Special Special Heavy Rain Heavy Rain Weather BriefingWeather Briefing

03/08/201203/08/2012

www.srh.noaa.gov/shv/briefingwww.srh.noaa.gov/shv/briefing

Keith StellmanKeith StellmanWarning Coordination Warning Coordination

MeteorologistMeteorologistNational Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana

Overview****Significant Rainfall Event Setting up across the Significant Rainfall Event Setting up across the

regionregion****

Setup:Setup: Best Heavy Rainfall Setup since October 2009Best Heavy Rainfall Setup since October 2009 Stalled FrontStalled Front High Precipitable Water (99High Precipitable Water (99thth percentile) percentile) Cutoff upper level lowCutoff upper level low

ImpactsImpacts Flooding/Flash Flooding PossibleFlooding/Flash Flooding Possible

Thur PM->Friday AMThur PM->Friday AM Saturday -> SundaySaturday -> Sunday

Severe Weather Threat ThursdaySevere Weather Threat Thursday Damaging WindsDamaging Winds HailHail

National Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana

Current Satellite/Water Current Satellite/Water VaporVapor

National Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana

L Note the plume of moisture Note the plume of moisture from the Pacificfrom the Pacific

Cold Front dropping southCold Front dropping south

Radar @ 945Radar @ 945 Strong Strong

Storms Storms developingdeveloping

Expect Expect this area this area to fill as to fill as the day the day progressesprogresses

Thursday PMThursday PM Northern Northern

half of half of the areathe area

Along/ Along/ north I-north I-2020

1”- 1”- 3” ..isolat3” ..isolated 3” – ed 3” – 4”4”

Overnight ->Friday AMOvernight ->Friday AM

Southern Southern half of the half of the regionregion

Along/ Along/ south I-20south I-20

1”- 1”- 3” ..isolate3” ..isolated 3” – 4”d 3” – 4”

Precip Precip through through

Friday AMFriday AM Slight-> Slight->

ModeratModerate risk of e risk of excessivexcessive rainfall e rainfall i.e. Flash i.e. Flash FloodingFlooding

Excessive Rainfall Outlook

SPC slight risk area

SPC slight risk area

Severe Weather Threat – Thursday/Thursday PMSevere Weather Threat – Thursday/Thursday PM

Primary Threats:Primary Threats:1.1.Damaging WindsDamaging Winds2.2.HailHail3.3.Very isolated tornado threatVery isolated tornado threat

Friday-Friday NightFriday-Friday Night Front shifts Front shifts

southsouth

Break for Break for areas north areas north of I-20of I-20

Biggest Biggest threat area threat area Deep East Deep East TX-> coastTX-> coast

Friday PM – Saturday AMFriday PM – Saturday AM Rain begins Rain begins

re-re-developing developing SE TX SE TX coastcoast

Continued Continued break for break for areas north areas north of I-20of I-20

Biggest Biggest threat area threat area Deep East Deep East TX-> coastTX-> coast

Rainfall Forecast Rainfall Forecast Friday AM – Saturday AMFriday AM – Saturday AM

Heaviest Heaviest rainfall rainfall expected to expected to the south of the south of the regionthe region

May clip Deep May clip Deep East East TX/Central LA TX/Central LA with 1”-2”with 1”-2”

Saturday AM - Saturday Saturday AM - Saturday PMPM

Front Front aligns itself aligns itself north-> north-> south south across east across east TXTX

Rainfall Rainfall increasing increasing across East across East TXTX

Saturday PM – Sunday Saturday PM – Sunday AMAM

Heavy Heavy Rainfall Rainfall expected expected overnight overnight overspreadoverspreading the ing the entire entire region.region.

Heavy in Heavy in East TX / East TX / NW LA/ SW NW LA/ SW AR/ SE OKAR/ SE OK

Rainfall Forecast Rainfall Forecast Saturday AM – Sunday AMSaturday AM – Sunday AM

Heaviest Heaviest rainfall rainfall expected expected across western across western half along the half along the north/south north/south frontfront

1”- 3” ..isolated 1”- 3” ..isolated 3”-4”3”-4”

Sunday AM – Sunday PMSunday AM – Sunday PM Front Front

begins begins moving moving east with east with strong strong upper level upper level system system kicking outkicking out

Rainfall Rainfall increasing increasing across East across East TXTX

1”- 3” 1”- 3” possiblepossible

Sunday PM – Monday AMSunday PM – Monday AM Finally…Finally…

heavy rain heavy rain moving out moving out and ending and ending in the in the eastern eastern half of the half of the regionregion

Rainfall Forecast Rainfall Forecast Sunday AM – Monday AMSunday AM – Monday AM

Heaviest Heaviest rainfall rainfall expected expected across SW across SW AR/Western AR/Western LA/ Deep LA/ Deep East TXEast TX

1”- 3”1”- 3”

Computer Model Total Rainfall Computer Model Total Rainfall Forecast Forecast (ECMWF)(ECMWF)

Swath of 5”-Swath of 5”-7” 7” +extending +extending from Lufkin from Lufkin -> Marshall -> Marshall -> -> Texarkana /Texarkana /HopeHope

Computer Model Total Rainfall Computer Model Total Rainfall Forecast Forecast (GFS)(GFS)

Swath of 5”-Swath of 5”-6” East TX-6” East TX->NW LA->NW LA->SW AR>SW AR

Note the Note the consistency consistency in the in the location of location of the heavy the heavy rain axisrain axis

Some perspective on the Some perspective on the amountsamounts

Top 10 Wettest March – SHV Top 10 Wettest March – SHV (1874-2011)(1874-2011)Rank Value Rank Value

Ending Date Ending Date 1. 11.99 3/31/1945 2. 11.67 3/31/1876 3. 9.93 3/31/1912 4. 9.31 3/31/1922 5. 9.30 3/31/1934 6. 9.27 3/31/1874 7. 9.00 3/31/1888 8. 8.72 3/31/1997 9. 8.04 3/31/1894 10. 7.90 3/31/2000

*** We could break the top 10 wettest

MarchRainfalls this

weekend!!

Precipitable Water (inches)Precipitable Water (inches)A measure of the amount of moisture in the A measure of the amount of moisture in the

atmosphereatmosphere

Max 1.75”Max 1.68”

Thursday Night Sunday

Forecasts from the GFS computer model

Climatology of Climatology of Precipitable WaterPrecipitable Water

X

This event falls inside the 99th percentile and approaches the maximum value observed in March..based on the forecast PW values

Impacts

National Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana

River ImpactsRiver Impacts Sabine, Neches, Sulphur/ portions of the Red Sabine, Neches, Sulphur/ portions of the Red

system most at risk.system most at risk. Minor to some moderate flooding Minor to some moderate flooding

Depends on location of heaviest rainfall & Depends on location of heaviest rainfall & duration at which the rain fallsduration at which the rain falls

Other ImpactsOther Impacts Flooding/Flash Flooding PossibleFlooding/Flash Flooding Possible

Thur PM->Friday AMThur PM->Friday AM Saturday -> SundaySaturday -> Sunday

Severe Weather Threat ThursdaySevere Weather Threat Thursday Damaging WindsDamaging Winds HailHail

NEXT CONFERENCE CALL:

Possibly Friday 3/9 Time Possibly Friday 3/9 Time TBDTBD

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National Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana