WKU Meteorology

Tuesday has been overcast and cool thus far, with afternoon temperatures in the lower 50s. A shortwave trough (Figure 1) is currently affecting Bowling Green’s weather, and it is expected to continue to dig southeast to further affect the forecast for Tuesday night into early Wednesday morning. Before the clouds set in from the northwest Tuesday morning, the temperature did fall to 34 °F. Current enhanced infrared satellite imagery (Figure 2) shows the heavier cloud cover over Illinois, Indiana, and western Kentucky.

Figure 1

Rain showers over these same areas will move southeast this evening into tonight, so expect a wet and chilly evening as you watch election results roll in. Cloudy skies will remain through the night and through half of Wednesday. Overnight lows will be in the lower 40s.

Figure 2

The clouds will persist until Wednesday afternoon, so expect highs only around 50 degrees. A ridge of high pressure begins building into the region Wednesday night into Thursday, and this feature will produce warming each day into the weekend. The NAM (Figure 3) shows surface temperatures rising back into the mid 60s by Friday.

Figure 3

Bowling Green, KY Forecast:

Tuesday Night: Rain. Cloudy, with a low around 42.

Wednesday: Cloudy in the morning, partly sunny in the afternoon and evening. High 50.

Wednesday Night: Clear. Low 32.

Thursday: Sunny. High 58.

Friday: Sunny. High 65.

What a nice week to end October and move into November.  Skies have been generally sunny all week despite temperatures that have been slightly below average.  Temperatures should be in the mid-60s for this time of year in Bowling Green but highs have been in the 50s to near 60 this week.  As for overnight lows, Bowling Green fell to 30 degrees Thursday morning which is one of the coldest nights we’ve had thus far this fall.  There has been a gradual warm up in temperatures this week and this slow warm up should continue into this Saturday before yet another trough dips down to encompass southern Kentucky by Sunday.  As the trough and the jet stream dips to our south, slightly cooler air will once again filter into our area.  Until then however we will be on the southern edge of a trough but very near the southern edge of the jet stream as a ridge tries to build in. Generally when this jet moves to our north we warm, and when it moves to our south we cool down, thus this week with the jet stream virtually speeding by directly above us temperatures have been fairly consistent and neither warm nor cold.

NAM 300 mb heights/winds forecast for Saturday afternoon. Temperatures will gradually warm thanks to being on the south side of jet stream but overall temperatures will be relatively neither warm or cold.

Thus until the trough dips in on Sunday expect temperatures to be warming ever so slightly. A shortwave is expected to move through Saturday afternoon ahead of the trough which could bring enough lift to create a few showers.  Rain chances Saturday afternoon are about 40% though any rain that does fall should be very light with a 0.1 of an inch of rain at the very most.  The system lacks a strong forcing mechanism as warm thermal advections and positive vorticiy advections will be very weak if present at all.

NAM forecast vertical velocity (rising air) at 7 pm Saturday. Increased vertical velocity here in southern Kentucky at this time just ahead of the shortwave (yellow dashed lines) indicates rising air and thus a chance of rainfall.

In summary, expect a very slow warm up through Saturday followed by increased cloudiness as rain chances enter the picture Saturday afternoon.  Cooler air will once again try to spill its way in by Sunday.  Looking longer term into early next week, models somewhat disagree to the strength of another trough axis moving through, nevertheless, more troughing is expected and thus cool weather will likely continue.

Daily Forecast:

Friday: Low: 40  High: 63  Mostly sunny skies with increasing high clouds late in the day.  Northwest winds will become more northerly; speeds from 4-9 mph.

Saturday: Low: 35 High: 64  Mostly cloudy skies will become overcast with a 40% chance of rain after noon.  Rain will be light with up to a 0.1 of an inch possible.  Winds from the north-northeast turning to the north at 5-10 mph.

Sunday (Daylight Savings Time Ends: Fall Back): Low: 41  High: 57  Partly to mostly sunny with light north winds between 3-8 mph.

After an exceptionally warm week last week, colder air made a return to the Commonwealth Friday and the colder temperatures and clouds stuck around for much of the weekend.  The cold front that ushered in the colder weather weakened as it moved to our east thanks to a very strong low pressure system moving up the east coast named Hurricane Sandy.  Speaking of Hurricane Sandy, this tropical system will quickly become extra-tropical as it gets absorbed into a negatively tilted trough that currently extends from southwest Ontario down into Kentucky.  The system is expected to make landfall somewhere along the New Jersey shoreline Monday evening and wreak havoc on much of the northeast and mid-Atlantic states.  Any impacts for us here in Kentucky??  Despite what you may initially think, our weather for much of this week will actually be controlled by post-tropical cyclone Sandy, but will she bring us a trick or a treat?  The biggest impact on central Kentucky will be blustery winds.  Winds will likely be sustained between 20-25 mph on Monday and between 25-30 mph on Tuesday; winds could gust between 35-40 mph.

NAM sea-level pressure and surface winds in knots for mid-day Tuesday. Winds are expected to be between 25-30 mph with gusts over 35 mph!

Sandy will also force the trough to stay put and thus we here in Kentucky will remain fairly cool.  Overall, low temperatures will fall into the 30s while highs will only be reaching into the low to mid 50s.  Skies should stay predominately clear however, as south-central Kentucky will be located in an area of dry air throughout most of the week. Occasionally some high clouds may move in from the east off of Sandy though the clouds should stay mainly to the east of I-65.

A conveyor belt of dry air will move over western and central KY bringing dry weather and sunny skies. Meanwhile eastern KY will deal with clouds and rain/snow.

Overall the week will be nice and sunny and if you can overlook the strong winds and cooler temperatures you might consider the weather a treat.  As for eastern parts of Kentucky… Sandy Snow???  Now there’s a trick! Winter storm warnings have been posted for Pike, Letcher & Harlan Counties in extreme eastern KY as up to a foot of snow is possible in some of the higher elevations near the VA border; as of Sunday night light snow had already began to fall in these locations.

00Z NAM forecast total snowfall. Heavy Snow is expected over eastern Kentucky near the Virginia border. Winter storm warnings are posted for 3 counties in southeast KY.

Glancing into the later part of the week for us here in central KY, no rainfall is expected and a gradual warm-up should occur as the trough begins to break down..

Daily Forecast:

Monday: Low: 32  High: 54  Sunny skies and windy.  Winds will be from the northwest increasing from around 8 mph early to between 20-25 mph in the afternoon.

Tuesday: Low: 38  High: 57  Mostly Sunny with occasional high clouds.  Windy!  Winds will be from the northwest between 25-30 mph and winds could gust between 35-40 mph.

Wednesday (Halloween): Low: 31  High: 56  A beautiful sunny day and not as windy.  West winds between 12-16 mph.

Thursday: Low: 35  High: 58  A few clouds are possible early before becoming mostly sunny.  West-northwest winds between 8-12 mph.

The past couple of days have been pretty boring, but a great chance to enjoy the beautiful leaves and sunshine. The upper level ridge allowing this persistent pattern will begin to break down tomorrow into Friday. A deepening trough from the west is approaching our area bringing strong winds aloft beginning early Friday into the weekend. The pesky ridge is looking to block the main flow of wind to just north of the area. This will reduce the amount of lift over our area. With the surface ridge over our area this past week, the moisture values are less than spectacular. Moisture inflow is shown to be relevant Thursday night into Friday as the surface high finally scoots east. This isn’t too promising since the front is depicted by the NAM and GFS to roll through the area early Friday. There is some discrepancy with the frontal passage though. The mention of upper air blocking earlier makes me think the frontal movement will slow down as time progresses, which is supported by the SREF model. This is coupled with the surface low moving to the far north into Canada’s Hudson Bay. Considering these facts and how it will occur in the morning, indicating a lower temperature gradient, the front should still have enough steam to pass our area. The timing is the issue.

Everything in consideration, I’m predicting an early afternoon frontal passage. Therefore, high temperatures will not reach as high as today or tomorrow. The amount of precipitation is in question. The models are not showing a high probability of precipitation thanks to the diminishing lift and lack of moisture in our area. The front will bring cooler temperatures, but its intensity will be weakening.

The GFS 10/24 18Z run valid Friday 10/26 at 15Z. It supports both the precipitation and timing predicted for our area.

After the frontal passage, cold air will filter into the region. Lows Friday are looking to drop to the lower 40’s to upper 30’s. Highs on Saturday and Sunday will hover in the 50’s, while the lows hang in the 30’s. Clouds will clear out after the frontal passage Friday as a high pressure settles into our area for the weekend.

Highlights:    High     Low      Precipitation
Thursday:     81         62               0.0
Friday:         72         41                0.1
Saturday:     54         31                0.0
Sunday:       59          37               0.0

Forecaster: Austin Boys

Current conditions have Bowling Green under the dominance of a surface high pressure system. As Chris stated in the previous forecast, it will linger around through the middle of the week. There is an upper level ridge situated over the central US preventing the influence of any disturbances into our area. This looks to change into Thursday as the ridge begins to break down. The surface high pressure is then depicted by both the NAM and GFS to progress eastward.

The SPC Mesoscale Analysis 850 mb temperatures, dewpoints above 50 degrees F, and heights valid 11pm 10/21. The moisture axis across the central US is clearly visible, as well as the high pressure shielding our area.

Our start to the week is not a complete snooze. The picture above shows the strong moisture axis stretching from the Texas Gulf coast into eastern Oklahoma northeastward into Missouri, Iowa, and Illinois. This inflow of warming temperatures and higher moisture values looks to continue across that area into the middle of the week. This is significant because there is a low pressure system shown to develop along a stalled cold front boundary in the Great Plains. Models depict the associated warm front to extend across the lower Great Lakes eastward starting tomorrow into Wednesday. The low pressure system is not shown to progress eastward but to the north since our area will be shielded by the persistent dome of high pressure, leaving us with little chance of rain.

With this said, expect a dry and beautiful start to the week. Temperatures will stay consistent with today with a slight warming trend. Highs in the upper 70’s and lower 80’s and lows in the lower 50’s. Get outdoors and enjoy the weather, or lack thereof.

Forecaster: Austin Boys

The last shortwave along the back side of the upper level cut-off low over the upper Midwest was over central Illinois and Indiana earlier this morning and has continued to dive southward towards Cincinnati.  In return, cloud cover has continued into the afternoon hours and will hang tough into the early evening.  As the low continues its slow progression northeastward, conditions across the Commonwealth will begin to clear from west to east.

Visible Satellite produced and provided by simuawips valid for Saturday 18Z.

By tonight, skies will be mostly clear as the surface high pressure moves into our area.  In return cool overnight lows will be anticipated as temperatures drop into the upper 30’s to around 40 degrees.  As we look to wrap up the weekend, Sunday appears to be a start of a very nice stretch of fall time weather for the Bluegrass.  The stubborn ridge will hang tough over the region bringing sunny and warmer conditions over the next few days.  In general, highs should remain in the low to mid 70’s with overnight lows in the 50’s with sunny conditions.

Warmer conditions have flooded much of the region for the past couple of days as highs have gradually warmed into the low to mid 70’s across the area.  Mostly sunny conditions have ruled the skies for Wednesday as those fall time colors have began to really show across the area.  We wrapped up the weekend on a wet and windy note as a system worked its way though the region bringing showers and very windy conditions.  The front eventually tracked its way through the state and pushed eastward as a ridge of high pressure begin to build over Central Plains and into the Ohio Valley by Monday.  In return, pleasant and cooler conditions returned to the Bluegrass to kick off the week.

We now turn our attention towards a similar set up that we had this past Sunday.  The 250 mb heights and winds map shows an upper level cut-off trough slowly tracking eastward over the Dakota’s.  Jet streaks have been very strong with upper level winds reaching 100-120 knots over parts of the Central Plains as the trough continues to dig.

250 mb Heights and Winds map valid for 06Z Thursday.

The trough will continue its progression eastward and in return drape a cold front from parts of Minnesota down into Missouri and Oklahoma.  Similar to the last set up we had on Sunday, the lack of instability seems to be the main problem with the development of widespread severe storms.  Surface-500 mb bulk shear map shows strong mid-level winds over the Central Plains ranging from 50-80 knots.  At 700mb the atmosphere continues to show a saturated upper level which is important for the development of these showers and storms.  Surface dewpoints lack a bit but range from 50-60 degrees as precipitable water values range from 1.1-1.5 inches over parts of western and south-central KY.  The SPC’s latest outlook outlines the possibility for severe weather over parts of the Central Plains as those areas are under a SLIGHT risk for severe storms this evening.  The risk also includes far Western Ky counties as well as the line of showers and storms could potentially affect those areas as the front continues to slide eastward.

Storms that do develop over parts of Missouri, Arkansas, and Louisiana will develop and track eastward ahead of the front. With the lack of instability over our area, the storms are expected to weaken considerably as they approach lesser amounts of instability.  Nonetheless, given the strong wind fields aloft, some of the convection overnight could pose a wind threat as these storms may be able to transfer some of that higher momentum air down to the surface.  These storms will have a decent amount of moisture to work with as QPF amounts range from 0.5-1.0 inches for the area.  In addition to the showers and storms, the pressure gradient will tighten up over the region bringing south to southwest winds across the area around 15-25 mph with gust up to 35-40 mph. The latest HPC forecast gives a good idea of precipitation amounts expected.

Latest HPC map showing widespread rainfall amounts across the area.

As the system tracks through the Ohio Valley region later tonight, expect mainly windy conditions with light to moderate rain over the area.  Expect lows to drop down in the low 50’s under cloudy skies as the chance for showers will loom later tonight and into your Thursday morning.  Look for partly cloudy skies across the area with highs struggling to hit the mid 60’s.  Clouds look to hang tough heading into Thursday evening as lows drop into the low to mid 40’s with light winds from the south.  By Friday, look for dry conditions to prevail as partly sunny skies are expected.  Highs will be a tad cooler as temperatures struggle to reach the mid 60’s with winds from the southwest around 10-20 mph.

Saturday kicked off the weekend on a relatively nice note.  A cool morning eventually led to partly sunny skies and slightly warmer conditions across the region.  Highs across the area quickly warmed up after a chilly start as temperatures topped out in the mid to upper 70’s statewide.  A warm front moving through the region brought somewhat of a change back to above normal conditions after much of the week offered cooler than average temperatures.  This noticeable change will come behind gusty southerly winds as high pressure begins to shift towards the Atlantic and low pressure develops across the Central Plains.

HPC/NOAA Current Surface Analysis

Current surface analysis shows the development of the low over the Central Plains with the cold front extending into parts of the Oklahoma/Texas panhandle.  The warm front stretches from parts of South Dakota over to Ohio and in return has continued to advect the warmer air over the region.  Heading into the evening and overnight hours, the current set up will allow for a milder low than we’ve seen lately. Low’s are expected to bottom out around the 60 degree mark for Bowling Green, as other areas across the state will see temperatures drop into the upper 50’s under mostly cloudy skies. Pressure gradients will tighten up overnight bringing very windy conditions across the area. Expect sustained winds around 15-25 mph with the possibility of winds gusting up to 40+ mph.

Looking ahead for your Sunday, a cold front will move across the Ohio Valley region Sunday afternoon/evening.  Ahead of this front, expect a line of showers and storms to develop in the warm sector.  Surface-500mb bulk shear winds showing strong values ranging 40-50 knots leading to the possibility of decent development of storms.

Surface-500mb Bulk Shear Map valid for 18Z Sunday. Areas over the Ohio Valley region showing strong wind values ranging from 40-50 knots.

Instability over the area will remain the key factor in the development of any strong to severe storms.  CAPE values continue to lack but still look to provide enough energy with values ranging from 750-1300 J/Kg.  Southerly flow will allow temperatures to warm in the mid to upper 70’s as dew points climb into the mid 60’s.  Precipitable water amounts range from about 1.4-1.8 inches statewide with relative humidity values reaching greater than 70%.  The latest SPC forecast shows some agreement as the forecast shows s SLIGHT risk for much of the state for Sunday.

SPC Categorical Outlook for Sunday. Showing a SLIGHT risk for severe storms across the Commonwealth.

The low will continue to track towards the northeast into northern Illinois and eventually over the Great Lakes region by Sunday night.  The cold front will slide through the area bringing a slight risk of storms with the main threat of heavy rain, gusty winds, and the possibility of hail.  As far as the amount of precipitation expected with these storms, the HPC seems to think a decent rainfall will occur. Areas just to our west could receive a decent amount of rainfall ranging from 1-2 inches, with higher amounts to the north.

HPC’s QPF map showing a decent rainfall for the Central Plains area extending northward into the Great Lakes region.

The front should arrive by the late afternoon/evening hours and will continue to track eastward across the state.  Rain should move out of the area overnight Sunday night with cooler temperatures filtering in from the northwest.  Expect lows in the mid-50’s with clearing skies and light northwest winds around 5-10 mph.

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Outlook:

Monday: Mostly sunny…High: 67.  Northwest winds 5-10 mph.

Monday Night: Patchy fog after 4am. Otherwise, mostly clear…Low: 44. Light and variable winds.

Tuesday: Mostly sunny…High: 68. Light and variable winds.

Tuesday Night: Partly Cloudy….Low:49. Southwest winds around 5 mph.

Moving into the weekend, we will see a strong shortwave trough continue to advance east over our area. This disturbance will have weakened somewhat upon arrival but will still allow for the development of severe weather across Western Kentucky.

The lacking factor in this set up will be instability. CAPE parameters are lacking looking through the day Sunday with values less than 750 j/kg^1.  This is likely due to forecast overcast skies Sunday that will inhibit any daytime heating and air mass destabilization. With this in mind, we are looking at a linear squall line even for Western Kentucky with the biggest threats being damaging winds and hail though an isolated squall line tornado is not out of the question. The Storm Prediction Center has placed Bowling Green in the slight risk for Sunday. Taking a look at the probabilistic  outlook, we see Bowling Green in a 15% chance for severe storms Sunday.

A strengthening pressure gradient out ahead of the system will contribute to a strong low level jet and gusty Sunday. A high wind advisory may need to be issued into the day Sunday. Temperatures will take a dip after the passage of the cold front Sunday night with surface ridging building in behind.

Sunday Forecast Overview:

High, 75. Low, 56. Gusty winds throughout the day with thunderstorm development in the late afternoon. Main threats high wind and hail. Storm to continue into the night with rain ending in the early hours Monday morning.

We have experienced a cool week here in Warren County with frost advisory most mornings and cools starts to the day. Tonight a Freeze Advisory has been issued by the NWS in Louisville valid until 8 am CDT tomorrow. Tonight, we will have clear skies over the area allowing the temperature to drop lower than previous forecast lows. Overnight, an area of high pressure with slide over the area and move out to the east into Thursday. This will keep our skies mostly clear and morning lows low.

 Our next chance for showers and thunderstorms will come Thursday night as another trough axis swings through the upper levels. A merging/splitting pattern of the polar jet and subtropical jet will provide enhanced difluent flow aloft which will provide some upper level support for thunderstorm development. Moisture will again be somewhat limited with northerly winds advecting dry air from a cold air mass over the great lakes and Dakotas over our area. A warm front will move north from the south west and cause and increase in clouds by Thursday night. This will allow us to warm temperatures a few degrees as the warm front passes Friday-Saturday and winds shift from the north west to the south east gradually into Thursday night.

Looking into the weekend, we see a powerful system develop off the west in the form of a cut off low that develops off the west coast and slowly wobbles our way with fast moving winds circulating through it at the 500 mb and 250 mb levels. This system will drag over the Rockies and develop an associated surface low as it passes over the mountains and into the lower plains. As this system progresses, the low will be reabsorbed into the polar jet flow Saturday night into Sunday as it progresses towards our area. The next forecast update will detail the expectations for this system further.

Forecast Overview:

Thursday: High, 65. Low, 50. Clouds increasing into the night as another weather system moves in. 30% chance of showers and thunderstorms Thursday night.

Friday: High, 70. Low, 50. Left over precipitation will move out with temps warming back up.