Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/27/21
Area Forecast Discussion
National Weather Service Binghamton NY
838 PM EDT Tue Oct 26 2021
.SYNOPSIS...
A strong low pressure system has brought periods of rain to our
area, which will end tonight. Flash flooding and river
flooding is ongoing. Dry and seasonably mild weather returns
Wednesday afternoon through Thursday.
&&
.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
820 PM Update...
Surface observations and RUC13 analysis show the surface low
over northern NJ has weakened into an open trough, which still
extends back to the northwest into the Finger Lakes region.
However, while low level convergence remains strong across this
boundary, upper level support is quickly diminishing as a
shortwave trough/vort max rotating around the parent upper low
over the Delmarva moves into south-central PA (clearly visible
on mesmerizing water vapor satellite imagery). One hour rainfall
rates have greatly diminished over the past hour as the precip
band has pivoted into western NY. Additional rainfall is working
in from the northeast, but gauge reports show 1 hour rainfall
amounts of just a few 0.01s of an inch. Further south, radar
mosaic from surrounding sites shows clear downsloping effect
over Delaware and Sullivan Counties, limiting precip amounts
west of the Catskills. Some moderate rainfall is working back
into Pike County at the head of the "firehose" stretching back
into the Atlantic, too far south to benefit from the Catskills`
shadowing. However, even here rainfall amounts are generally
around 0.10 to 0.15 inches an hour over nearby Ulster County and
NW New Jersey. More concerning rainfall rates can be found over
western Long Island, and are expected to stay out of our CWA.
Precip coverage may appear to increase in the next few hours as
the western part of this complex system weakens, allowing the
dryslot over the Southern Tier and NE PA to fill in. But
rainfall rates will be light, and coverage will become spottier
and more showery towards Midnight.
In terms of the flooding threat, additional rainfall is not
expected to be much of a contributing factor. It`s all just
runoff and possible reservoir releases going forward.
4 pm update...
Rain continues with many warnings out for flooding. A cut-off
low is centered over PA while a deepening surface low is off of
Cape Cod. Both are slowly moving east. An inverted trough
extends northwest into the area from the surface low. This is
providing convergence over the area. Deep warm moist air is
being funneled along the surface trough into our area. As the
upper low captures the coast low and both move east the moisture
stream and rain will end late evening. Rainfall slowly tapers
off from south to north. With the coastal low, the Poconos and
Catskills will have breezy winds of 10 to 20 mph with gusts to
30.
Clouds will still wrap around from the northeast on Wednesday
but we will be dry. High pressure builds in from Quebec as
upper level heights build late Wednesday into Wednesday night.
As the drier air comes in skies will clear Wednesday night.
Temperatures will only fall into the 40s tonight. Wednesday
warms into the mid and upper 50s and lower 60s with some late
day sun. With the drier air temperatures fall into the mid and
upper 30s and lower 40s Wednesday night.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
300 PM Update:
A trough digging into the central US will result in mid and upper
level ridging across NY and PA on Thursday. Dry air aloft will keep
the region partly cloudy with temperatures getting back to
seasonably warm. Increasing southerly flow Thursday night into
Friday increases the cloud cover along with precipitation moving
back in late Friday as a warm front lifts into the region. Most
models have the warm front progressive with a several hour period
with preliminary QPF of 0.5 to 1 inch. With recent rainfall
localized flash flooding is a concern once again Friday afternoon
into Friday night. As the trough moves into the northeast Friday
night, a surface low moves in keeping clouds and rain showers going
into Saturday morning.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
300 PM Update:
The upper level trough slowly propagates through the northeast
this weekend with unsettled and cooler weather. NW flow early
next week with cool 850 mb temps results in chances of lake
effect rain showers along and north of I 90 early next week.
Still little to no chance of any overnight freezes in the long
term.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Precip will continue to fill back in over much of the area over
the next few hours before diminishing in coverage, however
rainfall rates will be much lighter, allowing visibilities to
generally increase. Ceilings will be more problematic, with MVFR
to IFR expected most of the night, but with a lot of
variability, even brief VFR in some areas.
Ceilings will improve to VFR at SYR and RME before dawn, and
between 14Z and 19Z elsewhere.
Outlook...
Wednesday night through Thursday...Mainly VFR.
Friday through Sunday...Restrictions likely with rain returning.
&&
.BGM WATCHES/WARNINGS/ADVISORIES...
PA...Flash Flood Watch until midnight EDT tonight for PAZ038>040-
043-044-047-048-072.
NY...Flash Flood Watch until midnight EDT tonight for NYZ045-046-
055>057-062.
&&
$$
SYNOPSIS...MPH/TAC
NEAR TERM...MPH/TAC
SHORT TERM...AJG
LONG TERM...AJG
AVIATION...MPH/TAC
Area Forecast Discussion
National Weather Service Denver/Boulder CO
835 PM MDT Tue Oct 26 2021
.UPDATE...
Issued at 829 PM MDT Tue Oct 26 2021
A strong upper level trough was moving across this evening, with
the best precip coverage, over the plains and Palmer Divide.
Closer to the I-25 Corridor the winds had a more NNW component
which was causing downslope and far less coverage of precip. In
the mtns were still seeing areas of light snow. Overall, most
precip thru midnight will move eastward, with some lingering rain
over the far ern plains until 09z or so.
As far as winds, had some brief strong winds late in the aftn but
speeds have generally been under warning criteria early this
evening. Best subsidence doesn`t arrive until after midnight. Latest
HRRR still shows a few areas may see gusts to 60 mph. One area
would be mainly near the WY-NE border area thru midnight. Meanwhile
a 2nd area would be over Lincoln county. Thus have left High Wind
Warnings as is.
UPDATE Issued at 608 PM MDT Tue Oct 26 2021
The Red Flag Warning for fire weather zones 246, 247, and 249
was allowed to expire due to recovering humidity ranging from
70-80 above warning criteria. Gusty winds will continue through
Wednesday afternoon.
&&
.SHORT TERM...(This evening through Wednesday)
Issued at 232 PM MDT Tue Oct 26 2021
Satellite imagery showing the upper level trough axis tracking
east over Colorado at this time. Radar and web cameras indicate a
lull in snowfall over the central and north central Colorado
mountains. As the trough axis shifts over eastern Colorado, snow
will form over the mountains due to increasing northwest flow and
cold air advection leading to good orographic lift. New snowfall
for the mountains is expected to be 3-6 inches with up to 8 inches
around Rabbit Ears Pass. Current Winter Weather Advisory still
looks on track. As temperatures fall this afternoon and evening,
mountains roads will become slick, mainly after sunset.
Over the plains, a second front drops southward late this
afternoon and QG ascent moves overhead. This will bring rain
showers from late afternoon through the evening. Downslope flow
will limit the rain west of I-25. For the Palmer Divide area,
temperatures should get cold enough for snow later this evening.
Can`t rule out some slushy roads over higher parts of I-25. Main
impact this evening will be strong winds behind the second cold
front. Models showing winds just off the surface reaching 40-60
knots. Strong cold air advection leading to steep low level lapse
rates should help these stronger winds mix to the surface. The
High Wind Warning begins at 6pm, may need to move it up an hour or
two over far northern Colorado since the front will arrive a
little earlier than expected.
By Wednesday morning, the trough and precipitation associated
with it will be east of Colorado. Strong northwest flow aloft will
be over the state. Expect windy conditions to prevail over the
mountains and eastern plains with gusts to 45 mph. Looks to be
enough moisture embedded in the northwest flow aloft for light
snow over the north central mountains. Additional snowfall over
the mountains should be less than 3 inches. The warmest
temperatures Wednesday will be found from Fort Collins to Fort
Morgan due to downslope flow off the Cheyenne Ridge where highs
will be around 60 degrees. Elsewhere across northeast Colorado,
highs should be in the mid 50s.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 232 PM MDT Tue Oct 26 2021
Colorado will be under a moderate northwest flow pattern Wednesday
night and Thursday. There will still be enough upstream mountain
level moisture to generate continued chance of snow showers for
the mountains along with continued gusty winds. Expect a warming
trend across the plains Thursday and Friday along with dry
conditions as high pressure ridge shifts across the state. For
Saturday, the flow shifts more westerly but still generally dry
conditions and seasonable temperatures.
Changes are still expected from late weekend through early next week
as next upper trof drops southward from the Northern Rockies.
Initial cold front looks to drop southward across the plains for
cooler temperatures on Sunday but still on the dry side. The GFS
is showing a slower trend in this development with the upper trof
with the main bulk of the precipitation not showing up until late
Monday and Tuesday time frame. Temperatures for this event look to
be turning to all snow, even across lower elevations as 700mb
temperatures drop to -11c Monday evening. The new 12 European run
also is showing similar timing now with the GFS also targeting
Monday night and Tuesday morning for snowfall. Both GFS/European
showing some snow accumulation over all of Northern Colorado for
the first snow of the season for the majority of the plains. Still
6-7 days out, so won`t get too excited yet but certainly the potential
is there. For now will carry slightly higher snow chances, into the
chance category. Will also drop high temperatures on Friday into
the lower to mid 40s, but may end up being even colder.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 829 PM MDT Tue Oct 26 2021
Clearing of rain showers and lower cloud decks will begin by
Wednesday morning. The upper level low will push into Nebraska
keeping all terminals gusty until 00Z Wednesday evening. Winds
will continue north to northwesterly flow. The strongest wind
gusts will occur 18Z-00Z Wednesday up to 28kts. By Wednesday
evening, wind will shift west to northwest with SCT to FEW cloud
decks at 10k ft.
&&
.FIRE WEATHER...
Issued at 232 PM MDT Tue Oct 26 2021
A cold front will bring a wind shift to the west mid afternoon and
falling temperatures. This will lead to higher relative humidities
as well. A second cold front will bring northerly winds and rain
showers for this evening. The Red Flag Warning may be canceled
sooner than 6pm due to higher humidities behind the cold fronts.
Gusty north winds will prevail Wednesday, but humidities are
expected to be higher than today and above red flag warning
criteria.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until midnight MDT tonight for COZ042-044-
048>051.
Winter Weather Advisory until midnight MDT tonight for COZ031.
High Wind Warning until 3 AM MDT Wednesday for COZ046-047.
&&
$$
UPDATE...RPK
SHORT TERM...Meier
LONG TERM...Entrekin
AVIATION...AD
FIRE WEATHER...Meier
Area Forecast Discussion
National Weather Service Dodge City KS
1021 PM CDT Tue Oct 26 2021
...Updated Synopsis...
.SYNOPSIS...
Issued at 1019 PM CDT Tue Oct 26 2021
The upper level trough located in eastern Colorado will continue
to move east through the night and bring the leading edge of a
cold front through western Kansas. Winds behind the front are
already gusting over 30 mph and we should expect stronger winds as
we go into the day on Wednesday. Elsewhere the line of storms is
located from Hays to Medicine Lodge and will continue to move
eastward into central Kansas over the next hour.
&&
.SHORT TERM...(This evening through Wednesday)
Issued at 314 PM CDT Tue Oct 26 2021
Active weather situation across the central High Plains tonight into
Wednesday, and a lot of uncertainty to the forecast as well. A strong
upper level shortwave trough was moving over the Four Corners region
at midday. Ahead of this system, surface low pressure was deepening
over northeast Colorado. A warm front extended southeast from the
low through far southwest Kansas into southwest Oklahoma. A dry
line extended south from the warm front across the Texas Panhandle.
Strong southerly flow is advecting higher dewpoints into the central
Plains with increasing SBCape nosing up into south central and
portions of southwest Kansas. Latest short term models continue to
show the warm front/dryline sharpening up just west of Dodge City
late this afternoon and early evening. CAMs are showing thunderstorm
initiation along this line by around 7-8 pm with storms moving and
developing rapidly northeast through the mid to late evening.
While we may see a narrow window of opportunity for supercell
thunderstorms, some parameters like deep layer shear nearly
parallel to the boundary and some backing to the winds with height
through the mid levels would suggest that storms should evolve
into a line fairly quickly this evening. Initial threats of large
hail up to golf ball size and damaging wind gusts would switch
more to a damaging wind threat as the evening progresses. A few
QLCS tornadoes are still possible this evening as the 0-3km bulk
shear is a little more orthogonal to the boundary and expected
convective line. The severe threat should be moving out of the
Dodge City forecast area by 11pm to midnight.
As the upper system continues east tonight, a strong cold front
will push through southwest and central Kansas through the late
evening and overnight hours. Am concerned that there will be a
period of high winds for a few hours behind the front as low
level cold air advection develops. RAP and NAM model output shows
a strong isallobaric gradient behind the front which could result
in some post frontal wind gusts around 60 mph for areas over far
southwest Kansas along the Colorado border. Winds should die down
somewhat as the gradient relaxes later tonight. Model soundings
show mixing up through 700 mb during the day on Wednesday with
45-50 knot winds in the upper levels of the mixed layer. Some of
the MOS guidance is also suggesting sustained 40 mph winds by
midday Wednesday. With this in mind, have issued a High Wind
Warning from late this evening through mid afternoon Wednesday for
southwestern sections of the area.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 314 PM CDT Tue Oct 26 2021
The upper wave continues to deepen into an upper low as it moves
into the mid Mississippi Valley on Thursday. On the backside of
the low, there will be a fairly deep layer of unidirectional flow
over the central High Plains which will lead to another day of
strong north winds across the forecast area. At this time, it
appears winds should stay below high wind criteria but this will
have to be watched.
Friday and Saturday will see upper level ridging over the central
Plains with quiet weather and near seasonal temperatures in the
60s. By Saturday, an upper level ridge builds over western Canada
while to the east, an upper level trough moving east along the
US/Canadian border. This will push a cold front south into the
central Plains as early as Saturday afternoon or evening. An even
stronger trough will dig south out of Canada into the northern
Plains by Sunday night and Monday which will push even colder
temperatures into the central Plains. Highs in Monday may only be
in the 30s and 40s and we could be getting our first taste of
winter weather by Monday night and Tuesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 645 PM CDT Tue Oct 26 2021
Thunderstorms beginning to develop over southwest Kansas will
continue to become more numerous and strengthen as they move
northeast through the early evening. Thunderstorms would impact
the Dodge City and Hays terminals between 01z-04z with large hail
damaging wind and possible tornadoes. Garden City and Liberal
should remain west of any thunderstorms. A strong cold front will
move through southwest Kansas around and after midnight. Strong
northerly winds will develop behind the front and continue into
Wednesday. Some blowing dust could develop especially at Garden
City and Liberal during the day.
&&
.FIRE WEATHER...
Issued at 314 PM CDT Tue Oct 26 2021
Critical fire weather conditions have developed over far southwest
Kansas this afternoon as humidity levels have dropped into the
10-15 percent range and winds gust to around 35-40 mph as far east
as Ulysses and Hugoton. Will keep the Red Flag Warning in place
until expiration time. Near critical fire weather conditions are
expected to redevelop on Wednesday as strong northerly winds develop
and humidity levels fall to around 20 percent or so.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 44 62 42 61 / 60 10 10 0
GCK 43 62 39 60 / 30 10 0 0
EHA 42 63 39 62 / 20 10 0 0
LBL 44 64 41 62 / 20 10 0 0
HYS 45 59 42 59 / 60 20 10 0
P28 51 61 46 63 / 50 20 10 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 5 PM CDT /4 PM MDT/ Wednesday for KSZ061-
074>076-084>086.
&&
$$
SYNOPSIS...Tatro
SHORT TERM...Gerard
LONG TERM...Gerard
AVIATION...Gerard
FIRE WEATHER...Gerard
Area Forecast Discussion
National Weather Service North Platte NE
651 PM CDT Tue Oct 26 2021
.SHORT TERM...(This evening through Wednesday night)
Issued at 320 PM CDT Tue Oct 26 2021
Short term forecast concerns are high winds and thunderstorms.
Currently, a sfc low pressure system is centered over the Rockies,
with a warm front out ahead of it extending from far NE colorado
southeastward to TX, and a cold front just behind extending from
central CO into the Pacific. This enter system has broadly moved SE.
At upper levels, there is a sharp trough over the Rockies moving
east.
As of 18Z, sfc flow is from the southeast. This flow has advected in
Gulf moisture, allowing dwpts to reach into the upper 50s, and even
60s in some spots. This moisture will be beneficial to thunderstorm
potential this evening. Also as of 18Z, a frontal boundary sat over
the WY/NE border, with fairly moderate 850 FGEN that has kicked up
some drizzle over the CO/WY border. This 850 mb lee cyclogenesis is
expected to continue to strengthen over the next few hours. It will
move through with the system, and provide lift to initiate storms.
ATTM, initiation looks in earnest around 00Z, though some showers
could kick up in the panhandle prior.
As for svr potential tonight, CAMs advertised a decent amount of
instability this morning, however there is a decent cap that will
need to be broken first. Likewise, clouds lingered around longer
today than previously thought. This is why SPC trimmed back their
previous outlook, leaving potions of the WFO only in slight risk.
Nevertheless, ~1000J/kg of MUCAPE was advertised in central Neb by
both RAP and HRRR models, as well as about 50 kts of shear. As such,
expecting an isolated severe storm (or a couple), but likely not a
widespread event. The biggest hazard will be damaging winds, with
the lesser chance of large hail. Precip looks to leave tomorrow
morning/ by the noon hour. Storm total precip of .25-.75" is
possible, with localized spots of lesser amounts (SW Neb) and higher
amounts (N central Neb).
Besides this storm, the UL trough strengthened since the last
forecast. As it continues to move east, it increase wind speeds for
the CWA as it tightens pressure gradients. Sustained winds up to 35
mph are expected for SW Neb and portions of the Panhandle. This,
along with the potential for gusts up to 60 mph, has prompted a High
Wind Warning for this evening, from 6 PM- 12 AM MDT. In the hours
just before and just after, winds will still be gusty and erratic.
Additionally, gusty and erratic winds are likely across the entire
CWA.
Behind the system, winds will shift to northwesterly, and skies will
clear by Wednesday afternoon. The NW winds bring in some cooler air,
and highs will only be able to reach into the 50s across the area.
This will persist into the overnight hours, with lows near freezing.
Similarly, behind the system much drier air will work its way across
Western Nebraska, with dwpts slated to be in the 20s/30s.
.LONG TERM...(Thursday through Tuesday)
Issued at 320 PM CDT Tue Oct 26 2021
The strong winds look to persist through Thursday.
Yet, high pressure and subsequent height rises will work their way
across the Plains behind the current troughing features, bringing
for quiet weather until the weekend.
That said, on Saturday a sharp sfc trough will come through the
Plains, bringing much cooler air in for next week. This means below
normal highs are expected for Halloween. The troughing seems to
linger for a few days. As the system moves through, it brings the
potential for precipitation Sunday/Monday, mainly in the Panhandle.
The WSUP viewer displayed just under a 60% chance for this
precipitation to be snow in the Panhandle. However, it may end up
being a mix. The ptype will need to be monitored to see if October
ends up snow-free or not.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 649 PM CDT Tue Oct 26 2021
A powerful cold front is moving across western and north central
Nebraska this evening, leading to periods of MVFR to IFR
conditions through the night. Rain showers with rumbles of
thunder are currently developing in southwest Nebraska and the
Panhandle. Rain showers and isolated thunderstorms will continue
to develop into the evening. For KVTN and KLBF, the greatest
possibility for precipitation appears to be until midnight.
Ceilings should begin to improve tomorrow morning around sunrise.
Strong winds out of the north to northwest can be expected tonight
through the day tomorrow.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 1 AM CDT /midnight MDT/ Wednesday for
NEZ022-056>058-069-070.
&&
$$
SHORT TERM...Sinclair
LONG TERM...Sinclair
AVIATION...Meltzer
Area Forecast Discussion
National Weather Service New Orleans LA
635 PM CDT Tue Oct 26 2021
.AVIATION (00Z Taf Cycle)...
Conditions will start off mostly VFR tomorrow but will begin to
fall apart as strong to possibly severe storms sweep through the
area. The timing of these storms remains early afternoon through
late evening hours tomorrow. Where strong storms set up,
terminals can expect to see gusty winds and low ceilings/visibility.
Once storms have dissipated ceilings will creep back up to
VFR/MVFR conditions in the early morning hours on Thursday. /TDB/
&&
.PREV DISCUSSION... /issued 451 PM CDT Tue Oct 26 2021/
SHORT TERM (This evening through Thursday Night)...
Quite the nice day across the area thanks to a recent weak
frontal passage which has introduced drier air and mostly sunny
skies. As mentioned in the morning update, what is left of
Tropical Storm Rick in the EPAC - now just a weak shortwave in the
mid to upper-levels - continues to spread cirrus in from the
west. We will see clouds continue to increase overnight, becoming
partly to mostly cloudy by daybreak with better cloud coverage
across the Atchafalaya Basin west of I-55. Didn`t venture too far
away from deterministic NBM MinT`s for Wednesday morning, but
there could be a small window with clear (enough) skies and nearly
calm winds for radiative cooling to bring low temperatures a bit
below deterministic NBM, primarily along the northshore/coastal MS
drainage basins. Notched temps down to follow this potential, but
overall no hazardous weather concerns in the next 12 hours.
The major focus for this discussion will be the potential for
severe weather Wednesday and Wednesday night, so let`s dive right
into it. Analyzing the H5 pattern shows a sharp, high amplitude
trough pushing east from the Rockies into the central US.
Downstream of this trough, the remnant energy associated with Rick
has spread out to the north underneath a sharp ridge axis draped
generally meridional along the MS river valley. The evolution of
this trough transitions from neutral to eventual negative tilt,
and closes off over Oklahoma to upper Texas, maximizing downstream
divergence and attendant height falls over our CWA. Meanwhile at
the surface, rapid cyclogenesis will be ongoing over the central
US, reaching sub-1000mb and dives southeast. What is left of the
cold front that pushed through yesterday steadily returns back
northeast as a warm front daybreak Wednesday, and sets the stage
for a complicated forecast. First, analyzing HREF members all day
today portrays several different scenarios that could alter or
change the extent/magnitude of severe weather potential. As
mentioned for the previous few days now, there has been the idea
of coastal convection igniting in the northwestern Gulf in
associated with supportive low-level frontegentics/convergence
with the warm front aided by environmental dynamic ascent. Without
explaining each member, this overall seems meteorologically
reasonable. However, other individual members of the HREF
(omitting the HRW FV3 due to overdone convective feedback) have
started to trend slightly back from the idea of convective
initiation ahead of the line. Taking a closer look at the
reasoning behind this (picking the NAM3KM) does not necessarily
illustrate much in the way of any reason to suppress convection,
as there is much more dynamic forcing mechanisms available to
support cells developing along the front, similar to the way the
HRRR portrays. As mentioned earlier, surface pressure/height falls
and localized convergence nearby the surface warm front should be
enough to ignite this convection, coupled with intensifying
downstream divergence and the eastward evolution of a 40-50kt LLJ
which all appears to be enough to spark cells early, the only
caveat is lingering dry air in the surface to H6 layer with this
dry airmass currently in place, but moistens quickly even north
of the boundary throughout the morning. 12-15Z Wednesday, we
should start to see some isolated cells developing offshore south-
central coastal Louisiana, with a strong to potentially severe
QLCS racing east into eastern Texas. Weak cells will steadily
increase in coverage mid to late-AM in response to increasing
dynamic ascent, with greater confidence going into early
afternoon. Also mentioned in the discussion yesterday was doubt in
how far north the warm front could climb, dragging a warm sector
characterized by upper 60 to lower 70 Td`s north into the area.
This boundary may be slow to drift northeast initially early
Wednesday, but should accelerate given aforementioned increasing
dynamic ascent /low- level flow, meaning the likelihood of any
stratiform precip shield as depicted in the NAM yesterday appears
relatively unlikely. Given how recent trends in the HRRR appear
most meteorologically reasonable, local sounding analysis across
the area illustrates several shear and instability parameters
honing in on the likelihood of severe thunderstorms. Breaking it
down by threat:
Damaging winds: As mentioned earlier, a QLCS or squall line will
be racing quickly east, even accelerating in forward speed into
southwestern LA late AM/early PM. Eventually entering our NW CWA
between ~1-3PM. A strengthening 40-50kt LLJ will accompany this
line of storms, with downward flux transport likely to aid in
damaging wind potential to the surface. For now, a squall line (or
QLCS with several line segments) will race east across the CWA
from 1-3PM through 8-10PM. Keep in mind, timing could be on the
earlier side due to model`s typical poor handling of cold-pool
propagated convective systems such as this, meaning if timing is
to shift or change any, it could be slightly earlier. But overall,
damaging wind gusts >60mph will be possible at any portion of the
line. Depending on how far north the warm front travels will
determine the northward extent of severe wind potential, but
typically, strong forcing can overcome lack in instability,
leading to enough downward potential to produce damaging winds
even as far north as southwestern Mississippi, but will be moreso
unlikely anywhere north of the warm front boundary as the frontal
inversion "cuts off" surface downward transport. Where this sets
up will be monitored.
Tornadoes: Low-level shear focused within the warm sector will be
maximized to around 0-1km SRH of 150-220m2/s2 with 0-3km SRH in
the 350-450m2/s2 range which will support organized, rotating
updrafts in any cells out in the warm sector. If cells develop and
interact with the warm front drifting northeast Wednesday
morning/afternoon, boundary interactions including localized
enhanced low-level shear may produce a heightened risk of a
tornado. The question remains just how much overall coverage of
cells/supercells will be possible. Overall, expect a messy multi-
storm mode event, with cell/line interactions. One thing to note,
alternative parameters including the SCP/STP are not entirely
extreme, which should limit any significant tornado risk but will
be closely watched.
Localized Flooding: Not to overshadow this risk, but given multi-
storm mode potential, some areas may pick up 1-2 inches of total
rainfall, likely locally higher in isolated locations.
Fortunately, antecedent soil conditions are overall dry, so the
risk for widespread flash flooding issues will be minimal, but
non-zero.
The line of strong to severe storms will quickly race out of our
area Wednesday evening/night, likely exiting our far eastern CWA
around 8 to 10PM. Ofcourse, timing will be watched especially
since this line will likely continue to accelerate east. The
actual cold front will be lagging this convection, about a few
hours behind but could develop a thin line of showers, just
depends on any lingering moisture. One thing to also watch
following the severe weather risk will be if gusty winds develop
on the back side of the stratiform precip shield out ahead of the
eastward racing front. There are some indications of a low-level
inversion on the backside, and the placement of the LLJ maximum
right on the backside of the precip shield, this could be enough
to support wake-low development and maintenance leading to gusty
winds Wednesday evening/night.
Next forecast challenge will be cloud cover on Thursday. Blends
for now are keeping only patchy Cu wrapping around the backside of
the low, possibly reaching down to the I-10/12 corridor. For now,
coverage amount remains the main question but should sky cover be
thicker than currently anticipated, this could lead to cooler
MaxT`s. Otherwise, will adjust if model trends catch on any more
confident trend. KLG
LONG TERM (Friday through Monday)
Over all the long term pattern looks good for Halloween weekend.
After the low pressure system pushes to the east, cold air advection
causes temps to decrease. A tight pressure gradient does remain in
the lower levels causing the gusty winds to continue through
Saturday. In addition to this the upper level winds switch to the
north on Sat, helping to bring in dry air and decreasing PoPs. -KO
AVIATION... (18Z TAF Discussion)
Conditions begin at VFR and remain that way for the bulk of the
forecast. As the front approaches Wednesday afternoon cloud cover
increases and cloud heights decrease. -KO
MARINE...
Weak to occasionally breezy easterly flow will persist tonight,
eventually transitioning more from the southeast and increasing
through early Wednesday. Surface winds reach Small Craft Advisory
criteria for zones west of the MS river early to mid-morning
Wednesday, increasing to the east throughout the day. Strong
southeasterly onshore flow will persist through the rest of
Wednesday into Thursday as a line of storms passes through. For
now, there is the potential for severe thunderstorms beginning
Wednesday morning through Wednesday night, with the main threats
being locally strong wind gusts >=34kt and waterspouts. This
convection will be followed by a strong cold front passage late
Wednesday night into early Thursday, with strong winds likely to
reach gale force beginning after midnight Thursday for zones west
of the MS river, spreading east through the morning and rest of
the day. High winds, followed by building waves/seas will continue
through the day on Thursday, Friday and upcoming weekend with
persistent westerly flow, with winds and waves/seas steadily
diminishing going into early next week. KLG
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 59 79 57 69 / 0 90 70 20
BTR 65 81 57 71 / 10 100 50 10
ASD 58 83 61 75 / 0 90 90 10
MSY 68 83 63 74 / 10 90 80 10
GPT 59 81 63 75 / 0 80 100 20
PQL 56 81 62 74 / 0 70 100 20
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Gale Watch from late Wednesday night through Friday afternoon
for GMZ550-552-570-572.
Small Craft Advisory from 10 AM Wednesday to 1 AM CDT Thursday
for GMZ550-552-570-572.
Gale Watch from Thursday morning through Friday afternoon for
GMZ536-538-555-557-575-577.
Small Craft Advisory from 4 PM Wednesday to 7 AM CDT Thursday
for GMZ536-538-555-557-575-577.
Small Craft Advisory from 4 PM Wednesday to 4 PM CDT Friday for
GMZ530-532-534.
MS...None.
GM...Gale Watch from late Wednesday night through Friday afternoon
for GMZ552-570-572.
Small Craft Advisory from 10 AM Wednesday to 1 AM CDT Thursday
for GMZ552-570-572.
Gale Watch from Thursday morning through Friday afternoon for
GMZ538-555-557-575-577.
Small Craft Advisory from 4 PM Wednesday to 7 AM CDT Thursday
for GMZ538-555-557-575-577.
Small Craft Advisory from 4 PM Wednesday to 4 PM CDT Friday for
GMZ532-534.
&&
$$