Almanack Weather Prognosticator Chad Merrill
August: Return of Beneficial Rainfall
July 30, 2022 - Inflated water bills to keep up with the lack of rainfall best describes the summer of 2022. As we look ahead to August, what are the main driving weather patterns for western Maryland and the Potomac Highlands and are heat and dry weather relief on the way?
The main mechanism driving the pattern so far this summer is a continuation of La Nina, the cooling of the Equatorial Pacific. Historically, La Nina summers bring less than average rainfall to western Maryland and the Potomac Highlands. There is light at the end of the tunnel, however. Reviewing analog or best matching previous La Nina patterns in August shows the likelihood of near to above average rainfall. Cumberland averages 3.2 inches in August while Garrett County typically sees 4.0 inches of rain. This also matches the most recent decadal trend for August rainfall in the region. Five to six out of the last 10 years measured more rainfall than average in Garrett and Allegany county.
The Atlantic tropics have been unusually quiet since very short-lived Tropical Storm Colin developed along the Carolina coast in early July. There will likely be an influx of tropical systems in August. On the list of names, we should at least get to Fiona by the turn of the calendar to September. We expect moisture from one of the southern-tracking systems to team up with a front and bring downpours to the northern Appalachians, best chance around August 22-23.
Cumberland averages a high temperature of 86.1 degrees in August and Oakland typically sees a monthly average high temperature of 78.5 degrees. There is a total guarantee based on recent climatology and La Nina trends for warmer than average high temperatures in August. Additionally, there is a strong signal for a positive phase of the East Pacific Oscillation through mid-August. This favors well-above average temperatures from the Great Lakes to the Mid-Atlantic and Northeast. The oscillation will become negative for August’s second half, which will promote a return to average temperatures.
As far as dangerously hot weather with heat indices exceeding 90 degrees in Garrett County and 100 degrees east of Route 36, we are targeting August 11 to 16 as the best chance for the hottest weather of the month. This coincides with the transition of the East Pacific Oscillation from a negative to positive phase.
The summer heat wave is setting records in the southern Plains. On several occasions earlier this month, the Electric Reliability Council of Texas (ERCOT) hit record peak demand due to the persistent dangerously hot pattern in the southern Plains. August offers no relief to the above-average temperatures in this part of the country either. The saving grace to break the heat wave would be a tropical system or stalled front, both of which would likely produce flooding rain.
Another pattern making national news headlines is the record wet monsoon in the Southwest U.S. Each year, a southerly flow develops in early July that brings an influx of moist air into the desert Southwest and produces daily occurrences of afternoon showers and thunderstorms. This year’s monsoon season got off to a running start in mid-June and has continued unabated through July. Rainfall in August will likely be near to above average, so the drought will continue to get chipped away in New Mexico and Arizona.
While the tropics will become active and likely three named storms will develop in the Atlantic basin, the prospect for a landfalling hurricane is quite low in August. As mentioned earlier, the most likely scenario to unfold is tropical moisture from a system offshore to get funneled into a front heading for the East. There doesn’t appear to be an upside risk for significant rainfall amounts in the Southeast from a tropical system in August.
What’ll unfold across western Maryland and the Potomac Highlands as we turn the corner to September and meteorological autumn? We’ll be tracking the patterns and provide our next monthly weather outlook update just as the kids head back to the classroom in late-August.