Updated 915am CT – Wednesday / 21 February 2018
… Much Colder Air Arrives … Rain Doesn’t Materialize in the Overnight Hours …
… As a Classic Overrunning Pattern Develops, Rains Now Developing …
… Unsettled Weather Pattern Continues Late Week into the Weekend …
On the Weather Map…
On the surface map… the leading edge of surface based shallow arctic cold air has now advanced as far south as the Texas coastal plains. As a result of this surface weather pattern, our surface winds are northerly.
On the upper air map… a broad deep trough, or line, of counter clockwise rotating upper air low pressure extends southwestward from west of Hudson Bay into the western half of the USA and adjoining areas of northwest Mexico and the Baja Peninsula. As a result of the upper air weather pattern, the 30,000 foot winds over our local area are south southwesterly 60 to 70 mph.
What I am Seeing As I Look Ahead…
After a complete forecast bust overnight locally, as it regards precipitation occurrence and amounts, I have to retreat a second and try to gather my thoughts about the dynamic weather pattern in place across the area. The numerical computer guidance and even some of the National Weather Service national rainfall guidance overnight for south central Texas was miserably bad and since I use this as input in my forecast, my forecast ended up being miserably bad. Even though I realize that weather forecasting is an imperfect science, I still consider my forecast through the overnight hours to be especially bad. For that, I apologize. I hope I’ll learn a bit from this and I can improve/sharpen my forecast skills as a result.
So where are we this morning? The surface based much colder arctic air has moved as far southeast as the central Texas coastal plains this morning. This was actually where the short range high resolution atmospheric computer modeI data had a better handle on the situation and I realized that last evening with my mid evening weather update.
The warm and deep moisture flow off the Gulf of Mexico is still there, however; it’s overriding up and over the top of this colder surface based air which only extends up to around 3,000 feet overhead of our area based on the upper air data and data from the National Weather Service Doppler weather radar sites at New Braunfels and Granger.
Rain has been slow to develop over the area (at least through 8 to 9am this morning), but, as we speak, rain showers and thunderstorms are being more numerous especially in areas to our south through southwest. This is occurring as an upper air low pressure disturbance, being ejected by the counter clockwise rotating trough to our distant west, move more overhead and creates atmospheric lift in what is still a warm and moist air mass above the cooler based surface air. As a result, the forecast bust was overnight, not today, with rain showers and thunderstorms now starting to really get developed.
Since the precipitation is not surface based but rooted in the warmer air aloft, I think we will see rainfall amounts overall not as heavy as earlier thought. I still think we’ll see an inch or less today with additional rains tonight into tomorrow averaging as much as an another inch, but in most cases probably a little less.
By late tomorrow into tomorrow night, the cold front, that moved southeastward through the area in the predawn hour earlier today, will begin to sweep back northwestward as a warm front that will pass back north of the area by Friday with much warmer conditions returning. Remember that upper level disturbances will be continuing to move east northeastward overhead with rain and thunderstorm chances continuing as well.
By Saturday, yet another cold front will sweep through the area with numerous rain showers and thunderstorms expected. Rainfall Friday Through Saturday locally will average 1 inch based on the latest guidance (which I don’t exactly have the greatest confidence in at this point).
Once this front moves through, I expect rain chances to decrease (not to completely disappear) with even some breaks in the clouds Sunday into the earliest part of next week. Temperatures, which will cool a few degrees in the wake of the Saturday cold front, will slowly warm once again by the first part of the new week.
Have a good Wednesday..
Meteorologist Troy Kimmel
Contact me:
tkimmel@austin.utexas.edu
http://www.facebook.com/troykimmel
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Updated 845am CT… Wednesday / 21 February 2018
TODAY…. Cloudy and unseasonably cool with numerous rain showers and thunderstorms with an associated lightning risk. Localized urban flood problems may result. An 80% chance of rain; rainfall will average 1 inch or less. Temperatures remaining in the 40s. Northerly wind 8 to 15 mph.
TONIGHT…. Cloudy with numerous rain showers and isolated thunderstorms with an associated lightning risk. A 70% chance of rain early decreasing to 50% late; where rainfall occurs, it will average 1/4 to 1/2 inch. Low 38. Northerly wind 5 to 12 mph.
THURSDAY…. Cloudy and unseasonably cool with rain showers and isolated thunderstorms with an associated lightning risk. A 50% chance of rain early increasing to 70% by mid and late morning; additional rainfall will average 1/4 to 1/2 inch. High 52. North northeasterly wind 5 to 10 mph.
THURSDAY NIGHT…. Some patchy fog developing. Cloudy with numerous rain showers and isolated thunderstorms with an associated lightning risk. A 70% chance of rain; rainfall will average 1/4 to 1/2 inch. Low 48. Light northerly wind becoming more easterly after midnight.
FRIDAY…. Cloudy and warmer with scattered rain showers and thunderstorms. A 60% chance of rain; where rainfall occurs, it will average 1/4 to 1/2 inch. High 70. Light east southeasterly wind becoming south southeasterly in the afternoon.
FRIDAY NIGHT…. Cloudy with scattered rain showers and thunderstorms. A 60% chance of rain; rainfall will average 1/4 to 1/2 inch. Low 62. South southeasterly wind 5 to 12 mph.
SATURDAY…. Mostly cloudy with numerous rain showers and thunderstorms with an associated lightning risk as a cold front passes in the afternoon. A 60% chance of rain; where rainfall occurs, it will average 1/4 to 1/2 inch. High 73. South southeasterly wind 5 to 12 mph becoming west northwesterly by afternoon.
SATURDAY NIGHT…. Partly to mostly cloudy and cooler with a few lingering rain showers. A 20% chance of rain; where rainfall occurs, it will average trace amounts. Low 48. Northerly wind 5 to 12 mph.
SUNDAY…. Isolated rain showers early. Partly cloudy. A 20% chance of rain; where rainfall occurs, it will average trace amounts. High 65. North northeasterly wind 5 to 10 mph becoming easterly in the afternoon.
SUNDAY NIGHT…. Partly cloudy. Low 48. Light east northeasterly wind.
MONDAY…. Partly cloudy. High 69. Easterly wind 5 to 10 mph becoming more southeasterly by afternoon.
MONDAY NIGHT…. Partly cloudy. Low 50. Light wind.
TUESDAY…. Partly cloudy. High 70. Light south southeasterly wind.
NATIONAL WEATHER SERVICE / 8 TO 14 DAY OUTLOOK
Valid Wednesday / 28 February 2018 through Tuesday / 06 March 2018…
Temperature… Near to Slightly Above Average
Precipitation… Slightly Above Average
AUSTIN SUNSET/SUNRISE TIMES…..
Sunrise this morning (21 February)………………………………….. 7:05 am
Sunset this evening (21 February)……………………………………. 6:24 pm
Sunrise tomorrow (22 February)………………………………………. 7:04 am
Sunset tomorrow (22 February)……………………………………….. 6:25 pm