Graupel and Lightning Forecasting in the 1.5km UKV Model Jonathan Wilkinson © Crown copyright Met Office

Introduction Rightly or wrongly, high-resolution NWP models are capable of resolving thunderstorm cells. Parametrizations of lightning flash rate have been appearing in the literature over the last few years. Traditional forecasting of thunderstorms done with forecaster rules (e.g. CAPE or looking at tephigram profiles) Good for Cb but no necessarily good for lightning. Can we develop an “electric scheme” (or lightning diagnostics) for use in the UM? © Crown copyright Met Office

Prognostic Graupel Available as an option in the UM for some time. Code has recently been modified to increase graupel mass by a factor of 10 by including a missing process (snow-rain collection). Graupel currently expected to be in the operational model from end November 2012 and should be included in the 1.5 km UKV configuration. Looking at graupel diagnostics now. Possible candidates are: GWP (kg m-2) Altitude of the peak graupel (m) © Crown copyright Met Office

Lightning parametrization In this talk, show results from McCaul et al (2009). Most relations require prognostic graupel to parametrize cloud-to-ground flash rate. We are assessing a number of parametrizations: Price and Rind (1992, JGR-A) Deierling et al (2008, JGR-A) McCaul et al (2009, Weather and Forecasting) Dahl et al (2011, MWR) (The variables r1 and r2 are tuneable constants) © Crown copyright Met Office

Results: DYMECS and London Olympics © Crown copyright Met Office

A DYMECS lightning case: 1300-1900 UTC on 07/08/11 Sferics UKV © Crown copyright Met Office

Why forecasters were concerned Opening ceremony started at 9pm. UKV model shows showers near London at both 8pm and 9pm. Would these produce lightning that may disrupt the ceremony? 8pm 9pm © Crown copyright Met Office

Results- lightning at 07 UTC UKV ATDnet Lightning in channel captured © Crown copyright Met Office

Results- opening ceremony (20 UTC) UKV ATDnet UKV correctly forecasts No lightning for London area. © Crown copyright Met Office

Summary Current Status: Major Questions: We are well on the way to developing an operational lightning forecasting capability within the UM. Intention is to be able to do long-term comparisons of a number of different lightning schemes and show which is the best for different areas of the world. Current lighting scheme has only been tested in the UKV. Major Questions: How does this perform in other models and areas outside the UK? How does the algorithm perform in marginal situations? How good is the UKV model at getting graupel in the correct places at the correct time? How much electrical activity is in COPE-like storms? © Crown copyright Met Office

Summary Data sets or model improvements?: Understand UK lightning cases- use COPE or DYMECS data to see which storms initiate lightning- what makes them different from non-lightning storms? Improve UKV using COPE and DYMECS data on UK storms. Provide trial lightning forecasts for COPE? King Air wishing to avoid lightning situations at all costs. BAe-146 required time on the ground after a lightning strike last summer. © Crown copyright Met Office

Questions and answers © Crown copyright Met Office