Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 300353
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1153 PM EDT WED JUL 29 2015


.AVIATION...

ONGOING DRY AIR ADVECTION UNDER LIGHT W-SW WINDS WILL SUSTAIN CLEAR
SKIES THROUGH DAYBREAK. GROWTH OF THE BOUNDARY LAYER DUE TO DAYTIME
HEATING ON THURS WILL CAUSE A STEADY INCREASE IN WESTERLY WIND
SPEEDS LATE THURS MORNING INTO EARLY AFTERNOON. GIVEN EXPECTED
MIXING DEPTHS FREQUENT GUSTS OVER 20 KNOTS ARE EXPECTED.

//DTW THRESHOLD PROBABILITIES...

* LOW IN WESTERLY WIND GUSTS EXCEEDING CROSSWIND THRESHOLDS THURSDAY
  AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 338 PM EDT WED JUL 29 2015

SHORT TERM...THROUGH TONIGHT

LINE OF SHOWERS AND THUNDERSTORMS WILL CONTINUE TO MOVE ACROSS
SOUTHEAST MICHIGAN AS THE COLD FRONT PROGRESSES EAST. JUICY AIRMASS
AHEAD OF THE FRONT...TEMPS IN THE UPPER 80S/NEAR 90 AND DEWPOINTS IN
THE LOW 70S...WILL CONTINUE TO PROVIDE FUEL FOR STORMS...BUT
STRENGTH AND ORGANIZATION WILL REMAIN LIMITED BY MID-LEVEL LAPSE
RATES NEAR 6 C/KM AND WEAKER SHEAR VALUES. A FEW STRONGER WIND GUSTS
TO 50 MPH ARE POSSIBLE WITH THE STRONGER STORMS. A BRIEF PERIOD OF
VERY HEAVY RAINFALL IS LIKELY...AND COULD LEAD TO PONDING ON AREA
ROADWAYS OR FLOOD-PRONE AREAS.

BEHIND THE FRONT...DEWPOINTS HAVE BEEN QUICKLY DROPPING INTO THE
LOW/MID 50S. THIS WILL PUT A QUICK END TO SHOWER/TSTORM
THREAT...ENDING FOR ALL BUT THE FAR EAST PORTION OF THE AREA BY 6
PM...AND COMBINED WITH SLIGHTLY COOLER TEMPS WILL PROVIDE MORE
COMFORTABLE CONDITIONS (LOWER HEAT INDICES) FOR THIS EVENING AND
TONIGHT. THIS IS DESPITE ACTUAL MIN TEMPS ONLY EXPECTED TO RUN 3-5
DEGREES COOLER THAN LAST NIGHT...WITH READINGS IN THE 60S FORECAST.

LONG TERM...

EXPANSION OF THE SUBTROPICAL RIDGE INTO THE GREAT BASIN AND
EVENTUALLY THE PACIFIC NORTHWEST AS THE IMPRESSIVE OCCLUDED LOW OVER
FAR NW ONTARIO SETS UP OVER HUDSON BAY WILL USHER IN A PERIOD OF LOW
AMPLITUDE NORTHWEST FLOW THROUGH FRIDAY. MUCH DRIER AIR WILL FUNNEL
INTO THE GREAT LAKES REGION AROUND THE NE PERIPHERY OF THE EXPANSIVE
HIGH ENCOMPASSING THE WESTERN US DEPRESSING DEWPOINTS INTO THE 50S
FOR THURS AND FRI. 850MB TEMPERATURES WILL SETTLE IN THE LOW TO MID
TEENS DURING THIS TIME WHICH WILL SET THE STAGE FOR SIGNIFICANT
DIURNAL BOUNDARY LAYER GROWTH TO 6-7KFT UNDER ABUNDANT LATE JULY
HEATING. ADIABATIC MIXING WILL SUPPORT HIGH TEMPERATURES ON THE
WARMER SIDE OF NORMAL ALONG WITH GUSTY AFTERNOON WINDS FROM THE
WEST. THIS WILL PARTICULARLY BE THE CASE ON THURSDAY WHEN CLOSER
PROXIMITY TO THE ONTARIO CYCLONE WILL CONTRIBUTE TO AN ENHANCED
GRADIENT THROUGH THE COLUMN AND GUSTS APPROACHING 30 MPH...ALTHOUGH
FRIDAY COULD BE SIMILARLY BREEZY DEPENDING ON EXTENT OF MIXING. A
WEAK EMBEDDED SHORTWAVE WILL CONTRIBUTE TO LITTLE MORE THAN ENHANCED
CU OVER THE THUMB ON THURSDAY AS THE ATMOSPHERE REMAINS QUITE DRY.

SLIGHTLY STRONGER WAVE ALONG THE CYCLONIC SIDE OF A STRENGTHENING
JET MAX WILL DEEPEN AS IT PROPAGATES SE INTO THE AREA LATE FRIDAY
INTO FRIDAY NIGHT. SLIGHTLY BETTER SYSTEM MOISTURE HERE AS IT IS
MODELED TO DRAW UPON THE THETA-E RESERVOIR SITTING OVER THE CENTRAL
PLAINS. WELL-MIXED ENVIRONMENT INCREASES CONFIDENCE IN A CONVECTIVE
RESPONSE ONCE MID-LEVEL MOISTURE QUALITY BEGINS TO INCREASE, BUT ANY
SHOWERS WILL BE HIGH BASED AND CAPE DENSITY WILL STAY ON THE LOW
SIDE. HOWEVER, MODERATE WIND FIELD AND VERY DRY AIR THROUGH THE
LOWEST 5KFT COULD PRODUCE SOME HEFTY WIND GUSTS FROM OTHERWISE
UNIMPRESSIVE CONVECTION. WILL CONFINE HIGHER CHC POPS TO NORTH OF
THE I-69 CORRIDOR WHERE DYNAMIC FORCING WILL BE BEST. STEEP LAPSE
RATES ALOFT WILL SUPPORT CARRYING POPS WELL INTO THE EVENING.

AVOIDED MOS GUIDANCE AND LEANED TOWARD WARMER HIGHER RESOLUTION RAW
OUTPUT IN THE LOW 60S FOR LOWS GIVEN THE EXPECTATION FOR MIXED
CONDITIONS TO EXIST EACH NIGHT.

BROAD UPPER TROUGH WILL BE SITUATED OVER THE NORTHERN TIER OF THE
EASTERN HALF OF THE CONUS THIS WEEKEND INTO EARLY NEXT WEEK.
SHORTWAVE ENERGY ROTATING THROUGH THE LONGWAVE TROUGH WILL PROVIDE
FOR SHOWER/TSTORM CHANCES WITH 12Z SUITE INDICATING THE BEST
POTENTIAL ON SUNDAY AND MONDAY...THOUGH CANNOT RULE OUT SOME
ACTIVITY SATURDAY. TROUGH AXIS SHIFTS EAST TUESDAY FAVORING DRY
CONDITIONS UNDER NORTHWESTERLY UPPER FLOW.

MARINE...

A PASSING COLD FRONT WILL BRING A PARTIAL COVERAGE OF THUNDERSTORMS
TO THE WATERS THIS EVENING FOR SAGINAW BAY AND POINTS EAST AND
SOUTH. ISOLATED STORMS APPROACHING SEVERE LIMITS WILL BE POSSIBLE
THROUGH 8 P.M. LOCAL TIME. MODERATE SOUTH BREEZE WILL THEN VEER TO A
WNW DIRECTION TONIGHT INTO THURSDAY BEHIND THE FRONT. WIND GUSTS OF
25 KNOTS OVER LAND WILL LIKELY CARRY INTO AT LEAST A PORTION OF THE
NEARSHORE ZONES. SMALL CRAFT ADVISORIES HAVE THEREFORE BEEN ISSUED
FOR ALL NEARSHORE ZONES FOR THURSDAY. ISOLATED GUSTS TO NEAR-GALES
WILL BE POSSIBLE ACROSS THE NORTHERN TIP OF LAKE HURON DURING THIS
TIME. A SIMILAR SETUP MAY NECESSITATE ADDITIONAL ADVISORIES DURING
THE DAY FRIDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY FROM 2 PM TO 8 PM EDT THURSDAY FOR LHZ442-443.

     SMALL CRAFT ADVISORY FROM 11 AM TO 8 PM EDT THURSDAY FOR LHZ421-422-
     441.

LAKE ST CLAIR...SMALL CRAFT ADVISORY FROM 2 PM TO 8 PM EDT THURSDAY FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY FROM 2 PM TO 8 PM EDT THURSDAY FOR LEZ444.

&&

$$

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


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