Possible Pattern Change Next Week

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Since the last post, we were expected to see a weak to moderate strength storm later Tuesday into Wednesday this week as a trough dug into the western U.S. Well, as everyone (probably) knows, that storm didn’t do much for us, thus I didn’t put out an updated post.

The ridge that chewed up this system will remain in place through the weekend into early next week, amplifying over the weekend into early next week as a deep trough digs into the east-central Pacific, advecting some warmer mid-level temperatures northward ahead of the trough as it slowly nudges the ridge south. This will bring above-normal temperatures from late this week into early next week.

Warm temperatures being advected ahead of a deep surface low int he eastern Pacific. MSLP, 850mb winds and temperatures plotted through the 18z GFS valid for Monday.

Warm temperatures being advected ahead of a deep surface low int he eastern Pacific. MSLP, 850mb winds and temperatures plotted through the 18z GFS valid for Monday.

Drought update:

While the early-month atmospheric river has helped a little, bumping up reservoirs a bit and boosting the high-sierra snowpack by a few extra feet… we are still in an extreme drought. The atmospheric river earlier in the month has 1: caused a small drop in coverage of D3 (extreme) drought conditions (with no change to D4 (exceptional) drought condition coverage), and 2: brought 30 day precipitation from average values up to the 50 – 100% range on average. Before the AR event, 30 to 6 month precipitation percent of average was between 0 and 10 percent of normal. However, it is key to note this is just in the last 30 days… we’ve seen extremely low precipitation since early last year, though we’ve been dealing with some form of drought the last few years. One 30 day period of just near normal precipitation doesn’t do a whole lot to a multi-year drought.

Precipitation departure from normal over the last 30 days.

Precipitation departure from normal over the last 30 days.

20140211_CA_trd

Possible pattern change:

It’s growing increasingly likely we will see some sort of precipitation event next week as the deep trough in the eastern Pacific as aforementioned nudges our current ridge out of place by the middle of next week. As this occurs, a deep low associated with the trough off the western U.S. coast rotates several shortwaves into northern California, bringing rounds of precipitation and gusty winds to the region. It is possible that one of the few deep lows within the longwave trough in the eastern Pacific could actually slam into California later in the week, bringing perhaps the most intense precipitation and wind.

February 19th

Model agreement is surprisingly strong given this event is 7+ days out, however track, timing, and strength of individual systems is still needing to be refined.

ESRL/NCEP global ensembles indicate rather high potential for a decent precipitation event between Wednesday and Sunday next week, as well as anomalously low SLP values over the eastern Pacific. The GFS ensembles are also indicating a rather deep low off the western U.S. coast with an extremely deep low in the Gulf of Alaska, both of each connected in the same trough. ECMWF ensemble mean is rather close to that of the op-ECMWF, also indicating a deep low off the western U.S. coast between Thursday and Friday, after an initial shortwave Wednesday that opens the door for the stronger system Thursday/Friday based on current timing.

Mean precipitation for around Thursday via the NCEP ensembles.

Mean precipitation for around Thursday via the NCEP ensembles.

Not really worth it to go into precipitation and wind details at the moment given every model is different solution wise. Nonetheless, a period of wetter, windier weather appears likely from Wednesday into the weekend, with potentially a good bit of snow in the mountains.

I’ll surely have additional updates on this change over the coming days as models refine their solutions and hopefully close in one general idea. Expect the next update between this weekend and Monday depending on the way models act, with much more information regarding the possible pattern shift.

Stay tuned!

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