## 5 Weather Forecasting Models
### The Next Leap  
The World Meteorological Organization (WMO) is a specialized agency of the United Nations (UN) tasked with establishing and maintaining an integrated Earth system observation network. This global network is composed primarily of state-operated weather and climate monitoring resources from the WMO's 187 member states. Its objective is to provide reliable weather and climate data to a wide range of end-users [26]. For the first time, a  
Figure 5: 3D Precipitation Structure—Courtesy of Tomorrow.io. privately held entity will possess weather monitoring resources at a scale comparable to those of state-level infrastructure, contributing additional value to the WMO's operational capabilities and global observation efforts. Tomorrow.io, a U.S.-Israeli startup specializing in advanced weather technology, is poised to revolutionize global weather and climate monitoring by deploying the world's first dedicated constellation of 30 weather observation satellites. The company aims to launch at least 20 of these satellites into low Earth orbit (LEO) by the end of 2025. The constellation will include two primary sensor types:  
1. Active Ka-Band Radars  
These radars will be placed at an altitude of 550 km in sub-synchronous, mid-inclination orbits. They will operate in the Ka-Band frequency range of 35.5 to 36 GHz, offering distinct advantages over lower-frequency systems. Specifically, Ka-Band operation enhances sensitivity to both low and high-intensity precipitation, improves detection of vertically integrated liquid water content compared to Ku-Band radars, and enables accurate estimation of a wide range of surface precipitation intensities. The shorter wavelength also allows for the use of smaller antenna and radio frequency (RF) components, optimizing satellite design. The radars will provide horizontal resolution of 5 km \(\times\) 5 km and vertical resolution of 250 m. Each radar is designed for a mission lifespan of approximately 5 years. 2. Passive Microwave Radiometers  
These instruments will also be deployed at 550 km in mid-inclination orbits, operating within the 91 to 204 GHz frequency range. The radiometers will offer horizontal resolutions of 26 km \(\times\) 28 km at 91 GHz and 14 km \(\times\) 17 km at 204 GHz. The higher operating frequencies enhance the ability to detect atmospheric water vapor, cloud liquid water, and precipitation profiles. Each radiometer is designed with a mission lifespan of approximately 3 years. This constellation will establish the first global, near-real-time sensing network capable of providing high-resolution precipitation measurements and atmospheric profiles. The resulting data will support a wide range of applications, including advanced severe weather alerts, early warning systems, and emergency management operations (as illustrated in Figure 6). For discussion purposes, the U.S National Weather Service defines tornadoes, severe thunderstorms, flash floods, and urban and small stream flooding (which is not life-threatening) as severe weather events. The service monitors these phenomena and issues warnings to the public, primarily to prevent any unfortunate loss of life [27]. For instance, it is well established that environmental moisture plays a critical role in the intensification of tropical cyclones and hurricanes (both classified as forms of tropical storms) by facilitating convection and precipitation outside the storm system. In a study on the impact of environmental moisture on tropical cyclone intensification, [PERSON], of the California Institute of Technology, illustrated this concept, stating:  
_\"Enhanced environmental moisture ahead of a northwestward-moving storm induces a dry air intrusion into the inner core, limiting storm intensification. In contrast, increased moisture in the rear quadrants favors intensification by supplying additional moisture to the inner core and promoting storm symmetry, with primary contributions originating from moisture increases in the boundary layer.