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The EPAC pattern has flipped into a very wet mode, finally!  Several days ago this event was initially pointing to just a NORCAL event, but charts are now consistently showing the warm/wet zonal type flow spreading over NORCAL and …into portions of CENCAL.  The isohyetal (lines of equal rainfall) gradient over CENCAL is significant, with moderate to occasionally heavy rains suggested over the Delta and into the Tuolumne and Stanislaus River basins with up to 2 inches, which rapidly diminishes toward the south, with portions of Kern Co depicted with receiving only >0.1 inch.  This storm series is great news for an ailing NORCAL, and a prayer answered for at least parched NORCAL!  If the QPF’s verify for the Northern Sierra with the forecasted 7-9 inches during the next 7-10 Days, that would bring the monthly average for February close to normal/average…for the month of February.  This does not mean an end to the Drought however, because not only was precip absent during December and January, the Long Range GFS cuts off most of the moisture during the remainder of the 16 Day Outlook for NORCAL, and after this weekend completely dries out most of CEN/SOCAL thru Feb 21st, the third week of February.   For more precise QPF amts please refer to the QPF charts illustrated below.  We count our blessings and are thankful that this warm/wet flow pattern has finally knocked down the RRR High Pressure ridge and will put a substantial amt of water into Trinity, Shasta, Oroville and Folsom reservoirs.  The main event of Fri/Sat/Sun is powered by a wide Atmospheric River initially full of 1.25 in PWAT Atmospheric Moisture which flows into CA on a SW flow …without the support of 500mb dynamics, and only producing precip due to ‘upslope glide’ along the SW flow pattern.  This pattern is most difficult for charts to depict correctly due to the lack of dynamic lift that is absent in the 500mb charts.  The lower 700mb layer of the atmosphere will be the primary driving force advecting the warm/moist subtropical moisture into CA.  The western facing slopes of the Coast Range and Sierra will ramp up orographic lift to enhance heavy rainfall into the higher elevations.  Snow levels will be high.  By Friday night the core of the Atmospheric River with 1.5 inch PWAT’s noses onshore into the North Bay region, aiming at the northern Sierra producing copious rains which gradually sag southward into CENCAL on Sunday, then rapidly drop into SOCAL on Sunday night with diminishing rainfall to the north.  Another Atmospheric River surge develops into far NORCAL again next Wednesday and Thursday producing another dose of rainfall for portions of NORCAL.  The RRR High Pressure ridge with warm 582dm heights dominates CA from Friday, Feb 14th thru Tuesday, Feb 18th with possible record-setting warm temps!   On Wednesday, Feb 19th a weak trough digs into NORCAL producing some brief showers and cooling temps back down over most of CA, with High Pressure returning over CA on Thu/Fri, Feb 20/21st.





Days 1-7;


Wed, Feb 5th                Clear skies in the morning allow for a frosty morning with the coldest Ag Stations reaching 28° or lower.  Increasing high clouds spread thru NORCAL and into CENCAL during the day, with increasing chances of warm rains spreading SE from Cape Mendocino southward into portions of CENCAL overnight.  This moisture is riding down the eastern flank of the RRR High Pressure ridge which is being cut-off in the middle by a break-thru of the Southern Branch Jet Stream beneath the main High Pressure cell which is migrating northward into the Bering Sea.  This allows for the development of a zonal-type flow pattern a low latitudes to FINALLY penetrate the 8 week old RRR High Pressure ridge.


Thu, Feb 6th                 While moderate warm rains continue over NORCAL and portions of CENCAL, the moist NW flow pattern over CA gradually diminishes, and weak High Pressure offshore produces a developing longwave trough pattern which extends from Hawaii NE toward the OR/CA border region attached to a long-fetched Atmospheric River (AR) which contains PWAT’s of up to 1.25 inch.  Warm rains commence again near Cape Mendocino after midnight.


Fri, Feb 7th                   As the offshore High Pressure relaxes, the Atmospheric River ramps up with an onshore flow bringing Hawaiian moisture with PWAT’s of up to 1.5 inches into NORCAL producing heavy rainfall with high elevation snow levels.  CENCAL is on the southern fringe zone of this activity with mod/heavy rains in the northern districts rapidly diminishing to partly cloudy skies over most of Kern Co.  The Sierra receive heavy amts of orographically enhanced precip, which tapers off dramatically over the Southern Sierra.  Overnight the heavy precip continues into NORCAL down to Monterey to YNP.


Sat, Feb 8th                  The synoptic pattern remains similar with weak High Pressure over SOCAL and the Atmospheric River (AR) continuing to feed a steady flow of subtropical moisture into NOR/CENCAL with PWAT’s jumping up to 1.5 inches. This will increase precip efficiencies over the Sierra and Coast Range where orographically enhanced precip will generate copious amts of rainfall, with high snowlevels.  Overnight the moist flow retracts northward slightly with precip focused mostly into NORCAL.  Note the 700mb chart below ↓ depicts a strong well-defined Atmospheric River reaching into CA, without the dynamic support of the GOA Low Pressure which is quite far away.  Instead, this precip event will be primarily produced by upslope glide and enhanced by orographic uplift near western facing slopes.



Sun, Feb 9th                 The charts indicate the Atmospheric River (AR) supply of moisture feeding into CA is chopped off west of CA and the remainder of the moist flow moves into NORCAL with torrentially heavy rainfall showing on charts.  Rainfall amts rapidly taper off to the south over CENCAL.  Overnight the rains over NORCAL diminish as the event comes to an end.  High Pressure offshore rebuilds west of CA.


Mon, Feb 10th              The rebuilding RRR High Pressure ridge offshore temporarily shunts the moist flow northward into the PACNW, while CA dries out.  Overnight the RRR High Pressure ridge once again weakens as another Atmospheric River from Hawaii re-connects to the SW flow pattern, producing heavy rains into Vancouver, BC and the WA coastline, with further development of the AR to the west of NORCAL.  


Tue, Feb 11th               As the High Pressure continues to weaken over NORCAL, the redeveloping AR begins to advect warm rains back into extreme NW CA.  The longwave trough pattern over the NE PAC maintains the long fetched SW flow pattern carrying the AR into CA. Overnight the moist flow enhances and spreads over most of NORCAL down to the North Bay region to Tahoe with light to moderate rains, while skies over CENCAL are partly cloudy.         


Days 8-16, Long Range into Fantasyland OutlookDay 8 begins;



Wed, Feb 12th shows the long fetched Atmospheric River (AR) stretching back to the Dateline, with warm rains flowing into southern Canada down to Monterey Bay to YNP with cloudy skies thru the rest of CENCAL.  Overnight High Pressure offshore SOCAL rebuilds which shunts the moisture feed northward into the CA/OR border.


Thu, Feb 13th shows High Pressure west of SOCAL allows the long-fetched AR to continue to bring mod/heavy rainfall into NORCAL from Pt Arena northward with partly cloudy skies over CENCAL.  Overnight rains over NORCAL diminish and skies over CENCAL begin to clear.


Fri, Feb 14th Valentine’s Day shows the RRR High Pressure ridge rebuilding over CEN/SOCAL as the cloudiness diminishes over NORCAL.  Overnight strong 582dm heights move inland over Pt Conception, commencing a heat wave for CEN/SOCAL.


Sat, Feb 15th shows strong 582dm heights moving northward over CA to SFO to YNP with rapidly increasing temps for CEN/SOCAL with fair skies over all of CA as the storm track diverts northward into the PACNW and BC, Canada.  With the GOA Low Pressure maintaining the tight SW flow gradient tapping into the subtropics near Hawaii.   Overnight the subtropical connection is severed, however the trough in the GOA remains.


Sun, Feb 16th shows strong 582dm heights maintaining over SFO to YNP with continued warming temps over CEN/SOCAL with fair/dry conditions over all of CA.


Mon, Feb 17th shows the 582dm heights dropping down to SLO to Kings Cyn, as the GOA trough advances eastward toward 140W with a SW flow pattern developing over NORCAL. Temps over CEN/SOCAL remain warm, under fair/dry conditions, while rains commence into WA again.


Tue, Feb 18th shows the trough axis is over 140W with High Pressure shifting into the 4-Corners region, with light rains reaching into southern OR, with partly cloudy skies over NORCAL and fair skies over CENCAL with a cooling trend initiating.  Overnight as the trough advances eastward some light rainfall reaches into NORCAL, with partly cloudy skies as far south as SFO.


Wed, Feb 19th shows a developing wave along the frontal boundary enhances rainfall into NORCAL with mod/heavy rate near Cape Mendocino NE into the Klamath River basin in portions of the Shasta basin with partly cloudy skies for the rest of NORCAL.  Overnight the trough and frontal boundary spread into the rest of NORCAL down to SFO to Tahoe with lighter rains.


Thu, Feb 20th shows the trough axis moves into the Great Basin with diminishing cloudiness over NORCAL with flat pressures offshore.  CENCAL remains mostly fair.  Overnight High Pressure noses into NORCAL, which shunts the storm track northward into the PACNW and SW Canada.


Fri, Feb 21st shows the RRR High Pressure ridge rebuilding offshore CA, with the storm track flowing NE into SW Canada, and fair/warm conditions over CA.



Special Notations;


Forecast guidance suggests the ‘biggest storm event of the season’ reaching into CA during the next 4 days, Thu to Sun, with heavy warm air advection type rains soaking NORCAL with significant much need precip which during the next 7-10 Day period should bring most NORCAL precip Stations close to normal/average for the month of February.  This is great news, but does not erase the Drought situation due to the lack of rainfall during Dec/Jan.  One month of normal rains will not end the Drought for NORCAL but it will definitely help put a dent into it.  On the other hand, the situation for CENCAL remains more tenuous.  It would help if the activity over NORCAL during the next 4 days could spread further south about 100-150miles and drench the Southern Sierra, but the current forecast charts do not depict that happening.  Nonetheless we are grateful for whatever rainfall we can get, even though it is warm …at least it is putting water into the basins.  The proposed 4-Day mini-heat wave beginning on Valentines Day’s will not only stop the rains, but will also increase evapotranspiration rates, and will not be the best for the precious snowpack.  Longer Range Outlooks show the return of the Hudson Bay Low Pressure which has been the dominant force driving this unusual season.  If that does verify then we could be looking at the RRR High Pressure ridge also returning for an extended period.





Day 1 – 5 QPF:

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

Wed shows light amts of precip spreading into the northern coastal region between the North Bay and Cape Mendocino with up to 0.5 inch, and with 0.2 inch from near the Klamath River basin southward along the coast to near Napa to Gilroy and the Santa Lucia’s, with >0.1 inch from near Tule Lake southward to the Reno area to YNP then SW to near SLO, including the Merced region of the SJV.

Thu shows up to 1+inches for the Santa Lucia’s along the Central Coast, with 0.75-1.0 inch of precip along portions of the NW coastal region, the Monterey Bay region and the higher terrain of the Central Coast, and in the Sierra from the Feather River basin southward to the Kings River basin and with 0.6 inch for the Kaweah and upper Kern River basins, with 0.2 to 0.3 inch for the Great Valley, diminishing to >0.1 inch for the SW portion of Kern Co.

Fri shows heavy precip confined to NORCAL, north of Santa Cruz to Stockton to YNP, with up to 2 inches into the wet spots along the NW Coastal region and into the Feather River basin, with up to 1 inch for most of the Northern Coastal region, the Shasta River basin and the northern Sierra from the Feather River southward to the Stanislaus River basin, and up to 0.75 to 1 inch for the SAC region the Santa Cruz Mts and into the YNP region, with 0.5 inch down to the Santa Lucia’s to Stockton, to the North Fork of the Kings River basin, with 0.2 inch from near San Simeon to Merced to the Kaweah River basin and >0.1 inch from near Santa Barbara north to near Lemoore to the Tule and lower Kern River basins.  Most of Kings and Kern Co are dry.

Sat shows heavy rains over NORCAL with up to 3+ inches for the northern coastal region in the Eel and Russian River basins with up to 2 inches for most of the Eel and Russian River basins, and the Feather, Yuba and American River basin of the Sierra.  With up to 1 inch for most of the north coast southward to Santa Cruz, stretching across the SAC/Delta/Stockton region, and from the Shasta River basin SE thru the northern Sierra down to YNP.  With up to 0.5 inch from Big Sur east to near Modesto to the Kings River basin and up to 0.2 inch from near San Simeon to Fresno to the northern portion of the Kaweah River basin and up to >0.1 inch from Arroyo Grande NE to Tulare Lake eastward to near Johnsondale in the Kern River basin.

Sun shows continued heavy rains into portions of NORCAL with up to 2 inches designated for portions of the Feather, Yuba and American River basins with up to 1 inch for the Russian River basin to the north Bay region, across the SAC region, and from Mt Lassen southward into the Merced and northern portion of the San Joaquin River basin, with up to 0.75 inch for the coast from Watsonville northward to the Smith River basin, all of the Shasta River basin and from the northern Sierra foothill region SE into the upper Kings River basin, with up to 0.5 inch covering all of NORCAL, and down to the Santa Lucia’s to near Modesto to the Kaweah River basin, with up to 0.2 inch from San Simeon to Fresno, and the Tule River and northern Kern River basin, with >0.1 inch from near Lompoc north to Lost Hills then east to Delano and then into the Isabella region, with most of Kern Co remaining dry.






16-Day QPF estimates (from the 12Z GFS) for;

Days 1-8 shows heavy rains up to 9 inches into the Feather River basin and a dramatic drop-off of rainfall over CENCAL with heavy amts into the northern districts and down to >0.1 inch into SW Kern Co.


Days 9-16 shows light amts of precip up to 1 inch for the NW coastal region of CA with rapidly diminishing amts to the south, with CEN/SOCAL remaining dry.


Wednesday’s comparison QPF charts;

Wednesday’s 12Z 9am GFS 384hr, 16Day QPF Chart, depicting up to 5-6 inches for the NW Coastal region over to the Shasta region, up to 4-5 inches from the North Bay region northward, with 3-4 inches from the South Bay toward Tahoe, and up to 2-3 inches from near Big Sur to YNP.  The rainfall amts diminish significantly between Big Sur to Santa Maria along the Coast and from near Madera/Fresno southward into Kern Co.   



Wednesday’s 0Z 9pm GFS 384hr, 16Day QPF Chart, depicting a larger aerial coverage of heavy rains into NORCAL, with up to 5-7 inches forecast for a large section of NORCAL, with localized amts in the orographically enhanced regions of up to 8-9 inches.  The 0Z chart also corresponds to the earlier 0Z model run which illustrates a rapid decrease of precip over CENCAL with a significant reduction of rainfall between Big Sur and Santa Maria along the coast, and between the northern SJV near Stockton versus the amts suggested over Kern Co, with Stockton showing up to 3.0 inches and Bakersfield showing up to 0.25 inch.  This steep gradient will be very interesting to watch via radar as the event occurs.






Water Vapor 4KM Image of the West Coast Monday, February 3rd, 2014, shows a slug of subtropical cloudiness reaching into NORCAL on a NW to SE directional pathway.



Visible Satellite Image of the CA Monday, February 3rd, 2014, shows approaching subtropical cloudiness reaching into NORCAL, with upslope cloudiness along the Eastside SJV into the Sierra foothills.  SOCAL remains mostly clear.




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

559-696-9697                559-433-7316