Figure 1: GFS 500 hPa height (orange) and absolute vorticity (green) in the initialization for 0000 UTC 23 October 2003
Figure 2: UKMET 500 hPa height (orange) and absolute vorticity (green) in the initialization for 0000 UTC 23 October 2003
Part I
In Part 1 of this case, the forecaster will make a day-5 forecast for Tallahassee, Florida (TLH) after examination of forecast guidance based on initial conditions at 0000 UTC 23 October 2003.
Section 1a: Synoptic Setting, 0000 UTC 23 October 2003
Examine Figures 1 and 2 below, which show the GFS and UKMET 500 hPa height and absolute vorticity patterns in the models' initialization for 0000 UTC 23 October 2003.
Figure 1: GFS 500 hPa height (orange) and absolute vorticity (green) in the initialization for 0000 UTC 23 October 2003
Figure 2: UKMET 500 hPa height (orange) and absolute vorticity (green) in the initialization for 0000 UTC 23 October 2003
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Now test your initial condition analysis skills by answering the following multiple choice question.
Answer a) is incorrect. The GFS (Fig. 1) and the UKMET (Fig. 2) handle the shortwave trough off the Washington/Oregon coast (130°W) differently. The GFS has the vorticity center with this wave located farther north than does the UKMET, placing it near the border of Washington and Oregon. The UKMET has the trough extending farther south along the Oregon coast. The GFS has a stronger and more localized vorticity center with this trough, while the UKMET shows weaker vorticity values and more of an elongated region of vorticity.
Answer b) is incorrect. The cut-off low in the Gulf of Alaska (150°W) has a vorticity center at its core, as well as several vorticity centers surrounding it. These centers are all stronger in the UKMET than in the GFS.
Answer c) is correct. The cut-off low to the south of the western tip of the Aleutian Island chain (175°W) is more intense in the UKMET (two closed contours) than in the GFS (one closed contour).
Answer d) is correct. The vorticity center in the eastern Pacific around 12°N and between 100°W and 110°W is much more clearly defined in the UKMET and placed farther west (109°W versus 105°W in the GFS).