000
FXUS63 KLOT 191946
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
246 PM CDT SUN MAY 19 2013

.MESOSCALE DISCUSSION...
1111 AM CDT

THE MAIN CHALLENGES WILL BE THE CHANCES FOR CONVECTIVE ACTIVITY OVER
THE NEXT FEW DAYS. FOR TODAY IT APPEARS THAT MOST IF NOT ALL OF THE
AREA WILL REMAIN DRY. AIRCRAFT SOUNDINGS AND VARIOUS MODEL ANALYSIS
INDICATE THAT AN EML CAPPING INVERSION HAS SET UP ACROSS MOST OF
NORTHERN ILLINOIS WITH 700 MB TEMPERATURES NEAR 10C. WITH THE MID
LEVEL ENERGY EXPECTED TO REMAIN WEST OF THE AREA DURING THE DAY
TODAY...I DO NOT SEE ANYTHING THAT WILL ALLOW FOR CONVECTION TO
BREAK OUT ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA
DURING THE DAY TODAY. WITH THAT BEING SAID...A COUPLE OF STRONG
THUNDERSTORMS HAVE DEVELOPED ACROSS FAR NORTHEASTERN MISSOURI AND
FAR WEST CENTRAL ILLINOIS OVER THE PAST HOUR. THESE STORMS ARE
DEVELOPING ALONG THE WESTERN PERIPHERY OF THE EML...WHERE COOLER MID
LEVEL TEMPERATURES ARE IN PLACE. I EXPECT THESE STORMS TO MOVE TO
THE NORTH-NORTHEAST. STORMS WILL LIKELY CONTINUE TO DEVELOP WEST OF
THE AREA ACROSS IOWA THROUGH THE AFTERNOON AS THE MID LEVEL FLOW
REMAINS STRONGER AND MORE DISTURBED. ALTHOUGH IT IS NOT OUT OF
THE QUESTION THAT SOME OF THIS ACTIVITY COULD AFFECT NORTHWESTERN
ILLINOIS AND POSSIBLY SOME OF MY FAR WESTERN COUNTIES LATER THIS
AFTERNOON...THE OVERALL THREATS FOR CONVECTION THROUGH THIS
AFTERNOON SHOULD RAPIDLY DECREASE TO THE EAST. WE WILL KEEP THE
FORECAST DRY AS A RESULT...BUT WILL KEEP AN EYE ON THE CONVECTIVE
ACTIVITY TO THE SOUTHWEST TO SEE IF ANY POPS WILL BE NEEDED FAR WEST
LATER TODAY.

A MORE SUBSTANTIAL DISTURBANCE...ASSOCIATED WITH THE UPPER JET
ACROSS THE SOUTHWEST CONUS THROUGH THE TEXAS PANHANDLE...IS FORECAST
TO PUNCH EAST-NORTHEASTWARD ACROSS MISSOURI TONIGHT. THIS LOOKS TO
INDUCE VEERING LOW LEVEL JET AND MID LEVEL HEIGHT FALLS ACROSS THE
AREA INTO MONDAY MORNING. THIS COULD RESULT IN A COMPLEX OF
CONVECTION MOVING ACROSS THE AREA LATER TONIGHT INTO MONDAY MORNING
WITH A WEAKENING CAP...AND THIS ACTIVITY COULD RESULT IN A SEVERE
THUNDERSTORM RISK FOR PORTIONS OF THE AREA INTO MONDAY.

KJB

&&

.DISCUSSION...
501 AM CDT

FORECAST FOR TODAY INTO LATE IN THE WEEK PRIMARILY HINGES ON HOW
LONG IT TAKES FOR THE UPPER LOW THAT HAS BEEN FORMING OVER UT
YESTERDAY AND OVERNIGHT TO REACH AND THEN FINALLY MOVE EAST OF THE
LOCAL AREA.

MODEL RUNS OVER THE LAST COUPLE OF DAYS HAVE ALL BEEN GRADUALLY
SLOWING ITS EASTWARD PROGRESS AND ARE QUITE SIMILAR IN LOCATION OF
THE UPPER LOW AS IT MOVES VERY SLOWLY ENE ACROSS THE PLAINS. MODELS
ARE ALSO VERY SIMILAR IN THE GRADUAL WEAKENING OF THE UPPER LOW
DURING TUE NIGHT AND WED AS IT MOVES TO THE UPPER MIDWEST...AND WITH
THE REMAINING UPPER TROUGH STILL HANGING BACK ACROSS THE GREAT
LAKES...OH VALLEY AND MS VALLEY DURING THU.

WITH THE VERY SLOW PROGRESSION OF THIS SYSTEM ACROSS THE CENTRAL
U.S. THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS WILL HANG OVER THE
LOCAL AREA FROM LATE TODAY TIL AT LEAST THU BEFORE THE UPPER TROUGH
MOVES FURTHER OVER THE GREAT LAKES AND MIDWEST. ECMWF 00Z RUN IS
MOST AGGRESSIVE WITH EASTWARD PROGRESS DURING THE LATTER PART OF THE
WEEK...AS WAS THE PREVIOUS 12Z RUN.

OTHER MODELS ARE SLOWER WITH ABSORBING THE GREAT LAKES UPPER
TROUGH INTO THE DEEP VORTEX PROGGED TO SETTLE SOUTHWARD OVER
EASTERN CANADA AND NORTHERN NEW ENGLAND WED THROUGH FRI BUT ALL
HAVE THE UPPER TROUGH AXIS MOVING E OF THE LOCAL AREA BY FRI WITH
A SURFACE RIDGE SPREADING SSE ACROSS THE REGION THU NIGHT THROUGH
SAT.

AHEAD OF THE SLOW MOVING SYSTEM VERY WARM AND MOIST AIR WILL
CONTINUE TO SPREAD FROM THE SOUTHERN AND CENTRAL PLAINS NNE
ACROSS THE MID MS VALLEY TODAY AND TONIGHT. FORECAST LOCAL
TEMPERATURE PROFILES SHOW A CAPPING INVERSION IN PLACE TODAY BUT
ERODED AWAY THIS EVENING. SURFACE DEW POINTS HAVE HELD STEADY
ACROSS THE AREA DURING THE OVERNIGHT AND WILL GRADUALLY RISE AS
INCREASING SE TO SSE LOW LEVEL FLOW ADVECTS MID 60S DEW POINTS
OVER THE AREA. WITH RISING LOW LEVEL MOISTURE...THE REMOVAL OF
THE CAP AND SLIGHT COOLING IN THE MID LEVELS BY THIS EVENING CAPE
VALUES CLIMB TO 1.0 TO 1.5K BY LATE AFTERNOON AND TO 1.5 TO 2.0K
DURING THE EARLY EVENING.

ALL MODELS SHOW INDICATIONS OF A SHORT WAVE TROUGH ROTATING ACROSS
NORTHERN MO AND IA TONIGHT. THIS WILL PROVIDE LARGE SCALE UVV TO
SUSTAIN CONVECTION EXPECTED TO BE ONGOING UPSTREAM THIS AFTERNOON
AND SPREADING OVER THE MID MS VALLEY DURING THE AFTERNOON. WITH
INSTABILITY AND UPPER FORCING CHANCES FOR THUNDERSTORMS WILL
SPREAD OVER MUCH OF FA LATE THIS AFTERNOON AND THIS EVENING...
ESPECIALLY THE NW HALF.

CONVECTIVELY INDUCED VORT MAXIMA ARE LIKELY TO MOVE NE AND E UP
AND OVER THE UPPER RIDGE...CURRENTLY OVER THE MS VALLEY...AS THE
RIDGE SHIFTS GRADUALLY E TO THE WESTERN GREAT LAKES AND THE LOWER
OH VALLEY BY 00Z. HOWEVER...WITH A CAP IN PLACE DURING THE
DAYTIME FORESEE ONLY SLIGHT CHANCES OF STORMS REACHING THE
WESTERN FA BEFORE LATER AFTERNOON.

MODELS USUALLY HAVE TROUBLE WITH IDENTIFYING AND MAINTAINING
MINOR DISTURBANCES ROTATING AROUND AN UPPER LOW...ESPECIALLY WHEN
NUMEROUS STRONG THUNDERSTORM COMPLEXES FORM. GIVEN LARGE
UNCERTAINTY IN WHEN ANY DISTURBANCES WILL BE MOVING OVER THE
LOCAL AREA WILL HAVE TO USE A BROAD BRUSH WITH POP VALUES MON
THROUGH THU AS IDENTIFYING TIMES OF ANY PEAKS AND LULLS IN
CONVECTIVE OCCURRENCE MINIMAL AT BEST IN THIS PATTERN.

CIRRUS FROM PLAINS THUNDERSTORMS HAS BEEN SPREAD E OVERNIGHT BUT
DISSIPATING AS IT REACHES THE UPPER RIDGE AXIS JUST W OF THE FA
AT PREDAWN. EXPECT A GRADUAL INCREASE IN HIGH CLOUDINESS AS THE
DAY PROGRESSES WITH THE RIDGE AXIS MOVING E OF THE FA BY EARLY
EVENING. WITH SUFFICIENT SUN BEFORE THICKER CLOUDS SPREAD E TEMPS
LIKELY TO HIT MID 80S AND POSSIBLY UPPER 80S...EXCEPT FOR ALONG
THE LAKE WHERE THE SE LOW LEVEL WINDS WILL KEEP LAKE COOLED AIR AT
THE IL SHORE.

WITH 850HPA TEMPS PROGGED TO REMAIN AROUND VALUES SEEN TODAY FOR
MON...GIVEN SOME SUN TEMPS ARE LIKELY BE SIMILAR TO TODAY OR EVEN
A DEGREE OR TWO WARMER AS TEMPS TO START OUT IN THE UPPER 60S AT
SUNRISE MON. INCREASING CONVECTION AND SHIFT EASTWARD OF THERMAL
AXIS BY TUE WILL RESULT IN TEMPS IN THE UPPER 70S AND LOWER 80S...
AND CONTINUED COOLING OFF MID AND LATE WEEK. BY FRI WITH THE LARGE
SURFACE RIDGE BUILDING SSE OVER THE AREA AND MUCH COOLER AIR
SPREADING DOWN FROM CENTRAL CANADA HIGHS ARE EXPECTED TO BE IN THE
MID AND UPPER 60S INLAND...WITH AREAS NEAR THE LAKE IN THE 50S AND
LOWER 60S WITH A MODERATELY STRONG ALMOST FULL-FETCH FLOW DOWN THE
LAKE AND ACROSS NW IND AND NE IL.

TRS

&&

.AVIATION...

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

* SOUTHERLY WINDS GUSTING TO AROUND 20 KT. GUSTS DIMINISHING THIS
  EVENING...THEN INCREASING AND BECOMING GUSTY AGAIN ON MONDAY.

* CHANCE OF TSRA OVERNIGHT.

PAW

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

AREAS OF TSRA HAVE DEVELOPED WELL TO THE WEST OF THE TERMINALS
OVER PORTIONS OF EASTERN IOWA AND WESTERN ILLINOIS. HIGH
PRESSURE IN PLACE OVER THE TERMINAL AREAS ALONG WITH WARM
TEMPERATURES ALOFT HAVE PREVENTED THESE TSRA FROM MAKING MUCH
PROGRESS TO THE EAST. THE HIGH WILL GRADUALLY DRIFT TO THE EAST
AND SOME TSRA MAY BE APPROACHING RFD BY LATE EVENING...AND THE
REST OF THE TERMINALS DURING THE OVERNIGHT HOURS. THEN IT LOOKS
LIKE THERE MAY BE A BREAK IN THE ACTION BEFORE ANOTHER ROUND OF
TSRA DEVELOPS ON MONDAY.

PAW

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

* MEDIUM TO HIGH CONFIDENCE IN WIND TREND THIS AFTERNOON INTO
  MONDAY.
* MEDIUM CONFIDENCE IN POTENTIAL FOR TSRA OVERNIGHT.

PAW

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

MONDAY NIGHT...PERIODS OF TSRA.
TUESDAY...PERIODS OF TSRA.
WEDNESDAY...LIKELY TSRA DURING THE DAY. CHC OF SHRA IN THE EVENING.
THURSDAY...CHC OF SHRA/TSRA EARLY.
FRIDAY THROUGH
SATURDAY...VFR.

BEACHLER

&&

.MARINE...
159 PM CDT

THE MAIN WEATHER MAKER FOR THE NEXT FEW DAYS WILL BE THE SURFACE
LOW...CURRENTLY ACROSS THE PLAINS. THIS STORM SYSTEM IS EXPECTED TO
MOVE EAST-NORTHEASTWARD TOWARDS THE MID MISSOURI VALLEY TONIGHT INTO
MONDAY MORNING. AS IT DOES SO...AN ASSOCIATED SURFACE WARM
FRONT...EXTENDING EASTWARD ACROSS NORTHERN ILLINOIS AND
INDIANA...WILL MOVE NORTHWARD ACROSS AT THE SOUTHERN HALF TO TWO
THIRDS OF THE LAKE LATER TONIGHT AND ON MONDAY. IN THE WAKE OF THIS
FRONT...THE WINDS WILL SHIFT MORE SOUTHERLY AND SHOULD INCREASE UP
TO 15 TO 25 KT BY MONDAY. HOWEVER...TO THE NORTH OF THIS
FRONT...WINDS WILL PRIMARILY REMAIN EASTERLY AT AROUND THE SAME
MAGNITUDE.

THE OTHER CONCERN WILL BE THE THREAT FOR PERIODS OF DENSE MARINE FOG
LATER TONIGHT AND INTO AT LEAST THE FIRST PART OF THE WEEK. AS
THIS WARM FRONT LIFTS OVER THE LAKE...MUCH HIGHER DEW POINTS WILL
MOVE OVER THE RELATIVELY COLD WATER...POSSIBLY RESULTING IN SOME FOG
DEVELOPMENT.

IT APPEARS THAT THE SURFACE LOW WILL SLOWLY MOVE EASTWARD ACROSS THE
MID MISSISSIPPI VALLEY AND TO NEAR SOUTHERN LAKE MICHIGAN BY MID
WEEK AND THEN CONTINUE EASTWARD ACROSS THE LOWER GREAT LAKES REGION
LATER IN THE WEEK. THIS SHOULD ALLOW WARM FRONT TO SHIFT BACK
SOUTHWARD WITH TIME DURING THE WEEK. DURING THIS TIME...THE WIND
DIRECTIONS WILL PRIMARILY BECOME EAST NORTHEASTWARD 15 TO 25 KT
NORTH OF THE FRONT. LATER IN THE WEEK...AS THE SURFACE
LOW PASSES EAST OF LAKE MICHIGAN...THE WINDS STILL LOOK TO BE RATHER
STOUT UP TO 30 KT OUT OF THE NORTH FOR A PERIOD AS A GOOD AREA OF
HIGH PRESSURE BUILDS EASTWARD ACROSS ONTARIO AND THE UPPER GREAT
LAKES REGION.

KJB

&&

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

$$

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