George R. Kasica
San Antonio Forecast Day #3 - 0600Z January 25 to 0600Z January 26, 2007

The third day of the forecasting period was Thursday, January 24th and the time period it covered was again from 0600Z on the 25th to 0600Z on the 26th, this again was due to the fact that San Antonio, Texas is 6 hours behind the time in Greenwich, thus the offset of 6 hours rather than a midnight to midnight time frame.

The big picture for the area was much less complicated than the earlier forecasts. The system that had been causing such difficulty in making a forecast for the previous day had moved off to the east and the real challenge for this period wouldn't be precipitation, but instead the temperature forecast and wether or not the skies would clear during the period and allow for enhanced warning and cooling as a result.

Below you can see the 24 hour forecast for cloud cover over the US which was valid at 12Z on 1/25/07. Both of the models referenced in this image (the AVN and the WRF) indicated that there would be none or very few clouds in the area of San Antonio for the following day. Assuming this to be a correct forecast the possibility for very warm or cool temperatures certainly existed.

(12Z 1/24/07 24 hour cloud forecast chart courtesy of the Pennsylvania State e-Wall - click for full sized image)

Looking at the 12Z and 18Z MOS outputs below (click for full view) you can see that the models were quite consistent again in the temperature and wind speed predictions so I felt comfortable in taking something of a consensus of the 4 forecast values and I went with a high of 60, low of 38 and a wind speed of 10 kts (15 mph), which I admit I did raise just a bit in the event there were any higher gusts during the day.

12Z GFS High 59F Low 36F Wind 8 kts
12Z ETA High 61F Low 37F Wind 8 kts
12Z NGM High 62F Low 37F Wind 7 kts
18Z GFS High 57F Low 36F Wind 8 kts

Looking towards the precipitation forecast the 12Z  and 18Z FOUS outputs did not indicate any measurable precipitation on any of the three outputs during the time period of the forecast, though one (the 12Z NAM FOUS) did indicate a 6 hour total of 0.22" for the period ending at 6Z on 1/25/07, just as our forecast period would be stating. As a result of this I chose to go with 0.00" of precipitation wit the assumption that the precipitation would end before the forecast period began.

The actual results for the day (click for METARS and climate summary) were close to what I had forecast with a high of 64, a low of 36 and a maximum wind speed of 13 mph with out any precipitation being recorded. The detailed METARS showing the high and low temperatures in degrees Celsius are shown below. In the first line from 1753Z, the low temperature is shown in the group of numbers starting with 2 in bold blue underline which indicated that the low temperature occurred sometime in the last 6 hours. The next 0 indicates that the following temperature is above zero and the last pair of 22 indicates a temperature of 2.2C or 36F. The second line indicated the days high temperature within 6 hours of 2353Z (in this case looking at the detailed METARs we find it actually got recorded in the 2053Z METAR shown below in the third detail line). The next zero indicated the reading was again above zero and the following 178 indicated a temperature of 17.8C or 64F  To decipher the third detail line look for the red highlighted group starting with a T. The following zero, like in the 1 and 2 groups above it, indicates a reading above 0 and the 178 stands for 17.8C or 64F.

KSAT 251753Z 03008KT 10SM CLR 15/03 A3041 RMK AO2 SLP290 T01500033 10150 20022 58002
KSAT 252353Z 14007KT 10SM CLR 13/02 A3031 RMK AO2 SLP255 T01280017 10178 20128 55007

KSAT 252053Z VRB03KT 10SM CLR 18/M01 A3033 RMK AO2 SLP260 T01781006 56029

This third day of forecasting the results were far better than the previous two days, mainly due to the fact that I started to trust the models a bit more in terms of accuracy and not try to outguess them, but rather take the information and seek more of a consensus or average value for the various readings. However, on the other hand, the forecast situation was also far simpler than the previous two days as there was little if any chance of precipitation and the weather pattern was one that the MOS forecasts were fairly good at handling correctly.

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