First Widespread Freeze Arrives; Wetter Pattern Sets In

By:  Aaron Wilson

Much of Ohio experienced frost or freeze conditions this past Friday and/or Saturday night. In fact, many locations dropped below 30°F (Table 1), with unofficial observations as cold as 26°F! How does this compare to typical first freeze dates?

Figure 1 shows the climatological median date (50^th percentile; 1980-2010) occurrence for the first 32°F in the fall. Ohio’s dates vary widely, as early as the last week in September in some of the colder valleys of the northeast hills (light blue) to as late as the first week of November (brown) in the far east. However, much of Ohio experiences first freeze during the second and third weeks of October. So, this year’s first freeze appears to be right on schedule across the north and a bit early for areas of southern and southwest Ohio.

Figure 1: Climatological date of median first 32°F freeze for the years 1980-2010. The median is defined as the 50th percentile.

Forecast

A stalled boundary is currently draped across Ohio. This boundary is providing a focus for shower activity, bringing the heaviest widespread rainfall that we have seen in Ohio since Labor Day. CoCoRaHS observations show that 0.5-1.25” of rain has fallen in the last 24 hours, with additional rain showers expected Monday night into Tuesday morning. This frontal boundary will lift north of the region by Wednesday afternoon, but not before providing the opportunity for additional showers through Wednesday morning. Highs will warm into the mid to upper 70s for mid to late week, perhaps even low 80s across the south on Thursday, with dry conditions expected through Friday morning. A strong cold front will approach the region on Friday, bringing a line of showers and storms through late in the day. Behind this front, much cooler air will filter back into the region, with highs in the 50s and 60s and overnight lows in the 30s and 40s expected this weekend.  The weekend should remain dry before damp, chilly conditions return early next week. The Weather Prediction Center is currently forecasting 0.50-1.25” of rain across most of Ohio for the next 7 days, with greatest totals in the far southwestern counties (Fig. 2).

Figure 2: Forecast precipitation for the next 7 days. Valid from 8 p.m. Monday October 19, 2020 through 8 p.m. Monday October 26, 2020. Figure from the Weather Prediction Center.

The latest NOAA/NWS/Climate Prediction Center outlook for the 8-14 day period (October 27 – November 2) shows below average temperatures and above average precipitation are likely (Fig. 3). Normal highs during the period are in the upper-50s to low-60s, lows in the upper-30s to low-40s, with about 0.85” of rainfall per week.

Figure 3: Climate Prediction Center 8-14 Day Outlook valid for October 27 – November 2, 2020 for left) temperatures and right) precipitation. Colors represent the probability of below, normal, or above normal conditions.