Memphis, Tennessee

New DISCUSSION, AVIATION, FIRE WEATHER

• Isolated rain chances will return this afternoon, becoming more widespread by Sunday morning. There is also a low (30%) chance of thunder Sunday morning.
• After a brief break from the rain on Monday, showers and thunderstorms return to the forecast for Tuesday into Wednesday.

A change in our long-standing dry weather pattern is finally upon us after a month of arid weather through the month of October. An upper trough along the leading edge of enhanced subtropical southwesterlies will swing across the Mississippi River Valley today and Sunday. Height falls and weak DPVA will aid in mid-level ascent while moisture increases throughout the column. Morning upper air observations from both LZK and OHX show that moisture is abundant above 500 mb with lingering drier layers below. For now, this will lead to mainly virga over the Mid-South, but steady, southerly low-level moisture advection will soon allow for rain to reach the surface this evening. So, expect mainly scattered rain showers this evening during Halloween trick-or-treating. Later in the night, low-level warm advection is forecast to bring 850 mb theta e values high enough to produce 500 - 1000 J/kg MUCAPE as far north as interior portions of West Tennessee early Sunday morning. Therefore, a few thunderstorms are not out of the question, mainly after Midnight Sunday and into Sunday morning. MUCAPE values will decrease through Sunday after the upper trough exits the region and upper level heights begin to rise, warming much of the profile above 700 mb and leading to a steady decrease in the coverage of showers and thunderstorms. Forecast rainfall accumulation values currently sit around an inch, especially near the Tennessee River.

Shortwave ridging is forecast to build in over the region in response to increased low-level warm advection ahead of a new system over the Rockies early this upcoming week. Expect highs, which will remain largely in the 60s and low 70s this weekend, to jump into the mid 70s Monday and Tuesday with dry weather. While this is occurring the trough will finish phasing with the jet streak within the subtropical southwesterlies located behind this weekend`s trough, eventually ejecting out of the Rockies late Monday. A third trough will dive south out of Canada and into the northern Plains after this point, tugging the ejecting trough further north, leaving behind weaker, open flow across the southern Plains. This area of weaker flow will then become pinched off and less progressive, losing amplitude as it nears the Mid-South Wednesday. Additionally, the surface cyclone will more closely follow the amplified portion of the upper pattern through the Midwest and Great Lakes with only a stalling cold front and a nebulous area of surface low pressure over our region; a trend that has only gained momentum in the last day. The end result is increasing uncertainty in previously forecast rainfall amounts as the NBM 48 hour rainfall values for Tuesday through Wednesday are now approaching 1.5". For now expect around another inch next week with the potential for big swings towards massive under- and over-performance of rainfall.

The forecast dries out through the end of the period as the upper troughing lifts north and east away from the region and upper ridging brings in mid-level subsidence. A new shortwave trough will eject from the Rockies and travel towards the Mid-South late Thursday. However, with no substantial frontal passage earlier in the week, no surface temperature gradient will be present to produce surface cyclogenesis. This will aid in keeping the forecast dry and mild towards the end of the period.

VFR conditions are expected to prevail for the start of the 18Z TAF period. A southern stream trough will move across the Lower Mississippi Valley later this afternoon into Sunday, resulting in an increase in rain showers with time. There is moderate to high confidence for MVFR and IFR conditions developing late tonight into Sunday morning. PROB30 groups were introduced for MEM and TUP overnight into Sunday morning with the presence of marginal but sufficient elevated instability for a few elevated thunderstorms. E/SE winds will prevail for much of the period.

Fire weather danger will begin to lessen through the next 48 hours as low level humidity returns alongside wetting rains and extensive cloud cover. Minimum relative humidity values are forecast to surge well above 40% beginning Saturday afternoon, remaining at this level through the remainder of the forecast period with two rounds of wetting rains; this weekend and the middle of next week. Therefore, elevated fire danger is not expected through the forecast.

AR

None.

MO

None.

MS

None.

TN

None.