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NRL Monterey, Marine Meteorology Division
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NRL Monterey, Marine Meteorology Division
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| LEIPPER INVERSION BASE STATISTICS (LIBS) PHASE 1 to 2
TRANSITION The LIBS (Leipper Inversion Base Statistics) objective fog forecasting method has been introduced in the Fog Forecasting Method (LIBS) study. A full explanation of LIBS can be found in Leipper (1995). LIBS is a conceptual model approach that focuses on the redevelopment of the marine boundary layer (MBL) following a synoptic scale offshore flow pattern regime over the California coastal area. The conceptual model
includes a four phase synoptic and mesoscale sequence of: A similar sequence of clear to fog to stratus overcast has been documented to occur over offshore water areas under return flow following an offshore flow regime. REFERENCE: Liepper, D.F., 1995: Fog forecasting objectively in the California coastal area using LIBS. Wea Forecasting, 10, 741- 762. |
| Figure 1 NOGAPS SLP tau 12 VT 12/19/00Z | Figure 2 GOES VIS 12/19/21Z |
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| Figure 1 is a tau 12 NOGAPS SLP forecast verifying at 0000Z on 19 December 2000, showing the extention of the Northeast Pacific anticyclone over the western interior of the U.S. and the resulting general offshore flow pattern over all of California and Baja Mexico. This offshore flow pattern had persisted for 2 or 3 days prior to the time of Figure 1. Moderate Santa Ana wind conditions had been experienced in favored Southern California areas. Figure 2 shows the resulting extensive clear area over the offshore waters of California. This condition had also persisted for 2 or 3 days. | |
| Figure 3 GOES Southern California VIS 12/19/21Z | Figure 4 GOES Central California VIS 12/19/21 Z |
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| Figures 3 and 4 show the beginning formation of fog/stratus, in locations well offshore, reflecting the initial transition from phase 1 to 2 of the LIBS conceptual model. | |
| Figure 5 COAMPS 54 km Sfc tau0 VT 12/20/00 Z | Figure 6 COAMPS 54 km Sfc tau12 VT 12/20/12 Z | Figure 7 COAMPS 54 km Sfc tau24 VT 12/21/00 Z | |
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| Figures 5 thru 7 show a sequence of COAMPS 54km grid size sea level pressure, air temperature, and wind forecasts from basetime 20/00Z with verifying times from 20/00Z to 21/00Z at 12 hour increments. This sequence illustrates the ability of COAMPS to forecast the return of an onshore flow regime, and the transition to LIBS conceptual model phase 2. | |||
| Figure 8 KNUC (San Clemente) Aviation Forecast Meteogram for 20/00 Z - 21/00 Z | Figure 9 KNZY (North Island) Aviation Forecast Meteogram for 20/00Z - 21/00 Z |
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| The COAMPS 24 hour forecast sequences from basetime 20/00Z for San Clemente Island and North Island are depicted in meteogram format in Figures 8 and 9. The forecast of the return of fog/stratus and saturated MBL conditions at San Clemente (Figure 8) is shown. The fog/stratus cloud is first indicated at about 20/1700Z in the near surface humidity (top panel) and low cloud % (panel 4)for the San Clemente area. The North Island meteogram (Figure 9) does not indicate the forecast return of fog/stratus during this 24hr period. Note that at the time these meteograms were generated, neither a COAMPS internal nor post-processing fog versus low cloud algorithm was yet in use. | |
| Figure 10 Southern California GOES VIS 20/1645 Z | Figure 11 Southern California GOES VIS 20/2130 Z |
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| Satellite imagery of the SOCAL area near the time that fog/stratus is
shown in the San Clemente forecast meteogram (Figure 8) is provided as
verification of the COAMPS forecast. The 20/1645Z NOAA Vis image (Figure
10) shows an elongated fog/stratus patch extending southeastward from the
San Clemente Island area. Fog/stratus patches are also shown off Point
Conception. Figure 11, a NOAA Vis image from 20/2130Z shows increasing fog/stratus coverage extending southeastward from Point Conception, over the outer Channel Islands, and onward to near northern Baja California. The sharp eastern boundary of the fog/stratus, from near offshore San Diego and southward, likely reflects the convergence between offshore flow and the returning onshore flow pattern. | |
| Figure 12 KNZY (North Island) Aviation Forecast Meteogram for 20/12Z - 21/12 Z | Figure 13 KNUC (San Clemente) Aviation Forecast Meteogram for 20/12 Z - 21/12 Z |
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| Meteograms based on the 20/12Z base time COAMPS run, 12 hours after the run time of Figures 8 and 9, for North Island and San Clemente are shown in Figures 12 and 13. This 24hr forecast indicates the continuing development of LIBS phase 2. The cloud cover panel for North Island shows the forecast for low clouds for about 3 hours duration during the 03Z to 05Z period. The 24 hour aviation meteogram for San Clemente Island clearly shows a developing MBL and increasing fog/low cloud conditions. | |
| Figure 14 Southern California NRL Low Cloud Image GOES 21/1530Z | Figure 15 San Clemente Meteogram VT 21/0000Z to 22/0000Z | Figure 16 COAMPS 10m winds tau12 VT 21/1200Z |
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| The return of wide spread fog/stratus to the Southern California offshore
waters and coastal areas on the day following that shown in figures 10
through 13 above is shown in Figure 14. This NRL Low Cloud image was
recorded at 07:30am (1430Z based on daylight savings +7 time factor) on
Thursday 21 December. This reflects the condition discribed as the LIBS
conceptual model enters Phase 3: "Continued onshore flow with deepening
MBL and the fog lifting to form a low overcast". Figure 15 shows the San
Clemete Meteogram and conditions as forecast by COAMPS during the period
of 21/0000Z through 22/0000Z. The COAMPS 54km 12hr surface forecast,
verifying at 21/1200Z (21/05:00am), showing the return of the onshore flow
regime is seen in Figure 16. Important Conclusions: | ||
Author: Ron Englebretson Last Updated: Wed Dec 18 12:23:54 2002 Produced by: The Composer (Ver: 1.1.2 ) |
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