National Report of the UK ( , 950 Kb) - LCRS

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Met Office forecasting
methods for fog and low cloud
B.Golding
Head of Forecasting Research
Met Office, UK

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NWP
Site-specific model
Nowcast system
Manual techniques
Outline

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Unified Model NWP
UK mesoscale model
– ~12.5km grid, 38 levels
– v5 (June 2002): non-hydrostatic, semi-implicit, semi-
Lagrangian
– conserved thermodynamic variables, two phase cloud,
CAPE closure convection
– predicted aerosol
– visibility recently upgraded to allow for rain and snow as well
as cloud water
– verification shows skill limited to large scale fog events

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SSFM
Single column UM with 70 levels
Uses local upwind topography/land use
Verification shows skill limited by lack of local
data input
Used as input trial product generation in
AutoTAF and Autotext

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High resolution land use and
orography data

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SSFM graphical output

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Stansted TAF visibility accuracy, Oct
99 - Jan 00

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Autotext example
Predicción para MADRID 320016 válida desde 00:00 el
21/02/2002 hasta 12:00 el 22/02/2002
Madrugada
Cielo: despejado
Temperatura: temperaturas sin cambio a 4 grados C
Viento: oeste girando al noroeste 3
Tiempo: seco
Visibilidad: buena

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Precipitation
Nimrod
– 2km England & Wales, updated every 15 mins
– 5km Europe, updated hourly
Cloud: 15km, NW Europe, updated hourly
Visibility: 5km NW Europe, updated hourly
Others: lightning, wind, pressure
All nowcasts to 6 hours ahead

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Nimrod - Cloud
– 15km grid, 29 horizontal levels
– analysis uses METEOSAT imagery and surface
observations with forecast first guess
– precipitating cloud moved with precipitation
vectors
– non-precipitating cloud moved with model layer
wind
– merged with mesoscale model cloud forecast

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Nimrod cloud data
Surface visual & instrumental
observations define lower cloud
layers
Satellite images define
highest cloud layer
Model forecast & surface visual
cloud type observations define
intermediate cloud layers

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Nimrod cloud base forecast

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Nimrod - visibility
5km grid; liquid water temperature and total water
variables
analysis based on METEOSAT / AVHRR imagery and
surface observations
nowcast is persistence
merged with mesoscale model forecast
hill fog added from cloud forecast
used as input to Time & Place product

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Visibility Analysis
x
x
x x
x
x
x
x x
Observations
Satellite area
of fog/low cloud

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Nimrod visibility forecast

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Manual techniques
Saunders or Craddock & Prichard used to forecast
fog point, and hence fog formation with a cooling
curve
Jefferson or Barthrum used to predict fog clearance
temperature, and hence fog clearance with a warming
curve
Both temperatures better predicted by SSFM
Problem is with cooling/warming curve shape,
especially in presence of cloud
Local experience can be a major benefit

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Summary
Guidance provided by NWP, SSFM, Nimrod
Experimental automated services on trial
Manual forecast techniques unhelpful
High impact forecasts (e.g. TAFs) require
human experience and judgement

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Met Office Plans
in Fog & Low Cloud
Forecasting
Brian Golding
Head of Forecasting Research
Met Office, UK

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Nowcasting - Nimrod
Main areas
Site-specific modelling - SSFM
Downscaling
High Resolution NWP

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Nimrod plans
MSG - improved low cloud/ fog detection,
especially at night, replace use of AVHRR
Review of performance in progress
Considered use of grid of Single Column
Models, but expected to be overtaken by Hires
NWP

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SSFM
Initialisation using local obs
Kalman Filter error correction for visibility
Cloud ensemble

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High resolution NWP
New non-hydrostatic UM
HR-NWP project will focus on convective
precipitation
Experiments have shown much improved fog
prediction with a 3km grid length
If confirmed, expect to implement in 2006
Comparisons with SSFM & Nimrod

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Downscaling
Simple model used to downscale winds taking
account of local topography
Would like a similar tool for fog, but no definite
work planned currently

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Summary
Enhance SSFM with data assimilation and
statistical post-processing for aerodromes and
other point forecasts
Enhance Nimrod with MSG data and
improved algorithms for land and sea
transport
Implement fine scale NWP to represent nonlinear
interactions that are critical to accurate
fog and low cloud prediction