Bowling Green, along with much of the Mid South, continues to experience abnormally dry conditions. Since the first of the year, Bowling Green is experiencing a rainfall deficit of 3.42 inches, 2.44 of that deficit being since the first of March. Some much needed rain is on the way for this evening and into the early morning hours of tomorrow as well. This rain is in association with a cold front and a storm system tracking across The Great Lakes with an additional low centered over northeast Texas. Over the next 24 hours the front will track across The Mid South bringing light to moderate rain to much of the area. Some thunderstorm activity can be expected, but conditions are not favorable for severe weather. The SPC has a 5% risk delineated for much of the Contiguous United States east of The Mississippi River as well as the Southern Plains.
An overall quiet weather pattern has been in place for the past few days, with the jet stream over the northern tier of states in the Contiguous United States. In general this pattern reflects what is normally seen sometime around mid to late May as opposed to mid April. As today progresses, The GFS and the NAM want to progress a trough across The Plains, which could spell severe weather for The Red River Valley all the way north and eastward into southern Iowa including much of Oklahoma, a good portion of eastern Kansas, and a good portion of western Missouri. A standard Slight Risk is in place for these areas, from the SPC. As the week comes to a close, activity from this afternoon in The Plains along with the trough will increase rain chances for The Mid South. Rain chances are on the increase for Friday and into Saturday. No severe weather is expected with this activity, however, as the conditions are nowhere near favorable for such activity. This rain will, however, be a welcome sight as much of The Mid South is running abnormally dry.
On this date fourteen years ago, April 16, 1998, the city of Bowling Green was devastated by a very potent supercell thunderstorm that produced baseball-size hail. The storm developed in Logan County, and very quickly produced a tornado that would track across southern Warren County, clip the northern tip of Allen County, cross Barren River Lake, and track the entire width of Barren County before dissipating. The tornado produced F3 damage at its peak intensity. The long track supercell then produced a brief F2 tornado in Metcalffe County, produced another F3 tornado that raked across northern Adair County, and then produced another brief F2 tornado at the end of the track of the F3 in Adair County.
The F3 tornado in Warren County hit rural areas of the county, thus allowing it to be mostly overshadowed by the tremendous hail damage in the city of Bowling Green, which experienced a direct impact from the hail core of this very intense supercell.
On that same day, Nashville’s central business district was directly impacted by an F3 wedge tornado as well. This outbreak of tornadoes came only a week after an outbreak of tornadoes impacted The Deep South, with suburbs of Birmingham, AL being hit by an F5 tornado. On Apirl 16, 1998, an F5 tornado occurred near Lawrenceburg, TN. It is known as “The Forgotten F5” because it was widely overlooked due to the impacts on Nashville as well as Bowling Green.
Today’s weather setup does not look to be as active as fourteen years ago. The decaying remnants of a very expansive squall line in association with a rather potent low pressure system that is tracking across the northern Great Lakes moved through the region this morning widely stabilizing the environment. The cold front should pass through the region by late afternoon into the early evening. While the majority of convective activity looks to occur in far eastern Ohio, much of West Virginia, Pennsylvania, and New York with a small region of favorable conditions in the southern tip of Texas, which is currently verifying (the northern region should verify later today) as delineated by The SPC, some minor convective activity could be triggered in The Mid South and The Ohio Valley today by the passing cold front.
Both the NAM and the GFS seem to be in better agreement for 36 hours out from the 12Z run. Both are forecasting a widespread rain event, with the only difference being the GFS is wanting to soak the Deep South with heavier rain as opposed to the NAM. For The Mid-South this event looks to mainly bring steady to heavy rain, and maybe some thunderstorms, however, no significant convective activity is expected, as it appears clouds will hinder any major diurnal heating in the warm sector.
Also, for the long term forecast, the GFS is suggesting a change in the pattern, bringing a polar vortex over Canada, based on the 500-mb vorticity and heights plot. Granted this is 144 hours out, but it is definitely something to consider for long term forecasting. However, it is also important to note that the NAO is still forecast to remain positive, and not much change in the AO is expected either.
While the Winter of 2010-2011 had a La Niña, it also saw anomalously negative NAO and AO throughout much of its entirety. Winter 2011-2012 has seen La Niña as well, only as anomalously negative as NAO and AO were last winter, this winter they have been as anomalously positive, and that pattern does not look to break any time soon.
As for the short term, a shortwave is moving through the area triggering some shower activity, albeit of a more scattered nature, and mainly in Tennessee.
Shower activity should continue throughout the day. A more organized and widespread event can be expected over the weekend. The 06Z run of the NAM and GFS have moved the arrival of this system to Saturday as opposed to Sunday, with the NAM being a bit more progressive at 84 hours out than the GFS. The GFS wants to keep the ridging intact with the NAM breaking the ridging down.
As observed on the 84 hour 1000-500mb Thickness/MSLP charts from the 06Z run, the NAM also is more aggressive with the precipitation, as well and has the system being better organized as well. One consensus of the models is that this will definitely be a rain event, as has been the recurring theme of many storm systems over the past several weeks.
The mild winter influenced by La Niña and very positive NAO and AO continues as a ridge of high pressure is in place over the East Coast providing solid warm air advection into the Mid South this morning.
The day will start off cold, but the southerly flow will bring in more warm and moist air and allow temperatures to reach into the upper 50s, and set the stage for a rain event come mid week as a trough will pass through the area by Thursday. Temperatures will rebound quickly and a second system will send a wave of energy through the mid south bringing bigger chances of rain for Sunday.
For the midweek event, the GFS is not as aggressive as the NAM is with the cold air. Based on the abnormally warm nature of the pattern in place, a solution closer to the GFS is a good bet. As for the Sunday precipitation, the GFS is suggesting a very warm set-up—much too warm for any wintry precipitation. There could even be the chance for severe weather on Sunday, but that is a very remote possibility as of now. The SPC does not have anything plotted for Sunday in regards to convective activity.
Monday evening began a pattern of continual precipitation throughout the Mid-South, and the rainfall amounts for the past 24 hours have been rather impressive in the Mid-South, with the bulk of the precipitation having fallen from thunderstorms at around 2am. The Warren County Kentucky Mesonet Site has measured 1.83 in. of rain since midnight, and The National Weather Service in Louisville issued this graphic of interpolated precipitation data through today.
The rain will be coming to an end later today, and will be followed by a sharp cool down as the cold front finally progresses through the area and the cold Canadian air moves into the area. However, forecast models have been persistent with building a ridge over the Southeast again, thus supporting more unseasonable warmth for next week.
The severe weather threat has diminished dramatically. The lack of instability from diurnal heating has clearly taken its toll on the squall line, and the decay is quite evident in a recent radar image. What can be expected from this decayed squall line is still some gusts upward of 30-40 mph at the very most as well as very heavy rain.
Some breaks in the cloud cover have been occurring, which was expected based on earlier runs of the RUC showing a patch of drier air at 700mb moving through the area. However, the limited amount of sunlight that has been allowed to come through the cloud cover will not be enough to increase instability at the surface. Any storms that fire and move through today and into tonight are going to be heavily driven on dynamics. It is very likely that there will be limited convection with the storms; however, the high wind threat is very real with this system. Thus, there does not need to be any major convective activity to have a “thunderstorm” wind event. The main tornado threat continues to be well north of the Mid-South; however, there is an outside chance of low-topped supercells forming. Lack of surface based CAPE, however, will be a major inhibiting factor on these storms should they develop.
With a decent ridge in place over the Southeastern CONUS and a deep positively-tilted long wave trough axis over the Western CONUS, today looks very mild once again. Ridging over the Southeastern CONUS similar to what is in place currently could likely be a recurring pattern based on what the forecast models suggest—the GFS in particular. If that is indeed the case, Thanksgiving week could be rather mild. This pattern also brings with it regular rain chances to the Mid-South, Ohio Valley, and points northward as well, with the Southeastern CONUS remaining relatively dry.
Today, however, the Storm Prediction Center has felt the need to issue a Slight Risk for severe weather for The Mid South and The Ohio Valley, much of Indiana and Ohio as well.
The main threat for the Mid South today will be from high winds, with a very low end tornado threat in place as well. The main threat for tornadoes is up in Indiana as well where the wind shear will be at its strongest, and winds will likely be backed at the surface as well.
Currently there is a cloud deck at about 850mb as the moisture is very rich at that level right now. There is a chance that the cloud deck will clear out toward mid to late morning and allow for some insolation. In general, the storm mode for today looks like more linear, based on the latest RUC Sounding.
What is also clear from both soundings is saturation at or just below 850mb, suggesting a cloud deck in place throughout the day. This will definitely limit diurnal heating from the sun, which could prove to limit severe potential; however, the dynamics in place are rather impressive. The wind shear is in place.
The current RUC Hodograph suggests linear storm mode for today, as does the forecast hodograph at 19Z by the RUC. Winds at the surface should remain mainly out of the south and veering with height, today.
In conclusion, the cloud cover for today could prove to be an inhibiting factor to establish any significant surface based CAPE; however the dynamics and shear in place are far too impressive to ignore. If any severe weather does occur today, it will very likely be more dynamically driven.