Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/12/18
Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
717 PM CDT Tue Sep 11 2018
.DISCUSSION...Updated for latest aviation discussion below.
.AVIATION...Satellite and radar images as well as surface
observations indicate scattered convection continues across
central portions of the CWA early this evening. A mix of
low/mid/high clouds were across the Rio Grande valley. Ceilings
were near 2100ft at KEBG to near 7500ft at KBRO. VISIBILITIES
were near 3SM with heavy rain at KEBG. Expect VFR to MVFR
conditions across the Rio Grande valley through the rest of the
evening into early Wednesday morning as the 500mb trough across
southwest Texas brings some drier air aloft across the western
portions of the CWA tonight but low to mid mid level moisture will
remain high across the eastern portions. Brief MVFR to IFR
conditions can be expected with showers and thunderstorms in the
vicinity of local aerodromes the rest of this evening into early
Wed morning. &&
.PREV DISCUSSION... /issued 353 PM CDT Tue Sep 11 2018/
SHORT TERM (Tonight through Wednesday Night): Some signs showing
now that the current heavy rain event is beginning to wind down.
Current water-vapor satellite imagery showing that much drier mid-
level air has overspread roughly the NW 2/3rds of the CWA, flowing
in from the WSW around the mid-level low centered in the vicinity
of SJT. Latest HRRR run also suggesting that any heavier bands of
showers/thunderstorms along the coast tonight may stay just
offshore. That being said, have opted to retain the Flash Flood
watch for Hidalgo/Brooks counties eastward through 12Z tomorrow.
Flash Flood Guidance for central/western Hidalgo and southwestern
Brooks counties remains quite low due to nearly saturated soils,
so it won`t take much additional rain to produce problematic
runoff. WPC continues to highlight a Slight Risk of excessive
rainfall in a narrow coastal strip as well.
Recent trends in visible imagery show that a compact surface low
near the Starr/Hidalgo county border has begun to open up and/or
lift NE a bit, along the old frontal boundary. This could still
help trigger some "wrap-around" showers and thunderstorms over the
Ranchlands and coastal counties from this evening into the overnight
period. Have begun walking PoP`s back a bit over the next 24 hours,
especially out west, per latest MOS/blend numbers. GFS is really
wanting to dry out the mid-levels tonight, but not completely .
buying into this solution. Will focus best coverage and amounts in
the coastal counties, toward midnight and later, as has been the
case the past several nights.
Models show better consensus in some fairly sharp drying aloft for
Wednesday, again especially to the west. H25 trough axis passes
tonight, with mid-level low mentioned above finally progged to fill
over south-central TX. PW`s come down to 1.6-1.7" west to ~2.0"
along the coast, vs. 2.2" observed in BRO 18Z sounding today. Hence,
will hold PoP`s in scattered category and remove mention of heavy
rain for daytime Wednesday and beyond. Temps should recover to the
low 90`s (except at the immediate coast), perhaps back to the mid-
90s in the Zapata-Falcon dam area where there should be much more
A little uncertainty in the forecast for later Wednesday night.
Models trying to regenerate some more "wrap-around" precip over the
N. Ranchlands/coastal counties. NAM sags the old H5 vort max into
the western CWA, pulling some richer PW back inland. MOS guidance
rather unimpressed, though, so have kept rain chances generally 30%
or lower for land areas.
LONG TERM (Thursday through Tuesday): All eyes on the potential
development of the disturbance centered just north of the Yucatan
peninsula Tuesday afternoon for what it may (or may not) do for
Deep S. Texas and the Rio Grande Valley during the first few days
of the long term (Thursday through Saturday). Concentrated the
focus on this period with few changes made beyond Saturday night
At this point, uncertainty reigns for most parameters and
potential impacts, and confidence for all but direct coastal
impacts from waves/swell/tides is low (medium for these). There
are some subtle signs that do offer some possibilities for what
may actually occur and the sensible weather that comes with it.
First...and for what it`s worth...global deterministic models
(GFS,ECWMF, UKMET, Canadian GEM) all carry a circulation, with
relatively modest pressure falls, to the coast somewhere along the
Coastal Bend. The elongated look of the disturbance as well as a
jump to the north-northwest to just north of the Yucatan peninsula
rather than along the Peninsula may have helped to guidance to
"lean" toward the mid Texas coast vs. the Lower Texas coast.
Second, there remains notable wind shear in the western Gulf,
courtesy of the overnight convection and an eastward nudge of the
`atmospheric river` that brought the flooding rains to parts of
the region and the end of the drought/dryness to others. That wind
shear, should it be present even if weakened, would argue for the
model consensus slow development of the system. A quick look at
intensity forecasts suggest the potential for a depression or
tropical storm at this point.
That said, if the shear does relax over the next 36 to 48 hours,
the system has a better shot to intensify, with plenty of deep
layer moisture in the envelope as well as peak warm temperatures
in the 29-30C range (September in the Gulf). If that were to
happen, the ability of the cyclone to track a bit farther south
might improve as the 500 mb ridge between Florence and the
southern Plains could become just dominant enough to bring more of
a westward, than northwestward, movement.
Because of the uncertainty, it`s just a bit too soon to bite off
on any one solution, and better just to lean in a little bit
toward the pragmatic answer which does favor a more northwest
movement and slower intensification at this point.
With this in mind, have followed the WPC/NHC idea for moderate
rain chances and more modest QPF for the region, with slightly
higher amounts on a southeast to northwest line along the coast
(South Padre to Falfurrias) and lesser values in the populated mid
Valley, which could use a break after the big rains since last
Beyond Saturday night/Sunday the 500 mb ridge returns, and should
bring more sunshine and temperatures a few degrees above average
with modest east to southeast flow.
One situation that bears watching is how rainfall potential
develops across the Rio Grande Plains by Saturday afternoon and
night. Models favor the area along/west of the Rio Grande between
Laredo and Del Rio to get bigger rainfall, and WPC`s forecast does
the same. Such a situation could create additional flood waves
down the Rio Grande, which might affect areas north of Falcon in
Zapata but more importantly push additional water into Falcon
Reservoir, such that percentage of capacity, Texas share, could
head toward 50% or higher as was the case in late September 2017.
That`s always great news for irrigation come late winter and
Potential Impact Confidence:
Elevated rip current and some tidal run up...medium. Forecast
tides are at astronomical higher levels, and an additional foot or
foot+ of increase could produce 1 to 1.5 feet of water at the
typical shoreline interface, which would push water up to the dune
line at high tide.
MARINE: (Now through Wednesday Night): A weak pressure gradient will
continue through Wednesday, with a stalled frontal boundary in the
area, which will maintain light to occasionally moderate winds and
seas generally 3 feet or less. Deep tropical moisture will continue
to support scattered to numerous showers and scattered
thunderstorms, with possible brief heavy downpours, locally gusty
winds, and isolated to occasional cloud-to-water lightning. Winds
may back to a more NE direction Wednesday night as a tropical wave
moves into the western Gulf of Mexico. At this time, speeds don`t
appear to reach SCEC level in the short-term, but will have to
monitor in case the tropical system develops more organization and
tightens the gradient offshore. Could see some 4-ft. waves offshore
by that time as well.
Thursday through Sunday Night...much will depend on the
evolution of the disturbance, both for intensity and track. A
straight ECMWF/Canadian solution would bring northeast, then
north, then northwest winds with the passage of the system
followed by south to southeast winds Saturday and Sunday which
could be the highest of all periods. A modest system - for
example, a tightly wrapped tropical storm that makes landfall
north of Corpus - would keep wind speeds 10 knots or less until
the back side when south/southeast winds could kick up to 15-20
knots. Waves/seas are highly dependent on where and how quickly
the system develops, and theoretically could range from 2 to 4
feet ahead of the cyclone to 4 to 6 feet in the longer fetch
southeast flow behind it. A stronger system, even if tight, would
be able to kick out swells and higher waves propagating to the
Lower Texas coast...but how high cannot be determined at this
TX...Flash Flood Watch until 7 AM CDT Wednesday for TXZ250-251-
This product is also available on the web at:
Area Forecast Discussion
National Weather Service State College PA
1048 PM EDT Tue Sep 11 2018
A slow moving cold frontal boundary will stall just to the
southeast of the state tonight. The region will remain in a
moist easterly flow between a high to our north and the
circulation associated with Hurricane Florence well off to our
There is the potential for the region to be impacted by rain
from (the future remnants of) Hurricane Florence by the weekend
or more likely next week, though the eventual track and timing
of the storm are still very uncertain.
.NEAR TERM /THROUGH WEDNESDAY/...
Meso analysis indicates the occlusion associated with the long
dissipated Gordon has all but dissipated. Looking at the 950mb
dewpoints suggests the best support for a frontal boundary, the
old warm front, extends from southern New England SW into NRN
I lowered POPs overnight looking at the HRRR taking the scattered
showers over portions of the lower and mid Susq Valley moving
out and not much new expected through early Wednesday morning.
The airmass is still rather humid with dewpoints in the 60s, so
prospects for significant drying are not promising. With plenty
of cloudcover, overnight lows will remain on the mild side
ranging from the mid 50s over the north to mid 60s over the
Clouds and scattered showers look to hang around Wednesday as a
deep easterly flow develops south of the sprawling high off to
.SHORT TERM /WEDNESDAY NIGHT/...
High pressure trying to nose in from the NW looks like it will
be thwarted by a stalled front just off to the SE, keeping low
level moisture trapped in place which will keep clouds
plentiful. Low level flow turning around to the S/SE won`t help
the situation either, and will feed development of generally
light showers, becoming a bit more numerous each day through
Friday as flow gradually increases. Timing / placement of
these banded showers a tough task when trying to indicate
enhanced PoPs over next couple of days, but generally highest
likelihood will be over the south and east. Mesoscale models
will aid in focusing/enhancing PoPs further during a sliding
12-24hr window. The best chance of staying dry Wed will be NW
of a line from Clearfield to Mansfield.
Temps remain pretty constant for next several days, with highs
pretty much in the 70s and lows pretty much in the 60s.
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Frontal boundary that pushed slowly east across the region
Monday (in the wake of the remnants of what was once Tropical
Storm Gordon during the middle of last week), has stalled out
across the Susq Valley and Scent PA, and will slowly weaken and
retreat back to the northwest over the next few days as an
inverted trough well in advance and to the NW of powerful
All model and EFS guidance indicates scattered to numerous
showers and perhaps a isolated/brief low-topped afternoon tsra
Thursday and Friday, with high temps climbing back to near, or
slightly above normal under a persistent, but mainly light east
to southeast llvl flow.
Still, slightly diverging medium range U.S. and EC guidance
occurs with respect to the timing and ultimate track of powerful
Hurricane Florence as she nears the NC coast later Thursday into
Friday, then either stalls for 24 to 48 hours or drifts slowly
west or SW.
There will likely be some significant differences in sensible
weather conditions from north to south acrs PA with the
thickest layered clouds, best chance for drizzle or some periods
of light rain, and a slightly gusty east to SE sfc wind limited
to the southern tier or half of PA Sat and Sunday. A fair amount
of sunshine, pleasant near-normal high temps, low humidity and
Blended in about 50-70 percent weighting of the Operational EC
and EC ensembles (which have shown the most consistency run to
run over the past few days, along with its slightly more
southern landfall and inland track compared to the GFS/GEFS and
official TPC track). That being said, and integrated into the
regional CWA forecast, will paint just a slight chc for some Fri
night/Sat morning drizzle and low clouds across mainly the
southern part of the PA and otherwise just isolated rain
As the greatly weakened remnants of Florence beings to drift
north through a weakness across the Ohio River Valley, that
exists between two large areas of upper level high pressure, it
will bring an increasing chance for showers and TSRA with bands
of locally heavy rain possible Monday through Tuesday night
(especially across the western half of the state that
experienced the heaviest rain from the recent passage of the
remnants of TS Gordon).
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
The boundary remains stalled with showers through eastern PA as
of 00Z Radar. MVFR cigs overall dominate the skies with only UNV
and IPT IFR. While a brief period of VFR should continue, cigs
and vsbys will drop tonight due to low level moisture trapped
under the inversion. This will bring widespread IFR reductions
overnight along with patchy fog. Expect conditions to drop
between 05Z to 07Z.
Light low level flow turning to the S/SE tomorrow will make it
tough for conditions to improve much. Latest SREF and HREF
models due show some improvement from IFR to MVFR by late
morning. However MVFR should continue through tomorrow afternoon
with scattered VFR possible again with scattered showers. We`ll
repeat that MVFR during the day and IFR at night cycle through
the end of the week as showers become more numerous each day.
Hurricane Florence will impact the Carolinas/Mid Atlantic region
late week and this weekend. A high pressure area building to our
north looks to potentially advect some drier air in Sat/Sun with
improving conditions at least for the central/northern sections.
Wed...AM low cigs/fog possible. MVFR/VFR cigs with sct showers.
Thu-Fri...Patchy AM fog possible. MVFR/VFR cigs. Scattered to
numerous showers. Isold PM tsra impacts possible.
Sat-Sun...Patchy AM fog possible. PM rain/low cigs possible
Spotty showers today should not allow for renewed rises on area
streams/rivers. Smaller streams and creeks are retreating this
afternoon, with rivers and some larger streams still experiencing
at least minor flooding (we`ve got 15 river points still in
flood at 18z). The West Branch Susq R is still going to be
rising significantly into Wed. The Juniata basin, easily the
hardest hit area, peaked with moderate to major flooding and is
now generally falling. Beech Creek (West Branch basin) cresting
in Major flood category. Much of that water did an end-around
the Sayers Dam, falling in the Marsh Creek and Beech Creek
basins. Those points are now falling.
NEAR TERM...La Corte
Area Forecast Discussion
National Weather Service Wilmington NC
640 PM EDT Tue Sep 11 2018
Hurricane Florence, a powerful category four storm, will
approach the Carolinas Thursday through Friday. Catastrophic
impacts from wind, flooding rainfall, and storm surge flooding
are expected to develop for portions of the eastern Carolinas.
Florence may linger through the weekend with the potential for
flooding rainfall continuing.
.NEAR TERM /THROUGH TONIGHT/...
As of 500 PM Tuesday...Hurricane Watch and Storm Surge Watch
have been upgraded to a Hurricane Warning and Storm Surge
Warning for all coastal counties and a few inland counties, for
Major Hurricane Florence forecast to impact the area Thursday
through at least Friday. Current radar shows mainly inland
scattered showers and thunderstorms along and south of the I-95
corridor. Convection is following an outflow boundary along the
leading edge, heading towards the northwest. The HRRR has
initialized quite well with ongoing convection and its solution
depicting continued northwest movement with erosion on the
southeastern edge. Most shower and thunderstorm activity should
dissipate by 00Z or shortly thereafter. Overnight lows should be
quite close to guidance, so didn`t stray too far. Only made
slight changes to drop temps a degree or 2 in locations that
touched 70 last night. Before the night is over, models show
nocturnal convection moving inland. Thus, have maintained low
end POPS from the previous forecast.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
As of 330 PM Tuesday...Wednesday will give us one final day to
prepare for the arrival of category four Hurricane Florence.
Partly cloudy skies, scattered showers, and continued warm/humid
conditions are forecast. Adding 3-5 degrees to MOS high
temperatures at inland sites has been a winning strategy over
the past several weeks, and I`ll continue do this this
The first outer bands of showers from Florence could push
onshore before daybreak Thursday in the Cape Fear area.
Thickening clouds and more rain bands will spread inland during
the day, with winds anticipated to reach tropical storm force
in the Cape Fear area during the afternoon.
Conditions will go downhill in a hurry Thursday night as the
center of Florence approaches the coast. I don`t have much to
add beyond what the National Hurricane Center and Weather
Prediction Center have forecast for the area. The very dry
antecedent conditions we`ve had over the past six weeks won`t
buy us much reprieve from flooding given the exceptional
rainfall amounts expected along the coast north of Myrtle Beach.
Just Thursday night alone 8-10 inches of rain will probably
fall in the Cape Fear area, with additional heavy rain
continuing into Friday.
This will likely be the storm of a lifetime for portions of the
Carolina coast, and that`s saying a lot given the impacts
we`ve seen from Hurricanes Diana, Hugo, Fran, Bonnie, Floyd,
and Matthew. I can`t emphasize enough the potential for
unbelievable damage from wind, storm surge, and inland flooding
with this storm.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 330 PM Monday...So much uncertainty with the extended
especially early depending on the evolution of Hurricane
Florence. I did increase pops, cloud cover, and QPF amounts at
least for Friday. The weekend remains a toss up as well as
guidance wants to linger the vortex inland. Here again I
increased the relevant parameters albeit at a more muted clip.
The next mid latitude trough and front to possibly impact the
region may arrive next week although this far out in time
confidence is low.
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 00Z...Convection winding down and is mainly out of the CWA.
Tonight, some convection could possibly drift onshore, best chance
ILM. Mainly MVFR fog is expected. Wednesday, lots of subsidence
ahead of Hurricane Florence, so expect only isolated convection
along the resultant boundary.
Extended Outlook...Mainly VFR through Wednesday outside of ISOLD
showers and TSTMs. Patchy morning MVFR fog possible. Hurricane
Florence will begin to affect the area Thursday with increasing
wind and wind-shear, and deteriorating ceilings/visibilities,
continuing into Friday.
NEAR TERM /THROUGH TONIGHT/...
As of 500 PM Tuesday...Hurricane Watch has been upgraded to
Hurricane Warning for our local coastal waters, for
Major Hurricane Florence forecast to impact the area Thursday
through at least Friday. Light onshore winds are expected
tonight along with a small but very long period swell from
Hurricane Florence. Scattered showers will develop mainly after
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 330 PM Tuesday...The approach of category four Hurricane
Florence is the single concern in this period. Long-period
swells ahead of the storm will increase in amplitude throughout
the day Wednesday, creating extremely hazardous conditions in
inlets during outgoing tides. Situations like this in the past
have created large breaking waves 10-20 miles from shore along
Frying Pan Shoals. Hurricane-force winds will overspread the
area Thursday afternoon and evening.
LONG TERM /FRIDAY THROUGH SUNDAY/...
As of 330 PM Tuesday...Obviously the evolution of Hurricane
Florence will be dictating conditions with rugged seas and
either hurricane or tropical storm force winds basically
through the entire period.
As of 330 PM Tuesday...Depending on the exact landfall position
of Florence, there is some potential that a new all-time low
barometric pressure reading for Wilmington could be established.
Operational models are showing forecast pressures anywhere from
948 to 965 mb in the eye of the storm as it approaches the
coast. Here are the current records for Wilmington.
1 Hurricane Floyd 9/16/1999 959.7 mb 28.34"
2 Hurricane Fran 9/5/1996 961.4 mb 28.39"
3 Hurricane Donna 9/11/1960 962.1 mb 28.41"
4 Hurricane Bonnie 9/26/1998 969.9 mb 28.64"
5 Nor`easter 3/6/1932 970.2 mb 28.65"
More at https:/weather.gov/ilm/Top_20_Storms
SC...Hurricane Warning for SCZ054>056-058-059.
High Rip Current Risk until 8 PM EDT this evening for SCZ054-
High Rip Current Risk from Wednesday morning through Wednesday
evening for SCZ054-056.
NC...Hurricane Warning for NCZ105>110.
High Rip Current Risk until 8 PM EDT this evening for NCZ106-
High Rip Current Risk from Wednesday morning through Wednesday
evening for NCZ106-108-110.
Hurricane Watch for NCZ087-096-099.
MARINE...Hurricane Warning for AMZ250-252-254-256.
Area Forecast Discussion
National Weather Service Wilmington OH
1021 PM EDT Tue Sep 11 2018
High pressure over New England and southeast Canada extending
back into the Midwest will keep mostly dry conditions across the
area through the week. Temperatures will be slowly moderating
each day as warmer air returns with a light southerly flow, as
well as increased humidity. A few showers may develop on
Thursday and Friday with the increased moisture, primarily over
central and eastern Ohio, but most locations will remain dry.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Clouds persist across all but the northwest corner of the
forecast area. RAP continues to show this area clouding up as
thermal trough slowly shifts northwest overnight. Forecast lows
look on track.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Weak low level warm advection will continue on Wednesday which
should erode the thermal trough to some degree -- and allow for
low clouds to slowly break up. Unfortunately for sunshine
lovers, thickening mid/high level clouds on southwesterly flow
aloft and a near-continuous stream of sheared mid level
vorticity from the Gulf Coast to the Ohio Valley will train
through the area. Result will be still plenty of clouds, though
there should be more sunshine than recent days. Could even see a
sprinkle out of mid level echoes tied to the stronger vort
maxes pushing through this weak southwesterly flow on Wednesday
afternoon into Wednesday evening, but most areas will not see
measurable rain. Temperatures were held a little cooler than
statistical guidance given today`s poor MOS performance under
thicker clouds. So have run on the cooler side for highs on
Wednesday, and the warmer side on Wednesday night.
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Expansive mid and upper level ridge will stretch from the southern
Plains into New England late this week into the weekend. This will
keep the Ohio Valley region mainly dry with a warming trend. Highs
on Thursday to range from 80 to 85, with lower and middle 80s
expected Friday through Sunday. Boundary layer CAPES of 1000-1500
j/kg develop Thursday thru Saturday. Forcing is weak but isolated
showers or thunderstorms can not be ruled during the afternoons,
with the best chance across our far eastern areas. Will limit pops
to slight chance category during peak heating.
Large spread in the model solutions and therefore a good deal of
uncertainty exists in the forecast late this weekend into early next
The portion of the ridge over the Ohio Valley gradually breaks down
and weakens. This will be a big player in determining the track of
the remnants of Florence. 12Z deterministic GFS solution has trended
closer to the previous ECMWF deterministic and ensemble solutions,
which takes the remnants further west into the Ohio Valley. Latest
ECMWF is still south but slow with movement.
Due to the weak steering flow and therefore the uncertainty will
limit pops to chance category. Will allow these pops to develop into
the southeast Sunday and across the entire region Sunday night into
Monday and Tuesday. Due to lack of instability will not mention
thunder at this time. Clouds and pcpn will affect temperatures with
highs generally in the upper 70s.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
VFR ceilings at the start of the period will likely lower
slightly overnight, just enough to reach MVFR at all sites
except the Cincinnati area. Ceilings will gradually lift on
Wednesday morning with this deck eventually becoming scattered
later in the TAF period.
OUTLOOK...No significant weather expected.