Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 050755
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
355 AM EDT TUE MAY 5 2015

.SHORT TERM... TODAY AND TONIGHT

A WET 24 HOUR PERIOD IS SETTING UP OVER SOUTHERN LOWER MICHIGAN
TODAY THROUGH TONIGHT. THE TRI CITIES AND NORTHERN THUMB MAY ESCAPE
THE BULK OF THE RAINFALL TODAY BUT THE REST OF SE MICHIGAN STANDS TO
PICK UP A PROLONGED PERIOD OF SHOWERS AND THUNDERSTORMS. THE SURFACE
FRONT WILL REMAIN SOUTH OF THE OHIO BORDER THROUGH THE PERIOD SO
THUNDERSTORMS WILL BE THE ELEVATED VARIETY AND MAINLY CONTRIBUTE TO
LOCALLY HEAVY DOWNPOURS. RAINFALL TOTALS LOCALLY AROUND 1 INCH WILL
BE POSSIBLE BY SUNRISE WEDNESDAY.

WIDESPREAD SHOWERS AND THUNDERSTORMS ARE ALREADY UNDERWAY OVER THE
MIDWEST AND WILL SPREAD TO THE NORTH AND EAST DURING THE REST OF THE
MORNING. THIS AREA OF CONVECTION ORIGINATED ALONG THE FRONT OVER THE
CENTRAL PLAINS DURING PEAK HEATING YESTERDAY AND HAS SINCE GROWN
LARGE ENOUGH AND PERSISTENT ENOUGH TO SUPPORT MCV DEVELOPMENT ALOFT
AND AN AREA OF SURFACE PRESSURE FALLS OVER IOWA AND MISSOURI. THE
WAVE IS JUST STRONG ENOUGH TO SUPPORT A WEAK LOW LEVEL JET FUELING
ACTIVITY OVER NORTHERN ILLINOIS WHICH WILL CONTINUE TO DEVELOP INTO
SOUTHERN LOWER MICHIGAN AS THE LOW TO MID LEVELS OF THE FRONT
STRENGTHEN WITH TIME. CONVECTIVE DEBRIS IN SATELLITE IMAGERY SHOWS
THE ENTRANCE REGION OF A 120 KNOT UPPER JET ANALYZED IN MODEL DATA
AT 250 MB. THIS FEATURE IS POSITIONED FAVORABLY OVER THE GREAT LAKES
TO GENERATE STRONG FRONTOGENESIS THROUGH TODAY WHILE THE LARGE SCALE
FRONTAL POSITION REMAINS STATIONARY AND THEN DRIFTS SLOWLY NORTHWARD
TONIGHT. CROSS SECTIONS OF MODEL DATA FROM THE POSITION OF THE
SURFACE FRONT EXTENDING NORTHWARD TO THE UPPER JET AXIS SHOW THE
STEEPEST PORTION OF THE AGEOSTROPHIC CIRCULATION SETTING UP THROUGH
CENTRAL SECTIONS OF OUR AREA BY AFTERNOON THROUGH THIS EVENING. DEEP
CONVECTIVE INSTABILITY ABOVE THE FRONTAL SURFACE COMBINED WITH
PRECIPITABLE WATER RISING TO ABOUT 1.25 INCHES WILL ENSURE
WIDESPREAD COVERAGE OF SHOWERS WITH EMBEDDED THUNDERSTORMS. LOCALLY
HEAVY RAINFALL WILL ALSO BE POSSIBLE DUE TO THE PERSISTENCE OF THIS
TEXTBOOK UPPER JET ENHANCED FRONTAL CIRCULATION AND THE CONVECTIVE
NATURE OF THE PRECIPITATION PATTERN. SO THEN WHAT COULD GO WRONG IN
THIS FORECAST? THE POTENTIAL FOR SURFACE BASED CONVECTION OVER
INDIANA AND OHIO...COMBINED WITH THE TENDENCY FOR ELEVATED
INSTABILITY TO BECOME LESS EFFECTIVE DURING THE DAY...COULD LEAD TO
A WEAKENING TREND IN THE PATTERN OVER SE MICHIGAN DURING THE
AFTERNOON INTO THIS EVENING. SHOULD THIS OCCUR...IT WOULD DO MORE TO
REDUCE THE POTENTIAL FOR HEAVY RAINFALL IN OUR AREA AND POSSIBLY
ALTER THE LOCATION OF THE MOST PERSISTENT SHOWERS AND OVERALL QPF...
BUT MOST AREAS WILL SEE A LENGTHY PERIOD OF RAIN AS THE MORNING RAMP
UP WOULD CARRY OVER INTO THE AFTERNOON JUST BASED ON INERTIA.

PROGRESSION OF THE UPPER LEVEL RIDGE AND THE ENTRANCE REGION OF THE
UPPER JET WILL NUDGE THE MID LEVEL FRONTAL ZONE TO THE NORTH AND
EAST OVERNIGHT. THIS WILL BRING THE TRI CITIES AND NORTHERN THUMB
MORE INTO THE PATTERN OF REMAINING SHOWERS AND WILL BE THE FAVORED
LOCATION FOR ANY NOCTURNAL REDEVELOPMENT. THE AXIS OF LIKELY POPS
OVER SE MICHIGAN IS PLACED ALONG THE 850 MB THETA-E GRADIENT WHICH
IS WELL AGREED UPON BY THE 00Z MODEL CYCLE AND IS THE MOST FAVORED
LOCATION FOR RENEWED DEVELOPMENT OF NOCTURNAL ELEVATED INSTABILITY
AND SUPPORT FOR SHOWERS THROUGH SUNRISE WEDNESDAY.

&&

.LONG TERM...WEDNESDAY THROUGH MONDAY

SE MICHIGAN WILL RESIDE ALONG THE IMMEDIATE DOWNSTREAM SIDE OF AN
ELONGATING UPPER RIDGE ON WEDNESDAY.  THE RESULTING WEAKLY SHEARED
WEST-NORTHWEST FLOW WILL SUSTAIN A PERTURBED 850-925 MB FRONTAL ZONE
ACROSS THE REGION.  MODELS TRENDING SLIGHTLY STRONGER WITH THE
ASCENT/CONVERGENCE THROUGH THIS LAYER...SUGGESTING THE EXISTING
FRONTAL SLOPE WILL POTENTIALLY BE MORE ACTIVE.  THIS WILL SUPPORT
THE INCLUSION OF A LOWER END POP.  GREATER POTENTIAL FOR SHOWER
PRODUCTION DURING THE MORNING PERIOD...BEFORE BOTH THE MOISTURE
QUALITY AND AVAILABLE FORCING DIMINISHES AS THE INBOUND UPPER RIDGE
MAKES BETTER INROADS.  SUBSTANTIAL CLOUD COVER WITHIN PERSISTENT LOW
LEVEL EASTERLY FLOW WILL CAP THE DIURNAL TEMPERATURE RESPONSE TO
SOME DEGREE...REGARDLESS OF SHOWER COVERAGE.  ABSENT OF A LARGER AND
PERSISTENT COVERAGE OF SHOWERS TO DISRUPT THE HEATING CYCLE...
EXISTING THERMAL PROFILE WILL SUPPORT HIGHS GENERALLY WITHIN THE MID
AND UPPER 60S RANGE.

UPPER RIDGE STEADILY BUILDS INTO LOWER MICHIGAN WEDNESDAY NIGHT...
580 DM AT 500 MB MARKING THE RIDGE AXIS CENTERING OVERHEAD BY EARLY
THURSDAY MORNING.  THIS PROGRESSION WILL SEND SE MICHIGAN INTO THE
WARM SECTOR BY THURSDAY...SOLID DEPTH TO THE EMERGING SOUTHWEST FLOW
CONTINUING TO POINT TOWARD HIGHS MAKING A RUN INTO THE LOWER 80S.
DRY/STABLE PROFILE STILL INFLUENCED BY EXITING UPPER RIDGING WILL
RESULT IN LITTLE MORE THAN A STANDARD DIURNAL CU FIELD.

CLOSED LOW CURRENTLY PARKED OVER THE DESERT SOUTHWEST WILL LIFT
NORTHEAST THROUGH THE LATTER HALF OF THE WEEK...EVENTUALLY SHEARING
OVER THE TOP OF THE UPPER RIDGE STAGNATING ALONG THE EAST COAST.
THIS LOWERING HEIGHT FIELD WILL BEGIN TO EASE AN ATTENDANT FRONTAL
BOUNDARY EASTWARD WITHIN THE FRIDAY AND SATURDAY WINDOW.  GENERAL
TIMING ACROSS THE MODEL SPECTRUM SUGGESTS FRIDAY WILL REMAIN
CHARACTERED BY THE PRE-FRONTAL WARM SECTOR...WITH ANY POSSIBLE LATE
DAY/EVENING CONVECTIVE CHANCES ARRIVING TOO LATE TO DISRUPT ANOTHER
DAY WITH HIGHS IN THE 80S.  POTENTIAL IS THERE FOR AN ACTIVE PERIOD
HEADING INTO THE UPCOMING WEEKEND...FRONTAL BOUNDARY EVENTUALLY
ALIGNING OVER OR NEAR THE REGION FOR AN EXTENDED TIME AS THE AXIS
BECOMES PARALLEL TO THE MEAN FLOW.  THIS PATTERN WOULD SHAVE A FEW
DEGREE OFF PROSPECTIVE HIGHS THIS WEEKEND RELATIVE TO THE
THU/FRI WARMTH...STILL NEAR TO ABOVE NORMAL THROUGH THIS TIME.

&&

.MARINE...

SHOWERY CONDITIONS WITH THE CHANCE OF THUNDERSTORMS WILL EXIST UNDER
PERSIST EAST TO NORTHEAST FLOW OVER THE SOUTHERN LAKE HURON BASIN
AND POINTS SOUTHWARD THROUGH TONIGHT.  FAVORABLE MARINE CONDITIONS
ACROSS NORTHERN LAKE HURON DURING THIS TIME AS HIGH PRESSURE BUILDS
INTO THE REGION.  MODEST WAVE AND WIND CONDITIONS THROUGH THE
MIDWEEK PERIOD AS HIGH PRESSURE SUSTAINS A WEAK GRADIENT.

&&

.AVIATION...ISSUED 1154 PM EDT MON MAY 4 2015

VFR CONDITIONS OVERNIGHT WILL GIVE WAY TO MVFR AND MOST LIKELY IFR
CIGS AT TIMES ON TUESDAY AS AN AREA OF RAIN AND POSSIBLE EMBEDDED
TSRAS...MOVE INTO AREA AS A SHORTWAVE TRACK ALONG STALLED BOUNDARY
JUST SOUTH OF THE TERMINALS. THIS FRONTAL BOUNDARY REMAINS PRETTY
MUCH IN PLACE INTO THE END OF THE FORECAST SO EXPECT LOWER CIGS AND
SOME REDUCED VSBYS AS LOW LEVEL MOISTURE INCREASES AND POOLS ALONG
THIS BOUNDARY. AFTER THE MAIN PUSH OF SHOWERS DURING THE DAY...SOME -
SHRAS WILL LINGER INTO THE EVENING TUESDAY AS WELL.

FOR DTW...SHOWERS WILL WORK INTO TERMINAL BY AROUND NOON AND WHILE
THE MOST CONCENTRATED AREA OF SHOWERS APPEARS TO SHIFT JUST NORTH OF
DTW...PERIODIC SHOWERS WILL BE A GOOD BET THROUGH THE DAY AND ON
INTO THE EVENING. LIGHT NE WINDS WILL BECOME EAST AND HOLD PRETTY
STEADY THROUGH THE END OF THE FORECAST...PERHAPS VEERING MORE TO THE
ESE WITH TIME LATE.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CEILINGS BELOW 5000 FT AFTER 16Z-18Z TUESDAY.

* LOW FOR THUNDERSTORMS AFTER 16Z-18Z TUESDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...BT
LONG TERM....MR
MARINE.......MR
AVIATION.....DG


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