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Area forecast discussion...updated 
National Weather Service Fort Worth Texas 
1136 am CST Sat Nov 21 2009 


Aviation... 
18z taf package 
persistent cloud cover continues across North Texas this morning 
with ceilings varying from VFR to IFR. Most sites east of 
Interstate 35 are now reporting VFR while locations along and west 
of Interstate 35 are reporting IFR. Either way...expect ceilings 
to improve to bkn050 during the early afternoon hours at all sites 
as an upper level trough continues to shift into East Texas and 
breaks in the clouds help heat the lower levels of the atmosphere. 
With the slow eastward advancement of the upper level 
trough...models are indicating that a layer of moisture around 850 
mb will remain in place today and will keep broken VFR ceilings in the 
taf through 22/02z. Clouds should then scatter and eventually 
become clear overnight. 


Other concern for the overnight hours is the development of fog 
due to moisture on the ground and light winds overnight. Will 
prevail 3 sm at all sites beginning at 22/07-08z but lower kact 
into IFR near daybreak. There is a chance that the metroplex will 
see IFR visibilities as well. Conditions should improve by late 
morning Sunday. 


82/jld 


&& 


Update... 
this morning/S visible satellite loop shows there are breaks in the 
clouds across the northeastern and far north central parts of 
North Texas. The clearing line to the west of an Abilene to San 
Antonio line as of 11 am. As the upper level trough over East 
Texas moves eastward this afternoon and evening...we should see 
the clearing line progress eastward. Have bumped up this afternoon/S 
temperatures a few degrees across the extreme western zones where 
sunshine later this afternoon should allow temperatures to warm 
into the middle to upper 60s. Light winds...a wet ground and 
clear/clearing skies should allow for some fog to develop late 
tonight. Thus have introduced fog into the forecast for late 
tonight through middle morning Sunday for most of the forecast area. 


58 


&& 


Previous discussion... /issued 448 am CST Sat Nov 21 2009/ 


Today...areas of light drizzle are expected to continue to develop 
across much of North Texas through the morning hours. This light 
precipitation will reduce visibilities so placed mention of fog in 
the morning forecast as well. A more organized area of stratiform 
rainfall exists in the Waco area early this morning...and this 
seems to correlate well with large scale forcing for ascent 
associated with the upper level shortwave trough located over 
southeastern Texas. This upper level feature is expected to move off to 
the northeast today bringing subsidence through North Texas bringing 
light precipitation to an end by this afternoon. Models show upper 
and middle level clouds dissipating quickly as subsidence builds over 
North Texas...however low clouds are expected to be a bit more 
resilient and will begin to dissipate during middle afternoon hours. 
Today's highs are tricky as breaks in the cloud cover are likely to 
cause temperatures to rise above the lower 60s that are in the 
forecast...however at forecast time low level stratus continued to 
expand north and west of the County Warning Area...so low clouds look likely to 
hang in for much of the day. 


Tonight through Monday...skies look to clear out tonight if not 
during the late afternoon hours...and a dry forecast looks in store 
for this period as weak upper level ridging builds over the Southern 
Plains. The next strong upper level disturbance is expected to 
move into the northwestern Continental U.S. During the day on 
Sunday...bringing cyclogenesis over the central and northern 
plains and bringing a return to low level southerly flow over 
North Texas. Southerly flow looks to continue through the day on 
Monday...and 24-36 hours of southerly winds will send some Gulf 
moisture back north through the County Warning Area and into MO valley by Monday 
evening. 


Monday night and Tuesday...the strong shortwave trough looks to 
move into the plains and then into the Great Lakes region by 
Tuesday evening. This will send a cold front south through North Texas 
beginning Monday night and moving south through the entire forecast 
area by Tuesday afternoon. While Gulf moisture is expected to 
return to the Southern Plains...did not place thunderstorms in the 
forecast as the Gulf moisture return is somewhat shallow in nature 
and the bulk of the large scale forcing for ascent remains well 
north of the Red River per 00z model guidance. Regardless...think 
low level moisture is sufficient to allow rain shower activity to 
develop along the cold front as it moves through the area. For now 
do not expect heavy rainfall or any severe weather associated with the 
front. Drier air behind the front should bring a return to mostly 
clear skies by Tuesday evening. 


Extended forecast...another strong shortwave trough is expected to 
dig into the back of the exiting trough over the Great Lakes 
region Wednesday and Wednesday night. This would normally bring a 
back door type cold front through the Southern Plains...but chances 
are the upper trough will only send a reinforcing shot of 
cool...dry air through the region. With meridional flow remaining 
over the plains in between these two systems a return to southerly 
flow and associated moisture return seems unlikely at this 
time...so did not bring much in the way of clouds or precipitation into 
the County Warning Area with this second feature. Beyond Thursday the models begin 
to diverge on solutions in the large scale flow pattern...with too 
much uncertainty in any one solution have maintained a dry 
forecast for now as any return of good quality Gulf moisture seems 
unlikely with two shots of cool...dry air coming in earlier in the 
forecast period. 


Cavanaugh 


&& 




Preliminary point temps/pops... 
Dallas-ft. Worth, Texas 62 46 67 47 70 / 20 0 0 0 0 
Waco, Texas 62 46 68 49 70 / 40 0 0 0 0 
Paris, Texas 61 43 66 45 67 / 20 0 10 0 0 
Denton, Texas 62 44 67 45 69 / 20 0 10 0 0 
McKinney, Texas 63 43 66 45 68 / 20 0 10 0 0 
Dallas, Texas 62 47 67 50 69 / 20 0 0 0 0 
Terrell, Texas 63 43 67 45 69 / 20 0 0 0 0 
Corsicana, Texas 63 44 68 48 70 / 40 0 0 0 0 
Temple, Texas 62 47 69 47 70 / 30 0 0 0 0 


&& 


Forward watches/warnings/advisories... 
none. 


&& 


$$ 


82/58 

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