309 AM CST
AN ACTIVE FEW DAYS LAY AHEAD WITH THE MAIN FORECAST CONCERNS
CENTERED AROUND WINDS AND PRECIP CHANCES. EARLY MORNING WATER VAPOR
IMAGERY SHOWS A CORRIDOR OF FAIRLY FLAT UPPER FLOW OVER THE EASTERN
HALF OF THE COUNTRY WITH SLIGHT UPPER RIDGING TRANSLATING EASTWARD
ACROSS THE NORTHERN PLAINS AND UPPER MISSISSIPPI RIVER VALLEY. TO
THE WEST...A SERIES OF SHORTWAVES ARE LINED UP WITH ONE DIGGING INTO
WESTERN MONTANA AND ANOTHER MOVING ALONG THE SOUTHEASTERN ALASKAN
COAST TOWARD FAR NORTHERN BRITISH COLUMBIA. ANOTHER UPPER TROUGH IS
CUT OFF FROM THIS NORTHERN STREAM OF FLOW JUST OFF THE CALIFORNIA
COAST AND WILL PLAY A ROLE IN PRECIP CHANCES FOR OUR AREA EARLY NEXT
WEEK. AT THE SURFACE...LOW PRESSURE WAS OBSERVED JUST NORTHEAST OF
LAKE SUPERIOR. ANOTHER SURFACE LOW IS DEVELOPING OVER SOUTHERN
SASKATCHEWAN/CENTRAL MONTANA AS A RESULT OF THE AFOREMENTIONED UPPER
SHORTWAVE WITH A SUBTLE WARM FRONT/TROUGH ANALYZED FROM THE LOW
ARCHING SOUTHEASTWARD ACROSS NORTHERN ILLINOIS AND INDIANA. THIS LOW
WILL BE KEY IN BRINGING INCREASING WINDS TO THE REGION TONIGHT AND
SUNDAY.
TODAY...AM EXPECTING A MILDER DAY TODAY WITH WARM ADVECTION ONGOING
EARLY THIS MORNING. SOUTH WINDS WILL INCREASE EARLY THIS AFTERNOON
AND BECOME SOMEWHAT GUSTY AS THE PRESSURE GRADIENT TIGHTENS WITH THE
SURFACE LOW DEEPENING OVER THE NORTHERN PLAINS. MIXING TO BETWEEN
950 AND 925 MB IS EXPECTED TODAY RESULTING IN GUSTS AROUND 20 KT AT
TIMES AND HIGHS IN THE MID 50S NORTH TO UPPER 50S SOUTH OF
INTERSTATE 88...WITH A FEW AREAS POSSIBLY REACHING 60 DEGREES MAINLY
SOUTH OF INTERSTATE 80 THANKS TO THE BREEZY SOUTH-SOUTHWEST WINDS.
TONIGHT THROUGH SUNDAY NIGHT...THE SURFACE LOW WILL MOVE FROM
EASTERN NORTH DAKOTA INTO WESTERN ONTARIO TONIGHT WHILE DEEPENING
INTO THE 980-985 MB RANGE. WINDS AND TEMPS WILL BE TRICKY AS THEY
WILL BE DICTATED BY THE DECOUPLING OF THE BOUNDARY LAYER THIS
EVENING. AM THINKING THAT DECOUPLING MAY OCCUR WITH SUNSET LATE THIS
AFTERNOON ALLOWING GUSTS TO DIMINISH BUT THE TIGHTENING PRESSURE
GRADIENT WILL KEEP SUSTAINED WIND SPEEDS UP. THIS WOULD LEAD TO
LITTLE DROP OFF IN TEMPS THIS EVENING. A WEAK UPPER WAVE LOOKS TO
LIFT NORTHEASTWARD ACROSS THE AREA THIS EVENING BRINGING MODEST MID
LEVEL COOL ADVECTION FOR A SHORT TIME AND MAY SERVE AS A CATALYST
FOR MIXING TO RE-DEVELOP LEADING TO A RETURN OF WIND GUSTS. THE
CONCERN IS THAT THE LOW LEVEL JET RAMPS UP SIGNIFICANTLY THIS
EVENING WITH FORECAST SOUNDINGS INDICATING 30+ KT WINDS STARTING
AROUND 600 FT AGL AND 40+ KT WINDS AT 1000 FT WITH A PEAK AT AROUND
60 KT UP AROUND 2500 FT. ITS NOT OUT OF THE QUESTION THAT 30 KT
GUSTS COULD OCCUR OVERNIGHT. ANOTHER WARM FRONT LOOKS TO QUICKLY
CROSS THE AREA EARLY SUNDAY MORNING WITH A LOW LEVEL THERMAL AXIS
CRESTING THE AREA. WINDS BECOME A BIGGER ISSUE SUNDAY AS MIXING
COMMENCES. THE LOW WILL BE LIFTING NORTHEASTWARD TOWARDS SOUTHERN
HUDSON BAY AND LIKELY BE SOMEWHERE AROUND 980 MB. PEAK LOW LEVEL
WINDS DO SUBSIDE BUT A DEEP LAYER OF 40-50 KT WINDS CONTINUES INTO
EARLY SUNDAY AFTERNOON. MIXING SUPPORTS GUSTS TO NEAR 40 KT DURING
THE DAY WITH POTENTIAL FOR A BRIEF PERIOD OF HIGHER GUSTS OF 45 KT
OR POSSIBLY HIGHER AS THE COLD FRONT PASSES AROUND MIDDAY. PRECIP
CHANCES ARE NOT IMPRESSIVE WITH DEEP LAYER MOISTURE LACKING SO WILL
CONTINUE WITH SLIGHT AND LOW CHANCE POPS BUT THESE MAY EVEN BE TOO
HIGH. WINDS WILL DIMINISH OVER LAND AREAS SUNDAY EVENING.
MONDAY THROUGH WEDNESDAY...THE COOL FRONTAL BOUNDARY WILL WEAKEN AND
WASH OUT TO THE SOUTH AND EAST OF THE AREA SUNDAY NIGHT INTO MONDAY
BUT STILL BE INTACT ENOUGH TO KEEP A BELT OF POOLED MOISTURE FROM
THE LOWER LAKES INTO CENTRAL ILLINOIS. THE ALASKAN UPPER WAVE WILL
DAMPEN BUT THE NORTHERN STREAM WILL BEGIN TO PHASE WITH THE
CALIFORNIA CUTOFF UPPER LOW. A LEAD SHORTWAVE WILL EJECT
NORTHEASTWARD FROM THE CENTRAL PLAINS AHEAD OF THE DEVELOPING
LONGWAVE TROUGH AXIS AND PUSH A WEAK SURFACE TROUGH ALONG THE OLD
FRONT/AREA OF POOLED MOISTURE MONDAY. THIS SHOULD PUSH THE MOISTURE
NORTHWARD AND BACK INTO MOST OF THE FORECAST AREA MONDAY MORNING.
THIS WILL SUPPORT INCREASED RAIN CHANCES...PRIMARILY ACROSS THE
SOUTHEAST TWO-THIRDS TO THREE-QUARTERS OF THE AREA MONDAY. THE
LARGER SCALE UPPER TROUGH WILL SWING ACROSS THE AREA AS IT AMPLIFIES
TUESDAY WITH ANOTHER SURFACE LOW MOVING FROM THE UPPER MISSISSIPPI
RIVER VALLEY INTO WESTERN ONTARIO. ANOTHER SHARP COLD FRONT WILL
CROSS THE AREA LATER TUESDAY AFTERNOON OR EARLY TUESDAY EVENING.
ANOTHER PERIOD OF GUSTY WINDS IS EXPECTED WITH THE STRONG COLD
ADVECTION AS H85 TEMPS FALL BACK TO THE -6 OR -8 C RANGE INTO
WEDNESDAY FROM THEIR ABOVE ZERO C READINGS PRIOR TO THAT.
THURSDAY AND FRIDAY...DRIER WEATHER WILL RETURN INTO THURSDAY AS
HIGH PRESSURE MOVES SOUTH OF THE AREA BUT THE UPPER FLOW PATTERN
WILL REMAIN ACTIVE JUST TO THE NORTH OF THE AREA. THEREFORE CANNOT
RULE OUT A WAVE MOVING CLOSE ENOUGH TO THE AREA TO KICK OFF SOME
SHOWERS ESPECIALLY AS WARM ADVECTION RETURNS THURSDAY NIGHT. THE
UPPER FLOW WILL TURN SOUTHWESTERLY SUGGESTING A RETURN TO MORE
ACTIVE WEATHER NEXT WEEKEND THOUGH WE SHOULD SEE AN UPSWING IN TEMPS
BY THAT TIME.
MDB
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* SOUTH WIND GUSTS OF 20 TO 25 KTS THROUGH TONIGHT AND SOUTHWEST
WINDS UP TO 40 KTS BY SUNDAY AFTERNOON.
* LOW-LEVEL WIND SHEAR TONIGHT.
* LOW CLOUD LIKELIHOOD LATE TONIGHT INTO SUNDAY MORNING.
//DISCUSSION...UPDATED 18Z...
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 18Z...
* HIGH CONFIDENCE IN PERIODIC SOUTH WIND GUSTS TO 20 KTS THROUGH
DAYBREAK SUNDAY.
* HIGH CONFIDENCE IN SOUTHWEST GUSTS REACHING AT LEAST 35 KTS ON
SUNDAY AFTERNOON...WITH POTENTIAL FOR SOME OF THESE GUSTS
ALREADY IN THE MORNING.
* HIGH CONFIDENCE IN 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.
//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.
&&
$$
