Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/12/20
Area Forecast Discussion
National Weather Service Charleston SC
1030 PM EST Fri Dec 11 2020
High pressure will prevail through late Saturday. A cold front
will then move through the region Monday with a coastal low
pressure system to likely impact the area mid week. Cooler and
drier high pressure should then return starting Wednesday
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 1025 PM: Based on latest observations and HRRR run, I will
update the forecast to add a mention of patchy fog along the
lower SC coast. Otherwise, no change needed to the forecast.
As of 840 PM: Recent IR satellite images indicated that cirrus
cloud cover was increasing across the forecast area this
evening. The combination of persistent cloud cover and warming
llvl thicknesses should keep temperatures generally steady,
cooling by only 1-2 degrees through the rest of the night. Given
the limited cooling, dewpoint depressions should remain between
1 to 2 degrees. The forecast update will feature less mention of
patchy fog across the region, retained the mention of fog along
the lower Altamaha River.
As of 6 PM: Based on satellite trends, I expect that cirrus will
increase across the forecast area through the night. The
forecast update will feature slight changes to hourly sky and
High pressure will prevail as a coastal trough lingers across
the area tonight. The rest of the afternoon will remain rain
free with plenty of sunshine. Overnight, upper-level moisture
will return from the west and there will be an increase in
cirrus clouds across the area. While some models hint at some
light showers offshore, significant dry air (PWATs ~0.5-0.8
inches) should limit any measurable rainfall. Therefore, have
left out any mentionable POPs. With less radiational cooling
tonight, lows will be in the mid to upper 40s inland and low to
mid 50s along the coast.
There could be another round of fog tonight, even though ingredients
seem less favorable than the previous night/morning. Even so, winds
are expected to become calm in most places and the condensation
pressure deficits will be favorable for fog formation. Therefore,
due to persistence and some hints in the models, have added
patchy fog to the forecast.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
High confidence that high pressure will bring mostly dry and
unseasonable warm weather through the weekend with a cold front to
move through Monday. Although there will be a few showers around
starting Saturday night due to a bit better moisture and upper
forcing, the best rain chances/amounts will come Monday when a more
potent storm system impacts the area. Instability will be limited
but can`t rule out a few weaker storms. Rain amounts should
generally be about a quarter of an inch or less, although could be a
bit higher, especially northern and western areas near the Pee
Dee/Midlands/CSRA. It will also be breezy on Monday.
Temperatures will remain above normal through the period, likely
peaking Sunday afternoon with more clouds and rain holding
temperatures down on Monday. Should see temperatures more steady or
even rising Sunday night due to the increasing low-level warm
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
A cold front will move offshore Monday night, leading to drier
weather and colder temperatures. A weak coastal trough is
expected to form on Tuesday, bringing some showers to the
immediate coast. Though, inland areas will remain dry. Some
showers are possible everywhere on Wednesday as a weak front
moves through. High pressure will yield dry conditions and cold
temperatures on Thursday.
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Flight conditions across the terminals is forecast to remain
generally VFR through the 0Z TAF period. A period of ground fog
is possible at both KSAV and KCHS during the predawn hours.
Otherwise, expecting SCT to BKN cirrus with calm winds tonight
and steady SW winds during the daylight hours on Saturday.
Extended Aviation Outlook: Moderate to high confidence this period
at KCHS/KSAV. Some restrictions are possible starting late Saturday
night and then moreso Sunday night into Monday as a storm system
impacts the area. Breezy conditions and a few weak storms are
possible Monday, mainly through mid afternoon before a cold front
moves through. Additional restrictions are then possible Tuesday and
Wednesday as a coastal storm system impacts the area.
Rest of today and tonight: As a coastal trough lingers over the
area, high pressure will prevail overnight. A southerly flow
will persist with winds 5-10 kt. Seas will be 1-2 ft.
Saturday through Wednesday: Moderate to high confidence through the
period with high pressure expected to prevail until a cold front
moves through Monday and a coastal storm likely impacts the area mid
week. Wind/sea conditions are expected to stay below Small Craft
Advisory levels through Sunday night before Small Craft Advisories
are then likely needed Monday into at least Tuesday. There is a
small chance that a marginal Gale Warning will even be needed
Monday, mainly for the offshore GA waters and Charleston County
High astronomical tides due to the lunar perigee and new moon
could yield minor coastal inundation as early as Sunday morning
along the southern SC coast. More significant inundation is
possible starting Tuesday when winds will be more favorable,
maybe even extending southward along the GA coast.
Area Forecast Discussion
National Weather Service Lincoln IL
854 PM CST Fri Dec 11 2020
Issued at 528 PM CST Fri Dec 11 2020
A rainy night is in store across central and southeast
Illinois...with overnight low temperatures ranging from the upper
30s in the Illinois River Valley to the upper 40s near the Indiana
border. The rain will gradually come to an end by Saturday
Issued at 854 PM CST Fri Dec 11 2020
0230z/830pm surface analysis shows a 1006mb low over northeast
Missouri with a warm front extending into central Illinois. Based
on latest wind fields, it appears the front stretches from just
south of Danville to north of Rantoul. S/SE winds and temps in the
middle 50s prevail south of the boundary, while NE winds and much
cooler readings in the lower to middle 40s are noted north of the
front. Rain has overspread all of central and southeast Illinois,
with hourly rates of one tenth to one quarter of an inch observed
on MRMS data. The rain will continue for the balance of the
evening into the first part of the overnight before gradually
tapering off toward dawn across the S/SW KILX CWA. 00z NAM and
HRRR both indicate a faster departure of the rain on Saturday,
which seems reasonable given drying trend on upstream radar across
central/western Missouri. Have updated PoPs Saturday to reflect
the rain ending everywhere except across the Illinois River Valley
by noon. Further west, a trailing deformation zone will keep
chance PoPs in the forecast through the remainder of Saturday
afternoon along/west of the Illinois River.
.SHORT TERM...(This evening through Saturday)
ISSUED AT 302 PM CST Fri Dec 11 2020
Radar data showed continued rain development over MO and moving
northeast into Illinois. Moisture channel imagery showed the
shortwave in western KS with diffluence in the upper level flow
over the mid MS valley area. Surface analysis shows low center
over west central MO which is progged to move east northeast over
central IL tonight. Models have sped up the movement of the short
wave and the surface low, so that it moves quicker over IL tonight
and so the lift and period of lift is shorter with the result
being lower pcpn amounts. Amounts have dropped to 1/2 to 1 inch
now with some locally higher amounts. 850mb moisture transport
displayed in the SPC mesoscale page still shows good advection
from MO into IL. Precip water amounts still around 1 inch.
Pcpn moving out by Saturday afternoon but with only weak low level
northerly flow over the area.
.LONG TERM...(Saturday night through Friday)
ISSUED AT 302 PM CST Fri Dec 11 2020
Next shortwave approaching region late Sunday into Monday, but
goes by mainly to the south of the area as seen in the progs. Then
another minor wave goes by mainly over southern IL on Tuesday
night. Pattern then is benign through rest of week.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 540 PM CST Fri Dec 11 2020
Light rain continues to spread northeastward across central
Illinois late this afternoon: however, ceilings have been slow to
lower. 23z/5pm obs show a large pocket of VFR ceilings persisting
east of the Illinois River...with only KPIA down to IFR. Radar
trends suggest the heavier rain upstream across Missouri/southwest
Illinois will eventually saturate the airmass from the top-down,
resulting in lowering ceilings as the evening progresses. Based on
latest obs and HRRR forecast, have introduced IFR ceilings at
KSPI/KDEC after 02z...then further northeast to KCMI after 09z.
Predominant rain will come to an end from south to north across
the area by late Saturday morning into the afternoon...with
ceilings rising to MVFR at KCMI by around 15z and further west to
KSPI by 17z. Further west/northwest, IFR will linger through the
remainder of the 00z TAF period at both KPIA and KBMI.
Area Forecast Discussion
National Weather Service Tallahassee FL
917 PM EST Fri Dec 11 2020
Previous forecast appears to be on track. Patchy fog will be
possible overnight but shouldn`t be as dense or widespread as
.PREV DISCUSSION [625 PM EST]...
.NEAR TERM [Through Saturday]...
Surface high will push east into the Atlantic overnight as the
next upper wave and associated cold front approach. This will help
keep winds and thus temperatures up for most of the area along
with much less in the way of fog. The exception will be in the
eastern Big Bend and southern GA where there will be a better
chance for decoupling leading to areas of fog and cooler temps
than the rest of the region. Increasing moisture off the Gulf
could bring isolated late night showers to the western Panhandle
per latest HRRR and 12Z deterministic guidance.
Front will continue to slowly approach our SE AL counties late
Saturday but most if not all of the showers associated with the
front should hold off until Saturday Night. Saturday will be very
mild with most locations away from the coast well into the 70s for
highs. Low shower PoPs carried only in the far west.
.SHORT TERM [Saturday Night Through Sunday Night]...
An upper level shortwave trough moving northeast from Missouri
into Illinois on Saturday with the associated surface low centered
over Michigan. These systems to our north will keep precip
chances for our region at a minimum. There will be a weak ridge
above us on Sunday, keeping temperatures relatively warm in the
low to mid 70s across the region with lows remaining in the upper
50s low 60s by Sunday night.
.LONG TERM [Monday Through Friday]...
A second upper level shortwave trough over the Pacific NW on
Saturday is expected to dive south towards north central Texas by
Sunday. Cyclonegenesis at the surface is expected to develop in
eastern Texas by Sunday night and move east along with the
shortwave trough aloft. At this time, global models maintain a
weakly unstable environment across our region ahead of the cold
front passage with the low pressure system. Showers can develop
across the area by Monday but, the nature as to how widespread the
activity will be is uncertain. The forecast details will become
more apparent in the coming days.
After the passage of the cold front, temperatures will range from
the mid 40s for lows to the 60s for highs. By Tuesday, another
shortwave trough will quickly move through the southern US; but
with little recovery time from Monday, there will likely not be
enough moisture for this system to produce measurable
precipitation. This front will however, introduce a reinforcement
of cold air with highs reaching the upper 50s. Lows will be
seasonal with the much of the region falling to the low 40s.
[Through 00Z Sunday]
Mostly VFR conditions are expected through the period. Some fog
may be possible overnight, but not expecting it to be as dense as
Favorable boating conditions are expected to continue through
today, with Cautionary conditions are expected to start Friday
night ahead of a cold front. By Sunday, Winds are expected to drop
into more favorable boating conditions briefly before once again
increasing to cautionary conditions on Monday ahead of the next
system. Swells through this time are not expected to increase much
beyond 1-2 feet, with swells occasionally reaching 3 feet through
Hazardous fire weather conditions are not expected over the next
With widespread rainfall totals of less than an inch expected
over the next week, there are currently no significant flooding
concerns at this time.
.SPOTTER INFORMATION STATEMENT...
Spotter activation is not requested. However, spotters are always
encouraged to safely report significant weather conditions when they
occur (while following all local, state, and CDC guidelines) by
calling the office or tweeting us @NWSTallahassee.
.PRELIMINARY POINT TEMPS/POPS...
Tallahassee 49 73 56 74 59 / 10 0 10 10 30
Panama City 59 73 61 73 59 / 10 10 10 10 30
Dothan 52 72 56 72 55 / 10 20 20 20 50
Albany 48 73 56 73 57 / 10 0 10 10 40
Valdosta 45 73 55 75 58 / 10 0 10 10 20
Cross City 47 72 57 76 59 / 10 0 0 0 10
Apalachicola 59 72 60 72 61 / 10 0 10 10 20