Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 210156
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
856 PM CDT WED MAY 20 2015

.UPDATE...
ISSUED AT 856 PM CDT WED MAY 20 2015

A SHORTWAVE TROUGH ASSOCIATED WITH PRECIPITATION THIS
AFTERNOON/EVENING IS CURRENTLY OVER NORTHEASTERN IL ACCORDING TO
WATER...RAPIDLY MOVING EAST. SHOWERS WILL LINGER JUST ANOTHER HOUR
OR TWO IN THE SOUTHEASTERN PORTION OF THE FORECAST AREA NEAR
LAWRENCEVILLE BEFORE THE FEATURE MOVES COMPLETELY OUT OF THE ARE.
CLOUDY CONDITIONS WILL REMAIN MOST OF THE NIGHT AS ANOTHER
SHORTWAVE APPROACHES NORTHERN IL FROM SOUTHERN MN. QUITE COOL AIR
OVER THE REGION THAT RESULTED IN HIGHS IN THE UPPER 40S AND 50S
WILL REMAIN...WITH LOWS REACHING THE LOW 40S OR EVEN SOME UPPER
30S. CLOUD COVER AND LIGHT CONTINUOUS SURFACE WINDS FROM THE NORTH
WILL PREVENT TEMPERATURES FROM FALLING FURTHER OVERNIGHT. UPDATES
THIS EVENING TO SPEED UP EXIT OF PRECIPITATION FROM THE AREA...BUT
OTHERWISE FORECAST OVERNIGHT IS LARGELY ON TRACK.

&&

.SHORT TERM...(TONIGHT)
ISSUED AT 205 PM CDT WED MAY 20 2015

2 PM SURFACE MAP SHOWED LOW PRESSURE OVER SOUTH CENTRAL MISSOURI.
LARGE PRECIPITATION SHIELD HAS EXTENDED NORTH AND EAST FROM THE LOW
ASSOCIATED WITH A WEAK UPPER WAVE. NORTHEAST WIND FLOW HAS RESULTED
IN PLENTY OF DRY AIR THAT NEEDS TO BE CHEWED UP FIRST...AND WITH
TEMPERATURES IN THE MID TO UPPER 40S ACROSS THE NORTHERN CWA...WE
HAVE HAD SOME SLEET MIXED IN WITH THE RAIN AT TIMES DUE TO
EVAPORATIVE COOLING. BACK EDGE OF THE RAIN SHIELD TIMED TO LARGELY
BE NEAR THE I-57 CORRIDOR BY 7 PM. WILL LINGER MOST OF THE
MENTIONABLE POP`S EAST OF THIS AREA EARLY EVENING WITH SOME LIGHT
SHOWERS AS FAR WEST AS I-55, BUT MOST OF THE CWA SHOULD BE DRY BY
MID EVENING. SOME CLEARING WILL TRY TO TAKE PLACE OVERNIGHT ACROSS
THE NORTHWEST CWA...BUT THE APPROACH OF AN UPPER TROUGH CURRENTLY
OVER SOUTHEAST SOUTH DAKOTA SHOULD BRING KEEP SKIES AT LEAST PARTLY
CLOUDY. TEMPERATURES MAINLY SHOULD BE IN THE 40-45 DEGREE RANGE FOR
LOWS...BUT SOME UPPER 30S ARE FEASIBLE UP AROUND GALESBURG.

.LONG TERM...(THURSDAY THROUGH WEDNESDAY)
ISSUED AT 205 PM CDT WED MAY 20 2015

HIGH PRESSURE WILL INTENSIFY IN THE WAKE OF TODAYS SYSTEM AND SETTLE
DOWN INTO THE MISSISSIPPI VALLEY BEFORE MOVING OFF TO THE EAST
FRIDAY NIGHT AND SATURDAY. TEMPS ON THURSDAY WILL BE INHIBITED BY
LINGERING CLOUDINESS ACROSS SOUTHEASTERN FORECAST AREA. SUNSHINE AND
CLIMBING 850 TEMPS SHOULD ALLOW TEMPS TO REBOUND TO NEAR NORMAL BY
FRIDAY.

AS THE HIGH PUSHES EAST...RETURN FLOW QUICKLY DEVELOPS SATURDAY
ENABLING DEEP MOISTURE TO SATURATE THE AREA BY SATURDAY NIGHT.
SUBSIDENCE FROM 500MB SHORTWAVE RIDGE AND LACK OF A TRIGGER INHIBITS
CONVECTIVE DEVELOPMENT SATURDAY...BUT WITH THE RIDGE AXIS MOVING
EAST OF THE STATE SATURDAY NIGHT RAIN CHANCES SHOULD INCREASE
RAPIDLY. PRECIP WATER IS PROGGED BY THE 12Z GFS TO CLIMB ABOVE 1.5
IN BY 12Z SUNDAY AND APPROACHING TWO INCHES BY 12Z MONDAY.

LONGWAVE TROUGH CONTINUES IN THE FLOW PATTERN OVER THE WESTERN
STATES THROUGH EARLY NEXT WEEK WITH EJECTED WAVES MOVING NORTHEAST
INTO THE MIDWEST.  THE COLD FRONT ASSOCIATED WITH THE INITIAL WAVE
OVER THE WEEKEND IS EXPECTED TO STALL OUT EAST TO WEST ACROSS THE
REGION FOR AT LEAST THE FIRST PART OF THE WORKWEEK.  THE INTERACTION
BETWEEN THE FRONT...THE OCCASIONAL WAVES...AND CONTINUED MOIST FLOW
OFF THE WESTERN GULF SHOULD PRODUCE AN UNSETTLED PERIOD.  BIGGEST
UNCERTAINTY IS WHERE THE FRONT WILL LAY OUT AS IT IS OSCILLATED BY
WAVE PASSAGE AND FEEDBACK FROM CONVECTION. ALONG AND NORTH OF THIS
BOUNDARY WILL LIKELY SEE LIKELY POPS WHILE ACTIVITY WILL BE MORE
SCATTERED IN THE WARM SECTOR. SOME SEVERE WEATHER SEEMS LIKELY NEAR
THE BOUNDARY AS WELL WITH THE INCREASED SHEAR...AND POOLING OF
MOISTURE NEAR THE BOUNDARY...AND BOTH ECMWF AND GFS SUGGESTING CAPES
>2000 J/KG BY WEDNESDAY AFTERNOON. AGAIN WE WILL HAVE TO MONITOR
FUTURE RUNS TO REFINE WHERE WE EXPECT THE FRONT AND OTHER CONVECTIVE
BOUNDARIES TO LAY OUT.

TEMPS WILL LIKELY REMAIN ABOVE NORMAL THROUGH THE PERIOD DESPITE
THE PRECIP AND CLOUDS. TEMPS AT 850 MB ARE CONSISTENTLY 13-18C IN
THE LATEST LONG-RANGE MODELS. GFS FROM 12Z DOES SHOW A BIT MORE
RANGE TO LOW-LEVEL TEMPS THAN EARLIER RUNS...BUT GIVEN THE
UNCERTIANTY SEE LITTLE TO MAKE ME FEEL COMFORTABLE PINPOINTING
WHICH DAY WILL BE A BIT COOLER/WARMER THAN ANOTHER.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 657 PM CDT WED MAY 20 2015

RAIN SHOWERS FROM AROUND KMTO-KCMI EASTWARD WILL EXIT CENTRAL IL
TO THE EAST BY AROUND 03Z...THEREFORE NO FURTHER MENTION WAS
NEEDED IN 00Z TAFS. AREAS OF LOW CEILINGS IN THE MVFR RANGE AND
LOCAL IFR LINGER BEHIND THIS AREA...ESPECIALLY FROM AROUND I-72
SOUTHWARD. MODEL GUIDANCE SUGGESTS MVFR CIGS MAY LINGER MUCH OF
THE NIGHT TO THE SOUTH...BUT IS MUCH LESS AGGRESSIVE WITH CEILINGS
TO THE NORTHWEST WITH DRIER NORTHWESTERLY FLOW AFFECTING THAT
AREA FIRST. WITH DAYTIME HEATING THURSDAY...ANY LOW CEILINGS
SHOULD LIFT...WITH FORECAST SOUNDINGS INDICATING A SHALLOW
CUMULUS LAYER AROUND 4 KFT AGL LIKELY. WINDS NNE7-10 KTS GRADUALLY
SHIFTING TO WNW THROUGH THE 24 HOUR TAF FORECAST PERIOD.


&&

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

$$

UPDATE...ONTON
SHORT TERM...GEELHART
LONG TERM...BARKER
AVIATION...ONTON


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