Fast Forecast

WEATHER FOR BUSINESS

We supply weather data to businesses

Free Weather Plugin

Add this forecast to your website



Local Weather

Willow Springs 14 Day Long Range Forecast

14 Day weather providing an extended long range forecast outlook for Willow Springs

Illinois, United States Of America

Long range weather outlook for Willow Springs includes 14 day forecast summary:

The forecast for Willow Springs in the coming two weeks is predicting the average daytime maximum temperature will be around 3°C, with a high for the two weeks of 10°C expected on the morning of Wednesday 11th. The mean minimum temperature will be -2°C, dipping to its lowest on the morning of Tuesday 17th at -13°C. Expect the coming 14 days to have some days seeing a little precipitation and some days with rain, sleet or snow. The current forecast indicates Sunday 15th will have the most precipitation with an accumulation of around 34.0mm. On the whole winds are likely to be moderate.

DayLocal TimeDirSpeed/
Gust		Temp/
Feels Like		HumidityPressureCloud AmountPrecip AmountWeather
Tue 10
Mar		00:00

SSW
SSW

 9 / 14 mph 61 / 61°F 96% 1007 mb
Low level cloud: 93%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
93%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
03:00

SSW
SSW

 8 / 15 mph 58 / 56°F 96% 1008 mb
Low level cloud: 70%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
69%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
06:00

SW
SW

 6 / 12 mph 58 / 57°F 98% 1009 mb
Low level cloud: 89%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

NE
NE

 5 / 6 mph 58 / 57°F 84% 1011 mb
Low level cloud: 98%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
97%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

ENE
ENE

 11 / 12 mph 48 / 43°F 70% 1012 mb
Low level cloud: 86%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: low
86%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

ENE
ENE

 9 / 11 mph 52 / 48°F 67% 1010 mb
Low level cloud: 15%
Mid level cloud: 8%
High level cloud: 3%
Most Significant Cloud Type: low
18%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

ENE
ENE

 8 / 15 mph 52 / 49°F 82% 1007 mb
Low level cloud: 40%
Mid level cloud: 15%
High level cloud: 18%
Most Significant Cloud Type: low
47%
Expect 0.2 In of precipitation over the past 3 hours.
0.2 In
21:00

E
E

 6 / 12 mph 50 / 48°F 92% 1005 mb
Low level cloud: 48%
Mid level cloud: 47%
High level cloud: 47%
Most Significant Cloud Type: low
69%
Expect 0.3 In of precipitation over the past 3 hours.
0.3 In
Wed 11
Mar		21:00

NW
NW

 13 / 15 mph 37 / 29°F 63% 1020 mb
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
Thu 12
Mar		00:00

NNW
NNW

 10 / 11 mph 35 / 28°F 63% 1022 mb
Low level cloud: 0%
Mid level cloud: 2%
High level cloud: 0%
Most Significant Cloud Type: medium
2%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
03:00

W
W

 6 / 8 mph 33 / 27°F 72% 1022 mb
Low level cloud: 0%
Mid level cloud: 8%
High level cloud: 0%
Most Significant Cloud Type: medium
8%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
06:00

W
W

 7 / 9 mph 32 / 26°F 73% 1023 mb
Low level cloud: 0%
Mid level cloud: 29%
High level cloud: 0%
Most Significant Cloud Type: medium
29%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

WNW
WNW

 9 / 11 mph 38 / 31°F 57% 1023 mb
Low level cloud: 18%
Mid level cloud: 1%
High level cloud: 0%
Most Significant Cloud Type: low
18%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

WNW
WNW

 9 / 11 mph 43 / 38°F 34% 1022 mb
Low level cloud: 0%
Mid level cloud: 2%
High level cloud: 15%
Most Significant Cloud Type: medium
2%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

WSW
WSW

 10 / 11 mph 47 / 42°F 27% 1019 mb
Low level cloud: 0%
Mid level cloud: 16%
High level cloud: 12%
Most Significant Cloud Type: medium
16%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

SSW
SSW

 8 / 10 mph 46 / 42°F 38% 1015 mb
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
21:00

S
S

 15 / 20 mph 45 / 38°F 47% 1011 mb
Low level cloud: 0%
Mid level cloud: 100%
High level cloud: 20%
Most Significant Cloud Type: medium
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Fri 13
Mar		00:00

S
S

 21 / 30 mph 44 / 36°F 51% 1002 mb
Low level cloud: 0%
Mid level cloud: 81%
High level cloud: 42%
Most Significant Cloud Type: medium
82%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
03:00

SW
SW

 22 / 31 mph 46 / 37°F 53% 999 mb
Low level cloud: 46%
Mid level cloud: 49%
High level cloud: 32%
Most Significant Cloud Type: low
67%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
06:00

WSW
WSW

 26 / 37 mph 49 / 42°F 48% 995 mb
Low level cloud: 0%
Mid level cloud: 11%
High level cloud: 1%
Most Significant Cloud Type: medium
10%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

W
W

 23 / 27 mph 42 / 32°F 44% 1000 mb
Low level cloud: 20%
Mid level cloud: 35%
High level cloud: 0%
Most Significant Cloud Type: low
32%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

W
W

 24 / 28 mph 43 / 33°F 47% 1003 mb
Low level cloud: 98%
Mid level cloud: 100%
High level cloud: 0%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

WNW
WNW

 19 / 22 mph 44 / 35°F 43% 1009 mb
Low level cloud: 13%
Mid level cloud: 45%
High level cloud: 0%
Most Significant Cloud Type: medium
80%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

NW
NW

 13 / 16 mph 42 / 35°F 43% 1015 mb
Low level cloud: 7%
Mid level cloud: 17%
High level cloud: 2%
Most Significant Cloud Type: low
12%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
21:00

NW
NW

 9 / 10 mph 40 / 35°F 48% 1019 mb
Low level cloud: 0%
Mid level cloud: 5%
High level cloud: 9%
Most Significant Cloud Type: medium
5%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
Sat 14
Mar		00:00

N
N

 5 / 6 mph 37 / 32°F 52% 1020 mb
Low level cloud: 0%
Mid level cloud: 24%
High level cloud: 32%
Most Significant Cloud Type: medium
25%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
03:00

N
N

 4 / 5 mph 35 / 31°F 53% 1022 mb
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
06:00

ENE
ENE

 7 / 8 mph 31 / 24°F 79% 1022 mb
Low level cloud: 35%
Mid level cloud: 100%
High level cloud: 67%
Most Significant Cloud Type: medium
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

ESE
ESE

 7 / 9 mph 31 / 24°F 85% 1023 mb
Low level cloud: 99%
Mid level cloud: 100%
High level cloud: 51%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
12:00

ESE
ESE

 8 / 9 mph 35 / 28°F 76% 1021 mb
Low level cloud: 95%
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
15:00

E
E

 9 / 11 mph 36 / 29°F 78% 1019 mb
Low level cloud: 55%
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
18:00

E
E

 11 / 13 mph 36 / 28°F 85% 1018 mb
Low level cloud: 67%
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
21:00

ENE
ENE

 13 / 17 mph 35 / 26°F 92% 1016 mb
Low level cloud: 96%
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
Sun 15
Mar		00:00

ENE
ENE

 13 / 17 mph 34 / 25°F 97% 1012 mb
Low level cloud: 100%
Mid level cloud: 84%
High level cloud: 100%
Most Significant Cloud Type: low
100%
Expect 0.2 In of precipitation over the past 3 hours.
0.2 In
03:00

ENE
ENE

 14 / 19 mph 34 / 24°F 97% 1009 mb
Low level cloud: 100%
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

NE
NE

 14 / 18 mph 34 / 25°F 96% 1006 mb
Low level cloud: 100%
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
09:00

NE
NE

 18 / 24 mph 32 / 21°F 95% 1005 mb
Low level cloud: 99%
Mid level cloud: 71%
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

NE
NE

 18 / 23 mph 31 / 19°F 95% 1006 mb
Low level cloud: 93%
Mid level cloud: 98%
High level cloud: 72%
Most Significant Cloud Type: low
100%
Expect 0.2 In of precipitation over the past 3 hours.
0.2 In
15:00

NNE
NNE

 21 / 29 mph 30 / 17°F 95% 1006 mb
Low level cloud: 83%
Mid level cloud: 52%
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

N
N

 22 / 31 mph 28 / 14°F 93% 1013 mb
Low level cloud: 78%
Mid level cloud: 57%
High level cloud: 0%
Most Significant Cloud Type: low
98%
Expect 0.2 In of precipitation over the past 3 hours.
0.2 In
21:00

N
N

 17 / 23 mph 26 / 13°F 90% 1017 mb
Low level cloud: 88%
Mid level cloud: 92%
High level cloud: 40%
Most Significant Cloud Type: low
100%
Expect 0.1 In of precipitation over the past 3 hours.
0.1 In
Mon 16
Mar		00:00

NNW
NNW

 13 / 18 mph 20 / 7°F 85% 1021 mb
Low level cloud: 37%
Mid level cloud: 100%
High level cloud: 36%
Most Significant Cloud Type: low
76%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
03:00

NNW
NNW

 10 / 14 mph 17 / 5°F 87% 1023 mb
Low level cloud: 29%
Mid level cloud: 32%
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

NW
NW

 8 / 9 mph 15 / 4°F 87% 1025 mb
Low level cloud: 0%
Mid level cloud: 2%
High level cloud: 0%
Most Significant Cloud Type: medium
2%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
09:00

NW
NW

 9 / 11 mph 16 / 5°F 81% 1026 mb
Low level cloud: 5%
Mid level cloud: 4%
High level cloud: 0%
Most Significant Cloud Type: low
6%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
12:00

WNW
WNW

 12 / 14 mph 22 / 10°F 78% 1026 mb
Low level cloud: 100%
Mid level cloud: 14%
High level cloud: 0%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
15:00

WNW
WNW

 11 / 13 mph 24 / 13°F 78% 1025 mb
Low level cloud: 82%
Mid level cloud: 100%
High level cloud: 0%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
18:00

WNW
WNW

 7 / 10 mph 21 / 13°F 87% 1026 mb
Low level cloud: 23%
Mid level cloud: 99%
High level cloud: 0%
Most Significant Cloud Type: medium
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
21:00

W
W

 3 / 6 mph 15 / 11°F 97% 1027 mb
Low level cloud: 89%
Mid level cloud: 100%
High level cloud: 0%
Most Significant Cloud Type: low
100%
Expect 0.0 In of precipitation over the past 3 hours.
0.0 In
DayLocal TimeDirSpeed/
Gust		Temp/
Feels Like		HumidityPressureCloud AmountPrecip AmountWeather
Tue 17
Mar		00:00

ENE
ENE

 8 / 16 mph 28 / 20°F 62% 1025 mb
Low level cloud: 55%
Mid level cloud: 50%
High level cloud: 100%
Most Significant Cloud Type: low
84%
0.0 In
06:00

NNW
NNW

 8 / 17 mph 26 / 17°F 56% 1031 mb
Low level cloud: 0%
Mid level cloud: 0%
High level cloud: 0%
Most Significant Cloud Type: high
0%
0.0 In
12:00

WNW
WNW

 8 / 16 mph 26 / 18°F 32% 1028 mb
Low level cloud: 3%
Mid level cloud: 100%
High level cloud: 0%
Most Significant Cloud Type: medium
100%
0.0 In
18:00

NW
NW

 2 / 4 mph 37 / 36°F 32% 1031 mb
Low level cloud: 0%
Mid level cloud: 8%
High level cloud: 32%
Most Significant Cloud Type: medium
9%
0.0 In
Wed 18
Mar		00:00

SSE
SSE

 6 / 12 mph 25 / 18°F 75% 1032 mb
Low level cloud: 88%
Mid level cloud: 100%
High level cloud: 33%
Most Significant Cloud Type: low
100%
0.0 In
06:00

SSE
SSE

 9 / 19 mph 28 / 19°F 89% 1022 mb
Low level cloud: 84%
Mid level cloud: 48%
High level cloud: 35%
Most Significant Cloud Type: low
100%
0.0 In
12:00

SSE
SSE

 5 / 11 mph 33 / 28°F 96% 1024 mb
Low level cloud: 100%
Mid level cloud: 46%
High level cloud: 0%
Most Significant Cloud Type: low
100%
0.0 In
18:00

NNE
NNE

 8 / 16 mph 33 / 27°F 88% 1023 mb
Low level cloud: 100%
Mid level cloud: 9%
High level cloud: 0%
Most Significant Cloud Type: low
100%
0.0 In
Thu 19
Mar		00:00

N
N

 3 / 6 mph 33 / 30°F 96% 1022 mb
Low level cloud: 88%
Mid level cloud: 86%
High level cloud: 100%
Most Significant Cloud Type: low
100%
0.0 In
06:00

N
N

 2 / 5 mph 27 / 25°F 97% 1030 mb
Low level cloud: 60%
Mid level cloud: 1%
High level cloud: 0%
Most Significant Cloud Type: low
59%
0.0 In
12:00

ESE
ESE

 4 / 10 mph 34 / 30°F 100% 1024 mb
Low level cloud: 87%
Mid level cloud: 100%
High level cloud: 100%
Most Significant Cloud Type: low
100%
0.0 In
18:00

SE
SE

 2 / 4 mph 42 / 41°F 95% 1028 mb
Low level cloud: 1%
Mid level cloud: 2%
High level cloud: 100%
Most Significant Cloud Type: medium
9%
0.0 In
Fri 20
Mar		00:00

E
E

 4 / 8 mph 37 / 33°F 100% 1023 mb
Low level cloud: 100%
Mid level cloud: 45%
High level cloud: 2%
Most Significant Cloud Type: low
100%
0.0 In
06:00

SSE
SSE

 9 / 19 mph 36 / 29°F 97% 1019 mb
Low level cloud: 100%
Mid level cloud: 100%
High level cloud: 0%
Most Significant Cloud Type: low
100%
0.0 In
12:00

ESE
ESE

 2 / 4 mph 38 / 38°F 100% 1023 mb
Low level cloud: 86%
Mid level cloud: 24%
High level cloud: 100%
Most Significant Cloud Type: low
100%
0.0 In
18:00

NNW
NNW

 3 / 7 mph 41 / 39°F 100% 1016 mb
Low level cloud: 100%
Mid level cloud: 0%
High level cloud: 97%
Most Significant Cloud Type: low
100%
0.0 In
Sat 21
Mar		00:00

ESE
ESE

 1 / 2 mph 38 / 38°F 100% 1021 mb
Low level cloud: 93%
Mid level cloud: 2%
High level cloud: 16%
Most Significant Cloud Type: low
100%
0.0 In
06:00

NNW
NNW

 3 / 6 mph 38 / 36°F 99% 1018 mb
Low level cloud: 90%
Mid level cloud: 0%
High level cloud: 17%
Most Significant Cloud Type: low
100%
0.0 In
12:00

E
E

 4 / 8 mph 42 / 40°F 96% 1020 mb
Low level cloud: 91%
Mid level cloud: 6%
High level cloud: 81%
Most Significant Cloud Type: low
100%
0.0 In
18:00

NNE
NNE

 5 / 10 mph 53 / 52°F 83% 1019 mb
Low level cloud: 10%
Mid level cloud: 5%
High level cloud: 13%
Most Significant Cloud Type: low
13%
0.0 In
Sun 22
Mar		00:00

NE
NE

 7 / 14 mph 39 / 35°F 99% 1015 mb
Low level cloud: 92%
Mid level cloud: 24%
High level cloud: 82%
Most Significant Cloud Type: low
100%
0.0 In
06:00

NE
NE

 10 / 21 mph 39 / 32°F 83% 1026 mb
Low level cloud: 30%
Mid level cloud: 7%
High level cloud: 29%
Most Significant Cloud Type: low
35%
0.0 In
12:00

NNE
NNE

 10 / 20 mph 41 / 35°F 96% 1010 mb
Low level cloud: 100%
Mid level cloud: 21%
High level cloud: 93%
Most Significant Cloud Type: low
100%
0.1 In
18:00

ENE
ENE

 6 / 13 mph 52 / 51°F 55% 1024 mb
Low level cloud: 0%
Mid level cloud: 3%
High level cloud: 6%
Most Significant Cloud Type: medium
3%
0.0 In
Mon 23
Mar		00:00

NE
NE

 13 / 28 mph 35 / 26°F 89% 1017 mb
Low level cloud: 100%
Mid level cloud: 66%
High level cloud: 100%
Most Significant Cloud Type: low
100%
0.1 In
06:00

SSE
SSE

 10 / 21 mph 45 / 39°F 76% 1018 mb
Low level cloud: 0%
Mid level cloud: 5%
High level cloud: 1%
Most Significant Cloud Type: medium
5%
0.0 In
12:00

NE
NE

 13 / 27 mph 37 / 29°F 63% 1026 mb
Low level cloud: 98%
Mid level cloud: 27%
High level cloud: 29%
Most Significant Cloud Type: low
100%
0.0 In
18:00

SW
SW

 10 / 20 mph 77 / 79°F 60% 1008 mb
Low level cloud: 0%
Mid level cloud: 1%
High level cloud: 0%
Most Significant Cloud Type: high
0%
0.0 In
Tue 24
Mar		00:00

E
E

 11 / 22 mph 34 / 26°F 62% 1030 mb
Low level cloud: 2%
Mid level cloud: 46%
High level cloud: 93%
Most Significant Cloud Type: medium
55%
0.0 In
06:00

SW
SW

 10 / 21 mph 65 / 65°F 70% 1008 mb
Low level cloud: 0%
Mid level cloud: 0%
High level cloud: 1%
Most Significant Cloud Type: high
0%
0.0 In
12:00

ESE
ESE

 9 / 19 mph 37 / 30°F 48% 1024 mb
Low level cloud: 7%
Mid level cloud: 100%
High level cloud: 35%
Most Significant Cloud Type: medium
100%
0.0 In
18:00

SW
SW

 3 / 7 mph 82 / 84°F 50% 1006 mb
Low level cloud: 0%
Mid level cloud: 3%
High level cloud: 11%
Most Significant Cloud Type: medium
3%
0.0 In
Wed 25
Mar		00:00

SSE
SSE

 8 / 18 mph 45 / 40°F 94% 1014 mb
Low level cloud: 76%
Mid level cloud: 46%
High level cloud: 0%
Most Significant Cloud Type: low
91%
0.0 In
06:00

ESE
ESE

 4 / 9 mph 59 / 59°F 87% 1010 mb
Low level cloud: 1%
Mid level cloud: 8%
High level cloud: 0%
Most Significant Cloud Type: medium
9%
0.0 In
12:00

SW
SW

 17 / 36 mph 76 / 78°F 54% 1008 mb
Low level cloud: 0%
Mid level cloud: 2%
High level cloud: 0%
Most Significant Cloud Type: medium
3%
0.0 In
18:00

SSW
SSW

 11 / 22 mph 81 / 82°F 49% 1005 mb
Low level cloud: 0%
Mid level cloud: 19%
High level cloud: 0%
Most Significant Cloud Type: medium
19%
0.0 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