743 
fxus63 kdtx 240816 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
416 am EDT Thursday Jul 24 2008 


Short term...today 


The large high pressure system currently extending from Lake 
Superior through the Tennessee Valley will build across lower Michigan and 
the Ohio Valley today as the upper low to the east of the state 
slowly lifts off to the northeast. The current water vapor loop 
shows a fairly strong short wave trough rotating around the back 
side of the upper low. This short wave is now rotating into eastern 
Upper Michigan and is forecast to slide across Southeast Michigan between 12z and 18z. 
The airmass across the state is quite dry. Thus far...this short 
wave has only been able to produce some scattered Alto cumulus across 
northern lower Michigan. Latest model soundings suggest this will also be 
the case as this wave enters the forecast area late this morning. 
Building middle level heights and confluent flow aloft in the wake of 
the short wave will ensure plenty of afternoon sunshine across the 
forecast area. After a relatively cool start to the day...model 
soundings indicate a dry and well mixed boundary layer by afternoon 
with maximum temperatures rising to the lower 80s across most of the forecast 
area. 


&& 


Long term...tonight through Wednesday 


Surface high pressure poised to our south will continue to provide 
dry weather overnight. Southerly flow will however build in late and 
start transporting warm air and moisture back into lower Michigan. 
Trended temperature forecast towards the low end of guidance given 
early clearing before clouds start working their way back in late 
night. Should see temperatures ranging from the middle 50s to low 60s. 


Upper low over Ontario/Quebec will lift a little northeast on Friday 
as approaching upper trough pushes into MN/WI. This system will then 
get pulled up into the upper low over Canada as blocking ridge 
extending into the North Atlantic halts the eastward progress of the 
two systems. Resultant surface trough will move into Wisconsin on 
Friday and then across lower Michigan Friday night. Warm front will 
settle over the northern Great Lakes Friday/Friday night...where 
upper diffluence and left exit region forcing will focus 
precipitation. This will keep the heaviest precipitation north of 
the forecast area...over the u.P. And Northern Lake Huron. For our 
area...will see few showers/thunderstorms develop Friday with 
isentropic ascent remaining very weak as the warm sector asserts 
itself. With lack of a strong focusing mechanism...shallow moisture 
and only weak instability...will continue to carry only isolated 
probability of precipitation. Chance for showers/thunderstorms will increase overnight as the 
trough axis and front start to approach...and as jet dynamics become 
slightly more favorable across Southeast Michigan. Nocturnal timing 
and the low-level jet remaining to our north over Canada...per NAM 
solution...will limit both thunderstorm coverage and 
strength...warranting only a chance pop. Cold front will push 
through on Saturday with showers/thunderstorms spreading into the area 
ahead of it before all activity pushes into Ohio by evening. Have 
trended the forecast towards an northward-adjusted version of the 
GFS...as it seems to have a good handle on things synoptically but 
remains an outlier with dropping shortwave energy too far south into 
Michigan by Saturday. 


Forecast for Sunday remains dry as upper low continues to spin over 
Ontario/Quebec. Although...a few recent model runs have dropped 
additional shortwave energy down through the Great Lakes. 


Am becoming a little more hesitant with keeping forecast for next 
week so "nice"...but high degree of uncertainty with individual 
features makes it hard to add precipitation to the forecast for any 
one particular period. Highest probably of dry pleasant weather will 
be Monday and Monday night as surface high pressure finally extends 
into the Great Lakes from the west. Models have again backed off a 
little on the eastward progression of the central Continental U.S. Upper ridge 
through the beginning of next week. This trend does make sense given 
the strength and amplitude of the upper ridge currently over the 
Atlantic. This creates uncertainty with the placement of the 
upstream Continental U.S. Ridge and the upper low over Canada...and more 
importantly the middle-latitude baroclinic zone across the eastern half 
of the country. Recent runs of both the GFS and Euro have brought at 
least one mesoscale convective system through the region at some point middle week...with wide 
variations in day to day placement. Both models have shown a trend 
towards another shortwave trough pushing through southern Canada and 
the northern plains around Tuesday. Southward progress of this 
trough and resultant low pressure system will definitely need to be 
watched towards the middle of next week...and probability of precipitation may need to be 
added soon to cover this next system. For now...prefer the GFS 
solution of tracking the upper level energy across or north of 
Michigan vs the unseasonable Euro solution of diving the energy 
south of the region. 


&& 


Marine... 


Latest observations over Southern Lake Huron show northwesterly 
winds gusting up to 20 knots. This wind direction will continue to 
produce waves in the 3 to 5 feet range over the Lake Huron waters 
from Port Austin to Harbor Beach early this morning. Winds and waves 
will decrease during the day as high pressure builds in from the 
west. 


&& 


Previous discussion...issued 102 am EDT Thursday Jul 24 2008 


Aviation... 


VFR clear conditions will be in place over Southeast Michigan this morning 
with just some high thin clouds moving in during the afternoon. 
Light northwest winds will gradually turn toward the southwest by 
middle afternoon as surface high pressure slides from the Midwest into 
the Ohio Valley. 


&& 


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


Lake Huron... 
Small Craft Advisory...nearshore waters from Port Austin to Harbor 
Beach...until 11 am Thursday. 


Lake St Clair...none. 
Michigan waters of Lake Erie...none. 


&& 


$$ 


Short term...SC 
long term....hlo 
marine.......SC 
aviation.....Bt 




You can obtain your latest National Weather Service forecasts online 
at www.Weather.Gov/Detroit (all lower case). 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)