Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/14/19
Area Forecast Discussion
National Weather Service Columbia SC
1049 PM EST Fri Dec 13 2019
Cold air damming across the area through the overnight. Another
period of rain expected overnight. The low will be northeast of
the area Saturday and drying will begin in a westerly flow with
breezy conditions expected. Weak high pressure will bring dry
weather and moderating temperatures Sunday into Monday. The next
system will bring rain to the forecast area late Monday through
Tuesday as another cold front moves across the region. Drier,
cooler weather is expected for the remainder of the long term.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Areas of fog have developed across the area in the wake of the
first round of rain with visibilities dropping to around 1-2
miles or less. Decided to issue a special weather statement to
handle the threat for now but if vsbys continue to lower to one
quarter mile for a extended period time a dense fog advisory may
Regional radar imagery showing another area of rain moving
through central GA at this time associated with an upper trough.
The upper trough is forecast to become negatively tilted as it
moves through the region and bring another round of potentially
moderate to heavy rainfall with isolated thunderstorms possible.
This event is expected to be relatively brief compared to the
long duration event from today though which will limit
additional rainfall totals. Strong dynamics associated with the
trough acting on relatively high PWAT air mass (1.2-1.3 inches)
with a tropical connection may support heavy rainfall which
could result in additional flooding after midnight, especially
in areas along and north of I-20 where many locations reported
well over 3 inches of rain today. Flash Flood Watch remains in
effect from midnight to 7am. Updated hourly pops to reflect the
min in rainfall this evening and ramping back up to categorical
later tonight. Temperatures will be relatively steady through
the night ranging from the upper 30s through mid 40s under wedge
conditions, extensive cloud cover and additional precipitation.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
An upper level low will cross over the southern Appalachians and
portions of the forecast area on Saturday. The majority of the
moisture will push northeast of the FA after sunrise. Drier low
level air and westerly winds will move in late morning,
suggesting any lingering showers will be light. Although the
chance of measurable rainfall will decrease through the day,
there may be scattered sprinkles even into the afternoon as the
upper level low moves over the area.
A Lake Wind Advisory is in effect for Saturday. The surface low
will deepen as it exits the CWA causing the pressure gradient
over the area to tighten. The HRRR suggests 10m wind gusts will
generally range from 25 to 30 kts in the afternoon with a few
higher gusts possible over the lakes. Lows should be around 40
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Dry, high pressure will be over the region Sunday with temperatures
a couple of degrees warmer than Saturday. An upper level trough
develops over the central US early next week. The associated
surface low will lift into the Northeast, bringing a cold front
into the Southeast late Monday through Tuesday. Warm, moist
advection ahead of the front, synoptic scale ascent and lift
along the front supports likely to categorical PoPs. Expect the
front to shift east by Tuesday night with rain chances
diminishing, skies clearing, and temperatures falling into the
30s. Dry high pressure will build back into the region for
Wednesday and Thursday, but temperatures will be several degrees
below normal behind the front. Highs will be in the low to mid
50s with lows in the 30s for the remainder of the long term.
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
LIFR through tonight.
Surface wedge pattern in place, with associated widespread low
CIGS. Radar indicating batch of moderate rain has pushed east of
the TAF sites providing a relative lull in the precipitation in
the near term. Nonetheless, given wedge and diurnal effects,
VSBY restrictions of 1 to 2 miles still expected in
drizzle/fog. Another batch of heavier showers are expected to
move through later tonight as a second wave of low pressure
moves by. Behind the low, winds will shift to west and increase,
eventually allowing the low cloudiness to scour out late
morning to early afternoon Saturday. VFR with breezy conditions
expected Saturday afternoon.
EXTENDED AVIATION OUTLOOK...A cold front will bring showers and
associated restrictions Monday night and Tuesday.
GA...Lake Wind Advisory from 7 AM Saturday to 1 AM EST Sunday for
Flash Flood Watch until 7 AM EST Saturday for GAZ040-063>065.
SC...Lake Wind Advisory from 7 AM Saturday to 1 AM EST Sunday for
Flash Flood Watch until 7 AM EST Saturday for SCZ018-020-021-
Area Forecast Discussion
National Weather Service Jacksonville FL
918 PM EST Fri Dec 13 2019
...AREAS OF DENSE FOG EARLY TONIGHT...
...ISOLATED SEVERE THUNDERSTORMS POSSIBLE LATE TONIGHT...
Warm front extends from roughly GNV-SGJ this evening. Front will
continue to lift northward, reaching the Altamaha River by 06Z.
Lull in precipitation noted in the JAX forecast area per mosaic
radar composite as shortwave energy quickly exits northeast of the
forecast area. Saturated boundary layer and light winds have
allowed areas of dense fog to develop with visibilities 1/4 mile
or less near and just north of the warm front. A Dense Fog
Advisory now in effect for these areas until around 07Z to 08Z as
well as for the nearshore coastal waters north of St Augustine.
Improvement expected thereafter as southerly winds increase.
Another strong shortwave trough will traverse the area late tonight
with precipitation coverage increasing again. Latest HRRR bullish
with broken squall line in advance of cold front reaching the
Suwannee Valley by 06Z and the Atlantic coast around 10Z. SPC has
tweaked the slight risk footprint to include areas along and south
of Highway 84. Bulk shear increases to 50 knots, highlighting
damaging wind potential as main threat. An isolated tornado and
large hail possible. Instability lacking somewhat but GFS forecast
soundings paint 500-1000 J/KG CAPE values across the south half
of County Warning Area. 0.25 to 0.75 inch of rainfall expected.
The cold front will push south and east of the inland zones by
12Z, shifting winds westerly and ending the thunderstorm threat as
drier air filters in from the west. Scattered to numerous
thunderstorms expected over the marine zones Saturday morning as
the cold front pushes offshore.
.PREV DISCUSSION [635 PM EST]...
.NEAR TERM [Through Tonight]...
An upper level shortwave along the northern-central Gulf waters
with a vertically stacked deepening low below it is keeping the
southeast in a soggy weather pattern this afternoon. A quasi-
stationary front is stretched out from roughly St. Augustine
southwest to Gainesville, with available instability north of this
boundary capped by a thick deck of low level clouds. However,
just to the south of this boundary lies an untapped instability
source with of MLCAPE 500-800 J/kg. Not a rager, but enough to
kick storm generation up a notch along boundaries. As the Gulf low
swings northeastward this evening, that boundary will push north
as a warm front moving through our area and dynamics will become
more favorable for the development of severe weather. By the time
midnight rolls around, we`ll have 0-6 km shear of 50-60 kts, which
will help organize thunderstorms that develop in the warm sector
of the system and at least pose a wind threat. With 0-1 km shear
of 30-40 kts, unfortunately these storms will also be posing a
threat for nighttime tornadoes. The time frame of midnight to 7
AM means that it`s a good idea to make sure you have your Weather
Radio set to alert tonight and your WEA notifications enabled on
your phone before going to bed tonight just in case.
.SHORT TERM [Saturday Through Sunday Night]...
By Saturday morning, the remaining storms will likely pick up
some steam and exit the area quickly through the remaining
morning hours, rendering a drier, breezy afternoon with highs in
the mid 60s to low 70s. Temperatures Sat night behind the cold
front will be near normal, in the low-mid 40s. High pressure will
build eastward Sunday, leading to calmer winds and similar
temperatures to Saturday.
.LONG TERM [Monday Through Friday]...
The break in rain chances will be brief, however, with our next
front developing and moving in by Monday night. At that point,
another upper level shortwave trough will push into the Srn
Plains, developing a cold front out in the lower MS Valley. This
cold front will move into the Southeast and TN Valley on Tuesday,
reaching our area Tues evening/night. Behind this cold front, much
a colder, drier air will advect into the area. Highs Wed through
Friday behind the front will be in the mid 50s to low 60s and
overnight lows will be in the 30s.
[Through 00Z Sunday]
Latest HRRR run bullish with broken squall line late tonight.
07Z-09Z window for strong, possibly severe, thunderstorms at KSSI
and JAX metro TAFS, and 08Z-10Z for KGNV and KSGJ. Opted to
include VRB20G30KT group in TEMPO group to highlight wind gust
potential with 0-6KM Bulk Shear near 50 kts. Potential for LLWS
but appears marginal at this time. Otherwise, ceilings bounced to
VFR at KGNV and KSGJ this afternoon in the warm sector, but
should drop back to IFR by 03Z. Along and north of the boundary,
LIFR/IFR ceilings at JAX Metro TAFS and KSSI to persist throughout
the night. With the passage of the cold front 09Z- 12Z...winds
shift westerly with ceilings lifting to MVFR Saturday morning,
then VFR around noon Saturday as low PW air (less than 0.50 inch)
filters into the forecast area from the west.
Strong southwest winds tonight will become more westerly in the
wake of a cold front Saturday morning. A strong pressure gradient
along this front will continue small craft conditions over our
offshore waters through Saturday afternoon, possibly into the
overnight period. After that, we`ll have a brief quiet period with
winds around 10 knots through Tuesday until another front
approaches the area mid-week.
A quasi-stationary boundary in place today is keeping very light winds
in place at the surface and leading to low daytime dispersion values.
This will push north overnight as a warm front, with a cold front
sweeping in west to east later in the night and early tomorrow morning.
Heavy showers and scattered thunderstorms will accompany these fronts,
which will make for wet fuels, diminishing the threat for red flag
conditions when drier air moves in behind the front.
A much needed 1-3" of rainfall fell this morning, mostly in
extreme SE GA and eastern portions Nassau and Duval counties in
FL. Although we`ve been in a quiet period through much of the day,
showers and scattered thunderstorms will ramp up again in the
evening and overnight hours, bringing another 1-2" of rain to the
area. This may lead to isolated flooding in low-lying areas and
those with poor drainage.
.PRELIMINARY POINT TEMPS/POPS...
AMG 48 63 41 66 45 / 100 10 0 0 0
SSI 56 66 46 65 52 / 90 20 0 0 0
JAX 58 70 45 69 50 / 90 20 0 0 0
SGJ 60 71 48 69 53 / 80 30 0 0 0
GNV 59 70 45 71 50 / 80 20 0 0 0
OCF 60 73 45 72 50 / 90 20 0 0 0
FL...Dense Fog Advisory until 2 AM EST Saturday for Baker-Bradford-
Clay-Coastal Duval-Coastal Nassau-Coastal St. Johns-
Hamilton-Inland Duval-Inland Nassau-Inland St. Johns-
Northern Columbia-Southern Columbia-Suwannee-Union.
High Rip Current Risk until 4 AM EST Saturday for Coastal Duval-
Coastal Flagler-Coastal Nassau-Coastal St. Johns.
GA...Dense Fog Advisory until 2 AM EST Saturday for Brantley-Coastal
Camden-Coastal Glynn-Inland Camden-Inland Glynn-
Northeastern Charlton-Western Charlton.
High Rip Current Risk until 4 AM EST Saturday for Coastal Camden-
AM...Small Craft Advisory until 4 PM EST Saturday 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-Waters from St. Augustine to Flagler Beach FL from 20
to 60 NM.
Dense Fog Advisory until 3 AM EST Saturday for Coastal waters
from Altamaha Sound to Fernandina Beach FL out 20 NM-
Coastal waters from Fernandina Beach to St. Augustine FL
out 20 NM.
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
1022 PM EST Fri Dec 13 2019
An area of low pressure to the south will lift north just
inland from the coast tonight. The low will continue to lift
north of the region Saturday pushing a cold front through
eastern North Carolina. High pressure will build in briefly
Sunday and Monday, followed by another cold front on Tuesday.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 1015 PM Friday...Widespread precipitation continues across
the region with the heaviest rainfall now occurring over the
Sound Region. Rain coverage may thin out a bit after midnight,
but latest HRRR and 3km NAM shows precipitation filling back in
toward morning, so will continue with high likely to categorical
PoPs overnight. Warm frontal boundary continues to hug the coast
with temperatures hovering around 60 degrees on the Crystal
Coast, mid 60s Outer Banks, but mainly upper 40s to lower 50s
inland. Still enough low CAPE values for isolated thunder near
the coast for the next several hours. Patches of dense fog will
also remain likely for the next few hours given the very moist
airmass with a nearly saturated sounding and precipitable water
values of almost 1.7 inches.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
As of 230 PM Fri...Sfc low will continue to lift north of the
area early Sat with front pushing through in the afternoon.
Active weather will continue for the first part of Sat, with
widespread rain and isolated storms (along the coast). Some
convective banding is possible, however most of the instability
should remain just offshore limiting the severe potential, but
still couldn`t rule out some strong wind gusts or isolated
rotating cells. Precip chances will be quickly decreasing late
morning and early afternoon as westerly flow develops and drier
air moves in behind the front. As the upper level trough moves
across the area in the afternoon, some isolated showers are
possible across the coastal plain and a bit further east, though
coverage looks minimal at this time. Mild temps with highs in
the lower 60s.
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
As of 240 AM Fri...Dry and mild conditions are expected Sunday
and Monday. Another cold front will cross the area Tuesday,
bringing additional chances for rain, as well as cooler
temperatures for Wednesday and Thursday.
Sunday and Monday...Upper level trough will move out of the
region Sunday morning, with heights quickly rebounding. High
pressure will move in from the west, and settle in offshore late
Sunday through Monday. Expect high temps on Sunday to reach the
upper 50s to low 60s across the area, and be even milder on
Monday, reaching the mid to upper 60s.
Tuesday...A stronger cold front will move through the region on
Tuesday afternoon ahead of a potent upper level trough. Dry
conditions are expected through early morning when showers move
into the area from the west. Widespread rain is expected from
mid morning through at least late evening, with perhaps a few
rumbles of thunder as well. Temperatures will remain mild
ahead of the front, reaching the mid to upper 60s for high
temps. Then behind the front, temps will quickly drop into the
50s and eventually all the way into the upper 30s to low 40s by
Wednesday and Thursday...An expansive longwave trough will
remain over the region for this period, leading to below
average temperatures. Strong CAA will persist through at least
Thursday morning, leading to high temps only reaching the mid to
upper 40s Wednesday and then maybe a couple of degrees warmer
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Short Term /through 00Z Sunday/...
As of 7 PM Friday...Not much change in the current aviation
forecast as widespread rain coupled with patches of dense fog
through this evening and the overnight hours into Saturday
morning will lead to IFR/LIFR ceilings. Conditions will be
improving late Saturday morning and afternoon, and should return
to VFR by late Saturday afternoon. Westerly wind gusts increase
to 15-20 kt behind the front Sat afternoon.
Long Term /Saturday night through Wednesday/...
As of 315 AM Fri...VFR conditions through Tuesday morning when
another cold front moves into the area and may bring another
period of MVFR/IFR conditions through late Tuesday.
Short Term /through Saturday/...
As of 1020 PM Friday...Warm frontal boundary near the coast
playing havoc with wind direction at late evening, with mostly
NE over Sounds and inland waters, but more SE/S along the coast.
Winds speeds are also quite variable with less than 10 knots at
Duck, but gusts to 33 knots at Diamond Buoy. Most guidance shows
SE/S winds increasing overnight as area of low pressure forms
and moves inland of the NC coast tonight and early Saturday.
As winds increase tonight seas will build to 6 to 11
feet...highest outer central wtrs. Could see areas of fog
develop across the coastal waters overnight into Saturday
morning, becoming locally dense at times. Could see some gale
force gusts develop across the waters south of Oregon Inlet
Saturday morning and early afternoon. Front will move through
the waters by Saturday afternoon with winds becoming westerly
20-25 kt gusting to 30 kt. Seas will remain 6-11 ft. Added
Albemarle, Croatan/Roanoke Sounds, and Alligator Rvr to SCA
beginning early Sat evening with increasing westerly winds.
Long Term /Saturday night Through Wednesday/...
As of 315 AM Fri...Then winds subside briefly Sunday through
Monday morning, before increasing out of the S at 15-25 kts
early Monday night. Winds 20-25 kts continue Tuesday as another
cold front moves through the coastal waters.
Seas subsiding to 5-8 ft on Sunday. Seas then briefly become
3-5 ft Sunday night and Monday, before increasing to 6-9 ft
Monday night through Tuesday.
MARINE...Small Craft Advisory from 8 AM Saturday to 7 AM EST Sunday for
Small Craft Advisory from 5 PM Saturday to 5 AM EST Sunday for
Small Craft Advisory until 5 PM EST Sunday for AMZ152-154.
Small Craft Advisory until noon EST Sunday for AMZ150-156-158.
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
755 PM EST Fri Dec 13 2019
Water vapor satellite imagery and 500mb analysis maps show a pretty
strong jet streak situated over portions of Southern LA, AL and the
Florida Panhandle. This is associated with a negatively tilted
shortwave trough axis propagating to the ENE towards the FL
peninsula. Across much of the state, conditions remain fairly
warm and humid. Dewpoints are running in the upper 60s to low 70s
in the wake of what has now become a stationary front. The 0Z
sounding also shows a weak veering wind profile, indicative of
WAA. Combining this WAA with synoptic-scale PVA, this is the
perfect environment for large-scale ascent. Indeed this has
already been proven to be true with the earlier line of showers
that passed through.
However, conditions have stabilized somewhat for the moment,
allowing the atmosphere to recover and regroup for round two. What
can also be noted in the 0Z sounding is a pretty decent capping
inversion around 820mb. This explains why much of the earlier shower
activity likely fell apart (in combination with several other
factors like SSTs along the shelf). Despite the inversion, the
atmosphere has a fairly deep well-mixed layer just above and just
below the inversion...suggesting significant positive buoyancy
once once this begins to erode.
While some directional shear is noted in the sounding at the moment,
and some weak directional shear will continue to exist, what there
will be more of tonight is speed shear. RAP soundings from 6Z onward
show little directional shear and only around 30kts of speed shear
in the first 3km. This does not make for a particularly high threat
for tornadoes, but rather for an environment that could support some
damaging wind gusts across portions of West Central and SW Florida.
Suffice all that to say, a line of storms is likely to approach the
peninsula in the early hours of Saturday morning, bringing the
potential for some damaging wind gusts and an isolated tornado in
the overnight hours to the peninsula. This risk diminishes further
to the South as convection moves father away from the most favorable
environment. Timing sets up for areas North of Tampa Bay to see the
greatest threat between 1AM and 5AM and from Tampa Bay Southward
from around 4AM to 11AM. The current forecast remains on track, and
no major changes have been made.
Conditions remain VFR ahead of an approaching cold front. A line of
storms will likely set up overnight and push towards terminals,
leading to brief MVFR/IFR conditions, but timing is still not an
absolute certainty. For now, will leave VCTS in and later TAFs will
add TEMPO/Prevailing groups as necessary to provide a more accurate
representation of timing. Conditions could become temporarily MVFR,
but after the passage VFR will prevail. Winds out of the SW
generally 10kts or less overnight will turn out of the NW by the
An approaching cold front will bring the potential for showers and
thunderstorms overnight into coastal waters with the potential for
gusty winds, heavy rain, and possible waterspouts. A potential for
sea fog still exists for the Nature Coast, but this will likely be
short-lived and patchy in nature. Cautionary statements are in
effect for outer waters tonight, but conditions will begin to settle
down after the front passes tomorrow.
.Preliminary Point Temps/PoPs...
TPA 78 67 75 55 / 50 70 30 0
FMY 81 68 79 56 / 20 40 60 0
GIF 78 66 76 52 / 30 50 50 0
SRQ 79 67 78 55 / 30 60 50 0
BKV 78 63 74 48 / 60 70 20 0
SPG 77 68 75 57 / 50 70 40 0
FL...High Rip Current Risk from 7 AM EST Saturday through Saturday
evening for Coastal Charlotte-Coastal Hillsborough-Coastal
Lee-Coastal Manatee-Coastal Sarasota-Pinellas.