412 PM CDT
A LITTLE MORE COVERAGE IN SHOWERS HAS BEEN CREEPING UP EAST OF
INTERSTATE 39 THIS AFTERNOON. THE SUNSHINE WARMING LOWER
LAYERS...COUPLED WITH THE COLD AIR JUST OFF OF THE BL ARE ALLOWING
LOWER LEVEL LAPSE RATES TO EXCEED 7 C/KM. THIS COUPLED WITH THE
LOW FREEZING LEVELS AND LOW HAIL GROWTH ZONE WILL ALLOW FOR A FEW
OF THE MORE 'CONVECTIVE' AND SHALLOW SHOWERS TO BE SUPPORTIVE OF
SMALL HAIL. SO FAR THIS AFTERNOON THERE HAVE BEEN A FEW REPORTS
OF PEA OR SMALLER SIZED HAIL FROM THE MORE ORGANIZED LOOKING
SHOWERS...BUT COVERAGE WILL BE VERY LIMITED AND WILL KEEP ANY
GRAUPEL MENTION OUT OF THE ZONES UNLESS THERE IS BIGGER UPTICK IN
COVERAGE AND INTENSITY. ACTIVITY SHOULD WANE ONCE THE SUN FALLS
BELOW THE HORIZEN. UPDATED GRIDS AND ZONES HAVE BEEN SENT.
SHEA
&&
.PREV DISCUSSION...
327 PM CDT
AFD...SHORT TERM...THIS EVENING THROUGH MONDAY...
THE BIG NEWS FOR EVERYONE DEPRESSED BY THE WEATHER OVER THE LAST
WEEK OR SO IS WE ARE FINALLY GOING TO GET A BREAK AND A MUCH
DESERVED WARM-UP...BUT NOT UNTIL SUNDAY AND ESPECIALLY MONDAY.
MAIN CONCERNS WITH THIS FORECAST PACKAGE ARE EXTENT OF LAKE EFFECT
SHOWERS LATER THIS AFTERNOON AND TONIGHT...COLD TEMPERATURES AND
FROST IN OUTLYING AREAS TONIGHT...AND ANOTHER NIGHT OF COLD
TEMPERATURES ON SATURDAY NIGHT. THIS WILL BRING THE POTENTIAL FOR A
MORE WIDESPREAD FROST.
ON WATER VAPOR IMAGERY THIS AFTERNOON...DEEP MIDLEVEL TROUGH DIGGING
EAST INTO CENTRAL GREAT LAKES...WITH LARGE RIDGE OVER WESTERN CONUS.
AT THE SURFACE...LOW PRESSURE HAS MOVED EAST TO EASTERN GREAT
LAKES...WITH A VERY LARGE AREA OF HIGH PRESSURE STRETCHING FROM
WESTERN ONTARIO DOWN THROUGH THE CENTRAL PLAINS. THIS HAS ALLOWED
WINDS TO CONTINUE TO SUBSIDE AS PRESSURE GRADIENT RELAXES. WAVE
HEIGHTS ALONG LAKESHORE WILL ALSO SLOWLY FALL...SO LAKESHORE FLOOD
WARNINGS AND STATEMENTS WILL BE ALLOWED TO EXPIRE AT 400 PM. MAIN
STORY THIS AFTERNOON IS VERY COOL AIRMASS CONTINUING TO SPILL INTO
REGION. SECOND SHOT OF EVEN COLDER AIR IS PUSHING IN THIS AFTERNOON
WITH ARRIVAL OF THERMAL TROUGH. THIS HAS STEEPENED LAPSE RATES AND
ALLOWED STRATOCU FIELD TO BLOSSOM OVER LAND. AS OF THIS WRITING...
SOME SPOTTY LIGHT SHOWERS AND SPRINKLES HAVE DEVELOPED OUT OF THIS
STRATOCU FIELD...SO ADDED IN SOME SLIGHT POPS TO COVER THIS
DEVELOPMENT THIS AFTERNOON.
MORE SIGNIFICANTLY...NORTHERLY FLOW OF COLD AIR OVER WARM LAKE HAS
SPURRED LAKE EFFECT SHOWER DEVELOPMENT INTO NORTHWEST INDIANA.
ACTIVITY DID NOT REALLY GET GOING UNTIL SECONDARY CAA SURGE THIS
AFTERNOON...WHICH INCREASED LAKE SURFACE TEMP TO 850 MB DIFFERENTIAL
TO A SUFFICIENT DEGREE. SHOWERS WILL FOCUS MAINLY ON PORTER COUNTY
INTO EARLY TONIGHT...AND THIS IS WHEN LAKE EFFECT PARAMETERS WILL BE
MOST FAVORABLE. LAKE INDUCED CAPE OF WELL OVER 500 J/KG...
EQUILIBRIUM LEVELS WELL OVER 10KFT...AND DECENT OMEGA AND MOISTURE
IN UNSTABLE LAYER WILL SUPPORT AT LEAST LIKELY POPS FOR LAKE
EFFECT SHOWERS...TAPERING TO CHANCE OVER LAKE COUNTY INDIANA. MAY
NEED TO MONITOR TO BUMP UP POPS OVER PORTER COUNTY THIS EVENING.
LATER TONIGHT...GUIDANCE IS HINTING AT NEARSHORE CONVERGENCE FARTHER
EAST...WHICH SHOULD LAKE EFFECT PARAMETERS REMAIN AS
FAVORABLE...WOULD ENTAIL A WELL-DEFINED PLUME OF SHOWERS INTO LAKE
COUNTY INDIANA AND POSSIBLY AS FAR WEST AS FAR EASTERN COOK COUNTY
AS WINDS TURN DUE NORTHERLY OR JUST EAST OF NORTH. HOWEVER...NAM AND
GFS BUFKIT SOUNDINGS BOTH SUGGEST LAKE EFFECT SET-UP BECOMING LESS
FAVORABLE AFTER MIDNIGHT...WITH SUBSIDENCE FROM RISING MIDLEVEL
HEIGHTS AND HIGH PRESSURE NOSING IN FROM THE NORTH CAUSING FALLING
INVERSION HEIGHTS. CAPPED POPS AT CHANCE IN NORTHWEST INDIANA AND
FAR EASTERN COOK COUNTY...AND BROUGHT SLIGHT CHANCE POPS WEST TO
VICINITY OF MIDWAY AIRPORT DUE TO EXPECTATION OF SHOWERS WEAKENING.
LAKE EFFECT SHOWERS WILL NEED MONITORING TONIGHT FOR NEAR-TERM
UPDATES GIVEN SOME UNCERTAINTY OVER EVOLUTION. KEPT A SLIGHT CHANCE
FOR LAKE SHOWERS TO CONTINUE INTO EARLY SATURDAY MORNING FOR EASTERN
COOK COUNTY AND LAKE COUNTY INDIANA...WITH ANY ACTIVITY COMPLETELY
SHUTTING OFF BY MID-MORNING SATURDAY.
OUTSIDE OF LAKE EFFECT CLOUDS AND PRECIP...AS HIGH BUILDS IN FROM
NORTH...SKIES WILL CLEAR. LOW LEVEL AIR-MASS IS VERY DRY AND QUITE
COLD...WITH 850 MB TEMPS FALLING TO BELOW 0C...SO LOWS IN THE LOW TO
MID 30S ARE EXPECTED FOR NORTHWEST AND NORTH CENTRAL ILLINOIS.
EXTENT TO WHICH BOUNDARY LAYER DECOUPLES AND NORTHERLY WINDS
DIMINISH FOR THESE AREAS WILL DETERMINE IF AND HOW MUCH FROST CAN
DEVELOP. FOR NOW...OPTED NOT TO HOIST FROST HEADLINES AND CARRIED
PATCHY FROST IN GRIDS THROUGH EARLY SATURDAY MORNING. WILL MENTION
IN HWO.
DESPITE MIDLEVEL HEIGHTS CONTINUING TO RISE ON SATURDAY...850 MB
THERMAL TROUGH WILL BE OVER AREA...WITH TEMPS OF 0 TO -2C. THIS WILL
TRANSLATE TO HIGHS ONLY IN THE MIDDLE AND UPPER 50S...THOUGH SKIES
WILL BE MOSTLY SUNNY OUTSIDE LINGERING LAKE EFFECT CLOUDS. SURFACE
RIDGE AXIS WILL MOVE OVERHEAD ON SATURDAY...SETTING UP FOR A
POSSIBLY EVEN COLDER NIGHT THAN TONIGHT...ESPECIALLY WELL OUTSIDE
CHICAGO. LIGHT WINDS AND CLEAR SKIES WILL SPELL NEARLY OPTIMAL
RADIATIONAL COOLING CONDITIONS. DID NOT GO QUITE AS COLD AS PREVIOUS
FORECAST WITH LOW TEMPS BUT STILL WENT BELOW GUIDANCE...ESPECIALLY
IN NORMALLY COLDER SPOTS. LOW TO MID 30S ARE IN THE CARDS AWAY FROM
THE LAKE...SO FROST COVERAGE WILL LIKELY BE MORE WIDESPREAD. OPTED
NOT TO ISSUE A FREEZE WATCH...AS THOUGHT IS FREEZING TEMPERATURES
WILL NOT BE WIDESPREAD ENOUGH.
AFTER COLD START ON SUNDAY MORNING...TEMPERATURES ALOFT WILL
STEADILY WARM...SO ONCE MIXING COMMENCES...AFTERNOON TEMPERATURES
WILL REACH THE MID 60S...WITH UPPER 60S SOUTH OF I-80. SUNDAY WILL
START A STRETCH OF BEAUTIFUL FALL WEATHER...WITH MIDLEVEL RIDGE
BUILDING OVER AREA AND SURFACE RIDGE REMAINING NEARBY. AIR-MASS WILL
REMAIN QUITE DRY AND LONG NIGHT THIS TIME OF YEAR WILL LEAD TO
ANOTHER COOL NIGHT SUNDAY NIGHT...BUT NOT AS COLD AS SATURDAY NIGHT.
AND THEN FINALLY THE WEATHER WE HAVE ALL BEEN WAITING FOR ON MONDAY.
SUNNY SKIES AND HIGHS IN THE LOW 70S...WITH EVEN SOME MID 70S
POSSIBLE OVER FAR SOUTHERN CWA. WENT A BIT ABOVE GUIDANCE ON
MONDAY...AS DRY AIR MASS AND FULL SUNSHINE SHOULD SUPPORT EFFICIENT
WARMING.
RC
LONG TERM...MONDAY NIGHT THROUGH FRIDAY...FAIRLY QUIET WEATHER
IS IN STORE NEXT WEEK AS STRONG UPPER RIDGE SLOWLY WORKS EAST ACROSS
THE REGION. UNDER THE INFLUENCE OF THE UPPER HIGH...EXPECT TO SEE
PLENTY OF SUNSHINE AND ABOVE NORMAL TEMPERATURES AS H85 TEMPS WARM
INTO THE 13-16C RANGE...AND PERSIST THROUGH THE WEEK. AT THE
SURFACE...A GRADUAL WARMING TREND IS EXPECTED THROUGH THE
PERIOD...AS AFTERNOON HIGHS GO FROM LOW TO MID 70S TUESDAY...TO MID
AND UPPER 70S BY THURSDAY. BY FRIDAY...UPPER RIDGE IS EXPECTED TO
SLIDE EAST OF THE AREA AS LONGWAVE TROUGH BEGINS TO APPROACH FROM
THE WEST. AMONGST EXTENDED GUIDANCE AND GLOBAL ENSEMBLE
MEMBERS...THERE IS FAIRLY HIGH AGREEMENT LENDING TO HIGHER
CONFIDENCE IN FAIR/WARM WEATHER PERSISTING THROUGH THE END OF THE
WEEK. THE ECMWF IS MUCH SLOWER IN BRINGING THE UPPER TROUGH TOWARDS
THE END OF THE WEEK...BUT THIS SOLUTION WOULD ONLY KEEP THE NICE
WEATHER AROUND LONGER. BMD
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 1920Z...
* NORTHWEST WINDS GUSTING TO 25-28 KT AT TIMES THIS AFTERNOON.
* SCATTERED -SHRA POSSIBLE LATE THIS AFTERNOON.
* SCT-BKN SKIES 3500-4500 FT.
* POTENTIAL FOR LAKE EFFECT SHRA LATER TONIGHT/SATURDAY MORNING.
* POTENTIAL FOR 2000-3000 FT LAKE EFFECT CIGS OVERNIGHT THROUGH
SATURDAY MORNING.
MDB
//DISCUSSION...UPDATED 1920Z...
WEAK UPPER WAVE AND STEEP LAPSE RATES HAVE RESULTED IN SCATTERED
SHOWER DEVELOPMENT ACROSS SOUTHERN WI WHICH ARE QUICKLY MOVING
SOUTHWARD. HAVE ADDED VCSH TO THE ORD/MDW/DPA TAFS FROM 21-00Z AND
IT IS POSSIBLE THAT THESE MAY IMPACT THE TERMINALS FOR BRIEF
PERIODS AND BRING ENOUGH RAIN TO AT LEAST WET THE RUNWAYS.
ACTIVITY WILL DIMINISH WITH SUNSET.
FROM 18Z...
NORTH TO NORTH-NORTHWEST WINDS CONTINUE EARLY THIS AFTERNOON AND
EXPECT THAT GUSTS WILL INCREASE TO AROUND 25 KT OR SLIGHTLY
HIGHER...WITH GUSTS OF 25-30 KT CONTINUING AT GYY. SCT-BKN LOWER
END VFR SKIES WILL CONTINUE THROUGH THE AFTERNOON WITH SKIES WELL
INLAND OF THE LAKE SEEING CLEARING AS THE SUN SETS. AREAS NEAR THE
LAKE AND ACROSS MUCH OF NORTHWEST INDIANA WILL SEE AT LEAST
SCATTERED SKIES CONTINUE THIS EVENING...WITH BROKEN SKIES PROBABLY
PREVAILING AT GYY THANKS TO THE LAKE. LAKE EFFECT SHOWERS WILL
BECOME MORE LIKELY INTO THE EVENING AND ESPECIALLY TONIGHT WITH
CURRENT RADAR MOSAIC SHOWING SOME DEVELOPMENT TRYING TO ORGANIZE
DOWN THE LONG AXIS OF THE LAKE. INITIAL ACTIVITY SHOULD STAY JUST
EAST OF GYY BUT WILL LIKELY DRIFT WESTWARD WITH TIME. MAY BE A
LITTLE SLOW ON THE VCSH MENTION THERE BUT ITS NOT COMPLETELY CLEAR
HOW QUICKLY THE BANDS WILL INTO THE EVENING. CONFIDENCE IS BETTER
IN LAKE EFFECT SHRA EVOLUTION INTO TONIGHT. LOW LEVEL FLOW WILL
BECOME SLIGHTLY EAST OF NORTH WITH CONVERGENCE SETTING UP ON THE
WESTERN SHORE OF THE LAKE. THIS WOULD SUPPORT A WESTWARD MOVEMENT
TO ANY ACTIVITY THIS EVENING AND OVERNIGHT. THIS WILL BRING AT
LEAST THE CHANCE FOR SHRA TO THE ILLINOIS SHORELINE OVERNIGHT INTO
SATURDAY MORNING WITH ACTIVITY POSSIBLY MOVING AS FAR INLAND AS
ORD/MDW. STILL SOME QUESTION IF DEVELOPMENT WILL CONTINUE
OVERNIGHT WITH PARAMETERS WANING A BIT BUT WILL STICK WITH VCSH
MENTION AT ORD/MDW. MVFR CIGS ARE ALSO POSSIBLE THERE...AS WELL AS
DPA. SHRA ACTIVITY SHOULD SHUTOFF BY EARLY AFTERNOON ALLOWING
SCATTERING OF SKIES. FURTHER INLAND...INCLUDING RFD...SKIES WILL
PROBABLY BE MOSTLY CLEAR WITH SOME STRATOCU POSSIBLY DEVELOPING
LATE MORNING. WINDS WILL BE LIGHTER WITH SOME GUSTS TO NEAR 20 KT
POSSIBLE DURING THE AFTERNOON.
MDB
//ORD AND MDW CONFIDENCE...UPDATED 1920Z...
* HIGH CONFIDENCE IN WIND FORECAST.
* MEDIUM-HIGH CONFIDENCE THAT -SHRA WILL MOVE INTO THE AREA
21-22Z...MAY DIRECTLY AFFECT TERMINALS FOR BRIEF PERIODS...BUT
ACTIVITY IS WIDELY SCATTERED.
* HIGH CONFIDENCE IN CEILING FORECAST THIS AFTERNOON.
* MEDIUM CONFIDENCE IN LAKE EFFECT SHRA AT LEAST BEING IN THE
VICINITY OF THE AIRPORT LATE TONIGHT AND SATURDAY MORNING.
* MEDIUM-HIGH CONFIDENCE IN LAKE EFFECT CEILINGS LATE TONIGHT AND
SATURDAY MORNING BUT LOW CONFIDENCE IN THEM BEING BELOW 3000 FT.
MDB
//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...
SATURDAY NIGHT THROUGH THURSDAY...VFR.
MDB
&&
.MARINE...
143 PM CDT
MARINE FORECAST CONCERNS ARE FOCUSED ON GRADUAL DECREASE IN STRONG
NORTHERLY WINDS ACROSS LAKE MICHIGAN...HIGH WAVES AND ASSOCIATED
STORM/GALE/SMALL CRAFT ADVISORY HEADLINE ISSUES INTO SUNDAY.
LOW PRESSURE CONTINUES TO FILL NEAR TORONTO ONTARIO EARLY THIS
AFTERNOON. THIS LOW WILL CONTINUE TO WEAKEN AS IT DRIFTS EAST ACROSS
UPSTATE NEW YORK THIS EVENING...AND EVENTUALLY REFORMS OFF THE EAST
COAST. AS THIS OCCURS...HIGH PRESSURE OVER WESTERN ONTARIO AND THE
UPPER MIDWEST WILL SLOWLY DRIFT SOUTHEAST ACROSS THE NORTHERN AND
WESTERN GREAT LAKES AND THE MID MISSISSIPPI VALLEY THROUGH SUNDAY
MORNING. THIS WILL ALLOW CONTINUED GRADUAL WEAKENING OF THE SURFACE
PRESSURE GRADIENT ACROSS LAKE MICHIGAN.
AFTER THIS MORNINGS GUSTS IN EXCESS OF 50 KTS...AND WAVES HIGHER
THAN 20 FT PER BUOY AND SHIP OBS...WINDS HAVE SETTLED TO 35-40 KTS
FOR THE MOST PART ACROSS THE OPEN WATERS AND THE SOUTH SHORE WITH
WAVES NOW IN THE 12-15 FOOT RANGE PER LATEST BUOY OBS. THUS HAVE
ALLOWED THE STORM WARNING TO EXPIRE AS OF 1 PM CDT...REPLACED BY A
GALE WARNING WHICH WILL RUN THROUGH 1 AM CDT SATURDAY BASED ON
CONSISTENT MODEL GUIDANCE. WITH EXPIRATION OF GALE WARNINGS
TONIGHT...WILL HAVE TO HOIST SMALL CRAFT ADVISORIES FOR THE ILLINOIS
AND INDIANA NEARSHORE WATERS. LONG NORTHERLY FETCH AND CONTINUED
RATHER GRADUAL DECLINE IN WIND SPEEDS WILL HELP TO MAINTAIN WAVES
WELL ABOVE 4 FT PARTICULARLY ALONG THE INDIANA SHORE INTO SUNDAY
MORNING. WILL LIKELY BE ABLE TO KEEP ILLINOIS SHORE SMALL CRAFT
ADVISORIES A LITTLE SHORTER...WITH A SLIGHTLY MORE FAVORABLE FETCH
FOR ALLOWING WAVES TO SUBSIDE.
WINDS AND WAVES SHOULD BE MUCH LOWER FROM SUNDAY INTO THE MIDDLE OF
NEXT WEEK...AS BLOCKING PATTERN ALOFT ALLOWS HIGH PRESSURE RIDGE TO
LINGER ACROSS THE CENTRAL PART OF THE NATION AND THE WESTERN LAKES.
IN FACT WIND DIRECTION FORECAST BECOMES A BIT UNCERTAIN DUE TO VERY
WEAK GRADIENT DURING THIS PERIOD.
RATZER
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ744-LMZ745-LMZ777-
LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 1 AM
SATURDAY.
GALE WARNING...LMZ741-LMZ742-LMZ743 UNTIL 10 PM FRIDAY.
SMALL CRAFT ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 1 AM SUNDAY.
&&
$$
