AP-LM--CHI-IL Lake Michigan Area Forecast Discussion, LM
000
FXUS63 KLOT 151533
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1033 AM CDT WED JUL 15 2015
.UPDATE...
1027 AM CDT
NO REAL BIG CHANGES TO GOING FORECAST FOR TODAY. HOWEVER...DID
MAKE SOME MODIFICATIONS TO SKY TRENDS THROUGH THE AFTERNOON.
EARLY MORNING LOW STRATUS IS STILL LINGERING ACROSS COOK COUNTY
AND PORTIONS OF NORTHWEST INDIANA. THESE CLOUDS WILL LIKELY ERODE
OVER THE NEXT COUPLE OF HOURS AS DRIER AIR CONTINUES TO MOVE
THROUGH THE AREA. LOW CLOUDS FURTHER SOUTH IN EAST CENTRAL
ILLINOIS MAY HOLD ON A TAD LONGER AS THEY APPEAR TO HAVE SOME
DIURNAL COMPONENT TO THEM. OTHER LOCATIONS IN MOSTLY SUNNY SKIES
THIS MORNING WILL LIKELY BECOME MORE PARTLY CLOUDY...AS HIGH LEVEL
CIRRUS MAY CONTINUE EASTWARD TOWARD NORTHERN ILLINOIS THROUGH
MIDDAY.
RODRIGUEZ
&&
.SHORT TERM...
328 AM CDT
THROUGH TONIGHT...
QUIET WEATHER IS IN STORE AS HIGH PRESSURE CENTERED OVER THE
NORTHERN GREAT LAKES SLOWLY SHIFTS EAST THROUGH TONIGHT. THERMAL
PROGS SUPPORT HIGHS IN THE UPPER 70S TO AROUND 80 INLAND...WHILE
ONLY AROUND 70 ALONG THE SHORE DUE TO LIGHTER BUT CONTINUED
ONSHORE WINDS. SOME UNCERTAINTY IN CLOUD COVER AS THERE HAVE BEEN
PATCHY LOW CLOUDS OVERNIGHT IN NORTHWEST INDIANA AND SOUTHERN HALF
OF COOK COUNTY. NAM BASED GUIDANCE TRIES TO EXPAND IT EAST THROUGH
MID DAY BEFORE DISSIPATING. WITH NOT MUCH TEMPERATURE ADVECTION
AND STRONG JULY SUN...LOW STRATUS SHOULD MIX OUT THIS MORNING. DO
EXPECT SCATTERED TO BROKEN CUMULUS CLOUDS TO REDEVELOP WITH
HEATING OF DAY...ESPECIALLY IN SOUTHERN THIRD OF CWA WHERE BETTER
MOISTURE WILL EXIST AT TOP OF MIXED LAYER. DESPITE UNIFORM
NORTHEAST FLOW TODAY...THERE WILL BE A LAKE BREEZE PUSH IN THE
AFTERNOON THAT SHOULD CREATE A LAKE SHADOW EFFECT AS IT MOVES
INLAND.
HIGH CLOUD DEBRIS FROM MCS OVER KANSAS AND NEBRASKA THAT IS
ROUNDING STRONG MIDLEVEL RIDGE OVER SOUTHERN PLAINS WILL START TO
MOVE IN DURING THE EVENING HOURS AND THEN INCREASE AND GRADUALLY
LOWER TOWARD DAYBREAK THURSDAY. HAVE MAINTAINED A DRY FORECAST
THROUGH EARLY THURSDAY...THOUGH SOME GUIDANCE/NAMELY ECMWF IS A
BIT QUICKER WITH NEXT SHORT WAVE APPROACHING FROM WEST. BANKING ON
INFLUENCE OF DEPARTING HIGH PRESSURE TO KEEP THINGS DRY. LOWS WILL
BE A BIT BELOW SEASONAL FOR THE WARMEST TIME OF YEAR...IN THE MID
50S TO LOWER 60S.
RC
&&
.LONG TERM...
328 AM CDT
THURSDAY THROUGH TUESDAY...
THURSDAY WILL SEE A SHORT WAVE TROUGH ADVANCING EASTWARD ON THE
NORTH SIDE OF THE WELL-ESTABLISHED UPPER HIGH/RIDGE ACROSS THE
SOUTHERN PLAINS. THERE IS A FAIR AMOUNT OF NWP DISCREPANCY IN
LATITUDE ON HOW THIS TRANSLATES AND CORRESPONDING DETAILS. THE
GENERAL TREND THE PAST SIX ACTIVE AND WET WEEKS HAS BEEN FOR
GUIDANCE TO BE TOO FAR NORTH IN THE DAY 2-3 PERIOD WITH AREAS OF
CONVECTION/MCS ACTIVITY. THIS PLAYS INTO THURSDAY BECAUSE AT LEAST
A COUPLE AREAS OF REGIONAL CONVECTION ARE EXPECTED TO BE ONGOING
EARLY IN THE MORNING WITHIN WARM ADVECTION AND FORCING AHEAD OF
THE AFOREMENTIONED TROUGH. THERE ARE SOME INDICATIONS THAT SOME OF
THE ACTIVITY BY 12Z COULD BE AS FAR SOUTH AS MISSOURI AND AS FAR
EAST AS NORTHWEST/NORTH CENTRAL ILLINOIS...AND THOSE MESOSCALE
DETAILS WILL LIKELY PLAY INTO FORECAST ON THURSDAY. SO HAVE LEANED
TOWARD A MORE SOUTHERN NWP SOLUTION FOR THURSDAY AND THURSDAY
NIGHT...SUCH AS THE 00Z EC AND SOMEWHAT THE 00Z GFS. ALSO HAVE
CONTINUED TO SUPPORT THE CHANCE OF SOME SHOWERS AND POSSIBLY A FEW
STORMS MOVING INTO AND POSSIBLY WELL INTO THE CWA THURSDAY MORNING
WITHIN WARM ADVECTION...WITH POPS FURTHER EAST THAN MOST NWP
SOLUTIONS INDICATE.
THURSDAY SHOULD SEE PLENTY OF HIGH AND PROBABLY MID CLOUD COVER TO
KEEP TEMPERATURES FROM CONSIDERABLY WARMING DESPITE A SURFACE WARM
ADVANCING/EVOLVING NORTHWARD IN RESPONSE TO A SURFACE LOW ACROSS
NORTHERN OR CENTRAL IA AT MIDDAY. WITH ASCENT AND FORCING ALOFT
IMPROVING THROUGH THE DAY AND CONTINUED MOIST ASCENT ON 25-35 KT
850MB FLOW...STORM CHANCES WILL GRADUALLY INCREASE. THERE IS
EXPECTED TO REMAIN A CAP ON SURFACE-BASED CONVECTION FOR MUCH OF THE
DAY...HOWEVER THAT MAY WEAKEN LATE IN THE DAY AND INTO EARLY-MID
EVENING IF STRONG ENOUGH RETURN FLOW OR SOME CLEARING OCCURS.
DEPENDING ON INSTABILITY...WHICH RIGHT NOW LOOKS LIMITED...A
SCATTERED SEVERE STORM POSSIBILITY CENTERED A LITTLE NORTHWEST OF
THE AREA COULD EXIST FURTHER EAST INTO EVENING ESPECIALLY
CONSIDERING THE DYNAMICS...BUT AGAIN INSTABILITY MAY LIMIT
CONVECTION COVERAGE AND POTENCY.
GRADUAL HEIGHT RISES ARE FORECAST TO SLOWLY ADVANCE NORTHWARD FRIDAY
AND FRIDAY NIGHT WITH A LOW-LEVEL THERMAL RIDGE AND INCREASING DEW
POINTS INTO THE 70S PUSHING INTO THE REGION AS WELL. THIS WILL
BEGIN A WARM AND HUMID PERIOD INTO THE WEEKEND. NWP SOLUTIONS HOLD
ONTO SCATTERED STORM PRECIP CHANCES ON FRIDAY BUT ANY FORCING
LOOKS PARTICULARLY LOW AMPLITUDE AND A FOCUS LOOKS WEAK...SO NOT
PARTICULARLY CONFIDENT ON THAT OCCURRING AND EVEN LESS CONFIDENT
ON SATURDAY...WITH ONLY THE EC REALLY INDICATING A SUBTLE SHORT
WAVE INDUCING SOME PRECIP. THE 850MB TEMPERATURES FORECAST BY THE
00Z GFS AND EC ARE AT 22C ON SATURDAY INTO EARLY SUNDAY WHILE THE
EC IS MORE AROUND 19C-20C. THE FORMER SUPPORTS CORRELATING
SURFACE HIGHS IN THE MID 90S AS AN AVERAGE OF REANALYSIS DATA FOR
THIS TIME OF YEAR...BUT WITH UNCERTAINTIES THAT COME ALONG WITH
BEING ON THE NORTH EDGE OF A RIDGE AND NOT PARTICULARLY STRONG
CAPPING FORECAST...ALONG WITH THE TRENDS THIS SUMMER...HAVE
CONTINUED TO BE CONSERVATIVE WITH FORECAST HIGHS THIS WEEKEND AND
INDICATE AROUND 90. THE HIGH DEW POINT AIR LOOKS MORE CONFIDENT
GIVEN GUIDANCE SOLUTIONS AND WET GROUND OVER UPSTREAM AREAS WITHIN
THE LOW-LEVEL FLOW. FORECAST APPARENT TEMPERATURES...WHILE
DETERMINISTIC AND SEVERAL DAYS OUT YET...DO INDICATE HEAT
ADVISORY CRITERIA FOR A PORTION OF THE AREA ON SATURDAY.
MTF
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 14Z...
* NORTHEAST WINDS TODAY.
* SMALL CHANCE FOR SHRA THURSDAY PRIOR TO 18Z.
RC/RODRIGUEZ
//DISCUSSION...UPDATED 12Z...
GENERALLY QUIET AVIATION CONDITIONS TODAY AND TONIGHT WITH HIGH
PRESSURE SPREADING SOUTHEASTWARD FROM THE NORTHERN GREAT LAKES.
AREA OF MVFR CIGS CURRENTLY AT MDW AND GYY HAS BEEN DEVELOPING
HOLES AND STRONG JULY SUN SHOULD ERODE THE CLOUD DECK THIS
MORNING..BUT CANNOT RULE OUT A BRIEF PERIOD OF MVFR AT ORD.
FURTHER INLAND...EXPECTING A FEW TO SCT CU CLOUDS.
MAIN QUESTION TODAY IS WHETHER NORTHEAST WINDS WILL REACH 10 KT
AT ORD. FORECAST SOUNDINGS SUGGEST PREVAILING SPEEDS WILL BE CLOSE
TO BUT GENERALLY LESS THAN 10 KT. A LAKE BREEZE IS EXPECTED TO
PUSH INLAND THIS AFTERNOON...AND WHILE IT MAY HAVE BRIEF 7/810 KT
SPEEDS WITH IT...NOT EXPECTING MUCH MORE THAN THAT. WINDS WILL
DIMINISH THIS EVENING AS AREA WILL REMAIN UNDER INFLUENCE OF HIGH
PRESSURE...THEN PICK UP OUT OF THE SOUTH-SOUTHEAST ON THURSDAY AS
THE HIGH SLIDES EAST AND LOW PRESSURE APPROACHES FROM THE WEST.
THERE IS A SMALL CHANCE FOR SHRA THURSDAY MORNING...BUT TOO LOW TO
MENTION IN THE ORD 30 HR TAF. BETTER CHANCE FOR SHRA/TSRA WILL BE
NEAR RFD AND POSSIBLY NOT UNTIL LATE IN THE DAY OR THE EVENING FOR
THE EASTERN TERMINALS.
RC
//ORD AND MDW CONFIDENCE...UPDATED 14Z...
* HIGH IN GENERAL WITH WIND TRENDS...MEDIUM IN PREVAILING SPEEDS
REMAINING AT GENERALLY LESS THAN 10 KT.
* LOW IN ANY SHRA ON THURSDAY PRIOR TO 18Z.
RC/RODRIGUEZ
//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...
THURSDAY NIGHT...DECENT CHANCE FOR SHRA/TSRA AND ASSOCIATED VSBY
IMPACTS.
FRIDAY THROUGH MONDAY...PERIODIC CHANCES FOR SHRA/TSRA AND
ASSOCIATED VSBY IMPACTS...OTHERWISE VFR OUTSIDE OF ANY PRECIP.
TUESDAY...VFR.
RC
&&
.MARINE...
435 AM CDT
NORTHERLY WINDS HAVE BEEN A BIT SLOW TO SUBSIDE ON THE SOUTHERN
TIP OF THE LAKE...KEEPING WAVES ELEVATED. SHOULD STILL BE ABLE TO
EXPIRE SMALL CRAFT ADVISORY AT 10 AM AS PLANNED WITH WINDS
CONTINUING TO DIMINISH DUE TO HIGH PRESSURE SPREADING SOUTHEAST.
THERE COULD BE A BRIEF INCREASE IN NORTHERLY GUSTS TO CLOSE TO 20
KT ALONG THE EASTERN SHORE OF THE LAKE THIS AFTERNOON. HIGH
PRESSURE WILL SLIDE EAST TONIGHT AND LOW PRESSURE WILL APPROACH
FROM THE PLAINS...TURNING WINDS SOUTHEAST. INCREASING PRESSURE
GRADIENT WILL STRENGTHEN SOUTHEAST WINDS TO 10 TO 20 KT ON
THURSDAY AND THEN 15 TO 25 KT ON THURSDAY NIGHT. GENERALLY LIGHTER
SOUTH AND SOUTHWEST WINDS ARE IN STORE THROUGH THE WEEKEND AFTER
THE LOW PRESSURE CROSSES THE LAKE THURSDAY NIGHT INTO
FRIDAY...WITH WEAK HIGH PRESSURE CENTERED OVER THE EASTERN LAKES
AND A LOW PRESSURE TROUGH SLOWLY APPROACHING FROM THE PLAINS.
RC
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ006-ILZ014 UNTIL 1 PM WEDNESDAY.
IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 1 PM WEDNESDAY.
LM...NONE.
&&
$$
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Delivered by Weather Underground Inc. Wed Jul 15 2015 11:33AM EDT