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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
604 PM EST Thursday Mar 11 2010 




Aviation... 


A stalled low pressure system over Iowa will push a weak frontal 
boundary across the region overnight bringing rain showers to all of 
the taf sites. Scattered showers at the onset will be handled by 
tempo groups...before the steadier rain arrives by 04-05z which will 
be handled in the prevailing group. Abundant low level moisture will 
result in IFR ceilings through most of the night with some patchy 
fog reducing visibilities as well. Conditions will improve to MVFR 
Friday morning as drier air filters into the area. 


&& 


Previous discussion...issued 339 PM EST Thursday Mar 11 2010 


Short term...tonight 


Broad area of vertically stacked low pressure is currently stalled 
across the upper Mississippi Valley. This will slowly drag an 
occluded front across the western Great Lakes overnight bringing a 
chance of rain to our County Warning Area. Thin ribbon of moisture associated with 
nocturnal convection over Arkansas is trying to make its way into 
Michigan but it is encountering some drier air as seen on this 
mornings 12z DTX sounding. Moisture availability will not be much of 
an issue by later tonight though as strong south-southeasterly winds 
advect higher dewpoints into the area...increasing precipitable water values to over 
one inch. Main limiting factor for precipitation will be a lack of 
good forcing. Thermal advection is weak at best with little to no 
isentropic lift. Upper level dynamics will be sufficient with a vorticity 
maximum rotating around the upper low but it will be too far west to 
produce significant rainfall over our area...especially across The 
Thumb and eastern County Warning Area. Nevertheless...expect most areas along and 
west of the i75 corridor to see rainfall tonight. Will continue to 
mention the possibility of a few thunderstorms as BUFKIT soundings 
suggest there will be around 200 j/kg of elevated instability 
tonight. Min temperatures are expected to be in the upper 40s...which is 
supported by upstream surface dewpoints of similar values. 


Long term...Friday through next Thursday 


The key features of interest for the next several days will be the 
deep upper low now over Iowa and the strong wave now traversing 
Texas. While there are some significant differences with respect the 
track and intensity of this wave over Texas...the current 
representation on satellite would support the deeper GFS and NAM 
solutions which lift this wave into the lower Tennessee/Ohio valleys 
on Friday...then phase it with the deep upper low now over Iowa. 
This will lead to a broad upper low over the middle Mississippi 
Valley by Saturday morning...which is forecast to gradually move 
to the East Coast by Sunday. 


The wave forecast to lift up the Tennessee/Ohio valleys on Friday 
will lead to surface cyclogenesis across southern Illinois/Indiana. 
The bulk of the large scale ascent will remain focused south of the 
state through much of the day. Residual early morning showers 
associated with the overnight low level Theta-E ridge and potential 
for some late day moisture convergence will warrant a low chance of 
showers on Friday. Overall...the lack of significant forcing and middle 
level drying later in the morning will keep the bulk of the day 
precipitation free...with some peaks of sun expected. Residual morning low 
clouds and slightly cooler air in the low levels should restrict 
highs temperatures to the 50s for most of the forecast area. 


Short wave energy over the southeast US and strong upper jet support will 
lead to surface cyclogenesis across the eastern Seaboard this 
weekend. The 12z model suite continue to indicate that this pattern 
will establish strong Atlantic moisture transport from the middle 
Atlantic/New England into the southern Great Lakes/Northern Ohio 
valley. Periodic large scale enhancement from weak middle level short 
wave impulses and deep layer moisture convergence will continue to 
warrant a high probability of rain Friday night through the day 
Saturday and into Sat night. Although the models have trended 
farther south with the highest quantitative precipitation forecast over the last couple of 
runs...the potential still exists for some heavier rainfall amounts 
in light of the moisture transport. Model solutions /the GFS in 
particular/ have trended a bit faster in tracking the upper low off 
the East Coast late in the weekend. In light of these trends...will 
back off on the chances of rain slightly on Sunday. The clouds and 
rain will keep daytime temperatures suppressed in the 40s over much of the 
weekend. 


Middle level heights will then build across the region early next weak 
as the upper low lifts off the East Coast. This will allow high 
pressure and much drier air to filter into the forecast area. A weak 
cold front is forecast to drop south across the area during the middle 
week period as an upper low slides across eastern Canada. A dry 
forecast will however be maintained given the lack of moisture 
expected along this boundary. Low level cold air advection is also 
expected to be very weak. The combination of ample sunshine and 
respectable mixing depths should allow daytime temperatures to remain above 
seasonal norms Monday through Thursday. 


Marine... 


Low pressure currently over Iowa will weaken and shift southward 
before merging with another low moving out of the Gulf Coast and 
into the Ohio Valley. This will result in easterly winds continuing 
into the weekend. However...with relatively warm air over the Cold 
Lakes...it will be difficult for stronger winds to mix down to the 
surface. Small craft advisories may be needed heading into Sunday as 
the winds strengthen and become more northeasterly. 


&& 


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


&& 


$$ 


Aviation.....Kurimski 
short term...agd 
long term....SC 
marine.......agd 




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