Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/27/24
Area Forecast Discussion
National Weather Service La Crosse WI
645 PM CDT Thu Sep 26 2024
.KEY MESSAGES...
- Quiet weather continues through the short term. Favorable
conditions for valley fog late tonight into Friday morning.
- Forecast remains dry (90-100%) through the weekend. Trends
continue to indicate the mid-level low and remnants of
Hurricane Helene remain southeast of the area with mid-level
ridging influencing the Upper Mississippi River Valley.
- More seasonable temperatures expected next week.
&&
.DISCUSSION...
Issued at 138 PM CDT Thu Sep 26 2024
Quiet weather continues through the short term. Favorable
conditions for valley fog late tonight into Friday morning.
High pressure and mid-level ridging located over much of the
central United States will continue to influence the Upper
Mississippi River Valley this afternoon and overnight. Clear
skies and calm to light winds are expected through Friday as a
result of these features leading to another valley fog scenario
late tonight into Friday morning. Will need to continue to
monitor the trends for the potential for valley fog Friday
night into Saturday morning, as there will be a decreased depth
of the light wind layer as seen in RAP soundings. Overall, a
persistence forecast is the expectation in the short term.
Forecast remains dry (90-100%) through the weekend. Trends
continue to indicate the mid-level low and remnants of Hurricane
Helene remain southeast of the area with mid-level ridging
influencing the Upper Mississippi River Valley.
The aforementioned high pressure and mid-level ridging will
continue to influence the Upper Mississippi River Valley through
the weekend as a mid-level cutoff low centered over southern
Illinois slowly shifts eastward and merges with the remnants of
Hurricane Helene. The ECMWF Ens/GEFS/GEPS depict these features
remaining to the southeast of the region and continue to trend
towards a dry solution for the weekend with probabilities of
0-10%.
More seasonable temperatures expected next week.
Model guidance depicts a mid-level shortwave trough diving into
the region early next week. This trough is expected to drag a
cold front southeast through the area Monday night into Tuesday.
However, ample dry air in place over much of the region as well
as better dynamics across northern Minnesota and Wisconsin,
precipitation chances are only 0-15% during this timeframe with
Taylor County being the focus of the higher end chances. Cooler
air will succeed the front, allowing for more seasonable
temperatures into the middle of next week.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 645 PM CDT Thu Sep 26 2024
Valley fog for Friday morning continues to remain the primary
aviation concern throughout the forecast period with high pressure
in place allowing for relatively clear skies, light low-level winds,
and falling dewpoint depressions. Minimal adjustments have been made
to the KLSE TAF with forecast trends remaining on track for periods
of IFR/LIFR fog around and just before sunrise. The main question
over the next 6-12 hours remains how dewpoint depressions will trend
and if they will favor 1/4SM. Currently, the dewpoint depression at
KLSE is 22 degrees as of 25.23z, which is marginally favorable for
1/4SM per local research. If this trends similar to previous nights,
likely would favor a more intermittent 1/4SM as opposed to longer
duration dense fog. As a result, opted to hold off on any tempo for
1/4SM this forecast issuance but will likely need to introduce it
for the 26.06z issuance assuming dewpoint depressions behave
similarly to previous nights.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
DISCUSSION...Falkinham
AVIATION...Naylor
Area Forecast Discussion
National Weather Service Grand Rapids MI
922 PM EDT Thu Sep 26 2024
.KEY MESSAGES...
- Gusty winds Friday
- Rain chances Saturday through Tuesday
- Drier and cooler mid-week next week
&&
.UPDATE...
Issued at 922 PM EDT Thu Sep 26 2024
Cirrostratus covers much Lower Michigan east and south of
Ludington, a little farther northwest than the 12z HREF was
suggesting. Some models including the HRRR and ARW have been
trying to saturate the near-surface layer late tonight around
Lansing to Mount Pleasant, though this may be overdone as winds
just above the surface will increase to 15-20 knots which should
lessen the fog threat along with the high clouds. The only patchy
fog mention will be in northern Clare county (and to the north)
where winds are weaker and cirrus thinner.
&&
.DISCUSSION...
Issued at 228 PM EDT Thu Sep 26 2024
- Gusty winds Friday
The low level pressure gradient increases considerably tonight
and more so on Friday. Looking at Bufkit and mixing heights for
tomorrow, we may see gusts into the 35 to 40 mph range, especially
south of I-96. These values are supported by the latest ensemble
gusts from the various models. Such values commonly lead to
isolated power outages. No headlines at this time but we will
mention the stronger gusts in social media posts. It`s worth
noting that if we do mix slightly deeper than forecast, gusts
could start to reach into the advisory level, which will need to
be monitored with future forecasts.
- Rain chances Saturday through Tuesday
Run to run consistency remains high with regards to the main players
in the weather. The main players are the upper low centered
currently near the Bootheel of Missouri, and what is left of
Hurricane Helene as it gets absorbed by the upper low.
The majority of the weather with the upper low and remnants of
Helene is expected to remain south of Michigan as the upper low
wraps Helene to the WNW, and the upper high tries to hold on over
the area. The systems will be close enough that Southern Lower will
see occasional rain shower chances Saturday through Monday with
additional moisture moving overhead, and impulses on the northern
periphery of the low rotating from east to west across Lower
Michigan. Can not rule out some thunder late Saturday. The better
chance of some thunder will be Sunday and Monday afternoons during
peak heating.
The upper low will get a kick then by late Monday by another
stronger upper jet and upper trough digging into the middle portion
of the country. This trough will bring a fairly decent fall cold
front through Monday night/Tuesday. A few showers/storms will be
possible along the front, but there will not be good moisture to
interact with it, as it will be swept out with the weekend low.
- Drier and cooler mid-week next week
Once the front moves through earlier on Tuesday, a decent amount of
cool fall air will surge in from the NW. Max temperatures can be
expected to be 10 degrees cooler or so for Wednesday into Thursday.
Strong subsidence building in over the area will assure dry weather
for Wednesday and Thursday.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 755 PM EDT Thu Sep 26 2024
VFR conditions will prevail through the TAF period, with only
high level cloudiness expected. As hurricane (or remnants of)
Helene move into the Ohio Valley by late Friday, ENE winds will
increase across southern Lower MI between the approaching tropical
system and surface high pressure to the north. Wind gusts in
excess of 25 kts are likely by midday, particularly along the
I-94 corridor (AZO/BTL/JXN).
&&
.MARINE...
Issued at 228 PM EDT Thu Sep 26 2024
The pressure gradient will be on the increase tonight and more so
on Friday. The winds up around 925 mb are shown to increase to 40
knots or higher over the southern parts of the nearshore area
Friday morning. While we are not forecast to mix to that level
over the water, the winds will increase considerably. At this
time, most of the guidance supports gusts to 30 knots for the
southern half of the marine area, where we will issue a small
craft advisory. The main period for higher wind speeds is from 12z
Fri to 12z Sat. For the north half, it`s not until Fri evening
that the winds may reach into hazardous levels, so we will hold
off on any headlines there. With an offshore component to the
wind, the waves will be limited in height until closer the the 5
nm mark.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 8 AM Friday to 8 AM EDT Saturday for
LMZ844>846.
&&
$$
UPDATE...CAS
DISCUSSION...MJS/NJJ
AVIATION...Smith
MARINE...MJS/Thielke
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1115 PM EDT Thu Sep 26 2024
.SYNOPSIS...
Tropical Cyclone Helene will move quickly north through Georgia
through the overnight hours, bringing continued heavy rainfall,
significant flooding and strong winds through Friday morning. After
the storm departs Friday afternoon, expect a calmer weekend with
temperatures near seasonal normals.
&&
.NEAR TERM /THROUGH FRIDAY/...
***A MAJOR RAINFALL EVENT FOR THE SOUTHERN APPALACHIANS AND VICINITY
IS OCCURRING WITH THE POTENTIAL FOR WIDESPREAD AND CATASTROPHIC
FLASH FLOODING***
As of 1111 pm...No significant changes to the array of Watches,
Warnings and Advisories in effect.
A Tornado Watch has been issued for the area from Greenwood
to Union SC to the Charlotte Metro area through 12Z Friday,
in anticipation of improving tornado potential in the overnight
hours. In these situations, it`s best to get the Watch out before it
gets too late in the evening. While the thermodynamic environment
is not particularly conducive at this time...the sfc-based and
most-unstable CAPE was generally 100 J/kg or less southeast of
I-85... the latest HRRR suggest that 300-500 J/kg or so may work
in from the southeast, particularly into the southern portions
of metro CLT after 05Z or 06Z. Needless to say, the low level and
deep layer shear will remain more than adequate as Helene makes its
approach from the south through the overnight hours. The tornado
threat may continue through late Friday morning if the RAP and HRRR
are correct, as they bring a plume of 500 J/kg CAPE into the area
along/E of I-77 as the main circulation of Helene lifts northward
in the morning.
Meanwhile...the rain rain rain came down down down...across the
entire forecast area for the better part of the day. The radar loop
shows a brief lull moving up from the south, so we should get a
break for an hour or two. Even so, the increasing moist upslope
flow will likely force more light to moderate rain as the lull
moves in, so the rain won`t really taper off, or not long enough
to matter. More showers and a few storms were already filling in
over the Coastal Plain. Needless to say, a 100pct will suffice
for the precip prob overnight.
As to the wind...no change to earlier thinking. The leading edge
of the significant wind gust potential will lift north across the
region from roughly 08Z to 11Z, maximizing from 10Z to 14Z south to
north. Indications of strong tropical storm force gusts continue in
the most recent guidance. Outside the mtns, there is some concern
that a very shallow stable boundary layer will keep the strongest
gusts from reaching the surface, but there will still be frequent
50kt gusts in many locations. Officially, the gust forecast will
not change until after the 11 pm Advisory. The mountains will have
no such protection. It seems likely that peaks and ridgetops will
get frequent gusts to hurricane force. These winds will combine
with saturated soils and down widespread swaths of trees, producing
structural damage and knocking out power for many communities.
Otherwise...confidence is high that rainfall intensity will pick
back up after 06Z as the bands set up perpendicular to the NC
mtns. This will likely add an additional 8- 10 inches of rain across
the Blue Ridge and should high-end flooding, which may eventually
require flood warnings with the EMERGENCY designation. All the
ingredients are in place for numerous landslides and several
damaging debris flows over the mountains as the final bursts of
very high rainfall rates move across the region. Reservoirs along
the Catawba River chain are also running high and there could be
breaching problems as enuf water may not be able to be released
beforehand. Please remain vigilant to any warnings issued this
evening and overnight as conditions can worsen rather quickly.
The system will continue to advance north of the forecast area late
Friday morning thru the afternoon. Improving weather conditions are
in store Friday afternoon as the column dries quickly from above,
however, the impacts and effects of this system will last thru
the weekend.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 200 PM Thu: By Friday evening, Helene`s center will be
northwest of the Appalachians and interacting with the lower OH
Valley upper low. The CWA should be pretty much entirely in the dry
slot of the transitioning system, but the low will be positioned to
allow vort lobes to swing across the mountains, and we accordingly
keep a small PoP generally west of I-26 and northwest of I-85. 850mb
flow will continue to be southerly/upslope, and although the dry
slot will bear PWATs well under an inch initially, those values
may rebound toward daybreak Saturday. That said, the moisture
Fri night will be beneath a deep subsidence inversion and rainfall
rates/amounts are expected to pale in comparison to those earlier in
the day, so it is unlikely there will be any new flood or landslide
impacts, except perhaps on slopes made unstable by the earlier
rainfall. Gusty winds will continue particularly in higher terrain
overnight, where frequent gusts of 25-30 mph will remain possible
into Saturday morning; shallow instability may still tap into 20+
kt winds in some lower elevations over the western half of the area.
By Saturday morning, the sfc/upper low will be stacked, and
Helene should be no longer distinguishable from a regular inland
closed low. Heights will continue to rise early Saturday but then
fall a bit from the west as another vort lobe rotates over the
CWA. Convective layer deepens and appears a little more viable
in our west, so PoPs expand across the mountains again. PWATs may
rebound over 1.5 inches but CAPE does look to remain no more than
a couple hundred joules. Effective shear looks unlikely to support
a severe threat; locally heavy rain could redevelop as well as a
localized flood risk. WPC maintains Marginal Risk excessive rain
outlook for the mountains on Saturday, which seems reasonable in
light of antecedent conditions. All of the above factors will be
in play again Sunday, just shifted slightly further north/east,
so PoPs end up similar but expanded slightly in those directions.
Temps will be mild, slightly above normal for the Piedmont each
afternoon, and slightly below over the cloudier mountains.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 230 PM Thu: Sunday night the upper low looks to begin to
rejoin the westerlies, at least partially, although the process is
slow and somewhat unsettled weather will continue through Monday
if not Tuesday. Some guidance depicts pattern almost getting to
a Rex block, with the remnant upper low beneath the eastern CONUS
ridge, but it looks somewhat transient. We retain small PoPs over
the northwest half of the CWA both days due to the upper low, but
with less potential enhancement from vort lobes. Rainfall rates are
likely to be light and currently appear unlikely to hinder recovery
efforts. Temperatures trend slightly warmer through Wednesday,
but remain within a couple degrees of normal in all locations.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Widespread IFR/LIFR cig/vis will continue
across the western Carolinas this evening, with occasional MVFR
holes, under an expansive rain shield still well ahead of the
circulation around fast-moving and powerful Helene. Will continue
with the strategy of moving a four-hour TEMPO group ahead with
semi-regular amendments to handle the changes. A developing radar
trend looks like a bit of a lull moving up from the south over
the next 2-4 hours, but the strength of the upslope flow and very
high moisture content will probably keep the light precip and at
least MVFR/IFR restrictions in place. Finally, the rain shield with
Helene will arrive in the pre-dawn hours, with intense bursts of
rain that bring vis down to IFR/LIFR. As this happens, basically
after the end of whatever operations are conducted this evening,
the wind will increase dramatically, with the potential for frequent
gusts of 50kt or higher toward daybreak as the center of circulation
lifts quickly northward over GA. Winds aloft will be even stronger,
with intense LLWS possible. The center moves past and winds veer
around quickly between daybreak and mid-morning. Guidance suggests
a quick end to the precip restrictions after 14Z or so, with the
lowest ceiling restrictions scattering out around midday. Lots
more details were glossed over on the back end.
Outlook: The remnants of Helene will move north of the area Friday
evening. Isolated to sct mainly diurnal convection will be possible
thru the weekend.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Flood Watch through Friday afternoon for GAZ010-017-018-026-
028-029.
Tropical Storm Warning for GAZ010-017-018-026-028-029.
NC...Flood Watch through Friday afternoon for NCZ033-035>037-
048>053-056>059-062>065-068>072-082-501>510.
Tropical Storm Warning for NCZ033-048>053-056-058-059-062>065-
068>071-082-501>510.
Wind Advisory until 2 PM EDT Friday for NCZ035>037-057-072.
SC...Flood Watch through Friday afternoon for SCZ008>014-019-
101>109.
Tropical Storm Warning for SCZ008>014-019-101>109.
&&
$$
SYNOPSIS...PM
NEAR TERM...PM/SBK
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...PM
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1200 AM EDT Fri Sep 27 2024
.KEY MESSAGES...
- The remnants of tropical system Helene will bring a widespread,
soaking rain event into Friday.
- Flash flooding could result from the remnants of Helene, but the
overall potential may be limited by its quick movement.
- Wind gusts of generally 40 to 60 mph are expected at times from
late tonight into Fri as the remnants of Helene pass by.
&&
.UPDATE...
Issued at 1200 AM EDT THU SEP 26 2024
Showers continue across eastern Kentucky at midnight and are
still expected to increase in intensity from southeast to
northwest through 4 AM EDT. Forecast is on track.
UPDATE Issued at 847 PM EDT THU SEP 26 2024
Showers, mainly light, continue to stream northward across eastern
Kentucky this evening while Hurricane Helene, now a category 4
hurricane, churns toward the Florida Panhandle. Expect waves of
showers to continue drifting across eastern Kentucky. The overall
intensity of the rainfall should tick up gradually from the
southeast, especially after midnight, as Hurricane Helene lifts
across the Florida Panhandle and through Georgia. Overnight PoP/T
forecast has been refined with the latest hi-res model solutions.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 455 PM EDT THU SEP 26 2024
Late this afternoon, an upper level ridge was centered to the
west of Bermuda with another upper level ridge extending from the
Southern Rockies to the upper MS Valley. An upper level low was
centered near the confluence of the MS and OH Rivers while Major
Hurricane Helene continues to move north in the northeastern Gulf
of Mexico and headed toward northwest portions of FL. A nearly
stationary frontal zone remains from low pressure in Quebec to
the upper OH Valley to eastern KY to northwest FL to the
northwestern Gulf of Mexico. The upper level low continues to
interact with the boundary and moisture transported into the
region for a continued precursor rain event (PRE). Rain continues
to move from eastern TN north into much of eastern KY at this
time.
Tonight and Friday, the upper level low is expected to move south
to northeastern MS/northwest AL with this upper low and Hurricane
Helene more or less moving into Fujiwhara fashion with Helene
tracking quickly across northwest and FL and southern and central
GA. This will then move across the Southern Appalachian region
and then to the Cumberland Plateau through early to mid afternoon
on Friday, gradually weakening and becoming extratropical. Bands
of rain more closely associated with Helene are expected to cross
the region tonight through Friday morning as the pressure
gradient also increases between Helene and high pressure north of
the eastern Great Lakes vicinity. These winds will have a
downslope component a times, but PW will rise near or in excess of
2 inches tonight remain at those levels into the morning before
dry slotting works northwest on Friday afternoon. As Helene nears,
a general additional soaking rainfall should occur areawide. Some
locally more intense rain of 3 or more inches could occur in a
band somewhere across eastern KY per some CAM runs, though a
general 1 to 2.5 inches of rain expected through Friday evening.
Winds and wind gusts are also a concern and in addition to a flood
watch in effect generally south of the Mtn Pkwy. Areas generally
south of the Mtn Pkwy have either had more rain over the past 3
days and/or are expected to have the highest totals on average.
12Z HREF mean wind gusts increase to 40 mph or higher across the
highest terrain along the VA border toward midnight with the
stronger gusts progression to the north and northeast through the
remainder of the night. Some of this is not expected to be realized
in the deeper valleys before sunrise. However, 12Z HREF mean
brings wind gusts to near or in some instances than 60 mph
northwest across much of the area Friday morning to early Friday
afternoon, before gradually slackening. Momentum is likely to mix
down as a dry slot moves in behind a morning band of rainfall.
Higher elevation locations will experience a longer period where
stronger wind gusts are possible from late tonight into early
Friday afternoon. A High Wind Warning was issued for Bell, Harlan,
and Letcher County from 11 PM tonight to 8 PM on Friday with
another tier of High Wind Warnings to the north and west 2 AM on
Friday to 8 PM on Friday which generally has elevations of 1500
feet or higher or where soil moisture is highest/heavier rain has
fallen over the past 3 days or so. A Wind Advisory was issued for
areas further northwest, but gusts to around 60 mph area possible
especially in the eastern Bluegrass region and on ridges and
further adjustments to headlines may be needed. 12Z HREF
probabilties of 60 mph gusts or higher are significant over much
of the area at 50 to 100 percent. The 18Z HRRR wind gusts are in
general agreement with the HREF values. So in summary, tonight,
the strongest wind gusts of 40 mph or more are expected in the
High Wind Warning area later tonight, especially on ridges, with
wind gusts peaking across the region during Friday morning to mid
afternoon on Friday.
From late Friday into Friday night, the upper level low and Helene
will gradually merge with the combined low meandering over the
Lower OH Valley region. Following a relative lull in chances for
showers on Friday afternoon and evening with the dry slotting,
moisture is progged to increase from west to east late Friday
night with an associated increase in shower chances from west to
east.
.LONG TERM...(Saturday through Thursday)
Issued at 225 PM EDT THU SEP 26 2024
The forecast period begins with the area still largely under the
impacts of the remnants of Hurricane Helene. At upper-levels, the
remnants of Helene will begin to merge with a largely stationary cut-
off circulation that`s been situated over western Kentucky through
much of this week. As the two systems merge into one circulation,
shower and storm chances will persist through the day Saturday and
linger through the weekend. Models continue to remain in rather good
agreement going into next week with the circulation getting picked
up by the mean flow and ejecting out of the area by Monday morning
but lingering PoP chances will exist through the end of the period
as an upper-level trough, moving through southern Canada, drags a
cold front through the region Tuesday afternoon which will then
usher in cooler and drier weather for the middle of next week.
Overall, the forecast period will be highlighted by multiple rounds
showers and storms. Shower and thunderstorm chances drop a little
bit with the merging of the closed circulation and the remnants of
Helene but chances (40-70%) exist through the weekend. Temperatures
through the period will remain rather seasonal as highs are forecast
to in the upper-60s to upper-70s. Overnight lows, will be warmer
with the insulation of the system overhead but with the approach of
a cold front on Tuesday, cooler temperatures and fall-like weather
will be in place for the end of the period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 815 PM EDT THU SEP 26 2024
Variable aviation conditions were observed at TAF issuance time as
areas of low clouds and showers continued impact eastern
Kentucky. Conditions range generally between IFR and VFR on
average, but localized LIFR was present at a few terminals closer
to the Virginia border. A rumble of thunder is possible overnight,
but confidence in any affecting a particular TAF site remains too
low the mention. An uptick in the rainfall rates should occur in
bands ahead of Helene tonight as well as on Friday morning. Winds
will average from the east at 5 to 10 KT to begin the period and
then become east and northeast at 10 to 20 KT, with gusts up to
around 30KT by 12Z. Winds should increase from the northeast
between 12Z to 18Z to as high as 15 to 25KT and begin to trend to
the southeast for southern locations to end the with gusts up up
into the 35 to 50KT range through at least 19Z. LLWS will also be
a threat later tonight into Friday morning, as well, with winds
as high as 50 KT a thousand feet off the sfc generally blowing
from the east or northeast and then trending toward southeast
after 18Z.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 5 AM to 8 PM EDT Friday for KYZ044-050>052-
058>060-068-069-079-083-104-106>109-111-112-114-119.
Flood Watch through Friday evening for KYZ058-068-069-079-080-
083>088-107>120.
High Wind Warning until 8 PM EDT Friday for KYZ080-084>086-110-
113-115>117-120.
High Wind Warning until 8 PM EDT Friday for KYZ087-088-118.
&&
$$
UPDATE...GEERTSON
SHORT TERM...JP
LONG TERM...VORST
AVIATION...GEERTSON/JP