724 PM CDT
SHOWERS AND THUNDERSTORMS CONTINUE TO DEVELOP IN AN AREA OF
CONVERGENCE FROM THE WESTERN CHICAGO METRO AREA SOUTHWESTWARD INTO
NORTHEASTERN MISSOURI. STORM ORGANIZATION HAS INCREASED QUICKLY AS
DEEPER LAYER SHEAR INCREASES IN THE PRESENCE OF A LOW LEVEL JET AND
AN UPPER SHORTWAVE ARRIVES FROM THE WEST. ACTIVITY WILL CONTINUE TO
RACE EASTWARD AT 40-50 MPH OVER THE NEXT FEW HOURS THEN LIKELY
EXHIBIT A WEAKENING TREND BEYOND THAT. EXPECT THE BEST COVERAGE OF
MOST INTENSE CELLS TO REMAIN SOUTH OF INTERSTATE 88 DURING THAT TIME
WITH WIND GUSTS INTO THE 40 MPH RANGE AND SMALL HAIL POSSIBLE. A
MARGINAL SEVERE HAIL THREAT DOES EXIST FOR A SHORT TIME WITH THE
BETTER ORGANIZED STORMS GENERALLY WEST OF INTERSTATE 55. ADDITIONAL
SHOWER/ISOLATED THUNDER ACTIVITY WILL REMAIN POSSIBLE AHEAD OF THE
SURFACE LOW AND COLD FRONT WHICH IS STILL ACROSS EASTERN IOWA. HAVE
UPDATED SHORT TERM GRIDS TO REFLECT THE PROGRESSION OF THE
SHOWERS/STORMS WITH MINIMAL CHANGES TO THE FORECAST LATER TONIGHT.
UPDATED PRODUCTS ALREADY OUT.
MDB
//PREV DISCUSSION...
227 PM CDT
PRECIP CHANCES/TIMING ARE THE MAIN FORECAST CHALLENGE OVER THE NEXT
FEW DAYS AS DEEPENING UPPER TROUGH SHIFTS SOUTHEAST ACROSS THE
REGION.
IN THE NEAR TERM...BAND OF ELEVATED SHOWERS IS WEAKENING AS THEY
MOVE ACROSS THE EASTERN CWA THIS AFTERNOON...IN ASSOCIATION WITH MID
LEVEL SHORT WAVE TROUGH RIPPLING THROUGH THE FAST FLOW LEADING INTO
BROAD EASTERN CONUS UPPER RIDGE. SOUNDINGS FROM UPSTREAM RAOB SITES
THIS MORNING DEPICTED VERY DRY PROFILES...ALBEIT WITH A DEEP LAYER
OF STEEP LAPSE RATES...INDICATIVE OF RELATIVE TROUBLE OF PRODUCING
TOO MUCH IN THE WAY OF SIGNIFICANT PRECIP THIS AFTERNOON.
PRECIP POTENTIAL SHOULD INCREASE THIS EVENING HOWEVER...THANKS TO
INCREASING LARGE SCALE ASCENT WITH APPROACH OF SHORT WAVE TROUGH
CURRENTLY TRACKING ACROSS NORTHERN MISSOURI. FORECAST SOUNDINGS
INDICATE INCREASED MID LEVEL ASCENT WILL HELP TO ERODE MID-LEVEL
INVERSION. IN ADDITION...TIME/HEIGHT SECTIONS DEPICT RELATIVELY
STRONG LOW LEVEL UVM/OMEGA WHICH APPEAR TO BE A RESULT OF
STRENGTHENING LOW LEVEL FRONTOGENESIS ALONG BAROCLINIC FRONTAL ZONE
AND MASS CONVERGENCE IN VICINITY OF THE LOW LEVEL FRONT AND LOW.
EROSION OF WARM MID LEVEL TEMPS DURING THE EVENING ALSO RESULTS IN
SOME ELEVATED CAPE...ROUGHLY 250-500 J/KG PER 12Z WRF. THEREFORE THE
POTENTIAL FOR THE RENEWED DEVELOPMENT OF SHOWERS AND A FEW
THUNDERSTORMS APPEARS LIKELY AS THE LOW AND TRAILING COLD FRONT
SLIDE ACROSS THE AREA. PRECIP THREAT SHOULD DIMINISH FROM THE
NORTHWEST OVERNIGHT AS THE FRONT SLOWLY SAGS SOUTHEAST...AND THE
FRONTOGENETIC FORCING DECREASES WITH THE PASSAGE OF THE SHORT WAVE
TROUGH PER WRF/GFS PROGS.
WITH FORCING ON THE DECLINE AND FRONT PUSHING SOUTHEAST OF THE CWA
WEDNESDAY MORNING SHOULD SEE A RELATIVE LULL IN ANY ORGANIZED PRECIP
THREAT...THOUGH PRESENCE OF ELEVATED BAROCLINIC ZONE NORTH OF THE
COLD FRONT AND DIGGING UPPER TROUGH OVER THE UPPER MIDWEST SUGGESTS
A LITTLE SCATTERED LIGHT RAIN STILL POSSIBLE WEDNESDAY MORNING.
HEIGHT FALLS ARE ON THE INCREASE AGAIN WEDNESDAY AFTERNOON INTO
THURSDAY HOWEVER...AS UPPER TROUGH DIGS AND SHARPENS ACROSS THE
AREA. THE STRONGEST/DEEPEST FORCING PER MODEL TIME/HEIGHT SECTIONS
REMAINS ACROSS THE SOUTHERN PARTS OF THE CWA CLOSER TO THE MID LEVEL
FRONTAL ZONE...THOUGH THE COLD POOL WITH THE UPPER TROUGH REALLY
STEEPENS UP LAPSE RATES IN A DEEP LAYER FROM THE SFC TO AROUND 650
MB ON THURSDAY PER WRF FORECASTS. THUS HAVE MAINTAINED A MORE
UNIFORM POP ACROSS THE AREA THURSDAY. LOW LEVEL COLD ADVECTION ALSO
GRADUALLY INCREASES THE POTENTIAL FOR SOME LAKE EFFECT SHOWERS TO
DEVELOP OVER AND DOWNWIND OF THE LAKE WEDNESDAY NIGHT AND
THURSDAY...WITH NORTHERLY WIND PROFILES EVEN FAVORING THE IL SHORE
FOR A TIME BEFORE LOW LEVEL FLOW WEAKENS. PRECIP THREAT SHOULD END
BY THURSDAY NIGHT AS UPPER TROUGH FINALLY PASSES...AND SURFACE HIGH
PRESSURE RIDGE SPREADS IN FROM THE WEST.
COLDEST NIGHTS DURING THE PERIOD LOOK TO BE THURSDAY NIGHT AND
FRIDAY NIGHT...WITH LIGHT WINDS...CLEAR TO PARTLY CLOUDY SKIES AND
COLDER AIR MASS SUPPORTING TEMPS IN THE 30-35 RANGE AWAY FROM THE
CITY.
IN THE LONG TERM...GUIDANCE IN GENERAL AGREEMENT IN BRINGING ANOTHER
DIGGING SHORT WAVE ACROSS THE UPPER MIDWEST/WESTERN LAKES FRIDAY.
MAIN COLD POOL PASSES NORTH OF THE REGION AND HAVE HELD PRECIP OUT
OF THE FORECAST AT THIS POINT...THOUGH WILL HAVE TO SEE HOW THAT
SYSTEM EVOLVES OVER THE NEXT FEW DAYS.
RATZER
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 06Z...
* IFR CIGS THROUGH AT LEAST MID MORNING.
* POSSIBLE REDUCED VSBY...MOST LIKELY IN MVFR RANGE OR BETTER.
LENNING
//DISCUSSION...UPDATED 06Z...
TSRA ACROSS NORTHEAST ILLINOIS AND NORTHWEST INDIANA HAS MOVED
EAST AWAY FROM THE AREA...AND IFR CEILINGS MOVING IN ON NORTH
WINDS HAVE ARRIVED A BIT EARLIER THAN PREVIOUSLY EXPECTED. THIS
ACTIVITY IS ASSOCIATED WITH A FRONTAL ZONE AND CENTER OF LOW
PRESSURE SITTING OVER THE AREA. THE FRONT WILL SLIDE EAST TODAY
BUT NORTH WINDS WILL PERSIST THROUGH THE TAF PERIOD. DESPITE THE
DRIER AIR MASS BEHIND THE RETREATING FRONT...LOW CEILINGS WILL BE
SLOW TO CLEAR OUT THIS MORNING. IMPROVEMENT TO MVFR IS EXPECTED BY
MID MORNING AS THE MORE SATURATED BOUNDARY LAYER AIR GRADUALLY SLIDES
SOUTH AND EAST WITH THE FRONT. A FEW STATIONS ACROSS THE AREA ALSO
ARE REPORTING REDUCED VSBYS AT TAF TIME...BUT WINDS SHOULD BE
STRONG ENOUGH TO PROVIDE ENOUGH MIXING OVERNIGHT TO KEEP THESE AT
THE HIGH MVFR RANGE. TEMPO GROUPS MAY YET BE WARRANTED...BUT CIGS
WILL CONTINUE TO DETERMINE FLIGHT CATEGORIES.
LENNING
//ORD AND MDW CONFIDENCE...UPDATED 06Z...
* HIGH CONFIDENCE ON IFR CIGS OVERNIGHT...BUT LOW CONFIDENCE ON
WHEN THEY WILL IMPROVE.
* MEDIUM CONFIDENCE THAT VSBYS STAY AT MVFR OR BETTER OVERNIGHT.
LENNING
//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...
THURSDAY...CHANCE OF SHRA...OTHERWISE VFR.
FRIDAY...VFR.
SATURDAY...VFR.
SUNDAY...VFR.
MONDAY...VFR.
RODRIGUEZ
&&
.MARINE...
215 AM CDT
THE SURFACE LOW AND COLD FRONT HAVE JUST ABOUT CLEARED THE SOUTHERN
FRINGE OF LAKE MICHIGAN THIS MORNING. THUS THE PREDOMINATE FLOW IS
NOW OUT OF THE NORTH AT 20 TO 25 KT ACROSS THE LAKE. THE COLD AIR
MOVING ACROSS THE LAKE SHOULD CONTINUE TO KEEP THE WINDS ELEVATED
THROUGH MUCH OF THE DAY. DUE TO THE IDEAL LONG NORTH TO SOUTH
FETCH...WAVES OF 6 TO 9 FEET ARE EXPECTED ALONG THE INDIANA AND
ILLINOIS NEAR SHORE WATERS TODAY. CONDITIONS WILL GRADUALLY
IMPROVE TONIGHT INTO THURSDAY AS A BROAD AREA OF HIGH PRESSURE
SETS UP ACROSS THE CENTRAL CONUS.
THE ONLY WEATHER CONCERNS OVER THE NEXT FEW DAYS WILL BE A SLIGHT
POTENTIAL FOR A WINDOW OR TWO OF WATERSPOUTS. THE FIRST WINDOW
APPEARS TO BE THURSDAY MORNING AS AN UPPER TROUGH AND COLD POOL MOVES
ACROSS THE LAKE. THIS COULD SET UP A PERIOD OF FAVORABLE
THERMODYNAMIC CONDITIONS EARLY THURSDAY...WHEN A LAND BREEZE
CONVERGENCE ZONE WOULD LIKELY BE IN PLACE. A SIMILAR SETUP MAY OCCUR
FRIDAY NIGHT AS ANOTHER UPPER TROUGH AND COLD POOL MOVES ACROSS LAKE
MICHIGAN. IN SPITE OF THIS...THE MENTION OF WATER SPOUTS HAVE BEEN
LEFT OUT OF THE FORECAST FOR NOW DUE TO THE RATHER SMALL WINDOW.
HOWEVER...LATER FORECASTS MAY NEED TO ADD THE MENTION IF THE
CONDITIONS CONTINUE TO APPEAR FAVORABLE.
KJB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 3 AM THURSDAY.
&&
$$
