Area Forecast Discussion
Issued by NWS Jacksonville, FL

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000 FXUS62 KJAX 160054 AFDJAX Area Forecast Discussion National Weather Service Jacksonville FL 854 PM EDT Tue Oct 15 2019 .UPDATE... Latest analysis shows nearly stationary front near the I-10 corridor with the best instability over northeast FL, although weak, supporting a little more convective echoes per radar trends with scattered showers and an isolated embedded thunderstorm or two. SB CAPE instability is about 400-800 J/kg over northeast FL, which will more or less remain intact overnight based on latest forecasts from RAP. Further north over southeast GA, better rain chances exist as shortwave disturbances traverse that area from west to east, enhancing lift and spreading stratiform rains and embedded showers there. A few storms will be possible overnight but weak lapse rates and little instability aloft should keep them brief and isolated. As sfc frontal wave over TN valley consolidates and moves east- northeast tonight, the frontal boundary near I-10 will push northward. Scattered to numerous showers and an isolated storm expected and not expecting much change in the forecast at this time. Lows in the upper 60s to lower 70s tonight. && .AVIATION... [Through 00Z Thursday] Multilayered clouds with periods of showers and possible isolated thunderstorm expected through Wednesday aftn, with MVFR at times for SGJ and SSI in the near term. Additional showers expected by Wed morning and MVFR vsby and cigs will be possible from around 09z-15z. T.-storm chances are too small to include in the TAFs at this time. && .PREV DISCUSSION [357 PM EDT]... .NEAR TERM [Through Wednesday]... Stationary front over SE Georgia this afternoon is the focus for areas of rain with embedded showers and a few thunderstorms, primarily along and north of the front over SE Georgia. Mid/upper level impulses riding east in zonal flow over the SE U.S. will prevent the front from moving much through tonight. As a result, the highest rain chances will remain over SE Georgia for much of the near term, along with a chance of a couple of stronger thunderstorms late this afternoon through the overnight, especially given the 30-40 knot wind maximum at 850 mb moving through the area and increasing shear/helicity values. Locally heavy rainfall will be enhanced tonight by a surface low pressure area moving east along the front, with the Weather Prediction Center placing SE Georgia in a marginal risk for excessive rainfall through sunrise Wednesday. South of the front, scattered showers and thunderstorms developing over the Florida panhandle this afternoon will move east and approach NE Florida towards sunset, although timing suggests that this activity will likely weaken due to loss of daytime heating and associated instability. Nevertheless, there should be enough dynamics to support scattered showers and a few thunderstorms across NE Florida through the overnight. As is the case north of the front, there could be a strong storm or two late this afternoon, especially from Lake City west. On Wednesday, a sharp mid-level trough anchored over the Great Lakes is expected to move east and sweep a longwave trough through the SE states, acting to move the front east/south across our area as the day progresses. Chances for showers and thunderstorms will persist during the first half of the day, with 40- 50 kt mid-level flow providing enough support for a few thunderstorms along and ahead of the advancing front. Lack of low level convergence along the front and unidirectional flow should preclude widespread stronger storms. Rain chances decrease from west to east during the afternoon as the front moves through, with most of the rain chances confined to our southernmost counties by the end of the day on Wednesday where the front is expected to lie at that time. Low temperatures tonight will remain in the upper 60s to lower 70s, and high temperatures reaching the 80s (warmest across NE Florida) on Wednesday. .SHORT TERM [Wednesday Night Through Friday Night]... Clearing skies and cooler air will overspread the region Wednesday night in the wake of the front, with dry and pleasant conditions on Thursday as continental high pressure builds in from the NW. Low temperatures Wednesday night will drop into the 50s north and west of JAX, and 60s from JAX south. High temperatures on Thursday will remain in the 70s over much of the area, with lower 80s south of JAX. The clear skies will not last long, however, as a closed mid-level low pressure area over Texas and a surface low over the extreme western Gulf of Mexico help to spread mid and high level moisture back over the area late Thursday night. This trend towards cloudier skies will continue on Friday as the mid/upper low moves slowly E-NE. Clouds should thicken during the day on Friday, especially over NE Florida, with light rain possibly affecting far southern areas by Friday night. Models differ somewhat in the timing of the deeper moisture and precipitation onset, with the GFS faster/earlier than the ECMWF and Canadian model, as well as the regional NAM. With these timing differences in mind, will introduce low rain chances Friday night mainly south of I-10. Low temperatures Thursday night will dip into the 40s over SE Georgia away from the coast, and 50s elsewhere. Highs on Friday will be in the 70s, then moderating lows Friday night about 5-7 degrees warmer than the previous night as clouds increase across the area and flow turns E-SE advecting warmer air. .LONG TERM [Saturday Through Early Next Week]... The low pressure over the Gulf of Mexico and SE U.S. will lift NE this weekend, and the wind flow will turn southerly across the area in response. Models again showing some differences in the location of the axis of deeper moisture return, with the GFS farther east and the ECMWF a little to the west. All in all, expect scattered showers and a few thunderstorms to return to the region this coming weekend, especially on Sunday. This trend looks to continue into early next week, as models are in good agreement at this time on a deep longwave trough setting up over the eastern U.S. and the next cold front approaching the area. Temperatures will warm up quite a bit and highs will return to the 80s during this time frame, along with humid conditions. .MARINE... Showers and thunderstorms will gradually increase over the next 24 hours as the stationary front over the SE Georgia waters eventually moves SE and through the local waters Wednesday night. Increasing S to SW wind to 20 knots or greater will result in a Small Craft Advisory starting overnight and continuing through Wednesday afternoon. Following the frontal passage Wednesday night, wind turns NW to N and gradually decreases to 10 to 15 knots on Thursday, then NE-E 10 knots on Friday. High pressure will move over the western Atlantic this weekend, and wind will turn SE to S and increase to around 15 knots for this coming weekend. Seas will peak at 5 feet over the offshore waters Wednesday, then remain mainly in the 2-4 ft range Thursday into the upcoming weekend. Rip Currents: Persisting long period swells will result in a moderate risk through Wednesday. .FIRE WEATHER... Cloudy and mainly wet/humid conditions tonight, then gradually drying on Wednesday as a cold front moves through the area. Minimum relative humidity values drop below 35 percent on Thursday, mainly north of a St. Augustine to Gainesville line. Transport winds and dispersion values will increase Wednesday and remain at moderately high levels on Thursday. .HYDROLOGY... River levels will remain elevated along the St Johns River with continued minor flooding in Putnam county during high tide into tonight. && .PRELIMINARY POINT TEMPS/POPS... AMG 67 81 50 73 48 / 80 30 0 0 0 SSI 72 83 59 74 58 / 70 40 10 0 0 JAX 71 87 59 78 56 / 70 50 10 0 0 SGJ 72 86 65 78 61 / 20 60 20 0 0 GNV 71 86 62 79 56 / 60 90 20 0 0 OCF 72 86 66 82 59 / 50 80 20 0 0 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...Coastal Flood Advisory until 6 AM EDT Wednesday for Putnam. GA...None. AM...Small Craft Advisory from 2 AM to 5 PM EDT Wednesday for Waters from Altamaha Sound GA to Fernandina Beach FL from 20 to 60 NM-Waters from Fernandina Beach to St. Augustine FL from 20 to 60 NM. && is the U.S. government's official web portal to all federal, state and local government web resources and services.