Update: Wednesday, 3 March: 1:00 p.m.
The shortwave is slowing down in the models..not ejecting into west Texas until after dark on Sunday evening. If these trends are correct then much of central and western Texas will simply see a thick deck of low level clouds and a bunch of rain on Sunday. Any severe potential won’t occur until after dark as the shortwave moves in from the west.
As the shortwave ejects into eastern Texas/Louisiana on Monday there may be some severe potential there. But timing is clearly an issue, so it’s too early to talk about anything specific.
You know if I’m spending this much time talking about marginal setups a week in advance now, I can’t imagine how I’ll handle this blog once classic Spring setups occur. Or maybe I’m just bored with the weather I get up here in New England for the next few weeks….
- Jim
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Update: Tuesday, 2 March: 2:00 p.m.
Severe potential increasing for Texas on Sunday, but important questions remain unanswered…
The GFS Ensemble has been consistent in forecasting a shortwave to eject into the southern Plains on Sunday, March 7. The GFS Operational model has shown some inconsistencies, but the latest run (12z March2) is in line with the GFS Ensemble solution. Both bring a shortwave into western Texas by Sunday evening, with a surface low over eastern Colorado and a dryline over the high plains of west Texas. Deep layer shear would support supercells as well as possible tornadoes. However, moisture continues to be an issue. [Note: European models are slower to eject the shortwave and suggest it may not reach the southern Plains until Monday, but preference is placed with the GFS Ensemble solution.]
As mentioned in the previous update the Gulf of Mexico will be be robbed of quality moisture (surface dewpoints in the 60s) this week as strong cold fronts give it a beating (so to speak). But the southwestern Gulf will retain dewpoints in the upper 50s to lower 60s by Friday evening. Then all day Saturday and all day Sunday southeasterly flow is expected at the surface from the western Gulf into Texas. This will allow for low level moisture to ride up the high terrain of southern and western Texas by Sunday afternoon/evening.
As a result the GFS is forecasting low to mid 50s dewpoints to reach the lower Texas panhandle/southwestern Texas (Midland to Lubbock line) by late Sunday afternoon. The moistening boundary layer combined with 500mb height falls in the afternoon/evening ahead of the shortwave should contribute to modest CAPE, supportive of severe storms given the deep layer shear. {Note: Low to mid 50s dewpoints are supportive of supercells and tornadoes over the high terrain of west Texas known as the caprock. In this area, and other areas of the high plains, excessively high dewpoints are not necessary to support supercell thunderstorms and even tornadoes.}
But alas there is a big problem – low level cloud cover. As low to mid 50s dewpoints surges into southern, central and western Texas Saturday night into Sunday a thick low level cloud deck will form. This is even more evident given the high soil moisture values present across much of central and southern Texas. The GFS indicates this with it’s high 850mb relative humidity values on Sunday across Texas. It also develops lots of precipitation along and just north of the nose of the low level moisture Sunday morning through midday Sunday.
But one good thing I can say about cloud cover is according to the GFS there won’t be a cirrus deck over western Texas, as the models indicates a clear slot moving through by midday.
So if the early March sunshine can erode the thick, low level cloud deck over western Texas on Sunday then there’s the potential for supercells (and maybe even tornadoes) to fire along the dryline over west Texas. There’s a lot going against this setup, but the potential is there.
Stay tuned…..
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Update: Monday, 1 March: 10:00 a.m.
Moisture hope…
One thing I completely neglected to consider was the current soil moisture anomalies across the southern Plains and the Gulf Coast. See the image below for Feb 28 soil moisture anomalies. It’s very interesting to see very high soil moisture anomalies over Texas – in particular central to southern Texas. This is the region where low level moisture often times sneaks up from the western and southwestern Gulf.
Soil Moisture Anomalies February 28.
The Gulf is going to get beaten pretty bad over the next few days with strong cold fronts. But after looking at a few model solutions it appears the extreme southwestern Gulf will not take a direct hit. Below is the GFS surface dewpoints forecast for Friday evening (March 5). Notice how there are still 60F dewpoints over the southwestern Gulf. When moisture begins the painful process of trying to lift north and northwest over the weekend, these 60F dewpoints will have the luxury of advecting over very wet soil in southern and central Texas. This presents more hope for adequate moisture to support severe potential on Sunday, March 7 ahead of the shortwave across the southern Plains.
GFS surface dewpoints forecast valid Friday evening March 5 (00z March 1 run)
- Jim
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Sunday, 28 February: 9:30 p.m.
Well it’s interesting that the GFS Operational model is forecasting a strong storm system to dig in the Plains the weekend of March 6 and 7. This storm system is a product of an active southern jet stream thanks to El Nino. Some storm chasers are already getting pretty excited about the potential for a chase day somewhere across the southern Plains the weekend of March 6/7. I can’t blame them either. It’s been a long, cold winter for many and we are all more than ready for the first good chase setup of the Spring.
Below is the 12z Feb 28 GFS Ensemble mean surface pressures forecast for Sunday evening on March 7. It is forecasting a pretty deep surface low over the central Plains, which would bring the potential for a decent chase setup across much of the central to southern Plains if enough boundary layer moisture can return north from the Gulf of Mexico.
GFS Ensemble mean surface pressures from 12z Feb 28 valid Sunday evening, March 7
But current dewpoints (see image below) across the Gulf of Mexico range from the 30s over the northern Gulf to the lower 60s across the southwestern Gulf. Meanwhile over the next five days strong cold fronts are expected to further starve the Gulf and even Caribbean from deep moisture. The sea surface temperatures are even running a bit below normal, which means it will take longer than normal for constant sunshine over the Gulf to result in rich dewpoints.
Surface dewpoints valid Sunday evening February 28
So for now I’m not too optimistic about the severe potential around March 6-8 across the Plains, but we’ll see. Things can change and moisture can sometimes return in surprising ways.
Stay tuned…..
- Jim
