Program Status for 12 February 2001

Spiral descent at 33N, 120.5W 0610 UTC found warm frontal shear and stability between 700-750mb in heavy precip.

     P(mb)  WndSpd(kt)  WndDir(deg) Temp(degC)
     700      20          138        -7.3
     750      16           51        -5.1
     850      26            2        -0.2
     900      30            0         1.9

MSLP 1003.8 mb

No echoes evident NW of the rainband line extending from Pt Conception.

Widespread stratiform precip, 35-40dBz bright band, bright band is ~2.5km above surface.

Heavy stratiform precip south of Channel Isles. Western edge is sharp and at 0400 was east of Pt Conception. NEasterly flow extends far offshore. No orographic forcing near Santa Barbara. Proceeding to 33N, 120.5W for radar surveillance leg from there to 123W, 36N (West of Monterey).

We also interpret this as a warm frontal over- running area.

Doing a microphysics stack in the stratiform precip south of the channel islands. Doing stacks at 6, 9, 12, and 15 thousand feet.

winds: 52deg, 11kt
air temp: 7.0degC, dewpt temp: 2.7degC

winds: 55deg, 13kt
air temp: 6.5degC, dewpt temp: 5.7degC

winds: 34deg, 14kt
air temp: 6.9degC, dewpt temp: 5.2degC

winds: 34deg, 12kt
air temp: 6.7degC, dewpt temp: 4.7degC

winds: 14deg, 9kt
air temp: 6.4degC, dewpt temp: 4.7degC

winds: 98deg, 9kt
air temp: 5.9degC, dewpt temp: 1.8degC

Low-level jet at 600m: 25kt, 180deg

at 950mb: 23kt, 175deg
air temp: 9.6degC, 6.4g/kg

at 1000ft: 8g/kg, mslp:1004.6mb

Spiral occurred within heavy precipitation.

winds: 224deg, 41.2kt
air temp: -22.6degC ,dewpt temp:-23.8degC

winds: 239deg, 60kt
air temp: -34.3degC, dewpt temp: -37.3degC

Broad area of 40-50 dBz echos.

winds: 257deg, 94kt (steady at 94kt)
air temp: -30.3degC, dewpt temp: -55.1degC

winds:258deg, 91kt
air temp: -30.9degC , dewpt temp: -49.3degC

winds: 241deg, 75kt (as high as 90kt seen)
air temp: -36.1degC, dewpt temp: -39.5degC

Precip increasing as we move South from pt 4 (32N, 125W). Embedded cells to 50 dBz. Strong bright band a few hundred meters off of the surface.

air temp: -35.2degC, dewpt temp: -56.1degC

just turned at point 3.
pt 5 is moved to 28.5N, 121.5W

winds 256deg, 26kt
air temp: -34.7degC, dewpt temp: -50.0degC

Things really starting to ramp up in S. Calif.; just got off the phone with LOX and they're considering going to Flood Warning. Warm frontal boundary setting up across S. LA Basin acting now increasingly acting as a focusing mechanism for heavy precip. Warm frontal passage occurred at Avalon between 05 and 06Z; now reporting winds up to 31 knots from the SSE with a rapidly falling pressure and heavy rain. Mesoscale circulation seems to be focusing in L.A. Basin area...if low-level boundary were to move in from offshore (with shift to SW winds behind it), and if could get just abit more unstable, would be a near-classic set-up for an L.A. Basin tornado. However, at this time instability looks like it will remain too marginal and low-level wind shift to SW will probably not reach coast. Would have been a great event for 2 airplanes...or even one plane with 2 crews (so it could be turned around and sent back out).

0630Z Weather Update

Sulphur Mountain (KVTX) radar indicates that strongest rainfall---about 50 dBz--has moved inland into the Ventura county mountains, north-northeast of Oxnard. Large area of 35-45 dBz extends south of Santa Barbara and west-southwest of Santa Ana. Hourly rainfall reports at 06Z had several in the 0.15-0.25 inch range. The highest report in the past hour was 0.47 inch at the Signal Hill city hall in the San Gabriel Valley.

Infrared satellite loops place the low near 35N/124W. The low has become more diffuse during the past hour. Cold cloud-top enhancement become more widespread off the southern California coast and inland over the Ventura and Kern county mountains, with cloud top temperatures around -50c. Offshore cold enhancement region rotating toward the Los Angeles-Anaheim coastal area, and spreading south toward San Diego.

GS

0530Z Weather Update

Satellite water-vapor loops show the low near 35N/124W. The area of cloud enhancement is over eastern two-thirds of the Santa Barbara channel region. Cold cloud-top enhancement becoming evident along the Ventura county coast, with cloud top temperatures around -50 C. Hourly rainfall amounts through 05Z generally 0.16 inch or less, except for 0.35 inch at Refugio, in Santa Barbara county. Sulphur Mountain (KVTX) and Santa Ana (KSOX) radars show large area of 35-45 dBz extending from east of Santa Barbara to Anaheim, with a few 50 dBz returns along the coast southwest of Oxnard.

GS

9 pm PST 12 Feb

At 0430Z, would guesstimate from sat image triple pt somewhere vicnity of 31N, 121W. Sat suggests max dynamics shifting south -- eta may turn out to be right afterall, in having max precip work southward a bit overnight and Tues morning. To + 3 hr eta (valid 03Z) shows max omega over Orange Co of 18 ubar/sec trailing to second max near 29.3N, 120.63W. By 12Z Tues, peak is along northern Baja coast about 100 mi south of SAN, reaching 33 ubar/sec! ...but new secondary max omega develops over San Bernadino mtns, approx. 26 ubar/sec. If flight time permits, might be interesting to sample area near triple point -- where fronts should be most intense. As you had back home, would be interested to hear how far north precip extends under cloud shield (northern extension of high clouds now north almost to Monterey).

No lightning activity noted throughout event thus far vicinity S. Calif, though nldn has just recently picked up a couple of strikes at distant locations: one with a cell at 38.2N, 124.9W, the other with a cell at 33.7N, 126.75W.

Warren

0430Z Weather Update

Infrared satellite loops show low centered about 100 miles west of Monterey. Latest Sulphur Mountain (KVTX) radar shows a large area of 35-45 dBz from Oxnard to approximately 50 nmi south, with smaller areas near Santa Monica, and between San Diego and San Clemente Island, heading for Los Angeles. Heaviest rains are occurring along leading edge of area of cloud enhancement on satellite loops. Hourly rainfall reports, including METARS, continue generally 0.08 inch or less; highest report was 0.24 inch at Live Oak Dam in the Los Angeles county mountains.

GS

8:30 pm PST 12 Feb

Center of coldest cloud tops on IR (approx. -52C) now moving into LA Basin. ASOS show widespread light to moderate rain, undoubtedly heavier on mtn slopes, with light offshore surface flow throughout the Basin. Proto warm front seems to be intersecting the coast somewhere around N San Diego Cty and offshore to a bit north of buoy 47 (32.4, 119.5), which had an apparent warm frontal passage between 02Z and 03Z.

Just fyi...7 of the drops made it into the Eta model initialization (though may not have helped it much!) and we are getting 03Z and 06Z soundings from San Diego (big thanks to Ivory). 03Z SAN sounding shows 0.75 in precip water and a close to saturated, moist-neutral layer to about 550 mb.

0330Z Weather Update

Sulphur Mountain (KVTX) radar showing two areas of light to moderate precipitation. One area coming onshore at this time from Los Angeles south to San Clemente; the other from Santa Barbara to east of Oxnard. Returns mostly 25-35 dBz with an area of 40 dBz south of Oxnard. A small area of 40 dBz also southwest of San Clemente. Highest rainfall reported past hour was 0.43 inch at San Antonio Ridge, in Santa Barbara county. Rainfall over Ventura and Los Angeles counties, and eastern San Luis Obispo county past hour generally 0.13 inch or less.

IR satellite loop shows the low centered near 36N/124W. The area of enhancement centered near 33N/121W showing signs of weakening the last few frames. The water vapor loop shows a dry slot becoming wrapped into the circulation around the low at 30N/124W, along the back edge of the enhanced cloud region.

GS/DW

630PM PST Satellite and Radar Discussion

Light rain continuing over the area from San Luis Obispo county south through Los Angeles county. Rainfall amounts in the past hour generally 0.08 inch or less; highest report was 0.31 inch at the Calleguas Creek at Chuci, in coastal Ventura county.

IR satellite loops show the low center near 35N/124.5W. The offshore area of enhancement is coming onshore near Point Conception. Rapidly developing cloud enhancement occurring over the LA basin, extending across the San Gabriel Mountains and the Mojave Desert into southwestern Nevada.

Weak blocking flow indicated in the California Bight by the Goleta profiler. At 02Z it shows southeast wind at 10 knots from the surface through 1500 m. Southeast to East-Southeast wind of 5 to 10 knots to a depth of 600 m has been present since 21Z.

GS/DW

5:45 pm PST 12 Feb

IR sat for region of development off S. Calif shows massive growth in areal coverage of cold cloud tops continues. A few scattered pixels now at -51C; now extensive area of cloud tops colder than -40C. If you get this message in time, suggest following modifications to flight path (if possible). (1) Extend path segment from pt 4 to pt 5 *past* present pt 5 (I have as 28, 123) another 50 or 60 km to get to leading edge of cloud band (unless no indication of precip that area). Then suggest you move pt 6 from present 32.5, 120 to approx. 33.5, 120.5 if possible to get further under cold cloud top area. Would imagine LOX and SAN would be very interested in precip rates and low-level air characteristics under this rapidly expanding cloud mass -- not sure if pt 5 to pt 6 is sched for low-altitude, but that would seem best.

530 PM Satellite and Radar

Light showers have developed over San Luis Obispo, Santa Barbara, Ventura and Los Angeles counties. Rainfall amounts 1600-1700 PST mostly 0.05 inch or less, though locally as much as .20 in the LA metro area, and the mountains and eastern valleys of Ventura county. Highest amount past hour was 0.28 inch at Rocky Peak in Ventura county.

Satellite loops show the low center about 150 miles west of Monterey. Leading edge of cloud shield located at 32N/122W. IR loop shows area of enhancement centered 33N/132W, Leading edge of enhanced area will reach Santa Barbara south coast next hour. Extrapolation of movement shows center of enhanced area will hit Ventura county in 2-3 hours.

GS/DW

4:30 pm PST 12 Feb

Max precip amounts from 9:15 am to 3:15 pm PST: SB and Ventura County: a few reports of 0.2 to 0.5 inches mtns of east SB Co and Ventura Co. LA County: highest report 1.65 inches at Live Oak Dam (south slope of San Gabriel's I think). Also 1.06 inches at Opid's Camp (south slope of San Gabriels). Highest in Orange Cnty Mtns 0.45 inches. 0.70 inches at Big Bear.

Radar shows broad general region of precip streaming into S. Calif. coast from SW. Highest reflectivties of 40-45 dbz in coastal extreme southern Orange Co/extreme northern San Diego Co, San Gabirel and San Bernadino Valleys along slopes of San Gabriel Mtns, and vicinity of Santa Monica mtns (here max less, more like 35-40 dbz). Many large holes in (genearlly weaker) reflectivity field offshore.

Flood or Flash Flood Watches have been issued by both Oxnard and San Diego WFOs for most of coastal region of S. Calif through Tues. am. Both offices also mentioning possibility of thunderstorms and San Diego has issued a marine weather statement mentioning possibility of waterspouts. Flood Watch issued by Oxnard starts 10 pm tonight, no starting time specified by San Diego.

San Diego WFO just issued NOW for increasing rain, working southwards during the early evening. Indicate possible max precip rates of > 0.25 in/hr.

Warren

3 pm PST 12 Feb

Over past couple of hours, has become more difficult to precisely define vort center -- probably multiple vort max developing in region of interaction with baroclinic leaf. At 2:45 pm, best sat estimate of primary center location is 31.42N, 127.28W. May have been just a shade too far west with 2 pm location -- perhaps 127.60 rather than 127.80. Probably another vort max near 32.33N, 126.39W and perhaps others in that general area as well. Hard to project where any particular vort max will be at 00Z or later given multiple centers and complex interaction. SW'most of these 2 apparently mvg SE approx. 25-27 knots while one near 32.22, 126.39 moving slowly east.

Also...just received e-mail from Dave Danielson: after discussion with Ivory approx. 12:30 pm, both now feel heaviest precip may occur north of where indicated by Eta -- in L.A. vicinity and perhaps northward along coast towards SBA.

2:15 pm PST 12 Feb

At 22Z, vis and ir sat indicate upper-level vort max centered near 31.75N, 127.80W. Sat also indicates significant interaction now occurring between vort max and baraoclinic leaf, with rapid cooling of baroclinic leaf cloud tops. Appearance is of developing instant occlusion. Between 19z and 22z, lowest cloud top temps in IR have gone from -30C to -45C! AT 22Z, one element with -45C top centered at 32.26N 123.73W, second centered at 31.44N 123.72W (actually -46C in center). Sat suggests developing instant occluded front intersects NW edge baroclinic leaf approx. 31.25N 125.43W.

1130AM PST MON FEB 12 2001
Short Term (Mon - Wed)Discussion

Eta seemed to have a good initializaion of the 500mb vorticity field, though both the Avn and Eta had too broad of a depiction of the upper level trough over California. Southern California will be the focus of weather activity in the short term.

The surface low along the Central California coast this morning will drop slowly south through tuesday. Compared to yesterday morning's run...the models have changed their solution of conditions for today and tonight. Maximum precipitation should be tonight rather than today. According to the Meso Eta a plume of nearly 1.00 inch precipitable water will be focused on the vicinity of Long Beach. Also significant instability offshore this afternoon as a vort rotating around the upper low catches up with the front and develops. Should see an increase in precipitation rates around 7 pm. Lifted Index forecast to be -8 with Cape values of 1300 to 1400 J/Kg. Instability not as strong by the time this feature reaches the Southern California coast overnight but still impressive. Rainfall should gradually decrease on tuesday through wednesday as the low weakens, while high pressure ridges across the pacific northwest.

Long Term (Thu-Mon) Discussion

Extended models continue to be a bit divergent but the MRF and the UKMET want to bring a low out of the nothern pacific to the central coast of California by Friday night. This solution would incorporate subtropical moisture that would head toward California by southwest flow. With higher PW values and good onshore flow, it could be a very wet weekend.

DW/Ertl