809 
fxus63 kapx 212311 
afdapx 


Area forecast discussion 
National Weather Service Gaylord Michigan 
711 PM EDT Thursday Aug 21 2008 


Aviation...increasing moisture will gradually lower ceilings 
/toward 8-10kft/ through the night as upper level wave drifts just west 
of the area...and should provide at least scattered rain showers 
for ktvc/kpln. Wind shear also a concern at these sites as low 
level jet Cranks up after 06z. Better coverage of showers and 
storms expected for all areas on Friday as moisture surges into 
the area. Ceilings still generally VFR...although areas of MVFR 
ceilings possible around thunderstorms. 


Jk 
&& 


Previous discussion... /issued 357 PM EDT Thursday Aug 21 2008/ 


Synopsis...the remnants of upper level ridging across northern 
Michigan will give way overnight as a pronounced upper low 
low/shortwave advances through Iowa/Illinois this afternoon and 
eventually slips west of the area overnight. A strong cold front 
will then make a run at the area late Saturday before high pressure 
once again takes over through much of next week. 


Short term (tonight and friday)... /issued 357 PM/ 


Primary forecast concerns focused on precipitation potential through the 
period. Late afternoon satellite/radar pics tell the story for 
tonight...as upper low over Iowa/Illinois this afternoon on track to slip just 
west of the area tonight. Late afternoon regional radar shows fairly 
healthy area of precipitation advancing into WI along axis of modest 
305-310k isentropic ascent/700-500mb qg upward forcing... while 
second area trails back into southern Indiana in channel of strong 
850-700mb Theta-E advection. Aforementioned features will continue 
to slip almost due north tonight on the backside of strong deep 
layer ridge over the East Coast...with pronounced isentropic 
upglide/downglide couplet over Lake Michigan arguing to a sharp cutoff to 
precipitation chances over the apx County Warning Area. At this juncture...appears 
sufficient lift will be in place to provide scattered showers for 
the far western County Warning Area after 03z...though overall moisture profiles 
sub-700mb rather unimpressive (i.E. Dry downstairs). Farther 
east...difficult to foresee any significant precipitation chances through 
the night...though not completely zero given healthy shot of 
Theta-E advection arriving after 06z. Thunder chances not terribly 
impressive with scant middle level lapse rates (thanks to saturation) 
though influx of moisture down low (tipping of low level lapse 
rates upward) could provide a few rumbles as evidenced by upstream 
nldn plots this afternoon. Temperatures much warmer with ongoing warm 
advection... mainly low/middle 60s. 


For Friday...tricky precipitation forecast. Airmass should be basically the 
complete opposite of that in place the past few days...with upstream 
dew points well into the 60s (if not near 70) gliding north tonight. 
Basic problem for additional convective initiation will be lack of 
defined trigger mechanism as overnight wave/qg support shears out 
into Ontario and low level flow way too strong for any lake 
component to wind. However...strongly believe additional convective 
will fire given simple airmass arguments...namely prognosticated uptick in 
850-700mb moisture transport on the backside of sprawling East Coast 
high and localized forcing on the higher terrain. Upstream radars 
already bear this out with long axis of convecting strung out from 
Louisiana into southern Missouri and difficult to ignore NAM/sref 
forecasts of rather high probability of precipitation. Severe potential rather minimal with only 
modest lapse rates (too warm aloft) and scant wind fields. Even with 
expected better cloud cover...should have little trouble reaching 
the 80s most spots with better shot of warm advection ahead of 
approaching cold front. 


Lawrence 


Long term (friday night through thursday)... /issued 357 PM/ 


A lot of this forecast rests on what Fay does or doesn't 
do, as a tropical system can put a halt on the movement of the 
systems coming across the continent. 


Friday night...initial convection with 500 mb shortwave trough looks 
to be shearing out, with the cold front bearing down on the Great 
Lakes. The cold front begins to really bring in the chance for rain 
showers and thunderstorms. 


Saturday...the front passes through the state during the day. The 
front looks fairly strong with the thermal packing, reinforced by 
the 500 mb wave. So tried to split the day to show the front passing 
through instead of having one full day of rain. 


Saturday night...the front leaves the region. The subsidence behind 
the front looks pretty strong as the surface high builds into the 
western Great Lakes pretty quickly. So will go with rapidly lowering 
chances for precipitation. 


Sunday...Sunday morning the a second 500 mb shortwave pushes into 
the region. The GFS, ECMWF, and NAM all have the 850-700 mb moisture 
relative humidity near 70% with the +3c or so 850 mb temperature. With the northwest flow 
and the qg forcing, would expect at the least, sprinkles and 
self-destruct sunshine. Have some very small chance for sprinkles in 
the evening, the things dry out again. 


Extended (monday through thursday)...with the slow movement of Fay, 
will have to put in the caveat that this forecast may not pan out 
due to the models inability to handle the tropical systems. With 
that said, if Fay stays suppressed to the south then...Monday strong 
high pressure moves into the Great Lakes, and dries things out. This 
looks like it would allow temperatures to rebound. Tuesday, the surface 
high would continue to control the weather. Wednesday, temperatures 
get back to 80 degrees as the high moves to the east and the return 
flow begins to warm things. Thursday, we get into a similar scenario 
like we have today, front in The Rockies and Central Plains with 
tropical moisture moving into the region and the remnants of Fay 
moving into the Tennessee Valley. Will allow for the chance of 
thunderstorms, but it will more than like be dry over most of 
northern Michigan. 


Lutz 


Marine... /issued 357 PM/ 


No concerns through Friday...though winds will be on the increase 
over the water in advance of an approaching cold front. Decent 
shot at small craft conditions Friday night into Saturday as flow 
Cranks up just ahead of the front. 


Lawrence 


&& 


Apx watches/warnings/advisories... 
Michigan...none. 
Lm...none. 
LH...none. 
Ls...none. 
&& 


$$