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000
FXUS63 KDTX 071629
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1129 AM EST FRI MAR 7 2014


.AVIATION...

//DISCUSSION...

LIGHT SOUTH TO SOUTHWEST FLOW WILL ACCOMPANY TRANQUIL VFR CONDITIONS
INTO TONIGHT. DEEPER LOW LEVEL MOISTURE ASSOCIATED WITH A WEAK COLD
FRONT WILL THEN SPREAD INTO THE AREA FROM NORTH TO SOUTH RESULTING
IN DETERIORATION OF CONDITIONS TO AT LEAST LOW MVFR BY SATURDAY
MORNING. THERE REMAINS SOME POTENTIAL FOR LIGHT NON-ACCUMULATING
SNOWFALL, BUT THE COMBINATION OF WEAK FORCING AND MID-LEVEL DRY AIR
SUFFICIENTLY LIMITS CONFIDENCE TO WARRANT OMISSION OF -SHSN FROM THE
18Z SET OF TAFS.

//DTW THRESHOLD THREATS...

* NONE.

&&

.PREV DISCUSSION...ISSUED 343 AM EST FRI MAR 7 2014

SHORT TERM...TODAY AND TONIGHT

PLEASANT DAY ON TAP AS WE BECOME LOCATED IN BETWEEN THE EXITING SFC
RIDGE AND A WEAK COLD FRONT ENTERING THE WESTERN GREAT LAKES. THIS
PUTS US INTO A REGION OF DEEP LAYER SW FLOW...SFC TO 800 MB...FOR
MUCH OF THE DAY. THERMAL PROFILES IN MODEL SOUNDINGS ADVERTISE A
LAYER FROM ABOUT 950MB-700MB ABOVE ZERO MAXING OUT AROUND 3C.
COMBINED WITH THE SUBSTANTIALLY DRY AIRMASS FROM THE EXITING RIDGE
AND WE WILL HAVE A GOOD AMOUNT OF HEATING TODAY. HIGH CLOUDS...AOB
15KFT...WILL STREAM INTO THE LATER IN THE DAY BUT ONLY AFTER SEVERAL
HOURS OF ADVECTIVE AND RADIATIVE HEATING HAS WORKED OVER THE AREA.
ONLY MINOR TWEAKS TO TODAYS HIGHS...STILL IN THE UPPER 30S TO LOW
40S WHICH IS SLIGHTLY ABOVE MOST GUIDANCE.

CHANGES COMING DURING THE OVERNIGHT HOURS AS A WEAKENING FRONTAL
BOUNDARY DROPS THROUGH LOWER MI. THE BEST FRONTAL FORCING LIFTS OFF
TO THE NW AS THE FRONT DROPS THROUGH AFTER 06Z. THE FGEN BAND THAT
DOES PASS THROUGH LOOKS VERY FRACTURED AND DISORGANIZED. LOOKING AT
A CROSS SECTION VIEW THERE IS A LAYER OF OMEGA ALOFT THAT TRIES TO
WORK ITS WAY TO THE LOW LEVELS WHILE THE FRONT PASSES BUT EVEN THAT
WEAKENS DURING THE TRIP. MUCH OF THIS IS TIED TO THE FACT THAT THE
JET ENERGY IS TRANSITIONING. THE ORIGINAL JET MAX AIDING IN THE
PRECIP UPSTREAM CURRENTLY LIFTS OFF TO THE NE WITH THE LOW BUT
ANOTHER MAXIMUM DEVELOPS RIGHT OVERHEAD STARTING CLOSE TO 12Z
SATURDAY. THE DEPTH OF DRY AIR WITH A LAYER OF DEWPOINT DEPRESSIONS
AROUND 15-20C FROM THE SFC THROUGH 700MB...MUCH OF THE MOISTURE
EARLY ON WILL GO TO SATURATING THE COLUMN FROM THE TOP DOWN DURING
THE EVENING HOURS. THE DEEP WARM LAYER BROUGHT UP THE QUESTION OF
PTYPE. BY THE TIME SATURATION OF THE LOW LEVELS OCCURS...THE COLUMN
HAS ALREADY BEGUN TO COOL OFF LEAVING ONLY A SHALLOW LAYER ABOVE 0C
ALOFT. WITH THE SATURATION STEMMING FROM ALOFT ALL THE PRECIP IS
STARTING OFF AS SNOW WITH THE FRONT. THE WET BULB POTENTIAL SHOULD
FORCE THE LAST OF THE WARM AIR TO COOL OFF ALLOW THE FLAKES TO FALL
TO THE SFC. THERE IS A CHANCE THAT THE LEAD EDGE OF THE BAND COULD
PRODUCE A QUICK BURST OF SNOW PELLETS BEFORE FLAKES TAKE OVER BUT
THAT SHOULD BE THE EXTENT OF THE INFLUENCE OF THE WARM LAYER. SO
WILL KEEP THE PTYPE AS SNOW THROUGH THE FRONT. ALL THIS SAID...ONLY
EXPECTING A DUSTING UP TO A TENTH OR TWO BEFORE SUNRISE AS THE DRY
AIR SHOULD USE UP MOST OF THE MOISTURE. A CHANCE POP WILL CONTINUE
FOR 06-12Z TONIGHT.

LONG TERM...

THE COLD FRONT WILL FINISH SLIDING THROUGH SE MICHIGAN DURING
SATURDAY MORNING. MODERATE SURFACE TEMPERATURE CONTRAST WILL BE
MAINTAINED AS THE BOUNDARY EXITS THE REGION BUT THE DYNAMICS OF THE
FRONTAL CIRCULATION WILL CONTINUE TO SUFFER FROM BEING LEFT BEHIND
BY THE WAVE OVER EASTERN CANADA. MODEL INDICATIONS OF MOISTURE
QUALITY ARE GOOD JUDGING BY SPECIFIC HUMIDITY AROUND 3 G/KG IN THE
850-700 MB LAYER BUT THIS WILL BE OFFSET BY THE DRY NEAR SURFACE
LAYER AND THE SHALLOW NATURE OF THE FRONTAL STRUCTURE WITH HEIGHT.
MODEL CROSS SECTIONS INDICATE A VERY SHALLOW FRONTAL SLOPE IN
THETA-E FROM THE SURFACE TO 700 MB BY 12Z SATURDAY WITH PLAN VIEW
DEPICTIONS OF 2D FGEN WEAKENING WITH TIME IN RESPONSE TO THE
WEAKENING UPPER JET AND EASTWARD DEPARTURE OF SHORT WAVE DYNAMICS.
IN THIS ENVIRONMENT, THE NAM INDICATES A SURPRISINGLY UPRIGHT
AGEOSTROPHIC CIRCULATION NEAR THE OHIO BORDER, LIKELY TOO MUCH SO
CONSIDERING THE BROAD AND WEAK UPPER JET LEFT OVER THE AREA IN
LOCALLY ZONAL FLOW ALOFT. PREFER THE GFS DEPICTION IN THIS CASE
WHICH IS CONSIDERABLY MORE SHALLOW LEAVING THE VERTICAL MOTION
FIELD MOSTLY WITHIN THE HIGHER STATIC STABILITY REGION BELOW 500
MB. ON THE OTHER HAND, AND TYPICAL OF THE GFS, ITS 6 HR QPF IS TOO
GENEROUS WITH NEARLY 0.10 INCH LIQUID EQUIVALENT DURING SATURDAY
MORNING. INSTEAD, PLAN TO MAINTAIN A CHANCE POP ALONG AND SOUTH OF
INTERSTATE 69 LINGERING INTO EARLY AFTERNOON NEAR THE OHIO BORDER.

THE FRONT WILL DROP MAX TEMPS BACK DOWN BELOW NORMAL VALUES, WHICH
ARE RANGING FROM THE UPPER 30S AT MBS TO LOWER 40S AT DTW HEADING
INTO THE SECOND WEEK OF MARCH, BUT ANYTHING ABOVE FREEZING IS
WELCOME COMPARED TO RECENT DAYS EVEN IF COUPLED WITH MIN TEMPS
NEAR SINGLE DIGITS BY SUNDAY MORNING. A REBOUND IS THEN EXPECTED
SUNDAY INTO MONDAY WITH GOOD MODEL AGREEMENT ON THE ARRIVAL OF THE
NEXT NORTHERN STREAM LOW PRESSURE SYSTEM. THIS WILL GENERATE SOME
SOUTHWEST RETURN FLOW IN THE LOW LEVELS BEFORE THE WAVE WASHES OUT
OVER WESTERN QUEBEC IN FAVOR OF YET ANOTHER SYSTEM FROM CENTRAL
CANADA BY MONDAY. THIS SYSTEM WILL MAINTAIN A SIMILAR SURFACE WIND
PATTERN OVER LOWER MICHIGAN ADDING SOME CONFIDENCE TO THE
TEMPERATURE REBOUND DURING THE FIRST HALF OF NEXT WEEK. THE KEY
HERE IS THAT, WHILE PREDICTABILITY IS LOW ON THE INDIVIDUAL SHORT
WAVES, THE TRACK OF EACH SYSTEM IS SOLIDLY OVER CANADA WITH
LIMITED POTENTIAL FOR SUBSTANTIAL COLD ADVECTION UNTIL MID WEEK.
THAT IS WHEN THE LARGE SCALE UPPER AIR PATTERN IS SHOWN TO AMPLIFY
ENOUGH FOR A MEANINGFUL SURGE OF COLD AIR BY WEDNESDAY, JUST AS
THE NEXT SOUTHERN STREAM WAVE MOVES INTO LOWER MISSISSIPPI VALLEY.
FORECAST CONFIDENCE IS MUCH GREATER ON THE RESULTING BELOW NORMAL
TEMPERATURE TREND IN THE GREAT LAKES COMPARED TO PRECIPITATION
CHANCES. THE GFS AND ECMWF HAVE A LOT OF SPREAD IN THE UPPER AIR
FORECAST IN TERMS OF PHASING OF THE WESTERLIES. THE ECMWF IS
STRONGER IN THAT REGARD WITH ITS SOLUTION BRUSHING OUR AREA WITH
SNOW ON THE NORTH FLANK OF THE SYSTEM WEDNESDAY. THE GFS IS LESS
AMPLIFIED WITH SOME SUPPORT FROM THE CANADIAN AND BOTH ARE FAR
ENOUGH SOUTH FOR SNOW TO MISS OUR AREA. RECENT HISTORY LEANS THE
FORECAST TOWARD THE GFS GIVEN THE TENDENCY FOR THE LONG WAVE RIDGE
OUT WEST TO EASILY/QUICKLY TAKE ON OMEGA BLOCK CHARACTER SHORTLY
AFTER A NEW ROUND OF AMPLIFICATION.

MARINE...

MODEST SOUTHERLY FLOW AND MILD TEMPERATURES BY RECENT STANDARDS
WILL DEVELOP OVER THE REGION TODAY AND TONIGHT. THIS WILL BE
FOLLOWED BY A COLD FRONT OF AVERAGE STRENGTH PASSING THROUGH THE
NORTHERN LAKES TONIGHT AND SOUTHERN LAKES SATURDAY MORNING. MODERATE
NORTHERLY FLOW OVER THE MOSTLY ICE COVERED LAKE HURON WILL BE
GENERALLY LESS THAN 25 KNOTS. SOUTHWEST WINDS WILL INCREASE AGAIN
SUNDAY AND MONDAY AS TWO WAVES OF LOW PRESSURE TRACKS THROUGH
SOUTHERN CANADA. THIS WILL KEEP TEMPERATURES ON THE MILD SIDE UNTIL
A STRONGER FRONT MOVES THROUGH THE REGION BY WEDNESDAY.

&&

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

&&

$$

AVIATION.....JVC
SHORT TERM...DRK
LONG TERM....BT
MARINE.......BT


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