Weather2 on Twitter Weather2 on Facebook Weather2 on YouTube Weather2 blog

WEATHER FOR BUSINESS

We supply weather data to businesses

Free Weather Plugin

Add this forecast to your website



Local Weather

Gelyn 14 Day Long Range Forecast

14 Day weather providing an extended long range forecast outlook for Gelyn

Gwynedd, United Kingdom

Long range weather outlook for Gelyn includes 14 day forecast summary:

The outlook for Gelyn in the two weeks ahead shows the average daytime maximum temperature will be around 21°C, with a high for the two weeks of 25°C expected on the afternoon of Friday 27th. The mean minimum temperature will be 10°C, dipping to its lowest on the morning of Thursday 19th at 8°C. Expect the following 14 days ahead to have some days seeing a little precipitation and some days with rain. Predictions are Friday 20th will have the most precipitation with an accumulation of around 8.0mm. On the whole winds are likely to be light.

DayLocal TimeDirSpeed/
Gust
Temp/
Feels Like
HumidityPressureCloud AmountPrecip AmountWeather
Thu 19
Jul
18:00

NW
NW

4 / 5 mph 69 / 66°F 68% 1018 mb
Low level cloud: 46%
Mid level cloud: 1%
High level cloud: 0%
Most Significant Cloud Type: low
46%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
21:00

N
N

1 / 3 mph 57 / 56°F 89% 1018 mb
Low level cloud: 1%
Mid level cloud: 1%
High level cloud: 0%
Most Significant Cloud Type: high
0%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
Fri 20
Jul
00:00

SE
SE

1 / 2 mph 49 / 49°F 90% 1018 mb
Low level cloud: 0%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: high
0%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
03:00

SSE
SSE

4 / 7 mph 46 / 45°F 92% 1017 mb
Low level cloud: 0%
Mid level cloud: 1%
High level cloud: 4%
Most Significant Cloud Type: high
4%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
06:00

S
S

4 / 8 mph 55 / 53°F 91% 1016 mb
Low level cloud: 11%
Mid level cloud: 12%
High level cloud: 21%
Most Significant Cloud Type: low
17%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
09:00

SW
SW

9 / 10 mph 67 / 65°F 71% 1016 mb
Low level cloud: 24%
Mid level cloud: 33%
High level cloud: 32%
Most Significant Cloud Type: low
39%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
12:00

WSW
WSW

8 / 9 mph 63 / 62°F 82% 1014 mb
Low level cloud: 72%
Mid level cloud: 66%
High level cloud: 95%
Most Significant Cloud Type: low
100%
Expect 0.03 In of precipitation over the past 3 hours.
0.03 In
15:00

SW
SW

6 / 8 mph 58 / 57°F 98% 1014 mb
Low level cloud: 92%
Mid level cloud: 86%
High level cloud: 7%
Most Significant Cloud Type: low
100%
Expect 0.22 In of precipitation over the past 3 hours.
0.22 In
18:00

SW
SW

5 / 6 mph 58 / 57°F 99% 1014 mb
Low level cloud: 91%
Mid level cloud: 78%
High level cloud: 0%
Most Significant Cloud Type: low
100%
Expect 0.05 In of precipitation over the past 3 hours.
0.05 In
21:00

W
W

2 / 3 mph 58 / 59°F 99% 1015 mb
Low level cloud: 90%
Mid level cloud: 43%
High level cloud: 0%
Most Significant Cloud Type: low
100%
Expect 0.01 In of precipitation over the past 3 hours.
0.01 In
Sat 21
Jul
00:00

N
N

3 / 4 mph 58 / 59°F 99% 1015 mb
Low level cloud: 85%
Mid level cloud: 46%
High level cloud: 65%
Most Significant Cloud Type: low
100%
Expect 0.01 In of precipitation over the past 3 hours.
0.01 In
03:00

NNW
NNW

4 / 6 mph 55 / 55°F 98% 1015 mb
Low level cloud: 81%
Mid level cloud: 10%
High level cloud: 46%
Most Significant Cloud Type: low
100%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
06:00

NW
NW

4 / 5 mph 57 / 55°F 96% 1015 mb
Low level cloud: 58%
Mid level cloud: 44%
High level cloud: 32%
Most Significant Cloud Type: low
77%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
09:00

NW
NW

4 / 4 mph 60 / 60°F 84% 1016 mb
Low level cloud: 79%
Mid level cloud: 79%
High level cloud: 21%
Most Significant Cloud Type: low
100%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
12:00

NW
NW

6 / 7 mph 66 / 63°F 72% 1016 mb
Low level cloud: 46%
Mid level cloud: 11%
High level cloud: 5%
Most Significant Cloud Type: low
50%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
15:00

NW
NW

8 / 9 mph 68 / 65°F 68% 1016 mb
Low level cloud: 43%
Mid level cloud: 15%
High level cloud: 32%
Most Significant Cloud Type: low
52%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
18:00

NW
NW

7 / 8 mph 66 / 63°F 76% 1017 mb
Low level cloud: 39%
Mid level cloud: 16%
High level cloud: 39%
Most Significant Cloud Type: low
49%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
21:00

NW
NW

3 / 7 mph 53 / 51°F 94% 1018 mb
Low level cloud: 14%
Mid level cloud: 7%
High level cloud: 0%
Most Significant Cloud Type: low
16%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
Sun 22
Jul
00:00

NW
NW

1 / 3 mph 49 / 49°F 95% 1018 mb
Low level cloud: 10%
Mid level cloud: 15%
High level cloud: 0%
Most Significant Cloud Type: low
15%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
03:00

WSW
WSW

2 / 4 mph 48 / 49°F 95% 1018 mb
Low level cloud: 41%
Mid level cloud: 49%
High level cloud: 0%
Most Significant Cloud Type: low
58%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
06:00

WSW
WSW

2 / 3 mph 57 / 58°F 95% 1018 mb
Low level cloud: 73%
Mid level cloud: 70%
High level cloud: 0%
Most Significant Cloud Type: low
98%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
09:00

W
W

3 / 4 mph 64 / 63°F 88% 1018 mb
Low level cloud: 90%
Mid level cloud: 57%
High level cloud: 0%
Most Significant Cloud Type: low
100%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
12:00

W
W

5 / 6 mph 69 / 68°F 81% 1018 mb
Low level cloud: 83%
Mid level cloud: 27%
High level cloud: 0%
Most Significant Cloud Type: low
92%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
15:00

W
W

6 / 6 mph 72 / 70°F 79% 1017 mb
Low level cloud: 78%
Mid level cloud: 16%
High level cloud: 0%
Most Significant Cloud Type: low
83%
Expect 0.01 In of precipitation over the past 3 hours.
0.01 In
18:00

W
W

5 / 5 mph 73 / 70°F 79% 1017 mb
Low level cloud: 47%
Mid level cloud: 15%
High level cloud: 1%
Most Significant Cloud Type: low
52%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
21:00

SW
SW

4 / 8 mph 60 / 58°F 97% 1018 mb
Low level cloud: 40%
Mid level cloud: 27%
High level cloud: 4%
Most Significant Cloud Type: low
100%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
Mon 23
Jul
00:00

S
S

5 / 10 mph 56 / 56°F 98% 1018 mb
Low level cloud: 57%
Mid level cloud: 46%
High level cloud: 3%
Most Significant Cloud Type: low
100%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
03:00

SSW
SSW

6 / 11 mph 57 / 56°F 99% 1017 mb
Low level cloud: 80%
Mid level cloud: 42%
High level cloud: 12%
Most Significant Cloud Type: low
100%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
06:00

SSW
SSW

8 / 10 mph 61 / 61°F 98% 1017 mb
Low level cloud: 93%
Mid level cloud: 38%
High level cloud: 11%
Most Significant Cloud Type: low
100%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
09:00

SSW
SSW

9 / 11 mph 64 / 64°F 94% 1016 mb
Low level cloud: 88%
Mid level cloud: 32%
High level cloud: 17%
Most Significant Cloud Type: low
100%
Expect 0.01 In of precipitation over the past 3 hours.
0.01 In
12:00

SW
SW

10 / 11 mph 65 / 65°F 88% 1015 mb
Low level cloud: 91%
Mid level cloud: 25%
High level cloud: 3%
Most Significant Cloud Type: low
99%
Expect 0.01 In of precipitation over the past 3 hours.
0.01 In
15:00

SW
SW

10 / 12 mph 69 / 68°F 75% 1015 mb
Low level cloud: 84%
Mid level cloud: 4%
High level cloud: 0%
Most Significant Cloud Type: low
85%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
18:00

SW
SW

7 / 8 mph 65 / 64°F 91% 1014 mb
Low level cloud: 89%
Mid level cloud: 46%
High level cloud: 1%
Most Significant Cloud Type: low
100%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
21:00

SW
SW

6 / 9 mph 61 / 61°F 99% 1015 mb
Low level cloud: 91%
Mid level cloud: 46%
High level cloud: 4%
Most Significant Cloud Type: low
100%
Expect 0.01 In of precipitation over the past 3 hours.
0.01 In
Tue 24
Jul
00:00

SSW
SSW

7 / 11 mph 61 / 61°F 99% 1014 mb
Low level cloud: 91%
Mid level cloud: 46%
High level cloud: 17%
Most Significant Cloud Type: low
100%
Expect 0.02 In of precipitation over the past 3 hours.
0.02 In
03:00

WNW
WNW

3 / 4 mph 60 / 60°F 98% 1014 mb
Low level cloud: 88%
Mid level cloud: 32%
High level cloud: 32%
Most Significant Cloud Type: low
100%
Expect 0.03 In of precipitation over the past 3 hours.
0.03 In
06:00

NNW
NNW

2 / 4 mph 60 / 59°F 97% 1014 mb
Low level cloud: 47%
Mid level cloud: 2%
High level cloud: 6%
Most Significant Cloud Type: low
48%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
09:00

W
W

3 / 4 mph 66 / 64°F 80% 1015 mb
Low level cloud: 68%
Mid level cloud: 3%
High level cloud: 0%
Most Significant Cloud Type: low
68%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
12:00

W
W

8 / 9 mph 67 / 65°F 69% 1015 mb
Low level cloud: 36%
Mid level cloud: 1%
High level cloud: 18%
Most Significant Cloud Type: low
38%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
15:00

W
W

8 / 9 mph 68 / 67°F 61% 1015 mb
Low level cloud: 1%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: high
0%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
18:00

W
W

5 / 6 mph 69 / 67°F 67% 1016 mb
Low level cloud: 1%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: high
0%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
21:00

W
W

2 / 4 mph 50 / 50°F 91% 1017 mb
Low level cloud: 10%
Mid level cloud: 0%
High level cloud: 21%
Most Significant Cloud Type: low
12%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
Wed 25
Jul
00:00

SE
SE

3 / 6 mph 48 / 47°F 94% 1017 mb
Low level cloud: 5%
Mid level cloud: 2%
High level cloud: 1%
Most Significant Cloud Type: low
6%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
03:00

SSE
SSE

3 / 7 mph 47 / 45°F 95% 1017 mb
Low level cloud: 11%
Mid level cloud: 3%
High level cloud: 3%
Most Significant Cloud Type: low
12%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
06:00

S
S

4 / 6 mph 55 / 52°F 93% 1018 mb
Low level cloud: 21%
Mid level cloud: 5%
High level cloud: 12%
Most Significant Cloud Type: low
23%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
09:00

SW
SW

7 / 8 mph 66 / 64°F 71% 1018 mb
Low level cloud: 27%
Mid level cloud: 6%
High level cloud: 32%
Most Significant Cloud Type: low
32%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
12:00

SW
SW

8 / 9 mph 71 / 68°F 65% 1017 mb
Low level cloud: 16%
Mid level cloud: 9%
High level cloud: 12%
Most Significant Cloud Type: low
20%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
15:00

WSW
WSW

7 / 8 mph 71 / 69°F 65% 1016 mb
Low level cloud: 6%
Mid level cloud: 8%
High level cloud: 9%
Most Significant Cloud Type: low
9%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
18:00

SW
SW

5 / 6 mph 69 / 67°F 73% 1016 mb
Low level cloud: 2%
Mid level cloud: 7%
High level cloud: 19%
Most Significant Cloud Type: medium
13%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
21:00

SSW
SSW

3 / 6 mph 55 / 54°F 93% 1017 mb
Low level cloud: 2%
Mid level cloud: 7%
High level cloud: 69%
Most Significant Cloud Type: medium
16%
Expect 0.00 In of precipitation over the past 3 hours.
0.00 In
DayLocal TimeDirSpeed/
Gust
Temp/
Feels Like
HumidityPressureCloud AmountPrecip AmountWeather
Thu 26
Jul
00:00

S
S

3 / 6 mph 50 / 50°F 91% 1018 mb
Low level cloud: 3%
Mid level cloud: 10%
High level cloud: 0%
Most Significant Cloud Type: medium
18%
0.00 In
06:00

W
W

7 / 10 mph 54 / 52°F 95% 1011 mb
Low level cloud: 85%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
85%
0.00 In
12:00

NW
NW

2 / 3 mph 78 / 81°F 69% 1015 mb
Low level cloud: 39%
Mid level cloud: 31%
High level cloud: 0%
Most Significant Cloud Type: low
49%
0.03 In
18:00

W
W

9 / 11 mph 63 / 64°F 76% 1010 mb
Low level cloud: 41%
Mid level cloud: 1%
High level cloud: 9%
Most Significant Cloud Type: low
41%
0.00 In
Fri 27
Jul
00:00

ENE
ENE

2 / 4 mph 60 / 60°F 95% 1017 mb
Low level cloud: 11%
Mid level cloud: 33%
High level cloud: 5%
Most Significant Cloud Type: medium
64%
0.03 In
06:00

E
E

6 / 12 mph 61 / 61°F 91% 1014 mb
Low level cloud: 0%
Mid level cloud: 48%
High level cloud: 98%
Most Significant Cloud Type: medium
51%
0.05 In
12:00

S
S

6 / 8 mph 78 / 81°F 70% 1017 mb
Low level cloud: 7%
Mid level cloud: 48%
High level cloud: 98%
Most Significant Cloud Type: medium
72%
0.05 In
18:00

SSW
SSW

7 / 14 mph 73 / 77°F 85% 1011 mb
Low level cloud: 0%
Mid level cloud: 16%
High level cloud: 32%
Most Significant Cloud Type: medium
17%
0.46 In
Sat 28
Jul
00:00

E
E

4 / 9 mph 62 / 62°F 96% 1014 mb
Low level cloud: 1%
Mid level cloud: 19%
High level cloud: 96%
Most Significant Cloud Type: medium
23%
0.02 In
06:00

SSW
SSW

6 / 7 mph 61 / 61°F 98% 1013 mb
Low level cloud: 86%
Mid level cloud: 2%
High level cloud: 33%
Most Significant Cloud Type: low
100%
0.00 In
12:00

WNW
WNW

9 / 12 mph 71 / 71°F 78% 1013 mb
Low level cloud: 76%
Mid level cloud: 28%
High level cloud: 0%
Most Significant Cloud Type: low
85%
0.05 In
18:00

WSW
WSW

4 / 6 mph 69 / 69°F 81% 1011 mb
Low level cloud: 51%
Mid level cloud: 11%
High level cloud: 20%
Most Significant Cloud Type: low
56%
0.03 In
Sun 29
Jul
00:00

W
W

3 / 5 mph 54 / 55°F 98% 1016 mb
Low level cloud: 66%
Mid level cloud: 20%
High level cloud: 0%
Most Significant Cloud Type: low
100%
0.01 In
06:00

SSW
SSW

6 / 8 mph 58 / 57°F 97% 1012 mb
Low level cloud: 85%
Mid level cloud: 5%
High level cloud: 0%
Most Significant Cloud Type: low
100%
0.00 In
12:00

SW
SW

6 / 6 mph 69 / 69°F 63% 1015 mb
Low level cloud: 59%
Mid level cloud: 44%
High level cloud: 6%
Most Significant Cloud Type: low
74%
0.00 In
18:00

WNW
WNW

7 / 9 mph 65 / 65°F 78% 1012 mb
Low level cloud: 37%
Mid level cloud: 7%
High level cloud: 42%
Most Significant Cloud Type: low
44%
0.03 In
Mon 30
Jul
00:00

SSW
SSW

6 / 8 mph 59 / 58°F 97% 1014 mb
Low level cloud: 60%
Mid level cloud: 4%
High level cloud: 8%
Most Significant Cloud Type: low
62%
0.05 In
06:00

NNW
NNW

7 / 11 mph 57 / 55°F 95% 1015 mb
Low level cloud: 83%
Mid level cloud: 16%
High level cloud: 57%
Most Significant Cloud Type: low
95%
0.00 In
12:00

SW
SW

8 / 9 mph 65 / 65°F 81% 1012 mb
Low level cloud: 63%
Mid level cloud: 41%
High level cloud: 7%
Most Significant Cloud Type: low
77%
0.02 In
18:00

NNW
NNW

12 / 14 mph 63 / 63°F 73% 1017 mb
Low level cloud: 58%
Mid level cloud: 8%
High level cloud: 10%
Most Significant Cloud Type: low
61%
0.02 In
Tue 31
Jul
00:00

S
S

7 / 13 mph 56 / 54°F 98% 1011 mb
Low level cloud: 56%
Mid level cloud: 16%
High level cloud: 78%
Most Significant Cloud Type: low
100%
0.01 In
06:00

NNW
NNW

9 / 15 mph 51 / 48°F 86% 1021 mb
Low level cloud: 32%
Mid level cloud: 0%
High level cloud: 32%
Most Significant Cloud Type: low
35%
0.00 In
12:00

S
S

12 / 15 mph 68 / 68°F 84% 1008 mb
Low level cloud: 62%
Mid level cloud: 30%
High level cloud: 11%
Most Significant Cloud Type: low
74%
0.03 In
18:00

NNW
NNW

12 / 14 mph 60 / 60°F 69% 1021 mb
Low level cloud: 3%
Mid level cloud: 5%
High level cloud: 37%
Most Significant Cloud Type: medium
16%
0.00 In
Wed 01
Aug
00:00

SSE
SSE

8 / 13 mph 61 / 61°F 97% 1003 mb
Low level cloud: 53%
Mid level cloud: 47%
High level cloud: 69%
Most Significant Cloud Type: low
78%
0.20 In
06:00

NNW
NNW

11 / 19 mph 53 / 49°F 94% 1017 mb
Low level cloud: 68%
Mid level cloud: 52%
High level cloud: 66%
Most Significant Cloud Type: low
94%
0.19 In
12:00

WNW
WNW

9 / 15 mph 65 / 65°F 84% 1005 mb
Low level cloud: 56%
Mid level cloud: 20%
High level cloud: 19%
Most Significant Cloud Type: low
65%
0.27 In
18:00

NW
NW

13 / 15 mph 57 / 54°F 96% 1011 mb
Low level cloud: 79%
Mid level cloud: 50%
High level cloud: 52%
Most Significant Cloud Type: low
100%
0.41 In
Thu 02
Aug
00:00

WNW
WNW

5 / 6 mph 57 / 56°F 93% 1014 mb
Low level cloud: 58%
Mid level cloud: 46%
High level cloud: 0%
Most Significant Cloud Type: low
74%
0.05 In
06:00

W
W

7 / 14 mph 54 / 52°F 98% 1011 mb
Low level cloud: 85%
Mid level cloud: 63%
High level cloud: 0%
Most Significant Cloud Type: low
100%
0.28 In
12:00

W
W

8 / 9 mph 58 / 57°F 58% 1020 mb
Low level cloud: 19%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
18%
0.02 In
18:00

WSW
WSW

8 / 9 mph 58 / 56°F 96% 1014 mb
Low level cloud: 85%
Mid level cloud: 47%
High level cloud: 36%
Most Significant Cloud Type: low
100%
0.13 In
Fri 03
Aug
00:00

SSW
SSW

4 / 9 mph 49 / 47°F 87% 1024 mb
Low level cloud: 3%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
3%
0.00 In
06:00

SW
SW

5 / 9 mph 53 / 51°F 96% 1017 mb
Low level cloud: 44%
Mid level cloud: 25%
High level cloud: 0%
Most Significant Cloud Type: low
52%
0.04 In
12:00

WSW
WSW

10 / 11 mph 65 / 65°F 63% 1025 mb
Low level cloud: 54%
Mid level cloud: 13%
High level cloud: 9%
Most Significant Cloud Type: low
59%
0.00 In
18:00

WSW
WSW

6 / 7 mph 64 / 64°F 74% 1018 mb
Low level cloud: 8%
Mid level cloud: 21%
High level cloud: 0%
Most Significant Cloud Type: low
15%
0.01 In

The day label given represents the local day relative to the local time for the location you are looking at.
(More Info)

Day

This time is corrected for local time zones and where possible for daylight saving times.
(More Info)

Local Time

The wind direction we use on this page is the direction the wind is coming from, given in a 16 point compass format.
(More Info)

Dir

This refers to the sustained average wind speed, normally averaged over a period of 10 minutes for up to 3 hrs.
(More Info)

Speed/
Gust

Temperature from our forecast perspective are fairly well defined, they are what we would expect to measure in a standard meteorological screen (in other words, shaded and well ventilated) at 2 metres above ground level.
(More Info)

Temp/
Feels Like

The relative humidity is the percent of saturation humidity, generally calculated in relation to saturated vapour density.
(More Info)

Humidity

The value given is a total predicted for the previous 3 hrs and includes the time of the forecast being looked at.
(More Info)

Precip Amount

The total amount of cloud as a percentage is derived from looking at cloud cover throughout the atmosphere and estimating how these combine when looked at from the ground.
(More Info)

Cloud Amount

Here we try to capture the feel of the weather as an image – it will never be perfect but is useful for a quick overview.
(More Info)

Weather

When we measure for forecast air pressure we are normally doing this relative to a certain height and most commonly relative to Mean Sea Level.
(More Info)

Pressure