FXUS63 KDTX 120519
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1219 AM EST SAT DEC 12 2009
.AVIATION...
MAINLY CLEAR SKIES WILL PERSIST INTO THE EARLY PORTIONS OF
SATURDAY. THE WESTERLY FLOW WILL SLOWLY BACK TO SOUTHWESTERLY AS
THE NEXT SYSTEM APPROACHES FROM THE WEST. THE ONLY IMPACT WILL BE
AN INTRODUCTION OF MID AND HIGH CLOUD COVER LATER ON SATURDAY.
DEEPER MOISTURE WILL BE MAKING INROADS INTO THE FORECAST AREA AT THE
END OF THE PERIOD.
&&
.PREV DISCUSSION...ISSUED 333 PM EST FRI DEC 11 2009
SHORT TERM...TONIGHT
LAKE EFFECT SLOWLY WINDING DOWN ACROSS FAR SOUTH LAKE MICHIGAN.
THIS IS IN RESPONSE TO THE SURFACE RIDGE BUILDING INTO LOWER
MICHIGAN...THE ACCOMPANYING DRY AIR FROM 925 MB TO 850 MB...AND THE
START OF SOME WARM AIR ADVECTION IN THAT SAME LAYER. WILL CARRY THE
SNOW SHOWERS NORTH OF 8 MILE EARLY THIS EVENING...THEN EXPECT A
CLEARING TREND. WITH THE DRY AIR AND WINDS BACKING TO THE
SSW...EXPECT MOST OF SOUTHEAST MI TO BECOME CLEAR OR MOSTLY CLEAR
OVERNIGHT.
MOS IS TRENDING WARMER FOR TONIGHTS LOWS...AND EVEN SUGGEST SOME
STEADY OR SLOWLY WARMING TEMPS LATER TONIGHT IN RESPONSE TO THE
WARMER SSW FLOW AND THAT WARM AIR ADVECTION. THINK THAT WITH THE
CLEARING SKIES AND SURFACE RIDGE...WINDS WILL DECOUPLE ENOUGH TO BE
IN THE 5 TO 8 KT RANGE OVERNIGHT. THERE IS NOT A BIG SURGE OF
MOISTURE EITHER...AND SURFACE DEW POINTS WILL AT LEAST BE AROUND 10
TO THE LOWER TEENS. THEREFORE...WILL GO AT LEAST AS COLD AS THE
GFS/MAV MOS NUMBERS TONIGHT.
LONG TERM...SATURDAY THROUGH THURSDAY
THE WEATHER PATTERN ACROSS SOUTHEASTERN MICHIGAN WILL REMAIN BUSY AS
THE CONSOLIDATED POLAR JET CORE LIFTS BACK NORTHWARD AND WAVERS IN
VICINITY. THIS FLOW PATTERN WILL BRING SEVERAL OPPORTUNITIES FOR
PRECIPITATION DURING THE NEXT WEEK...AS SHORTWAVE ENERGY WILL TAKE
AIM OF THE GREAT LAKES. IN GENERAL...THE CWA WILL RESIDE ON THE
COOL SIDE OF THE BOUNDARY...DESPITE THE BRIEF WARMUP DURING THE
SUN-MON NIGHT TIME PERIOD.
EXPECTING A SUN SPLASHED SKY FOR DECEMBER STANDARDS TOMORROW AS
RELATIVE HUMIDITIES THROUGHOUT THE COLUMN WILL BE LACKING. NOT
REALLY FRIGHTENED BY THE POTENTIAL FOR TRAPPED MOISTURE UNDER THE
STRENGTHENING INVERSIONS EITHER WITH THE PRECEDING AIRMASS HEAVILY
INFLUENCED BY SUBSIDENCE. STILL SOME QUESTION AS TO HOW DEEP THE
NEAR SURFACE MIXED LAYER WILL BECOME...BUT GIVEN POOR DECEMBER
SUN/925 TEMPS THAT WARM SOME 10C THE NEXT 24 HOURS...FEEL EITHER
SIDE OF 30 IS ATTAINABLE. WANTED TO REMAIN A FEW DEGREES BELOW
GUIDANCE...GIVEN THE TYPICAL OVER AGGRESSIVE TENDENCY OF THE MODELS
AND A MUCH MORE STABLE SOUTHERLY FLOW.
THE NEXT SYSTEM OF CONSIDERABLE INTEREST WILL ARRIVE OVER THE GREAT
LAKES LATE SATURDAY NIGHT. A COUPLE OF THINGS TO WATCH FOR WILL BE
THE DEVELOPMENT OF A DEFORMATION SWATH THAT TRACKS FROM THE CENTRAL
PLAINS TO NORTHERN LOWER MICHIGAN...AND THE ACTUAL INGESTION OF A
MODIFIED GOMEX AIRMASS WHICH CLIPS THE SOUTH. WHILE THERE ARE HINTS
OF THESE FEATURES WITHIN THE MODEL SUITE...THERE REMAINS SOME SOLID
DIFFERENCES IN HOW THIS EVENT WILL UNFOLD. MORE SPECIFICALLY THE
THERMAL PROFILE. THE NAM ADVECTS A SUBSTANTIAL WARM LAYER INTO THE
CWA QUICKLY...WHILE THE GFS REMAINS BORDERLINE IN REGARDS TO MIXED
PRECIPITATION. THE FEELING IS PRECIPITATION WILL ARRIVE VERY LATE
SATURDAY NIGHT...INITIALLY THWARTED BY THE DRY AIR IN RESIDENCE. WET
BULB COOLING AT THE ONSET WILL KEEP THE LOW TO MIDLEVEL THERMAL
PROFILE COMFORTABLY LEFT OF THE 0C ISOTHERM...BEFORE QUICKLY WARMING
RIGHT AT/AROUND 12Z. THEREFORE...DECIDED NOT TO INTRODUCE A FREEZING
RAIN MENTION THIS ISSUANCE WITH THE IDEA THE WET BULB COOLING WILL
BUY SOME TIME. RELATIVELY WEAKER SOUTHWEST FLOW AND DEEP 8 KFT LAYER
ABOVE ZERO SHOULD ALLOW SURFACE TEMPERATURES TO WARM ABOVE FREEZING.
WHILE IN AGREEMENT WITH THE PREVIOUS FORECASTER THAT A OVERALL GREAT
SETUP IS LACKING...THERE IS A 6-9 HR WINDOW WHERE THINGS LOOK
DECENT. DEEP SATURATED AIRMASS THROUGH 13K FT AND A WONDERFULLY
MODELED THETA E STRUCTURE SWEEPING THROUGH THE CWA (MODELS EVEN HAVE
SUPERBLY DEFINED SUBSIDENT SIGNATURE). BUMPED POPS CONSIDERABLY FOR
THE EVENT WITH LIKELYS FAR NORTH FOR SNOW IN DEFORMATION AND HIGH
CHANCE SOUTH. EXPECTING THE BULK OF THE SNOW TO MISS TO THE
NORTH...BUT AN INCH/POSSIBLY TWO FOR NORTHERN BAY/MIDLAND COUNTIES.
THE LACK OF ANY SUBSTANTIAL GRADIENT/ADVECTIONS BEHIND THE SUNDAY
SYSTEM WILL KEEP THE FRONTAL ZONE NEAR LOWER MICHIGAN. THIS WILL
ALLOW THE NEXT WAVE/REMNANT PIECE OF THE POLAR VORTEX TO SCRAPE ALONG
THE NORTHERN PORTIONS OF THE GREAT LAKES MONDAY NIGHT AND TUESDAY.
DEFINITELY FAVOR THE THE STRONGER GFS SOLUTION...AS BAROCLINICITY
AND MODELED THERMAL SUPPORT IS HIGH. THE SHEARED OUT NATURE OF THE
PV ANOMALY AND POSITIONING OF THE JET CORE WILL KEEP THE SURFACE LOW
TRACK TO THE NORTH. WITH THAT SAID...GOOD FRONTAL DYNAMICS
ISENTROPIC ASCENT SHOULD CLIP THE FAR NORTHERN PORTIONS OF THE CWA.
CONDITIONS SHOULD COOL DOWN AGAIN TUES-THURS AS AN ARCTIC
AIRMASS...VERY SIMILAR TO THE ONE EXPERIENCED NOW...WILL SWEEP
ACROSS LOWER MICHIGAN...HIGHS IN THE TWENTIES...LOWS SINGLE DIGITS
TO LOWER TEENS.
MARINE...
SURFACE RIDGE MOVES THROUGH THE SOUTHERN LAKES OVERNIGHT WHICH WILL
CAUSE THE WINDS TO DECREASE BELOW GALES AND END THE LOW WATER IN
LAKE ERIE TOO. WINDS INCREASE AGAIN...ESPECIALLY OVER SAGINAW BAY
AND LAKE HURON ON SATURDAY WITH SOUTH SOUTHWEST FLOW. THAT WILL
LIKELY MEAN AN EXTENDED PERIOD OF SMALL CRAFT INTO SATURDAY EVENING.
ANOTHER LULL IN THE WIND IS EXPECTED FOR SUNDAY AND INTO EARLY
MONDAY.
A STRONG STORM PASSES THROUGH THE NORTHERN LAKES ON MONDAY NIGHT AND
BEHIND THAT THE WEST TO NORTHWEST WINDS WILL INCREASE AS ARCTIC AIR
RUSHES BACK OVER THE LAKES. THIS WILL BE THE NEXT POTENTIAL GALE
EVENT AND WILL HAVE WINDS TO 30 KTS IN THIS FORECAST.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...SAGINAW BAY AND THE NEARSHORE WATERS FROM
PORT AUSTIN TO HARBOR BEACH...UNTIL 10 PM SATURDAY.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
AVIATION.....MANN
SHORT TERM...RBP
LONG TERM....CB
MARINE.......RBP
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