In the short term forecast period the moist Atmospheric River which has been drenching the PACNW and portions of NORCAL with heavy/warm subtropical rainfall should taper off by Wednesday, with a transition to a well advertised amplified pattern beginning on Wednesday into Thursday. The recent forecast models have continued with good consistency toward this transition to a more amplified western trough/ridge pattern regime that ends the zonal-type AR storm activity over NORCAL and the PACNW as the pattern buckles and the amplification occurs. Before the big buckling, the PACNW will continue to pile up more moist onshore flow precip with enough zonal component to spread snows all the way into the Rockies. The positive PNA pattern should cut off the concentrated plume of moisture into the PACNW. The model spread is still somewhat moderate for the leading features embedded within the fast flow aloft for the beginning of March, but it is encouraging to see basic model agreement with the GFS and EC models nearly in synch with each other on the large scale pattern solutions. Model progs show the massive RRR High Pressure ridge firmly anchored over the WCONUS by next weekend, with above normal temps thru March 5th. The model spread also shows the possibility for the AR development described above on Sat, Mar 1st to ramp up into a rather robust feature which could bring a significant amt of rainfall into portions of NOR/CENCAL, once again…although models are flip/flopping as to whether the strength of the AR does develop into a potentially strong event or whether it remains weak. It appears highly likely that most of CENCAL and all of SOCAL will end the month of February with record-setting dryness, compounding the deepening seriousness of the CA Drought
Warm rains reach into portions of NORCAL on Tuesday as the basic flow pattern undergoes a fundamental change into a more amplified ridge/trough configuration which may shut the storm door into CA for the remainder of Feb and into the beginning of March according to some models, and not by others. By Friday and over the weekend strong High Pressure is dominant over the WCONUS. The most recent longer range outlook charts remain consistently dry for most of CA during Week #2 with mild temps. The GFS 384hr 16Day Outlook now extends thru the end of the month of February into March 5th with a most interesting period timed around March 1st, as some models hint at the potential development of a strong AR Event possibly reaching into NORCAL and portions of CENCAL with heavy rains…this scenario is issued with low confidence. The final week of February should end the “February Monthly Summary” for the Northern Sierra Index…above normal, being the first time in 14 months with an above average monthly total. That’s the good news. Now the not so good news …it appears as though the month of February will end with a worsening Drought deficit for the Central Sierra and especially for the Southern Sierra as the recent heavy rains which have drenched portions of NORCAL have been mostly absent over the Southern Sierra region and above average temps are once again creating conditions with high evaporation rates.
PRECIP past 24hrs over NORCAL; 0.44 Gasquet and Elk Valley, 0.21 Crescent City, 0.13 Somes Bar, 0.08 Orick, Hoopa, Orleans, 0.07 Big Hill, 0.05 Arcata, 0.04 Sand Flat, 0.02 Sawyers Bar
Tue, Feb 18th As a weak trough axis nears the PACNW coastline a newly attached AR supplying rains gradually spread southward thru the PACNW into portions of NORCAL with up to 1+ inch along the far NW Coastal region, with lighter amts down to near the Russian River basin up to Redding and then down into the American River basin with >0.1 inch, while partly cloudy to sunny skies remain over CENCAL. Overnight the RRR High Pressure ridge begins to rebuild near 140W which realigns the flow pattern over NORCAL to the NW as rains taper off further south into NORCAL and begin to diminish as temps begin to lower slightly due to the cooler NW flow pattern.
Wed, Feb 19th The trough axis moves into the Great Basin and deepens, the High Pressure builds onshore over CA with a drying trend in the north, while fair skies continue over CEN/SOCAL With a tightening pressure gradient, the NW onshore flow pattern brings higher wind speeds with BLOWING DUST along the Westside. Overnight another disturbance flows into the PACNW from the NW.
Thu, Feb 20th 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. Overnight the pressure gradient over CA tightens over the PACNW with increased NW winds while CA develops a weaker flow pattern aloft.
Fri, Feb 21st The RRR High Pressure ridge pushes further north into Alaska and shifts closer to the West Coast with a lighter NW flow pattern with fair skies and warmer temps. Overnight the RRR High Pressure ridge continues to intensify and moves closer toward the West Coast.
Sat, Feb 22nd 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 bringing lots of moisture eastward to about 140W where it is blocked and forced to turn abruptly northward toward Alaska.
Sun, Feb 23rd The RRR High Pressure ridge axis runs northward from offshore the West Coast up into Alaska and the Yukon, with the mid-section of the ridge is allowing the southern branch Jet Stream to punch into the base of the ridge, bringing some 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.
Mon, Feb 24th The RRR High Pressure ridge axis remains over the West Coast with the southern branch Jet Stream piercing into the mid-section of the ridge and bringing increasing warm air advection rainfall into the PACNW. A large trough carves out in the GOA down to near 40N 140W with an abundance of moisture flowing across the PAC basin at low latitudes and then splitting into 2 pieces near 40N 135W with the bulk of the moisture field tearing off and heading northward into southern Alaska. Meanwhile NORCAL becomes partly cloudy while CEN/SOCAL remain fair/dry. Overnight the storm approaches the PACNW, as the High Pressure ridge migrates eastward into the Great Basin.
Days 8-16, Long Range into Fantasyland Outlook; Day 8 begins;
Tue, Feb 25th shows the RRR High Pressure ridge 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 ridge. A moist south flow pattern develops well ahead of the storm with increasing clouds over NORCAL and perhaps a few showers. Fair skies prevail over CEN/SOCAL.
Wed, Feb 26th shows the High Pressure remains anchored over the Great Basin, with a zonal-type moist flow pattern reaching with weak mid-section of the ridge with warm rains into the PACNW and NORCAL with partly cloudy skies over CENCAL and fair, sunny skies over SOCAL. Overnight the 700mb charts show a continuation of the low level moisture stream reaching into the PACNW and NORCAL with cloudy skies spreading over CENCAL.
Thu, Feb 27th shows the High Pressure ridge axis aligned SE to NW across the Great Basin NW into Alaska with a small Low Pressure cell west of Vancouver pumping a nearly continuous stream of moisture into the PACNW and portions of NORCAL, while CENCAL remains partly cloudy. Overnight the rains in the north begin to taper off.
Fri, Feb 28th shows the RRR High Pressure ridge rebounding offshore CA as a minor shortwave trough digs into NV with a NW flow pattern over CA, as skies begin to clear. Overnight the ridge axis moves onshore over CA.
Sat, Mar 1st shows the RRR High Pressure ridge axis continues to shift eastward over CA and into the Great Basin with a SW flow pattern offshore approaching the PACNW with heavy warm rains commencing into the SW Canada and the WA coastline, supplied by an developing long-fetched Atmospheric River (AR) originating from near Hawaii flowing NE into the Low Pressure storm in the GOA. Overnight while the High Pressure remains dominant over CA the heavy rains continue into the PACNW…attached to the AR. By the way, during the last forecast discussion we mentioned that the WPAC produces a Tropical Cyclone and it is still on the charts during this chart cycle though it has changed locations.
Sun, Mar 2nd shows the High Pressure ridge weakening as the axis shifts into the Great Basin, with a tight SW flow pattern forming over CA carrying the remnant left-over’s of the AR thru NORCAL and trailing SW offshore west of CENCAL. CAUTION: Some models shows this AR Event more robust, and possibly bringing significant rains into CA. If this does not materialize then fair skies continue to dominate over CEN/SOCAL. Overnight the remnant left-over’s of the AR pass thru CENCAL with perhaps a few showers.
Mon, Mar 3rd shows the RRR High Pressure ridge rebuilding offshore west of CA as a weak shortwave trough continues to pass thru CA and into the Great Basin. The 500mb and 700mb charts are discontinuous with the 700mb feature well to the east, while the 500mb chart lags behind and therefore lack confidence in this time frame. Overnight High Pressure noses into NORCAL with an offshore NE flow pattern for CENCAL.
Tue, Mar 4th shows the RRR High Pressure once again dominant over CA and up into the PACNW, while the storm track is diverted northward into southern Canada. Overnight the ridge steepens significantly with colder air sliding southward from BC, Canada into the PACNW.
Wed, Mar 5th shows an intensifying High Pressure ridge offshore, jutting northward into western Canada, with the downwind flank bringing cold air southward into the Great basin as a cold/dry north flow pattern develops over CA.
Station New Record Old Record__
Sandberg 69° (Ties) 69° set in 1977
Las Vegas 81° 79° set in 1996
Big Bear 46° 36° set in 2003 Record Max Min
Palomar 51° (Ties) 51° set in 1958 Record Max Min
Day 1 – 5 QPF:
At 12Z (9am) Saturday thru the period Wednesday night (Thursday @4am) shows;
Mon shows up to 0.75 inch of precip into the wet spots in the higher elevations of Del Norte Co, with rapidly diminishing amts to the south dropping down to >0.1 inch reaching Pt Arena and the Eel River basin and into the Trinities northward to Crater Lake, OR. The remainder of CA stays DRY.
Tue shows increased precip into NORCAL, with up to 1.5 inches falling into the higher terrain of the Smith River basin, diminishing to 1 inch for the Klamath River basin, down to 0.5 inch for the Eel River basin and into portions of the Shasta River basin, with 0.2 inch from near the South Fork Eel River basin NE to Susanville, and >0.1 inch from near the Russian River basin northward to Redding then SE into the Sierra to near the I-80 corridor. The remainder of CA stays DRY.
Wed shows much lighter amts of precip over NORCAL with >0.1 inch into the Klamath River basin eastward into the Shasta River basin and throughout the NE quadrant of the State, then southward into the northern Sierra to near Kirkwood. The remainder of CA stays DRY.
Thu shows CA DRY.
Fri shows CA DRY.
5DAY ACCUMULATION CHART:
Saturday’s 7 Day Chart; shows up to 1 inch for the far NW Coastal Region into Del Norte Co, with rapidly diminishing amts to the south, with 0.5 inch from near Fort Bragg to the Shasta River basin and a portion of the Feather River basin, with 0.25 inch from near Pt Arena to Red Bluff to near Blue Cyn, with >0.1 inch from near the Russian River basin to Chico to near Kirkwood. The remainder of CA stays DRY.
16-Day QPF estimates (from the 0Z GFS model) for;
Days 1-7; shows NORCAL receiving up to 1 inch for the far NW Coastal Region into Del Norte Co, with rapidly diminishing amts to the south, with 0.5 inch from near Fort Bragg to the Shasta River basin and a portion of the Feather River basin, with 0.25 inch from near Pt Arena to Red Bluff to near Blue Cyn, with >0.1 inch from near the Russian River basin to Chico to near Kirkwood. The remainder of CA stays DRY.
Days 8-16; shows most of CA
Monday’s 0Z 9pm GFS 384hr, 16Day QPF Chart, depicting a moderately wet NORCAL, semi-wet CENCAL, and dry SOCAL. With up to 3-4 inches for the NW Coastal region diminishing to 0.75 inch from the North Bay into the Feather River basin and up to 0.5 inch from San Jose to near Lake Tahoe, 0.25 inch from near Monterey to Modesto to near Kirkwood, with >0.1 inch from near Morro Bay to Cedar Grove.
Water Vapor 4KM Image of the West Coast Monday, February 17th, 2014, shows a westerly flow pattern crossing CA with occasional high cloudiness.
Visible Satellite Image of the CA Monday, February 17th, 2014, shows high cloudiness crossing over CA, with thicker clouds over the NW Coastal region.
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