Weather

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fxus63 kdtx 061510 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
1105 am EDT Monday Oct 6 2008 


Update... 


Updated to lower temperatures a few degrees and delay clearing a bit based 
on satellite/radar trends and new guidance. Middle level forcing will 
continue to weaken as it pushes southwestward during the afternoon 
as entrance region of upper jet moves to the east. High pressure 
dropping south into Ontario will send drier air filtering in from 
the northeast this afternoon which will erode cloud cover from 
northeast to southwest across Southeast Michigan. Light rain is 
transitioning to sprinkles across the far southeast corner and 
should be gone by early afternoon. 


&& 


Aviation... 


Light showers will continue to develop this morning along a 
weakening elevated frontal boundary draped across lower Michigan... 
but impacts will remain mimimal with conditions holding at VFR at 
all taf sites. Middle level cloud deck will linger into the afternoon 
before scattering out by evening as high pressure centered over 
Ontario builds south. This high will maintain an easterly wind 
through the taf period. 


&& 


Previous discussion...issued 531 am EDT Monday Oct 6 2008 


Short term...today 


Latest water vapor and upper air analysis showing southeast lower Michigan 
sandwiched between the back end of an upper trough axis swinging 
across southern Ontario/Quebec and upper ridging extending into the 
middle MS valley. An elongated area of weak isentropic accent and middle 
level frontogenesis supporting a narrow corridor of very light rain 
stretching from east-central WI into the southern third of the 
forecast area. Both the 12z NAM and GFS indicate this forcing will 
quickly diminish through the morning hours...allowing any lingering 
precipitation to rapidly taper off. The rather modest looking moisture 
profiles...as well as current radar trends...would suggest little 
more than a couple hundredths of rain at most. Highest probability of precipitation will 
focus within the Owosso-Howell-Ann Arbor corridor...with no mention 
toward The Thumb. 


Residual high cloudiness will gradually thin through the afternoon 
as the large scale forcing wanes and upper ridging builds toward the 
region. Some increasing insolation late will help counter a 
predominant low level easterly flow resulting from high pressure 
centered over southern Ontario. Rising upper heights will allow the 
airmass to moderate despite the easterly flow...although perhaps not 
quite to the extent projected by either the NAM or GFS. Generally 
will see highs around or just below seasonal norms...with readings 
mainly in the lower 60s (upper 50s in the thumb). 


Long term... 


Not a whole lot of changes made to the previous forecast...as 
milder temperatures remains the weather story. 


The trend of the upper level longwave trough over The Rockies is to 
be a bit faster/more progressive as the day shift expected. The 
upper wave at the bottom of the trough struggles to cutoff from the 
northern stream...with zonal flow becoming established over the 
northern Continental U.S. On Wednesday. Models (00z UKMET/gfs) showing some 
semblance of a weak surface low/wave or at the very least a surface 
trough (nam/european) lifting northeast through lower Michigan 
during Wednesday...and have raised probability of precipitation to 50 percent. Day shift 
already introduced chance probability of precipitation late Tuesday night which also looks 
good as sharp 850-700 mb Theta-E gradient moves in around 12z 
Wednesday. In the meantime...rather amplified upper level ridge in 
place on Tuesday will provide a mild day as low level warm advection 
kicks in...allowing 850 mb temperatures to reach and exceed 12 c. The mav 
guidance looks good...upper 60s to around 70 on Tuesday. Clouds and 
showers on Wednesday will probably hold maximum temperatures down a bit...in 
the middle 60s. However...with the weak cold front washing out on 
Thursday...upper 60s to near 70 degrees seems attainable once again 
as 925 mb temperatures seen warming into the low to middle teens. 


Marine... 


A prolonged period of easterly winds will develop across all marine 
areas today as high pressure builds across the eastern Great Lakes 
and low pressure moves through the plains. These winds moving 
across the Long Lake Huron fetch will result in higher waves today. 
These conditions will develop across the Michigan waters of Lake 
Erie by tonight and small craft advisories are now in effect here as 
well. Waves will gradually diminish on Tuesday as winds shift 
toward the southeast and decrease. An approaching cold front will 
bring the next chance of rain on Wednesday...although wind and wave 
conditions will remain generally favorable across all marine areas. 


&& 


DTX watches/warnings/advisories... 
Michigan...none. 


Lake Huron... 
Small Craft Advisory...Saginaw Bay and the nearshore waters from 
Port Austin to Port Sanilac...until 10 am Tuesday. 


Small Craft Advisory...nearshore waters from Port Sanilac to Port 
Huron...from 2 PM Monday to 10 am Tuesday. 


Lake St Clair...none. 
Michigan waters of Lake Erie... 
Small Craft Advisory...from 6 PM Monday to 10 am Tuesday. 


&& 


$$ 


Update.......drc 
aviation.....Mr 
short term...mr 
long term....sf 
marine.......mr 




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