Area Forecast Discussion
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000
FXUS63 KLOT 191737
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1237 PM CDT SUN APR 19 2015

.UPDATE...
952 AM CDT

I MADE SOME UPDATES TO THE FORECAST FOR TODAY TO RAISE
TEMPERATURES AND PUSH OFF THE TIMING OF THE RAIN CHANCES.

WATER VAPOR IMAGERY INDICATES OUR MID/UPPER LEVEL DISTURBANCE OF
INTEREST FOR LATER TODAY NOW LIFTING NORTHWARD ACROSS WESTERN
KENTUCKY. THIS FEATURE IS CURRENTLY SUPPORTING AN AREA OF
NORTHWARD MOVING SHOWERS ACROSS SOUTHERN PORTIONS OF ILLINOIS AND
INDIANA. THEREFORE...THIS AREA OF SHOWERS WILL GRADUALLY WORK
NORTHWARD ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA
DURING THE AFTERNOON. IT APPEARS THE THREAT FOR THUNDERSTORMS WILL
BE VERY LOW WITH THIS ACTIVITY...WITH TRENDS SUGGESTING NO
LIGHTNING STRIKES OVER THE PAST FEW HOURS...SO I HAVE REMOVED THE
MENTION OF SUCH THIS AFTERNOON. IN ADDITION...WITH THE SLOWER
ONSET OF PRECIP TODAY...IT APPEARS TEMPERATURES WILL BE ABLE TO
WARM TO NEAR 70 IN MOST AREAS AWAY FROM LAKE MICHIGAN...SO I
RAISED HIGH TEMPERATURES TODAY.

KJB

&&

.SHORT TERM...
340 AM CDT

THROUGH MONDAY...

UPPER AIR ANALYSIS EARLY THIS MORNING DEPICTS DEEP UPPER LEVEL LOW
PRESSURE NOW PUSHING INTO WESTERN KANSAS. MULTIPLE VORT MAXES ARE
ROTATING AROUND THE LOW. THE STRONGEST OF THESE EXIST IN TEXAS AND
THROUGH THE CENTRAL PLAINS...WITH SOME SMALLER SCALE WAVES EXTENDING
INTO EASTERN MO/FAR WESTERN IL WERE SOME SCATTERED THUNDERSTORMS
WERE ONGOING. A NORTHERN STREAM SHORTWAVE IS ENTERING THE NORTHERN
PLAINS WITH SOME SHOWERS OUT AHEAD OF IT AS WELL. AT THE
SURFACE...THE COLD FRONT THAT PASSED THROUGH NORTHEAST ILLINOIS AND
NW INDIANA SATURDAY HAS PUSHED INTO CENTRAL ILLINOIS...BUT HAS
LIKELY COMPLETED ITS SOUTHWARD RETREAT AND HAS WASHED OUT OVER THE
PAST FEW HOURS. OVER THE LOCAL AREA...MUCH DRIER NE FLOW EXISTS WITH
DEWPOINTS IN THE MID TO UPPER 20S IN THE CITY TO NEAR 40
SOUTH...THOUGH DEWPOINTS ARE POOLING ALONG THE FRONT IN THE UPPER
40S JUST SOUTH OF THE LOT CWA. THE SURFACE LOW THAT IS EXPECTED TO
DEVELOP FROM THE SOUTHERN STREAM SHORTWAVE IS ALSO TAKING SHAPE OVER
THE SOUTHERN STATES WITH A WARM FRONTAL BOUNDARY EXTENDING FROM
WESTERN ARKANSAS THROUGH THE LOWER TENNESSEE VALLEY. AN EXPANSION OF
LOWER CLOUD TOPS ON IR IMAGERY ALONG AND AHEAD OF THE WARM FRONT IS
OCCURRING.

LOW LEVEL WARM/MOIST ADVECTION WILL CONTINUE ITS SLOW PROGRESSION
NORTHWARD UNDER MODEST SOUTH/SOUTHEAST FLOW. DEEPER MOISTURE/LIFT
REALLY HOLD OFF UNTIL THE AFTERNOON PERIOD ACROSS MOST OF THE AREA.
A SOMEWHAT COMPLICATED EVOLUTION AS A MAIN SURFACE LOW CENTER IS
FORECAST TO STRENGTHEN AS IT LIFTS NORTH THROUGH INDIANA TODAY THEN
FURTHER STRENGTHEN TONIGHT INTO MONDAY WHILE SEVERAL ADDITIONAL
SURFACE LOWS DEVELOP AND EVENTUALLY MERGE WITH THE MAIN LOW CENTER.
THE SURFACE LOW WILL EVENTUALLY BECOME DRIVEN BY A COMBINATION OF
THE SW FLOW AHEAD OF THE SOUTHERN STREAM UPPER LOW AND THE
NORTHERN STREAM SHORTWAVE.

OF NOTE LATER TODAY...EXPECT COVERAGE OF SHOWERS TO INITIALLY BE
SLOW GIVEN THE DRIER AIR PLACE...BUT INCREASING ASCENT ALOFT...LOW
LEVEL SSE ISENTROPIC ASCENT AHEAD OF THE LOW AND WRAPPING AROUND THE
CLOSED CIRCULATION EXTENDING THROUGH 850 AND EVEN 700 MB COMBINED
WITH MODEST LOWER LEVEL FGEN SHOULD ALLOW FOR A BLOSSOMING OF
SHOWERS ACROSS THE AREA LATER THIS AFTERNOON AND EVENING. THE
HIGHEST PWAT AXIS EXPANDS ACROSS INDIANA TODAY BUT SHOULD GET
WRAPPED INTO NE ILLINOIS. RAP MOST UNSTABLE CAPE VALUES RELATIVELY
LOW BUT DO EXPAND FROM SE TO NW THIS AFTERNOON AND THIS COUPLED WITH
THE PUNCH FROM THE DRY SLOT OF THIS SYSTEM MAY ENABLE A FEW T-STORMS
AS WELL...SO SOME OF THE SHOWERS WILL HAVE A MODEST KICK TO THEM IN
THE MODERATE/HEAVY RAINFALL DEPARTMENT. EXPECT THAT NORTH CENTRAL
ILLINOIS MAY BE UNDER A BIT OF SQUEEZE PLAY FROM THESE TWO
SYSTEMS...THUS WHILE SHOWERS ARE STILL EXPECTED...HIGHER CONFIDENCE
EXISTS IN COVERAGE FARTHER EAST.

THIS EVENING THE FIRST MAIN SHORTWAVE WILL BE PASSING NE WHILE THE
MAIN SOUTHERN STREAM ENERGY PASSES EAST THROUGH THE OHIO
VALLEY...AND THE NORTHERN STREAM SHORTWAVE LAGS BEHIND BACK IN
MN/IA. THERE IS ALSO THE LOSS OF DEEPER MOISTURE...THEREFORE EXPECT
SHOWERS TO TAPER/END/TURN TO DRIZZLE POSSIBLY OVERNIGHT FOR A TIME.
THEN MONDAY MORNING WE GET THE COUPLED UPPER LEVEL FORCING FROM THE
NORTHERN STREAM LOW AND SURFACE COLD FRONT WHICH WILL LIKELY BRING
ANOTHER ROUND OF SHOWERS MONDAY MORNING. SHOWERS WILL EASE MONDAY
AFTERNOON. IT WILL BE QUITE BREEZY/WINDY BEHIND THE FRONT ON MONDAY
IN THE COLD ADVECTION REGIME.

KMD

&&

.LONG TERM...
340 AM CDT

MONDAY NIGHT THROUGH SATURDAY...

THE THEME OF THE EXTENDED WILL BE THE UNSEASONABLY COOL WEATHER. A
HIGH AMPLITUDE PATTERN WILL BE IN PLACE WITH STRONG UPPER LEVEL
RIDGING EXTENDING WELL NORTH INTO THE CANADIAN ROCKIES AND SIMILARLY
HIGH AMPLITUDE RIDGING IN THE NORTH ATLANTIC. THAT LEAVES OUR
NORTHERN STREAM SHORTWAVE FROM SUNDAY/MONDAY WITH NO WHERE TO GO.
THIS WILL KEEP MUCH OF THE EASTERN HALF OF THE COUNTY...INCLUDING
OUR REGION...UNDER COOL NORTHWEST FLOW. THIS PATTERN ALSO FAVORED
STRONGLY SHEARED OUT AND ELONGATED VORT MAXES TO PIVOT THROUGH
BRINGING PERIODS OF SHOWERS. WITH PWAT VALUES QUITE LOW IN THIS
AIRMASS...MUCH OF THE PERIOD WILL BE DRY AND EVEN THE SHOWERS SHOULD
NOT BE VERY STRONG. BUT MORE IMPORTANTLY...SEASONAL AVERAGE
HIGHS/LOWS FOR LATE APRIL ARE THE LOWER 60S (MID 60S SOUTH) AND
LOWER 40S RESPECTIVELY...AND MUCH OF THIS PERIOD WILL FEATURE HIGHS
IN THE 50S AND LOWS IN THE MID 30S...POSSIBLY COOLER A NIGHT OR TWO
IF WINDS ARE LIGHTER. TEMPERATURE ANOMALIES ARE NOT THAT EXTREME
THOUGH...SO RECORD COLD IS NOT ANTICIPATED.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* EAST WINDS 10-14 KT BCMG NORTH LESS THAN 10 KT THIS EVENING.

* RAIN ARRIVES 21-22Z WITH 5SM VSBY WITH HEAVIER SHOWERS.

* CIGS LOWER TO MVFR LATE THIS AFTN THEN TO IFR THIS EVENING
  THROUGH EARLY MONDAY MORNING.

* SCATTERED SHOWERS OVERNIGHT WITH ANOTHER ROUND OF -SHRA EARLY
  MONDAY MORNING.

* GUSTY WEST WINDS WITH MAX GUSTS ARND 30 KT MONDAY AFTN.

JEE

//DISCUSSION...UPDATED 18Z...

RAIN IS SLOWLY PUSHING NORTH AND IS JUST SOUTH OF I-80 AT THIS
TIME. MVFR AND LOWER CIGS ARE OVER CENTRAL AND SOUTHERN IL AND
INDIANA BUT ALSO PUSHING NORTH. ADJUSTED PRECIP AND CIG TIMING
BASED ON RADAR AND SATELLITE TRENDS. MVFR VSBY WILL BE TIED TO THE
HEAVIER RAIN SHOWERS...AND CIGS WILL LOWER TO MVFR LATE THIS AFTN
AND THEN TO IFR THIS EVENING. ALL GUIDANCE MEMBERS SHOW IFR CIGS
ACROSS THE TERMINALS.

WILL EITHER SEE SCATTERED SHOWERS OR A BREAK IN RAIN AFTER
MIDNIGHT TONIGHT WITH ANOTHER ROUND OF RAIN PUSHING WEST TO EAST
EARLY MONDAY MORNING.

EAST WINDS BCM NORTHEAST ARND 10 KT LATE THIS AFTN AND BACK TO NW
BY 03Z. WINDS CONTINUE TO BACK TO WEST BY EARLY MONDAY MORNING.
GUSTY WINDS FOLLOW THE BAND OF RAIN SHOWERS...WITH 20G30KT
EXPECTED BY MONDAY AFTERNOON. THINKING THE GUSTY WINDS AND DRIER
AIR WILL HELP CIGS LIFT LATE MONDAY MORNING AND AFTN...BUT HAVE
MEDIUM CONFIDENCE IN HOW QUICKLY CIGS LIFT TO VFR.

JEE


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN RAIN SHOWERS THIS AFTERNOON AND EVENING.

* HIGH CONFIDENCE IN MVFR CIGS...MEDIUM CONFIDENCE IN MVFR CIG
  TIMING AND OCCURRENCE AND TIMING OF IFR CIGS.

* HIGH CONFIDENCE IN WIND TRENDS OVERNIGHT...MEDIUM CONFIDENCE IN
  TIMING OF BACKING WINDS.

* MEDIUM CONFIDENCE IN HOW QUICKLY CIGS LIFT TO VFR MONDAY.

* HIGH CONFIDENCE IN ALL OTHER FORECAST PARAMETERS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...MVFR BECOMING VFR.

TUESDAY...SLGT CHANCE PM SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

FRIDAY...MAINLY VFR. CHC PM SHRA.

SATURDAY...MAINLY VFR.

BEACHLER

&&

.MARINE...
257 AM CDT

LOW PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY LIFT NORTHEAST
TOWARDS THE LOWER GREAT LAKES REGION TONIGHT/EARLY MON. GUIDANCE
CONTINUES TO INDICATE THE GRADIENT WILL TIGHTEN ACROSS THE
LAKE...HOWEVER THIS APPEARS TO BE MORE FOCUSED ALONG THE SOUTHERN
TIP OF THE LAKE. WITH THE CONTINUED EASTERLY WINDS...IT IS
POSSIBLE MARGINAL SMALL CRAFT CONDITIONS MAY DEVELOP FOR THE
ILLINOIS SHORELINE LATER TODAY INTO TONIGHT. THE LOW PRESSURE WILL
THEN APPROACH THE LAKE AND BRIEFLY WEAKEN THE GRADIENT EARLY MON.
THEN AS THE LOW LIFTS NORTHEAST LATER IN THE DAY MON...IT WILL
DEEPEN AND MERGE WITH ANOTHER LOW...WHICH WILL CREATE A TIGHT
GRADIENT OVER THE LAKE AND INCREASING WEST/NORTHWEST TUE. AFTER
TUE THE DOMINANT WIND DIRECTION WILL BE NORTHWEST THROUGH MID-
WEEK...BEFORE RELAXING TO THE WEST. THIS WILL ALLOW HIGHER WAVES
TO BE FOCUSED IN THE SOUTHERN HALF OF LAKE MICHIGAN THROUGH MID-
WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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