Scientific Forecaster Discussion
000 FXUS64 KJAN 091103 AAA AFDJAN Area Forecast Discussion...UPDATED National Weather Service Jackson MS 503 AM CST Mon Dec 9 2019 .UPDATE... Updated for 12Z aviation discussion && .AVIATION... 12Z TAF discussion: Variable IFR/MVFR conditions early this morning will become predominantly MVFR by mid morning and VFR this afternoon into the early evening. Isolated showers will begin developing by late morning with more widespread rainfall developing during the evening and continuing through the end of the period as a cold front enters the region from the northwest. Just ahead and behind the front, IFR/MVFR conditions will develop during the evening and overspread the area overnight with the southward movement of the front./GG/ && .DISCUSSION... Through tonight: WV imagery this morning showing our next weather maker in the form of a mid level wave dropping south through southern CA into northwestern Mexico. In advance, a large swath of moisture has been tapped from west of Baja and is being funneled northeastward across the southern CONUS in increasingly southwest mid level flow. Already, mid/high level cloudiness has built into the region. At the surface, high pressure remains centered off the east coast while a shallow cold front approaches the MS valley from the Plains. The tightening pressure gradient ahead of the boundary will allow low level winds to increase today, especially over the open areas of the ArkLaMiss Delta. As the southwest flow aloft continues and low level winds increase today, moisture levels will increase steadily in the column, enough so for showers to be possible by late morning/afternoon over the south and west. Coverage of showers will increase from the northwest tonight as convergence along the frontal boundary encounters increasing low level moisture. Some thunder looks possible over the south where model soundings are indicating 300-500 J/kg of skinny CAPE ahead of the boundary. With the mid level energy moving into the region after midnight, backing winds aloft will allow widespread isentropic rains to break out, especially overtop the passing boundary./GG/ Tuesday Night through Sunday: Really the only period of interest for the remainder of the week will be Tuesday into Tuesday night as the anticipated shortwave trough swings east over our region and a colder post-frontal air mass seeps in from the northwest. With the right entrance region of the upper-level jet positioned overhead into Wednesday night, frontogenesis through the mid- levels should continue to support precipitation falling behind the cold front. Drier air will gradually work in aloft and at the surface as the trough axis moves eastward, but there may be enough of a window for a wintry mix to develop in the cooling air mass. Looking at forecast soundings especially across northern Mississippi and southeast Arkansas, the column will be awfully close to the tipping point between all rain and all snow, with precipitation rates being increased due to dynamics aloft. Given the uncertainties of just how much of a warm layer will remain aloft, and if low-level temps can chill to near freezing, weather type has been set at a mix of rain or snow mixing into areas generally around the US Highway 82 corridor and northwards. Have also included a light accumulation of snow up to around one quarter of an inch in those areas, but warmer ground temperatures and the likelihood of standing puddles, etc. before any kind of transition can occur will probably limit much if any accumulation. Will also include a "Limited" threat area for winter weather to the Hazardous Weather Outlook text and graphics for this potential. For areas to the south of this zone, a little light wintry mix cannot be ruled out as precip tapers off Tuesday night, but confidence in a change over is much lower to include in the weather grids at this time. The rest of the forecast is relatively low key, with a gradual warming trend ahead of the next shortwave trough passage over the weekend. A chance for showers will return to parts of the forecast area Friday into Saturday as this system passes, but at this time do not anticipate thunderstorms or winter weather to be of any concern for the weekend. /NF/ && .PRELIMINARY POINT TEMPS/POPS... Jackson 73 50 53 35 / 29 89 100 96 Meridian 72 55 63 36 / 18 75 100 99 Vicksburg 76 47 50 34 / 26 89 100 84 Hattiesburg 74 60 69 40 / 20 60 98 98 Natchez 76 52 54 36 / 28 89 100 93 Greenville 72 41 43 30 / 21 84 100 55 Greenwood 71 44 45 30 / 21 88 100 73 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...None. LA...None. AR...None.