045  
FXUS63 KDTX 221103  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
703 AM EDT FRI SEP 22 2017  
   
AVIATION
 
 
ANY LIGHT FOG WILL DISSIPATE BY MID MORNING. A STRONG UPPER LEVEL  
RIDGE IN PLACE WILL MAINTAIN MOSTLY CLEAR SKIES THROUGH THE ENTIRE  
TAF PERIOD. WINDS WILL ALSO BE VERY LIGHT (UNDER 10 KNOTS) OUT OF THE  
SOUTHEAST TO SOUTH. THERE IS A VERY LOW CHANCE FOR A THUNDERSTORM TO  
GO UP LATE IN THE DAY, BUT IF A STORM DOES DEVELOP, IT WOULD LIKELY  
OCCUR WEST OF THE TAF SITES. ANOTHER CHANCE FOR FOG TONIGHT,  
ESPECIALLY YIP/DTW WITH THE POTENTIAL LIGHT FLOW COMING OFF LAKE  
ERIE.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* NONE.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 427 AM EDT FRI SEP 22 2017  
 
DISCUSSION...  
 
THE FIRST DAY OF FALL (EQUINOX AT 402 PM EDT) WILL ARRIVE WITH A  
CONVINCING MID SUMMER FEEL OF RECORD OR NEAR RECORD HIGHS AGAIN  
THIS AFTERNOON. EARLY MORNING SATELLITE IMAGERY AND MODEL ANALYSIS  
FIELDS INDICATE THE UPPER LEVEL RIDGE AXIS CENTERED DIRECTLY OVER  
LOWER MICHIGAN WHERE IT WILL REMAIN THROUGH THE WEEKEND. THE 00Z  
MODEL PACKAGE IS IN GOOD AGREEMENT SHOWING 500 MB HEIGHT NEAR 590  
DM THROUGH SATURDAY AND EVEN APPROACHING 592 DM DURING SUNDAY  
WHILE BROADENING IN SCALE FROM THE GREAT LAKES TO THE NEW ENGLAND  
STATES AND MID ATLANTIC COAST. THE CORRESPONDING SURFACE HIGH WILL  
ALSO STRENGTHEN AND BROADEN OVER THE NEXT FEW DAYS AND PROVIDE A  
LIGHT SOUTH WIND OVER THE REGION WITH AN ONSHORE COMPONENT INTO  
THE THUMB AND INTO THE DETROIT METRO AREA. THE COOLING EFFECT OF  
THE ONSHORE FLOW WILL BE LIMITED AND CONFINED CLOSER TO THE  
SHORELINE AS THE LAKE TEMPERATURES ARE AT WARM SEASON PEAK. THIS  
WAS DEMONSTRATED YESTERDAY WHERE BAD AXE REACHED 90 WHILE PORT  
HOPE ONLY MANAGED 84 FOR HIGH TEMPS. INTERIOR SECTIONS FROM FLINT  
TO THE TRI CITIES WILL REMAIN WARMEST WITH ANOTHER ROUND OF HIGHS  
IN THE LOWER 90S LIKELY AS BOUNDARY LAYER MIXING REACHES CLOSER TO  
825 MB IN THAT AREA. THE RAP SOUNDING FOR MBS AS AN EXAMPLE  
OFFERS A MIXED LAYER TO 815 MB AT 16 C TRANSLATING TO SURFACE  
TEMPS OF 91-93 F, RIGHT IN LINE WITH READINGS THAT OCCURRED  
THURSDAY AFTERNOON. THESE READINGS COMBINED WITH DEWPOINT NEAR 70  
WILL MAKE HEAT INDEX IN THE MID TO UPPER 90S POSSIBLE FOR A FEW  
HOURS DURING MID AFTERNOON. THIS IS SHORT OF HEAT ADVISORY  
CRITERIA (HEAT INDEX = 100) BUT WARM ENOUGH TO HIGHLIGHT FOR THE  
TIME OF YEAR. PRECAUTIONS WILL BE MENTIONED IN FORECAST MESSAGING  
FOR TODAY THROUGH THE WEEKEND.  
 
THE HIGH TEMPERATURE RECORDS FOR TODAY: 89 MBS, 90 FNT, 91 DTW  
ALL SET IN 1941.  
 
AS WARM AS SURFACE TEMPERATURES WILL BE DURING THE AFTERNOON,  
READINGS ABOVE THE SURFACE ONLY APPROACH THE VALUES CONSIDERED  
WARM ENOUGH TO FIRMLY CAP OFF CONVECTION, 20 C/850 MB AND 10 C/700  
MB. HOWEVER, A DEEPER EXAMINATION OF MODEL SOUNDINGS DOES SHOW A  
MORE CONVINCING WARM LAYER AROUND 800 MB THAT WILL BE DIFFICULT TO  
BREAK ON JUST SURFACE HEATING ALONE. THE BUILDING UPPER LEVEL  
RIDGE AND BROADENING HIGH PRESSURE AT THE SURFACE DO NOT OFFER ANY  
ADDITIONAL LARGER SCALE SUPPORT TO AUGMENT PEAK HEATING. HIGH  
RESOLUTION CAM OUTPUT DOES SHOW SOME SPECKS OF CONVECTION OVER  
INTERIOR SECTIONS DURING MID TO LATE AFTERNOON WHICH WILL BE  
MONITORED BEFORE ADDING TO THE FORECAST.  
 
AFTER THE MID SUMMERLIKE WEEKEND, EXPECT TEMPERATURES TO REMAIN WELL  
ABOVE NORMAL THROUGH MONDAY AND TUESDAY BEFORE THE NEXT FRONT  
ARRIVES WITH COOLER AIR WEDNESDAY INTO THURSDAY. GLOBAL MODELS TIME  
THE SYSTEM TO ARRIVE ROUGHLY LATE WEDNESDAY. THERE REMAINS ABOUT 12  
HOURS OF SPREAD AMONG THE DETERMINISTIC SOLUTIONS LIKELY ORIGINATING  
IN THE ONSET OF THE LARGE SCALE PATTERN SHIFT. THIS TRANSITION WILL  
STRONGLY DEPEND ON THE TIMING OF NEW HEIGHT FALLS OVER THE NORTH  
PACIFIC AND ASSOCIATED WEST COAST RIDGE DEVELOPMENT. SUCH A STRONGLY  
AMPLIFIED LONG WAVE PATTERN IS USUALLY SLOWER TO BREAK DOWN FAVORING  
A LATER FRONTAL PASSAGE IN THE GREAT LAKES. THE NEW FORECAST  
DATABASE HAS A CHANCE POP ON WEDNESDAY AND A STRONG COOLING TREND  
DURING THE SECOND HALF OF THE WEEK. THESE ELEMENTS ARE BOTH GOOD  
MARKERS FOR THE CHANGE BACK TOWARD NORMAL LATE SEPTEMBER  
TEMPERATURES THAT THE FRONT WILL BRING SUBJECT ONLY TO SOME TIMING  
ADJUSTMENTS IN UPCOMING FORECASTS.  
 
MARINE...  
 
VERY STRONG UPPER LEVEL RIDGE WILL BE SITUATED OVER THE CENTRAL  
GREAT LAKES THROUGH THE WEEKEND, LEADING TO LIGHT WINDS (UNDER 15  
KNOTS) AND LOW WAVES, ALONG WITH VERY WARM AND DRY CONDITIONS. THE  
WARM AND QUIET PATTERN LOOKS TO PERSIST INTO EARLY NEXT WEEK AS  
WELL.  
 

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

 
 

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