Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 032225
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
525 PM CDT SUN MAY 3 2015

.SHORT TERM...
303 PM CDT

THROUGH MONDAY...

COMPACT BUT FAIRLY VIGOROUS MCV MOVING INTO NORTHWEST ILLINOIS
MID AFTERNOON WILL CONTINUE TO PUSH ACROSS FAR NORTHERN ILLINOIS
THROUGH EARLY THIS EVENING. CONVECTION HAS RE-FLARED ENTERING INTO
THE DIURNALLY FAVORABLE PERIOD AND WITH WEAK DESTABILIZATION
TAKING PLACE IN ADVANCE OF THE MCV WOULD ANTICIPATE SHOWERS AND
THUNDERSTORMS TO CONTINUE TO MARCH STEADILY EASTWARD ACROSS MAINLY
NORTHERN HALF OF THE CWA...LIKELY MOVING OUT ONTO THE LAKE EARLY
THIS EVENING.

SHOULD SEE A LULL IN THE CONVECTION FOR A TIME IN THE WAKE OF THE
MCV BEFORE CHANCES OF SHOWERS AND THUNDERSTORMS BEGIN TO RAMP BACK
UP AGAIN LATER TONIGHT WITH THE APPROACH OF THE COLD FRONT FROM
THE NORTHWEST. GUIDANCE CONTINUES TO HIT QPF PRETTY HARD LATE
TONIGHT INTO FIRST HALF OF THE DAY MONDAY AND AM MAINTAINING
LIKELY POPS...BUT GIVEN THAT WE WILL BE ENTERING A TYPICAL
CONVECTIVE DOWNTIME AM QUITE LEARY ABOUT ABOUT SHOWERS AND
THUNDERSTORMS BEING AS WIDESPREAD AND PRECIPITATION HEAVY AS MODEL
WOULD SUGGEST.

SYNOPTIC FRONT...POTENTIALLY MODIFIED BY CONVECTION TONIGHT INTO
MONDAY MORNING...WILL BE IN THE PROCESS OF MAKING ITS WAY
SOUTHWARD MONDAY AND LIKELY GET AN ADDED BOOST FROM THE LAKE.
MODELS DIFFER ON TIMING OF THE FRONTAL PASSAGE MONDAY AND THIS
TIMING UNCERTAINTY ALONG WITH THE POTENTIAL FOR CONVECTION AND/OR
CONVECTIVE DEBRIS ADD A LOT OF UNCERTAINTY TO THE TEMPERATURE
FORECAST FOR MONDAY. WHEN THE LAKE ENHANCED FRONT MOVES THROUGH
LOOK FOR TEMPS ALONG THE SHORE TO CRASH INTO THE 50S TO PERHAPS
40S RIGHT ALONG THE SHORE. CANNOT RULE OUT SOME MARINE FOG AS WELL
GIVEN THE COLD MARINE LAYER ENCOUNTERING 55F+ DEWPOINTS.

COULD SEE SOME DIURNAL REDEVELOPMENT OR RE-INTENSIFICATION OF
CONVECTION MONDAY AFTERNOON ALONG THE FRONT...BUT GUIDANCE SUGGESTS
BETTER LARGE SCALE ASCENT WILL BE MOVING AWAY FROM THE STALLING OUT
FRONTAL BOUNDARY DURING THE AFTERNOON. AHEAD OF THE FRONT
TEMPERATURES SHOULD ONCE AGAIN SOAR INTO THE 70S...POTENTIALLY LOWER
80S WHERE RAIN AND CLOUD COVER HOLD OFF AND ALLOW FOR BETTER
HEATING.

IZZI

&&

.LONG TERM...
303 PM CDT

MONDAY NIGHT THROUGH SUNDAY...

QUASI-STATIONARY FRONT LIKELY TO TAKE UP RESIDENCE OVER THE AREA
MONDAY NIGHT AND POTENTIALLY THROUGH WEDNESDAY NIGHT DEPENDING ON
YOUR GUIDANCE OF CHOICE. CONVECTION WILL LIKELY ULTIMATELY PLAY A
ROLE IN FRONTAL TIMING...BUT CERTAINLY THE SLOWER NORTHWARD ADVANCE
ADVERTISED BY THE WRF-NAM WOULD SEEMS REASONABLE BASED ON THE
EXPECTED PERIODIC MCS ACTIVITY. ONE SUCH MCS LOOKS TO POTENTIALLY
AFFECT THE AREA MONDAY NIGHT INTO EARLY TUESDAY MORNING...BEFORE
RAIN CHANCES WITH THE FRONT DWINDLE A BIT AS UPPER HEIGHTS RISE
PLACING THE MORE FAVORED VORT TRACK WELL NORTH AND REMOVED FROM THE
FRONTAL BOUNDARY.

THERE IS THE POTENTIAL FOR FOG NORTH OF THE BOUNDARY MONDAY NIGHT
REALLY THROUGH WEDNESDAY...PARTICULARLY AT NIGHT INLAND AND JUST
ABOUT ANYTIME NEAR THE LAKE.

FRONT IS PROGGED TO BEGIN HEADING BACK NORTHWARD WEDNESDAY AND PLACE
THE MAJORITY OF OUR CWA IN THE WARM AND HUMID AIR MASS. THE ONE
POTENTIAL EXCEPTION WEDNESDAY COULD BE THE ILLINOIS LAKEFRONT WHERE
SOUTHEAST WIND CUTTING OFF THE LAKE COULD PREVENT THE FULL EFFECTS
OF THE WARMTH FROM REACHING THE BEACHES. BY WEDNESDAY NIGHT AND
THURSDAY A STRONGER SOUTHERLY FLOW SHOULD SEND THE FRONT WELL NORTH
INTO WISCONSIN WITH UNSEASONABLY WARM AND HUMID AIR MASS OVER THE
ENTIRE CWA THURSDAY THROUGH FRIDAY.

FRONT DOES LOOK TO SAG SOUTHWARD INTO THE VICINITY OF OUR CWA OVER
THE WEEKEND BRINGING THE THREAT OF OCCASIONAL SHOWERS/STORMS AND
PROBABLY SETTING UP A LARGE TEMPERATURE GRADIENT ONCE AGAIN WITH
WINDS OFF THE LAKE NORTH OF THE BOUNDARY POTENTIALLY KEEPING
LAKESIDE AREAS RATHER CHILLING WHILE LOCATIONS SOUTH OF THE FRONT
REMAIN WARM/HUMID.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* PERIOD OF TSRA LATE AFTN/EARLY EVENING.

* WINDS LIKELY BECOMING NE-E BEHIND STORMS FOR A FEW HOURS.

* CHANCE OF SHRA/TSRA MID EVENING THRU EARLY MORNING.

* SHRA WITH SCATTERED TSRA FROM DAYBREAK THRU LATE MORNING.

* WIND SHIFT TO NORTHEAST LATE MONDAY MORNING/EARLY MONDAY
  AFTERNOON.

MS/RATZER

//DISCUSSION...UPDATED 22Z...

AREA OF RA/TSRA ASSOCIATED WITH MCV CIRCULTATION OVER NORTHERN IL
WILL CONTINUE TO MOVE EAST AND ACROSS THE CHI TERMINALS OVER THE
NEXT FEW HOURS. GUSTY SOUTH-SOUTHWEST AHEAD OF STORMS WILL
DIMINISH...AND LIKELY BECOME NORTHEAST AND THEN EAST INTO THIS
EVENING IN WEAK MESO-HIGH BEHIND THE SYSTEM. WINDS WILL LIKELY
BECOME SOUTH-SOUTHWEST AGAIN TONIGHT...THOUGH PERHAPS NOT UNTIL
LATE EVENING/OVERNIGHT.

RATZER

PREVIOUS 18Z DISCUSSION...

MULTIPLE FORECAST CONCERNS THIS PERIOD WITH RELATIVELY LOW
CONFIDENCE OVERALL. UPPER WAVE CURRENTLY MOVING ACROSS EASTERN IA
WILL MOVE ACROSS NORTHERN IL THIS AFTERNOON. THUNDERSTORMS ACROSS
FAR NORTHWEST IL AND EASTERN IA HAVE BEEN WEAKENING AS THEY MOVE
EAST INTO MORE STABLE AIR THOUGH SHOWERS HAVE MADE IT AS FAR EAST
AS DPA. THIS AREA OF SHOWERS MAY AFFECT ORD OVER THE NEXT FEW
HOURS. ADDITIONAL SHOWERS ARE POSSIBLE THRU LATE AFTERNOON OR
EARLY EVENING AS THIS WAVE MOVES ACROSS THE AREA. CONFIDENCE
REGARDING COVERAGE IS LOW ENOUGH TO MAINTAIN JUST VICINITY MENTION
FOR NOW. BEST CHANCE OF ANY THUNDER WOULD BE AT RFD AND STILL LOW
ENOUGH TO NOT MENTION AT THIS TIME.

APPEARS THERE WILL BE A BREAK IN PRECIP POTENTIAL EARLY THIS
EVENING BUT THERE REMAINS QUITE A BIT OF DISAGREEMENT ABOUT HOW
MUCH WARM AIR ADVECTION SHRA/TSRA MAY DEVELOP OVER THE AREA LATER
THIS EVENING. SHORT TERM/HI RES GUIDANCE SUGGESTS NEW DEVELOPMENT
WILL OCCUR ON THE BACK SIDE OF THIS WAVE BY MID EVENING...PERHAPS
AS EARLY AS 02Z AND POSSIBLY CONTINUING THRU 07Z-09Z. GIVEN THE
LONGER PERIOD OF POSSIBLE ACTIVITY AND LOW CONFIDENCE IN BOTH
OCCURRENCE AND COVERAGE...OPTED TO STAY DRY IN THE TAFS DURING
THIS TIME PERIOD...BUT THIS WILL NEED TO BE MONITORED CLOSELY
LATER THIS AFTERNOON INTO THIS EVENING.

A COLD FRONT WILL MOVE ACROSS THE WESTERN GREAT LAKES TONIGHT AND
INTO NORTHERN IL BY MID/LATE MONDAY MORNING. ADDITIONAL SHOWERS
AND THUNDERSTORMS WILL DEVELOP AHEAD OF THIS FRONT AND MOVE ACROSS
THE TERMINALS MONDAY MORNING. MEDIUM CONFIDENCE THIS WILL OCCUR SO
MAINTAINED PREVAILING MENTION BUT DURATION AND START/END TIMES
WILL LIKELY REQUIRE REFINEMENT. CIGS WILL EVENTUALLY LOWER INTO
MVFR EITHER WITH THE PRECIP OR ONCE WINDS TURN NORTHEAST OFF THE
LAKE. FAIRLY CONFIDENT WIND SHIFT TO THE NORTHEAST WILL HAPPEN...
BUT LOW CONFIDENCE AGAIN WITH TIMING. CMS

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH FOR TSRA IN VCNTY LATE THIS AFTERNOON/EARLY EVE.
* MEDIUM FOR SHRA/SCATTERED TSRA DAYBREAK THRU LATE MONDAY
  MORNING.
* HIGH FOR WIND SHIFT MIDDAY MONDAY...MEDIUM FOR TIMING.

CMS/RATZER

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

MONDAY NIGHT-TUESDAY...SHRA WITH PERIODS OF TSRA LIKELY. MVFR
                       LIKELY AT TIMES. EAST-NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA. SOUTHEAST WINDS.
THURSDAY...VFR. SOUTH WINDS.
FRIDAY-SATURDAY...CHANCE OF TSRA. SOUTH WINDS.

MTF

&&

.MARINE...
253 PM CDT

BRISK SOUTH-SOUTHWEST WINDS PREVAILING ACROSS LAKE MICHIGAN WILL
EASE THIS EVENING.  A VERY STABLE VERTICAL PROFILE RESULTING FROM
THE WARM MOIST AIRMASS ADVECTING NORTH OVER COLD LAKE WATER ALSO IS
INHIBITING BETTER TRANSFER OF HIGHER MOMENTUM AIR ALOFT TO THE LAKE
SURFACE.

WITH WINDS EASING OFF THIS EVENING WILL ALLOW SMALL CRAFT ADVISORY
TO EXPIRE AS SCHEDULED.  RELAXING PRESSURE GRADIENT OVERNIGHT IN
ADVANCE OF APPROACHING COLD FRONT WILL CAUSE WINDS TO SLACKEN
FURTHER OVERNIGHT.  THE COLD FRONT ITSELF DROPS SOUTHEAST ACROSS
ABOUT THE NORTH HALF OF THE LAKE BY 0700-0800 CDT MONDAY... AND THEN
REACHES THE FAR SOUTH END OF THE LAKE BY MID AFTERNOON MONDAY.

WINDS WILL BECOME NORTHWEST AND THEN QUICKLY NORTH BEHIND THE FRONT
MONDAY... AS THE FRONT THEN STALLS JUST SOUTH OF LAKE MICHIGAN
MONDAY NIGHT.  WINDS ACROSS THE LAKE WILL BECOME NORTHEAST TO EAST
LATER MONDAY NIGHT AND TUESDAY... BEFORE THE FRONT LIFTS BACK NORTH
AS A WARM FRONT TUESDAY NIGHT AND WEDNESDAY.  GIVEN THE PRESENCE OF
A WARM MOIST AIRMASS WOULD EXPECT FOG TO DEVELOP OVER THE LAKE
TUESDAY INTO WEDNESDAY. AS THE FRONT THEN LIFTS BACK NORTH... THIS
WILL SET THE STAGE FOR SOUTHERLY WINDS ON THE LAKE FOR MUCH OF LATE
WEEK.

ED F

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 7 PM SUNDAY.

&&

$$

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