809 
fxus63 kdtx 181745 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
145 PM EDT Friday Jul 18 2008 




Aviation... 


A weak frontal boundary will remain nearly stationary across central 
lower Michigan into tonight. An overcast deck of middle clouds is 
present along this boundary with a few scattered light showers 
possible at fnt/mbs this afternoon. An isolated thunderstorm is also 
possible but chances are low and will exclude from the taf until we 
see development upstream. Outside of a shower...VFR conditions are 
expected through tonight with chances of rain showers increasing at 
all taf sites by late Saturday morning. 


&& 


Previous discussion...issued 351 am EDT Friday Jul 18 2008 


Short term...today. Forecast focus on precipitation chances. 


A weak cold front will slowly move southward into the County Warning Area today. The 
models are in good agreement keeping the precipitation out of the southern 
County Warning Area during the morning and early afternoon. Given the model 
agreement will keep the southern County Warning Area dry through 18z. During the 
afternoon the models diverge as the GFS/European model (ecmwf) keep the precipitation across 
the north while the NAM places the precipitation farther south. Will keep 
probability of precipitation in across the southern County Warning Area during the afternoon with the model 
disagreement. 


Severe potential today should be minimal as the best convective available potential energy will be 
further north with continued weak shear. MOS temperatures are fairly 
close and in line with the previous forecast so little chance is 
anticipated with high temperatures with another warm muggy day in 
store for southeastern Michigan. 


Long term...tonight through Thursday 


Little change was made overall to inherited forecast. Fairly zonal 
flow with embedded shortwaves still expected through Sunday. Middle 
latitude baroclinic zone currenly draped across Lake Huron will 
continue to sink southward...and most likely stall over the central 
part of the forecast area this evening. GFS and Euro are consistent 
with this scenario...however the NAM...an outlier...is now dragging 
the front further south and stalling it closer to the Ohio border. 
Will keep with the GFS/Euro/previous forecast and keep the highest 
probability of precipitation north of the city of Detroit. Stalled out boundary will 
continue to serve as a focus for showers/thunderstorms in the warm humid 
airmass Saturday and Saturday night...though the expectation is for 
thunderstorm coverage to increase as models continue to advertise a 
more organized shortwave trough developing upstream of the Great 
Lakes as energy ejects out of the upper low over British Columbia 
and races eastward across southern Canada. GFS/NAM/Euro all hint at 
possible upstream mesoscale convective system development both Sat and Sat night with 
activity then spreading eastward over the baroclinic zone and 
across lower Michigan. 


Medium range models support a continued chance of convection on 
Sunday as a bigger shortwave trough and surface low pressure system 
approach. Models then exhibit some differences with how quickly the 
trough exits east into southern Ontario/New England...and how strong 
any shortwaves that drop out of Canada and into lower Michigan 
Monday and Tuesday will be. Given the inconsistencies and drier 
candian airmass will keep forecast dry from Monday night 
Onward...with the expectation that the upper ridge building over the 
central Continental U.S. Will eventually extend into the western Great Lakes. 


Marine... 


A weak cold front will slowly move from Northern Lake Huron to 
Central Lake Huron today...then into Southern Lake Huron tonight. 
Strong thunderstorms will develop along the front with the potential 
for torrential rains...wind gusts to 40 knots and locally higher 
waves today. In addition...synoptic winds of 10 to 20 knots will 
cause higher waves across the open waters of central and Southern 
Lake Huron today. 


Winds and waves will then subside tonight and into Saturday as the 
frontal boundary stalls across Southern Lake Huron. 


&& 


DTX watches/warnings/advisories... 
Michigan...none. 
Lake Huron...none. 
Lake St Clair...none. 
Michigan waters of Lake Erie...none. 


&& 


$$ 


Aviation.....Kec 
short term...kurimski 
long term....hlo 
marine.......kurimski 




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at www.Weather.Gov/Detroit (all lower case).