313
FXUS63 KDTX 130739
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
339 AM EDT TUE AUG 13 2013
.SHORT TERM... TODAY AND TONIGHT
POST FRONTAL COLD ADVECTION WILL DOMINATE THE WEATHER IN SE MICHIGAN
TODAY. ALONG WITH THE IMPACT ON TEMPERATURES, THE MAIN CONSEQUENCE
WILL BE A SUBSTANTIAL INSTABILITY INDUCED CLOUD FIELD AND EVEN A FEW
LIGHT RAIN SHOWERS DURING THE PEAK OF AFTERNOON SURFACE HEATING. THE
NEW 00Z MODEL DATA HAS REASONABLY CAPTURED THE COLD AIR UPSTREAM
INDICATED BY UPPER AIR OBSERVATIONS. NORTHERN ONTARIO OBS SITES AT
MOOSONEE/CWZC AND PICKLE LAKE/CWPL INDICATE +1C AT 850MB AND -22C AT
500 MB RESPECTIVELY ILLUSTRATING THE MAGNITUDE OF THE COLD AIR. THE
MODELS PIVOT THE LOW AND MID LEVEL THERMAL TROUGH OVER LOWER
MICHIGAN DURING THE DAY BUT WITH SLIGHTLY LESS MAGNITUDE BY EVENING.
STILL, A -18C 500 MB TEMP WOULD BE A RECORD FOR THE DATE WITH 850 MB
TEMP NEAR -5C ONLY A COUPLE DEGREES SHY. IT IS NO SURPRISE THAT
MODEL SOUNDINGS INDICATE PLENTY OF INSTABILITY IN THE LOW LEVELS
WITH ENOUGH MOISTURE TO MAINTAIN CONSIDERABLE CLOUD COVER. IN
ADDITION, THERE IS GOOD POSITIVE AREA INDICATED DUE TO ENVIRONMENTAL
LAPSE RATE AVERAGING NEAR DRY ADIABATIC FROM CLOUD BASE TO EQL, GOOD
ENOUGH TO MAINTAIN THE CHANCE OF SHOWERS IN THE GOING FORECAST AS
MAX TEMPS ATTEMPT A RUN AT 70.
THE STRONG DIURNAL DEPENDENCY OF THE CLOUDS, ALONG WITH MORE NEUTRAL
LOW LEVEL FLOW, WILL RESULT IN A CLEARING TREND DURING THE EVENING.
POCKETS OF STRATOCU WILL REMAIN POSSIBLE, ESPECIALLY IN THE THUMB
REGION OFF OF LAKE HURON, BUT COVERAGE SHOULD BE LOW ENOUGH FOR
MOSTLY CLEAR SKY OVER INTERIOR SECTIONS OF THE AREA. LINGERING
GRADIENT WIND WILL PREVENT IDEAL RADIATIONAL COOLING AND MAKES
GUIDANCE TEMPS IN THE MID TO UPPER 40S LOOK REASONABLE WITH LOWER
50S IN THE DETROIT METRO AREA. RECORD LOWS FOR WEDNESDAY MORNING
ARE: DTW 48/1964, FNT 41/1964, MBS 44/1964.
&&
.LONG TERM...WEDNESDAY THROUGH NEXT MONDAY
BROAD AND DEEP LONGWAVE TROUGH WILL CONTINUE TO SIT OVER THE GREAT
LAKES THROUGH THE WEEKEND ALTHOUGH IT WILL UNDERGO SOME
MODIFICATION. THE STRONG SHORTWAVE OVER SOUTHERN ONTARIO/QUEBEC WILL
LIFT NE AWAY FROM SE MI ON WEDNESDAY TAKING WITH IT THE UNSEASONABLY
COLD MID LEVEL COLD POOL AND BEST UPPER LEVEL DYNAMICS. WITH THE
SHIFT NE...THE NEXT SHORTWAVE TO ROTATE THROUGH THE TROUGH WILL STAY
OVER CANADA AVOIDING SOUTHERN MI FOR THE FIRST TIME IN A WHILE. AS A
RESULT OF THE SHORTWAVE LIFTING OUT OF THE AREA...HEIGHTS WILL
SLOWLY RISE THROUGH THE WEEK. ALTHOUGH THE PATTERN WOULD SUGGEST THE
AMPLIFIED WEST COAST RIDGE WOULD SLIDE EAST BEHIND THE DEPARTING
WAVE...A WEAK SHORTWAVE DIVING INTO THE BASE OF THE TROUGH LOOKS TO
DEVELOP A CUTOFF LOW OVER THE MID MISSISSIPPI VALLEY FRIDAY. WITH
THE FLOW OVER THE CONUS NEGLIGIBLE (LONGWAVE PATTERN TRENDING ZONAL
ACROSS CANADA) AND THE BERMUDA HIGH HOLDING FIRM OFF THE EAST
COAST...THIS LOW WILL EVER SO SLOWLY DRIFT THROUGH THE OHIO VALLEY.
DOWN AT THE SFC...HIGH PRESSURE WILL DROP OVER THE GREAT LAKES FROM
CANADA AND WILL PERSIST THROUGHOUT THE EXTENDED PERIOD. INITIALLY ON
WEDNESDAY WE WILL BE ON THE EASTERN PERIPHERY WHICH WILL PRODUCE
N/NW FLOW OVER THE AREA. WITH THE MID LEVEL COLD POOL STILL OVER THE
EASTERN GREAT LAKES AND 850 MB TEMPS IN THE MID SINGLE DIGITS...LOOK
FOR ANOTHER CHILLY DAY WITH TEMPS STRUGGLING TO TOUCH 70 FOR MOST
LOCATIONS. IN ADDITION...THE COLD AIR AND FAVORABLE FETCH WILL LEAD
TO A SLIGHT CHANCE OF PRECIP OVER LAKE HURON DUE TO THE RELATIVELY
WARM WATER. THE NW FLOW SHOULD KEEP THE RAIN OFF SHORE BUT MAY
INITIALLY COME CLOSE TO THE EASTERN THUMB. THAT IS THE MOST
EXCITEMENT WE WILL DEAL WITH FOR THE NEXT SEVERAL DAYS. THE SFC HIGH
WILL DRIFT OVER MI AND THEN TO THE EAST THROUGH THE WEEKEND. WITH
1000-500MB HEIGHTS ON THE RISE AND A DRY AIRMASS...LOOK FOR MOSTLY
CLEAR/SUNNY SKIES AND A GRADUAL WARMING TREND. BY THE END OF THE
WEEKEND OR EARLY NEXT WEEK...WE WILL FALL UNDER THE WESTERN EDGE OF
THE HIGH WHICH WILL LEAD TO SOUTHWESTERLY FLOW AND WAA. THIS SHOULD
BRING US BACK TO NORMAL FOR TEMPS TO START THE NEXT WEEK.
&&
.MARINE...
SMALL CRAFT ADVISORIES REMAIN IN EFFECT TODAY AND TONIGHT AS COOL
NORTHERLY WIND OF MODERATE INTENSITY WILL PRODUCE ROUGH MARINE
CONDITIONS, ESPECIALLY OVER THE SOUTH HALF OF LAKE HURON. IN
ADDITION TO GUSTY WIND AND HIGH WAVES, THE COOL AIR FLOWING OVER THE
WARM WATER WILL INCREASE POTENTIAL FOR WATERSPOUT FORMATION. MODEL
SOUNDINGS OVER THE OPEN WATERS OF SOUTHERN LAKE HURON INDICATE
STRONG CLOUD BASE ACCELERATION WITH LAKE TO 850 MB DELTA-T AROUND
15C AND CLOUD DEPTH OF AROUND 7500 FEET. THESE ARE ENTRY LEVEL
PARAMETERS THAT SUGGEST POTENTIAL WORTHY OF A CHANCE MENTION IN THE
FORECAST MAINLY FOR TONIGHT. SURFACE HIGH PRESSURE WILL THEN BUILD
MORE FULLY OVER THE LAKES BY WEDNESDAY WITH LIGHTER WIND AND
IMPROVED WAVE CONDITIONS THROUGH THE END OF THE WEEK AND INTO THE
WEEKEND.
&&
.AVIATION...ISSUED 1203 AM EDT TUE AUG 13 2013
//DISCUSSION...
WITH SHRAS/TSRAS SHIFTING SOUTHEAST OF THE AREA...ATTENTION TURNS TO
MVFR STRATUS AND/OR FOG OVERNIGHT IN WAKE OF PASSING COLD FRONT.
LATEST OBS INDICATE PATCHY DEVELOPMENT JUST PRIOR TO THE FRONTAL
PASSAGE. WILL ADJUST 06Z TERMINALS AS SUCH...WITH GENERALLY VFR
CONDITIONS LATER AND JUST A TEMPO PERIOD FOR ANY PATCHY LOW
CEILINGS. HIGH PRESSURE WILL BRING GRADUALLY CLEARING SKIES LATER
TODAY WITH CIGS INITIALLY LIFTING AND THEN CLEARING OUT
ALTOGETHER BY THE END OF THE FORECAST PERIOD.
FOR DTW...THERE STILL MAY BE A PERIOD OF SUB 4000 FOOT CIGS LATE
TONIGHT THROUGH THE MORNING WITH PATCHY FOG AS WELL...BUT TRENDS
SUGGEST ANY LOWER CIGS IN THE WAKE OF THE COLD FRONT WILL BE SHORT
LIVED.
//DTW THRESHOLD THREATS...
* MEDIUM CONFIDENCE IN CEILING BELOW 5000 FT TONIGHT.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
HURON INCLUDING OUTER SAGINAW BAY...UNTIL 4 AM WEDNESDAY.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
SHORT TERM...BT
LONG TERM....DRK
MARINE.......BT
AVIATION.....DG
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).