NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION. Privacy and Cookie policy

FXUS63 KLMK 081129 AFDLMK

Area Forecast Discussion National Weather Service Louisville KY 629 AM EST Fri Dec 8 2023

Updated Aviation Discussion

================================================================ Key Messages

- Strong storm system to affect the region Saturday and Sunday

- Heavy rainfall and a few strong storms Sat afternoon/eve

- Colder air returns Sunday

- Dry with seasonable temps for much of next week

================================================================


Short Term
(Today and tonight)
Issued at 257 AM EST Fri Dec 8 2023

Synopsis...Broad cyclonic flow associated with an amplifying longwave trough will extend across the CONUS during the next 24-36 hours. This trough will be accompanied by several shortwave energy impulses and notably strong cyclonic vorticity advection aloft. The northernmost stream wave is responsible for the development of an occluding cyclone moving from the northern Plains to the Midwest and subsequent pressure gradient reinforcement. On the other hand, the southernmost stream wave will be more dynamic, and therefore impactful, given the influence of a Pacific jet streak rounding the base of the trough. Last but not least, a secondary and smaller vorticity impulse/mid-level speed max will eject from the southern Plains towards the Mid Mississippi Valley Friday night helping drive a weak surface low and enhanced LLJ across the region.

Today...The combination of a broken layer of upper-level clouds and decent southerly flow has kept temperatures running a few degrees above the forecast. Nonetheless, satellite imagery shows partial clearing taking place as clouds move to the east, so it is expected that temperatures fall quicker during the rest of the night. Only caveat to the previous reasoning could be the effect of low-level clouds approaching from Western Kentucky and the Deep South related to the onset of theta-e advection and shallow lifting. Otherwise, decaying LLJ extending across the Wabash Valley will keep winds around 10 to 15 mph through around 8/14Z. Rest of today will be dry and initially sunny, but anticipate increasing clouds from west to east this afternoon as the LLJ gradually increases PW values beneath 700-mb capping inversion. In addition, highs were adjusted a few degrees up to account for the ongoing warm air advection pattern.

Tonight...Rain chances will begin to increase after midnight thanks to low-level convergence and moisture advection associated with the enhanced LLJ ahead and along the mid-level speed max and attendant weak surface cyclone. The shower activity will be characterized by shallow cells with meager instability. Therefore, lightning chances are ruled out before 9/12Z with model probabilities (SREF, NBM, HRRR) of less than 10 percent. One important thing to note in forecast soundings is the erosion of the capping inversion which hints at better nocturnal mixing and higher wind gusts overnight.

Long Term
(Saturday through Thursday)
Issued at 311 AM EST Fri Dec 8 2023

Saturday through Sunday Night...

A broad southwest flow will be in place by Saturday morning as a northern stream upper trough axis shifts from the northern Plains into the Great Lakes. A surface cold front is expected to be oriented from roughly Chicago to St. Louis to just west of Little Rock by early Saturday morning. For the morning and early afternoon hours of Saturday, cloudy skies with scattered rain showers are expected. Given the broad southwest flow, plenty of moisture will be streaming into the region, so periodic bouts of heavier rainfall will be possible with the showers. As the front draws closer, gradient winds will pick up and wind gusts of 25-30 mph will be possible in the afternoon. Temperatures are expected to warm into the low-mid 60s.

Higher impact weather is expected to develop by late Saturday afternoon into Saturday evening as the surface cold front pushes into central KY as deeper layer shear overspreads the region from the southwest. Secondary upper level wave within the southern stream will force cyclogenesis across west TN with the surface low riding northward along the cold front. This low will likely cross central KY during the evening hours. The overall setup continues to have quite the spread within the short term higher resolution guidance. The convective setup is the classic high shear/low instability setup that we typically see. A look through model proximity soundings across the CWA shows this quite well with decent shear for organized severe weather, but instability still looks rather meager. Enough instability and forcing will be present for some thunderstorms, but the best combination of shear/instability for severe weather will reside a bit to our south and west. Given the thermodynamic and kinematic parameters, the main risk of severe would be damaging winds in any stronger storm that develops. If some line segments can develop, there is a small, but non-zero threat of QLCS embedded mesovortices within the line. Current SPC day 2 risk has much of the region in a marginal risk. This seems appropriate given the parameters. However, we generally think the highest risk of any severe weather will likely reside across far southern KY Saturday evening. Given anomalously high PWATs and expected forcing, moderate to heavy rainfall will be possible Saturday evening. Given the recent dryness, we do not expect FFG values to be exceeded, though ponding of water on roadways and some quick rises on area creeks and streams will be possible. Rainfall amounts of 1-2 inches are likely with the highest QPF swath running from roughly Bowling Green northeast through Lexington. The threat of thunderstorms will rapidly decrease by late evening as the cold front pushes east. Plenty of post frontal precipitation will linger and colder air will drop into the region from the northwest. By sunrise Sunday, temps will range from the upper 30s over our SW Indiana counties to the mid-upper 40s in areas east of I-65.

For Sunday, surface cold front will continue to head eastward and ongoing precipitation is likely to be in progress Sunday morning but this precipitation will diminish rather quickly from west to east during the morning and into the afternoon hours. Highs temps for Sunday will likely be right at midnight with temps throughout the day hanging out in the upper 30s to around 40. As colder air aloft comes into the region, lapse rates will steepen through the afternoon and additional light rain showers, perhaps mixed with a little snow at times will be possible. Some additional snow flurries may persist into Sunday evening mainly over the northeast sections until further drying within the column commences. Lows Sunday night will be colder with readings dropping into the mid 20s.

Monday through Thursday...

Upper trough axis should be well to our east on Monday with the region remaining in a northwest flow. The upper level flow will become zonal by midweek with some ridging building in aloft for the late part of the week. Generally speaking, next week looks to be dry with slow moderating temps from Monday onward with seasonal readings expected. Coldest day of the week will be Monday with highs in the upper 30s to the lower 40s, with overnight lows in the 20s. Temps will bump back up by Tuesday with highs in the the upper 40s to the lower 50s. Similar highs are expected for Wednesday and Thursday. Overnight lows here will generally be in the upper 20s/lower 30s.

Extended Forecast Discussion...

Moving beyond Thursday, dry weather looks to start off the extended period. Signal analysis shows a signal crossing the area around Sat/Sun (12/16-17) with another signal crossing around 12/24-25. In terms of the teleconnection pattern, the very beginning of the period looks to feature a +NAO/Neutral AO/+EPO/+PNA pattern. What is more interesting to watch early next week is the development of strong pressure anomalies across southern Siberia (north of Tibet).
This will likely result in a positive east-Asian mountain torque which will likely result in the Pacific jet becoming very strong and gradually extending well into the Pacific. Negative height anomalies are expected to persist across AK in the extended period resulting in the +EPO pattern continuing.

While most of the dynamical modeling shows the MJO orbiting into the cooler phases of 7/8 towards Christmas, I have concerns that the Pacific jet may remain strong during the period keeping the +EPO pattern in place. If that is the case, a flood of modified Pacific air will continue to affect the CONUS in the near term. It does appear that a retraction and decrease in the Pac Jet will come about towards late December with ridging building into AK setting the stage for the EPO to drop with the well advertised colder pattern for the central/east US developing towards year end.

Aviation
(12Z TAF Issuance)
Issued at 627 AM EST Fri Dec 8 2023

Impacts/Confidence: - Medium confidence in brief period of LLWS for HNB & SDF this morning - High confidence in gusty SW winds today and tonight - High confidence in MVFR ceilings late tonight

Discussion...VFR conditions will prevail during most of this TAF period with MVFR ceilings taking over by the end of the forecast.
Although the first half of the morning will feature SKC, satellite imagery already shows expanding low-level cloud cover over the Mid Mississippi Valley in response to enhancement of the LLJ. Such cloud layer will eventually translate through the region and although the cloud base will stay around 5 kft, there is a non-zero chance of MVFR ceilings at HNB around noon. Furthermore, ongoing LLWS at HNB and SDF will subside around 8/14Z as daytime mixing begins and gusty SW winds between 18-22 kts carry on through the afternoon. For tonight, a weak low pressure system tracks north and west of the OH Valley supporting wind gusts and MVFR ceilings. There is also a chance of another LLWS mention, but the presence of wind gusts overnight lowers the confidence at this moment.

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

toggle option: (graph/table)

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

Louisville, KY,