2007_09_19_archive

Weather 101: What Are Computer Models?

Some popular questions I get from time to time have to do with

computer models. You may have heard of the GFS, the WRF, the GFDL, the

HWRF, the NOGAPS, the UKMET, the ECMWF, the CMC, and more but what are

they and which one is 'better' than the others?

First off, what are computer models? Computer models are simulated

forecasts of what a computer thinks the weather will be like over a

period of time. Think of them as simulations.

Each computer model will forecast weather for a different amount of

time, based on the data it ingests, the mathematical equations that

the computer running these forecasts needs to process, and the amount

of detail or resolution that is required to run the forecast. Some

computer models, such as the Global Forecast System (GFS) run

forecasts out to 16 days while other models, such as the Rapid Update

Cycle (RUC) will only run for 12 hours.

Here is a brief tutorial on what models are out there, how long they

forecast for, and how often they update. These only cover the major

'free' computer models that one can access through a bevy of sites,

including the models page here at Phillyweather.net which provides a

number of different computer forecast model links.

MODEL Stands For How often/day How many hours Best used

RUC Rapid Update Cycle Hourly 12 Nowcasting / current weather

SREF Short Range Ensemble Forecast 4 times daily

(03, 09, 15, 21Z) 87 Short term

WRF Weather Research and Forecast 4 times daily

(00, 06, 12, 18z) 84 Short term

UKMET United Kingdom Meteorological 2 times daily 120 Comparison

forecasting to other models

GEM (Canadian) Global Environmental Multiscale 2 times daily 144

Comparison forecasting to other models

EURO European Model 2 times daily 240 Weather pattern analysis

GFS Global Forecast System 4 times daily 384 Weather pattern

analysis/comparison forecasting

NOGAPS Navy Operational Global Atmospheric Prediction System 2 times

daily 144 Comparison forecasting to other models

Some other computer models that are not included here are the GFDL

which is a hurricane model that is run based off of GFS input, the NAM

(which has been effectively replaced by the WRF), and the MM5 which is

a mesoscale model run in several different formats.

These computer models ingest observation data (temperature, wind

direction and speed, humidity, pressure, and more) from the surface

and the upper atmosphere and the supercomputers that these forecast

models run from will generate forecasts a certain number of times per

day, with two or four times being the most common number of times

these forecasts are generated.

Whenever a storm is close at hand, some of the shorter range computer

models are more useful. The RUC, which runs hourly, is useful to

determine possible precipitation trends with storms. It is a higher

resolution model and is only intended to forecast for 12 hours as its

main purpose is to serve as a nowcasting tool. By the way,

"nowcasting" is defined as short range forecasting that can utilize

primarily radar, satellite, and surface observations in forecasting.

The RUC is a useful side tool but should not be relied upon solely for

a nowcast. The WRF model is another solid type of short-term model and

can sometimes spot a change in 'forecasted' track for a storm before

the GFS or other computer models do.

Regarding long range forecasts, some forecast models are better than

others. For instance, the EURO and GFS are better at spotting mid and

upper level atmospheric pattern changes than the NOGAPS or the Global

models are. However, these other models can spot occasional storms

before the GFS or EURO catch on to seeing them. In forecasting, you

will typically see meteorologists rely upon the GFS or EURO for

midrange and longer range forecasts as these computer models typically

perform the best at seeing what changes can take place in the

atmosphere.

Meteorologists use the different computer models out there and can

make a forecast based partially on the forecasts these computer models

make. However, the computer models are only guidance into what could

happen and it is important to note that accuracy can sometimes vary

widely. That's why good meteorologists will rely upon other tools such

as surface observations in other parts of the country and climatology

(past performance in similar situations) to come up with a forecast.

Technorati Tags: Weather 101, computer models, long range forecasting,

weather patterns

written by Tom @ 6:22 PM |

Stepping Up The Ladder

Weather in Philadelphia started out cool this week but as everyone and

their brother has told you the temperatures are on their way up.

Today's high of 79 in Philadelphia was the warmest in a few days and

we should see temperatures continue to warm up through Saturday. I'm

forecasting temperatures in the 80's for the next 3 days with the

potential for upper 80's on Saturday here in Philadelphia. This could

be a week long stretch of warmth here in Philadelphia as temperatures

could be 80 or above through next Wednesday.

The culprit? A weak and somewhat zonal jet stream that is situated far

to our north. With the lack of blocking in the upper level pattern we

will continue to see high pressure ridges to our south and the main

storm track from the Midwest through Eastern Canada. This high

pressure ridge is an extension of the same stubborn Bermuda high that

has kept our weather dry for the majority of the last several weeks

here in the Delaware Valley.

Technorati Tags: weather patterns, warmth

written by Tom @ 6:03 PM |

Septembr 20th, 2007 Forecast

Here is what we saw today:

...and here is what we will see tomorrow:

If you look real close to the top of the picture, you will see a

cloud. Thursday will quite likely be a carbon copy of today with

almost completely clear skies and tons and tons of sunshine. As high

pressure continues to move off of the coast we will see temperatures

climb for the next few days, with a frontal boundary coming through on

Saturday to 'cool' us off from the mid and upper 80's on Saturday into

the lower 80's on Sunday. Temperatures at night will also moderate

over the next few days, from the mid and upper 50's tonight to the mid

60's on Friday night as warmer air will have made its way into the

region.

Weather and Business Do Mix: CNBC had Paul Walsh of Storm Exchange on

during Squawk on the Street earlier today. He was discussing "Fall

Weather Risk" and he asserted that 30% of the market was subject to

weather related risk.

It's Not Just Here: People in the Pacific Northwest complain about the

weather, too.

Hoping for Cold: Buffalo is hoping that it will be cold on New Years

Day so they can play hockey at outdoor Ralph Wilson Stadium against

Pittsburgh.

Technorati Tags: daily forecast, CNBC, business, NHL Outdoor Hockey,

Buffalo

written by Tom @ 5:41 PM |