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 050900
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
400 AM CDT TUE MAY 5 2015

.SHORT TERM...
329 AM CDT

THROUGH TONIGHT...

A LOOSELY-DEFINED AND NON-INTENSE MCS IS MOVING ACROSS NORTHERN
ILLINOIS DURING THE PREDAWN WITHIN A BROAD ZONE OF WARM ADVECTION.
RADAR MOSAIC AND VAD WIND PROFILER DATA INDICATE THE PRESENCE OF
A MID-LEVEL SHORT WAVE THAT LIKELY MAY BE CONVECTIVELY-ENHANCED
HELPING TO FOCUS THE BULK OF THE RAIN AND EMBEDDED THUNDER. BASED
ON RADAR TRENDS...HAVE GONE A LITTLE FURTHER SOUTH WITH RAIN AND
THUNDER CHANCES THROUGH 9 AM OR SO COMPARED TO THE SUITE OF HIGH-
RESOLUTION GUIDANCE. OVERALL EXPECT THE COVERAGE OF PRECIPITATION
TO CONSIDERABLY DIMINISH DURING THE MID TO LATE MORNING HOURS
WITH THE WAVE PASSING NORTHEAST. TRAILING SHOWERS AND A FEW
STORMS ARE LIKELY TO LINGER ALONG AND NORTH OF I-80 DURING THE
LATTER MORNING.

WHILE THE MID-LEVEL FLOW IS EXPECTED TO BECOME LESS DISTURBED BY
AFTERNOON PER WATER VAPOR ANALYSIS AND RAP AND NAM
FORECASTS...THE CHANCES FOR AFTERNOON CONVECTION LINGER IN THE
HIGH PWAT AIR /1.4 INCHES +/. THESE CHANCES WILL BE ATTACHED TO
OUTFLOWS/CONVERGENCE ZONES TRAILING THE MORNING SHORT WAVE AND
ITS CONVECTION...AS WELL AS THE SYNOPTIC CONVERGENCE ALONG THE
STATIONARY FRONT THAT EARLY THIS MORNING IS ROUGHLY NEAR I-74.
THIS FEATURE IS EXPECTED TO CREEP NORTHWARD THIS MORNING WITH THE
DECAY OF CONVECTION AND HEATING IN THE WARM SECTOR. THIS FRONT
WILL SEPARATE TEMPERATURES LIKELY AROUND 80 IN THE SOUTHERN
FORECAST AREA TO THE COOLER AND CLOUDY 60S IN NORTHEAST
ILLINOIS...WITH EVEN LOWER TO MID 50S ALONG THE LAKE SHORE. DEW
POINTS IN THE LOWER-MID 60S ALONG THE BOUNDARY WILL PROVIDE
MARGINAL BUT SOME MIXED LAYER INSTABILITY NEAR THE BOUNDARY THIS
AFTERNOON. CONVECTIVE ALLOWING MODELS GENERALLY SHOW DEVELOPMENT
THIS AFTERNOON BUT VARY WIDELY IN COVERAGE. WITH WEAK MID-LEVEL
FLOW AND BUILDING HEIGHTS NOT EXPECTING ANYTHING SEVERE AND HAVE
GONE WITH SCATTERED OR CHANCE WORDING DEPENDING ON THE AREA. THE
PRESENT MOST FAVORED FOCUS THIS AFTERNOON LOOKS TO BE ALONG I-80
AND JUST NORTH OF...BUT THAT COULD CERTAINLY SHIFT OR BE MORE
DIFFUSE...AND THE DAY SHIFT WILL BE ABLE TO BETTER ASSESS POST-
MORNING CONVECTIVE TRENDS.

MODELS AGREE ANY SHOWERS/STORMS THIS AFTERNOON WILL WANE IN THE
EVENING BEING MORE DIURNALLY DRIVEN. THE FRONTAL BOUNDARY WILL
LIKELY NOT MAKE TOO MUCH PROGRESS NORTH DURING THE
NIGHT...HANGING AROUND I-80 OR SO. THE HIGH ABSOLUTE MOISTURE
ALONG THE BOUNDARY COULD RESULT IN FOG ACROSS THE AREA...SOME OF
WHICH MAY BE DENSE AND LINGER INTO EARLY WEDNESDAY MORNING. HAVE
ADDED SOME GENERAL MENTION INTO THE FORECAST FOR THE TIME BEING.

MTF

&&

.LONG TERM...
329 AM CDT

WEDNESDAY NIGHT THROUGH MONDAY...

ATTENTION IN THE LONG RANGE IS FIRST ON THE IMPRESSIVE EARLY MAY
WARMTH THAT WILL MAKE IT FEEL LIKE SUMMER IN SOME PLACES WEDNESDAY
AND AREAWIDE THURSDAY AND POTENTIALLY FRIDAY TOO. THE UPPER JET
PATTERN COMING IN FROM THE PACIFIC ON WEDNESDAY INTO THURSDAY
CARVES A MORE AMPLIFIED PATTERN...FAVORING BUILDING HEIGHTS AND
LOW-LEVEL SOUTHERLY FLOW TO INCREASE. GIVEN ALREADY ABOVE-NORMAL
TEMPERATURES UP TO CENTRAL ILLINOIS IN RECENT DAYS...THIS SYNOPTIC
PATTERN WILL FAVOR REPLENISHING AND ADDING TO THAT WARMTH AS WELL
AS SPREADING IT NORTH.

THE FRONTAL BOUNDARY IS LIKELY TO BREAK DOWN SOMEWHAT ON WEDNESDAY
AS JUST BROAD SOUTHERLY FLOW BEGINS. THIS FLOW WILL NOT BE STRONG
ENOUGH TO PREVENT LAKE COOLED AIR TO LIKELY REMAIN OVER NORTHEAST
ILLINOIS AND POSSIBLY EVEN FAR NORTHWEST INDIANA. APART FROM THE
MID 60S TO MID 70S IN THESE AREAS...LOWER TO POSSIBLY MID 80S ARE
EXPECTED ACROSS THE SOUTHERN AND FAR WESTERN FORECAST AREA.

THURSDAY WILL SEE SOUTH-SOUTHWEST WINDS INCREASE ENOUGH TO PREVENT
ANY LAKE COOLING. A THERMAL RIDGE DEFINED BY 925MB TEMPERATURES
OF 18C-19C AND 850MB TEMPERATURES OF 13-14C. USING REANALYSIS DATA
SINCE 1979...WHEN THESE WARM OF TEMPERATURES HAVE BEEN EXPERIENCED
IN THE FIRST HALF OF MAY IT YIELDS AN AVERAGE HIGH OF 83 DEGREES
AT CHICAGO OHARE. WITH SUNSHINE HIGHLY LIKELY ON THURSDAY GIVEN
THE AMPLIFIED FLOW KEEPING CIRRUS/DEBRIS AWAY ON MODEL
SOLUTIONS...HAVE BOOSTED TEMPERATURES TO THESE VALUES AND EVEN
SLIGHTLY HIGHER. SOME UPPER 80S ARE CERTAINLY POSSIBLE GIVEN THIS
PATTERN. THE RECORD HIGH FOR CHICAGO ON THURSDAY MAY 7TH IS 87
DEGREES SET IN 1964.

THE SECOND FOCUS ON THE LONG RANGE IS CONVECTIVE CHANCES. THE
POTENTIAL BEGINS FRIDAY WITH A NORTHERN STREAM FRONT EASING TOWARD
THE AREA...WHICH WILL COOL TEMPERATURES FOR SATURDAY AND POSSIBLY
SUNDAY TOO...ESPECIALLY FOR LAKE ADJACENT AREAS. AS THE UPPER-
LEVEL SOUTHWESTERLY FLOW INCREASES LATER IN THE WEEKEND...STORM
CHANCES WILL INCREASE AS HIGH PWAT AIR IS AGAIN FORECAST TO
ESTABLISH ITSELF ACROSS THE CORN BELT REGION. TIMING OF SHOWERS
AND STORMS LOOK TO AGAIN BE TIED TO MID-LEVEL IMPULSES WHICH CAN
OFTEN BE SUBTLE...WHICH DIMINISHES PREDICTABILITY AT THIS
POINT...SO CONTINUE WITH CHANCES.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* RAIN CONTINUES THROUGH THE MORNING. A FEW CLAPS OF THUNDER ARE
  NOT OUT OF THE QUESTION THROUGH DAYBREAK.

* EAST WINDS INCREASE TO 10-11 KT THIS MORNING AND AFTERNOON.

* IFR CIGS ARE EXPECTED BY 12Z AND NOT EXPECTING CIGS TO LIFT TO
  MVFR UNTIL THIS EVENING IF NOT LATER.

* ANOTHER CHANCE OF SHOWERS AND PERHAPS A THUNDERSTORM THIS AFTN.

JEE

//DISCUSSION...UPDATED 06Z...

THE MESSY PATTERN CONTINUES. A SWATH OF SHOWERS AND A FEW
THUNDERSTORMS ARE SLOWLY PUSHING NORTHEAST AND WILL IMPACT ALL OF
THE TERMINALS. LIGHTNING STRIKES ARE FEW AND FAR BTWN SO KEPT
VCTS GOING THROUGH 12Z. IT IS STILL RATHER DRY OUT THERE DESPITE
THE RAIN...SO MVFR CIGS ARE ADVANCING SLOWLY. ALL GUIDANCE MEMBERS
INDICATE THE IFR CIGS TO OUR WEST WILL INFILTRATE THE TERMINALS
EARLY THIS MORNING. THE FRONT CURRENTLY OVER CENTRAL IL WILL
REMAIN SOUTH OF THE TERMINALS TODAY...WHICH SHOULD ME WE ARE
LOCKED INTO IFR CIGS UNTIL THE FRONT LIFTS NORTH WEDNESDAY
MORNING. WINDS WILL BE OUT OF THE EAST AS WELL.

GUIDANCE ALSO HINTS AT ANOTHER ROUND OF SHOWERS AND PERHAPS A
THUNDERSTORM THIS AFTERNOON SO PUT A PROB30 IN AS CONFIDENCE IS
NOT OVERLY HIGH GIVEN HOW MESSY THE PATTERN IS.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE IN SHOWERS THROUGH THIS MORNING AND ONLY A FEW
  LIGHTNING STRIKES THROUGH DAYBREAK. MEDIUM-LOW CONFIDENCE IN
  OCCURRENCE AND COVERAGE OF -SHRA AND TSRA THIS AFTN.

* MEDIUM-HIGH CONFIDENCE IN VSBY...STRONGER DOWNPOURS COULD LOWER
  VSBY TO 2SM.

* MEDIUM-HIGH CONFIDENCE IN CIGS DROPPING TO IFR THIS MORNING.
  MEDIUM CONFIDENCE IN CIGS LIFTING TO MVFR THIS EVENING AS THEY
  COULD REMAIN IFR OVERNIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

WEDNESDAY...SLIGHT CHANCE TSRA. MAINLY VFR. SOUTHEAST WINDS.

THURSDAY...VFR. SOUTH WINDS.

FRIDAY...CHANCE TSRA. MAINLY VFR. SOUTH WINDS.

SATURDAY...CHANCE OF TSRA WITH BRIEF MVFR...THOUGH MAINLY VFR.
SOUTHWEST WINDS BECOMING EAST-NORTHEAST.

SUNDAY...CHANCE OF TSRA. BRIEF MVFR  POSSIBLE. SOUTHEAST WINDS.

RATZER

&&

.MARINE...
212 AM CDT

A STATIONARY FRONT IS OVER CENTRAL IL AND IT WILL REMAIN SOUTH OF
THE LAKE UNTIL IT LIFTS NORTH AS A WARM FRONT WEDNESDAY.
THEREFORE...NORTHEAST TO EAST WINDS WILL BECOME SOUTH WEDNESDAY
NIGHT BEHIND THE WARM FRONT.  HIGH PRESSURE CURRENTLY OVER LAKE
SUPERIOR SHIFTS EAST OF LAKE MICHIGAN WEDNESDAY AND REMAINS OVER THE
EASTERN SEABOARD THROUGH THE WEEK.  SOUTH WINDS UP TO 20 KT AT TIMES
ARE EXPECTED THROUGH FRIDAY.  THE NEXT LOW FORMS OVER THE NORTHERN
ROCKIES WEDNESDAY AND MOVES OVER ONTARIO THURSDAY NIGHT AND FRIDAY.
THE LOWS COLD FRONT SWEEPS OVER THE LAKE SATURDAY AND WINDS BECOME
NORTH BEHIND THE FRONT.

JEE

&&

.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.