Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 040447
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1147 PM CDT SUN MAY 3 2015

.UPDATE...
ISSUED AT 852 PM CDT SUN MAY 3 2015

CONVECTION CONTINUES TO FIRE THIS EVENING ALONG A FRONTAL
BOUNDARY EXTENDING FROM NORTHWEST ONTARIO INTO THE CENTRAL
PLAINS. THE NORTHERN PORTION THE LINE, WELL NORTH OF THE FORECAST
AREA, IS MAKING THE MOST RAPID EASTWARD PROGRESS. THIS IS NOT
SURPRISING GIVEN THE STRONGER WIND FIELDS IN THAT AREA, AND THE
FORECAST WEST-EAST ORIENTATION OF THE FRONTAL BOUNDARY THAT IS
ANTICIPATED BY LATER TOMORROW.

A FEW LIGHT SHOWERS ARE PUSHING INTO THE WESTERN PORTIONS OF THE
FORECAST AREA WELL IN THE PRE-FRONTAL WARM SECTOR, AND THIS SHOULD
CONTINUE TO WANE WITH THE LOSS OF DIURNAL HEATING. THE CONVECTION
ALONG THE FRONT WILL CONTINUE TO PUSH TOWARD AT LEAST THE NORTHERN
PORTION OF THE AREA BY LATE TONIGHT AS THE UPPER-LEVEL WAVE
HELPING TO DRIVE THEM MOVES THROUGH. HOWEVER, THEY SHOULD ARRIVE
IN A SUBSTANTIALLY WEAKENED STATE CONSIDERING THE LOSS OF DIURNAL
INSTABILITY AND FORECAST WEAKENING OF THE LOW-LEVEL JET BY THE
TIME THEY ARRIVE.

GOING FORECAST IS IN GOOD SHAPE OVERALL. MOST SIGNIFICANT
ADJUSTMENTS NEEDED ARE TOWARD PRECIPITATION TRENDS, MOST NOTABLY
TO REMOVE THUNDER MENTION FROM THIS EVENING AND DELAY ARRIVAL OF
THE UPSTREAM CONVECTION A BIT.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 250 PM CDT SUN MAY 3 2015

A WEAKENING SHORT WAVE OVER EASTERN IA AND NW IL BY MS RIVER WILL
LIFT INTO SE WI BY SUNSET AND KEEP BEST CHANCES OF SHOWERS AND
THUNDERSTORMS NORTH OF I-80 THROUGH SUNSET WITH JUST ISOLATED
SHOWERS AND POSSIBLE THUNDERSTORMS OVER THE IL RIVER VALLEY. CHANCES
OF SHOWERS AND THUNDERSTORMS WILL INCREASE DURING THE NIGHT
ESPECIALLY OVERNIGHT OVER THE IL RIVER VALLEY WITH SLIGHT CHANCES
EXTENDING AS FAR SE AT CHARLESTON/MATTOON BY SUNRISE MONDAY AS YET
ANOTHER SHORT WAVE OVER EASTERN NEBRASKA TRACKS EAST TOWARD THE
IA/IL BORDER BY 12Z/7 AM MONDAY. SPC KEEPS RISK OF SEVERE STORMS NW
OF IL OVER NORTHERN IA, SE MN AND INTO CENTRAL WI THROUGH DAYBREAK
MONDAY WHERE BETTER FORCING WILL BE AS COLD FRONT PUSHES SE INTO
CENTRAL PARTS OF WI/IA BY SUNRISE MONDAY. STAYED CLOSE TO MET/MAV
GUIDANCE LOWS TONIGHT IN THE UPPER 50S AND LOWER 60S WITH COOLEST
READINGS IN EASTERN/SE IL. BREEZY SSW WINDS 15-25 MPH THIS AFTERNOON
WILL DIMINISH SOUTH 7-14 MPH AFTER SUNSET.

.LONG TERM...(MONDAY THROUGH SUNDAY)
ISSUED AT 250 PM CDT SUN MAY 3 2015

MAIN FORECAST CHALLENGE WILL BE POSITION OF FRONTAL BOUNDARY AND
HIGHER RAIN CHANCES LATER TONIGHT THRU MONDAY NIGHT. REMNANTS OF
TODAY`S MCV SHOULD PUSH OFF TO OUR NORTHEAST PUSHING THE SHOWERS
EVEN FURTHER AWAY FROM THE FORECAST AREA THIS EVENING. WEAK UPPER
LEVEL DISTURBANCE OVER THE MISSOURI VALLEY HAS A FEW SHOWERS
ASSOCIATED WITH IT BUT THE LAST FEW RUNS OF THE RAP AND HRRR HAVE
BACKED OFF SOME ON ANY ORGANIZED SHOWER AND THUNDERSTORM THREAT WITH
THAT FEATURE. IT STILL APPEARS OUR MAIN THREAT WILL COME LATER
TONIGHT AND THRU THE MORNING HOURS OF MONDAY WITH REDEVELOPMENT
TAKING PLACE LATER TOMORROW AFTERNOON INTO THE EVENING RIGHT ALONG
THE STALLED FRONTAL BOUNDARY. HAVE TRENDED MORE TOWARDS THE HIGH
RESOLUTION MODEL SOLUTIONS FROM THE NSSL-ARW AND 4KM NAM-WRF WITH
RESPECT TO FRONTAL POSITION ON MONDAY AND ASSOCIATED PRECIP CHANCES
ALONG IT. THE HIGHER POPS WILL REMAIN ACROSS THE NORTHERN HALF OF
THE FORECAST AREA BEFORE THE BOUNDARY SHIFTS BACK NORTH LATE TUESDAY
INTO WEDNESDAY AS UPPER LEVEL RIDGING BUILDS ACROSS THE REGION.

SEVERE THREAT WILL BE TIED TO THE POSITION OF THE BOUNDARY MONDAY
AFTERNOON AND EVENING WITH THE NAM-WRF INDICATING A 40-45 KT LOW
LEVEL JET SETTING UP TONIGHT FROM NORTHERN MISSOURI NORTHEAST INTO
NORTHERN IL WITH THE STRONGER 850 MB THETA-E ADVECTION AND MOISTURE
TRANSPORT LOCATED FROM NORTHEAST MISSOURI INTO NORTHERN IL. STORMS
SHOULD DEVELOP WELL OUT TO OUR WEST AND NORTHWEST LATER THIS EVENING
AND THEN TRANSLATE EAST AND SOUTHEAST INTO OUR NORTHERN AREAS BY
LATE EVENING OR DURING THE EARLY MORNING HOURS OF MONDAY. IF A
DECENT COLD POOL DEVELOPS LATER TONIGHT...THOSE STORMS MAY TRACK
FURTHER SOUTH AND AFFECT THE POSITION OF THE SYNOPTIC SCALE BOUNDARY
IN OUR AREA ON MONDAY/MONDAY EVENING. WITH THE WEST TO EAST BOUNDARY
LOCATED ACROSS A PORTION OF THE FORECAST AREA MONDAY AFTERNOON AND
EVENING...LOOK FOR STORMS TO FIRE AGAIN ALONG THE INSTABILITY AXIS
WHICH SHOULD BE ALIGNED FROM NORTHERN MISSOURI INTO WEST CENTRAL IL
BY MID AFTERNOON. MIXED LAYER CAPES OF 1500-2000 J/KG AND EFFECTIVE
SHEAR VALUES OF 25 KTS SHOULD PROMOTE STORM ORGANIZATION WITH
ISOLATED STRONG WIND GUSTS AND HAIL POSSIBLE WITH 700-500 MB LAPSE
RATES OF 6.5-7 DEG/C DEPICTED ON SOUNDINGS TOMORROW AFTERNOON ACROSS
THE NORTH. SCATTERED STORMS SHOULD CONTINUE MONDAY NIGHT AND THEN
BEGIN TO EDGE NORTHWARD BY TUESDAY AS THE UPPER LEVEL RIDGING BEGINS
TO AMPLIFY ACROSS THE MIDWEST.

ONCE THE 500 MB RIDGE BUILDS OVER THE AREA ON TUESDAY...SHOWER AND
THUNDERSTORM CHANCES WILL SHIFT NORTH CLOSER TO THE RETREATING
SURFACE BOUNDARY. OUR NEXT THREAT WILL BE ASSOCIATED WITH A LEAD
SHORTWAVE TROF THAT IS FORECAST TO EJECT NORTHEAST INTO THE SOUTHERN
AND CENTRAL PLAINS ON THURSDAY WITH THE HIGHEST POPS...AT LEAST
INITIALLY...ACROSS THE WEST AS MODELS SUGGEST MOST OF THE STRONGER
LIFT AND INSTABILITY WILL SHIFT MORE NORTH THAN EAST. HOWEVER...OUR
AREA WILL BE UNDER A SOUTHWEST FLOW ALOFT LATE IN THE WEEK AND INTO
NEXT WEEKEND WITH A DEEPER UPPER LEVEL LOW FORECAST BY MEDIUM RANGE
MODELS TO PUSH OUT OF THE PLAINS AND INTO THE MIDWEST BY LATE IN THE
WEEKEND. UNFORTUNATELY...THIS TYPE OF A PATTERN THIS TIME OF YEAR
BRINGS DAILY CHANCES FOR SHOWERS AND STORMS BUT AT LEAST THE
TEMPERATURES WILL REMAIN ABOVE NORMAL.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1142 PM CDT SUN MAY 3 2015

WEAKENING LINE OF SHOWERS/STORMS APPROACHING CENTRAL ILLINOIS FROM
THE NORTHWEST LATE THIS EVENING. FURTHER WEAKENING IS ANTICIPATED
AND THEY MAY NOT REACH THE BULK OF THE LOCAL TERMINALS. KPIA AND
KBMI STAND THE BEST CHANCE OF SEEING STORMS. ADDITIONAL CONVECTION
OVER THE CENTRAL PLAINS IS MOVING MORE OF AN EASTERLY DIRECTION
AND THESE MAY IMPACT A PORTION OF THE REGION AS WELL VERY LATE
TONIGHT OR MONDAY MORNING. HOWEVER, IN BOTH CASES, COVERAGE BY THE
TIME THEY GET HERE IS NOT EXPECTED TO BE HIGH, SO HAVE GONE WITH A
VCSH/VCTS MENTION FOR NOW. ASIDE FROM ANY OF THIS CONVECTION,
EXPECT VFR CONDITIONS TO PREVAIL FOR MOST OF THE 06Z TAF VALID
TIME. EXPECT MOST OF THE ADDITIONAL DEVELOPMENT ON MONDAY TO STAY
MOSTLY TO THE NORTH OF THE AREA, ALONG A STALLED FRONTAL BOUNDARY,
ALTHOUGH KPIA AND KBMI STILL STAND THE BEST CHANCE OF BEING
IMPACTED.

&&

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

$$

UPDATE...BAK
SHORT TERM...07
LONG TERM...SMITH
AVIATION...BAK



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