Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 240144
Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
844 PM CDT Mon Mar 23 2015
ISSUED AT 830 PM CDT MON MAR 23 2015
Main concern late tonight thru the mid morning hours of Tuesday
will be the threat for a brief period of freezing rain over
parts of west central and central IL. Shortwave that produced
the period of sleet and freezing rain over our far northern
counties early this morning has pushed well to our east this
evening with weak high pressure moving across the area in its
wake. Meanwhile, our next weather system is taking shape over
the Central Plains with elevated convection already developing
in the warm advection pattern ahead of the strong upper wave.
That upper wave and the developing precip will shift east tonight
and approach our area in the 11z-14z time frame and based on the
last several runs of the RAP, it appears there will be a brief
period of light freezing rain across west central IL extending
into parts of central IL thru mid morning.
Will be making some adjustments to the coverage of the light
freezing rain late tonight over extreme western IL and shift the
threat into central IL during the 12z-15z time frame. Have also
adjusted the temps down a few degrees, especially across the
north for late tonight and thru the mid morning hours of Tuesday.
The rest of the forecast looks on target. The ZFP update should
be out by 900 pm.
.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 346 PM CDT MON MAR 23 2015
PRECIPITATION ASSOCIATED WITH TODAY`S SHORTWAVE HAS EXITED TO
THE EAST. LOW LEVEL CLOUD COVER REMAINS IN ITS WAKE. STRONG
HIGH PRESSURE REMAINS IN PLACE ACROSS THE EASTERN GREAT LAKES
WHICH TENDS TO SUGGEST THAT THE CLOUDS WILL LINGER MUCH OF THE
NIGHT IN SPITE OF SOME POTENTIAL CLEARING TO THE SOUTH. WITH THE
HIGH IN PLACE TONIGHT...LOW LEVEL DRY ENE FLOW WILL KEEP A COOL
LOW LEVEL AIR MASS IN PLACE.
ATTENTION SHIFTS TO THE UPPER TROUGH ENTERING THE SOUTHERN ROCKIES.
THERE WILL BE SOME LEAD SHORTWAVE ENERGY PUSHING EAST THROUGH
THE CENTRAL PLAINS AND MID MISSOURI VALLEY TONIGHT. STRONG LOW LEVEL
WARM ADVECTION/ISENTROPIC LIFT INTO THE LOW-MID LEVEL FRONTAL ZONE
WILL RESULT IN SHOWERS TO MOVE INTO ILLINOIS LATE TONIGHT INTO
TOMORROW MORNING. THERE IS SOME WEAK INSTABILITY ABOVE 700-600 MB
AS THESE SHOWERS ROLL IN WHICH MAY RESULT IN A FEW EMBEDDED
THUNDERSTORMS...ESPECIALLY SOUTH OF I-72. MEANWHILE NORTH OF
I-74 AND CLOSER TO I-72...SURFACE TEMPERATURES LOOK TO DIP BELOW
FREEZING TONIGHT INTO EARLY TUESDAY MORNING. THEREFORE RAIN/FREEZING
RAIN CONCERNS COME INTO PLAY. CONFIDENCE IS NOT SUPER HIGH ON ICE
ACCUMULATIONS GIVEN THE WARMER GROUND CONDITIONS...BUT IT IS
CERTAINLY CONCERN EAST OF I-55 WHERE PRECIPITATION HAS A BETTER
CHANCE OF COMING IN DURING THE COOL HOURS OF THE NIGHT AND EARLY
MORNING. BY MID-LATE MORNING THE LOWER LEVEL WARMING WILL ALLOW
SURFACE TEMPS TO BE ABOVE FREEZING AREA-WIDE.
THERE MAY BE A LULL IN THE SHOWER ACTIVITY IN AFTERNOON AS THE
MID LEVEL BAROCLINIC ZONE SHIFTS NORTH AND THE LEAD WAVES MOVES
EASTWARD. THE SURFACE WARM FRONT WILL EVENTUALLY MOVE NORTH THROUGH
THE CWA DURING THE AFTERNOON AND MORE SO THE EVENING HOURS.
.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY) ISSUED AT 346 PM CDT
MON MAR 23 2015
THE CENTER OF LOW PRESSURE LIFTING OUT OF THE SOUTHERN PLAINS
WILL CROSS THE LOCAL AREA TUESDAY NIGHT AND QUICKLY PUSH WELL TO
THE NORTHEAST BY NOON WEDNESDAY. UNCERTAINTY IN THE EXACT TRACK OF
THE LOW WILL CREATE CHALLENGES FOR LOW TEMPERATURE FORECASTS AND
THE NORTHERN EXTENT OF THUNDERSTORM ACTIVITY...WITH THE BEST
CHANCE OF THUNDER BEING IN THE TUESDAY EVENING HOURS AS THE LOW
CENTER AND UPPER TROUGH AXIS MOVE OVERHEAD.
AFTER A BRIEF DRY PERIOD WEDNESDAY...AND AT LEAST PART OF
WEDNESDAY AFTERNOON...ANOTHER WEAKER DISTURBANCE WEDNESDAY
NIGHT FOLLOWS QUICKLY ON THE HEELS OF THE TUESDAY NIGHT SYSTEM.
THIS TOO SHOULD QUICKLY CLEAR TO THE EAST AFTER DAYBREAK THURSDAY.
WITH THE PASSAGE OF THE FRONTAL ZONE ASSOCIATED WITH THE SECOND
SYSTEM...COOLER AIR SETTLES INTO THE AREA UNDER A BROAD DOME OF
HIGH PRESSURE FOR THE REMAINDER OF THE WEEK AND EARLY WEEKEND. BY
LATE SUNDAY THE DOMINANT AREA OF COOL HIGH PRESSURE SLIDES INTO THE
SOUTHEAST CONUS ALLOWING MILDER AND MORE HUMID RETURN FLOW TO BEGIN
WORKING BACK INTO THE MIDWEST. WITH THE RETURN OF HIGHS IN THE 50S
OR WARMER COMES INCREASED CHANCES OF PRECIPITATION FOR LATE IN THE
WEEKEND...BUT AT THIS RANGE AM ONLY CONFIDENT ENOUGH ON TIMING AND
EXTENT TO INCLUDE CHANCE POPS.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
ISSUED AT 620 PM CDT MON MAR 23 2015
Our next weather system is expected to bring deteriorating conditions
once again late tonight and especially during the morning. Low VFR
to MVFR cigs dominate the area and expect most of our TAF sites to
be MVFR by 04z and continue into tomorrow morning with precip
developing across west central IL by dawn. Main forecast concern
tomorrow morning will be with precip type as a few models suggest the
threat for a period of freezing rain across PIA and BMI. Last several
runs of the RAP forecast soundings suggest precip will be slower to
arrive than originally thought as drier air in the low and mid levels
impedes the initial surge of rain. However, by late morning in most
areas, we should see the rain overspread the forecasts sites with
cigs lowering to IFR by afternoon. Surface winds will be northeast to
east tonight at 10 to 15 kts and mostly out of the east on Tuesday
at 10 to 15 kts.