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Area forecast discussion...updated 
National Weather Service Fort Worth Texas
1005 PM CDT Monday Apr 20 2015

Update...
not a great deal of change to the current forecast for the
remainder of tonight. Ample high level moisture has spread into
North Texas from the southwest resulting in nearly overcast skies
south of Interstate 20. This may help keep temperatures a couple of
degrees warmer than previously forecast so have raised overnight
lows a tad. Also increased cloud cover for the remainder of the
night.

A cluster of showers and a few thunderstorms is ongoing across the
Texas Panhandle late this evening. This should continue to move
southeast but will likely weaken as it does. There may still be
some ongoing elevated activity that moves into North Texas early
Tuesday morning. In addition...some elevated showers and possibly
a thunderstorm may develop farther south during the day Tuesday as
slightly better moisture moves into the region where steep lapse
rates will reside. Toned down the probability of precipitation a little during the day
tomorrow to 20-30 percent but better rain/storm chances arrive middle
to late week.

Dunn

&&

Aviation...
/issued 720 PM CDT Monday Apr 20 2015/

For the 00z tafs...elevated rain showers or thunderstorms on
Tuesday are the primary forecast concern.

A relatively dry low-level air mass in place across the region
will keep conditions VFR through tomorrow morning. VFR conditions
are likely to hold throughout the day on Tuesday as well...however
elevated moisture return may result in some scattered showers or
thunderstorms developing across the region after 15z tomorrow.
Models are not consistent with the onset or placement of this
elevated convection tomorrow...however most models show some
elevated precipitation develop by the late morning hours of the
day.

Forecast soundings indicate some shallow cape for air lifted from
the 850 mb level or about 1 mile above ground level. Confidence in scattered
precipitation developing on top of the dfw area is not high at
this time...so chose to highlight the most likely period for
precipitation with a mention of vcsh from 15 to 22z. May have to
add a mention of thunderstorms in the vicinity or just a couple of hours of persistent
thunder if confidence increases that this elevated convection will
develop right on top of the dfw area.

Aside from the potential for elevated showers and storms near
airports tomorrow...VFR conditions and southerly flow is expected
to persist throughout the day.

Cavanaugh

&&

Previous discussion... /issued 345 PM CDT Monday Apr 20 2015/

After a quiet and dry period yesterday through tonight...rain
chances return to the forecast on Tuesday. The forecast through
Friday is muddled and challenging due to discrepancies between
the models. Part of the issue with the models and the forecast for
the next few days is that the disturbances and/or atmospheric
elements that are key to different forecast elements are not being
well sampled over the Pacific Ocean or Mexico. The overall
confidence in the forecast through Friday is moderate that we
will see thunderstorms in the region Tuesday through Friday and
some of these storms are likely to be severe...but confidence in
the specifics is low. Now we just have to answer the
where...when...and threats questions. I think it is safe to say
that the forecast will have daily changes and it is important this
week to check the latest updates each day.

Tonight will be a quiet night with mostly clear skies and light
winds. The winds across the region are already starting to turn to
the south...and south to southeast winds will prevail across all
of the region by daybreak. Some high clouds will be
present...mainly across the southern counties of the County Warning Area. Low
temperatures will range from the middle 40s to lower 50s.
Thunderstorms may trek across western Oklahoma and/or northwest
Texas late tonight but are not expected to reach North Texas.

Elevated showers and thunderstorms are possible across the region
on Tuesday. Hi resolution model guidance and forecast soundings
support elevated thunderstorms across the southern third of the
region during the day tomorrow. The lift for these storms comes
from isentropic lift around the 300k level. Sufficient elevated
instability may result in some gusty winds or small hail with
these storms. Elsewhere...a suite of other models including the
4km WRF and European model (ecmwf) indicate elevated showers and thunderstorms
will be possible. Will carry a 30-40 pop across the area all day
tomorrow but confidence is low in exactly where showers/storms
will occur. North of Interstate 20...virga may be observed with
any elevated activity in the morning hours. Also on
Tuesday...thunderstorms are expected to develop on the dryline to
our west during the afternoon hours. Right now it looks like the
dryline will be too far west for these storms to affect our
western counties but will leave a 20 pop in the evening hours for
this slight chance.

Better chances for severe weather may occur on Wednesday.
Thunderstorms are likely to form along a warm front just north of
the Red River and may track into north or northeast Texas. As also
mentioned in the Storm Prediction Center day3 outlook...storm Mode is uncertain for
Wednesday. Isolated supercells may develop near this boundary but
there is also support that an mesoscale convective system will develop and track
southeast. In addition...at the surface...the dryline may be
closer to our western border as a surface low moves into northwest
Texas during the afternoon hours. North Texas will be warm and very
unstable /cape values exceeding 3000 j/kg with deep layer shear
values over 40 kts/ and any embedded disturbance in the zonal
flow aloft would be enough to spark isolated to scattered
convection near the dryline and possibly elsewhere if any
other boundaries are present. We should be able to better refine
storm evolution as we approach Wednesday but the key message at
this time is a good part of the area could be under a threat for
severe storms.

The chance for rain continues on Thursday with the surface low
located in our western zones and indications of another
disturbance moving overhead. The best chances for storms on
Thursday would likely be across our eastern zones...ahead of the
surface low...and severe storms will again be possible.
Instability parameters and shear values are greater Thursday
afternoon than they are forecast to be for Wednesday. We will
have to be aware of any boundaries left over in the area for
additional foci for thunderstorm development Thursday.

On Friday...a large upper level low will swing into the plains
from Baja California bringing US another chance for storms before a front
sweeps through the region. The latest run of the European model (ecmwf) and
Canadian have slowed the timing of this system over the GFS. The
GFS has the highest chances for rain in the morning hours while
the other models focus more in the afternoon hours. Due to the
discrepancies will keep 50-60 probability of precipitation but extend the coverage area
and timing into Friday night. Once again...severe weather will be
possible but will be dependent on timing and evolution/Mode. The
atmosphere will be very unstable once again.

While it is too difficult to dive into specific details for storm
evolution...Mode...and severity in the Wednesday through Friday
time frame...it looks like it could be an active period with
threats for large hail...damaging winds...isolated tornadoes...and
flooding. At this time...a widespread outbreak is not expected on
any of these days.

A front will sweep through the area behind the storms on Friday
resulting in a pleasant weekend for all of north and central
Texas. The GFS is quick to return moisture and develop more storms
Sunday night as another upper level system and front moves through
the plains. This seems too fast for the moisture return but will
keep a 20 pop in the forecast for Sunday night.

Jldunn

&&

Preliminary point temps/pops...
Dallas-ft. Worth, Texas 52 75 63 76 66 / 0 20 10 40 40
Waco, Texas 50 77 64 80 66 / 0 20 10 30 30
Paris, Texas 48 74 58 75 61 / 10 30 20 40 50
Denton, Texas 49 76 62 76 63 / 5 30 20 40 40
McKinney, Texas 48 74 62 75 63 / 5 20 20 40 40
Dallas, Texas 52 76 64 76 66 / 0 20 10 40 40
Terrell, Texas 49 75 63 75 64 / 0 20 10 40 40
Corsicana, Texas 50 76 63 77 67 / 0 30 10 30 30
Temple, Texas 52 78 65 79 67 / 5 20 10 30 20
Mineral Wells, Texas 49 78 62 79 63 / 5 20 10 30 30

&&

Forward watches/warnings/advisories...
none.

&&

$$

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