Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Friday 31 July 2020

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain clear, dry and stable through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 12 C this afternoon, 6 C this evening and 5 C tomorrow morning. Winds will be from the ENE at 5-15 mph for today, increasing to 10-20 mph for the night. Seeing will be near 0.45-0.5 arcseconds, while precipitable water is expected to be in the 0.8-1 mm range for the night.

Graphical Summary

Discussion
A distinct inversion will continue to cap low-level moisture near 8 thousand feet and ensure a dry/stable summit-level air mass through the next 4 nights. There is a chance that a patch of moisture will drift into the area, weakening the inversion and increasing the risk for fog/high humidity at the summit for Tuesday night. Daytime clouds will be minimal and short-lived through Tuesday, but could pick up on Wednesday.

Skies will remain predominately clear for tonight, but there is a chance for thin patches of light cirrus moving in from the east and/or south through the remainder of the forecast period.

Precipitable water is expected to linger just below 1 mm for tonight, briefly increase toward 2 mm for early tomorrow evening, then slip back to 1 mm as that night progresses and settle in near 0.8 mm for Sunday and Monday night. There is a chance that it will increase to 3+ mm for Tuesday night.

While winds aloft will maintain a relatively light/laminar easterly flow throughout most of the forecast period, there is a chance for periods of light low-level turbulence, induced by a slight increase in winds just above the summit. Nevertheless, better than average seeing (near 0.5 arcseconds) should prevail over the next 4 nights. There is a possibility that an influx of moisture and perhaps instability could degrade seeing for Tuesday night.

A deep ridge will continue to sit to the north of the state before the upper portion begins to fall apart as the tropical upper-tropospheric trough (TUTT) begins to take shape around the middle part of next week. Nevertheless, subsidence associated with the ridge will easily maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass through at least Monday night. There is a chance that redevelopment of the TUTT combined with an influx of tropical wave/moisture will weaken/lift the inversion toward 12-13 thousand feet and increase the risk for fog and high humidity at the summit for Tuesday night. Regardless, prior to this, a stable air mass combined with relatively laminar easterly flow at and above the summit will minimize free atmospheriec turbulence and should allow for better than average seeing. There is a chance for minor low-level turbulence as winds just above the summit creep toward 20 mph, which could result in slight degradation/variability in seeing over the next 4 nights. PW, for the most part, will also benefit from the deep subsidence and settle in below 1 mm over most of this time. The only exception could be as a patch of mid/upper-level moisture scrapes through, increasing PW toward 2 mm for tomorrow evening. However, the influx of moisture may further degrade seeing and raise PW (perhaps significantly) for Tuesday night.

Astronomical Observing Quality Guidance
Seeing/CN2 Images are not available today. Sorry for the inconvenience.
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
02 pm HST
Fri 31 Jul
08 pm HST
Fri 31 Jul
02 am HST
Sat 01 Aug
02 pm HST
Sat 01 Aug
08 pm HST
Sat 01 Aug
02 am HST
Sun 02 Aug
02 pm HST
Sun 02 Aug
08 pm HST
Sun 02 Aug
02 am HST
Mon 03 Aug
02 pm HST
Mon 03 Aug
02 am HST
Tue 04 Aug
02 pm HST
Tue 04 Aug
02 am HST
Wed 05 Aug
00 UTC
Sat 01 Aug
06 UTC
Sat 01 Aug
12 UTC
Sat 01 Aug
00 UTC
Sun 02 Aug
06 UTC
Sun 02 Aug
12 UTC
Sun 02 Aug
00 UTC
Mon 03 Aug
06 UTC
Mon 03 Aug
12 UTC
Mon 03 Aug
00 UTC
Tue 04 Aug
12 UTC
Tue 04 Aug
00 UTC
Wed 05 Aug
12 UTC
Wed 05 Aug
Cloud Cover (%) 0 to 20 0 to 5 0 to 5 0 to 20 0 to 10 0 to 20 10 to 30 0 to 20 0 to 20 0 to 20 0 to 20 0 to 20 0 to 20
Cloud Height (km) above sea level N/A N/A N/A N/A 9.5-10 9.5-10 9-10 9.5-10 9.5-10 9.5-10 9-10 9.5-10 9.5-10
Chance for Fog/Precip (%) 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 25/5
PW (mm, summit upward) 0.8 to 1.2 0.8 to 1 0.8 to 1 1 to 2 1.5 to 2 1 to 1.5 0.8 to 1.2 0.7 to 0.9 0.7 to 0.9 0.8 to 1.2 0.8 to 1 1 to 2 2 to 4
Mean Seeing (arcsecs) N/A 0.45 ± 0.1 0.5 ± 0.1 N/A 0.55 ± 0.1 0.5 ± 0.1 N/A 0.45 ± 0.1 0.5 ± 0.1 N/A 0.45 ± 0.1 N/A 0.65 ± 0.15
Summit Temp (°C) 12 6 5 10.5 5.5 5 10 4.5 4.5 9.5 3.5 8.5 2
Wind Dir/Speed (mph)
    Summit (615 hPa)
    19,000 ft (500 hPa)
    24,500 ft (400 hPa)
    31,000 ft (300 hPa)
    35,000 ft (250 hPa)
    40,000 ft (200 hPa)
    46,000 ft (150 hPa)
    54,000 ft (100 hPa)

E/5 to 15

E/10 to 20

E/10 to 20

E/10 to 20

E/10 to 20

E/10 to 20

ESE/10 to 20

E/10 to 20

E/10 to 20

E/5 to 15

NE/5 to 15

E/10 to 20

E/10 to 20


 Rise and Set times for the Sun and Moon
Night (HST)
Sun Set
Twilight End
Twilight Beg
Sun Rise
Moon Rise
Moon Set
Illum (%)
RA
Dec
Fri.Jul.31/Sat.Aug.01
19:08
20:18
4:38
5:48
N/A
4:16
94
18 52.6
-24 44
Sat.Aug.01/Sun.Aug.02
19:08
20:17
4:39
5:49
17:41
5:13
98
19 51.4
-23 59
Sun.Aug.02/Mon.Aug.03
19:07
20:17
4:39
5:49
18:32
6:11
100
20 48.0
-21 56
Mon.Aug.03/Tue.Aug.04
19:07
20:16
4:40
5:50
19:19
N/A
99
21 41.6
-18 50
Tue.Aug.04/Wed.Aug.05
19:06
20:15
4:41
5:50
20:01
N/A
97
22 32.0
-14 55


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Friday 31 July (0300 UTC Saturday 1 August) 2020.
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