Examine the GFS and UKMET forecast graphics carefully and note differences in the handling of vorticity centers that are important for the TLH day-5 forecast. Which of the following are accurate statements in this regard? Choose all choices that apply, then click Done. (To undo a selection, click the choice again.)
Discussion
The correct answers are b) and d). By 1200 UTC 25 October 2003, the anticipated retrogression in the longwave pattern over the Pacific and western North America has occurred in both models. The vorticity center off the coast of Washington/Oregon in the initialization of 0000 UTC 23 October 2003 has moved over the longwave ridge and into the central U.S. near Colorado in both models. The vorticity center that was initially located to the south of the western tip of the Aleutian Island chain (175°W) has moved to southeastern Alaska (60°N, 140°W) in the GFS but noticeably farther eastward (60°N, 135°W) in the UKMET. The vorticity center associated with Patricia, which by this time has weakened into a depression (See Table 1), is farther to the northeast and more clearly defined in the UKMET than in the GFS.
By 0000 UTC 26 October 2003, the UKMET begins to dig the Colorado vorticity center into New Mexico, while the GFS moves it southeastward into a NE/SW trough through North Texas. Thus, the central U.S. trough is beginning to hang back in the UKMET. The vorticity center with Tropical Depression Patricia continues to be much better defined in the UKMET as it moves northeastward, and for the first time there is the hint that this vorticity center might be picked up by the New Mexico trough and vorticity center in the UKMET. The vorticity center that had been at 60°N and 140°W (GFS) or 135°W (UKMET) continues to move more rapidly in the UKMET, as it is now moving southeastward toward the central U.S. longwave trough, while it is located in the longwave ridge line in the GFS. So, there are already indications that the GFS and UKMET models may have different solutions for the evolution of the central U.S. trough and the future progress of Tropical Depression Patricia.