.DISCUSSION...
342 PM CST
THE MAIN ISSUES CONTINUE TO BE WITH THE WINDS...ESPECIALLY ON SUNDAY
AND PRECIPITATION CHANCES AND AMOUNTS ON MONDAY.
WATER VAPOR IMAGERY EARLY THIS AFTERNOON INDICATES A POTENT NORTHERN
STREAM SHORT WAVE DIGGING SOUTHEAST ACROSS THE NORTHERN ROCKIES.
ASSOCIATED WITH THIS DISTURBANCE IS A POTENT SURFACE LOW OF 990 MB
ACROSS THE JAMES RIVER VALLEY OF NORTH DAKOTA. AS A
CONSEQUENCE...SOUTHERLY WINDS HAVE INCREASED ACROSS THE CENTRAL
CONUS DOWN STREAM OF THIS LOW AND UPSTREAM OF HIGH PRESSURE ACROSS
THE SOUTHEASTERN STATES. AREA PROFILER INDICATE A STOUT 40+ LOW
LEVEL JET ALREADY DEVELOPING ACROSS THE MID MISSISSIPPI RIVER
VALLEY. THIS TREND WILL IN THE WINDS WILL CONTINUE TONIGHT INTO
SUNDAY AS THE SURFACE LOW DEEPENS INTO THE SUB 985MB RANGE AS IT
MOVES NORTHEASTWARD ACROSS WESTERN ONTARIO.
LOW LEVEL MOISTURE WILL BE ON THE INCREASE LATER TONIGHT INTO SUNDAY
MORNING AS THE LOW LEVEL JET CONTINUES TO TRANSPORT MOISTURE
NORTHWARD FROM THE GULF. MODEL BUFFER SOUNDINGS SUGGEST THAT AS
ISENTROPIC ASCENT INCREASES ACROSS THE AREA THAT A LOWER CLOUD DECK
WITH DEVELOP ACROSS THE AREA BY EARLY SUNDAY MORNING. THERE COULD
ALSO BE A FEW SHOWERS OR AREAS OF DRIZZLE DURING THE EARLY TO MIDDLE
PART OF THE DAY. HOWEVER...BY FAR THE MAIN CONCERNS WITH THIS SYSTEM
WILL BE THE WINDS. IT APPEARS THAT THE SURFACE WINDS WILL REMAIN
ELEVATED TONIGHT. I AM A LITTLE CONCERNED THAT THERE COULD BE SOME
GUSTY WINDS TONIGHT...IN SPITE OF THE UNFAVORABLE TIME OF DAY. IT
APPEARS THAT THERE WILL NOT BE MUCH OF A NOCTURNAL INVERSION...AND
WITH THE WINDS SCREAMING ABOVE THE SURFACE IT MAY NOT BE HARD TO GET
SOME OF THAT MOMENTUM TO THE SURFACE.
DURING THE DAY ON SUNDAY...AS MENTIONED ABOVE THERE WILL LIKELY BE
SOME LOWER CLOUDS AND AREAS OF DRIZZLE DURING THE MORNING. THERE WAS
SOME CONCERN THAT THIS COULD LIMIT OUR MIXING POTENTIAL AND HENCE
OUR OVERALL THREAT FOR GETTING ADVISORY CRITERIA WINDS. HOWEVER...I
AM STILL EXPECTING THAT AS THE FRONT APPROACHES THE AREA TOMORROW
AFTERNOON THAT A GOOD DRY PUNCH OF AIR WILL QUICKLY ERODE THIS DECK
OF CLOUDS AND ALLOW US TO MIX THE MUCH STRONGER WINDS ALOFT. IN
ADDITION TO THIS...IT APPEARS THAT NORTHERN ILLINOIS WILL EXPERIENCE
FAVORABLE ISALLOBARIC PRESSURE RISES OF 9 TO 10 MB/6HR WITH THE
SURFACE FRONTAL PASSAGE SUNDAY AFTERNOON. MODEL BUFFER SOUNDINGS
ALSO LOOK VERY FAVORABLE FOR WIND GUSTS OF 40+ KT WITH MEAN BOUNDARY
LAYER WINDS IN EXCESS OF 40 KT. WITH THIS IN MIND...I HAVE ISSUED A
WIND ADVISORY FOR SUNDAY FOR WINDS OF 25 TO 35 MPH WITH GUSTS TO 50
MPH. I INCLUDED ALL BUT MY 3 FAR NORTHWEST COUNTIES IN AND AROUND
THE ROCKFORD AREA. IT STILL APPEARS TO BE A WINDY DAY IN THESE
AREAS. HOWEVER...DUE TO SOME UNCERTAINTIES ON THE STRENGTH OF THE
WINDS ACROSS MY NORTHWEST...I HAVE LEFT THEM OUT OF THE ADVISORY AT
THIS TIME.
THE WINDS SHOULD QUICKLY ABATE BY SUNDAY EVENING AND THEN THE OTHER
CONCERN WILL BE THE THREAT FOR RAINFALL ON MONDAY. THE WEATHER
PATTERN WILL REMAIN ACTIVE EARLY NEXT WEEK AS ANOTHER SERIES OF MID
LEVEL DISTURBANCES RACES EASTWARD WITHIN THE FAST NORTHERN STREAM
FLOW. THIS SHOULD DRIVE A WEAK SURFACE WAVE NORTHEASTWARD ALONG A
SURFACE BOUNDARY ACROSS CENTRAL ILLINOIS AND NORTHWESTERN INDIANA ON
MONDAY. ALTHOUGH THERE IS STILL SOME DISAGREEMENTS ON THE
NORTHWESTERN EXTENT OF THIS RAINFALL EVENT...IT DOES APPEAR THAT THE
SOUTHEASTERN 1/2 TO 2/3RDS OF MY CWA WILL HAVE GOOD CHANCES OF
EXPERIENCING SOME RAINFALL FROM THIS SYSTEM AS GOOD LARGE SCALE
FORCING FOR ASCENT OCCURS ACROSS THE AREA. THERE COULD EVEN BE A FEW
THUNDERSTORMS ACROSS PORTIONS OF EAST CENTRAL ILLINOIS AND PORTIONS
OF NORTHWESTERN INDIANA...CLOSER TO THE WARM SECTOR.
THIS WAVE WILL QUICKLY EXIT THE AREA MONDAY NIGHT...ESSENTIALLY
PUSHING THE SURFACE FRONTAL ZONE AND MAIN FOCUS FOR ADDITIONAL
RAINFALL FARTHER SOUTH ACROSS PORTIONS OF THE OHIO VALLEY AND
LOWER MISSISSIPPI VALLEY. THEREFORE...AS THE SOUTHERN STREAM UPPER
LOW...CURRENTLY OFF THE SOUTHERN CALIFORNIA COAST...EJECTS
EASTWARD ACROSS THE SOUTHERN MISSISSIPPI VALLEY...IT APPEARS THE
MAIN HEAVY RAINFALL EVENT WILL REMAIN SOUTH OF MY CWA ON TUESDAY.
THE FOCUS FOR MY AREA ON TUESDAY AND WEDNESDAY WILL BE WITH REGARDS
TO ANOTHER STRONG SYSTEM MOVING ACROSS SOUTHERN CANADA AND THE UPPER
MISSISSIPPI VALLEY. THIS STORM LOOKS TO PUSH ANOTHER STRONG COLD
FRONT ACROSS THE AREA LATE TUESDAY AFTERNOON AND EVENING. BEHIND
THIS FRONT...IT APPEARS THAT SOME OF THE COLDEST AIR THUS FAR THIS
SEASON COULD MOVE ACROSS THE AREA FOR WEDNESDAY AS A 1030 MB HIGH
BUILDS IN ACROSS THE LOWER MISSOURI VALLEY. TEMPERATURES AT 850 MB
AROUND -10 DEGREES CELSIUS COULD MOVE ACROSS SOUTHERN WI AND
NORTHERN ILLINOIS BY WEDNESDAY AFTERNOON. THIS WOULD LIKELY KEEP
SURFACE TEMPERATURES IN THE 30S IN MOST AREAS ON WEDNESDAY.
THEREFORE...I LOWERED TEMPERATURES A FEW DEGREES DURING THIS PERIOD
TO MATCH THIS THINKING.
LATER NEXT WEEK INTO NEXT WEEKEND IT APPEARS TEMPERATURES WILL
REBOUND AS ANOTHER TROUGH DIGS ACROSS WESTERN NORTH AMERICA.
DOWNSTREAM UPPER LEVEL RIDGING ACROSS THE SOUTHEASTERN CONUS SHOULD
SETUP SOUTHWEST FLOW ALOFT ACROSS THE CENTRAL PORTION OF THE COUNTY.
THIS LOOKS TO SET THE STAGE FOR ANOTHER ACTIVE WEATHER PATTERN
ACROSS THE AREA WITH MORE DECENT CHANCES FOR RAIN AND SOME WIND.
KJB
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 21Z...
* SOUTH WIND GUSTS OF UP TO 25 KTS BEFORE SUNSET...POSSIBLY GUSTS
AFTER SUNSET.
* SOUTHWEST WINDS UP TO 40 KTS BY SUNDAY AFTERNOON.
* LOW-LEVEL WIND SHEAR TONIGHT.
* LOW CLOUD LIKELIHOOD LATE TONIGHT INTO SUNDAY MORNING.
RC/MTF
//DISCUSSION...UPDATED 21Z...
WITH GOOD MIXING AND TIGHTENING PRESSURE GRADIENT...INCREASED
SUSTAINED WINDS TO 15 KT AND GUSTS TO UP TO 25 KT AT THE NE IL AND
NW IN TAF SITES. RFD HAS NOT SEEN GUSTS YET BUT EXPECT GUSTS IN 20
KT RANGE BEFORE SUNSET. 0200Z START TIME FOR LLWS STILL LOOKS
GOOD. REMOVED GUSTS MUCH OF OVERNIGHT DUE TO EXPECTATION THAT
INVERSION BELOW LLWS WILL BE STOUT ENOUGH TO PREVENT MIXING DOWN
OF GUSTS. HOWEVER...CONTINUING INCREASE IN PRESSURE GRADIENT MAKE
THIS AN UNCERTAIN FORECAST. NAM...RUC AND GFS MODEL SOUNDINGS SHOW
25 KT+ WINDS ONLY A FEW HUNDRED FEET ABOVE SURFACE...SO IT IS
POSSIBLE OCCASIONAL GUSTS MAY OCCUR OVERNIGHT AND SUSTAINED WINDS
MAY NEED TO BE REVISED UPWARDS A FEW KNOTS.
RC
18Z DISCUSSION...
LOW PRESSURE WILL CONTINUE TO DEEPEN AS IT EVOLVES EAST ALONG THE
INTERNATIONAL BORDER OF ND/MN INTO TONIGHT. THIS WILL LEAD TO A
TIGHTENING PRESSURE GRADIENT ACROSS THE TAF SITES TONIGHT AND KEEP
SUSTAINED WINDS UP...POTENTIALLY EVEN INCREASING SLIGHTLY.
OCCASIONAL GUSTS TO 20 TO 25 KTS ARE LIKELY. ALSO BECAUSE OF THE
LOW DEEPENING...A SOUTHWEST LOW-LEVEL JET WILL FOCUS ATOP THE
AREA WITHIN THE 1500 TO 3000 FT LAYER. SPEEDS AS HIGH AS 55-60 KTS
ARE POSSIBLE IN THIS LAYER OVERNIGHT...POTENTIALLY CREATING PLANE
SPACING ISSUES THROUGH LOW-LEVEL WIND SHEAR. THESE STRONG
SOUTHERLY WINDS JUST OFF THE SURFACE TONIGHT WILL STEER MOISTURE
BACK AND WITH THAT WILL COME THE LIKELIHOOD OF MVFR AND POSSIBLY
IFR CEILINGS. AT LEAST SOME SCATTERED MORNING CLOUDS ARE
EXPECTED...WITH BROKEN CEILINGS BECOMING MORE FAVORED THAN THE
LAST FORECAST. SCATTERED LIGHT SHOWERS AND AREAS OF DRIZZLE ARE
POSSIBLE...MOST FAVORED SOUTH OF THE TAF SITES. AS THE
AFOREMENTIONED LOW PRESSURE WRAPS DRY AIR IN FROM THE WEST...THE
CLOUDS SHOULD PUSH EAST BY AFTERNOON. WITH THAT DRY SURGE HOWEVER
WILL COME EVEN GUSTIER AND HIGHER IMPACT SOUTHWEST SURFACE
WINDS...POTENTIALLY UP TO 45 KTS.
//ORD AND MDW CONFIDENCE...UPDATED 21Z...
* HIGH CONFIDENCE IN SOUTH WIND GUSTS UP TO 25 KT PRIOR TO SUNSET.
LOW CONFIDENCE IN GUSTS AFTER SUNSET.
* HIGH CONFIDENCE IN SOUTHWEST GUSTS REACHING UP TO 40 KTS ON SUNDAY
AFTERNOON...WITH POTENTIAL FOR SOME OF THESE GUSTS ALREADY IN
THE MORNING.
* HIGH CONFIDENCE IN LLWS FORECAST...AT LEAST 45 KT SOUTHWEST
FLOW WITHIN THE 1500 TO 3000 FT LAYER TONIGHT.
* LOW CONFIDENCE IN MORNING LOW CLOUDS AT ORD WITH MEDIUM
CONFIDENCE AT MDW. HIGH CONFIDENCE THAT ANY CLOUDS WILL SCATTER
BY EARLY TO MID AFTERNOON.
RC/MTF
//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...
SUNDAY NIGHT...VFR. SLOWLY DIMINISHING WINDS.
MONDAY...CHANCE SHRA. MVFR CIGS POSSIBLE.
TUESDAY...VFR LIKELY. BREEZY WEST WINDS.
WEDNESDAY...VFR.
THURSDAY...VFR. SLIGHT CHANCE SHRA LATE.
FRIDAY...CHANCE SHRA AND MVFR CIGS.
MTF
&&
.MARINE...
217 PM CST
DEEPENING LOW PRESSURE MOVING ACROSS THE INTERNATIONAL BORDER OF
MN TONIGHT AND INTO WESTERN ONTARIO ON SUNDAY WILL HAVE A LARGE
INFLUENCE ON LAKE MICHIGAN. SMALL CRAFT ADVISORY CONDITIONS ARE
BEING SPORADICALLY OBSERVED ALREADY...WITH 25 KT GUSTS SEEN ON OR
NEAR THE ILLINOIS SHORE. SOUTHERLY WIND SPEEDS WILL ONLY BE ON THE
INCREASE INTO TONIGHT WITH GALE CONDITIONS EXPECTED TO DEVELOP
PRIOR TO MIDNIGHT INCLUDING IN THE NEAR SHORE AREAS. THE WIND
DIRECTION MAY VARY SOME BETWEEN SOUTH AND SOUTHWEST ALL THE WAY
THROUGH SUNDAY MORNING...BECOMING A MORE DEFINED SOUTHWEST BY
SUNDAY AFTERNOON. HIGHER END GALES TO 45 KTS ARE MOST LIKELY AFTER
MORNING CLOUDS SCOUR AND THE COLD FRONT PASSES...WHICH IS EXPECTED
DURING THE EARLY TO MID AFTERNOON ON SUNDAY. THE MOST FAVORED
PORTION OF THE LAKE TO SEE THESE IS THE SOUTHERN HALF. SOME OF
THESE HIGHER END GUSTS COULD BE SEEN IN THE NEAR SHORE ZONES AS
WELL...PRIMARILY FROM NORTHERLY ISLAND AROUND TO MICHIGAN CITY.
WHILE GALES WILL SLOWLY SUBSIDE LATER SUNDAY NIGHT...THE OVERALL
PROGRESSIVE PATTERN OF LOW PRESSURES WILL CONTINUE THROUGH EARLY
WEDNESDAY. THE NEXT ROUND OF GALES IS FAVORED ON TUESDAY NIGHT AS
LOW PRESSURE MOVES EAST NEAR OR OVER LAKE SUPERIOR DRIVING A WELL-
DEFINED COLD FRONT EAST ACROSS LAKE MICHIGAN. WESTERLY GALES TO 35
KTS AT THIS TIME ARE FAVORED OVER THE NORTHERN HALF OF THE LAKE.
MTF
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND ADVISORY...ILZ005-ILZ006-ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-
ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-ILZ039...8
AM SUNDAY TO 6 PM SUNDAY.
IN...WIND ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019...8 AM SUNDAY
TO 6 PM SUNDAY.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-
LMZ874-LMZ876-LMZ878...9 PM SATURDAY TO 9 PM SUNDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 9 PM SATURDAY.
&&
$$
