Discussion
The tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure the summit remains dry and stable for the next 3 nights. There is a chance that a patch of deep low-level moisture will briefly pass through the area, lift/weaken the inversion and increase the risk for fog and high humidity at the summit for Monday night; precipitation is unlikely. The inversion is set to recover again by late Tuesday morning, allowing dry/stable conditions to return again for that night. Daytime clouds will be minimal and short-lived through the weekend, but could pick up for Monday, only to taper again for Tuesday and Wednesay.
While the bulk of the high clouds will continue to shift to the western skies, there is a possibility for patches of mid-level clouds lingering near/over the summit area for the next 2 nights. Clear skies should prevail for most of Sunday, Monday and Tuesday night, but there is a possibility for short-lived summit-level clouds building in from the east mainly for Monday evening.
Precipitable water is expected exceed 4 mm for the next 2 nights, then slip toward 2 mm for Sunday night. There is a chance for large variability in PW for Monday evening, but it may drift to 1-1.5 mm by the end of that night and into Tuesday night.
Winds at and above the summit will remain quite light, resulting in minimal dynamic turbulence and probably allowing for good/excellent seeing over much of the weekend. However, easterly winds are expected to deepen/strengthen, which will likely stir up boundary layer turbulence and contribute to poor/bad seeing for Monday and Tuesday night.
Little change since the morning forecast...The surface ridge will continue to sit in the NE Pacific, while the mid-level ridge expands to the NW before also shifting to the NE Pacific as the weekend progresses. Nevertheless, strong/steady subsidence associated with the ridge will help maintain a well-defined tradewind inversion at or below 8 thousand feet and ensure the summit remains dry and stable through at least the weekend. An upper-level low to the west of the state will continue to draw high cloud out of the tropics, but will also shift westward in response to an upper-level ridge building in from the east. This should help to open up skies (as these clouds slip westward) , though there is a chance for patches of mid-level clouds lingering in the area over the next 2 nights. Despite this, light winds are set to build in overhead with upper-ridge, which will help to minimize free atmospheric turbulence probably through the weekend. This, combined with a stable air mass and light summit winds, should allow for good/excellent seeing during that time, particularly for Saturday and Sunday night. However, the upper-level ridge is expected to shift off toward the SW and weaken as a new upper-level low develops to the east early next week. The low will have little to no direct impact on the stability of the atmosphere for the early part of next week, but may (indirectly) contribute to the deepening/strengthening of NE flow over the Big Island. This could push summit-level winds toward 20-30 mph, enough to stir up boundary layer turbulence and contribute to poor/bad seeing for Monday and Tuesday night. In addition, a patch of low-level moisture/clouds, deepened by the developing low and riding in with the trades, could briefly lift/weaken the inversion and allow for fog/high humidity at the summit, mainly around Monday evening.
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