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fxus63 kdtx 131700 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
1200 PM EST Sat Mar 13 2010 




Aviation... 


Predominately low MVFR ceilings will continue this afternoon as 
showers continue to rotate through Southeast Michigan. There will 
periods of VFR and high IFR ceilings in heavier showers...but 
more widespread IFR conditions are expected tonight...as cold 
advection takes place. Rather strong northeast winds (10-15 knots 
gust to 20 knots) through the period should keep the surface mixed 
enough to hold visibilities in the MVFR/VFR category. Increasing boundary 
layer depths tomorrow should allow ceilings to climb back into low 
MVFR. There will probably be scattered showers around with the 
steep low level lapse rates...but did not put in the tafs until 
timing and location can be better pinned down. 




&& 


Previous discussion...issued 404 am EST Sat Mar 13 2010 


Short term...today 


Latest upper air/RUC and water vapor analysis showing a broad middle 
level circulation pivoting southeast across the Missouri bootheel. 
The northern extension of this system will remain firmly entrenched 
across Southeast Michigan today. Extensive moisture plume continues to 
rotate around the northern/eastern periphery. A widespread area of 
rainfall moving west-northwest through the Ohio Valley remains 
focused within an axis of better moisture advection/isentropic 
ascent and in the vicinity of a weakening surface low and residual 
frontal boundary draped across that region. The northern extension 
of this now beginning to expand across the border per latest radar 
trends. 


Rain will expand in coverage across the entire region today under 
continued moisture advection /pw values over .75"/ within a 
persistent/deep easterly flow. Any enhancement provided by weak 
shortwaves embedded within the broad cyclonic flow will bring the 
potential for a period of widespread moderate rain...with latest 
model consensus keying in on the afternoon hours. Despite limited 
mixing today...a tight pressure gradient with 950 mb winds reaching 
30 knots will bring gusty conditions making for a rather raw day. 
The solid overcast/rain and minimal mixing will limit the diurnal 
thermal response today. Highs will struggle to climb much above 
the morning lows...with readings hovering 40s. 


Long term...tonight through next Friday 


Deep cyclonic flow will grip southeastern Michigan for the latter 
half of the weekend...providing for a continuation of cooler and 
unsettled conditions. Model guidance differs with regards to the 
thermal profile beginning tonight. Not very impressed with either of 
the 00z initializations to the GFS/NAM. Generally...both are too 
warm with the cold pool across the Central Plains/upper 
Midwest...and too cold with the large warm sector ahead of the main 
pv anomaly over southeastern US. This is noteworthy as freezing 
heights will come crashing overnight to around 1500-2000 feet. This 
near surface warm layer is rather deep but something to keep in 
mind. Thus...light rain is expected to be the dominant activity 
although may see some drizzle activity as middle to upper level 
saturation will vary. With an abundance of low level 
moisture...established deformation forcing...and some upper level 
jet support....nudged categorical probability of precipitation upward...with quantitative precipitation forecast on the 
order of .10 - .20 inches. 


Jet axis...cyclonic flow...and inbound shortwave energy requires the 
mention of light rain for Sunday. Very steep lapse rates are 
expected to develop by the afternoon hours through 5 kft. This 
signals that an uptick in shower activity may occur during the 
afternoon due to the diurnal boost. Highs on Sunday will struggle in 
the middle 40s with brisk easterlies. 


Rising midlevel heights will dictate the weather across southeastern 
Michigan early this upcoming week before a solid surface ridge 
builds for the end of the week. Expect dry and sunny conditions 
throughout...with temperatures creeping a couple of degrees upward 
each day. With the strength of the surface high 
pressure...prototypical springtime lows of below freezing are to be 
expected. 


Marine... 


A low pressure system centered over the Ohio Valley will maintain 
a stronger easterly flow across the central Great Lakes through 
tonight. This will lead to gusts to 25 knots...while the prolonged 
onshore flow allows waves to build in excess of 4 feet along the 
nearshore waters of Lake Huron and outer Saginaw Bay. The low over 
the Ohio Valley will Transfer to the middle Atlantic coast during the 
weekend and move well offshore by Sunday...allowing winds to 
decrease and waves to slowly subside. High pressure building into 
the western Great Lakes early next week should result in relatively 
light winds. 


&& 


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


Lake Huron... 
Small Craft Advisory...nearshore waters from Port Austin to Port 
Huron including outer Saginaw Bay...until 8 PM Sunday. 


Lake St Clair... 
Small Craft Advisory...until 8 am Sunday. 


Michigan waters of Lake Erie... 
Small Craft Advisory...until 8 am Sunday. 


&& 


$$ 


Aviation.....Sf 
short term...mr 
long term....cb 
marine.......mr 




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