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

- Long-Duration Cold Weather Outbreak Continues through Early Next Week. Hard Freezes Inland & Light Coastal Freezes Tonight. Light Freeze & Frost for Inland Locations on Thursday Night. Protect People, Pets, Plants, and Practice Safe Heating

- Record Cold & Dangerously Low Wind Chills Saturday Night & Early Sunday Morning. Lows in the Teens Possible Inland and Lower 20s at Coastal Locations. Windy Conditions Expected from Saturday Afternoon through Sunday Morning. Life-threatening Wind Chills (Single Digits) Possible Saturday Night & Early Sunday Morning

- Gale Conditions this Weekend for the Atlantic Coastal Waters

- Saturday and Saturday Evening Snowfall Potential Decreasing. Probabilities for Minor Impacts (Transportation) of 15-25% Across Southeast GA

NEAR TERM /THROUGH THURSDAY/

Rest of today into early this evening, shortwave trough will move across parts of the forecast area and then southeast of the area tonight. Highs expected to reach into the 50s this afternoon all areas. Weak ridging aloft will move in late in the wake of this system and anticipate clear skies across most areas. At the surface, high pressure ridge will shift off to the northeast from the central Gulf coast to the TN Valley resulting in low level flow flow to turn from northwest to more northerly. Dry cold front will move off the coasts of Carolinas but not have sensible weather affects to land zones. The anticipate light winds tonight will set up another night of subfreezing temperatures for most areas so a freeze warning remains in effect. The exception will be from parts of eastern Duval southward along the northeast FL coast to Flagler county where drainage/northwest flow will keep the temps just above freezing there. In more sheltered locations in these areas, areas to widespread frost is likely with lows in the lower to mid 30s so frost advisory is in effect as well.

SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/

Flow aloft will become zonal by Thursday afternoon, as our region will be downstream of shortwave troughing that will be migrating eastward across the Ozarks and the Tennessee Valley. Meanwhile, surface high pressure will gradually weaken over our region and will slide off the southeastern seaboard on Thursday night. Following another frosty start to the day, fast zonal flow will spread thin cirrus cloud cover will overspread our region by the early afternoon hours, with thicker high altitude cloudiness expected by the late afternoon and evening hours, especially across southeast GA. Decreasing wind speeds and rising heights aloft will allow highs to rebound to the lower 60s for inland locations south of Interstate 10, while highs elsewhere remain in the mid to upper 50s. Decoupling winds and a lingering dry air mass will likely result in another light freeze for inland southeast GA, the Suwannee Valley and for inland locations along the I-10 corridor, where lows will fall to the lower 30s. Areas to widespread frost are expected for inland locations, where lows elsewhere will fall to the mid 30s, while a light onshore breeze developing at coastal locations likely keeps lows in the upper 30s and lower 40s.

Deepening troughing over the Upper Midwest and the Great Lakes region will begin digging southward on Friday, with Arctic high pressure diving southward from the Canadian Prairies into the northern Plains states in the wake of this trough. This deepening trough will initially induce weak cyclogenesis over the northeast Gulf / Apalachee Bay on Friday afternoon. Cloud cover will thicken and gradually lower on Friday afternoon and evening from west to east, with a few showers possible for locations near the Suwannee / Alapaha / Ocmulgee / upper Altamaha Rivers towards sunset. Developing south to southwesterly low level flow will finally boost highs to near late January climatology, with highs generally climbing to the 60-65 degree range across southeast GA and the mid to upper 60s for northeast and north central FL.

Deep troughing will keep digging southeastward through the Ozarks, Tennessee, and Ohio Valleys on Friday night. Deepening southwesterly flow downstream of this digging trough will allow for a modest surge in moisture values from late Friday afternoon through around sunrise on Saturday, allowing for widely scattered showers to progress across northeast and north central FL on Friday night, with coverage likely to be more isolated in nature across southeast GA, where model soundings indicate that PWATS will remain below 0.75 inches. Rainfall amounts are expected to remain below one quarter of an inch at most locations. As weak surface low pressure crosses north central FL and then emerges over the Atlantic waters towards midnight, low level flow will become northwesterly, with cold air advection late on Friday night dropping lows into the mid to upper 30s for inland southeast GA, with 40s expected elsewhere.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Deep troughing positioned over the Tennessee Valley early on Saturday morning will pivot across the Deep South on Saturday night and Sunday, with 500 millibar heights (around 20,000 feet) falling to around 525 dekameters, which is around 5 standard deviations below normal for our area. This anomalously deep trough diving into our region will result in rapid deepening of low pressure off the North Carolina Outer Banks by Saturday night. Northwesterly winds will strengthen across our region as low pressure rapidly deepens (perhaps as low as 970 millibars by Sunday afternoon) off the southeastern seaboard. The deep trough migrating across our region will allow for precipitation to wrap around the west side of the developing surface low, potentially sending enough moisture for snow flurries over portions of southeast GA and along the I-95 corridor by late Saturday afternoon and evening. The extent of available moisture over our area remains in question, while accumulating snowfall appears more likely closer to the developing winter storm system over the coastal Carolinas and Delmarva region. We'll continue to watch the development of this "wrap-around" moisture that could brush our area, with uncertainty remaining in the potential bombogenesis to the northeast of our area.

Wind advisories will likely be needed for the I-95 corridor and possibly for our entire area by Saturday afternoon as our local pressure gradient rapidly tightens. Low and mid level cloud cover will likely be slow to erode due to the "wrap-around" moisture potentially infiltrating our area, keeping highs in the 40s for southeast GA and the Suwannee Valley, with lower 50s expected elsewhere. Highs will likely occur during the late morning or early afternoon hours, with temperatures falling through the 30s across inland southeast GA and the 40s elsewhere during the afternoon hours, with strong winds dropping wind chill values into the 20s during the afternoon hours for inland southeast GA and the I-10 corridor by late afternoon and the 30s for locations south of I-10.

Arctic high pressure spilling southward through the Plains states on Saturday will gradually weaken as it builds eastward along the northern Gulf coast by Sunday afternoon. A very tight local pressure gradient and strong cold air advection will drive Arctic air and dangerously cold weather into our area as skies clear from northwest to southeast on Saturday night. Wind Advisories will likely remain in place along the I-95 corridor throughout the night, with frequent 40-45 mph gusts possible at coastal locations. Extreme Cold Watches will likely be required for our entire area on Saturday night, as lows likely fall below daily records for February 1st. Actual air temperatures will fall to the upper teens for inland locations along and north of I-10, with low and mid 20s forecast elsewhere. Breezy conditions inland and windy conditions for locations along and east of I-95 will drive wind chill values down to the single digits area- wide and perhaps near zero across inland southeast GA towards sunrise on Sunday.

Strong low pressure will accelerate northeastward off the U.S. eastern seaboard on Sunday afternoon and evening as gradually weakening Arctic high pressure builds eastward along the northern Gulf coast. Breezy northwesterly winds will continue on Sunday, and cold air advection will counter sunny skies, with highs only climbing to the 40-45 degree range for most locations. Wind chills will remain in the 30s throughout the afternoon hours, possibly not climbing above freezing all day in southeast GA and coastal northeast FL. Weakening Arctic high pressure will then migrate east- southeastward on Sunday night, settling over the FL peninsula towards sunrise. This will allow our local pressure gradient to loosen, and winds at inland locations will likely diminish overnight, resulting in a long duration hard freeze that will likely extend all the way to coastal locations. Long-term model blends currently indicate that lows will fall to the 20-25 degree range at most locations by sunrise on Monday, with widespread frost likely inland and a light offshore breeze at coastal locations likely dropping wind chills back into the teens.

Anomalously deep troughing will lift northeastward and away from our region early next week. Dry northwesterly flow on Monday and Monday night will turn northerly by Tuesday as another high surface ridge builds over the Tennessee Valley. Slowly rising heights aloft will allow temperatures to gradually rebound early next week, with highs mostly in the 50-55 degree range on Monday and 55-60 by Tuesday. Decoupling winds at inland locations and a lingering very dry air mass will likely allow for another long duration, potentially hard freeze on Monday night and early Tuesday morning inland, with a light freeze extending to coastal locations. Temperatures should remain above freezing by Tuesday night and early Wednesday morning for coastal locations, with a light freeze appearing likely for inland locations.

AVIATION /00Z THURSDAY THROUGH 00Z FRIDAY/

VFR conditions will prevail through the forecast period. Light to calm winds will continue through tonight and then building to about 5 to 10 knots sustained from out of the northeast on Thursday.

MARINE

High pressure will continue to shift to the north tonight and then northeast of the area by Thursday. A dry cold front will move off the coast of the Carolinas tonight and result in briefly elevated winds to Exercise Caution Levels through Thursday morning. A Gulf low pressure system is then expected to develop in the Gulf on Friday, and cross Florida and push into the local waters Saturday, then move off to the northeast Sunday. As this low intensifies Saturday, Gale conditions are likely to develop. The strong northwest to north winds are forecast to subside by late Monday as high pressure builds into the region.

Rip Currents: A moderate to low risk today and Thursday. Surf will lower from near 2-3 feet today, to 1-2 feet by Thursday.

FIRE WEATHER

- Critically Low Humidity Inland this Afternoon and Thursday - Marginally Low Daytime Dispersion Values Inland on Thursday - High Daytime Dispersion Values Area-Wide this Weekend - Elevated Nighttime Dispersion Values Area-Wide Saturday Night

Breezy northwesterly transport winds will continue to funnel a cold and dry air mass into our region, resulting in near critically low humidity values at most inland locations this afternoon and again on Thursday afternoon. Transport winds will shift to northerly while gradually weakening on Thursday, with low mixing heights yielding poor to marginally low daytime dispersion values, especially at inland locations. Transport winds will shift from easterly early on Friday morning to southwesterly by the afternoon hours, with gradually increasing speeds and mixing heights creating fair to good daytime dispersion values at most locations.

Chances for showers will increase on Friday night, followed by strengthening northwesterly surface and transport winds on Saturday, especially during the afternoon hours. These strong winds will yield very high daytime dispersion values by Saturday afternoon. Strong and gusty northwesterly surface and transport winds on Saturday night will yield very high nighttime dispersion values area-wide, and speeds will only gradually diminish by Sunday afternoon, with high daytime dispersion values continuing. An Arctic air mass will filter into our region on Saturday night, with critically low humidity values expected at inland locations on Sunday afternoon.

FOG POTENTIAL AND OTHER REMARKS: Widespread frost is expected area- wide tonight and early Thursday morning, followed by areas to widespread frost at inland locations late Thursday night and early Friday morning.

CLIMATE

Daily records challenged by the arctic cold air outbreak are below:

Record Low Maximum Temperatures:

Saturday, January 31: JAX 40/1909 CRG 43/1977 GNV 47/1909 AMG 44/1948

Sunday, February 1: JAX 42/1900 CRG 44/1980 GNV 41/1909 AMG 42/1980

Record Low Temperatures:

Sunday, February 1: JAX 24/1977 CRG 29/1977 GNV 25/1977 AMG 22/1977

Monday, February 2:

JAX 23/1979 CRG 27/1980 GNV 25/1980 AMG 19/1951

PRELIMINARY POINT TEMPS/POPS

AMG 27 55 30 60 / 0 0 0 10 SSI 32 54 42 60 / 0 0 0 0 JAX 29 59 35 65 / 0 0 0 10 SGJ 34 57 43 66 / 0 0 0 0 GNV 28 62 35 68 / 0 0 0 0 OCF 27 63 35 68 / 0 0 0 0

JAX WATCHES/WARNINGS/ADVISORIES

FL...Freeze Warning from 11 PM this evening to 9 AM EST Thursday for FLZ021-023-024-030-031-035-120-136-220-236-322-422- 425-522. Freeze Warning from 1 AM to 9 AM EST Thursday for FLZ038-124- 132-137-140-225-232-237-240-340-533-633. Frost Advisory from 2 AM to 9 AM EST Thursday for FLZ125-138- 233-325-333-433. GA...Freeze Warning from 11 PM this evening to 9 AM EST Thursday for GAZ132>136-149-151>153-162-163-165-250-264-350-364. Freeze Warning from 1 AM to 9 AM EST Thursday for GAZ154-166. MARINE...None.