Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KDTX 171947
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
347 PM EDT FRI OCT 17 2014

.SHORT TERM... AFTERNOON THROUGH TONIGHT

A BROAD SURFACE LOW PRESSURE SYSTEM AND ASSOCIATED COLD FRONT
REMAINS SPRAWLED ACROSS THE GREAT LAKES AND EASTERN CANADA DURING
THE AFTERNOON. THE SURFACE FEATURES ARE TIED TO DUAL UPPER LEVEL
CIRCULATIONS THAT WILL PIVOT EASTWARD TONIGHT RESULTING IN THE
PASSAGE OF THE COLD FRONT THROUGH SE MICHIGAN. THE FIRST ELEMENT IN
THE FORECAST WILL BE ENTRY LEVEL CONVECTIVE POTENTIAL FOLLOWED BY
OVERALL COVERAGE OF SHOWERS DURING THE NIGHT AND THEN THE PACE OF
COLDER AIR ARRIVING THROUGH SUNRISE SATURDAY.

MID AFTERNOON MESO ANALYSIS INDICATES 700-500 MB LAPSE RATES
EXCEEDING 7 C/KM OVER WISCONSIN ASSOCIATED WITH THE 500 MB COLD POOL
AROUND -20C. THE COLD AIR ALOFT IS STILL TRAILING THE LOW LEVEL
THETA-E RIDGE...ABOUT OVERHEAD OF SE MICHIGAN AT PRESS TIME...BY A
WIDE ENOUGH MARGIN TO CAUSE A MINIMAL DIURNAL RESPONSE TO SHOWER
DEVELOPMENT. HOWEVER...AN ISOLATED THUNDERSTORM CAN STILL NOT BE
RULED OUT AS THERE DOES REMAIN ENOUGH POTENTIAL FOR POOLING OF
BETTER MOISTURE ALONG THE COLD FRONT DURING THE EVENING JUDGING FROM
THETA-E FIELDS FROM THE SURFACE TO 925 MB IN BOTH THE NAM AND RAP
MODELS. BOTH OFFER MINIMAL SURFACE BASED CAPE AND SLIGHTLY NEGATIVE
SURFACE TO 500 MB LI PRIOR TO 03Z. WHERE THIS FAILS TO GENERATE A
THUNDERSTORM...IT IS LIKELY TO RESULT IN NUMEROUS SHOWER COVERAGE AS
FAR SOUTH AS THE I-69 CORRIDOR AND GENEROUS SCATTERED COVERAGE
TOWARD THE OHIO BORDER THROUGH THE EARLY OVERNIGHT HOURS.

COVERAGE OF SHOWERS WILL DIMINISH TOWARD SUNRISE BUT CLOUDS WILL
PERSIST AS COLDER AIR SURGES INTO SE MICHIGAN. THE PACE OF COLD
ADVECTION WILL BE RAPID BASED ON UPSTREAM SURFACE OBS COMPARED WITH
LOW LEVEL MODEL TEMPERATURE FIELDS...BUT CLOUDS AND A WELL MIXED
BOUNDARY LAYER WIND WILL LIKELY PREVENT MIN TEMPERATURES FROM
REACHING THE 30S.

&&

.LONG TERM...

SOUTHEAST MICHIGAN WILL ALREADY BE IN THE GRIPS OF THE THERMAL
TROUGH BY 12Z SATURDAY MORNING. ONLY LIGHT COLD ADVECTION WILL
CONTINUE THROUGH THE DAY WITH 850MB TEMPS PROGGED TO GRADUALLY FALL
FROM AROUND -1C TO AS LOW AS -3C BY AFTN. STEEP LAPSE RATES OWING TO
COLD AND WELL-MIXED NW FLOW ALONG WITH ADEQUATE BOUNDARY LAYER
MOISTURE WILL SUPPORT EXTENSIVE STRATOCU FOR THE BALANCE OF THE DAY.
OVERCAST CONDITIONS WILL BE ACCOMPANIED BY A MODEST PRESSURE
GRADIENT WITHIN WHICH WINDS CAN BE EXPECTED TO GUST TO AROUND 20 MPH
OR HIGHER..HIGHER ALONG THE SHORELINE OF THE EASTERN THUMB WHERE
FLOW WILL BE OFF OF LAKE HURON IN ADDITION TO SOME ENHANCED DOWNWARD
TRANSPORT FURTHER NORTH. THIS WILL EFFECTIVELY CONFINE HIGH
TEMPERATURES OVER MOST OF THE AREA TO THE UPPER 40S AND YIELD WIND
CHILLS OF 40-44 DEGREES DURING PEAK HEATING. HURON AND SANILAC
COUNTY WILL STRUGGLE INTO THE MID 40S.

SHORTWAVE RIDGING WILL RAPIDLY BUILD IN SATURDAY NIGHT RESULTING IN
AGGRESSIVE SCOURING OF MID-LEVEL MOISTURE AND BUILDING SURFACE HIGH
PRESSURE ACROSS THE WESTERN AND CENTRAL GREAT LAKES. THIS WILL LEAD
TO AN EVENTUAL DISSIPATION OF BOUNDARY LAYER STRATOCU, BUT GIVEN THE
STRENGTH OF THE INVERSION PREFERRED TO DEPICT THIS DISSIPATION AS
GRADUAL WITH MOSTLY CLOUDY SKIES PERSISTING THROUGH THE FIRST HALF
OF THE NIGHT. WHEN TAKEN INTO CONSIDERATION WITH THE RESPECTABLE
NWLY SURFACE PRESSURE GRADIENT ALONG THE EASTERN PERIPHERY OF THE
BUILDING SFC HIGH, FELT EVIDENCE WAS COMPELLING ENOUGH TO WARRANT
GOING WARMER THAN GUIDANCE SAT NIGHT DUE TO POOR RADIATING
CONDITIONS. THE COLD AIRMASS WILL STILL, HOWEVER, ALLOW ALL
LOCATIONS TO FALL INTO THE 30S WITH A FEW WESTERN LOCATIONS PERHAPS
TOUCHING THE UPPER 20S BY EARLY SUNDAY MORNING.

HIGH PRESSURE WILL THEN DOMINATE THROUGH SUNDAY WITH MOSTLY SUNNY
SKIES AND A REBOUNDING THERMAL FIELD SUPPORTING HIGH TEMPERATURES IN
THE LOW 50S. LOW AMPLITUDE UPPER ENERGY WITH ORIGINS IN THE GULF OF
ALASKA WILL EVENTUALLY UNDERGO SOME AMPLIFICATION AS IT PROPAGATES
INTO THE GREAT LAKES WITHIN THE LARGER SCALE TROUGH BY LATE SUNDAY
NIGHT. THIS WILL BRING A LATE DAY INCREASE IN MID/UPPER CLOUDS ALONG
WITH A CHANCE OF SHOWERS WITHIN DEVELOPING WARM ADVECTION OVERNIGHT
SUNDAY.

SHOWER CHANCES WILL CONTINUE INTO MONDAY AS THE UPPER ENERGY AND ITS
SURFACE REFLECTION PROPAGATE NEAR/THROUGH THE LOCAL REGION. THIS UPPER
DISTURBANCE WILL LIKELY CUT OFF OVER THE NORTHEAST/MID ATLANTIC
STATES BEGINNING TUESDAY NIGHT WHILE HIGH AMPLITUDE RIDGING BUILDS
OVER THE UPPER MISSISSIPPI RIVER REGION LEAVING SE MI IN UPPER-LEVEL
NORTHERLY AND INCREASINGLY SUBSIDENT FLOW. SOME LAKE-EFFECT SHOWERS
APPEAR POSSIBLE TUESDAY BEFORE SURFACE HIGH PRESSURE BUILDS
IN...PROMOTING A DRY WEATHER AND A WARMING TREND MID/LATE NEXT WEEK.

&&

.MARINE...

EXPECT GUSTS TO NORTHWEST GALES TONIGHT THROUGH SATURDAY AS A COLD
FRONT USHERS COLDER AIR INTO THE GREAT LAKES. MODERATE SOUTHWEST
FLOW TODAY WILL QUICKLY TURN TO THE NORTHWEST THIS EVENING AND RAMP
UP TO GALES LATE TONIGHT. CENTRAL LAKE HURON WILL SEE WIDESPREAD
GUSTS TO GALES WITH THE OCCASIONAL WIND GUST AS HIGH AS 40 KNOTS
POSSIBLE. GALE WARNINGS ARE THEREFORE IN EFFECT FOR NEARLY ALL OF
LAKE HURON...INCLUDING THE EXPOSED NEARSHORE ZONES FROM PORT AUSTIN
TO PORT SANILAC. SIGNIFICANT WAVE HEIGHTS OVER THE SOUTHERN LAKE
HURON WILL BUILD TO AROUND 10 FEET BY EARLY SATURDAY MORNING. WINDS
IN THE PARTIALLY SHELTERED ZONES OF SAGINAW BAY AND THE NEARSHORE
ZONES FROM PORT SANILAC TO PORT HURON MAY APPROACH MARGINAL GALES AT
TIMES...BUT WILL STRUGGLE TO SUSTAIN TRUE GALE CONDITIONS. SMALL
CRAFT ADVISORIES REMAIN IN EFFECT FOR THESE LOCATIONS.

&&

.AVIATION...ISSUED 1258 PM EDT FRI OCT 17 2014

//DISCUSSION...

A NARROW WINDOW OF VFR WILL DEVELOP DURING THE AFTERNOON IN BETWEEN
THE MORNING MVFR CEILING AND MVFR/IFR CONDITIONS WITH THE COLD FRONT
TONIGHT. THIS WILL OCCUR ALONG WITH AN INCREASINGLY GUSTY WESTERLY
FLOW BUT GENERALLY LESS THAN 25 KNOTS BEFORE TURNING NORTHWEST AFTER
PASSAGE OF THE COLD FRONT. EARLY AFTERNOON OBSERVATIONS OVER THE
NORTHERN GREAT LAKES SUPPORT MODEL DEPICTIONS OF A GREATER SHOWER
CONCENTRATION THROUGH THE MBS TO FNT AREA BUT WITH EQUALLY GOOD
POTENTIAL FOR A SHORT PERIOD OF FOG AND LOW CEILING ALL AREAS AS THE
COLD FRONT MOVES THROUGH THE REGION. THUNDERSTORM POTENTIAL IS TOO
LOW TO INCLUDE IN ANY OF THE TERMINAL FORECASTS.

MVFR CEILING WILL PERSIST THROUGH THE LATE NIGHT AND SATURDAY
MORNING AS STEADY NORTHWEST WIND CARRIES COLDER AIR INTO SE
MICHIGAN. EXPECT MVFR CEILING TO MIX UP OR SCATTER OUT INTO VFR FROM
MBS DURING LATE MORNING TOWARD DTW BY EARLY AFTERNOON.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET MUCH OF THE TAF PERIOD.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...
     GALE WARNING...LHZ362-LHZ363...FROM MIDNIGHT SATURDAY TO 4 PM
     SATURDAY.

     GALE WARNING...LHZ441-LHZ442-LHZ462-LHZ463-LHZ464...FROM 4 AM
     SATURDAY TO 4 PM SATURDAY.

     SMALL CRAFT ADVISORY...SAGINAW BAY...FROM MIDNIGHT SATURDAY TO 4 AM
     SUNDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT SANILAC TO PORT
     HURON...FROM 4 AM SATURDAY TO 4 AM SUNDAY.

LAKE ST CLAIR...NONE.

MI WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...BT
LONG TERM....JVC/DT
MARINE.......JVC
AVIATION.....BT


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








USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.