Model Guidance Trending a Little Later With Arrival of Halloween Showers & Storms – Timeline of What to Expect

Halloween…it’s right around the corner and everyone is finalizing their costumes and trick-or-treating plans. Unfortunately we may be contending with some showers and a few storms around prime trick-or-treating time in parts of the Tennessee Valley.  We’ve been talking about this storm system and the potential for storms on Halloween for several days and now and model guidance continues to come into better agreement on timing, but there are still some discrepancies.  As of right now, it looks like the main line of showers and storms will likely move into northwest Alabama sometime late Thursday afternoon/early evening.  Below are two images of both the European (ECMWF) and GFS model guidance valid 7:00 pm Thursday evening, showing the main line of storms already in northwest Alabama.

Rain will likely start crossing the state line into northwest Alabama between 5:00-6:00 pm, but that time frame could easily change.  Unfortunately an hour/two difference in shower/storm arrival can mean a BIG difference in Halloween plans, which makes forecasting this storm system extremely tough.  Below is our most recent thinking for how things will play out Wednesday night into Halloween.  It is important to understand that the timing could change between today and tomorrow and will likely change between now and Halloween.  Right now we are just trying to give you an idea of what to expect, so you can be prepared for a dry or wet forecast.

Wednesday Night:

Clouds and moisture will continue to increase ahead of the approaching storm system, with a strong southerly wind Wednesday night pumping in moisture from the Gulf of Mexico.  Dew points are expected to rise into the low to mid 60s by Thursday afternoon and evening (indicated by the meteogram below), adding more fuel for storm development and substantial downpours.

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Halloween (Thursday):

It will be a mild morning for late October standards, with many towns starting out the day in the low to mid 60s, thanks to stout southerly wind, which will increase throughout the day.  A sustained wind of 20-30+ mph is likely, with higher gusts possible, which means a wind advisory will likely be needed.  Wind speeds will be even greater in the higher terrain of northeast Alabama and the issuance of a high wind warning could become necessary.  Below is a look at the the forecast wind speeds over the next several days, with the circled area highlighting gusts greater than 30-40+ mph Thursday afternoon and night.

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A few showers will be possible ahead of the main line of showers and storms, with the bulk of the rain expected to hold off until the late afternoon/evening.  As stated above, the main band of rain will likely move into northwest Alabama between 5:00-6:00 pm and track east through the rest of the Tennessee Valley during the evening and overnight.  This means trick-or-treaters could get an hour or so of trick-or-treating in during the mid-late afternoon time frame.  Again a one to two hour timing difference with the onset of rain will make a huge impact between an hour or two of dry trick-or-treating time, or a washout in northwest Alabama.  If you live west of I-65, it will be a good idea to have and indoor contingency plan in case showers and storms move in earlier, but keep in mind rain may hold off until later in the evening as well.

Towns, especially east of I-65 may sneak by with two or more hours of dry trick-or-treating time, before the showers and storms roll in, the key word is “may”, it’s not a guarantee by any stretch.  Showers will remain possible ahead of the main band of rain.  No matter where you live, you need to prepare for the possibility of rain during prime trick-or-treating time.  Showers and storms will gradually shift east overnight and taper off Friday morning.

Strong/Severe Potential:

The Storm Prediction Center has outlined and area of concern in their Day 4 Severe Weather Outlook, that includes northwest Alabama, but the threat for severe storms still remains minimal for the Tennessee Valley.

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The best dynamics with this storm system will be well to the north of the Tennessee Valley, with a somewhat weakening trend as the storms progress east.  There will be a higher chance for strong storms in Mississippi and Tennessee, but a few strong or isolated severe storms cannot be ruled out, especially in northwest Alabama, mainly due to high wind.  Heavy rain and frequent lightning will be likely as the band of rain moves through.  Rain totals will range mostly between 0.75-1.50, to up to 2.0″+ in communities that get under the heaviest downpours.

- Jennifer Watson

Twitter: @JWatson_Wx

Facebook: Jennifer Watson WHNT