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Predicted Heavy Rain Event is Underway; DFW Rainfall Record Broken

➡︎ Update History: Initial Forecast (Sunday 10/18) & Updates 2 through 5 | Update #6 | Update #7

Forecast Verification and Records Tied or Broken

◙  Record #1 [Broken] 2.58 inches of rain at DFW on Thursday 10/22 shattered the previous record for the date (2.19″) set in 1908.

◙  Record #2 [Broken] 3.55 inches of rain at DFW on Friday 10/23 shattered the previous record for the date (2.38″) set in 1920.

◙  Record #3 [Broken] the 2-day rainfall stands at 6.13 inches which is now the all-time greatest 2-day total ever recorded during the month of October.  It is the 11th greatest 2-day total ever recorded at anytime during the year (all months considered).  Records date back 117 years to 1898.


Update #7 Friday 10/23 4 pm

***Round 3 Developing to the South/Southwest***
***A Few Marginally Severe Thunderstorms Possible***
***Rain Ending Tomorrow/Colder***

Round 3 is forming on radar to the south and southwest as predicted. This area will expand in coverage and intensity over the next few hours as it overspreads North Texas.

◙  The lull has allowed for some afternoon heating which has enhanced atmospheric instability. I believe a few thunderstorms could become marginally severe, meaning that they will be capable of producing hail or downburst winds that barely meet severe criteria (1-inch diameter hail and/or winds of 58 mph or stronger).

◙  I do not expect widespread severe thunderstorms, but don’t be surprised if you hear a warning or see some hail, especially over the western half of the area.

◙  Atmospheric precipitable water content continues near the 99th percentile for this time of year.  As I’ve been saying this week, when deep tropospheric moisture content is this high, thunderstorms are capable of producing rainfall rates in the range of 1 to 3 inches per hour.

◙  I am forecasting widespread 3 to 5 inches of rain tonight, with isolated higher amounts.  Flash flooding will become a threat once again this evening through the overnight.

◙  Also, thunderstorms will be capable of producing frequent to excessive cloud to ground lightning. As we saw last night, the lightning can cause power outages and affect outdoor events.

◙  The greatest coverage of persistent rain and thunderstorms tonight (highest rainfall totals) will be SOUTH of a line from Decatur to Denton to McKinney.  If you recall my rainfall graphics from Wednesday, I concentrated the heaviest storm-total amounts in that area.

➡︎ How does Hurricane Patricia factor in?
• In my forecast this morning, I explained that the excessive atmospheric moisture that we have right now is not directly associated with Patricia. I have manually traced the high theta-e air (equivalent potential temperature) to the western Caribbean and a northward moisture flux through the western Gulf of Mexico into Texas.

• Tomorrow, the remnants of Patricia will move into northern Mexico and a surface low will deepen along the Gulf coast (a hybrid between the remnants of Patricia and the vigorous upper-level disturbance arriving from the west).

• As the surface pressure falls along along the coast, it will induce convergence (i.e., air flowing into the developing surface low) which will cause the excessive moisture over North Texas to retreat southward.  At the same time, a cold front will move through North Texas with cooler/drier air advecting in during the afternoon.

• All of this means that the heavy rain event will be over and the heavy rain should be south of the metroplex by early afternoon tomorrow.

• This is an exercise in atmospheric dynamics, but I feel the need to explain some of it because of so much scuttlebutt attempting to blame the heavy rain on Patricia.

Ok, so long story short:
1) Rain/thunderstorms overspreading N. TX this afternoon/evening

2) Heavy rain tonight (3 to 5 inches possible, especially south of a Decatur to Denton to McKinney line)

3) Heavy rain *ending* tomorrow, turning colder.  Light rain may linger into the evening. Temperatures only in the upper 50s to lower 60s by mid/late afternoon

4) Sunday: Mostly cloudy with a high in the upper 50s to lower 60s

-Chris Robbins, Meteorologist, M.S., iWeatherNet.com

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Update #6 Friday 10/23 7 am

***Flash Flooding Possible Today/Tomorrow***
***Record Rainfall Again Today***
***Rain Ending Saturday Night/Much Colder***

Good morning North Texas. I have been working on the forecast since midnight. It’s definitely complex.

  1. Earlier this week, I predicted record rainfall with this upper low. Yesterday and overnight, widespread 2 to 4 inches of rain fell across North Texas. DFW Airport received 2.58 inches of rain yesterday, shattering the previous record for October 22 (2.19″) set 107 years ago (1909).

  2. Last night’s upper air sounding from Fort Worth revealed atmospheric precipitable water content well above the 99th percentile for this time of year and was the 5th highest on record for the month of October in the 65-year database.

  3. The excessive, deep tropospheric moisture will persist through tomorrow. However, as the remnants of Hurricane Patricia cross over the mountains of northern Mexico tomorrow and approach the northwestern Gulf of Mexico, the main upper-level disturbance and a cold front will move through North Texas.

  4. Subsequently, the deep moisture will retreat southward toward the remnant circulation and the atmospheric precipitable water content over North Texas will drop during the day. This process will bring the heavy rain event in  North Texas to an end during the afternoon as cooler air moves in.

  5. Temperatures will fall tomorrow afternoon, possibly into the upper 50s by sunset (especially from the metroplex northward). Highs on Sunday will struggle into the lower 60s and northern/western areas may stay in the 50s.

  6. As for today (Friday 10/23), areas of rain and thunderstorms will develop with the next disturbance. With PWATS > 99th percentile (unrelated to Patricia), rainfall rates today will be in the range of 1 to 2 inches per hour (locally higher).

  7. I expect development south and west of the metroplex very soon, increasing in coverage and intensity this morning.

  8. I am forecasting widespread 3 to 5 inches of rain today, with embedded amounts as high as 10 inches by midnight.

  9. Another rainfall record will be broken today.

  10. It is impossible to pinpoint those extreme amounts with precision, but I will be watching the radar for persistent thunderstorms that train over the same areas.

  11. People in flood-prone areas are obviously at the highest risk. However, flash flooding can also occur in urban areas hampering travel (especially during rush hour this evening).

I will post updates as necessary.
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