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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
650 am EST Monday Nov 23 2009 


Latest update...aviation... 


Synopsis...(438 am EST Monday Nov 23 2009) 
the warmer than normal temperatures will continue into middle week as 
southerly winds prevail. The chance of rain returns by Tuesday 
night into Wednesday as low pressure enters the western Great 
Lakes. It will become cooler behind this system and some snow could 
mix in with the rain by late Wednesday night into Thanksgiving day. 
At this point little to no snow accumulation is expected. 


&& 


Short term...(438 am EST Monday Nov 23 2009) 
(today through wednesday) 
the main focus early in the short term was on fog potential. Then 
attention turns to the rain chances that will arrive Tuesday night 
into Wednesday. 


Light fog was widespread across the County Warning Area this morning...however winds 
of 20-25 knots in the boundary layer was keeping any dense fog at a 
minimum. The mixing has resulted in a stratus deck that covers much 
of the area early this morning. These clouds are rather shallow and 
it will be a tough call as to whether the low November sun angle 
will be able to burn off these low clouds through the day. This 
appears most doubtful across areas south of I-96 where moisture will 
advect northward from the wave over southern Ohio. In fact...I have 
added the possibility of a sprinkle to the southeast County Warning Area by late 
afternoon/early evening. A few peaks of the sun may occur over the 
NE County Warning Area however...where the moisture will remain shallow and enough 
mixing may scour out some of the clouds. 


By late tonight weak upper ridging will slide through. This will 
help relax the pressure gradient and fog appears like a good bet 
again tonight. This could become dense across any area that briefly 
clears. 


Will remove all probability of precipitation in the western County Warning Area for Tuesday as a slower 
trend continues with the ejection of the plains low. This should be 
another repeat of today where...with little flow...we may struggle 
to see much daytime clearing. 


A stacked low pressure will be over southeast Iowa by Tuesday evening. It 
will move slowly NE to Northern Lake Michigan by Wednesday evening. 
With it remaining to our west we will stay on it/S warm side and 
only rain is expected initially. As with systems of this type...a 
slower solution usually wins out. So have bumped back the 
likely/categorical probability of precipitation until late Tuesday night and continued them 
into Wednesday. It appears that the left exit region of the upper 
jet stays to our west...so heavy rain is not expected. 


&& 


Long term...(438 am EST Monday Nov 23 2009) 
(wednesday night through sunday) 
100-130 knots upper level jet diving south from central Canada through 
the northern plains will help carve out a long wave trough over the Great 
Lakes region for Thanksgiving. The result will be colder air and 
showery precipitation in the form of mixed rain and snow showers. 


While the air prognosticated at 800 mb around -5c supports snow on 
Thanksgiving...the surface temperatures are still prognosticated to be near 40f which 
supports mostly rain. The best opportunity to experience any wet 
snow would be Thursday night and early Friday when surface temperatures will be 
a little cooler and the closed upper low will still be nearby. 
Nothing significant in terms of accumulation is expected at this 
point. 


The longwave trough/cold air is prognosticated to move east of the area 
Friday and Friday night as the next upstream system digs into the 
northern rockies. Upper ridging in between these two troughs will reside 
over the Great Lakes region Saturday and Sunday...which should 
promote dry conditions with slightly above normal temperatures. 


&& 


Aviation...(650 am EST Monday Nov 23 2009) 
widespread IFR/LIFR stratus with bases below 1k feet formed 
overnight and will likely linger through 14-16z. It/S uncertain 
however whether the stratus will totally scatter out and go VFR by 
18z or just gradually lift to an MVFR deck with a few breaks in it. 
Have opted to forecast the latter in the tafs since it is late November 
and the sun angle does little to help with mixing out stratus. 


It is Worth noting the idea shown by the hrrr RUC model and that is 
that the stratus will clear from southeast to northwest this 
morning. This solution is certainly gaining some credence since 
current satellite fog imagery shows that most of Ohio is fog/stratus 
free and low level trajectories are from the southeast. If this 
starts to happen... will amend the tafs and time the clearing line 
into the area. 


More fog/stratus issues are likely again tonight... with IFR 
category or lower a possibility again. 


&& 


Marine...(438 am EST Monday Nov 23 2009) 
areas of fog will be an issue early this morning and again late 
tonight. Winds and waves however will remain fairly low... 
especially for Nov. 


&& 


Hydrology...(438 am EST Monday Nov 23 2009) 
rainfall from Tuesday night and Wednesday will be rather light with 
most areas receiving between a quarter and a half inch of rain. 
This should have little impact on Hydro. 


&& 


GRR watches/warnings/advisories... 
Michigan...none. 
Lm...none. 


&& 


$$ 


Synopsis: jk 
short term: jk 
long term: Meade 
aviation: Meade 
marine: jk 
hydrology: jk