Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220346
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1146 PM EDT THU MAY 21 2015


.AVIATION...

THE COLD FRONT WILL CONTINUE TO PUSH SOUTH ACROSS THE AREA OVER THE
NEXT FEW HOURS...PASSING THROUGH METRO DETROIT BETWEEN 08Z AND 09Z.
THE FRONT WILL BE MARKED BY A WIND SHIFT TO THE NORTHWEST. HIGH
BASED CLOUDS WITH A FEW LIGHT SHOWERS/SPRINKLES WILL PRECEDE THE
FRONT. POST FRONTAL DRY AIR ADVECTION WILL THEN CLEAR SKIES OUT
DURING THE EARLY MORNING HOURS.


//DTW THRESHOLD PROBABILITIES...

* NONE.

&&

.PREV DISCUSSION...ISSUED 911 PM EDT THU MAY 21 2015

UPDATE...

A BAND OF SCT TO ISOLD SHOWERS CONTINUES TO MOVE ACROSS THE
SAGINAW VALLEY AND THUMB REGION THIS EVENING IN ADVANCE OF THE SFC
COLD FRONT NOW PUSHING INTO CNTL LOWER MI. THE NARROW RIBBON OF MID
LEVEL FRONTAL FORCING SUSTAINING THESE SHOWERS WILL CONTINUE TO
MOVE SOUTH ACROSS THE AREA TONIGHT IN ADVANCE OF THIS FRONT. THE
00Z DTX SOUNDING SHOWED FAIRLY STEEP MID LEVEL LAPSE RATES. THIS
WILL AID THE WEAKER LARGER SCALE FORCING AND REMAINS SUPPORTIVE OF
SOME SHOWERS PUSHING SOUTH DURING THE REST OF THE EVENING INTO THE
FIRST HALF OF THE OVERNIGHT. THUS FAR COVERAGE AND INTENSITY OF
THE SHOWERS HAS BEEN SOMEWHAT INSIGNIFICANT. GIVEN CURRENT RADAR
TRENDS AND EXPECTED FRONTAL FORCING TONIGHT...SEE NO REASON TO
EITHER INCREASE OR DECREASE POPS FROM LOW CHANCE. THE ONLY MAJOR
UPDATE WILL BE TO END THE SHOWERS A LITTLE EARLIER IN THE NIGHT
GIVEN THEIR CURRENT SOUTHWARD PROGRESSION.

PREV DISCUSSION...ISSUED 353 PM EDT THU MAY 21 2015

SHORT TERM... AFTERNOON AND TONIGHT

AN UPPER LEVEL WAVE WITH LITTLE TO NO SURFACE REFLECTION WILL
CONTINUE TO EXIT THE OHIO BORDER REGION DURING THE REST OF THE
AFTERNOON. THIS FEATURE HAS BEEN VERY EFFICIENT IN THE GENERATION OF
MID AND HIGH CLOUDS OVER ALL SE MICHIGAN ON TOP OF SHALLOW CUMULUS.
THE WESTERN EDGE OF THE CLOUD PATTERN LINES UP WELL WITH THE AXIS OF
500 MB VORTICITY MAXIMUM IN MODEL DATA AND SUGGESTS THE HIGH CLOUDS
WILL EXIT EASTWARD TOWARD SUNSET.

THE CLEARING OF HIGH CLOUDS WILL START FIRST IN THE TRI CITIES BUT
WILL BE SHORT LIVED AS THE COLD FRONT APPROACHES FROM THE NORTHERN
GREAT LAKES. THE FRONT WILL POSE A CHALLENGING FORECAST FOR COVERAGE
AND INTENSITY OF SHOWERS OVER OUR AREA TONIGHT. THE LATEST SET OF
MODEL RUNS PREDOMINANTLY SUPPORT A STRONG DIURNAL DEPENDENCE ON THE
SHOWER MORPHOLOGY DURING THE EVENING. THE NAM REMAINS AT THE HIGH
END OF BOTH COVERAGE AND INTENSITY EVEN AS DAYTIME HEATING SUPPORT
TRENDS DOWNWARD DURING THE EVENING. THIS IS SOMETHING TO MONITOR AS
THERE IS SOME POTENTIAL FOR THE PATTERN TO EVOLVE MORE STRONGLY OVER
SOUTHERN LOWER MICHIGAN DURING THE NIGHT. LOW LEVEL THETA-E
ADVECTION WILL FIRST COMBINE WITH DAYTIME HEATING TO STEEPEN LAPSE
RATES UPSTREAM DURING THE LATE AFTERNOON INTO THE EVENING. DEEP
CYCLONIC FLOW ON THE SOUTH FRINGE OF THE UPPER LOW OVER CANADA WILL
SUPPORT FURTHER SUPPORT BROAD SCALE LIFT WITHIN THE FRONTAL ZONE.
THERE IS THEN GOOD MODEL AGREEMENT ON THE 850 MB THETA-E
RIDGE/UPSTREAM GRADIENT SHARPENING CONSIDERABLY OVER LOWER MICHIGAN
AFTER MIDNIGHT... MAINLY SOUTH OF THE I-69 CORRIDOR TO THE OHIO
BORDER. THIS IS A GOOD QUALITATIVE INDICATION OF FRONTOGENESIS IN
THE LOW LEVELS TO GO ALONG WITH NOCTURNAL STEEPENING OR MAINTAINING
700-500 MB LAPSE RATES NEAR 7 C/KM BY INCREASING MOISTURE FROM
BELOW. FOR NOW...THE FORECAST POPS ARE INCREASED MORE INTO THE
CHANCE RANGE WHILE MONITORING DURING THE EVENING FOR THE OPPORTUNITY
TO RAISE INTO THE LIKELY RANGE OVERNIGHT. THE FRONT AND ATTENDANT
MOISTURE WILL THEN EXIT TO THE SOUTH AND EAST BEFORE SUNRISE FRIDAY.
POST FRONTAL COLD ADVECTION WILL DROP MIN TEMPS IN THE UPPER 30S TO
LOWER 40S MOST LOCATIONS BUT A STEADY GRADIENT WIND IN THE 5-10 MPH
RANGE WILL MITIGATE FROST CONCERNS.

LONG TERM...

LARGE UPPER LEVEL LOW EXITING JAMES BAY THIS AFTERNOON...DROPPING
SOUTHEAST INTO SOUTHERN QUEBEC. THE BULK OF THE COLD AIR WILL SLIP
TO OUR EAST INTO NEW ENGLAND...BUT SOUTHEAST MICHIGAN WILL BE ON THE
OUTER FRIDGE OF THIS LARGE/COLD CIRCULATION. CONSEQUENTLY...THERE
WILL BE A SUBSTANTIAL SOUTHWEST TO NORTHEAST TEMPERATURE
GRADIENT...ENHANCED BY THE DIFFERENTIAL HEATING OF LAND/MARINE AREAS
DURING THE FRIDAY...WITH 850 MB TEMPS RISING TO ZERO ACROSS EASTERN
THUMB REGION...TO 4 C ACROSS FAR SOUTHWEST (PER 12Z
EURO)...SUGGESTING MID 50S TO MID 60S FOR HIGHS ACROSS THE CWA.

UPPER LEVEL NORTHWEST CONFLUENT FLOW FRIDAY EVENING WITH SURFACE
HIGH PRESSURE IN PLACE WILL PROVIDE A FAVORABLE RADIATING
NIGHT...ALTHOUGH THE CENTER OF THE HIGH SLIDING INTO THE EASTERN
OHIO VALLEY/MID ATLANTIC STATES OVERNIGHT WHICH SHOULD ALLOW FOR
RETURN FLOW/WARM ADVECTION TO COMMENCE...AND AT LEAST STABILIZE THE
FALL IN TEMPERATURES...BUT NOT BEFORE MANY AREAS FALL INTO THE 30S.

QUICK RECOVERY/BIG DIURNAL TEMPERATURE SWING ANTICIPATED FOR
SATURDAY AS UPPER LEVEL RIDGE BUILDING OVER THE AREA...COUPLED WITH
THE FAVORABLE LOW LEVEL SOUTHWEST/WEST FLOW COMBINES WITH NEAR FULL
LATE MAY INSOLATION...SENDING TEMPS UP AROUND 70 DEGREES BASED ON
850 MB TEMPS SLIGHTLY EXCEEDING 7 C.

CONTINUED WARM ADVECTION AND INCREASING HIGH CLOUDS EXPECTED TO HOLD
MINS UP AROUND 50 DEGREES SATURDAY NIGHT.

WARM AND INCREASINGLY MOIST PATTERN WILL BE IN PLACE SUNDAY THROUGH
AT LEAST THE MIDDLE OF NEXT WEEK. THIS WILL OCCUR AS RETURN FLOW
SETS UP ON THE BACK SIDE OF THE EASTWARD-MOVING SURFACE HIGH WHILE A
BROAD AREA OF LOWER PRESSURE SETS UP OVER THE GREAT PLAINS. THIS
PATTERN FAVORS GULF MOISTURE ADVECTION INTO THE GREAT LAKES REGION.
CONTINUE TO TARGET SUNDAY NIGHT/EARLY MONDAY FOR THE BEST FORCING
SIGNAL AS A LOW-LEVEL WARM FRONT TRAVERSES THE REGION. HAVE ENTRY
LEVEL CHANCE POPS FOR SUNDAY AS MOISTURE ADVECTION LOOKS TO
STRENGTHEN LATE IN THE DAY...BUT THERE IS STILL A GOOD CHANCE THAT
MOST OF THE DAY WILL REMAIN DRY. TOUGH TO PINPOINT PRECIP TIMING FOR
EARLY NEXT WEEK BUT...WITH A VERY MOIST AIRMASS IN PLACE AND
PERIODIC SHORTWAVES EMBEDDED IN UPPER SOUTHWESTERLY FLOW...CHANCE
POPS WILL COVER IT.

MARINE...

A COLD FRONT SLIPPING SOUTH THROUGH THE CENTRAL GREAT LAKES THIS
EVENING AND TONIGHT WILL ALLOW FOR AN INCREASE IN NORTHWEST
WINDS...REACHING BETWEEN 20 TO 25 KNOTS OVER THE OPEN WATERS OF LAKE
HURON. HOWEVER...WINDS WILL DIMINISH QUICKLY ON FRIDAY AS HIGH
PRESSURE AGGRESSIVELY BUILDS BACK INTO MICHIGAN BY EVENING. WINDS
WILL THEN REMAIN LIGHT INTO SATURDAY AS HIGH PRESSURE REMAINS IN
CONTROL. WARMER AIR STREAMING INTO THE REGION WILL PROVIDE FOR
FAVORABLE BOATING CONDITIONS ON SUNDAY AS WELL BEFORE THE THREAT
FOR SHOWERS AND THUNDERSTORMS RAMPS UP AS WE HEAD INTO MONDAY.

&&

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

$$

AVIATION.....SC
UPDATE.......SC
SHORT TERM...BT
LONG TERM....SF/DT
MARINE.......SF


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


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