Tuesday, July 28, 2015

Heat Warning tomorrow, then watch for falling dewpoints!

As of early this afternoon, temperatures climbing into the mid 90s and high dewpoints (a measure of humidity) combined to meet the NWS definition of excessive heat (heat indices of 110°+), and the Heat Advisory that was in effect was upgraded to an Excessive Heat Warning. That warning continues through 8pm Wednesday, as we have one more very hot and humid day to deal with tomorrow. In fact, there's little relief overnight as the projected low in the city is 81°, which would tie the record warmest low temperature for July 29.

You've no doubt heard about the cold front that will move through the region Wednesday night. Many times in the summer, moisture and heat "pool" ahead of these fronts, resulting in hot and humid days. This is exactly what we expect tomorrow as temperatures once again reach the upper 90s with dewpoints in the mid 70s to near 80 in some spots in the Delta, making it feel much like it did today, if not a bit hotter!

So what about rain chances? Unfortunately, it appears the best chance of thunderstorms will remain to the east of the metro with only a slight (20%) chance locally on Wednesday and Wednesday night. Part of the reason for the low rain chance is that upper level high pressure will continue to be strong, limiting the support for storms, despite the presence of a front. Even the front itself will have little in the way of converging air along it, which would typically aid in making the air rise and increasing chances of storms.

The GFS computer model forecast at the jet stream level Wednesday evening shows the strongest wind well north of the area and a broad area of high pressure over the south-central U.S. The strong high will prevent any organized storms from affecting the region as the cold front passes.

The good news arrives Thursday as the front clears the area and drier air begins to push into the region. Temperatures will also peak about 5-7° lower than ahead of the front, so although it will still be hot (lower 90s), dewpoints will be a good 10° cooler, in the mid 60s. So rather than feeling like 110°, low 90s will FEEL like low 90s! I think we can live with that!

Looking towards the weekend, although temperatures will remain near or slightly above seasonal norms (lower to mid 90s), dewpoints & afternoon humidity values will remain below normal, so it should be a little easier to get the yard work done or get in a run! The long-range outlook continues the hot pattern into next week but with continued mid 60s dewpoints, thus heat indices should remain below the danger levels seen the past couple of weeks.

Be conscious of the heat for one more day, then we can look forward to hot without the humidity!

Erik Proseus
MWN Meteorologist

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