Garrett’s Blog: Planning Around Halloween Rain

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Another weekend, another rain chance. Like last weekend, this system will also cause another round of heavy, soaking rain with over an inch possible.

The weekend system is still several days away but I wanted to share with you the current forecast trend to help you plan as the weekend gets closer.

Before we dig into the model precipitation, let’s take a look at what’s causing the rain.

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Saturday: Rising air in the atmosphere causes rain. Some of the highest ascent is found in the left-front and right-rear quadrant of pockets in the upper level flow called “jet-streaks”. The left-front quadrant passing over us in the overnight and the right-rear in the morning Saturday. High humidity from the Gulf is being pumped around the high pressure and into our area. This is a strong signal for high rain chances on Saturday morning (especially early) with a clearing from west to east as the trough of low pressure lifts to the northeast.

Saturday’s rain would be heavy and last for hours with a few rumbles of thunder and totals around 1-2″.

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Sunday: Another source of rising air is low pressure. An upper low will be directly overhead Sunday with more rain chances.

The rain on Sunday will be more scattered and won’t be as widespread as Saturday. It’ll also be of shorter duration.

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The rain forecast from the Weather Prediction Center is around .50-1.25″ over the next 5 days. The majority of which will fall on Friday night into Saturday morning.

And now to the model data; for extended forecasting we use “global spectral models” there are 2 leading models: The ECMWF & GFS. Both show rain this weekend but the timing is different.

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Saturday morning: Heavy rain in the area via the ECMWF model.

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Saturday evening: The ECMWF shows most of the rain gone. This scenario matches the upper wind data and seems most reasonable.

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Saturday morning: The GFS showing rain across the area lifting northeast

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Saturday evening: The GFS is developing another area of rain on Saturday night. With the absence of upper level lifting and the upper low still to the west… this solution seems questionable.

So… as of midweek, here’s what the forecast looks like. Keep in mind that better data will arrive with the short-term models later this week with the timing of the rain becoming more clear.

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