Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KLOT 041815
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
115 PM CDT MON MAY 4 2015

.UPDATE...1111 AM CDT

A SOMEWHAT DISORGANIZED COLD FRONT DRAPED ACROSS THE AREA FROM
SOUTHWEST TO NORTHEAST WILL DROP TOWARD CENTRAL ILLINOIS THIS
AFTERNOON. SCATTERED TO ISOLATED SHOWERS PERSISTED SOUTH OF THIS
FEATURE LATE THIS MORNING...BUT WEAK CONVERGENCE ALONG THE
BOUNDARY ALONG WITH POOLING OF MOISTURE MAY SUPPORT INCREASED
COVERAGE THIS AFTERNOON DURING PEAK DIURNAL HEATING. MORE
EFFECTIVE MOISTURE CONVERGENCE DEVELOPS LATE THIS EVENING INTO
THE OVERNIGHT HOURS AS THE FRONT BEGINS TO LIFT BACK NORTH.

DESPITE INCREASING INSTABILITY NEAR THE FRONT THIS AFTERNOON AND
TONIGHT...DEEP LAYER SHEAR IS NOT FAVORABLE FOR SUPPORTING
WIDESPREAD ORGANIZED CONVECTION...BUT ISOLATED STRONGER STORMS
COULD PRODUCE SOME SMALL HAIL.

LENNING

&&

.SHORT TERM...
331 AM CDT

THROUGH TUESDAY...

CONVECTION ASSOCIATED WITH AN APPROACHING COLD FRONT IS MOVING FROM
NORTHWEST TO SOUTHEAST THROUGH NORTHERN IL THIS MORNING. ITS WELL
DEFINED GUST FRONT STRETCHES FROM SOUTHERN LAKE MI THROUGH PONTIAC
IL WITH SCATTERED STORMS FORMING ALONG THE GUST FRONT. A BROADER
AREA OF SHOWERS LAGS BEHIND THE GUST FRONT AND LATEST RADAR IMAGERY
SUGGESTS THE AREA OF SHOWERS IS QUICKLY DISSIPATING.  TWO ADDITIONAL
CONVECTIVE COMPLEXES ARE FURTHER WEST OVER NORTHEAST IOWA AND
NORTHWEST MISSOURI AND THE IOWA COMPLEX MAY PLAY A PART IN WHAT
HAPPENS THIS MORNING.

THINKING WE WILL SEE ADDITIONAL SCATTERED SHOWER AND THUNDERSTORM
DEVELOP ALONG THE GUST FRONT AS IT PLOWS THROUGH THE REST OF THE CWA
EARLY THIS MORNING. MUCH LESS CONFIDENT ON HOW LONG THE SHOWERS WILL
PERSIST OVER NORTH CENTRAL IL AND IF THEY WILL EVEN REACH NORTH EAST
IL AND NW INDIANA. THE ONGOING CONVECTION OVER NORTHEAST IOWA MAY
SHIFT EAST PRODUCING SHOWERS ALONG THE IL/WI STATE LINE...OR IT MAY
DISSIPATE AND WE SEE A DRY MORNING OUTSIDE OF THE CONVECTION ALONG
THE GUST FRONT. SINCE CONFIDENCE IS VERY LIMITED...DECIDED TO KEEP A
LOW END CHANCE TO SLIGHT CHANCE OF RAIN THROUGH MID MORNING.

THE COLD FRONT WHICH CURRENTLY STRETCHES FROM NORTHEAST WI THROUGH
SOUTH CENTRAL IA WILL SLIDE THROUGH THE CWA THIS MORNING AND THEN
STALL OVER LASALLE COUNTY IL THROUGH BENTON COUNTY INDIANA LATE THIS
AFTERNOON.  SHORT TERM GUIDANCE SUGGESTS CAPE WILL INCREASE THIS
AFTERNOON SO HAVE LIKELY POPS SPREADING ACROSS THE CWA THIS AFTN.
HAVE MEDIUM CONFIDENCE IN HOW FAR NORTH THE CONVECTION WILL REACH.
CURRENTLY HAVE LIKELIES OVER THE I-88 CORRIDOR BUT THE NORTHERN
EXTENT MAY REMAIN SOUTH OF I-88.

A MID LEVEL WAVE PUSHES NORTH INTO IOWA THIS EVENING AND EXPECTING
IT TO FORCE THE NEXT ROUND OF STORMS. EXPECTING SHOWERS AND AND A
FEW EMBEDDED THUNDERSTORMS TO COVER THE CWA BY LATE THIS EVENING.
STORMS SHOULD REMAIN TIED TO THE STALLED FRONT TUESDAY AND HAVE
MEDIUM-LOW CONFIDENCE IN HOW CONVECTION WILL BEHAVE. THINKING THE
NOCTURNAL WAVE OF STORMS WILL DISSIPATE AS THEY LIFT NORTH AWAY FROM
THE FRONT...WHILE ADDITIONAL SCATTERED CONVECTION WILL FESTER ALONG
THE FRONT. KEPT AT LEAST A LOW END CHANCE OVER THE WHOLE CWA EVEN
THOUGH AREAS NORTH OF I-80 MAY BE DRY TUESDAY AFTERNOON.

FOR TEMPS...TODAY SHOULD BE A BIT COOLER WITH THE COLD FRONT MOVING
THROUGH SO HAVE HIGHS AROUND 70 ALONG THE IL/WI STATE LINE AND THEN
IN THE UPPER 70S SOUTH OF I-80. WINDS SHOULD TURN ONSHORE ALONG THE
LAKE KEEPING TEMPS IN THE MID 60S TO AROUND 70.  TUESDAY LOOKS EVEN
COOLER IF YOU ARE NORTH OF THE FRONT WITH HIGHS IN THE 60S...AND
ONLY IN THE 50S ALONG THE LAKE. SOUTH OF THE FRONT...LOCATIONS
SHOULD BE IN THE UPPER 70S TO LOW 80S. BREAKS IN CLOUD COVER COULD
LEAD TO A FEW SITES GETTING INTO THE MID 80S.

JEE

&&

.LONG TERM...
331 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE STATIONARY FRONT BEGINS TO SHIFT NORTH AS A WARM FRONT TUESDAY
NIGHT AND COULD SEE ISOLATED TO SCATTERED SHOWERS AND PERHAPS
THUNDERSTORM DEVELOPMENT NORTH OF THE FRONT.  CAPE VALUES DROP OFF
QUICKLY OVERNIGHT SO NOT EXPECTING WIDESPREAD THUNDERSTORM
DEVELOPMENT.

WE ARE IN THE WARM SECTOR WEDNESDAY WITH SOUNDINGS SHOWING NO CAP AND
A FEW HUNDREDS OF J/KG OF CAPE. ISOLATED TO SCATTERED THUNDERSTORM
DEVELOPMENT IS POSSIBLE ESPECIALLY WED AFTN NORTH OF A RENSSELAER
TO RFD LINE. TEMPS WILL BE WARMER AWAY FROM THE LAKE WITH HIGHS IN
THE LOW TO MID 80S. IT WILL BE IN THE MID TO UPPER 60S ALONG THE
LAKE.  GUIDANCE FEATURES A FEW LOBES OF VORTICITY MOVING ALONG THE
UPPER LEVEL RIDGE...BUT THEY SHOULD REMAIN WEST OF THE CWA. THIS
WOULD LEAD TO A DRY NIGHT WEDNESDAY NIGHT...BUT IF THE VORTS SHIFT
EAST...COULD SEE SCATTERED SHOWER DEVELOPMENT.

THE NEXT SURFACE LOW FORMS OVER THE UPPER PLAINS/MIDWEST THURSDAY
MORNING AND REACHES SOUTHERN ONTARIO FRIDAY MORNING. ITS COLD FRONT
STALLS OVER NORTHERN IL SUNDAY MORNING.  THEREFORE LOOKING AT
ANOTHER ACTIVE PERIOD WITH MULTIPLE PERIODS OF SHOWERS AND
THUNDERSTORMS LATE THIS WEEK THROUGH THE WEEKEND.  THE FORECAST
LOOKS ODDLY SIMILAR TO WHAT WE WILL GO THROUGH EARLY THIS WEEK.
TEMPERATURES START ABOVE NORMAL IN THE 80S AWAY FROM THE LAKE
THURSDAY AND THEN COOL TO THE 70S SATURDAY AND SUNDAY. A LAKE BREEZE
WILL KEEP TEMPS ALONG THE LAKE IN THE 60S.  FOR WHAT IT IS
WORTH...WPC IS FORECASTING UPWARDS OF 3 INCHES OF RAIN OVER THE NEXT
7 DAYS.

JEE

&&

.AVIATION...

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

* WNW WINDS QUICKLY TURNING NORTHEAST THIS AFTERNOON LIKELY
  INCREASING TO 10 KT OR SLIGHTLY HIGHER THROUGH EARLY AFTERNOON
  BEFORE EASING THIS EVENING.

* A BRIEF PERIOD OF MVFR CIGS AROUND 2500-3500 FT THROUGH MID
  AFTERNOON.

* SMALL CHANCE OF -SHRA THIS AFTERNOON...BUT CHANCES OF
  SHRA/EMBEDDED TS SHARPLY INCREASING BY LATE EVE INTO OVERNIGHT.

* MVFR AND POSSIBLE IFR CONDITIONS WITH EAST WINDS TUESDAY
  MORNING.

KMD

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

VARIBLE NORTHWEST WINDS PREVAIL UNDER A FAIRLY LIGHT PRESSURE
GRADIENT REGIME. MEANWHILE...WINDS AS OF 18Z HAD ALREADY SHIFTED
TO ENE ALONG THE LAKEFRONT. A COMBINATION OF NORTHERLY WINDS FROM
THE SOUTHWARD MOVING FRONT AND LAKE BREEZE WINDS WILL ALLOW WINDS
INLAND TO SHIFT TO NE IN THE COMING HOURS. CONFIDENCE ON SPECIFIC
WIND DIRECTION IS NOT SUPER HIGH...BUT SHOULD BE IN THE ENE-NNE
DIRECTION AND EXPECT IT TO BE 10 KT OR SLIGHTLY HIGHER WITH THE
INITIAL PUSH.

MVFR CIGS WILL ALSO HOLD FOR AT LEAST THE NEXT FEW HOURS UNTIL THE
COLD FRONT ARRIVES. A FEW HIGH RESOLUTION MODELS SUGGEST A SHOWER
OR TWO IS POSSIBLE ACROSS NE IL THIS AFTERNOON...BUT LOW
CONFIDENCE IN THIS SO HELD IT OUT OF THE TAFS. THEN THE EVENING
PERIOD INITIALLY LOOKS ON THE QUIETER SIDE BEFORE SUBTLE SHORTWAVE
IN WSW FLOW ALOFT ALLOWS THE SOUTHWARD SHIFTING COLD FRONT TO MOVE
BACK NORTHWARD. EXPECT INCREASING COVERAGE OF SHOWERS AFTER 4Z-6Z
FROM SOUTHWEST TO NORTHEAST. LOCALLY HEAVY DOWNPOURS SEEM THE MOST
LIKELY HAZARD...WITH SOUNDINGS SUGGESTING AT LEAST WEAK ELEVATED
CAPE SUPPORTING EMBEDDED TS. CONFIDENCE ON TS COVERAGE IS LOW BUT
HIGH ON SHOWERS DURING THE 6Z-12Z PERIOD. THE BOUNDARY STALLS OUT
ALLOWING -SHRA TO BE POSSIBLE DURING THE MORNING HOURS AS
ADDITIONAL WEAK SW FLOW ENERGY PROPOGATES THROUGH. INCREASED
DEWPOINTS IN THE COOLER AIR MASS NORTH OF THE FRONT WILL PROMOTE
LOW MVFR TO POSSIBLY IFR CONDITIONS TUESDAY MORNING.

KMD


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

* MEDIUM-HIGH IN NORTHEAST WINDS THIS AFTERNOON BUT MEDIUM ON
  TIMING AND WHEN SPEEDS WILL INCREASE OVER 10 KT.

* MEDIUM-HIGH IN CIGS HOLDING AROUND 2500-3500 FT THROUGH MID-LATE AFTERNOON.

* MEDIUM-HIGH ON TIMING OF SHRA TONIGHT AND LOW-MEDIUM ON THUNDER
  COVERAGE.

* HIGH IN EAST WINDS TUESDAY MORNING AND MEDIUM-HIGH IN MVFR
  CONDITIONS. LOW-MEDIUM IN WHETHER IFR WILL OCCUR.

KMD

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT-WEDNESDAY...CHANCE OF STORMS. LIGHT EAST WINDS.
THURSDAY...CHANCE OF STORMS DURING THE NIGHT. SOUTH WINDS.
FRIDAY...CHANCE OF STORMS. SOUTH WINDS.
SATURDAY-SUNDAY...CHANCE OF STORMS. WINDS BECOMING NORTHEAST.

MTF

&&

.MARINE...
257 AM CDT

A COLD FRONT WILL ADVANCE SOUTHWARD ACROSS THE REGION THIS
MORNING REACHING THE FAR SOUTHERN PART OF THE LAKE BY EARLY
AFTERNOON. THIS WILL TURN WINDS TO THE NORTH-NORTHEAST. WHILE THE
LAKE HAS WARMED CONSIDERABLY IN THE PAST FEW WEEKS...THE COOLER
AIR BEHIND THE FRONT COMBINED WITH THE HIGH MOISTURE ALONG IT MAY
GENERATE FOG NAMELY ACROSS THE SOUTHERN PART OF THE LAKE. WINDS
WILL TURN EASTERLY LATER TONIGHT AND INTO TUESDAY AND THEN BACK TO
THE SOUTHEAST AND SOUTH TUESDAY NIGHT INTO WEDNESDAY AS THE FRONT
RETURNS NORTHWARD AS A WARM FRONT. A WARM SECTOR WILL REMAIN OVER
THE LAKE DURING THURSDAY AND FRIDAY MEANING STABILITY SHOULD KEEP
GUSTS MAINLY IN THE 20-25 KT BALLPARK DURING THAT TIME.

MTF

&&

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

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.