000 FXUS63 KDTX 201126 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 625 AM EST THU JAN 20 2005 .AVIATION... UPDATE SATELLITE AND RADAR IMAGERY INDICATE RESPECTABLE VERTICAL MOTION GOING ON IN THE MID LEVEL FRONTAL ZONE OVER SOUTHERN LAKE MICHIGAN THIS MORNING. COOL CLOUD TOPS AND SOME CONVECTIVE LOOKING RADAR PATTERNS SUGGEST AT LEAST SOME ELEVATED INSTABILITY IN THE EXIT REGION OF THE UPPER JET. HIGHER PRECIP RATES ASSOCIATED WITH THIS FORCING WILL BATTLE DRY AIR IN THE LOW LEVELS OVER SE MICHIGAN DURING THE MORNING WITH LOTS OF VIRGA ON RADAR. MOUNTING EVIDENCE SUGGESTS THAT SOME MVFR VISIBILITY RESTRICTIONS WILL BE POSSIBLE THIS AFTERNOON WITH LIGHT SNOW NEAR THE OHIO BORDER, JUST TO THE WEST AND SOUTH OF DTW. PLAN TO CARRY A SHORT TEMPO FOR 5 MI -SN AROUND NOON. EXPECT VFR CONDITIONS OVER THE REST OF SE MICHIGAN THROUGH THIS AFTERNOON. TONIGHT, THERE IS A CHANCE OF MVFR CEILINGS AND SOME FLURRIES AROUND FNT AND MBS AS NE FLOW FROM LAKE HURON PRODUCES SOME STRATOCU. NE FLOW FROM ONTARIO WILL KEEP CEILINGS VFR AROUND DETROIT. && .SHORT TERM... ISSUED AT 425 AM TODAY OUR FIRST MILD CONCERN IN THE SHORT TERM IS THE BACKDOOR FRONT MOVING THROUGH SE MICHIGAN THIS MORNING. THIS WILL BE HELPED THROUGH THE AREA BY THE UPPER JET MAX THAT IS MOVING THROUGH THE SOUTHERN LAKES AND THE SURFACE REFLECTION MOVING INTO ILLINOIS BY TONIGHT. THE FRONT HAS SOME LAKE MOISTURE TO WORK WITH THAT HAS BEEN GOOD ENOUGH FOR FLURRIES IN THE THUMB SINCE MIDNIGHT, AND EXPECT THEY WILL WORK SOUTH DURING THE MORNING AND COMBINE WITH WHATEVER CAN REACH THE GROUND FROM THE UPPER SUPPORT ASSOCIATED WITH THE JET CIRCULATION. PLENTY OF DRY AIR BETWEEN 850 AND 700 MB WILL ENSURE THAT THIS IS MINIMAL WITH A LOT OF VIRGA EXPECTED ON RADAR THROUGH THE DAY. THIS DRY AIR IS ALSO CUTTING INTO THE LAKE EFFECT ALONG WITH MARGINAL INSTABILITY. ETA-12 MODEL FORECAST SOUNDINGS SUGGEST EQUILIBRIUM LEVEL (EQL) LESS THAN 4 KFT THIS MORNING WITH DELTA-T AROUND 17C. OBSERVATIONS FROM THE CANADIAN EXETER RADAR SHOW NUMEROUS BUT WEAK CELLULAR SNOW SHOWERS IN ONTARIO AS THE LOW LEVEL FLOW LINGERS FROM THE NORTH. THIS WILL BE GOOD ENOUGH FOR NUMEROUS SNOW SHOWER COVERAGE BY THIS AFTERNOON AS THE LOW LEVEL FLOW BECOMES FROM THE NE AND THE GRADIENT WEAKENS. THIS SHOULD ALLOW A FEW SNOW BANDS TO FORM WITHIN THE LAKE INDUCED PRESSURE TROF WHICH WILL MOVE INLAND WITH SOME LIGHT ACCUMULATION, ABOUT AN INCH, IN THE THUMB COUNTIES. AS COLDER AIR FILTERS INTO THE REGION TONIGHT, LAKE EFFECT CONDITIONS WILL BECOME MORE FAVORABLE IN THE THUMB, WITH A CHANCE AT SCATTERED SNOW SHOWERS FARTHER INLAND. BOTH EQL AND INSTABILITY WILL INCREASE WITH TIME AND WILL BE AUGMENTED BY INCREASED MID LEVEL MOISTURE FOR POTENTIAL SEEDING OF THE LAKE CONVECTION. ETA-12 FORECAST SOUNDINGS SHOW EQL REACHING NEAR 7 KFT BY 06Z WITH DELTA-T AROUND 21C AND CAPE LOOKING PRETTY FAT EVEN WHEN ADJUSTED FOR A COOLER SURFACE PARCEL. IT DOES LOOK LIKE GRADIENT FLOW WILL BE WEAK ENOUGH FOR A LAKE INDUCED SURFACE PRESSURE TROF TO HELP FOCUS BANDING, AND THIS TROF MAY BE DUE TO LAKE CONVECTION IN THE MODEL AT THIS POINT, BUT IT IS STILL DIFFICULT TO DETERMINE PRECISELY HOW THAT WILL LINE UP. THE LARGER SCALE SURFACE RIDGE WILL BE BUILDING INTO GEORGIAN BAY AND THAT WILL TEND TO FORCE THINGS CLOSER TO THE THUMB SHORELINE OVERNIGHT WITH THE CONVERGENCE HELPING TO FOCUS BANDS. PLAN TO GIVE 2 TO 4 INCH ACCUMS A CHANCE TO WORK OUT WITH SOME SPILLING OVER INTO FRIDAY MORNING BEFORE THE PATTERN BREAKS DOWN IN ADVANCE OF THE NEXT SYSTEM. && .LONG TERM... LONG TERM FOCUS DOMINATED BY THE CLIPPER THAT AFFECTS THE REGION THIS WEEKEND. ETA/GFS STILL OFFERING SLIGHTLY DIFFERING SOLUTIONS... WHICH LEAD TO BIGGER DIFFERENCES AS FAR AS SNOWFALL POTENTIAL. GFS HAS CONTINUE TO SLOWLY TREND FARTHER SOUTH WITH THE TRACK OF THE SYSTEM...WHILE THE ETA MAINTAINS A STRONGER LOW FARTHER NORTH. WEAK CONSENSUS FAVORS THE GFS...WHICH HAS ALSO BEEN LESS ERRATIC THAN THE ETA WITH THE HANDLING OF THIS SYSTEM. HOWEVER A QUICK LOOK AT THE 00Z/20 ECMWF SHOWS ITS SOLUTION IS PRETTY SIMILAR TO THE ETA...FARTHER NORTH AND A BIT STRONGER. ALSO INTERESTING IS THAT THE 00Z CANADIAN GLOBAL...WHICH IS CLOSER TO THE GFS SOLUTION...IS RATHER DIFFERENT FROM THE 00Z CANADIAN REGIONAL ACROSS THE PLAINS AT F48/00Z SATURDAY. THE REGIONAL MARKS OFF A COUPLE OF WEAK SURFACE LOWS...WITH THE NORTHERN LOW SIMILAR TO THE ETA/GFS POSITION NEAR THE SD/MN/IA BORDER AND WITH A COMPROMISE STRENGTH. HOWEVER THE GLOBAL ONLY HAS A MUCH WEAKER INVERTED TROUGH THAT FAR NORTH...WITH ONE LOW NEAR OKLAHOMA. 00Z MM5 IS ALSO SIMILAR TO THE ETA AT F48. PERHAPS THE FINER GRIDSCALE MODELS ARE ABLE TO RESOLVE SOME IMPORTANT FEATURE BETTER THAT LEAD TO THE DOWNSTREAM DIFFERENCES. ALTHOUGH THE 00Z RUC13 IS MORE LIKE THE GLOBAL GEM AT F48...SO THAT MAY NOT BE THE CASE. SHORTWAVE CURRENTLY OFF THE NORTHWEST COAST TRACKS ACROSS THE NORTHERN PLAINS ON FRIDAY. EXPECT SOME DEGREE OF SURFACE DEVELOPMENT UNDER UPPER DIVERGENCE IN RIGHT-ENTRANCE OF 300MB JET. PRETTY DECENT FRONTOGENESIS/DEFORMATION AS WELL ASSOCIATED WITH THIS FEATURE...IN ADDITION TO ISENTROPIC LIFT/Q-VECTOR CONVERGENCE WITH WARM ADVECTION/DPVA AHEAD OF THE SYSTEM. GFS PRETTY CONSISTENT WITH QPFS 0.33/6H...WHICH IS IN LINE WITH 3-4G/KG SPECIFIC HUMIDITIES ALONG 290K/295K ISENTROPIC SURFACES. HOWEVER AS THE SYSTEM APPROACHES THE UPPER MISSISSIPPI VALLEY...STRONGER/COMPACT SHORTWAVE DROPS SOUTH OUT OF THE CANADIAN PRAIRIES. MODELS HAVE BEEN TRENDING CONSISTENTLY FASTER WITH THIS FEATURE...WHICH THEN HELPS TO CARVE OUT A LONGWAVE TROUGH ACROSS THE EASTERN CONUS. THIS FASTER WAVE IS ALSO RESPONSIBLE FOR THE FARTHER SOUTH TRACK TO THE INITIAL CLIPPER...AS IT DROPS HEIGHTS FASTER ACROSS THE REGION. ONCE THESE TWO SYSTEMS BEGIN TO INTERACT...WE LOSE TO THE GOOD AGEOSTROPHIC CIRCULATION FROM THE UPPER JET AND THE HEAVIER BANDED SNOW WEAKENS WITH LOSS OF THE BETTER FRONTOGENESIS/DEFORMATION. CONSEQUENTLY THE GFS INSTEAD PAINTS A RATHER WIDESPREAD YET MEAGER 0.25 QPF ACROSS SOUTHEAST MICHIGAN FOR THE ENTIRE EVENT. FEELING IS THAT DESPITE THE INTERACTION OF THE TWO SYSTEMS...WE COULD STILL SEE SOME HEAVIER SNOW. HOWEVER GIVEN UNCERTAINTY AS TO AMOUNTS AS WELL AS EVEN THE TRACK OF THE SYSTEM...WILL HOLD OFF ON ANY HEADLINES AT THIS POINT. BEST POTENTIAL WILL BE ACROSS THE SOUTHERN CWA. FOR NOW WILL KEEP HIGH LIKELY POPS ACROSS THE AREA...AND SNOW ACCUMULATIONS RANGING FROM AROUND ADVISORY TO NEAR WARNING IN THE SOUTH TO NEAR/JUST BELOW ADVISORY IN THE NORTH. WITH A SOMEWHAT FASTER TREND COULD SEE SNOW END DURING THE DAY SATURDAY...BUT TOO MUCH UNCERTAINTY IN THE EVOLUTION OF THE SYSTEM TO PIN THAT DOWN AT THIS POINT. ETA/GFS BOTH SHOW A BRIEF PERIOD OF POTENTIAL LAKE EFFECT BEHIND THE SYSTEM ON SATURDAY NIGHT. DEEP MOISTURE SLOWLY STRIPS OUT THROUGH THE NIGHT...BUT WITH CYCLONIC LOW-LEVEL FLOW PERSISTING. WEAK CONVERGENCE AND MODEST LOW-LEVEL LAPSE RATES...ENOUGH TO KEEP A LOW CHANCE FOR SNOW SHOWERS IN. POTENTIAL QUICKLY DIMINISHES THROUGH THE NIGHT THOUGH...AS INVERSION HEIGHTS COME CRASHING DOWN AS RIDGING SURFACE/ALOFT BUILD ACROSS THE REGION. IN ADDITION TO TRENDED FASTER WITH THE COMPACT SHORTWAVE DROPPING OUT OF CENTRAL CANADA...GFS HAS ALSO BEEN TRENDING STRONGER WITH THE SURFACE HIGH BUILDING DOWN ACROSS THE PLAINS IN BEHIND IT. SURFACE RIDGE FROM THIS HIGH BUILDS ACROSS THE STATE ON SUNDAY...WITH LOW-LEVELS QUICKLY DRYING OUT AND FLOW BACKING AROUND TO THE SOUTHWEST. NEXT SHORTWAVE STILL ON TRACK TO SWING THROUGH THE REGION ON MONDAY. THIS SYSTEM IS SOMEWHAT WEAKER THAN EARLIER ONES...WITH LIMITED MOISTURE AND LITTLE SURFACE REFLECTION. CURRENT FORECAST WITH CHANCE SNOW SHOWERS MONDAY/MONDAY NIGHT LOOK ON TRACK. && .DTX WATCHES/WARNINGS/ADVISORIES... .MI...NONE. .LAKE HURON...SMALL CRAFT ADVISORY LAKE HURON NEARSHORE TODAY. .LAKE ST CLAIR...NONE. .MI WATERS OF LAKE ERIE...NONE. && $$ BT/BRAVENDER