WEATHER FOR BUSINESS

We supply weather data to businesses

Free Weather Plugin

Add this forecast to your website



Local Weather

Cefn Glas 14 Day Long Range Forecast

14 Day weather providing an extended long range forecast outlook for Cefn Glas

The Vale Of Glamorgan, United Kingdom

Long range weather outlook for Cefn Glas includes 14 day forecast summary:

Over the next 14 days the Cefn Glas forecast suggests the average daytime maximum temperature will be around 9°C, with a high for the two weeks of 11°C expected on the afternoon of Thursday 18th. The average minimum temperature will be 6°C, dipping to its lowest on the morning of Saturday 20th at 4°C. The next 14 days will have some days seeing a little precipitation and some days with rain. It looks like Monday 15th will have the most precipitation with an accumulation of around 46.0mm. On the whole winds are likely to be moderate. The strongest wind will be experienced on the morning of Friday 19th, coming from a south westerly direction, and reaching around 26mph. However, the forecast suggests maximum gusts on Thursday evening.

DayLocal TimeDirSpeed/
Gust
Temp/
Feels Like
HumidityCloud AmountPrecip AmountWeather
Sun 14
Dec
06:00

SSW
SSW

13 / 23 mph 47 / 41°F 83%
Low level cloud: 0%
Mid level cloud: 69%
High level cloud: 34%
Most Significant Cloud Type: medium
70%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

SSW
SSW

13 / 21 mph 49 / 44°F 83%
Low level cloud: 0%
Mid level cloud: 46%
High level cloud: 79%
Most Significant Cloud Type: medium
49%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

SSW
SSW

14 / 20 mph 51 / 46°F 80%
Low level cloud: 0%
Mid level cloud: 44%
High level cloud: 71%
Most Significant Cloud Type: medium
46%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

SSW
SSW

15 / 21 mph 52 / 47°F 82%
Low level cloud: 14%
Mid level cloud: 76%
High level cloud: 9%
Most Significant Cloud Type: medium
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

S
S

15 / 23 mph 51 / 46°F 85%
Low level cloud: 19%
Mid level cloud: 95%
High level cloud: 12%
Most Significant Cloud Type: medium
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
21:00

SSW
SSW

18 / 35 mph 49 / 43°F 85%
Low level cloud: 85%
Mid level cloud: 88%
High level cloud: 48%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Mon 15
Dec
00:00

SSW
SSW

18 / 36 mph 48 / 42°F 88%
Low level cloud: 82%
Mid level cloud: 97%
High level cloud: 97%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
03:00

SSW
SSW

18 / 38 mph 47 / 40°F 91%
Low level cloud: 100%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: low
100%
Expect 0.2 In of precipitation over the past 3 hours.
0.2 In
06:00

SSW
SSW

19 / 38 mph 46 / 39°F 93%
Low level cloud: 100%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: low
100%
Expect 0.4 In of precipitation over the past 3 hours.
0.4 In
09:00

SSW
SSW

18 / 27 mph 49 / 42°F 95%
Low level cloud: 93%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: low
100%
Expect 0.4 In of precipitation over the past 3 hours.
0.4 In
12:00

S
S

13 / 17 mph 51 / 46°F 95%
Low level cloud: 100%
Mid level cloud: 100%
High level cloud: 86%
Most Significant Cloud Type: low
100%
Expect 0.3 In of precipitation over the past 3 hours.
0.3 In
15:00

SSE
SSE

11 / 13 mph 52 / 49°F 97%
Low level cloud: 97%
Mid level cloud: 100%
High level cloud: 84%
Most Significant Cloud Type: low
100%
Expect 0.3 In of precipitation over the past 3 hours.
0.3 In
18:00

W
W

8 / 9 mph 51 / 48°F 97%
Low level cloud: 99%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: low
100%
Expect 0.2 In of precipitation over the past 3 hours.
0.2 In
21:00

W
W

5 / 6 mph 50 / 48°F 93%
Low level cloud: 99%
Mid level cloud: 100%
High level cloud: 99%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Tue 16
Dec
00:00

NNW
NNW

3 / 4 mph 47 / 47°F 94%
Low level cloud: 81%
Mid level cloud: 71%
High level cloud: 98%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
03:00

NE
NE

5 / 7 mph 47 / 45°F 92%
Low level cloud: 66%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
06:00

N
N

6 / 8 mph 45 / 42°F 90%
Low level cloud: 15%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: medium
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

NNE
NNE

5 / 9 mph 45 / 42°F 84%
Low level cloud: 0%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: medium
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

NW
NW

5 / 7 mph 47 / 44°F 79%
Low level cloud: 0%
Mid level cloud: 100%
High level cloud: 33%
Most Significant Cloud Type: medium
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

NNW
NNW

5 / 7 mph 47 / 44°F 81%
Low level cloud: 0%
Mid level cloud: 3%
High level cloud: 41%
Most Significant Cloud Type: medium
4%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

N
N

4 / 6 mph 46 / 44°F 85%
Low level cloud: 0%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: high
0%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
21:00

NNW
NNW

4 / 7 mph 42 / 40°F 84%
Low level cloud: 0%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: high
0%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Wed 17
Dec
00:00

NW
NW

4 / 7 mph 41 / 38°F 83%
Low level cloud: 0%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: high
0%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
03:00

NW
NW

2 / 4 mph 39 / 39°F 83%
Low level cloud: 0%
Mid level cloud: 20%
High level cloud: 5%
Most Significant Cloud Type: medium
19%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
06:00

SW
SW

6 / 13 mph 40 / 36°F 87%
Low level cloud: 3%
Mid level cloud: 20%
High level cloud: 32%
Most Significant Cloud Type: medium
28%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

SSW
SSW

9 / 15 mph 42 / 37°F 87%
Low level cloud: 11%
Mid level cloud: 66%
High level cloud: 100%
Most Significant Cloud Type: medium
99%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

SSW
SSW

13 / 19 mph 47 / 41°F 84%
Low level cloud: 10%
Mid level cloud: 57%
High level cloud: 100%
Most Significant Cloud Type: medium
88%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

SSW
SSW

14 / 22 mph 48 / 42°F 84%
Low level cloud: 71%
Mid level cloud: 79%
High level cloud: 70%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

SSW
SSW

13 / 20 mph 48 / 43°F 86%
Low level cloud: 94%
Mid level cloud: 70%
High level cloud: 4%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
21:00

SSW
SSW

13 / 20 mph 48 / 43°F 91%
Low level cloud: 100%
Mid level cloud: 97%
High level cloud: 72%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
Thu 18
Dec
00:00

SSW
SSW

13 / 22 mph 49 / 43°F 92%
Low level cloud: 100%
Mid level cloud: 88%
High level cloud: 32%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
03:00

S
S

10 / 17 mph 48 / 43°F 94%
Low level cloud: 100%
Mid level cloud: 99%
High level cloud: 15%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
06:00

SSE
SSE

15 / 29 mph 47 / 40°F 87%
Low level cloud: 94%
Mid level cloud: 100%
High level cloud: 33%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
09:00

SSE
SSE

19 / 27 mph 49 / 42°F 88%
Low level cloud: 53%
Mid level cloud: 20%
High level cloud: 8%
Most Significant Cloud Type: low
61%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

SSE
SSE

23 / 27 mph 51 / 45°F 88%
Low level cloud: 100%
Mid level cloud: 13%
High level cloud: 32%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

S
S

27 / 41 mph 52 / 46°F 85%
Low level cloud: 56%
Mid level cloud: 43%
High level cloud: 86%
Most Significant Cloud Type: low
81%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

SSW
SSW

27 / 43 mph 51 / 44°F 91%
Low level cloud: 97%
Mid level cloud: 99%
High level cloud: 85%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
21:00

SW
SW

25 / 31 mph 49 / 42°F 78%
Low level cloud: 20%
Mid level cloud: 71%
High level cloud: 100%
Most Significant Cloud Type: medium
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Fri 19
Dec
00:00

SW
SW

28 / 42 mph 47 / 38°F 75%
Low level cloud: 27%
Mid level cloud: 3%
High level cloud: 99%
Most Significant Cloud Type: low
39%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
03:00

WSW
WSW

28 / 40 mph 47 / 38°F 84%
Low level cloud: 93%
Mid level cloud: 44%
High level cloud: 91%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
06:00

WSW
WSW

18 / 26 mph 47 / 40°F 83%
Low level cloud: 83%
Mid level cloud: 46%
High level cloud: 100%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

WSW
WSW

15 / 22 mph 47 / 41°F 85%
Low level cloud: 77%
Mid level cloud: 31%
High level cloud: 6%
Most Significant Cloud Type: low
88%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

SW
SW

12 / 17 mph 48 / 42°F 86%
Low level cloud: 36%
Mid level cloud: 20%
High level cloud: 1%
Most Significant Cloud Type: low
43%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

SW
SW

9 / 14 mph 47 / 43°F 87%
Low level cloud: 9%
Mid level cloud: 15%
High level cloud: 0%
Most Significant Cloud Type: low
14%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

SW
SW

7 / 12 mph 45 / 41°F 89%
Low level cloud: 15%
Mid level cloud: 29%
High level cloud: 0%
Most Significant Cloud Type: low
25%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
21:00

SW
SW

5 / 10 mph 44 / 41°F 88%
Low level cloud: 8%
Mid level cloud: 1%
High level cloud: 0%
Most Significant Cloud Type: low
8%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Sat 20
Dec
00:00

SSW
SSW

4 / 7 mph 42 / 40°F 90%
Low level cloud: 34%
Mid level cloud: 1%
High level cloud: 0%
Most Significant Cloud Type: low
34%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
03:00

S
S

1 / 2 mph 40 / 40°F 90%
Low level cloud: 40%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
40%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
06:00

E
E

4 / 8 mph 39 / 36°F 92%
Low level cloud: 26%
Mid level cloud: 2%
High level cloud: 0%
Most Significant Cloud Type: low
26%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

E
E

5 / 8 mph 42 / 38°F 92%
Low level cloud: 14%
Mid level cloud: 6%
High level cloud: 0%
Most Significant Cloud Type: low
16%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

ESE
ESE

5 / 6 mph 45 / 42°F 83%
Low level cloud: 5%
Mid level cloud: 15%
High level cloud: 0%
Most Significant Cloud Type: medium
29%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

ESE
ESE

6 / 7 mph 46 / 43°F 86%
Low level cloud: 1%
Mid level cloud: 5%
High level cloud: 0%
Most Significant Cloud Type: medium
6%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

SSE
SSE

8 / 10 mph 45 / 41°F 89%
Low level cloud: 18%
Mid level cloud: 8%
High level cloud: 0%
Most Significant Cloud Type: low
20%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
21:00

SE
SE

11 / 19 mph 43 / 37°F 87%
Low level cloud: 62%
Mid level cloud: 65%
High level cloud: 93%
Most Significant Cloud Type: low
96%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
DayLocal TimeDirSpeed/
Gust
Temp/
Feels Like
HumidityCloud AmountPrecip AmountWeather
Sun 21
Dec
00:00

WSW
WSW

23 / 42 mph 49 / 41°F 96%
Low level cloud: 84%
Mid level cloud: 45%
High level cloud: 0%
Most Significant Cloud Type: low
99%
0.0 In
06:00

E
E

3 / 6 mph 42 / 40°F 91%
Low level cloud: 19%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: medium
100%
0.0 In
12:00

N
N

1 / 1 mph 44 / 44°F 72%
Low level cloud: 0%
Mid level cloud: 100%
High level cloud: 34%
Most Significant Cloud Type: medium
100%
0.0 In
18:00

E
E

4 / 6 mph 50 / 49°F 89%
Low level cloud: 22%
Mid level cloud: 26%
High level cloud: 0%
Most Significant Cloud Type: low
31%
0.0 In
Mon 22
Dec
00:00

WNW
WNW

8 / 12 mph 47 / 43°F 90%
Low level cloud: 5%
Mid level cloud: 30%
High level cloud: 0%
Most Significant Cloud Type: medium
42%
0.0 In
06:00

NE
NE

5 / 8 mph 43 / 40°F 88%
Low level cloud: 25%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
24%
0.0 In
12:00

ESE
ESE

17 / 31 mph 47 / 40°F 89%
Low level cloud: 88%
Mid level cloud: 25%
High level cloud: 98%
Most Significant Cloud Type: low
100%
0.0 In
18:00

NE
NE

7 / 11 mph 49 / 46°F 84%
Low level cloud: 16%
Mid level cloud: 1%
High level cloud: 1%
Most Significant Cloud Type: low
16%
0.0 In
Tue 23
Dec
00:00

E
E

13 / 24 mph 45 / 39°F 89%
Low level cloud: 53%
Mid level cloud: 22%
High level cloud: 0%
Most Significant Cloud Type: low
60%
0.0 In
06:00

N
N

5 / 8 mph 43 / 40°F 75%
Low level cloud: 93%
Mid level cloud: 20%
High level cloud: 0%
Most Significant Cloud Type: low
100%
0.0 In
12:00

E
E

13 / 26 mph 46 / 40°F 86%
Low level cloud: 73%
Mid level cloud: 14%
High level cloud: 1%
Most Significant Cloud Type: low
77%
0.0 In
18:00

SW
SW

2 / 4 mph 50 / 51°F 73%
Low level cloud: 73%
Mid level cloud: 14%
High level cloud: 0%
Most Significant Cloud Type: low
78%
0.0 In
Wed 24
Dec
00:00

ENE
ENE

22 / 43 mph 44 / 36°F 92%
Low level cloud: 87%
Mid level cloud: 57%
High level cloud: 99%
Most Significant Cloud Type: low
100%
0.0 In
06:00

W
W

4 / 7 mph 42 / 40°F 77%
Low level cloud: 60%
Mid level cloud: 12%
High level cloud: 0%
Most Significant Cloud Type: low
64%
0.0 In
12:00

E
E

17 / 33 mph 46 / 38°F 94%
Low level cloud: 82%
Mid level cloud: 86%
High level cloud: 33%
Most Significant Cloud Type: low
100%
0.1 In
18:00

ESE
ESE

2 / 3 mph 53 / 53°F 78%
Low level cloud: 8%
Mid level cloud: 2%
High level cloud: 0%
Most Significant Cloud Type: low
8%
0.0 In
Thu 25
Dec
00:00

E
E

12 / 24 mph 43 / 36°F 92%
Low level cloud: 40%
Mid level cloud: 46%
High level cloud: 21%
Most Significant Cloud Type: low
58%
0.0 In
06:00

ENE
ENE

4 / 7 mph 39 / 36°F 82%
Low level cloud: 0%
Mid level cloud: 1%
High level cloud: 54%
Most Significant Cloud Type: high
53%
0.0 In
12:00

E
E

9 / 18 mph 47 / 43°F 86%
Low level cloud: 12%
Mid level cloud: 46%
High level cloud: 26%
Most Significant Cloud Type: medium
80%
0.0 In
18:00

ENE
ENE

5 / 8 mph 48 / 46°F 79%
Low level cloud: 0%
Mid level cloud: 6%
High level cloud: 6%
Most Significant Cloud Type: medium
5%
0.0 In
Fri 26
Dec
00:00

E
E

6 / 11 mph 44 / 41°F 89%
Low level cloud: 19%
Mid level cloud: 60%
High level cloud: 1%
Most Significant Cloud Type: medium
100%
0.0 In
06:00

ENE
ENE

5 / 9 mph 38 / 34°F 84%
Low level cloud: 47%
Mid level cloud: 3%
High level cloud: 6%
Most Significant Cloud Type: low
48%
0.0 In
12:00

ENE
ENE

1 / 2 mph 48 / 48°F 85%
Low level cloud: 11%
Mid level cloud: 52%
High level cloud: 2%
Most Significant Cloud Type: medium
84%
0.0 In
18:00

ENE
ENE

6 / 9 mph 44 / 41°F 86%
Low level cloud: 59%
Mid level cloud: 3%
High level cloud: 21%
Most Significant Cloud Type: low
62%
0.0 In
Sat 27
Dec
00:00

NE
NE

14 / 30 mph 42 / 34°F 87%
Low level cloud: 96%
Mid level cloud: 46%
High level cloud: 33%
Most Significant Cloud Type: low
100%
0.0 In
06:00

E
E

6 / 10 mph 41 / 37°F 86%
Low level cloud: 93%
Mid level cloud: 6%
High level cloud: 5%
Most Significant Cloud Type: low
95%
0.0 In
12:00

ENE
ENE

17 / 35 mph 45 / 38°F 78%
Low level cloud: 1%
Mid level cloud: 3%
High level cloud: 0%
Most Significant Cloud Type: medium
5%
0.0 In
18:00

E
E

6 / 9 mph 46 / 43°F 93%
Low level cloud: 75%
Mid level cloud: 6%
High level cloud: 20%
Most Significant Cloud Type: low
79%
0.0 In
Sun 28
Dec
00:00

ENE
ENE

13 / 26 mph 40 / 33°F 87%
Low level cloud: 5%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
4%
0.0 In
06:00

S
S

8 / 14 mph 42 / 37°F 89%
Low level cloud: 27%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: medium
100%
0.0 In
12:00

NE
NE

9 / 19 mph 45 / 40°F 85%
Low level cloud: 58%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
58%
0.0 In
18:00

NW
NW

8 / 13 mph 48 / 45°F 78%
Low level cloud: 13%
Mid level cloud: 60%
High level cloud: 100%
Most Significant Cloud Type: medium
99%
0.1 In
Mon 29
Dec
00:00

NNE
NNE

4 / 7 mph 45 / 44°F 87%
Low level cloud: 0%
Mid level cloud: 4%
High level cloud: 10%
Most Significant Cloud Type: medium
4%
0.0 In
06:00

SSW
SSW

3 / 5 mph 39 / 38°F 78%
Low level cloud: 12%
Mid level cloud: 19%
High level cloud: 15%
Most Significant Cloud Type: low
20%
0.0 In
12:00

ENE
ENE

7 / 15 mph 47 / 43°F 70%
Low level cloud: 0%
Mid level cloud: 0%
High level cloud: 7%
Most Significant Cloud Type: high
7%
0.0 In
18:00

SSW
SSW

29 / 50 mph 51 / 43°F 80%
Low level cloud: 99%
Mid level cloud: 62%
High level cloud: 0%
Most Significant Cloud Type: low
100%
0.4 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