Over the last few days, operational models have been trending more and more towards solutions that show severe weather striking the area on Tuesday.  The Storm Prediction Center has now changed its forecasted “slight risk” area for Tuesday from an area that was contained in the ArkLaTex to one that now extends well into Kentucky.

Severe weather is becoming increasingly likely for Kentucky on Tuesday

Early Tuesday morning, a positively-tilted trough will swing into the area, providing the necessary momentum to push a front that is currently stalled across the state back to the north again as a warm front.  As it does so, most of Kentucky will be in the warm sector of the storm, allowing for a progressively destabilizing atmosphere to take hold in the region.  Mositure will increase ahead of the storm’s trainling cold front, with forecasted dew points in the low 60s.  An elongated area of vorticity and increased shear hint at a developing QLCS across Missouri, Arkansas and Illinois that will likely affect the Warren County area after dark.  With bulk shear values of 40-60 knots, damaging winds ahead of bowing segments of the squall line are the most probable convective mode to impact the region.

The 06z NAM Model forecasted 1000-500 mb shear.

The models are differing as to the timing of the arrival of the system.  The 06z ECMWF and the latest run of the NAM are showing a slowing storm, while the 06z runs of the GFS and NAM show the main line affecting us just after sundown on Tuesday.  Nonetheless, heavy rains and the downward transfer of high momentum winds will make for a stormy evening Tuesday, which could possibly last into Wednesday morning.  The latest forecasted rainfall totals by the HPC show well over an inch of rain falling across the western half of the state, with isolated totals being greater than that.

Heavy rains are going to fall for most of the day Tuesday.

The strong ridge off to our east that has provided for the warm weather and gusty conditions over the last few days will prevent any tornadic activity for our region.  A relatively stable boundary layer will provide a hostile environment for the sustenance of any convective activity across the Ohio Valley.

Currently the Mid-South is sitting on the ascending side of a ridge axis located over New England with a deep positively tilted trough digging over Arizona.  The trough will continue to dig eastward into the southern plains today with a surface low developing in west Texas this afternoon as well.  The low will make its way from Texas northeastward to the Great Lakes region by Tuesday evening.  A closed upper level low over Bermuda is causing the whole synoptic pattern to become quasi-stationary as the upper level low will gradually retrograde westward, inhibiting much eastward progression of the ridge over the Mid-South.  This will cause the trough to continue to dig in the west, eventually not being able to push the ridge causing the low to become negatively tilted and eject northeast towards the Great Lakes. Late Tuesday night into Wednesday morning is when this system will affect our region with possible strong thunderstorms and showers.

Until the middle of the week, the Mid-South region can expect today and Tuesday to be mild with a high today of 71 and Tuesday 72 as southerly flow starts to develop ahead of this system.  Lows will stay a bit warmer than recent nights due to the southerly flow, expect a low tonight of 47 and Tuesday 51.  Winds will increase through the day to become out of the south at 10 mph with gusts between 15-20 mph possible.  Today and Tuesday we will remain under mostly clear skies as the region remains under a ridge.  Tuesday evening the clouds will start to make its way into the region as the ridge finally pushes eastward and a cold front approaches bringing showers/Thunderstorms to the region after midnight on Tuesday into Wednesday.

There is some severe potential for the region as the vertical shear is quite impressive, however there is little to no instability ahead of the front over the Mid-South.  Will monitor the potential for severe weather and update if needed, but not expecting much in the way of severe weather at the moment.  Models will pick up on what to expect in the coming hours.  The region can expect to see around 0.25″-0.40″ of precipitation from this system Tuesday night and Wednesday.  Wednesday you can expect a high of 60 and a low dropping drastically to 35 overnight with winds around 9 mph from the south before the front and turning west after the frontal passage.

A broad upper level ridge will dominate the pattern over the eastern half of the U.S. for the next several days, leading to picture perfect fall weather over the weekend for the mid-South. Highs in the middle to upper 60s are expected tomorrow and Sunday under mostly clear skies. These clear skies and light winds will provide ideal radiational cooling conditions, so overnight lows are expected to drop down into the middle 30s tonight and tomorrow night. These conditions will also be favorable for cold air drainage into Kentucky’s valleys and large overnight temperature spreads between adjacent ridgetops and valleys. This phenomenon can be monitored in real time using temperature data at the Kentucky Mesonet web site.

GFS 250 mb height and wind speed forecast for 1:00 PM Saturday, showing upper level ridging over the eastern U.S.

With quiet weather the rule locally and nationally, this is a good time to share a few links to other web sites that may be of interest to readers of this blog. The first link is to the University of Wisconsin’s Cooperative Institute for Meteorological Satellite Studies (CIMSS) blog, which provides selected satellite imagery of current meteorological events and provides a sampling of the numerous applications that satellite-derived products can have in weather analysis and forecasting. Another great source of information on current weather events is Dr. Jeff Masters’ blog at Weather Underground; Dr. Masters does a great job of compiling information and statistics and gears his writing toward a general audience while remaining faithful to the science of meteorology. Closer to home, the WKU StormTopper Network is a great source of information on local weather, and the network also maintains Facebook and Twitter pages. Finally, you can “like” the new Western Kentucky University Meteorology Facebook page to receive meteorology stories of interest in your Facebook news feed.

After a beautiful start to the week, the weather will turn dreary tomorrow. An upper-level disturbance and associated surface low will progress through the region, bringing widespread rainfall and holding high temperatures in the mid 50s. A few embedded thunderstorms also can’t be ruled out. Anywhere between a quarter and a half inch of rainfall is expected before the system exits the area tomorrow night.

NAM 500mb height and vorticity forecast for 4 PM tomorrow, showing upper level low over the region

After the system clears the area tomorrow night, high pressure will quickly build back in from the west. This will result in a return to pleasant weather and seasonable temperatures for the weekend, with highs around 60 on Friday increasing to the mid 60s on Saturday and Sunday. Nighttime temperatures will not be quite as cold as they were earlier this week, with lows in the upper 30s and lower 40s expected over the weekend.

Zonal flow aloft and high pressure at the surface will make for a pleasant start to the week in the mid-South. Highs in the mid to upper 60s and lows in the upper 30s are expected today through Wednesday under mostly clear skies. On Thursday, an upper level trough will approach the region from the west, bringing with it a chance for some showers.

One region that did not experience tranquil conditions over the weekend is the Northeast. A freak October snowstorm dropped a swath of heavy snow from West Virginia to Maine Saturday through Sunday, breaking numerous records in the process. For many locations, it was the largest October snowfall on record; a good summary of the storm from Weather Underground can be found here. Some of the remarkable records set by the storm: Concord, New Hampshire received 22.2″ of snow, which was not only the all-time daily and monthly October snowfall record (both previously 3″) but was also the third-largest storm total snowfall on record, regardless of month. Central Park received 2.9″, breaking the previous October record of 0.8″ set in 1925. The big “winner” was Peru, Massachusetts, which recorded a whopping storm total of 32″. An interactive map of snowfall totals can be found here.

Visible satellite animation from Sunday morning, showing departing Nor'easter and fresh snow cover

The early-season timing of the storm meant that it had an even larger impact that these amazing statistics would suggest. The heavy, wet nature of the snow, combined with the fact that many trees still had some or all of their leaves, caused widespread tree damage and power outages throughout the Northeast. At the height of the storm, over 3.1 million customers were without power in the region. The governor of Connecticut declared a State of Emergency, and that state’s Department of Transportation said that the storm knocked down five times as many trees as Hurricane Irene earlier this year. So while the snowfall totals in this storm weren’t quite as high as some of the memorable Northeast blizzards of recent years, the unusual timing and widespread tree damage will ensure that “Snowtober” won’t soon be forgotten.

Snow at the NWS Gray, Maine office, which received 12.9"

Highlights

Trough digging into the eastern U.S. bringing with it much cooler temps

Chances of rain through Fri.

Discussion

Currently, there is a trough of low pressure beginning to dig into the eastern U.S. that will change up the weather for the short term. A cold front currently over northern Indiana will pass through BG late tonight cooling off temperatures and bringing in some much needed rain.  Today’s temperatures will max out around 76 with a slight chance or rain.  The best chance of rain comes tomorrow with temperatures topping out in the mid 50′s for Thursday and Fri and lows staying in the low 40′s.

Since the weather is relatively tame today, we will take a moment to discuss the long term outlook leading into this winter.

For long term climatic outlooks The Climate Prediction Center compares various climactic oscillations as well as atmospheric teleconnections, along with some history, to use past events with similar conditions as an analogy to the current state of the atmosphere.

That being said, the CPC has issued there report for the Central Region of the U.S., which includes KY. From following changes in the El Nino/Southern Oscillation. ENSO and the change in Sea Surface Temperatures across the Pacific Ocean, is considered to be one of the major players in sensible weather here in the United States.

From verifications of SST anomolies and forecasted products from this summer. Modeled guidance as well as the CPC both agree that a weak La Nina will persist and strengthen slightly through the beginning of winter.

Based on prior history and the fact that Texas has had record drought, this will likely cause the polar jet to stay mostly across the northern United States and more zonal causing an above normal chance of precipitation in the Pacific Northwest. This is to be taken with a huge grain of salt, as other factors such as the North Atlantic Oscillation can have changes in the sensible weather from week to week. This is a 3 month forecast.

The upper level trough currently responsible for the cloudy and wet conditions across the state of Kentucky will continue to keep clouds overhead throughout the day today and most of the day on Thursday.  A stray shower or two cannot be ruled out as moisture continues to wrap around the deepening cyclone at the surface on Thursday with rain chances diminishing throughout the day.  Highs Thursday look to remain slightly cool in the mid to upper 50′s. Into the afternoon on Thursday high pressure will begin to build in behind the surface trough and be the dominating factor over the coming weekend with lows reaching the mid 30′s.  Expect highs in the lower 60′s this weekend with lows approaching the freezing mark to mid 30′s.  Temperatures will be comfortable during the day; but will cool quite efficiently under clear skies in association with a dry mid-level atmosphere and northwest flow in the mid-levels.  A frost advisory may be issued into Saturday night and Sunday night as the cold air mass and high pressure system settle into the region.

High pressure system building over the region Saturday morning

Sounding showing temperatures approaching the freezing mark and dry slot in mid-levels Saturday morning