923  
FXUS63 KDTX 220830  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
330 AM EST SAT NOV 22 2014  
   
SHORT TERM
 
TODAY AND TONIGHT  
 
TEMPERATURES ARE STILL IN THE LOW TO MID 20S EARLY THIS  
MORNING...WITH SURFACE DEW PTS IN THE LOWER TEENS.  
WITH THIS AMOUNT OF LOW LEVEL DRY AIR IN PLACE...BOUNDARY LAYER WET  
BULB TEMPERATURES LOOK TO REMAIN BELOW FREEZING THROUGH THE MORNING  
HOURS...PER 00Z NAM. MEANWHILE...WATER VAPOR IMAGERY SHOWS MID LEVEL  
WAVE/CIRCULATION LIFTING INTO THE WESTERN GREAT LAKES...WHICH WILL  
ALLOW FOR SUBSTANTIAL SURGE OF WARM AND MOIST AIR TO ARRIVE THIS  
MORNING...WITH 850 MB DEW POINTS RISING TO BETWEEN 4-5 C. THIS WILL  
LEAD TO SOME INSTABILITY...AS SHOWLATER INDEX FALLS TO AROUND ZERO  
...WITH GOOD MID LEVEL (700-500 MB) LAPSE RATES IN EXCESS OF 7 C/KM  
WORKING THROUGH SOUTHERN LOWER MICHIGAN. DUE TO THE CONVECTIVE  
NATURE OF THE ACTIVITY...TOUGH TO GAUGE QPF AREAL COVERAGE...AS  
ESPECIALLY THE 00Z GFS IS LIKELY OVERDONE. STILL...BASED ON UPSTREAM  
RADAR TRENDS...65-80 PERCENT POPS APPEAR APPROPRIATE...AND HAVE  
ELECTED TO EXTEND FREEZING RAIN ADVISORY SOUTH...AS A QUICK GLAZE OF  
ICE APPEARS LIKELY WITH THE FROZEN GROUND. SELF-LIMITING  
PROCESS/LATENT HEAT RELEASE FROM THE FREEZING RAIN WITH NO COLD AIR  
FEED WILL ASSURE TRANSITION TO JUST COLD RAIN AS THE DEEP AND STRONG  
SOUTHWEST FLOW OVERSPREADS THE AREA...AND THE WARMER RAIN DROPS TAKE  
HOLD. ALTHOUGH ACTIVITY MAY TAPER OFF TO DRIZZLE THIS  
AFTERNOON...ANOTHER DEEPER SURGE OF MOISTURE TONIGHT...PW VALUES  
INCREASING TO 1 INCH SHOULD ASSURE FURTHER ADDITIONAL LIGHT  
RAIN/DRIZZLE...AS MERGING HEIGHT FALLS TAKE PLACE OVER THE CENTRAL  
CONUS...BACKING THE FLOW OVER THE MISSISSIPPI RIVER VALLEY. WITH  
FORECASTED (SEE EURO) SURFACE DEW PTS OF 40 F COMING OVER COLD/SNOW  
COVERED GROUND OVER SOUTHERN LOWER MICHIGAN...ZONES WILL CONTAIN  
SOME MENTION OF FOG. THE COLD SNOW COVERED GROUND IS ALSO EXPECTED  
TO INHIBIT THE MIXING DEPTHS TODAY...AND THINK WIND GUSTS WILL BE  
HARD PRESSED TO EXCEED MUCH PAST 20 KNOTS...DESPITE THE GOOD LOW  
LEVEL JET (50 KNOTS).  
 

 
   
LONG TERM
 
 
 
SUNDAY...COMPACT SOUTHERN STREAM MID LEVEL WAVE NOTED ON WATER VAPOR  
THIS MORNING EJECTING EASTWARD ACROSS NORTHERN MEXICO WILL STEADILY  
LIFT NORTHEAST AND EVENTUALLY ACROSS THE GREAT LAKES BY SUNDAY  
NIGHT. MOIST LOW LEVEL SOUTHERLY FLOW ALONG THE EASTERN FLANK OF  
THE MAIN HEIGHT FALLS WILL MARK CONDITIONS LOCALLY IN ADVANCE OF  
THIS SYSTEM ON SUNDAY. A RENEWED PERIOD OF STRONGER MOIST  
ISENTROPIC ASCENT WILL TRANSLATE FROM SOUTH TO NORTH ACROSS THE  
REGION DURING THE FIRST HALF OF THE DAY. THIS PROCESS WILL IMPROVE  
THE OVERALL MOISTURE QUALITY /PW AROUND 1 INCH/...IN ADDITION TO  
SUPPORTING SOME LIGHT SHOWER DEVELOPMENT DURING THIS TIME. A BRIEF  
LULL IN THE FORCING FOR MIDDAY WILL PROVIDE THE GREATEST WINDOW FOR  
A BETTER THERMAL RESPONSE. A BACKGROUND OF WEAK WARM AIR ADVECTION  
WILL COUNTER THE LACK OF MIXING AND INSOLATION POTENTIAL...ALLOWING  
HIGHS TO MAKE A RUN TOWARD THE 50 DEGREE MARK.  
 
SUNDAY NIGHT...STRONG MID LEVEL DYNAMICS ANCHORED BY STOUT LEFT EXIT  
REGION UPPER JET FORCING...DIVERGENCE AND INCREASING CVA ATTENDANT  
TO THE INBOUND WAVE WILL SWEEP ACROSS SE MICHIGAN SUNDAY NIGHT.  
THIS FORCING INTO THE EXISTING VERY MOIST AMBIENT ENVIRONMENT WILL  
RESULT IN A 6-9 HOUR PERIOD OF WIDESPREAD RAINFALL FOR THE ENTIRE  
REGION OVERNIGHT. QPF AMOUNTS WITHIN THE .5" TO .75" RANGE LOOK  
ATTAINABLE GIVEN THE UNDERLYING STRENGTH OF ASCENT...MOISTURE DEPTH  
AND OVERALL RESIDENCE TIME. A FIRM SOUTHEAST GRADIENT WILL CONTAIN  
TEMPERATURES IN THE LOWER AND MIDDLE 40S THROUGH THE NIGHT.  
 
MONDAY...00Z NAM REMAINS OUTSIDE THE MODEL CONSENSUS WHICH HOLDS  
WITH A MUCH DEEPER SURFACE LOW AS IT TRACKS FROM THE SOUTH END OF  
LAKE MICHIGAN THROUGH NORTHERN LAKE HURON DURING THIS TIME. 00Z GFS  
SEEMINGLY TOO AGGRESSIVE WITH THE RESPONSE /966 MB CENTER AT 18Z MON  
NORTH OF THE STRAITS/...OWING TO MORE PRONOUNCED PHASING OF THE LEAD  
PV FEATURE WITH A TRAILING NORTHERN STREAM TROUGH THAT BECOMES  
NEGATIVELY TILTED. THE NET RESULT IS A MORE SIZABLE DIFFERENCE IN  
HANDLING THE DETAILS IN THE WAKE OF THE EXITING MAIN MOISTURE PLUME  
HEADING INTO MONDAY. SLIVER OF MILDER PRE-COLD FRONTAL AIR WILL  
EXIST MONDAY MORNING...THE TRAILING COLD FRONTAL PASSAGE MOST LIKELY  
COMMENCING DURING THE LATTER HALF OF THE DAY. AT THIS POINT...MAIN  
ELEMENT OF CONCERN BECOMES THE WIND POTENTIAL MONDAY AFTERNOON AND  
EVENING...AS THE ENSUING ADVECTIVE PROCESS BUILDS THE CONVECTIVE  
LAYER DEPTH INTO AN ALREADY FIRM WIND FIELD JUST OFF THE SURFACE. A  
PERIOD OF GOOD 280-285K ISENTROPIC DESCENT WITH 35 TO 40KT WINDS  
WITHIN THIS LEVEL WOULD SUGGEST PEAK GUSTS IN EXCESS OF 35 MPH ARE  
ATTAINABLE...WITH AN UPTICK TO HEADLINE WORTHY GUST POTENTIAL  
CERTAINLY PLAUSIBLE. WINDOW FOR STRONG CONVERGENCE ALONG THE  
FRONTAL SLOPE AND WITH THE PASSAGE OF THE TRAILING WAVE WILL  
MAINTAIN A CHANCE FOR SHOWERS INTO MONDAY...PARTICULARLY DURING THE  
FIRST HALF OF THE DAY. PRE-FRONTAL TEMPERATURES PEAK IN THE UPPER  
40S-LOWER 50S...STRONGER COLD AIR ADVECTION AWAITING THE BETTER  
HEIGHT FALLS TOWARD EVENING.  
 
TUESDAY AND BEYOND...SUBSTANTIAL SOUTHWARD EXPANSION OF THE LOWER  
HEIGHT FIELD WILL SPELL ANOTHER EXTENDED STRETCH OF BELOW NORMAL  
TEMPERATURES STARTING TUESDAY. PLACEMENT OF AN ENERGETIC NORTHERN  
PACIFIC JET CORE SOUTHEAST AND NEAR/OVER THE GREAT LAKES WILL BRING  
THE POTENTIAL FOR A PERIODICALLY ACTIVE PATTERN THROUGH THE UPCOMING  
HOLIDAY WEEKEND. POTENTIAL FOR LIGHT SNOW SHOWERS TUESDAY WITHIN A  
MOIST CYCLONIC FLOW...AUGMENTED BY THE MOISTURE FLUX OFF LAKE  
MICHIGAN. WEAK SHORTWAVE WORKING THROUGH THE NORTHWEST FLOW IS  
FORECAST TO DEEPEN WITHIN FAVORABLE UPPER JET SUPPORT ON  
WEDNESDAY...LONG RANGE MODEL GUIDANCE ALLOWING THIS WAVE TO SHIFT  
INTO SOUTHEAST MICHIGAN BY THANKSGIVING. WHILE SUBJECT TO CHANGE  
YET AT THIS TIME SCALE...LATEST TRENDS WOULD BRING THE POTENTIAL FOR  
A LIGHT ACCUMULATING SNOWFALL WITH THIS SYSTEM FOR THE HOLIDAY.  
 

 
   
MARINE
 
 
SOUTHWEST WINDS WILL REMAIN STRONG THROUGH THE FIRST HALF OF TODAY.  
GUSTS TO GALES OR NEAR GALES WILL EXIST OVER CENTRAL PORTIONS OF  
LAKE HURON THROUGH THE MORNING PERIOD. WINDS WILL EASE SLIGHTLY  
THIS AFTERNOON AS THE OVERALL GRADIENT SLACKENS. A MODEST SOUTHERLY  
WIND WILL EXIST TONIGHT AND SUNDAY IN ADVANCE OF STRENGTHENING LOW  
PRESSURE. SOME INCREASE IN SOUTHEAST WINDS WILL OCCUR AS THIS LOW  
TRACKS FROM SOUTHERN LAKE MICHIGAN TO THE STRAITS SUNDAY NIGHT. THE  
COMBINATION OF AN INCREASING GRADIENT AND THE RETURN OF COLDER AIR  
WILL BRING THE POTENTIAL FOR GALES ACROSS ALL MARINE AREAS BY MONDAY  
AFTERNOON AND EVENING.  
 

 
   
AVIATION
 
ISSUED 1150 PM EST FRI NOV 21 2014  
 
//DISCUSSION...  
 
A WARM FRONT...INITIALLY ELEVATED...WILL LIFT UP INTO LOWER MICHIGAN  
LATE TONIGHT AND SATURDAY. THIS WILL ALLOW A WARMER LAYER OF AIR TO  
SETTLE IN OVER SUB-FREEZING AIR AT THE SURFACE...POTENTIALLY LEADING  
TO FREEZING RAIN AND SLEET AS MOISTURE AND LIFT ARRIVE WITH THE  
FRONT. A PERIOD OF FREEZING RAIN OR SLEET WILL BE POSSIBLE BEFORE 14-  
16Z BEFORE STRONGER WARM AIR ADVECTION COMMENCES AND PRECIPITATION  
CHANGES TO ALL RAIN. THE FRONT WILL ALSO ALLOW CEILINGS TO FALL TO  
MVFR...WITH POSSIBLY A DROP TO IFR MID-MORNING SATURDAY.  
 
IN ADDITION...THE LOW-LEVEL JET WILL NOSE INTO THE AREA LATE TONIGHT  
AND REMAIN OVERHEAD ON SATURDAY...RESULTING IN A STRONG CORE OF 40-  
50 KT WINDS ABOVE 1500 FEET. LOW-LEVEL WIND SHEAR IS EXPECTED AFTER  
08Z AT ALL OF THE TAF SITES AND WILL LAST THROUGH THE DAY ON  
SATURDAY.  
 
//DTW THRESHOLD THREATS...  
 
* HIGH CONFIDENCE IN CEILINGS FALLING BELOW 5000 FEET AFTER 09Z.  
 
* MEDIUM CONFIDENCE WITH AT LEAST A LITTLE FREEZING RAIN AT ONSET OF  
PRECIPITATION BETWEEN 10Z-14Z SATURDAY. HIGH CONFIDENCE  
PRECIPITATION WILL THEN CHANGE TO RAIN DURING THE MID-MORNING.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...FREEZING RAIN ADVISORY UNTIL 11 AM EST THIS MORNING FOR MIZ060>063-  
068>070-075-076-082-083.  
 
FREEZING RAIN ADVISORY UNTIL NOON EST TODAY FOR MIZ047>049-053>055.  
 
LAKE HURON...GALE WARNING UNTIL 11 AM EST THIS MORNING FOR LHZ362-363-421-462-  
463.  
 
SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LHZ441-442.  
 
SMALL CRAFT ADVISORY UNTIL 11 AM EST THIS MORNING FOR LHZ422.  
 
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...NONE.  

 
 

 
 
SHORT TERM...SF  
LONG TERM....MR  
MARINE.......MR  
AVIATION.....KURIMSKI  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MI Page Main Text Page