Potomac has chilly winters and warm summers. A typical July afternoon reaches 87°, a January night drops to 26°, and about 6 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normalsUpdated once a decade
☀️
July high
87°
139th coolest of 536 Maryland towns
❄️
January low
26°
254th coldest of 536 Maryland towns
💧
Rain + melted snow
44 in
153rd driest of 536 Maryland towns
🌨️
Snow a winter
6 in
29th least snowy of 508 Maryland towns
A normal year
What a year in Potomac feels like
❄️
Winter
45° / 28°
Typical high / low · 3 days with an inch or more of snow
🌷
Spring
65° / 44°
Typical high / low · Last frost around Apr 9
☀️
Summer
85° / 65°
Typical high / low · 44 days reach 90° in a normal year
🍂
Fall
67° / 47°
Typical high / low · First frost around Oct 31
10°
20°
40°
50°
60°
70°
80°
90°
100°
32°
42°
26°
46°
27°
54°
34°
66°
44°
74°
53°
82°
62°
87°
67°
85°
66°
78°
59°
67°
47°
56°
37°
46°
30°
JanJFebFMarMAprAMayMJunJJulJAugASepSOctONovNDecD
32°, freezingBar runs from the typical overnight low up to the afternoon high
Best months to be outsideAprMayJunSepOctHighs of 62–84° and lows of 40° or more
Month by month
Potomac weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
Month
High
Low
Rain + melt
Snow
Wet days
Snow on ground
30-yr range
January
42°
26°
3.0"
2.9"
10
2
26° – 41°
February
46°
27°
2.7"
1.4"
9
2
26° – 44°
March
54°
34°
3.7"
0.7"
12
1
38° – 54°
April
66°
44°
3.4"
0
11
0
51° – 60°
May
74°
53°
4.3"
0
12
0
59° – 70°
June
82°
62°
4.3"
0
10
0
68° – 77°
July
87°
67°
4.4"
0
10
0
72° – 80°
August
85°
66°
3.7"
0
10
0
70° – 79°
September
78°
59°
4.3"
0
10
0
65° – 73°
October
67°
47°
3.8"
0
9
0
53° – 63°
November
56°
37°
3.2"
0
9
0
40° – 52°
December
46°
30°
3.6"
0.8"
11
1
29° – 49°
Year
65°
46°
44.5"
5.8"
123
6
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain & snow
Rain and snow in Potomac
Potomac gets 44 inches of rain and melted snow a year. July is the wettest month and February the driest. Rain or snow falls on about 123 days a year. Snow covers the ground about 6 days of the year.
💧
44 in
Rain + melted snow a year
More rain than 67% of U.S. towns
❄️
6 in
Snow in a normal winter
Less snow than 78% of U.S. towns
⛄
6 days
With 1"+ of snow on the ground
Fewer than 72% of U.S. towns
Rain + melted snow by month
Inches of water
4.4"
JFMAMJJASOND
Snowfall by month
Inches of snow
2.9"
JFMAMJJASOND
Frost & the growing season
About 202 frost-free days a year
In half of years the last 32° night comes by April 9 and the first one by October 31. That leaves about 202 frost-free days for gardens, longer than 73% of U.S. towns.
🌱 Apr 9
🍂 Oct 31
202 frost-free days
JFMAMJJASOND
🥶
96
nights at or below 32° in a normal year
🧊
0
nights below 0° in a normal year
🔥
44
days that reach 90° in a normal year
Freezing nights by month
Average nights at or below 32°
JFMAMJJASOND
90° days by month
Average days at 90° or more
JFMAMJJASOND
Heating & cooling
Heating and cooling a home in Potomac
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Potomac, 77% of that work is heating and 23% is cooling.
🔥
4,506 heating degree daysLess heating than 74% of U.S. towns
❄️
1,338 cooling degree daysMore cooling than 74% of U.S. towns
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
Around Potomac
Potomac and its neighbors
Potomac borders 7 towns with climate data. January nights across them vary by 0.7°. Rockville has the coldest January nights (25°) and Cabin John the hottest July afternoons (88°). Potomac’s January low is 26° and its July high 87°.
Compared with every U.S. town and city on TownTapestry, each counted once.
Then and now
Warmer than it used to be
+1.7°1991–2020 average vs. the 20th century (1901–2000)
The last 30 years in Potomac averaged 1.7° warmer than the 1900s. The biggest change is in December (+2.9°). The shift is larger than in 81% of U.S. towns.
❄️ Winter+2.2°now 36°, was 34°
🌷 Spring+1.4°now 54°, was 53°
☀️ Summer+1.7°now 75°, was 73°
🍂 Fall+1.4°now 57°, was 56°
Change by month1991–2020 average minus 1901–2000 average, at Potomac’s spot on NOAA’s grid
+1.0°
+2.9°
JanJFebFMarMAprAMayMJunJJulJAugASepSOctONovNDecD
Year to year
How much a month can swing
A normal is an average, and real years wander around it. December swings the most: between 1991 and 2020 its average temperature ranged from 29° to 49°. September is the most reliable, staying within 7°.
20°
30°
40°
50°
60°
70°
80°
90°
JanJFebFMarMAprAMayMJunJJulJAugASepSOctONovNDecD
Coldest to warmest month in 30 yearsNormal
Questions
Common questions about Potomac’s climate
What is the coldest month in Potomac?
January, with a typical high of 42° and a low of 26°.
What is the hottest month in Potomac?
July, with a typical high of 87° and a low of 67°. About 44 days a year reach 90°.
How much snow does Potomac get?
About 6 inches in a normal winter, most of it in January.
When is the first frost in Potomac?
In half of years the first 32° night comes by October 31, and the last spring frost by April 9.
What is the rainiest month in Potomac?
July, with 4.4 inches of rain and melted snow. The year totals 44 inches.
📍Temperatures and rainfall come from NOAA’s gridded climate normals for Potomac itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Dalecarlia Rsvr, MD (7 mi) away. Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.