Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 011954
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
354 PM EDT WED OCT 1 2014

.SHORT TERM...TONIGHT

SOUTHEASTERN MICHIGAN WILL REMAIN UNDER THE SPELL OF THE STRONG
SURFACE ANTICYCLONE TONIGHT OVER PORTIONS OF EASTERN QUEBEC AND
CANADIAN MARITIMES WITH A SUBSTANTIAL SURFACE RIDGE EXTENDING BACK
INTO THE GREAT LAKES REGION. THIS FEATURE WILL CONTINUE TO DIRECT A
SOUTHEASTERLY LOW TROPOSPHERE FEED INTO THE STATE DESPITE A WEAK
MIDLEVEL RIDGE SLIDING OVERHEAD. THIS UPPER LEVEL RIDGE WILL
ESSENTIALLY CAUSE THE PATTERN LOCALLY TO REMAIN STAGNANT THROUGH THE
OVERNIGHT...DISALLOWING MUCH IN THE WAY OF ADVECTIONS OR AIRMASS
TURNOVER. CLOUD TRENDS THIS AFTERNOON HAVE BEEN SLUGGISH IN MANY
AREAS WITH A TRANSITION FROM STRATUS TO CUMULOFORM. THERE HAS BEEN A
RAPID CLEARING TREND OVER PORTIONS OF SOUTH CENTRAL LOWER MICHIGAN
BUT SUSPECT THIS TO SLOW DOWN AND NOT MAKE MUCH INROADS TO
SOUTHEASTERN MICHIGAN BEFORE SUNDOWN. INSTEAD...EXPECT VERTICAL
CLOUD CIRCULATIONS TO DEEPEN YET OVER THE NEXT 4 HOURS WHICH WILL
SUPPORT GREATER CONVECTIVE ELEMENT SPACING AND INTRODUCE GREATER
CLOUD SCALE SUBSIDENCE AND ENTRAINMENT OF DRY AIR ALOFT. THIS SHOULD
SET THE STAGES FOR A RAPID CLEARING TREND IN MANY AREAS POST SUNSET
WITH NOCTURNAL COOLING.

NAM AND LATEST HRRR NWP IS VERY SUPPORTIVE OF FOG TONIGHT WITH A
MUCH BETTER PROFILE FOR NEAR SURFACE SATURATION IN COMPARISON TO
YESTERDAY MORNING. GIVEN THE AFOREMENTIONED LACK OF ADVECTIONS ALONG
WITH THE CONTINUATION OF GREENUP ACROSS THE AREA...HIGH AMBIENT
MOISTURE IN THE BACKGROUND SHOULD SUPPORT FOG FAIRLY EARLY
TONIGHT...I.E. SHORTLY AFTER MIDNIGHT. EXPECTATIONS ARE FOR FOG TO
DEVELOP ACROSS PORTIONS OF ONTARIO...PORT HURON AND THE EASTERN
THUMB BEFORE SPREADING WESTWARD. MODELS ARE ALSO SHOWING A SIGNAL
THAT AREAS SOUTH AND EAST OF THE TERRAIN IN HIGHER SURFACE PRESSURE
AREAS COULD VERY WELL BE A FAVORABLE ZONE FOR FOG DEVELOPMENT. GIVEN
THERMODYNAMIC STRUCTURE...DENSE FOG WILL BE POSSIBLE. CONFIDENCE IS
NOT 100 PERCENT AS IT SELDOM IS...AND WILL GIVE LATER SHIFTS THE
FLEXIBILITY ON ANY POSSIBLE HEADLINE DECISIONS.

&&

.LONG TERM...

THE NORTHERN PORTION OF THE EXISTING LONGWAVE TROUGHING NOW
ENCOMPASSING MUCH OF THE WESTERN CONUS WILL UNDERGO SUBSTANTIAL
AMPLIFICATION OVER THE NEXT 48 HOURS.  THIS PROCESS WILL COMMENCE AS
STRONG SHORTWAVE ENERGY AND AN ATTENDANT 140 KT UPPER JET CORE
CURRENTLY OVER BRITISH COLUMBIA DIG INTO THE LOWER HEIGHT FIELD.
STRENGTHENING DYNAMICS ATTENDANT TO A LEAD WAVE UNDERCUTTING THE
AMPLIFYING TROUGH WILL BRING A PERIOD OF ACTIVE WEATHER TO END THE
WORK WEEK.  THE DEEPENING PROCESS WILL THEN LEAVE A CLOSED LOW
CONFIGURATION CENTERED JUST TO THE NORTH FOR THE UPCOMING
WEEKEND...SPELLING A CONSIDERABLY COLDER AND UNSETTLED PERIOD.

A DEEPER SOUTHWESTERLY FLOW TAKES HOLD ON THURSDAY AS THE
GRADUALLY EXPANDING HEIGHT FALLS NUDGE THE EXISTING UPPER RIDGE TO
THE EAST.  THIS PROCESS WILL MIX OUT ANY LINGERING FOG THROUGH LATE
MORNING...WITH THE ENSUING INCREASE IN MID LEVEL WARM AIR AND
THETA-E ADVECTION PROMPTING A STEADY THICKENING OF A HIGH BASED
CLOUD DECK DURING THE FIRST HALF OF THE DAY.  DESPITE THE WARMING
THERMAL PROFILE...A LINGERING SOUTHEAST SURFACE WIND AND LIMITED
MIXING DEPTH WILL MUTE THE OVERALL RESPONSE SLIGHTLY.  IN ACCORDANCE
WITH THE GOING FORECAST...WILL CONTINUE TO TEMPER EXPECTATIONS WITH
HIGHS OF LOW TO MID 70S.  TANGIBLE FORCING THROUGH THE DAYLIGHT
PERIOD REMAINS LESS DEFINED LOCALLY...THE AREA LARGELY REMOVED TO
THE EAST FROM THE MAIN CORRIDOR OF ASCENT LOCKED ONTO THE
THETA-E RIDGE AND PRIMARY TRAJECTORY OF ANY LOWER AMPLITUDE SHORTWAVE
ENERGY FUNNELING THROUGH THE MEAN SW FLOW.  THERE REMAINS THE
POTENTIAL FOR THIS AXIS TO CREEP FAR ENOUGH EAST TO SUPPORT SOME
LIGHT SHOWER DEVELOPMENT...PARTICULARLY ACROSS THE TRI-CITIES.  LOW
CHANCE POPS REMAIN APPROPRIATE FOR THIS AREA GIVEN THE HIGH DEGREE
OF UNCERTAINTY.

THE INCREASING INTERACTION BETWEEN THE AFOREMENTIONED SOUTHERN
WAVE EJECTING NORTHEAST OUT OF THE SOUTHERN PLAINS AND THE DEEPENING
LOW ACROSS THE DAKOTAS WILL PROMPT RAPID SURFACE CYCLOGENESIS AND A
STRENGTHENING OF THE ATTENDANT COLD FRONT UPSTREAM BY THURSDAY
NIGHT.  THE DOWNSTREAM PROPAGATION OF A STRENGTHENING WIND FIELD
/50 KTS AT 850MB/ EMBEDDED WITHIN THE WARM SECTOR AND AT THE EDGE OF
THE INBOUND LOWER HEIGHT FIELD WILL LIKELY PROMOTE AN EXPANSION IN
PRECIPITATION COVERAGE THROUGHOUT THE MIDWEST BY LATE THURSDAY.
THIS FORCING REMAINS FORECAST TO TRACK THROUGH SE MICHIGAN LATE
THURSDAY NIGHT AND EARLY FRIDAY...A CORRESPONDING STEADY INCREASE IN
PRECIPITATION CHANCES COMMENCING DURING THIS TIME.  DEEPEST ASCENT
IN PLACE DURING THE FIRST HALF OF FRIDAY...A PERIOD OF SOLID UPPER
DIVERGENCE AND CVA WORKING INTO A MOISTENING PRE-FRONTAL
ENVIRONMENT.  EXISTING MID LEVEL INSTABILITY CERTAINLY SUFFICIENT TO
SUPPORT A THUNDER MENTION...A FEW STRONGER GUSTS A POSSIBILITY GIVEN
THE WIND FIELD SHOULD BEST CORES CAPITALIZE ON THE LIMITED
INSTABILITY.

SURFACE LOW DEEPENS TO 993 MB AS IT TRACKS NORTH OF LAKE SUPERIOR ON
FRIDAY.  THE OVERALL AMPLITUDE OF THIS SYSTEM CONTINUES TO FAVOR A
SLOWER DOWNSTREAM PROGRESSION OF THE MAIN HEIGHT FALL CENTER...WITH
THE CORRESPONDING COLD FRONTAL PASSAGE NOW EXPECTED EARLY FRIDAY
AFTERNOON.  A TRAILING PERIOD OF CVA AS THE STRONGER HEIGHT FALLS
COMMENCE AND COLD AIR ADVECTION ENSUES WILL SUSTAIN SCATTERED TO
NUMEROUS POST-FRONTAL SHOWER PRODUCTION LATE FRIDAY AND FRIDAY
NIGHT.

AMPLIFIED UPPER LEVEL TROUGH WILL BE SUSTAINED BY A 130 TO 140KT JET
THAT DIPS SOUTH OF THE GREAT LAKES INTO THE TENNESSEE VALLEY THROUGH
THE WEEKEND. THE UPPER LOW BECOMES CLOSED AT 500MB...BOTTOMING OUT
AROUND 538 DAM. EVEN AFTER SYNOPTIC RAIN ENDS ON SATURDAY...STEEP
LAPSE RATES IN PLACE WILL ALLOW FOR A 20 TO 30 PERCENT CHANCE FOR
RAIN SHOWERS EACH DAY IN THE EXTENDED PERIOD. STRONG GEOSTROPHIC
WIND COMPONENT WILL ALSO BE IN PLACE MOST OF THE PERIOD WITH DAYTIME
GUSTS OVER 20 MPH BEING COMMON.

&&

.MARINE...

SOUTHEAST WINDS WILL STEADILY INCREASE THURSDAY AND THURSDAY NIGHT
AS STRENGTHENING LOW PRESSURE TRACKS ACROSS LAKE SUPERIOR.  THIS
WILL RESULT IN A PERIOD OF GUSTY CONDITIONS FOR PORTIONS OF SOUTHERN
AND CENTRAL LAKE HURON BY LATE THURSDAY NIGHT AND EARLY FRIDAY.  THE
POTENTIAL EXISTS FOR SOME GUSTS OF UP TO 30 KNOTS...ALTHOUGH THE
ARRIVAL OF WARMER AIR WILL MAINTAIN A HIGHER DEGREE OF STABILITY
NEAR THE SURFACE.  THERE WILL BE A SLIGHT CHANCE FOR THUNDERSTORMS
AS WIDESPREAD SHOWERS MOVE THROUGH DURING THIS TIME.  A GUSTY
WESTERLY WIND FOR THE WEEKEND AS SEASONABLY COLD AIR OVERSPREADS THE
LAKES REGION.

&&

.AVIATION...ISSUED 147 PM EDT WED OCT 1 2014

//DISCUSSION...

RESIDUAL CYCLONIC FLOW IN ADDITION TO A RELATIVELY MOIST
SOUTHEASTERLY FLOW IS MAINTAINING A FAVORABLE ENVIRONMENT FOR
BOUNDARY LAYER CLOUD TODAY. LACK OF ADVECTION DURING THE NEXT 6
HOURS WILL MAKE CLEARING TRENDS VERY SLUGGISH. LATEST SATELLITE
IMAGERY SUPPORTS A CONVERSION OF CLOUD INTO CUMULOFORM AND CELL
BASED CONVECTIVE ELEMENTS. EXPECT DEEPENING CONVECTIVE CIRCULATIONS
TO LEAD TO A GREATER CLOUD SCALE SUBSIDENCE COMPONENT WHICH WILL
HELP NOCTURNAL COOLING PROCESSES THIS EVENING IN ALLOWING CLOUDS TO
DISSIPATE. PROVIDED THAT CLOUD COVER LESSENS TONIGHT...THE CONTINUED
LACK OF DRY AIR ADVECTION WILL THEN ALLOW THE POTENTIAL FOR FOG
DEVELOPMENT. CONFIDENCE IN COVERAGE AND TIMING IS LOW AT THIS
POINT...ALTHOUGH MODEL SOUNDINGS DO SUGGEST THAT DEVELOPMENT COULD
HAPPEN RATHER QUICK...SOMETIME SHORTLY AFTER MIDNIGHT.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT PERSISTING THIS
AFTERNOON.

* LOW TO MEDIUM CONFIDENCE IN CEILINGS BELOW 200 FT AND/OR
VISIBILITIES BELOW A HALF MILE AFTER MIDNIGHT.

&&

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

&&

$$

SHORT TERM...CB
LONG TERM....MR/MM
MARINE.......MR
AVIATION.....CB


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





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