Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 202249
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
649 PM EDT WED MAY 20 2015


.AVIATION...

THE LARGE REGION OF RADAR RETURNS NOW ADVANCING INTO SW LOWER MI IS
ASSOCIATED WITH AN UPPER LEVEL SHORT WAVE. THIS SYSTEM WILL ROTATE
ACROSS SE MI LATE THIS EVENING INTO THE OVERNIGHT. VERY DRY LOW
LEVEL AIR WILL KEEP THE BULK OF THESE RETURNS VIRGA AND/OR LIGHT
RAIN....MAINLY SOUTH OF FNT. CEILINGS WILL SLOWLY LOWER DURING THE
NIGHT AS THIS SYSTEM TRACKS THROUGH THE REGION. GIVEN THE DEGREE
OF LOW LEVEL DRY AIR...CIG HEIGHTS ARE EXPECTED TO REMAIN VFR.

FOR DTW...THE EXTENT OF RADAR RETURNS UPSTREAM WILL SUPPORT THE
INCLUSION OF SOME LIGHT RAIN IN THE TAF. THE STRONGEST FORCING WILL
ARRIVE AFTER 02Z AND END SHORTLY AFTER 06Z. RAPID COOLING OF THE SUB
CLOUD LAYER WITHIN THE RAIN/VIRGA WILL PROVIDE A CHANCE FOR PERIODIC
CEILINGS DROPPING BELOW 5K FT TONIGHT.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN CEILINGS DROPPING BELOW 5000 FT LATE THIS EVENING AND
  OVERNIGHT.

&&

.PREV DISCUSSION...ISSUED 336 PM EDT WED MAY 20 2015

SHORT TERM...TONIGHT

SHORTWAVE TROUGH LIFTING ACROSS THE UPPER MS VALLEY THIS AFTERNOON
IS DRIVING EXTENSIVE MID-LEVEL COVER INTO THE AREA WITH OVERCAST
CONDITIONS EXPECTED AREAWIDE SHORTLY. ABUNDANCE OF DRY AIR IN THE
LOWER ATMOSPHERE IS PRODUCING WIDESPREAD VIRGA UPSTREAM. ORGANIZED,
BUT SHALLOW, CORRIDOR OF MID-LEVEL FGEN FOCUSED AROUND 700MB ALONG
THE LEAD EDGE OF THE IMPINGING THETA-E GRADIENT HAS SUSTAINED AN
AREA OF HIGHER INTENSITY SHOWERS NORTH OF CHICAGO FOR SEVERAL HOURS
NOW. THIS BAND OF FORCING WILL TRANSIT THE SOUTHERN THIRD OF THE CWA
03-06Z. WITH PLENTY OF DRY AIR IN THE LOWEST 6KFT, MEASURING
POTENTIAL WILL LARGELY DEPEND ON HOW WELL SHOWERY NATURE OF PRECIP
IS MAINTAINED AS THE WAVE WRAPS INTO THE WESTERN GREAT LAKES TONIGHT.

SATELLITE TRENDS AND MODEL PROGS SUGGEST DECENT CLEARING POTENTIAL
EXISTS POST-06Z AS THE BATCH OF MID-CLOUD DEPARTS EAST AND THE LOWER
LEVEL MOISTURE AXIS REMAINS LARGELY TO THE SOUTH. A BRIEF PERIOD OF
POTENTIALLY FAVORABLE RADIATING CONDITIONS COULD DEVELOP,
PARTICULARLY GIVEN WIDESPREAD DEWPOINTS THIS AFTERNOON IN THE LOW
20S NORTH OF I-69. HOWEVER, THIS PERIOD WILL COINCIDE WITH A
GRADUALLY INCREASING PRESSURE GRADIENT AHEAD OF A COLD FRONT THAT
WILL BE POSITIONED ACROSS LAKE SUPERIOR BY SUNRISE. THUS, EVEN IF
RADIATING OVERACHIEVES AND TEMPERATURES FALL INTO THE LOWER/MID 30S,
SUSPECT GRADIENT WILL BE SUFFICIENT TO INHIBIT FROST FORMATION.
FURTHER NEGATIVE CONTRIBUTIONS TO FROST POTENTIAL INCLUDE RECENT
GREENUP AND GROUND TEMPERATURES STILL IN THE 50S. LEFT MENTION OF
PATCHY FROST ACROSS THE EASTERN THUMB WHERE GRADIENT WILL REMAIN
WEAKEST THROUGH SUNRISE.

LONG TERM...THURSDAY THROUGH NEXT TUESDAY

CONDITIONS WILL REMAIN DRY THROUGH THE DAY ON THURSDAY WITH HIGHS
STARTING TO REBOUND BACK INTO THE MIDDLE TO UPPER 60S.  WEAK HIGH
PRESSURE WILL SLOWLY BE REPLACED BY UPPER LEVEL TROUGHING THAT WILL
BE SWINGING DOWN ACROSS THE GREAT LAKES REGION LATER THURSDAY AND
INTO THE OVERNIGHT HOURS.  AN ASSOCIATED COLD FRONT WILL ALSO BE IN
THE PROCESS OF TRANSVERSING ACROSS THE AREA THURSDAY NIGHT.  LATEST
CROSS SECTIONS SHOW SHALLOW FORCING IN THE LOWEST LEVELS WITH THE
FRONTAL PASSAGE WHILE KEEPING PRECIPITATION CONFINED TO MAINLY THE
SOUTHERN TWO THIRDS OF THE CWA.  POPS WERE LOWERED TO TAKE INTO
ACCOUNT THE WEAKER FORCING AND LACK OF MOISTURE.  BEST CHANCES TO
SEE SOME RAIN SHOWERS WILL MAINLY FALL IN THE 03Z TO 09Z FRIDAY TIME
WINDOW.  THE FRONT THEN QUICKLY EXITS FRIDAY MORNING BRINGING YET
ANOTHER DRY DAY.  WINDS WITH THE FRONT WILL INCREASE BEHIND THE
FRONTAL PASSAGE AS WINDS SHIFT FROM THE SOUTHWEST TO NORTHWEST BY
FRIDAY.  WITH THE NORTHWEST FLOW ON FRIDAY...HIGHS ONLY LOOK TO REACH
INTO THE UPPER 50S ACROSS THE THUMB AREA INTO THE MIDDLE 60S SOUTH.

REMAINDER OF THE FORECAST WILL BE A TRANSITION FROM DRY WEATHER
UNDER A LARGE SURFACE ANTICYCLONE SATURDAY TO A WARMER AND MORE
UNSETTLED PERIOD SUNDAY INTO EARLY NEXT WEEK. HEIGHT RISES ARE
FORECAST TO OCCUR LOCALLY AS A LARGE UPPER TROUGH MOVES EASTWARD OUT
OF THE WESTERN US. WARM...MOIST ADVECTION INTO THE GREAT LAKES WILL
ACCOMPANY THIS PROCESS WITH A NICE FEED OF GULF MOISTURE BOOSTING
PWAT VALUES TO AOA 1.5 INCHES BY SUNDAY NIGHT /PER 12Z GFS/. TIMING
OF INDIVIDUAL ROUNDS OF PRECIP IS UNCERTAIN AT THIS POINT BUT THE
BEST CHANCES LOOK TO FOCUS AROUND THE SUNDAY NIGHT/MONDAY TIMEFRAME
DURING THE PASSAGE OF THE LOW-LEVEL WARM FRONT.

MARINE...

QUIET CONDITIONS WILL HOLD THROUGH TONIGHT AND INTO THURSDAY BEFORE
A COLD FRONT MOVES THROUGH THE REGION OVERNIGHT ON THURSDAY.
SOUTHWESTERLY WINDS ON THURSDAY WILL SWITCH TO THE NORTHWEST
THURSDAY NIGHT AS THE FRONT SLIDES THROUGH.  WINDS THEN CALM BACK
DOWN ON FRIDAY WITH QUIET WEATHER CONDITIONS RETURNING TO THE GREAT
LAKES REGION THROUGH THE MAJORITY OF THE WEEKEND.

&&

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

$$

AVIATION.....SC
SHORT TERM...JVC
LONG TERM....SS/DT
MARINE.......SS


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


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