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000
FXUS63 KILX 130809
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
309 AM CDT MON MAY 13 2013

.DISCUSSION...
ISSUED 309 AM CDT MON MAY 13 2013

SHORT TERM...TODAY THROUGH TUESDAY

THERMAL MODERATION BEGINS TODAY AS SFC RIDGE AXIS EDGES EAST AND LIGHT
RETURN FLOW DEVELOPS BY LATE DAY. ELEVATED WARM ADVECTION MID/HIGH
CLOUDS ALREADY EVIDENT IN IR SAT IMAGERY OVER THE DAKOTAS INTO
WESTERN IA EARLY THIS MORNING...AND THIS ACTIVITY IS EXPECTED TO
SPILL DOWN ACROSS THE CWA THROUGH THE DAY. MORE FOCUSED ISENTROPIC
LIFT AND THETA-E ADVECTION FOR ANY SPRINKLES OR LIGHT SHOWERS
SHOULD REMAIN JUST TO OUR NORTH LATER TODAY AND TONIGHT. HIGHS ARE
EXPECTED TO BE A FEW DEGREES BELOW NORMAL...GENERALLY 65-70 WITH
WARMEST READINGS IN WEST CENTRAL IL. STRONGER LOW AND MID LEVEL
WARM ADVECTION COMMENCES ON TUESDAY AS SOUTH TO SOUTHWEST FLOW
STRENGTHENS AHEAD OF A COLD FRONT ADVANCING THROUGH THE UPPER
MIDWEST. LATE AFTERNOON 850 MB TEMPS REACH 18-22 C AND THIS
SUPPORTS WIDESPREAD MID 80S AIDED BY PLENTY OF STRONG MID-MAY SUN.

LONG TERM...WEDNESDAY THROUGH SUNDAY

THE PATTERN THROUGH THE EXTENDED FORECAST FEATURES ZONAL MID LEVEL
FLOW WITH A QUASI-STATIONARY BOUNDARY WAVERING ACROSS THE MIDWEST.
THIS FAVORS FREQUENT CHANCES OF SHOWERS AND THUNDERSTORMS AND
ABOVE NORMAL TEMPS. THE INITIAL COLD FRONT MOVES INTO THE CWA ON
WEDNESDAY...AND HAVE HIGHER CHANCE POPS FOR THE CENTRAL AND
SOUTHERN CWA WHERE THE FRONT IS EXPECTED TO BE DURING PEAK DIURNAL
HEATING. SOME INCREASE IN LIFT WILL ALSO BE PROVIDED BY AN OPEN
MID LEVEL SOUTHERN STREAM TROF WHICH SHIFTS THROUGH THE LOWER/MID
MISSISSIPPI VALLEY LATE WED /GFS/ OR THU /ECMWF/.  LOW PRESSURE IS
FORECAST TO DEVELOP OVER THE HIGH PLAINS FRIDAY AHEAD OF A MORE
SIGNIFICANT TROF SETTING UP OVER THE WESTERN US. THIS WILL SEND
THE FRONT BACK NORTH AS A WARM FRONT WITH ATTENDANT SHOWER/STORM
CHANCES FOR THE END OF THE WEEK. IF THIS FRONT CAN SHIFT FAR
ENOUGH NORTH...SEVERAL PERIODS OF DRY WEATHER WOULD BE POSSIBLE
AND THIS IS SUGGESTED BY THE 00Z ECMWF. MEDIUM RANGE MODELS AND
ENSEMBLES SHOW THE MAIN LOW TO BE A SLOW MOVER...TRACKING THROUGH
THE UPPER MIDWEST LATE IN THE WEEKEND OR EARLY NEXT WEEK. THUS
WILL HAVE TO KEEP SOME MENTION OF POPS IN THROUGH SUNDAY GIVEN
DIFLUENT MID LEVEL FLOW...WARM AND RATHER HUMID AIR IN PLACE...AND
UNCERTAINTY IN BOUNDARY LOCATION. FORECAST CHALLENGE WILL BE TO
PIN DOWN HIGHER POPS AND POTENTIAL DRY PERIODS FRI-SUN AS THE
PATTERN EVOLVES.

25
&&

.AVIATION...
ISSUED 1118 PM CDT SUN MAY 12 2013...FOR THE 06Z TAFS

A WIDE RIDGE OF HIGH PRESSURE WILL DOMINATE THE WEATHER OVER THE
NEXT 24 HOURS...WITH VFR CONDITIONS. LITTLE TO NO CLOUD COVER IS
EXPECTED...WITH AC OR CIRRUS CLOUDS POSSIBLE FROM TIME TO TIME AS
THEY ROLL OVER THE UPPER RIDGE IN THE PLAINS.

FROST CONDITIONS REMAIN POSSIBLE LATER TONIGHT AS CALM WINDS AND
CLEAR SKIES ALLOW TEMPS TO DIP INTO THE MID 30S. TRAVEL SURFACES
COULD BECOME SLIPPERY WITH ANY FROST CONDITIONS JUST BEFORE
SUNRISE.

WINDS WILL BE VARIABLE THE REST OF THE NIGHT...DUE TO A VERY WEAK
PRESSURE GRADIENT NEAR THE RIDGE AXIS. AVE WIND DIRECTION SHOULD
REMAIN WESTERLY THROUGH SUNRISE. WINDS SHOULD REMAIN MAINLY WEST
ON MONDAY...UNTIL THE RIDGE MOVES FARTHER TO THE EAST OF IL AND
SOUTH-SOUTHWEST WINDS DEVELOP EARLY MONDAY EVENING. WIND SPEED MAY
EVEN INCREASE TO 10KT BEFORE SUNSET AS A RESULT OF INCREASING
PRESSURE GRADIENT.

SHIMON
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY UNTIL 7 AM CDT THIS MORNING FOR ILZ027>031-
036>038-040>057-061>063-066>068-071>073.

&&

$$