Latest Forecast for Mauna Kea Observatories
5 PM HST Wednesday 28 October (0300 UTC Thursday 29 October) 2020
Warnings
Fog and ice
Chance for thunderstorms and flurries
Strong winds
Cloud Cover and Precipitation Forecast
There is a high risk for fog, ice and patches of thick clouds in the area, while a narrow band of cirrus develops overhead throughout the night. Isolated convection may also pop up in the area and deposit flurries at the summit, particularly this afternoon and into the evening hours.
Summary of Key Meteorological Variables
Summit temperatures will be near -2 C, with winds from the WSW at 30-45 mph. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, through the night.
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Graphical Summary
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Discussion
Although the upper half of the atmosphere is expected to dry out over the next 12 hours, persistent instability and low-level moisture will keep the inversion rather indistinct and elevated probably well into the weekend. As a result, there is a high risk for periods of fog, ice and even light flurries at the summit particularly over the next 3 nights; this risk will subside as the weekend progresses. There is also a high probability for isolated convection in the are area, mainly during the afternoon hours along the Big Island slopes. Extensive daytime clouds are expected probably throughout the forecast period.
There is a possibility for lingering patches of thick clouds in the area over the next 2 nights, and residual cirrus from any afternoon convection may persist over/near the summit over the next 5 evenings. In addition, a narrow band of cirrus flowing out of the SW is expected to set up over the summit for tonight and into tomorrow evening, then will sag subtly southward through the latter night and into Friday night. More widespread banding clouds will eventually pass along the eastern skies and could be visible from the summit for the following 2 nights.
Precipitable water is expected to exceed 4 mm over the next 2 nights, slip toward 2 mm for Friday night, then increase back to 3-4 mm for the following 2 nights.
A mixture of boundary layer turbulence, free atmospheric turbulence and persistent instability will contribute to bad seeing for at least the next 4 nights. There is a possibility that seeing will improve as the atmosphere begins to stabilize and mid-level flow tapers for Sunday night.
No change since the morning forecast...The low to the north will remain quasi-stationary/steady to the north, displacing the ridge well off to the south for at least another 48 hours. While the low is then set to take off toward the NE on Friday, it will leave a large trough in its wake, which will eventually be reinforced by a short-wave trough passing through over the weekend. This will prevent the ridge from rebounding northward and allowing mostly an unstable air mass to persist in the area throughout the forecast period. Fortunately, the bulk of the upper-level moisture will continue to slide off toward the east over the next 6 hours. However, this persistent instability, combined with residual low-level moisture in the area will keep the inversion rather indistinct/elevated, likely resulting in more fog, ice and high humidity at the summit throughout much of the next 5 nights. Flurries are also possible, but it will mostly be linked with afternoon convection that may pop up along the Big Island slopes and persist into the evening hours. There is a chance that isolated convection may flare up at night, should a pocket of upper-level diffluence along the south side of the low and on the eastern side of the incoming SWT pass through (mainly over the next 2 nights and again on Saturday night). In addition to this, a tight wind gradient along the southern flank of the low and on the large trough will keep winds near 35-40 mph, with stronger gusts, well into the weekend.
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