Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Fort Worth Texas
1154 PM CST sun Dec 28 2014
main concern is the likely development of a low cloud/fog bank
across East Texas tonight. Low level winds turn more easterly and
could bring this low cloud bank or fog westward during the
morning hours. Once the sun rises it will work to prohibit this
westward movement...but a lingering IFR cloud bank may impact
dfw/Dal/gky taf sites middle-late morning. Have included a tempo for
IFR ceilings at just Dal from 14 to 17z...where probability would be
highest but confidence on this is lower than usual and will need
to be monitored.
Otherwise VFR will prevail through Monday evening with generally
light S/southeast winds and just some high clouds.
Winds will turn more easterly Monday night and with higher
moisture to the east and upslope flow...this should allow for the
redevelopment of low clouds and fog...this time impacting all of
the taf sites sometime after 6z. Confidence in this again is not
high...but NAM soundings are very aggressive in low level
saturation indicative of LIFR cigs/fog.
did a quick update to add patchy freezing fog to areas generally
east of an Emory-Cameron line for the rest of the night.
Temperature/dewpoint spreads already very small in these areas where
cloudcover dispersed around sunset. Given the passage of a
shortwave with no accompanying frontal passage today...fog may become a good bet in
these areas...with some freezing on exposed surfaces possible toward
morning. Rest of forecast looks good.
Previous discussion... /issued 316 PM CST sun Dec 28 2014/
precipitation continues to wane across our southeast counties as a
shortwave aloft passes across the area this afternoon. Subsidence
behind this feature has allowed for sunny skies across the
northwest counties. Highs were pushing close to 50 degrees in the
northwest while lingering in the upper 30s and lower 40s across
the southeast. Winds were light north and northwest less than 10
miles per hour as a surface ridge settled into the area.
We expect a quiet weather period Monday into Tuesday despite an
Arctic front arriving late Monday night and early Tuesday morning.
Monday will likely be the warmest day as we see partly sunny
conditions and the return of south winds. Highs should push well
up into the 50s with even lower 60s across central Texas where
brief southwest flow in the lowest levels will occur. But the
warmth won't last long as the Arctic front arrives by sunrise
Tuesday and Ushers in a shallow...but very cold airmass. There
will be little going on aloft with shortwave ridging occurring in
advance of an upper level low deepening over the Great Basin of
Nevada and Utah.
With the shallow Arctic airmass remaining in place middle-late
week...the forecast becomes challenging beginning Wednesday and
heading into at least the morning hours Thursday. A lead shortwave
will eject northeast out of the southwest U.S trough and induce
warm air advection and isentropic lift beginning across central Texas late
Tuesday night into Wednesday. Determining precipitation types and
impacts remains very challenging. A look at model bufr soundings
show there will be some drier air below 800mb to initially overcome
and not much of a warm layer aloft around that same level. Very
light rain or sleet appear the most reasonable...though some
spotting freezing rain could occur where temperatures remain a few
degrees below freezing across the southwest counties.
The southwest U.S upper low does begin to progress east toward
West Texas Thursday into Friday. Despite increasing warm air advection overnight
Wednesday night into Thursday...areas north through west of dfw
may remain at or below freezing with some potential wintry mix
possible at least through morning hours Thursday. We have adjusted
for this possibility...but a lot will be involved regarding how
the environment reacts to the increasing warm air advection and approaching
large-scale ascent. We do believe by afternoon that all locations
will be above freezing with only a cold rain expected into
The upper low will begin moving more readily by Friday morning and
through the day...though this is where models really diverge on
track and strength...with the GFS further north and fastest...the
Euro deeper and slower over northwest Texas and western OK..and the
Canadian about as fast as the GFS...but tracking right over North
Texas. Have basically left this period alone with the potential
for widespread rain with embedded and elevated thunderstorms.
Like the previous forecast...we went with an average on speed and
track of the system with a west to east end to rainfall chances
Friday night as a cold front moves through. If the European solution
holds...rain chances would need to be introduced across the northeast
half of the region through Saturday morning.
We will continue to fine tune the forecast late this week as the
atmosphere becomes more resolved by upper air soundings in the
coming days. For next week...deep longwave cyclonic flow envelops
the central U.S with an indication of more Arctic air could be on
the way for early January.
Preliminary point temps/pops...
Dallas-ft. Worth, Texas 31 58 34 42 31 / 0 5 5 5 5
Waco, Texas 27 61 33 45 31 / 5 5 5 5 5
Paris, Texas 29 52 33 43 28 / 0 5 5 5 5
Denton, Texas 28 58 28 41 27 / 0 5 5 5 5
McKinney, Texas 27 55 28 42 27 / 0 5 5 5 5
Dallas, Texas 32 58 35 43 31 / 0 5 5 5 5
Terrell, Texas 29 56 34 44 31 / 0 5 5 5 5
Corsicana, Texas 30 58 35 45 33 / 5 5 5 5 5
Temple, Texas 28 62 34 45 33 / 5 5 5 5 5
Mineral Wells, Texas 29 59 28 39 27 / 0 5 5 10 10