Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 251307
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
807 AM CDT MON MAY 25 2015

.UPDATE...756 AM CDT

COMPACT NEGATIVELY TILTED TROUGH AXIS IS SLIDING NORTHEAST THROUGH
IOWA AND WESTERN ILLINOIS. EASTERN EDGE OF THE TROUGH WILL MOVE
THROUGH NORTHEAST ILLINOIS THIS MORNING. NOTED UPTICK IN SHOWER
ACTIVITY ASSOCIATED WITH THIS WAVE IS PRODUCING MORE ORGANIZED BUT
STILL LARGELY SCATTERED SHOWERS. STILL TRACKING THIS FEATURE WILL
BRING THE BEST CHANCE FOR SOME BRIEF DOWNPOURS IN THE COMING
HOURS...AND THESE WILL SPREAD INTO THE WEST METRO AREA IN THE NEXT
HOUR...SPREADING INTO CHICAGOLAND SHORTLY THERE AFTER. THE CLOUDS
PRODUCING THE SHOWER ACTIVITY ARE SHALLOW AND MID LEVEL LAPSE
RATES ARE SUBPAR...THUS THUNDER SHOULD BE LIMITED AT BEST. SOME
WEAK INSTABILITY IS NOTED SOUTH OF I-80 WHICH DOES NOT PRECLUDE AN
ISOLATED STRIKE IN ANY STRONGER ACTIVITY.

REGARDING WINDS...WITH THE BROKEN TO OVERCAST LOW CLOUD
DECK...MIXING IS BEING LIMITED AND GETING GUSTS TO AROUND 30 KT OR
SO. ANY STRONGER GUSTS WOULD BE IN THE NEXT HOUR BEFORE A RAPID
DROP OFF LATER THIS MORNING.

KMD

&&

.SHORT TERM...
345 AM CDT

THROUGH MONDAY NIGHT...
FOR THE REMAINDER OF THE NIGHT AND INTO MONDAY MORNING...PCPN
CHANCES CONTINUE TO WANE AS LATEST RADAR TRENDS ONLY SHOW SOME SCT
SHRA WHICH ARE DECREASING IN INTENSITY.  IN SPITE OF DEWPOINTS IN
THE LOW 60S...AND A STRONG LOW LEVEL JET...50 KT AT 925 MB...THERE
IS AN ELEMENT LACKING WHICH IS SEEMS TO BE PREVENTING THE
MAINTENANCE OF SHRA/TSRA OVER NERN IL/NWRN IN.  THE MAIN MISSING
ELEMENTS IS FORCING.  THE SFC AND UPPER LEVEL LOW ARE WAY TO THE
WEST...OVER THE NRN PLAINS. THE SHORTWAVE CLIMBING UP THE NWRN
PERIPHERY OF THE HIGH AMPLITUDE RIDGE IS BEING SLOWED BY THE HIGH
AMPLITUDE...AND IS BEING FORCED TO A MORE WLY TRACK THROUGH THE
UPPER MISSISSIPPI VALLEY THAN PREVIOUSLY ANTICIPATED.  SO...FOR THE
REMAINDER OF THE OVERNIGHT HOURS AND THE DAYTIME HOURS MONDAY...HAVE
BACK OF TO ISOLD-SCT SHRA.  WILL KEEP ISOLD TS MENTION FOR THE LATE
MORNING HOURS...THROUGH AROUND NOON...WITH THE DAYTIME HEATING...BUT
CONFIDENCE IN ANY TS IS RATHER LOW AT THIS TIME.  BY THIS
AFTERNOON...A MID LEVEL DRY SLOT IS EXPECTED TO MOVE ACROSS THE
REGION...FURTHER LIMITING PCPN CHANCES AND IT IS QUITE LIKELY THAT
THE REGION WILL REMAIN DRY THROUGH THE DAY.  HOWEVER...WHILE THE
PCPN CHANCES ARE DIMINISHING...THE LIKELIHOOD OF STRONG WINDS IS
STILL A CONCERN.  WITH THE DIMINISHING PCPN CHANCES...LESS SKY COVER
THAN PREVIOUSLY ANTICIPATED IS ALSO POSSIBLE.  A STRONG SWLY
PRESSURE GRADIENT IS SETTING UP ACROSS THE REGION BETWEEN SFC
RIDGING ACROSS THE SERN CONUS AND AND LOW PRESSURE FROM THE UPPER
MISSISSIPPI VALLEY TO THE WESTERN PLAINS.  THE STRONG GRADIENT WILL
HELP DRIVE THE SFC WINDS AND THE DIMINISHING CLOUD COVER COULD HELP
ENHANCE DEEP LAYER MIXING...TAPPING STRONGER WINDS ALOFT.  SUSTAINED
25-25 MPH WINDS ARE LIKELY WITH GUSTS OF 30-35 MPH.
ALSO...PERSISTENT WARM/MOIST ADVECTION AT THE SFC WILL BRING
TEMPERATURES INTO THE LOW TO MIDDLE 80S WITH DEWPOINTS IN THE LOWER
60S.

FOR MONDAY NIGHT...THE BREEZY CONDITIONS WILL PERSIST INTO THE AS
THERE SHOULD BE LITTLE CHANGE TO THE SFC AND UPPER LEVEL PATTERNS.
THE UPPER RIDGE WILL LOSE A LITTLE AMPLITUDE AS SHORT WAVE ENERGY
OVERTOPS THE RIDGE...BUT GENERAL TROUGHING WILL PERSIST ACROSS THE
UPPER MISSISSIPPI VALLEY THROUGH THE CENTRAL PLAINS.  THE NEXT
CHANCE FOR PCPN WILL HOLD OFF UNTIL LATE TONIGHT/EARLY TUESDAY
MORNING AND THE NEXT SHORTWAVE LIFTS OUT OF THE SRN PLAINS AND INTO
THE MIDDLE MISSISSIPPI VALLEY.  AMPLE LOW LEVEL MOISTURE WILL
ALREADY BE IN PLACE SO IT WILL JUST A MATTER OF WHEN THE FORCING
WILL GET HERE.  AGAIN...THERE IS SOME CONCERN THAT THE FORCING WILL
BE TO THE WEST...WITH THE SHORTWAVE TRACKING THROUGH THE MIDDLE
MISSISSIPPI VALLEY AND INTO WI.  SO...WILL CARRY CHANCE POPS FOR THE
REGION...WITH LIKELY POPS APPROACHING THE PONTIAC AREA BY EARLY
TUESDAY MORNING.  THE PERSISTENT WARM/MOIST ADVECTIVE PATTERN AND
BREEZY CONDITIONS SHOULD KEEP TEMPERATURES FROM DROPPING OFF
SIGNIFICANTLY OVERNIGHT AND LOWS SHOULD BE IN THE MIDDLE TO UPPER
60S.

KREIN

&&

.LONG TERM...
239 AM CDT

TUESDAY THROUGH SUNDAY...

TUESDAY THROUGH WEDNESDAY...
500MB TROUGH AXIS WILL SLOWLY PIVOT EAST ACROSS THE CENTRAL PLAINS
INTO THE MID-MISSOURI VALLEY TUE...WITH A SFC WAVE SLIDING NORTH
ACROSS IOWA INTO CENTRAL WISC LATE TUE. THE SFC FEATURE IS NOT
EXPECTED TO BE STRONG...HOWEVER THE GRADIENT DOES TIGHTEN WITH
MODEST HEIGHT FALLS IN THE LOWEST LAYERS OF THE ATMOSPHERE. SOME
INSTABILITY DOES REMAIN ALONG WITH RELATIVELY MOIST SFC CONDS AS
DEW PTS WILL REMAIN IN THE UPR 50S/LOW 60S. PWAT VALUES WILL ALSO
HOVER JUST OVER 1 INCH...WHICH IS SEASONAL. WILL HOLD ONTO MENTION
OF RAIN AND THUNDER...BUT COULD SEE THIS MAINLY FOCUSED IN THE TUE
MORNING TIMEFRAME.

WITH CONSIDERABLE SOLAR SHIELDING PROGGED FOR TUE...TEMPS MAY
STRUGGLE TO WARM BEYOND THE MID/UPR 70S. BUT WITH GUIDANCE HINTING
AT A DRY SLOT LIFTING NORTHEAST ACROSS THE REGION TUE EVE...THIS
COULD INTRODUCE SOME EROSION TO THE CLOUD COVER IN THE AFTN HOURS
TUE AND ALLOW SOME SFC HEATING TO OCCUR AND PUSH TEMPS TO ARND 80.

GUIDANCE LIFTS THE DRY SLOT OVERHEAD LATE TUE NGT...WITH THE 500MB
TROUGH AXIS ARRIVING ARND DAYBREAK WED AND LIFTING EAST ACROSS LOWER
MICHIGAN. THIS WILL BRING DRY ONLY SLIGHT CHANCE POPS AS WEAK SFC
RIDGING BEGINS TO NUDGE EAST ACROSS THE MISSOURI VALLEY TOWARDS THE
FORECAST AREA MIDDAY WED. IT IS POSSIBLE THAT ENOUGH DRY AIR
INFLUENCE COULD ALLOW FOR REMOVAL OF THE SLIGHT CHANCE POPS WED
AFTN. THERMAL TROUGH LAGS BEHIND THE FRONTAL BOUNDARY WED...SO TEMPS
COULD STILL WARM BACK TO ARND 80 AND PERHAPS THE LOW 80S IN THE
SOUTHERN CWFA.

THURSDAY THROUGH SUNDAY...
ANTI-CYCLONIC FLOW ARRIVES THUR WITH AT LEAST ONE PERIOD OF DRY
WEATHER EXPECTED FOR NORTHERN IL/NORTHWEST IN. ONLY A COUPLE
ENSEMBLE MEMBERS CONTINUE TO PROG POPS ALONG THE SOUTHERN FORECAST
AREA THUR...BUT COULD SEE THIS TRENDING DRY IN THE NEXT FEW
SOLUTIONS. WITH WARM TEMPS ALOFT EXPECTED THUR AND THIN CLOUD
COVER...THUR HIGHS COULD PEAK IN THE LOW 80S.

THEN FOCUS TURNS TOWARDS THE UPCOMING WEEKEND AND A PATTERN SHIFT
AWAY FROM THE WARM/HUMID CONDITIONS. ENSEMBLES SHOW MINIMAL SPREAD
IN THE LATE WEEK PERIODS...WITH THE UPSTREAM RIDGE OVER
ALASKA/WESTERN CANADA AND A DOWNSTREAM MID-LVL RIDGE ACROSS THE
SOUTHEAST CONUS. BOTH OF THESE FEATURES IN TIME BEGIN TO
WEAKEN...WITH THE LONGWAVE PATTERN TRANSITIONING INTO A SEMI-ZONAL
ORIENTATION BY THE SECOND HALF OF THE WEEKEND.

OPER GUIDANCE HAS BEEN CONSISTENT WITH PROGGING A ROBUST 500MB
TROUGH TO SLIDE SOUTH FROM CENTRAL CANADA FRI...ALONG WITH A STRONG
CANADIAN SFC RIDGE ON IT/S HEELS. WITH A CHANNEL OF MOISTURE
REMAINING ACROSS THE SOUTHERN PLAINS STRETCHING NORTHEAST THROUGH
THE UPPER MIDWEST...THIS BOUNDARY WILL BECOME ACTIVE WITH A SFC WAVE
DEVELOPING ACROSS THE SOUTHERN PLAINS. THIS LOW WILL THEN LIFT
NORTHEAST TOWARDS THE CWFA FRI WITH A COLD FRONT ARRIVING ACROSS THE
FORECAST AREA SAT. WINDS LOOK TO SHIFT TO THE NORTH...WITH MUCH
COOLER AIR SLIDING SOUTH AND LIKELY KNOCKING TEMPS BACK TO SUB-
SEASONAL CONDS IN THE UPR 60S/NEAR 70 DEGREE RANGE SAT/SUN. IF
NORTHEAST WINDS MATERIALIZE...NEXT WEEKEND AREAS ADJACENT TO LAKE
MICHIGAN ALONG THE IL/IN SHORELINE COULD BE LOCKED IN THE UPR 50S TO
LOW 60S FOR HIGHS WITH A COLD FLOW OFF OF LAKE MICHIGAN.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* STRONG AND GUSTY SOUTH WINDS THROUGH EARLY EVENING.

* CHANCE SHRA/TSRA LATE TONIGHT THROUGH TOMORROW.

KREIN

//DISCUSSION...UPDATED 12Z...

MAIN CONCERN FOR TODAY WILL BE STRONG...GUSTY SOUTH WINDS. AS OF
11Z THIS MORNING...WINDS ARE ALREADY GUSTING TO 25-30KT AND EXPECT
THAT WITH DEEPER MIXING LATER THIS MORNING...SHOULD BE ABLE TO TAP
INTO A 50 KT LOW LEVEL JET TO MIX DOWN GUSTS TO 35 KT OR EVEN
SLIGHTLY HIGHER. THE STRONG LOW LEVEL JET SHOULD MOVE OFF TO THE
EAST BY EARLY AFTERNOON...SO WHILE WINDS SHOULD STILL BE STRONG
AND GUSTY...PEAK GUSTS SHOULD LOWER TO ARND 25KT.

WITH THE PERSISTENT FETCH OF LOW LEVEL MOISTURE INTO THE
REGION...A LAYER OF MVFR STRATOCU HAS OVERSPREAD THE REGION.
EXPECT THAT BASES SHOULD NOT LOWER MUCH LESS THAT 1800FT AGL.
THERE IS SOME UNCERTAINTY AS TO THE DURATION OF THE MVFR CLOUD
LAYER...BUT WITH LITTLE CHANGE TO THE OVERALL PATTERN THROUGH THE
DAY...THERE IS A CHANCE THAT THE MVFR CIGS COULD HANG IN THROUGH
MUCH OF THE DAY. HOWEVER...THERE IS ALSO A CHANCE THAT STRONGER
MIXING IN THE AFTERNOON HOURS COULD ALLOW FOR THE MVFR DECK TO
SCATTER OUT.

LATEST RADAR TRENDS INDICATE THAT AN AREA OF SHRA LIFTING NEWD
FROM CNTRL IL INTO INDIANA. THE TRAJECTORY OF THE PCPN AREA SHOULD
KEEP THE BULK OF THE PCPN EAST AND SOUTH OF GYY...THOUGH A FEW SCT
SHRA AREA NOT OUT OF THE QUESTION. ALSO...SOME SHRA ASSOCIATED
WITH A MID LEVEL IMPULSE LIFTING NORTH THROUGH IOWA AND INTO WRN
WI IS GENERATING SCT SHRA AS WELL. IT IS ALSO POSSIBLE THAT RFD
COULD SEE A FEW SHRA THIS MORNING...BUT THE PROBABILITY IS TOO LOW
TO INCLUDE IN THE TAF AS THE LATEST RADAR TRENDS INDICATE A
WEAKENING TREND THERE.

A SECONDARY LOW IS EXPECTED TO DEVELOP OVER THE UPPER MISSOURI
VALLEY THIS EVENING...KEEPING A MODEST PRESSURE GRADIENT OVER THE
REGION. SO MODERATE...GUSTY WINDS SHOULD PERSIST WELL INTO
TONIGHT. ANOTHER STRONG MID LEVEL IMPULSE IS EXPECTED TO TRACK
THROUGH THE MIDDLE MISSISSIPPI VALLEY AND INTO WISCONSIN LATE
TONIGHT...BRINGING A RENEWED CHANCE FOR SHRA/TSRA TO THE REGION
LATE TONIGHT AND TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* MEDIUM TO HIGH CONFIDENCE THAT THE TERMINALS SHOULD REMAIN
  DRY...THOUGH THERE IS A SMALL CHANCE FOR SOME SHRA INVOF THE
  TERMINALS THROUGH THE MORNING HOURS.

* MEDIUM CONFIDENCE IN CIG TRENDS.

* MEDIUM CONFIDENCE IN PCPN TIMING LATE TONIGHT.

KREIN

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

TUESDAY NIGHT...SHRA LIKELY/CHANCE TSRA. GUSTY SOUTHWEST WINDS.

WEDNESDAY...CHANCE OF SHRA/TSRA EARLY. WEST WINDS TURNING EAST.

THURSDAY...CHANCE SHRA/TSRA LATE. SOUTHEAST WINDS.

FRIDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. SOUTHWEST WINDS
BECOMING NORTHEAST OVERNIGHT.

SATURDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. NORTHEAST
WINDS.

SUNDAY...CHANCE TSRA. MVFR POSSIBLE. NORTHEAST WINDS.

KREIN

&&

.MARINE...
304 AM CDT

LOW PRESSURE WILL BE STEADILY LIFTING NORTH ACROSS THE MISSOURI
VALLEY THIS MORNING...REACHING LAKE SUPERIOR BY THIS EVENING AND
CONTINUING TO SLIDE EAST/NORTHEAST TOWARDS QUEBEC BY TUESDAY
MORNING. A FRONTAL BOUNDARY WILL REMAIN OVER THE FAR NORTHERN
PORTIONS OF LAKE MICHIGAN. MEANWHILE GUSTY SOUTHERLY WINDS ARE
EXPECTED TO INCREASE THIS MORNING...WITH OCCASIONAL GALES FOR THE
NEARSHORE WATERS OF IL/IN. ACROSS THE OPEN WATERS...EXPECT THE
WARM/MOIST AIR TO STRUGGLE TO REACH THE SFC OF THE LAKE WITH SOME
DEGREE OF LAKE STABILITY. WAVES WILL STEADILY BUILD ACROSS THE
NORTHERN HALF OF THE LAKE AS A RESULT OF THE LONG FETCH. STILL
FEEL THAT GUSTS WILL REACH 30KT ACROSS THE LAKE...HOWEVER
CONFIDENCE HAS DIMINISHED SLIGHTLY AS NEW GUIDANCE HAS BECOME A
LITTLE LESS WITH THE WIND FIELDS. NONETHELESS...WAVES FOR THE
NORTHERN HALF OF THE LAKE WILL LIKELY TOP OUT IN THE 4 TO 7 FT
RANGE WITH OCCASIONAL WAVES REACHING 9 FT THIS AFTERNOON/EVENING.

THE GRADIENT QUICKLY DIMINISHES THIS EVENING...BUT EXPECT
SOUTHERLY WINDS TO PERSIST. THIS WILL ALLOW WAVES TO SUBSIDE TO 3
TO 5 FT. ANOTHER LOW WILL ARRIVE TUE...WITH WINDS NUDGING BACK UP
HOWEVER WARM AIR WILL CONTINUE TO FLOW ACROSS THE LAKE AND COULD
FURTHER ENHANCE THE LAKE STABILITY AND KEEP WAVES FROM BUILDING TO
LARGE.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 9 AM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 3
     PM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...3 PM MONDAY TO 4 AM TUESDAY.

&&

$$

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