Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 182057
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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...

&&

.AVIATION...ISSUED 1205 PM EST TUE NOV 18 2014

//DISCUSSION...

A GENERAL WEST-SOUTHWEST WIND FIELD WILL PERSIST THROUGH THE
REMAINDER OF THE AFTERNOON...KEEPING THE MORE NUMEROUS SNOW SHOWER
ACTIVITY AT PTK AND FNT. SOME ADDITIONAL MINOR ACCUMULATIONS ARE
POSSIBLE AT FNT...WHERE THE SNOW SHOWERS SHOULD BE A LITTLE MORE
INTENSE. THE LOW LEVEL WIND FIELD WILL BACK TOWARD THE SOUTH THIS
EVENING INTO THE OVERNIGHT. THIS WILL CAUSE THE REMNANT SNOW SHOWERS
TO LIFT UP TO MBS. THE COLD AIR WILL SUSTAIN A DEEP ENOUGH MIXED
LAYER TO HOLD WIND GUSTS IN THE 25 TO 30 KNOT RANGE THIS AFTERNOON.
WIND GUSTS ARE EXPECTED TO DROP OFF THIS EVENING AS COOLING IN THE
BOUNDARY LAYER REDUCES THE MIXING POTENTIAL.

FOR DTW...THE SOUTHWEST FLOW WILL HOLD THE BULK OF THE SNOW
SHOWERS/FLURRIES NORTH OF METRO THIS AFTERNOON. DAYTIME HEATING HAS
INTERACTED WITH A SHALLOW MOISTURE LAYER TO SUSTAIN WIDESPREAD
STRATO CU FIELD...WHICH HAS BEEN GRADUALLY LIFTING TO 3000-3500FT.
GIVEN THE EXTENT OF CLOUDS UPSTREAM...EXPECT THESE WILL HOLD
THROUGH A GOOD PORTION OF THE AFTERNOON. SOME DRIER AIR LIFTING UP
FROM THE SOUTH THIS EVENING AND THE SUBSEQUENT LOSS OF DIURNAL
MIXING IS EXPECTED TO LEAD TO SOME DEGREE OF A CLEARING TREND OVER
METRO DETROIT. THERE DOES HOWEVER REMAIN A GOOD DEGREE OF
UNCERTAINTY AS TO HOW QUICKLY THE LOW CLOUDS WILL CLEAR OUT.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT THROUGH THIS AFTERNOON.
  LOW CONFIDENCE TONIGHT.

* HIGH CONFIDENCE IN PTYPE OF SNOW.

&&

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

     GALE WARNING UNTIL 10 PM EST THIS EVENING FOR LHZ361-421-422-
     441>443.

LAKE ST CLAIR...GALE WARNING UNTIL 10 PM EST THIS EVENING FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WARNING UNTIL 10 PM EST THIS EVENING FOR LEZ444.

     LOW WATER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR LEZ444.

&&

$$

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


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



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