Plaincast

Messages

Scattered showers and thunderstorms continue this afternoon and evening. Heavy downpours and gusty winds are anticipated, but severe weather is unlikely.

Heat and humidity continue for the next several days. Temperatures and heat indices elevate through the weekend.

Discussion

Routine summer time programming continues for the region as high temperatures today reach just about seasonal normals although clouds and showers may slow the thermal ascent. A high over low block continues to dominate the pattern over the central CONUS. General southerly flow across the center of the country propels a gradual, yet continual, increase in warm air and moisture across the area.

Moisture transport is expected to expand northward today which when coupled with increased warm air advection and diurnally enhanced instability is likely to generate some air mass thunderstorms this afternoon and evening. Some subtle vorticity advection aloft and slight low level convergence will create just enough lift to initiate convective development. Shear and mid level lapse rates are fairly meager which curtails expectation of robust convection; however, abnormally high precipitable water values of 2-2.5 inches (>90 Percentile) do present an opportune environment for isolated heavy rain showers. These downpours could result in rainfall rates of 1-2 inches per hour, with locally higher rate possible, which may lead to some flash flooding and pooling from runoff. Storm motions are also quite slow which may exacerbate impacts of heavy rainfall. Storms are expected to be fairly pulse like with updrafts developing and raining out fairly quickly. Unfortunately, coverage of these storms is expected to be scattered so some may receive all of the rain and some none. The good news is those that receive the rain should experience a temporary cooldown from the heat as highs reach the 90s for most and heat index values reach 95-100 degrees. However, it is likely that post storm conditions will feel more muggy and uncomfortable as fresh rainfall evaporates. Rain chances through the rest of the week look fairly marginal. There is some indication for potential MCS activity mainly over the eastern parts of the region early Friday morning; however, much of the activity is expected to remain further east.

As the week rolls on ridging continues to dominate. The low over the US/MEX border shrinks and meanders southward. This continues the flow of warm air and moisture into the region steadily raising highs into the mid to upper 90s by the weekend. Heat indices raise in kind with expectations of around 100F by the weekend peaking around 100- 105F Monday. Current guidance suggests a 70+ percent chance of exceeding 100F heat indicies and a 25 percent chances of advisory level heat indicies on Sunday and Monday.

More of the same is expected in the extended forecast. Additional rain chances return with a passing system early Tuesday morning, but again, the main activity is expected to remain further east. Extended guidance does show a potential for a break from the heat mid next week as a dramatic push of cooler air is anticipated to move southward from interior Canada. This looks to significantly alter the pattern over the CONUS. However, with such notable impact expected at this forecast scale, it is important to account for potential deviations as those will significantly affect the long term outlook.