Current Conditions
Temp7.7 C
RH12 %
WindENE 4 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 23 September (0300 UTC Saturday 24 September) 2016
Warning(s)
Fog/high humidity
Chance for rain
Cloud Cover and Fog/Precipitation Forecast
There is a very high risk for fog and light rain at the summit, particularly during the first half of the night. There is also a possibility for patches of mid/summit-level clouds in the area as well as isolated to scattered high clouds to the south through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C, with winds from the SSE at 5-15 mph for the night. Precipitable water is expected to exceed 4 mm, while seeing will be likely be near 0.8-1 arcsecond.
Discussion
The atmosphere below 18 thousand feet will remain fairly saturated through this evening, then will slowly dry out as the inversion rebuilds near 7 thousand feet through Saturday and into Sunday. There is a chance that the inversion will breifly weaken/lift toward 12-13 thousand feet again during the latter night, then quickly recover near 6 thousand feet for Monday and Tuesday night. Consequently, there is risk for fog, high humidity and perhaps light rain at the summit over the next 3 nights (tonight and Sunday night in particular). The summit will remain dry and stable for the early part of next week. Extensive daytime clouds are expected for today, but should taper a bit over the weekend and become minimal and short-lived for the early part of next week.

There is a possibility for patches of mid/summit-level clouds in the area as well as isolated to scattered high clouds to the south for tonight. The former set of clouds are expected to dissipate and shift southwestward through tomorrow, but the high clouds to the south are slated to spread to the western skies and may drift over the summit area for Saturday night. These clouds will dissipate and drift off toward the west through Sunday, leaving predominately clear skies for the remainder of the forecast period.

Precipitable water is expected to exceed 4 mm for tonight and probably most of tomorrow night, then will slip toward the 2-3 mm range for Sunday night and probably toward 1.25-1.5 mm for the early part of next week.

Despite relatively calm skies in the free atmosphere throughout most of the forecast period, there is a very good chance for poor seeing due to low-level moisture and minor low-level turbulence for tonight. There is a potential for good/excellent seeing as deep subsidence builds over the area mainly for Saturday night and early Sunday evening. There is a chance for minor mid-level turbulence which could disrupt seeing during the latter half of Sunday night and Monday night (still better than average seeing will likely prevail).

No change since the morning forecast...The patch of mid/low-level moisture/clouds responsible for the fog at the summit is set to push westward as a relatively deep ridge fills in form the east over the next 24 hours. While this should help rebuild the inversion near 7 thousand feet during this time, there is a very good chance that moisture (fog/high humidity) will continue to be an issue through tonight. Predominately dry/stable conditions and calm skies should prevail once the upper-level ridge settles in over the summit for tomorrow night. This may allow for another round of good/excellent seeing probably for the remainder of the forecast period. However, there is a possibility that the upper-level low to the far NE will destabilize a patch of low-level clouds over the next 24 hours. This patch is set to drift in with the NE trades, arriving around late Sunday evening. Although I suspect this is a little overdone, models have been quite consisitent with the batch of clouds and expects the inversion to lift toward 12-13 thousand feet for that night. This could allow for another round of short-lived fog and/or periods of high humidity at the summit for that night. Normal dry and stable conditions are expected to return to the summit once this patch shifts off toward the SW for the early part of next week.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Fri Sep 23 - 8 PM60-804-995 / 601SE/5-150.7-1.310-15
Sat Sep 24 - 2 AM40-605-875 / 401SE/5-150.6-110-15
2 PM40-604-660 / 156WNW/0-10NaN6-10
8 PM30-508-910 / 02NW/0-100.35-0.454-6
Sun Sep 25 - 2 AM40-608-1010 / 02.5WNW/5-150.35-0.454-6
2 PM40-604-540 / 08NE/5-15NaN3-6
8 PM10-308.5-930 / 54ENE/10-200.35-0.452-3
Mon Sep 26 - 2 AM0-20Clear60 / 103.5NNE/5-150.4-0.62-3
2 PM0-20Clear10 / 08.5NE/5-15NaN1.5-2.5
Tue Sep 27 - 2 AM0-10Clear0 / 03.5ENE/0-100.45-0.651-2
2 PM0-20Clear0 / 08.5SE/5-15NaN1.5-2.5
Wed Sep 28 - 2 AM0-10Clear0 / 03SSE/0-100.4-0.61-2
2 PM0-20Clear0 / 07ESE/5-15NaN2-4
Rise and Set times for the Sun and Moon
Night (HST) Sun Set Twilight End Twilight Beg Sun Rise Moon Rise Moon Set Illumination (%) RA DEC
Sun Sep 25 - Mon Sep 26 18:24 19:28 4:59 6:03 2:25 N/A 19 8 53.4 14 21
Mon Sep 26 - Tue Sep 27 18:23 19:27 4:59 6:03 3:19 N/A 12 9 44.3 11 31
Tue Sep 27 - Wed Sep 28 18:22 19:26 4:59 6:03 4:11 N/A 6 10 33.3 8 12
Wed Sep 28 - Thu Sep 29 18:21 19:25 4:59 6:04 5:02 17:12 2 11 20.6 4 33
Thu Sep 29 - Fri Sep 30 18:20 19:24 5:00 6:04 5:52 17:51 0 12 06.7 0 46
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 26 September 2016.
Additional Information
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