303  
FXUS63 KDTX 241759  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
1259 PM EST TUE JAN 24 2017  
 
   
AVIATION
 
 
THE SLOW IMPROVEMENT TO MVFR CEILINGS WILL CONTINUE THROUGH THE  
EARLY AFTERNOON AS A RIDGE OF HIGH PRESSURE SLOWLY BUILDS INTO  
MICHIGAN AND NORTHWEST WINDS INCREASE TO 7-10 KNOTS. THE RIDGE WILL  
BECOME CENTERED OVERHEAD THIS EVENING, FAVORING A LOWERING OF  
CEILINGS/VIS ONCE AGAIN AS IT ALSO BECOMES MORE DIURNALLY FAVORABLE.  
SOME QUESTION AS TO HOW LOW VISIBILITY WILL GO (LIFR VERSUS VLIFR)  
AS WEAK SOUTHEAST GRADIENT STARTS TO TIGHTEN AROUND 12Z NEAR THE  
DETROIT-AREA TERMINALS DUE TO AN APPROACHING LOW PRESSURE SYSTEM.  
PERSISTENCE AND QUESTIONABLE PERFORMANCE OF FORECAST MODELS IN  
RECENT DAYS FAVORS A MORE PESSIMISTIC FORECAST AT THIS TIME. SHOWERS  
ASSOCIATED WITH THE AREA OF LOW PRESSURE MAY BEGIN TO AFFECT THE  
AREA WITH RAIN/SNOW SHOWERS BETWEEN 15-18Z, HOWEVER MOST RAIN  
SHOWERS LOOK TO HOLD OFF UNTIL AFTER 18Z.  
 
FOR DTW...IMPROVING TREND IS EXPECTED TO CONTINUE THROUGH THE  
AFTERNOON, WITH LOW POTENTIAL FOR A BRIEF PERIOD OF LOW-END VFR  
CONDITIONS IN THE VERY EARLY EVENING. CONDITIONS ARE EXPECTED TO  
DETERIORATE AGAIN BY LATE EVENING AS CONDITIONS BECOME CALM UNDER  
THE INFLUENCE OF HIGH PRESSURE. THIS SHOULD PROMOTE THE  
REDEVELOPMENT OF LIFR TO VLIFR CEILINGS DURING THE EARLY MORNING  
HOURS. THERE IS SOME QUESTION AS TO HOW LONG THOSE CONDITIONS WILL  
HOLD AT DTW HOWEVER AS APPROACHING LOW PRESSURE BEGINS TO INCREASE  
THE SURFACE PRESSURE GRADIENT AROUND 12Z.  
 
FAVORS A MORE PESSIMISTIC  
 
//DTW THRESHOLD PROBABILITIES...  
 
* HIGH FOR CEILING 5000 FT OR LESS THROUGH THE FORECAST.  
 
* MODERATE FOR CEILING AOB 200 FEET/VISIBILITY AOB 1/4SM AT TIMES  
THROUGH MID MORNING.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 245 AM EST TUE JAN 24 2017  
 
DISCUSSION...  
 
WEAK MID-LEVEL DEFORMATION AND LARGE SCALE ASCENT ARE KEEPING THE  
RESIDENT SURFACE TROUGH ACTIVE WITH LIGHT RAIN SHOWERS THIS MORNING.  
00Z NWP AND THE LATEST RAP/HRRR GIVE EVERY INDICATION IN FAVOR OF A  
PERSISTENCE FORECAST THROUGH AT LEAST 18Z OR SO AS ENVIRONMENTAL  
FORCING/MOISTURE VARIABLES WILL REMAIN ESSENTIALLY UNCHANGED.  
UPSTREAM RIDGING IN ADVANCE OF THE WAVE EMERGING OVER THE FRONT  
RANGE THIS MORNING WILL EVENTUALLY SHUNT THE MOISTURE AXIS EAST 18-  
21Z AND SHUT DOWN FORCING BRINGING AN END TO RAIN AND GIVING WAY TO  
OVERCAST LOW CLOUDS AS THE SUBSIDENCE INVERSION STRENGTHENS AND  
TRAPS LOW-LEVEL MOISTURE. CLOUDS AND RAIN WILL KEEP TEMPS MUTED  
AROUND 40 DEGREES, WARMER THAN AVERAGE BUT LESS THAN WOULD BE  
OTHERWISE SUGGESTED BY THE WARM AIRMASS OVER THE REGION.  
 
CYCLOGENESIS IS CURRENTLY UNDERWAY IN EASTERN COLORADO AS A PV  
ANOMALY PIVOTS ACROSS THE FRONT RANGE. THIS ENERGY WILL RAPIDLY  
SHEAR NORTHEAST ALONG THE NORTHERN PERIPHERY OF A STRONG UPPER JET,  
REACHING THE GREAT LAKES TONIGHT. LONG-STANDING NWP CONSENSUS AT  
THIS POINT FOR A SURFACE LOW TRACK EITHER OVER OR JUST NORTH OF THE  
AREA ENSURING A STOUT SOUTHERLY FLOW COMPONENT AT THE SURFACE FOR  
THE BALANCE OF WEDNESDAY. LEAD EDGE OF HIGHER THETA-E AIRMASS IN THE  
MID-LEVELS MAY FORCE A ROUND OF RAIN SHOWERS ACROSS THE CWA AS EARLY  
AS WEDNESDAY MORNING BEFORE TEMPS RISE INTO THE 40S TO NEAR 50 NEAR  
THE OHIO BORDER. ONGOING ISENTROPIC ASCENT WILL SUPPORT THE BEST  
CHANCE OF STRATIFORM RAIN ACROSS THE FAR NORTH WHILE A RUMBLE OF  
THUNDER OR TWO IN THE WARM SECTOR IS NOT OUT OF THE QUESTION ALONG  
THE PRE-FRONTAL TROUGH ON WEDNESDAY AFTERNOON. LINGERING DEFORMATION  
SUPPORTS A CHANGE OVER TO SNOW AS COOLER AIR WRAPS INTO SOUTHEAST  
MICHIGAN BY THURSDAY MORNING.  
 
DEVELOPING RIDGE OVER THE WEST COAST IS A HIGH CONFIDENCE FEATURE  
HEADING INTO THE MEDIUM RANGE AS LOW PRESSURE CLOSES OFF OVER THE  
ALEUTIANS. A PERIOD OF LONGWAVE TROUGHING EXPECTED TO DOMINATE THE  
REMAINDER OF THE FORECAST PERIOD. MORE SEASONABLE NW FLOW IS SHOWN  
TO BE LARGELY CONFLUENT IN NATURE FOR THE NEXT SEVERAL DAYS.  
TRANQUIL WX LIKELY WITH JUST THE OCCASIONAL SNOW CHANCE AND HIGHS  
NEAR AVERAGE VALUES OF 30 DEGREES.  
 
MARINE...  
 
WEAK HIGH PRESSURE WILL MOVE OVER THE CENTRAL GREAT LAKES TODAY  
FOLLOWED CLOSELY BY THE NEXT LOW PRESSURE SYSTEM MOVING IN FROM THE  
CENTRAL PLAINS WEDNESDAY. LIGHT SOUTHERLY WIND WILL DEVELOP AHEAD OF  
THIS SYSTEM WHICH WILL BECOME VARIABLE AS THE LOW MOVES THROUGH  
CENTRAL LOWER MICHIGAN AND SOUTHERN LAKE HURON WEDNESDAY NIGHT.  
OTHER THAN A WINTRY MIX OF PRECIPITATION, THIS SYSTEM WILL PRESENT  
LITTLE IMPACT ON MARINE CONDITIONS UNTIL THURSDAY WHEN IT LEAVES  
BEHIND COLDER NORTHWEST WIND LIKELY REACHING 30 KNOTS ACROSS THE  
REGION. THE COLDER AND WINDY CONDITIONS WILL THEN LAST THROUGH  
FRIDAY AND INTO THE WEEKEND.  
 

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

 
 

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