Latest Forecast for Mauna Kea Observatories
5 PM HST Tuesday 14 November (0300 UTC Wednesday 15 November) 2017

Warnings
Chance for fog, ice and high humidity
Moderate winds

Cloud Cover and Precipitation Forecast
There is a risk for fog, high humidity and ice particularly as the night progresses; precipitation is unlikely but there is also a possibility for patches of mid-level clouds dropping down from the north through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this afternoon and -2 C for the night. Winds will be from the west at 15-30 mph, with seeing near 0.8-0.9 arcseconds. Precipitable water is expected to exceed 4 mm through the night.

Graphical Summary

Discussion
The tradewind inversion is expected to weaken/lift toward 12 thousand feet as patches of moisture and instability fill in from the north, raising the stakes on fog, high humidity and ice at the summit between late this afternoon and early tomorrow evening. The odds on moisture is expected to diminish as the the inversion rapidly rebuilds near 10 thousand feet through tomorrow night and settling in near 8 thousand feet for Thursday night. However, there is a chance that inversion will lift back toward 12-13 thousand feet, which could increase this risk again for Friday and perhaps Saturday night; precipitation is unlikely throughout the forecast period. Extensive afternoon clouds are possible for tomorrow, then will become minimal and short-lived for Thursday and Friday, only to briefly pick up again for Saturday, then taper for Sunday.

There is a possibility for small patches of mid/upper-level clouds dropping down from the north for tonight. Clear skies will prevail for much of tomorrow night and probably Thursday night, but thin strands of high clouds may spread in from the west and drift over the summit area for Friday night; clear skies will prevail for Saturday night.

Precipitable water is expected to exceed 4 mm for tonight, then abruptly drop below 1 mm by late Wednesday evening, eventually bottoming out near 0.6-0.65 mm for much of Thursday. There is a good chance that it will begin to increase early Friday morning, then linger in the 2-3 mm range for much of the weekend.

Turbulence in various layers of the atmosphere as well as an influx of moisture/instability will likely contribute to poor seeing for at least the next 2 nights. There is a chance that seeing will return toward more average-like values as the atmosphere stabilizes and only moderate upper-level turbulence prevails for Thursday night. However, another round of boundary layer turbulence and perhaps moisture/instability could degrade seeing again for Saturday night.

Longer term wind/seeing forecast has changed a bit since the morning....While the low-level ridge will persist to the NNW of the state through the week, a relatively deep short-wave trough embedded within a larger quasi-stationary trough to the north is expected to pass through between late this afternoon and early tomorrow evening. This SWT will likely bring instability and patches of fairly deep low-level moisture/clouds to the area, help elevate/weaken the inversion and increase the risk for fog, ice and high humidity at the summit during this time. In addition, boundary layer turbulence and/or mid/upper-level turbulence will likely contribute to poor seeing during this time. Very dry air (and eventually calmer skies) is expected to fill in as the SWT shifts off to the east through Wednesday night. This will not only help to rebuild the inversion near 8-10 thousand feet and diminish the risk for fog/ice at the summit, but could also allow PW to plummet toward 0.5-0.6 mm for much of Thursday. Seeing will also respond to departure of the trough and improve toward more average-like values for that night. Unfortunately, the ridge is expected retreat northward a tad as another passing SWT enhances the large-scale trough around the early part of the weekend. This could allow more moisture/instability to return/build in the area, which may weaken/elevate the inversion again and increase the risk for fog/ice at the summit for Friday and Saturday night. There is also a chance that this SWT will help increase summit-level winds again, stirring up boundary layer turbulence and disrupting seeing again during those night.

Astronomical Observing Quality Guidance
05 pm HST Tuesday 14 November (03 UTC Wednesday 15 November)CN2
08 pm HST Tuesday 14 November (06 UTC Wednesday 15 November)CN2
11 pm HST Tuesday 14 November (09 UTC Wednesday 15 November)CN2
02 am HST Wednesday 15 November (12 UTC Wednesday 15 November)CN2
05 am HST Wednesday 15 November (15 UTC Wednesday 15 November)CN2
08 am HST Wednesday 15 November (18 UTC Wednesday 15 November)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
08 pm HST
Tue 14 Nov
02 am HST
Wed 15 Nov
02 pm HST
Wed 15 Nov
08 pm HST
Wed 15 Nov
02 am HST
Thu 16 Nov
02 pm HST
Thu 16 Nov
08 pm HST
Thu 16 Nov
02 am HST
Fri 17 Nov
02 pm HST
Fri 17 Nov
02 am HST
Sat 18 Nov
02 pm HST
Sat 18 Nov
02 am HST
Sun 19 Nov
02 pm HST
Sun 19 Nov
06 UTC
Wed 15 Nov
12 UTC
Wed 15 Nov
00 UTC
Thu 16 Nov
06 UTC
Thu 16 Nov
12 UTC
Thu 16 Nov
00 UTC
Fri 17 Nov
06 UTC
Fri 17 Nov
12 UTC
Fri 17 Nov
00 UTC
Sat 18 Nov
12 UTC
Sat 18 Nov
00 UTC
Sun 19 Nov
12 UTC
Sun 19 Nov
00 UTC
Mon 20 Nov
Cloud Cover (%) 0 to 20 0 to 20 60 to 80 0 to 20 0 to 5 0 to 20 0 to 5 0 to 5 0 to 20 10 to 30 40 to 60 0 to 20 0 to 20
Cloud Height (km) above sea level 5-7 5-7 4-8 N/A N/A N/A N/A N/A N/A 9.5-10 4-5 N/A N/A
Chance for Fog/Precip (%) 40/5 60/10 75/20 40/5 10/0 0/0 0/0 0/0 0/0 25/5 40/10 20/5 0/0
PW (mm, summit upward) 4 to 6 4 to 6 4 to 8 1 to 2 0.6 to 1 0.6 to 1 0.6 to 1 1 to 2 2 to 4 2 to 3 3 to 6 1.5 to 2.5 1.5 to 2.5
Mean Seeing (arcsecs) 0.8 ± 0.2 0.9 ± 0.2 N/A 0.85 ± 0.2 0.75 ± 0.15 N/A 0.65 ± 0.1 0.6 ± 0.1 N/A 0.9 ± 0.2 N/A 0.9 ± 0.2 N/A
Summit Temp (°C) -2 -2 2 -1 -1 4 0 -0.5 3 -3 1 -3 3
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)

W/15 to 30

W/15 to 30

WNW/10 to 20

NW/5 to 15

WNW/5 to 15

WNW/5 to 15

WNW/5 to 15

WSW/10 to 20

W/15 to 30

WSW/25 to 40

W/25 to 40

WSW/25 to 40

W/30 to 45


 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
Tue.Nov.14/Wed.Nov.15
17:52
18:59
5:15
6:21
4:02
N/A
9
13 16.0
-3 30
Wed.Nov.15/Thu.Nov.16
17:52
18:59
5:15
6:22
4:53
16:27
4
14 02.8
-7 32
Thu.Nov.16/Fri.Nov.17
17:51
18:58
5:15
6:23
5:44
17:06
1
14 49.8
-11 12
Fri.Nov.17/Sat.Nov.18
17:51
18:58
5:16
6:23
6:34
17:46
0
15 37.3
-14 23
Sat.Nov.18/Sun.Nov.19
17:51
18:58
5:16
6:24
7:25
18:28
1
16 25.4
-16 57


Forecast issued by: Ryan Lyman
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