Tuesday, March 28, 2017

Severe Weather Risk Overnight

Forecast Discussion
…risk of strong and/or severe thunderstorms across central and south central Texas late tonight into early Wednesday morning
…strongest storms will be capable of producing large hail, strong gusty winds, torrential downpours, and dangerous cloud to ground lightning…
…an isolated tornado cannot be ruled out, but does not appear to be likely at this time…
…overall, 0.50-1.50 inches of rain can be expected across the area…flooding threat appears to be low at this time given the progressive (fast-moving) nature of this storm system…

Severe Weather Threat
The Storm Prediction Center (SPC) has placed areas along and west of the I-35 corridor (including the Austin Metro Area) under a SLIGHT RISK for severe weather late this evening and overnight...MARGINAL RISK for areas south and east of Austin.

The greatest threat for severe weather and tornadoes will be across west Texas and especially northwest Texas from Abilene to Wichita Falls to Childress where they are under a MODERATE RISK for severe weather (red shaded region).


Understanding Severe Risk Categories 
…the slight risk outlook is considered a threat level 2 in the 5 threat severe weather outlook system.
1.      Marginal
2.      Slight
3.      Enhanced
4.      Moderate
5.      High
(See chart below for a more detailed understanding of each threat level)


Detailed Forecast Explanation
A potent upper level low pressure system and its attendant cold front will move from west to east across the area during the overnight hours tonight lifting the warm, muggy, and unstable air mass currently in place across the area. The lift associated with this low pressure system at the mid and upper levels of the atmosphere will work together with surface lift provided by an eastward moving cold front to produce a line of thunderstorms across west Texas that will march east towards central Texas late tonight/early Wednesday morning. Some of the embedded storms within this line of storms are expected to be severe as they move across the area late tonight (especially across the Hill Country).

Storm Timeline
10pm to Midnight | Storms approach the western Hill Country
Midnight to 2am | Storms moving through the Hill Country…approaching Travis, Hays, and Williamson Counties
2am to 5am | Storms moving through the I-35 corridor and counties just east of the I-35 corridor
5am to 7am | Storms moving through eastern areas of central Texas
After 7am | Storms exiting the area to the east as drier and more stable air infiltrates the region from the west…clearing skies expected midday Wednesday

Forecast Radar (2 a.m. Wednesday morning)

Wednesday, March 22, 2017

Thunderstorm Risk Friday

Weather Re-Cap 
Good Evening Folks! It's another warm and breezy March afternoon across the area. Wednesday's official high temperatures are coming in at 83°F at both Camp Mabry and Austin Bergstrom International Airport. We started the day on a very mild note with temperatures in the mid to upper 60s.

An approaching upper level Pacific storm system (currently located along the west coast) is traveling east and will be increasing our chances for showers and thunderstorms across the area late Thursday into Friday. Ahead of Friday's storm chance, breezy southerly winds can be expected across central and south central Texas on Thursday. Southerly winds gusting 25-30 mph will be possible. Those southerly winds will be transporting plentiful amounts of Gulf of Mexico moisture into the area out ahead of Friday's showers and thunderstorms.

Friday Severe Weather Risk
Overall, the severe weather risk is looking to be fairly low for all of central Texas on Friday, however, one or two strong/potentially severe storms cannot be ruled out along and especially east of the I-35 corridor.

The Storm Prediction Center (SPC) has placed the area in the MARGINAL to SLIGHT Risk category for potential severe weather on Friday. The Marginal Risk area encompasses the eastern Hill Country down through San Antonio and to the Gulf Coast. The Slight Risk area encompasses areas from Austin to the north and east.

MARGINAL RISK = DARK GREEN SHADED AREA (5% risk of severe weather)

  • Isolated severe thunderstorms possible (limited in duration and/or coverage/intensity)
  • Low tornado risk
  • Hail up to 1" in diameter (quarter-sized)
  • Thunderstorm wind gusts of 40-60 mph

SLIGHT RISK = YELLOW SHADED AREA (15% risk of severe weather)

  • Scattered severe storms possible (short-lived and/or not widespread, isolated intense storms possible)
  • One or two tornadoes possible
  • Reports of strong winds/wind damage possible
  • Hail of about 1" in diameter possible, isolated 1.5-2" possible
Severe Weather Threat Map (valid late Thursday Night into Friday)


Storm Timeline
Per the latest forecast model guidance, a line of storms is likely to develop across west Texas late Thursday night and push east towards the I-35 corridor during the overnight hours. The high resolution North American Forecast Model has the line of storms moving through the: 
  • Hill Country between 4-9 a.m. CDT Friday morning and pushing 
  • through the I-35 corridor, including the Austin and San Antonio Metro Areas between 9-NOON CDT Friday
  • and 1-5 p.m. CDT for areas east of Austin.
Forecast Radar 10 a.m. CDT Friday (shows a line of storms along the I-35 corridor from Dallas to San Antonio)


Forecast Rainfall Accumulation
Generally less than an inch for most, 0.25-0.50 is a good bet for most locations (especially along and east of the Highway 281 corridor)...higher totals east, lower totals west

After Friday's Storms
Showers and thunderstorms should come to an end along the I-35 corridor by early Friday afternoon with clearing skies expected from west to east during the afternoon hours, a weak cool front will move through the area late Friday night/early Saturday morning and usher in some slightly cooler and drier air into the area for the first half of the weekend...lows in the 50s expected early Saturday morning and again on Sunday morning with highs in the 80s...storm chances increase a bit Sunday night with another disturbance and again for the middle of next week. Plenty of time to watch that. 









Monday, March 20, 2017

Hello Spring!

Forecast Discussion

Spring officially arrived at 5:28 a.m. this morning! Meteorological spring officially began back on March 1st.

Surface high pressure centered over the Gulf of Mexico and surface low pressure located over northwestern Oklahoma are creating breezy southerly winds over central Texas this afternoon. As of 4 p.m. CDT, the temperature at Camp Mabry is 84°F and 84°F at the airport. Where the air is drier 
out across north and west Texas, temperatures have soared into the lower 90s.


More of the same is set to continue for the majority of this week. Late night low clouds will give way to partly cloudy and warm afternoons in the 80s. Southerly winds will stay on the breezy side through the week. Southerly winds will keep the humid Gulf air in place and really limit the amount of cooling during the overnight hours. Lows only expected to bottom out in the lower to middle 60s.

Storm Chances late Thursday & Friday
Storm chances increase towards the end of the work week, peaking on Friday as an upper air disturbance and its associated surface frontal system move across the area from west to east. As it stands right now, the best dynamics for thunderstorms (some of which have the potential to become strong and/or severe) look to remain north of central and south central Texas. That will need to be monitored closely in the days to come. Storms would develop out to our west late Thursday and spread east into the I-35 corridor Friday morning into Friday afternoon. I’m putting storm chances right at 50% for Friday. Latest forecast model rainfall accumulation is indicating less than a half an inch, with the majority of totals coming in around 0.25 inches. Drier conditions will move into the area behind Friday’s potential storms for the upcoming weekend.  

The Storm Prediction Center out of Norman, Oklahoma has gone ahead and kept areas north and east of central Texas under a risk area for potential severe thunderstorms on Friday. Yellow shaded region = potential severe weather risk area. Remember, a thunderstorm is considered to be severe if it is producing hail of at least one inch in diameter, and/or winds of 58 mph or greater, and/or a tornado. Lightning intensity and rainfall intensity DO NOT determine if a storm is severe.