August

National Weather Service Grand Forks

Weather & Climate Review

August-September 2020

Table 1 August 2020 Temperature and Precipitation Statistics

Figure 1

August Daily

Departure from

Normal

Temps at Thief

River Falls, MN

Blue Bars = Colder than Normal Days & Red Bars = Warmer than Normal Days

Table 1 shows the August average temperature (AveT), departure from normal temperature (TDept), precipitation (Pcpn), departure

from normal precipitation (PDept), and snowfall (Snow) for 10 climate stations. The August average temperature was pretty close to

normal at all sites. Precipitation amounts were variable, from 0.79 inches at Devils Lake to 5.07 inches at Bemidji. Figure 1 plots the

daily departure from normal temperatures in August 2020 at Thief River Falls, MN. There were a fair number of cooler than normal

days between August 1st and 17th. This was followed by a little over a week of above normal temperatures (August 19th-26th).

At Fargo-Moorhead (our longest running climate site), no record events occurred in August. Records

Figure 2 August Observed Precipitation Figure 3 August Percent of Normal Precipitation

Figure 2 gives an August precipitation estimate for all of eastern North Dakota and the northwest quarter of Minnesota. The most

precipitation (5 to 15 inches) fell across southeast North Dakota into adjacent areas of northwest and west central Minnesota (red

and magenta colors). To show how variable summer precipitation patterns can be, the two black circles in Figure 2 show how close

the highest (magenta/10-15 inches) and lowest (light green/0.50-1.00 inches) precipitation areas are to each other. Figure 3 shows

the August precipitation as a percent of normal. The higher precipitation totals (red and magenta colors in Figure 2) were about

200 to 400 percent of normal (dark blue to magenta colors in Figure 3).

FARGO FARGO

In Table 1, (ND) DVL = Devils Lake, NWS GF = NWS Grand Forks, GFK

= GF Airport, RDR = GF Air Force Base, FAR = Fargo, (MN) BDE =

Baudette, PKD = Park Rapids, BJI = Bemidji, TVF = Thief River Falls,

Y63 = Elbow Lake.

Temperature Precipitation

Figure 4 CPC Temp Outlook Figure 5 Observed Temp Figure 7 Observed Pcpn

The August temperature (Figure 4) and precipitation (Figure 6) outlooks issued by the Climate Prediction Center (CPC) in late July

are shown above. Compare these with the observed August departures from normal temperatures (Figure 5) and precipitation

(Figure 7).

Figure 8 Monthly Departures from

Normal Temps at Fargo, ND Figure 9 Monthly Departures from

Normal Pcpn at Fargo, ND

The monthly average August 2020 temperature was pretty close to

normal at Fargo (Figure 8). After a drier than normal May and June at

Fargo, July and August both had above normal precipitation (Figure

9).

Looking at just the Fargo climate site (FAR), Figures 8 and 9 show how August 2020 fits into the previous 5 months.

Figure 8 plots the monthly departures from normal temperatures at Fargo. The blue bars represent months that were

colder than normal, while the red bars represent months that were warmer than normal. Figure 9 plots the monthly

departures from normal precipitation at Fargo. The green bars represent months that were wetter than normal, while the brown

bars represent months that were drier than normal.

6 Month

Trend

Figure 6 CPC Pcpn Outlook

Convective Warnings

In August, 83 Severe Thunderstorm, 18 Tornado, and 8 Flash Flood

Warnings were issued by the NWS in Grand Forks (Figure 10). On

August 14th, surface low pressure moved across South Dakota into

western Minnesota (Figure 11). During the mid-afternoon, five dis-

tinct tornadoes occurred over Grant County, Minnesota (a Mayville

radar image from 3:37 pm is shown in Figure 12). Of the five torna-

does, there were three EF-0 tornadoes, 1 EF-1 tornado, and 1 EF-2

tornado. The EF-2 tornado tracked about 14 miles, from 9 miles

west of Barrett to 6 miles east-northeast of Elbow Lake. The torna-

do snapped or uprooted numerous trees, snapped several power

poles at 4 different locations, and chewed up corn fields. Figure 10 Number of August 2020 Convective Warnings

Figure 12 Mayville Radar 3:37 PM August 14, 2020 Figure 11 Surface Map 1 PM August 14, 2020

The latest Climate Prediction Center (CPC) temperature (Figure 13) and precipita-

tion (Figure 14) outlooks for September 2020 are shown to the left. For eastern

North Dakota and the northwest quarter of Minnesota, the CPC is forecasting high-

er probabilities for below normal temperatures and precipitation.

Figure 13 Temperature Figure 14 Precipitation

September

Last Year

&

Normals

Table 2 September 2019 Temperature and Precipitation Statistics

Figure 16 Normal Temps September 1 Figure 19 September 2019 Data Figure 17 Normal Temps September 30 Figure 18 Normal September Pcpn

As a comparison to normal values, Figure 19 shows various observed data from last September (2019). As an example, in Fargo

(FAR), 4.47 inches of precipitation (green box) fell. The highest temperature was 88 degrees (red number), while the lowest tem-

perature was 33 degrees (blue number).

So what are normal temperatures in September? Figure 16 shows normal highs and lows on September 1st for selected cities

across eastern North Dakota and northwest Minnesota. Figure 17 shows how normal highs and lows change by September 30th.

As an example, at NWS Grand Forks on September 1st, the normal high is 76 and the normal low is 52. By September 30th at NWS

Grand Forks, the normal high falls to 63 and the normal low falls to 40. Figure 18 shows the normal precipitation amounts at the

same sites as Figures 16 and 17. As an example, the normal precipitation at NWS Grand Forks in September is 2.05 inches.

Figure 15 September 2019 Convective Warnings

Per Table 2, September 2019 average temperatures were above normal at every site but Devils Lake. Monthly pre-

cipitation amounts were above normal at every site, but especially at NWS Grand Forks. This was the start of the

wet fall. September 2019 was a fairly busy month for convective warnings (Figure 15), with a total of 50 Severe

Thunderstorm, 5 Tornado, 11 Flash Flood, and 7 Areal Flood Warnings issued. The busiest period was September

20th-21st.

B

Miscellaneous

The winning picture in our August photo contest (a shelf cloud) was taken by Cori Greendahl Morberg (Page 1, top right). Does it

seem like this summer has had a lot of active weather? The statistics prove it. From Figure 20, 2020 has had a total of 352 Severe

Thunderstorm, Tornado, and Flash Flood warnings, the most since 2010 (which had 311). Figure 21 looks at just Severe Thunder-

storm and Tornado warnings, and goes back to 1986. It shows that 2001 and 2002 were the busiest years, and were back-to-back.

2001 had 452 warnings and 2002 had 393 warnings.

Figure 20 Warning Numbers 2010-2020

352

Total

311

Total

Figure 21 Warning Numbers 1986-2020