Latest Forecast for Mauna Kea Observatories
5 PM HST Monday 16 April (0300 UTC Tuesday 17 April) 2018

Warnings
High humidity
Chance for fog

Cloud Cover and Precipitation Forecast
There is a chance for periods of fog as humidity lingers near 60-80% through the night. Broken mid/upper-level clouds will continue to linger in the area and/or fill in from the SW throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near -1 C, with winds from the NNW at 5-15 mph for the night. Seeing will be near 0.7-0.8 arcseconds, while precipitable water is expected to exceed 4 mm through the night.

Discussion
While the inversion will continue to restrengthen near 8 thousand feet over the next 12-24 hours, persistent mid-level moisture may still allow for periods of fog as humidity lingers near 60-80% for tonight and perhaps tomorrow night. A return of low-level moisture and upper-level instability may erode the inversion again, raise humidity toward 80-100% and increase the risk for extensive fog, ice and flurries at the summit as well as convection in the area for Wednesday, Thursday and Friday night. Some daytime clouds are possible over the next 2 days, then will likely turn extensive with the possibility for afternoon convection along the slopes for the remainder of the forecast period.

Broken mid/upper-level clouds will continue to linger in the area and/or drift in from the SW contributing to extensive cloud cover for tonight. More organized, widespread high clouds are set to fill in from the SW through tomorrow, with thicker/deeper clouds following suit on Wednesday. This will likely result in mostly overcast skies for Tuesday night through the weekend.

Precipitable water will continue to exceed 4 mm throughout the forecast period.

Persistent mid-level moisture combined with light/moderate turblence in the free atmosphere will contribute to poorer than average seeing over the next 2 nights. An increase in moisture, instability and turblence will likely further degrade seeing for the following 3 nights.

Little change since the morning forecast....The tropical upper tropospheric trough (TUTT) and an embedded low is set to shift off toward the west, allowing the atmosphere to stabilize a bit and the inversion to rebuild near 8 thousand feet over the next 48 hours. Unfortunately, mid-level moisture will continue to linger in the area, which will likely contribute to high humidity/PW and perhaps short-lived fog over the next 2 nights. In addition, a strong sub-tropical jet will persist overhead, shuttling more high clouds in from the SW and allowing moderate turbulence to prevail in the free atmosphere probably throughout most of the forecast period. While the embedded low to the west is expected to fall apart late tomorrow, the TUTT is set to return eastward, bringing widespread instability and moisture back to the area by late Wednesday morning. This will likely help dismantle the inversion and allow the atmosphere to become saturated, contributing to another round of extensive fog, ice and flurries at the summit and convection in the area for Wednesday, Thursday and Friday night. Longer term projections suggests that the TUTT will weaken and shift back off toward the west, which could allow the atmosphere to stabilize and dry out over the weekend.