WKU Meteorology

Highlights

For This Weekend

• Highs in the upper 30’s
• Lows in the lower 20’s

The weather pattern currently in place looks to hang around for at least the short term.  While a weak cold front will push through the area throughout the afternoon today which will provide a very small chance for precipitation, high pressure will build in behind it providing clear to most sunny skies throughout the weekend.  Highs Saturday and Sunday look to reach the upper 30’s to lower 40’s while lows will hover around the lower 20’s.  Bundle up if you have to go out at night!

In other news, following the round of heavy precipitation we received in November and December, many cities in the state have broken records for a rainfall total for a year.  The following graphic depicts new records set around the state.  (Provided by the NWS)

As you can see, for the year of 2010-2011, this is the 7th wettest year on record for Bowling Green, the 2nd wettest in Lexington, and this year will become the wettest year in recorded history for the city of Louisville.

Highlights

• Chance of Precipitation early/mid-day Wednesday
• Rain chances diminishing throughout the week
• Temperatures returning to near normal

The three day totals for the previous precipitation event has taken a toll on the waterways of Kentucky, with many counties including Warren County currently under a flood warning.  Remember to not try and cross flooded roadways and passages.  A graphic provided by the National Weather Service shows the rain distribution totals from December 4th-6th.

A high amplitude trough transitioning to a negative tilt, which signifies a trough reaching maturity, will quickly race across the region, bringing with it a chance of precipitation early Wednesday.  A mix bag of precipitation cannot be ruled out, but accumulations will be minimal, most likely less than a tenth of an inch.

NAM 500mb Absolute Vorticity

Passing of the trough will bring about clearing skies and sunshine in the afternoon with highs reaching in the mid 40’s, and lows falling into the mid 30’s.  Thursday will bring about mostly sunny skies in the mid 40’s with lows becoming quite chilly in the mid 20’s under the influence of cold air advection by the passing of the trough and radiative cooling under clear skies.

An update for the weekend will come on Thursday.

Looking at the 15z run of the RUC model, the severe weather threat for today seems almost non-existent.  An already rain-cooled air mass will not receive any extra convective energy from the sun as cloud cover will be extensive throughout the day.  This will put an end to any significant threat for the Bowling Green area and state of Kentucky.

Clouds will stop any real severe threat today

Despite the absence of a meaningful severe weather threat today, heavy rains are still probable across much of the state.  The latest 500 mb analysis puts the rain-shield sitting across the region continuing its movement toward the northeast.

Storms will continue to swing around the trough axis toward the northeast, placing most of KY under the heavy rains for the remainder of the day

PWAT values are very high and could mean that very high amounts of rain will fall before the night is over.  By tomorrow morning, SREF guidance suggests that close to 1 inch of rain will fall.  Bowling Green has already recorded 0.3 inches at the mesonet station, so the SREF forecast of around 0.85 inches by tomorrow morning is not completely out of the question.

Very high precipitable water amounts will lead to very heavy precipitation today and into tomorrow.

Damaging winds may still be possible today and this evening, as bulk shear values still range between 40 and 60 knots.  Some momentum transfer is possible, but winds are not expected to meet severe criteria.

Shear values could indicate some strong winds later tonight.

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.

The sounding itself is not the most ideal, as there is a rather robust cap from 700mb up to 500mb.  However, that is expected to erode significantly by the afternoon hours.

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.