Atmospheric River moves on shore later today…Latest model runs trend Bullseye further north to Tahoe…..Much colder storms expected next week……

Latest Update on the AR this Saturday morning the 7th:

 

  1. The AR will be out of the Mammoth Area between 11:00am and Noon.. A few showers may linger….
  2. No snow is expected in the Town of Mammoth
  3. Little if any snow is expected on Mammoth Mt following the system…..Above 9500 feet there may be an inch or two.
  4. Cooler air is following the rain, and precipitation should be mostly over by the time the rain ends.

 

Two more windy systems will move in mid-week. They will be colder and snow fall will be in the light category. 1 to 3 inches Tuesday night. and the system for Wednesday night into Thursday storm will bring the best chance of 6” plus of snowfall on Mammoth Mountain

 

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Some great news this morning…..

 

The good news this morning is that model consensus shows that the AR will affect the Northern Sierra with the greatest precipitation totals while the southern portion of the Central Sierra will have mainly moderate amounts. Computer generated QPF now showing up to three inches of water over the crest with about 2 inches in town and about an inch of water along the highway 395 corridor.  Rain is likely to reach the sierra crest up to 12,000 before the snow level comes down to 9000 on Saturday.  Additionally,  there is the suggestion that snowfall amounts will be in the 6 to 12 inch range on the mountain Saturday and a few inches possible in town. Down the road….two colder storms look likely to bring light to moderate snowfall Tuesday into Wednesday AM and again Wednesday night into Thursday. The Wednesday/Thursday system looks stronger than the Tuesday night storm and may bring enough snow in town for a plow.

Precipitation may begin as snow around Midnight tonight, even in town Friday, until our air mass becomes saturated later in the day, so do not be surprised if we get a couple of inches of snowfall early Friday before it turns to rain….

 

Dr Howard and the Dweebs………………….:-)

The Atmospheric River Drums beating stronger now for Friday into Saturday as high PWAT’s move toward Hawaii then Central and Northern CA Friday….

Tuesday 4:00PM

 

Stage is set for record or near record strength “AR” for the Central Sierra, “For the Month of April”. Rain and very high elevation snowfall will increase both in coverage and intensity Friday into Saturday. PWAT of 1.5 to 2.00 inches forecasted Early Saturday AM adjusted for climatology are some 500% of normal for Oakland, CA, nearing all time values for early April.  Although this atmospheric river is in the strong category and would be moderate to strong for any time of the Winter, the fact that it is coming within the strength forecasted in April is very unusual.  QPF amounts are in the 3 to 5 inches range over the west side of the sierra and up to the crest. Amounts in the town of Mammoth are likely to be in the 2:00 to 3:00 inches of rain with some light snowfall accumulations in town Saturday afternoon…..At the end of the storm. This storm may be similar to the storm we had last November 17th , 2017 when the top of Mammoth Mt picked up 4 to 5 feet at 11,000 feet and set up the snow pack in the upper bowls for the winter.  However, it is more likely to be in the range of 1 to 2 feet as most of the precip will fall as rain before it get cold enough to snow.

 

The Dweeber……………..:-)

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Tuesday AM:

More comments from WSFO Redwood City:

An excerpt from this WSFO mornings discussion.

Just look at the last AR event that shifted N impacting the Central Coast and not as much on Santa Barbara. That being said the 00Z suite of models bring rather impressive PWATs to the Bay Area by 12Z Friday and increase them through the day. PWAT values of 1.8-2″ are actually being forecast. To put that in perspective that is nearly 500% of normal, 7 to 9 standard deviations and nearing all-time record values for KOAK (Oakland) sounding climatology. AR guidance puts IVT values 700-1000+ kg/m/s, which clearly fits in the moderate to strong and possibly extreme categories. Simply put, WOW.

 

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Monday AM:

Comment from WSFO Redwood City, CA this Morning….

Indications are that the leading edge of a very well organized long fetch of subtropical moisture will first arrive later Thursday, an atmospheric river with maximum integrated water vapor transport values meeting or temporarily exceeding 1,000 kg/m/s from Friday into Saturday. On a scale from 1 (weak) to 5 (exceptional) this atmospheric river will last approximately 48 hours at category 3 or category 4 which means it`ll be borderline mostly hazardous with respect to hydro considerations, but also of course bring beneficial rain.

 

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Sunday PM:

The second strongest MJO of the year has created strong westerly wind bursts north of the equator near 150 East. The RIMM Phase Space has the envelope of upper divergence over the western pacific. There maybe a connection of the MJO to the strong -WPO as a blocking high over AK and the Bering Sea is now established in the 5 day means.  MJO composites show the block in a couple of Lagged composites for Phase 8 in April, However, the MJO is still officially in late Phase 7.

An eastward extension of the East Asian subtropical jet moves north of Hawaii and couples with a weak branch of the polar mid-week. Thereafter, the coupled jets shifts east to the west coast. This ties in with the strengthening MJO as it shifts into Phase space 8 then 1. Looking at the GFS and ECMWF’s PWAT’s,  the AR will extend from the Solomon Island to Hawaii this week and eventually reach Northern and Central CA regions Friday into Saturday AM. In the Fetch well off shore are PWATs in the 1.5 to 2 inch range. The moisture fetch is not subtropical, but rather tropical. So precipitation Friday will likely be rain except for only the highest elevations of the Sierra.  There is a colder system following the tropical AR for Saturday afternoon so the freezing level will lower and rain will turn to snow later Saturday afternoon in town. On another note, the AK blocking highs early in the winter were not associated with a California AR. The pattern across the pacific was all Meridional flow. That has now changed to Zonal Flow which is more like what we had the winter of 2017.

Potentially this could be a big deal with Hydro-Concerns. However, the key will be the forcing or the lack of in the AR Friday and where the AR spends most of its time.

So where the thinking is at the moment is that there will be little forcing Friday AM but lots of moisture and then strong forcing by Early Saturday morning. Also the GFS has the main part of the river into the Central CA area and the Euro has it near Tahoe.  Amounts in the meat of the AR could easily be 5 or 6+ inches of water. Most areas are in the 2 to 3 inch range at this time.  More confidence in where to place the Bull’s-eye by this Tuesday or Wednesday……Stay Tuned.

 

Dr Howard and the Dweebs………………..:-)

Spring has Sprung w/Warming Trend in full swing; 50s and low 60s possible the next 3 to 5 days….MJO Amping Eastward spells excitment for possible pattern change to wet….

Friday:

 

Models continue trend of focusing main thrust of Precipitation of an approaching “AR” for next Friday over Northern CA and Central CA. Snow levels look very high, at and above 9000 feet.  So rain a good bet for the town if the models hold on to that idea for next week, The MJO is amplified in phase spaces 7 and remains amped through phase 1. So above normal temperatures are likely under the subtropical high….. highs at 8000 ft will range depending upon cloud cover between 57 and 62 degrees in Mammoth with lows in the 30s. These temps are primarily for just above the nighttime inversion..

 

 

The Madden Julian Oscillation is Amping now in phase 7, and accordingly,  the Eastern Pacific Ridge is Amping as well along the west coast bringing the warm up. This upper ridge will move over CA Friday and weaken due to short wave action and peak out the warming trend with highs about 60 . Lots of high cloudiness will result over the weekend, however, temps will remain above normal.  Highs in the upper 50s in Mammoth and upper 70s in Bishop. lows in the 30s at resort levels.

The MJO is forecasted to translate east over the following two weeks. For week one, that means a continuing period of warmer than normal temps according to the RIMM composites.  As the MJO shifts from Phase 8 to 1 and possibly 2, the composites suggest the possibility of precipitation moving back into the Southern half of CA and the teleconnection WPO going negative with the “possibility of a blocking high near or just east of the Bering Sea. Undercutting of the westerlies with zone flow, may make it to the central west coast thereafter.  This brings the possibility of an AR as well. Although It is still too soon to count on from a climate perspective, it is interesting that both ECMWF and GFS global models suggest a strong negative phase of the WPO developing (Upper Level High Pressure blocking)  during the first week of April. In fact the standard deviation of normal for the -WPO is off the chart for the ECMWF and about -5 Deviation of normal for the GFS for that same time period.  Their ensemble members during the 2nd half of next week support a possible AR during the time frame Thursday and Friday next week.

On another note, DWP just posted the update on the Mammoth Pass water wise. It indicated that the pass was 95% of normal for the water year ending April 1st.   Again this is just telemetry and I suspect that when the manual survey is done, it will be considerably less.  Nevertheless, it is certainly encouraging! It shows that the pass went from about 5 inches up until the 3rd week of February to 40.5 inches. Now that’s amazing…almost a Miracle?  Again, this does not include the final manual core sampling that will likely be taken just after the first of April. Also noted that the Central Sierra was 70% of normal to date with about 16 inches of water eq. (Quite a difference).   I feel that the main point here,  is that Mammoth Pass possibly picked up the lions-share of the last AR event in California.

 

Enjoy the great weather over the coming days with spring conditions returning to the lower slopes…..

Get it while its cold……………..

 

Dr Howard and the Dweebs……………………..:-)