Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 161955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT WED APR 16 2014

.DISCUSSION...
313 AM CDT

WEATHER WITHOUT ANY SIGNIFICANT IMPACTS LOOKS TO BE THE RULE THROUGH
THE EARLY PART OF THE WEEKEND WITH MUCH OF THE ATTENTION ON
TEMPERATURES AND WIND SPEEDS TODAY AND THEN SMALL CHANCES FOR
PRECIPITATION THURSDAY NIGHT AND FRIDAY.

TODAY AND TONIGHT...
THE UPPER TROUGH RESPONSIBLE FOR THE CHILLY DAY YESTERDAY IS
ADVANCING EAST OVER EASTERN CANADA AND NEW ENGLAND AND IS
RESPONSIBLE FOR PORTIONS OF AT LEAST 22 STATES UNDER FREEZE WARNINGS
THIS MORNING! STRONG MID-LEVEL DRYING IS SEEN ALL THE WAY DOWN TO
THE NORTHERN GULF AND AT THE SURFACE THE DRY AIR HAS ADVANCED
SOUTHWARD ALL THE WAY INTO THE GULF WITH SEVERAL PLATFORMS/BUOYS
REPORTING DEW POINTS IN THE 30S. SO BASICALLY THE GULF IS NOT
AVAILABLE FOR THE NEXT SYSTEM PASSING ACROSS THE REGION TONIGHT AND
THAT WILL BE A MAIN REASON WE LOOK TO REMAIN PRECIPITATION FREE.
THIS SYSTEM IS A FAIRLY WELL-DEFINED LOW AMPLITUDE UPPER WAVE THAT
IS MOVING EAST ACROSS SD THIS MORNING AND WILL FOLLOW ITS PARENT JET
STREAK/DIVERGENCE ALOFT TO THE EAST NORTHEAST OVER THE UPPER GREAT
LAKES TONIGHT WHERE A SNOW STORM IS FORECAST ACROSS NORTHERN WI/U.P.
OF MICHIGAN.

THE QUICK EASTWARD PROGRESSION OF THE SYSTEM SURFACE LOW BY
AFTERNOON WILL TIGHTEN THE PRESSURE GRADIENT ACROSS THE LOCAL AREA.
WHILE THERE WILL BE SOME HIGH CLOUDS...MIXING WILL AID THE PRESSURE
GRADIENT IN CREATING SUSTAINED SPEEDS AROUND 20 MPH AND GUSTS PLUS
10 MPH OF THAT. SOME 35 MPH GUSTS SHOULD EVEN BE REALIZED IN NORTH
CENTRAL IL. TEMPERATURES LOOK TO BOUNCE BACK 15 DEGREES OR EVEN
HIGHER THAN YESTERDAY GIVEN WARMING OF THE BOUNDARY LAYER AND
LOW-LEVEL ADVECTION. A SLIGHT COMPONENT OFF THE LAKE INTO CITY OF
CHICAGO AND NORTHWARD WILL KEEP THESE LAKE ADJACENT AREAS A HANDFUL
OF DEGREES COOLER...BUT COMPARED TO 33 DEGREES YESTERDAY...THE
FORECAST OF AROUND 50 TODAY FOR THESE LOCATIONS SHOULD BE WELCOME.
OUTLYING AREAS LOOK TO REACH THE MID 50S. UPSTREAM DEW POINTS ARE IN
THE UPPER TEENS TO MID 20S ACROSS DOWNSTATE IL/IN INTO THE TENNESSEE
RIVER VALLEY...SO EXPECTING A FAIRLY DRY AIR MASS TODAY WITH
HUMIDITY IN THE 25-35 PERCENT RANGE IN MOST AREAS.

AS THE UPPER WAVE PASSES TO THE NORTH TONIGHT THE PACIFIC MOISTURE
REMAINS NORTH AS WELL AND THE WARM AIR ADVECTION ASCENT HERE REMAINS
WITHIN A LOW PWAT ATMOSPHERE. WOULD NOT BE SURPRISED TO SEE SOME
RADAR ECHOES/VIRGA ACROSS FAR NORTHERN IL BUT THAT SHOULD BE ABOUT
IT. WITH MORE CLOUD COVER TONIGHT AND SOUTHERLY WINDS OF 10-20 MPH
CONTINUING...LOWS LOOK TO ONLY DIP INTO THE LOWER-MID 40S.

THURSDAY AND FRIDAY...
THE SYSTEM SURFACE FRONT/TROUGH IS EXPECTED TO MOVE INTO THE
FORECAST AREA THURSDAY MORNING AND BECOME STATIONARY. THIS DOES NOT
LOOK TO BE A VERY PRONOUNCED BAROCLINIC BOUNDARY. HAVE CONSIDERABLY
LOWERED CLOUD COVER DURING THURSDAY MORNING AND EARLY AFTERNOON AND
WITH THAT BOOSTED TEMPERATURES SOME...WITH 55 TO 60 PROBABLE. A
SHEARING UPPER WAVE IS EXPECTED TO MOVE NORTHEAST OVER THE BOUNDARY
THURSDAY NIGHT. A LOOK AT THE DPROG/DT...OR TREND...OF SEVERAL
MODELS OVER THE PAST FOUR CYCLES SHOW CONSIDERABLY LESS FORCING AND
MOISTURE AVAILABILITY FOR PRECIPITATION. HAVE CONTINUED THE FORECAST
TREND TO CUT BACK POPS BUT ALSO TO CONFINE THE AREA WHERE
CONVERGENCE/FRONTOGENESIS IS DEPICTED NEAR THE BOUNDARY. BY FRIDAY
THE ENVELOPE OF GUIDANCE HAS FORCING EAST OF THE AREA...HOWEVER ONE
FINAL SEPARATE MID-LEVEL IMPULSE SEEN ON THE NCEP MODELS PASSES OVER
THE AREA FRIDAY AFTERNOON. CONTINUE A SMALL CHANCE OF RAIN SHOWERS
WITH THIS. THE NORTH TO NORTHEAST FLOW BEHIND THE FRONT ON FRIDAY
SHOULD LEAD TO A DECENT TEMPERATURE DIFFERENCE FROM NEAR THE LAKE TO
OUTLYING AREAS...WITH MID 40S TO MID 50S PRESENTLY FORECAST ACROSS
THAT CROSS SECTION. LOCAL CLIMATOLOGICAL RESEARCH FAVORS SUCH A
SPREAD THIS TIME OF YEAR WITH ONSHORE FLOW.

THIS WEEKEND INTO EARLY NEXT WEEK...
WHILE THE FLOW IS PROGRESSIVE ACROSS THE FAR NORTHERN CONUS/SOUTHERN
CANADA IT LOOKS TO BE FAR ENOUGH NORTH TO HAVE LITTLE INFLUENCE ON
THE AREA SATURDAY AND POTENTIALLY EVEN SUNDAY...ESPECIALLY IF GOING
TOWARD THE EC AND GEM WHICH WE HAVE LEANED OUR FORECAST. THESE
MODELS INDICATE THAT A CLOSED UPPER LOW OVER THE SOUTHEAST U.S.
DEPICTED BY MODELS LATE IN THE WEEKEND MAY LEAD TO A SLOWING OF THE
NEXT SYSTEM TO APPROACH THE AREA FROM THE ROCKIES...MORE SO SUNDAY
NIGHT AND MONDAY. TEMPERATURES LOOK TO BE BACK TO NORMAL SUNDAY AND
MONDAY.

MTF

&&

.AVIATION...

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

* STRONG AND GUSTY SSE WINDS CREATING CROSSWIND ISSUES ON EAST-
  WEST RUNWAYS.

* POSSIBLE LLWS TONIGHT WHEN GUSTS RELAX IN MORE STABLE
  CONDITIONS.

LENNING

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

A LOW PRESSURE CENTER LIFTING ACROSS IOWA INTO WISCONSIN TODAY AND
TONIGHT WILL SUPPORT GUSTY SSE WINDS OVER THE LOCAL TERMINALS TODAY.
GUSTS SHOULD DIMINISH OVERNIGHT WITH SFC COOLING AND BETTER LOW
LEVEL STABILITY...THOUGH STRONG WINDS ALOFT MAY CREATE MARGINAL
LLWS CONDITIONS. WINDS GRADUALLY TURN SOUTHWEST TOWARD MORNING
THEN AROUND TO THE WEST LATE TOMORROW AFTER THE LOW CROSSES LAKE
SUPERIOR AND A TRAILING COLD FRONT PASSES THROUGH THE AREA. PRECIP
CHANCES WITH THIS SYSTEM APPEAR LOW UNTIL LATE TOMORROW.

LENNING

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

* GENERALLY HIGH CONFIDENCE IN ALL ELEMENTS THOUGH LESS SURE
  ABOUT LLWS TONIGHT. GUSTS MAY ALSO RELAX A BIT EARLIER THAN 03Z.

LENNING

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

THURSDAY NIGHT...CHC RAIN. MVFR PSBL.
FRIDAY...SLT CHC RAIN. MVFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.
TUESDAY...VFR.

BMD

&&

.MARINE...
203 PM CDT

LOW PRESSURE...CURRENTLY ACROSS FAR WESTERN IOWA...WILL SHIFT
NORTHEASTWARD ACROSS THE UPPER LAKES REGION BY LATE
THURSDAY...WHILE WEAKENING. THIS WILL RESULT IN A CONTINUATION OF
THE SOUTH-SOUTHEASTERLY WINDS ACROSS THE LAKE TONIGHT AROUND 30 KT
RANGE. HOWEVER...AS A WEAK FRONTAL BOUNDARY MOVES ACROSS THE LAKE ON
THURSDAY...THE WINDS ABATE AND BECOME WEST-NORTHWESTERLY BY THURSDAY
EVENING. GENERALLY LIGHT NORTHERLY FLOW IS EXPECTED FRIDAY AND INTO
EARLY SATURDAY AS A WEAK SURFACE RIDGE OF HIGH PRESSURE BUILDS OVER
THE LAKE. THE WINDS LOOK TO INCREASE AGAIN OUT OF THE
SOUTH-SOUTHEAST LATER SATURDAY/SATURDAY EVENING AS THIS SURFACE
RIDGE SHIFTS EAST OF THE LAKES AND ANOTHER LOW TAKES SHAPE ACROSS
THE PLAINS.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM THURSDAY.

&&

$$

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