISSOURI TO SURGE NORTHWARD ON SUNDAY.  UNTIL THAT
TIME...A PRONOUNCED DRY LAYER WILL PERSIST BELOW 850MB.  AS A
RESULT...ANY SHOWERS THAT DEVELOP TO THE W/SW THIS AFTERNOON AND TRY
TO LIFT INTO WEST-CENTRAL ILLINOIS WILL LIKELY EVAPORATE.  HRRR
SHOWS THIS TREND QUITE WELL...WITH LITTLE MORE THAN SPRINKLES
SPREADING INTO THE ILLINOIS RIVER VALLEY FROM LATE EVENING INTO THE
OVERNIGHT HOURS.  HAVE THEREFORE MAINTAINED A DRY FORECAST THROUGH
MIDNIGHT...WITH JUST A SLIGHT CHANCE FOR SHOWERS WEST OF I-55 LATE
TONIGHT TOWARD DAWN SUNDAY.  DUE TO THE CLOUD COVER AND A
SOUTHEASTERLY BREEZE...OVERNIGHT LOW TEMPERATURES WILL ONLY DROP
INTO THE UPPER 50S AND LOWER 60S.

.LONG TERM...(SUNDAY THROUGH SATURDAY)
ISSUED AT 255 PM CDT SAT MAY 23 2015

RAIN CHANCES WILL BEGIN TO INCREASE ON SUNDAY...AS WESTERN CONUS
UPPER LOW GRADUALLY LIFTS TOWARD THE NORTHERN PLAINS.  WIDESPREAD
CONVECTION AHEAD OF THIS SYSTEM ACROSS OKLAHOMA/TEXAS TONIGHT INTO
EARLY SUNDAY MAY TEND TO BLOCK THE NORTHWARD FLOW OF DEEP MOISTURE
INTO THE MIDWEST.  AS A RESULT...ONLY SCATTERED CONVECTION IS
EXPECTED TO DEVELOP ACROSS CENTRAL ILLINOIS.  WILL RAISE POPS TO
LIKELY ACROSS THE ILLINOIS RIVER VALLEY BY AFTERNOON...BUT WILL ONLY
FEATURE SLIGHT CHANCE POPS ALONG/EAST OF I-57.

BEST BET AT WIDESPREAD RAINFALL IS STILL ON TRACK FOR SUNDAY NIGHT
INTO MONDAY...AS MOISTURE PLUME AHEAD OF THE ADVANCING LOW SHIFTS
EASTWARD INTO ILLINOIS.  SHOWERS AND THUNDERSTORMS WILL BECOME
LIKELY ACROSS THE BOARD SUNDAY NIGHT...BUT WILL SHIFT EASTWARD A BIT
MORE QUICKLY ON MONDAY THAN PREVIOUSLY FORECAST...AS PER 12Z MAY 23
MODELS.  NAM/GFS/ECMWF ALL SHOW PRECIP ACROSS THE AREA MONDAY
MORNING...THEN QUICKLY PUSH IT EASTWARD INTO INDIANA DURING THE
AFTERNOON.  WITH PRECIP ENDING FROM WEST TO EAST AND SKIES BECOMING
PARTLY SUNNY...ATMOSPHERE WILL BECOME MODERATELY UNSTABLE BY MONDAY
AFTERNOON/EVENING.  NAM SBCAPE VALUES CLIMB ABOVE 2000J/KG: HOWEVER,
WEAK 0-6KM BULK SHEAR OF ONLY 20-25KT AND A LACK OF STRONG SYNOPTIC
FORCING SHOULD LEAD TO A MOSTLY DRY AFTERNOON AND EVENING.  STILL
NEED TO WATCH OUT FOR ANY POTENTIAL MESOSCALE BOUNDARIES LEFT BEHIND
BY EARLY DAY CONVECTION...AS ADDITIONAL STORMS COULD CERTAINLY FIRE
IN THE UNSTABLE ENVIRONMENT.  AT THIS POINT...NO MODEL IS SHOWING
THIS SOLUTION...SO WILL GO WITH A DRY PERIOD MONDAY
AFTERNOON/EVENING.

VIGOROUS SHORT-WAVE TROUGH EVIDENT ON LATEST WATER VAPOR IMAGERY
OVER NORTHERN CALIFORNIA WILL ROUND THE BASE OF THE WESTERN CONUS
TROUGH AND LIFT INTO ILLINOIS ON TUESDAY.  MODELS ARE IN RELATIVELY
GOOD AGREEMENT WITH THE SPEED/TIMING OF THIS FEATURE...WITH THE GFS
BEING SLIGHTLY FASTER THAN THE ECMWF. GIVEN THE ARRIVAL OF STRONGER
LIFT ASSOCIATED WITH THE WAVE...HAVE BROUGHT POPS BACK INTO THE
PICTURE LATE MONDAY NIGHT...THEN HAVE GONE WITH LIKELY POPS
EVERYWHERE ON TUESDAY.

ONCE THE WAVE PASSES...THE REMAINDER OF THE WEEK WILL BE VERY WARM
AND HUMID WITH NO ORGANIZED CONVECTION.  WILL MAINTAIN SLIGHT/LOW
CHANCE POPS WEDNESDAY THROUGH FRIDAY IN CASE A SUBTLE WAVE NOT
CURRENTLY PICKED UP BY SYNOPTIC MODELS RIPPLES THROUGH THE AREA
WITHIN THE BROAD SOUTHWESTERLY FLOW PATTERN.  BETTER CHANCES FOR
RAIN WILL LIKELY HOLD OFF UNTIL NEXT WEEKEND...WHEN BOTH THE GFS AND
ECMWF SHOW A MORE SIGNIFICANT NORTHERN-STREAM WAVE PUSHING A FRONTAL
BOUNDARY INTO ILLINOIS BY NEXT SATURDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 639 PM CDT SAT MAY 23 2015

VFR CONDITIONS EXPECTED UNTIL AROUND 18Z...THEN SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS WILL SPREAD EASTWARD ACROSS CENTRAL IL
PRODUCING POTENTIAL FOR ISOLATED MVFR OR WORSE CIGS/VSBY. SPATIO-
TEMPORAL DETAILS OF SUB-VFR CONDITIONS ARE UNCERTAIN AT THIS TIME
AND COVERAGE LOOKS TO BE NON-PREDOMINANT...SO HAVE INCORPORATED
VCSH/VCTS WITH SCATTERED CB AT 2.5-3.5 KFT AGL IN LATER TAF
PERIOD TO ACCOUNT FOR CONVECTIVE ACTIVITY. WINDS SE 8-10 KTS
OVERNIGHT...INCREASING TO 15-20 KTS AND BECOMING SOUTHERLY LATE
MORNING SUNDAY.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...BARNES
AVIATION...ONTON


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