Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 172336
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
636 PM EST MON NOV 17 2014

.AVIATION...

//DISCUSSION...

COLD WESTERLY WINDS OFF LAKE MICHIGAN WILL MAINTAIN A FAVORABLE
ENVIRONMENT FOR NUMEROUS SNOW SHOWERS TO SHIFT ACROSS THE DETROIT TO
FLINT CORRIDOR BOTH TONIGHT AND ON TUESDAY.  RECENT RADAR RETURNS
INDICATE PERIODIC DIPS INTO IFR CAN BE EXPECTED WITHIN ANY HEAVIER
SNOW SHOWERS.  BOTH THE COVERAGE AND DURATION OF THESE CONDITIONS
CURRENTLY REMAIN TOO LOW TO PROVIDE A MORE DEFINITIVE PREVAILING
GROUP OF IFR AT ANY ONE LOCATION.  THE MOST INTENSE AND GREATEST
COVERAGE OF LAKE EFFECT SNOW SHOWERS IS EXPECTED TO EMERGE LATE
TONIGHT INTO TUESDAY MORNING.  OUTSIDE OF THESE SNOW SHOWERS...
CONDITIONS WILL RECOVER INTO VFR WITHIN AN EXTENSIVE CANOPY OF LAKE
STRATUS.  AN EASTWARD PUSH OF MVFR CEILING REMAINS PLAUSIBLE...
PARTICULARLY LATE TONIGHT AND EARLY TUESDAY.  GUSTY WEST-SOUTHWEST
WINDS INTO THE 25 KNOT RANGE WILL HOLD THROUGH TUESDAY.

FOR DTW...INTERMITTENT DISRUPTIONS TO VISIBILITY /IFR/ WILL CONTINUE
THROUGH THE NIGHT AS SNOW SHOWERS MOVE THROUGH THE AIRSPACE.
LIMITED DURATION OF ANY ONE SNOW SHOWER WILL CONTAIN THE OVERALL
ACCUMULATION POTENTIAL...A DUSTING TO HALF INCH AMOUNTS POSSIBLE
THROUGH TUESDAY MORNING.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT THROUGH TUESDAY.

* HIGH CONFIDENCE IN PTYPE OF SNOW.

&&

.PREV DISCUSSION...ISSUED 353 PM EST MON NOV 17 2014

SHORT TERM... LATE AFTERNOON THROUGH TUESDAY

ARCTIC AIR SURGING INTO THE GREAT LAKES WILL MAKE LAKE EFFECT SNOW
AND COLD WIND CHILL THE PRIMARY CONCERNS IN THE FORECAST TONIGHT
THROUGH TUESDAY. A WINTER WEATHER ADVISORY IS IN EFFECT TONIGHT
THROUGH NOON TUESDAY GENERALLY ALONG AND BETWEEN INTERSTATE 69 AND
94 CENTERED ON THE 96/59 CORRIDOR. THIS IS TO COVER LAKE EFFECT
ACTIVITY THAT WILL MOVE EASTWARD FROM LAKE MICHIGAN IN POCKETS
DURING THE EVENING THEN STEADILY INCREASE IN COVERAGE AND INTENSITY
OVERNIGHT WITH A PEAK ROUGHLY BETWEEN 3 AM AND 9 AM TUESDAY MORNING.
SNOW SHOWER COVERAGE WILL DIMINISH TO THE NORTH THROUGH THE SAGINAW
VALLEY AND TO THE SOUTH TOWARD THE OHIO BORDER IN A TYPICAL WESTERLY
FLOW CONFIGURATION. WHILE THE SNOW SHOWERS WILL BE CONCENTRATED
THROUGH CENTRAL SECTIONS...COLD TEMPERATURES WILL BE WIDESPREAD
ACROSS THE REGION AND TAKE WIND CHILL DOWN INTO THE RANGE FROM ZERO
TO ABOUT 5 BELOW BY SUNRISE.

COLD WESTERLY FLOW OVER LAKE MICHIGAN WILL BE THE PRIMARY DRIVING
FORCE FOR THE LAKE EFFECT EVENT BUT WILL BE MODULATED UPWARD BY A
SHARP UPPER LEVEL TROUGH MOVING OVERHEAD DURING THE NIGHT THAT WILL
BRING A NEAR RECORD COLD CORE ALOFT OVER THE REGION. THERE IS GOOD
MODEL AGREEMENT ON THE 500 MB COLD CORE OBSERVED OVER CENTRAL CANADA
AT 12Z TO MOVE OVER SE MICHIGAN BY 12Z TUESDAY AVERAGING -41C. THIS
COMPARES TO THE RECORD LOW OF -34C FOR NOVEMBER 18 AND TIES -41C FOR
THE ENTIRE MONTH IN THE DTX UPPER AIR DATABASE. THE COLD AIR ALOFT
AND THE DYNAMIC SUPPORT ASSOCIATED WITH THE TROUGH WILL LEAD TO A
SURGE IN THE ALREADY GOOD START TO LAKE EFFECT UNDERWAY DURING THE
DAY. THE MAIN SOURCE OF UNCERTAINTY LIES WITH THE STRENGTH OF THE
LOW LEVEL WIND FIELD ACTUALLY BEING A LIMITING FACTOR FOR ORGANIZED
AND PERSISTENT BANDS. GUSTY WIND IS EXPECTED TO CONTINUE THROUGH THE
NIGHT IN A WELL MIXED BOUNDARY LAYER THAT WILL TEND TO REDUCE THE
STRENGTH OF LOW LEVEL WIND CONVERGENCE IN THE LEE OF LAKE MICHIGAN.
AT THE SAME TIME...CONVECTIVE DEPTH APPROACHING 10 KFT WILL HAVE A
SURFACE DELTA THETA-E OF 2-4C...WHICH IS A GOOD MEASURE OF CAPE
DENSITY ADEQUATE FOR NUMEROUS CLUSTERS OF INTENSE LAKE EFFECT SNOW
SHOWERS TO SURVIVE THE TRIP ACROSS LOWER MICHIGAN. MODEL SOUNDINGS
INDICATE CONVECTIVE DEPTH BEING MAINTAINED FROM THE LAKESHORE INTO
SE MICHIGAN AS THE UPPER WAVE SLIDES OVER THE REGION MARKING THE
PEAK OF THE EVENT FOR THE ADVISORY. IF NOT AN ORGANIZED BAND...THEN
NUMEROUS CLUSTERS OF HEAVY LAKE EFFECT SNOW SHOWERS ARE EXPECTED TO
RESULT IN LOCALIZED ACCUMULATION OF 3 TO 4 INCHES MAINLY IN THE 6
HOUR PERIOD BETWEEN 3 AM AND 9 AM. THIS IS ENTRY LEVEL FOR ADVISORY
ISSUANCE BUT COUPLED WITH MORNING COMMUTE TIMING TIPS THE SCALE IN
FAVOR OF HEADLINE ISSUANCE.

SUBSIDENCE INDUCED BY THE PASSAGE OF THE UPPER TROUGH IS EXPECTED TO
FORCE A CONSIDERABLE DECREASE IN LAKE EFFECT COVERAGE AND INTENSITY
BY TUESDAY AFTERNOON. NUMEROUS SNOW SHOWERS THROUGH THE ADVISORY
AREA WILL BECOME WEAKER AND MORE SCATTERED AS ACTIVITY STRUGGLES TO
MOVE THROUGH SW LOWER...ESPECIALLY AS DIURNAL BOUNDARY LAYER MIXING
INCREASES DURING PEAK HEATING...SUCH AS IT IS WITH MAX TEMPS
ONLY REACHING THE LOWER 20S.

LONG TERM...

..WIDESPREAD SNOW ON WEDNESDAY...

PRONOUNCED ANTI-CYCLONIC FLOW/SURFACE RIDGE BUILDING IN TUESDAY
NIGHT WILL TAPER OFF AND PUSH ANY REMNANT LAKE MICHIGAN BAND/PLUME
NORTH. INCREASING HIGH CLOUDS FROM NEXT STORM SYSTEM WILL LIKELY
PREVENT TEMPERATURES FROM CRATERING HOWEVER...AND WILL HOLD TEMPS IN
THE TEENS. WATER VAPOR IMAGERY SHOWS NEXT STRONG POLAR PV ANOMALY
DESCENDING SOUTH THROUGH NUNAVUT THIS AFTERNOON...WITH A STRONG BUT
COMPACT UPPER WAVE/JET STREAK OVER FAR NORTHERN BRITISH COLUMBIA
ALSO COMING OUT OF WESTERN CANADA. THE INTERACTION OF THESE TWO
FEATURES AS THEY COME THROUGH THE AREA ON WEDNESDAY IS COMPLICATING
THE FORECAST A BIT WITH THE PLACEMENT OF THE SURFACE LOW...BUT MODEL
CONSENSUS IS FOR THE MAIN LOW TO TRACK WELL NORTH OF SOUTHEAST
MICHIGAN...THROUGH THE NORTHERN GREAT LAKES. EVEN SO...THERE SHOULD
BE A GOOD BURST OF SNOW WITH GOOD ISENTROPIC ASCENT AND VERY
EFFICIENT SNOW TO LIQUID RATIOS...AS 850-700 MB LAYER RESIDES IN THE
-11 TO -14 C RANGE...WITH SPECIFIC HUMIDITIES AROUND 2 G/KG.
WITH LIFT FOR APPROXIMATELY 6 HRS BEFORE THE MATURE DRY SLOT PUNCHES
THROUGH...SNOWFALL ACCUMULATIONS AROUND 2 INCHES APPEARS LIKELY FOR
MAJORITY OF SOUTHEAST MICHIGAN...WITH SOUTHWEST TRAJECTORY OFF LAKE
MICHIGAN POSSIBLY ENHANCING AMOUNTS IN TRI-CITIES REGION/NORTHERN
THUMB REGION. 850 MB TEMPS DROPPING BACK DOWN INTO THE NEGATIVE
UPPER TEENS WITH CYCLONIC WESTERLY FLOW WILL BRING CONTINUE CHANCE
OF LIGHT SNOW SHOWERS WEDNESDAY NIGHT...WITH CLOUDS AND WINDS
EXPECTED TO HOLD MINS UP AROUND 20 DEGREES.

LAKE RESPONSE EXPECTED TO CONTINUE THURSDAY WITH 850 MB TEMPS AROUND
-16C AND STRONG WESTERLY LOW-LEVEL FLOW. THIS SHOULD SUSTAIN SOME
DEGREE OF SNOW SHOWER ACTIVITY THROUGH THE DAY WHILE TEMPERATURES
TOP OUT ONLY IN THE MID-20S. SURFACE HIGH WILL ATTEMPT TO BUILD IN
AT NIGHT AS UPPER LEVEL FLOW BECOMES MORE NORTHWESTERLY. THIS COULD
CAUSE TEMPS TO DIP QUITE LOW THURSDAY NIGHT...ESPECIALLY IF AREAS OF
CLEARING CAN DEVELOP. THE STORY FOR THE REMAINDER OF THE PERIOD WILL
BE A LONG-AWAITED WARMING TREND AND ACCOMPANYING PRECIPITATION
CHANCES...WITH THE MAGNITUDE OF THE WARMING AND THE TIMING OF THE
PRECIP STILL CLOUDY. THIS WILL OCCUR AS THE PERSISTENT UPPER LOW
FINALLY LIFTS TO THE NORTHEAST WITH RISING HEIGHTS OVER THE LOCAL
AREAS IN ITS WAKE. 12Z GFS/EURO IN DECENT AGREEMENT WITH A WAVE
EJECTING NORTHWARD FROM TEXAS TO THE UPPER MIDWEST DURING THE
WEEKEND...BUT WITH GEFS MEMBERS STILL ALL OVER THE PLACE WILL
DECLINE ON LIKELY POPS IN ANY ONE PERIOD. PTYPE COULD BE AN ISSUE
EARLY ON /SATURDAY AND SATURDAY NIGHT/ AS SURFACE COLD AIR MAY BE
TOUGH TO RETREAT WHILE MILDER AIR STREAMS IN ALOFT. TEMPS COULD
RETURN BACK TO NEAR NORMAL BY LATE IN THE WEEKEND.

MARINE...

A HIGH END WESTERLY GALE EVENT REMAINS ON TRACK OVER LAKE HURON TONIGHT THROUGH TUESDAY
EVENING ...AS VERY COLD AIRMASS CONTINUES TO ADVECT INTO THE CENTRAL GREAT LAKES.
AN OCCASIONAL GUST TO STORM FORCE IS NOT OUT OF THE QUESTION DURING THE PEAK OF
THE EVENT DURING TUESDAY. THE OFFSHORE FETCH WILL SPARE NEARSHORE LOCATIONS THE EFFECTS
OF THE LARGEST WAVES BUT SIGNIFICANT WAVE HEIGHTS WILL EASILY SURPASS 10 FEET FOR
SEVERAL HOURS OVER CENTRAL LAKE HURON. MAXIMUM WAVE HEIGHTS WILL APPROACH 20 FEET.
 WIDESPREAD SNOW SQUALLS CAN BE EXPECTED OVER THE OPEN WATERS OF LAKE HURON.
LOW WATER LEVELS ARE A CONCERN FOR BOTH SAGINAW BAY AND LAKE ERIE...AND LOW
WATER ADVISORY HAS BEEN ISSUED.

ANOTHER LOW AND COLD FRONT WILL PASS THROUGH THE REGION ON WEDNESDAY...AND ANOTHER
ROUND OF GALES IS POSSIBLE WEDNESDAY NIGHT INTO THURSDAY OVER THE
OPEN WATERS OF LAKE HURON.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR MIZ060-061-068-
     069-075.

LAKE HURON...GALE WARNING UNTIL 4 AM EST WEDNESDAY FOR LHZ362-363-462>464.

     GALE WARNING FROM 11 PM THIS EVENING TO 10 PM EST TUESDAY FOR
     LHZ361.

     LOW WATER ADVISORY UNTIL MIDNIGHT EST TUESDAY NIGHT FOR LHZ422.

     GALE WARNING UNTIL 10 PM EST TUESDAY FOR LHZ421-422-441>443.

LAKE ST CLAIR...GALE WARNING FROM 11 PM THIS EVENING TO 10 PM EST TUESDAY FOR
     LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WARNING FROM 11 PM THIS EVENING TO 10 PM EST TUESDAY FOR
     LEZ444.

     LOW WATER ADVISORY UNTIL MIDNIGHT EST TUESDAY NIGHT FOR LEZ444.

&&

$$

AVIATION.....MR
SHORT TERM...BT
LONG TERM....SF/DT
MARINE.......SF


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