Wednesday Midday Forecast Thoughts

Late this morning, visible satellite imagery shows a clear sky with just a few high level, wispy cirrus clouds across the state of Mississippi. A southeasterly wind flow, however, will gradually increase our moisture content over the next couple of days; subsequently, we'll see a gradual increase in cloud cover by the end of the week in advance of our next storm system. 

An active southern branch of the jet stream has established itself from California eastward toward the nation's midsection. Some ridging is seen trying to nudge in from the southeast, so temperatures will actually warm up slightly through the end of the week. We'll see readings near 70 degrees by your Friday! 

By Saturday, a strong upper-level trough will be evolving across the eastern half of the country, sending a strong cold front our way. Moisture will have increased throughout the week, so some showers are possible especially Saturday morning. However, the big story is the cold blast of air that will accompany this cold frontal passage. 

MOS is not handling this bout of cold air well at all. I think raw guidance has a much better handle on the situation. Strong arctic high pressure (~1038mb) will build in behind this front, and lows Sunday morning will dip well down into the 20s! 

It looks like we have some interesting weather issues setting up next week. Of course, this is a week out, but models agree on a low pressure moving northeast along the Gulf Coast during the middle of the week next week. The GFS (shown above) shows some precipitation on the backside of the low.

A quick peek at forecast soundings show a saturated dendritic growth zone, but some warming and drying in the 1-2km layer. However, we are saturated at the surface as well as below freezing. So, based on this sounding alone, I would expect some freezing drizzle or light freezing rain as the system ejects to the northeast. It should be noted that the Euro has a similar setup, except it's a good 6-12 hours faster than the GFS…so I'll be watching trends throughout the week and providing more updates as the weather situation gets clearer! 

Have a great hump day Wednesday! 

IW

Friday Midday Forecast

We've certainly had a rainy start to our Friday across the GTR as rain has filled in nicely across the area this morning. Why all this rain? 

Here's the 500mb vorticity analysis. There is a short wave in the mid-levels of the atmosphere, and the associated fort max is located on the AR/LA border. Significant downstream uplift from this feature is likely driving force  for the rain this morning. 

Also, if you notice in the surface observations, a weak surface low seems to be spinning up over parts of southwestern Alabama, just to the southeast of Meridian, MS. Additionally, a psuedo-warm front-type structure extends to the northeast, and moisture is, in essence, overrunning this feature and is also combining with the aforementioned uplift to produce widespread rain this morning. 

Here's the potent shortwave for the last part of the weekend. Notice a slight negative tilt to the trough, with over a 100kt wind max in the base of this trough that is progged to spread across the Ohio River Valley. 

This shortwave will bring some severe weather from the Tennessee Valley all the way to the Great Lakes. 

The primary dynamics associated with this system will be well to our north, but the SPC has included us here in the GTR in their standard slight risk of severe weather. An analysis of the severe weather parameters reveal, again, the highest threat will be to our north. 

But, instability will be higher (relatively) than the past few events we have. Forecasted CAPE values are between 500-1000 J/KG but with weaker dynamics. 

The 0-6km shear values are much higher to our north, but notice the shear vectors are due west across our area. This suggests the deep layer wind field will be flowing across the approaching frontal boundary, so isolated supercell storms seem to be the most probable convective mode, especially for areas in north MS into the Ohio River Valley. 

For us here in the GTR, I can't rule out an isolated severe storm, but the highest threat will be in areas to our north. 

Have a great Friday, and stay dry!

IW

Monday Afternoon Forecast Thoughts

We're enjoying a very pleasant, warm day across the GTR and really the entire Southeast. The sky is mostly clear and it feels great. But notice off to our northwest the blue dots and much colder temperatures; that's associated with a frontal system that will be bringing in the coldest air so far this Fall season to our area by the middle of the week. 

The NAM/GFS are in remarkable agreement through the middle of the week with the timing of this frontal passage. I think we will see clouds increase overnight tonight into tomorrow morning, but with such dry air in place, I don't see much chance of rain…but I suppose a sprinkle is possible! 

Also notice the very strong (1044mb) area of high pressure building in behind this front. That strong pressure gradient that results will cause our winds to be rather gusty tomorrow, maybe exceeding 20-25mph at times. Temperatures will also be struggling to get out of the 50s with strong cold air advection. 

The GFS/NAM also are in good agreement with the temperature forecasts as well. With the core of the high pressure not too far to our northwest, and a clear sky, radiational cooling will be highly effective in lowering our temperatures into the upper 20s area wide Tuesday night. The only potential caveat to this freeze would be the winds staying up higher than forecast overnight which would probably result in temperatures reaching the low 30s but creating wind chill readings well down in the lower 20s. 

This high will be firmly entrenched across the Southeast. As a result, we'll see another night (Wednesday) of sub-freezing temperatures across the GTR. Both evenings we should see temperatures range from 25 to 30 for most spots, so take preventive measures to protect sensitive plants or pets. 

It looks like the pattern will get a little progressive toward the weekend. The cold conditions will not last long, and we'll see temperatures rebounding into the 60s and upper 60s by Saturday. The flow aloft will evolve to southwesterly, and it looks like individual pieces of energy could bring some rain chances to our forecast late Friday lasting through the first part of next week, stay tuned! 

IW

Thursday Morning Forecast Thoughts

The parent trough that brought us the showers last night has since lifted well of to our north and east this morning. However, the base of the trough still is close enough to our area, and when combined with subtle PVA remaining, some clouds are hanging around and will likely persist through the overnight hours. However, they are certainly not widespread and we've got about a 95% blue, sunny sky! 

High pressure is forecast to be right on top of us tonight. With efficient radiational cooling and calm winds, temperatures will bottom out in the mid 30s for most locations. But, I wouldn't be surprised to see some areas of north-central Mississippi get close to the freezing mark! 

By tomorrow, the GFS is forecasting more of a flat ridge in place across the area with a piece of energy associated with the subtropical jet over the Gulf of California. Friday should be a nice, sunny day with moderating temperatures with highs in the 60s; it should feel fantastic! 

By Saturday, despite a very dry low level airmass, some mid-level PVA associated with the aforementioned piece of energy in the Gulf of California will bring us some clouds by Saturday, but no rain is expected thanks to the dry surface airmass. 

The GFS is forecasting a fairly strong long wave trough over the eastern half of the country by the first part of next week. Because moisture return will be weak, albeit nonzero, we probably can squeeze out a few showers but for now, no widespread rain is expected. 

Looking ahead past this trough, the NAO is forecasted to go mostly negative once again. The Euro and GFS both suggest very strong high pressure associated with a rather cold airmass by the middle and end of next week, which would support this negative NAO forecast. Some of the raw temperature guidance suggests we'll be well down below freezing into the 20s! Brrrr! We'll watch things, stay tuned! 

IW

Monday Morning Forecast Thoughts

Visible satellite imagery shows a fetch of clouds representing a channel of low and mid-level moisture originating in the eastern Pacific. This is in advance of our next storm system that is organizing over the Four Corners region. 

A longwave trough will be evolving eastward by Tuesday while a ridge of high pressure in the mid-levels of the atmosphere will be anchored over the Florida Peninsula. This type of setup favors a funneling of moisture in from the eastern Pacific, and this is already seen in visible imagery shown above.

Meanwhile, the low-level airmass will remain dry through at least Wednesday. You can see the cold front off to our west and associated showers. Notice the tightly packed isobars across the GTR/Southeast - this suggests slowly retreating high pressure and a residual wedging effect, especially for areas just to our east. 

So, through Wednesday, all of our clouds will be high based into the mid/upper levels of the atmosphere thanks to the dry characteristics of the low level airmass. 

Most models agree that a band of rain will work in here Wednesday evening into the predawn hours of Thursday. Models aren’t quite as bullish on overall precipitation this go-around as they were last week, but they might be undergoing it just a tad (I’ll show PWATs below). By the same token, the models could actually be spot on thanks to the relatively delay in our surface moisture flux that will not commence until Wednesday afternoon. 

Still, we cannot ignore these high PWAT values (exceeding 2” here in the GTR). But also, just like last time, this might be an event where the heaviest rain will be confined to the Delta of Mississipppi into southwest MS/central Louisiana. 

Behind this system, strong high pressure builds into the Tennessee Valley Friday morning. This will likely lead to temperatures falling to around 40 or into the upper 30s, marking the return of the crisp, cool feeling we saw this past weekend!

IW