Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 272141
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
ISSUED BY NATIONAL WEATHER SERVICE CHICAGO IL
341 PM CST Tue Jan 27 2015

.SHORT TERM...(Through Wednesday afternoon) 
ISSUED AT 255 PM CST TUE JAN 27 2015

MAIN CHALLENGE IN THE SHORT/NEAR TERM REVOLVES AROUND CLOUD COVER
TONIGHT...WINDS AND TEMPS ON WEDNESDAY. A SURFACE RIDGE IS IN PLACE
OVERHEAD...AND SATELLITE PICTURES SHOW LOWER CLOUDS ERODING FROM THE
NORTHEAST THIS AFTERNOON AS DRIER AIR FILTERS IN.  BEST CHANCES FOR
EROSION WILL BE FOR EASTERN AREAS WHERE THIS DRIER AIR IS MAKING
BETTER HEADWAY. RAW MODEL GUIDANCE CONTINUES TO ADVERTISE CLEARING
MUCH SOONER THIS EVENING AREA-WIDE...WHILE RAP TIME HEIGHTS SUGGEST
IT WILL TAKE UNTIL LATER TONIGHT FOR THIS TO OCCUR...ESPECIALLY
NORTH OF I-72. MODEL SOUNDINGS SUGGEST THAT THIS LOWER LEVEL
MOISTURE WILL REMAIN TRAPPED BELOW A SUBSIDENCE INVERSION...AND THAT
IT WILL AT LEAST HOLD FIRM THROUGH THE EVENING HOURS. CLOUD BEARING
WINDS WILL BE TURNING MORE NORTHERLY AS WELL...WHICH WOULD SUPPORT
CLOUDS HANGING ON ALONG AND WEST OF HIGHWAY 51. SURFACE HIGH
PRESSURE TONIGHT WILL SHIFT OFF THE EAST TONIGHT AS THE UPPER RIDGE
IN THE PLAINS MOVE EAST AND CONTINUES TO DEAMPLIFY. EXPECT WINDS TO
SHIFT TO THE SE OVERNIGHT...WITH LOWS IN THE EAST IN THE UPPER TEENS
TO NEAR 20...WITH 20S HOLDING WEST WHERE CLOUD COVER IS EXPECTED TO
BE MORE PREVALENT.

THURSDAY...ATTENTION SHIFTS TO UPPER LEVEL LOW PRESSURE MOVING
THROUGH THE GREAT BASIN THIS AFTERNOON. THE UPPER TROUGH MOVES INTO
THE PLAINS RIDGE WHILE ADDITIONAL PACIFIC ENERGY MOVES INTO THE
NORTHERN PLAINS. LOW LEVEL WARM ADVECTION ENSUES IN THE
SOUTHWESTERLY FLOW AHEAD OF THESE SYSTEM .IT APPEARS THAT NOT ALL OF
OF THIS LOW LEVEL WARMING WILL NOT TRANSLATE TO THE SURFACE WITH A
FAIRLY STRONG INVERSION HOLDING...BUT DO EXPECT SOME WARMING FROM
TODAY`S READINGS...ESPECIALLY FOR SOUTHERN AND WESTERN AREAS WHERE
MID 40S LOOK LIKE A DECENT BET. AREAS NORTH AND EAST WILL REMAIN ON
THE COOLER SIDE STRUGGLING TO REACH 40. AHEAD OF THESE TWO
DISTURBANCES SURFACE LOW PRESSURE OF 1005 MB COMBINES WITH THE
DEPARTING HIGH TO CREATE A MODEST PRESSURE GRADIENT ACROSS THE AREA.
A VERY STRONG LOW LEVEL JET SETS UP LATE IN THE AFTERNOON...BUT
GIVEN THE LOW LEVEL INVERSION...EXPECT A BREEZY DAY WITH GUSTS IN
THE 25 KT RANGE.

KMD

&&

.LONG TERM...(Wednesday Night through Tuesday)
ISSUED AT 340 PM CST TUE JAN 27 2015

WEDNESDAY NIGHT THROUGH SATURDAY...

A WINDY AND MILD NIGHT IS IN STORE ON WEDNESDAY NIGHT AS LOW
PRESSURE QUICKLY MOVES JUST NORTH OF THE CWA. STRONG PRESSURE
FALLS DUE TO TIGHTENING GRADIENT BETWEEN ADVANCING LOW AND
DEPARTING HIGH PRESSURE TO THE EAST WILL RESULT IN SUSTAINED
SOUTHERLY WINDS IN THE MID TO HIGH TEENS WITH GUSTS OF 20-25 KT.
TEMPERATURES SHOULD DROP SOME IN THE EVENING BUT THEN ARE LIKELY
TO SLOWLY RISE TOWARD DAYBREAK. THERE IS A DECENT VORT MAX
ASSOCIATED WITH APPROACHING SHORT WAVE TROUGH...BUT GUIDANCE IS
FAIRLY DRY WITH EXCEPTION OF ECMWF AND NAM. MAINTAINED SLIGHT TO
LOW END CHANCE POPS FOR LIGHT RAIN MAINLY AFTER MIDNIGHT. MAY NEED
TO ADD DRIZZLE TO GRIDS.

COLD FRONT TRAILING FROM THE LOW PRESSURE WILL SWEEP ACROSS THE
AREA FROM NW TO SE OVERNIGHT INTO THURSDAY MORNING...SHIFTING
WINDS FROM SOUTHWEST TO NORTHWEST...AND COLD ADVECTION RAMPING UP
BEHIND IT. HAVE LOW POPS FOR MOST OF THE CWA IN THE MORNING...BUT
ANY PRECIP WOULD LIKELY BE LIGHT RAIN DESPITE COLD ADVECTION AS
SURFACE TEMPERATURES WOULDNT COOL QUICK ENOUGH FROM EARLY HIGHS IN
THE UPPER 30S TO MID 40S...WARMEST FAR SOUTHEAST. BIGGER STORY
WILL BE STRONG ISALLOBARIC PRESSURE RISES BEHIND FRONT RESULTING
IN NORTHWEST WINDS GUSTING TO 30-35 MPH MUCH OF THE MORNING AND
AFTERNOON. WINDS WILL GRADUALLY DIMINISH THURSDAY NIGHT AS
EXPANSIVE HIGH PRESSURE SPREADS SOUTHEAST. EXPECT LOWS IN THE
UPPER TEENS TO MID 20S BY EARLY FRIDAY...RECOVERING TO SLIGHTLY
BELOW CLIMO LOW-MID 30S UNDER LARGE CANADIAN HIGH. THE HIGH WILL
SLIDE SOUTHEAST ON SATURDAY...ALLOWING TEMPS TO WARM SLIGHTLY TO
THE MID TO UPPER 30S.

SATURDAY NIGHT THROUGH TUESDAY...

ATTENTION TURNS TO EJECTION OF CLOSED UPPER LOW OVER THE DESERT
SOUTHWEST AS MORE OF AN OPEN WAVE SATURDAY NIGHT INTO
SUNDAY...WITH ASSOCIATED WEAK SURFACE LOW POSSIBLY MOVING TOWARD
THE LOWER OR MID MS VALLEY THEN OH VALLEY BY SUNDAY EVENING. WITH
IT BEING STILL OVER 100 HRS OUT...GUIDANCE VARIES ON PLACEMENT OF
SURFACE LOW...BUT DECENT AGREEMENT IN OPERATIONAL MODELS AND
ENSEMBLES OF BROAD WARM ADVECTION/ISENTROPIC ASCENT WITH THIS
SYSTEM. THIS YIELDS THE POTENTIAL FOR FAIRLY LONG DURATION
PRECIPITATION. AT THIS POINT...THERMAL PROFILES APPEAR COLD ENOUGH
FOR SNOW ACROSS THE CWA...BUT FARTHER NORTHWEST/STRONGER LOW COULD
INTRODUCE P-TYPE CONCERNS...ESPECIALLY IN THE FAR SOUTHEAST. WAY
TOO EARLY TO DISCUSS POTENTIAL SNOW ACCUMULATIONS...BUT THIS
PERIOD BEARS WATCHING. BEHIND THIS SYSTEM...MODELS HAVE BEEN
WAFFLING ON INTENSITY OF A POTENTIAL SHOT OF ARCTIC AIR EARLY NEXT
WEEK AS PIECE OF POLAR VORTEX ROTATES SOUTH OF HUDSON BAY. BRUNT
OF THE ARCTIC BLAST MAY BE DIRECTED FARTHER EAST...BUT STILL LOOKS
LIKE THERE COULD BE A PERIOD OF WELL BELOW NORMAL TEMPERATURES
EARLY NEXT WEEK.

RC

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 1141 AM CST TUE JAN 27 2015

MAIN AVIATION CONCERN REVOLVES AROUND EXISTING MVFR AND IFR CIGS.
IFR CIGS ARE BECOMING LESS COMMON ACROSS THE TERMINALS AS DRIER
AIR SLOWLY FILTERS IN FROM THE NORTHEAST. EXPECT KBMI WILL HANG
ONTO IFR A BIT LONGER BEFORE TRANSITION MVFR CIGS IN THE 1000-1500
FT RANGE. CHALLENGE THEN TURNS TO HOW QUICKLY THE LOWER CLOUD BASE
ERODES. HRRR AND RAP GUIDANCE ARE A BIT MIXED TO HOW QUICKLY THIS
OCCURS. THE GENERAL FEELING IS THAT SOMETIME THIS EVENING THE MVFR
DECK WILL LIFT ABOVE 2000 FT AND SCATTER OUT AS THE HRRR
SUGGESTS...BUT CONFIDENCE ON THIS TIMING IS MEDIUM. HIGHEST CONFIDENCE
ON TIMING THIS OCCURRENCE IS AT KCMI AND EASTERN LOCATIONS WHERE
DRIER AIR WILL MORE READILY ADVECT IN. MEANWHILE THE RAP AND NAM
HOLD ONTO THE CLOUDS THROUGH 6Z OR SLIGHTLY LATER AS A LOW LEVEL
INVERSION REMAINS IN PLACE. WINDS OVERNIGHT WILL VEER TO THE
SOUTHEAST AND WEAKEN BEFORE STRENGTHENING TOMORROW MORNING. SOME
PATCHY FOG MAY DEVELOP AFTER CLOUDS CLEAR BUT HELD OFF ANY MENTION
AT THIS POINT.


&&

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

$$

SHORT TERM...kmd
LONG TERM...RC
AVIATION...KMD





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