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 22Z...
* WINDS SHIFTING MORE TOWARDS THE SOUTHWEST THROUGH THIS EVENING
WITH GUSTS SLOWLY DIMINISHING.
* VFR CEILINGS LOWERING CLOSER TO 4KFT THIS EVENING WITH SHOWERS
ALSO POSSIBLE DURING THIS TIME FRAME.
RODRIGUEZ
//DISCUSSION...UPDATED 18Z...
LIGHT SHOWER ACTIVITY TO BE ON THE WANE QUICKLY THIS AFTERNOON AND
END FOR ALL EASTERN TERMINALS WITHIN THE VICINITY OF 19-20Z. WIND
FORECAST HAS PROVED TO BE AS BIG OF A CHALLENGE AS THE AFTERNOON
PRECIP. PRESSURE FALLS BEHIND THE WARM FRONT ACROSS WEST CENTRAL
MICHIGAN ALLOWED WINDS AT ORD/MDW TO PULL AROUND TO THE SOUTHWEST
FOR A SHORT TIME...BUT AS THE PRESSURE FALLS SHIFTED NORTH AND
EAST...MAIN SYNOPTIC FLOW TOOK OVER...KEEPING WINDS OUT OF THE
SOUTH. AS THE SURFACE LOW THAT IS PRESENTLY ACROSS SOUTHWESTERN
IOWA...SLIDES EAST...WINDS WILL BEGIN TO SHIFT TO THE SOUTHWEST
AND WILL LIKELY BE WITHIN THE 220 TO 240 RANGE BEYOND 00Z.
FORECAST GUIDANCE CONTINUES TO INDICATE THE NEXT CHANCE FOR PRECIP
WILL BE AROUND THE TIME FRAME THAT THE LOW MOVES ACROSS NORTHERN
ILLINOIS. THERE WILL BE SUFFICIENT INSTABILITY TO BE REALIZED FOR
THUNDER BUT THE OVERALL DYNAMICS ARE NOT THE MOST IMPRESSIVE OVER
THE TERMINALS. THINKING THAT THERE WILL BE AGAIN SHOWER ACTIVITY
WITH SOME EMBEDDED THUNDER AND WILL ONLY KEEP THE SHRA WITH CB
MENTION ONLY AT THIS TIME. BEHIND THE FRONT...WINDS WILL TURN
NORTHERLY AND GUST INTO THE LOW 20S AGAIN. NAM MET GUIDANCE IS
TRYING TO TAKE THE CIGS DOWN TO CAT 2 /LIFR/ AT THEIR LOWEST
TOMORROW MORNING....WHILE THE GFS MAV IS CONTENT AT HIGH END IFR.
FOR NOW...SIDING MORE WITH GFS CIGS AT THEIR WORST DUE TO FORECAST
MIXING THAT MAY HELP TO KEEP BASES UP AND THE FACT THAT THE
CLOSEST IFR OR LOWER CIGS ARE ACROSS NORTH DAKOTA OR DEEP INTO
CANADA.
SHEA
//ORD AND MDW CONFIDENCE...UPDATED 22Z...
* HIGH CONFIDENCE WITH WIND SPEED AND DIRECTION.
* HIGH CONFIDENCE WITH VFR CEILING TRENDS AND MEDIUM CONFIDENCE
WITH PRECIP TIMING.
RODRIGUEZ
//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...
WEDNESDAY NIGHT...VFR WITH SLT CHC SHRA.
THURSDAY THROUGH FRIDAY...VFR. PATCHY MVFR WITH CHC SHRA.
SATURDAY THROUGH MONDAY...VFR.
JEE
&&
.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.
&&
$$
