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FXUS63 KLMK 021052 AFDLMK

Area Forecast Discussion National Weather Service Louisville KY 652 AM EDT Thu May 2 2024

Updated Aviation Discussion

KEY MESSAGES

* Very warm today with highs in the mid-to-upper 80s, with a few 90 degree readings possible.

* Widespread showers and scattered thunderstorms Friday, mainly in the afternoon and evening. Brief heavy rain and lightning.

* Rain/storm chances decrease for Saturday, but forecast confidence remains low at this time.

SHORT TERM /THROUGH TONIGHT/
Issued at 342 AM EDT Thu May 2 2024

Quiet conditions are present across central KY and southern IN this morning as earlier convection to our west has subsided, leaving residual scattered high clouds over the area. Temperatures as of 07Z are primarily in the 60s, with a few cooler locations cracking the upper 50s within the last hour or two. Between now and sunrise, no significant weather is expected with calm or light winds continuing and temperatures expected to fall into the upper 50s and low-to-mid 60s.

Unseasonably warm temperatures will be the main feature in today's forecast with highs expected to be about 15 degrees above normal for this time of year. A frontal boundary which moved into southern and central IN on Wednesday is expected to lift north during the morning today as a warm front as mid-level ridging over the eastern one- third of the CONUS amplifies. Increasing heights aloft, light southerly flow, and limited low level cloud cover will allow temperatures to go several degrees higher this afternoon than on Wednesday. High temperatures this afternoon should top out in the mid-to-upper 80s in most locations, with a few spots potentially reaching 90 degrees. NBM probabilities of reaching 90 degrees approach 60-70% within the Louisville urban heat island, as well as within some of the deeper river valleys. Heat index values aren't particularly concerning, mainly due to the fact that dewpoints are expected to mix out into the upper 50s and lower 60s during the afternoon hours.

Outside of the warm temperatures today, winds should remain fairly light as the approaching sfc low from the west is not particularly deep, with the pressure gradient only supporting 5-10 mph southerly winds. 00Z high resolution model guidance (most notably, the HRRR)
does try to develop a few showers and thunderstorms late this afternoon, mainly along and north of I-64. Model sounding data does show greater than 1000 J/kg SBCAPE across much of the area; however, there is not much of a triggering mechanism present across the region, and the HRRR does have a tendency to be quite aggressive with convective initiation in steep lapse rate environments. As a result, will continue with silent PoPs through the evening hours tonight, though one or two brief showers or a storm cannot be ruled out.

Tonight, a weak perturbation in the mid-level flow will swing northeast across the mid-Mississippi Valley and into the lower Ohio Valley. This will help to nudge an elongated cold front close to the region by Friday morning. Increasing moisture, especially below 700 mb, will help to increase PW values from around 1" this afternoon to 1.3-1.5" by sunrise Friday. Within this moisture advection regime, scattered rain showers are expected to push into the region late tonight, with the onset of widespread rain not expected until after midnight. The probability of thunder should remain low (20% or less) tonight, as soundings show that the moisture advection in the mid- levels will greatly reduce instability. Temperatures should remain mild tonight, with lows only expected to fall into the 60s.

LONG TERM /FRIDAY THROUGH WEDNESDAY/
Issued at 342 AM EDT Thu May 2 2024

Quasi-zonal pattern with flat ridging over the southeast CONUS will yield a period of warm but at times muggy and unsettled weather.
High confidence in rain on Friday, and moderate confidence in rain on Tuesday. Notably low confidence in between, with most of the uncertainty having to do with timing.

Friday and Friday Night...Approaching cold front will interact with a moist air mass and a few disturbances in deep SW flow. Look for widespread showers to expand west to east across the Ohio Valley during the morning and continue through the evening. It's important to note that there will be breaks in the rain, but any heavier shower or embedded thunderstorm will produce brief moderate to heavy rainfall. Weak mid-level flow and modest lapse rates will limit any severe potential.

Saturday and Saturday Night...Low-confidence forecast as it depends greatly on the progression of the front on Friday night. Still looks like the front lays out somewhere across Kentucky, and there's enough post-frontal subsidence for at least few dry hours. However, model agreement is not good with roughly half the NBM ensemble members showing measurable precip, and the 00Z NAM12 lifting an upper shortwave out of the Deep South along the slow-moving front.
Our official forecast will include a 40-50% chance for showers, and at least a slight chance for thunderstorms at anytime during the day. However, do not expect rain or storms to last that long in any given location. Another, possibly better, shot at precip comes Sat night as another weak cold front moves in from the NW.

Sunday into Next Week...Daily rain chances continue through the forecast period as a parade of disturbances continues but remains difficult to time. Best potential for organized storms appears to be Tuesday, as a deep occluding cyclone over the Dakotas takes on quite a negative tilt, with a strong secondary low over the mid- Mississippi Valley driving a cold front into the Ohio Valley. Still fairly low confidence in severe wx at this point, but we still have several days to sort out the details.

AVIATION /12Z TAFS THROUGH 18Z FRIDAY/
Issued at 651 AM EDT Thu May 2 2024

VFR conditions are expected today with little more than scattered high clouds expected to stream across the region from west to east.
Winds will veer from southeasterly to southerly later this morning, with speeds increasing to between 6-10 kt for the afternoon hours.
An occasional 15-20 kt gust cannot be ruled out at BWG/HNB as slightly stronger winds aloft approach from the west late this afternoon.

Tonight, moisture will increase in the low levels of the atmosphere, with ceilings gradually building downward after sunset. Light to moderate rain showers are expected to accompany this surge of moisture, though rain rates should primarily be light enough to avoid causing impactful VIS reductions. After 06Z tonight, model guidance indicates the potential for MVFR/IFR ceilings, first at HNB and BWG before pushing east to around SDF by sunrise Friday.
However, confidence is still relatively low in exactly how far ceilings will drop, so we'll go with a VFR forecast for now at all sites except for HNB, where there is slightly higher confidence in reduced ceilings. Rain showers will spread eastward Friday morning, but the bulk of the rain chances should not arrive at LEX/RGA until around or just after the end of the current forecast period.

LMK WATCHES/WARNINGS/ADVISORIES
KY...None.
IN...None.

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