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……………..:-)


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.



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.



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………………..:-)