Current Conditions
Temp8.7 C
RH30 %
WindSSW 8 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Friday 23 October 2020
Warning(s)
Chance for fog/high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a moderate risk for periods of fog and high humidity, particularly for the second half of the night; precipitation is unlikely and skies will remain clear.
Summary of Key Meteorological Variables
Summit temperatures will be near 6.5 C this afternoon, 1.5 C this evening and 1 C tomorrow morning. Winds will be from the south at 10-20 mph for today, easing to 5-15 mph for the night. Seeing will start out near 0.4 arcseconds, but could become more variable and degrade toward 0.6 arcseconds as the night progresses. Precipitable water is expected to exceed 4 mm through the night.
Discussion
There is a chance that the inversion will weaken/lift toward 12 thousand feet, increasing the risk for periods of fog and high humidity at the summit over the next 2 nights, particularly for early tomorrow morning; precipitation is unlikely. The inversion is expected to recover near 7-8 thousand feet by sunrise Sunday, ensuring the summit remains dry and stable for that night and perhaps into early Monday evening. However, an abrupt increase in widespread moisture will increase the risk for fog, high humidity, ice and light flurries at the summit through the latter night and will eventually saturate the air mass for Tuesday night. Some afternoon clouds and perhaps isolated convection along the Big Island slopes are possible over the next 2 days, then will become minimal and short-lived for Sunday and Monday, only to turn extensive again for Tuesday and Wednesday.

Predominately clear skies will prevail through at least midnight Saturday, but high clouds are set to quickly spread in from the west by sunrise Sunday. These clouds will thicken and become more widespread over the next 2-3 days, contributing to extensive cloud cover for Sunday night and probably overcast skies for the following 2 nights.

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

While skies will remain predominately calm in the free atmosphere and allow seeing to linger near 0.4-0.5 arcseconds for this evening, an elevated/weakened inversion could contribute to a degradation and/or variation in seeing for the second half of the night. A minor increase in mid-level turbulence may push seeing toward 0.5-0.6 arcseconds for Saturday and Sunday night, while an widespread influx of deep moisture and eventually instability will likely result in poor/bad seeing for the following 2 nights.

The mid/low-level ridge will continue to sit over the Big Island, while the low to the north loses its surface reflection and lifts out of the area as it is replaced by a new large trough digging in from the NW over the weekend. While subsidence associated with the ridge will still prevail in the area into next week, a relatively deep band of moistture trailing from the departing/weakening low will move in from the east over the next 24-36 hours. This band is expected to elevate/weaken the inversion and could increase the risk for periods of fog and high humidiaty the summit over the next 2 nights, but particularly for tomorrow evening. There is also an outside chance that daytime heating, combined with leading/trailing moisture surrounding the band may allow afternoon convection to develop along the Big Island slopes through tomorrow. The inversion is set to recover as this band of moisture exits westward probably by midnight Saturday, ensuring dry/stable conditions for Sunday night. However, the new aformentioned trough digging in from the NW will begin to send widespread high clouds in from the west and SW, contributing to extensive cloud cover for that night. Deeper clouds/moisture may eventually fill in from the SW as the trough draws closer to the state, blanketing summit skies for the early part of next week. There is a chance that this moisture combined with instability associated with the trough will eventually erode the inversion and drastically increase the risk for fog, high humidity, ice and flurries at the summit as early as Monday night and especially Tuesday night. There is a chance that these conditions will persist into Thursday.
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 Oct 23 - 2 PM20-404-4.525 / 56.5SSW/10-20NaN4-8
8 PM0-20Clear40 / 101.5S/5-150.35-0.554-6
Sat Oct 24 - 2 AM0-20Clear60 / 151S/5-150.45-0.754-6
2 PM60-804-565 / 206.5SSE/5-15NaN4-8
8 PM0-20Clear40 / 51.5E/0-100.4-0.63.5-4.5
Sun Oct 25 - 2 AM0-209.5-1020 / 51ESE/0-100.45-0.653.5-4.5
2 PM60-809-100 / 06.5SE/5-15NaN4-6
8 PM60-808-100 / 01.5SE/5-150.45-0.654-6
Mon Oct 26 - 2 AM60-807-100 / 01SE/5-150.4-0.64-6
2 PM80-1006-100 / 05SE/5-15NaN4-8
Tue Oct 27 - 2 AM80-1005-1065 / 30-1SE/15-300.6-1.16-10
2 PM80-1004-1095 / 602SW/20-35NaN10-15
Wed Oct 28 - 2 AM80-1004-1095 / 60-2SW/20-351-210-15
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
Fri Oct 23 - Sat Oct 24 18:01 19:06 5:06 6:11 N/A 0:49 58 20 57.4 -21 29
Sat Oct 24 - Sun Oct 25 18:01 19:06 5:06 6:11 N/A 1:43 68 21 49.1 -18 12
Sun Oct 25 - Mon Oct 26 18:00 19:05 5:07 6:12 N/A 2:35 77 22 37.8 -14 10
Mon Oct 26 - Tue Oct 27 17:59 19:05 5:07 6:12 N/A 3:25 84 23 24.1 -9 37
Tue Oct 27 - Wed Oct 28 17:59 19:04 5:07 6:13 N/A 4:14 91 0 08.7 -4 45
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Friday 23 October (0300 UTC Saturday 24 October) 2020.
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