Many Heat Advisories have been issued for the Brazos Valley this summer due to the intense heat we've been experiencing due to prolonged high pressure overhead, but this week parts of the Brazos Valley will be under an Excessive Heat Warning. What's the difference?
Different weather service offices use different criteria, so it's possible that even when conditions are similar across the Brazos Valley, one area may be under a Heat Advisory and another an Excessive Heat Warning or nothing at all, so it's important to keep that in mind.
Put simply, an Excessive Heat Warning is more urgent than a Heat Advisory. It's generally (remember that different offices may have slightly different criteria) issued when a heat index over 105° is forecast for more than three hours for at least two consecutive days, or if a heat index of at least 115° is forecast at all. Also, when an Excessive Heat Warning is issued, you can expect overnight lows to only drop to around 80°. This doesn't give your body a chance to cool itself down easily and heat exhaustion or heat stroke is likely if you don't take precautions.
An Excessive Heat Watch is generally issued when Excessive Heat conditions are expected with in 36 hours. The Warning will usually be issued within 12 hours of the expected Excessive Heat. The Excessive Heat is expected Tuesday through Thursday.
As of Tuesday afternoon, Leon, Milam and Robertson counties are under an Excessive Heat Watch until Thursday evening. The rest of us are under a Heat Advisory.
Less severe, but still important is the Heat Advisory. In this case, heat indices are expected to reach at least 105 (or 108 depending on your forecasting office) degrees, but not greater than 115 for less than three hours per day and overnight lows are forecast to remain above 80° (or the upper 70s depending on your forecasting office).
For an Excessive Heat Warning to be issued, conditions have to be downright dangerous. If you don't have to be outdoors, don't be. If you do, try and limit outdoor activities to the morning or late evening hours when the heat won't be as intense. If you don't have air conditioning, try to spend the hottest hours of the day somewhere that does. Drink plenty of water and be sure to check on elderly neighbors and relatives.
Highs this week could be as high as 105 and heat indices will likely top out around 110 or even higher.