Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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 260739
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
239 AM CDT TUE MAY 26 2015

.SHORT TERM...
255 PM CDT

THROUGH TUESDAY...

SHOWERS CONTINUE TO DIMINISH AS WE GET ON THE SUBSIDENT SIDE OF THE
DEPARTING UPPER TROUGH AXIS THAT WILL QUICKLY EXIT TO THE NORTHEAST
TONIGHT. SURFACE LOW PRESSURE IS PUSHING INTO UPPER MICHIGAN WHILE
LEAVING MODEST PRESSURE RISES IN ITS WAKE. WIND GUSTS TO 30 TO
LOCALLY 35 MPH WILL CONTINUE THROUGH THE AFTERNOON. EXPECT TO SEE
A LITTLE MORE BLUE SKY THROUGH THE AFTERNOON/EARLY EVENING WHICH
WILL ALLOW TEMPERATURES TO SLOWLY INCH UPWARD TO THE UPPER 70S TO
LOW 80S...THOUGH WITH MOIST SW FLOW EXPECT THESE LOWER CLOUDS TO
LINGER AROUND A BIT LONGER.

THE ACTIVE PATTERN CONTINUES ACROSS THE AREA FOR THE NEXT 24 HOURS.
SEVERAL UPPER LEVEL LOW PRESSURE SYSTEMS ARE NOTED IN AFTERNOON
WATER VAPOR IMAGERY. THE FIRST IS OVER THE NEBRASKA PANHANDLE...WITH
ASSOCIATED LEADING SHORTWAVE ENERGY TRIGGERING SOME SHOWERS AND T-
STORMS ACROSS IOWA...THEN THE BIGGER SHOWS TO THE SOUTH WITH THE
COMPLEX OF STRONG/SEVERE THUNDERSTORMS ASSOCIATED WITH A NEGATIVELY
TILTED TROUGH IN THE TEXAS. THE NORTHERN SHORTWAVE IS EXPECTED TO
CONTINUE DEVELOPING SHOWERS AND STORMS ACROSS IOWA AND INTO FAR
WESTERN ILLINOIS AND WISCONSIN. SOME OF THIS MAY CLIP OUR FAR
NORTHWESTERN COUNTIES...INCLUDING THE ROCKFORD AREA...BUT FEEL AT
THIS POINT THAT IT SHOULD LARGELY BE OFF FARTHER NW. HAVE HELD OFF
AND KEPT THIS ACTIVITY OUT OF AREA.

THEN TONIGHT THE LOWER LEVEL FRONTAL BOUNDARY ASSOCIATED WITH THE
NORTHERN WAVE WILL SAG SOUTHEAST TOWARD THE AREA LATE TONIGHT. MUCH
OF THE GUIDANCE THEN BRINGS THE SOUTHERN SHORTWAVE TOWARD OUR AREA
LATE TONIGHT AND MORE SO ON TUESDAY ON A DECENT UPPER LEVEL JET. THE
LARGE SUITE OF GUIDANCE KEEPS THESE TWO LOWS SEPARATE...ALLOWING
MUCH OF THE NORTHERN STREAM SHOWERS/STORMS TO LARGELY REMAIN OUT OF
AREA...BUT THEY MAY BEGIN TO AFFECT AREAS WEST OF I-39 IN ILLINOIS
OVERNIGHT.

TUESDAY MORNING IS WHEN BETTER CHANCES OF SHOWERS AND SCATTERED
THUNDERSTORMS WOULD BE. THIS MID MORNING/EARLY AFTERNOON PERIOD
FEATURES MODEST LOW/MID LEVEL ISENTROPIC LIFT/PW VALUES APPROACHING
1.5 INCHES AND THETA-E RIDGE NOSING IN FROM THE SOUTH. WE SHOULD
HAVE SOME SHOWERS AND THUNDERSTORMS MOVING FROM SOUTH TO NORTH
DURING THIS TIME FRAME.  DEPENDING ON THE INTERACTION OF THESE TWO
SYSTEMS AND IF THINGS SLOW DOWN A BIT...BETTER INSTABILITY WILL BE
TAPPED INTO IN THE AFTERNOON. THE NAM WOULD SUGGEST THIS
SOLUTION...WHILE THE GLOBAL GFS/ECMWF SUGGEST THE MID-MORNING TO
EARLY AFTERNOON PERIOD WOULD BE THE MOST LIKELY PERIOD WHERE DEEPER
MOISTURE IS AVAILABLE AND CO-LOCATED WITH THE UPPER FORCING.
CONFIDENCE ON TIMING IS ONLY MEDIUM WHICH REQUIRED CARRYING AN
EXTENDED PERIOD OF LIKELY POPS FOR MUCH OF THE DAY.

KMD

&&

.LONG TERM...
229 AM CDT

WEDNESDAY THROUGH MONDAY...

WEDNESDAY THROUGH THURSDAY...
OPEN 500MB WAVE WILL BE LIFTING NORTHEAST ACROSS THE UPPER MIDWEST
INTO ONTARIO AND EVENTUALLY QUEBEC...WITH HEIGHTS SLOWLY INCREASING
WED AFTN. SFC FEATURES REMAIN DISORGANIZED WED...WITH A BOUNDARY
SLOWLY SHIFTING EAST. OPER GUIDANCE DIFFERS ON HOW QUICKLY PRECIP
WILL DEPART THE REGION. ENSEMBLE DATA SUGGESTS HOLDING ONTO CHC TO
SLIGHT CHC POPS MAINLY FOR THE CENTRAL/EASTERN CWFA WED/WED EVE.
ALTHOUGH WITH SOME HINT OF SFC HEIGHTS NUDGING UP...IT IS POSSIBLE
THAT SOME DRY AIR COULD FILTER IN AND KICK PRECIP EAST BY MIDDAY AND
ALLOW FOR A MAINLY DRY WED. SFC WINDS WILL BE TURNING SOUTHWEST TO
WEST...KEEPING AN OFFSHORE FLOW FOR LOCATIONS CLOSE TO LAKE
MICHIGAN. TEMPS SHOULD YET AGAIN TOUCH UPR 70S TO ARND 80 WED...IF
CLOUDS AND PRECIP CAN PUSH EAST BY MIDDAY...SOME CLEARING WOULD
ALLOW SFC TEMPS TO PUSH A COUPLE DEGREES WARMER INTO THE LOW 80S IN
SOME LOCATIONS. LATE IN THE EVENING THE GRADIENT SLACKENS
FURTHER...AND COULD ALLOW A LATE DAY ONSHORE FLOW TO DEVELOP FOR
AREAS ADJACENT TO LAKE MICHIGAN.

MID-LVL FLOW BEGINS TO FLATTEN AS A WEAK SFC RIDGE BECOMES ORIENTED
FROM WESTERN QUEBEC SOUTH THROUGH THE EASTERN OHIO RIVER VALLEY.
THIS WILL GENERALLY ALLOW A SOUTHERLY FLOW...ALTHOUGH THE GRADIENT
IS NOT VERY STRONG. THIS SHOULD SET THE STAGE FOR A LAKE
BREEZE/ONSHORE FLOW TO DEVELOP THUR. TIMING COULD END UP BEING
SLIGHTLY EARLIER GIVEN THE LIGHT SFC GRADIENT. GUIDANCE HAS BEEN
CONSISTENT IN HOLDING PRECIP WEST/SOUTH OF THE FORECAST AREA
THUR...AS A RESULT OF THE WEAK SFC RIDGING. SO ONE MORE MILD DAY
WITH HIGHS WARMING BACK INTO THE UPR 70S/LOW 80S...HOWEVER AS
PREVIOUSLY NOTED...A LAKE BREEZE IS LIKELY TO DEVELOP. THIS WILL
BLEED THE MUCH COOLER MARINE AIR WEST ACROSS NORTHEAST IL AND
DOWNTOWN CHICAGO. IF THE TIMING IS EARLIER IN THE DAY THUR...TEMPS
MAY NOT WARM BEYONG THE LOW/MID 60S ALONG THE CHICAGO LAKEFRONT.

FLOW THEN TURNS SOUTHERLY THUR NIGHT WITH THE MORE PROGRESSIVE FLOW
IN THE MID-LVLS PUSHING THE RIDGING EAST. A RETURN FLOW MOISTURE
WILL CONTINUE TO BE FOCUSED ACROSS THE CENTRAL CONUS THUR EVE...WITH
A SLOW MOVING FRONTAL BOUNDARY NUDGING EAST THUR NIGHT TOWARDS
WESTERN IL. THIS FRONTAL BOUNDARY WILL BECOME ENERGIZED AS A ROBUST
500MB VORT MAX BREAKS SOUTH FROM CENTRAL CANADA LATE THUR NIGHT.

THIS SHOULD ALLOW FOR AN ATMOSPHERIC RIVER TO DEVELOP FROM THE
SOUTHERN PLAINS STRETCHING NORTH THROUGH THE MID-MISSOURI VALLEY
INTO THE WESTERN GREAT LAKES EARLY FRI MORNING.


FRIDAY THROUGH EARLY NEXT WEEK...
ENSEMBLES CONTINUE TO PROG A ROBUST TROUGH SLIDING SOUTH FROM
CENTRAL CANADA FRI. THIS COUPLED WITH DOWNSTREAM MID-LVL RIDGING
ACROSS THE SOUTHEAST CONUS WILL STRENGTHEN THE FRONTAL BOUNDARY
THAT WILL BE ORIENTED FROM THE SOUTHERN PLAINS STRETCHING
NORTHEAST THROUGH THE GREAT LAKES REGION INTO WESTERN QUEBEC.

THIS SETUP IS IDEAL FOR THE DEVELOPMENT OF AN ATMOSPHERIC RIVER WITH
ABUNDANT LOW LEVEL MOISTURE AND EFFICIENT PRECIP PRODUCING
CONVECTION.

OPER GUIDANCE HAS BEEN RELATIVELY CONSISTENT WITH BRINGING A SERIES
OF WAVES ALONG THE SLOW MOVING FRONTAL BOUNDARY FRI AFTN/EVE...THEN
THE BOUNDARY SHOULD SLIDE EAST WITH WINDS QUICKLY VEERING
NORTH/NORTHEAST FOR SAT AND USHERING IN MUCH COOLER AIR TO THE
REGION.

CURRENT INDICATIONS ARE THAT HIGHS SAT MAY STRUGGLE TO WARM BEYOND
THE UPR 50S ACROSS NORTHEAST IL/NORTHWEST IN...WITH ONLY LOW 60S
ELSEWHERE. STRONG SFC RIDGE WILL REMAIN NORTH OF THE REGION...SO THE
PRIOR FRONTAL BOUNDARY MAY BECOME QUASI-STATIONARY FOR THE WEEKEND
ALONG THE OHIO VALLEY AND CONTINUE TO FEED PRECIP CHANCES TO THE
SOUTHERN CWFA.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SOUTH-SOUTHWEST WINDS OF AROUND 40 KT AT 1000 FT
  OVERNIGHT...SETTING UP LOW LEVEL WIND SHEAR.

* MVFR CEILINGS PROBABLE AT TIMES TUESDAY WITH A CHANCE FOR
  TEMPORARY IFR.

* PERIODS OF SHRA WITH PERIODIC TSRA FROM LATE TUESDAY MORNING
  THROUGH THE AFTERNOON.

* NEAR DUE SOUTH WINDS ON TUESDAY WITH PERIODIC GUSTS POSSIBLE
  AND SOME VARIABILITY BETWEEN SOUTHEAST AND SOUTHWEST.

KREIN

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

GUSTY SOUTH-SOUTHWEST WINDS HAVE DIMINISHED TO 10 KT OR LESS AND
BECOME SOUTHERLY. A LOW-LEVEL JET WILL DEVELOP OVERHEAD WITH
SSWLY-SWLY WINDS OF 40 KT TO 45 KT FLOW AT 1500-2000 FT UNTIL
ARND 12Z. SOME THUNDERSTORMS MAY DEVELOP THROUGH OVERNIGHT AHEAD
OF A FRONT FROM NRN MO THROUGH ERN IA AND INTO WI. THESE STORMS
WILL ONLY MAKE SLOW PROGRESS EASTWARD DUE TO THE STRONG SSWLY-SWLY
WINDS ALOFT SO...AND STORMS THAT DO DEVELOP SHOULD REMAIN NORTH
AND NORTHWEST OF AREA TAF SITES...THOUGH THERE IS A CHANCE THAT A
FEW STORMS COULD APPROACH THE RFD TERMINAL AREA VERY LATE
TONIGHT.

AS AN MID LEVEL DISTURBANCE MOVING FROM THE SOUTHERN PLAINS TO
NRN IL BY TUESDAY AFTERNOON MAY BRING ANOTHER ROUND OF SHOWERS
WITH SCT EMBEDDED THUNDERSTORMS TO THE REGION. UPPER LEVEL FORCING
FROM THE MID LEVEL DISTURBANCE AND AN UPPER LEVEL JET STREAM WILL
ENHANCE THE LIKELIHOOD FOR SHRA AND THE CHANCE FOR TSRA...WITH THE
MOST LIKELY CHANCE FOR ACTIVITY FROM 15Z THROUGH 02Z. SOME
UNCERTAINTY REMAINS IN PINNING DOWN THE EXACT PERIOD FOR THE
TSRA...SO WILL MAINTAIN THE GOING TEMPO FOR LATE MORNING THROUGH
EARLY AFTERNOON. HOWEVER...THE PCPN ACTIVITY COULD BE SHIFTED OR
EXPANDED IN TIME.

WINDS WILL BE SOUTHERLY ON TUESDAY...THOUGH DIRECTION MAY BE A BIT
VARIABLE AROUND CONVECTIVE ACTIVITY...THOUGH A GENERALLY SOUTHERLY
DIRECTION SHOULD PREVAIL THROUGH THE NIGHT AND MUCH OF THE DAY
TUESDAY. SOME GUSTINESS IS POSSIBLE THROUGH THE ENTIRE DAY...WITH
THE LATEST GUIDANCE SUGGESTING THAT WINDS COULD STRENGTHEN AND
BECOME EVEN MORE GUSTY THROUGH THE NIGHT TOMORROW NIGHT WITH WINDS
VEERING SWLY AS SURFACE LOW PRESSURE MOVES NORTHEAST ACROSS
SOUTHERN WISCONSIN.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH CONFIDENCE IN 40-45 KT SSWLY-SWLY FLOW ALOFT OVERNIGHT...BUT
  MEDIUM IN TRUE LLWS OCCURRING.

* HIGH CONFIDENCE IN WIND TRENDS OVERNIGHT AND TUESDAY MORNING.
  MEDIUM IN WIND TRENDS TOMORROW EVENING.

* MEDIUM CONFIDENCE IN MVFR CIGS TUESDAY MORNING WITH LOWER
  CONFIDENCE IN DURATION AND HOW LOW CIGS WILL DROP.

* HIGH CONFIDENCE IN SHOWERS AND AT LEAST A PERIOD OF TSRA. LOW
  CONFIDENCE IN SPECIFIC TSRA TIMING AND IMPACT ON THE TERMINALS
  WITH MULTIPLE ROUNDS POSSIBLE BETWEEN 15Z AND 02Z.

KREIN

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

WEDNESDAY...CHANCE OF TSRA. WEST WINDS.
THURSDAY...SLIGHT CHANCE OF TSRA LATE AT NIGHT. SOUTHEAST WINDS.
FRIDAY...INCREASING CHANCE OF TSRA THROUGH THE DAY AND NIGHT.
         SOUTHWEST WINDS.
SATURDAY...SHRA LIKELY WITH A CHANCE OF TSRA. NORTHEAST WINDS.
SUNDAY...CHANCE OF SHRA. EAST WINDS.

MTF

&&

.MARINE...
229 AM CDT

WARM MOIST AIR CONTINUES TO FEED NORTH ACROSS THE LAKE
TODAY...WHICH MAY HELP TO FURTHER ENHANCE ANY AREAS OF FOG THAT
HAVE ALREADY DEVELOPED. IT IS POSSIBLE PATCHY DENSE FOG MAY
DEVELOP...ALTHOUGH WINDS MAY BE JUST STRONG ENOUGH TO LIMIT THE
COVERAGE AND INTENSITY OF THE FOG. A SURFACE LOW PRESSURE SYSTEM
WILL BE LIFTING NORTH ACROSS EASTERN IOWA INTO CENTRAL WISCONSIN
THIS EVENING. THE GRADIENT WILL TIGHTEN ACROSS THE
CENTRAL/SOUTHERN PORTIONS OF THE LAKE...WHICH WITH WARMER
NEARSHORE WATERS EXPECT SOME SLIGHTLY BETTER MIXING TO OCCUR.
FURTHER OUT ACROSS THE OPEN WATERS THE WATER REMAINS COLD AND
EXPECT THE STABILITY TO MAKE IT DIFFICULT TO MIX TO THE SFC THE
HIGHER GUSTS. HIGH PRESSURE THEN ARRIVES LATE WEDNESDAY WITH LIGHT
WINDS DEVELOPING. THEN HIGH PRESSURE SHIFTS EAST THURSDAY
NIGHT...WITH SOUTHERLY WINDS DEVELOPING AGAIN FRIDAY. A FRONTAL
BOUNDARY WILL APPROACH LAKE MICHIGAN LATE FRIDAY NIGHT THEN
STEADILY SLIDE SOUTH ALONG THE LAKE. THIS WILL ALLOW WINDS TO
QUICKLY VEER FROM SOUTH TO NORTH/NORTHEAST SATURDAY. ALONG WITH
THIS QUICK WIND SHIFT WILL BE COOLER AIR SLIDING SOUTH OVER THE
LAKE. WAVES SHOULD EASILY BUILD SATURDAY FOR THE CENTRAL/SOUTHERN
PORTIONS OF THE LAKE.

BEACHLER

&&

.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.