Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/27/22
Area Forecast Discussion
National Weather Service Charleston SC
951 PM EDT Mon Sep 26 2022
High pressure will build over the region tonight into Tuesday.
Tropical cyclone Ian could impact the region from mid week into
early this weekend.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
A large mid level trough centered over the Great Lakes will
continue to extend into the region tonight. A cold front is
still not that far inland from the US-17 corridor, and is
designated mainly by winds that are west and northwest, and dew
points that are in the upper 50s to upper 60s. This is opposed
to winds that are southerly further east, and dew points are 70F
or greater. The front will slide off the coast after midnight.
No significant changes with the mid evening update. Latest HRRR
shows that any convection that is able to occur will be over
the Atlantic. This is where the "best" moisture convergence and
MLCAPE will be situated in advance of the cold front. Instead
over land sections we look for just scattered to broken clouds
between about 5 and 10K feet, where the bulk of the moisture is
found. In addition, the large cirriform outflow from Hurricane
Ian will start reaching some of our southeast Georgia counties,
especially during the overnight period.
Min temps look to range from the mid and upper 50s far inland to
the lower and middle 60s over the coastal zones.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday: The cold front will slowly push east across the western
Atlantic through the day. In the wake of the front, dry high
pressure will build over the region from the west. Temperatures are
expected to range close to normals, generally in the low to mid 80s.
Wednesday: Canadian high pressure will push from the Northern Plains
to the Great Lakes Region, ridging south along the east facing
slopes of the Appalachians. TC Ian is forecast to track north off
the Gulf Coast of the FL Peninsula. The pressure gradient across the
forecast areas will steepen through the day, resulting in
strengthening NE winds. The NE flow will keep the forecast area
under dry air during the morning, over the inland counties through
the afternoon. However, moisture will build in from the east from
the top-down. GFS indicates that a warm front will sharpen over the
Gulf Stream, drifting towards the GA/SC coast. Isolated to scattered
showers may reach the coast, especially the GA coast, Wed PM. High
temperatures will be noticeably cooler from Tuesday, generally in
the mid 70s, some spots in the low 70s.
Thursday: The pressure gradient across the nearshore waters will
tighten, GFS indicates nearly a 7mb gradient Thursday afternoon.
Based on forecast soundings and blended models, tropical storm force
winds and gusts are expected across the marine zones, possibly on
the beaches. The warm front will near the coast Thursday night,
likely leading to winds to gradually weaken. A thick band of
moderate to heavy showers and thunderstorms are expected to develop
over the Gulf Stream as the warm front pushes over the nearshore
waters. Daytime temperatures may range in the low 70s.
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Thursday through Friday will be the primary period for any TC Ian
impacts. The warm front is timed to reach the coast Thursday night,
pushing inland during the day on Friday. The air mass east of the
warm front will feature PWs in excess of 2.1 inches and deep surface
based instability. The combination of deep frontogenesis, tropical
moisture, and instability should yield periods of moderate to heavy
rainfall rates Thursday night into Friday. (See Hydro section below)
In addition, hodographs near the coast at daybreak Friday show 0-1
km SRH in excess of 500 m2/s2 with weak instability, possibly
resulting in a time window for tornadoes/waterspouts Friday morning.
Bands of heavy rainfall will stream off the Atlantic around the
circulation of TC Ian through Friday.
The center of Ian is forecast to track across inland across SE GA
Friday night into Saturday morning. The passage of Ian should bring
numerous showers and thunderstorms across the CWA. By Saturday
afternoon, a cold front followed by a dry slot is expected to swing
across the region late Saturday, resulting in decreasing rainfall
rates and wind gusts. Sunday and Monday, a lingering pool of
moisture may result in mainly diurnal showers with near normal
Refer to the National Hurricane Center for the latest Ian
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Any isolated showers that occur with the cold front early
tonight look to be offshore. So we did not show anything other
than VFR with the 00Z TAF set for KCHS, KJZI and KSAV.
Extended Aviation Outlook: VFR. Gusty winds are likely Wednesday
through Friday at all terminals. Periods of moderate to heavy rain
possible Thursday night through Friday which could lead to periods
of flight restrictions due to low vsbys.
Tonight: A cold front will push offshore and east of the waters
tonight. Winds will shift from the south/southwest this evening
to the north overnight following frontal passage. Speeds will
top out around 15 or 20 knots, so below small craft advisory
criteria. Seas will average 2-3 feet. There will be a few
showers and t-storms with the cold front, mainly between 11 PM
and 2 AM on the nearshore waters and after midnight on the
outer waters. DCAPE values are forecast to be around 1000-1200
J/kg, meaning that there is a risk for some gusty winds in the
Monday through Saturday: High pressure building in from the west
through Tuesday. Conditions should remain below Small Craft Advisory
criteria through Tuesday. The marine zones will remain between high
pressure ridging in from the north and Tropical Cyclone Ian
Wednesday into Thursday. Conditions will deteriorate rapidly
Wednesday night through and late week. Tropical storm force NE winds
are forecast to develop across the marine zones Wednesday night
through Thursday. The circulation of TC Ian will spread across the
waters on Friday, likely remaining as tropical storm force. Seas
will increase to around 5-11 feet across the nearshore waters out to
20 nm and 12-15 ft across the outer Georgia waters from 20-60 nm.
Marine interests should stay informed of the latest official
forecasts for Tropical Cyclone Ian through the upcoming week.
Conditions will gradually improve over the weekend.
Marine Impacts: Moderate risk for rip currents expected along all
area beaches on Wednesday. Conditions mid to late week along all
beaches may lead to High Surf (5 ft breakers), Beach Erosion, and an
elevated risk for rip currents. The worst conditions are expect from
late Wednesday night through Friday evening.
TC Ian is forecast to near the Gulf coast of FL Thursday evening. A
warm front associated with Ian`s circulation will swing over the
Gulf Stream, likely leading to a band of heavy showers and
thunderstorms to develop. The environment will support an organized
band of showers/thunderstorms over the coastal waters, pushing
onshore Friday morning. This initial band could produce intense
rainfall rates. Later on Friday, bands of convection will sweep
onshore with the circulation of Ian through the day on Friday,
possibly into Friday night. Periods of moderate to heavy rain may
linger into Saturday morning, decreasing Saturday afternoon. Storm
total rainfall is forecast to range from 5 to 7 inches generally
along and east of I-95, some locally higher amounts.
The rainfall may overlap with periods of significant coastal
flooding, exacerbating any fresh or salt water flooding.
The combination of astronomical forcing and gusty winds will likely
lead to minor coastal flooding during both high tides on Wednesday.
Winds may strengthen to near tropical storm force along the coast
Wednesday night through Thursday. The gusty winds would likely
increasing tidal departures Wednesday into Thursday. By mid-day
Thursday, major coastal flooding is forecast to develop along the
SC/GA coast by mid-day Thursday. The significant coastal flooding is
expected continue with the Thursday evening and Friday morning high
tides. It is possible with the surging winds associated with the
convection, that moderate to major coastal flooding continue into
Area Forecast Discussion
National Weather Service Gray ME
1050 PM EDT Mon Sep 26 2022
A trough of low pressure will continue unsettled conditions over
the region early this week, with daily rounds of rain showers
punctuated by dry spells between. Thunderstorms will be possible this
evening, but the rest of the activity should be ordinary
showers mostly concentrated over the mountains, though not
exclusively. A cold front sweeps across the region around
midweek, bringing in drier and breezier weather through late
week with high pressure building in from the west.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
1050 PM Update...Little change to the going forecast at this
hour. The bulk of shower and thunderstorm activity has moved
into northern ME. Patchy fog will then develop tonight.
655 PM Update...Arching broken line of showers and a few
thunderstorms continues to push eastward across NH and this hour
and should gradually weaken with time. Have adjusted PoPs a
little bit based on latest radar mosaic loops, but otherwise,
little change to the going forecast.
Current water vapor imagery shows a highly amplified pattern across
North America with ridge along the West Coast up through Alaska and
a down stream long wave trough centered to the west of New England.
A short wave and vort max rotating through the trough is providing
forcing for ascent over New England with additional forcing from the
left exit region of a jet streak sliding across southern New
England. Surface heating has led to around 500 J/kg of SB CAPE
to develop with pockets up to 1000 J/kg per the latest SPC
mesoanalysis. Enhanced mid to upper flow will bring effective
Bulk Shear to 35-45 kts from late this afternoon through this
CAMs suggest low topped convection will blossom over the next
couple of hours in the mountains followed by a north to south
linear segment reaching the CT Valley around 5 PM and sliding
east reaching the NH/ME border around 8 PM. The HRRR has been
very consistent with this linear segment while other CAMs are
less bullish with more in the way multi cell clusters. Shower
and thunderstorm activity will spread northeastward after 8 pm
and will weaken with the loss of heating. SPC continues a
Marginal Risk for severe storms across northern and western
zones with model soundings showing inverted-V profiles and
relatively steep mid-level lapse rates around 6.5-7C/km. Dry
air aloft will likely limit convective coverage while storms
that do form will bring the threat of gusty winds and possibly
some small hail. Latest wind gust data from the HRRR suggests
gust potential will approach 40 mph with the linear segments
across New Hampshire. So while the overall environment is not
entirely conducive for widespread severe storms a few SPS storms
seems possible and cannot rule out an isolated severe storm.
Coverage will be greatest across northern and western zones
while areas down stream of the mountains will see widely
scattered showers and possibly an isolated thunderstorm.
Shower and thunderstorm activity wanes this evening with the loss of
heating and subsidence moving in behind the departing short
wave. Subsidence and residual low level moisture will bring the
threat of patchy fog first along the Mid Coast to the Capital
District of Maine spreading west along with patchy fog within
interior valleys. Lows tonight will range from the 40s in
northern and western zones to the 50s for areas near the coast.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
The high amplitude ridge/trough pattern continues into Tuesday
and Tuesday night, although the trough over the eastern CONUS
takes on a more positive tilt. This will shift the best forcing
well offshore with the 12Z guidance showing subtle short wave
ridging sliding over southern areas Tuesday afternoon. Areas
south of the mountains look to remain mostly dry with skies
turning partly to mostly sunny during the afternoon. As we
remain under broad cyclonic flow aloft there will be more clouds
in the mountains with slight chances for showers. Highs will
range from the low 60s north to low 70s across southeastern NH
and SW Maine.
Onshore flow will keep dewpoints elevated into the 50s along the
coast up towards the Capital District of Maine Tuesday night.
Mesoscale models are in decent agreement that fog will develop
again near in these areas Tuesday night with 12Z HREF also
suggesting reduced visibility from fog across much of the area
during the pre-dawn hours. Otherwise no weather impacts are
expected Tuesday night with continued chances for showers in the
mountains. Lows will range from the mid 40s north to near 50
degrees near the coast.
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
The persistent upper level trough will continue to slowly pivot over
New England to start our the long range portion of the forecast on
Wednesday. A broad frontal zone will also cross the region. This
will once again trigger a few scattered rain showers with northern
areas being the primary focus. The most cloud cover will be in the
upslope regions of the mountains with the coastline having more
sunshine. With mostly sunny skies the coastline will be above normal
for this time of the year as temperatures top out in the lower 70s
in a few communities.
The rain showers will mix with a few snow showers across the highest
peaks before ending Wednesday night. Drier air will enter the region
on Thursday as high pressure begins to build over the Northeast. It
will be breezy in a cold air advection pattern as well as having a
well mixed layer. This pattern will likely mix down lower dew points
We will likely have some radiational cooling Thursday night as the
surface high begins to build overhead. It will remain dry on Friday
with seasonable temperatures and light winds. A warming trend will
follow on Saturday as winds become southwest. 12Z operational models
and ensemble solutions suggest a backdoor cold front will approach
the region late Saturday night into Sunday. This system will likely
be moisture starved with limited or no precipitation associated with
it. The remains of TC Ian will then likely exit the East Coast early
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Short Term...Scattered showers and thunderstorms develop over
the mountains this afternoon. A band of showers and
thunderstorms over upstate NY will push east into New Hampshire
this evening reaching Maine around 00Z and will then weaken
with the loss of heating as they spread further into Maine.
These SHRA/TSRA will bring the threat of brief restrictions with
the best chances at KHIE, KLEB, and KCON. Behind this band of
showers there will be brief window of LLWS at KRKD. Subsidence
and low level moisture will bring the threat of fog late tonight
at KHIE, KLEB, KRKD, and KAUG. Conditions improve to VFR Tuesday
followed by another night of patchy fog bringing potential for
restrictions to most terminals in the pre-dawn hours Wednesday
Long Term...MVFR conditions in scattered showers will continue
over northern areas on Wednesday into Thursday. Otherwise, VFR
conditions are expected through the long range period.
Short Term...South to southwest flow and seas building to 5-6
will bring SCA conditions to the outer waters late this evening
and tonight. Winds subside late tonight while seas remain
elevated into Tuesday morning. Winds and seas then remain below
SCA thresholds Tuesday and Tuesday night.
Long Term...Winds and seas will remain below SCA thresholds
through the period. Winds switch behind a cold front to the
northwest on Thursday.
MARINE...Small Craft Advisory until 10 AM EDT Tuesday for ANZ150-152.
Small Craft Advisory until 5 AM EDT Tuesday for ANZ154.