Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221803
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
103 PM EST SAT NOV 22 2014

.AVIATION...

//DISCUSSION...

LOW PRESSURE ORGANIZING OVER CENTRAL CANADA AND THE PLAINS STATES
TODAY WILL MAINTAIN MILDER SOUTHERLY WIND OVER SE MICHIGAN THROUGH
SUNDAY. LOW LEVEL WIND SHEAR REMAINS IN PLACE BELOW 2000 FEET IN
THIS PATTERN ENHANCED BY LIMITED BOUNDARY LAYER MIXING. CEILING
WILL BE NO BETTER THAN MVFR THROUGH THE PERIOD COMBINED WITH
INTERVALS OF IFR IN BOTH CEILING AND VISIBILITY DEPENDING ON MILD
AIR INTERACTIONS WITH SNOW COVER. THE LATEST OBSERVATIONAL DATA
SUGGESTS THIS IS MOST LIKELY SUNDAY MORNING AS INCREASING SURFACE
DEWPOINT COMBINES WITH THE NEXT SURGE OF RAIN SHOWERS. EXPECT THE
SHOWERS TO LAST OFF AND ON INTO SUNDAY AFTERNOON WITH A MODEST
IMPROVEMENT TO LOW END MVFR CEILING DURING THE DAY.

FOR DTW... PRECIPITATION TYPE WILL REMAIN FIRMLY IN THE FORM OF ALL
RAIN GOING FORWARD IN THE FORECAST TODAY THROUGH SUNDAY.
TEMPERATURES WILL CONTINUE A STEADY RISE EVEN AFTER SUNSET TONIGHT
WITH READINGS IN THE LOWER TO MID 40S BEFORE THE NEXT SURGE OF RAIN
SHOWERS BEGINS SUNDAY MORNING.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING BELOW 5000 FEET.

* HIGH CONFIDENCE IN RAIN AS PRECIPITATION TYPE TODAY THROUGH
  SUNDAY.

&&

.PREV DISCUSSION...ISSUED 1130 AM EST SAT NOV 22 2014

UPDATE...

WARMER AIR SURGING INTO SE MICHIGAN HAS ELIMINATED THE FREEZING
RAIN HAZARD BY LIFTING TEMPS INTO THE MID AND UPPER 30S ACROSS
THE REGION. UPSTREAM OBSERVATIONS DURING THE LATE MORNING INDICATE
EVEN WARMER AIR ON OUR DOORSTEP WITH READINGS IN THE UPPER 40S TO
LOWER 50S ENTERING CENTRAL AND SOUTHERN INDIANA. WE WILL LIKELY
NOT WARM UP THAT MUCH BASED ON THE PACE OF SURFACE WARM ADVECTION
OVER SNOW COVER IN OUR AREA BUT MID TO UPPER 40S LOOK REACHABLE.

COVERAGE OF SHOWERS WILL CONTINUE DIMINISHING DURING THE
AFTERNOON WITH A DRIZZLE COMPONENT ADDED DUE TO MID LEVEL
SUBSIDENCE BETWEEN SHORT WAVES ALOFT. THIS WILL KEEP CONDITIONS
DAMP AND CLOUDY WITH FOG ALSO BECOMING MORE NOTICEABLE AS THE
INCREASINGLY MILD AIR FLOWS OVER THE SNOW COVER.

PREV DISCUSSION...ISSUED 330 AM EST SAT NOV 22 2014

SHORT TERM...TODAY AND TONIGHT

TEMPERATURES ARE STILL IN THE LOW TO MID 20S EARLY THIS
MORNING...WITH SURFACE DEW PTS IN THE LOWER TEENS.
WITH THIS AMOUNT OF LOW LEVEL DRY AIR IN PLACE...BOUNDARY LAYER WET
BULB TEMPERATURES LOOK TO REMAIN BELOW FREEZING THROUGH THE MORNING
HOURS...PER 00Z NAM. MEANWHILE...WATER VAPOR IMAGERY SHOWS MID LEVEL
WAVE/CIRCULATION LIFTING INTO THE WESTERN GREAT LAKES...WHICH WILL
ALLOW FOR SUBSTANTIAL SURGE OF WARM AND MOIST AIR TO ARRIVE THIS
MORNING...WITH 850 MB DEW POINTS RISING TO BETWEEN 4-5 C. THIS WILL
LEAD TO SOME INSTABILITY...AS SHOWLATER INDEX FALLS TO AROUND ZERO
WITH GOOD MID LEVEL (700-500 MB) LAPSE RATES IN EXCESS OF 7 C/KM
WORKING THROUGH SOUTHERN LOWER MICHIGAN. DUE TO THE CONVECTIVE
NATURE OF THE ACTIVITY...TOUGH TO GAUGE QPF AREAL COVERAGE...AS
ESPECIALLY THE 00Z GFS IS LIKELY OVERDONE. STILL...BASED ON UPSTREAM
RADAR TRENDS...65-80 PERCENT POPS APPEAR APPROPRIATE...AND HAVE
ELECTED TO EXTEND FREEZING RAIN ADVISORY SOUTH...AS A QUICK GLAZE OF
ICE APPEARS LIKELY WITH THE FROZEN GROUND. SELF-LIMITING
PROCESS/LATENT HEAT RELEASE FROM THE FREEZING RAIN WITH NO COLD AIR
FEED WILL ASSURE TRANSITION TO JUST COLD RAIN AS THE DEEP AND STRONG
SOUTHWEST FLOW OVERSPREADS THE AREA...AND THE WARMER RAIN DROPS TAKE
HOLD. ALTHOUGH ACTIVITY MAY TAPER OFF TO DRIZZLE THIS
AFTERNOON...ANOTHER DEEPER SURGE OF MOISTURE TONIGHT...PW VALUES
INCREASING TO 1 INCH SHOULD ASSURE FURTHER ADDITIONAL LIGHT
RAIN/DRIZZLE...AS MERGING HEIGHT FALLS TAKE PLACE OVER THE CENTRAL
CONUS...BACKING THE FLOW OVER THE MISSISSIPPI RIVER VALLEY. WITH
FORECASTED (SEE EURO) SURFACE DEW PTS OF 40 F COMING OVER COLD/SNOW
COVERED GROUND OVER SOUTHERN LOWER MICHIGAN...ZONES WILL CONTAIN
SOME MENTION OF FOG. THE COLD SNOW COVERED GROUND IS ALSO EXPECTED
TO INHIBIT THE MIXING DEPTHS TODAY...AND THINK WIND GUSTS WILL BE
HARD PRESSED TO EXCEED MUCH PAST 20 KNOTS...DESPITE THE GOOD LOW
LEVEL JET (50 KNOTS).

LONG TERM...

SUNDAY...COMPACT SOUTHERN STREAM MID LEVEL WAVE NOTED ON WATER VAPOR
THIS MORNING EJECTING EASTWARD ACROSS NORTHERN MEXICO WILL STEADILY
LIFT NORTHEAST AND EVENTUALLY ACROSS THE GREAT LAKES BY SUNDAY
NIGHT.  MOIST LOW LEVEL SOUTHERLY FLOW ALONG THE EASTERN FLANK OF
THE MAIN HEIGHT FALLS WILL MARK CONDITIONS LOCALLY IN ADVANCE OF
THIS SYSTEM ON SUNDAY.  A RENEWED PERIOD OF STRONGER MOIST
ISENTROPIC ASCENT WILL TRANSLATE FROM SOUTH TO NORTH ACROSS THE
REGION DURING THE FIRST HALF OF THE DAY.  THIS PROCESS WILL IMPROVE
THE OVERALL MOISTURE QUALITY /PW AROUND 1 INCH/...IN ADDITION TO
SUPPORTING SOME LIGHT SHOWER DEVELOPMENT DURING THIS TIME.  A BRIEF
LULL IN THE FORCING FOR MIDDAY WILL PROVIDE THE GREATEST WINDOW FOR
A BETTER THERMAL RESPONSE.  A BACKGROUND OF WEAK WARM AIR ADVECTION
WILL COUNTER THE LACK OF MIXING AND INSOLATION POTENTIAL...ALLOWING
HIGHS TO MAKE A RUN TOWARD THE 50 DEGREE MARK.

SUNDAY NIGHT...STRONG MID LEVEL DYNAMICS ANCHORED BY STOUT LEFT EXIT
REGION UPPER JET FORCING...DIVERGENCE AND INCREASING CVA ATTENDANT
TO THE INBOUND WAVE WILL SWEEP ACROSS SE MICHIGAN SUNDAY NIGHT.
THIS FORCING INTO THE EXISTING VERY MOIST AMBIENT ENVIRONMENT WILL
RESULT IN A 6-9 HOUR PERIOD OF WIDESPREAD RAINFALL FOR THE ENTIRE
REGION OVERNIGHT.  QPF AMOUNTS WITHIN THE .5" TO .75" RANGE LOOK
ATTAINABLE GIVEN THE UNDERLYING STRENGTH OF ASCENT...MOISTURE DEPTH
AND OVERALL RESIDENCE TIME.  A FIRM SOUTHEAST GRADIENT WILL CONTAIN
TEMPERATURES IN THE LOWER AND MIDDLE 40S THROUGH THE NIGHT.

MONDAY...00Z NAM REMAINS OUTSIDE THE MODEL CONSENSUS WHICH HOLDS
WITH A MUCH DEEPER SURFACE LOW AS IT TRACKS FROM THE SOUTH END OF
LAKE MICHIGAN THROUGH NORTHERN LAKE HURON DURING THIS TIME.  00Z GFS
SEEMINGLY TOO AGGRESSIVE WITH THE RESPONSE /966 MB CENTER AT 18Z MON
NORTH OF THE STRAITS/...OWING TO MORE PRONOUNCED PHASING OF THE LEAD
PV FEATURE WITH A TRAILING NORTHERN STREAM TROUGH THAT BECOMES
NEGATIVELY TILTED.  THE NET RESULT IS A MORE SIZABLE DIFFERENCE IN
HANDLING THE DETAILS IN THE WAKE OF THE EXITING MAIN MOISTURE PLUME
HEADING INTO MONDAY.  SLIVER OF MILDER PRE-COLD FRONTAL AIR WILL
EXIST MONDAY MORNING...THE TRAILING COLD FRONTAL PASSAGE MOST LIKELY
COMMENCING DURING THE LATTER HALF OF THE DAY.  AT THIS POINT...MAIN
ELEMENT OF CONCERN BECOMES THE WIND POTENTIAL MONDAY AFTERNOON AND
EVENING...AS THE ENSUING ADVECTIVE PROCESS BUILDS THE CONVECTIVE
LAYER DEPTH INTO AN ALREADY FIRM WIND FIELD JUST OFF THE SURFACE.  A
PERIOD OF GOOD 280-285K ISENTROPIC DESCENT WITH 35 TO 40KT WINDS
WITHIN THIS LEVEL WOULD SUGGEST PEAK GUSTS IN EXCESS OF 35 MPH ARE
ATTAINABLE...WITH AN UPTICK TO HEADLINE WORTHY GUST POTENTIAL
CERTAINLY PLAUSIBLE.  WINDOW FOR STRONG CONVERGENCE ALONG THE
FRONTAL SLOPE AND WITH THE PASSAGE OF THE TRAILING WAVE WILL
MAINTAIN A CHANCE FOR SHOWERS INTO MONDAY...PARTICULARLY DURING THE
FIRST HALF OF THE DAY.  PRE-FRONTAL TEMPERATURES PEAK IN THE UPPER
40S-LOWER 50S...STRONGER COLD AIR ADVECTION AWAITING THE BETTER
HEIGHT FALLS TOWARD EVENING.

TUESDAY AND BEYOND...SUBSTANTIAL SOUTHWARD EXPANSION OF THE LOWER
HEIGHT FIELD WILL SPELL ANOTHER EXTENDED STRETCH OF BELOW NORMAL
TEMPERATURES STARTING TUESDAY.  PLACEMENT OF AN ENERGETIC NORTHERN
PACIFIC JET CORE SOUTHEAST AND NEAR/OVER THE GREAT LAKES WILL BRING
THE POTENTIAL FOR A PERIODICALLY ACTIVE PATTERN THROUGH THE UPCOMING
HOLIDAY WEEKEND.  POTENTIAL FOR LIGHT SNOW SHOWERS TUESDAY WITHIN A
MOIST CYCLONIC FLOW...AUGMENTED BY THE MOISTURE FLUX OFF LAKE
MICHIGAN.  WEAK SHORTWAVE WORKING THROUGH THE NORTHWEST FLOW IS
FORECAST TO DEEPEN WITHIN FAVORABLE UPPER JET SUPPORT ON
WEDNESDAY...LONG RANGE MODEL GUIDANCE ALLOWING THIS WAVE TO SHIFT
INTO SOUTHEAST MICHIGAN BY THANKSGIVING.  WHILE SUBJECT TO CHANGE
YET AT THIS TIME SCALE...LATEST TRENDS WOULD BRING THE POTENTIAL FOR
A LIGHT ACCUMULATING SNOWFALL WITH THIS SYSTEM FOR THE HOLIDAY.

MARINE...

SOUTHWEST WINDS WILL REMAIN STRONG THROUGH THE FIRST HALF OF TODAY.
GUSTS TO GALES OR NEAR GALES WILL EXIST OVER CENTRAL PORTIONS OF
LAKE HURON THROUGH THE MORNING PERIOD.  WINDS WILL EASE SLIGHTLY
THIS AFTERNOON AS THE OVERALL GRADIENT SLACKENS.  A MODEST SOUTHERLY
WIND WILL EXIST TONIGHT AND SUNDAY IN ADVANCE OF STRENGTHENING LOW
PRESSURE.  SOME INCREASE IN SOUTHEAST WINDS WILL OCCUR AS THIS LOW
TRACKS FROM SOUTHERN LAKE MICHIGAN TO THE STRAITS SUNDAY NIGHT.  THE
COMBINATION OF AN INCREASING GRADIENT AND THE RETURN OF COLDER AIR
WILL BRING THE POTENTIAL FOR GALES ACROSS ALL MARINE AREAS BY MONDAY
AFTERNOON AND EVENING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR LHZ421-441.

     SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LHZ442.

LAKE ST CLAIR...NONE.

MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....BT
UPDATE.......BT
SHORT TERM...SF
LONG TERM....MR
MARINE.......MR


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


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