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Sunday Evening Weather Blog: Marvelous Monday then Wet Wednesday?

By: Meteorologist Ray Hawthorne Email
By: Meteorologist Ray Hawthorne Email

A large dome of high pressure extending from the Red River Valley of Minnesota and North Dakota all the way to the Northern Gulf of Mexico will supply us with fair conditions tonight and Monday. A weak cold front moved through the area late Saturday night, but it brought some very dry air into the region. In fact, the relative humidity dropped to between 10 and 15 percent in several locations Sunday afternoon! There is another weak cold front stretching from the Virginia Capes through North Georgia and Alabama on its way to the Arklatex region. The air behind this second front is even drier (if one can believe that). Dewpoints are in the single digits above and below zero over parts of the Tennessee Valley into the Midwest behind it. The numerical models forecast this new front to make it into South Georgia before it stalls out and loses its identity on Monday morning. There is no moisture for this thing to work with, so rain is out of the question. Instead, a weak pressure gradient will cause nearly calm winds under clear skies and dry air overnight into early Monday. These are the ingredients that cause temperatures to plummet and I do expect a light freeze (generally 2 hours or less) in the low-lying areas away from downtown and the coast. Patches of frost should also form since the temperature will fall to near the dewpoint.

There are two systems we are going to watch going into midweek. The first is an upper-level low now over Baja California. Some high clouds well ahead of this system are expected to move into our area late Monday afternoon. These clouds will slowly lower and thicken Monday night and Tuesday. The upper-level low will weaken quite a bit as it approaches us on Tuesday and a lot of the lift generated by it will go toward removing the pre-existing dry air in the atmosphere. As a result, just scattered showers are anticipated (at most) by late in the day. This same disturbance may have better moisture and instability to work with over the Florida Peninsula, where a cluster of heavier rain and thunderstorms could develop. Many of the models forecast this cluster to move toward the coastal Carolinas Tuesday night and Wednesday.

The second shortwave is now over British Columbia. It is expected to dive into the Southern Plains before scooting eastward along the Northern Gulf coast on Wednesday. Upward vertical motion out ahead of this disturbance would give us a better opportunity of showers and perhaps thunderstorms Tuesday night into Wednesday morning. The complicated part of this forecast is this: how much moisture will the first system (read above) "steal" from the second system? That is always hard to judge, especially 2 or 3 days in advance. The Storm Prediction Center in Norman, OK, backed off on the severe weather threat over our area. The first system would be most likely to produce severe convection over the Florida Peninsula where the air will be most unstable and the deep-layer wind fields will be strongest. However, the latest GFS run does show weak instability ahead of the second shortwave on Wednesday morning. The vertical wind profiles are favorable for rotating updrafts, so we'll have to see if future model runs continue to point toward some destablization, but that is questionable at this point.

Sunshine, dry air, cool mornings and seasonably warm afternoons are on tap for Thursday and Friday. So as it stands now, the weather is looking good for you and your lover on Valentine's Day (that's Thursday if you've already forgotten!)

One more quick thing that I will delve into during later blogs: many of the models are showing another strong Pacific system approaching us next weekend.


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