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 290850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
350 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

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

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.

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

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

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

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

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

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

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.