415  
FXUS63 KDTX 011117  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
717 AM EDT WED APR 1 2015  
   
AVIATION
 
 
IFR STRATUS BETWEEN MTC AND PHN WILL BE MONITORED FOR POSSIBLE  
IMPACT AT DET BUT IS NOT EXPECTED TO REACH THE OTHER TERMINALS AS A  
WEAK SURFACE PRESSURE TROUGH DISSIPATES DURING THE MORNING. THE  
RESULTING LIGHT WIND FIELD WILL GRADUALLY TURN LIGHT FROM THE  
SOUTHEAST DURING THE AFTERNOON WITH JUST SOME MID AND HIGH CLOUDS  
INCREASING MAINLY IN THE MBS TO FNT REGION. VFR CONDITIONS WILL  
CONTINUE TONIGHT BUT THE WIND WILL INCREASE FROM THE SOUTH. A WARM  
FRONT DEVELOPING OVER THE OHIO VALLEY WILL PRESENT A LOW LEVEL  
WIND SHEAR SCENARIO OVER SE MICHIGAN BY LATE EVENING THROUGH  
SUNRISE THURSDAY.  
 
FOR DTW... EARLY SUNSHINE WILL QUICKLY DISSIPATE MVFR FOG AND ANY  
CEILING BELOW 5000 FT WILL BE EQUALLY SHORT. THAT LEAVES NO OTHER  
CONCERNS OUTSIDE OF LOW LEVEL WIND SHEAR DEVELOPMENT TONIGHT.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* LOW FOR CEILING AOB 5000 FEET EARLY THIS MORNING.  
 

 
   
PREV DISCUSSION
 
ISSUED 347 AM EDT WED APR 1 2015  
 
SHORT TERM... TODAY AND TONIGHT  
 
THE UPPER LEVEL IMPULSE SLIDING THROUGH THE EASTERN GREAT LAKES WILL  
CONTINUE TO THE ATLANTIC COAST DURING THE EARLY MORNING. THIS WILL  
LEAD TO A CLEARING TREND OVER SE MICHIGAN AS THE MODEST SURFACE  
PRESSURE REFLECTION FILLS. THE EXCEPTION TO MONITOR WILL BE IN THE  
THUMB WHERE MID CLOUDS WILL BE LAST TO EXIT AND WHERE SOME POTENTIAL  
FOR LAKE INFLUENCED STRATOCU WILL OCCUR DUE TO WEAK ONSHORE FLOW. A  
GENEROUS AMOUNT OF SUNSHINE IS EXPECTED ELSEWHERE TO AID IN WARMING  
TEMPERATURES THROUGH THE MORNING.  
 
THE GREAT LAKES AND SE MICHIGAN WILL COME UNDER THE INFLUENCE OF  
LARGER SCALE WEATHER FEATURES THROUGH THE REST OF THE DAY AND  
TONIGHT. SATELLITE IMAGERY AND MODEL ANALYSIS FIELDS SHOW THE UPPER  
RIDGE OVER THE PLAINS SET TO PROGRESS STEADILY EASTWARD AND  
STRENGTHEN SURFACE HIGH PRESSURE OVER THE APPALACHIANS. THIS WILL  
BIAS THE LOW LEVEL WIND FIELD TOWARD AN EASTERLY DIRECTION UNTIL  
LATE IN THE DAY WHICH WILL ADD SOME COMPLEXITY TO THE MAX TEMP  
FORECAST OUTSIDE OF THE TYPICAL SHORELINE AND DOWNRIVER AREAS. THE  
THUMB SHORELINE WILL STRUGGLE IN THE 40S...BUT THERE IS POTENTIAL  
FOR OVERACHIEVEMENT THROUGH INTERIOR AREAS BASED ON LOW LEVEL  
THICKNESS WARMING COMPARED TO HOW WELL READINGS RESPONDED TO  
AFTERNOON SUN YESTERDAY. THERE WILL BE SOME MID AND HIGH CLOUDS TO  
CONTEND WITH DURING THE AFTERNOON ASSOCIATED WITH THE ELEVATED WARM  
ADVECTION PATTERN THAT IS HELPING DRIVE THE RIDGE EASTWARD. MODEL RH  
FIELDS INDICATE THESE CLOUDS WILL MAINLY AFFECT THE TRI CITIES AND  
NORTHERN THUMB LEAVING THE DOOR OPEN FOR MAX TEMPS TO TOUCH 60  
INTERIOR TOWARD THE OHIO BORDER.  
 
THE MAIN THEME FOR TONIGHT WILL BE CONTINUED DEVELOPMENT OF  
SOUTHERLY GRADIENT WIND OVER THE REGION DRIVEN BY THE LARGE LOW  
PRESSURE SYSTEM MOVING FROM THE PLAINS TO UPPER MIDWEST. MODEL  
DEPICTIONS OF PRECIPITATION REMAINING NORTH OF OUR AREA LOOK  
REASONABLE GIVEN ACTIVITY WILL BE TIED TO MID LEVEL ISENTROPIC  
ASCENT. MID AND HIGH CLOUDS LINGERING OVER OUR AREA WILL DEVELOP  
NORTHWARD AS WELL BEFORE THICKENING FROM THE WEST LATE. THE  
EVOLUTION OF THE WIND FIELD THEN HAS THE LOOK OF LATE EVENING MIN  
TEMPS IN THE UPPER 30S THUMB TO MID 40S INTERIOR RISING OVERNIGHT  
TOWARD 50 INTERIOR AND WELL BACK INTO THE 40S ELSEWHERE BY SUNRISE  
THURSDAY.  
 
LONG TERM...  
 
A BUSY END OF THE WEEK IS EXPECTED WITH THE FOCI OF THE FORECAST  
INVOLVING THE POTENTIAL FOR THUNDERSTORMS/HEAVY RAINFALL ON THURSDAY  
AND THE POTENTIAL FOR ACCUMULATING SNOW ON FRIDAY.  
 
THE PROGRESSIVE HIGH AMPLITUDE RIDGE AXIS WILL BE DIRECTLY OVER  
SOUTHEASTERN MICHIGAN AT THE START OF THE PERIOD THURSDAY. IN  
RAPID SUCCESSION...THE RIDGE AXIS WILL PUSH EASTWARD ALLOWING FOR  
THE INFLUENCE OF CYCLONIC FLOW TO ENCROACH UPON CWA FROM THE WEST.  
POINT OF CONTENTION FOR THIS PERIOD HAS BEEN THE TIMING OF  
PRECIPITATION INTO LOWER MICHIGAN. STILL POOR INTER-MODEL  
AGREEMENT ON ONSET WITH MODELS SEEMINGLY HALF AND HALF ON WHETHER  
OR NOT PRECIPITATION WILL BEGIN BEFORE NOON. STILL PREFER A DRY  
MORNING BEFORE POPS RAMP UP SUBSTANTIALLY FOR THE AFTERNOON.  
REASONS ARE: UPSTREAM ELEVATED NOCTURNAL PRECIPITATION IS EXPECTED  
TO BE BACK ACROSS WISCONSIN AT 12Z...WILL NEED TIME TO PUSH OUT  
RESIDUAL NEAR SURFACE RIDGING/DRY AIR...AND EASTERN EDGE OF JET  
ALOFT AND SHORTWAVE ENERGY ARE NOT FORECASTED TO ARRIVE UNTIL THE  
AFTERNOON. THINGS LOOK GOOD FROM A PROBABILITY OF PRECIPITATION  
PERSPECTIVE AS CONVECTIVE INSTABILITY WILL BE IN PLACE AS WELL AS  
A SYNOPTIC SCALE TRIGGER IN A WIDE RANGING OCCLUDED FRONT  
STRUCTURE. NAM IS STILL SUGGESTING UPWARDS OF 700 J/KG OF ELEVATED  
CAPE...HOWEVER...RAW DATA IS ALSO SUGGESTING A SFC DEWPOINT OF  
BETWEEN 55 AND 60 DEGREES. THIS IS ALMOST CERTAINLY OVERZEALOUS  
AND STUCK CLOSER TO THE OFFERED MOS VALUES OF THE UPPER 40S TO  
NEAR 50 DEGREES. STEEP LAPSE RATES BETWEEN 800-600MB CONTINUES TO  
SUPPORT A CHANCE FOR THUNDERSTORMS. DEPTH OF MOISTURE (PWATS OF  
1.25-1.30 INCHES) AND LOW COLUMN STABILITY IS ALL LINING UP FOR  
WHAT COULD BE A WINDOW FOR SOME HEAVY RAINFALL. ONE LARGE NEGATIVE  
WILL BE WORKING ON RAINFALL AMOUNTS WILL BE STORM MOTION TO THE  
EAST NORTHEAST AT 55 TO 60 KNOTS. LATEST SWODY2 KEEPS MUCH OF  
SOUTHEASTERN MICHIGAN UNDER A DESIGNATION OF MARGINAL.  
 
THE MAIN BAROCLINIC ZONE IS EXPECTED TO BECOME POSITIONED SOUTHEAST  
OF THE AREA OVER PORTIONS OF OHIO AND INDIANA THURSDAY NIGHT.  
 
A TRAILING UPPER LEVEL JET STREAK AND PV ANOMALY IS ALSO FORECASTED  
TO EJECT OUT OF THE FOUR CORNERS REGION THURSDAY NIGHT. MODELS  
REALLY DO SHOW AN ORGANIZED COUPLING OF THIS TRAILING JET STREAK  
WITH THE MAIN BRANCH OVER THE UPPER MIDWEST FROM THE START.  
EVOLUTION OF THIS COUPLING JET STRUCTURE ONLY INCREASES IN STRENGTH  
MOVING INTO THE DAY FRIDAY AS THE LEAD/GREAT LAKES BRANCH UNDERGOES  
A TRANSITION TO ANTICYCLONIC CURVATURE. PV PHASING OVER THE MID  
MISSISSIPPI RIVER VALLEY TIPS THE SCALES INTO CYCLOGENESIS ALONG  
THE OHIO RIVER ON FRIDAY. A GOOD FRONTAL WAVE SETUP WITH A SWATH  
OF DEFORMATION SNOWFALL STRIPING ALONG THE NORTHERN PROXIMITY OF  
THE DEEPENING LOW CENTER. THERE STILL REMAINS A HIGH AMOUNT OF  
UNCERTAINTY WITHIN THE MODEL DATA ON WHETHER OR NOT A SIGNIFICANT  
AMOUNT OF PRECIPITATION WILL FALL OVER SEMICH. PATTERN RECOGNITION  
SUGGESTS THE BOOK HAS NOT BEEN WRITTEN YET AS THERE IS SOME  
POTENTIAL FOR PRECIPITATION TO MISS THE AREA TO THE SOUTH DUE TO A  
GREATER SOUTHERN PV CONTRIBUTION FROM CONVECTION/LATENT HEAT  
RELEASE. THE MOVE THIS FORECAST PACKAGE WAS TO INCREMENTALLY  
INCREASE POPS WHILE INTRODUCING A RAIN/SNOW MENTION FOR THE  
DAYLIGHT HOURS ON FRIDAY. CERTAINLY A TIME PERIOD TO WATCH FOR  
FORECAST EVOLUTION.  
 
MARINE...  
 
HIGH PRESSURE TODAY WILL PROVIDE LIGHT WINDS AND LOW WAVES.  
SOUTHERLY WINDS WILL INCREASE TONIGHT AHEAD OF A COLD FRONT...WHICH  
IS EXPECTED TO MOVE THROUGH LATE THURSDAY. WARM SOUTHERLY FLOW WILL  
INCREASE TO 20 TO 25 KNOTS DURING THE DAY THURSDAY BUT STABILITY  
WILL LIMIT WIND GUST POTENTIAL.  
 

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

 
 

 
 
AVIATION.....BT  
SHORT TERM...BT  
LONG TERM....CB  
MARINE.......CB  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).  
 
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