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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 201118
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
718 AM EDT MON MAY 20 2013


.AVIATION...

-- Changed Discussion --
//DISCUSSION...

DEEP RIDGING WILL MAINTAIN PREDOMINANTLY VFR CONDITIONS AND LIGHT
WINDS INTO AT LEAST EARLY THIS AFTERNOON. INCREASING LOW-LEVEL
MOISTURE WILL POSE A SLIGHT RISK OF MVFR FOG BETWEEN THROUGH
15Z...MAINLY AT THE METRO AIRPORTS. BY LATE THIS MORNING...DIURNAL
MIXING WILL CONTRIBUTE TO SE WINDS GUSTING TO 20 KTS ALONG WITH A
SCT CU FIELD DEVELOPING AROUND 4KFT AGL. CIGS WILL GRADUALLY EVOLVE
TOWARD A BROKEN COVERAGE IN THE 4-5KFT RANGE BY MID/LATE AFTERNOON
AS SHOWERS & TSTORMS APPROACH THE AREA. CONFIDENCE IN TSTORM IS IN
THE MEDIUM RANGE...AND HIGHLY DEPENDENT ON INSTABILITY AND A TRIGGER
MECHANISM DURING THE LATE AFTERNOON AND EARLY EVENING HOURS. EVEN IF
THUNDERSTORMS DEVELOP...CONFIDENCE IS STILL LOW WITH REGARD TO THE
POTENTIAL FOR TSRA TO IMPACT ANY ONE LOCATION. WITH THIS IN
MIND...FEEL THAT THE CONTINUATION OF A PROB30 FOR TSRA AT ALL
LOCATIONS BEST REPRESENTS CONFIDENCE LEVEL. SHOWERS AND EMBEDDED
THUNDERSTORMS ARE EXPECTED TO CONTINUE INTO THE OVERNIGHT
HOURS...HOWEVER THUNDER COVERAGE WILL BE EVEN LOWER THAN LATE THIS
AFTERNOON AND THIS EVENING.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN CEILINGS BELOW 5KFT AFTER 21Z.

* LOW CONFIDENCE THAT A THUNDERSTORM WILL IMPACT KDTW AIRSPACE AFTER
  21Z.
-- End Changed Discussion --

&&

.PREV DISCUSSION...
-- Changed Discussion --
ISSUED 351 AM EDT MON MAY 20 2013

SHORT TERM...TODAY AND TONIGHT

UPPER LEVEL RIDGE AXIS WILL BE IN PLACE ACROSS THE CENTRAL GREAT
LAKES THIS MORNING. HOWEVER A HEALTHY SURGE OF HIGHER THETA-E AIR IN
THE 925 TO 850 MB LEVEL AND SYSTEM RELATIVE ISENTROPIC LIFT AT 310K
WILL TRACK THROUGH MICHIGAN DURING THE EARLY MORNING HOURS WITH
SEVERAL LOCAL AND NWP MODELS GENERATING SHOWERS BETWEEN 09-15Z.
DESPITE THE LOW LEVEL LIFT...THE UPPER LEVEL RIDGING AND DRY AIR IN
PLACE ARE A CONCERN AS WELL AS THE THETA-E SURGE WEAKENING AS IT
MOVES THROUGH THE AREA. WITH THESE FACTORS IN MIND POPS IN THE LOW
CHANCY RANGE SEEM APPROPRIATE AS THE LOW LEVEL LIFT CANNOT BE
COMPLETELY DISCARDED. MUCAPE VALUES EARLY THIS MORNING WILL BE
AROUND 1000 J/KG...WARRANTING THE INCLUSION OF THUNDER WITH THE RAIN
SHOWERS. GIVEN THE ELEVATED NATURE OF THIS MORNINGS CONVECTION AND
WEAK WIND FIELD THROUGH THE SOUNDING...SEVERE WEATHER IS NOT
EXPECTED TO BE AN ISSUE WITH THE EARLY DEVELOPMENT IF IT
MATERIALIZES.

AFTER THIS INITIAL SURGE THERE WILL BE A QUIET PERIOD LATER THIS
MORNING AND INTO THE EARLY AFTERNOON HOURS WITH THE RIDGE AXIS STILL
OVER THE CENTRAL GREAT LAKES...ALLOWING HIGH TEMPERATURES TO GET
INTO THE MIDDLE TO UPPER 80S AWAY FROM THE GREAT LAKES AS 850 MB
TEMPERATURES RISE INTO THE MIDDLE TO UPPER TEENS.

LATER THIS AFTERNOON AND INTO THIS EVENING A PIECE OF SHORTWAVE
ENERGY TRACKS THROUGH THE CENTRAL GREAT LAKES WHILE THE
AFOREMENTIONED RIDGE SLIDES EAST TOWARDS THE EASTERN GREAT LAKES AND
THE 850 MB LOW LEVEL JET CRANKS TO AROUND 30 KNOTS WITH THE NOSE
POINTED TOWARDS SOUTHEAST MICHIGAN. MUCAPE VALUES DURING THIS PERIOD
HOVER AROUND 2000 J/KG WITH 0-6KM BULK SHEAR VALUES OF 20 TO 30
KNOTS. SLIGHT RISK FOR SEVERE WEATHER CONTINUES WITH THE SPC DAY ONE
OUTLOOK WITH THE MAIN CONVECTIVE MODE EXPECTED TO BE LINEAR
STRUCTURES WITH SUPERCELLS POSSIBLE GIVEN THE DIRECTIONAL TURNING IN
THE LOW LEVELS. DAMAGING WINDS AND LARGE HAIL ARE EXPECTED TO BE THE
MAIN THREAT...WITH SOME ISOLATED TORNADOES POSSIBLE IF CONVECTION
CAN FIRE EARLY ENOUGH AND TAKE ADVANTAGE OF THE BETTER INSTABILITY
AND LOW LEVEL SHEAR.

WITH ONGOING CONVECTION OVERNIGHT AND ABUNDANT CLOUD COVER IN THE
WARM SECTOR...OVERNIGHT LOWS ARE EXPECTED TO STAY IN THE 60S TONIGHT.

LONG TERM...TUESDAY THROUGH SUNDAY

ACTIVE WEATHER PATTERN OVER SE MI TUESDAY THROUGH WEDNESDAY NIGHT
WITH STRONG TO SEVERE STORMS POSSIBLE ON TUESDAY. SHOWERS WILL TAPER
OFF THURSDAY BEFORE A STRONG CANADIAN HIGH PRESSURE SYSTEM BUILDS
INTO THE REGION THROUGH THE HOLIDAY WEEKEND LEAVING US COOL AND DRY.
MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT OVERALL WITH THE LARGE
SCALE PATTERN AND THE STACKED LOW PRESSURE SYSTEMS OVER THE NORTHERN
PLAINS. THIS DOES NOT LEAD TO A HIGH CONFIDENCE FORECAST THOUGH AS
PERIODS OF SHOWERS AND THUNDERSTORMS WILL BE FORCED BY SMALL SCALE
SHORTWAVES ROTATING AROUND THE PARENT UPPER LOW WHICH ARE DIFFICULT
TO TIME THIS FAR OUT.

TUESDAY...LOOKS LIKE MULTIPLE ROUNDS OF STORMS WILL PASS THROUGH SE
MI THIS DAY. FIRST WE MAY HAVE TO DEAL WITH A CONVECTIVE COMPLEX
LINGERING INTO THE MORNING HOURS FROM THE OVERNIGHT. MAY TRY TO
CLEAR OUT DURING THE EARLY AFTERNOON BEFORE A SHORTWAVE ROUNDING THE
BASE OF THE UPPER LEVEL TROUGH REACHES THE AREA. MEANWHILE A SFC LOW
PRESSURE CENTER LOOKS TO TRACK THROUGH NORTHERN MI. THE
AFTERNOON TIMING WILL BE FAVORABLE FOR STORMS TO DEVELOP WITH A
STRONG DIURNAL COMPONENT INCREASING LOW LEVEL LAPSE RATES. OTHER
FAVORABLE PARAMETERS ARE MUCAPE VALUES PEAKING AROUND 1500 J/KG...30
TO 40 KNOTS OF EFFECTIVE SHEAR...STRONG LOW/HIGH LEVEL LAPSE
RATES...SHOWALTER INDEX AROUND -1...AND UPPER LEVEL SUPPORT AS WELL
WITH THE JET INCHING CLOSER TO MID MI AND WEAKENING UPPER LEVEL
DIFFLUENCE. HIGH PWATS REACHING 1.6 INCHES WILL SUPPORT HEAVY
RAINFALL AS WELL. SPC HAS INCLUDED SE MI IN THE SLIGHT RISK AREA
WHICH SEEMS MORE THAN WARRANTED AT THIS TIME.

MODELS HAVE BEEN ADVERTISING ANOTHER LULL TUESDAY NIGHT FOR A COUPLE
RUNS NOW...INCLUDING THE MOST RECENT 00Z ECMWF...SO FEEL COMFORTABLE
WITH THE INHERITED CHANCE POPS.

BY WEDNESDAY...THE ENTIRE PATTERN BECOMES MUCH MORE PROGRESSIVE AS
OUR ONCE CUT OFF UPPER LOW BEGINS PHASING WITH NORTHERN STREAM
TROUGHING OVER ONTARIO. BY NOW THE SFC LOW HAS BEEN VERY SHEARED OUT
WITH SEVERAL NEW CENTERS TRYING TO FOR ALONG THE MAIN BAROCLINIC
ZONE. THE STRONGEST OF WHICH LOOKS TO FORM OVER THE CENTRAL
MISSISSIPPI VALLEY. SHOWERS AND THUNDERSTORMS WILL BE LIKELY ONCE
AGAIN AS THIS LOW LIFTS NE INTO THE REGION. ISENTROPIC ASCENT WILL
INCREASE OVER THE STATE DUE TO THE LOW RUNNING INTO WARM FRONT THAT
HAS BEEN DRAPED OVER NORTHERN MI THROUGH THE WEEK. THE TRIPLE POINT
WILL PASS NORTHEASTWARD SOMEWHERE CLOSE TO THE MI/OH BORDER IN THE
EVENING.

AFTER DEALING WITH SOME LINGERING SHOWERS ON THE BACKSIDE OF THE
SYSTEM...HIGH PRESSURE WILL DROP IN FROM CANADA PUTTING AN END TO
THE WET STRETCH OF WEATHER. IT WILL ALSO USHER COOLER TEMPS...IN THE
60S...BACK INTO THE GREAT LAKES. TROUGHING OVER BOTH COASTS WILL
HELP AMPLIFY THE RIDGE OVER THE CENTRAL CONUS THROUGH THE WEEKEND.

MARINE...

A LOW PRESSURE SYSTEM OVER THE NORTHERN 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 SCATTERED THUNDERSTORMS TODAY THROUGH
THURSDAY. WINDS WILL SHIFT TO THE NORTH ACROSS ALL WATERS BY
THURSDAY MORNING...AS THE LOW AND TRAILING COLD FRONT PUSH OFF TO
THE EAST.
-- End Changed Discussion --

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....KURIMSKI
SHORT TERM...KURIMSKI
LONG TERM....DRK
MARINE.......KURIMSKI


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