Near-real time CAPE East of the Rockies combining Hyperspectral IR Satellite Sounding and ASOS Surface Stations: Part II Methodology and Preliminary Results

Near-real time satellite data can give forecasters the extra edge they need to issue timely and accurate watches and warnings. The Convective Available Potential Energy (CAPE) is a measure of atmospheric instability computed from vertical profiles of temperature and water vapor used the National Weather Service Storm Prediction Center (NWS SPC). CAPE can give forecasters valuable information as to the stability of the atmosphere and therefore the potential for severe weather. The value of using satellite vertical soundings from hyperspectral infrared sensors has been recognized at the NOAA Hazardous Weather Testbed workshops held at the NWS SPC (http://hwt.nssl.noaa.gov/).

Satellite overpass times from EUMETSAT METOP IASI at 10:30am/pm and NASA AQUA AIRS, Suomi-NPP CrIS, and JPSS J1 at about 1:30am/pm occur conveniently between the operational 0 and 12 UTC NWS radiosondes. Since the day’s first in-situ measurements are taken in the early morning there is a need for forecasters to see the SkewT vertical profiles of temperature and water vapor updated from the 6am (0 UTC) soundings. In addition to more temporal coverage, satellite date can provide spatial coverage between NWS radiosonde launch sites. Automated Surface Observing System (ASOS) stations currently operate routinely as U.S. airports and provide surface meteorological measurements at 1 minute intervals reported in METAR format.

A set of ASOS surface stations east of the Rocky Mountains is used to extract hourly averaged temperature and dewpoint temperature each hour. These point data are smoothed to a 0.7x0.7 degree grid using a 2-dimensional convolution which fills in the values between stations. A similar gridding is applied to the satellite Level 2 soundings for ascending (daytime) and descending (nighttime) overpasses. The gridded ASOS surface observation and IR sounder profiles are merged before computing surface CAPE values. The merging technique is validated in Part I of this two-part paper. Contour plots of CAPE from the merged observations dataset are presented compared with corresponding reanalysis fields from numerical weather prediction (NWP) models.

Using the resources of the SSEC we are able to demonstrate a near-real time estimate of the CAPE in the U.S. east of the Rocky Mountains using the direct broadcast reception facility at UW-Madison and access to NASA real-time data streams. A preliminary demonstration of near-real time CAPE using JPSS satellite data is intended to be made available via a restricted web page at SSEC. More information is available upon request.