Conventional satellite imagery depicted an upper low digging slowly southeast into the Central Rockies. Meanwhile, an active subtropical jet was focused farther south underneath it lifting northeast across northern Mexico and downstream across the wind across the Gulf Coast states.
GOES Sounder Air Mass RGB animation showing the evolution of heavy thunderstorms over the Gulf Coast centered near Houston (0600 UTC 04/16/15 – 0600 UTC 04/17/15).
While there was broad warm air advection, instability and a very moist airmass focused across the western Gulf Coast region, there were no identifiable features on the larger scale in conventional satellite imagery that suggested a forcing mechanism for organized convection to initiate. However, upon closer inspection of morning GOES-RGB airmass imagery, a subtle and small scale, but identifiable feature appeared that reflected a shortwave impulse. This impulse was tracked crossing the Rio Grande river at 12Z/16, and in conjunction with deep moisture and diurnal instability proved to be the catalyst for increasingly organized convection after 18Z/16 that continued past 00Z/17 along the Upper Texas coast and coastal areas of southern Louisiana. The result was 4 to 8 inches of rain, and flash flooding in the suburbs of Houston, TX.
GOES Sounder Air Mass RGB valid at 1200 UTC on 04/16/15. The red circle denotes the subtle shortwave that initiates downstream convection.
GOES-13 Water Vapor image valid at 1215 UTC on 04/16/15. The red circle denotes the same shortwave identified in the Air Mass RGB image.
GOES Sounder Air Mass RGB image valid at 1800 UTC on 04/16/15.
GOES-13 Water Vapor image valid at 1815 UTC on 04/16/15.
GOES Sounder Air Mass RGB valid at 0000 UTC on 04/17/15.
GOES-13 Water Vapor image valid at 0015 UTC on 04/17/15.
The NSSL 24-hour QPE product valid at 1200 UTC on 04/17/15.
While most of us thaw out after a rough February into the first week of March, winter weather-wise, the Southern Hemisphere is boiling with deep convection that has spawned three tropical cyclones near Australia and the South Pacific, one tropical cyclone in the West Pacific (a twin of sorts to TC Pam in the South Pacific), and an invest area near the coast of southern Brazil. There is a weak El Nino that is centered near the dateline in the West Pacific and there is currently a strong westerly wind burst associated with the current state (Phase 6 moving to 7) of the Madden-Julian Oscillation (MJO). TC Pam and TS Bavi look to have formed near this burst as part of the overall monsoon trough that straddled the equator. TC Nathan may have also formed due to the strength of the monsoon trough, while TC Olwyn formed well to the west on the other side of Australia.
I have put together some animations and a snapshot of the of the four storms near Australia and Guam.
MTSAT-2 Infrared satellite image of four concurrent tropical cyclones in the western Pacific and eastern Indian Oceans valid at 2032 UTC on 03/11/2015.
A four day animation that shows the development of TC Pam, TC Nathan, TC Olwyn, and TS Bavi valid from 03/08/15 to 03/11/15.
MTSAT-2 Infrared Satellite imagery with GLD-360 lightning strikes overlaid showing the lightning distribution (cloud-to-ground and some intra-cloud) associated with all four tropical cyclones valid from 1432 UTC on 03/10/2015 to 2032 UTC on 03/11/2015.
Finally, a new invest area has been identified near the southern coast of Brazil on the tail end of a mid-latitude storm system. This is rare, but not unprecedented as this area occasionally sees subtropical development during the Southern Hemisphere summer. The RGB Air Mass animation below shows the system still developing, but appears to be embedded in a cold core system as indicated by the orange, red, and purplish coloring. There is a significant amount of upper-level dry air that the system has to fight through, but water temperatures are slightly above normal (+0.5C), so some additional development is possible (thank you to Dr. Jeff Masters for the information).
SEVIRI RGB Air Mass animation of Invest 90Q in the South Atlantic valid on 03/11/2015.
Thanks for reading! I’ll try to follow up on these systems as they develop.
So, we have all probably noticed that it has been cold lately. Well, due to the ample snow cover over much of the U.S. at this time, the baroclinic zone is sharpening over the lower Mississippi and Ohio River Valleys this afternoon with the aid of shortwave energy coming out of a cutoff low located over the Southwest U.S. One of the Ocean Prediction Center forecasters, Tim Collins, noted the strong contrast in temperature on either side of this zone in the RGB Air Mass image from MODIS below.
MODIS RGB Air Mass image of the strong baroclinic zone valid on 03/04/15.
Note the orange and purplish coloring to the north (above) of the moisture plume (cirrus, etc). This delineates the colder, drier air advancing south and east, while to the south (below) of the clouds there is a greenish coloring that denotes warmer mid-tropospheric air associated with a ridge of high pressure aloft over the Gulf of Mexico and Southwest Atlantic.
MODIS Water Vapor image to compliment the RGB Air Mass image valid on 03/04/15.
For contrast, the above image is the ~6.7 um water vapor channel from MODIS. Notice that north of the moisture plume you can see evidence of the lower tropopause and cold air by the relative smoothing noted in the image (lighter blue coloring due to the enhancement). To the south of the moisture plume, you can see the dry air at ~400-500 mb associated with the ridge over the Gulf of Mexico.
This baroclinic zone will continue to sharpen overnight and produce a significant snowstorm for many in the central and eastern US into tomorrow.
