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fxus63 kdtx 221701 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
1201 PM EST sun Nov 22 2009 


Aviation... 


Much like yesterday...it will take most of the afternoon for 
visibilities and ceilings to improve into VFR category. Once the sun 
sets...good raditional cooling will kick in...allowing surface 
visibilities to begin to crash...as surface dew points are running 
high early this afternoon (mid 40s). Tonight there will be a 
stronger southeast wind...which may lead to LIFR ceilings vs 
visibilities...but either way we appear destined to fall into the LIFR 
category as southeast flow comes of Lake Erie/St Clair/Southern 
Lake Huron. Improvements in the visible/ceilings will be slow 
tomorrow...and probably won't see VFR conditions until after 18z. 




&& 


Previous discussion...issued 336 am EST sun Nov 22 2009 


Short term...today 


Low stratus/fog continue to slowly build southwest through the County Warning Area 
early this morning...and expect most of the area to be mostly cloudy 
with areas of fog by daybreak. With weak November sunshine...it will 
then take much of the morning to burn of this stratus/fog...so only 
expect a gradual transition to partly sunny skies by afternoon. The 
temperatures will be able to climb into the low/middle 50s again as the 
airmass has not changed appreciably...but this will be dependent on 
the eventual evolution of the stratus/fog and adjustments may be 
needed in some areas if clouds take longer to scour out. 


Long term...tonight through next Saturday 


Forecast concerns for the extended period again center around fog 
development Monday and Tuesday mornings and the middle week low 
pressure system that will affect Michigan. 


Middle level ridging and associated surface low pressure system will 
continue to affect Southeast Michigan through Monday evening as it moves eastward 
over New England. It will eventually be replaced by a series of 
shortwaves and amplified longwave trough by early midweek. The middle 
levels will remain dry until this trough begins to influence the 
airmass aloft early Tuesday as shown by NAM bufr soundings and 
BUFKIT. The low levels on the other hand will remain very moist 
leading to potential fog development both Sunday and Monday nights. 
The pressure gradient remains weak between the outgoing high and 
incoming low pressure systems keeping the winds weak through this 
period. Model soundings continue to show boundary layer decoupling 
each night at around 950mb under the continued middle level subsidence 
from the exiting high. A slight easterly component to the low level 
flow will act to reinforce the already moist boundary layer. 
Potential does exist for this fog to become dense as a lack of day 
time heating will allow temperatures to drop fairly quickly after sunset. 


Not much has changed with the middle week storm system from previous 
model runs. It seems that the GFS is slowing down a bit bringing it 
more in line with the European model (ecmwf)...which has been the favored model 
solution thus far. They both show the middle level trough becoming 
increasingly amplified on Monday over the central rockies then 
becoming more of a cutoff circulation over the Central Plains. There 
are still many questions though regarding the evolution of this 
trough and low as to how cutoff it will become from the main stream 
and how a secondary shortwave sliding down the backside of this main 
low will affect the trough. This will affect the propagation speed 
of the trough and when it will arrive over Southeast Michigan. It will also 
affect how cold the airmass will be that is brought in with the 
trough. The models have been tapering back the amount of cold air 
and holding it back until later in the as they slow the main feature 
down. At this point it looks like the precipitation will move in Tuesday 
night in the form of rain with the best chances during the day on 
Wednesday. Precipitation chances remain through Friday transitioning to a 
rain/snow mix Thursday night as the coldest air moves in on the 
backside of the low. 


Marine... 


High pressure will remain in place over the central Great Lakes this 
weekend...resulting in light/variable winds. There will be a gradual 
increase in southeast winds Monday into Tuesday as the high retreats 
east away from the area. The pattern becomes active again middle/late 
next week as a strong shortwave and associated jet streak dig into 
the upper Midwest and lead to the development of a large upper level 
low over/near the region. This time frame will bring unsettle 
weather and higher wind and waves. 


&& 


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


&& 


$$ 


Aviation.....Sf 
short term...dg 
long term....drk 
marine.......dg 




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