Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211102
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
702 AM EDT MON JUL 21 2014


.AVIATION...

//DISCUSSION...

THE PATCHY FOG ACROSS THE AREA IS SHALLOW AND WILL RAPIDLY DIMINISH
BETWEEN 12Z AND 13Z AS DIURNAL HEATING GETS UNDER WAY. OTHERWISE...A
WEAK SURFACE GRADIENT OVER SE MI WILL MAINTAIN LIGHT WINDS THROUGH
THE TAF PERIOD. WARMING ALOFT WILL ALSO LIMIT THE DEGREE OF
AFTERNOON CUMULUS DEVELOPMENT.


//DTW THRESHOLD THREATS...

* NONE.

&&

.PREV DISCUSSION...ISSUED 402 AM EDT MON JUL 21 2014

SHORT TERM...TODAY AND TONIGHT

WITH A WELL MIXED DAYTIME BOUNDARY LAYER YESTERDAY...THE MOISTURE
DEPTH THIS MORNING WILL BE CONSIDERABLY MORE SHALLOW COMPARED TO SUN
MORNING. THUS EARLY MORNING FOG WILL BE MORE PATCHY IN NATURE AND
MORE PREVALENT IN LOW LYING FOG PRONE AREAS. MID LEVEL HEIGHTS WILL
BE ON THE RISE TODAY...AN EXTENSION OF THE BUILDING SUBTROPICAL
RIDGE OVER THE SRN ROCKIES/SRN PLAINS. THE SUBSEQUENT INCREASE IN
MID LEVEL TEMPS WILL FURTHER CAP THE ATMOSPHERE OVER SE MI...
HINDERING ANY CONVECTIVE DEVELOPMENT. MODEL SOUNDINGS DO SUGGEST
ENOUGH MOISTURE TO RESULT IN SOME SHALLOW CU FORMATION... LIKELY
ENHANCED BY LAKE BREEZE BOUNDARIES. GIVEN THE LIGHT WIND FIELD AS A
RESULT OF THE WEAK SFC GRADIENT OVER SE MI... LOW LEVEL WARM AIR
ADVECTION WILL REMAIN QUITE WEEK TODAY. NONETHELESS... AMPLE
AFTERNOON MIXING UNDER THE BUILDING MID LEVEL RIDGE WILL BOOST
DAYTIME HIGHS A COUPLE DEGREES WARMER THAN OBSERVED YESTERDAY /MID
80S/. THE LOW LEVEL SOUTHWEST GRADIENT WILL INCREASE TONIGHT IN
RESPONSE TO LOW PRESSURE TRACKING INTO MINNESOTA. THE RESULTING
LIGHT WINDS WILL SUPPRESS RADIATIONAL COOLING...SUPPORTING MIN TEMPS
ONLY DOWN INTO THE MID/UPPER 60S.

LONG TERM...TUESDAY THROUGH SUNDAY

THE LONG TERM PACKAGE CENTERS ON THE HOT WEATHER TUESDAY FOLLOWED BY
THE POTENTIAL FOR THUNDERSTORMS TUESDAY NIGHT AND WEDNESDAY MORNING.

MODEL DATA HAS SHOWN GREAT CONTINUITY WITH REGARDS TO THE LARGE
SCALE PATTERN EVOLUTION FOR THE MIDDLE OF THE WEEK. MORE
SPECIFICALLY...THE PROGRESSIVE UPPER LEVEL RIDGE STRUCTURE OVER
EASTERN NORTH AMERICA WILL BE VERY SHORT-LIVED GIVING WAY TO AN
AMPLIFYING UPPER LEVEL TROUGH BY LATE WEDNESDAY. SO WHILE THIS DOES
GIVE GOOD CONFIDENCE WITH THE BEGINNING AND END STATES...HOW WE GET
THERE REMAINS A LITTLE MORE MUDDLED. THIS IS ESPECIALLY TRUE FOR HOW
THE CONVECTION WILL ORGANIZE OR EVOLVE TUESDAY AND TUESDAY NIGHT.

TUESDAY...NWP DEPICTS A VENTING OF THE WESTERN NORTH AMERICA THERMAL
RIDGE...SENDING AN EML PLUME THROUGH THE CENTRAL GREAT LAKES.
FORECASTED H85 TEMPS ARE EXPECTED TO REACH 20C BY THE EVENING
HOURS...THE NAM AN OUTLIER WITH A CONSPICUOUSLY COOLER COLUMN BELOW
H7. THIS WILL LEAD TO A CAPPED THERMODYNAMIC ENVIRONMENT THROUGHOUT
THE DAYLIGHT HOURS. NOT CONFIDENT THE MODELS ARE IN TUNE WITH HOW
DRY THE ATMOSPHERE WILL ACTUALLY BE DURING THIS TIMEFRAME.
DYNAMICALLY...THE MODELS ARE NOT SUGGESTING MUCH IN THE WAY OF
ACTIVE SUBSIDENCE...HOWEVER...THE UPPER LEVEL RIDGE AXIS WILL NEED
TO MIGRATE THROUGH THE THE STATE AND POINTS NORTHWARD 18-00Z.
ANTICYCLONICALLY CURVED FLOW TO START THE DAY ALONG WITH DEPICTIONS
OF THE MODELED RH FIELD FEEL THAT HIGH CLOUD ARRIVING FROM UPSTREAM
CONVECTION WILL NOT PERSIST IN AN OPAQUE STATE. SO...AGAIN WENT
ALONG WITH THE PREVIOUS FORECASTER BY FORECASTING HIGH TEMPERATURES
A DEGREE OR TWO WARMER THAN MOS. FORECASTED HIGHS ARE EXPECTED TO
REACH A DEGREE WITHIN THE 90 DEGREE MARK. LOW TO MID 60S DEWPOINTS
WILL CERTAINLY BE FELT...BUT NOTHING OPPRESSIVE. HEAT INDICES ARE
FORECASTED TO REACH THE LOW 90S.

TUESDAY NIGHT...THUNDERSTORM POTENTIAL/COVERAGE/VIGOR IS HEAVILY
DEPENDENT ON UPSTREAM EVOLUTION. WHAT THE MODELS HAVE BEEN
SUGGESTING WITH SOME REGULARITY IS THE MAIN MCS AND CONVECTIVELY
ENHANCED SURFACE LOW STRUCTURE WILL SLIDE EASTWARD THROUGH THE LAKE
SUPERIOR REGION/U.P. TO NORTH OF LAKE HURON. FEEL CONFIDENT IN THIS
HAPPENING WITH THE MAIN UPPER LEVEL JET STREAK/RIGHT ENTRANCE REGION
DYNAMICS LOCATED WAY UP NORTH...OVER JAMES BAY AND EASTERN CANADA.
THE MAIN SURFACE COLD FRONT AND SURFACE TROUGH WHICH WILL MEET A
FAIR AMOUNT OF RESISTANCE OVER THE CENTRAL LAKES TUESDAY...SHOULD
THEN SETTLE STEADILY SOUTHWARD THROUGH LOWER MICHIGAN TUESDAY NIGHT.
THERE IS SOME DISCONTINUITY WITH THE FRONTAL SURFACES WITH THE
SURFACE FEATURE SOUTH OF CWA BY 12Z...THE 850MB SURFACE LAGGING BACK
ACROSS THE SAGINAW VALLY AT THE SAME TIME. THE ASPECT OF THE FORECAST
THAT HAS HIGH CONFIDENCE IS THAT SHEAR OVER SOUTHEASTERN MICHIGAN
WILL BE RELATIVELY LOW. WINDS WITHIN THE ENTIRE COLUMN ARE EXPECTED
TO REMAIN BELOW 40 KNOTS WITH 0-6KM BULK SHEAR STRUGGLING TO REMAIN
ABOVE 20 KNOTS. THE INSTABILITY MAXIMUM IS FORECASTED TO RETREAT TO
THE SOUTHWEST DURING THE OVERNIGHT AS THERE IS NO SUSTAINED EML
PUSH. THROW IN A VEERED OUT LOW TO MIDLEVEL WIND PROFILE...AND THE
PROSPECTS FOR A WIDESPREAD SEVERE WEATHER OUTLOOK IS SERIOUSLY
QUESTIONED. AN ISOLATED STRONG TO SEVERE STORM WILL BE POSSIBLE
GIVEN MUCAPES TRYING TO HOLD NEAR 1000 J/KG. NOTE...SWODY2 FAILS TO
INCLUDE SEMICH IN THE 5 PERCENT CONTOUR IN THE PROBABILISTIC OUTLOOK.

MARINE...

A BROAD REGION OF HIGH PRESSURE EXTENDING ACROSS SOUTHEAST LOWER MI
AND THE EASTERN LAKES WILL MAINTAIN LIGHT WINDS AND FAVORABLE WAVE
CONDITIONS SOUTHERN LAKE HURON...LAKE ST. CLAIR AND LAKE ERIE WHILE
NORTHERN LAKE HURON WILL MAINTAIN A LIGHT S-SE WIND. LIGHT S-SW
WINDS WILL DEVELOP ON MONDAY AND STRENGTHEN A LITTLE ON TUESDAY IN
ADVANCE OF A SLOW MOVING FRONTAL BOUNDARY OVER THE NORTHERN PLAINS.
WARM AIR ADVECTION WILL LEAD TO STRONG STABILITY OVER THE LAKES
DURING THIS TIME FRAME. THIS WILL KEEP WINDS GENERALLY AT OR BELOW
15 KNOTS.

A COLD FRONT WILL PASS THROUGH THE REGION TUESDAY NIGHT OR
EARLY WEDNESDAY...PROVIDING A CHANCE FOR THUNDERSTORMS. THERE IS
LIKELY TO BE A NOTABLE WIND SHIFT TO THE N-NW WITH THE PASSAGE OF
THE FRONT WITH UNSTABLE CONDITIONS DEVELOPING. THIS WILL LEAD TO
WINDS 15 TO 25 KNOTS AND BUILDING WAVES...ESPECIALLY FOR LAKE HURON.

&&

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

&&

$$

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


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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).






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