Special Special SevereWeather SevereWeather & & Heavy Rain Heavy Rain Weather Weather

BriefingBriefing03/19/201203/19/2012

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 Severe Weather and Rainfall Event Significant Severe Weather and Rainfall Event

Setting up across the regionSetting up across the region****

Setup:Setup: Cutoff – slow moving upper lowCutoff – slow moving upper low Stalled FrontStalled Front High Precipitable Water (99High Precipitable Water (99thth percentile) percentile) Soils prepped from the recent rainsSoils prepped from the recent rains

ImpactsImpacts Serious Flooding/Flash Flooding!!Serious Flooding/Flash Flooding!! Tues AM->Thu AMTues AM->Thu AM Severe Weather Threat Late Monday/Early Severe Weather Threat Late Monday/Early

TuesTues Damaging Winds – Strong!Damaging Winds – Strong! Tornadoes (primarily East TX/SE OK/SW AR)Tornadoes (primarily East TX/SE OK/SW AR)

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

Strong Polar Jet diving Strong Polar Jet diving Down the backside of this lowDown the backside of this low

Strong ridge holding strong Strong ridge holding strong East of the areaEast of the area

H

Radar @ 1045 AM Radar @ 1045 AM MondayMonday

Strong Strong Storms Storms developingdeveloping

Expect this Expect this line to line to shift east shift east slowly with slowly with stronger stronger stormsstorms

Monday PMMonday PM Upper Upper

level low level low beginninbeginning to cut g to cut off.off.

Waves of Waves of storms storms moving moving across across west/NW west/NW areasareas

L

7 PM 10 PM

1 AM 4 AM

MondayPM

Thru

Tuesday AM

Model RadarSimulation

Precip Precip through through Tues 7 Tues 7

AMAM High High

Risk Risk of of excessivexcessive e rainfall rainfall i.e. i.e. Flash Flash FloodingFlooding

Excessive Rainfall Outlook

SPC Mod

erat

e ris

k are

a

SPC Mod

erat

e ris

k are

aSevere Weather Threat – Monday PM/Tuesday AMSevere Weather Threat – Monday PM/Tuesday AM

Primary Threats:Primary Threats:1.1.Damaging WindsDamaging Winds2.2.TornadoesTornadoes

Tuesday PMTuesday PM Front Front aligns aligns along along Sabine Sabine River from River from north-north->south>south

Storms Storms train over train over the same the same areasareas

Low cuts Low cuts off over off over west TXwest TX

7 AM

Tuesday AM

Thru

Tuesday PM

Model Radar

Simulation

10 AM

1 PM

4 PM

Note kinks in line

Rainfall Forecast Rainfall Forecast Tuesday AM – WednesdayAMTuesday AM – WednesdayAM

Axis of heavy Axis of heavy rains along rains along LA/TX LA/TX border and border and SW ARSW AR

3”- 3”- 6” ..isolated 6” ..isolated 8”8”

SPC Slight risk areaSPC Slight risk area

Severe Weather Threat – TuesdaySevere Weather Threat – Tuesday

Primary Threats:Primary Threats:1.1.Damaging WindsDamaging Winds2.2.TornadoesTornadoes

Increased Risk in Orange outlined areasIncreased Risk in Orange outlined areas

Wednesday PMWednesday PM Heavy Heavy

Band shifts Band shifts into into Eastern LAEastern LA

Low still Low still cutoff over cutoff over TXTX

Rainfall Rainfall over in TX. over in TX. Ongoing in Ongoing in LA, S AR.LA, S AR.

Rainfall Forecast Rainfall Forecast Wednesday AM – Thursday AMWednesday AM – Thursday AM

Heaviest axis Heaviest axis expected expected across across Eastern LA.. Eastern LA.. US 165 US 165 CorridorCorridor

2”- 3” …2”- 3” …isolated 4”isolated 4”

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

Note the heavy axis in East TXNote the heavy axis in East TXSW AR/ SE OKSW AR/ SE OK

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

2 Swaths of 2 Swaths of 5”-8” 5”-8”

This model This model has shown has shown the highest the highest amounts amounts through the through the forecastforecast

Computer Model Total Rainfall Computer Model Total Rainfall Forecast Forecast (NAM)(NAM)

1 large 1 large Swath of Swath of 5”-8” with 5”-8” with a max of a max of 9”-10”9”-10”

This model This model has been has been the the Western Western mostmost

Computer Model Total Rainfall Computer Model Total Rainfall Forecast Forecast (NAM)(NAM)

1 large 1 large Swaths of Swaths of 5”-8” with a 5”-8” with a max of 9”-max of 9”-10”10”

This model This model has been has been the Western the Western mostmost

Computer Model Total Rainfall Computer Model Total Rainfall Forecast Forecast (SREF)(SREF)

1 large 1 large Swath of Swath of 5”-8”5”-8”

This is a This is a combinatiocombination of n of numerous numerous model runsmodel runs

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

week!!

Month to date:3.41” – SHV6.68” – LFK6.42” – MLU3.03” – TYR3.03” – TXK2.43” - DEQ

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 1.77”Max 1.80”

7 AM Tues Wed AM

Forecasts from the GFS computer model

GFS model Indicating 85 kt low level jet

Believability?

Climatology of Climatology of Precipitable WaterPrecipitable Water

X

This event falls above 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, Red Sabine, Neches, Sulphur, Red

system..including parts of the Red, Upper system..including parts of the Red, Upper OuachitaOuachita

Moderate flooding most areas…Some Major Moderate flooding most areas…Some Major (Sulphur)(Sulphur)

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 Significant Flash Flooding Significant Flash Flooding

Tues AM->Thu AMTues AM->Thu AM Severe Weather Threat Severe Weather Threat

Late Mon/Early TuesLate Mon/Early Tues Damaging Winds - StrongDamaging Winds - Strong TornadoesTornadoes

NEXT CONFERENCE CALL:

Possibly Friday 3/20 Time Possibly Friday 3/20 Time TBDTBD

www.srh.noaa.gov/shv/www.srh.noaa.gov/shv/briefingbriefing

National Weather Service Shreveport, LouisianaNational Weather Service Shreveport, Louisiana