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 02Z...
* SHOWERS ENDING OVER THE NEXT COUPLE OF HOURS.
* NORTHERLY WINDS INCREASING IN WIND SPEED TONIGHT.
* VFR CEILINGS BECOMING LOW END MVFR LATER TONIGHT...WITH AN
INCREASED POSSIBILITY OF IFR CEILINGS MORE TOWARDS EARLY
WEDNESDAY MORNING.
RODRIGUEZ
//DISCUSSION...UPDATED 00Z...
LATEST RADAR IMAGERY SHOWING AN AREA OF SHOWERS AND THUNDERSTORMS
FINALLY BLOSSOMING ACROSS PORTIONS OF WESTERN ILLINOIS. THIS IS IN
RESPONSE TO A MID LEVEL WAVE MOVING ACROSS AN AREA OF LOW LEVEL
CONVERGENCE AT THE SURFACE. EXPECT THESE SHOWERS TO MOVE TO THE
EAST WITH TIME EARLY THIS EVENING...WITH THE BULK OF SHOWERS AND
THUNDERSTORMS TO STAY SOUTH OF THE TERMINALS. ALTHOUGH...THE
NORTHERN FRINGE OF THESE SHOWERS COULD POSSIBLY REACH THE
TERMINALS BEFORE THEY EXIT TO THE EAST THIS EVENING. BEST
INSTABILITY CURRENTLY REMAINS TO THE WEST OF THE TERMINALS...WHERE
SEVERAL LIGHTNING STRIKES HAVE BEEN REPORTED. CURRENT THINKING IS
THAT THIS BETTER INSTABILITY WILL REMAIN TO THE WEST/SOUTH OF THE
TERMINALS KEEPING ANY THUNDER AWAY FROM THE TERMINALS. ALTHOUGH
WITH BETTER FORCING MOVING OVER THE TERMINALS AND THIS INSTABILITY
NOT TOO FAR AWAY...IT WOULD NOT BE OUT OF THE QUESTION FOR A STRAY
RUMBLE OF THUNDER. THEN AREA OF LOW PRESSURE AND SURFACE BOUNDARY
TO PUSH THROUGH IN THE OVERNIGHT HOURS WITH SOUTHERLY WINDS
QUICKLY SHIFTING TO THE NORTH. AS COLDER AIR MOVES IN FROM THE
NORTH...WIND GUSTS SHOULD INCREASE AND REMAIN THROUGH MUCH OF
WEDNESDAY. WITH THIS COLDER AIR MASS MOVING IN...CEILINGS WILL
ALSO BE FALLING WITH CEILINGS FALLING CLOSE TO THE 1KFT RANGE
EARLY WEDNESDAY MORNING. THERE ARE CURRENTLY SOME IFR CEILINGS
BEING REPORTED UP NORTH AND ALTHOUGH PREVAILING IFR IS NOT
ANTICIPATED AT THIS TIME...IT DOES REMAIN A SLIGHT POSSIBILITY
EARLY WEDNESDAY MORNING. THESE LOW END MVFR CEILINGS WILL REMAIN
BUT SLOWLY RISE ON WEDNESDAY BEFORE THEY LIFT BACK TO VFR.
RODRIGUEZ
//ORD AND MDW CONFIDENCE...UPDATED 02Z...
* HIGH CONFIDENCE WITH SHOWERS AND TRENDS.
* HIGH CONFIDENCE WITH WIND SPEED AND DIRECTION.
* MEDIUM CONFIDENCE WITH CEILINGS AND THE DOWNWARD TREND TOWARDS
LOW END MVFR/IFR.
RODRIGUEZ
//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...
217 PM CDT
LOW PRESSURE OVER IOWA THIS AFTERNOON WILL CONTINUE TO MOVE
EAST...PUSHING ACROSS SOUTHERN LAKE MICHIGAN OVERNIGHT. OUT AHEAD OF
THE LOW...STRONG PRESSURE FALLS AND A TIGHT PRESSURE GRADIENT WILL
ALLOW WINDS TO ACCELERATE...WITH 15 TO 25 KT SOUTH TO SOUTHWEST
WINDS AND OCCASIONAL 30 KTS NOT OUT OF THE QUESTION SOUTH OF THE
WARM FRONT WHICH IS STRADDLING LAKE MICHIGAN. OVER THE NORTHERN HALF
OF THE LAKE...GUSTY NORTHEASTERLY WINDS ARE IN PLACE. WINDS SHOULD
DIMINISH SOMEWHAT OVERNIGHT ACROSS THE SOUTH HALF OF THE LAKE AS THE
LOW MOVES THROUGH...BUT THEN PICK UP AGAIN BEHIND A TRAILING COLD
FRONT OUT OF THE NORTHEAST AND THEN NORTH. THERE WILL BE A SHORT
WINDOW DURING THE TRANSITION OF SOUTHERLY TO NORTHERLY WINDS...ON
THE ORDER OF A FEW HOURS...WHERE WIND SPEEDS WILL FALL BELOW SMALL
CRAFT ADVISORY CRITERIA...HOWEVER HAVE OPTED TO SIMPLY EXTEND THE
CURRENT ADVISORY THROUGH TOMORROW INSTEAD OF HAVING TWO HEADLINES.
WINDS WILL THEN TAPER OFF TOMORROW EVENING...WITH WAVES FOLLOWING
SUIT SHORTLY THEREAFTER. WE SHOULD FALL BELOW ADVISORY CRITERIA
DURING THE OVERNIGHT HOURS WEDNESDAY NIGHT. BMD
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 3 AM THURSDAY.
&&
$$
