textproduct: Jacksonville

KEY MESSAGES

For the latest NE FL and SE GA Daily Key Messages please visit: https:/www.weather.gov/media/jax/briefings/nws-jax-briefing.pdf

- Scattered Strong to Isolated Severe Storms Possible this Afternoon and Evening, Mainly along the I-95 and U.S. Highway 301 Corridors. Potential Hazards: Damaging Wind Gusts, Small Hail, Frequent Lightning Strikes, and Heavy Downpours.

- Scattered Severe Storms on Monday. Potential Hazards: Damaging Wind Gusts, Tornadoes, and Large Hail.

- Wind Chill Values Fall to the 20s and Lower 30s Area-Wide late Monday Night and Early Tuesday Morning.

- Light Freeze and Widespread Frost for Inland Southeast GA & Suwannee Valley on Tuesday Night and Early Wednesday Morning.

- Small Craft Advisory Conditions Late Tonight through Tuesday Afternoon.

UPDATE

Main Highlights through Tonight:

- Scattered Strong to Isolated Severe Storms Possible this Afternoon and Evening, Mainly along the I-95 and U.S. Highway 301 Corridors. Potential Hazards: Damaging Wind Gusts, Small Hail, Frequent Lightning Strikes, and Heavy Downpours.

- Small Craft Advisory Conditions Begin Late Tonight Offshore.

Early afternoon surface analysis depicts strong low pressure (991 millibars) that was pivoting across the Upper Midwest, with a trailing cold front crossing the southern Plains states. Meanwhile, a warm front has lifted northward across the Altamaha River in southeast GA. Aloft...a veering wind profile has been established across our region, which is downstream of a trough that was digging southeastward from the Plains states towards the Mississippi Valley. The morning sounding at Jacksonville revealed steepening lapse rates above 650 millibars (around 12,500 feet) and seasonably cool mid-level temperatures (around -13 degrees Celsius at 500 millibars), with a very dry troposphere above 750 millibars. Latest GOES-East derived Total Precipitable Water imagery indicates that deeper moisture is surging northward from the FL peninsula in the wake of the warm frontal passage, with PWATS above 1.5 inches located near and south of Interstate 4, while values across northeast and north central FL rising to about 1.25 inches. Meanwhile, a drier air mass remains in place closer to the warm front, where PWAT values were closer to 0.75 inches across inland portions of southeast GA.

Low stratus ceilings were gradually eroding for locations north of Waycross in southeast GA, with some sea fog noted over the near shore Atlantic waters in coastal southeast GA. Mostly mid- level cloud cover was located along the I- 95 and U.S. Highway 301 corridors in north central and northeast FL, while fair skies prevailed for the Suwannee Valley and much of inland southeast GA to the south and southwest of Waycross. Temperatures have soared to the upper 70s and lower 80s across most of northeast and north central FL at noon, with 70s prevailing across southeast GA. Dewpoints ranged from around 60 for interior southeast GA and the Suwannee Valley to the mid and upper 60s elsewhere at 16Z.

Deeper moisture surging northward from the FL peninsula this afternoon will combine with an existing warm and unstable air mass over our area to develop scattered to numerous thunderstorms during the mid to late afternoon hours along the I-95 and U.S. Highway 301 corridors in north central and northeast FL. This activity will likely be initially triggered by the inland moving Atlantic sea breeze boundary over coastal Flagler and St. Johns Counties, with this activity then interacting with convective outflow boundaries emanating northward from central FL to increase the coverage and intensity of showers and thunderstorms for locations south of I-10 through late afternoon. Convective outflows moving north and northwestward will then spread activity towards coastal southeast GA and the Okefenokee Swamp towards sunset. Given cool mid-level temperatures and steep lapse rates already in place, along with ML CAPE values in excess of 2,000 j/kg, storms may pulse and become strong or even briefly severe in these areas into the evening hours. The Storm Prediction Center has maintained a Marginal (level 1 out of 5) Risk for severe thunderstorm development across our area, with downburst winds of 40-60 mph and small hail being the primary threats later today, along with frequent lightning strikes and locally heavy downpours. Highs should reach the mid to upper 80s for inland locations, with 70s expected at coastal locations from Jacksonville Beach northward.

Troughing will continue to deepen as it takes on a more neutral tilt tonight over the Upper Midwest, Great Lakes, and Mississippi Valleys. Southwesterly flow aloft will also continue to deepen downstream of this trough and its associated powerful cold front across our region, with flow aloft also becoming increasingly diffluent towards sunrise on Monday. Widespread showers and thunderstorms ongoing early this evening across the I-95 and U.S.- 301 corridors will tend to weaken towards midnight as activity attempts to build northwestward towards the Suwannee Valley and interior southeast GA. Strong to isolated severe storms will remain possible early this evening, with a break in activity expected to be short-lived overnight as the cold front enters the southeastern states and moisture levels continue to increase ahead of this strong boundary. A wave of showers and thunderstorms may develop over Apalachee Bay and the northeast Gulf during the predawn hours, with this activity rapidly spreading inland across the Suwannee Valley and southeast GA towards sunrise. Strong warm air advection and gusty southerly winds will keep lows in the mid to upper 60s tonight area-wide.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Main Highlights This Period:

- Warming trend late in the period.

Surface high pressure will be centered to the north northeast Tuesday night through Wednesday. Freezing temperatures inland expected north of I-10. Winds will be fairly light, so frost is expected for all but coastal NE FL. Temperatures will begin to moderate Wednesday, but remain below average.

The region will be between a ridge of high pressure to the northwest and a trough of low pressure Wednesday night through Thursday night. The dry weather will continue during this time, with temperatures coming closer to normal.

The surface high pressure ridge will build overhead of the region Friday into Friday night, as temperatures rise above normal.

The high will sink to the south over the weekend, but dry weather will continue with temperatures continuing above normal.

AVIATION /12Z SUNDAY THROUGH 12Z MONDAY/

VFR conditions are expected to prevail through around 20Z. Showers and thunderstorms will develop late this afternoon and continue into the evening hours at the regional terminals. Confidence in timing of impacts remains low enough to maintain PROB30 groups from around 21Z through around 04Z for MVFR conditions during heavier downpours, in addition to brief wind gusts up to 30 knots. We will shift these PROB30 groups to TEMPO groups for the 18Z TAF issuance and will aim to narrow the impact window for these MVFR or lower impacts that are likely later today and into this evening. Showers and thunderstorms should depart our area by 05Z Monday, with IFR ceilings likely developing in the wake of this activity by 08Z. Southeast to southerly surface winds will increase to 5-10 knots at the regional terminals by 15Z, with southerly winds of 10-15 knots and gusty then prevailing at the inland terminals. A pinned Atlantic sea breeze boundary positioned east of I-95 will move across the coastal terminals before 19Z, shifting surface winds to southeasterly around 15 knots and gusty. Southerly surface winds will prevail after the conclusion of this evening's convective impacts, with speeds remaining sustained at 10-15 knots overnight at the coastal terminals and 5-10 knots inland after 06Z.

MARINE

A warm front situated over the Georgia coastal waters will lift northward this afternoon as a strong low pressure center pivots from the Upper Midwest towards the Great Lakes states. Showers and thunderstorms will develop late this afternoon and will continue this evening, with strong to isolated severe storms possible. This storm's system's cold front will enter the southeastern states late tonight, crossing our local waters on Monday afternoon. Southerly winds will strengthen over the offshore waters adjacent to northeast Florida late this afternoon, where Small Craft Advisories are expected to develop overnight. Southerly winds will strengthen near shore this evening, and Small Craft Advisory conditions will likely develop by the late morning or early afternoon hours on Monday. Strong to severe thunderstorms are forecast to impact our local waters on Monday, with the potential for damaging wind gusts, waterspouts, and large hail.

Winds will shift to westerly during the passage of the strong cold front on Monday afternoon, with strong northwesterly winds forecast on Monday night and Tuesday morning throughout our local waters as high pressure builds into the southeastern states. Winds will shift to northerly on Tuesday afternoon and then northeasterly by Wednesday as high pressure shifts northeastward towards the Mid- Atlantic coast. This strengthening high pressure center will wedge down the southeastern seaboard later this week, creating another round of Small Craft Advisory conditions on Wednesday night and Thursday. Winds and seas are expected to diminish by Friday afternoon.

Rip Currents: Moderate risk of rip currents expected Today with South to Southeast flow at local beaches along with surf/breakers of 2-4 ft along with a greater impact from potential storm activity this afternoon and evening. Developing strong offshore flow on Monday will knock surf down slightly to 2-3 ft, but a Moderate risk of rips will continue.

FIRE WEATHER

- Inland Minimum Humidity Values Below 30 Percent Tuesday Through Thursday

- Area of High Daytime Dispersion Sunday through Tuesday and again Thursday through Saturday

A strong cold front will move southeast across the area on Monday. Showers and thunderstorms can be expected ahead of the front Tonight, with potential for strong to severe storms along front during the day Monday. High pressure will be the prevailing weather feature Tuesday through Sunday.

FOG POTENTIAL AND OTHER REMARKS: Significant fog potential is not expected Tonight. Thunderstorm chances through Monday, with chances for strong to severe storms. The greatest chance for the severe weather will be during the day Monday. A frost/freeze is forecast for Tuesday night, mainly inland areas north of I-10.

PRELIMINARY POINT TEMPS/POPS

AMG 67 75 33 54 / 40 90 10 0 SSI 65 76 38 54 / 70 80 10 0 JAX 67 83 37 57 / 70 80 10 0 SGJ 66 80 40 58 / 80 80 20 0 GNV 67 81 37 59 / 60 90 10 0 OCF 67 82 38 59 / 60 90 10 0

JAX WATCHES/WARNINGS/ADVISORIES

FL...None. GA...None. MARINE...Small Craft Advisory from 8 AM Monday to 11 AM EDT Tuesday for AMZ450-452-454. Small Craft Advisory from 2 AM Monday to 2 PM EDT Tuesday for AMZ470-472-474.