Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 190446
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1146 PM EST TUE NOV 18 2014


.AVIATION...

//DISCUSSION...

SOUTHWEST WINDS WILL CONTINUE TO BACK TOWARD THE SOUTH
OVERNIGHT...CONFINING SNOW SHOWERS TO THE MBS AREA. A LOW PRESSURE
SYSTEM WILL BRING WIDESPREAD SNOW SHOWERS TO THE TAF SITES ON
WEDNESDAY AS ANOTHER BLAST OF COLD AIR ADVECTS INTO THE CENTRAL
GREAT LAKES. THIS SYSTEM WILL BRING A GENERAL 1 TO 3 INCHES OF SNOW
TO THE TAF SITES ON WEDNESDAY AS CONDITIONS FALL TO IFR. BEHIND THE
LOW LIGHT SNOW SHOWERS AND FLURRIES WILL PREVAIL LATE WEDNESDAY
AFTERNOON AND INTO THE EVENING HOURS AS CONDITIONS IMPROVE TO MVFR.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT LATE WEDNESDAY
  MORNING AND EARLY AFTERNOON THROUGH WEDNESDAY NIGHT.

* HIGH CONFIDENCE IN PTYPE OF SNOW.

&&

.PREV DISCUSSION...ISSUED 357 PM EST TUE NOV 18 2014

SHORT TERM...TODAY AND TONIGHT

LOW CONVECTIVE DEPTH OF LAKE EFFECT SNOW BANDS HAS LIMITED THE
REFLECTIVITY RELIABILITY FOR THE CENTER PART OF THE STATE THIS
AFTERNOON. VISIBLE SATELLITE SHOWS 2 MODERATE LAKE EFFECT BANDS
REACHING INTO THE CWA...WITH A THIRD BAND SPUTTERING OUT AS IT
REACHES WASHTENAW COUNTY. THE NORTHERN TWO BANDS SPARKED SPS
ISSUANCE I-69 NORTHWARD...BUT ACCUMS SHOULD REMAIN UNDER ONE
INCH. THE CONTINUED BACKING OF THE LOW LEVEL WIND FIELD WILL
ENCOURAGE BANDING TO LIFT NORTHWARD THROUGH THE EVENING.
THIS WILL PUT THE SAGINAW VALLEY IN THE FAVORABLE AREA TO SEE LIGHT
SNOW THROUGH TONIGHT.

AS SOUTH TO SOUTHWEST WINDS CROSS LAND AREAS IN INDIANA BEFORE
REACHING THE CWA...THEY WILL DRAW IN DRIER AIR. THIS POSES THE
CHANCE FOR SLIGHT CLEARING IN OUR SOUTHERN AREAS. HAVE DROPPED MIN
TEMPS IN THE SOUTH DUE TO THIS EFFECT. DETROIT WILL BE PUSHING NEAR
RECORD LOW VALUES (9F IN 1880) AS CLEARING DROPS THE FORECAST MIN
TO NEAR 10F. FLINT IS ALSO FLIRTING WITH THE RECORD (13 IN 1986)
TONIGHT WITH TEMPS DROPPING TO THE LOW TEENS.

HIGH WINDS WILL SLACKEN A BIT AFTER SUNDOWN...BUT EXPECT OVERNIGHT
GUSTS TO BE IN THE 15 TO 20 MPH RANGE. THIS COULD CAUSE SOME
DRIFTING AND BLOWING SNOW...BUT THE REAL DANGER IS WIND CHILL.
APPARENT TEMPERATURE WILL RANGE FROM 0 TO -5F FROM M-59 SOUTHWARD
TONIGHT...AND ALSO IN THE THUMB REGION. OUTSIDE OF THOSE
AREAS...CLOUD COVER SHOULD KEEP TEMPS FROM DROPPING OFF AS MUCH.

LONG TERM...WEDNESDAY THROUGH NEXT TUESDAY

UPPER ENERGY SEEN ON WATER VAPOR STRETCHING FROM VICTORIA ISLAND
CANADA INTO MANITOBA WILL CONSOLIDATE AND FORM AN UPPER TROUGH OVER
ONTARIO AND THE NORTHERN GREAT LAKES TONIGHT THROUGH WEDNESDAY. THE
UPPER TROUGH AXIS WILL THEN MOVE ACROSS LOWER MICHIGAN LATE
WEDNESDAY NIGHT INTO THURSDAY. THIS WILL PROVIDE ANOTHER ROUND OF
SNOW TOMORROW...FOLLOWED BY A REINFORCING BLAST OF ARCTIC AIR
WEDNESDAY NIGHT INTO THURSDAY WHICH WILL RE-INVIGORATE LAKE EFFECT
PROCESSES.

SURFACE TROUGH WILL GET PUSHED ACROSS THE AREA TOMORROW AHEAD OF THE
UPPER SYSTEM. A WEAK ELEVATED WARM FRONT WILL LIFT ACROSS SOUTHEAST
MICHIGAN DURING THE LATE MORNING AND AFTERNOON IN ADVANCE OF THE
SYSTEM...PROVIDING ISENTROPIC ASCENT (AND PERHAPS A LITTLE WEAK FGEN
IN THE 700-850MB LAYER PER 12Z NAM) TO GENERATE SNOW. LIFT FROM THE
FRONT COMBINED WITH LIFT AHEAD OF THE SURFACE/UPPER TROUGH LOOKS TO
BE MAXIMIZED RIGHT IN THE DENDRITIC GROWTH ZONE. MOISTURE LOOKS GOOD
WITHIN THIS LAYER AS WELL...WITH SPECIFIC HUMIDITIES RANGING BETWEEN
1-2 G/KG UP THROUGH 600MB. WITH THE ARRIVAL OF FORCING AND
MOISTURE...EXPECTING ACCUMULATING SNOW TO SPREAD INTO SOUTHEAST
MICHIGAN AROUND 9-10 AM...AND TAPER OFF AROUND 4-5 PM AS ISENTROPIC
ASCENT REALLY STARTS TO WEAKEN PER NAM/GFS. VERY COLD AIRMASS STILL
IN PLACE SHOULD ALLOW FOR GOOD SNOW TO LIQUID RATIOS (15:1-20:1).
STILL EXPECTING TO SEE BETWEEN 1 AND 3 INCHES OF SNOW LATE TOMORROW
MORNING THROUGH TOMORROW AFTERNOON.

COLD FRONT ON THE BACKSIDE OF THE SURFACE TROUGH WILL THEN PUSH
ACROSS THE AREA WEDNESDAY EVENING. COLD AIR RUSHING IN BEHIND THE
FRONT WILL INCREASE LAPSE RATES AND ALLOW THE BOUNDARY LAYER TO
DEEPEN...NOT ONLY CREATING A MORE FAVORABLE ENVIRONMENT FOR LAKE
EFFECT SNOW OFF LAKE MICHIGAN...BUT ALSO ALLOWING GUSTS TO 35 MPH TO
DEVELOP AS A STRONGER CORE OF WINDS ALOFT IS ABLE TO MIX DOWN TO THE
SURFACE. VERY STEEP LAPSE RATES (9-10 C BELOW 850MB)...SATURATION ON
MODEL SOUNDINGS FROM OFF THE LAKE BELOW THE INVERSION HEIGHT NEAR
850MB (ALL WITHIN THE DGZ)...AND GOOD WESTERLY FLOW WILL PROVIDE A
FAVORABLE LAKE-EFFECT SET UP WEDNESDAY NIGHT THROUGH THURSDAY. BANDS
SHOULD CARRY INTO THE EASTERN PART OF THE STATE...WITH WESTERLY FLOW
FAVORING AREAS BETWEEN I-69 AND I-94. ADDITIONAL ACCUMULATIONS ARE
POSSIBLE BOTH PERIODS...BUT LIKE LAST NIGHT...ACCUMULATIONS WILL BE
SPOTTY IN NATURE AS BANDS AND EMBEDDED CONVECTION FLUCTUATE. THIS
WILL NOT BE PURELY LAKE EFFECT HOWEVER...AS THE UPPER TROUGH AXIS
MOVING ACROSS THE AREA LATE WEDNESDAY NIGHT THROUGH EARLY THURSDAY
WILL ALSO CONTRIBUTE TO LIGHT SNOW SHOWERS.

TEMPERATURES WILL REMAIN WELL BELOW NORMAL OVER THE NEXT FEW DAYS
WITH SOME RECOVERY TOMORROW EXPECTED TOMORROW AS WARMER AIR TRIES TO
SNEAK IN AHEAD OF THE TROUGH...BEFORE H850 TEMPERATURES FALL BACK
DOWN TO -16C BY THURSDAY. GUSTY WINDS COMBINED WITH THE COLD ON
THURSDAY WILL HOLD WIND CHILLS INTO THE SINGLE DIGITS MOST OF THE
DAY.

THE STORY FOR THE REMAINDER OF THE FORECAST WILL BE THE WARMING
TREND AND ACCOMPANYING PRECIPITATION CHANCES. THIS WILL OCCUR AS THE
PERSISTENT UPPER TROUGH PLAGUING MUCH OF THE EASTERN CONUS SHIFTS
EAST WITH RISING HEIGHTS IN ITS WAKE. FIRST...ONE MORE DAY OF VERY
COLD TEMPERATURES FRIDAY AS THE THERMAL TROUGH IS SLOW TO EXIT. WARM
AND MOIST ADVECTION WILL ENSUE FRIDAY NIGHT INTO SATURDAY WITH
MODELS DEPICTING SATURATION AND LIGHT QPF BY SATURDAY. THIS MAY POSE
SOME PTYPE ISSUES EARLY SATURDAY AS MILDER AIR OVERRUNS THE COLDER
SURFACE AIR WHICH MAY BE SLOW TO DISLODGE. GLOBAL MODELS ARE IN
GENERALLY GOOD AGREEMENT WITH PROGRESSION OF A WAVE LIFTING
NORTHWARD FROM TX AND ACCOMPANYING SURFACE LOW...THOUGH SOME TIMING
DIFFERENCES EXIST. BEST DYNAMICS LOOK TO BE IN THE SAT NIGHT/SUNDAY
TIMEFRAME...WITH LIKELY POPS ACCORDINGLY. 850 MB TEMPS INCREASE TO
+6C SO ALL RAIN IS EXPECTED. HIGH TEMPS LOOK TO RETURN BACK TO NEAR
NORMAL BY SUNDAY. RAIN CHANCES LINGER INTO MONDAY AS WE STAY
DOWNSTREAM OF THE LONGWAVE TROUGH.

MARINE...

WHILE THERE HAS BEEN A SLIGHT DOWNWARD TREND NOTED IN RECENT MARINE
OBSERVATIONS...GALE FORCE GUSTS UP TO 40 KNOTS ARE STILL BEING
REPORTED AS OF 19Z. WINDS WILL GRADUALLY WEAKEN BELOW GALE FORCE
DURING THE COURSE OF THE NIGHT AS THE GRADIENT RELAXES. THIS WILL BE
THE RESULT OF THE DEEP LOW PRESSURE SYSTEM OVER QUEBEC LIFTING
NORTHEAST. WINDS WILL THEN BACK TO THE SOUTH WEDNESDAY MORNING AS
LOW PRESSURE DEVELOPS OVER THE WESTERN GREAT LAKES. THE LOW IS
FORECAST TO DEEPEN AS IT TRACKS ACROSS LAKE HURON AND INTO QUEBEC
WED NIGHT INTO THURSDAY. THIS WILL RESULT IN A VEERING OF THE WINDS
BACK TOWARD THE WEST AND A GOOD CHANCE THAT A NEW ROUND OF GALE
WARNINGS WILL BE NEEDED WED NIGHT INTO THURSDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...GALE WARNING UNTIL 4 AM EST WEDNESDAY FOR LHZ362-363-462>464.

     SMALL CRAFT ADVISORY UNTIL 4 AM EST WEDNESDAY FOR LHZ422-442-443.

     SMALL CRAFT ADVISORY UNTIL 7 AM EST WEDNESDAY FOR LHZ421-441.

LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 4 AM EST WEDNESDAY FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 4 AM EST WEDNESDAY FOR LEZ444.

     LOW WATER ADVISORY UNTIL 4 AM EST WEDNESDAY FOR LEZ444.

&&

$$

AVIATION.....KURIMSKI
SHORT TERM...MM
LONG TERM....HLO/DT
MARINE.......SC


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



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