000
FXUS63 KDTX 172018
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
418 PM EDT SAT MAY 17 2008
.SHORT TERM...THROUGH TONIGHT
LARGE UPPER LOW REMAINS TO OUR NORTH OVER CANADA...WITH SMALLER
UPPER SHORTWAVES ROTATING AROUND THE SYSTEM. COMPLICATED FORECAST
FOR THIS EVENING AS OVERNIGHT AS WE LOOK TO THREE MAIN PLAYERS AND A
LOT OF INSTABILITY TO DICTATE OUR WEATHER.
THE FIRST FEATURE OF INTEREST IS THE BOUNDARY THAT CURRENTLY EXTENDS
WEST TO EAST FROM NORTHERN LIVINGSTON COUNTY THROUGH SOUTHERN ST
CLAIR COUNTY. THIS HAS BEEN KICKING UP SHOWERS AND A FEW
THUNDERSTORMS THIS AFTERNOON. THREAT FROM THIS FIRST ROUND WILL BE
CONFINED TO ROUGHLY ALONG AND SOUTH OF M-59...WITH THE MAIN THREAT
BEING SMALL HAIL AND GUSTS TO 35 MPH (AS HAS ALREADY BEEN REPORTED).
FREEZING LEVEL FROM 6500-7000 FEET WILL MAKE SMALL HAIL A LIKELIHOOD
AS STORM UPDRAFTS REALLY WON`T NEED TO GET TOO STRONG FOR HAIL
GENERATION...SEVERE HAIL IS ALSO POSSIBLE WITH THE -20 C LAYER ONLY
AT AROUND 15000 FEET. DRY SUBCLOUD LAYER WILL ALSO KEEP A MARGINAL
THREAT FOR SEVERE WINDS AROUND THIS EVENING.
NEXT FOCUS FOR THUNDERSTORMS ARRIVES THIS EVENING (AFTER 21Z) AS A
WEAK SURFACE TROUGH OVER NORTHERN LAKE MICHIGAN MOVES DOWN AND EAST
ACROSS LOWER MICHIGAN. AIRMASS FROM M-59 SOUTHWARD HAS BEEN WORKED
OVER SOMEWHAT BY EARLIER CONVECTION...WHILE AREAS NORTH OF HERE SAW
A FAIR AMOUNT OF HEATING TODAY. NORTHERN AREAS WILL BE OF GREATER
CONCERN FOR SEVERE THREAT TONIGHT...WITH THE THREAT AGAIN BEING
LARGE HAIL AND STRONG WIND GUSTS. MOST THUNDERSTORMS SHOULD AT LEAST
BE CAPABLE OF PRODUCING WIND GUSTS TO 35 KNOTS AND SMALL HAIL.
SBCAPE VALUES FOR MBS (TEMP OF 67 AND TD OF 31) CURRENTLY RUNNING
AROUND 700 J/KG. THIS ROUND OF STORMS MAY BE A LITTLE STRONGER
INITIALLY (UNTIL WE LOSE HEATING)...ESPECIALLY WITH -27 C COLD POOL
MOVING IN ALOFT TO FURTHER STEEPEN LAPSE RATES.
FINALLY...WILL SEE ANOTHER COLD FRONT PUSH DOWN INTO CENTRAL LOWER
MICHIGAN AS ANOTHER SHORTWAVE TROUGH ROTATES DOWN AROUND THE MAIN
UPPER LOW AND ACROSS THE NORTHERN GREAT LAKES. INSTABILITY SHOULD BE
WANING AT THIS POINT...BUT A FEW RUMBLES OF THUNDER WILL STILL BE
POSSIBLE WITH GOOD LIFT/CONVERGENCE AHEAD OF THE FRONT AND STRONG
UPPER COLD POOL.
&&
.LONG TERM...SUNDAY THROUGH SATURDAY
SAME BASIC SCENARIO REMAINS IN PLAY TODAY. A MUCH COOLER AIRMASS
WILL FILTER INTO THE REGION FOR SUNDAY AS A MAJOR SHORTWAVE NORTH OF
THE GREAT LAKES DROPS SOUTHEAST THROUGH THE MEAN UPPER TROUGH...AND
PULLS A STRONG COLD FRONT THROUGH THE REGION. FORECAST HIGHS IN THE
50S STILL SEEM REASONABLE...WITH AREAS FROM THE SAGINAW VALLEY INTO
THE THUMB PROBABLY HOLDING IN THE LOWER 50S AS H85 TEMPERATURES ARE
FORECAST TO DROP TO AROUND -5C BY EVENING. SCATTERED SHOWERS WILL
REMAIN A POSSIBILITY WITH THIS FEATURE...AND WILL MAINTAIN SHOWER
CHANCES ON SUNDAY. WITH THE COLD FRONTAL PASSAGE SO EARLY...DO NOT
PLAN ON ADDING A MENTION OF THUNDER ATTM.
WITH COLD POOL PIVOTING THROUGH THE EASTERN GREAT LAKES ON SUNDAY
NIGHT...LINGERING SHOWERS MAY DOT AREAS MAINLY FROM THE THUMB ON
NORTHEAST INT LAKE HURON. ANY ACTIVITY WILL COME TO AN END OVER THE
REGION ON MONDAY AS A WEAK RIDGE OF HIGH PRESSURE BUILDS IN FROM THE
WEST IN ADVANCE OF THE NEXT APPROACHING SHORTWAVE. THIS WAVE WILL
RENEW THE CHANCE OF SHOWERS LATE MONDAY NIGHT INTO TUESDAY. WILL
MAKE A MINOR ADJUSTMENT TO HOLD OFF NO A MENTION OF LIGHT SHOWERS
UNTIL OVERNIGHT MONDAY NIGHT...BUT OTHERWISE MAINTAIN THE CURRENT
FORECAST.
DURING THE MONDAY/TUESDAY TIMEFRAME...TEMPERATURES WILL MODERATE
SOMEWHAT...RISING BACK INTO THE LOWER/MID 60S AS THE COLDEST POOL OF
AIR SLIDES OFF TO THE EAST AND WARM AIR ADVECTION ENSUES IN ADVANCE
OF THE AFOREMENTIONED SHORTWAVE. AS FOR LOW TEMPERATURES...AFTER A
CHILLY NIGHT SUNDAY NIGHT WITH LOWS GENERALLY IN THE UPPER 30S...THE
TEMPERATURES WILL EDGE BACK UP INTO THE LOWER/MID 40S.
IN BEHIND THIS SHORTWAVE...A REINFORCING SURGE OF COLD AIR WILL
TRUNCATE THIS MODERATING TREND. WILL HAVE TO ADJUST THE FORECAST
DOWNWARD SEVERAL DEGREES ON WEDNESDAY BACK INTO THE LOWER/MID 60S
(WITH 50S ALONG THE LAKE HURON SHORE). WILL ALSO ADD A MENTION OF
SHOWERS AS THIS DISTURBANCE TRACKS THROUGH THE AREA.
TO THE END FORECAST...WITH MAINTAIN THE IDEA OF A SLOW/STEADY TREND
TO MILDER WEATHER...BACK TO AROUND NORMAL ON DAY 7. MODELS CONTINUE
TO WAVER IN JUST HOW FAR EAST THE WESTERN RIDGE WILL BUILD DURING
THE LAST HALF THE THE WEEK. TRENDS TODAY ARE MOST DEFINITELY SLOWER
AS COMPARED TO 12Z MODEL RUNS YESTERDAY...SO HIGHS PREDOMINANTLY IN
THE 60S SOUNDS REASONABLE INTO FRIDAY...WITH PERHAPS A BREAK ABOVE
THE 70 DEGREE MARK BY SATURDAY. THIS IS STILL A FEW DEGREES BELOW
NORMAL FOR LATE MAY. MODELS ARE NOT EXACTLY BULLISH ON SHOWER AND
THUNDERSTORM CHANCES LATE IN THE WEEK...AND WILL PULL THE CHANCE OF
SHOWERS/THUNDERSTORMS THURSDAY/FRIDAY WITH GFS/ECWMF SHOWING A LARGE
SURFACE RIDGE BUILDING SOUTH THROUGH THE GREAT LAKES.
&&
.MARINE...
GALE WARNING FOR NORTHERN LAKE HURON HAS BEEN CANCELLED AS WIND
GUSTS HAVE FAILED TO MATERIALIZE...LIKELY DUE TO STABILIZING EFFECT
OF THE COOLER WATERS. ELSEWHERE SMALL CRAFT ADVISORIES REMAIN IN
EFFECT WITH WINDS GUSTING TO 25 KNOTS. STRONG WINDS WILL CONTINUE
ON NEARSHORE AREAS ON SUNDAY AS A TIGHT PRESSURE GRADIENT REMAINS
IN PLACE BETWEEN LOW PRESSURE OVER QUEBEC AND BUILDING HIGH
PRESSURE OVER THE UPPER MIDWEST.
&&
.PREV DISCUSSION...ISSUED 150 PM EDT SAT MAY 17 2008
AVIATION...
AREA OF CLOUDS HAS DEVELOPED FROM FNT SOUTHWARD IN ASSOCIATION
WITH A WEAK BOUNDARY MOVING SOUTHWARD ACROSS LOWER MICHIGAN.
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON
WITHIN THIS AREA OF CLOUDS...WITH IMPACTS BEING FELT AT
FNT...DTW...AND DET THROUGH 23Z. BEHIND THIS BOUNDARY AND AREA OF
CLOUDS...WILL SEE DECREASED CLOUD COVER AND DRY WEATHER UNDERNEATH
AN AREA OF SUBSIDENCE. THIS EVENING...AFTER 21Z...THE NEXT AREA OF
CLOUDS AND SHOWERS/THUNDERSTORMS CURRENTLY OVER LAKE MICHIGAN WILL
MOVE TOWARDS MBS AND THEN CONTINUE SOUTHWARD IF IT HOLDS TOGETHER.
THUNDERSTORMS TODAY MAY CONTAIN STRONG WIND GUSTS AND HAIL...WITH
SEVERE STORMS POSSIBLE. TOP END GUSTS COULD APPROACH 60 KNOTS.
ANOTHER COLD FRONT WILL ARRIVE DURING THE EARLY MORNING...BRINGING
ANOTHER CHANCE OF SHOWERS AND MVFR CEILINGS.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
HURON INCLUDING SAGINAW BAY...UNTIL 8 AM MONDAY.
LAKE ST CLAIR...
SMALL CRAFT ADVISORY...UNTIL 8 PM SUNDAY.
MI WATERS OF LAKE ERIE...
SMALL CRAFT ADVISORY...UNTIL 8 PM SUNDAY.
&&
$$
SHORT TERM...HLO
LONG TERM....99
MARINE.......HLO
AVIATION.....HLO
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
