Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 192019
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
319 PM CDT TUE AUG 19 2014

.DISCUSSION...
304 PM CDT

WARMER AND MORE HUMID CONDITIONS ARE STILL EXPECTED AS WE GO THROUGH
THE REST OF THE WEEK WITH THE BIGGEST CHALLENGE BEING THE
DETERMINATION OF THE EXTENT OF SHOWER AND THUNDERSTORM ACTIVITY.
AFTERNOON WATER VAPOR IMAGERY SHOWS AN UPPER TROUGH OVERHEAD OF THE
LOCAL AREA MAKING GRADUAL PROGRESS TO THE EAST. BROAD LOW-AMPLITUDE
RIDGING IS IN PLACE OVER THE ROCKIES AND HIGH PLAINS WHILE A BROAD
UPPER TROUGH MOVES ACROSS WESTERN CANADA. A CUTOFF UPPER LOW IS
SPINNING SOUTHWARD DOWN THE CALIFORNIA COAST. THIS RIDGE/TROUGH
COMBINATION WILL AMPLIFY OVER THE NEXT FEW DAYS AND MAKE EASTWARD
PROGRESS. AT THE SURFACE...LOW PRESSURE IS OVER NORTHERN MICHIGAN IS
DRAGGING A COOL FRONTAL BOUNDARY/TROUGH SOUTHEAST ACROSS THE LOCAL
AREA.

TONIGHT AND WEDNESDAY...THE UPPER TROUGH OVER THE AREA TODAY WILL BE
SLOW TO MOVE EAST INTO WEDNESDAY KEEPING CYCLONIC FLOW OVERHEAD
THROUGH THE MORNING. THE BULK OF THE CONVECTIVE ACTIVITY IS NOW OFF
TO THE EAST WITH MORE SPOTTY DIURNALLY DRIVEN ACTIVITY WORKING INTO
THE NORTHERN CWA AND MAY SEE SOME ADDITIONAL ACTIVITY INTO CENTRAL
AREAS BEFORE DISSIPATING THIS EVENING. OTHERWISE...WATER VAPOR SHOWS
A WEAK WAVE ROUNDING THE PERIPHERY OF THE UPPER LOW OVER MINNESOTA
THIS AFTERNOON AND THIS SHOULD ROTATE OVER THE LOCAL AREA TONIGHT
AND MAY TRIGGER SOME ADDITIONAL SHOWERS. THE CHANCE DOES NOT LOOK
THAT GREAT ESPECIALLY WITH A MODESTLY DRIER AIRMASS IN PLACE BEHIND
THE AFTERNOON TROUGH. CYCLONIC FLOW REMAINS OVERHEAD WEDNESDAY
MORNING BUT SHIFTS TO THE EAST SO AM NOT EXPECTING PRECIP ACTIVITY
GIVEN THE POOR DIURNAL SUPPORT THEREFORE MUCH OF THE DAY WEDNESDAY
SHOULD BE DRY. HIGHS WILL WARM INTO THE LOW TO MID 80S BUT A LAKE
BREEZE SHOULD COOL LAKESHORE AREAS DURING THE AFTERNOON.

WEDNESDAY NIGHT THROUGH FRIDAY...THE UPPER RIDGE WILL MOVE FROM THE
HIGH PLAINS AND SLOW ITS EASTWARD PROGRESS OVER THE LOCAL AREA BY
FRIDAY. IT WILL AMPLIFY AS IT MOVES EASTWARD HELPING TO SHARPEN THE
ASSOCIATED MID LEVEL BAROCLINIC ZONE WHICH WILL MOVE NORTHEAST
ACROSS THE FORECAST AREA STARTING BY WEDNESDAY EVENING. WITH A
STRONG PUSH OF MOISTURE AND A WEST TO SOUTHWEST LOW LEVEL JET
DEVELOPING WEDNESDAY EVENING SHOULD SEE A DECENT COVERAGE OF SHOWERS
AND THUNDERSTORMS DEVELOP AND MOVE ACROSS THE AREA INTO THURSDAY
MORNING. BETTER ORGANIZATION COULD RESULT WITH THE PASSAGE OF ANY
SHORTWAVE EJECTING FROM THE AMPLIFYING BUT STILL BROAD WESTERN
TROUGH. LESS CONFIDENT IN PRECIP CHANCES FROM LATE THURSDAY THROUGH
FRIDAY AS THE RIDGE AXIS WILL BE OVER THE AREA BUT THE RIDGE LOOKS
TO BE BROAD ENOUGH THAT THE MORE ACTIVE FLOW AROUND THE PERIPHERY
WILL BE IN CLOSE PROXIMITY. ULTIMATELY A WARM FRONTAL BOUNDARY WILL
LIKELY SET UP TO THE NORTH EXTENDING FROM LOW PRESSURE ACROSS THE
CENTRAL/NORTHERN PLAINS BUT CONVECTION MAY INFLUENCE HOW FAR
NORTH-SOUTH THIS BOUNDARY MOVES WHICH WILL AFFECT POPS AND POSSIBLY
TEMPS AS WELL. WILL CONTINUE WITH THE IDEA OF THE BOUNDARY REMAINING
NORTH LEADING TO HIGHS IN THE MID AND UPPER 80S THURSDAY AND UPPER
80S TO AROUND 90 FRIDAY. THE FLOW MAY BE WEAK ENOUGH TO ALLOW SOME
LAKE INFLUENCE TO COOL SHORELINE AREAS SOMEWHAT. ANY OUTFLOW FROM
STORMS OVER OR NORTH OF THE AREA COULD IMPACT TEMPS AS WELL.

SATURDAY AND BEYOND...THE WESTERN TROUGH WILL EVENTUALLY TRACK EAST
ACROSS THE NORTHERN PLAINS BREAKING DOWN THE RIDGE BUT THE SPEED
WITH WHICH THIS OCCURS IS STILL IN QUESTION. AT THIS POINT THE RIDGE
LOOKS TO FURTHER AMPLIFY OVER THE WEEKEND WHICH COULD KEEP THINGS
DRY BUT GUIDANCE HAS FLUCTUATED ON THE AMPLITUDE. WILL KEEP LOW POPS
SATURDAY AND SUNDAY...MAINLY NORTH CLOSER TO THE MORE ACTIVE FLOW
AROUND THE TOP OF THE RIDGE. TEMPS IN THE UPPER 80S TO AROUND 90
WILL CONTINUE ALONG WITH THE HUMIDITY. AS THE UPPER TROUGH MOVES
EAST SURFACE LOW PRESSURE WILL LIKELY DEVELOP ACROSS THE NORTHERN
PLAINS AND DRAG A COLD FRONT INTO THE AREA EARLY NEXT WEEK. THE
OVERALL UPPER PATTERN WILL BE DE-AMPLIFYING SO THE FRONT MAY STALL
OUT SOMEWHERE NEAR THE AREA BUT STILL QUITE A WAYS OUT THERE FOR ANY
KIND OF CONFIDENCE IN THIS.

MDB

&&

.AVIATION...

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

* ISOL SHRA POSSIBLE THIS AFTERNOON.

* WESTERLY WINDS GUSTING TO AROUND 20 KT THROUGH EARLY EVENING.

* POTENTIAL FOR MVFR VIS IN BR LATE TONIGHT INTO WED MORNING.

RODRIGUEZ

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

LATEST RADAR IMAGERY SHOWING AREA OF THUNDERSTORMS EXITING TO THE
EAST OF THE TERMINALS...BUT WITH GYY THE ONLY TERMINAL BEING
IMPACTED AT THIS TIME. THIS WILL CONTINUE EAST OVER THE NEXT HOUR
WITH GENERALLY DRY CONDITIONS THEN EXPECTED OVER THE NEXT SEVERAL
HOURS. ISOL TO WIDELY SCATTERED SHOWERS ARE STILL DEVELOPING OVER
FAR NORTHERN ILLINOIS AND SOUTHERN WISCONSIN...OUT AHEAD OF FRONT
STRETCHED FROM SOUTHERN WISCONSIN TO EASTERN IOWA. THIS WILL
LIKELY CONTINUE INTO THE AFTERNOON AS THIS FRONT DROPS TO THE
SOUTHEAST...BUT EXPECT IT TO REMAIN LIMITED IN COVERAGE AS BETTER
LIFT ALOFT IS LOST. ONLY HAVE VCSH MENTIONED DUE TO ANTICIPATED
COVERAGE...BUT WILL NEED TO CONTINUE MONITORING THE POTENTIAL FOR
A STRAY SHOWER AND EVEN AN OUTSIDE POSSIBILITY FOR A BRIEF/ISOL
STORM TO MOVE OVER THE TERMINALS. CEILINGS STILL HOVERING AROUND
MVFR/VFR...BUT WITH VFR CEILINGS EXPECTED THIS AFTERNOON THROUGH
THE REST OF THE FORECAST PERIOD. FAIRLY MOIST CONDITIONS LINGERING
TONIGHT COULD ALLOW FOR FOG DEVELOPMENT...AND HAVE CONTINUED
MENTION OF THIS IN THE TAF.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH ISOL SHRA DEVELOPING AROUND THE
  TERMINALS THIS AFTERNOON.

* HIGH CONFIDENCE WITH WIND SPEED AND DIRECTION.

* MEDIUM CONFIDENCE WITH MVFR VIS OCCURRING LATE TONIGHT INTO
  WEDNESDAY MORNING.

RODRIGUEZ

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

WEDNESDAY NIGHT THROUGH SUNDAY...PERIODIC CHANCES FOR TSRA AND
OCNL REDUCED CIGS/VIS.

SUNDAY NIGHT THROUGH MONDAY...VFR. WX NIL.

&&

.MARINE...
319 PM CDT

GENERALLY QUIET CONDITIONS OVER THE LAKE THROUGH THE WEEKEND WITH
RESPECT TO WINDS AND WAVES...AND PERIODS WHERE DIRECTIONS IN THE
NEARSHORE AREAS WILL BE CONTROLLED BY LAKE BREEZE INFLUENCES BY
DAY. A WARM AND MOIST AIR MASS WILL OVERSPREAD THE REGION AND
UPPER LEVEL DISTURBANCES COULD RESULT IN THUNDERSTORM COMPLEXES
CROSSING THE LAKE AT TIMES...MAINLY FROM WEDNESDAY NIGHT THROUGH
SATURDAY. THE POTENTIAL EXISTS FOR SOME OF THESE COMPLEXES TO
PRODUCE GUSTY WINDS AND LOCALLY HIGHER WAVES...AS WELL AS FREQUENT
CLOUD TO WATER LIGHTNING.

RC

&&

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

$$

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