Latest Forecast for Mauna Kea Observatories
5 PM HST Tuesday 17 April (0300 UTC Wednesday 18 April) 2018
Warnings
Chance for fog/high humidity
Cloud Cover and Precipitation Forecast
There is a small risk for fog and high humidity, mainly during the first half of the night; precipitation is not expected. Broken to overcast mid/upper-level clouds will continue to fill in from the WSW through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near -0.5 C this evening and 0 C tomorrow morning. Winds will be light and from the north, with seeing near 0.7-0.75 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
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Graphical Summary
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Discussion
While the tradewind inversion will continue to restrengthen, persistent mid-level moisture may still permit for periods of high humidity and perhaps short-lived fog mainly for this evening; precipitation is not expected. Unfortunately, building instability will help erode the inversion again through tomorrow night, allowing the atmosphere to become saturated early Thursday morning and late Friday night. This will significantly increase the risk for fog, ice and flurries at the summit as well as isolated convection in the area during that period. There is a good chance that the atmosphere will begin to stabilize while the inversion rebuilds near 10-12 thousand feet, which should help to reduce the risk for moisture at the summit as the weekend progresses. Some afternoon clouds are possible for today, then could pick up tomorrow, turn extensive for Thursday and Friday, then slowly taper over the weekend.
Broken to overcast high clouds will continue to pour in from the SW, contributing to extensive cloud cover, if not overcast skies, probably through the next 5 nights. There is also a possibility for thicker/summit-level clouds in the area mainly between late Wednesday night and early Saturday morning.
Precipitable water will continue to linger near or exceed 4 mm through at least Friday night, but could slip toward 3 mm for Saturday night.
Persistent mid-level moisture combined with light/moderate turblence in the free atmosphere will contribute to poorer than average seeing for much of tonight. An increase in moisture, instability and turblence will likely further degrade seeing for the following 3 nights. There is a chance that seeing could return toward more average-like values for as the atmosphere dries and moderate turbulence prevails in the free atmosphere for Saturday night.
No change since the morning forecast...Although the mid-level ridge will remain weak/indistinct into the weekend, the tropical upper-tropospheric trough will continue to shift westward for another 12-18 hours, allowing the low-level ridge to reinstate large-scale subsidence in the area for tonight. This should help rebuild the inversion near 7-8 thousand feet and decrease summit-level humidity as well as the risk for fog/ice at the summit as the night progresses. Unfortunately, a very persistent sub-tropical jet along the SE flank of the TUTT will linger over/near the Big Island and will continue to shuttle high clouds over the summit area probably throughout the forecast period. Furthermore, the TUTT is set to shift back eastward through tomorrow, which will likely destabilize the air mass, erode the inversion and allow the atmosphere to become mostly saturated between late Wednesday night and early Saturday morning. This will likely contribute to inoperable conditions, with extensive fog, ice, high humidity and light flurries plaguing the summit during that period (Thursday night in particular). Isolated convection is also possible in the area, especially along the slopes during the afternoon hours and just offshore near sunrise. The air mass is expected to restabilize again once the TUTT flattens out and a mid-level ridge begins to slowly fill in from the west over the weekend. Still, lingering instability associated with the TUTT may limit the inversion from strengthening much until Sunday, while more high clouds fill out of the SW late in the weekend and for the early part of next week.
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