Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 251942
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
342 PM EDT MON APR 25 2016

.DISCUSSION...

INCREASINGLY AGITATED CU OVER SOUTHWEST LOWER MICHIGAN SIGNALS THE
ARRIVAL OF DEEPER MID-LEVEL MOISTURE, THE LEAD EDGE OF WHICH IS
SUPPORTING A FEW LIGHT SHOWERS INVOF THE THUMB. ARRIVAL OF THIS
MOISTURE DURING PEAK HEATING WILL BRING AN INCREASING CHANCE OF
SHOWERS BETWEEN NOW AND 00Z OVER MOST OF SOUTHEAST MICHIGAN. THE
ENVIRONMENT WILL REMAIN LARGELY CAPPED THROUGH THIS TIME SO THERE
EXISTS ONLY A VERY LOW CHANCE OF THUNDER THIS AFTERNOON.
NONETHELESS, A DEEP AND VERY WELL-MIXED BOUNDARY LAYER SPORTING DRY
ADIABATIC LAPSE RATES THROUGH THE LOWEST 5KFT WILL SUPPORT STRONG
WIND GUST POTENTIAL WITHIN ANY ORGANIZED SHOWER DEVELOPMENT. THE
LACK OF INSTABILITY AND AND WEAK AMBIENT WIND FIELD THIS AFTN WILL
LIMIT POTENTIAL TO LESS THAN 50 MPH.

ATTENTION FOR THE REMAINDER OF THE NIGHT TURNS TO THE COLD FRONT
READILY EVIDENT IN VISIBLE IMAGERY OVER SOUTHERN WISCONSIN AND
WESTERN ILLINOIS WHERE CONVECTIVE INITIATION IS JUST GETTING
UNDERWAY. CONVECTION WILL INCREASE IN COVERAGE AND INTENSITY
COINCIDENT WITH DIURNAL DESTABILIZATION, BUT WILL LIKELY BECOME
ELEVATED AND LARGELY SUPPORTED BY THE STRENGTHENING LLJ AS IT
CROSSES LAKE MICHIGAN THIS EVENING. INCREASING LLJ TO 30-40KTS WILL
STEEPEN MID-LEVEL LAPSE RATES AND SUPPORT PERSISTENCE OF NOCTURNAL
CONVECTION AS IT WORKS ACROSS SE MICHIGAN 02-06Z. SURFACE-BASED
INSTABILITY WILL BE NON-EXISTENT NORTH OF THE SURFACE FRONT AND
QUITE LIMITED TO THE SOUTH GIVEN NOCTURNAL TIMING. THE EXCEPTION
WILL BE THE FAR SOUTHWEST PORTIONS OF THE CWA CURRENTLY HIGHLIGHTED
IN THE 1630Z SPC SLIGHT RISK AREA. A FEW HUNDRED J/KG CAPE
PERSISTING DURING THE SUNSET HOURS WILL YIELD AN OPPORTUNITY FOR
UPSTREAM CONVECTION TO PROPAGATE INTO THE AREA CARRYING A BETTER-
DEFINED WIND THREAT PRIOR TO BECOMING ELEVATED. NORTH AND EAST,
WITHIN THE MARGINAL RISK AREA/STILL SOUTH OF THE SURFACE WARM FRONT,
THE RATHER SHALLOW NOCTURNAL INVERSION WILL NOT BE IMPERVIOUS TO
DOWNDRAFTS, WHICH COULD BE ON THE STRONGER SIDE GIVEN THE AMPLE LOW-
LEVEL DRY AIR IN PLACE IN THE PRE-STORM ENVIRONMENT. A LOW END
SEVERE RISK THEREFORE EXISTS THROUGH ABOUT 06Z FOR ALL LOCATIONS
SOUTH OF I-69. NORTH OF THE I-69 CORRIDOR, THE STRONGLY FORCED
ENVIRONMENT WILL HELP OFFSET THE LACK OF ELEVATED INSTABILITY, SO
SUB-SEVERE HAIL CANNOT BE RULED OUT.

COLD FRONT WILL WORK THROUGH THE CWA BY 18Z TUESDAY LEADING TO A
SIZEABLE HIGH TEMPERATURE GRADIENT ACROSS THE CWA...NEAR 70 ALONG
THE OHIO BORDER AND UPPER 40S IN THE THUMB. STEEP LAPSE BOUNDARY
LAYER RATES SUPPORTED BY ONGOING CAA AND THE INTRUSION OF SHALLOW
MOISTURE PRESENTLY EVIDENT BY LOW CLOUDS ON VIS IMAGERY OVER THE
NORTHERN GREAT LAKES WILL SUPPORT PATCHY DRIZZLE IN ADDITION
OVERCAST SKIES FOR MUCH OF THE DAY...WITH THE EXCEPTION OF LOCATIONS
SOUTH OF I-94/SOUTH OF THE COLD FRONT. COOL AIRMASS CHARACTERIZED BY
H85 TEMPS IN THE SINGLE DIGITS WILL SUPPORT HIGHS IN THE 50S ON
WEDNESDAY. DRY RESIDENT AIRMASS AND CONFLUENT FLOW ALOFT WILL
SUPPORT MOSTLY CLEAR SKIES FOR MOST OF WEDNESDAY.

LOW PRESSURE SYSTEM WILL SLIDE SOUTH OF THE OHIO BORDER ON THURSDAY
ALLOWING RAIN TO SPREAD NORTHWARD ACROSS SOUTHERN LOWER MICHIGAN. AN
ISOLATED THUNDERSTORM IS ALSO A POSSIBILITY THURSDAY AFTERNOON AS
BETTER INSTABILITY WORKS INTO OUR EXTREME SOUTHERN COUNTIES. STRONG
HIGH PRESSURE BUILDS SOUTHWARD OUT OF NORTHERN ONTARIO ON FRIDAY AND
REMAINS SITUATED OVER THE REGION FOR AT LEAST THE FIRST HALF OF THE
WEEKEND. MODELS ARE UNDECIDED FOR SUNDAY...EITHER KEEPING SOUTHEAST
MICHIGAN DRY OR HAVING A LOW PRESSURE SYSTEM /AND RESULTING RAIN/
FOR SUNDAY. WILL HAVE TO FINE TUNE THIS FORECAST FOR SUNDAY AS THE
WEEK PROGRESSES.

&&

.MARINE...

A FRONTAL BOUNDARY THAT WAS STALLED ACROSS THE CENTRAL GREAT LAKE
HAS DRIFTED SOUTHWARD THROUGH THE DAY. A LOW PRESSURE SYSTEM TO THE
WEST IS TRACKING ALONG THIS BOUNDARY WHILE PULLING A WARM FRONT INTO
THE SOUTHERN GREAT LAKES...WHICH WILL PHASE WITH THE EXISTING FRONT.
THIS HAS RESULTED IN EASTERLY FLOW ACROSS ALL OF THE EASTERN LAKES.
SOUTHWESTERLY FLOW WILL ATTEMPT TO LIFT OVER LAKE ERIE THIS EVENING
BUT THE LOW WILL TRACK RIGHT ACROSS SOUTHERN LOWER MICHIGAN WHICH
WILL KEEP PRIMARILY AN EASTERLY/NORTHEASTERLY FLOW. IN
ADDITION...SHOWERS WILL CONTINUE ALONG THE FRONT WITH A CHANCE OF
THUNDERSTORMS LATER THIS EVENING.

SMALL CRAFT ADVISORIES REMAIN IN EFFECT FOR A PORTION OF THE
NEARSHORE WATERS OF LAKE HURON INCLUDING SAGINAW BAY. WINDS AND
WAVES WILL BE MARGINAL...WITH THE EXCEPTION OF SAGINAW BAY ALREADY
GUSTING OVER 25 KNOTS...BUT SUSTAINED EAST/NORTHEAST FLOW OVER LAKE
HURON WILL CAUSE WAVE HEIGHTS TO BUILD ALONG THE SHORELINE. WINDS
WILL DECREASE WHILE BECOMING NORTHERLY ON TUESDAY AS HIGH PRESSURE
BEGINS TO MOVE BACK INTO THE REGION.

&&

.HYDROLOGY...

LOW PRESSURE AND AN ATTENDING COLD FRONT WILL MOVE THROUGH SOUTHEAST
MICHIGAN LATE TODAY INTO TONIGHT WITH NUMEROUS SHOWERS AND EMBEDDED
THUNDERSTORMS BECOMING INCREASINGLY LIKELY FROM LATE AFTERNOON INTO
THE EVENING HOURS. WHILE WIDESPREAD BASIN AVERAGE RAINFALL WILL
HOVER AROUND ONE QUARTER OF AN INCH...LOCALIZED RAINFALL AMOUNTS OF
ONE HALF TO THREE QUARTERS OF AN INCH WILL BE POSSIBLE FROM LATE
TODAY INTO EARLY TUESDAY MORNING. THE BULK OF THE RAIN IS FORECAST
BETWEEN 00-06Z TONIGHT WHEN THUNDERSTORMS WILL BE MOST LIKELY.

&&

.AVIATION...ISSUED 126 PM EDT MON APR 25 2016

CLOUDS ARE THICKENING AND CIGS ARE LOWERING THROUGH THE AFTERNOON AS
MOISTURE CONTINUES TO STREAM INTO THE REGION BEHIND A WARM FRONT AND
AHEAD OF THE APPROACHING LOW PRESSURE SYSTEM. THE INITIAL SURGE OF
MOISTURE WILL OCCUR BETWEEN 20Z-00Z WHICH MAY IGNITE A FEW SHOWERS
BUT MODELS HAVE CONTINUED TO SUGGEST COVERAGE/CONFIDENCE OF THESE
SHOWERS IS LOW ENOUGH TO EXCLUDE FROM THE TAFS. BETTER CHANCE OF
SHOWERS AND THUNDERSTORMS WILL COME AFTER 02Z WHEN THE COLD FRONT
BEGINS TO SWING THROUGH LOWER MICHIGAN. WILL CONTINUE TO HIGHLIGHT
THE 02Z-07Z WITH THE BEST CHANCE OF SEEING THUNDERSTORMS. IN THE
WAKE OF THE SYSTEM...CIGS AND VSBYS WILL DROP TO MVFR AND POSSIBLY
IFR FOR A PERIOD. MAY SEE SOME DRIZZLE EARLY TUESDAY BEFORE DRIER
AIR WORKS BACK INTO THE AREA.

FOR DTW...WARM FRONT SLOWLY APPROACHING FROM THE SOUTHWEST WHICH HAS
KEPT SOUTHEASTERLY FLOW AND DRIER AIR IN PLACE. THIS HAS KEPT CIGS
ABOVE 5KFT THUS FAR TODAY AND WILL CONTINUE FOR THE NEXT SEVERAL
HOURS. WINDS WILL SHIFT TO SOUTHWESTERLY ONCE THE FRONT LIFTS NORTH
AROUND 19Z-20Z. FORCING ALONG THE WARM FRONT MAY BE ENOUGH TO SPARK
A COUPLE SHOWERS BUT CHANCES ARE TOO LOW TO INCLUDE IN THE TAF AT
THIS TIME. BEST CHANCE WILL COME BETWEEN 03Z-07Z AS THE TRAILING
COLD FRONT SWEEPS THROUGH.

//DTW THRESHOLD PROBABILITIES...

* LOW IN THUNDERSTORMS AFFECTING TERMINAL THIS EVENING.

* MEDIUM IN CEILINGS BELOW 5000 FEET AFTER 06Z TUESDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY FROM 8 AM TO 4 PM EDT TUESDAY FOR LHZ442-443.

     SMALL CRAFT ADVISORY UNTIL 4 PM EDT TUESDAY FOR LHZ421-422-441.

LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

DISCUSSION...JVC/RK
MARINE.......DRK
HYDROLOGY....
AVIATION.....DRK


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).



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