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FXUS64 KMRX 031841 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 241 PM EDT Fri May 3 2024

New SHORT TERM, LONG TERM

SHORT TERM
(This evening through Saturday)
Issued at 240 PM EDT Fri May 3 2024

Key Message:

A few instances of small hail, gusty winds, and locally heavy downpours are possible this afternoon with showers and thunderstorms.

Discussion:

Currently showers and thunderstorms are traversing across much of the southeastern United States being aided by a shortwave moving through the Tennessee Valley this afternoon. As of this writing there is predominantly just rain showers, but increasing instability means we'll likely see more thunderstorms moving through the southern Appalachians through the rest of the evening.
Soundings and CAMs are still showing a few hundred (maybe up to near 1000) J/kg of MLCAPE the rest of this afternoon. Combine this with a fairly week lapse rate and very little shear, and the chances for widespread sever weather continue to look low. With that being said an individual thunderstorm could bring brief heavy rain, small hail, and gusty winds in areas that have destabilized this afternoon. With how slow these storms are currently moving and the possibilty of multiple storms over a small area, the biggest threat the rest of the afternoon/evening is likely to be flooding of low lying or poor drainage areas.

As we head into the overnight hours we should see a lull in activity, and although the threat of rain does not go away, but the risk of lightning and strong storms really decreases as the shortwave exits the area and the atmosphere becomes more stable overnight.

On Saturday we will likely see a similar story as today, with morning showers transitioning into afternoon thunderstorms with heavy rain, small hail, and gusty winds as the primary hazards in the strongest storms. Forecast soundings show a similar environment with weak to moderate CAPE and weak shear, so once again widespread severe weather looks unlikely.

LONG TERM
(Saturday night through next Friday)
Issued at 240 PM EDT Fri May 3 2024

Key Messages:

1. An unsettled pattern is expected through the extended period with daily scattered to numerous showers and storms. More organized convection is possible by Wednesday/Thursday of next week.

2. Temperatures will be generally above normal.

Discussion:

We start the period with a fairly weak upper level flow pattern over the region and a short wave moving through. Most model guidance suggest the short wave will exit by early Sunday, with short wave ridging building in. This may allow for less coverage of showers and thunderstorms Sunday afternoon, but it still looks like there will be enough moisture and instability for at least scattered convection. The upper level ridging looks to be short lived as another short wave aloft moves in Sunday night/Monday, along with more numerous showers and thunderstorms. Models suggest modest instability with MLCAPES likely around 100J/kg or less for both Sunday and Monday and shear will be on the weak side given the weaker flow. However some stronger storms with gusty downburst winds will be possible as well as locally heavy rainfall rates given the near 90th percentile PWATs (around 1.4 inches both days).

The unsettled pattern will continue for the Tuesday through Friday time frame, although timing of individual short waves in the flow is uncertain. Ensembles do suggest a more dynamic pattern developing with the upper jet nosing in from the west/northwest then dipping south, and mean 850 mb flow will likely increase to 30+ kts and may exceed 40 kts at some point during the period. In addition, a cold front is forecast to be moving in from the northwest by the end of the period. There are still model differences and timing questions, but the data does indicate that by Wednesday we will see an environment with potentially better thermodynamics and deep-layer shear sufficient for more organized convection than in the earlier part of the extended period. This will bear watching going forward.

The long term period will generally feature temperatures above seasonal normals, although precipitation timing/coverage may help to hold high temperatures down on some wetter days, and the cold front moving in Friday is expected to help hold temperatures Friday down closer to normal although timing that far out is of course still very uncertain.

AVIATION
(18Z TAFS)
Issued at 111 PM EDT Fri May 3 2024

Showers and thunderstorms can be expected in the southern Appalachian region through the rest of the daytime hours today.
Difficult to say exactly when a storm may impact a terminal and there could be several rounds of storms through the evening hours.
Expect mostly showers, but cannot completely rule out lightning in the vicinity of the airports. We should see a lull in activity overnight, with more widespread storms and lightning expected tomorrow.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 84 66 81 64 / 70 70 80 30 Knoxville McGhee Tyson Airport, TN 77 63 78 63 / 80 70 90 50 Oak Ridge, TN 76 63 78 62 / 90 60 90 40 Tri Cities Airport, TN 79 61 76 59 / 70 50 90 60

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

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