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Area forecast discussion 
National Weather Service Grand Forks ND 
844 PM CDT Friday Aug 29 2008 


Discussion... 
relatively zonal upper air pattern forecast to increase in amplitude 
tonight as upper level trough begins to dig in the Pacific 
northwest. Upper level jet will stay over southern Canada. Water 
vapor loop indicated an anticyclonic circulation center over the 
Idaho/Montana border moving east about 30 knots. 


High pressure over central ND will move to the Minnesota WI border by 
morning. Precipitable water around half an inch will increase a bit 
in the southwest zones tonight. Cross sections indicate moisture 
increases and warm advection to occur at middle levels tonight. Will 
tweak temperatures a bit tonight. Will update zones. 


&& 


Previous discussion.../issued 258 PM CDT Friday Aug 29 2008/ 


Main forecast challenges include increasing southerly winds this 
weekend and precipitation chances Sunday night into early next 
week. Operational models in fairly good agreement through the 
short term...so used a model blend for this forecast package. Due 
to good run-to-run consistency and the extent to which next weeks 
short wave trough digs south across the western Continental U.S....prefer 
the slower European model (ecmwf) early next week. This resulted in slight 
adjustments to the timing of precipitation...high temperatures and 
strength of southerly winds. 


For tonight...expect fair weather cumulus to quickly dissipate 
after sunset. Winds will be light...gradually shifting to the south 
as surface high pressure moves eastward over the Great Lakes. Under 
mostly clear skies...overnight lows will dip into the upper 40s to 
low 50s. 


Main concern tomorrow will be increasing winds. With surface high 
pressure across the Ohio Valley/Great Lakes and a developing trough 
across the intermountain west...low-level pressure gradient will 
strengthen across the northern plains. Both GFS/NAM show 925 hpa 
winds tomorrow afternoon near 30 kts with upwards of 40 kts at 850 
hpa. Sufficient boundary layer mixing should allow surface winds 
to reach 15 to 25 miles per hour with frequent gusts to 30 miles per hour...especially 
along and west of the Red River valley. Will brief future shifts 
on the possible need for a Wind Advisory. 


Did add slight chance probability of precipitation (20 percent) across Devils Lake basin 
tomorrow night into early Sunday morning. Developing surface 
trough will nose into north central North Dakota...providing weak 
low-level convergence. GFS/NAM also paint ml cape values from 500 
to 1000 j/kg with showalters -2 to -3 across the area at 06 UTC 
Sunday. Any storms to develop will be very isolated and are not 
expected to be severe. 


Focus then turns to strong Pacific short wave trough Sunday night 
into early next week. Successive model runs continue to slow 
forward speed of overall system...keeping precipitation chances 
west of the Red River valley through Monday. High temperatures 
Sunday will be quite warm...approaching 90 degrees in spots...with 
700 hpa thermal ridge moving overhead. Lows Sunday and Monday 
mornings also expected to be quite warm (mid to upper 60s) with 
ample boundary layer mixing overnight due to strong southerly 
winds. 


Long term (monday night through friday)... 
a strong frontal boundary will affect the region early in the 
period. The slightly slower European model (ecmwf) is preferred today...and this 
will mean an unsettled period Monday night-Wed. Thereafter colder air 
will filter into the region...and temperatures will fall below normal. 
Dry weather is expected on Thu/Fri...although we may have to watch 
for some showers under the cold pool and another wave for this 
timeframe as well. 


&& 


Aviation... 
a clear sky is expected overnight. GFS suggest a few middle clouds are 
possible around 10 thousand feet. Fog loop showing isolated patch of 
clouds over central ND. Will not mention isolated clouds overnight. 
Expect windy conditions Sat afternoon with potential gusts to 30-35 
knots. 


&& 


Fgf watches/warnings/advisories... 
ND...none. 
Minnesota...none. 


&& 


$$ 


Hoppes