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Area forecast discussion 
National Weather Service Fort Worth Texas
635 PM CDT Friday Apr 17 2015


For the 00z tafs...tracking the north/south oriented line of
thunderstorms moving east towards the dfw metroplex is the primary
forecast concern.

The line of storms just west of Tarrant County has been losing
intensity for the most part...and as a result has been
consistently slowly down with regards to its easterly progress.
The most intense part of the line is located over far southwestern
Tarrant County...moving east now at about 20 miles per hour. For the most
part this line of storms will be capable of producing 20 to 30 miles per hour
wind gusts...heavy rainfall...and frequent lightning as it moves
over area taf sites.

The more intense line of storms over far southern Tarrant County
will be capable of producing wind gusts of 40 to 45 miles per hour as well as
heavy rainfall and frequent lightning. This more intense line of
storms appears on track to move over kgky Airport...remaining just
south of kftw...kdfw...kafw...and kdal airports.

Will likely have to keep amending the tafs for timing
considerations as the storms roll across the dfw area. Behind the
main line of storms...light rain showers are expected to persist
for a couple of hours before all precipitation ends across the dfw

Other than storms...IFR ceilings are expected to build over north and
central Texas from the south early tomorrow morning. Did not see
any reason to change the timing of the onset of IFR ceilings from the
previous forecast...but may need to adjust the timing once storms
have dissipated...allowing for an evaluation of where outflow
boundaries end up. Did not have enough confidence in the timing of
storms on Saturday to include them in the tafs at this time.
Storms may once again threaten area taf sites tomorrow afternoon
or evening.



Previous discussion... /issued 310 PM CDT Friday Apr 17 2015/
a shortwave trough axis is now moving through Texas and upper
level lift is increasing over the region. As this lift interacts
with an axis of uncapped instability from roughly Wichita Falls to
Abilene and south into the lower Rio Grande Valley...scattered to
numerous thunderstorms have developed. While storm motion has been
generally appears that cold pools are beginning to
organize beneath the stronger clusters of storms with more
eastward motions noted with the cells in the northwest County Warning Area near well as the storm segments west and also south of San
Antonio. As the cold pools continue to develop... the eastward
motion will accelerate. Probability of precipitation will be highest this evening for the
northern part of the County Warning Area and also the southern part of the County Warning Area.
This is where the small line segments or clusters of storms are
most likely to track near. There is a chance a gap in the activity
will occur right across the central County Warning Area primarily due to the storm
clusters in south central Texas increasing in strength and
intercepting the best moisture and instability across our area.
Many locations will just experience light rain from anvil blow off
but where storms do track...well over 2 inches of rain is possible.
This activity will track mostly east of County Warning Area after midnight.

Surface based instability across North Texas is not very high
today...with local objective guidance showing generally only a few
hundred j/kg of energy. However instability just above the surface
is much higher...ranging from 1000-2000 j/ the strongest
cells will have enough instability for a severe hail and wind
threat. The Severe Thunderstorm Watch continues through 7 PM for
generally the western half of the County Warning Area. We and Storm Prediction Center will assess
storm trends before determining whether the a new severe watch
will be needed farther east this evening.

The atmosphere on Saturday will probably end up being significantly
worked over from the ongoing convection this evening and overnight.
Most models do forecast a strong mesoscale convective system to
track eastward through the Upper Texas coast and out into the northwest
Gulf by early morning...and given current radar trends across
south central Texas this seems likely. Often the subsidence in
the wake of an mesoscale convective system is not forecast well by computer models...and
this subsidence can extend several hundred miles northwest of the
parent mesoscale convective system. In addition...the primary shortwave trough axis also
exits to our east...and as a result the flow from the surface up
to 700mb becomes very weak and disorganized. This flow will
inhibit a replenishment of quality Gulf moisture back into the
region. Have lowered probability of precipitation a little for Saturday due to these
concerns. Having said that...the airmass will become weakly capped
and unstable by the afternoon hours with heating...and a dryline
will also approach the western zones. Therefore we do expect a few
showers and storms to fire across the western zones in the
afternoon...and track generally northeastward into the evening
hours. Again coverage will not be especially high...but there is a
low threat of severe wind/hail with this activity as adequate deep
layer shear and instability will exist.

A cold front will track across the region during the day on Sunday
and with south winds veering to the northwest during the midday
and afternoon hours...this should result in warm subsident
downslope flow. Temperatures will reach the 80s in most areas of
North Texas under sunny skies...and some temperatures near 90 may occur
across central Texas. Will add in a slight chance of afternoon
showers/storms over the far southeast zones where a moderately
unstable airmass will develop ahead of the front during the
afternoon hours.

Cooler and drier air will spread into the region Sunday night and
into Monday. Temperatures will drop into the middle 40s to middle 50s for lows
with highs only in the low to middle 70s Monday. Return flow will set
up during the day Tuesday...but it appears model guidance is a bit
too aggressive with quantitative precipitation forecast and have kept the forecast dry except for
generally the western zones.

Upper level westerly flow will continue over Texas from middle week
into next weekend. This does not lend much confidence in trying to
time the primary shortwave disturbances or determining when/whether
weak cold fronts will be able to make it into the County Warning Area. For now
have kept probability of precipitation low due to these concerns...but it appears
Wednesday night through Thursday night offer the slightly better
chances of rainfall. This is when the models are forecasting a
weak cold front to drop into the area from the northeast. Temperatures
from middle to late week will return to the upper 70s and near 80 for
highs with overnight lows muggy and in the 60s. The GFS shows
another front pushing through the region by Friday which scours
out our moisture...but the European model (ecmwf) has no such front and continues
chances of rain. Due to the discrepancy have dialed probability of precipitation down to
just a slight chance next Friday.



Preliminary point temps/pops...
Dallas-ft. Worth, Texas 62 79 61 81 51 / 50 30 20 5 5
Waco, Texas 62 78 60 86 49 / 50 30 20 10 5
Paris, Texas 63 75 60 80 48 / 60 30 30 20 5
Denton, Texas 60 79 58 80 48 / 60 30 20 5 5
McKinney, Texas 62 78 60 79 49 / 60 30 30 10 5
Dallas, Texas 62 81 63 82 53 / 50 30 20 5 5
Terrell, Texas 63 79 61 81 52 / 60 30 30 10 5
Corsicana, Texas 63 79 62 83 51 / 60 30 30 20 5
Temple, Texas 62 79 61 89 51 / 60 30 20 10 5
Mineral Wells, Texas 59 80 56 81 48 / 40 30 20 5 5


Forward watches/warnings/advisories...



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