Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 301110
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
710 AM EDT WED JUL 30 2014

.AVIATION...

//DISCUSSION...

AN UPPER LEVEL WAVE OF LOW PRESSURE WILL SLIDE ACROSS THE SOUTH HALF
OF LOWER MICHIGAN TODAY. THIS WILL PROMOTE THE REPLACEMENT OF MID
CLOUDS WITH LOWER CUMULUS DURING THE AFTERNOON AS DAYTIME HEATING
STRENGTHENS. A PASSING LIGHT SHOWER DURING THE MORNING WILL TEND TO
INCREASE INTENSITY BUT MAINLY THROUGH THE DTW CORRIDOR DURING THE
LATE AFTERNOON. THE MBS AND FNT AREA WILL BE DRY UNTIL POSSIBLY
LATER IN THE NIGHT WHEN THE NEXT UPPER LEVEL CIRCULATION PIVOTS DOWN
FROM NORTHERN ONTARIO. CONDITIONS WILL BE VFR AREA WIDE TODAY THROUGH
TONIGHT OUTSIDE OF A PASSING DOWNPOUR DURING THE AFTERNOON IN THE
DTW AREA.

FOR DTW... TIMING ON THE PASSAGE OF THE WAVE ALOFT WITH PEAK HEATING
FAVORS SHOWERS DEVELOPING OVERHEAD WITH ISOLATED TO SCATTERED
COVERAGE BEFORE MOVING TOWARD THE TOL AREA AND INCREASING BOTH
COVERAGE AND INTENSITY. EXPECT THUNDERSTORMS WILL REMAIN CLOSER TO
THE OHIO BORDER BY LATE AFTERNOON THROUGH MID EVENING.

//DTW THRESHOLD THREATS...

* MODERATE CONFIDENCE IN CEILING BELOW 5000 FEET TODAY.

&&

.PREV DISCUSSION...ISSUED 323 AM EDT WED JUL 30 2014

SHORT TERM... TODAY AND TONIGHT

PATCHY FOG WILL BE THE FIRST CONCERN IN THE FORECAST AS THE RAIN
YESTERDAY AND LAST NIGHT LEFT WET GROUND FOLLOWED BY LIGHT WIND AND
A DECREASE IN CLOUDS DURING THE EARLY MORNING. THE GREATEST
POTENTIAL FOR LOCALLY DENSE FOG WILL BE IN THE TRI CITIES DOWN TO
FLINT WHERE RADIATIONAL COOLING CONDITIONS WILL BE BETTER AND WHERE
MOST OF THE RAIN FELL. THIS WILL BE MONITORED FOR TRENDS IN DURATION
AND AREAL COVERAGE FOR HEADLINE POTENTIAL BEFORE SUNRISE.

THE FOCUS OF THE FORECAST FOR THE REST OF THE DAY WILL BE ON THE
SHORT WAVE ENERGY ROUNDING THE UPPER LOW OVER THE SOUTH END OF LAKE
MICHIGAN. COVERAGE OF SHOWERS SUPPORTED BY THIS FEATURE HAS
DECREASED CONSIDERABLY SINCE MIDNIGHT WITH THE LOSS OF DIURNAL
INSTABILITY. HOWEVER...THE WAVE REMAINS SUPERIMPOSED OVER THE WEAK
NORTHWEST-SOUTHEAST TEMPERATURE AND MOISTURE GRADIENT BEING
MAINTAINED BY THE LONG WAVE PATTERN. LOW TO MID LEVEL THETA-E
ADVECTION AHEAD OF THE SHORT WAVE TRACK HAS A CHANCE TO PRODUCE
SHOWERS THROUGHOUT THE MORNING AS WEAK MOISTURE TRANSPORT GENERATES
SOME ELEVATED INSTABILITY. DAYTIME HEATING WILL THEN ADD SURFACE
BASED INSTABILITY TO THE MIX WITH SOME ENHANCED CONVERGENCE WITHIN
THE SURFACE PRESSURE REFLECTION OF THE WAVE. THUNDERSTORM POTENTIAL
WILL BE SIMILAR TO YESTERDAY BUT WITH SLIGHTLY HIGHER SURFACE
DEWPOINT AND PERHAPS A DEGREE OR TWO INCREASE IN MAX TEMP. A 75/53
PARCEL THEN MODIFIES SURFACE BASED CAPE TO ABOUT 1300 J/KG IN NAM
SOUNDINGS. ALL THAT BEING SAID...EXPECT CHANCE POPS WILL COVER THIS
SCENARIO WHICH WILL AFFECT THE AREA GENERALLY SOUTH OF THE M59
CORRIDOR BUT LIMITED BY AN EARLY EASTWARD EXIT OF THE WAVE. THE 00Z
MODEL PACKAGE HAS A RELIABLE HANDLE ON THE SITUATION BASED ON
ANALYSIS FIELDS...AND FORECASTS SHOW GOOD TEMPORAL EVOLUTION THROUGH
THE OHIO BORDER REGION PLACING THE BULK OF AFTERNOON CONVECTION TO
OUR SOUTH AND EAST BEFORE PEAK SURFACE HEATING.

MID LEVEL SUBSIDENCE TRAILING THE OHIO BORDER WAVE WILL KEEP THINGS
DRY IN THE TRI CITIES DOWN NEAR FLINT DURING THE DAY...BUT THE NEXT
UPPER LEVEL FEATURE WILL ARRIVE SOON INTO TONIGHT. THIS SYSTEM IS
SHOWN CLEARLY IN EARLY MORNING WATER VAPOR IMAGERY OVER NORTHERN
ONTARIO AND LOOKS PLENTY CAPABLE OF SUPPORTING SHOWERS TONIGHT AS IT
MOVES THROUGH LOWER MICHIGAN. MODEL SOLUTIONS INDICATE THE
CIRCULATION WEAKENING FROM A VORTICITY PERSPECTIVE BUT NOT ENOUGH TO
OFFSET THE SHOT OF COLD AIR ALOFT IT WILL BRING DOWN OVER THE
REGION. THE WAVE WILL ALSO BE ABLE TO DRAW SOME LOW TO MID LEVEL
MOISTURE IN FROM THE WEST TO HELP GENERATE MODEST ELEVATED
INSTABILITY TO PROMOTE SCATTERED SHOWER DEVELOPMENT THROUGH SUNRISE
THURSDAY.

LONG TERM...THURSDAY THROUGH TUESDAY

UPPER LOW CONTINUES TO CHURN NEAR THE ONTARIO/QUEBEC BORDER...WITH
SEVERAL NOTABLE SHORTWAVES VISIBLE ON WATER VAPOR IMAGERY PIVOTING
AROUND THE MAIN SYSTEM. THE LARGER OF THE WAVES (ONE OVER NORTHERN
MICHIGAN AND THE OTHER OVER HUDSON BAY) WILL ROTATE ACROSS THE AREA
TODAY AND TONIGHT...CLEARING THE AREA TO THE EAST BY 12Z THUR. THE
CENTER OF THE UPPER LOW APPEARS TO BE LOCATED NEAR THE SOUTHERN END
OF ST JAMES BAY AT THE MOMENT. MODELS ARE FORECASTING THIS WILL DROP
THROUGH EASTERN ONTARIO THURSDAY AND THURSDAY NIGHT...PUSHING A
SURFACE TROUGH ACROSS NORTHERN MICHIGAN. THE PASSAGE OF THE TROUGH
SHOULD HELP FOCUS SHOWERS AND MAYBE SOME THUNDERSTORMS ONCE AGAIN
ACROSS SOUTHEAST MICHIGAN...WITH THE BEST COVERAGE DURING THE
AFTERNOON AND EVENING AS DIURNAL HEATING PEAKS. THERE IS SOME
UNCERTAINTY WITH DEVELOPMENT AND COVERAGE OF THUNDERSTORMS THROUGH
AT LEAST THE FIRST HALF OF THE DAY. GFS/NAM FORECAST SOUNDINGS HAVE
VARIED OVER THE PAST FEW RUNS BETWEEN A WEAK MID-LEVEL CAP HOLDING
AND NO CAP WITH A SKINNY CAPE PROFILE. THEY DO ADVERTISE A TREND FOR
THE ATMOSPHERE TO BECOME UNCAPPED BY LATE EVENING HOWEVER...WITH
COOLER AIR ALOFT SLIDING DOWN AS THE UPPER LOW DRAWS CLOSER. WILL
CONTINUE TO MENTION THUNDERSTORMS AFTER 15Z AND THROUGH THE
OVERNIGHT PERIOD.

SHORTWAVE ENERGY DIVING DOWN FROM SASKATCHEWAN AND MANITOBA WILL
THEN ALLOW A WEAK UPPER TROUGH TO FORM OVER THE MIDWEST AND WESTERN
GREAT LAKES EARLY FRIDAY. THIS TROUGH WILL THEN SLOWLY TRACK ACROSS
THE GREAT LAKES FRIDAY AND SATURDAY. SURFACE LOW ASSOCIATED WITH
THIS FEATURE IS EXPECTED TO WORK ACROSS THE SOUTHERN OHIO
VALLEY...HOWEVER SOME MID-LEVEL MOISTURE IS EXPECTED TO INCREASE
OVER MICHIGAN FRIDAY INTO FRIDAY NIGHT AS THE TROUGH APPROACHES AND
SOUTHWEST FLOW INCREASES SLIGHTLY...WITH SOME MOISTURE THEN
LINGERING INTO SATURDAY. THIS WILL ONCE AGAIN ALLOW SHOWERS AND
THUNDERSTORMS TO FORM AGAIN...ESPECIALLY EACH AFTERNOON/EVENING AS
WE REMAIN UNDER THE UPPER COLD POOL AND DIURNAL HEATING HELPS TO
INCREASE LAPSE RATES.

SHORTWAVE RIDGE IS EXPECTED TO BRIEFLY BUILD INTO THE AREA FOR
SUNDAY BRINGING A RESPITE FROM DAILY SHOWER/THUNDERSTORM CHANCES.
ANOTHER UPPER TROUGH IS THEN ADVERTISED BY MEDIUM RANGE MODELS TO
DROP ACROSS ONTARIO ON MONDAY...PUSHING ANOTHER SURFACE TROUGH
ACROSS THE WESTERN AND CENTRAL GREAT LAKES AND BRINGING SHOWERS AND
THUNDERSTORMS BACK.

TEMPERATURES THROUGH THE EXTENDED PERIOD ARE EXPECTED TO MODERATE A
BIT AS UPPER TROUGHING OVER THE AREA EXHIBITS A GENERAL WEAKENING
TREND. MAX TEMPS THURSDAY THROUGH EARLY NEXT WEEK SHOULD RUN IN THE
UPPER 70S TO NEAR 80...STILL BELOW NORMAL FOR THIS TIME OF YEAR.

MARINE...

WINDS WILL REMAIN FAIRLY LIGHT THROUGH THE END OF THE WEEK...WITH
THE MOST NOTABLE PERIOD OF WINDS OCCURRING FROM THE SOUTHWEST
THURSDAY AND THURSDAY NIGHT AS A WEAK TROUGH MOVES ACROSS THE
WESTERN AND CENTRAL GREAT LAKES. WINDS ARE STILL EXPECTED TO REMAIN
NEAR OR BELOW 10 KNOTS HOWEVER. OTHERWISE...EXPECT THE AREA TO
REMAIN UNDER A COOL PATTERN WITH SHOWERS AND THUNDERSTORMS
DEVELOPING EACH DAY...MOSTLY DURING THE AFTERNOON AND EVENING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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


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