AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
355 AM EDT SUN MAY 19 2013
.SHORT TERM...TODAY AND TONIGHT
SE MI STILL REMAINS UNDER THE INFLUENCE OF THE HIGH PRESSURE SYSTEM
OVER EASTERN CANADA WHILE A COLD FRONT DROPS INTO THE NORTHERN GREAT
LAKES AND A STATIONARY FRONT ACROSS THE OHIO VALLEY BEGINS MAKING A
MOVE NORTH. THE SOUTHERN BOUNDARY WILL BEGIN FEELING THE INFLUENCE
OF THE LARGE LOW PRESSURE SYSTEM OVER THE PLAINS AND LIFT NORTHWARD
THROUGH THE DAY. WAA IN THE 600 TO 700 MB LAYER WILL PROVIDE A NICE
CAP TODAY HELPING TO PREVENT ANY CONVECTION FROM INITIATING. THE
LINGERING DRY BOUNDARY LAYER WILL HELP AS WELL BUT AS WINDS SHIFT TO
MORE SOUTHERLY TODAY MOISTURE WILL BE INCREASING STEADILY THROUGH
THE DAY. MID LEVEL RIDGE AXIS WILL PASS OVER MI IN THE EVENING
AMPLIFYING IN RESPONSE TO THE DEEPENING TROUGH OVER THE PLAINS.
PRECIP CHANCES WILL EXIST VERY LATE TONIGHT FOR WESTERN LOWER MI AS
THE FRONT LIFTS NORTH...THE NOSE OF THE LLJ APPROACHES...WE ENTER
THE DIFFLUENT REGION OF THE MID LEVEL FLOW AND A SPOKE OF VORTICITY
LOOKS TO ROTATE AROUND THE LOW UP AND THROUGH THE AREA. SOME OF
THESE SHOWERS/THUNDERSTORMS MAY FIND THEIR WAY INTO OUR FAR WESTERN
COUNTIES THUS ONLY MODIFIED AN INHERITED AREA OF SLIGHT CHANCE POPS
HERE. THE DRY AIR OVER SE MI WILL MAKE IT HARD FOR THEM TO MAKE IT
TOO FAR EAST SO MOST LOCATIONS WILL LIKELY REMAIN DRY NOW THROUGH
SUNDAY NIGHT.
&&
.LONG TERM...MONDAY THROUGH SATURDAY
A CLOSED OFF MID LEVEL LOW PRESSURE SYSTEM WILL CONTINUE SPINNING
OVER THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY EARLY IN THE
WORKWEEK. THIS SYSTEM IS FORECAST TO LUMBER SLOWLY EAST AS THE WEEK
PROGRESSES...TRACKING OVER THE WESTERN GREAT LAKES BY WEDNESDAY AND
EVENTUALLY GETTING ABSORBED BY A LARGER NORTHERN WAVE OVER CANADA.
WHEN THIS OCCURS THE CLOSED LOW BECOMES A TROUGH THAT EVENTUALLY
TRACKS THROUGH THE CENTRAL GREAT LAKES REGION ON THURSDAY. MODEL
SOLUTIONS ARE AGAIN VASTLY DIFFERENT IN HANDLING THIS SYSTEM WITH
THE GFS MAINTAINING A SPLIT FLOW AND SLOWER MOVING LOW THROUGH
FRIDAY WHILE THE ECMWF ABSORBS THE LOW QUICKER BUT BRINGS A SHOT OF
NORTHERN STREAM PV ANOMALY THROUGH THE NORTHERN GREAT LAKES THURSDAY
AND FRIDAY. THIS POSES QUITE AN ISSUE REGARDING POPS AS THE TIMING
OF THESE FEATURES WILL BRING PERIODS OF HEAVY RAIN AS WELL AS QUIET
PERIODS DEPENDING ON THE MODEL SOLUTION. GIVEN THE MODEL UNCERTAINTY
WILL NOT VENTURE FAR FROM THE PREVIOUS FORECAST POPS FOR MUCH OF THE
WORK WEEK.
THE MAIN CHANGES TO THE FORECAST WILL BE TO TEMPERATURES. WITH A
LATER ARRIVAL OF SHORTWAVE ENERGY ON MONDAY SUNSHINE SHOULD BE ABLE
TO CREATE A DEEP MIXED LAYER WHICH TAKES ADVANTAGE OF 850 MB
TEMPERATURES IN THE MID TO UPPER TEENS TO BRING DAYTIME HIGHS WELL
INTO THE 80S AWAY FROM THE GREAT LAKES. ALTHOUGH THE MODELS SHOW THE
SURFACE WARM FRONT SINKING SOUTH MONDAY NIGHT WITH SHOWERS AND
THUNDERSTORMS...IT IS PROGGED TO MOVE BACK NORTH ON TUESDAY. THE
PUSH NORTH OF THE WARM FRONT SHOULD BRING ANOTHER DAY WITH HIGHS
REACHING OR EXCEEDING 80 DEGREES AS 850 MB TEMPERATURES REMAIN IN
THE MIDDLE TEENS. THE MAIN FACTOR KEEPING TEMPERATURES DOWN WILL BE
MORE CLOUD COVER AND ONGOING SHOWERS AND THUNDERSTORMS...HOWEVER THE
EXTREME SOUTHERN CWA HAS THE BEST SHOT AT HITTING THE MIDDLE 80S
WITH A BRIEF BREAK IN THE PRECIPITATION AND SOME FILTERED SUNSHINE.
THE SURFACE LOW TRACKS ALONG THE WARM FRONT LAID ACROSS CENTRAL
LOWER MICHIGAN ON WEDNESDAY. TEMPERATURES SHOULD BE ABLE TO GET INTO
THE 70S ONE LAST DAY BEFORE THE COLDEST AIR FILTERS IN BEHIND THE
DEPARTING LOW BY THE LATE PART OF THE WEEK. HIGH TEMPERATURES BEHIND
THE LOW ARE ONLY EXPECTED TO GET INTO THE 60S FOR THE LATE PART OF
THE WEEK AND INTO THE WEEKEND.
THIS COMPLEX SYSTEM WILL BRING SEVERAL ROUNDS OF SHOWERS AND
THUNDERSTORMS TO THE AREA DURING THE MONDAY THROUGH THURSDAY TIME
FRAME. MUCAPE VALUES WILL BUILD UP TO AROUND 2000 J/KG MONDAY AND
TUESDAY...INCREASING THE CHANCE FOR SEVERE WEATHER ACROSS SOUTHEAST
MICHIGAN. WITH SOUTHEAST SURFACE WINDS AND SOUTHWESTERLY WINDS ALOFT
THERE WILL BE QUITE A BIT OF DIRECTIONAL SHEAR IN THE LOWEST LEVELS
DURING THIS TIME...HOWEVER SPEED SHEAR IS NOT ALL THAT IMPRESSIVE ON
MONDAY AS SPEEDS IN THE COLUMN STRUGGLE TO REACH 20 KNOTS. TUESDAY
IS A DIFFERENT STORY WITH BETTER SPEED SHEAR IN ADDITION TO THE
DIRECTIONAL SHEAR AND MORE IMPRESSIVE HODOGRAPHS WITH HELICITY
VALUES EXCEEDING 300 AND EHI VALUES OF 2 TO 3. THE KEY FACTOR TO THE
SEVERE WEATHER POTENTIAL ON TUESDAY WILL BE IF A BREAK IN THE
ACTIVITY OCCURS AND BREAKS IN THE CLOUDS ALLOW FOR DESTABILIZATION
DURING THE AFTERNOON HOURS. THIS WOULD INCREASE THE THREAT FOR
SEVERE WEATHER...WHILE ONGOING ACTIVITY THROUGHOUT THE DAY WOULD
INHIBIT THE THREAT. IN ADDITION TO THE SEVERE WEATHER THREAT...HEAVY
RAIN WILL ALSO BE A THREAT AS PWAT VALUES REACH 1.80 TO 1.90 INCHES.
WITH A WEAKENING SYSTEM THE THREAT FOR ORGANIZED SEVERE WEATHER
WANES ON WEDNESDAY...HOWEVER MUCAPE VALUES LINGERING IN THE 1500
J/KG RANGE WILL CONTINUE THE THREAT FOR THUNDERSTORMS INTO WEDNESDAY
AS THE LOW TRACKS ALONG THE FRONTAL BOUNDARY. BY THURSDAY MUCAPE
VALUES SHRINK TO A FEW HUNDRED J/KG...WITH THE THREAT FOR AN
ISOLATED THUNDERSTORM EMBEDDED IN THE MAIN AREA OF SHOWERS BEING THE
MAIN THREAT ACROSS THE SOUTHERN CWA. HIGH PRESSURE EVENTUALLY ENDS
THE THREAT FOR PRECIPITATION FRIDAY AND SATURDAY AS A
COOL...DRY...STABLE AIRMASS SETTLES OVER THE CENTRAL GREAT LAKES
REGION.
&&
.MARINE...
WEAK SOUTHEASTERLY FLOW OVER THE LAKES WILL PROVIDE FAVORABLE MARINE
CONDITIONS THROUGH TONIGHT. A LOW PRESSURE SYSTEM OVER THE CENTRAL
PLAINS WILL DRIFT TOWARD THE GREAT LAKES LAYING OUT A WARM FRONT
ACROSS CENTRAL MI. THIS FRONT WILL STALL OVER THE AREA THROUGH
MIDWEEK AS THE LOW TRACKS ALONG IT. WINDS SOUTH OF THE FRONT WILL
REMAIN SOUTHERLY WHILE WINDS TO THE NORTH WILL BACK TO THE EAST AND
INCREASE SLIGHTLY. THIS WILL LEAD TO HIGHER WAVES OVER NORTHERN LAKE
HURON WHILE THE SOUTHERN BASIN...LAKE ST CLAIR AND LAKE ERIE KEEP
WAVES GENERALLY UNDER 2 FEET. THIS LOW WILL BRING A CHANCE OF
THUNDERSTORMS MONDAY THROUGH THURSDAY. A MID-WEEK WIND SHIFT TO
NORTHERLY CAN THEN BE EXPECTED AS A COLD FRONT PUSHES ACROSS AREA
WATERS.
&&
.AVIATION...ISSUED 1149 PM EDT SAT MAY 18 2013
//DISCUSSION...
A REGION OF VERY DRY LOW LEVEL AIR CIRCULATING AROUND THE HIGH
PRESSURE SYSTEM TO THE EAST OF THE REGION HAS HELD SURFACE DEWPOINTS
IN THE 40S ACROSS MUCH OF THE AREA THIS EVENING. THE LOW LEVEL FLOW
WILL TURN MORE TOWARD THE SOUTHEAST DURING THE COURSE OF THE MORNING
WHICH WILL ADVECT THE MID TO UPPER 50S DEWPOINTS NOW OVER NORTH
CENTRAL OHIO INTO SE MI. IT NOW APPEARS THAT THE BULK OF THE SURFACE
MOISTURE ADVECTION WILL OCCUR AFTER DAYBREAK. THIS SUPPORTS THE
REMOVAL OF ANY MENTION OF HAZE IN THE TAFS. OTHERWISE...AN UPPER
LEVEL RIDGE WILL MAINTAIN BENIGN AVIATION WEATHER CONDITIONS THROUGH
THE AFTERNOON.
//DTW THRESHOLD THREATS...
* NONE
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
SHORT TERM...DRK
LONG TERM....KURIMSKI
MARINE.......DRK
AVIATION.....SC
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