Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 261319
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
919 AM EDT THU MAR 26 2015

.UPDATE...
QUICK UPDATE TO ADD SNOW TO THE GRIDS FOR LENAWEE/MONROE COUNTIES.
BETTER RATES HAVE LED TO SNOW BEING THE PREDOMINANT P-TYPE
THERE...WHILE TO THE NORTH THE WARMER BOUNDARY LAYER/LACK OF
BETTER WET BULBING HAS KEPT PRECIP LIGHT RAIN. EVEN WHERE SNOWFALL
IS OCCURRING...ONLY LIGHT ACCUMULATIONS CONFINED TO GRASSY
SURFACES ARE EXPECTED WITH SFC TEMPS/DEWPOINTS AOA FREEZING. ONLY
HAZARD WILL BE VISIBILITIES DROPPING TO 1 MILE OR LESS.
OTHERWISE...PRECIP SHIELD STILL ON TRACK TO EXIT BY 15Z.

&&

.AVIATION...ISSUED 700 AM EDT THU MAR 26 2015

MORNING RAINFALL WILL REMAIN SOUTH OF PTK. AS FOR
PTK/FNT/MBS...THERE HAS BEEN SOME SIGNIFICANT DIMINISHING TREND TO
THE MVFR STRATUS DECK. THE ONSET OF DAYTIME MIXING SHOULD LEAD TO AN
EXPANSION OF THE CLOUD DECK JUST NORTH AND WEST OF THE
AREA...RESULTING IN A WIDESPREAD MVFR STRATO CU DECK THIS AFTERNOON.

FOR DTW...BASED ON CURRENT OBSERVATIONS...PRECIP TYPE LOOKS TO
REMAIN MOSTLY IF NOT ALL RAIN THIS MORNING WITH TEMPERATURES HOLDING
ABOVE FREEZING. SOME LOW END MVFR BASED CLOUDS HAVE BEEN OBSERVED
ON THE NORTHERN EDGE OF THIS RAIN. THESE LOWER CLOUDS ARE EXPECTED
TO BRUSH METRO EARLY THIS MORNING. THE RAIN WILL EXIT TO THE EAST OF
METRO BETWEEN 14Z AND 15Z...WITH CONDITIONS RAPIDLY IMPROVING IN ITS
WAKE.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS BELOW 5000 FT THIS MORNING. MEDIUM THIS AFTERNOON
  AND TONIGHT.

* MEDIUM IN PRECIPITATION TYPE BEING ALL RAIN THIS MORNING.

&&

.PREV DISCUSSION...ISSUED 326 AM EDT THU MAR 26 2015

SHORT TERM...TODAY AND TONIGHT

THE DYNAMIC RESPONSE ALONG A DEEP LAYER FRONTAL BOUNDARY EXTENDING
FROM THE SOUTHERN PLAINS INTO THE OHIO VALLEY IS BEING DRIVEN BY
UPPER LEVEL DIVERGENCE WITHIN THE ENTRANCE REGION OF A STRENGTHENING
UPPER JET MAX. THE REGIONAL RADAR LOOP HAS BEEN SHOWING THE ENTIRE
AREA OF RAIN LIFTING NORTHEASTWARD ACROSS IL/IN. THIS IS OCCURRING
AS THE UPPER JET MAX STRENGTHENS AND LIFTS NORTHWARD...PULLING THE
ELEVATED FRONT FARTHER TO THE NORTH AND EAST. SATELLITE/RADAR
COMPOSITE ALSO SHOWS A MID LEVEL SHORT WAVE IMPULSE OVER SOUTH
CENTRAL ILLINOIS. THIS FEATURE WILL CONTINUE ON A NORTHEASTWARD
TRACK INTO OHIO THIS MORNING...FURTHER AIDING THE NORTHEAST EXPANSION
OF THE PRECIP SHIELD.

THE MID LEVEL FRONTAL FORCING /700-600MB LAYER/ IS DRIVING THE
EXPANDING REGION OF RAIN ACROSS NRN INDIANA. THIS MID LEVEL ASCENT
WILL TRACK ACROSS FAR SE MI DURING THE 09Z TO 15Z TIME FRAME...WITH
THE PEAK FORCING EXPECTED AROUND 12Z. THERE IS A REGION OF
SUBSTANTIAL MID LEVEL DRY AIR WITHIN THE DESCENDING BRANCH OF THE
ELEVATED FRONTAL CIRCULATION. THIS HAS AND WILL CONTINUE TO SUPPORT
A SHARP CUT OFF TO THE PRECIP ON ITS NORTHERN EDGE. VARIOUS HIRES
MODEL SOLUTIONS /INCLUDING THE HRR...4KM WRF...NAM12 AND RAP/
SUGGEST THAT LOCALS GENERALLY ALONG AND SOUTH OF AN ANN ARBOR TO PORT
HURON LINE WILL SEE THE WIDESPREAD PRECIP...WITH CHANCES DROPPING
OFF RAPIDLY TO THE NORTH. WITH A DEEPER DRY LAYER ACROSS SE
MI...THERE WILL BE A GOOD DEGREE OF WET BULB COOLING AS THE PRECIP
EXPANDS INTO THE FORECAST AREA. NAM MODEL SOUNDINGS ACTUALLY SUGGEST
THE PRECIP WILL BE ALL SNOW BY 12Z. BASED ON SFC OBS...THE NAM SEEMS
A LITTLE TOO COOL IN THE BOUNDARY LAYER. THERE IS ALSO CONCERN THE
NAM MAY BE TOO STRONG WITH THE ASCENT. LEANING TOWARD THE RAP
THERMAL PROFILES...A MIX OF RAIN AND SNOW WILL BE CARRIED WITH NO
ACCUMULATIONS. THIS OF COURSE WILL BE MONITORED CLOSELY THIS MORNING.

WEAK LOW LEVEL COLD AIR ADVECTION TODAY WILL BE OFFSET A BIT BY
DIURNAL HEATING. THERE IS A CONSIDERABLE AMOUNT OF STRATUS ACROSS
THE REGION...NOT TO MENTION THE MID/HIGH CLOUDS ASSOCIATED WITH THE
MID LEVEL FGEN. THESE FACTORS WILL LIMIT DAYTIME MIXING DEPTHS AND
SUPPORT GUIDANCE MAX TEMPS OF LOW-MID 40S. A SURFACE COLD FRONT NOW
DRAPED ACROSS LAKE SUPERIOR WILL PUSH SOUTH ACROSS LAKE HURON THIS
EVENING AND INTO SE MI OVERNIGHT AS HIGH PRESSURE EXPANDS INTO UPPER
MI. THIS ALONG WITH A DEEPENING LONG WAVE TROUGH OVER THE GREAT
LAKES WILL LEAD TO AN INFLUX OF ARCTIC AIR INTO THE FORECAST AREA.
STEEPENING LOW LEVEL LAPSE RATES ALONG THE SFC FRONT AND LINGERING
LOW LEVEL MOISTURE WILL PROVIDE A CHANCE OF SOME SNOW SHOWERS
OVERNIGHT. THE HIGHEST CHANCES WILL BE ACROSS THE THUMB REGION WHERE
LOW LEVEL DELTA THETA E ACTUALLY SUGGEST THE AIRMASS WILL BE COLD
ENOUGH TO GENERATE SOME WEAK MOISTURE FLUX OFF THE OPEN WATERS OF
LAKE HURON...PERHAPS ENOUGH TO SUPPORT A DUSTING OF SNOW ACCUMS.

LONG TERM...FRIDAY THROUGH WEDNESDAY

DEEPLY AMPLIFIED LONGWAVE PATTERN SETTING UP ACROSS THE CONUS WITH A
WEST COAST RIDGE AND EAST COAST TROUGH TO HEAD INTO THE WEEKEND. BY
SATURDAY MORNING THE 850MB 0C ISOTHERM WILL HAVE MADE IT ALL THE WAY
TO THE FLORIDA PANHANDLE. OVER SOUTHERN MI WE WILL BE LOOKING AT
500/850MB TEMPS AROUND -35/-15C RESPECTIVELY FRIDAY THROUGH FRIDAY
NIGHT AS THE COLD POOL SINKS THROUGH THE REGION BEHIND AN ARCTIC
FRONT THAT MORNING. THIS SHOULD RESULT IN HIGHS FRIDAY ONLY AROUND
30 AND LOWS OVERNIGHT IN THE LOW TEENS. THE OTHER ISSUE FOR FRIDAY
WILL BE THE POTENTIAL FOR SOME LIGHT SNOW SHOWERS. AS THE COLD POOL
AND MID LEVEL TROUGH AXIS PASSES OVER...LAPSE RATES WILL STEEPEN AS
WITH MOISTURE TRAPPED IN THE LOWEST 7KT OF THE COLUMN. SHOULD BE
ENOUGH MOISTURE AND BROAD LIFT TO IGNITE AN AREA OF SHOWERS THROUGH
THE FRONT PART OF THE DAY. AS THE TROUGH PUSHES EAST...THE SHOWERS
WILL CEASE EXCEPT POSSIBLY OVER EASTERN THUMB WHICH COULD GET SOME
LAKE ENHANCED SNOW SHOWERS. WITH THE UPTICK IN NORTHERLY WINDS
BRINGING A SURGE OF COLD AIR OVER THE LAKE...NOW WITH A GOOD DEAL OF
OPEN WATER...MODELS ARE HINTING AT A CONVERGENCE BAND SETTING UP FOR
A FEW HOURS BEFORE WINDS BACK TO NW AND DRY AIR PUTS AN END TO IT.
NOTHING OVERLY IMPRESSIVE AT THIS TIME SO KEEPING ACCUMS TO A FEW
TENTHS. SOMETHING TO WATCH AS HIRES MODELS START COVERING THAT
TIMEFRAME.

SFC HIGH PRESSURE STARTS BUILDING OVER THE REGION FRIDAY
NIGHT...CENTERING ITSELF OVER LOWER MI ON SATURDAY. NOT MUCH
RECOVERY TEMPERATURE WISE AS COLD DOME IS STILL LOCKED OVERHEAD. BUT
A REDUCTION IN CLOUD COVER WILL ALLOW SOME ADDITIONAL HEATING INTO
THE MID 30S.

SATURDAY NIGHT WILL FEATURE A STRONG SHORTWAVE SURGING EASTWARD
ALONG THE US/CANADA BORDER WHICH WILL BREAK DOWN THE STEEP RIDGE
OVER THE WEST COAST. THIS WILL LEAD TO A MORE PROGRESSIVE PATTERN
FIRST SWEEPING A RIDGE ACROSS THE AREA ON SUNDAY...FOLLOWED QUICKLY
BY THE COLD FRONT EXTENDING SOUTH FROM THE RESULTANT LOW. WITH
TEMPERATURES IN THE LOW/MID 30S OVER NIGHT...THIS COULD RESULT IN
RAIN...SNOW...OR A MIX DEPENDING ON THE TIMING OF THE FRONT.

THE PROGRESSIVE PATTERN CONTINUES FOR THE FRONT HALF OF THE COMING
WORK WEEK WITH A SERIES OF CLIPPERS EMBEDDED IN THE NW FLOW TRACKING
NEAR THE AREA. THIS WILL BE SOMETHING TO WATCH IN THE COMING DAYS.
THE FLATTER FLOW WILL ALLOW THE WARM AIR TO LIFT FURTHER NORTH WHICH
WILL RESULT IN TEMPERATURES CLOSER TO NORMAL FOR LATE MARCH/EARLY
APRIL.

MARINE...

WESTERLY WINDS WILL BRIEFLY RELAX TODAY AS A FRONTAL BOUNDARY
BECOMES DRAPED THROUGH THE CENTRAL GREAT LAKES. WINDS WILL AGAIN
BECOME EXCITED OUT OF THE NORTH BEHIND THE FRONT TONIGHT THROUGH
FRIDAY. COLD AIR WILL REDUCE THE STABILITY OVER THE LAKE ALLOWING
FOR GUSTS OF 25 TO 30 KNOTS. IN ADDITION...THE FRONT AND INITIAL
COLD BURST BEHIND IT WILL PRODUCE SOME LIGHT SNOW SHOWERS TONIGHT
AND FRIDAY. THE SOUTHWARD MOVING FRONT WILL CLEAR THE REMAINDER OF
THE WATERS DURING THE DAY ON FRIDAY. WINDS WILL THEN DIMINISH LATE
FRIDAY NIGHT INTO SATURDAY AS HIGH PRESSURE BUILDS INTO THE REGION.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

UPDATE.......DT
AVIATION.....SC
SHORT TERM...SC
LONG TERM....DRK
MARINE.......DRK


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


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