textproduct: Memphis

SYNOPSIS

Issued at 234 AM CST Thu Dec 26 2024

Expect periods of showers and thunderstorms with intermittent lulls in precipitation through Saturday night. Any rainfall today will remain light, but more organized thunderstorms will bring a potential for gusty winds and locally heavy rainfall to the area tonight into early Friday. Another system will affect the area on Saturday with improving conditions Sunday and Monday. A gradual warming trend will continue into the weekend with temperatures topping out in the 60s Friday through Monday. Slightly cooler conditions are expected Tuesday of next week as rain chances return to the Mid-South.

DISCUSSION

(Today through Wednesday) Issued at 234 AM CST Thu Dec 26 2024

The first in a series of shortwave troughs is moving through the Lower MS Valley early this morning. Shortwave ridging in its wake will provide a bit of a lull in the rain chances much of today. Low-level isentropic ascent is not as strong as previous days and synoptic-scale subsidence in the wake of the trough axis should promote mostly dry conditions through at least mid-afternoon. However, the next shortwave trough will approach the area tonight. This wave is more potent that the previous and will provide substantial QG forcing that will overspread the CWA after sunset. HREF paintballs are consistent in bringing a quasi-linear MCS through the Mid-South tonight, reaching the MS River within a few hours either side 11 PM.

Surface-based instability is largely lacking with this setup with an isothermal (to slightly inverted) temperature profile in the lowest 1 km. Storms will likely be rooted at the top of this inversion where lapse rates are ~6.5 C/km which is hardly impressive. This means that updrafts will not be able to tap into the significant low-level helicity present on forecast hodographs, resulting in largely straight to slightly cyclonically curved plots. A few elevated supercells are possible should instability overachieve. Otherwise, tonight's convection will probably have more bark than bite with a generally low severe weather threat across the CWA. The most likely hazard is locally heavy rainfall. Widespread rainfall amounts of 1-2 inches are expected through midday Friday with localized amounts of 2-3 inches across the MS Delta.

Another fast-moving wave will swing across the Mid MS Valley Friday afternoon. Most of the dynamic forcing with this system will pass to our north and the short recovery time following the previous system will significantly limit organized convection. This will put the focus on the Saturday system which is currently progged to traverse the Ozarks during the afternoon/evening. The prevailing question mark with this system is how much instability will be realized. LREF (GEFS + EPS + GEPS members) mean SBCAPE for Saturday afternoon is generally 200-500 J/kg south of I-40 with 90th percentile values near 500-750 J/kg. Complicating this forecast is the potential for morning convection that could contaminate the thermodynamics, lending relatively low confidence to this forecast.

Effective bulk shear near 50 kts is sufficient to support organized convection should the instability pan out as advertised and a strong, veering wind profile is supportive of cyclonically curved hodographs with 250 m2/s2 of effective SRH. A conditional risk area is certainly not out of the question for the Day 3 period. In addition to the severe weather threat, we'll be watching the heavy rainfall potential, mainly east of the MS River. Rain chances will gradually end from west to east late Saturday night as a Pacific cold front traverses the region.

Expect mostly dry weather Sunday and Monday under a rapid quasi- zonal flow aloft. Highs are forecast to be in the 60s with lows in the 40s (compared to climatology of 50/35 at Memphis). A fast- moving trough will bring rain chances back to the area on Tuesday along with another cold front. This will knock temperatures back at or below normal by midweek as a longwave trough digs over the central CONUS. Morning lows are forecast to be back near the freezing mark by Thursday.

MJ

AVIATION

(06Z TAFS) Issued at 1100 PM CST Wed Dec 25 2024

VFR conditions will prevail for most of the remainder of the night. MVFR CIGS will then return to KJBR and KMEM between 10-15Z but will likely bounce back to VFR after 19-21Z. Biggest concern of the TAF period will be a line of convection that moves into KJBR and KMEM after 04Z but will impact the TAF sites for the remainder of the TAF period. CIGS and VSBYS will deteriorate with the line. Light SE winds overnight will increase to 10 KTS after 14-15Z. Speeds will increase further after 00Z. In addition, the low level jet will strengthen after sunset. Will keep mention of low level wind shear in at KMEM.

KRM

MEG WATCHES/WARNINGS/ADVISORIES

AR...None. MO...None. MS...None. TN...None.