Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | 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 292000
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.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 VISIBILITY 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 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

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

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 03Z/10PM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 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.