756  
FXUS63 KDTX 210800  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
300 AM EST TUE FEB 21 2017  
   
DISCUSSION
 
 
BAND OF SHOWERS STRETCHES FROM THE GULF OF MEXICO TO NORTHWEST  
ONTARIO AT PRESS TIME, THE NORTHERN BRANCH OF WHICH IS UNDERGOING A  
STEADY WEAKENING PHASE AS FORCING PEELS AWAY TO THE NORTHEAST.  
EXTRAPOLATION PUTS LIGHT RAIN SHOWERS ON THE DOORSTEP OF THE SAGINAW  
VALLEY AT 12Z. DIMINISHING TREND IS THEN FORECAST TO ACCELERATE  
THROUGH THE MORNING AS THE NORTHERN BRANCH WAVE CURRENTLY OVER  
NORTHERN WISCONSIN AND LAKE SUPERIOR PEELS AWAY AND THE LLJ WEAKENS  
AND VEERS OUT. AS A RESULT, TOOK ANOTHER WHACK AT THE INHERITED POPS  
AS CONFIDENCE IN SHOWERS REACHING THE SE HALF OF THE CWA IN ANY  
ORGANIZED FASHION IS REDUCED SINCE YESTERDAY. HIGH AND MID-LEVEL  
OVERCAST WILL DOMINATE IN THE WAKE OF ANY LIGHT RAIN. 925MB TEMPS  
INCREASING TO THE HIGH SINGLE DIGITS OVER THE SW PORTION OF THE CWA  
COMBINED WITH REDUCED RAIN POTENTIAL WILL MAKE FOR A GOOD  
OPPORTUNITY FOR HIGHS TO REACH THE LOW 60S ONCE AGAIN.  
 
THE LOW-LEVEL MOISTURE AXIS WILL REMAIN IN PLACE TONIGHT AS THE LEAD  
EDGE OF ENERGY PRESENTLY COMING ONSHORE IN THE PACIFIC NORTHWEST  
FORCES LEE CYCLOGENESIS OVER THE NORTHERN GREAT PLAINS THIS EVENING.  
STEADY SOUTHWEST GRADIENT AT THE SURFACE WILL SUPPORT DEWPOINTS  
PERHAPS REACHING THE LOW 50S WHILE STRENGTHENING WESTERLY FLOW ATOP  
THE STRENGTHENING INVERSION LAYER SETS UP A DECENT SHEAR LAYER FOR  
ENHANCED FORCING OF DRIZZLE DEVELOPMENT. WITH SUPPORT FROM EXISTING  
UPSTREAM OBS THIS MORNING AND THE ADDITION OF BETTER FORCING  
TONIGHT, ADDED BOTH FOG AND DRIZZLE TO THE FORECAST FOR THE LATTER  
HALF OF TONIGHT.  
 
AFOREMENTIONED LEE CYCLONE WILL TRACK WELL NORTH OF THE AREA ON  
WEDNESDAY, THE 00Z EC INDICATING A SLIGHTLY FLATTER SOLUTION AS IT  
GRAPPLES WITH ENERGY OFFSHORE IN THE EASTERN PACIFIC. STRENGTHENING  
SOUTHWEST GRADIENT AS THE LOW APPROACHES THE WESTERN GREAT LAKES MAY  
SUPPORT SOME GUSTS UPWARD OF 20 MPH. MEANWHILE, LATE FEB INSOLATION  
AND LOW-LEVEL WARMING SHOULD HELP MIX OUT LOW CLOUDS/DRIZZLE/FOG BY  
MID TO LATE WEDNESDAY MORNING. MID 60S SEEM LIKE A SURE BET WITH  
WARMER SPOTS POTENTIALLY MAKING A RUN TOWARD ALL-TIME FEBRUARY MARKS  
OF...  
 
DTW...70 (1999)  
FNT...68 (1999)  
MBS...67 (1930)  
 
WEAK HEIGHT FALLS ASSOCIATED WITH THE PASSING WAVE IS MODELED TO  
FORCE THE COLD FRONT JUST SOUTH OF THE MICHIGAN/OHIO BORDER FOR  
THURSDAY ALLOWING TEMPS TO FALL BACK TOWARD SUB-RECORD VALUES.  
DURING THIS TIME, JET ENERGY DIGGING SOUTH ALONG THE WEST COAST WILL  
DEEPEN THE EXISTING TROUGH AS IT TRANSLATES ACROSS THE ROCKIES.  
STRONG CYCLOGENESIS WILL RESULT. WEAKLY COUPLED JET STRUCTURE WILL  
EMERGE AS LONGWAVE PATTERN AMPLIFIES, DOMINATED BY THE SOUTHERN JET,  
ALLOWING ISENTROPIC ASCENT TO RAMP UP IN FULL FORCE IMMEDIATELY TO  
THE SOUTH. BAROCLINIC ZONE WILL LIFT BACK NORTH BRINGING WIDESPREAD  
STRATIFORM RAIN THURSDAY NIGHT INTO EARLY FRIDAY WITH A FEW RUMBLES  
OF THUNDER POSSIBLE AS H7-H5 LAPSE RATES STEEPEN COINCIDENT WITH  
STRENGTHENING LLJ NOSING INTO THE AREA. CONSENSUS IS ESSENTIALLY SET  
ON A WARM TRACK TO THE WEST OF THE CWA WITH THE VAST MAJORITY OF  
VARIABILITY ATTRIBUTABLE TO DIFFERENT INTENSITY OUTCOMES. SEVERAL  
LOW AMPLITUDE FEATURES OVER CANADA AND THE EASTERN PAC APPEAR TO BE  
PLAYING HAVOC WITH LARGER SCALE TROUGH EVOLUTION. THUS, WHILE  
CONFIDENCE IS SUFFICIENT FOR A HIGH POP SCENARIO, CONFIDENCE IN  
FRIDAY AFTERNOON HIGH TEMPERATURES AND FRIDAY EVENING/NIGHT SEVERE  
WEATHER VARIABLES REMAINS LOW. THIS IS LARGELY A RESULT OF  
UNCERTAINTY IN SURFACE WARM FRONT PROGRESS. WORTH NOTING THAT THE  
POTENTIAL EXISTS FOR ANOTHER RUN ALL-TIME FEBRUARY HIGHS WILL BE  
POSSIBLE GIVEN THAT WEDNESDAY'S AIRMASS WILL SIMPLY BE RE-SURGING  
BACK INTO THE AREA.  
 

 
   
MARINE
 
 
THE SOUTHEASTERLY GRADIENT HAS BEEN INCREASING OVERNIGHT WITH THE  
APPROACH OF A FRONTAL BOUNDARY. MEANWHILE, AN INFLUX OF VERY WARM  
LOW LEVEL AIR ATOP THE SHALLOW COOL LAYER OVER THE LAKE IS GREATLY  
LIMITING STABILITY. NONETHELESS, SOUTH-SOUTHEASTERLY WINDS ACROSS  
LAKE HURON WILL GUST UP TO 25 TO POSSIBLY 30 KNOTS AT TIMES DURING  
THE PRE DAWN HOURS GIVEN THE STRENGTH OF THE GRADIENT. THE FRONT IS  
FORECAST TO PASS ACROSS LAKE HURON THIS AFTERNOON AND INTO LAKE ERIE  
THIS EVENING. THERE WILL ACTUALLY BE A WEAKENING OF THE GRADIENT AS  
THE FRONT PASSES THROUGH TODAY BEFORE WASHING OUT OVER LAKE ERIE  
TONIGHT. THE RESULT WILL BE A MARKED WEAKENING IN THE WINDS DURING  
THE COURSE OF THE DAY AND EVENING.  
 
MODEST SOUTH-SOUTHWEST WINDS WILL THEN DEVELOP LATE TONIGHT AND  
PERSIST INTO WEDNESDAY NIGHT AS A SLOW MOVING LOW PRESSURE SYSTEM  
AND FRONTAL BOUNDARY PUSHES INTO THE NORTHERN GREAT LAKES. A  
STRENGTHENING LOW PRESSURE SYSTEM IS FORECAST TO LIFT INTO THE GREAT  
LAKES REGION ON FRIDAY, POTENTIALLY BRINGING GALE FORCE WINDS FRIDAY  
THROUGH SATURDAY.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 1158 PM EST MON FEB 20 2017  
 
AVIATION...  
 
VFR WILL CONTINUE THROUGH THE NIGHT AS HIGH CLOUDS THICKEN AND LOWER  
AHEAD OF THE NEXT FRONTAL SYSTEM. THIS WILL BE ACCOMPANIED BY  
SOUTHEAST SURFACE WIND HOLDING IN THE 5 TO 10 KNOT RANGE WHICH THE  
LATEST MODEL SOUNDINGS INDICATE WILL BE MARGINAL FOR A LLWS MENTION  
THROUGH THE MORNING.  
 
EXPECTATIONS FOR THE COLD FRONT REMAIN ON TRACK FOR LATE MORNING  
THROUGH THE AFTERNOON. LOW PRESSURE PARENT TO THE COLD FRONT WILL BE  
WELL NORTH OVER HUDSON BAY AND MOVING AWAY FROM THE GREAT LAKES. THE  
TRAILING COLD FRONT THAT IS LEFT BEHIND SHOWS SIGNS OF WEAKENING IN  
MODEL DATA AS IT APPROACHES SE MICHIGAN BUT APPEARS ABLE TO PRODUCE  
MVFR RAIN SHOWERS AT MBS FROM ABOUT MID MORNING THROUGH EARLY  
AFTERNOON. THE FRONT WILL THEN STRUGGLE TO SUPPORT RAIN LATER IN THE  
DAY BUT BORDERLINE MVFR/IFR CEILING WILL LINGER WITH THE HIGHER  
BOUNDARY LAYER MOISTURE CONTENT INDICATED UPSTREAM. SURFACE DEWPOINT  
IN THE LOWER TO MID 50S INTO SOUTHERN WISCONSIN IS PROJECTED TO  
REACH LOWER MICHIGAN AND COULD PRODUCE A MORE AGGRESSIVE INTRUSION  
OF IFR BY TUESDAY EVENING. THE DISSIPATING FRONTAL WIND SHIFT WILL  
BE FAVORABLE FOR MAINTENANCE OF LOW CLOUDS AND FOG IN LIGHT AND  
VARIABLE OR LIGHT SOUTHWEST WIND OVER THE REGION.  
 
FOR DTW... EASTERLY FLOW THAT LINGERED AROUND THE 100 DEGREE  
DIRECTION DURING THE EVENING WILL VEER TOWARD THE SOUTH DURING THE  
NIGHT WITH SPEED 10 KNOTS OR LESS. THE VEERING TREND WILL AT LEAST  
HELP SWITCH RUNWAYS BACK TO SOUTHWEST TRAFFIC OPERATIONS DURING THE  
MORNING. VFR WILL OTHERWISE PERSIST UNTIL THE REMAINS OF THE COLD  
FRONT ARRIVE DURING AFTERNOON.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* HIGH FOR CEILING 5000 FT OR LESS LATE MORNING INTO TUESDAY  
EVENING.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LAKE HURON...SMALL CRAFT ADVISORY UNTIL NOON EST TODAY FOR LHZ441-442.  
 
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...NONE.  

 
 

 
 
DISCUSSION...JVC  
MARINE.......SC  
AVIATION.....BT  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT.  
 
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