Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221704
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
104 PM EDT TUE JUL 22 2014


.AVIATION...

//DISCUSSION...

DEEPENING MIXED LAYER WILL CONTRIBUTE TO SOUTHWEST WIND GUSTS AROUND
20 KNOTS THIS AFTERNOON. WARM AIR ALOFT WILL CAP THUNDERSTORM
POTENTIAL THROUGH THE EARLY EVENING. HOWEVER, AN INCREASE IN
MID-LEVEL MOISTURE WILL CONTRIBUTE TO AN INCREASING PROBABILITY OF
THUNDERSTORMS BETWEEN ABOUT 03Z AND 09Z. FOR NOW, CONFIDENCE
CONTINUES TO WARRANT NOTHING MORE THAN A PROB30. COLD ADVECTION AND
LINGERING LOW-LEVEL MOISTURE IN THE WAKE OF THE FRONT IS EXPECTED TO
CONTRIBUTE TO AN MVFR LAYER OF STRATUS BY DAYBREAK WEDNESDAY...WITH
CIGS THEN FORECAST TO MIX UP TO VFR DURING THE MORNING.

FOR DTW...THE BEST CHANCE FOR THUNDERSTORMS WILL BE AFTER 05Z. THE
COLD FRONT WILL EXIT THE AREA BY 09Z WITH NORTHERLY WINDS FILLING IN
BEHIND.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE THAT A THUNDERSTORM WILL IMPACT KDTW

* MEDIUM CONFIDENCE IN CEILINGS BELOW 5KFT WEDNESDAY MORNING

&&

.PREV DISCUSSION...ISSUED 337 AM EDT TUE JUL 22 2014

SHORT TERM...TODAY AND TONIGHT

A CONVECTIVELY ENHANCED MID LEVEL WAVE OVER NRN MN IS SHOWING UP
NICELY ON THE SATELLITE/RADAR COMPOSITE. THIS WAVE WILL RACE EAST
ACROSS LAKE SUPERIOR TODAY...WITH THE ASSOCIATED SFC LOW TRACKING
EAST AS WELL. THIS SYSTEM WILL DRIVE AN ASSOCIATED COLD FRONT INTO
NRN LOWER MI THIS EVENING...THEN ACROSS SE MI LATE TONIGHT.

THE ATMOSPHERE REMAINS STRONGLY CAPPED FROM SRN MN ACROSS IOWA
COURTESY OF AN EML. AN EXTENSION OF THIS EML WILL SLIDE INTO LOWER
MI THIS AFTERNOON AND WILL ACT TO FURTHER STRENGTHEN THE CAPPING
INVERSION ALREADY PRESENT OVER SE MI /PER 00Z DTX RAOB/. THIS CAP
WILL HOLD THROUGH THE AFTERNOON AND SHOULD SUPPRESS CONVECTION OVER
SE MI THROUGH AT LEAST 00Z THIS EVENING. STRENGTHENING S-SW FLOW IN
ADVANCE OF THE FRONT WILL LEAD TO LOW LEVEL WARM AIR ADVECTION INTO
SE MI...WITH 850MB TEMPS FORECAST TO RISE TO +20C. MODEL SOUNDINGS
SUGGEST THE BOUNDARY LAYER WILL BECOME WELL MIXED THIS AFTERNOON
WHICH WILL RESULT IN HIGH TEMPS INTO THE UPPER 80S/LOW 90S. THE 00Z
MODEL INITIALIZATIONS SHOW AN AXIS OF LOWER DEWPOINTS FROM THE SFC
TO 850MB EXTENDING FROM ARKANSAS UP THROUGH NE ILLINOIS...AND ARE
SUPPORTED BY AVAILABLE SFC OBS AND 00Z RAOBS. THESE LOWER DEWPOINTS
WILL ADVECT INTO SE MI DURING PEAK AFTERNOON HEATING AND WILL RESULT
IN A DROP IN DEWPOINTS IN THE AFTERNOON. THIS WILL CUT BACK ON THE
HUMIDITY AND THUS KEEP HEAT INDICES CLOSE TO ACTUAL AIR TEMPS.

A DEEPENING OF THE LONGER WAVELENGTH TROUGH OVER NRN ONTARIO AND
QUEBEC TONIGHT WILL LOWER MID LEVEL HEIGHTS OVER SE MI AND WILL
ERODE THE CAPPING INVERSION. THIS WILL OCCUR AS THE COLD FRONT
ADVANCES THROUGH THE FORECAST AREA BETWEEN 03Z AND 09Z. A NARROW
AXIS OF HIGH LOW LEVEL MOISTURE WILL ACCOMPANY THE SFC
FRONT...LEADING TO 0-3KM MU CAPE OF 1K TO 1500 J/KG. CONVECTIVE
INITIATION WILL BE TIED TOWARD THE INCREASED BOUNDARY LAYER
CONVERGENCE AHEAD OF THE FRONT OR WITHIN ANY PRE FRONTAL TROUGHING.
WITH SOME UNCERTAINTY AS TO HOW QUICKLY THE EROSION OF THE MID LEVEL
CAP WILL OCCUR AND WITH WEAK LARGER SCALE DYNAMIC FORCING...NOTHING
HIGHER THAN CHANCE POPS TONIGHT SEEMS JUSTIFIED AT THIS TIME. WITH
0-6KM SHEAR ON THE ORDER OF 30 KNOTS AND GOOD CAPE DENSITY SHOWN ON
MODEL SOUNDINGS...CAN NOT RULE OUT AN ISOLATED SEVERE STORM TONIGHT
/WITH DAMAGING WIND AND HAIL BEING THE BIGGEST CONCERN/. THE BETTER
SEVERE POTENTIAL WILL BE SOUTHWEST OF THE AREA /IN THE REGION
OUTLINED IN THE SPC DAY 1 SLIGHT RISK/ WHERE INSTABILITY WILL BE
MUCH HIGHER.

LONG TERM...

THE WEATHER THROUGH THE END OF THE WEEK WILL BE DOMINATED BY A
STABLE CANADIAN HIGH PRESSURE SYSTEM. TEMPERATURES WEDNESDAY WILL BE
APPROXIMATELY 12 TO 15 DEGREES COOLER THAN TUESDAY...READINGS
RUNNING 4 TO 8 DEGREES COOLER THAN AVERAGE. DAYTIME TEMPERATURES ON
THURSDAY SHOULD BE EVEN COOLER...WORKING OFF A CHILLY START WITH
AFTERNOON VALUES STRUGGLING TO REACH THE MIDDLE 70S IN MANY
LOCATIONS.

WEDNESDAY...LATEST GUIDANCE CONTINUES TO ADVERTISE THE MAIN SURFACE
COLD FRONT SLIPPING ACROSS THE MICHIGAN/OHIO STATELINE SHORTLY AFTER
12Z. THE H85 EXTENSION IS SHOWN TO LAG BACK SLIGHTLY NORTH...BUT
EVEN THE MIDLEVEL FRONT DEPICTED TO EXIT THE CWA BY 15Z. AN
EFFICIENT NORTHERLY FLOW TRAJECTORY SHOULD SCOUR OUT NEAR SURFACE
THETA E FAIRLY QUICKLY. THROW IN DIURNAL MIXING PROCESSES AND
DEWPOINTS WILL DROP RAPIDLY INTO THE 50S. AS A RESULT OF THE LOWER
HEAT CAPACITY OF THE DRY AIR...LOWERED TEMPS A COUPLE OF DEGREES
ACROSS THE BOARD. THE SHORELINE AREAS NEAR LAKE HURON SHOULD BE
ESPECIALLY CHILLY...FACTORING NORTH WINDS OF 20 TO 25 MPH.

THURSDAY...VERY STEEP LAPSE RATES IN THE H7-H8 LAYER WILL LEAD TO AN
ACTIVE CUMULUS RESPONSE BY MIDDAY. VERY HIGH MIXING HEIGHTS OF UP TO
6000 FT AGL...WILL EAT INTO CONVECTIVE DEPTHS AND LEAD TO LEGITIMATE
POTENTIAL FOR PRECIPITATION.

MARINE...

THE MAIN ISSUE OF THE MARINE FORECAST IS THE STRONG SURGE OF
NORTHERLY WINDS THAT WILL IMMEDIATELY FOLLOW THE COLD FRONT SET TO
DROP ACROSS LAKE HURON. THE FRONT IS EXPECTED TO EMERGE OVER THE
STRAITS REGION VERY EARLY THIS EVENING...EXITING THE FAR SOUTHERN
LAKE HURON BASIN PRIOR TO DAYBREAK WEDNESDAY. A TIGHT PRESSURE
GRADIENT WILL THEN PERSIST OUT OVER LAKE HURON THROUGHOUT THE DAY.
WINDS OF UP TO 30 KNOTS WILL BE POSSIBLE TONIGHT THROUGH WEDNESDAY
AFTERNOON ALONG WITH WAVE HEIGHTS IN THE 3 TO 5 OR 4 TO 6 FOOT
RANGE. SMALL CRAFT ADVISORIES WILL EVENTUALLY BE NEEDED FOR THE
NEARSHORE WATERS OF LAKE HURON FROM PORT AUSTIN TO PORT
HURON...INCLUDING OUTER SAGINAW BAY. A RETURN TO MORE FAVORABLE
BOATING CONDITIONS WILL OCCUR THURSDAY AND FRIDAY AS A LARGE SURFACE
HIGH PRESSURE SYSTEM DOMINATES THE REGION.

&&

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

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
     HURON INCLUDING OUTER SAGINAW BAY...FROM 5 AM WEDNESDAY TO 10
     PM WEDNESDAY.

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

&&

$$

AVIATION.....JVC
SHORT TERM...SC
LONG TERM....CB
MARINE.......CB


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






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