240 AM CDT
EXTRAORDINARILY TRICKY FORECAST THE NEXT 24 HOURS WITH RESPECT TO
CLOUD COVER...PRECIP CHANCES...AND TEMPS.
WARM FRONTOGENESIS TAKING PLACE FROM NORTHERN IA EAST INTO SOUTHERN
WISCONSIN EARLY THIS MORNING WITH REGIONAL RADAR MOSAIC SHOWING
TRANSVERSE BANDS OF SHOWERS DEVELOPING ALONG/NORTH OF THE WARM FRONT
AND ON THE NOSE OF THE VERY STRONG 50-60KT LOW LEVEL JET. SOUTHERN
EXTENT OF THESE ELEVATED SHOWERS SHOULD REMAIN NEAR/NORTH OF THE
IL/WI LINE THIS MORNING.
HOWEVER...FORECAST FOR REMAINDER OF TODAY IS ANYTHING BUT STRAIGHT
FORWARD. SOUNDINGS FROM ACROSS THE CENTRAL PLAINS MON EVENING SHOWED
PRESENCE OF A VERY STOUT EML WHICH IS LIKELY TO BE ADVECTED EASTWARD
INTO THE MIDWEST TODAY BY THE DEEP WESTERLY FLOW ALOFT. AS THE STEEP
LAPSE BECOME JUXTAPOSED ABOVE A TONGUE OF MOISTURE (ALBEIT QUITE
MEAGER) BEING ADVECTED NORTHWARD BY THE SCREAMING STRONG LOW LEVEL
JET OUT AHEAD OF SUBTLE SHORTWAVE NOTED OVER KS EARLY THIS MORNING
AM CONCERNED THAT ACCAS FIELD WILL LIGHT UP OVER THE AREA THIS
MORNING. WHILE LOW LEVEL AIRMASS WILL BE SLOW TO MOISTEN
TODAY...PARCELS WITH SOMEWHAT GREATER MOISTURE CONTENT ORIGINATING
OVER THE SOUTHERN PLAINS WILL BE RAPIDLY ADVECTED NORTHWARD AND
ISENTROPICALLY LIFTED BY THE STRONG LOW LEVEL JET. MODELS ARE IN
GOOD AGREEMENT WITH THIS GENERAL SET-UP AND IN SHOWING VERY STRONG
NEARLY SATURATED ASCENT ON THE 305K SURFACE TODAY...WHICH GIVEN THE
STEEP LAPSE RATES COULD VERY WELL BE ENOUGH TO KICK OFF HIGH
ELEVATED SHOWERS (WITH MAYBE A ROGUE LIGHTNING STRIKE OR TWO). HAVE
BUMPED UP SKY COVER A BIT TODAY FROM PREVIOUS FORECAST AND EXPANDED
SLIGHT CHANCE POPS TO ENCOMPASS THE ENTIRE CWA.
SHORTWAVE AND ASSOCIATED MAXIMA IN LIFT SHOULD TRAVERSE THE AREA
RATHER QUICKLY TODAY...SO THAT PRECIP CHANCES SHOULD END THIS
AFTERNOON FROM WEST TO EAST WITH MODE MIXED SUNSHINE EXPECTED IN THE
WAKE OF THE WAVE. HAVE BASICALLY LEFT GOING TEMPS ALONE GIVEN THE
VERY LOW CONFIDENCE IN HOW CLOUD COVER AND POSSIBLE PRECIP WILL PLAY
OUT TODAY. BUST POTENTIAL FOR TEMPS TODAY IS CERTAINLY HIGHER THAN
AVERAGE FOR A 1ST PERIOD FORECAST WITH MORE SUNSHINE LIKELY LEADING
TO HIGHS EVEN WARMER THAN GOING GRIDS AND POSSIBLY EVEN FLIRTING
WITH RECORDS. EVEN IF ABOVE SCENARIO WITH THE CLOUD COVER AND
MID-LEVEL CONVECTION DOES PLAY OUT TODAY WOULD STILL ANTICIPATE
HIGHS TO GET INTO THE UPPER 60S TO MID 70S AS AIR MASS BEING
ADVECTED IN IS VERY WARM (STILL IN THE LOW/MID 60S AT 2 AM IN IOWA).
NUMERICAL GUIDANCE...PARTICULARLY THE HI-RES MODELS...ARE DEPICTING
STRONGER FORCING THIS EVENING WITH APPROACHING SHORTWAVE AND SFC
LOW. WHILE CAPE VALUES WILL BE WEAK DUE TO LESS THAN STELLAR
MOISTURE RETURN...THE VERY STEEP MID LEVEL LAPSE RATES COULD BE
ENOUGH TO SUPPORT SCATTERED THUNDERSTORMS BREAKING OUT THIS EVENING.
MANY OF THE HI-RES CONVECTIVE ALLOWING MODELS ARE BREAKING OUT
THUNDERSTORMS OVER NORTHERN ILLINOIS THIS EVENING...ENOUGH SO THAT I
FELT COMFORTABLE HITTING POPS A BIT HARDER IN THE GRIDS THOUGH STILL
TOO GUN SHY TO GO WITH LIKELYS.
ANY SHOWERS/STORMS WILL END FROM NW TO SE ACROSS THE AREA WED NIGHT
AS FRONT SETTLES SOUTH OF THE AREA...BEFORE SLOWING DOWN OR EVEN
STALLING OUT DOWNSTATE AS IT BECOMES MORE ALIGNED WITH THE UPPER
FLOW. MID-LEVEL FLOW IS THEN FORECAST TO BACK SOMEWHAT IN ADVANCE OF
DIGGING/AMPLIFYING NORTHERN STREAM SHORTWAVE AND COULD RESULT IN
SOME RAIN SPREADING BACK NORTH INTO MAINLY OUR SOUTHERN CWA
WEDNESDAY AFTERNOON AND EVENING. MEANWHILE...FAIRLY EXTENSIVE
STRATUS AND STRENGTHENING NORTHERLY FLOW/COLD AIR ADVECTION SHOULD
RESULT IN VERY LITTLE RECOVERY IN TEMPS FROM MORNING LOW WEDNESDAY.
SEASONABLY STRONG HUDSON BAY VORTEX PROGGED TO DEVELOP LATER THIS
WEEK LEAVING US IN A NORTHWEST FLOW ALOFT. SERIES OF SHORTWAVES
PIVOTING AROUND THE POLAR VORTEX COULD RESULT IN SOME INCREASE IN
CLOUD COVER AND MAYBE EVEN A SHOWER OR TWO...BUT OVERALL LOOKS TO BE
A FAIRLY DRY PATTERN WITH BELOW AVERAGE TEMPS INTO THE WEEKEND.
WHILE THE DETAILS ARE FUZZY...THERE ARE SIGNS IN THE MEDIUM RANGE
GUIDANCE THAT THE NORTHWEST FLOW WILL BREAK DOWN LATE IN THE WEEKEND
INTO EARLY NEXT WEEK WITH A RETURN TO NEAR IF NOT SLIGHTLY ABOVE
AVERAGE TEMPS.
IZZI
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* -SHRA ACTIVITY THIS AFTERNOON
* RA WITH EMBEDDED THUNDER THIS EVENING
* GUSTY NORTH WINDS WEDS
* IFR CIGS WEDS
SHEA
//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 18Z...
* MEDIUM CONFIDENCE IN WIND FORECAST
* LOW CONFIDENCE IN PRECIP FORECAST THIS EVENING/OVERNIGHT
* HIGH CONFIDENCE ON CLOUD TRENDS...LOW ON LOWEST EXTENT WEDS
SHEA
//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 10 PM TUESDAY.
&&
$$
