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fxus63 kdtx 080225 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
1025 PM EDT sun Sep 7 2008 


Update... 


Updated to reflect the latest precipitation trends after the loss 
of daytime heating. Showers from earlier in the evening are gone 
and we will have to wait for the cold front to arrive later in 
the night/early Monday morning and bring with it another chance of 
showers. There is an outside shot at a shower near Saginaw Bay 
due to the warm water adding some boundary layer instability, but 
this will be isolated. 


&& 


Previous discussion...issued 703 PM EDT sun Sep 7 2008 


Aviation... 


With the loss of daytime heating, showers will continue to diminish 
this evening and have little or no impact on aviation operations 
tonight. VFR conditions will be in place through the overnight 
hours until the cold front arrives from Wisconsin. This front will 
reach mbs around sunrise and will have just spotty patches of 
showers and MVFR ceiling before making its way through the rest of 
Southeast Michigan. A broken VFR ceiling is then expected later in the 
morning and early in the afternoon as the front slides eastward 
and southward. A light SW wind will increase modestly from the 
west behind the front, generally at 15 knots or less. 


Previous discussion...issued 342 PM EDT sun Sep 7 2008 


Short term...tonight 


Very weak upper shortwave is allowing for scattered development of 
showers and thunderstorms across northern and far central lower 
Michigan this afternoon...as quick shot of energy works on a moist 
and unstable atmosphere. Latest runs of the GFS and NAM both 
indicate that the best instability remains limited to The Thumb 
and Tri-Cities region and will keep a mention of showers/thunderstorms 
through early evening across this area only. 


Strong upper shortwave dropping through southwest Ontario will 
continue to push east-southeast across the northern Great Lakes 
overnight. This will push a surface trough and attendant cold front 
into central Michigan by 12z tomorrow. Cold front is currently very 
active across Minnesota and Wisconsin. GFS is the most aggressive 
with this little system and does seem to be better in line with what 
has been seen on upstream surface observations...radar...and 
satellite imagery. GFS indicates that showers and thunderstorms may 
extend down into the tri-cites and thumb early tomorrow morning as 
the cold front approaches. Have added low probability of precipitation to cover this. 
Otherwise...the rest of Southeast Michigan will see increasing 
clouds overnight as the surface trough approaches. 


Long term...Monday through next Sunday 


Quick system to impact the Great Lakes late Monday through Tuesday. 
Models are clustering around a weaker solution with the low moving 
across the southern portion of the forecast area Monday night. Still 
some support for a slower and stronger solution from the NAM...ruc13 
and even NGM. Not much to note on the initialization so will be 
going toward the model trends and support...which is toward the 
GFS...Gem...wrfhemi...and UK solution. 


With this system...there are very good dynamics. Right rear entrance 
region of 100 knots plus jet and strong shortwave provide plenty of 
upper support. To the north of the storms track there is deep and 
strong deformation...fgen...isentropic lift and moisture advection. 
Really have no issue with the models idea of inch plus rainfall just 
north of the surface low track. To the south of the track...there 
will be some instability with ml convective available potential energy getting up to 500 j/kg as 
surface dew points push toward 60f and 850 dew points get to 12c. Wind 
fields are impressive with 850 winds to 60 kts and a 75 jet core at 
500 mbs. This will lead to convection...maybe even an isolated 
threat of a severe wind gust south of the low track. At this 
point...that threat looks to be along and south of I-94 and more 
toward in and western Ohio. 


Behind the system for Tuesday morning...strong cold air advection 
will bring breezy/windy conditions. There will also be some help 
from an isallobaric component. Do not think that the any of the 
models have a particularly good handle on the wind...and will go 
somewhere between the GFS and ruc13 wind fields. This should yield 
enough wind for gales across much of Lake Huron and winds around 15 
kts across Southeast Michigan. There will be enough low level moisture for 
broken to overcast SC deck during the morning...which will really give the 
morning a raw middle autumn feel. Conditions improve during Tuesday 
afternoon as the surface high moves in quickly. This will bring 
plenty of dry air and relaxes the gradient by Tuesday afternoon. 


Will go with the cooler temperatures on Monday with plenty of clouds around 
both the low clouds in the wake of the overnight system...and then 
middle cloud in advance of the Monday storm. Monday nights low temperatures 
will be right at 12z as the cold air advection starts late at night. 
Still will go a couple of degrees warmer than guidance given the 
push of dew points near 60 in far southeast lower. For 
Tuesday...will go toward the warmer guidance even with the cold air 
advection...given the expected sunshine in the afternoon. It is 
still early to middle September after all. 


Tuesday night will be cool as high pressure settles over the Great 
Lakes. There will be some lake effect clouds off of Lake Huron for 
The Thumb coastal area...as land breezes set up a convergence area 
just off shore. Waterspouts will become a concern for Wednesday 
morning within this convergence area. Certainly enough instability 
and the convective cloud depth looks to be nearly 10k feet. 


Weather is quiet for Wednesday with the high over the Great Lakes. 
Then some differences for Thursday into next weekend. Next system 
and frontal boundary will move through Thursday night and Friday 
morning. Models have been more consistent about this timing and 
will take out probability of precipitation for the day on Thursday...except late afternoon 
for the Tri Cities area. For next weekend will follow HPC as the 
extended models are all over the place. 12z runs did not help either 
as GFS is now completely dry...while the European model (ecmwf) is a bit more 
consistent by being wetter for the second half of next weekend. 


Marine... 


Winds will remain predominately out of the southwest through early 
Monday...as a trough of low pressure moves across Lake Huron and 
high pressure holds south of the region. Persistent southwest flow 
with gusts up to 21 knots will allow waves over outer Saginaw Bay to 
build up to 3 feet by this evening...then subside by late Monday 
morning. 


Easterly winds will strengthen Monday night as a deepening low 
pressure system lifts up through lower Michigan. There is potential 
for gale force winds to develop across much of Lake Huron by early 
Tuesday morning as winds flip to the northwest and cooler air pours 
over the Warm Lake waters in the wake of this system. The gale watch 
has been expanded to include most of the open waters of Lake 
Huron...outer Saginaw Bay...and the Lake Huron nearshore waters Port 
Austin to Port Huron. While we anticipate winds to decrease to below 
gale force Tuesday afternoon...waves will remain high well into 
Tuesday night as cold air continues to push down into the region. 
Waves will subside quickly through late Wednesday as high pressure 
builds back into the region. With the cold air and high settling 
over the Great Lakes region...land breezes will set up a 
convergence area across Southern Lake Huron. Waterspouts will become a 
concern for Wednesday morning within this convergence area. 
Certainly enough instability and the convective cloud depth looks 
to be nearly 10k feet. 


&& 


DTX watches/warnings/advisories... 


Michigan...none. 


Lake Huron... 
gale watch...lhz362-lhz363-lhz421-lhz441-lhz442-lhz443-lhz462- 
lhz463-lhz464...from 4 am Tuesday to 2 PM Tuesday. 


Lake St Clair...none. 


Michigan waters of Lake Erie...none. 


&& 


$$ 


Update.......bt 
aviation.....Bt 
short term...hlo 
long term....rbp 
marine.......hlo/rbp 




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