Embedded Files
Now I've included the 00Z sounding from Fort Worth. It was taken twelve hours before the sounding we've been looking at. The overall weather pattern didn't change much at Fort Worth during that period, but what changes can be found in the sounding?
To me, the most obvious change is in the dew point. At 00Z the sounding is mostly dry, except for that layer of clouds around 400 mb, but at 12Z there are several other layers below that in which the dew point has risen to within ten degrees of the temperature. Comparing the two soundings, I would predict that while the 12Z observation features a high overcast, lower cloud decks will be moving into the area.
Here are the surface observations for a few hours after the time of the 12Z sounding:
KDAL 041051Z 10006KT 20SM SCT150 OVC250 06/02 A3024=KDAL 041150Z 10008KT 20SM SCT150 OVC250 08/02 A3023 RMK 10086 20057= KDAL 041250Z 12006KT 15SM BKN150 OVC250 07/02 A3026= KDAL 041350Z 11014KT 20SM OVC150 08/02 A3024 RMK OVC V BKN= KDAL 041450Z 11017KT 20SM FEW065 BKN120 OVC250 09/03 A3026= KDAL 041555Z 11021KT 20SM BKN065 BKN120 OVC250 10/03 A3025 RMK BKN065 V SCT= KDAL 041651Z 13022KT 20SM VCSH FEW050 BKN065 OVC120 11/02 A3024= The OVC250 corresponds to the cloud deck near 400 mb. Beneath that, another cloud deck at 15000 ft (near 500 mb) starts out scattered, but eventually lowers and thickens. A third cloud deck appears at 6500 ft (near 800 mb) by 15Z, and an even lower cloud deck appears in the most recent observation. What happened to the original cloud deck at 25000 ft? It's probably still there, but there's no way of seeing it from the ground through the lower clouds.
Temperature changes over the 12 hours are comparatively small. The biggest change, by far, takes place at the ground. There, the temperature at 00Z was 12 C and the temperature at 12Z was about 3 C. (These temperatures are taken from the soundings; the hourly observations, from within the city of Dallas, were a few degrees warmer.) Where an inversion would form by 12Z, the 00Z sounding's lowest 50 mb shows a temperature line almost parallel to the dry adiabats. This is known as a dry adiabatic layer, and is common during daytime. On this day, above the lowest 70 mb or so, it appears that the temperature of the atmosphere was unaffected by the daytime/nighttime transition.
Report abuse