Sunrise 6:36 AM   Sunset 8:29 PM Moonrise 4:33 AM   Moonset 6:06 PM

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FXUS64 KMRX 061846 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 246 PM EDT Mon May 6 2024

New SHORT TERM, LONG TERM

SHORT TERM
(This evening through Tuesday)
Issued at 244 PM EDT Mon May 6 2024

Key Messages:

1. Scattered to numerous showers/storms this afternoon/evening will diminish later tonight. A few storms mainly southern half may be strong to severe this afternoon/evening.

2. Scattered showers and storms expected again Tuesday, with a few strong to severe storms possible again mainly in the afternoon.

Discussion:

We will start the period with an MCV moving in from the west. We will see additional showers and thunderstorms this afternoon into at least the early part of tonight, with the greatest coverage likely to be across the central and north with the better forcing. However, the best instability and bulk shear will overlap across the south into central areas late this afternoon and evening, so a few storms especially south/central may become strong to severe with strong gusty winds and hail the main threats. Isolated supercellular structures also look possible in this environment, so there also is a very low risk of a brief tornado this afternoon/early evening again mainly southern half. Some isolated to scattered convection may linger for much of the night mostly north although this should be weaker as convective energy lessens.

Tuesday will see short wave ridging over the area although the axis will shift to our east during the day. Convective energy will build with heating and most sources indicate MLCAPES are likely to peak in excess of 1,500 J/kg with deep-layer shear reaching at least 30 to 35 kts. Overall model guidance including the CAMS suggests more isolated to scattered coverage, but given the thermodynamic and shear profiles there is a threat that some storms will become severe with damaging winds and large hail again the primary threats.

LONG TERM
(Tuesday night through next Monday)
Issued at 244 PM EDT Mon May 6 2024

Key Messages:

1. Unsettled weather with potential for strong to severe thunderstorms most likely late Wednesday. Increasing potential for isolated flooding in saturated locations.

2. Cold front to pass through Friday morning, with a cooler airmass settling in through the weekend.

Discussion:

Unsettled atmosphere continues, with not much changes from the overall thinking the last couple of days. Weak shortwave ridge will be headed out Tuesday night from the region, and a dual jet streak setup will be hanging over the central US, with a stronger polar jet to the north and a weaker subtropical jet nosing in across Texas into northern Mississippi. The largest question Tuesday night through Thursday is when do storms form and move into East Tennessee and surrounding areas. Long range CAM guidance is just moving into range for Tuesday night. There's some questions given the expected ridge in the short term period, but convection may redevelop in the evening across portions of the area, most likely Virginia and to our north and northeast. If convection does fire and then move in, there's enough shear by this time to support a severe storm, but the biggest question will be if a storm can translate that to the surface, given nighttime loss of instability and low level stability questions.

Wednesday is a big unknown daytime. The shear and instability should be present, but the last ingredient is lift and that seems to be lacking. The high res NAM is just within range and it doesn't show much activity aside from an errant left splitter. The larger global guidance does have some thunderstorm activity during the day on Wednesday, with the GFS and its ensemble being particularly aggressive, and the Euro ensemble more conservative. Should those more conditional storms fire, environment would be conducive to severe wind and hail. On a wider view, thunderstorms are expected to fire out over the Ohio River to Mississippi River intersection, and should grow upscale with time. These storms are higher confidence in origination and formation, and will move our direction heading into Wednesday night. Still, plenty of questions on when exactly they reach our area and how much instability will be present then. The most likely risk would be with damaging straight line winds in these storms. Assuming an overnight arrival (based off current guidance), low level instability could be hard to come by if an inversion sets up before the line arrives.

Timing arrival of the potential MCS or linear system will then influence how much recovery can take place into Thursday to allow for a final round of showers and thunderstorms. Stronger storms look to remain to the southeast of Tennessee outside our area on Thursday. Last thing of note to mention is high PWATs combined with the several days of thunderstorms and an expected MCS Wednesday night is still consistent with the potential for isolated flooding.
Thus far storm coverage has been intermittent enough to allow for efficient runoff, but flash flood guidance has dipped a bit, especially in northeastern Tennessee where 3 hour guidance has dipped to 2 inches. Locations that receive repeated rounds of thunderstorms may see minor or urban flooding issues.

Finally we get to the high confidence portion of the forecast. The GFS and Euro are in agreement (and their ensembles seem to match closely as well) with a cold front passing through the region on Friday morning. In association with the frontal passage, a longwave trough will settle in over the Eastern United States on through the weekend, 850mb temperatures are in the single digits in both sets of guidance. Checking Nashville sounding climatology, this is good for the 10th to 25th percentiles for this time of year. End result is this airmass will result in rather pleasant afternoons for the wider region! Shower chances are fairly low (20 to 30%) at this range over the weekend, and will come down to how much lift the rotating shortwaves in the overall trough can help generate showers. Apart from the potential for scattered showers, the weekend will be pleasant and calm.

AVIATION
(18Z TAFS)
Issued at 113 PM EDT Mon May 6 2024

Will see additional convection around during the period, with the best chance looking to be during the late afternoon/early tonight time frame. Will try to time highest probability period with VCTS and tempo thunder groups. Otherwise, there may be some MVFR or lower conditions with low clouds and/or fog around during the early morning hours, but probability of occurrence does not look high enough to include for now. Outside of any convection, will have a VFR forecast.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 66 86 69 87 / 30 30 60 60 Knoxville McGhee Tyson Airport, TN 63 84 67 83 / 60 30 60 50 Oak Ridge, TN 62 83 66 83 / 60 40 60 60 Tri Cities Airport, TN 60 81 64 81 / 60 30 60 50

MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.

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