Latest Forecast for Mauna Kea Observatories
5 PM HST Tuesday 19 February (0300 UTC Wednesday 20 February) 2019

Warnings
Fog/ice and snow
Strong winds
Chance for thunderstorms and heavy snow

Cloud Cover and Precipitation Forecast
Extensive fog, ice, clouds and light/steady rain/snow will continue to plague the summit through the night; there is also a chance for periods of thunderstorms and heavy rain/snow at virtually anytime.

Summary of Key Meteorological Variables
Summit temperatures will be near -1.5 C, with winds from the SSW at 50-70 mph for this evening, easing to 40-60 mph as the night progresses. Seeing and PW are expected to exceed 1 arcseconds and 4 mm, respectively, through the night.

Discussion
The atmosphere near the Big Island will remain saturated, allowing extensive fog, ice and snow/rain to plague the summit for at least tonight. There is also a possibility for periods of heavy snow/rain at the summit and convection in the area. While there is a possibility that the upper air mass will dry out, persistent instability combined with a fairly saturated air mass below 16 thousand feet will keep the inversion rather weak/indistinct probably into the weekend. Consequently, more periods of fog, ice and flurries are certainly possible during that period. Extensive daytime clouds are expected throughout the forecast period and there is a possibility for afternoon convection along the slopes particularly after today.

Thick clouds will continue to build in from the south and/or develop in the area blanketing summit skies for tonight. There is a good chance that these clouds will begin to break up through tomorrow, leaving very persistent/stagnant scattered to broken mid-level clouds to slowly dissipate in the area over the following 4 nights.

Precipitable water is expected to linger near or exceed 4 mm probably into early Saturday evening, then will slip toward 2 mm by sunrise Sunday.

A mixture of boundary layer and free atmospheric turbulence, as well as instability, moisture and/or an elevated inversion will contribute to poor/bad seeing throughout the forecast period.

Little change since the mroning forecast...A very persistent large-scale trough will continue to linger over or just west of the state and promote widepread instability in the area probably into latter part of the weekend. A somewhat equally incessant/steady embedded low to the NW will continue to draw deep moisture out of the south and over the eastern half of the state, before finally breaking down and lifting off toward the NNE over the next several days. Unfortunately, its trailing low-level frontal band will remain over the Big Island to gradually detrain into the surrounding atmosphere probably into the weekend. Nevertheless, the initial deep moisture advecting in from the south will contribute to inoperable conditions, with the possibility for quick moving patches of convection, which may deposit heavy snow at the summit over the next 12 hours. A tight wind gradient along the SE flank of the low will also result in strong winds at the summit probably through tomorrow night. There is a very good chance that the air mass above 16 thousand feet will dry out as the low lifts northward through tomorrow. However, relentless instability and moisture provided by large-scale trough and residual frontal band, respectively, will keep the inversion rather weak and indistinct and likely allow for more periods of fog, ice and flurries into the weekend. The lack of dynamic instability should limit the risk for heavy snow and nighttime convection beyond tonight. But, thermodynamic instability provided by daytime heating may still fire off afternoon convection along the Big Island slopes, especially with the depature of the thicker upper-level clouds after today.