327 AM CDT
BIGGEST FORECAST CHALLENGE THIS MORNING IS TRYING TO FIGURE OUT JUST
WHEN THE BEST RAIN CHANCES ARE THE NEXT SEVERAL DAYS.
COLD FRONT IS SLOWLY MOVING SOUTH THROUGH THE SOUTHERN CWA EARLY
THIS MORNING...WITH ITS PASSAGE MARKING ABOUT A 2 MONTH CHANGE IN
TEMPERATURES FROM READINGS MORE TYPICAL OF MID-SEPT TO THOSE MORE
TYPICAL OF EARLY TO MID NOV. STRATUS DECK IS SPILLING SOUTHWARD
BEHIND THE FRONT WITH RECENT ACARS SOUNDINGS OUT OF RFD SHOWING A
VERY STOUT (6-8C) TEMP INVERSION BASED NEAR 900MB. THOUGH SLOWLY
WEAKENING...FORECAST SOUNDINGS SUGGEST THAT THIS FRONTAL INVERSION
WILL REMAIN IN PLACE THROUGH THE DAY LIKELY MAKING ANY MIXING AND
SCOURING OUT OF THIS STRATUS DECK SLOW TO OCCUR. COMBINATION OF COLD
AIR ADVECTION AND LOW CLOUDS SHOULD MAKE ANY TEMP RECOVERY A VERY
DIFFICULT TASK WITH NOT MUCH TEMP CHANGE EXPECTED TODAY NORTHERN CWA
AND PROBABLY MORNING HIGHS AND FALLING TEMPS SOUTHERN COUNTIES.
GENERALLY EXPECTING A DRY START TO THE DAY TODAY THOUGH MODELS DO
SUGGEST THAT RAIN COULD BEGIN TO RE-DEVELOP THIS AFTERNOON OVER
MAINLY OUR SOUTHERN CWA AS SUBTLE SHORTWAVE OVER THE CENTRAL PLAINS
MOVES EASTWARD INTO THE MS VALLEY REGION. MORE SIGNIFICANT
POSITIVELY TILTED TROUGH OVER THE ROCKIES THIS MORNING IS THEN
FORECAST TO MOVE EASTWARD BRINGING WITH IT A POOL OF VERY CHILLY AIR
ALOFT. WARM AIR ADVECTION AND STRENGTHENING MID-LEVEL FRONTOGENETIC
CIRCULATION IN ADVANCE OF THIS WAVE SHOULD RESULT IN A RAMP UP IN
COVERAGE OF PRECIPITATION TONIGHT...AGAIN LIKELY FOCUSED MORE ACROSS
OUR SOUTHERN CWA. HAVE TRENDED POPS UPWARD SIGNIFICANTLY AND AM IN
GOOD AGREEMENT WITH MET/MOS GUIDANCE WITH CATEGORICAL POPS SOUTHERN
CWA.
OTHER CONCERN TONIGHT WILL BE WITH INCREASING CHANCE OF LAKE EFFECT
AND/OR LAKE ENHANCED SHOWERS OVER NE IL. CERTAINLY NOT THE MOST
IMPRESSIVE LAKE EFFECT SET-UP I'VE EVER SEEN...BUT WITH INCREASING
AND MOST IMPORTANTLY DEEPENING LAKE INDUCED INSTABILITY COMBINED
WITH SYNOPTIC SCALE ASCENT THINK THE THREAT OF LAKE EFFECT/ENHANCED
SHOWERS IS PRETTY HIGH LATER TONIGHT. AS UPPER TROUGH AND POCKET OF
VERY COLD AIR ALOFT (AOB -30C AT 500MB) ARRIVES EARLY THURSDAY
MORNING SHOULD SEE A SUBSTANTIAL STEEPENING OF THE LOW AND MID
LEVEL LAPSE RATES...WITH LAKE INDUCED INSTABILITY INCREASING
FARTHER (CAPES NEAR 500 J/KG) AS EQUILIBRIUM LEVELS (EL) RISE TO
15-20KFT. WITH THE EL PROGGED TO CLIMB TO WELL ABOVE THE -20C
LEVEL THERE IS A RISK OF ENOUGH CHARGE SEPARATION TAKING PLACE IN
THE CLOUDS TO ALLOW FOR A COUPLE THUNDERSTORMS NEAR THE LAKE EARLY
THURSDAY MORNING...PARTICULARLY IN LIGHT OF THE ENHANCED
CONVERGENCE THAT IS EXPECTED TO DEVELOP IN ASSOCIATION WITH LAND
BREEZE. WHILE SURFACE TEMPS WILL BE IN THE 40S AND SHOULD KEEP
PRECIP FROM SWITCHING TO SNOW...THE VERY LOW FREEZING LEVELS COULD
ALLOW THE MORE ROBUST UPDRAFTS TO RESULT IN SOME GRAUPEL LATER
TONIGHT INTO THURSDAY.
UPPER TROUGH AXIS AND ASSOCIATED BETTER ORGANIZED LARGE ASCENT IS
PROGGED TO PUSH EAST OF THE AREA BY THURS AFTERNOON...SO DESPITE THE
LINGERING COLD AIR ALOFT AND STEEP LAPSE RATES SUPPORT FOR
ADDITIONAL SHOWERS LOOKS TO DECREASE THURS AFTERNOON. WE LOOK TO BE
IN BETWEEN NW FLOW SHORTWAVES THURSDAY NIGHT BUT WITH LINGERING COLD
AIR ALOFT AND STEEP LAPSE RATES...CYCLONIC FLOW...AND ABSENCE OF
SIGNIFICANT LARGE SCALE SUBSIDENCE AM VERY LEERY OF MODEL
FORECAST SOUNDINGS WHICH WOULD SUGGEST CLEARING. HAVE BUMPED UP
CLOUD COVER IN THE SKY GRIDS WITH THE ANTICIPATION THAT THERE WILL
BE SOME PRETTY GOOD SIZED AREAS OF STRATOCUMULUS LINGERING
THROUGH THE NIGHT. FOR THIS REASON...HAVE GENERALLY GONE ABOVE MOS
GUIDANCE VALUES FOR LOWS...HOWEVER SHOULD SKIES ACTUALLY CLEAR OUT
THEN WINDS COULD DECOUPLE AND TEMPS FALL OFF ENOUGH TO POSE A
FROST RISK.
SOME SLIGHT MODERATION IN TEMPS IS EXPECTED FRIDAY IN ADVANCE OF THE
NEXT SHORTWAVE THATS PROGGED TO PINWHEEL AROUND THE HUDSON VORTEX.
COULD ONCE AGAIN SEE SOME SHOWERS DEVELOP IN ADVANCE OF THIS FEATURE
VERY LATE FRIDAY AFTERNOON INTO FRIDAY EVENING BEFORE IT MOVES EAST
OF THE AREA LATER FRIDAY NIGHT. SAME DILEMMA EXISTS FRIDAY NIGHT
WITH REGARDS TO CLEARING...WITH THE EXPECTATION THAT CLEARING COULD
BE SLOW TO OCCUR IF IT HAPPENS AT ALL...HAVE NUDGED TEMPS UPWARD
SOME.
MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT TO START THE WEEKEND BUT
THEN DIVERGE SUBSTANTIALLY IN THEIR HANDLING OF THE NEXT TROUGH.
REGARDLESS OF THE SOLUTION...IT DOES APPEAR THAT SOME MODERATION IN
TEMPS WILL TAKE PLACE OVER THE WEEKEND AS POLAR VORTEX AND ITS
ASSOCIATED NW FLOW LOOSENS ITS GRIPS. HAVE MAINTAINED A DRY FORECAST
THROUGH THE PERIOD AS MOISTURE LOOKS TO REMAIN LIMITED WITH ANY
SHORTWAVES THAT DO AFFECT THE AREA.
IZZI
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 10Z...
* DURATION OF IFR CIGS THIS MORNING...AND THEN MVFR FOR REMAINDER
OF DAY.
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 10Z...
* MEDIUM TO LOW CONFIDENCE ON DURATION OF IFR CIGS THIS MORNING...
BUT RECENT SLIGHT IMPROVEMENT AT MDW BODES WELL.
* MEDIUM CONFIDENCE ON MVFR CIGS FROM MID MORNING THRU THE DAY.
IMPROVEMENT TO VFR SEEMS UNLIKELY.
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.
&&
$$
