Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Tuesday 13 August 2019
Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, while scattered to broken high clouds fill in from the SW and contribute to periods of extensive cloud cover for tonight.
Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon, 3 C this evening and 2.5 C tomorrow morning. Winds will be from the ENE at 20-35 mph, while seeing will exceed 1 arcseconds. Precipitable water is expected to be in the 2-3 mm range for the first half of night and 1.75-2.25 mm range for the second half.
The tradewind inversion will continue to cap low-level moisture primarily near 7 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Some very minor afternoon clouds are possible through Thursday, then will become minimal and short-lived for Friday and over the weekend.
More scattered to broken high clouds are expected to flood out of the SW, contributing to periods of extensive cloud cover, perhaps even overcast skies over the next 2 nights. There is a good chance that these clouds will disperse a bit and shift subtly to the north, opening up skies for Thursday night. These remainder of these clouds will eventually rapidly sag southward through Friday night, through there is still a possibility for residual isolated patches in the area through the weekend.
Precipitable water is expected to start out in the 2-3 mm range for this evening, slip toward 1.75 mm by the end of the night and settle in near 1 mm for Wednesday and Thursday night, then increase back to 2 mm for the following 2 nights.
Despite relatively calm skies in the free atmosphere, moderate boundary layer turbulence will contribute to poor seeing probably throughout the forecast period.
The SW tip of the mid/low-level ridge sitting just north of the Big Island is expected to expand off toward the north and west, before becoming quasi-stationary/steady late tonight and probably for the remainder of the week. Strong subsidence associated with the ridge will help maintain a well-defined tradewind inversion primarily near 7 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Unfortunately, summit-level winds are expected to pick up as the ridge broadens over the next 12-24 hours, then likely hold steady near 20-30 mph into the weekend. The winds are projected to stir up boundary layer turbulence and contribute to poor seeing probably throughout the forecast period. In the upper atmosphere, a persistent tropical upper-tropospheric trough will continue to sit the NW of the state, though will hardly affect the stability of the atmosphere during its tenure. However, SW flow along the TUTT's SE flank, aka the sub-tropical jet, will continue to shuttle high clouds over the summit area, contributing to periods of extensive cloud cover or even overcast skies into Thursday evening. There is a good chance that these clouds will retract further northward as an short-wave trough embedded in the TUTT fills in from the NW through Thursday night. While this may actually help disband most of the clouds in the area, there is a chance that the short-wave trough will send the remaining more organized high clouds back over the summit area on Friday. Skies are set to open up again as the bulk of these clouds shift off toward the SE (with the short-wave and the STJ0 over the early part of the weekend.