Scientific Forecaster Discussion
000 FXUS64 KLIX 200516 AFDLIX Area Forecast Discussion National Weather Service New Orleans LA 1116 PM CST Tue Nov 19 2019 ...UPDATED AVIATION DISCUSSION... && ..EVENING UPDATE... /issued 718 PM CST Tue Nov 19 2019/ Performed a gridded forecast update this evening - with the main focus being forecast lows tomorrow morning/highs tomorrow afternoon and dense fog potential early AM. Taking a look at the latest 00Z HRRR guidance valid for 12Z tomorrow morning, comparing it to what was initialized in the 12Z run yesterday morning shows a similar overall atmospheric profile. Only notable difference is a slightly stronger surface subsidence inversion and a bit more of a southerly surface to low-level flow developing (to around 1,000ft AGL). Given this, areas of dense fog will likely develop again around the same areas as last night (generally along/west of I-55 including the southshore and coastal southern Louisiana). Will likely issue a Dense Fog Advisory later tonight before 10PM to get an early heads up for those traveling early tomorrow morning, with possible expansion where needed as observations indicate. Similar to last night, blended guidance continues to come in a bit too warm with overnight lows. Dropped temperatures slightly (not as much as last night) with focus on area drainages from the northshore east across the MS coast). Blended guidance still is struggling with afternoon highs a bit, as some locations today reached the mid to upper 70's - which confirms this cooler bias. Have manually bumped up highs tomorrow to a more realistic forecast. KLG .PREV DISCUSSION... /issued 332 PM CST Tue Nov 19 2019/ High pressure is in place and will persist through Thursday. This high pressure is bringing drier air and a bit warmer air into the region for the next few days. Wednesday and Thursday, winds will primarily be southerly, bringing in some moisture from the Gulf into the region as well. Friday and Friday night, a low pressure system will move through the area. Winds leading up to the event will remain southerly, continuing to fuel moisture into the area. Some upper level divergence will help to provide some lifting for the area Friday. The abundant moisture presence combined with the lifting will further be enhanced by the front, however, this front currently seems weak, looking at the models. As a result, there will likely be rain showers with the chance of a thunderstorm Friday and Friday night. If the front remains weak like the models show, then the threat of severe weather would be low. The main threat if the front remains weak would just be rain and scattered thunderstorms. In addition, some gusty winds and frequent lightning would be a concern Friday and Friday night as well. Saturday through the beginning of next week, high pressure builds in, which will help to stabilize the atmosphere. In general, this stable air will help to dry out the area, so the rain chances are pretty low for the beginning of next week again. MSW .AVIATION... .UPDATED 0516Z... Main focus tonight will be patchy dense fog, primarily for areas along and west of I-55 and especially south of I-10/12. Main impacts for area terminals will be periods of reduced visibility at the surface, leading to IFR/LIFR flight categories. Otherwise, any area fog will likely dissipate shortly after sunrise (or after 13-14Z) revealing prevailing VFR conditions throughout the day/rest of the forecast period. KLG .MARINE... Winds will be variable today, shifting to southeasterly tonight and tomorrow and calm (<15 knots). Winds will be southerly and light (<15 knots) through Saturday. Saturday through Sunday, winds will be stronger (15-20 knots) and northerly. Sunday through early Tuesday morning, winds will be northerly and calm (<15 knots). Tuesday through Wednesday, winds will be southerly and stronger (15-20 knots). Wave heights will correspond with the wind speeds. MSW .DECISION SUPPORT... DSS code: Blue. Deployed: None. Activation: None. Activities: Fog Advisory through 8AM. Decision Support Services (DSS) Code Legend Green = No weather impacts that require action. Blue = Long-fused watch, warning, or advisory in effect or high visibility event; Marginal risk severe or excessive rain. Yellow = Heightened impacts with short-fused watch, warning or advisory issuances; radar support for slight risk severe or excessive rain. Orange = High Impacts; Enhanced risk severe; nearby tropical events; HazMat or other large episodes. Red = Full engagement for Moderate to high risk of severe and/or excessive rainfall, or direct tropical threats; Events of National Significance. && .PRELIMINARY POINT TEMPS/POPS... MCB 45 75 50 74 / 0 0 0 0 BTR 46 78 53 77 / 0 0 0 0 ASD 44 75 50 75 / 0 0 0 0 MSY 51 75 56 75 / 0 0 0 0 GPT 47 72 52 72 / 0 0 0 0 PQL 43 75 49 75 / 0 0 0 0 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...Dense Fog Advisory until 8 AM CST Wednesday for LAZ046-049- 056>061-063-065>069. GM...None.