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Nowcast

• 

• Now as of 12:17 PM CDT on May 25, 2013

  Showers and isolated thunderstorms are occurring mainly along and west of the Interstate 35 corridor. The individual cells are moving to the north but overall expect shower and thunderstorm activity to increase across the region this afternoon. Most of the activity will remain scattered in nature but a broad area of widespread rain could develop south of Interstate 20 this afternoon. Lightning and locally heavy rainfall will be the main threats throughout the day but small hail and gusty winds may occur in stronger storms. Rainfall totals through 3 PM will range up to a quarter of an inch with isolated higher amounts. Otherwise...it will remain cloudy and humid with temperatures in the 70s and lower 80s.

Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Saturday
• 
• High: 81 °
• Low: 68 °
• Chance of T-Storms

• Sunday
• 
• High: 86 °
• Low: 68 °
• Partly Cloudy

• Monday
• 
• High: 86 °
• Low: 70 °
• Partly Cloudy

• Tuesday
• 
• High: 88 °
• Low: 68 °
• Partly Cloudy

• Wednesday
• 
• High: 84 °
• Low: 72 °
• Partly Cloudy

Area forecast discussion...updated 
National Weather Service Fort Worth Texas 
1247 PM CDT Sat may 25 2013 


Aviation... 
/18z tafs/ 


Concerns...thunder through the evening and MVFR ceilings through the 
period. 


A messy taf period continues with low confidence in cloud and 
precipitation trends for the next 18-24 hours. At all the taf 
airports...scattered to broken MVFR ceilings with bases between 
1200-2000 feet persist. However...IFR ceilings are being reported 
southwest of kact where light rain has persisted for much of the 
morning. Ceilings should lift above 2000 feet this afternoon and 
possibly into VFR category before the evening hours but the 
development of showers and thunderstorms in the region may affect 
improving cloud trends. Most of the precipitation this morning has 
remained west of the airports but radar indicates new development 
closer to the taf terminals. Expect isolated to scattered showers 
and thunderstorms to develop throughout the afternoon. Showers 
and thunderstorms could directly impact any of the airports this 
afternoon but think kact as the highest chances of being impacts 
by convection and included a tempo from 19-23z for thunderstorms and rain. Once 
again...expect most of the convective activity to decrease this 
afternoon and a fairly quiet and dry overnight period...but will be 
monitoring the movement of an upper level low over the region for 
any changes to rain/convective chances. Also will be monitoring 
for another area of widespread rain/storms to affect any of the 
airports later today. MVFR ceilings will likely return to all taf 
airports overnight between 09-11z. 


82/jld 


&& 


Update... 


The primary forecast challenge for the next 24 hours is determining 
where and when a middle-level low pressure system /MCV...caused by 
persistent thunderstorm activity that has dissipated/ will move 
over North Texas and bring US more thunderstorm activity. The middle- 
level low from yesterdays thunderstorm activity was difficult to 
locate this morning. 12z upper air analysis indicated middle-level 
cyclonic circulations from northwest Texas south to The Hill Country. 
It is possible that this cyclonic shear axis is yesterdays middle- 
level low...but sheared apart in the larger scale upper level 
ridge over the region. Just before noon...there was a band of rain 
showers and embedded storms extending from Stephenville south to 
the Austin and San Antonio areas which appeared to be associated 
with this shear axis. 


The more intense thunderstorms and rain showers were located at 
the far southern end of this line...causing widespread flooding 
around the city of San Antonio at the time of this discussion. Due 
to the persistence of intense rain shower and thunderstorm 
activity to the south of the County Warning Area...would expect that a new or 
reinforced middle-level low pressure system would develop around San 
Antonio sometime today. There has been some indication of weak 
cyclonic circulations in the lighter rainfall returns to the north 
of San Antonio...in between Temple and Austin. 


Middle-level low pressure systems are created by thunderstorms due 
to large amounts of latent heat released in the middle of the 
atmosphere due to water vapor condensing into water droplets or 
rain. Because this has been going on in an intense fashion near 
San Antonio all morning...think that a middle-level low pressure 
system will likely develop around San Antonio /if it has not 
already/ and become the dominant mesoscale feature driving rain 
and storm chances for North Texas over the next 24 hours. Through this 
afternoon just adjusted probability of precipitation to highlight areas south of 
Interstate 20 as having the highest rain chances today assuming 
the San Antonio low moves slightly east through 7 PM. 


Did not remove rain chances to the north because the weak 
cyclonic shear axis still exists as far north as Wichita 
Falls...so some rain and thunderstorm chances are still warranted 
north of Interstate 20 this afternoon. Severe weather chances 
remain small across all of North Texas as middle-level lapse rates are 
poor due to yesterdays thunderstorm activity and deep layer shear 
remains weak at this time. 


Cavanaugh 


&& 


Previous discussion... /issued 347 am CDT Sat may 25 2013/ 
radar/satellite loop indicates that the weak middle level low is 
likely located near Abilene and 00z 500mb analysis confirms it is 
warm-core in nature. As is often the case with warm-core 
lows...convection is firing before sunrise across The Hill 
Country within a weak low level jet axis where Theta-E advection 
and orographic lift are occurring. Short-term models such as the 
hrrr and RUC suggest that scattered convection will continue to 
expand northward from central Texas into the western zones during 
the morning hours. The GFS appears to be suffering from grid scale 
convective feedback which is resulting in very high quantitative precipitation forecast and 
contaminated mass fields...thus the GFS will not be used in the 
short-term. The NAM seems to be matching current trends and short- 
term models well and therefore it gives confidence to raise probability of precipitation 
today. We expect the best coverage of convection in the western 
zones this morning. Scattered convection will build/expand 
eastward into the eastern zones during the midday/afternoon hours. 
The airmass over the eastern zones will be a bit more unstable due 
to better insolation and a couple of strong storms with gusty 
winds will be possible...but due to weak shear the severe threat 
is low. Highs today in the western zones will only be in the upper 
70s to low 80s due to clouds/rain...with highs in the eastern 
zones reaching the middle 80s. Scattered convection will continue 
into the evening hours before dissipating with loss of heating. 


The warm core middle level low will be exiting the region to the 
northeast tonight...and therefore the rain chances will come to an 
end. Expect a dry Sunday with temperatures rebounding into the 
middle-upper 80s area wide. As an upper level trough develops across 
the inter-mountain west...a surface low will deepen in the High 
Plains Monday. This will bring breezy south winds to the region 
Monday which will likely persist through the week. Low temperatures will 
warm into the 70s area wide by midweek with highs generally in the 
middle 80s east to low 90s west. The southwest flow above the 
surface will bring a thermal inversion into the area. Thus the 
forecast looks dry unless/until forcing arrives to weaken the cap. 


Model guidance remains in poor to fair agreement regarding the 
evolution/ejection of the West Coast upper trough middle-late week. 
The European model (ecmwf) continues to show a very negatively tilted trough 
swinging through the region late Wednesday and Thursday which 
would Bode well for rain. But it continues to be the only model 
that shows the trough ejection like this...and frankly the 500mb 
pattern it presents just does not look realistic. If it were not 
for the European model (ecmwf) being the better of the long range models...I would 
discount it altogether and show a dry forecast on Thursday...but 
for now have retained the slight chance probability of precipitation. The GFS/UKMET/Gem 
forecasts show that the upper energy needed to break the cap will 
likely remain well northwest of the region. Furthermore...the 
dryline also looks like it will remain too far to the west...with 
the GFS showing it as far west as the Texas Panhandle. Storm motions 
will generally be northeast and this means storms would not even 
have a chance to propagate into the County Warning Area either. So in summary the 
rain chances on Thursday at this point are hinging on the European model (ecmwf) 
being correct...and this may be a bit of a long shot. 


Tr.92 






&& 




Preliminary point temps/pops... 
Dallas-ft. Worth, Texas 84 69 87 69 87 / 40 30 10 5 0 
Waco, Texas 83 68 87 68 89 / 50 30 10 5 0 
Paris, Texas 83 67 85 66 85 / 30 30 10 5 0 
Denton, Texas 84 67 86 68 87 / 40 30 10 5 0 
McKinney, Texas 84 67 85 68 87 / 30 30 10 5 0 
Dallas, Texas 85 71 87 70 89 / 40 30 10 5 0 
Terrell, Texas 84 67 86 68 88 / 40 30 10 5 0 
Corsicana, Texas 84 67 88 68 89 / 40 30 10 5 0 
Temple, Texas 82 67 87 68 88 / 60 20 10 5 0 
Mineral Wells, Texas 81 66 87 67 89 / 40 20 10 5 0 


&& 


Forward watches/warnings/advisories... 
none. 


&& 


$$ 


82/69