Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 14 January (0300 UTC Friday 15 January) 2021
Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, while isolated to scattered high clouds pass along the northern skies mainly during the first half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 0.5 C, with winds from the SE at 5-15 mph for this evening, easing and switching to a more SW direction through the night. Seeing will be near 0.5-0.6 arcseconds, while precipitable water is expected to be in the 2.5-3.5 mm range for the first half of the night and 2-3 mm range for the second half.
A fairly well-defined inversion will continue to cap low-level moisture near 7 thousand feet and ensure the summit remains dry and stable through at least Saturday night. Building instability will begin to erode the inversion and increase the risk for fog, ice and flurries at the summit through Sunday night and especially for Monday evening. Daytime clouds will be mimimal and short-lived through Saturday, but could pick up on Sunday, turn very extensive with the possibility for thunderstorms on Monday, then taper again through Tuesday.
THere is a chance for isolated to scattered high clouds passing along the northern skies for this evening. These clouds will shift eastward thereafter, leaving predominately clear skies through Sunday evening. Patches of mid/summit-level clouds may fill in from the WNW early Monday morning and may contribute to periods of extensive cloud cover (particularly along the northern half of the sky) before passing eastward through Tuesday.
Precipitable water is expected to slip into the 2.5-3 mm range for tonight, trend toward 1 mm through Friday night, increase back to 2-3 mm for Saturday night, and probably 3-4 mm through Sunday night and 4+ mm for Monday night.
Easing winds above the summit, combined with a drier more stable air mass will allow seeing to improve toward 0.5-0.6 arcseconds for tonight. There is a chance for a brief increase in winds, which could stir up boundary layer turbulence and contribute to a degradation in seeing for tomorrow evening. Seeing is set to improve again as winds subside through that night and eventually settle in near 0.5 arcseconds as relatively light/laminar northerly flow prevails in the free atmosphere for Saturday night. However, an increase in instability, boundary layer turbulence and the possibility for moisture and an elevated inversion will likely result in poor/bad seeing for Sunday and Monday night.
Little change since the morning forecast...The mid/low-level ridge will continue to sit over the state and stretch across most of the Pacific as the westerly jet retracts northward and maintains a fairly zonal orientation until early Sunday morning. This will allow strong steady large-scale subsidence to prevail in the area, which will help keep the inversion will established near 7 thousand feet and ensure a dry/stable (and predominately clear) air mass over the next 3 nights. The northward displacement of the jet will also allow turbulence to subside in the free atmosphere and seeing to improve toward better than average values for most of this time. There is a chance that summit-level winds will briefly pick up and disrupt seeing for as the ridge slips a tad northward for early tomorrow evening. A short-wave trough rapidly digging in from the NW is expected to kink the westerly jet and bring cold mid/upper-level air into the area as an upper-level low is deposited over the state late in the weekend and early part of next week. Thermodynamic instability associated with the low will help erode the inversion and increase the risk for fog, ice and flurries at the summit mainly between early Monday morning and early Tuesday morning. There is also a possibility that isolated convection will pop up in the area, especially along the northern skies around Monday afternoon/evening. Furthermore, a tight wind gradient along the SE flank of the trough/low could dramatically increase summit-level winds before the trough/low passes eastward around sunrise Tuesday. Winds are expected to quickly decrease, while the air mass stabilizes as the trough/low abruptly shifts eastward and retracts northward through Tuesday.