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Area forecast discussion...updated 
National Weather Service Fort Worth Texas
1240 PM CDT Wednesday Jul 30 2014

Update...
in the span of 24 hours...deep southerly flow has returned to
North Texas in response to a shortwave transiting Oklahoma and
Kansas. This moist upglide has resulted in widespread precipitation this
morning...the southern extent of which will continue to impact
northern and northeastern zones into the afternoon hours. The back
edge of the activity is still upstream across western Oklahoma and
adjacent parts of northwest Texas...and although the forthcoming
showers will be less intense...there will still be some additional
light rain well into the afternoon.

Once again today...there will be a sharp gradient with high
temperatures between the rainy areas and the sunny spots. Have
lowered high temperatures across the northern zones where rain
will persist this afternoon. The associated cloud shield will slow
the temperature rise elsewhere...but temperatures will still reach
the 90s across western and southern zones. There is some potential
for afternoon thunderstorms where surface heating is maximized...
but there is unlikely to be sufficient forcing along the thermal
discontinuity...which is not evident in the low-level wind fields.
Unlike Monday and Tuesday...there is no longer a frontal boundary
to focus convective initiation and realize the instability.

25

&&

Aviation...
/issued 659 am CDT Wednesday Jul 30 2014/

For the 12z tafs...VFR conditions are expected through the valid
forecast period...however flight operations are likely to be
affected by scattered rain showers over much of the next 24 to 30
hours.

A band of rain showers was moving directly at dfw Airport at the
time of this discussion. Despite the busy radar returns across the
region and headed over the metroplex...there have been no cloud to
ground or in cloud lightning strikes recorded across North Texas
so far this morning. As a result...went ahead and started off all
the metroplex area tafs with vcsh as opposed to thunderstorms in the vicinity as this trend
is expected to continue throughout the morning hours of the day.

Left vcsh in the tafs for several hours because the lift aloft is
expected to move slowly east over the area today. With a very
moist air mass already in place...and persistent lift
expected...could not find a good window to indicate a break in the
showers for the tafs this morning. There probably will be breaks
in the scattered rain shower activity...but it is difficult to
time those right now.

We should see precipitation diminish from west to east this
afternoon as models indicate some warm and slightly drier air
moving over the dfw area. Assuming this dry air leaves some cloud
cover in place...this dry air should cap off the atmosphere for
additional rainfall through this evening. If clouds clear out...we
could heat up rapidly...break the cap and get isolated to
scattered thunderstorms to develop near dfw area airports. This is
not expected to happen at this time as upper level clouds should
remain thick over the area.

By tonight the next round of precipitation is expected to slide
south of the Red River. This should bring another round of showers
to the dfw area just before midnight...hanging around through
sunrise Thursday morning. Thunderstorms cannot be ruled
out...however confidence in thunder was too low to bring into the
forecast at this time.

Around sunrise...a cold front is expected to push through the dfw
area which may be accompanied by a line of thunderstorms.
Confidence in the timing of this front is not great...models have
it moving through anywhere from 10 to 16z...so just left thunderstorms in the vicinity at
the end of the dfw taf after 12z at this time. Will have to adjust
this timing as the timing of the front is better resolved.

Cavanaugh




&&



Previous update...
update...
updated the probability of precipitation for today to account for current radar trends.
Additionally...updated quantitative precipitation forecast for tomorrow to account for the
continued model guidance hinting at a heavy rainfall event for our
northeast counties. A Flash Flood Watch may be warranted for areas
northeast of the dfw metropolitan for late tonight through Thursday if
model guidance continues this trend.

Ajs




&&



Previous discussion... /issued 409 am CDT Wednesday Jul 30 2014/
regional radars showed numerous rain showers extending from the
Texas Panhandle east-southeast along the Red River over to Wichita
Falls. This cluster of precipitation was likely associated with deep
warm...moist air advection over the area as evidenced by radar VAD
wind profiles showing wind direction veering with height from 925 to
700 mb in this area. This fairly deep warm air advection was likely
associated with a retreating/reorganizing frontal boundary in
response to a shortwave trough that was located along the
Colorado/New Mexico border per 08z/3am water vapor satellite
imagery.

This zone of strong low to middle-level warm air advection and lift is
expected to move slowly east along the Red River today. At least
scattered rain showers are expected to persist within this zone of
ascent as it moves east...and went ahead and left 30 to 40 probability of precipitation in
near the Red River throughout the day today as a result. Some high
resolution model guidance indicates that precipitation will extend
as far south as Interstate 20 today...so maintained at least a 20
pop down to just south of Interstate 20...including over most of the
dfw area. Rainfall is generally expected to remain light...but
periods of moderate to heavy rainfall will occur with any embedded
thunderstorm activity. Models consistently advertise precipitable
water values of 2 inches or slightly more within this zone of
ascent...so any deep convection/storms will be capable of very
efficient precipitation production.

The primary reason for thinking that thunderstorm activity will not
be more common along the Red River today is simply abundant cloud
cover which is already in place. If there are any breaks in the
clouds...thunderstorms will likely become more common...making
locally heavy rainfall more likely. However...with fairly persistent
lift in a very deep moist atmosphere...think that clouds will tend
to hold in today north of Interstate 20. Temperatures will likely
remain in the 80s again today for the dfw area. These unseasonably
cool temperatures will likely be more expansive today as the zone of
ascent and cloud cover is expected to be larger than yesterday.
Central Texas will likely still climb into the lower 90s at least
with more opportunities for sunshine with no organized lift expected
over these areas over the next 24 hours.

With the upper level ridge positioned over the Desert
Southwest...North Texas will be under northwest flow aloft. As
such...the organizing shortwave over the Colorado rockies is
expected to slide southeast today and bring elevated rain chances
to north and central Texas overnight Wednesday through much of the
day Thursday. Based on mass fields...model guidance has been gradually
shifting the focus of where the highest precipitation amounts
should be...further south out of northern Oklahoma and into southern
Oklahoma and North Texas...with the surface low prognosticated to reside
over northeast Texas early Thursday morning. A complex of
convection should develop and traverse south-southeast overnight tonight and
affect the region.

The precipitation gradient on Thursday is expected to be oriented
with higher amounts in the northeast and minimal rainfall totals
in the southwest. While most areas will only receive amounts in
the quarter to a half an inch range...locally higher amounts are
possible...especially for areas northeast of a Sherman to Canton
line. Forecast precipitable water values are expected to exceed 2
inches early Thursday morning for our northeast counties...which
is well above 150% of normal. Additionally...warm cloud depths
will be quite large...suggesting warm rain processes dominating
the situation. In such scenarios...rainfall totals can quickly add
up.

Once the shortwave exits the area on Friday...skies should clear
out and temperatures will gradually warm. However...with the
persistence of northwest flow expected to last several days...temperatures
will be slow to warm and should remain below the climatological
norm through the weekend. The upper level ridge will gradually
build eastward encompassing more of Texas early next week...and as a
result...expect a warm and dry forecast through early next week
once the aforementioned shortwave pushes southeast out of our area
on Friday.

Ajs/Cavanaugh




&&



Preliminary point temps/pops...
Dallas-ft. Worth, Texas 84 73 85 70 87 / 20 40 40 10 10
Waco, Texas 90 74 89 70 89 / 10 20 30 20 10
Paris, Texas 79 68 78 66 83 / 70 80 50 20 10
Denton, Texas 82 71 83 67 87 / 40 50 50 10 10
McKinney, Texas 82 71 82 66 85 / 50 70 50 10 10
Dallas, Texas 84 74 85 71 87 / 20 40 40 10 10
Terrell, Texas 85 72 83 68 86 / 20 50 50 20 10
Corsicana, Texas 88 73 87 69 87 / 20 30 30 20 10
Temple, Texas 92 72 90 70 90 / 10 10 40 20 10
Mineral Wells, Texas 86 69 84 67 86 / 20 30 30 10 10

&&

Forward watches/warnings/advisories...
none.

&&

$$

92/25

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