325 AM CDT
MODEL SOLUTIONS SHOW THAT THE SEASONALLY TYPICAL ACTIVE AMPLIFIED
UPPER PATTERN CURRENTLY OVER THE NORTHERN HEMISPHERE WILL PERSIST
THROUGH NEXT WEEK THOUGH BY LATER NEXT WEEK THE PATTERN ACROSS
CENTRAL NORTH AMERICA BECOMES MORE ZONAL. BEFORE THEN A COUPLE
OF DISTURBANCES WILL BRING CHANCES OF PRECIPITATION TO THE
AREA...AND IN THEIR WAKE PULL VERY COOL AIR CURRENTLY OVER NORTH
CENTRAL CANADA SOUTHWARD ACROSS THE UPPER MIDWEST AND THE GREAT
LAKES.
THE NEXT CHANCE FOR RAIN WILL COME OVERNIGHT TONIGHT THROUGH
SUNDAY MORNING AS THE SHORT WAVE OVER SOUTHERN B.C. AND NORTHERN
WA EARLY THIS MORNING CONTINUES ON A EAST- SOUTHEAST TRACK ACROSS
THE NORTHERN PLAINS AND REACHING THE UPPER MS VALLEY BY 12Z
SUNDAY. COMPARED TO THEIR PREVIOUS RUNS THE MODELS ARE ALMOST ALL
IN AGREEMENT IN DECREASING THE QPF AMOUNTS ACROSS THE AREA AS
LOWER LEVELS WILL REMAIN RATHER DRY WITH A SURFACE RIDGE PROGGED
TO REMAIN STRETCHED FROM THE NORTHERN ROCKIES SOUTHEASTWARD ACROSS
THE CENTRAL PLAINS. DESPITE DRY LOW LEVELS RADAR ECHOES ARE
SPREADING ACROSS MT IN THE MID LEVEL WARM ADVECTION AHEAD OF THE
SHORT WAVE TROUGH. METARS FROM UNDER THE ECHOES REPORTING MAINLY
MID LEVEL CLOUDS AND SOME LIGHT RAIN REACHING THE GROUND. EXPECT
A SIMILAR SCENARIO OVER THE LOCAL AREA LATE TONIGHT AND SUNDAY
MORNING.
AFTER DRY CONDITIONS FROM LATER SUNDAY INTO LATER MONDAY THE
THREAT OF RAIN RETURNS FOR MONDAY NIGHT INTO TUESDAY. THE STRONG
SHORT WAVE CURRENTLY OVER THE GULF OF AK PROGGED TO MOVE ACROSS
THE NORTHERN ROCKIES SUNDAY NIGHT IS SHOWN TO DIG DEEPER
SOUTHEASTWARD ACROSS THE PLAINS BY ALL THE MODELS. WITH THE SHORT
WAVE NOW EXPECTED TO BE FURTHER SOUTH THE THREAT OF RAIN ALSO
SHIFTS SOUTH MORE TO CENTRAL AND SOUTHERN IL...THOUGH HAVE KEPT
SLIGHT CHANCE POPS ALL THE WAY TO THE WI BORDER GIVEN THE
STRENGTH OF THE SYSTEM. THE UPPER TROUGH IS PROGGED TO SHARPEN
OVER THE MID AND LOWER MS VALLEY DURING LATE MONDAY NIGHT AND
TUESDAY AS ITS AXIS SLOWLY SHIFTS TO THE EAST.
THE PASSAGE OF THE UPPER TROUGH WILL BRING AN END TO THE RAIN
CHANCES FROM THE SYNOPTIC SYSTEM LATER TUESDAY AND TUESDAY NIGHT.
HOWEVER...A STRENGTHENING NORTH TO NORTH-NORTHEAST LOW AND MID
LEVEL FLOW DEVELOPS DURING TUESDAY AND INTO WEDNESDAY ADVECTING
VERY COOL AIR SOUTHWARD ACROSS THE REGION. TEMPERATURES ARE
FORECAST TO FALL TO AS COLD AS -10C AT 2.5KM AGL BY TUESDAY
EVENING AND WITH LAKE MI WATER TEMPERATURES RANGING FROM 13C
NORTH TO 17C SOUTH A DEEP UNSTABLE SETUP CONDUCIVE FOR LAKE
EFFECT RAIN SHOWERS WILL BE IN PLACE. WITH AN EASTERLY COMPONENT
TO THE FLOW THROUGH THE CLOUD BEARING LAYER TUESDAY NIGHT INTO
EARLY WEDNESDAY MORNING THE WESTERN SHORES OF SOUTHERN LAKE MI
ARE TARGETED FOR THE LAKE EFFECT RAIN...AS WELL AS FAR NORTHWEST
IN. THE FLOW BACKS TO NORTHERLY WEDNESDAY NIGHT WHICH IS EXPECTED
TO SHIFT THE LAKE EFFECT SHOWERS FURTHER EAST AND CONFINE THEM TO
JUST NORTHWEST IN. CONTINUED BACKING DURING THURSDAY ALONG WITH
WARMING MID LEVELS WILL RESULT IN THE SHOWERS DIMINISHING AS WELL
AS SHIFTING FURTHER EAST AND OUT OF THE LOCAL FORECAST AREA.
TEMPERATURES WILL BE AROUND CLIMATOLOGICAL NORMALS FOR MID
OCTOBER THE NEXT COUPLE DAYS BEFORE COOLER AIR ARRIVES DURING
TUESDAY WITH HIGHS MIDWEEK ONLY IN THE LOWER 50S NORTH AND LOWER
TO MID 50S SOUTH. OVERNIGHT LOWS OUTSIDE OF THE CHICAGO URBAN
HEAT ISLAND EXPECTED TO DIP TO MID 30S TO LOWER 40S. WITH THE
UPPER FLOW BECOMING MORE ZONAL LATE IN THE WEEK AS MENTIONED
ABOVE TEMPERATURES ARE EXPECTED TO START MODERATING.
TRS
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* GUSTY WEST WINDS THIS AFTERNOON.
* WIND DIRECTION EARLY SUNDAY MORNING.
RATZER
//DISCUSSION...UPDATED 18Z...
STRONG DEEPENING LOW PRESSURE CONTINUES TO LIFT SLOWLY AWAY FROM
THE AREA ACROSS EASTERN CANADA EARLY THIS AFTERNOON...THOUGH GUSTY
WEST WINDS CONTINUE ACROSS THE FORECAST AREA IN THE WAKE OF THIS
DEPARTING SYSTEM. SURFACE OBSERVATION TRENDS RELATE VERY WELL TO
MODEL FORECAST SOUNDING WIND PROFILES...WITH SUSTAINED WINDS
APPROACHING 20 KT AND GUSTS NEAR 30 KT EXPECTED TO CONTINUE THIS
AFTERNOON. COMBINATION OF LOSS OF DIURNAL MIXING AND A WEAKENING
OF THE SURFACE PRESSURE GRADIENT TOWARD EVENING SHOULD ALLOW WINDS
TO DIMINISH QUICKLY AND BACK WEST-SOUTHWEST AFTER SUNSET.
ATTENTION THEN TURNS TO A QUICK MOVING MID-LEVEL DISTURBANCE
APPROACHING FROM THE NORTHERN PLAINS LATER TONIGHT AND SUNDAY
MORNING. ASCENT PRODUCED BY THIS FEATURE IS PROGGED TO SPREAD MID-
LEVEL CLOUDS ACROSS THE REGION...WITH DRY LOW LEVEL AIR CURRENTLY
ACROSS THE AREA WORKING AGAINST DEVELOPMENT OF WIDESPREAD
PRECIPITATION AND LOWER CLOUD COVER. GUIDANCE IN GENERAL AGREEMENT
IN BAND OF LIGHT RAIN DEVELOPING FROM SOUTHERN MN TO SOUTHERN WI
OVERNIGHT AND PERHAPS JUST CLIPPING NORTHERN IL TERMINALS WITH A
LITTLE VFR LIGHT RAIN FROM A MID-DECK INTO SUNDAY MORNING. WHILE
THIS SCENARIO SEEMS FAIRLY LIKELY...CONFIDENCE ON COVERAGE AND
EXACT TIMING FOR OUR POINT FORECAST TERMINAL LOCATIONS IS MEDIUM
AT BEST. ANY LIGHT PRECIP SHOULD EXIT TO THE EAST-SOUTHEAST BY
SUNDAY AFTERNOON HOWEVER...WITH PASSAGE OF MID-LEVEL WAVE AND
SURFACE TROUGH/WEAK COLD FRONT.
SURFACE TROUGH WITH THIS SYSTEM IS EXPECTED TO BACK THE WINDS TO
THE SOUTHWEST OVERNIGHT...BEFORE VEERING BACK TO THE WEST-
NORTHWEST BY MID-LATE SUNDAY MORNING. SOME QUESTION AS TO DETAILS
OF WIND DIRECTION NEAR THE TROUGH AXIS EARLY SUNDAY...AS VARIOUS
GUIDANCE DEPICT EITHER AN OPEN TROUGH WITH A SIMPLE WIND SHIFT
FROM SOUTHWEST TO WEST-NORTHWEST...WHILE OTHERS INDICATE A
SLIGHTLY MORE ORGANIZED CYCLONIC CIRCULATION. HAVE INDICATED A
BRIEF PERIOD OF VARIABLE DIRECTION WITH TROUGH PASSAGE BASED ON
THIS...WITH WINDS IN EITHER CASE LESS THAN 10 KT EARLY SUNDAY
BEFORE TROUGH PASSES.
RATZER
//ORD AND MDW CONFIDENCE...UPDATED 18Z...
* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH THIS EVENING.
* MEDIUM-LOW CONFIDENCE IN PRECIP EXTENT/TIMING SUNDAY MORNING.
RATZER
//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...
SUNDAY THROUGH TUESDAY...VFR WITH PERIODIC RAIN CHANCES...SOME
MVFR POSSIBLE.
WEDNESDAY AND THURSDAY...VFR.
JEE
&&
.MARINE...
301 PM CDT
DEEP LOW PRESSURE WILL CONTINUE TO DRIFT VERY SLOWLY NEAR JAMES BAY
ONTARIO THROUGH MONDAY...WHILE SLOWLY FILLING AND WEAKENING. THIS
WILL MAINTAIN A STRONG WESTERLY GRADIENT ACROSS LAKE MICHIGAN...
THOUGH GRADUAL WEAKENING WILL OCCUR TONIGHT AS THE LOW STOPS
DEEPENING. UNFORTUNATELY...IT APPEARS THAT WINDS WILL RAMP UP AGAIN
TO GALE FORCE ON THE NORTHERN HALF OF THE LAKE SUNDAY AFTERNOON AS A
REINFORCING PUSH OF COOLER AIR WRAPS AROUND THE NEARLY STATIONARY
LOW. GALES WILL LIKELY PERSIST ON NORTHERN LAKE MICHIGAN INTO MONDAY
MORNING...BEFORE THE OLD LOW FINALLY BEGINS TO FILL MORE RAPIDLY AND
LIFTS OUT ACROSS QUEBEC. STRONG HIGH PRESSURE WILL BUILD SOUTHEAST
FROM THE CANADIAN PRAIRIES AND NORTHERN PLAINS MID-WEEK...WHICH WILL
MAINTAIN MODEST NORTHERLY WINDS ACROSS LAKE MICHIGAN THROUGH THE
LATER PARTS OF THE FORECAST 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-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 1 AM SUNDAY.
GALE WARNING...NEARSHORE WATERS UNTIL 7
PM SATURDAY.
&&
$$
