Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 21 February (0300 UTC Friday 22 February) 2019

Warnings
Chance for fog/ice and flurries
Moderate winds

Cloud Cover and Precipitation Forecast
There is a high risk for fog, ice, patches of clouds in the area and light flurries throughout the night. There is also an outside chance for brief periods of convection in the area, mainly for this afternoon and near sunrise tomorrow.

Summary of Key Meteorological Variables
Summit temperatures will be near -2 C, with winds from the WSW at 20-35 mph for the night. Seeing and PW are expected to exceed 1 arcseconds and 4 mm, respectively, through the night.

Graphical Summary

Discussion
A weak/indistinct inversion will allow the atmosphere below 13-15 thousand feet to remain fairly saturated, likely contributing to periods of extensive fog, ice, high humidity and periods of light flurries mainly over the next 3 nights. The atmosphere will begin to dry out and stablize as the inversion very slowly rebuilds around Sunday evening, decreasing this risk for that night and especially the following night. Extensive daytime clouds and possibily afternoon convection along the slopes are expected through the weekend, then will begin to taper for the early part of next week.

While skies overhead will remain predominately clear of organized high clouds throughout the forecast period, there is a possibility for patches of mid/low-level clouds in the area and perhaps lingering cirrus exhaust should afternoon convection develop along the slopes through Sunday evening.

Precipitable water is expected to linger near or exceed 4 mm through Saturday night, then will slip toward 1.5 mm for Sunday night, only to rebound back to 2-3 mm for Monday night.

A mixture of boundary layer and free atmospheric turbulence, as well as instability, moisture and/or an elevated inversion will contribute to poor/bad seeing throughout the forecast period.

No change since the morning forecast...A very broad/persistent mid/upper-level trough to the west will gradually progress eastward and destabilize the air mass before shifting east of the Big Island around Sunday night. In addition, a residual low-level frontal band sitting just east is set to build back overhead for the next 3 nights, then slip off toward the east with the trough on Sunday. Nonetheless, both features will keep the inversion rather weak/indistinct and allow the air mass below 13-15 thousand feet to remain quite saturated between early this afternoon and Sunday afternoon. This will likely result in extensive fog, ice, high humidity and periods of light flurries at the summit mainly over the next 3 nights. Daytime heating could also help fire off afternoon convection along the Big Island slopes, which could briefly deposit heavy precipitation at the summit through Sunday. The atmosphere is set to dry out and stabilize as the trough slips eastward early Sunday evening, which should help decrease the risk for moisture at the summit for that night and especially Monday night. However, there is a possibility that an short-wave trough will rapidly dig in from the north and deepen the large scale trough to the east of the state late Monday night. While the Big Island should remain on the more dry/stable portion of the trough/low, a very tight wind gradient between the trough's western flank and a building ridge to the west could result in a sharp increase in summit-level winds through Tuesday.

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
08 pm HST
Thu 21 Feb
02 am HST
Fri 22 Feb
02 pm HST
Fri 22 Feb
08 pm HST
Fri 22 Feb
02 am HST
Sat 23 Feb
02 pm HST
Sat 23 Feb
08 pm HST
Sat 23 Feb
02 am HST
Sun 24 Feb
02 pm HST
Sun 24 Feb
02 am HST
Mon 25 Feb
02 pm HST
Mon 25 Feb
02 am HST
Tue 26 Feb
02 pm HST
Tue 26 Feb
06 UTC
Fri 22 Feb
12 UTC
Fri 22 Feb
00 UTC
Sat 23 Feb
06 UTC
Sat 23 Feb
12 UTC
Sat 23 Feb
00 UTC
Sun 24 Feb
06 UTC
Sun 24 Feb
12 UTC
Sun 24 Feb
00 UTC
Mon 25 Feb
12 UTC
Mon 25 Feb
00 UTC
Tue 26 Feb
12 UTC
Tue 26 Feb
00 UTC
Wed 27 Feb
Cloud Cover (%) 20 to 40 20 to 40 80 to 100 20 to 40 20 to 40 80 to 100 20 to 40 0 to 20 60 to 80 0 to 20 40 to 60 0 to 20 20 to 40
Cloud Height (km) above sea level 4-5 4-5 4-8 4-5 4-5 4-8 4-5 4-4.5 4-7 N/A 4-5 N/A 4-4.24
Chance for Fog/Precip (%) 95/60 95/65 95/90 95/75 95/75 95/90 90/65 75/40 90/60 60/15 50/10 20/5 20/0
PW (mm, summit upward) 4 to 8 4 to 8 6 to 10 4 to 8 4 to 8 4 to 8 4 to 6 4 to 6 3 to 5 1 to 2 2 to 4 2 to 3 2 to 4
Mean Seeing (arcsecs) 1.2 ± 0.4 1.2 ± 0.4 N/A 1.2 ± 0.4 1.1 ± 0.4 N/A 1.0 ± 0.3 1.0 ± 0.3 N/A 0.8 ± 0.2 N/A 0.9 ± 0.3 N/A
Summit Temp (°C) -2 -2 1 -2.5 -3 0 -3 -4 0 -3 2 -3 0
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)

WSW/20 to 35

WSW/20 to 35

W/15 to 30

WSW/15 to 30

W/15 to 30

WSW/15 to 30

W/15 to 30

W/15 to 30

W/15 to 30

NNW/15 to 30

WNW/15 to 30

W/20 to 35

W/40 to 60


 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
Thu.Feb.21/Fri.Feb.22
18:33
19:38
5:33
6:38
20:51
N/A
88
12 55.3
-0 30
Fri.Feb.22/Sat.Feb.23
18:33
19:38
5:32
6:37
21:50
N/A
80
13 49.2
-5 46
Sat.Feb.23/Sun.Feb.24
18:34
19:38
5:32
6:36
22:48
N/A
70
14 41.9
-10 33
Sun.Feb.24/Mon.Feb.25
18:34
19:39
5:31
6:36
23:44
N/A
60
15 34.2
-14 37
Mon.Feb.25/Tue.Feb.26
18:35
19:39
5:30
6:35
0:39
N/A
50
16 26.3
-17 50


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Friday 22 February 2019.
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