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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
342 am EDT Thursday Jul 24 2008 


Latest update...all except aviation... 


Synopsis...(342 am EDT Thursday Jul 24 2008) 
it will be mostly sunny today with high pressure in control of our 
weather. Dry weather will continue tonight into Friday. An 
approaching front will bring our next chance of rain from late 
Friday through Friday night into early Saturday. 


&& 


Short term...(342 am EDT Thursday Jul 24 2008) 
(today through Saturday afternoon) 


High pressure will result in mostly sunny skies today. A dry airmass 
in place and subsidence will really limit cumulus potential. A few high 
clouds should advect in from the west-northwest over the top of the 500 mb ridge... 
but that will be about it for cloud cover. 


Short range numerical guidance has exhibited a cool bias with regard 
to maximum temperatures the past few days. For instance 00z and 06z mav 
guidance from the 23rd gave GRR an 80 maximum yesterday (met gave GRR a 
79)... and it was noted GRR made it all the way to 84 degrees 
yesterday. 


Today we will have abundant sun and develop deep mixing... resulting 
in afternoon dew pt values lower than what model guidance suggests. We 
believe dew points will tumble into the middle to upper 40s this afternoon 
(away from the lake). Maximum temperatures will generally surpass what 
numerical guidance suggests once again... so we raised the maximum temperature 
forecast slightly (by about 1-3 degrees). We went with a 83 maximum for GRR 
and I would not be surprised if it makes a run at 84-85. 


Model time height relative humidity forecasts suggest skies will be clear to partly 
cloudy tonight. Friday looks partly sunny... dry and warm as we get 
into a stronger SW flow warm air advection regime out ahead of the front. The best 
surface convergence will move across our County warning forecast area Friday night into early 
Saturday. Elevated instability is quite impressive... with 00z GFS 
guidance indicating 850 mb convective available potential energy will reach 1000-1500 j/kg with 850 
Li/S of around -2 to -4 Friday night. 


However the most vigorous positive vorticity advection will pass well north of our County warning forecast area 
across the Lake Superior region. Frontal timing is not the most 
favorable for severe weather either. Nevertheless... a few strong to 
severe storms cannot be ruled out given the magnitude of elevated 
instability... sufficient low level moisture and a forcing mechanism 
as the front approaches. A few lingering showers and storms Saturday 
morning across our southern County warning forecast area will be followed by partly sunny 
skies. 


&& 


Long term...(342 am EDT Thursday Jul 24 2008) 
(saturday night through wednesday) 
while on the face of it dry weather would be indicated for the 
western Great Lakes through the extended period (gfs 00z ensmelbes 
support this idea) there are some major questions of the validity of 
this idea. For some time now there has been a mean trough over the 
eastern United States with a ridge somewhere inland of the West 
Coast (looking at 30 day loop of global 500 heights) with the next 
down stream trough mostly near 140-150w. All the models and 
ensembles agree there will be some phasing of the northern and 
southerns steam near the Gulf of Alaska by late in this coming 
weekend. That would force the West Coast ridge inland by 15 degrees 
of longitude by Sunday. If that all happens than breaking Pacific 
upper waves... coming through long wave ridge... would have a better 
chance of bringing Pacific upper level waves into the Great Lakes 
next week. That would mean warmer and wetter conditions coming back 
to this area. The latest runs of the European model (ecmwf) and GFS support this idea 
with a decent system in the Tuesday to Wednesday time frame. The European model (ecmwf) for two 
days had rain in the western Great Lakes Sunday night but this was 
not on the 00z run tonight. 


One other major point... checking the msu ag stations in the area... 
the soil moisture has plunged in the past week. That happened even 
with the scattered showers coming through from time to time in the 
past week. That lower soil moisture (about half of what was in the 
soil a week ago) has lead to models under forecasting high 
temperatures over the past 3 day (days with more sunshine). I 
believe this condition will persist until it really starts raining 
again. More than likely our highs are under forecast on all days 
sunshine will prevail through our medium range forecast. 


Bottom line to all of this is while we have a dry forecast Sunday 
through Wednesday...and I did not change this... I have significant 
questions about the validity of that. However there is not enough 
model continuity for ME to chance to forecast at this point. I also 
did not change the high or low temperatures but I would expect most 
of the highs to be to cool sun through Wednesday if we get a the amount of 
sunshine we are currently forecasting to happen. The rub there 
through is if the upper ridge does get flattened by wave breaking 
from Pacific shortwaves... there would be more clouds and 
precipitation which would mean the highs would be fine but the lows 
would be to cold. Thus I am leaving all as is for now and calling 
the best we can do for now. 


&& 


Marine...(342 am EDT Thursday Jul 24 2008) 
west winds of 5 to 10 kts will back to the SW today and increase to 
10 to 15 kts. Wave action should be minimal (generally only around a 
foot or less). Wave heights will be higher in and near thunderstorm 
activity late Friday through Friday night. 


&& 


Aviation...(1145 PM EDT Wednesday Jul 23 2008) 
VFR conditions are expected the next 24 hours (06z-06z). Only some 
middle and high level clouds will affect the area...with bases above 
15000ft. Light winds tonight with high pressure overhead...giving 
way to westerly winds around 10 knots on Thursday. 


&& 


Hydrology...(342 am EDT Thursday Jul 24 2008) 
no significant Hydro issues are expected through the weekend. Our 
next chance of rain will come late Friday through Friday night into 
early Saturday. However basin average quantitative precipitation forecast amounts with that system of 
only a quarter to third of an inch are anticipated... which 
certainly would not be enough to cause Hydro issues. 


&& 


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


&& 


$$ 


Synopsis: Laurens 
short term: Laurens 
long term: wdm 
marine: Laurens 
aviation: Duke 
hydrology: Laurens 

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