094 FXUS62 KJAX 151444 AFDJAX Area Forecast Discussion National Weather Service Jacksonville FL 1044 AM EDT Tue Jun 15 2021 ...ISOLATED STRONG TO SEVERE STORMS POSSIBLE THIS AFTERNOON INTO EVENING... ...MAX HEAT INDEX VALUES TODAY WILL REACH 105 DEGREES IN SOME AREAS... .UPDATE... A cold front over central Georgia is shifting southward towards the area today and tonight. Scattered showers and storms develop ahead of the frontal boundary and along the sea breezes this afternoon into evening. A pocket of drier air is spreading into southeast Georgia with satellite PWAT estimates dropping into the 1.2-1.4". Best chance for storms this afternoon will be along and south of the FL/GA border where there is better moisture (JAX 12Z sounding PWAT = 2"). Moisture recovers over southeast Georgia later this evening which could support isolated showers and storms. Despite weak shear, there is ample CAPE and DCAPE to support occasional downbursts with strong/damaging outflow winds this afternoon into evening. Heavy downpours will also be possible which could cause minor flooding. Otherwise, hot and breezy day with highs in the low to mid 90s and heat indices between 100-105 possible. && .PREV DISCUSSION [724 AM EDT]... .NEAR TERM [Through Tonight]... Prevailing flow from out of the southwest ahead of the advancing frontal boundary will lead to showers and thunderstorms forming later this afternoon with a potential for strong isolated storms potentially forming in conjunction with developing dynamics aloft. Most likely areas for storms to develop span areas near the Florida-Georgia border and north and along the I-10 corridor. Storms are expected to clear out this evening. High temperatures for today are expected to lower to mid 90s with the highest temperatures expected to occur over southeast Georgia, with heat index values of 100 degrees expected throughout the forecast area. Overnight low temperatures will be in the lower 70s. .SHORT TERM [Wednesday through Thursday Night]... A potent shortwave trough diving southeastward from the eastern Great Lakes region on Tuesday night will pivot eastward across the Mid-Atlantic states, emerging offshore by Wednesday evening. This feature will briefly deepen troughing along the southeastern seaboard, driving another frontal boundary southward across southeast GA during the afternoon hours. An unseasonably dry air mass, featuring PWAT values falling to around 1 inch, will filter into inland portions of southeast GA by late afternoon, which will keep thunderstorm activity mostly confined to northeast and north central FL. Breezy low level west-southwesterly flow south of the FL/GA border will likely advect widely scattered convection developing over the FL Big Bend and Nature Coast eastward into the the Suwannee Valley and north central FL during the morning hours. Outflow boundaries from this morning convection should then migrate northward towards the I-10 corridor by early afternoon, which should trigger scattered to numerous thunderstorms. Coverage will be limited over north central FL during the afternoon hours as a cirrostratus shield over the Gulf of Mexico and the FL peninsula lifts northward, which will limit instability. Model soundings depict cooling mid-level temperatures as the base of the eastern U.S. trough migrates through our area, and downdraft CAPE values may approach 1,000 - 1,200 j/kg along the I-10 corridor as drier air aloft advects into our region. These factors should result in a few storms pulsing and becoming strong or even briefly severe, with damaging wind gusts of 40-60 mph, small hail and frequent lightning strikes being possible along the I-10 corridor. Fast westerly flow will result in a quick eastward storm motion on Wednesday afternoon, which will limit the risk for localized flooding. The drier air mass will allow highs to skyrocket to the mid 90s across inland southeast GA, while highs elsewhere generally reach the upper 80s to lower 90s. Upper troughing will depart the U.S. eastern seaboard by early Thursday, leaving our region with weakening northwesterly flow aloft. The aforementioned cirrostratus shield associated with widespread convection over the southern Gulf of Mexico and broad low pressure development in the Bay of Campeche will continue to overspread our area. The departing trough will result in a frontal boundary stalling near the FL/GA border on Wednesday night, with this feature gradually weakening on Thursday and then dissipating by Thursday night. An unseasonably dry air mass will remain in place over southeast GA, allowing inland lows to fall to the mid and upper 60s at inland locations by early Thursday morning. Evening convection will move offshore for locations south of the frontal boundary, with widely scattered convection again developing along the FL Big Bend and Nature Coasts during the overnight and predawn hours. Isolated convection will be possible over the western Suwannee Valley towards sunrise. Lows will fall to the low and mid 70s across northeast and north central FL. Weakening forcing along the decaying frontal boundary and a more subsident air mass overspreading our region from the south will limit convective coverage to widely scattered for northeast and north central FL on Thursday, with dry weather expected for most of southeast GA, where highs will soar to the mid 90s at inland locations. Our local pressure gradient will loosen, allowing for early development of the Atlantic sea breeze, which will keep coastal highs around 90. Highs will also remain around 90 for most of northeast and north central FL due to increasing cloud cover and afternoon convection. Convection will shift offshore before sunset, with thickening high cloud cover keeping lows in the upper 60s for inland locations north of I-10, with lows around 70 elsewhere, except mid 70s at coastal locations. .LONG TERM [Friday Through Tuesday]... Broad low pressure is forecast to only gradually organize late this week and early this weekend over the western or central Gulf of Mexico. Deep-layered southerly flow will develop locally as Atlantic ridging builds westward and extends its axis across south FL. Thick cirrostratus emanating from widespread convection that will be covering a good portion of the Gulf of Mexico should limit convective coverage on Friday to widely scattered, mainly for locations west of the U.S. Highway 301 corridor. Highs on Friday should reach the upper 80s to around 90 across northeast and north central FL, while a lingering dry air mass allows highs to climb to the lower 90s for inland southeast GA. We leaned on the wetter GFS solutions for the upcoming weekend and early next week, with widespread afternoon and evening convection expected along the I-75 corridor and throughout inland southeast GA on Saturday, followed by slightly higher coverage across all of southeast GA on Sunday as low pressure potentially gets steered eastward along the I-10 corridor in the Deep South. The forecast is low confidence due to uncertainty in how organized this low pressure center becomes before reaching the central Gulf Coast region this weekend. Cloud cover and inland convection should keep highs in the mid to upper 80s for most locations this weekend, with a tropical air mass advecting into our region on the heels of veering low and mid level winds, which will keep lows in the 70s. High temperatures may climb back into the lower 90s on Monday, with southwesterly low level flow likely focusing afternoon and evening convection along the I-10 and I-95 corridors. .AVIATION... [Through 12Z Wednesday] VFR conditions continue through the morning hours. Breezy southwesterly winds develop by late this morning reaching speeds around 12 knots and gusts near 20 knots through the day. Scattered showers and storms are expected to develop near the TAF sites this afternoon with a chance for the formation of isolated severe storms. Stronger storms could cause strong wind gusts and lower visibilities due to heavy downpours. Storms are expected to dissipate in the evening hours. .MARINE... A trough will move into region from the north today with the frontal boundary stalling over the area Wednesday and into Thursday. Wind speeds are expected to reach into Small Craft Advisory levels for offshore waters this Afternoon. A weak ridge will build to the east Friday into Saturday. Low pressure will track to the west then northwest of the region Sunday into Monday. Rip Currents: SE GA: Low today, Moderate Wednesday NE FL: Low through Wednesday .FIRE WEATHER... Breezy west-southwesterly surface and transport winds will develop shortly after sunrise for locations south of Interstate 10, with breezy westerly surface and transport winds expected north of I-10. These winds will create good dispersion values area-wide by the late morning hours. Strong to isolated severe thunderstorms will be possible this afternoon, with strong wind gusts, lightning, and small hail possible within stronger activity. A drier air mass will then filter into inland portions of southeast Georgia on Wednesday and Thursday, resulting in only isolated afternoon and evening thunderstorms for locations south of Waycross. Minimum relative humidity values may approach critical thresholds on Wednesday and Thursday afternoons for locations north of Waycross. Breezy westerly surface and transport winds will continue on Wednesday for locations south of Waycross. && .PRELIMINARY POINT TEMPS/POPS... AMG 96 69 93 66 95 / 30 30 10 10 0 SSI 94 76 90 74 89 / 20 20 30 30 10 JAX 95 73 93 70 92 / 60 30 60 30 30 SGJ 92 73 92 74 90 / 50 20 60 30 30 GNV 91 72 90 71 90 / 60 20 60 20 40 OCF 90 74 89 71 89 / 60 20 40 20 40 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...None. GA...None. AM...Small Craft Advisory from 6 PM this evening to 5 AM EDT Wednesday for Coastal waters from Altamaha Sound to Fernandina Beach FL out 20 NM-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. &&