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Area forecast discussion...updated 
National Weather Service Fort Worth Texas 
131 PM CDT Thursday Aug 21 2008 


Update... 
will issue a quick update to increase probability of precipitation in the southwest based on 
current radar trends. Instability should be sufficient to sustain 
scattered showers/storms through sunset. 


No other major changes at this time. 
79... 
&& 






Aviation... 
1233 PM 
dry air continues to work into the middle-levels of the atmosphere as 
subsidence behind the upper trough moves in. The primary areas for 
precipitation will be east and south of the metroplex where the best 
moisture remains. Coverage is too low to mention any precipitation for the 
metroplex tafs but will monitor the situation throughout the 
afternoon and amend tafs if necessary. 


Dont think we will see a complete repeat of this mornings IFR ceilings 
and MVFR visibilities. Moisture layer just off the surface will 
not be as deep and surface wind speeds will also be around 8 
knots keeping the air relatively mixed. But with saturated 
soils...cant rule out scattered low clouds and slight restrictions in 
visibility. 


85/New Hampshire 


&& 


Update... 
forecast looks on track...just minor changes to account for latest 
trends in clouds/dewpoints/winds. Removed probability of precipitation west of I-35 as 
area will be under a region of increasing heights/subsidence 
through the afternoon hours. Low level moisture (thus instability) 
will remain across the eastern County Warning Area...and coupled with drying aloft 
there is a low potential for wet microbursts this afternoon. 
Coverage of convection should remain near or less than 30 percent 
given lack of dynamic forcing that had been present the last 
several days. Tr.92 


&& 




Previous discussion... /issued 321 am CDT Thursday Aug 21 2008/ 
the upper level low that has brought beneficial but flooding rains 
to North Texas the past few days is now sliding into Kansas /per 
RUC analysis/. The associated trough extends south across Texas 
with the axis centered over the western half of the County Warning Area. Some weak 
shortwaves continue to move around the base of the trough. One 
shortwave is now exiting northeast Texas and is aiding in shower 
and thunderstorm development in our extreme NE County Warning Area. A stronger 
shortwave is forecasted to skirt the Red River this afternoon. The 
best chance for rain today will be across the eastern half of the 
County Warning Area...ahead of the trough axis and approaching shortwave...where 
lift will be strongest. Another potential player for today could 
be the left over boundary/surface trough running northeast to 
southwest across almost the middle of the County Warning Area. With some heating 
later today...showers and thunderstorms may develop along that 
boundary or any other residual boundaries. However...will have the 
highest probability of precipitation in the east. Precipitable waters  will remain near 2 inches in the 
east so heavy rainfall is still a threat today in that area. 


The weather pattern over the next several days will remain 
somewhat unsettled as the remnants of the upper level low never 
really leave the region and the upper level ridge to the west 
never really builds in. The upper level ridge only makes it as far 
as the Texas Panhandle before being halted. All models are in good 
agreement that energy from the trough will remain over northeast 
Texas and then drift back over North Texas over the next several 
days. Thus will keep 20-30 probability of precipitation in the forecast through the 
weekend with best chance for rain again in the east and southeast. 
Sunday looks to be the next best chance for rain across all of 
North Texas with the highest probability of precipitation along the Red River. By 
Monday...the upper level ridge gets nudged back west as Fay moves 
into the central gom coast and northerly flow aloft sets up. 
Models suggest that several weak disturbances will ride the 
northerly flow into Texas and will continue 20 probability of precipitation for the 
afternoon/evening hours through the remainder of the forecast. 


Have stuck close to guidance for high temperatures in the beginning 
of the forecast and then undercut guidance a degree or two for the 
last few days. High temperatures will mostly top out in the 
90s with a few scattered upper 80s this weekend. Reason for 
undercutting guidance on days 6 and 7 was thought MOS temperatures were 
too high for northerly flow. Overnight lows will continue to be 
in the upper 60s to middle 70s. 


82/jld 








&& 






Preliminary point temps/pops... 
Dallas-ft. Worth, Texas 91 74 94 75 92 / 20 10 10 10 30 
Waco, Texas 92 72 93 74 92 / 10 10 20 10 30 
Paris, Texas 87 70 91 71 90 / 40 10 30 10 30 
Denton, Texas 91 72 93 72 92 / 20 10 10 10 30 
McKinney, Texas 91 71 91 71 92 / 20 10 10 10 30 
Dallas, Texas 91 72 92 73 92 / 20 10 10 10 30 
Terrell, Texas 91 72 94 73 91 / 20 10 20 10 30 
Corsicana, Texas 91 72 93 73 93 / 20 10 20 10 30 
Temple, Texas 92 71 95 73 91 / 10 10 20 10 30 


&& 


Forward watches/warnings/advisories... 
none. 
&& 


$$ 


85/92/25