Josh Korotky noaa/nws, Pittsburgh, pa


НазваJosh Korotky noaa/nws, Pittsburgh, pa
Дата конвертації16.04.2013
Розмір536 b.
ТипПрезентации


Using Ensemble Probability Forecasts and High Resolution Models To Identify Severe Weather Threats

  • Josh Korotky

  • NOAA/NWS, Pittsburgh, PA

  • and

  • Richard H. Grumm

  • NOAA/NWS, State College, PA


Overview

  • Review a vigorous and a marginal severe weather event

    • Examine diagnostic fields from the NAM-WRF
    • Examine single and combined probability forecasts from the SREF
  • Examine threshold probabilities for:

    • CAPE
    • Storm-Relative Helicity (SRH)
    • Mean shear (total shear divided by shear depth)
    • The Energy Helicity Index (EHI)
    • The Supercell Parameter
    • The Significant Tornado Parameter
  • Examine the combined probability of MUCAPE > 1000 J/kg, effective bulk shear > 30/40 kts, and 3 hr. convective precipitation > .01 inch



Overview

  • This study illustrates the value of using diagnostic information from higher resolution models with probability information from SREF forecasts to better understand the nature of a severe weather threat potential

  • A forecast strategy is proposed:

    • Use ensemble data for assessing the likelihood of a severe weather event and the confidence level of NWP forecasts
      • Uncertainty information is critical for forecast users
    • Use climatological anomalies for evaluating the historical context of a model forecast
      • Important for users to appreciate possible impacts
    • Use high resolution model data for determining the timing, evolution, mode, and intensity of forecast convection, including important mesoscale structures and relevant forcing mechanisms
      • The devil is in the model details


SREF Configuration

  • EMC runs a 21 member multi-model, multi-analysis system with enhanced physics. The SREF is run four times daily at 03, 09, 15, and 21 UTC, with forecasts to 87 hours

  • The current SREF configuration:

    • 10 NAM-Eta members
    • 5 Regional Spectral Model (RSM) members
    • 6 WRF members
  • Why SREF?

    • SREF designed to address both initial state and model uncertainties






SPC SREF Forecasts April 02/09 UTC valid April (02-03)/(21 – 00) UTC

  • Single and combined probabilities - David Bright

  • http://www.spc.noaa.gov/exper/sref/







SREF Departures from Climatology and Probability Forecasts April 01/21Z valid April 02/00Z

  • Climate anomaly: SREF forecasts assessed relative to seasonal climatology; Rich Grumm

  • http://nws.met.psu.edu/ensembles/index.html

  • http://eyewall.met.psu.edu/ensembles/



SREF MSLP and PWAT Anomalies valid 00Z 03APR2006

  • Deepening surface cyclone

  • Central pressure forecast > 2 SD below climate normal over the upper Mississippi Valley

  • Moist air surging poleward

  • PWAT anomalies forecast 2 to 3 SDs above climate normal

  • CAPE anomaly + 2-3 SD (not shown)



Mean CAPE 1200-2500 Jkg-1

  • Mean CAPE 1200-2500 Jkg-1

  • Mean EHI 1-3 from Illinois to lower Mississippi Valley

  • Mean SRH 300-400+ m2s-2 along and north of a strong warm front

  • Mean SRH 200-300+ m2s-2 along and east of the cold front

  • Mean 1.5 km mean shear .009-.010+ s-1 (~30 kt) across the Mississippi Valley







SREF Summary

  • SREF departures from climatology indicate an anomalously deep cyclone with atypical moisture and instability in the warm sector

  • SREF forecasts indicate a high likelihood of severe weather… including a potential for supercells with significant tornadoes… across much of the lower and central Mississippi Valley on 2 April 2006

  • Additional SREF products (not shown) indicated considerable agreement among the ensemble members

  • Users need to know that forecast confidence is high for a high impact event



NCEP Operational NAM-WRF Graphics

  • 00 UTC and 1200 UTC:

    • http://www.emc.ncep.noaa.gov/mmb/mmbpll/nampll12_fullcyc_2mbtop/index.html
  • 0600 UTC and 1800 UTC:

    • http://www.emc.ncep.noaa.gov/mmb/mmbpll/opsnam_offtime/index.html


NAM-WRF and SREF

  • SREF: Greater than 90% probability of the surface dew point > 600 F across central and southern Mississippi Valley





NAM-WRF Forcing and Vertical Wind Shear (not shown)

  • NAM-WRF highlighted important forcing mechanisms in a forecast of significant low-level frontogenesis and strong moisture flux convergence along the frontal features

  • NAM WRF substantiated the SREF probabilities of a highly sheared environment and added details to magnitude and distribution of shear



NAM-WRF Instant and Convective Precipitation







Summary – Case 1

  • SREF graphics indicated the likelihood of a severe weather event with a high potential for supercells and tornadoes across the mid Mississippi Valley on 2 April 2006. EPS forecasts also indicated substantial agreement between the 21 SREF members… increasing confidence in the forecast

  • Climate anomalies indicated the event would be associated with an uncharacteristically deep surface cyclone and an anomalously moist warm sector

  • High resolution model data helped fill in the details of the mode, evolution, and intensity of forecast convection, and highlighted important mesoscale structures, including relevant forcing mechanisms



Overview – Case 2

  • A marginal severe weather event occurred across parts of the Ohio Valley and Pennsylvania on 4 October 2006



October 04, 2006 Ohio Valley Severe Weather

  • A frontal system moved southward across the Ohio Valley and PA during the late afternoon/evening of 10/04/06

  • Significant heating/destabilization were questionable because morning convection was expected across OH and PA

  • 35 to 45 kt mid-level flow was expected across the region ahead of front

  • SPC highlighted locally-damaging winds and some hail… with storms organized linearly along/ahead of the front











PWAT 2-3+ SD above climate norm….MSLP 1-2 SD above climate norm

  • PWAT 2-3+ SD above climate norm….MSLP 1-2 SD above climate norm







10/04/09Z valid 10/04/21Z



SREF Summary

  • SREF single and combined probabilities illustrate an environment marginally favoring severe weather from organized convection across the parts of the Ohio Valley and Pennsylvania on 10/04/06

  • Isolated supercells are possible but not probable. Tornadoes are unlikely

  • Main threat: damaging winds



AWIPS NAM-WRF Oct 04/12Z Valid Oct (04-05)/21Z



10/04/12Z valid 10/04/21Z









NCEP Operational NAM-WRF Graphics





NAM-WRF Summary

  • NAM-WRF depicts more unstable environment with greater shear than SREF

  • It appears high resolution model provides valuable additional information …especially when a marginal severe event is expected







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