New Remote Sensing Technologies

http://cimss.ssec.wisc.edu/goes/blog/about

NOAA’s Cooperative Institute for Meteorological Satellite Studies

(CIMSS), located at the University of Wisconsin – Madison’s

Space Science and Engineering Center (SSEC)

Forecasting Lake/Ocean Effect Snow

Forecasting Lake/Ocean Effect Snow

LOES are difficult phenomena to forecast: Mesoscale temporal/spatial resolution

I can predict thunderstorms will occur but can’t tell you exactly where.

Standard rawinsonde network lacks spatial/temporal resolution to adequately sample/observe this phenomenon.

Onset, intensity, orientation, exact location very sensitive to wind direction and thermal stratification in the lower troposphere.

Operational NWP is still not sophisticated enough to simulate the air-sea interface and lower atmospheric processes or resolve the physical scale of the snowbands.

Forecasting Lake/Ocean Effect Snow

Empirical Forecast Rules Assess:

Localized Instability. Depth of the mixed layer. Ambient moisture of the airmass. Wind direction and speed through mixed layer.

Then determine how long such conditions remain steady-state to sustain the snow band.

BUFKIT Guidance – Used at OSPC

Guidance product developed at NWSFO Buffalo that imports and displays hourly model sounding data from several models.

Numerical Weather PredictionMesoscale Modelling of LOES

Brief History of NWP and LOES

Date Model

Resolution Land/Sea Mask(Great Lakes)

pre 1980 LFM    ~160km  No Great Lakes

1980-90      NGM  ~ 80km 1-2 grid points per lake

1995-2000    

ETA  80km then 40km

A few more lake points

2000-2003 ETA  32km Even more lake points

2003-2005   ETA  12km Resolves lakes well.

2006 WRF   4-8km Well-defined Great Lakes??

2006 * YYZ 500m Individual Rolls

2007-09 WRF Ensembles Consensus Solutions* Research Cloud Model Being Run at The University of Toronto

Model Resolution

• It takes roughly 4 to 8 points to resolve a wave.

• To resolve a 20km wide snowband:– 20km / 4 points ~ 5km horizontal model resolution.

• Therefore, only the larger, single banded snows have any chance of being explicitly simulated by most operational NWP today.

Bua (2002) Outlined Success/Deficiency of a Mesoscale Model for a Single Band Event Using ETA-

12km.

• Precipitation deficiencies seen may result from:

– Latent and sensible heat fluxes from Lake Erie that were lower than occurred because surface winds used to calculate the fluxes were too light.

Sensible Heat (temperature) Flux Fs = rCDCp|V|(Tw-Ta)

Latent Heat (moisture) FluxFh= rCqLv|V|(qw-qa)

Model Wind - 250° at 10 ktsObserved Wind - 200° at 35 kts

ETA Model Simulation Cloud Water and Surface Wind – Observed Wind

Green – observed wind Blue – Model Wind

From Bua, 2002

ETA Model Simulation Results

• General Precipitation Deficiencies Result From:• Eta-12 surface winds underforecast by up to 20 kts• Latent and sensible heat fluxes that are too low,

perhaps by as much as a factor of 3.

• The steady state single lake effect snow band will thus get too little moisture and heat from below, which will result in:

• too little instability• too little convection• too little precipitation.

• Additionally, convective scheme does not draw moisture out of the boundary layer.

• Leaves it too moist and warm.

• This reduces the vertical gradient of moisture and temperature, and thus even further reduces already low latent and sensible heat flux from the lake.

ETA Model Simulation Results

• In spite of the physics limitations, the model captured the essence of the mesoscale circulation generated by the passage of cold air over Lake Erie.

• We can conclude that the Eta-12 got synoptic/gross scale features of the mesoscale environment correct, since it predicted a single snow band.

ETA Model Simulation Results

REGIONAL-SCALE ENSEMBLE FORECASTS

OF THE 7 FEBRUARY 2007 LAKE EFFECT SNOW EVENT

Justin Arnott and Michael EvansNOAA/NWS Binghamton, NY

Richard GrummNOAA/NWS State College, PA

What is the Northeast Regional Ensemble?

• 12 km Workstation WRF– 24 hr run length

• 2007-2008: 8 Members– 2 CTP members– 1 Operational

• Goal: Improve operational forecasts of lake effect snowfall

The Ensemble – 2008/09Office Core BCs Micro CPS #Z Lev

Operational NMM

NAM Ferrier BMJ 60

BGM ARW NAM Lin KF 31

CLE ARW GFS Lin KF 40

CTP-1 NMM

NAM Lin BMJ 31

CTP-2 ARW NAM Lin BMJ 31

BUF NMM

GFS Ferrier KF 31

BTV NMM

GFS Ferrier BMJ 31

Northeast Ensemble Project

• Case Study Conclusions

– Suggests ensemble approach to LES may be valuable

– Hone in on high-probability impact areas

– Highlight outlier (low-probability) outcomes

Summary

• NWP much improved but limited in abilities:– Initialization and data assimilation– Microphysics– Convective parameterization– Other factos

• As a result, QPF and subsequently, snowfall forecasts are a tremendous challenge.

Summary

• Better data initialization/assimilation, improved physics and other improvements will enhance our understanding and further the development of new and improved conceptual models.

• Development of more local expertise (e.g., focal point meteorologists to build local guidance packages, do case studies, etc.) will also lead to improved forecasts.

Summary