FXUS63 KDTX 221152
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
652 AM EST TUE DEC 22 2009
.AVIATION...
HIGH PRESSURE WILL CONTINUE TO BUILD FROM NORTHERN ONTARIO INTO
LOWER MICHIGAN TODAY. THE COLD AND DRY AIR WILL SCOUR OUT ANY
REMAINING BOUNDARY LAYER MOISTURE DURING THE MORNING RESULTING IN
VFR CONDITIONS ALL AREAS BY AFTERNOON. SATELLITE IMAGERY WILL BE
MONITORED FOR INDICATIONS OF STRATOCU MOVING BACK INTO THE AREA FROM
LAKE HURON AS THE WINDS TURN TOWARD THE NE, BUT THE ANTICYCLONIC
FLOW AND SUBSIDENCE ASSOCIATED WITH THE HIGH PRESSURE WILL ACT
AGAINST ANY CEILING FORMATION. THAT LEAVES SOME VFR CEILING AND
FLURRIES POSSIBLE AT DTW THROUGH ABOUT MID AFTERNOON AS A WAVE MOVES
THROUGH INDIANA AND OHIO. HIGH PRESSURE WILL THEN FOSTER A CLEARING
TREND TONIGHT BUT WITH SOME MVFR FOG POSSIBLE TOWARD SUNRISE
WEDNESDAY MORNING.
&&
.PREV DISCUSSION...ISSUED 423 AM EST TUE DEC 22 2009
SHORT TERM...TODAY
THE FIRST CONCERN IN THE FORECAST WILL BE LAKE EFFECT SNOW OCCURRING
IN THE THUMB MOSTLY BEFORE MID MORNING. SAMPLING RADAR DATA FROM
NORTHERN LOWER AND HERE IN SE MICHIGAN INDICATES CONVECTIVE DEPTH
NEAR 10 KFT IN ACTIVITY MOVING FROM BETWEEN APN AND OSC INTO HURON
COUNTY. THIS MATCHES UP WELL WITH 03Z-06Z MODEL FORECAST SOUNDINGS
WHICH ALSO INDICATE LAKE TO 850 MB DELTA-T NEAR 18C. THE MODEL
SOUNDINGS ALSO SHOW A RAPID DECREASE IN CONVECTION BY MID MORNING AS
DRY AIR MOVES IN FROM THE NORTH. SATELLITE IMAGERY OVER NORTHERN
LAKE HURON SUPPORTS THIS TREND AS WELL WITH A NOTICEABLE DECREASE IN
CLOUD COVERAGE. CONSIDERING THE LAKE EFFECT WILL BE FOCUSED IN THE
SURFACE TROUGH AND MOVING QUICKLY, ACCUMULATION WILL BE LIMITED TO
AN INCH OR TWO IN ANY ONE LOCATION. THE DRYING TREND BEHIND THE
SURFACE TROUGH ALSO SUGGESTS TRAILING SNOW SHOWERS WILL BE SCATTERED
AND LIGHT AS THE WINDS BECOME ONSHORE. THERE WILL BE SOME IMPRESSIVE
BURSTS OF SNOW INITIALLY AS THE SURFACE TROUGH MOVES DOWN THE
SHORELINE TOWARD PORT HURON BUT TOTAL ACCUMULATION LOOKS LIKE IT
WILL FALL JUST SHORT OF A 6 HOUR ADVISORY BEFORE DIMINISHING.
WHILE THE LAKE EFFECT IS GOING ON IN THE THUMB, A SHORT WAVE IS
MOVING THROUGH ILLINOIS AND INDIANA. BASED ON RADAR COMPOSITES TO
OUR WEST, THIS SYSTEM IS LIKELY TO BRING A DUSTING OF SNOW TO
LENAWEE AND MONROE COUNTIES DURING THE MORNING AS THE SYSTEM MOVES
THROUGH OHIO. THIS WAVE WILL BE SHEARING APART AND WEAKENING WITH
TIME BUT OBSERVATIONS OF 3/4SM IN SNOW IN THE CHICAGO AREA GIVE
SUPPORT TO A LIKELY POP LOW QPF FORECAST FOR AREAS NEAR THE OHIO
BORDER ON THE NORTHERN FRINGES OF THE DEEPER MOISTURE. THE FORECAST
WILL TREND DOWN TO A CHANCE FOR THIS AFTERNOON AS THE PRECIPITATION
THINS. ANY ACCUMULATION THERE WILL BE JUST AT TENTH OR TWO AT BEST.
LONG TERM...TONIGHT THROUGH NEXT MONDAY
SURFACE RIDGING WILL EXTEND THIS EVENING FROM THE LARGE SURFACE HIGH
PARKED OVER WESTERN ONTARIO DOWN TO THE VIRGINIAS. THIS RIDGE IS
EXPECTED TO PERSIST OVER SOUTHEASTERN MICHIGAN THROUGH MUCH OF THE
MIDWEEK...AND WILL ULTIMATELY PROVE A FORMIDABLE FOE FOR THE LEAD
PRECIPITATION OF THE IMPENDING UPPER MIDWEST STORM SYSTEM. DRY
CONDITIONS ARE ANTICIPATED WEDNESDAY AND THURSDAY WITH DAYTIME
TEMPERATURES A DEGREE OR TWO BELOW NORMAL.
THERE WERE NO IMPORTANT ISSUES WITH THE 00Z MODEL GUIDANCE. EACH OF
THE VARYING NWP CORES ARRIVED SLIGHTLY SLOWER AND WEST OF THEIR 12Z
COUNTERPARTS. THE CURRENT CONSENSUS LOW TRACK...SHARING GREATER
SIMILARITY TO THE EUROPEAN SOLUTION OF THE PAST FEW DAYS...IS FROM
OKLAHOMA WEDNESDAY MORNING...TO WESTERN IOWA THURSDAY EVENING...AND
TO NORTH CENTRAL WISCONSIN BY SATURDAY MORNING. COMPARING THIS
OPERATIONAL CONSENSUS WITH THE NEW NAEFS/FIM SUGGESTS THAT THERE MAY
ADDITIONAL ADJUSTMENTS NEEDED TO SLOW DOWN THE TIMING. WHAT IS
ESPECIALLY NOTEWORTHY OF THIS STORM...IS HOW QUICKLY THIS STORM WILL
GROW IN AREAL COVERAGE.
PRECIPITATION IS EXPECTED TO SPREAD INTO SOUTHEASTERN MICHIGAN
THURSDAY EVENING AS AN OLD TROWAL/WARM CONVEYOR IS CAST OFF TOWARD
THE CENTRAL LAKES. THE STRONG THETA E RIDGE IS NOT EXPECTED TO BE
COMPLETELY OCCLUDED...GIVEN THE PROXIMITY OF THE MODELED UPPER LEVEL
LEFT EXIT REGION DYNAMICS AND NEAR SURFACE TRIPLE POINT.
EXPECTATIONS ARE FOR QUITE THE UPWARD VERTICAL MOTION
RESPONSE/PRECIPITATION DUE TO VERY STRONG ISENTROPIC LIFT.
WET BULB COOLING EFFECTS ARE EXPECTED TO HAVE AN IMPACT THROUGHOUT
THE NIGHT AS A DEEP WARM LAYER (900-700MB) LIFTS RAPIDLY INTO LOWER
MICHIGAN. LOW CONFIDENCE CONTINUES IN REGARDS TO THE AMOUNT OF
PRECIPITATION THAT WILL FALL BEFORE SURFACE TEMPS WARM ABOVE
FREEZING. MORE SPECIFICALLY...UNKNOWNS REMAIN AS TO THE PRECIPITATION
INTENSITY AND WHAT SORT OF DOWNWIND INFLUENCE THE LAKES WILL HAVE ON
THE LOW LEVEL THERMAL PROFILE. ENVIRONMENTS CONDUCIVE FOR FREEZING
RAIN ARE DELICATE TO THERMODYNAMIC AND ADVECTIVE PROCESSES (LATENT
HEAT OF FREEZING/MODELS ACCURATE REPRESENTATION OF THE THERMAL
FIELDS). FOR THE FRIDAY FORECAST...OPTIMISTICALLY TURNED IT OVER TO
RAIN FOR MANY AREAS IN HOMAGE TO THE MODELED SOUTHERLY FLOW. WAS
ALSO SLOWER IN CHANGING IT TO ALL SNOW AS THE BELIEF IS THE MODELS
REMAIN TOO PROGRESSIVE. THE DRYSLOT IS EXPECTED TO MOVE IN LATE
FRIDAY EVENING/FRIDAY NIGHT WITH WRAP AROUND SNOW SHOWER CHANCES FOR
THE REMAINDER OF THE WEEKEND. THERE ARE LARGE DIFFERENCES WITHIN THE
MODEL SOLUTIONS FOR THE LATTER HALF OF THE WEEKEND IN REGARDS TO THE
EXTENT OF THE POLAR AIR INTRUSION TO FOLLOW.
MARINE...
HIGH PRESSURE BUILDING INTO LAKE HURON FROM NORTHERN ONTARIO TODAY
WILL START A PROLONGED PERIOD OF NORTHERLY WINDS ON LAKE HURON THAT
WILL LAST THROUGH WEDNESDAY. THE LONG FETCH DOWN THE LAKE WILL BUILD
WAVES OVER 4 FEET DESPITE THE MODEST WIND SPEED. A SMALL CRAFT
ADVISORY IS IN EFFECT FOR THE ROUGH WATER CONDITIONS.
A STRONG LOW PRESSURE SYSTEM IS THEN EXPECTED TO DEVELOP IN THE MID
MISSISSIPPI VALLEY DURING THURSDAY AND THURSDAY NIGHT. THIS SYSTEM
WILL GENERATE INCREASED EASTERLY WINDS OVER OUR AREA LASTING THROUGH
FRIDAY WITH THE POTENTIAL FOR GALE FORCE WINDS BY CHRISTMAS MORNING.
STRONG WESTERLY WINDS ARE THEN EXPECTED TO CONTINUE THROUGH THE
WEEKEND AS THIS SYSTEM TRACKS THROUGH THE GREAT LAKES AND INTO
CANADA.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
HURON INCLUDING OUTER SAGINAW BAY...UNTIL 5 AM THURSDAY.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
AVIATION.....BT
SHORT TERM...BT
LONG TERM....CB
MARINE.......BT
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
