Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 260857
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
357 AM EST THU FEB 26 2015

.SHORT TERM... TODAY AND TONIGHT

ANOTHER HIGH POP/LOW QPF/LOW ACCUMULATION SNOW EVENT IS UNFOLDING
MAINLY OVER THE SOUTH HALF OF SE MICHIGAN DURING THE MORNING. RADAR
COMPOSITE SINCE MIDNIGHT DEPICTS A PATTERN OF SNOW DEVELOPING
GRADUALLY WEST TO EAST AND SLOWLY ERODING THE DRY AIR IN RESIDENCE
AT LOW LEVELS OVER OUR AREA AS SHOWN IN THE 00Z DTX SOUNDING. THE
PATTERN WILL AFFECT ALL AREAS ALONG AND SOUTH OF THE I-69 CORRIDOR
TO THE OHIO BORDER BY 6 AM AND THEN LAST THROUGH LATE MORNING BEFORE
DIMINISHING. TOTAL ACCUMULATION AROUND A HALF INCH REMAINS ON TARGET
BY ABOUT NOON. THERE WILL ALSO BE A CHANCE OF SNOW SHOWERS OVER THE
NORTHERN THUMB AS INCREASING NORTHEAST WIND IS FLUXING SOME LOW
LEVEL MOISTURE FROM LAKE HURON. YESTERDAY`S VISIBLE SATELLITE
IMAGERY INDICATES SOME SLUSHY OPEN WATER AND EARLY MORNING
OBSERVATIONS AT BAD AXE HAVE SHOWN LIGHT SNOW SHOWERS OFF AND ON
THAT ARE WORTHY OF A SCATTERED/CHANCE POP.

SNOW HAS BEEN ABLE TO REACH THE GROUND FIRST BETWEEN THE I-69 AND M-
59 CORRIDORS UNDER THE MOST INTENSE MID LEVEL FRONTAL FORCING. MODEL
CROSS SECTIONS INDICATE MODERATE FGEN IN THE 700 TO 500 MB LAYER
WITH A SLIGHT COMPONENT OF ISENTROPIC ASCENT AND SHALLOW
AGEOSTROPHIC CIRCULATION LEADING THE FORCING AT ONSET. SPECIFIC
HUMIDITY INDICATED AROUND 1 G/KG WILL BE ADEQUATE IN THE MOISTURE
DEPARTMENT. THE MAIN LIMITING FACTOR WILL BE THE HIGH STATIC
STABILITY ALSO SHOWN IN CROSS SECTIONS THAT WILL TEMPER VERTICAL
MOTION RESPONSE TO THE FGEN. THIS BACKS MODEL QPF AMOUNTING TO ONLY
A FEW 100THS LIQUID EQUIVALENT FOR THE DURATION OF THE EVENT. THE
MICROPHYSICAL SCENARIO WILL ALSO KEEP FLAKES ON THE GRAINY SIDE OF
THE SPECTRUM. MODEL SOUNDINGS INDICATE THE TEMPERATURE PROFILE
HOVERING AT OR BELOW -20C THROUGHOUT THE ATMOSPHERE ABOVE THE
BOUNDARY LAYER. THE ONE THING TO MONITOR WILL BE SOME LATE
DEFORMATION FORCING SHOWING UP TOWARD THE END OF THE EVENT THAT
COULD HELP RATES FLARE UP SLIGHTLY. UPSTREAM OBSERVATIONS MATCH UP
WITH MODEL DATA TO SUGGEST THIS WILL SLIDE JUST SOUTH OF THE OHIO
BORDER MID TO LATE MORNING.

THE SYSTEM PRODUCING THE SNOW IN OUR AREA TODAY WAS RESPONSIBLE FOR
NUDGING ARCTIC AIR NORTHWARD YESTERDAY. NOW...AS THE WAVE DEPARTS
EASTWARD...ARCTIC AIR WILL LEAK BACK TODAY BEFORE SURGING MORE
STRONGLY INTO SE MICHIGAN TONIGHT. THE COLDER AND DRIER AIR WILL
COMBINE WITH A NORTHERLY WIND DIRECTION TO GENERATE A CLEARING TREND
DURING THE EVENING. THIS WILL SET THE STAGE FOR COLD ADVECTION EARLY
AND EFFECTIVE RADIATIONAL COOLING LATER THAT WILL TAKE MIN TEMPS
DOWN BELOW ZERO OVER THE ENTIRE AREA. THE COLDEST READINGS IN THE
NORTHERN THUMB COULD REACH THE -10 TO -15 RANGE WHILE READINGS
AROUND -5 WILL BE COMMON IN THE DETROIT METRO AREA. A WIND CHILL
ADVISORY MAY BE NEEDED FOR LATE TONIGHT DEPENDING ON HOW WIND SPEED
RESPONDS TO THE SURFACE RIDGE SLIDING OVER THE REGION.

RECORD LOWS FOR FEB 27
DETROIT AREA: -4  (1934)
FLINT AREA:   -14 (1994)
SAGINAW:      -8  (1934)

&&

.LONG TERM...FRIDAY THROUGH WEDNESDAY

UPPER TROUGH AXIS OVER THE CENTRAL GREAT LAKES WILL EXIT EAST EARLY
FRIDAY. THIS WILL ALLOW A STRONG DOME OF HIGH PRESSURE TO BECOME
CENTERED OVER THE OHIO VALLEY...PLACING LOWER MICHIGAN UNDER THE
INFLUENCE OF HIGH PRESSURE FRIDAY THROUGH SATURDAY. AS THE CENTER
SLIDES TO OUR SOUTH...FLOW WILL SHIFT TO THE WEST FRIDAY AND FINALLY
SOUTH BY SATURDAY. THIS WILL ALLOW FOR A GRADUAL MODERATION IN
TEMPERATURES AS H925 TEMPS RISE FROM -18 TODAY TO ABOUT -12 BY
SATURDAY. SUNSHINE AND INCREASING DAYLIGHT SHOULD HELP BOOST MAX
TEMPS INTO THE TEENS FRIDAY AND UPPER TEENS/NEAR 20 SATURDAY. LOWS
WILL REMAIN VERY COLD FRIDAY NIGHT...ESPECIALLY ACROSS THE SOUTHERN
PORTION OF THE FORECAST AREA WHERE THE RIDGE WILL PROVIDE CALM
WINDS. EXPECTING MINS BELOW ZERO ACROSS THE AREA...BUT LIGHT WINDS
SHOULD KEEP US JUST SHY OF A WIND CHILL ADVISORY. CLOUDS MOVING IN
AHEAD OF THE NEXT SYSTEM AND WARMER AIR ADVECTING INTO THE AREA
SHOULD THEN KEEP LOWS ABOVE ZERO SATURDAY NIGHT.

SHORTWAVE ENERGY NOW OVER NORTHERN ALASKA WILL DIVE DOWN TOWARDS THE
GREAT LAKES ON SUNDAY AS IT IS GUIDED BY THE VORTEX STRETCHING FROM
HUDSON BAY TO GREENLAND. THIS TROUGH WILL RIDE OVER A 925-850MB
FRONTAL BOUNDARY OVER THE OHIO VALLEY AND SOUTHERN GREAT LAKES
SATURDAY NIGHT...AS IT IS LIFTED NORTHWARD BY SOUTHERLY FLOW AHEAD
OF TROUGHING DEVELOPING OVER THE WEST COAST. THE SURFACE REFLECTION
(TROUGH) DOES NOT LOOK PARTICULARLY STRONG WITH THIS
SYSTEM...HOWEVER WE SHOULD SEE ISENTROPIC ASCENT RAMP UP IN THE
LOW/MID LEVELS ALONG WITH A PERIOD OF FGEN ON SUNDAY IN RESPONSE TO
PVA AND POTENTIALLY SOME FORCING FROM AN UPPER JET POSITIONING
ITSELF TO OUR SOUTH. THE TIMING OF THE STRONGEST FORCING IS STILL
UNCERTAIN...WITH THE GFS STILL RUNNING A LITTLE SLOWER WITH THE
ARRIVAL OF THE UPPER TROUGH. GFS DOES SHOW UPWARDS OF 0.5 INCHES OF
PW SURGING UP TO ABOUT THE I-69 CORRIDOR. ALTHOUGH THERE IS STILL
SOME VARIABILITY WITH THIS SYSTEM...AT THIS TIME IT LOOKS LIKE SNOW
WILL SPREAD INTO SOUTHEAST MICHIGAN LATE SATURDAY NIGHT AND CONTINUE
THROUGH SUNDAY. WITH THE CURRENT SET-UP HEAVIEST SNOW ACCUMULATIONS
SHOULD BE CLOSEST TO THE OHIO BORDER WHERE STRONGER FGEN FORCING
WILL SET UP. SOME AREAS COULD RECEIVE MORE THAN 3 INCHES...BUT THERE
IS STILL PLENTY OF TIME TO SORT OUT SNOW AMOUNTS AS WE WAIT FOR
FURTHER MODEL ADJUSTMENTS.

ENERGY EJECTING OUT OF THE WESTERN TROUGH WILL THEN SEND AN AREA OF
LOW PRESSURE UP ACROSS THE GREAT LAKES OR OHIO VALLEY DURING THE MID-
WEEK PERIOD. LATEST RUNS OF THE GFS/EURO/GEM CONTINUE TO SPREAD
PRECIPITATION INTO THE AREA DURING THE TUESDAY THROUGH EARLY
WEDNESDAY TIMEFRAME. THIS SYSTEM COULD POTENTIALLY BE WARMER THAN
THE PRECEDING ONE AS ENERGY DIVES DEEPER SOUTH AND WITH A PRECEDING
SHOT OF COLD AIR ABSENT. WILL CONTINUE TO FORECAST A LITTLE ON THE
COLD SIDE GIVEN TENDENCY THIS SEASON FOR A MORE DOMINANT NORTHERN
STREAM. MODELS HAD ORIGINALLY SHOWN THE WEEKEND SYSTEM AS A MIXED
PRECIP EVENT BUT THEN TRENDED MORE AMPLIFIED WITH NORTHERN STREAM
ENERGY. MEDIUM RANGE MODELS DO SHOW MORE ENERGY MOVING THROUGH
CENTRAL CANADA AND INTO QUEBEC WITH THE 00Z RUNS...AND WANT TO SEE
HOW THIS PLAYS OUT OVER THE NEXT DAY OR TWO BEFORE INTRODUCING RAIN
OR POSSIBLY FREEZING RAIN/SLEET TO THE FORECAST.

&&

.MARINE...

AN UPPER TROUGH WILL CONTINUE TO DROP THROUGH THE GREAT LAKES TODAY
AND TONIGHT. A STRONG DOME OF ARCTIC HIGH PRESSURE WILL MEANWHILE
DROP FROM CENTRAL CANADA INTO THE OHIO VALLEY BY FRIDAY AND REMAIN
THERE THROUGH SATURDAY. THIS WILL BRING FAIRLY LIGHT WINDS TO THE
AREA THROUGH THE END OF THE WEEK...ALTHOUGH WE WILL SEE SOME
INCREASE IN SPEED OVER LAKE HURON FRIDAY NIGHT IN RESPONSE TO A
TROUGH DROPPING ACROSS NORTHERN ONTARIO.

&&

.AVIATION...ISSUED 1203 AM EST THU FEB 26 2015

EXISTING WEAK SURFACE RIDGING WILL SUSTAIN A DRY LOW LEVEL
ENVIRONMENT EARLY THIS MORNING.  THIS WILL MAINTAIN VFR CONDITIONS
UNDER A THICKER CANOPY OF MID CLOUD.  THE DETROIT CORRIDOR REMAINS
IN LINE TO SEE A PERIOD OF LIGHT SNOW DEVELOPMENT MID AND LATE
MORNING HOURS...PONTIAC RESIDING ALONG THE NORTHERN PERIPHERY OF
THIS MOISTURE.  THIS WILL RESULT IN A PREDOMINANT PERIOD OF MVFR
CONDITIONS AT THESE LOCALES...WITH A NARROW WINDOW FOR A TEMPO
WORTHY IFR MENTION DURING THE PEAK.   A MODEST INCREASE IN THE
NORTHEAST GRADIENT WILL COMMENCE AT THE SAME TIME.

FOR DTW...POTENTIAL FOR LIGHT SNOWFALL WILL INCREASE AFTER 10Z-11Z.
PERIOD OF IFR MOST LIKELY CENTERED 12Z-15Z...WITH SNOWFALL THEN
TAPERING OFF 16Z-18Z.  ACCUMULATION LESS THAN HALF AN INCH.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CEILING BELOW 5000 FT LATE TONIGHT THROUGH THURSDAY
  MORNING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...BT
LONG TERM....HLO
MARINE.......HLO
AVIATION.....MR


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



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