Fig. 1. A) Base map showing flight operations areas used from mid January to late March 1998 during
the CALJET field experiment that was conducted out of Monterey, California during the strong El Niño
of 1997/98. B) Coastal observing network used during CALJET with terrain altitude shaded (500-1000
m: light, >1000 m MSL: dark).
Fig. 2. A) Scatterplot showing the correlation between the low-level-jet and orographic rainfall.
The wind measurements are from a coastal wind profiler at 12-m MSL at Bodega Bay, CA (BBY in Fig.
1b) and represent a layer average that is 500-m thick from 600-1100 m MSL. Only the component of the
wind normal to the local terrain orientation is used. The rain gauge was at 510 m MSL in the coastal
mountains 30 km north of the profiler site, and 10-km inland from the coast. The vertical profile of the
correlation coefficient from scatterplots such as shown here were also calculated for different layers, each
500 m thick, but centered at different altitudes. The observed correlation is greatest (~0.9) for layers
centered near the top of the LLJ at 1 km MSL, and then decreases dramatically for layers above 1.5 km
MSL, i.e., above the LLJ.
Fig. 3. 1500 UTC GOES-9 IR satellite image on 2 Feb. 1998 of a major developing storm during
CALJET with the flight track of the NOAA P-3 aircraft superimposed. Time (h, UTC) and dropsonde
locations (X) are marked. Low-level winds (below 850 mb) are shown, and key satellite features are
marked, including a cloud head that became the comma head as the cyclone developed, and two distinct
cloud bands (I and II) associated with the phasing of a cold-air disturbance (II) with a polar frontal wave
(I). The initial part of the flight was devoted to releasing dropsondes from near 500 mb in a pattern
designed to capture the meso-alpha-scale environment surrounding the LLJ. These data were then
transmitted via satellite and were assimilated into operational numerical models. After this, the aircraft
operated below 850 mb to document the low-level jet. The location of the strongest low-level jet winds
(80 kn at 900 m MSL) is marked near 16 UTC. This measurement was used by the hydrologist in the
Monterey NWS Weather Forecast Office to issue a flash flood warning that included Pescadero Creek and
provided 6-h lead time for a flash flood on that watershed (Fig. 4). (From Persson et al. 1999.)
Fig. 4. Hydrograph of stream flow observed by a stream gauge on Pescadero Creek near Santa Cruz,
California (see Fig. 3 for location) during a record-breaking flood of 2-3 February 1998. The flood stage
is shown, as is the previous record flood in 1983 during which several fatalities occurred. The time at
which a flash-flood warning was issued for the area based partly on the P-3 LLJ observation (Fig. 3) is
also marked. This warning provided over 6-h lead time before the river reached flood stage.
Fig. 5. Base map for the PACJET experiment that is to be conducted in early 2001 along the U. S. west
coast. The aircraft and ship operations areas are shown, as is the primary operations center at Monterey,
California. A secondary operations center will be located at Seattle, Washington and will be most active
during the 1-2 week period when the storm track takes storms to that region, and hence the P-3 aircraft
will operate out of Seattle.
Fig. 6. Quantitative precipitation verification for 6-h and 24-h forecast periods showing the decrease in
forecast accuracy for higher rain fall amounts and longer accumulation period. The assessment was made
for the area covered by the California/Nevada River Forecast Center (CNRFC) using forecasts and
observations of 6-h and 24-h accumulated rainfall based on numerical model output alone (the AVN and
ETA models) and on the operational QPF issued by the forecast offices. This figure was derived using
precipitation forecast threat scores presented in a formal NWS study of the QPF process (NWS 1999c).
Fig. 7. A prototype graphical synthesis of data gathered by a NOAA P-3 research aircraft during PACJET
regarding the position, intensity, motion, and other characteristics of a cold frontal rain band approaching
the U. S. West Coast, but that is still outside the range of the coastal NEXRAD network. All data
required for to create this synthesis could be observed in roughly 2 h during an appropriately designed
flight module and could be transmitted via satellite in real time. These real-time data could then be
displayed on a specialized web page that updates as new data becomes available. The data displayed here
are derived from lower fuselage radar surveillance scans, tail radar vertical cross sections, scanning radar
altimeter measurements of directional wave height spectra, flight-level in situ measurements, and
dropsondes, with key flight legs repeated to document system motion. The text message required to
convey this information via satellite would be composed by a flight scientist onboard the P-3 aircraft.
Most details shown in this schematic were derived from actual data gathered from P-3 missions during
CALJET.
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