Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Friday 14 September 2018
Cloud Cover and Precipitation Forecast
There is a small risk for short-lived fog/high humidity, mainly for early this evening and during the second half of the night; precipitation is not expected. High clouds may also creep in from the west and pass primarily along the northern skies throughout the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 6.5 C this afternoon, 2.5 C this evening and 2 C tomorrow morning. Winds will be from the NE at 5-15 mph, with seeing near 0.6-0.65 arcseconds. Precipitable water is expected to linger near 4-5 mm for the night.
There is a chance that lingering patces of instability and moisture will periodically lift the inversion toward 10-12 thousand feet and increase the risk for fog/high humidity mainly for early this evening and again during the second half of the night; precipitation is not expected. The inversion is expected more firmly established near 6-7 thousand feet through tomorrow, ensuring the summit remains dry and stable for that night, Sunday and probably Monday night. However, increasing instability may deepen the low-level cloud field and increase the risk for moisture at the summit around Tuesday/Wednesday. Some afternoon clouds and isolated convection are possible for today and perhaps tomorrow, then will become minimal and short-lived for Sunday and Monday, only to pick up again on Tuesday.
Scattered high clouds are expected to creep in from the west and pass mainly along the northern skies for tonight. More widespread clouds may fill in from the west and pass directly over the summit, contributing to periods of extensive cloud cover for Saturday, Sunday and probably Monday night. There is a chance that these clouds will shift to the southeast skies on Tuesday, but patches of thick clouds may spread in from the east during that night.
Precipitable water is expected to linger near 4 mm probably through the next 5 nights.
Relatively calm skies will prevail at and above the summit, and together with a drier more stable air mass should allow for better than average seeing probably through most of the next 4 nights. There is a possibility for some variability mainly if moisture briefly becomes an issue for early this evening and again near sunrise tomorrow. There is also a chance that pockets of minor turbulence will pass through the area and contribute to some fluctuations for Sunday and Monday night. A potential increase in upper-level turbulence/instability and summit-level moisture may degrade seeing for Tuesday night.
Although the ridge to the NNE is expected to reinstill large-scale subsidence in the area over the next several days, residual pockets of tropical moisture associated with Olivia combined with weak instability from the tropical upper-tropospheric trough (TUTT) lingering overhead may allow for the development of isolated convection along the slopes mainly for today. This could bring periods of fog/high humidity to the summit, which may persist into early this evening. There is also a chance that a small pocket of unstable low-level clouds will drift in from the NE and lift the inversion, increasing this risk toward the end night, but the odds are slim. Drier more stable conditions are expected to return to the summit as the TUTT and the remainder of Olivia shift off toward the west through tomorrow. However, the interaction between the two will continue to fire off deep convection way south of the state, and the TUTT's southern counterpart, the sub-tropical jet, is expected to stream the cirrus exhaust over the area, contributing to extensive cloud cover probably for Saturday, Sunday and Monday night. Eventually, a short-wave trough is set to dig in from the NNW and shift the TUTT back over the state, bringing more widespread instability to the area, which could deep the low-level cloud flow and increase the risk for moisture at the summit and perhaps convection in the area late Tuesday night. On the other hand, this incoming trough could help push the STJ off toward the SE, opening up skies a bit for that night.