Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 030501
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1201 AM EST TUE MAR 3 2015

.AVIATION...

VFR CONDITIONS THROUGH 13Z AS MID LEVEL CLOUDS THICKEN AND LOWER
WITH TIME.  PLUME OF DEEPER MOISTURE WILL THEN EXPAND ACROSS THE
REGION FROM LATE MORNING THROUGH THE AFTERNOON HOURS.  A PERIOD OF
ACCUMULATING SNOW IN MVFR/IFR ALL LOCATIONS 14Z-18Z...BEFORE A SOUTH
TO NORTH TRANSITION IN PTYPE DURING THE AFTERNOON.  SNOW
ACCUMULATION OF 1 TO 3 INCHES...HIGHEST AMOUNTS PTK NORTHWARD.   A
DEFINED 3-4 HOUR AFTERNOON WINDOW NOW IN PLACE TO HIGHLIGHT THE
POTENTIAL FOR FZRA AT ALL LOCATIONS EXCEPT MBS.   FINAL TRANSITION
TOWARD RAIN/DRIZZLE IN IFR AS SURFACE TEMPERATURES CLIMB ABOVE
FREEZING LATE AFTERNOON INTO THE EVENING.

FOR DTW...ONSET OF ACCUMULATING SNOWFALL STILL EXPECTED 14Z-15Z.
BURST OF MODERATE SNOW IN IFR INITIALLY MAY RESULT IN A QUICK INCH
OF ACCUMULATION LATE MORNING.  TRANSITION TOWARD A PERIOD OF FZRA/IP
CENTERED ON 17Z-20Z...THEN RA/DZ FROM MID AFTERNOON INTO THE
EVENING.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS BELOW 5000 FT AFTER 13Z TUESDAY MORNING.

* MEDIUM IN VISIBILITY BELOW 1/2 MILE IN FOG MID AFTERNOON INTO THE
  EVENING.

* HIGH IN SNOW AS DOMINANT PTYPE THROUGH 16Z...THEN TRANSITIONING TO
  FZRA/IP 17Z-20Z...AND RA/DZ AFTER 20Z.

&&

.PREV DISCUSSION...ISSUED 320 PM EST MON MAR 2 2015

SHORT TERM...TONIGHT

HIGH CLOUDS EMBEDDED WITHIN THE STRENGTHENING UPPER WIND FIELD ARE
ADVECTING ACROSS THE UPSTREAM LOW AMPLITUDE SHORTWAVE RIDGE AXIS AND
ARE RACING EAST ACROSS THE UPPER MIDWEST. THESE CLOUDS WILL PROVIDE
THE ONLY INHIBITION TO RADIATING FOR THE FIRST HALF OF THE NIGHT AS
SURFACE HIGH PRESSURE SLOWLY DEPARTS FROM THE REGION AND MAINTAINS A
LIGHT GRADIENT THROUGH 06Z. DURING THIS TIME, DECENT RADIATING
CONDITIONS SHOULD ALLOW TEMPERATURES TO FALL INTO THE TEENS
AREAWIDE. INCREASING SE FLOW AND THICKENING CLOUD COVER WILL BOUNCE
SURFACE TEMPS BACK UP TOWARD 20 DEGREES BY SUNRISE.

LONG TERM...TUESDAY THROUGH SUNDAY

MAIN FOUCS IS ON THE MIXED PRECIPITATION EVENT EXPECTED TUESDAY. IN
SUMMARY...WINTER WEATHER ADVISORY IS IN EFFECT BEGINNING 13Z. 1-2
INCHES OF SNOW/SLEET FOR I-94 COUNTIES AND SOUTH...WITH 2-4 INCHES
NORTH. ADDITIONALLY...UP TO 0.1 INCH ICE IS POSSIBLE FROM THE I-69
CORRDIOR SOUTHWARD. BRUNT OF THE EVENT IS EXPECTED BETWEEN 15-21Z.

GOOD INTERMODEL AND RUN-TO-RUN CONSISTENCY WITH THE GENERAL
EVOLUTION OF THE LARGE SCALE PATTERN AND TIMING OF LOCAL IMPACTS.
SHORTWAVE ENERGY WILL EJECT FROM THE SOUTHERN CA UPPER LOW AND ZIP
ACROSS THE PLAINS INTO THE GREAT LAKES TUESDAY. NO REAL PHASING
BETWEEN THIS ENERGY AND THE NORTHERN STREAM TROUGH DROPPING OUT OF
THE PRAIRIE PROVINCES...SO EXPECTING THIS EVENT TO BE A RELATIVELY
QUICK-HITTER. MOISTURE TRANSPORT IS EXPECTED TO BE EXCELLENT
BETWEEN THE DEPARTING SURFACE HIGH AND A BROAD AREA OF SURFACE LOW
PRESSURE ATTENDANT TO THE LARGE-SCALE UPPER TROUGH...WITH NAM
PROGS SHOWING PWAT NEAR 1 INCH ALONG THE OHIO BORDER FOR A BRIEF
PERIOD AROUND 21Z...AND CROSS SECTIONS SHOWING H85-H7 SPECIFIC
HUMIDITY OF 4-6 G/KG FROM 15-24Z. MAIN FORCING MECHANISM WILL BE
ISENTROPIC LIFT ALONG THE LOW/MID TROPOSPHERIC TEMPERATURE
GRADIENT.

DESPITE MODEL AGREEMENT WITH THE LARGE SCALE FEATURES AND
EVOLUTION...CONSIDERABLE UNCERTAINTLY REMAINS WITH RESPECT TO
THERMAL FIELDS AND RESULTING P TYPE. GENERAL PROGRESSION WILL BE
SNOW/SLEET TO FREEZING RAIN/RAIN. MODEL SOUNDINGS INDICATE A
CONSIDERABLE DRY LAYER BETWEEN H9 AND H7 MUST BE OVERCOME...SO LIFT
WILL INITIALLY GO TO SATURATING THE COLUMN. THE GOOD MOISTURE
TRANSPORT WILL BE ABLE TO OVERCOME THE DRY LAYER THOUGH WITH PRECIP
BREAKING OUT ROUGHLY 13-15Z AND QUICKLY SPREADING ACROSS THE REGION.
PRECIP SHOULD BE SNOW INITIALLY BEFORE THE WARM NOSE CENTERED AROUND
H8 POKES IN FROM SOUTH TO NORTH. THIS WILL CAUSE PRECIP TO MIX WITH
AND CHANGE TO SLEET AND FREEZING RAIN. SURFACE TEMPS ARE A TOUGH
CALL...WITH WAA BEING OFFSET BY WET BULBING. THERE DOES EXIST A
BRIEF WINDOW FOR FREEZING RAIN ALONG/SOUTH OF I-69 ROUGHLY 17-21Z AS
CURRENT FORECAST CALLS FOR SURFACE TEMPS TO REMAIN AOB FREEZING
UNTIL 18-21Z. HOWEVER...THIS DOES NOT APPEAR TO BE A CLASSIC SETUP
FOR A GOOD ICING EVENT GIVEN THE STRONG WAA /LACK OF LOW-LEVEL COLD
AIR RESUPPLY/ AND MARGINAL MAGNITUDE OF THE WARM NOSE. BACK ROADS
WILL LIKELY SEE GREATER IMPACTS THOUGH GIVEN FROZEN GROUND AND MAY
SEE LIQUID FREEZING ON SURFACES EVEN IF AIR TEMPS ARE ABOVE
FREEZING. MODERATE/LOCALLY HEAVY PRECIP IS POSSIBLE 15-21Z GIVEN THE
MOISTURE QUALITY AND REDUCED STATIC STABILITY ABOVE THE LOW-LEVEL
TEMPERATURE GRADIENT AS INDICATED BY CROSS SECTIONS...POSSIBLY
LEADING TO A MORE CONVECTIVE/SHOWERY LOOKING PRECIP SHIELD.

MODEL QPF CONSENSUS IS NOT GREAT WITH ECMWF SPITTING OUT A BROAD
0.25 AROSS THE AREA WHILE NAM APPEARS TO BE MORE AGRESSIVE WITH THE
DRY SLOT DRYING THINGS OUT OVER THE NORTH AND SHOWING ENHANCED
CONVECTION TO THE SOUTH OF THE DRY SLOT LEADING TO LOCALLY UP TO
0.50". OPTED FOR A COMPROMISE WITH 0.25" ACROSS THE NORTH TO 0.35"
ACROSS THE SOUTH...THOUGH GIVEN CONVECTIVE NATURE OF PRECIP IT WILL
LIKELY NOT END UP BEING A SMOOTH DISTRIBUTION. A COMBINATION OF THE
DRY SLOT ARRIVAL AND MAIN MOISTURE AXIS PEELING OFF TO THE EAST WILL
CAUSE PRECIP TO COME TO AN END 21-00Z. SOME POTENTIAL FOR DZ/FZDZ AS
THIS OCCURS. CAA ENSUES AFTER 00Z AS WINDS VEER WESTERLY...WITH LOWS
IN THE LOW/MID 20S BY 12Z WED.

LONG WAVE TROUGH AMPLIFICATION ACROSS THE WRN GREAT LAKES ON
WEDNESDAY WILL USHER IN ANOTHER ROUND OF ARCTIC AIR TO THE REGION
/850MB TEMPS ARE FORECAST TO DROP TO -22C BY 06Z THURS/. THIS WILL
RESULT IN WED HIGH TEMPS OCCURRING IN THE MORNING AND SLOWLY FALLING
DURING THE AFTERNOON AND EVENING. A STRONG BAROCLINIC ZONE ACROSS
THE ERN US AND LONG WAVE TROUGH AMPLIFICATION WILL INTENSIFY THE
UPPER JET STREAK OVER THE GREAT LAKES /190+ KTS/ ON WEDNESDAY. WHILE
THE FRONTAL DYNAMICS AND DEEP MOISTURE WILL RESIDE WELL SOUTH OF THE
STATE...A FAIR AMOUNT OF MID/HIGH LEVEL CLOUDS ARE LIKELY TO RESIDE
OVER SE MI. THIS ALONG WITH SOME LOW LEVEL MOISTURE ALONG A
SECONDARY SFC TROUGH POSITIONED ACROSS THE NRN GREAT LAKES MAY
SUSTAIN A GOOD DEAL OF CLOUDS WELL INTO WED NIGHT...SUPPORTING A
CONSERVATIVE APPROACH TO WED NIGHT MINS /AROUND ZERO/.

THURS WILL BE THE COLDEST DAY OF THE FORECAST PERIOD AS HIGHS MAY
STRUGGLE TO REACH 20 WITH A DEEP POOL OF ARCTIC AIR OVER LOWER MI.
SURFACE HIGH PRESSURE WILL THEN SLIDE INTO THE MID ATLANTIC ON
FRIDAY AS MID LEVEL HEIGHTS REBOUND ACROSS THE GREAT LAKES REGION.
WITH THE DEPARTURE OF THE DEEP COLD POOL TO THE EAST AND
STRENGTHENING SOUTHERLY FLOW...A MODEST WARMING TREND WILL OCCUR FRI
INTO SATURDAY. THE OVERALL LONG WAVE PATTERN THIS WEEKEND INTO EARLY
NEXT WEEK WILL CONTINUE TO FEATURE A LONG WAVE RIDGE OVER THE WEST
COAST AND TROUGH ACROSS THE GREAT LAKES/ERN CANADA. THE WAVELENGTH
WILL JUST NOT BE AS AMPLIFIED AS THE LAST MONTH. THIS AND SEVERAL
SHORTER WAVELENGTH PERTURBATIONS ROTATING INTO THE NRN GREAT LAKES
WILL HOLD TEMPS A LITTLE COLDER THAN EARLY MARCH MEANS DURING THE
LATER HALF OF THE FORECAST PERIOD.

MARINE...

THE DEPARTURE OF HIGH PRESSURE TO THE EAST AND APPROACH OF A LOW
PRESSURE SYSTEM WILL CAUSE SOUTHERLY WINDS TO DEVELOP TONIGHT. THE
SURFACE LOW IS FORECAST TO TRACK ACROSS THE STRAITS ON TUESDAY.
SOUTHERLY WINDS WILL INCREASE AS THIS LOW APPROACHES. WINDS WILL
THEN VEER TO THE WEST TUES NIGHT AS THE LOW DEPARTS TO THE EAST.
THERE WILL BE AN INCREASE IN THE WESTERLY WINDS ON WED AS ANOTHER
SURGE OF ARCTIC AIR OVERSPREADS THE LAKES. THERE IS A POTENTIAL FOR
GUSTS TO APPROACH GALE FORCE OVER FAR NORTHERN LAKE HURON ON
WEDNESDAY. THE CHANCES FOR ANY GALE FORCE GUSTS TO EXCEED TWO HOURS
IN DURATION DOES NOT APPEAR HIGH ENOUGH TO JUSTIFY A GALE WATCH
ATTM.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY FROM 8 AM THIS MORNING TO 7 PM EST THIS
     EVENING FOR MIZ047>049-053>055-060>063-068>070.

     WINTER WEATHER ADVISORY FROM 8 AM THIS MORNING TO 4 PM EST THIS
     AFTERNOON FOR MIZ075-076-082-083.

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

$$

AVIATION.....MR
SHORT TERM...JVC
LONG TERM....DT/SC
MARINE.......SC

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


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