Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Monday 16 April 2018

Warnings
High humidity
Chance for fog

Cloud Cover and Precipitation Forecast
There is a chance for periods of fog as humidity lingers near 60-80% through the night. Broken mid/upper-level clouds will continue to linger in the area and/or fill in from the SW throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this afternoon and -1 C for the night. Winds will be light and from the west for today, switching to more NNW direction for the night. Seeing will be near 0.7-0.8 arcseconds, while precipitable water is expected to exceed 4 mm through the night.

Graphical Summary

Discussion
While the inversion is set to restrengthen near 8 thousand feet over the next 24 hours, persistent mid-level moisture may still allow for periods of fog as humidity lingers near 60-80% for the next 2 nights. A return of low-level moisture and upper-level instability may erode the inversion again, raise humidity toward 80-100% and increase the risk for extensive fog, ice and flurries at the summit as well as convection in the area for Wednesday, Thursday and Friday night. Some daytime clouds are possible over the next 2 days, then will likely turn extensive with the possibility for afternoon convection along the slopes for the remainder of the forecast period.

Broken mid/upper-level clouds will continue to linger in the area and/or drift in from the SW contributing to extensive cloud cover for tonight. More organized, widespread high clouds are set to fill in from the SW through tomorrow, with thicker/deeper clouds following suit on Wednesday. This will likely result in mostly overcast skies for Tuesday night through the weekend.

Precipitable water will continue to exceed 4 mm throughout the forecast period.

Persistent mid-level moisture combined with light/moderate turblence in the free atmosphere will contribute to poorer than average seeing over the next 2 nights. An increase in moisture, instability and turblence will likely further degrade seeing for the following 3 nights.

The tropical upper tropospheric trough (TUTT) and an embedded low is set to shift off toward the west, allowing the atmosphere to stabilize a bit and the inversion to rebuild near 8 thousand feet over the next 48 hours. Unfortunately, mid-level moisture will continue to linger in the area, which will likely contribute to high humidity/PW and perhaps short-lived fog over the next 2 nights. In addition, a strong sub-tropical jet will persist overhead, shuttling more high clouds in from the SW and allowing moderate turbulence to prevail in the free atmosphere probably throughout most of the forecast period. While the embedded low to the west is expected to fall apart late tomorrow, the TUTT is set to return eastward, bringing widespread instability and moisture back to the area by late Wednesday morning. This will likely help dismantle the inversion and allow the atmosphere to become saturated, contributing to another round of extensive fog, ice and flurries at the summit and convection in the area for Wednesday, Thursday and Friday night. Longer term projections suggests that the TUTT will weaken and shift back off toward the west, which could allow the atmosphere to stabilize and dry out over the weekend.

Astronomical Observing Quality Guidance
05 pm HST Monday 16 April (03 UTC Tuesday 17 April)CN2
08 pm HST Monday 16 April (06 UTC Tuesday 17 April)CN2
11 pm HST Monday 16 April (09 UTC Tuesday 17 April)CN2
02 am HST Tuesday 17 April (12 UTC Tuesday 17 April)CN2
05 am HST Tuesday 17 April (15 UTC Tuesday 17 April)CN2
08 am HST Tuesday 17 April (18 UTC Tuesday 17 April)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
02 pm HST
Mon 16 Apr
08 pm HST
Mon 16 Apr
02 am HST
Tue 17 Apr
02 pm HST
Tue 17 Apr
08 pm HST
Tue 17 Apr
02 am HST
Wed 18 Apr
02 pm HST
Wed 18 Apr
08 pm HST
Wed 18 Apr
02 am HST
Thu 19 Apr
02 pm HST
Thu 19 Apr
02 am HST
Fri 20 Apr
02 pm HST
Fri 20 Apr
02 am HST
Sat 21 Apr
00 UTC
Tue 17 Apr
06 UTC
Tue 17 Apr
12 UTC
Tue 17 Apr
00 UTC
Wed 18 Apr
06 UTC
Wed 18 Apr
12 UTC
Wed 18 Apr
00 UTC
Thu 19 Apr
06 UTC
Thu 19 Apr
12 UTC
Thu 19 Apr
00 UTC
Fri 20 Apr
12 UTC
Fri 20 Apr
00 UTC
Sat 21 Apr
12 UTC
Sat 21 Apr
Cloud Cover (%) 70 to 90 60 to 80 60 to 80 70 to 90 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100
Cloud Height (km) above sea level 5-8 5-8 6-10 5-10 6-10 6-10 4-10 4-10 4-10 4-10 4-10 4-10 4-10
Chance for Fog/Precip (%) 75/25 50/10 40/10 60/15 30/10 30/10 80/60 90/80 95/90 95/90 95/90 95/90 95/90
PW (mm, summit upward) 6 to 10 6 to 10 6 to 10 6 to 10 6 to 10 6 to 10 8 to 12 8 to 12 8 to 12 8 to 12 8 to 12 8 to 12 8 to 12
Mean Seeing (arcsecs) N/A 0.75 ± 0.15 0.75 ± 0.15 N/A 0.7 ± 0.15 0.75 ± 0.15 N/A 1.0 ± 0.3 1.2 ± 0.4 N/A 1.5 ± 0.5 N/A 1.2 ± 0.4
Summit Temp (°C) 4 -1 -1 4 -0.5 -0.5 3 -1 -1.5 0 -2 0 -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)

W/0 to 10

NNW/0 to 10

NNW/5 to 15

NNW/5 to 15

NNW/0 to 10

SSW/0 to 10

SW/0 to 10

N/0 to 10

S/0 to 15

W/0 to 10

E/5 to 15

ENE/5 to 15

ENE/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
Mon.Apr.16/Tue.Apr.17
18:49
19:56
4:47
5:53
N/A
19:50
2
2 53.2
10 57
Tue.Apr.17/Wed.Apr.18
18:50
19:56
4:46
5:53
N/A
20:50
7
3 48.4
14 41
Wed.Apr.18/Thu.Apr.19
18:50
19:57
4:45
5:52
N/A
21:51
14
4 45.8
17 37
Thu.Apr.19/Fri.Apr.20
18:50
19:57
4:44
5:51
N/A
22:53
22
5 45.3
19 27
Fri.Apr.20/Sat.Apr.21
18:51
19:58
4:43
5:50
N/A
23:53
33
6 45.7
20 04


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Monday 16 April (0300 UTC Tuesday 17 April) 2018.
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