Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220830
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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.

&&

.AVIATION...ISSUED 1150 PM EST FRI NOV 21 2014

//DISCUSSION...

A WARM FRONT...INITIALLY ELEVATED...WILL LIFT UP INTO LOWER MICHIGAN
LATE TONIGHT AND SATURDAY. THIS WILL ALLOW A WARMER LAYER OF AIR TO
SETTLE IN OVER SUB-FREEZING AIR AT THE SURFACE...POTENTIALLY LEADING
TO FREEZING RAIN AND SLEET AS MOISTURE AND LIFT ARRIVE WITH THE
FRONT. A PERIOD OF FREEZING RAIN OR SLEET WILL BE POSSIBLE BEFORE 14-
16Z BEFORE STRONGER WARM AIR ADVECTION COMMENCES AND PRECIPITATION
CHANGES TO ALL RAIN. THE FRONT WILL ALSO ALLOW CEILINGS TO FALL TO
MVFR...WITH POSSIBLY A DROP TO IFR MID-MORNING SATURDAY.

IN ADDITION...THE LOW-LEVEL JET WILL NOSE INTO THE AREA LATE TONIGHT
AND REMAIN OVERHEAD ON SATURDAY...RESULTING IN A STRONG CORE OF 40-
50 KT WINDS ABOVE 1500 FEET. LOW-LEVEL WIND SHEAR IS EXPECTED AFTER
08Z AT ALL OF THE TAF SITES AND WILL LAST THROUGH THE DAY ON
SATURDAY.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS FALLING BELOW 5000 FEET AFTER 09Z.

* MEDIUM CONFIDENCE WITH AT LEAST A LITTLE FREEZING RAIN AT ONSET OF
  PRECIPITATION BETWEEN 10Z-14Z SATURDAY. HIGH CONFIDENCE
  PRECIPITATION WILL THEN CHANGE TO RAIN DURING THE MID-MORNING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...FREEZING RAIN ADVISORY UNTIL 11 AM EST THIS MORNING FOR MIZ060>063-
     068>070-075-076-082-083.

     FREEZING RAIN ADVISORY UNTIL NOON EST TODAY FOR MIZ047>049-053>055.

LAKE HURON...GALE WARNING UNTIL 11 AM EST THIS MORNING FOR LHZ362-363-421-462-
     463.

     SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LHZ441-442.

     SMALL CRAFT ADVISORY UNTIL 11 AM EST THIS MORNING FOR LHZ422.

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

$$

SHORT TERM...SF
LONG TERM....MR
MARINE.......MR
AVIATION.....KURIMSKI


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


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