709 
fxus64 kfwd 180057 aab 
afdfwd 


Area forecast discussion...updated 
National Weather Service Fort Worth Texas 
757 PM CDT Wednesday Mar 17 2010 


Update... 
upper low is moving across northeast Texas this evening and 
although there have been a few light radar returns associated with 
passing clouds...more significant convective activity appears very 
unlikely. 00z forward sounding indicates limited moisture and only a 
small amount of available instability. For tonight...will remove 
mention of isolated thunderstorms and make only some minor 
adjustments to the hourly gridded forecast. 


91/Dunn 


&& 


Aviation... 
00z taf package 


An upper level trough over eastern Oklahoma continues to slide 
south this evening. Some middle level moisture associated with the 
trough has resulted in a patch of middle level clouds moving through 
North Texas. After this patch of clouds moves south...generally 
sky clear is expected to prevail but a few small cumulus around 040 may 
develop Thursday afternoon. North winds are now established across 
the area as a surface high moves into the region. The winds will 
become light and variable overnight and eventually shift to the 
south late Thursday afternoon. Wind speeds will remain less than 
10 kts through the period and VFR will prevail. 


82/jld 


&& 


Previous discussion... /issued 343 PM CDT Wednesday Mar 17 2010/ 


19z water vapor imagery indicates that upper low continues to 
slide south through eastern OK towards North Texas. Sunny skies have 
allowed temperatures to climb into the lower 60s for much of North 
Texas however dew point values have mixed out into the upper 30s and 
skies remain mostly clear at forecast time. Models continue to 
indicate the best large scale forcing for ascent will spread over 
northeast Texas after 21z...so despite lack of an enhanced cumulus field 
will keep mention of isolated thunderstorms in the forecast for the late 
afternoon hours. Latest forecast soundings indicate only weak 
instability as the trough moves through the area...limiting 
overall potential for any organized convective weather. Additional 
heating will create more of an inverted v type sounding in the low 
levels however overall microburst potential continues to look 
minimal given maximum Theta-E difference with height of about 10 k. 
Any isolated storms that manage to develop should dissipate 
quickly with the loss of daytime heating...therefore we have about 
a 3 hour window of opportunity where storms may be possible. 


Tonight...the shortwave trough will move southeast through the 
forecast area spreading large scale forcing for subsidence over 
North Texas during the overnight hours. Any cloud cover should also 
dissipate quickly after sunset allowing for an ideal radiational 
environment tonight. Lows will likely dip into the upper 30s to 
near 40 degrees for most locations tonight as a result. 


Thursday through Saturday...upper level ridging will build into the 
Southern Plains on Thursday as another strong shortwave trough 
digs south over the western Continental U.S.. with the approach of the trough 
and upper level ridging over the Southern Plains...a quick return to 
low level southerly flow is expected by Thursday afternoon. As the 
trough approaches Lee side cyclogenesis will intensify over 
western Texas strengthening the low level pressure gradient and 
increasing low level southerly flow through Friday. 


By Friday afternoon persistent southerly flow is expected to 
bring a return of modified Gulf moisture into the Southern Plains 
and possibly an accompanying deck of Strata cumulus over North Texas 
by late Friday afternoon. The approaching storm system looks to 
move through the Southern Plains in two pieces. The first 
shortwave trough is a relatively weak upper level feature that will 
move over North Texas just after sunset on Friday. This appears to be 
a weaker southern stream trough that gets kicked out through the 
Southern Plains ahead of the much stronger upper trough digging 
southeast from the western Continental U.S.. this first trough will spread 
some large scale forcing for ascent over North Texas Friday night as 
well as allowing a cold front to begin to enter the region from 
northwest to southeast. Based on the degree of Gulf moisture that 
returns ahead of this system/cold front we should see a line of 
convection develop along the front and move southeast Friday 
night. In general expect these storms to be primarily elevated in 
nature as forecast soundings indicate that the cold front will 
need to push through before air parcels can reach their level of free convection Friday 
night. In general feel that any severe weather threat will likely 
be marginally severe hail which is typical with an elevated thunderstorm 
environment. 


The 12z guidance has lined up in generally good agreement on 
bringing the cold front through North Texas late Friday night through 
Saturday morning. Have placed the best probability of precipitation in across North Texas 
from 06 to 18z on Saturday near the expected frontal position at 
these times. Behind the cold front...would expect that 
precipitation would end quickly with fairly strong isentropic 
downglide/subsidence following frontal passage. The only real alternative to 
this solution was the 17/00z European model (ecmwf) which brought a fairly strong 
trowal region through North Texas behind the cold front late on 
Saturday and into Saturday night. With the 12z European model (ecmwf) further north 
and more neutrally tilted with the upper trough in line with other 
operational guidance have discounted this solution for now. 


Saturday night/Sunday morning...behind the cold front model 
guidance is consistent in indicating an unseasonably cold airmass 
will settle into North Texas. With a good radiational cooling 
environment looking to set up over the region Saturday 
night...temperatures could dip below freezing for portions of the 
County Warning Area by Sunday morning. May need to consider freeze watch or 
warning if this continues to look likely in the days ahead. 


Extended...only significant change was to introduce slight chance 
of thunderstorms into the forecast from Tuesday night into Wednesday as 
European model (ecmwf) and GFS both indicate another strong trough will move into 
the Southern Plains. Otherwise no significant changes made to 
previous forecast. 


Cavanaugh 


&& 


Preliminary point temps/pops... 
Dallas-ft. Worth, Texas 41 67 46 70 43 / 0 0 0 5 40 
Waco, Texas 40 67 45 71 46 / 0 0 0 5 40 
Paris, Texas 38 65 42 68 43 / 5 0 0 5 40 
Denton, Texas 37 67 45 70 42 / 0 0 0 5 40 
McKinney, Texas 38 66 43 69 42 / 0 0 0 5 40 
Dallas, Texas 42 67 46 70 42 / 0 0 0 5 40 
Terrell, Texas 40 67 44 69 45 / 0 0 0 5 40 
Corsicana, Texas 40 67 45 70 45 / 0 0 0 5 40 
Temple, Texas 39 68 43 71 47 / 0 0 0 5 30 


&& 


Forward watches/warnings/advisories... 
none. 


&& 


$$ 

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