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When we talk about July in Texas, most folks think of heat, humidity, and the occasional afternoon spent by the pond or pool. That mindset is going to change dramatically tomorrow when a rare meteorological phenomena occurs. The jetstream, which rolls upper level disturbances into the area, is draped up across the northern plains of the United States and Canada. In this scenario, we would usually hot and dry conditions. However, something very unusual is occurring in the atmosphere which will bring a unseasonably high chance of rain and possibly record-low temperatures to parts of Texas by Sunday and Monday. An upper level low pressure system is currently across the southeast United States. This low pressure system is going to retrograde to the west and be in the area by tomorrow afternoon. This is unusual because weather systems in the northern hemisphere usually move from west to east, not east to west. In this case with the jetstream so far north, this low pressure system will move west. I’ll spare you the meteorological reasoning behind this movement, but needless to say it doesn’t happen to often in a Texas summer.
The exact track of this upper level low will be crucial as it will determine which locations will receive the highest rainfall accumulations. We can’t determine the exact path the system will take at this point as it will depend on atmospheric factors we aren’t able to track more than a few hours out. With that in mind, a widespread and heavy rainfall event is expected to occur beginning on Sunday. This 5 day rainfall forecast from the Weather Prediction Center indicates the current thinking. Don’t expect it to play out exactly as this graphic shows and there will be variations in location and intensity of rainfall.
By tomorrow afternoon, the afternoon run of the high resolution North American Model (NAM) indicates rain will be occuring across portions of North and Central Texas. Where rain is falling, temperatures will only manage to climb into the upper 70s and lower 80s. High temperatures could even end up setting new records… for being the coolest high temperature to occur in July!
Rainfall intensity and coverage will increase Sunday night. We could begin to experience localized flooding problems during this time, but we’re still too far out to determine exact locations or areas threatened. Don’t think just because we’re in a drought that flooding cannot occur. I do believe we may have areas experiencing flooding by Monday, so we’re on alert for that possibility.
We’ll be here covering this unusual rain event from beginning to end. With such a tropical-like air-mass in place, severe weather does not look to be a problem. We could see a few strong storms with small hail and gusty winds, but this type of pattern favors heavy rain verses severe weather. One thing I will watch closely is any training of storms overnight in one location. Should we end up with an area that has storm after storm move over it, the threat of localized significant flooding is there. We’ve had that happen plenty of times with past summer systems. Enjoy this rain event, they don’t happen too often in the summer!
Unfortunately, those in South Texas don’t look to get much from this system. Outside of areas that are socked in with rain and clouds, temperatures will remain in the upper 90s and 100s.