Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Thursday 22 February 2018

Warnings
Fog, ice, high humidity, and flurries
Chance for convection and heavy snow

Cloud Cover and Precipitation Forecast
Fog, ice, high humidity, clouds and flurries are expected to plague the summit through the night. There is a possibility for convection in the area and periods of heavy snow throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near -1 C this afternoon and -3 C for the night. Winds will be from the SW at 5-15 mph for today, switching to ESE and increasing to 15-25 mph for the night. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively throughout the night.

Discussion
The atmosphere near the Big Island will remain saturated and unstable, allowing fog, ice, high humidity and flurries to plague the summit through the weekend and perhaps into Monday night. There is also a possibility for periods of heavy snow and convection in the area mainly through early Saturday morning (and especially through late this evening) There is a chance that a weak inversion will begin to slowly rebuild near 9 thousand feet through Saturday, which should help reduce the risk for convection near the Big Island thereafter (periods of moderate mostly uniform snow could still occur through Sunday evening. Extensive daytime clouds are expected throughout the forecast period.

Broken to overcast thick clouds will persist in the area, blanketing skies through at least Sunday evening. These clouds will begin to slowly breakdown thereafter, opening up skies a bit for early Monday evening. However, there is a possibility that more clouds will fill in from the west later that night.

Precipitable water is expected to exceed 4 mm throughout the forecast period.

A mixture of moisture, instability and turbulence throughout various layers of the atmosphere (including the boundary layer) will contribute to bad seeing through the next 5 nights.

The cut-off low will continue to strengthen and develop to the NW, destabilizing the air mass and drawing deep tropical moisture over the summit area probably through the weekend. This will likely keep the atmosphere quite saturated and cloudy, contributing to inoperable conditions through at least Sunday night. More focused instability in the area, combined with the fresh influx of moisture may also allow for the development of convection in the area, which could deposit heavy snow at the summit mainly through this evening and again around tomorrow afternoon/evening. The bulk of the convection will slide to the western skies as the low shifts subtly westward thereafter. Still, exhaust from the thunderstorms, combined with a saturated air mass, may still allow for moderate/stratiform snowfall at the summit through the weekend. There is a chance that the moisture around the Big Island will begin to detrain into the surrounding atmosphere, allowing a portion of the inversion to weakly rebuild near 9-10 thousand feet during the second half of the weekend and early part of next week. This could help drop mean summit-level humidity toward 60-80% and decrease the risk for fog, ice and especially flurries at the summit for Monday night.