398 
fxus63 kdtx 152335 
afddtx 


Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan 
735 PM EDT Wednesday Oct 15 2008 


Aviation... 


IFR conditions in place with periods of light-MDT rain to begin the 
taf period as low pressure tracking by to the south maintains a 
solid area of low level moisture. As this low shifts east...rain 
will taper off while conditions gradually improve toward MVFR 
overnight. Drier air moving in behind a cold front will bring VFR 
conditions on Thursday...with daytime heating generating a scattered-broken 
diurnal cumulus deck by afternoon. 


&& 


Previous discussion...issued 259 PM EDT Wednesday Oct 15 2008 


Short term...tonight 


Water vapor imagery and NAM/GFS dynamic tropopause maps show a very 
strong...but sheared out upper wave tracking east-NE through Iowa. 
Upper level confluent flow in place over the central Great 
Lakes...with just a progressive and weak surface low expected to 
track through or near Detroit early this evening. Rain did 
overspread much of Southeast Michigan around 2 PM as 
advertised...associated with the main moisture surge/isentropic 
ascent. The large scale forcing with the strong upper wave and 
925-850 mb fgen should assure additional rainfall into this 
evening...with a continued slight chance of thunderstorms south of 
M-59...as GFS indicating slightly negative surface-850 mb lifted indice's. 
With good subsidence late tonight and increasing northwest winds 
helping to dry out the column...looking for the rain to be mostly 
over by 6z...with skies even clearing out by 12z Thursday. GFS MOS 
guidance for mins looked reasonable (40s to near 50). 


Long term...Thursday through Wednesday 


A cooler and drier airmass will settle into the area in behind the 
current southernmost disturbance bringing showers to the area. As its 
northern stream counterpart continue into eastern Canada...the upper 
pattern will feature a broad trough over much of noam and allow high 
pressure to build into the region from Canada. Progressively cooler 
readings can be expected Thursday and Friday...with highs generally 
in the middle/upper 50s Thursday...and Lower/Middle 50s Friday. Will add 
the mention of patchy frost overnight Thursday night as well given 
widespread lows in the middle 30s. A better chance of widespread frost 
will come overnight Friday night as the high pressure settles right 
over the region...bringing ideal radiational cooling to much of the 
region. 


Beyond this...the upper level pattern becomes very progressive as a 
potent shortwave races into Canada from the Gulf/Alaska region and digs 
into the Great Lakes by early next week. This will bring a modest 
warmup on Sunday in south/southwest flow in advance of the system 
and then bring another shot of cooler air into the area during the 
day Monday on into Tuesday...before some moderation again ensues by 
the end of the forecast. Temperatures will push 60 on Sunday and 
again Monday before clouds and cold air advection bring cooling by 
late in the day. Tuesday will then by back into the Lower/Middle 50s. 
Do not plan on any changes at this time due to uncertainties in the exact 
timing. 


In terms of precipitation...will maintain a slight chance of light 
showers on Friday as a weak disturbance skirts the region just in 
advance of the building high pressure. The chance of showers will 
return Sunday night into Monday in advance/along the next northern 
stream system. 


Marine... 


Low pressure will zip through Lake St Clair this evening...with 
north/northwest winds increasing tonight in the lows wake. Marginal 
small craft conditions (gusts of 20 to 25 knots...waves 3-5 feet) 
are expected over the nearshore waters of Lake Huron...as well as 
out Saginaw Bay. Winds will slowly be decreasing during 
Thursday...but especially on Friday as an expansive area of high 
pressure settles over the Great Lakes region. Favorable boating 
conditions will then continue into Saturday as this high will be 
slow to exit. 


&& 


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


Lake Huron... 
Small Craft Advisory...nearshore waters from Port Austin to Port 
Huron including outer Saginaw Bay...from 2 am Thursday to 8 am 
Friday. 


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


&& 


$$ 


Aviation.....Mr 
short term...sf 
long term....dg 
marine.......sf 


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