1140 AM CST
THE AFTERNOON FORECAST IS IN GOOD SHAPE WITH MINIMAL CHANGES MADE.
THE MORNING CLOUD COVER LED TO A SLOW THERMAL CLIMB...BUT
AFTERNOON TEMPERATURES LOOK TO BOUNCE BACK TO NEAR THE FORECAST
HIGHS AS THE SHORT WAVE TAKES ITS MID-CLOUDS WITH IT INTO LOWER
MI. THE AFTERNOON WIND GUSTS LOOKS TO BE SLIGHTLY LOWER THAN
INITIALLY THOUGHT...DUE MAINLY TO A SHORTER DURATION OF MIXING
THANKS TO THE MORNING CLOUDS.
MTF
//PREV DISCUSSION...
320 AM CST
A FAIRLY ACTIVE FORECAST PERIOD WILL GET UNDERWAY WITH A WARMUP
COMMENCING TODAY AND CONTINUING THROUGH THE WEEKEND...WITH RAIN
CHANCES INCREASING LATE IN THE WEEKEND. HOWEVER...MODELS ARE HAVING
TROUBLE AGREEING ON HOW TO HANDLE SOME KEY FEATURES THAT WILL
DICTATE HOW AND WHEN PRECIP CHANCES EVOLVE. EARLY MORNING WATER
VAPOR IMAGERY SHOWS THE DEEP LONGWAVE TROUGH WHICH SWUNG ACROSS THE
AREA YESTERDAY NOW EXTENDING FROM HUDSON BAY ACROSS LAKE ONTARIO AND
OFF THE MID-ATLANTIC COAST. A FAIRLY FAST NORTHWESTERLY AND SLIGHTLY
RIDGED FLOW IS NOW IN PLACE FROM BRITISH COLUMBIA SOUTHEASTWARD
ACROSS THE LOCAL AREA. ALSO OF NOTE IS A CUTOFF CLOSED UPPER LOW OFF
THE CALIFORNIA COAST ALONG WITH A STRONG SHORTWAVE NOW MOVING
ONSHORE OVER CENTRAL BRITISH COLUMBIA. THESE FEATURES WILL BE KEY IN
DETERMINING OUR PRECIP CHANCES SUNDAY/MONDAY. AT THE
SURFACE...RIDGING IS QUICKLY APPROACHING FROM THE WEST WHILE LOW
PRESSURE ALONG THE CENTRAL SASKATCHEWAN/MANITOBA BORDER SENDS A
TROUGH SOUTHWARD INTO THE CENTRAL AND NORTHERN PLAINS.
TODAY AND SATURDAY...NORTHWESTERLY UPPER FLOW WILL REMAIN IN PLACE
AND STEADILY DE-AMPLIFY TONIGHT. HEIGHTS CONTINUE TO RISE AS A
RESULT WITH WARM ADVECTION UNDERWAY AS THE AFOREMENTIONED UPPER
TROUGH AXIS DEPARTS. SURFACE RIDGING WILL QUICKLY CREST THE AREA
THIS MORNING AND BE OFF TO THE EAST BY AFTERNOON. H85 TEMPS WILL
STEADILY WARM TO +3 OR 4 C. SOUTHWESTERLY WINDS WILL INCREASE BY
AFTERNOON AS THE RIDGE PASSES AS THE GRADIENT BETWEEN LOW PRESSURE
OVER SOUTHERN MANITOBA AND HIGH PRESSURE ALONG THE GULF COAST
TIGHTENS. MID LEVEL BAROCLINIC ZONE TIGHTENS BRIEFLY THIS MORNING
WITH A BAND OF MODEST FRONTOGENESIS PASSING OVERHEAD. THE BULK OF
THE FORCING AND MOISTURE REMAIN TO THE NORTH BUT SHOULD SEE A BAND
OF CLOUD COVER CROSS THE AREA WITH A MINIMAL CHANCE FOR A FEW FLAKES
OR SPRINKLES TO FALL AS WELL. CURRENT RADAR MOSAIC SHOWS LITTLE IN
THE WAY OF ACTIVITY TO THE WEST. MORNING CLOUD COVER WILL GIVE WAY
TO SOME SUNSHINE FOR THE AFTERNOON. THIS WILL COMBINE WITH THE
STRONG SOUTHWESTERLY WINDS...MID LEVEL WARM ADVECTION...AND DRY LOW
LEVELS TO ALLOW TEMPS TO WARM INTO THE MID 40S NORTH TO AROUND 50
ALONG AND SOUTH OF INTERSTATE 80. THE UPPER FLOW TURNS WESTERLY THEN
SOUTHWESTERLY SATURDAY WITH H85 TEMPS WARMING TO AROUND +8 C.
SOUTHWEST WINDS WILL CONTINUE TONIGHT AND WILL KEEP COOLING IN CHECK
SUPPORTING A MILDER START SATURDAY. THIS WILL SUPPORT HIGHS 7 TO 10
DEGREES WARMER THAN TODAY WITH SOME AREAS SOUTH OF INTERSTATE 80
REACHING 60 DEGREES WITH A FAIR AMOUNT OF SUNSHINE TO START THE DAY
WITH CIRRUS LIKELY ARRIVING DURING THE AFTERNOON.
SUNDAY AND MONDAY...FORECAST ISSUES ARISE SATURDAY NIGHT INTO SUNDAY
IN TERMS OF MODEL AGREEMENT. THE MAIN PROBLEM IS THE HANDLING OF THE
CUTOFF UPPER LOW OFF THE CALIFORNIA COAST AND THE SHORTWAVE COMING
ASHORE OVER BRITISH COLUMBIA. THE GENERAL CONSENSUS IS THAT THE
NORTHERN STREAM BRITISH COLUMBIA TROUGH WILL NOT PHASE WITH THE
CUTOFF UPPER LOW RESULTING IN A FASTER MOVEMENT OF THE NORTHERN
STREAM TROUGH. THE 12Z/10TH ECMWF WAS AN OUTLIER WITH SOME PHASING
OF THE TROUGH AND THE CUTOFF LEADING TO A WEAKER AND SLOWER NORTHERN
STREAM WAVE. THE 00Z/11TH ECMWF HAS JUST COME IN MORE ALONG THE
LINES OF THE OTHER MODELS WITH THE WAVE LIFTING TO THE NORTHWEST OF
THE AREA SUNDAY. LOOKING AT WATER VAPOR...IT APPEARS THAT THE
NORTHERN STREAM TROUGH WILL ZIP PAST THE CUTOFF TONIGHT OR SATURDAY
SUPPORTING GFS/NAM/SREF/GEM/GFS ENSEMBLE SOLUTIONS. DESPITE THIS
GENERAL AGREEMENT THERE ARE STILL TIMING DIFFERENCES WITH REGARD TO
HOW QUICKLY THE TROUGH ARRIVES SUNDAY MORNING BRINGING AN ASSOCIATED
COOL FRONTAL BOUNDARY ACROSS THE AREA WITH IT. THIS SYSTEM APPEARS
SIMILAR TO THE LOW FROM THIS PAST WEEKEND THAT TRACKED WELL NORTH OF
THE AREA. WILL CONTINUE WITH CHANCE POPS SUNDAY. EVEN GREATER
UNCERTAINTY EXISTS MONDAY THANKS TO CONTINUED DIFFERENCES IN THE
UPPER FLOW PATTERN. TROUGHING OF SOME DEGREE SHOULD BE IN PLACE BUT
DIFFERENCES IN THE AMPLITUDE AND PLACEMENT COMPLICATE THE PRECIP
FORECAST. WILL MAKE LITTLE CHANGE FOR NOW BUT THERE IS DECENT
SUPPORT FOR MUCH LOWER POPS...AT LEAST FOR NORTHWESTERN AREAS.
TUESDAY THROUGH THURSDAY...DESPITE THE DISCREPANCIES EARLY NEXT WEEK
THERE IS REASONABLE AGREEMENT THAT THE MAIN STORM TRACK WILL REMAIN
TO THE NORTH OF THE AREA FOR THE MIDDLE PART OF THE WEEK. THIS WILL
ALLOW COLDER AIR TO FILTER IN FROM THE NORTH WHILE KEEPING MOST IF
NOT ALL OF THE PRECIP TO THE NORTH WITH HIGH PRESSURE AT THE SURFACE
LOCALLY.
MDB
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 20Z...
* DURATION OF CURRENT 15 TO 20 KT SOUTHERLY WIND GUSTS.
* SOUTHERLY WIND GUSTS ON SATURDAY.
//DISCUSSION...UPDATED 18Z...
LOW PRESSURE LOCATED NORTH OF MN WILL CONTINUE TO MOVE EAST INTO
TONIGHT AND HAVE A WIDE INFLUENCE ACROSS THE GREAT LAKES
REGION...WITH WINDS INCREASING THIS AFTERNOON FROM THE SOUTH
ACROSS THE TAF SITES. SPORADIC GUSTS OVER 20 KTS SEEM PROBABLE FOR
IL TAF SITES BY MID TO LATE AFTERNOON. THESE GUSTS SHOULD DROP OFF
QUICKLY DURING THE EARLY EVENING. A VFR AND GENERALLY QUIET NIGHT
IS EXPECTED AT AIRPORTS...WITH FLOW ALOFT ONLY AROUND 30 TO 35 KTS
IN THE 1K TO 2K FT LAYER. THE PRESSURE GRADIENT WILL REMAIN TIGHT
INTO SATURDAY...WITH SOUTH SOUTHWEST WINDS AGAIN BECOMING GUSTY
DURING THE AFTERNOON. THESE SHOULD BE SLIGHTLY HIGHER THAN
TODAY...WITH A BETTER LIKELIHOOD OF SEEING AFTERNOON GUSTS IN
EXCESS OF 20 KTS.
//ORD AND MDW CONFIDENCE...UPDATED 20Z...
* HIGH CONFIDENCE THAT WIND GUSTS WILL REMAIN BELOW 25 KTS...AND
MEDIUM CONFIDENCE THAT GUSTS WILL SUBSIDE 00Z-01Z.
* MEDIUM CONFIDENCE IN SOUTHWEST GUSTS TO NEAR 25 KTS ON SATURDAY
AFTERNOON.
//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...
SATURDAY NIGHT...VFR. SLY WINDS INCREASING THROUGH THE NIGHT.
SUNDAY...CHANCE SHRA. CHANCE MVFR EARLY. WINDY. SWLY GUSTS TO
30KT IN THE AFTERNOON.
MONDAY...CHANCE SHRA AND MVFR CIGS.
TUESDAY...VFR. WX NIL.
WEDNESDAY...VFR. WX NIL.
THURSDAY...VFR. SLIGHT CHANCE SHRA LATE.
MTF
&&
.MARINE...
237 AM CST
AN ACTIVE PATTERN IS EXPECTED THROUGH THE WEEKEND INTO NEXT WEEK. A
RIDGE OF HIGH PRESSURE WILL MOVE ACROSS THE LAKE TODAY...ALLOWING A
BRIEF RESPITE FROM THE STRONGER WINDS...BUT THIS QUICK MOVING RIDGE
WILL BE CLOSELY TRAILED BY A RELATIVELY WEAK AREA OF LOW PRESSURE
TONIGHT WHICH WILL ALLOW WINDS TO PICK BACK UP TO AROUND 30 KT
ACROSS THE SOUTHERN PORTIONS OF THE LAKE...WHILE A BRIEF PERIOD OF
GALES ARE EXPECTED ACROSS THE NORTH. WILL UPGRADE THE GALE WATCH
TO A WARNING FOR LATE THIS AFTERNOON AND EVENING. ANOTHER WEAK
RIDGE WILL ALLOW WINDS TO DROP BACK BELOW GALES ON SATURDAY...
MEANWHILE ANOTHER STRONGER AREA OF LOW PRESSURE BEGINS TO DEEPEN
OVER THE CANADIAN PRAIRIES. WHILE THIS LOW IS EXPECTED TO STAY
NORTH OF THE GREAT LAKES...A COLD FRONT SWEEPING ACROSS THE LAKE
WILL USHER IN COLDER AIR AND DEEP MIXING. MODELS SUGGEST 50 TO 60
KT WINDS IN THE LOWEST FEW THOUSAND FEET JUST AHEAD OF THE FRONT.
SOME OF THIS MIXING DOWN TO THE LAKE SURFACE WILL RESULT IN GALE
FORCE WINDS. THESE WINDS WILL INCREASE FURTHER FOR A SHORT PERIOD
BEHIND THE FRONT AS LOW LEVEL LAPSE RATES STEEPEN. THERE IS A GOOD
INDICATION THAT SOME OF THESE WINDS COULD BE HIGHER END GALES
OF 45 KT. WINDS SHOULD DROP BACK BELOW GALE FORCE LATE SUNDAY
NIGHT...BUT BRISK WINDS ARE EXPECTED THROUGH MIDWEEK //ESPECIALLY
FARTHER NORTH// AS AN ACTIVE PATTERN PERSISTS. BMD
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
LMZ868 UNTIL MIDNIGHT SATURDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 3 AM SATURDAY.
&&
$$
