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fxus63 kgrr 201101 
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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
700 am EDT Sat Mar 20 2010 


Latest update...short term and aviation... 


Synopsis...(330 am EDT Sat Mar 20 2010) 
a strong cold front has moved through lower Michigan. A band of 
light rain and snow will slowly move south across the region today. 
Little accumulation is expected...but temperatures around 40 will be 
quite a change from the past several days. The cold air won't last 
long as temperatures in the 50s are expected by Monday. 


&& 


Short term...(700 am EDT Sat Mar 20 2010) 
(today through monday) 


The major forecast concerns is the snow into early afternoon. 


I did a quick update to the zones to account for the latest RUC 06z 
and RUC 08z plus the NAM from the 06z runs that show strong fgen in 
the 850 to 700 mb layer between now and 18z north of Interstate 96. 
Satellite loops show cloud tops cooling over northern Illinois...Central Lake Michigan 
and southeast WI at 630 am. The increased reflectivities on the composite 
radar loops suggest the trend on the models make sense. Both the RUC 
and NAM suggest from .15 to .25 inches of water will fall by 4 PM 
between Interstate 94 and Route 10. Also... given temperatures have 
fallen to near freezing by Interstate 96 and upper 20s by Route 10 I 
do believe the snow will accumulate on grassy surfaces this morning 
when snowfall rates should be the heaviest. 


The 130 knot jet entrance region north of Lake Superior...which is 
driving the fgen...will be east of the area by late afternoon and at 
that time this snow band will fall apart and the snow will come to 
an end. 


I adjusted the hourly surface temperature grids to keep them near freezing 
in the snow area through noon or so...which given the dew points 
coming in are in the teens...makes sense the temperatures will not 
rise at the surface until the snow stops. As a result of that I 
lowered the high temperatures a touch too. 


Previous discussion...the other main weather maker is the low that 
is developing in the Southern Plains. This occluded low is forecasted to move 
east-northeast through Kentucky to WV. The deformation precipitation that we see today 
should wind down late tonight across the far south. Then as the low 
over the southern US moves east-northeast toward Kentucky...precipitation will push back 
north. I am not convinced that we/ll see precipitation from that low in the 
southern County Warning Area but added a slight chance south of I-94 Sunday night and 
Monday. The rest of the County Warning Area will be dry. We/ll see increasing 
sunshine from south to north Monday 




&& 


Long term...(330 am EDT Sat Mar 20 2010) 
(monday night through friday) 
the short story forecast from Monday night through Friday is partly 
cloudy with unseasonably mild temperatures through the week. This is 
largely fostered by the continued split flow of the northern and 
southern stream polar jet. I see no reason to believe this will 
change in the near future. 


The next series of shortwaves on the northern and southern stream 
come through the longitude of the Great Lakes in the Wednesday time 
frame. The issue with the models with that system is how much can 
the northern stream dig into the Great Lakes verses how much can the 
southern stream shortwave that is currently moving into West Coast 
longwave ridge stop that from happening? The southern stream wave 
comes through the longwave ridge on the European model (ecmwf) with more energy then 
it does on the GFS. The result is the European model (ecmwf) build enough of a 
shortwave ridge in front of it to prevent the northern stream from 
digging so much as shown by the GFS. 


The European model (ecmwf) is in the Camp that allows the southern stream to rule the 
day while the GFS seems to want more northern stream energy. Part of 
the problem with the GFS is it kills to much of the upper wave 
energy as the system moves through the western ridge more. The European model (ecmwf) 
builds a better upstream ridge since it does not weaken the system 
as much as it moves through the longwave ridge. The better upstream 
ridge on the European model (ecmwf) in turn cuts off the polar front before it can 
really get through here. Either way I do not see much chance for 
precipitation Wednesday. So... I dropped the precipitation Wednesday 
night into Thursday since neither model show any potential for the 
precipitation anyway. Even the probability of precipitation I held onto for Wednesday is 
more than questionable. 


The next system comes in Friday and that has the same issue. That 
is... does the northern stream dig into the Great Lakes or does the 
next southern stream wave build enough of an upstream ridge to keep 
the cold air in canada? My only worry with all of this is that very 
dense cold air over southern Canada by middle week is not all that far 
form lower Michigan. Sometimes air that cold and dense has a way of 
coming this far south even through the models do not forecast it to. 
For now though... I vote for the southern stream to win but kept the 
grids mostly as is for now. 




&& 


Aviation...(700 am EDT Sat Mar 20 2010) 
I expect widespread IFR ceilings/visibility in snow over the I-96 taf sites 
middle to late morning before the fgen band falls apart by early 
afternoon. It is less assured that this snow band will get as far 
south as I-94 this afternoon. As a result I have the lowest 
ceilings/visibility in the I-96 taf group now. All sites should become VFR 
tonight as the northeast winds through 850 mb bring in the low level 
dry air. 


&& 


Marine...(330 am EDT Sat Mar 20 2010) 
Small Craft Advisory remains in effect today for the northern and far southern nsh areas. 
North winds will affect those areas with higher waves the most. As 
winds subside late in the day...waves will diminish. 


&& 


Hydrology...(330 am EDT Sat Mar 20 2010) 
water levels will continue to recede through the weekend. 
Precipitation from this next system is expected to remain under a 
quarter inch. 


&& 


GRR watches/warnings/advisories... 
Michigan....none. 
Lm....Small Craft Advisory today from St Joe to South Haven and from 
Whitehall to Manistee. 


&& 
$$ 


Synopsis: 93 
short term: 93 
long term: wdm 
aviation: wdm 
marine: 93 
hydrology: 93 

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