Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 192302
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
702 PM EDT FRI SEP 19 2014


.AVIATION...

//DISCUSSION...

A SOUTHERLY SURFACE GRADIENT WILL INCREASE DURING THE NIGHT WITH THE
APPROACH OF THE FRONTAL SYSTEM NOW MOVING INTO THE UPPER MIDWEST.
WINDS WILL WEAKEN AND MAINTAIN A SE COMPONENT THIS EVENING WITH THE
ONSET OF NIGHTTIME COOLING. AS THE GRADIENT STRENGTHENS OVERNIGHT
INTO FRI MORNING...WINDS WILL VEER TOWARD THE SOUTH AND INCREASE.
DAYTIME HEATING WILL FURTHER INCREASE THE WINDS BY LATE FRI
MORNING...CAUSING GUSTS TO EXCEED 20 KNOTS AT TIMES.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE IN THUNDERSTORM POTENTIAL FRIDAY AFTERNOON AND
FRIDAY NIGHT.

&&

.PREV DISCUSSION...ISSUED 342 PM EDT FRI SEP 19 2014

SHORT TERM...THIS AFTERNOON AND TONIGHT

VERY PLEASANT WEATHER WILL HOLD THROUGH THE EVENING AS TEMPERATURES
GRADUALLY DROP THROUGH THE 60S AS WE APPROACH SUNSET. THESE MILD
TEMPERATURES WILL PERSIST OVERNIGHT AS THETA-E RIDGE IN ADVANCE OF
APPROACH SHORTWAVE OVERSPREADS THE AREA. WITH THIS INCREASE IN
MOISTURE AND OVERALL CLOUD COVER...RADIATIONAL COOLING POTENTIAL WILL
BE GREATLY REDUCED. COMBINE THIS WITH STEADY WARM AIR ADVECTION AS
SOUTHWEST FLOW INCREASING AFTER MIDNIGHT AND LOW TEMPERATURES WILL
LIKELY HOLD IN THE 50S IN MOST...IF NOT ALL...LOCATIONS.

WHILE SHOWER POTENTIAL WILL BE RATHER MEAGER DURING THE PRE-12Z TIME
FRAME...WILL MAINTAIN A SLIGHT CHANCE FOR THE FAR NORTH TO NORTHWEST
CWA AS MOISTURE/LIFT GRADUALLY INCREASE WITH THE APPROACH OF THE
AFOREMENTIONED TROUGHING.

LONG TERM...

UPPER AIR PATTERN WILL CONTINUE TO AMPLIFY SATURDAY THANKS TO A
130KT JET STREAK DIGGING INTO THE MN/DAKOTAS REGION. COLUMN MOISTURE
WILL INCREASE MARKEDLY AS THE MOISTURE PLUME NOW EXTENDING INTO THE
NORTHERN PLAINS/SOUTHERN CANADA FOLDS EASTWARD. PWATS WILL INCREASE
TO 1.5-1.75 IN...NEAR +2SD FOR SEPTEMBER. LARGE SCALE FORCING FOR
ASCENT WILL INCREASE DURING THE DAY AS BETTER HEIGHT FALLS APPROACH
THE REGION. ADDITONALLY...ANOTHER JET STREAK DOWNSTREAM OF THE
TROUGH AXIS WILL STRENGTHEN DURING THE DAY...WITH ASSOCIATED RIGHT
ENTRANCE REGION FORCING TRANSLATING THROUGH THE AREA. THIS SETUP
SHOULD SUPPORT SHOWERS INCREASING TO SCATTERED TO NUMEROUS COVERAGE
BY THE AFTERNOON.

H5 WINDS OF AROUND 50 KT WILL SUPPORT BULK SHEAR VALUES AROUND 40
KT...MORE THAN ENOUGH TO WORRY ABOUT ORGANIZED CONVECTION AND SEVERE
WEATHER. LOW LEVEL JET WILL ALSO PEAK AROUND 30-40 KT DURING THE
AFTERNOON. LIMITING FACTOR TO SEVERE WEATHER...AND THUNDERSTORMS IN
GENERAL...IS INSTABILITY. A GOOD COVERAGE OF CLOUDS IS
EXPECTED...WHICH WILL DIMINISH MIXING DEPTHS AND MUTE THE SURFACE
TEMPERATURE RESPONSE DESPITE 925 MB TEMPS REACHING THE UPPER TEENS.
LOW-LEVEL CAPPING BECOMES A CONCERN AS WELL. MIDLEVEL LAPSE RATES
INCREASE SOMEWHAT...BUT ARE NOT TERRIBLY IMPRESSIVE AT AROUND 6.5
K/KM. ANOTHER LIMITING FACTOR FOR DEEP CONVECTION WILL BE THE LACK
OF ANY WELL-DEFINED BOUNDARY/SURFACE CONVERGENCE...AS THE MAIN COLD
FRONT WITH THIS SYSTEM WILL LAG BACK OVER NORTHERN LOWER MI/WI. WITH
SURFACE TEMPS IN THE 75-80F RANGE...AND DEWPOINTS INCREASING INTO
THE LOWER/MID-60S...AND THE AFOREMENTIONED LIMITING FACTORS...IT
LOOKS LIKE WE WILL STAY IN THE 500-750 J/KG MLCAPE RANGE. CANNOT
RULE OUT A FEW STORMS APPROACHING SEVERE LIMITS GIVEN THE SHEAR
EXPECTED...BUT WIDESPREAD SEVERE EVENT APPEARS UNLIKELY.

MAINTAINED CHANCE POPS SATURDAY NIGHT AS MOISTURE LINGERS AND
FORCING ASSOCIATED WITH THE INBOUND NOSE OF THE UPPER JET AND
IMPRESSIVE PV ANOMALY INCREASES LATE. RAISED POPS SUNDAY TO LIKELY AS THE
CORE OF THE MIDLEVEL COLD POOL /-21C AT H5/ MIGRATES OVER THE LOCAL
AREA DURING PEAK HEATING. AREA BUFR SOUNDINGS INDICATE UNCAPPED
PROFILES DEVELOPING WITH MLCAPE VALUES IN THE 500-1000 J/KG RANGE.
THIS SHOULD AGAIN SUPPORT THE DEVELOPMENT OF SCATTERED TO NUMEROUS
SHOWERS AND A FEW THUNDERSTORMS...WITH SOME SMALL HAIL POSSIBLE IN
THE MORE VIGOROUS UPDRAFTS GIVEN FREEZING LEVELS DROPPING TO AROUND
8KFT. MODELS DIFFER WITH HOW AGGRESSIVELY THE ANTICYCLONE BUILDS
INTO THE UPPER MIDWEST IN THE WAKE OF THIS SYSTEM SUNDAY NIGHT...BUT
PRECIPITATION SHOULD BE ON THE WANE SUNDAY EVENING WITH THE LOSS OF
DAYTIME HEATING.

THE WORK WEEK WILL START OFF QUITE COOL WITH LOW THETA E VALUES
INDICATING A COOL AND DRY AIRMASS. SURFACE HIGH PRESSURE WILL SLIDE
EAST...HELPING RETURN FLOW START TO WARM THE COLUMN BOTH TUES AND
WED. THIS WILL BRING NORMAL TEMPERATURE VALUES BACK TO THE AREA.
FLOW REMAINS RATHER WEAK...AND WE BECOME QUITE STAGNANT ALOFT BY THE
END OF THE PERIOD. THE LACK OF ANY UPPER WAVES OR MOISTURE ADVECTION
WILL KEEP A DRY FORECAST INTACT FOR THE EXTENDED FORECAST PERIOD.

MARINE...

SOUTHWEST FLOW WILL CONTINUE TO INCREASE TONIGHT INTO SATURDAY.
DESPITE THE WARM AIR WITH THIS SYSTEM...GUSTY WINDS WILL DEVELOP
GIVEN THE STRENGTH OF THE WIND FIELD AT LOW LEVELS OF THE
ATMOSPHERE. SHOWERS AND THUNDERSTORMS WILL ACCOMPANY THE WARMER AIR
SATURDAY AND SATURDAY NIGHT...WITH ADDITIONAL ACTIVITY EXPECTED
DURING THE DAY SUNDAY AS UPPER LEVELS COOL AND UNSTABLE CONDITIONS
DEVELOP. SOME SHOWERS MAY LINGER INTO SUNDAY NIGHT ALONG WITH A
RENEWED INCREASE IN WINDS BEFORE HIGH PRESSURE EXERTS MORE OF AN
INFLUENCE ON THE WATERS TO BEGIN NEXT WEEK.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...SAGINAW BAY AND THE NEARSHORE WATERS FROM
     PORT AUSTIN TO HARBOR BEACH...FROM 2 AM SATURDAY TO 8 PM
     SATURDAY.

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

&&

$$

AVIATION.....SC
SHORT TERM...DG
LONG TERM....DT/MM
MARINE.......DT


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