NUCAPS, Part One: Introduction

By Jorel Torres

The National Weather Service (NWS) has over 120 WFO (Weather Forecast Office) locations across the CONtinental United States (CONUS) where only a certain percentage of these offices produce and display RAwinsonde OBservations (RAOB). RAOB’s are important real-time observations for NWS forecasters where RAOB’s display an atmospheric stability profile, producing atmospheric measurements from the surface to the upper levels of the troposphere. RAOB’s not only assess the stability of the atmosphere, but can show levels of mixing (moist and dry air), the convective available potential energy (CAPE) needed for thunderstorm potential, determine precipitation type and can display the vertical wind profile; key parameters that are helpful for weather forecasting. The issue that comes into play is the lack of RAOB observations around the CONUS, which can become problematic for NWS forecasters. If a WFO does not produce any RAOB observations, forecasters at that WFO might rely on observations taken from WFO’s nearby, most in which are tens or hundreds of miles away. Consequently, there is a high probability the observation profile they utilize from a nearby WFO will be different than what would be seen at their own WFO; potentially causing inaccurate interpretation of real-time observations.

To help assist RAOB observations are NUCAPS (NOAA Unique Combined Atmospheric Processing System) satellite observations which combine the CrIS (Cross-Track Infrared Sounder) and ATMS (Advanced Technology Microwave Sounder) instruments on-board the Suomi-NPP satellite producing vertical temperature and moisture profiles of the atmosphere. Wherein NUCAPS and RAOB observations can be compared and displayed operationally for NWS forecasters in the Advanced Weather Interactive Processing System (AWIPS-II). Furthermore, NUCAPS can be seen as a complement to RAOB observations. RAOB observations occur every day at 00Z and 12Z only, while NUCAPS produces observations in between those hours, from 00Z-12Z and 12Z-00Z. The combination of NUCAPS and RAOB observations can further highlight the diurnal change in the vertical profile of the atmosphere since the atmosphere is always changing, and could benefit forecasters in severe weather nowcasting and the storm warning process. Additionally, NUCAPS has more observations to choose from compared to RAOB’s. Each NUCAPS observation (i.e., sounding) is approximately 50 kilometers (~30 miles) apart and are beneficial to WFO’s that do not produce RAOB observations. The differentiation between the number of RAOB observations to NUCAPS observations over the CONUS are shown in Figures 1A and 1B below.


Figure 1A: The display of NUCAPS observations across the CONUS shown in the AWIPS-II interface on 01 April 2016, @ 0846Z. Each filled circle is a NUCAPS sounding and the color dictates if the data is of good (green), ok (yellow), or bad (red) quality, respectively. It is important to note how many more NUCAPS observations there are in comparison to RAOB observations.


Figure 1B: The filled in blue circles indicate the locations where RAOB observations take place across the CONUS every day at 00Z and 12Z respectively. Notice how far away RAOB observations are from each other in comparison to NUCAPS observations.

NUCAPS expresses benefits for forecasters at WFO’s, however NUCAPS also has a few caveats. NUCAPS has trouble producing quality data when clouds are present in the atmosphere. Due to this limitation, a percentage of observations need to be modified by the forecaster, especially in the lower levels of the atmosphere where most clouds are present. Currently, this modification can be solved manually through the AWIPS-II interface, although it is cumbersome and can take too much time out of the forecaster’s daily operations. However, there are research studies that are ongoing that could help alleviate the manual modification and are working toward developing an automative process. One research study to note, is what is occurring at the Cooperative Institute for Research in the Atmosphere (CIRA) located in Fort Collins, CO, this spring and summer. CIRA is having a field campaign launching RAOB’s and comparing them to NUCAPS observations along the Colorado Front Range. The comparison of observations will be one step in the right direction in assessing what modifications are needed to produce better NUCAPS retrievals from satellite, which in turn, will increase forecaster’s confidence in its utility for weather forecasting. The field campaign starts in early May and will continue throughout the spring and summer of this year, 2016. For interested readers, look forward to future blog updates regarding the NUCAPS field experiment.

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