Area forecast discussion
National Weather Service Fort Worth Texas
348 PM CDT Friday may 24 2013
Discussion...
12z upper air analysis showed a well-defined middle-level low
pressure system near San Angelo this morning. Visible satellite
imagery and regional radars indicate that this low was moving
slowly to the northeast this afternoon with a nearly solid band of
showers and thunderstorms extending from Breckenridge South
through Austin on its eastern edge. According to a 19z aircraft
sounding around the dfw area the atmosphere remains largely
uncapped this afternoon with 1500 to 2500 j/kg of cape available
for storm growth.
Through tonight....aside from the middle-level low moving towards
the County Warning Area...the larger scale flow regime aloft over North Texas is
anticyclonic flow in weak ridging in place over the region. This
has left a moderate cape/very low shear environment in place over
North Texas which is more of a rain pattern we see in the Summer
months. Due to the very weak shear in place and little cap...think
a single cell to multicell storm Mode will continue through the
evening hours with a marginal severe weather threat in the form of
hail up to quarter size and downburst winds of 60 miles per hour. Locally
heavy rainfall may end up being the biggest hazard wherever storms
train over any one location for a couple of hours. The threat for
heavy rain and flooding is expected to remain localized through
this evening and will not be issuing any flood or Flash Flood
Watch with this forecast package. With the loss of daytime
heating...most high resolution guidance agrees in a sharp downward
trend to the coverage and intensity of storms associated with the
middle-level low.
Saturday...the middle-level low pressure system may be enhanced by
this afternoon and this evenings thunderstorm activity ongoing
across western counties of north and central Texas. Because the middle-
level low was created by thunderstorm activity yesterday...it
seems reasonable to assume that this feature will remain at least
as strong as it was today and should support some thunderstorm
chances across North Texas tomorrow. As a result left in a mention of
thunderstorms across all of North Texas through tomorrow evening. At
this time left precipitation chances at 20 percent because the
middle-level low may be right on top of the County Warning Area...where subsidence
and poor middle-level lapse rates are likely to reside. The middle-level
low is warm core...and does not contribute to destabilizing the
atmosphere as a result. With generally cloudy skies associated
with the low and weaker middle-level lapse rates...instability is
expected to be much weaker than it was today across North Texas which
will likely limit the amount of thunderstorm activity that we see.
Still cannot rule out isolated storms across the County Warning Area...especially
during the peak heating hours of the day. With many outdoor
activities likely to be ongoing during the start of Memorial Day
weekend...isolated storms producing lightning and locally gusty
winds can still be hazardous and should be taken seriously. This
is especially true if you happen to have plans out on area lakes
and reservoirs this weekend.
Sunday and Monday...the middle-level low is expected to meander east
in weak ridging aloft leaving subsidence in place over North Texas.
Subsidence should help get rid of the 70s dew points we have had
in place the past several days...although we will remain warm
under mostly sunny skies. With slightly drier air in
place...expect Monday to be a few degrees warmer than Sunday to
finish off Memorial Day weekend. Chances for thunderstorms look
low for now assuming subsidence does its job in drying out the
lower troposphere and placing a capping inversion over the region.
Mid-week...for Tuesday and Wednesday...the GFS and European model (ecmwf) agree
that we transition to southwest flow aloft as a large upper trough
builds over the western Continental U.S.. the large trough out west is
somewhat complex and composed of several large shortwaves...but at
least through Wednesday it seems that model consensus keep the
bulk of this strong energy north of the region. Southwest flow
aloft usually advects a Stout elevated mixed layer over the
region...and this is expected to help keep US dry through
Wednesday despite the resurgence of strong southerly low-level
flow and good Gulf moisture return.
On Thursday...went ahead and reintroduced 20 probability of precipitation into the
forecast because the European model (ecmwf) has been consistent in bringing a
strong shortwave trough over the South Plains. The GFS does not
support this...but in general has offered a wider spread of
solutions regarding this upper trough when compared to the European model (ecmwf).
While that does not guarantee the European model (ecmwf) will verify...at this
point wanted to side with the more consistent solution which would
bring a good chance of storms back into North Texas late next week.
Should this verify...some severe storms would be possible but it
is much too far out to worry about that right now. When confidence
in the large scale flow is low...confidence in smaller scale
details like severe storm hazards is extremely low. Will continue
to watch late next week in future forecasts.
Cavanaugh
&&
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 70 84 69 86 70 / 30 20 20 5 5
Waco, Texas 70 84 68 88 70 / 30 20 20 5 0
Paris, Texas 65 84 67 84 67 / 20 20 20 10 5
Denton, Texas 68 83 67 86 70 / 30 20 20 5 5
McKinney, Texas 69 85 68 86 68 / 30 20 20 5 5
Dallas, Texas 73 87 72 88 70 / 30 20 20 5 0
Terrell, Texas 70 87 69 88 68 / 20 20 20 5 0
Corsicana, Texas 70 85 69 88 69 / 30 20 20 5 0
Temple, Texas 69 83 68 86 70 / 30 20 20 5 0
Mineral Wells, Texas 67 82 67 87 69 / 30 20 20 5 0
&&
Forward watches/warnings/advisories...
none.
&&
$$
