The Hagerstown Almanack Monthly Weather Column

Hot and dry weather has punished western Maryland and the Potomac Highlands so far this summer, so is that a sign of what is next in August?

Following a negative phase of the Pacific North America pattern in the spring, a big flip to a positive phase occurred in June. It has remained strongly positive, except for a few dips. There is a strong signal for a warm summer in the Mid-Atlantic with a positive phase of this oscillation pattern. It allows the Bermuda high to ascend on the East Coast instead of being displaced farther off the coast. This also puts a lid on rainfall, which has contributed to our drought.

The Pacific North America pattern (PNA) looks to remain in a positive phase, with a few abbreviated dips in August. The signal for warmth is not as strong with a positive PNA in August, but it will contribute to the overall temperature regime.

Also, what happens in the Pacific is also influencing our weather. The Western Pacific Oscillation has gone far into the negative territory in July and contributed to our hot weather. The outlook calls for this pattern to continue into August, but not to the same magnitude as July. This is another factor, besides the Pacific North America Pattern, that would favor above average temperatures into August.

We’ve been straddling the neutral zone for ENSO (El Nino Southern Oscillation) and finally look to plunge into a weak La Nina by the end of August. The transition into La Nina favors warmer than average temperatures in August. The bigger question to answer is if we will make up for a lackluster summer in terms of rainfall. The teleconnection signals show we will finally see much needed rainfall, but historically, it takes a boat load of rain and cooler than average temperatures to completely break free from drought.

Following a lull in the tropics for the end of July, there are signs that Saharan dust will dissipate and favorable environmental conditions will allow for more tropical development in mid-August. We are much more likely by the end of August to benefit from tropical moisture, especially if it teams up with an approaching front or mid-latitude system.

The low down is that August will be warmer than average, but we will be visited by a couple of cold fronts to break the hot weather. The coolest period will be 20-24, which coincides with the highest frequency of the coolest morning and afternoon temperatures based on past observations. The hottest days will occur around August 6, 15 and end of August after the 24th. The drought, though, won’t completely break in August, so watering the garden will be a necessity.

While the grass will start to rejuvenate in patches, the leaves that have already changed color won’t revert back to luscious green. The streams and rivers will finally move away from near record low-levels, but we don’t see a risk to them returning to average by the end of August. The summer drought will likely contribute to an abbreviated, early foliage season with far less colors than the past two years.

A national perspective on what I believe will transpire with the weather includes the following: Drought-busting rain will likely sweep across the Lower Mississippi Valley, Southeast Atlantic Coast and Tennessee Valley. Afternoon temperatures will trend closer to average from Nashville, Tenn., to Miami. The frequent showers and storms will be brought on by a couple of cut-off southern troughs and likely at least two tropical systems. We will see Debby and Ernesto, perhaps Francine make headlines during the latter half of August.

 

While the southern Plains will also turn soggy, dry, hot weather will grip the Corn Belt to the northern Rockies in August. Drought development is likely along and north of I-70 while parts of the Texas Rio Grande Valley will see improving drought conditions.

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