Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 191954
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
354 PM EDT SAT JUL 19 2014

.SHORT TERM...THROUGH TONIGHT

WELL-DEFINED AREA OF UPPER LOW PRESSURE CAN BE SEEN ON WATER VAPOR
IMAGERY TRACKING NORTHWARD ACROSS LAKE HURON. WEAK MID-LEVEL
DEFORMATION ZONE DROPPING BACK DOWN AROUND THE WESTERN FLANK OF
THIS SYSTEM SHOULD STILL BE LINGERING DOWN FROM THE THUMB TO ABOUT
PTK PER 12Z GFS. THIS IS WHERE RADAR SHOWS A FEW LIGHT SHOWERS STILL
ONGOING. ACTIVITY GOT A BIT OF A BOOST FROM DAYTIME HEATING EARLIER
THIS AFTERNOON...BUT HAS REALLY DROPPED OFF IN THE LAST HOUR AS
FORCING WEAKENS AND STARTS TO LIFT NORTH. EXPECT LOW SHOWER COVERAGE
TO LINGER THROUGH THE EARLY EVENING BEFORE THE LOW MOVES TO THE
ONTARIO/QUEBEC BORDER AND HIGH PRESSURE NEAR THE NEW ENGLAND COAST
EXPANDS BACK INTO THE AREA.

HIGH PRESSURE AND DRIER ARRIVING IN THE LOW AND MID LEVELS SHOULD
ALLOW FOR LIGHT WINDS BY LATE THIS EVENING AND A CLEARING TREND TO
SKY COVER. NAM/RAP FORECAST SOUNDINGS HINT AT SOME SHALLOW FOG
FORMATION LATE TONIGHT AS A SHALLOW SURFACE-BASED INVERSION FORMS
AND SURFACE TEMPERATURES CRASH TO THE DEWPOINTS. THIS COULD BE
INFLUENCED BY OVERLY ZEALOUS MODEL QPF FOR TODAY...BUT DO SEE SOME
POTENTIAL FOR FOG TO DEVELOP AS THE SHALLOW INVERSION FORMS...WINDS
REMAIN LIGHT FROM OFF THE GREAT LAKES...AND SURFACE DEWPOINTS REMAIN
IN THE UPPER 50S TO NEAR 60. DID INCLUDE A PATCHY MENTION OF FOG FOR
THE FAR EASTERN PORTION OF THE AREA WHERE MORE SHOWERS OCCURRED
TODAY. OTHERWISE...WEATHER SHOULD BE QUIET TONIGHT WITH MINS IN THE
LOW/MID 50S TO NEAR 60.

&&

.LONG TERM... SUNDAY THROUGH NEXT SATURDAY

THE SHORT WAVE ALOFT OVER THE OHIO VALLEY TODAY CARVED OUT A
WEAKNESS WITHIN THE LARGER BACKGROUND OF BROAD SURFACE HIGH
PRESSURE. THE WEAKNESS IN THE PRESSURE FIELD WILL FILL IN BY SUNDAY
MORNING AS THE UPPER WAVE MOVES INTO THE NEW ENGLAND STATES AND
ALLOWS THE SURFACE HIGH TO REASSERT CONTROL OF THE WEATHER OVER SE
MICHIGAN. BASED ON THE UPSTREAM CUMULUS RESPONSE TODAY...THE CLOUD
FORECAST IS NUDGED TOWARD 50/50 COVERAGE IN OUR AREA DURING SUNDAY
AFTERNOON...BUT THAT IS ABOUT ALL THE FORECAST ADJUSTMENTS NEEDED AS
DRY CONDITIONS LOOK SOLID. DESPITE UPSTREAM CUMULUS DEVELOPMENT
WITHIN THE SURFACE RIDGE...CONCERN FOR SHOWERS OR STORMS IS EASED BY
12Z SOUNDINGS THAT INDICATE A RESPECTABLE CAPPING INVERSION THROUGH
THE MIDWEST OBSERVATION SITES. MODEL SOUNDINGS CAPTURE THIS WARMER
AIR ALOFT MOVING OVER LOWER MICHIGAN DURING PEAK HEATING SUNDAY
AFTERNOON ADDING CONFIDENCE TO THE EXPECTATION FOR DRY WEATHER. MORE
NOTABLE IS THE RETURN TO MORE TYPICAL JULY TEMPERATURES AND MODERATE
HUMIDITY. NO PROBLEM WITH GUIDANCE OFFERINGS IN THE LOWER 80S MOST
LOCATIONS AWAY FROM THE LAKE HURON SHORELINE.

UPPER LEVEL TROUGH DEVELOPMENT OFF THE PACIFIC COAST WILL LEAD TO AN
ARM OF THE SW U.S. UPPER RIDGE BUILDING INTO THE GREAT LAKES DURING
THE FIRST HALF OF NEXT WEEK. THIS WILL LEAD TO A TEXTBOOK BERMUDA
HIGH PATTERN AT THE SURFACE AND ASSOCIATED WARM TEMPERATURE/HIGH
HUMIDITY AIR MASS AFFECTING THE WEATHER IN SE MICHIGAN MONDAY AND
TUESDAY. THERE IS GOOD MODEL AGREEMENT ON THE LARGE SCALE UPPER AIR
FEATURES AND AREAL COVERAGE OF THE CUSTOMARY 10C 700 MB TEMPERATURE
EXPECTED TO CAP OFF CONVECTION. THIS ADDS SOME CONFIDENCE TO THE
TEMPERATURE FORECAST PUSHING 90 BY TUESDAY WITHOUT TOO MUCH WORRY
ABOUT THUNDERSTORM COMPLEXES GETTING IN THE WAY OF DAYTIME HEATING.
THIS LEVEL OF CONFIDENCE IS THEN ERODED ALONG WITH THE UPPER RIDGE
BY A SOUTHWARD INTRUSION OF THE WESTERLIES FROM CANADA BY TUESDAY
NIGHT. THE INCREASED WESTERLY FLOW ALOFT AND LOW LEVEL JET
DEVELOPMENT OVER THE PLAINS HAS THE LOOK OF AN MCS PATTERN BY THEN.

WEAK HIGH PRESSURE WILL BE IN PLACE FOR TUESDAY ALLOWING WARMER AND
MORE HUMID AIR TO FILTER INTO SOUTHEAST MICHIGAN. AT THIS TIME
TEMPERATURES ARE EXPECTED TO RISE INTO THE UPPER 80S BY TUESDAY
AFTERNOON ACROSS THE ENTIRE CWA. HOWEVER...A LOW PRESSURE SYSTEM
BUILDING OUT OF THE NORTHERN PLAINS WILL TRACK ACROSS THE NORTHERN
GREAT LAKES REGION ON TUESDAY NIGHT...DRAGGING A COLD FRONT ACROSS
SOUTHEAST MICHIGAN. THIS FRONT WILL BRING A CHANCE OF RAIN AND
THUNDERSTORMS ON TUESDAY NIGHT AND WEDNESDAY BEFORE HIGH PRESSURE
BUILDS OUT OF CANADA AND INTO THE GREAT LAKES RESULTING IN DRY
CONDITIONS THROUGH THE END OF THE WEEK. THIS HIGH NOT ONLY WILL
BRING DRIER WEATHER TO THE AREA...BUT ALSO COOLER TEMPERATURES
BEGINNING ON WEDNESDAY WITH HIGHS IN THE LOW TO MID 80S.
TEMPERATURES CONTINUE TO DROP THROUGH THE END OF THE EXTENDED PERIOD
WITH TEMPERATURES IN THE MID 70S ON THURSDAY AND FRIDAY.

&&

.MARINE...

WIND AND WAVE CONDITIONS WILL REMAIN FAVORABLE OVER THE NEXT FEW
DAYS THANKS TO SURFACE HIGH PRESSURE REBUILDING OVER THE GREAT LAKES
SUNDAY AND LINGERING NEARBY TO THE EAST MONDAY AND TUESDAY. LIGHT
SOUTH WIND WILL PROMOTE STEADILY INCREASING TEMPERATURES THROUGH THE
PERIOD WHICH WILL LEAD TO HIGH STABILITY OVER THE LAKES
CORRESPONDING TO LOW WAVE ACTION. UNSETTLED WEATHER IN THE FORM OF
INCREASED THUNDERSTORM ACTIVITY IS EXPECTED BY MID WEEK ALONG AND
AHEAD OF A COLD FRONT DUE TO MOVE THROUGH THE REGION WEDNESDAY.

&&

.AVIATION...

//DISCUSSION...

A SMALL AREA OF UPPER LEVEL LOW PRESSURE WILL CONTINUE TO LIFT
ACROSS FAR SOUTHEAST MICHIGAN THIS AFTERNOON. THIS WILL ALLOW
ADDITIONAL SHOWERS TO DEVELOP/SPREAD INTO THE AREA FROM THE EAST
THROUGH THE LATE AFTERNOON...WITH POTENTIAL FOR A FEW SHOWERS TO
LINGER INTO THE EVENING. AT 130 PM...SHOWERS WERE JUST BEGINNING TO
LIFT NORTH OF THE DTW/YIP AREA. A FEW MORE SHOWERS WILL BE POSSIBLE
THERE OVER THE NEXT FEW HOURS...BUT MOST OF THE FOCUS WILL SHIFT
SLIGHTLY NORTH TOWARD DET AND PTK. DRIER AIR WILL REMAIN IN PLACE AT
FNT AND MBS...AND CHANCES TO SEE A SHOWER THERE IS EXTREMELY LOW.
OTHERWISE...LOW-END VFR CEILINGS WITH OCCASIONAL DROPS TO MVFR CAN
BE EXPECTED THROUGH THE AFTERNOON FROM PTK SOUTH. HIGH PRESSURE OVER
THE NEW ENGLAND COAST WILL EXPAND BACK INTO MICHIGAN FOR
TONIGHT...ALLOWING A RETURN TO DRY CONDITIONS. ATTENTION WILL THEN
TURN TO POTENTIAL FOR SHALLOW FOG DEVELOPMENT TONIGHT AS WINDS GO
LIGHT AND SKIES BECOME MOSTLY CLEAR. LATEST FORECAST MODEL GUIDANCE
SHOWS SURFACE SATURATION LATE TONIGHT UNDER A SHARP SURFACE-BASED
INVERSION. THIS MAY BE DUE TO MODELS OVER-DOING PRECIPITATION/SOIL
SATURATION DURING THE DAY...BUT IT IS POSSIBLE THAT LINGERING
MOISTURE WILL JUST GET SQUISHED TO THE GROUND AS THE INVERSION FORMS
AND LOWERS CLOSE TO THE GROUND TONIGHT. WILL HAVE TO MONITOR
POTENTIAL THAT A FOG MENTION WILL BE NEEDED BETWEEN ROUGHLY 9-12Z.

FOR DTW...AREA OF SHOWERS WILL CONTINUE TO LIFT VERY SLOWLY NORTH
THROUGH 21Z. UNTIL THEN...A FEW SHOWERS ARE POSSIBLE BUT SHOULD BE
LIGHT ENOUGH TO HAVE LITTLE IMPACT ON OPERATIONS. CEILINGS HOWEVER
ARE EXPECTED TO REMAIN BELOW 5000 FEET THROUGH THE REMAINDER OF
THE AFTERNOON AND INTO THE EARLY EVENING.


//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE IN CIGS BELOW 5KFT THROUGH 00Z SUN.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...HLO
LONG TERM....BT/RK
MARINE.......BT
AVIATION.....HLO


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



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