Quick Post: Cool Storm Friday into Saturday, Another Possible Next Week, Wind Also Likely

Home / Active / Quick Post: Cool Storm Friday into Saturday, Another Possible Next Week, Wind Also Likely

Another moisture starved system is expected to drop into the southwestern U.S. late this week, similar to the one we had slide through over the weekend into Monday, except it appears it’ll take a slightly more westerly track, allowing a bit more moisture and lift to slide across northern California. The trough/upper-low will stretch out westward once again in a NE to SW oriented trough, with the trough axis extending from Idaho/Utah to northern/central California by Saturday. As the trough slides southward, showers will begin increasing in the mountains through the day Friday, with showers perhaps in the valley by the mid to late-afternoon into, overnight and into Saturday. Showers are expected to continue across the region, mainly in the mountains, through Saturday as the trough/upper-low slides southward, directly over northern California.

map-one

The cold pocket associated with the upper-low is currently forecast to feature -28 to -30c 500mb temperatures – which will steepen lapse rates a bit Friday and especially Saturday as the upper low slides directly overhead, equating to a bit of instability, especially when combined with partly cloudy skies due to the showery nature of precipitation with this system. A few thunderstorms can’t be ruled out both Friday afternoon/evening and Saturday afternoon & evening due to this instability – however a lack of upper-level flow over northern California will likely limit severe potential… but will monitor the track/positioning of the upper-low over the next couple of days to see if models adjust the position of the low.

0z GFS's forecast 500mb temperatures, valid Saturday afternoon as the upper low slides overhead.

0z GFS’s forecast 500mb temperatures, valid Saturday afternoon as the upper low slides overhead.

Snow levels Saturday and Sunday during the day look like they’ll be around 4000ft, but could drop down to 3000 – 3500ft overnight and/or in heavy convective showers or thunderstorms. Precipitation amounts won’t be very significant due to the lack of substantial moisture and the unfavorable/inland track of the system. Expecting nothing to a few hundredths in the valley, perhaps a few tenths or so if thunderstorms slide over some regions. In the mountains, a quarter to half an inch of liquid is generally progged, however local amounts up to an inch are possible where convection develops more frequently. Snowfall amounts are currently expected to range from a couple inches in some parts of the mountains above 4000ft, to around a foot above 5000 – 6000ft from around Highway-50 southward to Mariposa county.

map-two

Late Saturday into Sunday, as the trough/upper-low kicks southeastward deeper into the southwest, gusty northeast winds will develop behind the low as ridging tightens pressure gradients a good bit against the surface low that develops in the southwest. Appears some gusts in excess of 30mph will be possible in parts of the valley, while gusts in excess of 40mph are possible along favorable southwest facing slopes due as the northeast flow runs downslope perfectly through southwest-oriented slopes.

0z GFS's forecast surface wind gusts, valid early Sunday morning, depicting plenty of 30 - 40mph gusts along the east side of the valley and parts of the foothills and mountains north of Sacramento.

0z GFS’s forecast surface wind gusts, valid early Sunday morning, depicting plenty of 30 – 40mph gusts along the east side of the valley and parts of the foothills and mountains north of Sacramento.

There are serious model differences when it comes to next weeks pattern – with the ECMWF suggesting a somewhat similar setup to this Friday/Saturday’s system, while the GFS takes the upper low deeper inland into the Great Basin/Rockies, bringing us a significant wind event rather than a cold, showery setup. The GFS previously did follow the ECMWF, so we’ll have to see if the ECMWF is slow to follow the GFS or if the GFS dumped the solution too quickly. The GFS’s solution generates an offshore wind event with gusts potentially in excess of 40 – 45mph across a good chunk of the region, while the ECMWF has widespread showers and slow levels down into the foothills. There should be at least somewhat better agreement by later this week, and I’ll post another update if one of these two solutions becomes more prominent across the board, as either one would have some pretty decent impacts across the region.

Leave a Reply

%d bloggers like this: