Rain Next Week As Long Awaited Pattern Emerges

The wx fortunes of the entire contiguous USA will change by Day 7, when a powerful Jet Stream will punch into and thru the mid-section of the RRR High Pressure ridge, undercutting the freshly re-established blocking High Pressure ridge over Alaska. The West Coast will remain dry until the undercutting occurs early on Day 6. Thereafter, moisture should spread rapidly eastward across parched sections of CA, including the Southern Sierra via a negatively tilted trough and combined efforts of dynamic lift and orographics. Unlike the previous storm which drenched portions of NORCAL, this storm system does contain somewhat better upper level dynamics and a very wide plume of high 1.25 to 1.5 inch PWAT moisture field which should plow into the Southern Sierra at an optimum angle. Snow levels will be very high initially and then lower on Mar 1st. The longer range outlook shows this event is the biggie for the 16 Day period and could be the biggest of the season for portions of CENCAL. There are so many wx feature on the charts during this period that it adds to the list of ridiculous items occurring this winter season over North America; 1) the suggestion of a -50°C ARCTIC cold core near the Great Lakes is really surprising, 2) the suggestion of a February Tropical Cyclone in the WPAC is very rare, 3) the most troubling news from a climatological viewpoint is the new record high temp set at Needles, with the earliest 90° temp in that Stations 126 year history. This is one more case in point that we are dealing with an extraordinary season which some paleoclimatologist say is a 100year event, others say it is a 250year event and one UC Berzerkley professor suggests that it is a 500year event.

Mild and dry conditions with above average temps will persist thru early next week. The dry air over the region and the mild temps will keep fog formation to a minimum. As previously advertised, a long awaited pattern change next week is expected to provide CENCAL with a good soaking storm period. Although details and timings issues still abound in the models, particularly for CENCAL, the general trend is indicating a very wet storm to reach CA at the end of the month which produces up to 3 inches of precip for the Sierra near YNP and up to 1.5 to 2 inches for the northern portions of the SJV diminishing to about 0.5 inch into the Kern portion of the SJV. The forecast model tug-of-war between the EC versus the GFS shows the EC is faster than the GFS with the storm arrival as early as Wed, while the GFS is slower with arrival on Thu. Both models however are in basic synch with the high QPF’s which improves confidence. This could be the biggest storm of the Season for the Southern Sierra with up to 3 feet or more of snowfall at the higher elevations. The event is 7 Days away, so stay closely tuned in. If you have questions please contact us.

PRECIP past 24hrs over NORCAL; 0.40 Bonanza King, 0.35 Brush Creek, 0.27 Manzanita Lake, 0.28 Greek Store, 0.23 La Porte, 0.22 Lassen, 0.20 Snow Mtn, 0.17 De Sable, 0.16 Huysink, Strawberry Valley, Alleghany, Forni Ridge, 0.15 Blue Cyn, 0.12 Bucks Lake, Cohasset, 0.10 Covelo, 0.09 Ben Lomond, 0.08 Yorkville, Georgetown, 0.07 Alturas, Friend Mtn, Alpine Mdws, 0.05 Mt Shasta City, 0.04 Ruth Lake, Slate Crk, Hirz, Diddy Wells, Willits, Ukiah, Ft Steward, Arcata, Weed, Venado, Oroville Dam, Four Trees, Donner Lake, 0.03 Quincy, 0.02 Hawkeye, Mt Diablo, Ben Bolt, 0.01 Oroville, Hayfork, Crescent City, San Jose, SFO, Redwood City, Dublin.

FORECAST SUMMARIES

Days 1-7;

Thu, Feb 20^th The RRR High Pressure shifts to 140W and intensifies, as the trough to the east continues to travel into the mid section of the nation, providing CA with a drier NW flow pattern. The gentle slope of a NW flow pattern into the PACNW continues to bring light amts of rainfall into that region, while CA remains DRY. Overnight the High Pressure ridge steepens offshore at 140W and forges northward into the GOA, with a tight pressure gradient over the PACNW continuing to bring some shower activity into the PACNW, while CA develops a weaker flow pattern aloft with partly cloudy skies in the north.

Fri, Feb 21^st The RRR High Pressure ridge pushes northward into Alaska and shifts closer to the West Coast with a lighter NW flow pattern producing fair/dry conditions and warmer temps. Overnight the RRR High Pressure ridge continues to intensify and steepen with CA remaining fair/dry/warm.

Sat, Feb 22^nd Shows the massive RRR High Pressure ridge has rebuilt an effective blockade for the storm track which is now flowing into the Aleutians. However the southern branch Jet Stream is steadily encroaching eastward at the base of the ridge, with a zonal-type flow pattern across the WPAC following 40N, bringing lots of moisture eastward to about 150W where it is blocked and forced to turn abruptly northward toward Alaska. Overnight the southern branch Jet Stream begins to flow into the mid-section of the ridge aimed at the NORCAL coast.

Sun, Feb 23^rd The RRR High Pressure ridge axis runs northward from offshore the West Coast up into Alaska and the Yukon with a strong 558dm High Pressure cell over the Alaska/Yukon border, with the mid-section of the ridge gradually being pinched off and allowing the southern branch Jet Stream to punch thru the base of the ridge, bringing some warm/light rains into the WA coastline. While providing abundantly sunny skies over CA. Overnight the ridge axis moves onshore over the West Coast as Low Pressure begins to fill into the GOA and the westerly flow pattern begins to open the storm door into the PACNW and NORCAL. CEN/SOCAL remain fair and dry.

Mon, Feb 24^th The basic feature of the RRR High Pressure ridge axis remains over the West Coast and built up into Alaska. However, the mid-section of the ridge is becoming fully contaminated with moisture as the southern branch Jet Stream brings increasing warm air advection rainfall into the PACNW and far NW CA. A large trough carves out in the GOA down to near 43N 150W with an abundance of moisture flowing across the PAC basin at low latitudes at the base of the trough and then splitting into 2 pieces near 40N 135W with the bulk of the moisture heading toward the West Coast. This is a significant change from previous forecast model runs which earlier had shown the bulk of the moisture field shearing off and heading northward. While the mean position of the High Pressure ridge maintains its axis over CA, the portion of the ridge nearing CA is contaminated with warm advection moisture. Meanwhile NORCAL becomes partly cloudy while CEN/SOCAL remain fair/dry.

Tue, Feb 25^th The RRR High Pressure ridge remains dominant over the West Coast with the backside of the ridge containing a potent storm system full of moisture which is sluggishly moving eastward into the mid-section of the ridge with a very impressive moisture field. There are a series of 3 disturbances rotating around the base of the trough at very low latitudes with the first two being possible significant rain/snow producers for CA and the third is colder and slightly dryer. A moist south flow pattern develops well ahead of the storm with increasing clouds over NORCAL and perhaps a few showers with increasing high cloudiness over CENCAL. Fair skies prevail over SOCAL. Overnight the ridiculous High Pressure ridge shifts slightly east into the Great Basin which allows the offshore storm circulation to finally being moving onshore into NORCAL with rains moving south to north reaching Cape Mendocino first.

Special Notation; We have been discussing this feature for a while and initially it seemed far-fetched…and yet it still exists on today’s forecast charts, so therefore gaining momentum with confidence. Global scale charts show a Tropical Cyclone developing into the WPAC on Feb 25^th, near 10N 140E with sluggish directional motion, however it does intensify and could become a named Typhoon, which is extremely rare for February. February is the least favored month of the year for WPAC Typhoons. While the Tropical Cyclone (Possible February Typhoon) spins around it throws off a vast moisture field to the north which becomes fully entrained into the westerly flow patternand a developing MidPAC storm system as it crosses the Dateline on Feb 26^th. On the 27^th the developing storm near the Dateline is fully attached to anAtmospheric River (AR) which originates from the Tropical Cyclone. On the 28^th as the Tropical Cyclone appears to weaken, while the AR attachment with the PAC storm system remains well supplied by a subtropical plume, although somewhat weaker. On March 1^st the AR passes over Hawaii as the main storm center moves NE and the initial frontal boundary reaches 140W traveling east. Meanwhile the Tropical Cyclone continues to remain stationary and begins to reload the local SW PAC region with high PWAT’s, again. The Long Range charts indicate that this storm eventually reaches CA on late Sun, Mar 2^nd. What a journey…across the whole PAC basin from a rare February Typhoon…??? It will be very interesting to see if this crazy concept does verify…why not…nothing else about this winter season has been normal, so why not have a February Typhoon!

Wed, Feb 26^th The High Pressure continues to shift over the Great Basin, with the warm/moist flow pattern reaching into NORCAL with heavy rains along the NW Coastal region and lighter rainfall as far south as Monterey to the Delta to Tahoe and with partly cloudy skies spreading over the remainder of CENCAL and most of SOCAL staying clear. The heavy rainfall over NORCAL is aided by a minor shortwave 500mb vortmax which pivots NE offshore, but is close enough to produce dynamic forcing with resultant heavy rains. A secondary disturbance organizes further west of the first and it pivots toward the NORCAL coast overnight as the remnants of the first disturbance pass thru CENCAL with light showers possible for the Sierra. The approaching second disturbance becomes better organized overnight as it approaches the CA coast and is loaded with high PWAT atmosphere moisture content, with values of 1.25 inch reaching the Bay region and a widening core of up to 1.50 inch PWAT offshore west of CA. With the approaching systems originating from the subtropics, the snow levels into the Sierra will be quite high, at or above 7-8K, then lowering.

It is worth noting that for the first time this season the 500mb charts depict a -50°C ARCTIC cold core to sag southward thru central Canada. This monster makes the previous ARCTIC blasts the Great Lakes have experienced this winter look tame. It looks like the ARCTIC front gets close to Chicago and just clips the far northern NE States.

Special Notation; For Historical Significance…Chart depicting a very rare -50°C ARCTIC cold core over southern Canada, with the ARCTIC cold front past Minneapolis and approaching Chicago… this is amazing!

Days 8-16, Long Range into Fantasyland Outlook; Day 8 begins;

Thu, Feb 27^th shows the second stronger/wetter disturbance of the series reaching into NOR/CENCAL with heavy rains depicted by charts as supplied by a rich environment of 1.25 inch PWAT’s which ramp upwards to 1.50 inches as the day progresses (See PWAT chart below ↓). CENCAL remains on the southern fringe zone with rapidly diminishing rainfall gradient from the near Merced/Madera southward into Kern Co. The SW flow aloft provides excellent orographics for the Sierra, especially from Fresno Co (San Joaquin/Kings River basin) northward with high QPF’s expected which diminish further south. Overnight the heavy rains continue Fresno Co northward with lighter rains to the south.

PWAT’s of 1.5 inches moving onshore over the Central Coast region and with PWAT’s up to 1.25 inches flooding inland into CENCAL. This is a whole lot of water in the atmosphere!!!

Fri, Feb 28^th shows a shortwave trough and vortmax approaching the Central Coast with a tightening SW pressure gradient increasing the flow aloft. This feature adds upper dynamic lift support, as orographics continue to ramp up into maximum production of precip for the Sierra with high precip efficiencies. The initially high snow levels lower rapidly as the cold air aloft approaches. This event could produce a major SNOW DUMP for the Southern Sierra with up to 2-3 feet (or more) of snow at the higher elevations. Overnight the disturbance passes thru CENCAL with precip tapering off from the south and west, while the Sierra from the Kings River northward continue to receive mod/heavy snowfall with dramatic drops in the snowlevels. Overnight the heaviest activity occurs from Fresno Co northward with lighter amts into Tulare and Kern Co.

700mb Chart showing heavy rains over NOR/CENCAL on Fri, Feb 28^th.

Sat, Mar 1^st shows the last of the series of disturbances rolls into NOR/CENCAL down to the Tehachapi Mts with lighter precip rates and by late afternoon clearing skies spread onshore with rains diminishing. Building High Pressure ridging offshore provides a dry WNW flow pattern into CA overnight with cooler temps. Blocking High Pressure still resides into Western Canada with the Tropical Cyclone infused Low Pressure storm south of the Aleutian Islands.

Sun, Mar 2^nd shows the High Pressure ridge axis moving over the West Coast, followed quickly by a strong/moist SW flow pattern carrying the leading edge of the Tropical Cyclone moisture aimed at NORCAL. Skies over CA are fair and conditions are dry. Overnight the moisture field reaches onshore into the CA coastline with a brief shot of rainshowers from Monterey Bay northward.

Mon, Mar 3^rd shows High Pressure once again renewing its dominance along the West Coast, as the weakening disturbance pivots NE into the PACNW. Meanwhile the old Tropical Cyclone in the WPAC crosses 20N and continues to infuse the WPAC with high PWAT moisture. A deep and very large Low Pressure storm system is nearly stationary at 45N 160W with its precip flowing into southern Alaska. A long-fetched Atmospheric River (AR) reaches from near the ITCZ at the Dateline NE across Hawaii and is aiming at SOCAL.

Tue, Mar 4^th shows the main playing features as a strengthening High Pressure ridge along the West Coast, with a very large storm system in the NPAC which stretches from Russia into the Aleutians, with the SW flow ahead of the system pumping moisture into the Alaskan panhandle. The previously mentioned AR begins to flow northward on the backside of the West Coast ridge. The good old WPAC Tropical Cyclone has moved far enough north that it is now dissipating in colder waters with its large moisture field now attaching to the general westerly flow pattern.

Wed, Mar 5^th shows strong High Pressure over CA with a moist SW flow pattern over the top of the ridge reaching toward the PACNW with the trailing end of the AR still attached to the subtropical plume near Hawaii. Further west the remnant moisture field of the Tropical Cyclone is entrained into a developing MidPAC storm system with a rapidly developing baroclinic leaf structure that reaches 20° longitude from the Dateline to 160W at 40N. Overnight the trailing end of the plume crosses thru NORCAL with some light shower activity, with partly cloudy skies reaching into CA.

Thu, Mar 6^th shows a zonal-type flow pattern configuration over the PAC basin with less amplification of the ridge/troughs. The semi-resident Low Pressure south of the Aleutians continues to feed a conveyor belt of SW flow pattern into western Canada and the PACNW. CEN/SOCAL remain fair/dry/mild. Overnight the moist flow pattern reaches southward into NORCAL.

Fri, Mar 7^th shows a sharp increase in the High Pressure ridge along the West Coast, anchored by a strong 582dm High Pressure cell ½ way between Hawaii and CA. Skies over NORCAL begin to clear and sunny skies prevail over CEN/SOCAL.

TEMPS

NEW RECORDS

Station New Record Old Record__

Needles 90° 86° set in 1930 This is also the earliest 90° temp on record. The previous earliest 90° temps occurred on Feb 24, 1904.

PRECIPITATION FORECAST

Day 1 – 5 QPF:

At 12Z (9am) Wednesday thru the period Sunday night (Monday @4am) shows;

Wed shows much lighter amts of precip over the Coastal region of NORCAL with >0.1 inch and up to 0.2 inch into the from the Feather River to near the Stanislaus River, with a few showers over the Bay region >0.1 inch. The remainder of CA stays DRY.

Thu shows CA DRY.

Fri shows CA DRY.

Sat shows CA DRY.

Sun shows CA DRY.

5DAY ACCUMULATION CHART:

Wednesday’s 7 Day Chart; shows up to a precip focal point of 3.2 inches near Fort Bragg along the NORCAL coastal region, with a precip focal point of 2.7 inches to YNP/San Joaquin River basin, and a precip focal point of 1.9 inches for the Santa Lucia’s along the Central Coast. “Rainshadowing” is evident in the SJV with 1 inch suggested near the Delta diminishing down to 0.25 inch for portions of Kern Co.

16-Day QPF estimates (from the 0Z GFS model) for;

Days 1-7; shows up to a precip focal point of 3.2 inches near Fort Bragg along the NORCAL coastal region, with a precip focal point of 2.7 inches to YNP/San Joaquin River basin, and a precip focal point of 1.9 inches for the Santa Lucia’s along the Central Coast. “Rainshadowing” is evident in the SJV with 1 inch suggested near the Delta diminishing down to 0.25 inch for portions of Kern Co.

Days 8-16; shows most of CA wet, 3 inches in NORCAL, 1-2 inches over CENCAL and 0.25 to 1 inch for SOCAL.

Wednesday’s 0Z 9pm GFS 384hr, 16Day QPF Chart, depicting a very wet NORCAL, wet CENCAL, and some rainfall reaching into SOCAL. With up to 5 to 6 inches for the NW Coastal region diminishing to 4-5 inches for a large section of NORCAL, with up to 3-4 inches as far south as YNP, with rapidly diminishing totals over CENCAL, which range on the high side near Stockton with up to 2.5 inches suggested, dropping to about 1 inch for Kern Co. The bulk of this rainfall comes from one storm period which begins over NORCAL on Wed, Feb 26^th and spreads south into CENCAL by Thu, Feb 27^th and lasting thru Saturday night, Mar 1^st.