Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 26 May (0300 UTC Friday 27 May) 2016

Warnings
None

Cloud Cover and Precipitation Forecast
There is a small/moderate risk for fog and high humidity, mainly for early in the evening; precipitation is not expected. Banding cirrus will continue to pass over the area contributing to extensive cloud cover through this evening, then shift off toward the east during the second half of the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 0.5 C this evening and 0 C tomorrow morning. Westerly winds are set to increase to 10-20 mph by this afternoon and to 15-30 mph for the night. Seeing will likely be near 0.65-0.7 arcseconds, while precipitable water is expected to be in the 3-4 mm range for the night.

Graphical Summary

Discussion
While the upper atmosphere is expected to stabilize, the tradewind inversion will remain rather indistinct as mid/low-level moisture lingers in the area through Saturday afternoon. Consequently, there is a small/moderate risk for fog and high humidity over the next 2 nights (particularly during the early evening hours); precipitation is not expected. The inversion is set to strengthen near 6-7 thousand feet, ensuring the summit steers free of fog/precpitation for Saturday, Sunday and Monday night. Extensive daytime clouds are possible through Friday, but will taper over the weekend.

Banding high clouds will continue to pass over the area contributing to extensive cloud cover for this evening, then shift off toward the east during the second half of the night. This should leave relatively clear skies for most of Friday night, but another band may fill in from the south and could pass along the southern skies again (or even over the Big Island) between sunrise Saturday and early Sunday afternoon. This band is set to shift eastward thereafter, leaving clear skies for Sunday and Monday night.

Precipitable water is expected to linger in the 3-4 mm range through Sunday evening, then slip toward 2 mm for Monday and into Tuesday.

An increase in summit-level winds are expected to stir up light/moderate boundary layer turbulence and likely contribute to poore than average seeing over the next 3 nights. Winds are set to taper late in the weekend, which may allow seeing to return toward more average-like values for Sunday and especially Monday night.

Little change since the morning forecast...While the mid-level ridge will remain rather weak/indistinct probably well into next week, flow aloft will maintain a relatively zonal orientation, with the sub-tropical jet persisting over or just south of the Big Island during this time. This will help minimize the risk for upper-level instability in the area and allow the low-level ridge to govern the atmosphere near the state over the next 5 nights. Nevertheless, lingering mid/low-level moisture will prohibit the inversion from fully restrenghtening, which could permit the development of extensive afternoon clouds and perhaps (predominately evening) fog/high humidity over the next 48 hours. The inversion expected to strengthen near 6-7 thousand feet as this moisture finally detrains into the free atmosphere and/or is drawn to a trough developing far to the north late Saturday morning. This will ensure the summit steers free of fog/precipitation for the remainder of the weekend and early part of next week. Unfortunately, the STJ will gain access to high clouds coming out of the tropics and transport it along the southern skies mainly for this evening and again around Saturday night. In addition, a relatively deep ridge developing to the south of the STJ, will help strengthen summit-level winds, thus increasing boundary layer turbulence and contributing to poor seeing probably through Sunday evening. There is a good chance that seeing will improve again as the ridge/winds weaken for the early part of next week.

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 26 May
02 am HST
Fri 27 May
02 pm HST
Fri 27 May
08 pm HST
Fri 27 May
02 am HST
Sat 28 May
02 pm HST
Sat 28 May
08 pm HST
Sat 28 May
02 am HST
Sun 29 May
02 pm HST
Sun 29 May
02 am HST
Mon 30 May
02 pm HST
Mon 30 May
02 am HST
Tue 31 May
02 pm HST
Tue 31 May
06 UTC
Fri 27 May
12 UTC
Fri 27 May
00 UTC
Sat 28 May
06 UTC
Sat 28 May
12 UTC
Sat 28 May
00 UTC
Sun 29 May
06 UTC
Sun 29 May
12 UTC
Sun 29 May
00 UTC
Mon 30 May
12 UTC
Mon 30 May
00 UTC
Tue 31 May
12 UTC
Tue 31 May
00 UTC
Wed 01 Jun
Cloud Cover (%) 40 to 60 20 to 40 40 to 60 0 to 5 0 to 20 20 to 40 40 to 60 20 to 40 10 to 30 0 to 20 0 to 20 0 to 20 0 to 20
Cloud Height (km) above sea level 9-10 9-10 4-4.5 N/A 9.5-10 9-10 9-10 9-10 9-10 N/A N/A N/A N/A
Chance for Fog/Precip (%) 40/0 20/0 60/10 30/0 10/0 10/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0
PW (mm, summit upward) 3 to 4 3 to 4 3 to 6 3 to 4 3 to 4 3 to 6 3 to 4 3 to 4 3 to 6 2 to 4 1.5 to 2.5 1.5 to 2.5 2 to 4
Mean Seeing (arcsecs) 0.7 ± 0.2 0.65 ± 0.15 N/A 0.65 ± 0.15 0.6 ± 0.1 N/A 0.7 ± 0.2 0.65 ± 0.15 N/A 0.6 ± 0.1 N/A 0.55 ± 0.1 N/A
Summit Temp (°C) 0.5 0 5 0.5 0 5 0.5 0 6 2 8 3 9
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

W/15 to 30

WNW/15 to 30

W/10 to 20

W/15 to 30

WNW/15 to 30

W/15 to 30

W/15 to 30

WNW/10 to 20

NW/10 to 20

NNW/10 to 20

NE/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
Thu.May.26/Fri.May.27
19:05
20:17
4:21
5:33
23:00
N/A
71
20 52.2
-15 00
Fri.May.27/Sat.May.28
19:05
20:18
4:20
5:33
23:46
N/A
61
21 45.3
-11 57
Sat.May.28/Sun.May.29
19:06
20:19
4:20
5:33
0:31
N/A
50
22 38.2
-8 16
Sun.May.29/Mon.May.30
19:06
20:19
4:20
5:33
1:16
N/A
39
23 31.2
-4 05
Mon.May.30/Tue.May.31
19:07
20:20
4:20
5:33
2:01
N/A
29
0 24.8
0 23


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Friday 27 May 2016.
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