Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 192020
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
320 PM CDT SUN APR 19 2015

.SHORT TERM...
319 PM CDT

THROUGH MONDAY NIGHT...

AFTER ANOTHER WARM EARLY AFTERNOON ACROSS MUCH OF THE REGION RAIN IS
BEGINNING TO SPREAD NORTHWARD ACROSS SOUTHERN SECTIONS OF THE CHICAGO
METRO AREA AS OF THIS WRITING. THIS ACTIVITY WILL CONTINUE TO
OVERSPREAD THE REGION THROUGH THE AFTERNOON AND EVENING...WITH
TEMPERATURES LIKELY TO DROP BACK INTO THE UPPER 50S AND LOW 60S IN
THE RAIN.

THE MID-LEVEL DISTURBANCE...AND THE ASSOCIATED SURFACE SYSTEM WILL
QUICKLY SHIFT NORTHWARD OVER LOWER MICHIGAN OVERNIGHT...AND IT
APPEARS THAT THE RAIN WILL BECOME MORE SHOWERY AND INTERMITTENT OR
POSSIBLY JUST SOME DRIZZLE LATER THIS EVENING AND INTO THE EARLY
MORNING ACROSS MUCH OF THE AREA AS THIS INITIAL MID LEVEL
DISTURBANCE SHIFTS NORTH OF THE AREA AND SOME DRIER MID LEVEL AIR
SHIFTS OVER THE SOUTHEASTERN HALF OF MY AREA. SOME ADDITIONAL RAIN
SHOWERS ARE POSSIBLE AGAIN EARLY MONDAY WITHIN A REGION OF MID LEVEL
DEFORMATION AND RAP AROUND MOISTURE ASSOCIATED WITH THE DEEPENING
LOWER AND MID LEVEL LOW OVER THE UPPER GREAT LAKES REGION AND
SOUTHERN CANADA.

CONDITIONS SHOULD DRY OUT MONDAY AFTERNOON...WITH ONLY A SMALL
CHANCE OF AN ADDITIONAL SHOWER DEVELOPING AS COLDER AIR ALOFT
STEEPENS THE LOWER LEVEL LAPSE RATES. THE MAIN STORY DURING THE
AFTERNOON WILL BE THE WINDS. WINDS ARE EXPECTED TO INCREASE OUT OF
THE WEST-NORTHWEST DURING THE DAY AS STOUT SURFACE PRESSURE
GRADIENT SETS UP OVER THE REGION AS THE SURFACE LOW DEEPENS TO
AROUND 985 MB ACROSS ONTARIO MONDAY AFTERNOON. MODEL SOUNDINGS
SUGGEST GOOD AFTERNOON MIXING TO AROUND 850 MB SHOULD ALLOW FOR
GUSTS OF AROUND 30 KT AT TIMES...ESPECIALLY DURING THE AFTERNOON.
THESE WIND GUSTS SHOULD ABATE MONDAY EVENING...BUT STRONG WINDS
LOOK TO DEVELOP AGAIN ON TUESDAY. SEE LONG TERM DISCUSSION FOR
MORE INFO ON TUESDAY`S WINDS.

KJB

&&

.LONG TERM...
319 PM CDT

TUESDAY THROUGH SUNDAY...

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH BELOW NORMAL TEMPS
THROUGH THE FORECAST.

LARGE UPPER LEVEL CENTER WILL BE CENTERED ACROSS THE REGION AT THE
START OF THE PERIOD...AND REMAIN SITUATED THROUGH MUCH OF THE WORK
WEEK AS IT SLOWLY MOVES EAST. SEVERAL VORT LOBES ARE ANTICIPATED TO
WRAP AROUND THIS UPPER LEVEL LOW ON TUESDAY AND WITH STEEPENING
LAPSE RATES...EXPECT SKY COVER TO INCREASE THROUGH THE DAY WHILE
SCATTERED SHOWERS BECOME POSSIBLE...ESPECIALLY ACROSS NORTHERN
ILLINOIS. AS THIS OCCURS...LIKELY DEEP MIXING WITH STRONG FLOW ALOFT
WILL ALLOW FOR ANOTHER WINDY DAY. GUIDANCE IS SUGGESTING THAT
ADVISORY CONDITIONS COULD BE REACHED IN THE AFTERNOON...AND WILL
NEED TO CONTINUE MONITORING THIS POTENTIAL. ANY REMAINING PRECIP AND
CLOUD COVER SHOULD EXIT THE AREA TUESDAY NIGHT WITH DRY CONDITIONS
EXPECTED. SOME GUIDANCE DEVELOPS A SWATH OF PRECIP OVER THE CWA LATE
IN THE NIGHT INTO EARLY WEDNESDAY. HOWEVER...A MORE LIKELY SCENARIO
AT THIS TIME WOULD BE FOR DRY CONDITIONS AND SO HAVE LEFT OUT ANY
POPS AT THIS TIME. ONGOING CAA WILL MAKE FOR CHILLY CONDITIONS
TUESDAY NIGHT...WITH LOW TEMPS IN THE 30S. IF PRECIP WERE TO OCCUR
DURING THIS PERIOD...THESE COLDER CONDITIONS COULD SUPPORT THE
POTENTIAL FOR AT LEAST A RAIN SNOW MIX ACROSS NORTHERN ILLINOIS.
EXPECT DRY CONDITIONS WITH BELOW NORMAL TEMPS THROUGH THE REST OF
THE FORECAST PERIOD...WITH FORECAST HIGHS IN THE 50S. COLD NIGHT
TIME LOWS IN THE 30S COULD BECOME AN ISSUE LATE IN THE WORK WEEK AS
HIGH PRESSURE IS ANTICIPATED TO MOVE OVERHEAD...WITH LIGHTER WINDS
AND THE COLD TEMPS POSSIBLY CREATING A SETUP FOR FROST.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS ARND 10 KT BCMG NORTH LESS THAN 10 KT THIS EVENING.

* RAIN MOVING IN OVER THE NEXT 1-2 HOURS WITH MVFR VSBY. COULD
  HAVE PERIODS OF IFR VSBY WITH HEAVIEST SHOWERS.

* CIGS LOWER TO IFR LATE THIS AFTN THROUGH EARLY MONDAY MORNING.

* SCATTERED SHOWERS OVERNIGHT WITH ANOTHER ROUND OF -SHRA EARLY
  MONDAY MORNING.

* GUSTY WEST WINDS WITH MAX GUSTS ARND 30 KT MONDAY AFTN.

JEE

//DISCUSSION...UPDATED 18Z...

RAIN IS SLOWLY PUSHING NORTH AND IS JUST SOUTH OF I-80 AT THIS
TIME. MVFR AND LOWER CIGS ARE OVER CENTRAL AND SOUTHERN IL AND
INDIANA BUT ALSO PUSHING NORTH. ADJUSTED PRECIP AND CIG TIMING
BASED ON RADAR AND SATELLITE TRENDS. MVFR VSBY WILL BE TIED TO THE
HEAVIER RAIN SHOWERS...AND CIGS WILL LOWER TO MVFR LATE THIS AFTN
AND THEN TO IFR THIS EVENING. ALL GUIDANCE MEMBERS SHOW IFR CIGS
ACROSS THE TERMINALS.

WILL EITHER SEE SCATTERED SHOWERS OR A BREAK IN RAIN AFTER
MIDNIGHT TONIGHT WITH ANOTHER ROUND OF RAIN PUSHING WEST TO EAST
EARLY MONDAY MORNING.

EAST WINDS BCM NORTHEAST ARND 10 KT LATE THIS AFTN AND BACK TO NW
BY 03Z. WINDS CONTINUE TO BACK TO WEST BY EARLY MONDAY MORNING.
GUSTY WINDS FOLLOW THE BAND OF RAIN SHOWERS...WITH 20G30KT
EXPECTED BY MONDAY AFTERNOON. THINKING THE GUSTY WINDS AND DRIER
AIR WILL HELP CIGS LIFT LATE MONDAY MORNING AND AFTN...BUT HAVE
MEDIUM CONFIDENCE IN HOW QUICKLY CIGS LIFT TO VFR.

JEE

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

* HIGH CONFIDENCE IN RAIN SHOWERS THIS AFTERNOON AND EVENING.

* HIGH CONFIDENCE IN PERIODS OF MVFR VSBY...LOW CONFIDENCE IN
  OCCURRENCE AND PERSISTENCE OF IFR VSBY.

* HIGH CONFIDENCE IN IFR CIGS...MEDIUM CONFIDENCE TIMING AND
  PERSISTENCE.

* HIGH CONFIDENCE IN WIND TRENDS OVERNIGHT...MEDIUM CONFIDENCE IN
  TIMING OF BACKING WINDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST PARAMETERS.

JEE

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

MONDAY NIGHT...MVFR BECOMING VFR.

TUESDAY...SLGT CHANCE PM SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

FRIDAY...MAINLY VFR. CHC PM SHRA.

SATURDAY...MAINLY VFR.

BEACHLER

&&

.MARINE...
257 AM CDT

LOW PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY LIFT NORTHEAST
TOWARDS THE LOWER GREAT LAKES REGION TONIGHT/EARLY MON. GUIDANCE
CONTINUES TO INDICATE THE GRADIENT WILL TIGHTEN ACROSS THE
LAKE...HOWEVER THIS APPEARS TO BE MORE FOCUSED ALONG THE SOUTHERN
TIP OF THE LAKE. WITH THE CONTINUED EASTERLY WINDS...IT IS
POSSIBLE MARGINAL SMALL CRAFT CONDITIONS MAY DEVELOP FOR THE
ILLINOIS SHORELINE LATER TODAY INTO TONIGHT. THE LOW PRESSURE WILL
THEN APPROACH THE LAKE AND BRIEFLY WEAKEN THE GRADIENT EARLY MON.
THEN AS THE LOW LIFTS NORTHEAST LATER IN THE DAY MON...IT WILL
DEEPEN AND MERGE WITH ANOTHER LOW...WHICH WILL CREATE A TIGHT
GRADIENT OVER THE LAKE AND INCREASING WEST/NORTHWEST TUE. AFTER
TUE THE DOMINANT WIND DIRECTION WILL BE NORTHWEST THROUGH MID-
WEEK...BEFORE RELAXING TO THE WEST. THIS WILL ALLOW HIGHER WAVES
TO BE FOCUSED IN THE SOUTHERN HALF OF LAKE MICHIGAN THROUGH MID-
WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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