000
FXUS63 KDTX 150354
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1154 PM EDT TUE MAY 14 2013


.AVIATION...

//DISCUSSION...

A COLD FRONT WILL MOVE ACROSS SE MI BETWEEN 09Z AND 12Z THIS
MORNING. AMPLE INSTABILITY ALOFT WILL TRAVERSE SRN MI EARLY THIS
MORNING...LEADING TO SOME SCATTERED THUNDERSTORMS ALONG/IN ADVANCE
OF THE COLD FRONT. DRY AND STABLE AIR IN THE LOW LEVELS HOWEVER WILL
BE A MAJOR LIMITING FACTOR FOR WIDESPREAD THUNDERSTORM DEVELOPMENT.

FOR DTW...THE MOST PROBABLE TIME PERIOD FOR THUNDERSTORMS WILL BE
CENTERED AROUND 10 TO 12Z THIS MORNING. THE PASSAGE OF THE COLD
FRONT THIS MORNING WILL ALLOW WINDS TO TURN WESTERLY /AROUND 280
DEG/ BY 15Z...WITH GUSTS EXPECTED TO EXCEED 25 KNOTS THROUGH THE
AFTERNOON.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE ON THUNDERSTORM POTENTIAL BETWEEN 09Z AND 12Z THIS
MORNING.

* MEDIUM CONFIDENCE WESTERLY WIND GUSTS WILL EXCEED CROSS WIND
THRESHOLDS WEDNESDAY AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 740 PM EDT TUE MAY 14 2013

UPDATE...

THERE HAS THUS FAR BEEN NO SURFACE REPORTS OF RAIN ASSOCIATED WITH
THE RETURNS ACROSS THE WEST SIDE OF THE STATE GIVEN THE ABUNDANCE
OF LOW LEVEL DRY AIR. THESE RETURNS ARE ASSOCIATED WITH THE
LEADING EDGE OF A MID LEVEL THETA E PLUME. WHILE THE MID LEVEL MOISTURE
WILL ADVANCE ACROSS SE MI LATE THIS EVENING...EXPECT MAINLY JUST
SOME SPRINKLES AND/OR LIGHT RAIN SHOWERS. THE REGION OF DEEPER
CONVECTION WHICH HAS DEVELOPED ALONG A PREFERENTIAL SFC TROUGH
ACROSS IA AND SW WI IS LOCATED WITHIN A DEEP ELEVATED MIXED LAYER
/EML/. THIS EML WILL OVERSPREAD SE MI OVERNIGHT... LEADING TO
QUITE HIGH ELEVATED INSTABILITY /SHOWALTER INDICES OF -4 TO -7 C/.
MID LEVEL WESTERLY FLOW WILL INCREASE OVERNIGHT WHICH WILL ADVECT
THE MID LEVEL MOISTURE INTO SE MI. THIS COUPLED WITH THE ELEVATED
INSTABILITY /ENHANCED BY NOCTURNAL CLOUD TOP COOLING/ WILL REMAIN
SUPPORTIVE OF SOME SCATTERED THUNDERSTORMS LATE TONIGHT. IT NOW
APPEARS THE HIGHEST MID LEVEL MOISTURE WILL BE ACROSS THE SOUTHERN
SECTIONS OF THE FORECAST AREA...WHICH SUPPORTS AN UPDATE TO CARRY A
GENERAL SCATTERED POP ACROSS THE ENTIRE FORECAST AREA OVERNIGHT.
SOME OF THE THUNDERSTORMS WILL BE CAPABLE OF PRODUCING HAIL.

WHILE THE MAIN SYNOPTIC WARM FRONT EXTENDS FROM CHICAGO TO SRN
OHIO...A SECONDARY FRONTAL BOUNDARY HAS BECOME STATIONARY FROM
ALMA DOWN TO MONROE. E-SE FLOW TO THE EAST OF THIS BOUNDARY IS
BRINGING THE MARINE MODIFIED AIRMASS FARTHER INLAND. EXPECT ENOUGH
COOLING LATE THIS EVENING AND EARLY OVERNIGHT TO DROP TEMPS INTO
THE 40S AND 50S EAST OF THE BOUNDARY. THE MAIN WARM FRONT WILL
THEN LIFT INTO THE AREA BETWEEN 06Z AND 09Z...LEADING TO A
DRAMATIC RISE IN TEMPS. THE GRIDS HAVE BEEN UPDATED TO REFLECT
THESE CHANGES.

PREV DISCUSSION...ISSUED 357 PM EDT TUE MAY 14 2013

SHORT TERM...THROUGH TONIGHT

SURFACE WARM FRONT HAS PROGRESSED INTO LOWER MICHIGAN THIS
AFTERNOON...WITH SURFACE OBSERVATIONS SUGGESTING ITS PLACEMENT NOW
ALONG A LINE FROM WESTERN WAYNE COUNTY TO LANSING. BEHIND THE
FRONT...SOUTHWEST WINDS HAVE ALLOWED TEMPERATURES TO WARM WELL INTO
THE 70S. AREAS NORTH OF THE FRONT REMAIN IN THE 50S/60S OR EVEN 40S
CLOSE TO THE SHORELINE...IN PART DUE TO SOUTHEAST WINDS OFF THE
LAKES.

ELEVATED 925-850MB FRONT SHOULD STILL BE LYING OVER THE SAGINAW
VALLEY AND THUMB PER 12Z MODEL DATA...AND THIS IS SUPPORTED BY THE
GREATER ABUNDANCE OF MID-LEVEL CLOUDS SHOWN ON SATELLITE
OBSERVATIONS OVER THIS AREA. THE ELEVATED AND SURFACE FRONTS SHOULD
START TO LIFT MORE QUICKLY NORTHWARD TONIGHT AS THE UPPER WAVE OVER
SOUTHERN MANITOBA TRACKS INTO ONTARIO. SURFACE REFLECTION/TROUGH NOW
STRETCHES DOWN THROUGH MINNESOTA...BUT THE SOUTHERN EXTENT AND
ASSOCIATED COLD FRONT SHOULD PUSH INTO SOUTHEAST MICHIGAN VERY LATE
TONIGHT AND WEDNESDAY MORNING. MAIN QUESTION WILL BE PRECIPITATION
TIMING AND POTENTIAL TONIGHT AS THE WARM FRONT CONTINUES TO LIFT
NORTH TONIGHT AND AS THE COLD FRONT APPROACHES EARLY WEDNESDAY.

BEST POTENTIAL FOR PRECIPITATION LOOKS TO HOLD OFF UNTIL LATE
TONIGHT. HEALTHY 40-50 KNOT LOW LEVEL JET WILL SLIDE INTO MICHIGAN
OVERNIGHT AHEAD OF THE APPROACHING SYSTEM. NAM/GFS BOTH INDICATE
STRONG THETA-E ADVECTION OCCURRING OVERNIGHT WITH THE ARRIVAL OF THE
LLJ...PROMOTING STRONG ELEVATED INSTABILITY ABOVE ABOUT 850MB. 850
MB TEMPS LOOK TO RISE TO AN IMPRESSIVE 18-20C BY 12Z. MOISTURE
HOWEVER LOOKS FAIRLY ELEVATED...MOSTLY ABOVE 700MB ALONG AND SOUTH
OF THE I-69 CORRIDOR...AND THINK THIS WILL WORK TO LIMIT COVERAGE OF
SHOWERS AND THUNDERSTORMS. HAVE RETAINED HIGHER POPS ACROSS THE
SAGINAW VALLEY AND THUMB WHERE SLIGHTLY DEEPER MOISTURE WILL RESIDE
AND CLOSER TO FORCING FROM THE UPPER WAVE. THUNDERSTORMS WILL
CERTAINLY BE POSSIBLE...WITH GFS/NAM FORECAST SOUNDINGS SHOWING
STEEP LAPSE RATES (7-9 C/KM) WITHIN THE ELEVATED MIXED LAYER.

MIN TEMPS WILL LIKELY BE REACHED EARLIER IN THE NIGHT BEFORE THEY
LEVEL OFF OR START TO RISE LATE AS WARMER AIR ARRIVES. COLD FRONT
ACTUALLY HAS LITTLE THERMAL SUPPORT AS IT WORKS THROUGH EARLY WED
MORNING...AND WILL IN ACTUALITY BE MORE OF A WIND SHIFT. MINS LOOK
TO FALL INTO THE LOW 50S OVER THE THUMB AND INTO THE LOW 60S ACROSS
THE SOUTHERN AND WESTERN PORTION OF THE FORECAST AREA.

LONG TERM... WEDNESDAY THROUGH NEXT TUESDAY

STRONG SUBSIDENCE IS EVIDENT IN WATER VAPOR SATELLITE IMAGERY TODAY
IN THE WAKE OF THE LOW PRESSURE SYSTEM MOVING INTO NORTHERN ONTARIO.
THIS ADDS CONFIDENCE ON THE PACE OF PROGRESSION THROUGH SE MICHIGAN
ON BOTH THE PREFRONTAL LOW LEVEL MOISTURE AXIS AND THE COLD FRONT
ITSELF AS INDICATED IN THE LATEST MODEL DATA. THE MOISTURE AXIS WILL
SUPPORT POCKETS OF SHOWERS, AND EVEN A FEW THUNDERSTORMS, DURING
WEDNESDAY MORNING TO THE SOUTH OF INTERSTATE 69, MAINLY FROM
ACTIVITY LEFT OVER FROM EARLIER LOW LEVEL JET/WARM ADVECTION
FORCING. THERE IS A LOW CHANCE OF NEW DEVELOPMENT ALONG THE FRONT
ITSELF BUT INHIBITION CONCERNS REMAIN DUE TO A CAPPING LAYER OF WARM
AIR INDICATED AROUND 850 MB PEAKING AT ABOUT 21C BY MID MORNING IN
MODEL SOUNDINGS. THIS SUPPORTS THE GOING FORECAST THAT OFFERS NO
MORE THAN LOW CHANCE POPS THROUGH THE MORNING.

STEADILY VEERING LOW LEVEL FLOW AND THE DEEP LAYER SUBSIDENCE
TRAILING THE UPPER WAVE WILL DIRECT THE THETA-E RIDGE TO OUR SOUTH
AND EAST BY NOON. THIS WILL TAKE SHOWER POTENTIAL SOUTH OF THE
BORDER AND DEFLECT THE AIR MASS RESPONSIBLE FOR LOWER TO MID 90S MAX
TEMPS OVER THE MIDWEST TODAY, BUT AFTERNOON READINGS WILL REMAIN THE
PRIMARY FORECAST CHALLENGE FOR THE REST OF WEDNESDAY. THESE NUMBERS
WILL BE COMPLICATED BY THE PASSAGE OF THE SURFACE FRONT FROM ABOUT
MID MORNING IN THE TRI CITIES TO LATE AFTERNOON AT THE OHIO BORDER
WITH AN INFLUENCE FROM LINGERING CLOUDS. TIMING OF MEANINGFUL LOW
LEVEL COLD ADVECTION WILL ALSO BE SUBJECT TO DISRUPTION BY BOUNDARY
LAYER MIXING OF THE SHALLOW POST FRONTAL AIR MASS, BUT THIS APPEARS
TO BE LESS OF A CONCERN COMPARED TO DATA FROM PREVIOUS FORECAST
CYCLES. INSTEAD, THE SURFACE PRESSURE GRADIENT NOT ONLY HOLDS UP TO
SURFACE HEATING BUT NOW SUPPORTS NORTHWEST FLOW GUSTING TO 30 MPH BY
MID AFTERNOON. THIS SHOULD HELP ESTABLISH ENOUGH COLD AIR TO CONFINE
MAX TEMPS TO THE MID 70S IN THE SAGINAW VALLEY, BUT THE LOWER HALF
OF THE 80S LOOK REACHABLE FROM THE DETROIT AREA SOUTH WITH SOME
AFTERNOON SUNSHINE.

DRY CONDITIONS WILL SETTLE INTO THE GREAT LAKES WEDNESDAY NIGHT INTO
THURSDAY WITH HIGH PRESSURE OF PACIFIC ORIGIN AND TEMPERATURES AT OR
SLIGHTLY ABOVE NORMAL. SIGNS OF A BACKDOOR COLD FRONT ARE SHOWN IN
THE MODEL DATA OVER THE NORTHERN GREAT LAKES WITH A SOUTHWARD
RELEASE LIKELY THURSDAY NIGHT. COOLER AIR WITH THE ASSOCIATED
CANADIAN HIGH PRESSURE WILL CARRY MIN TEMPS DOWN A NOTCH BY FRIDAY
MORNING AND TRANSLATE INTO COOLER MAX TEMPS FRIDAY AFTERNOON BUT
STILL RIGHT AROUND NORMAL.

RAIN CHANCES WILL BE ON THE INCREASE DURING THE WEEKEND AS UPPER
LEVEL TROUGH DEVELOPMENT TAKES PLACE FROM THE PACIFIC COAST INTO THE
ROCKIES. THE GLOBAL MODEL SOLUTIONS ARE TRENDING TOWARD A SHARPER
AND FARTHER WEST CORRESPONDING UPPER RIDGE CENTERED OVER THE MIDWEST
AS LATE AS SATURDAY NIGHT. THIS WOULD GUARD SE MICHIGAN FROM SHOWER
ACTIVITY A LITTLE LONGER INTO THE WEEKEND SHOULD THE SLOWER/FARTHER
WEST PACIFIC COAST TROUGH DEVELOPMENT CONTINUE TO HOLD. A MODEST
REDUCTION IN POPS IS WORKED INTO THIS PACKAGE FOR SATURDAY BEFORE
THE UPPER RIDGE AXIS GETS CLOSE ENOUGH FOR WARM ADVECTION SHOWERS TO
REACH LOWER MICHIGAN. THE WARM ADVECTION PATTERN ALSO HAS POTENTIAL
TO THEN WARM MAX TEMPS BACK UP TOWARD 80 TO START NEXT WEEK.

MARINE...

A LOW PRESSURE SYSTEM WILL TRACK ACROSS THE NORTHERN GREAT LAKES
TONIGHT. THIS WILL ALLOW A WARM FRONT TO LIFT THROUGH THE AREA THIS
EVENING AND TONIGHT...MAINTAINING GUSTY SOUTHEAST WINDS. SPEEDS
SHOULD HOWEVER REMAIN BELOW 20 KNOTS. A WEAK COLD FRONT WILL THEN
PUSH ACROSS THE AREA LATE TONIGHT...HAVING LITTLE AFFECT ON
TEMPERATURES BUT SHIFTING WINDS TO THE SOUTHWEST AND BRINGING A
CHANCE FOR SHOWERS AND THUNDERSTORMS. SOUTHWEST WINDS WILL
STRENGTHEN TOMORROW IN THE WAKE OF THE LOW PRESSURE SYSTEM...AND AS
HIGH PRESSURE BUILDS INTO THE WESTERN GREAT LAKES. GUSTS IMMEDIATELY
ALONG THE SHORELINE MAY REACH JUST ABOVE 25 KNOTS...HOWEVER THE
RELATIVELY COLD WATERS OF THE GREAT LAKES WILL CREATE A VERY STABLE
ENVIRONMENT OFFSHORE...KEEPING GUSTS CLOSER TO 20 KNOTS. NO SMALL
CRAFT ADVISORIES ARE PLANNED...AS WESTERLY WINDS KEEP WAVE HEIGHTS
LOW ON THE WESTERN SIDES OF THE LAKES.

HIGH PRESSURE WILL SETTLE IN OVER THE AREA ON THURSDAY FOR QUIET
WEATHER AND LIGHTER WINDS.

&&

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

&&

$$

AVIATION.....SC
UPDATE.......SC
SHORT TERM...HLO
LONG TERM....BT
MARINE.......HLO


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