Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/08/18
Area Forecast Discussion
National Weather Service Bismarck ND
853 PM CDT Fri Sep 7 2018
Issued at 853 PM CDT Fri Sep 7 2018
Surface based convection that developed a few hours ago across far
southwest and far south central North Dakota continues to decay
with loss of daytime heating. 850mb southerly winds are forecast
per RAP/HRRR to quickly ramp up to between 35kt and 40kt across
western ND overnight. Low level moisture advection atop a northward
advancing warm front will lead to destabilization and elevated
convection across western and north central North Dakota through
the overnight period. Will tweak PoPs based on the latest NAM12
and CAM guidance for the overnight period. Overall forecast is on
UPDATE Issued at 544 PM CDT Fri Sep 7 2018
Latest surface map shows a stationary boundary roughly aligned
from Beach to Dickinson, Bismarck to Rugby. CAM`s continue to show
shower/thunderstorm development along and north of the stationary
boundary this evening then growing in coverage tonight. The favored
initial development this evening will be across western North
Dakota, then into north central North Dakota overnight. Locations
already south of the boundary such as south central and the James
River Valley will remain dry.
The thunderstorms are in response to an intensifying low level
jet/moisture advection which will result in elevated convection.
Hail up to the size of quarters will be the main threat. The HRRR
shows high based convection (10kft) with Effective Bulk Wind Shear
at Williston ranging from 35kt to 45kt between 03z and 07z.
Elevated CAPE ranges between 500 J/Kg and 1500 J/Kg, so enough
instability and shear to warrant isolated severe development. The
stationary front will transition into a warm front as low level
southerly winds increase and push the boundary to the northern
border by 12z Saturday, gradually pushing the elevated convection
across the border towards daybreak Saturday.
.SHORT TERM...(This afternoon through Saturday night)
Issued at 130 PM CDT Fri Sep 7 2018
Highs today will remain above normal, especially west and south,
with the influence of the cold frontal boundary clearing seen in
highs today, with 60s northeast to the upper 80s southwest.
Dewpoint temperatures will reflect more abundant moisture,
generally in the mid to upper 50s over all but the southwest,
where afternoon dewpoints in the mid 40s are expected.
Late this afternoon and into the evening hours, model consensus
has a shortwave trough propagating across our northwest and north
central. Additionally, the surface boundary located over parts of
the southwest and south central will continue to linger. These
two areas should serve as the main focus for thunderstorm
development across the forecast area late this afternoon into
tonight. Cape and shear are still forecast to be rather modest
(500 to 1500 J/kg MLCAPE and 25 to 35 knot 0-6 km bulk shear) but
this should be enough to spark at least an isolated severe storm
or two, capable of hail up to an inch in diameter. Slow storm
motions could also bring locally heavy rainfall with the stronger
Saturday will feature another progressive shortwave trough that
will bring yet another round of showers and storms across the
area. At the surface, expect thunderstorm development along a
pre-frontal trough. Regarding severe weather potential on
Saturday, confidence is decreasing as instability continues to
trend weaker in the guidance, while shear remains rather modest.
Still, we should see fairly widespread shower and thunderstorm
development by Saturday afternoon, and there will likely be enough
instability and shear present for a strong storm or two. Ahead of
the surface trough and approaching front, expect a strengthening
pressure gradient that will facilitate breezy conditions. Gusts
may approach 30 to 35 mph at times Saturday afternoon.
.LONG TERM...(Sunday through Thursday) Issued at 130 PM CDT Fri
Sep 7 2018
As the surface trough moves east and the trailing cold front
pushes across the state, thunderstorm chances will also translate
east, roughly along a line from the Turtle Mountains to the
southern James River Valley. This activity should diminish and/or
move out of the forecast area by the evening hours.
For the remainder of the extended, Monday through Thursday will
feature a gradual building ridge across the central part of the
country, with southwest flow aloft. This should ensure above
normal temperatures in the mid 70s into the lower 80s with some
chances for showers and thunderstorms. CIPS analogs and the NAEFS
ensemble remain consistent that summer will be hanging around for
a bit longer, forecasting above normal temperatures and continued
thunderstorm potential through the end of the long term and
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 544 PM CDT Fri Sep 7 2018
A stationary front draped over southwest ND and across south
central will move north tonight as a warm front. In doing so,
expect shower and thunderstorms to develop from near KDIK to KISN
and KMOT. Highest confidence right now is at KISN and have a tempo
group for -tsra between 04z and 08z Saturday. A vcts was added at
KDIK and KMOT respectively this evening into tonight. KBIS/KJMS
should remain dry. Behind the warm front Saturday, gusty southerly
winds sustained at around 20kt with gusts to 30kt for most of the
Issued at 1152 AM CDT Fri Sep 7 2018
Although there are fire weather concerns for Saturday across the
southwest, current forecasts still do not see critical fire
weather, but the forecast does bear watching.
The trend over the past few days shows increasing southerly winds
on Saturday, with sustained winds approaching 20 to 25 mph and
gusts as high 35 mph, across western and central North Dakota.
This trend continues, but the trend of stronger winds to move away
quickly from the lowest afternoon minimum relative humidity
values also continues. While forecast minimum relative humidity
has lowered a bit with today`s forecast package (20 to 25 percent
in the southwest), fire weather conditions still appear marginal
and borderline. Will continue to monitor, but thinking remains
that fire headlines are still not needed at this time.
Area Forecast Discussion
National Weather Service Columbia SC
1018 PM EDT Fri Sep 7 2018
Upper-level ridging over the region will weaken over the next
couple of days. Weak southeasterly flow will keep the region
in a moist air mass with a continued chance for mainly diurnal
showers and thunderstorms. Temperatures will remain at or above
normal into the weekend. Some cooling is expected Sunday
followed by above normal temperatures.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Low-level moisture will remain high because of the easterly
flow. Upper ridging will keep the moisture shallow. The SREF
guidance plus HRRR suggest the greatest potential for fog
development toward morning will be in the southeast section
closer to the moisture source. Overnight lows will again be in
the low to mid 70s.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
A low pressure system will be over the Mid-Mississippi Valley
Saturday with a front extending through the Tennessee valley
into the mid-Atlantic region. The local area will therefore
continue to experience warm southeasterly low-level flow. Mid-
level ridging could limit convection, with better chances along
the sea breeze to the southeast and closer to the front across
the Piedmont. The area will remain in the warm sector Sunday,
and there will be a greater chance of thunderstorms as the low
deepens and progresses eastward. Above normal temperatures will
persist Saturday with highs in the low to mid 90s. Increased
cloud cover Sunday could keep temperatures down and closer to
normal, with highs mainly forecast in upper 80s.
.LONG TERM /MONDAY THROUGH FRIDAY/...
The cold front is progged to stall west of the area Monday and
Tuesday. Scattered mainly afternoon and evening thunderstorms
will therefore continue. Temperatures will be above normal with
highs in the low 90s, and lows in the lower 70s.
Tropical Storm Florence is still forecast to be tracking west-
northwest south of Bermuda by early Tuesday. Refer to the NHC
for the latest track guidance. Much uncertainty exists near the
end of the forecast period due to the unknowns surrounding the
final track of the hurricane. Have kept a chance of convection
each day per model consensus.
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
VFR through 06Z. Moist easterly flow will continue across the
region. Fog/stratus with associated restrictions will again be
possible early Saturday morning...more probable at AGS/OGB 06Z-
13Z. Fog/stratus should improve with heating and mixing by mid
to late morning. Isolated/scattered diurnally driven convection
is expected to develop during the afternoon especially in the
vicinity of the seabreeze moving inland. Coverage is too low to
include in TAFs.
EXTENDED AVIATION OUTLOOK...Abundant low-level moisture and
onshore flow will continue the potential for late night and early
morning stratus. Flight restrictions are possible in scattered
afternoon/evening showers and thunderstorms.
Area Forecast Discussion
National Weather Service Jacksonville FL
954 PM EDT Fri Sep 7 2018
Latest analysis shows light easterly low level flow with weak
sfc moisture convergence over the ern zones. A weak sfc trough is
noted just inland from the coast at 9pm. A few showers dot the
marine zones so far this evening and with moist airmass per GOES
imagery and 00z JAX sounding (PWAT ~1.9 inches), anticipate
isolated to scattered convection later tonight and early Saturday
morning. The low POPs will be reserved for the coastal counties
but the highest rain chance will be over the marine zones. This
is in line with latest ensemble forecasts and HRRR guidance. No
thunder observed at the moment over the marine zones but instability
remains elevated with SBCAPE up to 2500-3000 J/kg so will
continue a low chance of t-storms overnight into Saturday morning.
Lows tonight in the lower to mid 70s, with some upper 70s
anticipated at the coast. Given dry air aloft, persistence and
SREF probabilities, will include patchy fog for the inland areas.
All afternoon/early evening convection has dissipated and
prevailing VFR at this time. Restrictions to MVFR vsby possible
late tonight for GNV and VQQ since winds are light to calm
tonight. There`s an outside chance of IFR too for GNV and VQQ but
MVFR is most probable. Coastal showers will start up again later
tonight and kept in VCSH for now after midnight. A round of
scattered showers and storms expected on Saturday.
East to southeast winds are 5-10 knots and seas about 2-4 ft.
Current forecast on track with little change. It is noted the bulk
of the wave energy is moving toward a swell component but periods
are about 10 seconds or less at this time. A few forerunners are
occurring though around 15 seconds at the Fernandina Beach buoy.
Will maintain long period swell as the dominant wave period
through the weekend per latest guidance and trends in buoy data.
Rip Currents: The long period ocean swell from distant TC
Florence will reach our local beaches through the weekend.
This swell will combine with high astronomical tides and onshore
breezes to produce a high risk of rip currents at all area beaches
on Saturday. Swell periods lengthen to 14-15 seconds on Sunday,
with life threatening rip currents expected to continue at area
beaches throughout next week.
Gauge sites along the coast and portions of the St. Johns River
basin are near action stage. As we near the new moon on Sunday,
water levels will trend up and a coastal flood advisory remains in
effect for Flagler, St Johns and Putnam counties at this time.
.PRELIMINARY POINT TEMPS/POPS...
AMG 70 90 72 91 / 0 30 10 40
SSI 78 87 78 87 / 30 40 30 30
JAX 72 89 73 89 / 20 30 10 40
SGJ 75 87 77 88 / 20 20 20 40
GNV 71 90 72 89 / 10 60 30 60
OCF 71 89 72 89 / 20 70 40 60
FL...Coastal Flood Advisory until 8 PM EDT Sunday for Coastal Flagler-
Coastal St. Johns-Inland Flagler-Inland St. Johns-Putnam.
Area Forecast Discussion
National Weather Service Louisville KY
938 PM EDT Fri Sep 7 2018
Issued at 925 PM EDT Fri Sep 7 2018
Decreased POPs overnight over all locations except southern Indiana.
The latest HRRR indicates the current convective cluster will
continue to migrate across southern Indiana overnight. Late tonight
we may see more isld-scattered activity over central KY mainly along
and west of I-65. Some light patchy fog is possible over portions
of south central and east central KY toward morning. Low temps look
to be on track in the upper 60s/lower 70s.
.Short Term...(This evening through Saturday)
Issued at 245 PM EDT Fri Sep 7 2018
Skies remained clear over southern Kentucky for much of today and
the clouds that were over southern Indiana and north central
Kentucky earlier have thinned out considerably, allowing the
attainment of convective temperatures. Isolated showers and a few
thunderstorms have developed in the humid air across Tennessee and
Kentucky and into southern Indiana. This activity will persist into
the early evening hours, then decrease after sunset. The few spots
that get caught under one of these cells could experience some heavy
downpours since the storms are moving slowly and there is plenty of
moisture in the atmosphere for them to work with.
Tonight clouds and rain chances will increase over southern Indiana
and western through northern Kentucky where there will be an
increase in isentropic lift and moisture ahead of former TS Gordon`s
remnants and north of an east-west warm front draped across
Kentucky. The best chances for heavy rain will remain to our west in
an area of better low level moisture transport.
On Saturday that east-west warm front will still be in place along
the length of Kentucky while Gordon`s circulation moves between
Paducah and St Louis. Widespread rain and embedded thunderstorms
with a heavy overcast can be expected north of the front. South of
the front scattered showers and storms will be possible in the
morning, with more thunderstorm activity developing in the afternoon
as the atmosphere destabilizes. The fact that we will be in the
right front quadrant of a former tropical system and will have a
warm front in the region raises the question of the possibility of
brief tornadoes. Right now it looks like the best chance of spin-ups
will be over the western half of Kentucky and along the warm frontal
boundary where EHI > 1 and shear is maximized. 0-1km SRH and 0-6km
bulk shear will increase as the day progresses, peaking around 100
m2/s2 (SPC SREF median value) and 30-40kt (GFS/NAM/EC) respectively.
.Long Term...(Saturday night through Friday)
Issued at 255 PM EDT Fri Sep 7 2018
...Flash Flooding Threat Through Sunday...
Main focus is on the flooding threat Saturday night into early
Sunday as the surface low, initially hung up near Cape Girardeau,
begins to eject eastward into southern Indiana. Heaviest rainfall
will be along and north of the track of the low pressure center, so
the current structure of the Flash Flood Watch remains in good
shape. Late Saturday night into Sunday still appears to be the prime
time for heavy rain and flash flooding.
Some concern early in the period with the potential for spinup
tornadoes due to easterly surface winds ahead of a northward-lifting
warm front. Lack of instability will be a substantial limiting
factor, so the primary hazard remains heavy rain/flooding. By
midnight Sat night, the front should be running roughly from
Vincennes to Cincinnati.
Forecast precip totals still running above 3 inches in the area
covered by the Flash Flood Watch, tapering down to around 1 inch
across south central Kentucky. The heaviest rain is still expected
to remain over the Wabash basin, thus limiting any lasting impact on
our mainstem rivers. We still expect plenty of short-duration
flooding along our smaller flashier streams anywhere that the
heaviest rain falls.
Sunday and Sunday night the deep moisture starts to taper off from
the west, as drier air wraps around behind the surface low lifting
into SE Michigan. By Sun evening our POPS will range from slight
chance west of I-65 to likely near the I-75 corridor, but the cutoff
will likely be sharper than that.
Monday will run unseasonably cool, especially in the daytime, as the
upper trof opens up and lifts out to the NE. Best chance for a dry
day appears to be Tuesday before our weak flow aloft becomes more
southerly again. Otherwise expect temps to gradually recover back to
climo, with diurnal 20-30% POPs for the latter half of the week.
.Aviation...(00Z TAF Issuance)
Issued at 645 PM EDT Fri Sep 7 2018
As T.D. Gordon approaches the region, chances for showers and storms
will increase through the TAF period.
SDF...VFR conditions are expected overnight with a VCSH possible
this evening. A better chance for rain and MVFR conditions should
arrive around 10Z. A morning t-storm and IFR conditions will also
be possible (tempo). Expect steady rains for much of the day
tomorrow with embedded t-storms and MVFR or possibly IFR conditions.
BWG...VFR conditions are expected through much of the TAF period
except in t-storms which could cause MVFR/IFR conditions. The best
t-storm chances exist tonight 5-9Z and tomorrow afternoon.
LEX...VFR conditions are expected tonight. Showers and MVFR
conditions should arrive around 12Z. Showers and t-storms will be
possible tomorrow afternoon with MVFR or IFR conditions.
HNB...Showers and t-storms at the terminal will continue to cause
MVFR or IFR conditions through 1Z. For the rest of the night expect
showers and perhaps an isld t-storm. A break in convection should
occur late tonight. MVFR cigs should return around 8Z.
Deteriorating conditions will begin around 10Z with the arrival of
steady rains and MVFR to IFR conditions through the end of the TAF
period. T-storm chances will be highest during the late morning and
afternoon hours tomorrow.
Winds of 4-9 kts will remain from the east at all TAFs except BWG
which will see southerly winds tomorrow afternoon. Higher gusts are
possible in t-storms.
IN...Flash Flood Watch from 8 AM EDT /7 AM CDT/ Saturday through
Sunday evening for INZ076>079-083-084-089>092.
KY...Flash Flood Watch from 8 AM EDT Saturday through Sunday evening