OPERATIONAL EVALUATION OF THE LAPS-MM5 \"HOT START\"

LOCAL FORECAST MODEL

Brent L. Shaw^1,^, Eric R. Thaler^2^, and Edward J. Szoke

*^1^NOAA Research-Forecast Systems Laboratory*

*Boulder, Colorado*

*\[In collaboration with the Cooperative Institute for Research in the
Atmosphere (CIRA),*

*Colorado State University, Fort Collins, Colorado\]*

*^2^NOAA National Weather Service Forecast Office*

*Boulder, Colorado*

1\. INTRODUCTION

Within the past few years, as computers have grown exponentially in
capability per unit cost, mesoscale numerical weather prediction (NWP)
models have been increasingly used as a \"real-time\" weather
forecasting tool by researchers and some operational agencies. It is now
possible for individual weather forecast offices (WFOs) to acquire a
relatively inexpensive cluster of personal computers on which to run
these sophisticated, high-resolution models to support their operations.

The Local Analysis and Prediction Branch of the NOAA Forecast Systems
Laboratory (FSL) has been focused on the problem of local-scale data
assimilation and NWP for several years. To address this goal, the Local
Analysis and Prediction System (LAPS, Albers et al. 1996) was developed
to provide a means to combine all available sources of meteorological
data, including radar, satellite, and locally acquired data (e.g., local
mesonets, etc.) into a single, coherent three-dimensional representation
of the atmosphere and sensible weather at high spatial and temporal
resolution. Alone, the analysis component of LAPS can be used as a
short-term \"nowcasting\" tool. When coupled with a forecast model, LAPS
can also provide quantitative forecasts.

During the summer of 2000, FSL began testing a new version of LAPS that
allows an NWP model to be diabatically initialized with all
microphysical species (cloud water, ice, rain, snow, and graupel)
present in the model initial conditions and in dynamic balance with the
model mass and momentum fields (Schultz and Albers 2001, McGinley and
Smart 2001). In the early fall, FSL began using this new technique to
initialize real-time simulations using the NCAR/PSU Mesoscale Model 5
(MM5). The output is made available on the Internet
(http://laps.fsl.noaa.gov) and on FSL\'s Advanced Weather Information
and Processing System (AWIPS) workstations for evaluation purposes and
is frequently used during local weather discussions. Due to its unique
diabatic initialization technique, it has been dubbed the \"hot start\"
MM5 forecast, hereafter referred to as \"MM5HOT\".

Although preliminary quantitative evaluation of these forecasts shows
improved skill in forecasting clouds and precipitation in the early
portion (0-6 h) of the forecasts compared to other initialization
methods (Shaw et al. 2001), an assessment of the operational utility of
the MM5HOT was desired.

Since the completion the new David Skaggs Research Center in Boulder in
1999, FSL and the Denver National Weather Service (NWS) WFO have been
collocated. This has provided for improved cooperation between FSL
researchers and NWS operational forecasters. This relationship allows
new tools and techniques under development by researchers within FSL to
be used and evaluated by operational forecasters. This feedback can then
be used to further improve the technology before potential full
technical transition occurs to the rest of the NWS offices.
Additionally, the forecasters benefit from having these additional tools
available to them to assist in daily operations. This paper discusses
the results of a collaborative effort that has been underway since
December 2000 to provide operational feedback on the MM5HOT forecasts.

2\. OPERATIONAL CONSIDERATIONS

For any tool to be useful in an operational environment, there are
several critical issues that must be addressed. First, the forecasters
must perceive that the tool has the potential to provide added value
during their forecast preparation. This is dictated by the vast amounts
of various tools and data sources available in the modern WFO due to
improved communications and computing technology. There is generally
insufficient time to consider all data sources, so those that are
perceived and/or demonstrated to add the most value will be the most
used. In the case of the Boulder WFO, the utility of a local model was
demonstrated during a cooperative experiment in which two mesoscale
models (RAMS and MM5) were run by FSL for evaluation during the winter
of 1996-1997 (Szoke et al. 1998). Following that experiment, a modified
version of the RAMS model was run in real time on a workstation within
the Boulder WFO for approximately two years, ending in the summer of
2000. Finally, the forecasters had a positive perception of the MM5HOT
as a result of seminars and personal communication with FSL staff.

Second, the tool must be easy to use in the operational environment
without extra steps that may not fit within the hectic pace of active
weather days. While it is generally easy to access web products, it is
not as convenient as having the grids available on the system where the
operational data and products are viewed and created. During the study
described in Szoke et al. (1998), the web products were frequently not
used due to this very reason. Thus, FSL worked with the Boulder WFO to
set up a mechanism to transfer the grids in a format that can be
displayed on their operational AWIPS workstations. Not only does this
make access easier, but it allows the forecasters to quickly assess the
forecast quality by overlaying satellite and radar imagery and
observations on the forecast fields. This was the single most important
step taken that led to the forecasters routinely using the model output.
![](media/image1.emf){width="3.120138888888889in"
height="2.504166666666667in"}

Third, the tool or data source must be available in a timely manner so
that the forecaster can consider it prior to putting together the final
forecast products. The MM5HOT runs on FSL\'s High Performance Computing
System (HPCS), a massively parallel Linux cluster of Compaq Alpha PCs.
Using 24 processors, the model is launched four times per day at 45 min
after the model initialization time, when the LAPS analysis is complete.
The complete 24-h forecast is available to the NWS forecasters on their
AWIPS workstations within 2 h of the model cycle time. This
configuration is run four times per day with cycle times of 0000, 0600,
1200, and 1800 UTC and provides hourly output for all 24 h of the
forecast at full spatial resolution. Although the use of the HPCS may
not be representative of a typical forecast office, a much smaller
cluster of Linux-based PCs (e.g., 6-8 processors) has become a very
powerful and relatively affordable solution that could provide similar
timeliness for a smaller domain configured for their county warning area
(CWA).

3\. LOCAL FORECAST CHALLENGES

Figure 1 shows the Boulder CWA of responsibility. The CWA covers an area
with highly varying topography, ranging from approximately 1050 m in the
northeastern portion (Platte River valley) to over 4200 m along the
Continental Civide. The Rocky Mountains in the western portion of the
area play a major role in the area\'s weather. Mountain wave activity
can produce localized wind storms, including Chinook wind events.
Additionally, two subtle areas of elevated terrain are oriented
east-to-west along the northern boundary (Cheyenne Ridge) and the
southern boundary (Palmer Divide). These two features modify local wind
flow to produce circulations often responsible for convergence zones
that produce or enhance localized areas of precipitation. This highly
variable topography makes the Boulder CWA an ideal location to employ a
mesoscale model to better capture and forecast small-scale weather
events.

4\. MODEL CONFIGURATION

The LAPS analysis and the latest version of MM5 (version 3, release 4)
were configured for the domain shown in Fig. 2, and consists of 125 by
105 horizontal grid points using a 10-km grid spacing. The LAPS analysis
used 21 vertical levels on constant pressure surfaces at 50-mb intervals
from 1100 mb to 100 mb. The forecast model uses 41 vertical sigma levels
(pressure-based terrain-following coordinate) with the finest resolution
near the boundary layer. Table 1 summarizes the physics options used for
the real-time forecast runs. These settings refer to the standard
options available in this release of MM5.

Table 1. MM5 run-time configuration.

  -----------------------------------------------------------------------
  **Convective Scheme**               Kain-Fritsch
  ----------------------------------- -----------------------------------
  **Microphysics**                    Schultz

  **PBL Scheme**                      Blackadar

  **Land Surface**                    5-Layer Soil Model

  **Radiation**                       RRTM

  **Time Step**                       30 seconds
  -----------------------------------------------------------------------

As a result of LAPS versatility to use virtually any source of
operational meteorological data, the real-time forecasts can benefit
from frequent assimilation of traditional data sources as well as those
only available within the local office. The following data sources are
routinely used in the analyses that initialize the real-time forecasts:
GOES imager and sounder radiances, WSR-88D reflectivity and VAD winds,
vertical wind profilers, aircraft observations (ACARS and PIREPs),
radiosonde reports, and surface observations (includes standard METAR
reports and several mesonets located throughout the region).

5\. RESULTS

![](media/image2.emf){width="3.122916666666667in" height="2.63125in"}

Although the MM5HOT forecasts have only been undergoing operational
evaluation since January 2001, preliminary feedback has been very
favorable. Most, if not all, of the forecasters evaluate the forecast
output when preparing the short-term forecasts, and it is frequently
mentioned in the area forecast discussions when the weather situation
dictates the need for mesoscale guidance. Additionally, confidence in
the forecast grids is high enough to warrant the use of the grids in the
Graphical Forecast Editor (GFE), a component of the Interactive Forecast
Preparation System (IFPS, Mathewson et al. 2000) developed at FSL and
being evaluated by the Boulder WFO. Through April 2001, the forecasters
have used the GFE to create hourly temperature, wind, and dewpoint
fields at the surface for display on their public web page. They have
the option to initialize these grids with any available model, and they
sometimes use the MM5HOT forecasts in this manner for the first 24-h
period.

Several benefits of using MM5HOT within the Boulder WFO have been
identified:

-   The MM5HOT does much better than the national models at forecasting
    local winds, particularly when they are modified due to subtle
    orographic effects. Examples of the model\'s ability to correctly
    diagnose and forecast the presence of the \"Longmont Anticyclone\"
    and the \"Denver Cyclone\" are discussed in Szoke and Shaw (2001).
    Forecaster feedback indicates that the model forecast of winds for
    the various airports along the Colorado Front Range urban corridor
    can often be used with little modification when preparing terminal
    forecasts.

```{=html}
<!-- -->
```
-   Mountain wave activity is handled much better by the local model
    than the national-scale models because of the increased vertical
    resolution and the pressure-based, terrain-following coordinate. In
    these situations, the model has been a great asset in determining
    the eastward extent of the mountain wave-induced winds. Often, these
    situations result in very strong westerly winds along the immediate
    Front Range areas with a rapid transition to weak easterly flow a
    few km east of the foothills. Additionally, the higher-resolution
    topography allows the model to better identify lower-elevation areas
    where a deeper boundary layer may preclude full downward mixing of
    the westerly momentum, despite these locations\' apparent favorable
    position relative to the mountain wave.

```{=html}
<!-- -->
```
-   The model does a good job of predicting localized precipitation
    patterns related to subtle orographic features (e.g., the Cheyenne
    Ridge and Palmer Divide) not represented well in the national-scale
    models.

```{=html}
<!-- -->
```
-   The surface temperature forecasts from the model do a much better
    job of representing significant differences due to subtle elevation
    differences not captured in the national-scale models. For example,
    in the presence of a Chinook wind situation, areas located in the
    Platte River valley will often not experience mixing of the drier,
    westerly winds all the way down to the surface, and will thus remain
    10-20 K cooler with calm or very light winds. The model frequently
    correctly forecasts these situations.

```{=html}
<!-- -->
```
-   In addition to the meteorological advantages, the WFO benefits from
    the flexibility inherent in running the model locally. Since the
    grids do not have to be transmitted on the Satellite Broadcast
    Network (SBN) like the national grids, the office is able to get
    every grid point of the output with a 1-h time increment. In
    contrast, NCEP is currently running the Eta with a 22-km grid
    spacing, but is only able to transmit the upper-level data on a
    coarser 40-km grid due to bandwidth limitations. Additionally,
    having the raw model output available locally allows additional
    variables to be displayed, such as the various prognosed
    microphysical fields and derived parameters such as visibility,
    cloud ceiling, etc. Traditionally, these fields must be inferred by
    the forecaster. Having them explicitly available from the model
    provides a new dimension to the use of model output in the forecast
    process. Furthermore, since LAPS is able to produce a complete,
    three-dimensional analysis every hour (or more frequently) due to
    its use of radar, satellite, wind profilers, and aircraft
    observations, the model can be initialized at any given hour of the
    day and run to any arbitrary forecast length. This allows the model
    to run at optimum times to meet the local office\'s production
    schedule. With the current national data production and distribution
    architecture, it would be impossible to tailor model production
    schedules to meet the exact needs of every WFO. Finally, the model
    configuration can be adjusted more quickly and on an \"as needed\"
    basis to provide the optimal results for the CWA\'s special forecast
    problems.

```{=html}
<!-- -->
```
-   From a scientific perspective, the forecasters are very interested
    in the model\'s ability to depict high-resolution weather phenomena
    that national-scale models cannot (either due to native resolution
    or communications bandwidth issues). This stimulation leads to
    improved understanding of the physical processes that are associated
    with various events, which presumably can lead to improved
    forecasts.

No assessment would be complete without finding negative aspects, and
there have been a few identified during this effort:

-   The model surface temperature forecasts tend to have a cold bias on
    sunny days during the peak heating period and tend to be too warm at
    night. The daytime bias can be as much as 5-10 K.

```{=html}
<!-- -->
```
-   There is an accentuated cold bias in the surface temperatures when a
    grid point is initialized with snow cover present and the actual
    snow melts during the time covered by the simulation. This is due to
    the land surface option currently exercised in the real-time runs,
    which does not allow the snow cover to change during the simulation.
    This may be mitigated through the use of a more advanced surface
    model option, and there are plans to do so.

```{=html}
<!-- -->
```
-   Although the model tends to do a good job forecasting local
    precipitation patterns, the actual amount of accumulated
    precipitation tends to be too high. The cause of this is being
    investigated.

```{=html}
<!-- -->
```
-   Convective cells generated by the model tend to have greater spatial
    coverage than observed, which is to be expected when using a
    grid-spacing as coarse as 10 km. This may be mitigated by running
    the model at sufficient horizontal resolutions to explicitly resolve
    convection (e.g., 1-3 km grid spacing).

```{=html}
<!-- -->
```
-   Although the use of the FSL HPCS allows the model simulations to be
    completed quickly, the use of a research-oriented computing system
    can lead to reliability problems not normally experienced with the
    national models. During peak usage, the model must wait in a job
    queue until processors are available. Additionally, the HPCS is on
    the cutting-edge of affordable supercomputing technology, and there
    have been growing pains in the use of this system which has been on
    line less than a year as of April 2001. On a positive note, the fact
    that the forecasters complain when the model is not available as
    expected is a testimony to the usefulness of the product.

Overall, based on verbal feedback from the NWS staff, the forecasts
produced by the MM5HOT have been beneficial in their daily operations
thus far.

6\. CONCLUSIONS

The use of a locally run mesoscale analysis and forecast system such as
the one discussed in this paper can add significant value to the
operational forecast process, particularly in areas where topographic
effects play a large role in localized weather phenomena. These benefits
are largely due to the following:

-   A locally run model offers more flexibility (physics options, cycle
    times, domain, etc.) than what can be provided by a centralized
    facility.

```{=html}
<!-- -->
```
-   Running a model locally eliminates the communications network as a
    limiting factor in determining the temporal and spatial resolution
    at which grids can be displayed.

```{=html}
<!-- -->
```
-   A locally run analysis system can take advantage of data sources
    that may not be available to a centralized facility and can run more
    frequent analyses for the local area.

Additionally, the MM5HOT system described in this paper has demonstrated
potential to improve explicit NWP forecasts of clouds and precipitation
in the 0-6 h period due to its unique diabatic initialization (Shaw et
al. 2001, Birkenheuer et al. 2001).

Planned work includes the installation of a similar system at three NWS
WFOs during the summer of 2001, as well as at the two USAF space launch
facilities. This will provide further opportunities for feedback from
the operational community. Additionally, the LAPS diabatic
initialization technique continues to be improved, and future tests will
include the use of other forecast models, such as the new Weather
Research and Forecast (WRF) model. As the ability to compute and store
data continues to increase exponentially, it is not an unrealistic
vision to imagine every operational local forecast office running a
mesoscale data assimilation and forecast system in the near future. This
could serve as a complementary tool to the national-scale NWP forecasts
produced at the centralized facilities and the various nowcasting tools
and techniques being developed.

**7. REFERENCES**

Albers, S., J. McGinley, D. Birkenheuer, and J. Smart, 1996: The Local
Analysis and Prediction System (LAPS): Analysis of clouds,
precipitation, and temperature. *Wea. and Forecast*., **11**, 273-287.

Birkenheuer, D., B. Shaw, S. Albers, and E. Szoke, 2001: Evaluation of
local-scale forecasts for severe weather of July 20, 2000. *18th
Conference on Weather Analysis and Forecasting*, Fort Lauderdale, FL,
Amer. Meteor. Soc., \[this volume\].

Mathewson, M., T. LeFebvre, and T. Hansen, 2000: The Interactive
Forecast Preparation System. *FSL Forum,* N. Fullerton, Ed., December
2000 issue, NOAA Forecast Systems Laboratory, Boulder, CO
(http://www.fsl.noaa.gov/\~vondaust/f200/).

.

McGinley, J. A., and J. R. Smart, 2001: On providing a cloud-balanced
initial condition for diabatic initialization. *14th Conference. on
Numerical Weather Prediction*. Fort Lauderdale, FL, Amer. Meteor. Soc.,
\[this volume\].

Schultz, P. and S. Albers, 2001: The use of three-dimensional analyses
of cloud attributes for diabatic initialization of mesoscale models.
*14th Conference. on Numerical Weather Prediction*. Fort Lauderdale, FL,
Amer. Meteor. Soc., \[this volume\].

Shaw, B. L., J. A. McGinley, and P. Schultz, 2001: Explicit
initialization of clouds and precipitation in mesoscale forecast models.
*14th Conference. on Numerical Weather Prediction*. Fort Lauderdale, FL,
Amer. Meteor. Soc., \[this volume\].

Szoke, E., J. A. McGinley, P. Schultz, and J. Snook, 1998: Near
operational short-term forecast from two mesoscale models. 12th
Conference on Numerical Weather Prediction, Phoenix, AZ, Amer. Meteor.
Soc., 320-323.

\_\_\_\_, and B. L. Shaw, 2001: An examination of the operational
predictability of mesoscale terrain-induced features in eastern Colorado
from several models. Ninth Conference on Mesoscale Processes, Fort
Lauderdale, FL, Amer. Meteor. Soc., \[this volume\].