Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/14/23
AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
1017 PM EDT Thu Apr 13 2023
.SYNOPSIS...
High pressure remains centered well off the Carolina coast
tonight. Low pressure approaches and moves across the area from
the southwest Friday into Saturday morning, bringing the chance
for showers and few thunderstorms. A cold front moves through
the area later Sunday into Monday.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 1015 PM EDT Thursday...
Late this evening, sfc high pressure was centered well off the
Mid Atlc coast. High clouds were starting to stream nwrd into
the region well in advance of low pressure over the Gulf coast
states and a warm front extending off the FL coast. Temps were
ranging through the 60s to near 70. Clouds will gradually
increase and thicken from SW to NE overnight into Fri morning
as low pressure and the warm front lift farther N. With the
increasing clouds and SW flow, remaining mild with lows in the
mid to upper 50s.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
As of 400 PM EDT Thursday...
Upper-level low continues moving gradually N into Friday.
Resultant S-SE flow will lead to pooling moisture along a sfc
boundary. Short-term guidance indicates a corridor of higher
instability may reside just SW of the local area (where sfc
temps are highest). An arcing line of convection is likely to
intensify some across central NC as it encounters the more
unstable air. There remains some differences among the hi-res
CAMs regarding how far N the instability gets, with the HRRR
more aggressive with the potential for sfc-based storms. Still,
there appears to be at least some potential for thunderstorms
mainly SW of a line from Farmville to Franklin to Ahoskie. The
strongest shear is also likely to remain to the S. SPC has
maintained a marginal risk across our SW counties (will
highlight in the HWO), with just a general thunder risk
elsewhere. The initial round of showers/storms looks to be
relatively short-lived and should be offshore by 18-21z. Given
the precip during the afternoon timeframe, highs should be
lowest (low 70s) where the most widespread rain and clouds are
(across the SW) and warmest (low 80s) across the N and NW
(where only light showers are possible). PoPs are likely-
categorical across the SW and chance elsewhere. A second round
of very scattered showers/storms are possible closer to sunset;
however, there is more uncertainty with this activity. Lows
Friday night around 60.
Upper-level ridging briefly recovers for later Sat and Sun.
Remnant scattered showers (and isolated storms) are possible Sat
afternoon. Highest chances across the N. Highs Sat in the mid
70s to around 80. A cold front approaches the area from the W
Sunday with highs surging again into the mid-upper 80s. PoPs
increase from W to E into the late evening. However, expect most
of the precip to hold off until the overnight. In terms of model
trends, most guidance have pushed back the frontal passage
timing into the early morning hours of Monday and are less
aggressive overall about precip coverage.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 330 PM EDT Thursday...
An upper-level trough will extend from the Great Lakes to the
southern Appalachians Sunday night, and progress east towards the
Northeast U.S. and Mid-Atlantic regions on Monday. The trough will
push a cold front through the region on Monday, bringing a chance of
showers and thunderstorms late Sunday and/or early Monday. However,
recent model guidance keeps best chance for storms across central VA
and locations north. Northwest flow will follow the cold front on
Monday and result in dry conditions through the long term forecast
period. Temperatures will fall to near seasonal averages Monday and
Tuesday before warming up to above average temperatures once
again.
&&
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
As of 815 PM EDT Thursday...
Mainly VFR conditions will prevail at the TAF sites this evening
through Fri morning, although expect increasing high and mid
level clouds from the SSW in advance of low pressure and a warm
front. That low pressure area and warm front will then lift
across the region Fri aftn into Sat morning, bringing the chance
for showers and a few tstms. This system may produce MVFR and
even IFR conditions during this time period.
Outlook: Isolated to sctd showers will be possible into Sat
evening, until an upper trough exits off the coast. A cold front
approaches from the west Sun into Sun night.
&&
.MARINE...
As of 330 PM EDT Thursday...
High pressure is centered off the Carolina coast this afternoon. The
wind is generally S-SW 5-10kt over open water, but is locally
variable nearshore with sea-breeze circulations in light flow. Seas
are ~2ft with ~1ft waves in the Bay. High pressure remains centered
off the coast tonight into Friday as low pressure slowly approaches
from the southwest. The wind becomes SW tonight and increases to 10-
15kt, before diminishing and becoming S Friday morning, and then
becoming SSE 8-12kt Friday afternoon/evening. Weak low pressure
pushes offshore Saturday with a cold front approaching from the west
by Sunday. Sub-SCA conditions are expected with generally light
southerly flow of 5-10kt. Seas are expected to be 2-3ft Friday
through the weekend, with 1ft to occasionally 2ft waves in the Bay.
SW flow increases Sunday night ahead of the cold front, with
marginal SCA conditions possible Monday night into Tuesday in the
wake of the cold front. Seas build to 3-4ft Monday night into
Tuesday, with 2-3ft waves in the Bay.
&&
.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...None.
&&
$$
SYNOPSIS...TMG
NEAR TERM...SW/TMG
SHORT TERM...SW
LONG TERM...CP
AVIATION...TMG
MARINE...AJZ/AM
Area Forecast Discussion
National Weather Service Columbia SC
1042 PM EDT Thu Apr 13 2023
.SYNOPSIS...
Moisture continues to spread across the forecast area along with
scattered showers. On Friday a a low pressure system will cross
the region along with numerous showers and a few thunderstorms.
Drier conditions come Saturday then the rain returns towards
the end of the weekend. Temperatures around to above average
through the period.
&&
.NEAR TERM /UNTIL 7 AM FRIDAY MORNING/...
Showers and an isolated rumble of thunder continue moving into
the forecast area from the south. Pwat values have increased to
an inch or greater over the central and southern Midlands and
the northern Midlands and Pee Dee will see this in the next
couple hours. Overnight expect scattered showers to continue
especially during the early morning hours as a weak warm
frontal boundary moves through the region. Some locally heavy
rain is possible however with expected storm motion do not
expect any hydro related issues. Instability overnight will be
low to moderate however with little dynamic forcing expect
thunder to remain limited. Overnight lows will generally be in
the low to mid 60s.
&&
.SHORT TERM /7 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Friday and Friday night: The upper low in the Tennessee River
Valley will weaken as it moves north. Ensemble and CAMs are in
good agreement that a dry slot will continue to move through the
Carolinas and Georgia Friday morning, providing a lull in
activity. At the same time, warm air will advect in as the low
heads north and will help to destabilize the Carolinas. Hi-res
deterministic and ensemble guidance continue to indicate mean
surface CAPE of 1000 J/kg with values near 1300 J/kg in the
northern and eastern Midlands. Showers and thunderstorms do not
look as widespread as previously thought but outliers such as
the HRRR continue to show higher max values near 2000J/kg. This
is likely overdone as HRRR, for example, show lower mid-level
lapse rates and higher moisture. Limiting factor will be the low
shear, around 25-30 kt from 0-6 km. Organized convection is not
out of the question and both hail and wind threat look low. Storm
Prediction Center continues a Marginal Risk (Category 1 of 5)
for severe weather for damaging wind and hail threat. Slow storm
motion and higher-than-average PWATs have prompted the Weather
Prediction Center to issue a Marginal Risk (Category 1 of 4) of
flash flooding for the northeastern end of the Midlands, which
makes sense given the best chance of deeper moisture and little
storm motion will be in this area. Highs in the mid to upper
70s given the warm air advection. Mild temperatures continue
overnight as the precipitation moves out of the region, with
lows only dropping to around 60.
Saturday and Saturday night: The system is expected to be in the
Mid- Atlantic region by Saturday morning, with weak ridging
moving over the Midlands and CSRA area. This will help to bump
temperatures up a few degrees to the lower 80s in the afternoon
and keep the area rain free. Although rain is not expected
through the day, residual low level moisture is expected to
remain in place, resulting in elevated humidity levels compared
to what we`ve had recently. With the higher moisture levels,
overnight lows are expected to once again be on the warmer side
in the lower 60s.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
An upper trough translating across the Upper Midwest is expected
to send a cold front across the Southeast on Sunday, sparking
some shower activity, with the potential for some thunderstorms
as well. Latest guidance continues to show that the front passes
through the region in the afternoon to evening timeframe. Given
the timing, there should be enough instability to support a
stronger storm or two. As of now, the shear values appear to be
borderline at best again, so the threat for severe weather seems
to be limited at this time. After the front passes on Sunday,
drier air and cooler temperatures move in to begin the workweek.
Then, a warming trend is anticipated through midweek.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Expect deteriorating conditions tonight.
As upper and surface lows, to our west, move N and NE through
Friday, a low level convergence boundary will move NE across the
forecast area (FA) tonight. Increasing moisture in a low level
SE flow, will promote shower activity and lowering CIGs/VSBYs
tonight.
In the near term, expect areas of light showers, with IFR to MVFR
CIGs. Later tonight, as the surface boundary pushes NE through the
FA, additional convective development expected, per a preponderance
of the latest high resolution models, as an upper level shortwave
moves through. This activity appears to favor CAE/CUB/OGB and may
remain east of AGS/DNL, with low confidence on whether current
convection over central GA will eventually affect AGS/DNL.
IFR CIGs currently at AGS/DNL, with MVFR elsewhere. Guidance
indicating deteriorating CIGS tonight, to possibly LIFR, with higher
probabilities of such at AGS/DNL per latest NBM/SREF. In addition,
as the boundary moves NE, low level winds may decrease some at
DNL/AGS, and possibly even at the other TAF sites late, while dry
air aloft moves in. This could promote lower VSBYs. Again, latest
NBM/SREF indicate higher probs of LIFR VSBYs at AGS/DNL. However,
latest GFSLAMP guidance more optimistic. For now, generally indicated
IFR at CAE/CUB/OGB and LIFR at AGS/DNL.
Gradual improvement expected Friday morning to midday. Diurnal
heating and some upper energy expected to promote scattered showers
and isolated thunderstorms Friday afternoon. Confidence of TS
hitting a TAF site not quite high enough this far out to include in
the TAFs at this time.
.EXTENDED AVIATION OUTLOOK...
Patchy fog/stratus possible Friday night/early Saturday. No
significant impacts to aviation expected Saturday/Saturday night.
Chance of showers Sunday. VFR, with breezy conditions possible,
Sunday night and Monday. VFR Tuesday.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
Area Forecast Discussion
National Weather Service Indianapolis IN
1156 PM EDT Thu Apr 13 2023
...Updated Aviation Discussion...
.Forecast Update...
Issued at 959 PM EDT Thu Apr 13 2023
Forecast is in decent shape this evening. High and some mid clouds
are increasing from the south from the low pressure system in the
southern states. Adjusted cloud cover as needed based on latest obs.
Radar has some weakening echoes moving into the far south from
weaker forcing on the periphery of the low pressure system. Fort
Knox, Kentucky did report some light rain from these echoes even
with large dewpoint depressions at the surface. However, at this
time, given the weakening nature of the echoes as they move into
central Indiana, feel that coverage of drops reaching the ground
will be too low to mention.
Made some tweaks to low temperatures based on latest trends, but no
significant changes were made.
&&
.Short Term...(This evening through Friday)
Issued at 257 PM EDT Thu Apr 13 2023
* Well above normal temperatures continue into Friday
* Increasing high clouds ahead of approaching weather systems
.This Evening and Tonight...
Forecast for this afternoon is on track, therefore little changes
made with today`s forecast package. High pressure is centered off
the coast of the Mid Atlantic states with a tropical low pressure
over Mississippi and another moving into Western Nebraska. This
pattern has resulted in weak southerly flow across the state with
subsidence under the high keeping skies clear. 18z IND ACARS
sounding shows a mixing height up to 1 km agl into a very dry layer
aloft. The forecast for falling RH values and steady dew points in
the 30s today has verified quite nicely. While RH values have
dropped significantly, winds have remained fairly light resulting in
little fire weather concerns today.
Overnight, conditions will remain similar, with no gusts as the PBL
decouples. Winds speeds staying around 5-8MPH throughout the night
and steady WSW advection will limit diurnal cooling some. However
increased cloud cover this evening into tonight, especially in the
upper levels as downstream moisture from the tropical low reaches
the region could have a more profound impact on temperatures. Kept
low temperatures in the mid 50s for tonight (around NBM75th
percentile) to account for increasing cloud cover and winds staying
slightly elevated.
.Tomorrow...
The tropical low across the Gulf Coast states Thursday continues its
weakening trend and slowly pushes north northeast within the weak
mean flow. The system erodes from the bottom up as it tracks towards
the Ohio and Tennessee Valleys with little to no surface reflection
as it makes its way this far north. The upper low reaches Kentucky
then turns northeastward toward West Virginia by tomorrow night.
Little impacts expected from this system across Indiana tomorrow,
however it will feel noticeably more humid than the past few days.
Moisture advection increases ahead of the system with dew points
rising from the 30s to the 50s by Friday afternoon. High clouds
associated with the expansive cloud shield push northward overnight
and into tomorrow across Indiana. RAP forecast soundings and cross
sections suggest high clouds increase and thicken through the day
keeping temperatures a few degrees cooler than today. With such a
warm airmass in place, expecting temperatures to still reach the mid
to upper 70s tomorrow, with the warmest temperatures along and north
of I-70 where clouds will be thinner.
&&
.Long Term...(Friday night through Thursday)
Issued at 257 PM EDT Thu Apr 13 2023
* Slight chance of rain on Friday
* Scattered showers and thunderstorms late Saturday into Sunday
* Cooler conditions on Monday
* Dry weather along with warming trend beginning Tuesday
Synoptic Pattern Overview
Currently, a large upper-level ridge resides over the Midwestern
United States. This has provided us with abundant sunshine and
above-average temperatures. To our south, a cut-off low pressure
system has developed in the Gulf of Mexico and moved inland. Out
west, a trough is beginning to dig into the intermountain west and
will progress eastward with time. The cut-off low to our south will
then open up and move northeastward ahead of the advancing trough.
Finally, the west coast trough is modeled to make its way into the
Plains and then the midwest, amplifying significantly as it does so.
By the time it reaches Indiana, it may already be in the occlusion
process. Afterward, broad ridging returns to the Plains and upper
Midwest.
Friday Night
The southern cut-off low, originating from the Gulf, will begin
lifting northward tonight. As it does so, moisture will begin
spreading northward as well. It is not out of the question that an
isolated shower or even a thunderstorm works its way into the area
during the day tomorrow. Chances of this appear quite low, however,
as the parent cyclone passes to our south and east. Upper-level
forcing seems almost nonexistent, as flow between the low and trough
to our west largely cancels out...leaving very little air flow
through the column. CAMs suggest that the best chance of any
shower/storm activity will be late in the afternoon, as surface
heating drives some meager amounts of CAPE around 500 J/kg. Given
the weak flow aloft, buoyancy-driven precip threat, will taper PoPs
downward after sunset as the PBL cools and instability is lost. Will
not remove PoPs entirely, however, as some hi-res members show
lingering showers into the night.
Saturday and Sunday
Any lingering showers from the cut-off low should be ending by
Saturday morning. Most the day thereafter should be dry, as weak
subsidence between the trough and low acts to inhibit shower
activity. Things change as the western trough makes its approach,
however. The nose of potent jet at the base of the trough begins to
edge into Illinois and Indiana by 00z. Diffluence aloft and PVA will
lead to some increased environmental lift, which may promote a few
isolated showers and thunderstorms late in the day.
The greatest threat for rain and storms looks to be overnight
Saturday and into Sunday, as the highly-amplified trough tilts into
the negative and swings into Indiana. Strong diffluent flow aloft,
strong PVA, and increasing low-level moisture all point towards
increasing precip potential after sunset as a potent cold front
makes its way eastward. Given the impressive dynamics aloft and
continued moisture advection, the nocturnal timing of the event
should not inhibit convective development.
In terms of severe potential, a few things stand out that point
towards a lower threat. First, the trough itself becomes highly
amplified, leading to generally southerly flow at all altitudes.
While speed shear is high, roughly over 50 kts, directional shear is
quite low. Boundary-parallel flow favors a linear storm mode.
Second, the nocturnal / early timing of the event. As mentioned
before, given the strong environmental forcing above and along the
front, the timing may not be enough to inhibit convective
development...it is enough to inhibit CAPE. Smaller CAPE and lapse
rates will lead to weaker thunderstorms less capable of strong
updrafts and downdrafts. Furthermore, BUFKIT soundings show a
shallow but potent surface inversion developing overnight. These two
factors work against a tornado threat. Thirdly, a rather weak LLJ
will limit downward momentum transfer in any storm that fires up, as
there will be rather weak flow to transfer downward. So while an
occasional wind gust is possible, mainly after the surface inversion
begins to weaken, the potential is not too impressive. To summarize,
while numerous showers and storms are likely, severe potential
appears low due to poor lapse rates, limited instability, and a weak
LLJ. Will need to monitor model trends, however, in case the arrival
of the trough / front is slower which would place the convective
activity more into Sunday afternoon. Recent model trends have slowed
down a bit with latest runs.
Once the showers and storms end Sunday morning, a strong cold front
will sweep through bringing an unfortunate end to our above-average
warmth. Temperatures will follow a non-diurnal curve, reaching their
max early before dropping into the low 50s during the afternoon.
Winds could be on the gusty side as well, as a surface low deepens
to our north. Guidance suggests gusts ranging from 25 to 30 kts at
times.
Monday
On Monday we will find ourselves in the broad cyclonic northwesterly
flow on the backside of the departing trough and surface low. BUFKIT
soundings show an optimal sounding for widespread stratocumulus with
possible showers and flurries. Therefore, expect a cold dreary day
on Monday compared to what we have seen recently. Model blends may
be a bit warm, given the robust CAA and signal for persistent
stratocu. Residual breeziness should contribute to the overall
unpleasantness of the colder air.
Tuesday through Thursday
Ensemble guidance shows the big cold upper-level trough departing
completely by Tuesday. Strong surface high pressure, passing to our
south, will provide large scale subsidence allowing for clearing
skies. While the day may begin with some lingering stratocu, it
should end mainly clear. Some high clouds may become apparent by
sunset in part from ridge-building out west.
Surface low pressure in the northern plains should work in tandem
with the high to our south to tighten the MSLP gradient, driving a
potent 850mb LLJ which will accelerate WAA. By Wednesday, as ridging
builds eastward, high temps look to return back into the 60s.
Further WAA may allow temperatures to jump into the 70s again by
Thursday.
&&
.Aviation...(06Z TAF Issuance)
Issued at 1156 PM EDT Thu Apr 13 2023
Impacts:
- VFR flying conditions with good confidence through the TAF period
Discussion:
Upper low will move across the Tennessee Valley today and
Appalachians tonight. This will bring some mid and high clouds to
the terminals. A brief very light shower or two are possible at
KBMG, but chances are too low to mention. Otherwise, high confidence
in VFR flying conditions.
Winds will be SE and then S less than 10 knots.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...50
Short Term...CM
Long Term...Eckhoff
Aviation...MK