Louisville, Kentucky

Updated Aviation Discussion

• Dry, mild weather continues through Halloween. Expect increasing clouds tonight through Saturday.
• Much needed rainfall is likely on Sunday as a weather disturbance moves through the region.
• Unsettled weather pattern is expected for the middle of next week, with breezy conditions and moderate to heavy rain showers at times Tuesday night through Wednesday night.

Today through Monday Night

Early morning satellite shows mostly cloudy skies across the region with a thickening deck of high cirrus overspreading the area. Temperatures were in the low-mid 50s in the Bluegrass with upper 50s and lower 60s in the I-65 corridor and points west. No significant weather is expected through sunrise.

For the daytime hours, mostly cloudy skies are expected across the region today thanks to a thick high overcast cloud layer. We`ll likely see a gradient in temperature this afternoon with lower 70s across southern Indiana and into the Bluegrass region of central Kentucky. Slightly warmer conditions are expected south of the WK/BG Parkways where highs should warm into the 73-78 degree range. For this evening, mostly cloudy skies will continue with clouds continuing to lower through the evening. Current forecast still calls for dry conditions with evening temperatures in the 60s. Overnight, moisture advection will continue across the region. Initially dry atmosphere will moisten up via the top-down process. Best precipitation chances look to be after midnight in the areas along and west of I-65 where we will continue to run chance PoPs though we`ll have likely PoPs along/west of the I-165 corridor. Lows tonight will solidly be in the 50s.

Moving into Sunday, a compact mid-level vort max is forecast to cross the Ohio Valley during the day. This feature will bring widespread rain showers to the region. A stronger low-level flow will remain just to our west/southwest where slightly heavier precipitation is expected. We`ll see a gradient of QPF across the region with the smallest amounts in the Bluegrass region where around a tenth of an inch can be expected. Higher precipitation totals will be confined to our far western areas (likely along/west of I-165) where a half to perhaps three quarters of an inch of rainfall is expected. Highs on Sunday will be cooler with readings in the lower 60s in areas west of I-65. Areas of east of I-65 will be a bit warmer with readings in the mid-upper 60s.

Compact shortwave trough axis will quickly move northeast of the region Sunday night with upper level heights quickly rising behind the system as a large upper trough comes out of the inter-mountain west. Monday looks to feature mainly dry conditions with highs warming into the mid-upper 60s. Lows Monday night will cool back into the lower 50s.

Tuesday - Friday

A large upper level trough axis will plow into the central Plains at the start of the period. Just ahead of the system we`ll remain under the influence of a sharp ridge axis just to our east. The ridge should keep much of Tuesday dry with continued strong moisture and warm advection. Temps on Tuesday will warm into the middle 70s, with some upper 70s down along the KY/TN border.

Upper trough axis looks to take on a slightly negative tilt by late Tuesday and into Wednesday. Strong warm advection and increasing isentropic upglide ahead of the vertically stacked sfc low and upper low should result in widespread rain showers overspreading the region late Tuesday and into the daytime hours on Wednesday. Moderate to occasionally heavy rainfall will be possible as this system pushes through. The threat of severe weather with this system is non-zero, though the better better jet dynamics will remain north of the region while better instability will be located well to our south. Low to mid-level shear will be quite impressive across the region, however, widespread cloud cover and ongoing precipitation will likely limit overall instability for organized severe. Surface cold front is likely to occlude across the region on Thursday. We could see a better shot of instability working in across the eastern sections of the region Thursday afternoon where a low-level risk of strong storms would be possible, though we still believe the better risk of organized severe will be across the Gulf coast states. Ongoing shower activity is likely to continue across the region through the day before diminishing in the evening. Highs Wednesday will likely be in the upper 60s to around 70, with highs mainly in the upper 60s on Thursday. Given our current short term drought conditions, rainfall with this system is not expected to result in flooding risks. However, ponding of water on roadways is possible Wed/Thu. Rainfall amounts of 1-2 inches with locally higher amounts will be possible during the period.

Upper low will rotate out of the region on Friday, however, a secondary perturbation will quickly move into the region behind the front. Right now, forcing for additional precipitation looks fairly light, but cloudy skies with perhaps some sprinkles/drizzle may linger into Friday morning. Seasonal air will filter into the region with highs on Friday warming into the mid-upper 60s.

Extended Forecast Discussion

On the hemispheric scale, a strong El Nino pattern persists and will likely continue for the next several months. Two ridges at 500 mb were noted and about 180 degrees apart. The first was located over the north Pacific and the other over in Scandinavia. Strong/persistent tropical activity over the western Pacific combined with very strong divergence up near 200 mb has led to strong wave-activity fluxes flowing northward from the tropics into the polar regions. The net result of this will be for intense warming in the stratosphere up near 10mb over the next week leading to a sudden stratospheric warming event. Much of the ensemble data agrees with this warming and it will likely perturb the PV and weaken it, perhaps splitting it (some solutions) or perhaps simply stretching it. This will likely be one of the earliest (if not the earliest) SSW to occur. The ramifications of this warming event are still unknown at this time. The main question here is whether there will be a downward reflection from the stratosphere back into the troposphere? Models pretty much diverge here on that, but I think we`ll just have to use the wait and see approach. The effects of this warming event will not affect our sensible weather in the immediate future. SSW events often will affect the flow pattern some 3-4 weeks after they occur. Typically, an SSW can/will weaken the PV and allow higher risks of colder air to work into the eastern US. That could still occur, depending if the PV gets displaced far enough south. So we would be looking at late November or early December to see any effects from this event.

In the meantime, the strong El Nino background state will continue. Pressure anomaly maps show a positive east-Asian mountain torque along with an MJO pulse pushing into the west Pacific. These two features will lead to a strengthening and longitudinal extension of the Pacific Jet. Typically, a +EAMT pattern leads to troughing over the eastern Pacific and western CONUS with subsequent downstream ridging in the central/eastern US. Given the El Nino state, the subtropical jet will remain active and strong through the month and will propel numerous disturbances across the CONUS with a risk of strong/severe storms from the southern Plains into the SE US. Given the strong Pacific flow and forecast high latitude blocking to the north, intrusions of cold air look to be fairly limited, especially with the Pacific jet flooding the CONUS with mild air.

Locally, we should continue to see normal to above normal temperatures through mid-late November. Given the expected stronger jet and multiple systems coming through, precipitation will likely average near normal.

The overall pattern may shift a bit toward the end of November and into December. However, this shift is dependent on whether we`ll see any downward propagation of warm temps aloft from the stratosphere into the troposphere from the early month SSW event. We`ll likely see blocking set up with the Euro ensembles showing the possible development of an -AO/-NAO/+PNA pattern. There is a bit more spread on how the Pacific will look as EPO forecasts still have a bit of spread here.

VFR conditions remain across the region with high overcast ceilings blanketing the area. Southeast to south winds remain light. Through the period, ceilings will lower through the VFR range as light rain moves northeast into the region tonight. Towards the end of the period into the next period, ceilings begin to fall into MVFR levels near HNB and BWG. Visibilities could also begin falling during periods of rain.

KY

None.

IN

None.