New Week Arrives on a Fair Note….Then a Return To Unsettled Weather Mid Week…..No Major Storms on the Horizon this Week….

Latest guidance favors the European Model which has the most consistent ensemble members and thus “Trumps” the GFS. (No pun intended)  The Wednesday night system looks pretty windy, with the potential for light to moderate precipitation.   There is another system out there for next Monday. Again the Euro seems to be handling the upper flow better with a slower approach and with better climatology showing a closed low associated with it. The Euro has another closed low system in back of it for the middle of next week as well.

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Monday AM the 9th:

The Dweebs Monday morning outlook is prefaced by the fact that we are approaching mid April now. Weather systems tend to move slower, become cut off from the westerlies at times and in general, model accuracy becomes ever more diminished with every calendar week ahead. The idea of trying estimate snowfall and rainfall amounts on a time scale of a week in the winter is much easier than at this time.  So as a result, more general outlooks for precip a week ahead will be issued and much subject to change.

We are currently in pattern that is highlighted by a series of smaller scale systems this week and next, that for the most part will bring lots wind at times;  little or no precip to generally light to moderate amounts of snowfall.  Light precip is defined as being 1 to 6 inches and moderate 6 to 18 inches of snow.  These are systems that have a fair amount of cold air.  The focus this week will be windy weather Tuesday afternoon and again Wednesday afternoon and night.  The Wednesday night into Thursday morning system holds the best chance for snowfall. The new 12Z Monday GFS has up to 1.2 inches on the west side of the Sierra, while last nights ECMWF had about 1/2 of that.  Best guess at this time is about 6 to 10 inches over the upper elevations by Thursday PM.

There will be periods of large swings of cooling and warming between weather systems. As a result, some of these weather systems will have strong thermal gradients and strong winds at times.

 

Dr Howard and the Dweebs………………………:-)

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The new week will offer a mixed bag of weather as the pattern remains progressive with a series of ridges and troughs migrating through the west coast. And typical for spring, some of these systems will bring windy weather over the upper elevations. A NW jet over the weekend will keep the upper elevations quite breezy as well…..Then a possibly stronger storm the following Sunday night into week 2. Overnight lows have now returned to below freezing and highs will wildly swing from the 60s to the 30s then 50s later this week.

 

Over all typical Spring April weather.  The mid-week storm may bring between 2 and 6 inches of snowfall

 

Dr Howard and the Dweebs…….:-)

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………………..:-)