STORM PREDICTION CENTER, (SPC) Norman, Oklahoma showing a Categorical Risk for Thunderstorms over much of CA on Friday. As the offshore upper level Low Pressure center and accompanying trough approach Monterey Bay, the exit region of a 95kt mid level Jet curves around the base of the system overspreading into CEN/SOCAL. This will result in a strong large scale ascent of the atmosphere Friday across much of CEN/SOCAL. In addition the mid-level Jet coupled with a 40-50ktlow level Jet will provide strong deep layered shear which should be sufficient for a marginal SEVERE threat during the afternoon. Forecast soundings near SAC southward into the LA Basin show 0-1 KM shear increasing to 25 to 30kts suggesting rotating Supercells may develop by afternoon. The greatest potential for a marginal tornado threat would exist with storms that move onshore into the LA basin where surface dewpoints will be in the 55° to 60° range. Strong Thunderstorms, possibly SEVERE could also erupt in areas of the SJV which sufficiently heat up during the late morning and early afternoon. If insufficient clearing does not allow for surface heating to occur, then the potential threat is lowered. The more clearing and higher the surface temps reached then the potential threat is raised. SJV Convection could begin in late morning hrs and continue into the evening hrs.
If possible, please take a camera with you to work on Friday in case SEVERE Thunderstorms hit your area, please record it and share it with us.
The second storm of the series is scheduled to arrive into CA tonight with heavy rains and a major SNOW DUMP for the Southern Sierra, the biggest of the season! The storm will be accompanied with gusty southerly winds thru Saturday. Conditions are favorable for Thunderstorms with a few of the strongest updrafts supporting possible SEVERE criteria. Rotating Supercells are suggested which could produce larger sized hailstones and/or funnel clouds or tornadoes, especially favoring from Fresno Co southward, but they may occur as far north as Merced Co. A quick and dirty look at convective parameters tomorrow morning is needed for fine-tuning.
The next 36 hours has the potential to be the biggest storm of the Season for such a widespread area of CA, and especially for the Southern Sierra with up to 1-3 feet or more of snowfall at the higher elevations above 7,000ft with gusty winds to 80mph along the Crest. Strong southerly winds will accompany the storm on Friday with the South Valley winds reaching as high as 30mph with gusts up to 50mph near the base of the Grapevine with strong adiabatic warming from the downsloping winds. Overnight temps in the extreme South Valley region could remain quite warm from these expected downsloping winds.
Longer range outlooks by the GFS are somewhat uncertain, and show another possible storm system arriving into NORCAL on MonPM, Mar 3rd which could bring rains as far south on Wed as the I-80 corridor according to the GFS, and further south according to the EC model on WedPM. The GFS Fantasyland Forecast shows a low confidence, cold core upper level ‘devil’ arriving on Day 15/16, valid on Wed/Thu, Mar 12th and 13th.
PRECIP past 24hrs over NORCAL; thru midnight Wednesday;
NORCAL; 2.52 Whispering Pines, 2.50 Stony Gorge Reservoir, 2.36 Hawkeye, 2.12 Fort Dick, 2.08 Konocti, 2.00 Yorkville, 1.92 Shasta Dam, 1.70 Redding, 1.64 Taylor Ridge, Angwin, 1.60 Lakeshore, 1.57 Santa Rosa, 1.56 St Helena, 1.52 Honeydew, 1.50 Red Bluff, 1.48 Trinity, 1.47 Saddle Camp, 1.46 Ukiah, Petaluma, 1.44 Cottonwood Crk, 1.40 Hirz, 1.36 Clear Crk, McCloud Dam, 1.33 DeSabla, 1.32 Slate Crk, Willits, 1.20 La Porte, 1.19 Corning, 1.16 Ogo Ranger Station, 1.12 Mt Shasta City, Boonville, 1.07 Lassen, 1.04 Vacaville, 1.03 Bucks Crk, 1.00 Bonanza King, Ruth Lake, 0.97 Cohasset, 0.84 Miranda, 0.80 Bridgeville, Oroville Dam, 0.76 Strawberry Valley, 0.75 Quincy, Fair Oaks, 0.74 Mud Springs, Friend Mtn, Chico, 0.71 Blue Cyn, 0.67 Auburn, Napa, 0.62 Donner Lake, 0.60 Leggett, Alpine Mdws, 0.57 Englebright Dam, 0.55 Rancho Cordova, 0.54 Marysville, 0.45 Crescent City, 0.44 Ft Seward, 0.43 Roseville, Elk Grove, 0.40 Pacific House, 0.36 Orick, 0.35 Folsom, 0.30 Arcata, 0.28 Forni Ridge, SAC
CENCAL; 4.25 Three Peaks, 3.98 Mining Ridge, 2.91 Central, 2.72 Mt Umunhum, 2.49 Ben Lomond, 2.32 Anderson Peak, 1.97 Loma Prieta, 1.73 Chews Ridge, 1.68 Las Tablas, 1.67 Ponciano Ridge, 1.56 Santa Margarita, 1.54 Wawona, 1.52 Telegraph Hill, 1.49 San Bruno, Los Trancos Preserve, 1.19 Shaver Lake, 1.10 Mt Madonna, 1.06 Green Spring, 1.04 Parkfield, 0.98 Bass Lake, Dinkey Crk, 0.97 Cambria, 0.94 Mariposa, 0.92 SF, 0.89 Minarets, 0.85 Black Springs, 0.83 Moffett Field, New Exchequer, 0.79 Gilroy, 0.78 Concord, 0.75 Watsonville, 0.72 Gianelli, 0.71 Salinas, 0.70 North Fork, 0.68 SJ, 0.66 YNP, Markleeville, 0.64 Paso Robles, Estrella, 0.60 Modesto, Peckinpah, 0.58 Arroyo Grande, 0.56 Camanche, Bradley, 0.53 Fence Mdw, 0.50 Merced, 0.49 Buchanan Dam, 0.45 OAK, 0.44 A.G. Wishon, Trimmer, 0.42 Madera, 0.41 Park Ridge, 0.36 Chilkoot Mdw, 0.35 Pinehurst, 0.34 Fresno, 0.33 Balch Camp, Peppermint, 0.32 Vandenberg, Buck Rock, 0.31 Cedar Grove, Johnsondale, 0.30 Wolverton, 0.28 Walker Cyn, 0.27 Hidden Dam, Santa Maria, Case Mtn, Tulare Lake, Lemoore, 0.26 Shadequarter, 0.25 Kettleman Hills, Pine Flat, 0.24 Mahogany, 0.23 Rogers Camp, 0.21 SLO, Ivanhoe, 0.20 Piute Pk, 0.19 Ash Mtn, Pascoes, 0.18 Hanford, 0.17 Visalia, 0.16 Lake Kaweah, 0.14 Oak Opening, Hanford, 0.13 Stockton, 0.11 Wofford Heights, 0.10 Kernville, Riverkern, 0.07 Isabella, Democrat, Lost Hills, Cuber, 0.06 Scofield, 0.05 Bishop, Cal Farms, 0.04 Carrizo, 0.03 Buena Vista Lake, Belridge, 0.02 Lake Success, Porterville, Cappello, 0.01 Bakersfield, Kern Cyn Powerhouse, Ducor, Zerker
SOCAL; 1.81 Refugio, 1.69 San Marcos Pass, 1.37 Upper Matiliga Cyn, 1.10 Old Man Mtn, 0.99 Santa Barbara, 0.92 Carpenteria, 0.80 Cachuma Dam, 0.68 Oxnard, 0.59 Sycamore Canyon, 0.48 Aliso Cyn, 0.36 Circle X Ranch, 0.32 Simi Valley, 0.28 Camp 9, 0.24 Van Nuys, 0.22 Lockwood, 0.16 Saugus, West Fork Heliport, 0.12 Santa Monica, 0.08 Hollywood, 0.07 Malibu, 0.04 Acton, San Gabriel Dam, Eaton Wash, LAX, San Gabriel Dam, 0.02 Lancaster, USC, 0.01 Hawthorne, Palmdale
Flash Flood Watch for the Santa Lucia Mts for Friday, with up to 8 inches of precip expected, following the heavy rains of up to 4.2 inches they received yesterday.
High Wind Warning for the Tehachapi Mts overnight into Friday afternoon for winds up to 40mph with gusts up to 70mph.
Fri, Feb 28th Charts for Friday show a dynamically strong storm system producing rains over most of CA, with heavier rains into portions of CEN/SOCAL. With an early morning FROPA, the heavy rains diminish as skies become partly cloudy and diurnal heating occurs. As the -24°C cold core moves near SFO and the cold front moves into SOCAL, CENCAL is placed in the left quadrant of the upper Jet Stream and Vort dynamics. This is a near classic set-up for Convection in the Great Valley with widespread Thunderstorms expected, with some of the strongest updrafts possibly producing strong Thunderstorms with SEVERE criteria. Convective Charts show chances of strong rotating Supercells, which could produce SEVERE THUNDERSTORMS with large hail, funnel clouds, and/or waterspouts or tornadoes. QPF charts show this storm could be the best single event of the season thus far for snow production in the Sierra with up to 2-3+ feet possible into the higher terrain and aSNOW DUMP for the Sierra Ski Resorts. The SW flow following FROPA will keep a moist onshore flow pattern advecting gradually diminishing shower activity into CA overnight as the Low Pressure center opens up into a trough configuration, with snowlevels dropping significantly as orographics keep the Sierra wet overnight.
Chart showing strong Thunderstorms over the SJV Friday afternoon from an intense 981mb Low Pressure -24°C storm center west of Monterey.
Sat, Mar 1st A new twist to the forecast for Saturday…While the upper levels of the atmosphere have opened the storm center into a trough configuration, the lower layer at 700mb still contains a close circulation which moves onshore over the Central Coast, mid Day. This could produce another day of Convective showers over the SJV, but probably not as powerful as Friday because of the lack of upper level dynamics which have shifted eastward. Expect continued showers over the SJV with orographics producing additional snowfall for the Sierra. Meanwhile further west, the large MidPAC storm slowly migrates eastward, with its long-fetched Atmospheric River trailing SW over Hawaii and then back to the originating WPAC Tropical Cyclone. Overnight as the system over CA slowly departs, the long fetched AR approaches NORCAL.
SPC Day 3 Categorical Thunderstorm Outlook for CA, indicating a categorical risk of Thunderstorms on Saturday from Monterey to Madera southward. The forecast intensity of SJV Thunderstorm activity appears less than Friday.
Special Notation; Tropical Cyclone Formation Alert for the WPAC. Tropical Cyclone “3W” is in the formation stages of possibly becoming a rare February named Typhoon SW of Guam. Currently located at 9N 148E moving SW at 16kts, with max sustained winds of 20kts.
As mentioned several times in recent forecasts we have been tracking the WPAC Tropical Disturbance and it still exists on today’s forecast charts with little overall change. Kudos to the GFS model which picked up on this rare event at least 11 Days ago! The global scale charts show a Tropical Cyclone developing in the WPAC late Thu, Feb 27th, near 9N 148E with SW directional motion. While the Tropical Cyclone spins around it manages to cast off a vast moisture field to the north which becomes fully entrained into the westerly flow pattern and into a developing MidPAC storm system as it crosses the Dateline on Feb 27th. By the 28th the PAC basin has 3 separate storm systems imbedded within the westerly flow pattern, including the developing Mid PAC storm which has crossed the Dateline and is fully attached to the Atmospheric River (AR) that is being generated by the Tropical Cyclone. On Mar 1st the Tropical Cyclone appears to strengthen, while the AR attachment to the PAC storm system remains intact to the subtropical plume, although somewhat weaker and stretched out, it passes over Hawaii. On Sun, Mar 2nd as the Tropical Cyclone continues to intensify, the leading edge of this incredibly long-stretched AR tropical moisture field reaches into the PACNW and NORCAL overnight. Meanwhile the Tropical Cyclone remains nearly stationary and begins to reload the local SW PAC region with high PWAT’s, again. Another rare oddity about this storm is that charts also show a near mirror image of another Tropical Cyclone forming almost due south of “3W” at 10S 155E…into the southern Hemisphere, while “3W spins at nearly equal distances from the Equator and not too far distant from the same longitude. On Mon Mar 3rd the juicy Mid PAC Low Pressure storm travels eastward nearing 150W with the advancing Atmospheric River (AR) stretched from the PACNW and NORCAL SW to Hawaii and beyond. The Tropical Cyclone’s new moisture field is now flowing northward into another storm which is brewing near 43N nearing the Dateline. High Pressure is depicted as keeping the AR nearly stationary over extreme NW CA producing heavy tropical rains on Mon, Mar 3rd. Meanwhile the Tropical Cyclone’s new moisture plume stretches from the storm itself at 20N near 145E …across most of the PAC basin with a wide, impressive Atmospheric River which approaches 160W by Tue, Mar 4th. On Wed, Mar 4th as the Tropical Cyclone dissipates, heavy rains commence again into NORCAL from moisture which originated from the old Tropical Cyclone. With High Pressure rebuilding along the West Coast this moisture is shunted NE into BC, Canada on Mar 7th. This is a very interesting long tale, which is rare for Feb/Mar, especially with the 6-Day longevity of the Cyclone and the continuous moisture pump that it provides into the PAC basin which brings copious amts of rainfall into the PACNW and NORCAL, which is the bottom line reason for paying so much attention to it.
Sun, Mar 2nd Weak, somewhat flat High Pressure ridging moves over the West Coast, with partly cloudy skies over CENCAL and rainshowers over NORCAL from the approachingAR which is connected to the Tropical Cyclone in the WPAC. While the High Pressure keeps most of the activity confined to NORCAL, some activity may spill into CENCAL…at least with partly cloudy to cloudy skies for the North Valley.
Mon, Mar 3rd As broad/flat High Pressure continues over the Great Basin, the long-fetched Atmospheric River (AR) that originated from the Tropical Cyclone in the WPAC continues to flow into NORCAL, with increasingly heavy rains. This AR/Tropical Cyclone feature has been long advertised with varying timing issues but is still on the charts and has been described in more detail above within the Special Notation. Overnight the Low Pressure trough located near 45N 155W continues to act as a conveyor belt for the AR moisture to continue streaming across the PAC basin, which is still originating from the intense Tropical Cyclone.
Tue, Mar 4th Charts show 2 separate Atmospheric Rivers (AR) crossing the PAC basin and each one has been or is currently supplied by the Tropical Cyclone in the WAPC! Pretty unusual! High Pressure ridge begins to rebuild over the West Coast with the moist onshore SW flow pattern continuing into the PACNW but shifting out of NORCAL. Partly cloudy skies exist over CENCAL. Overnight another slug of AR moisture from the WPAC Tropical Cyclone plows into the PACNW and far NW Coastal CA with heavy rains.
Wed, Mar 5th A strong zonal type, westerly flow pattern continues to race across the PAC basin with several imbedded disturbances traveling eastward toward the West Coast. The trailing end of the AR produces heavy rains into NORCAL, with cloudy to partly cloudy skies for CENCAL. Overnight the southern fringe remnant trailing end to the AR reaches into CENCAL with clouds only.
Thu, Mar 6th High Pressure rebuilds offshore west of CA with the zonal-type westerly flow buckling offshore the West Coast, while the core remnants of the old Tropical Cyclone are carrying an abundance of moisture toward the BC, Canada coastline. Skies over CA remain fair.
Days 8-16, Long Range into Fantasyland Outlook; Day 8 begins;
Fri, Mar 7th shows High Pressure dominant over the West Coast with the storm track diverted further north into BC, Canada with fair skies over CA.
Sat, Mar 8th shows High Pressure continues over the West Coast with a long-fetched SW flow carrying rains into the BC, Canada coast. CA remains fair, mild and dry.
Sun, Mar 9th shows High Pressure broadening its width across the WCONUS and offshore to the west, as the continuous feed of moisture into southern BC, Canada shifts further north.
Mon, Mar 10th shows High Pressure dominant over the West Coast as a Low Pressure trough pattern continues into the GOA with moisture reaching into the BC, Canada region.
Tue, Mar 11th shows High Pressure shifting inland into the Great Basin, with the approaching trough and westerly flow pattern moving closer toward the West Coast. With fair skies turning partly cloudy over NORCAL. Overnight a sharp shortwave trough digs southward from the GOA toward the West Coast. A SW flow over CA increases with clouds spreading into NORCAL with a few showers possible near Cape Mendocino.
Wed, Mar 12th shows the trough axis moving thru NORCAL with showers and with cloudiness spreading into CENCAL, but no rain. Overnight the trough shifts into the Great Basin with High Pressure moving onshore.
Thu, Mar 13th shows the High Pressure nosing into the PACNW, while the Great Basin trough digs further southward into NV and forms a large Low Pressure circulation centered over Las Vegas.
Fri, Mar 14th shows High Pressure along the West Coast tilting into the PACNW, while the Low Pressure over the SWCONUS remains. This produces an offshore E-NE flow pattern for CA. The storm track is diverted well to the north into BC, Canada.
Sat, Mar 15th shows the High Pressure migrating into the Great Basin as a new cold trough from the GOA digs SE toward CA, with a Low Pressure close circulation forming far west of CA. Tis the season for cut-off’s!
CME IMPACT: As expected, a CME hit Earth’s magnetic field today (Feb. 27th @ 1645 UT), and the impact has triggered geomagnetic storms around Earth’s poles. The CME is an after-effect of the X4.9 class solar flare reported on Feb. 25th. Visit http://spaceweather.com for updates about this developing space weather event.
Station New Record Old Record__
South Lake Tahoe 58° 57° set in 1995
Modesto 0.60 inch 0.45 inch set in 1951
Day 1 – 5 QPF:
At 12Z (9am) Thursday thru the period Monday night (Tuesday @4am) shows;
7 Day QPF Chart; showing up to 7.2 inches into Del Norte Co!
16-Day QPF estimates (from the 0Z GFS model) for;
Days 1-7; shows up to 7.2 inches for Del Norte Co with 4-5 inches into the Northern Sierra and 2-4 inches for the Southern Sierra, with up to 1.5 inches for the northern portions of the SJV diminishing to near 0.5 inch around the south end of the SJV near Bakersfield.
Days 8-16; shows mostly DRY conditions for CA with approx 0.2 inch in NORCAL, 0.1 inch in CENCAL, and >0.1 inch in SOCAL.
GFS 384hr, 16Day QPF Chart, depicting a wet State of CA with heavy rains continuing into NORCAL. With up to 3-4 inches for the Northern Sierra and 2-3 inches for the Southern Sierra with amts in the SJV ranging from approx 2 inches diminishing to 0.5 inch in Kern Co.
Water Vapor 4KM Image of the West Coast Thursday, February 27th, 2014, shows a dry slot over NV with the Wednesday storm system moving into CO. Further west is the approaching second storm system exhibiting a large baroclinic leaf structure ahead of the frontal boundary, with a tight
Visible Satellite Image of the CA Thursday, February 27th, 2014, shows a departing storm moving thru NV with a minor disturbance over NORCAL, while the South Valley region has mostly clear skies.
If you have any questions please call or text at any time of day or night.
Comments and suggestions always welcome.
Atmospherics Group International
Dan Gudgel Steve Johnson