Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 291703
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1203 PM EST THU JAN 29 2015


.AVIATION...

THE REGION OF PRECIP NOW MOVING ACROSS SW MI WILL ADVANCE ACROSS THE
TERMINALS EARLY THIS AFTERNOON. THE BULK OF THIS WILL FALL AS SNOW
FROM PTK NORTH AND RAIN/SNOW SOUTH. THERE IS A DEFINITE BACK EDGE TO
THIS PRECIP /MARKED BY THE END OF LARGER SCALE FORCING/. THIS BACK
EDGE WILL MOVE THROUGH SE MI BETWEEN 20Z AND 22Z. THE ASSOCIATED SFC
LOW WILL PASS EAST OF METRO DETROIT AFTER 19Z CAUSING A VEERING OF
THE WIND TOWARD THE W-NW WITH A MODEST INCREASE IN WIND SPEED.
SHALLOW COLD AIR ADVECTION UNDER A DEEP LOW LEVEL INVERSION WILL
SUSTAIN MVFR CIGS THROUGH WELL INTO THE OVERNIGHT. A SECONDARY COLD
FRONT...MARKED BY A PUSH OF ARCTIC AIR WILL ARRIVE LATE THIS EVENING
AND WILL CAUSE A DRAMATIC INCREASE IN THE WINDS /POSSIBLY GUSTING UP
TO 30 KNOTS AT TIMES/.

FOR DTW...ENOUGH WARM AIR IS IN PLACE OVER METRO DETROIT TO SUPPORT
RAIN MIXED WITH SOME SNOW AS THIS SECOND BATCH OF PRECIP ARRIVES
WITHIN THE NEXT HOUR. SFC TEMPS WILL REMAIN ABOVE FREEZING...SO NO
ACCUMULATIONS WITH ANY SNOW IS EXPECTED.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CIGS BELOW 5000 FT THIS AFTERNOON AND TONIGHT.

* MEDIUM IN PRECIPITATION BEING MOSTLY RAIN THIS AFTERNOON.

* MEDIUM IN WIND GUSTS EXCEEDING CROSS WIND THRESHOLDS TONIGHT.

&&

.PREV DISCUSSION...ISSUED 948 AM EST THU JAN 29 2015

UPDATE...

THE WATER VAPOR LOOP THIS MORNING SHOWS A SHORT WAVE NOW TRACKING
ACROSS CNTL INDIANA WITH A MID LEVEL TROUGH AXIS EXTENDING FROM
THE WRN UP INTO SRN MN. THE REGIONAL RADAR DATA SHOWS AN AREA OF
SNOW EXTENDING ACROSS NRN AND CNTL LOWER MI...WITHIN THE REGION OF
MID LEVEL DEFORMATION BETWEEN THESE TWO WAVES. THIS DEFORMATION
FORCING WILL BE DRIVEN ACROSS THE NORTHERN HALF OF THE FORECAST
AREA DURING THE LATER HALF OF THE MORNING INTO EARLY
AFTERNOON...LEADING TO SOME REDEVELOPMENT OF SNOW. FARTHER
SOUTH...RADAR DATA HAS BEEN SHOWING SOME RETURNS ACROSS SOUTHERN
LAKE MI. THESE ARE MORE CONVECTIVE IN NATURE IN LIGHT OF THE STEEP
MID LEVEL LAPSE RATES. THESE SHOWERS ARE OCCURRING WITHIN SOME
ADDITIONAL MID LEVEL DEFORMATION ALONG THE NORTHERN EDGE OF THE
OHIO VALLEY WAVE AND WILL AFFECT THE SOUTHERN HALF OF THE FORECAST
AREA LATE THIS MORNING AND AFTERNOON. THE EASTWARD ADVANCEMENT OF
THESE WAVES WILL ALLOW THE FORCING TO REMAIN PROGRESSIVE TODAY.
THERE MAY BE A BRIEF LULL IN PRECIP THIS AFTERNOON PRIOR TO SOME
ENHANCED MID LEVEL FGEN ARRIVING LATER THIS AFTERNOON AHEAD OF THE
NRN STREAM TROUGH AXIS.

THE ASSOC SFC LOW LOCATED ALONG THE IN/MI BORDER AS OF 14Z...WILL
LIFT INTO SE MI BY EARLY AFTERNOON. TEMPS AHEAD OF THIS LOW HAVE
RISEN INTO THE MID/UPPER 30S. THIS WARMER AIR WILL ADVECT INTO
METRO DETROIT. THE DEPTH OF THE WARM AIR LOOKS SUFFICIENT TO KEEP
PRECIP MAINLY LIQUID THROUGH MID AFTERNOON FOR METRO DETROIT
SOUTH /ALTHOUGH THERE MAY BE SOME BRIEF PERIODS OF SLEET IN ANY
HIGHER INTENSITY CONVECTIVE ELEMENTS/. THE WARM LAYER WILL BE MUCH
MORE SHALLOW FARTHER NORTH...SUPPORTING MAINLY SNOW. ADDITIONAL
SNOW ACCUMULATION OF AN INCH OR TWO WILL BE POSSIBLE ACROSS
MIDLAND/BAY/HURON COUNTIES WHERE FORCING WILL BE A LITTLE
STRONGER/MORE PERSISTENT. ACCUMS FARTHER SOUTH SHOULD BE MINIMAL.
COLDER AIR WILL ARRIVE LATE IN THE AFTERNOON WITH THE PASSAGE OF
THE MID LEVEL FGEN...FAVORING A PRECIP CHANGE OVER TO SNOW. THIS
FORCING LOOKS TO BE VERY BRIEF AND WEAK ENOUGH TO KEEP ACCUMS
MINIMAL IF ANY. AN UPDATED FORECAST WILL BE ISSUED SHORTLY TO
REFLECT THESE LATEST PRECIP TRENDS.

PREV DISCUSSION...ISSUED 242 AM EST THU JAN 29 2015

SHORT TERM...TODAY AND TONIGHT

A SHORTWAVE WILL TRACK FROM THE MID MISSISSIPPI VALLEY INTO THE
CENTRAL GREAT LAKES TODAY...SPREADING MOISTURE INTO THE AREA EARLY
THIS MORNING. 00Z KDTX SOUNDING SHOWS A VERY DRY LAYER IN PLACE OVER
LOWER MICHIGAN FROM 750 MB DOWN TO THE SURFACE...WHICH HAS KEPT A
BAND OF MOISTURE WITHIN REGION OF ISENTROPIC ASCENT IN ADVANCE OF
THIS THE MAIN SYSTEM ELEVATED OVERNIGHT.

FORCING ALONG THE LEAD EDGE OF THE VORTICITY CENTER WILL PROGRESS
EAST TO NORTHEAST INTO THE AREA FROM ITS CURRENTLY POSITION FROM
SOUTHWEST LOWER MICHIGAN INTO NORTHERN INDIANA. HOWEVER...BETWEEN
THE DRY LOW LEVELS STILL IN PLACE IN ADVANCE OF THIS BAND OF RAIN
AND SNOW...AND A MID LEVEL DRY SLOT TRAILING THIS FEATURE INTO THE
AREA...PRECIPITATION INTENSITY AND DURATION WILL BE LIMITED EARLY
THIS MORNING OVER MUCH OF THE CWA. ONLY THE NORTHERN THIRD TO HALF
OF THE CWA MAY RECEIVE 3 OR 4 HOURS OF PRECIPITATION...MAINLY SLEET
OR SNOW...ALONG THE NORTHERN EDGE OF THE DRY SLOT.

FURTHER SOUTH INTO METRO DETROIT AND POINTS SOUTH...A BRIEF ONE OR
TWO HOUR PERIOD OF LIGHT SHOWERS OR SLEET WILL CROSS THE AREA. WITH
TEMPERATURES IN THE MID 20S...ANY LIQUID THAT DOES FALL WILL MOST
LIKELY FREEZE ON SURFACES. AT THIS TIME...ONLY PATCHY SLICK SPOTS
ARE EXPECTED GIVEN THE LACK OF COVERAGE OF THE THE PRECIPITATION.
NO HEADLINES ARE ANTICIPATED AT THIS TIME.

AS THE SHORTWAVE CROSSES THE AREA TODAY...ADDITIONAL SNOW SHOWERS
WILL OCCUR AS COLDER AIR ASSOCIATED WITH THE WAVE OVERSPREADS THE
AREA. TEMPERATURES AT THE SURFACE WILL REMAIN AOA FREEZING FOR MUCH
OF THE AREA FROM LATE MORNING INTO THE AFTERNOON AS STRONGER COLD
AIR ADVECTION HOLDS OFF UNTIL THIS EVENING AND TONIGHT. TOTAL SNOW
ACCUMULATIONS OF AN INCH OR TWO WILL BE POSSIBLE DURING THE ENTIRE
PERIOD OVER THE NORTHERN CWA WITH MUCH LESSER AMOUNTS SOUTHWARD FROM
METRO DETROIT TO THE MICHIGAN AND OHIO STATE LINE.

COLD AIR WILL FILTER BACK SOUTH INTO THE AREA TONIGHT WITH THE LOW
TEMPERATURES RANGING FROM THE SINGLE DIGITS TO AROUND 10 DEGREE OVER
THE NORTH TO THE LOW/MID TEENS I-94 SOUTH. ANY REMAINING SNOW
SHOWERS WILL BE INSIGNIFICANT.

LONG TERM...

ARCTIC HIGH PRESSURE BUTTED AGAINST THE FRONT RANGE OF THE ROCKIES
IN ALBERTA THIS MORNING IS INTENSIFYING AS SHORTWAVE RIDGING
DEVELOPS DOWNSTREAM OF THE ALEUTIAN LOW. COLLAPSE OF UPPER SUPPORT
DUE TO INCREASING CONFLUENCE OVER NORTHWEST CANADA WILL FORCE THE
HIGH TO WEAKEN AND QUICKLY TRANSLATE SOUTHEAST INTO THE UPPER
MIDWEST THIS MORNING BEFORE SETTLING OVER THE OHIO VALLEY TONIGHT.
THIS WILL DRIVE A PERSISTENT NW GRADIENT ACROSS THE CWA THROUGH THE
FIRST HALF OF FRIDAY. COLD ADVECTION WILL EASE AS THE BROAD SURFACE
RIDGE AXIS TRAVERSES THE AREA, BUT WITH 925MB TEMPERATURES HOVERING
NEAR -17C, HIGHS WILL BE STUCK IN THE TEENS ON FRIDAY. RAPID
EASTWARD PROGRESS OF THE HIGH AND DRY NW FLOW, SUPPORTED BY
RELATIVELY DRY MOISTURE FIELDS IN THE 00Z NAM, SUGGEST THAT THIS
WILL BE THE CASE EVEN IN THE PRESENCE OF MOSTLY SUNNY SKIES OVER
MOST OF THE AREA. THE POTENTIAL EXCEPTION MAY BE ACROSS THE FAR NW
WHERE LAKE SUPERIOR-MICHIGAN PLUME WILL POTENTIALLY CONTRIBUTE TO A
MORE PERSISTENT STRATOCU DECK. FOR THIS SAME REASON, LOWS SHOULD
EASILY FALL INTO THE SINGLE DIGITS FRIDAY NIGHT, BUT HAVE A HIGHER
LIKELIHOOD OF REMAINING IN THE 10-15 DEGREES ACROSS THE FAR WEST.

A MOISTURE STARVED WAVE EMBEDDED IN NW FLOW WILL RACE ACROSS THE
GREAT LAKES EARLY FRIDAY BRINGING NOTHING MORE THAN A FEW SNOW
SHOWERS ACROSS THE FAR NORTH WITH NO ACCUMULATION EXPECTED.
DEVELOPING RETURN FLOW WILL PUSH HIGHS INTO AT LEAST THE UPPER 20S.

HIGH UNCERTAINTY FOR THE SECOND HALF OF THE WEEKEND. A SHORTWAVE,
WHICH HAS YET TO ACTUALLY DEVELOP, IS FORECAST BY THE SUITE OF
GUIDANCE TO EMERGE OUT OF THE ALEUTIAN LOW LATE TONIGHT AND COME
ONSHORE IN BRITISH COLUMBIA ON FRIDAY EVENING. THIS WAVE WILL
QUICKLY SHEAR TO SOUTHEAST AND INTERACT TO SOME DEGREE WITH A CLOSED
LOW OVER THE BAJA.

WHAT IS KNOWN IS THAT THERE IS A REASONABLE LIKELIHOOD FOR A
PROLONGED PERIOD OF LIGHT TO MODERATE ACCUMULATING SNOW TO DEVELOP
OVER A WIDE AREA GIVEN GIVEN THE BROAD AREA OF ISENTROPIC ASCENT AND
NORTHWARD TRANSPORT OF 4-5 G/KG H7 SPECIFIC HUMIDITY COURTESY OF
SOUTHERN STREAM INVOLVEMENT. THE KEY PLAYER IN THE LOCAL FORECAST
WILL BE JUST HOW AGGRESSIVELY THE NORTHERN BRANCH DIGS OVER MONTANA,
WYOMING, AND COLORADO SATURDAY INTO SATURDAY NIGHT. THE GREATER THE
INTERACTION WITH THE CLOSED LOW, THE GREATER SNOW PROSPECTS BECOME.
AS IT STANDS, THE NAM AND GEM ARE BY FAR THE MOST AGGRESSIVE. THE
ECMWF AND GFS ARE CONSIDERABLY LESS SO AND CONFINE ACCUMULATING SNOW
SOUTH OF THE OHIO BORDER. HOWEVER, THE LATTER TWO STILL MADE
NOTEWORTHY MOVES TOWARD MORE AGGRESSIVE SOLUTIONS AT 00Z IN
COMPARISON TO THEIR 12Z COUNTERPARTS. 00Z GFS ENSEMBLES ARE SPLIT
BETWEEN NORTH/SOUTH SOLUTIONS WITH THE OPERATIONAL GFS AND TWO
CONTROL RUNS REMAINING RIGHT IN BETWEEN AND CENTERING THE ACTION
ALONG/SOUTH OF I-80. GIVEN THAT THE S/W HAS YET TO EMERGE, TYPICAL
NWP PROBLEMS WITH CLOSED LOWS, AND GENERAL LOW MEDIUM RANGE
PREDICTABILITY THIS WINTER, WILL SIMPLY ALLOW THE BLENDED EXTENDED
GRIDS TO SPEAK FOR THEMSELVES AT THIS POINT.

MARINE...

FRESH TO STRONG SOUTHERLY WINDS WILL PERSIST FOR THE NEXT FEW HOURS
AS A WEAK LOW APPROACHES FROM THE WEST. GUSTS WILL BE LIMITED TO
AROUND 30 KNOTS GIVEN THE STABILITY OF WARM SOUTH FLOW. WINDS WILL
VEER TO THE NORTHWEST AND INCREASE CONSIDERABLY THIS EVENING INTO
TONIGHT. WIDESPREAD GALES ARE EXPECTED OVER LAKE HURON WITH GUSTS TO
STRONG GALES EXPECTED OVER CENTRAL AND SOUTHERN LAKE HURON WHERE
SIGNIFICANT WAVE HEIGHTS WILL EXCEED 12 FEET WITH HIGHER MAXIMUM
WAVE HEIGHTS. THE GALE WATCH HAS THEREFORE BEEN UPGRADED TO A
WARNING. CONSIDERABLE HEAVY FREEZING SPRAY WILL ACCOMPANY THESE
CONDITIONS AND A WARNING HAS BEEN ISSUED ACCORDINGLY. WINDS AND
WAVES WILL SUBSIDE FRIDAY AFTERNOON INTO FRIDAY NIGHT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...HEAVY FREEZING SPRAY WARNING FROM 7 PM THIS EVENING TO 7 PM EST
     FRIDAY FOR LHZ362-363-441-462.

     GALE WARNING FROM 7 PM THIS EVENING TO 10 AM EST FRIDAY FOR LHZ362-
     363-421-441-462.

     HEAVY FREEZING SPRAY WARNING FROM 10 PM THIS EVENING TO 7 PM EST
     FRIDAY FOR LHZ463-464.

     GALE WARNING FROM 10 PM THIS EVENING TO 10 AM EST FRIDAY FOR LHZ442-
     443-463-464.

     HEAVY FREEZING SPRAY WARNING FROM 7 PM THIS EVENING TO 4 AM EST
     FRIDAY FOR LHZ361.

     GALE WARNING FROM 7 PM THIS EVENING TO 4 AM EST FRIDAY FOR LHZ361.

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

$$

AVIATION.....SC
UPDATE.......SC
SHORT TERM...DG
LONG TERM....JVC
MARINE.......JVC


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



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