Monthly outlook for Markham, IL: average high 66.4°, average low 51.2°. That is 2.6° above the climate normal for October. Precipitation is expected on 3 days (about 0.5 inches), against a normal of 5 days and 1.7 inches. The warmest day looks like 16 October (81.6°), the coolest 22 October (43.1°).
66.4°/51.2°
Average high / low
+2.6°
Above normal
3 / 5
Wet days / normal
0.5 in
Precipitation this month
Ten-day blocks vs climate normal
Period
Forecast high
Normal
Difference
7 October – 16 October
72.1°
63.1°
+5°
17 October – 26 October
57.1°
58.5°
-0.8°
27 October – 5 November
at normal
54.8°
—
October records over 66 years
88.5°3 October 2025All-time high
26.1°26 October 1962All-time low
Climate normals and records are computed from the nearest reference point — Blue Island (4 mi).
Thu, 0870° / 54°0
70 °
Markham, Thursday, 8 October
Clear. High 70°, low 54°.
Pressure30.12 inHg
Wind5.4 mph NW
Humidity46%
Visibility6.2 mi
Dew point44°
Fri, 0972° / 50°0.01
72 °
Markham, Friday, 9 October
Light rain. High 72°, low 50°.
Pressure30.18 inHg
Wind7.4 mph SE
Humidity52%
Visibility6.2 mi
Dew point51°
Sat, 1080° / 59°0
80 °
Markham, Saturday, 10 October
Clear. High 80°, low 59°.
Pressure30.12 inHg
Wind8.7 mph S
Humidity54%
Visibility6.2 mi
Dew point57°
Sun, 1165° / 59°0.28
65 °
Markham, Sunday, 11 October
Rain. High 65°, low 59°.
Pressure29.91 inHg
Wind6.2 mph NE
Humidity91%
Visibility6.2 mi
Dew point59°
Mon, 1277° / 55°0.09
77 °
Markham, Monday, 12 October
Light rain. High 77°, low 55°.
Pressure29.83 inHg
Wind6.2 mph S
Humidity71%
Visibility—
Dew point60°
Tue, 1364° / 51°0.07
64 °
Markham, Tuesday, 13 October
Light rain. High 64°, low 51°.
Pressure29.94 inHg
Wind15.7 mph NW
Humidity60%
Visibility—
Dew point46°
Wed, 1461° / 51°0
61 °
Markham, Wednesday, 14 October
Partly cloudy. High 61°, low 51°.
Pressure30.21 inHg
Wind7.8 mph E
Humidity43%
Visibility—
Dew point36°
Thu, 1574° / 50°0
74 °
Markham, Thursday, 15 October
Overcast. High 74°, low 50°.
Pressure29.97 inHg
Wind13.9 mph S
Humidity31%
Visibility—
Dew point35°
Fri, 1682° / 58°0.02
82 °
Markham, Friday, 16 October
Light rain. High 82°, low 58°.
Pressure29.80 inHg
Wind13.1 mph W
Humidity57%
Visibility—
Dew point63°
Sat, 1758° / 48°0
58 °
Markham, Saturday, 17 October
Partly cloudy. High 58°, low 48°.
Pressure30.00 inHg
Wind12 mph W
Humidity50%
Visibility—
Dew point38°
Sun, 1852° / 47°0
52 °
Markham, Sunday, 18 October
Overcast. High 52°, low 47°.
Pressure30.03 inHg
Wind13.3 mph W
Humidity66%
Visibility—
Dew point37°
Mon, 1958° / 44°0
58 °
Markham, Monday, 19 October
Partly cloudy. High 58°, low 44°.
Pressure30.15 inHg
Wind9.3 mph W
Humidity54%
Visibility—
Dew point38°
Tue, 2063° / 46°0
63 °
Markham, Tuesday, 20 October
Clear. High 63°, low 46°.
Pressure30.15 inHg
Wind9.2 mph NW
Humidity42%
Visibility—
Dew point36°
Wed, 2155° / 48°0
55 °
Markham, Wednesday, 21 October
Partly cloudy. High 55°, low 48°.
Pressure30.30 inHg
Wind9 mph NE
Humidity45%
Visibility—
Dew point33°
Thu, 2257° / 43°0
57 °
Markham, Thursday, 22 October
Overcast. High 57°, low 43°.
Pressure30.30 inHg
Wind3.4 mph SE
Humidity39%
Visibility—
Dew point29°
From day 17 onward the outlook is built from 60-year climate statistics
Fri, 2359° / 46°0.13
59 °
Markham, Friday, 23 October
Climate normal for this date — 60-year average.
Average high59°
Average low46°
Average precipitation0.13 in
Chance of precipitation33%
Record high79° (1963)
Record low32° (1976)
Sat, 2458° / 46°0.12
58 °
Markham, Saturday, 24 October
Climate normal for this date — 60-year average.
Average high58°
Average low46°
Average precipitation0.12 in
Chance of precipitation40%
Record high78° (1963)
Record low27° (1981)
Sun, 2557° / 45°0.13
57 °
Markham, Sunday, 25 October
Climate normal for this date — 60-year average.
Average high57°
Average low45°
Average precipitation0.13 in
Chance of precipitation32%
Record high75° (1963)
Record low31° (2006)
Mon, 2656° / 45°0.11
56 °
Markham, Monday, 26 October
Climate normal for this date — 60-year average.
Average high56°
Average low45°
Average precipitation0.11 in
Chance of precipitation32%
Record high78° (1963)
Record low26° (1962)
Tue, 2756° / 44°0.09
56 °
Markham, Tuesday, 27 October
Climate normal for this date — 60-year average.
Average high56°
Average low44°
Average precipitation0.09 in
Chance of precipitation37%
Record high73° (2014)
Record low31° (1962)
Wed, 2856° / 43°0.06
56 °
Markham, Wednesday, 28 October
Climate normal for this date — 60-year average.
Average high56°
Average low43°
Average precipitation0.06 in
Chance of precipitation22%
Record high73° (1999)
Record low29° (1976)
Thu, 2956° / 43°0.06
56 °
Markham, Thursday, 29 October
Climate normal for this date — 60-year average.
Average high56°
Average low43°
Average precipitation0.06 in
Chance of precipitation20%
Record high79° (2024)
Record low30° (1980)
Fri, 3057° / 44°0.12
57 °
Markham, Friday, 30 October
Climate normal for this date — 60-year average.
Average high57°
Average low44°
Average precipitation0.12 in
Chance of precipitation30%
Record high78° (2024)
Record low29° (1988)
Sat, 3156° / 44°0.15
56 °
Markham, Saturday, 31 October
Climate normal for this date — 60-year average.
Average high56°
Average low44°
Average precipitation0.15 in
Chance of precipitation40%
Record high73° (1974)
Record low27° (2023)
Sun, 0155° / 43°0.18
55 °
Markham, Sunday, 1 November
Climate normal for this date — 60-year average.
Average high55°
Average low43°
Average precipitation0.18 in
Chance of precipitation43%
Record high73° (2016)
Record low23° (2019)
Mon, 0254° / 42°0.12
54 °
Markham, Monday, 2 November
Climate normal for this date — 60-year average.
Average high54°
Average low42°
Average precipitation0.12 in
Chance of precipitation40%
Record high73° (1961)
Record low25° (1991)
Tue, 0353° / 41°0.07
53 °
Markham, Tuesday, 3 November
Climate normal for this date — 60-year average.
Average high53°
Average low41°
Average precipitation0.07 in
Chance of precipitation25%
Record high72° (1987)
Record low19° (1991)
Wed, 0453° / 42°0.09
53 °
Markham, Wednesday, 4 November
Climate normal for this date — 60-year average.
Average high53°
Average low42°
Average precipitation0.09 in
Chance of precipitation27%
Record high71° (2015)
Record low18° (1991)
Thu, 0553° / 41°0.13
53 °
Markham, Thursday, 5 November
Climate normal for this date — 60-year average.
Average high53°
Average low41°
Average precipitation0.13 in
Chance of precipitation32%
Record high74° (1978)
Record low20° (1991)
About the monthly outlook
How accurate is a 30-day forecast?
The first 16 days come from weather models — reliable for the first 3–5 days and progressively less so after that. Days 17 through 30 for Markham, IL are built from the climate normal, the 60-year average, so they show typical weather for those dates rather than a specific forecast.
What does "above normal" mean?
We compare the forecast against the climate normal for those exact calendar days, computed from 60 years of observations. The deviation shows how much the coming month differs from a typical one.
Where do the 66-year records come from?
They are real temperature extremes recorded in Markham, IL since 1960: the highest and lowest reading for each calendar date, with the year it happened.
How often is it updated?
The forecast portion refreshes every hour; the climate portion is based on long-term data and stays stable.