Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/10/23
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
928 PM CDT Wed Aug 9 2023
.UPDATE...
Issued at 858 PM CDT Wed Aug 9 2023
Rather active earlier this evening with a few strong cells across
the region producing very localized 50-60 mph gusts and small
hail. That activity has since diminished. Been adjusting POPs
through the evening, as well as sky cover, to account for the
changing conditions. Latest runs of the HRRR still showing
potential for additional shower and thunderstorm activity late
tonight into the wee hours of the morning across the far eastern
CWA, so will keep POPs from previous shift in the forecast.
&&
.SHORT TERM...(This Evening through Thursday Night)
Issued at 130 PM CDT Wed Aug 9 2023
Forecast challenges revolve around precipitation chances tonight and
then again Thursday afternoon/evening.
At 1 PM CDT, skies were partly to mostly sunny. Temperatures are
warming through the 70s into the 80s and winds are light and
variable. There is some smoke aloft working through the region as
well. A weak cold front very slowly moving south is located
along/near the border of the Dakotas. MLCAPE values anchored on
the boundary are ~800-1100J/kg with deep layer shear holding
around ~30 knots.
Short-range guidance, including the latest CAMS, suggest a couple
of storms can be expected by early this evening working southeast
across the region. Then, later tonight into the early morning
hours on Thursday, there could be some elevated showers
developing/moving southeast across the Dakotas/Minnesota borders
region, likely forced from mid-level WAA and upper jet-streak
lift. Over the next 24 hours, the HRRR-Smoke output suggests the
smoke aloft will gradually diminish/get pushed east-southeast out
of the region.
On Thursday afternoon/evening, an area of low pressure (presently
out over British Columbia province) will work through the region,
sweeping a cold front over the CWA. Plenty of instability and shear
around tomorrow afternoon/evening, including a low level jet later
in the evening pointing up into eastern South Dakota. 12Z CAMS are
in agreement of isolated to scattered discrete (super) cells forced
on the cold front along/east of the Missouri River valley and then
gradually forming into a (broken) line of storms by the time they
are crossing over into Minnesota. So, perhaps, initially a large
hail threat that eventually transitions over into a strong/damaging
wind threat. SPC`s Day 2 marginal risk over this CWA his been
upgraded to a slight risk for a number of counties.
Temperatures tonight through Thursday night should be close to, to
perhaps a few degrees below, normal.
.LONG TERM...(Friday through Wednesday)
Issued at 130 PM CDT Wed Aug 9 2023
West to northwest flow aloft will remain in place through the
extended. This will mean elevated smoke from Canadian wildfires is
also expected to filter into the region through the middle of next
week.
A shortwave trough will clip through the northern Plains late Friday
and could bring a shower or two to the far northeastern cwa.
Otherwise, the region looks dry until Saturday night and Sunday when
sfc low pressure moves through the central Plains and an upper
trough digs into the northern Plains to Great Lakes region. Sfc high
pressure and upper ridging builds in behind this system on Monday. A
couple of fronts and lows could affect the region by the middle of
next week, but confidence in any placement is low at this time.
Normal to slightly below normal temperatures (upper 70s to 80s) are
forecast for the start of the extended. Highs will climb under the
ridge early next week before returning to near normal mid week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 639 PM CDT Wed Aug 9 2023
Terminals KABR,KATY,KPIR,KMBG
SHRA/TSRA continue across the area at 00Z, but dissipating and
decreasing in areal coverage by 01Z-02Z. KABR terminal affected
the most, and could see MVFR/IFR VSBY in the strongest of cells.
Otherwise, VFR conditions are forecast later tonight into
tomorrow. More TSRA expected late afternoon Thursday, with
potential for strong to severe storms. Best potential in KABR and
KATY.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
UPDATE...TMT
SHORT TERM...Dorn
LONG TERM...Wise
AVIATION...TMT
Area Forecast Discussion
National Weather Service La Crosse WI
1050 PM CDT Wed Aug 9 2023
.DISCUSSION...(This evening through Wednesday)
Issued at 228 PM CDT Wed Aug 9 2023
Key Messages:
- Isolated showers and storms this afternoon/evening. Cannot rule
out a stronger storm capable of small hail and gusty winds.
- Multiple rounds of showers and storms (50-80% chance) for Thu
night into Friday and then again Sunday.
- Seasonal temperatures for the remainder of the week, cooling
slightly for early next week.
This Afternoon/Tonight:
A modestly moist and unstable airmass exists across the forecast
area this afternoon with surface temps in the upper 70s to low 80s
and dewpoints in the low to mid 60s generating about 500-700 J/kg
of SBCAPE. The CAMs have all struggled to resolve the
thermodynamic profiles of this airmass, especially with their
dewpoint fields being 10+ degrees too low. As a result, the NAM--
of all the models-- is best depicting the boundary layer
conditions per a comparison with MSP ACARS soundings. Isolated
showers developed within this airmass by 17-18Z. However, the
boundary layer may dry further with daytime insolation and a
surface moist layer quite shallow, so updrafts will be fighting
narrow CAPE profiles and a dry lower troposphere that will act to
weaken updrafts through entrainment.
Effective shear values are only around 15-20 kts early this
afternoon, but do increase slowly through the afternoon as a 90-kt
jet and subtle shortwave wraps around a low north of Lake
Superior. With primarily linear hodographs through a lower hail
growth zone, one cannot rule out an organized cell capable of hail
up to around an inch in diameter. Upstream, a diffuse cold front
is sagging southward through central Minnesota and northwest
Wisconsin with several clusters of storms having fired along and
ahead of the boundary over the last few hours. These cells
propagate southeastward this afternoon, but confidence in how long
they will persist remains a near-term forecast challenge given
the current lack of deep shear. Convection should wane this
evening with the loss of daytime heating.
Thursday/Friday:
Upstream upper level ridging will keep pleasant and dry
conditions in place through the day on Thursday, though the ridge
axis does pass through by the afternoon and evening hours on
Thursday. Convection developing across the eastern Dakotas
propagates eastward into the western forecast area after midnight,
but will be on the decline as it begins to outruns the
instability corridor. The explicit CAM reflectivity outputs vary
in the coverage of the echos as they reach the forecast area, with
the northern locales showing the best likelihood of seeing
precipitation (60-80% chance).
The timing and evolution of the convection early Friday morning
will dictate the thunderstorm risk for Friday afternoon. A
seasonably strong upper tropospheric wave drives southeastward
through Minnesota Friday afternoon and should result in
redevelopment along and ahead of the surface cold front, but the
position of the front and the quality of the airmass over the
forecast area hinges heavily on how the previous event unfolds.
Some models try and develop convection back over southeast MN
while other solutions develop storms farther to the southeast over
WI and IL.
Saturday/Sunday:
Persistent northwest flow will result in a near carbon copy of
Thu/Fri for Sat/Sun. Saturday looks to be pleasant and dry ahead
of a low-amplitude shortwave ridge. A sharp trough digs
southeastward for Sunday, but confidence in the severe threat
remains low with the main question revolving around instability
profiles ahead of the wave and the timing of the wave itself.
Early Next Week:
The start of the week looks to feature a brief cool down behind
the Sunday cold front. Most ensemble members are pegging highs in
the mid-70s to around 80. This shot of cooler air will be short-
lived with a progressive pattern in place and shunting the upper
ridge eastward by Tuesday. This opens the door for another round
of showers and storms once cyclonic flow resumes on the backside
of the ridge late Tuesday into Wednesday.
&&
.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1050 PM CDT Wed Aug 9 2023
CIGS: sct-bkn mid/upper level VFR clouds expected into Thu night.
WX/vsby: CAMS continue to suggest some late night shra could spark
along a sfc front slowing sinking southward across the region. Very
isolated activity via latest radar imagery, showing a decreasing
trend. Meanwhile, some of the short term guidance trigger a few
showers Thu morning/early aft from a shortwave moving southeast out
of the northern plains. Issues with saturation and amount of forcing
lowers confidence in possible impacts for the TAF sites. Will hold
with a dry forecast for now.
Next shot for shra/ts will come with an upper level shortwave/sfc
warm front Thu night/early Fri morning.
Shifting gears back to late tonight, low T/Td spread and light sfc
winds will promote fog in the mississippi river valley. However,
SCT/BKN mid level clouds moving in overnight and the near sfc wind
goes light north at KLSE by 12z (bad for fog pushing onto the
airport). Depth of the light wind layer has been increasing in the
RAP over its lasts few runs...upwards of 2 kft. HRRR/NAM12 are
lower. As it sits, the clouds might be the biggest deterrent to 1/2SM
or less FG at KLSE. For now, will likely roll with BCFG and adjust
as the cloud/wind trends become more evident.
WINDS: generally westerly this evening, becoming more
northwest/north with passage of a sfc front near 06z. Speeds less
than 10kts through the period.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
DISCUSSION...Skow
AVIATION.....Rieck
Area Forecast Discussion
National Weather Service Columbia SC
901 PM EDT Wed Aug 9 2023
.SYNOPSIS...
A warm front will move into the area late tonight and expect
moisture to increase. A series of potent shortwaves bring the
risk for showers and thunderstorms on Thursday. Diurnally driven
convection returns Friday and into the weekend with typical
summertime heat.
&&
.NEAR TERM /UNTIL 7 AM THURSDAY MORNING/...
Frontal boundary appears to be located across central Ga into
the SC Low Country at 23z. This front is expected to move north
overnight into the central Midlands toward daybreak and expect
moisture to increase. Precipitable water may be near 2 inches by
daybreak. Mid level short wave trough moving east across TN/AL
this evening, will move through SC/east central GA overnight.
GFS suggests short wave will de-amplify a bit. Radar showing
convection ahead of the short wave trough in north GA. The
latest HRRR suggests this area of convection will diminish as it
approaches the area tonight. CAPE overnight is expected to be
limited. However, a few strong storms may be possible late
tonight in the SC Piedmont and north Midlands based on
statistical SSCRAM guidance. Raised the pops a bit toward
morning especially north and west of CAE. Temperatures tonight
will likely be slow to fall once the clouds build in with
forecast lows in the lower to mid 70s.
&&
.SHORT TERM /7 AM THURSDAY MORNING THROUGH SATURDAY/...
Thursday has the potential to be a rather busy convective day
with one or two rounds of strong to severe weather possible
across The Midlands and CSRA. The first shortwave trough is
forecast to bring a line of showers and thunderstorms into the
region during the morning hours followed by a second shortwave
during the afternoon.
The forecast model soundings are quite impressive for mid summer
with speed shear due to 700 mb winds 40-50 mph and downdraft CAPE
values of up to 1200 J/KG. There is some uncertainty on exactly
where these forecast convective line or lines set up and how
much the atmosphere stabilizes behind the first line which would
inhibit additional convection in the afternoon. The primary
hazard will be damaging wind gusts and a mode of broken line
segments and/or bows.
A frontal boundary stalls near or just to the south of the region on
Friday. The best chance for convection should be in the eastern
Midlands and lower CSRA. H5 heights and low level temperatures
increase on Saturday as ridging builds in from the west.
Apparent temperature values may approach 110 degrees across the
eastern Midlands, thus a Heat Advisory may be necessary.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
H5 heights and low level temperatures increase at the start of next
week which will lead to hot and humid weather conditions across
the Southeast U.S. Surface temperatures are expected to be in
the mid to upper 90s with dew points in the 70s on Sunday. A
Heat Advisory may be needed.
Ensembles show a strong upper level trough diving down into the Ohio
River Valley and Mid Atlantic States Monday through Tuesday for a
brief cooling trend with a good chance of organized convection along
a cold front on Monday or Monday Night.
There is a higher than normal probability of above normal H5 heights
and low level temperatures just beyond the forecast period.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
A shortwave trough and convection will approach the forecast
area tonight. Showers are expected to diminish this evening
before reaching the terminals so restrictions are unlikely.
Winds will stay up through the night ahead of the next system.
This will prevent fog formation. The next round of thunderstorms
may move into the area around 12Z tomorrow. Low to medium confidence
in the strength and coverage of convection, so we have opted
for VCSH in the TAFs on Thursday morning rather than including
TS. Low level winds will be strong as this line of
showers/storms moves across the area. Winds at 2,000 feet will
range from 30 to 40 kts. However, being associated with
convection LLWS is not appropriate. Breezy winds will continue
through the afternoon with another round of storms possible.
EXTENDED AVIATION OUTLOOK...Moisture increases late week and
into the weekend, increasing the chances for early morning
fog/stratus. Restrictions also possible in mainly diurnal
convection through the extended.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
Area Forecast Discussion
National Weather Service Caribou ME
955 PM EDT Wed Aug 9 2023
.SYNOPSIS...
High pressure crosses the region tonight through early
Thursday. A new low will approach from the west later Thursday
and lift across the area Thursday night into Friday. High
pressure will return on Saturday followed by another low on
Sunday.
&&
.NEAR TERM /THROUGH THURSDAY/...
955 pm update...
00z sounding from KCAR shows deep moist layer from surface up to
~9000ft that will likely take some time to erode tonight. Drier
air is starting to break clouds up across the northwest zones
with H8-H7 winds slowly backing to the west. Expect that clouds
will remain across the far northeast until close to daybreak and
this will keep temps up just a tad more than expected. Have
boosted overnight mins in the northeast by a degree or so to
account for cloud cover. Still retaining patchy dense fog over
the river valleys to the south of main axis of clouds due to
rain from yesterday. No other chgs needed at this time.
Prev discussion blo...
Late This Afternoon... The previous system has kicked well off
to our east, but we are still seeing cloudy/mostly cloudy skies
in NW flow and isolated to scattered showers, mainly over the
north. Breezy this afternoon generally from the NW.
Tonight...
Tonight, slightly drier air continues to work in from the west,
with weak shortwave upper level ridging. Expect decreasing
clouds and any showers dieing off early evening. Clouds will be
decreasing a lot faster over the southern 2/3 of the area than
over the far north. In fact, while Downeast will be mostly clear
tonight, the St John Valley could stay cloudy/mostly cloudy.
Can`t rule out patchy fog tonight, but got rid of it from about
Houlton north due to more clouds tonight. Also, there is still
somewhat of a pressure gradient and some decent winds just off
the surface, so although soil moisture is very high, there are
definitely some things working against us to get more than very
patchy fog.
Thursday...
High pressure moves off to the east as the next system
approaches. More sunshine will allow for warmer temps, with
highs in the upper 70s to mid 80s. Inland, expected isolated to
scattered shower and thunderstorm activity. Only barely enough
instability for thunder, and don`t expect anything strong. One
other thing to watch for tomorrow is smoke. There is a ribbon of
smoke from the James Bay fires stretching SE toward Burlington.
The HRRR smoke has this band elongating and moving NE through
our area during the day Thursday, with some smoke at the
surface. Not confident enough yet to put smoke in the forecast,
but it`s something to watch.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
A large upper level trough will continue to push a developing
triple point low across the Gulf of Maine. Model guidance has
been fairly inconsistent with the track and timing of this low.
The jet stream will be the driving force for this system. If the
high-res models and NAM are correct, then the track is expected
to move across coastal Downeast, funneling moisture from the
tropical flow to the south, which will increase QPF across the
south. If the extended guidance models are correct, then the
track is expected to move across the southern waters of the Gulf
of Maine, producing less QPF. Nevertheless, rain showers will
progress across the region throughout the night. Instability
should produce nighttime thunderstorms, mainly across the north
ahead of the frontal boundary. By Friday, the front will move
through the region, dropping temps and moving the moisture out
of the area by Friday night. Breezy W flow is expected to
continue through the afternoon with possible thunderstorms by
the afternoon.
For Friday night, very brief weak ridging will clear out the
majority of the clouds by late. Though the area will be moist
with cool nighttime temps, fog is not a concern as of this
update due to the continued gusty winds. Saturday should be
clear and breezy with temps in the low 70s.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The next low pressure system is expected on Monday with a strong
cold front moving across the area. 12Z guidance points to
instability to create thunderstorms. After a break on Monday and
Monday night, models point to the next storm system approaching
on Tuesday with heavy rainfall being a possibility, thought the
track is still uncertain.
&&
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
NEAR TERM: VFR over southern terminals tonight into tomorrow.
Aroostook terminals will be varying between MVFR and VFR this
evening before scattering out closer to 06z. Exception looks to
be KFVE where IFR cigs move back in after 07z. Thursday will see
VFR over all terminals.
SHORT TERM: Thursday night...VFR dropping to MVFR north. MVFR
dropping to IFR south. S wind around 5 kts.
Friday...MVFR north except for a period of VFR during the midday.
VFR south. Gusty W wind 10-15 kts.
Friday night...MVFR becoming VFR north. VFR south. W wind 5-10
kts.
Saturday...VFR. S-SW winds 5-10 kts.
Saturday night...VFR lowering to MVFR and possibly IFR south. S
wind 5-10 kts.
Sunday...IFR. SW wind 5-15 kts.
Monday...VFR. W winds 5-10 kts.
&&
.MARINE...
NEAR TERM: Cancelled small craft, as waves are generally below 5
feet now. W-SW wind 10-15 kts and seas 2-4 ft through Thursday
(below small craft), with little or no fog over the waters.
SHORT TERM: Winds and seas will approach SCA levels Friday
evening into Friday night with a few gusts up to 25 kts. Then
winds and seas will decrease by Saturday and remain below SCA
throughout the rest of the period.
&&
.HYDROLOGY...
A new weather system moving through late Thursday night into
Friday morning has the potential to bring additional heavy rain
and possibly some embedded thunderstorms. Given that the ground
will already be saturated, this additional rainfall has the
potential to bring some significant rises of small streams and
ponding of low lying areas.
&&
.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...None.
&&
$$
Near Term...Buster/Foisy
Short Term...LaFlash
Long Term...LaFlash
Aviation...Buster/Foisy/LaFlash
Marine...Buster/Foisy/LaFlash
Hydrology...
AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
633 PM CDT Wed Aug 9 2023
.Discussion...
Issued at 341 PM CDT WED AUG 9 2023
Key Messages:
- Limited Storm Chances in the Southern CWA
- Seasonable Temperatures Thursday, Warming This Weekend
- Precipitation Very Late Thursday; More Likely Friday Morning
Discussion:
The updated discussion at 1028am provided details on redevelopment,
primarily concerned for our southern counties. The clearing brought
in behind the MCV has increased insolation and increased instability
for areas south of Interstate 70, with MLCAPE values ranging between
750-1000 J/kg. Unfortunately MCI is a bit far north, and there have
not been any ACARS observations further south to get an idea of how
the boundary layer lapse rates have been responding, particularly in
our south. The H5 short-wave trough axis has been digging further
into the High Plains, and the surface cyclone has deepened and is
centered along the OK-TX Red River Valley, with surface troughing
extending ahead of this into southwest Missouri. Deep layer shear is
still present ahead of the mid-level vort max with 0-6km bulk shear
still around 40-45 kts. While there has been some level of
thermodynamic recovery in area of stronger shear, it appears that
the clearing did bring in some drier air around 700mb which perhaps
provided cap. On GOES Day Cloud Convection, there do appear to be a
few updrafts trying to initiate from Vernon to Benton County, MO,
but are failing to reach deep depths. This may confirm that there is
still a cap in place above a destabilizing boundary layer. While
there is still a decent environment in place from Linn [KS] to
eastern Henry [MO] Counties, it appears the better forcing with the
surface troughing is moving south of the forecast area. Subsequent
HRRR cycles since 15z today continue to push stronger updraft
initiation further south toward Interstate 44. The satellite trend
currently observed seems to support this. Therefore, only holding
onto slight chance POPs in our far south. While there is plenty of
CAPE and shear around, thinking the severe threat is extremely
limited for our area, as the storms will need time to mature and
will move out of the forecast area before becoming strong enough.
Should a robust updraft manage to start further north, strong winds
and hail around 1 inch could be possible, but expectations for this
are very low. As for the rest of the CWA north of Interstate 70,
expecting an area of H5 height rises and AVA behind the MCV that
should gradually clear out the stratiform cloud cover. A few light
showers could be possible given the increase in moisture from early
precipitation and convection, but north of Interstate 70 the forcing
is drastically decreasing. One final note for this evening and into
Thursday morning, clear skies with cooler temperatures, an increase
surface moisture, and calm winds will lead to fog potential across
much of the CWA. Will continue to monitor trends on GOES Nighttime
Microphysics Imagery as the evening progresses.
Thursday morning, expecting clear skies (though likely at least
patchy fog around). The main H5 trough that has been driving the
surface cyclone and active weather in the Ozarks Region to Tennessee
Valley will shift eastward. Eventually should see winds pick up a
bit ahead of this trough axis that should mixout patchy fog by the
late morning hours. Even with the brief H5 height rises and AVA
Wednesday Night, the subtle height falls with the main trough axis
passage may provide some passing clouds heading into Thursday
afternoon. Surface ridging though should extend eastward from the
developing high into the area, which will keep the forecast dry for
most of Thursday afternoon with relatively seasonable temperatures
across the area.
Late Thursday Night and into Friday morning, another H5 short-wave
trough is progged to drop out of the Northern Plains and increase
kinematic forcing across the middle and lower Missouri River Valley.
With previous H5 ridging, WAA will likely start late Thursday in the
evening and then continue into Friday. Therefore, a warm-moist
airmass may again be in place ahead of this feature that will
present the opportunity for rain shower and thunderstorm
development. GEFS probabilities for MUCAPE above 1000 J/kg are above
90 percent heading into Friday morning, especially for far northern
reach of the CWA. With a stronger vorticity maximum, potential for
deep layer shear will also be there. This may lead to the potential
for a few strong to severe storms. In the SWODY2 outlook, areas
along and north of Hwy. 136 are in the marginal, with the SWODY3
placing marginal risk across a large portion of the area. This is
shaped this way with convection crossing the 12z timeframe between
the Day 2 and Day 3 outlooks. For our area, this may become more of
a Friday morning event rather than Thursday late night, as current
GEFS and other ensemble probabilities focus greatest chances for at
least 0.10 inches of QPF between 12-15z Friday. However, the
propagation speed of the progged short-wave may change, and if it
speeds up could produce more prior to 12z Friday morning. This
mornings`s cycle of the 12z HREF mean with respect to QPF are also
in the same realm that most of this if favored after 12z Friday
morning. While the mid-level flow will likely be tad more
northwesterly, there is another short-wave perturbation in the
southwesterly CONUS that results in a surface cyclone, and turns low-
level flow southwesterly across much of the Southern Plains into the
middle Mississippi River Valley. This creates a WAA regime that will
send temperatures back into the upper 80s and potentially lower 90s,
along with increasing dewpoints. NBM probabilities for temperatures
at least 85F or higher are about 70 percent, with the 90th
percentile values Friday into Saturday around 93F across most of the
area. With increasing humidity, this may send heat index values into
the triple digits. One factor though will be cloud cover moving in
with the Friday vort max. But any areas of clearing may get quite
warm and muggy again.
Sunday into Monday, a stronger PV anomaly is progged to drop south
out of Canada with a strong H5 trough will bring active weather to
portions of the Upper Midwest. Would expect seasonably high values
of deep layer shear to be present with a warm unstable airmass
across the region that could support organized activity. This is
highlighted in the Day 5 portion of the extended severe weather
outlook. At this point, cannot pinpoint exact mesoscale details.
Synoptic scale ensembles though are indicating higher probabilities
for SBCAPE to exceed 1000 J/kg along with stronger convergence.
Depending on the exact track, these probabilities likely shift over
the next few days, but currently anticipate active weather
especially in northern and northeastern portions of the CWA Sunday
into Monday. Beyond the weekend, deterministic GFS/ECMWF have a
594dam high progged across the Southern Plains. However it does look
like flow across our region may be more zonal above the H5 ridge.
Temperatures more likely would remain seasonable, but if the ridge
were to amplify could see increasing temperatures. Toward the end of
next week, the 25th-75th percentile spread in the NBM for max
temperatures is between the lower 80s and the mid 90s, indicative of
the dependence on the amplification of the pattern.
&&
.Aviation...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 631 PM CDT WED AUG 9 2023
Abundant low level moisture, clear skies and light winds will lead
to the development of fog overnight. Fog is expected to buirn off
after 14Z Thursday with light winds.
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...NONE.
&&
$$
Discussion...Krull
Aviation...BT
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1041 PM CDT Wed Aug 9 2023
.SHORT TERM...(This Evening through Thursday Night)
Issued at 221 PM CDT Wed Aug 9 2023
A weak boundary near highway 14 and into parts of southwest MN may
aid in producing isolated thunderstorms late this afternoon into the
evening. Right now instability and shear look a bit limited so
severe storms are not expected but a bit of an inverted v sounding
does suggest some gusty wind potential with any storms that do
develop. Outside of this potential with light winds and a relatively
wet ground some patchy fog will be possible but not expecting it to
become widespread. Lows generally upper 50s to lower 60s.
Thursday will see mid and upper level ridging flatten as a wave
moves into the areas by late afternoon. A warm nose will extend into
central SD towards the James Valley my mid to late afternoon and
will likely serve as a focus for thunderstorm development. While the
GFS is a bit weak on instability both the RAP and Nam suggest
something close to 2000 J/kg CAPE in this area with some decent
directional shear in the lowest couple of km. This would likely
support a few stronger updrafts, but with fairly weak winds up to
about 250 mb the stronger updrafts would likely be limited in time a
bit. Would still expect the potential for 65 mph winds and hail to
golf ball however. The question after initial development then
becomes what potential there is that it becomes linear or it it
remains more of a broken line of convection. Right now with the
weaker mid and upper level winds and not a strong low level pool of
dry air it will remain more of a broken line with embedded stronger
updrafts. The models do hint at a brief uptick in the LLJ from about
0-3z which should aid in supporting some stronger updrafts through
sunset and possibly close to 6z Friday. The wave is mostly through
the area by 6-9z so that should be the end to any stronger updrafts.
.LONG TERM...(Friday through Wednesday)
Issued at 221 PM CDT Wed Aug 9 2023
Friday into Friday night will see a secondary wave with a bit
stronger punch of cool air move into the area. While capping appears
like it will hold Friday afternoon and evening, this time frame will
still need to be watched as strong unidirectional shear and a cap
that is not as strong as previous runs might allow for an isolated
severe storm to develop.
While most of the day Saturday should remain dry and warm, another
wave is expected to move into the area and bring a good chance for
showers and thunderstorms Saturday night into Sunday. At this time
any severe weather potential should be fairly isolated. Once this
wave passes northwest flow aloft becomes stronger and temperatures
will be cooler on Sunday and Monday. Highs mostly upper 70s to lower
80s.
Flat ridging builds back into the area for Tuesday and Wednesday
with temperatures likely near to above normal. There may be some
isolated shower and thunderstorm activity both days but forecasting
weak waves at this time frame is difficult.
&&
.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 1041 PM CDT Wed Aug 9 2023
Winds will be light and variable overnight, becoming southerly 5-10
mph with gusts around 15 mph after daybreak. After noon, winds
increase to 10 to 15 mph with 20 mph gusts. Winds drop off again
after sunset and become westerly by the end of the period.
The calm winds overnight will likely lead to fog development,
especially in low laying areas and southwestern MN where they
received some precipitation Wednesday evening. Expect the fog to
burn off within a couple hours after sunrise, but could reduce
visibility down to MVFR briefly.
Thursday afternoon thunderstorms could develop west of the James
river and move east through the evening. Some of these storms could
be strong to severe with strong wind gusts and large hail as the
primary threats. Thunderstorms are most likely between 23-06Z
Thursday evening into early Friday morning.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&
$$
SHORT TERM...08
LONG TERM...08
AVIATION...AJP
Area Forecast Discussion...CORRECTED
National Weather Service Goodland KS
747 PM MDT Wed Aug 9 2023
.UPDATE...
Issued at 721 PM MDT Wed Aug 9 2023
Overall forecast remains on track, I did make some minor tweaks to
overnight lows for tonight by warming a couple degrees over the
western CWA as more of a southwesterly wind component makes
itself more known. Mid morning tomorrow, a surface trough
associated with a low pressure system in South Dakota will slowly
move west to east across the area. As it does so, the pressure
gradient will tighten which will lead to breezy winds staring in
east Colorado before progressing into western Kansas. Forecast
soundings support wind gusts around 30 mph starting around 8am
and lasting through the evening. Thunderstorm potential for
tomorrow does exist. The surface trough will set up a surface
convergence boundary during the early to mid afternoon hours.
Isentropic analysis indicates the relative best indication for
initiation will occur in eastern portions of Thomas, Wallace
western Logan county; this lines up relatively well with recent
runs of the HRRR and RRFS. Supercells will again be favored with
effective wind shear of 40-50 knots, lapse rates around 7.5-7.8C
and MUCAPE of 2000 j/kg. Wind gusts up to 70 mph and hail up to
golf balls are the primary hazards; however coverage will be
isolated to widely scattered at best as overall forcing is rather
subtle. Peak time for storms looks to be from 2pm MT to 7pm MT.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 150 PM MDT Wed Aug 9 2023
Zonal flow aloft today and tomorrow will gradually shift to a
northwest flow as upper ridge migrates from the Southern Plains
today to the Great Basin by Saturday. Temperatures warm slightly
in the interim with highs in the low to mid 90s Thursday and
Friday, then back to around 90 on Saturday. Precipitation chances
will be lower than they have been recently but still in the
forecast. On Thursday, a weak shortwave aloft coming out of
Colorado appears to be enough for isolated to widely scattered
thunderstorms to initiate along a surface trough roughly along
Highway 83 in the late afternoon. Environmental parameters show
MUCAPE of around 2000 j/kg and 0-6 km shear of around 40 kts,
which should be sufficient for a marginal risk of severe storms in
eastern areas as shown by the latest SPC convective outlook.
Further west, cannot discount an isolated thunderstorm moving out
of northeast Colorado late in the afternoon as well, but
instability and shear parameters are much lower west of the
trough axis and not expecting them to be severe. Storms should
quickly weaken by early Thursday evening.
On Friday, storms will likely stay close to the Front Range with
rising heights aloft as the ridge axis makes its closest pass to
the area. By Saturday as the northwest flow tries to develop will
see a return to thunderstorm chances in the afternoon and evening
hours. The environment is forecast to have around 1500 j/kg of
instability and around 30 kts of deep layer shear, suggesting
another marginal risk for severe storms. Confidence is low
however, due to uncertainty in the forcing as the northwest flow
will be battling the ridge to the south and it is unclear which
will be dominant.
.LONG TERM...(Sunday through Wednesday)
Issued at 145 PM MDT Wed Aug 9 2023
Warmer, more seasonal temperatures are expected for this part of the
forecast. The upper level ridge will continue to build over the
western CONUS, and onto the Central Plains. This will push the
storm activity to the Northern Plains. However before the ridge
intensifies, there will be a chance for storms Sunday night as an
upper level short wave trough moves across the Plains.
During the week there will be upper level short wave troughs
rounding the ridge during the late afternoon through the evening.
Current model consensus forecast has low chances for rainfall, which
seems reasonable for the weather pattern.
Tuesday or Wednesday could be the warmest days of the week when the
ridge reaches its peak strength. Wednesday evening a strong cold
front may move through the Plains, which could bring chances for
rainfall with it.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 454 PM MDT Wed Aug 9 2023
VFR conditions are currently forecasted for each terminal through
this TAF period. Some moisture present around 5000 feet AGL is
present across the northeast position of the area which will
bring some mid level clouds near or over the KMCK terminal before
clearing out around 04Z. Winds will become breezy tomorrow at each
site as a surface trough moves across the area. Winds are
currently forecasted to be from the SW with gusts of 25-30 knots
possible, currently appearing to be a bit stronger at KGLD. Also
will need to watch for storm potential around the KMCK terminal
Thursday afternoon, confidence isn`t quite there to introduce into
the TAF at this time.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
UPDATE...Trigg
SHORT TERM...024
LONG TERM...JTL
AVIATION...Trigg
Area Forecast Discussion
National Weather Service Louisville KY
936 PM EDT Wed Aug 9 2023
.Forecast Update...
Issued at 934 PM EDT Wed Aug 9 2023
Current radar shows a WNW to ESE oriented line of ragged convection
moving NE across our northern CWA as lighter showers have exited to
our east. Expect increased shower and storm coverage overnight as
the LLJ strengthens. Flooding remains a concern as model soundings
show warm cloud depths around 10kft along with surface dew points
around 70F and PWATs around 1.90 inches (90th percentile), resulting
in efficient rain producing cells. For example, KY Mesonet in Oldham
County received 0.81" of rain in 30 minutes with the cells that just
passed through. Will have to keep an eye on any training convection.
Showers and storms should continue to develop as the LLJ strengthens
across the region. The strongest wind energy appears to move across
central TN, and latest CAM runs have been steering upstream MCV that
direction. Will still have to watch for possible severe weather
across our south western counties around BWG overnight, mainly from
midnight until 3am CDT. Damaging winds and possible tornadoes remain
the main threats.
No major changes were made to the going forecast, with only minor
adjustments made to the near term grids; therefore, no updated
products are necessary at this time.
&&
.Short Term...(This evening through Thursday)
Issued at 325 PM EDT Wed Aug 9 2023
Key Messages:
- Strong to Severe Storms Possible This Evening and Overnight.
- Localized flash flooding risk for portions of the area.
Synopsis...Positively-tilted shortwave trough will move from the
central Plains towards the lower Ohio Valley tonight as it deepens
due to interactions with a Canadian upper-low rotating towards the
Great Lakes region. As a result, chances of severe weather and flash
flooding will increase this evening and tonight associated with the
strong energy and dynamic fields of the mid-level wave which could
be tied to the following features: 1) convectively-augmented
vorticity lobe with attendant MCV ahead of the wave and 2)
strengthening LLJ ahead of a southward-sagging cold front. The best
window for experience any type of impacts from the weather would be
between 10/0-8Z.
Model Evaluation/Confidence...Bottom line up front: confidence in
timing, intensity, and coverage of strongest storms is medium (at
best). The 10/12Z HREF model suite has come into better agreement
regarding the timing of the QLCS feature potentially affecting south-
central Kentucky as difference in timing are about 2 hours. NAM
10/00Z was remarkably delayed and it has since caught up to the
model consensus; however, the convective mode is slightly different
than the rest. An important deviation with this latest run has been
the southward nudge of the QLCS feature over south-central KY. This
is something that RRFS has been hinting at for several runs and now
the HRRR and FV3 are showing, as well. If this trend actually
materializes, most of the embedded rotating elements in the line
might fall over the south side of the state border, diminishing some
of the severe risk for Kentucky. Accordingly, SPC has adjusted the
severe outlook by pushing the Slight risk towards the south. Another
point of contention is the QPF and thus the possibility of flash
flooding for southern IN and northern KY locations. Most of the
guidance consulted in the last 12 hours indicates that the bulk of
the precipitation should fall north of the aforementioned areas of
concern. However, models like NAM and RDPS still show swath of 2+
inches of rain while the HREF 24-hr LPMM and EAS fields locate
precipitation bullseye just north of the CWA boundary.
Through this evening...Isentropic lifting due to warm air advection
aided my mid-level lifting from vorticity lob is already forcing
scattered showers and isolated storms over Indiana. Surface
convergence due to the MCV`s circulation, convective temperatures in
the upper 70s to low 80s, and moderate surface-based instability
could aid in further storm initiation and maintenance during the
rest of the afternoon. Aside from lightning and brief periods of
moderate to heavy rainfall, HREF is indicating some negative updraft
helicity which combine with fair mid-level lapse rates and possible
dry-air entrainment could yield a chance of subsevere hail and
strong wind gusts. Probabilities of severe weather before 10/0Z are
low but not zero whatsoever.
Tonight...Severe weather and flash flood chances will increase after
10/0Z. The flash flooding risk was previously focused along south-
central KY, tied to the severe weather threat. But recent trends in
the QPF have indicated a second area of concern closer to southern
IN and northern KY. Training storms, efficient rainfall rates (aided
by mid-level rotation), and relatively low FFG could result in
localized areas of substantial runoff along those areas. ILN and IND
offices have issued flood watches for their respective forecast
areas, but decent model spread in the highest QPF axis (see section
above) has limited predictability, so decided to hold off from
issuing a watch for now and will keep monitor convective trends the
rest of the afternoon to further assess the situation. For example,
an important factor to watch will be clearing skies at the base of
the MCV which could reignite a line of repeating storms
potentially aligning across the northern row of counties.
The other area of concern is south-central Kentucky, where the QLCS
system (or part of it) should be moving tonight. A localized flash
flooding risk is possible in this area but higher FFG and faster
system speed will work against a higher flash flooding risk (WPC
currently has a Slight risk). Back to the severe weather, as
explained above, the overall risk has slightly shifted southward and
although this could mean the worst of the line will be further south
into TN, there is still a concerning threat of locally damaging
straight-line winds and a few tornadoes. One factor to note is that
the southward nudge that models are advertising could yield a
restricted buoyant sector along and ahead of the cold front with
negative impacts from decaying MUCAPE which in theory will imply an
increasingly hostile environment for storm maintenance. On the other
hand, this line will be forced by an strengthening LLJ feeding high-
theta air to the line, especially above the surface. Thus, RIJ
dynamics and sufficient effective inflow SRH/shear will account for
the wind and tornado risk.
Thursday...There will be some lingering showers and isolated storms
Thursday morning, especially over south-central KY, but overall the
trend is for this activity to go down during the morning with mostly
cloudy skies as an overcast stratus deck approaches from the north
right behind the severe storms. Skies will clear out in the
afternoon with west winds around 10-15 knots. As for temperatures,
highs will be in the low 80s.
.Long Term...(Thursday night through Wednesday)
Issued at 230 PM EDT Wed Aug 9 2023
Key Message...
- Best chances for organized storms on Saturday and Monday
Progressive quasi-zonal flow is expected through the weekend, with
sensible weather fairly typical of mid-August. The tropical air mass
remains in place Friday, so it`ll be warm and muggy, but rising
heights will help to keep us rain-free. A shortwave upper trof
pushing through the Great Lakes on Saturday will bring the potential
for scattered, mostly diurnal, showers and storms. Just enough
instability and modest shear will support mainly pulse threats, but
no clear signal for organized severe weather.
By Monday the pattern amplifies with a building ridge over the West
and a sharper but still progressive upper trof digging into the
Great Lakes. This will push a respectable cold front through the
Ohio Valley during the day Monday, with scattered to numerous
thunderstorms. Stronger dynamics with this system will support
better storm organization, but confidence in severe wx is limited as
timing could limit the instability.
Sfc high pressure and NW flow aloft Tue-Wed will bring some mild
weather for mid-August, with temps several degrees below normal and
dewpoints in the lower 60s.
&&
.Aviation...(00Z TAF Issuance)
Issued at 753 PM EDT Wed Aug 9 2023
Impacts:
- Showers and thunderstorms this evening
- MVFR/IFR conditions into Thursday morning
Discussion:
Current radar shows an area of increased convection blossoming
between HNB and FTK. As the LLJ increases this evening, expect
showers and storms to increase in coverage, affecting SDF, LEX, and
BWG through 10/05Z at SDF and 10/06Z at LEX. Winds will gradually
veer to WNW with the passing of the surface trough. Regional
observations show MVFR CIGs approaching HNB, with CIGs lowering
across all TAF sites by midnight. MVFR/IFR conditions will persist
into the daylight hours Thursday morning with slow and gradual
improvements by late morning into the early afternoon.
Confidence: Medium to high confidence for thunderstorms and MVFR/IFR
conditions. Medium confidence on timing of storms and
onset/improvement of flight categories.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...CG
Short Term...ALL
Long Term...RJS
Aviation...CG
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1055 PM CDT Wed Aug 9 2023
.UPDATE...
Issued at 844 PM CDT Wed Aug 9 2023
What breaks in the clouds that did occur this afternoon and
evening were not enough to provide sufficient surface heating to
help instability recover over southern portions of the CWA.
Capping noticed in RAP soundings and SPC mesoanalysis limited
updraft strength to the point that convection was and still is no
more than showers and a couple of weak thunderstorms.
Additionally, storm motion vectors favor the cluster of storms
currently over the MO-AR state line to continue moving to the
southeast away from the CWA. Therefore, the threat of strong to
severe thunderstorms has ended this evening. With the low- level
jet focusing south of the CWA tonight and drier air moving in via
weak northwesterly flow, rain chances are expected to gradually
diminish from northwest to southeast through the early overnight
hours. With the decreased chance for stronger storms capable of
locally heavy rainfall, the chance for flash flooding and other
hydrological impacts has ended and the Flood Watch cancelled.
Despite the drier air moving into the area, we continue to monitor
the potential for fog across the region tonight, though exactly
where it will be most impactful remains uncertain. However, fog is
most likely in areas that received recent rainfall, such as across
northeastern Missouri and west-central Illinois.
Elmore
&&
.SHORT TERM... (Through Friday)
Issued at 334 PM CDT Wed Aug 9 2023
Key messages for Tonight:
1) Second round of severe thunderstorms will threaten the region
late this afternoon through this evening and will mainly be over
southeast Missouri and southwest Illinois.
2) These storms will likely start off as discrete supercells then
grow upscale into a line. Initially they will be capable of all
severe hazards, then favor damaging winds and brief tornadoes as it
becomes linear as it exits the forecast area.
3) With PWATs around 2" and possible training of storms across the
far southern sections of our forecast area, we have issued a Flood
Watch for Reynolds, Iron and Madison counties through 06z Thursday.
Morning/early afternoon activity is exiting the forecast area as of
20z. Also, latest satellite images are indicating that the remnant
MCV is continuing to slide east along the I-70 corridor with breaks
in the overcast developing south of I-70. So expect the atmosphere
in this area will recover a bit with latest SPC mesoanalysis
indicating that surface based CAPEs could rebound back to between
1000 and 1500 J/kg late this afternoon in this area. Even though
latest ML lapse rates are rather weak, 0 to 6km bulk shear is around
50kts from the west, so with the increasing instability, decent deep
layer shear, and lift from a cold front that is sinking southeast
across the region this afternoon, expect thunderstorms will begin to
redevelop between 3 and 5 pm. Even through the storms will likely
form as discrete supercells, the orientation of the shear in
relation to the cold front will favor the storms to congeal into
more of a liner structure.
In the meantime, as the associated upper level shortwave lifts into
the Ohio, it will drag a surface low along the front into the Ohio
Valley with the front exiting by late this evening.
With all of these variables this afternoon/evening, there is still
some question about if any severe storms will develop over the
southern portions of the forecast area. Just a matter of an hour or
two sooner or later with the onset of development, could be the
difference between severe storms and locally heavy rain or nothing
at all. For now will keep categorical POPs south of I-70 through
this evening, before activity tapers off.
As for locally heavy rainfall and/or flooding, with PWs around 2
inches, saturated soundings and skinny CAPE profiles, storms that
develop will be efficient rainers. So if storms train along the
frontal boundary, mainly over far southern portions of the forecast
area, could see locally heavy rainfall/flooding. However, the
majority of the CAMs are now indicating that the storms could be a
bit more progressive, so only issued a Flood Watch until 06z
Thursday for Reynolds, Iron and Madison counties in Missouri.
Beyond this evening, expect dry and slightly warmer weather Thursday
and Friday.
Byrd
.LONG TERM... (Friday through Next Wednesday)
Issued at 334 PM CDT Wed Aug 9 2023
The pattern begins to change late this week, as an upper level ridge
builds over the western CONUS once again. So with northwest flow
aloft, will see a shortwave slide southeast into the area.
Associated surface low and cold front will move into the region late
in the day on Friday bringing in the next chance for rain. Even
though there are chances of showers and storms through the weekend
and into early next week, it will not be a complete washout. Beyond
Monday, dry and cooler weather expected on Tuesday and Wednesday.
Byrd
&&
.AVIATION... (For the 06z TAFs through 06z Thursday Night)
Issued at 1046 PM CDT Wed Aug 9 2023
Confidence is high in impacts at all local terminals tonight into
early Thursday morning. A departing storm system has left cool,
stable air in its wake, leading to the potential for fog tonight.
In fact, several area observations have already shown sudden
drops in visibility due to fog over the last couple of hours. At
least MVFR flight category is expected at all terminals, with
flight conditions likely dropping into IFR range at KUIN due to
recent rainfall contributing to ample low-level moisture for fog
development. I can`t rule out other local terminals dropping into
IFR range, but confidence in which terminals this would happen is
low at this point. Fog that develops is expected to clear as the
sun rises, with confidence high in VFR flight conditions through
the remainder of the period.
Elmore
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX
Area Forecast Discussion
National Weather Service Phoenix AZ
405 PM MST Wed Aug 9 2023
.UPDATE...
Updated Aviation
&&
.SYNOPSIS...
Thunderstorm chances will primarily remain limited to the higher
terrain areas north and east of Phoenix, while chances remain less
than 20% across the lower deserts. A drying trend will ensue through
the end of the week and into the upcoming weekend, with storm
chances limited to just the higher terrain areas of eastern Arizona.
A cooling trend in temperatures will be observed through Saturday,
with highs near to just slightly above normal for this time of the
year. A warming trend is anticipated beginning on Sunday and
continuing into next week with well above normal highs once again
returning back above 110 degrees across the lower deserts.
&&
.DISCUSSION...
Current WV imagery and RAP analysis show an area of low pressure,
stemming from former Tropical Storm Eugene, situated in the eastern
Pacific west of the Baja Peninsula, while an elongated subtropical
ridge remains over northern Mexico extending across the Gulf of
Mexico. As a result, southwesterly flow aloft is in place across the
Southwest CONUS. Embedded in this flow pattern is a weak disturbance
currently situated over northern Arizona. This disturbance has
allowed for active monsoonal conditions to develop to our north this
afternoon, with afternoon radar showing widespread thunderstorm
activity across the northern Arizona high terrain.
Across our forecast area, subsidence on the back side of this
disturbance is expected to inhibit any convective activity this
afternoon and evening. The best chances for any thunderstorms will
remain confined to orographic features, primarily east of Phoenix
across southern Gila County. An isolated thunderstorm can`t be ruled
out across the northern foothills as well. Across the lower deserts,
chances are expected to remain low (<20%) through the evening. The
12Z HREF paintball plots show good support for this idea with the
bulk of activity remaining confined to northern Arizona. Any
thunderstorm that were to develop in our area would be capable of
producing gusty outflows with the HREF showing upwards of a 30-50%
chance for outflow winds in excess of 35 mph across southern Gila
County today.
By Thursday, the area of low pressure situated west of Baja will
advance northward into southern California, allowing for drier
southwesterly flow to advect drier air into the region. The low
pressure system will become quasi-stationary along the southern
California Coast, while the subtropical ridge builds into the
southern Plains. This pattern will promote southerly flow across the
Desert Southwest, which can generally be more conducive for getting
better monsoonal moisture from Mexico. However, the close proximity
of the aforementioned low pressure system will promote drier air
advecting into the region, while the best thunderstorm chances will
remain confined across the eastern third of Arizona and into New
Mexico where better southeasterly flow with embedded weak
disturbances will be present. Limited monsoonal activity is expected
to persist through the forecast period with the best chances for any
thunderstorms remaining focused across the south- central Arizona
high terrain.
&&
.PREVIOUS DISCUSSION...
With the upper-level high pressure system situated well east of the
region and the upper-level trough moving into southern California,
high temperatures through the end of the week and into the upcoming
weekend will be noticeably cooler than what we have been
experimenting so far through much of the summer with highs generally
ranging between 102-109 degrees across the lower deserts. These
values are near to just slightly above normal for this time of the
year. Still, these temperatures will pose a moderate HeatRisk and
thus if partaking in outdoor activities, the necessary heat
precautions still need to be taken. By early to middle of next week,
ensembles are in good agreement in showing the high pressure ridge
eventually expanding westward leading to a warming trend and thus a
return to excessive heat conditions once again with highs back above
110 degrees across most of the lower deserts to potentially 115+
degrees across some areas, especially by the middle portion of the
week.
&&
.AVIATION...Updated at 2305Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major weather issues will exist through Thursday afternoon with
slightly lower than normal forecast confidence in wind trends.
Confidence is good west winds with gusts up to 25kt will hold
through the evening, however decaying outflow from storms well to
the northeast may result in an earlier than usual switch to easterly
around midnight. A periods of cross runway southerly winds in excess
of 10kt will be possible midday Thursday before completing the
westerly switch. Otherwise, a few mid/high cloud decks will be
common with storms remaining mostly over mountain locations well
removed from terminal locations.
Southeast California/Southwest Arizona including KIPL and KBLH:
Gusty winds will be the greatest weather concern through Thursday
afternoon under periods of mid/high clouds decks. Winds will be most
pronounced at KIPL this evening with 20-30kt gusts likely resulting
in more lofted dust before partially decoupling around midnight. At
KBLH, breeziness should be a bit more muted as south to southwest
winds gust to 20-25 kts into early evening. Isolated high based
showers/virga may develop across parts of Southwest AZ and along the
CO river just after midnight tonight, however probabilities of
directly affecting KBLH air space is too low to include in this TAF
package.
&&
.FIRE WEATHER...
Monsoonal moisture will linger through Thursday, with the best
thunderstorm potential relegated mainly across the higher terrain
areas of south-central Arizona. MinRH values will generally range
between 15-25%, while MaxRH values generally remain between 40-60%
most days. Aside from thunderstorms, winds will favor familiar warm
season patterns, except over Imperial County where late afternoon
and nighttime sundowner winds from the west with gusts at times
exceeding 30 mph can be expected during the next couple of days.
High temperatures through the weekend will be near to slightly above
normal with a warming trend expected by early next week.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Smith
PREVIOUS DISCUSSION...Lojero
AVIATION...18
FIRE WEATHER...Smith/Lojero
Area Forecast Discussion
National Weather Service Raleigh NC
956 PM EDT Wed Aug 9 2023
.SYNOPSIS...
An upper level trough will approach from the west tonight, and cross
the region Thursday morning through the evening. Weak high pressure
will build over the area on Friday, as an upper level disturbance
moves overhead. A hotter air mass will move in over the weekend.
&&
.NEAR TERM /TONIGHT/...
As of 956 PM Wednesday...
Modified the arrival time of POPs a bit earlier in the west compared
to the previous forecast given observational and model trends.
Otherwise, the inherited forecast is on track tonight.
A potent mid-level short-wave was observed over central TN/KY
driving showers through the Smokies/Nantahala mountains this
evening. A weak MCV was evident in this region on radar (handled
decently by the 22Z RAP) pushing eastward across the mountains. This
feature will push east across our area over the next several hours
ahead of the more potent mid-level short wave previously mentioned.
Associated scattered showers may develop across the west as early as
07Z as this weak feature pushes through. Given these observational
trends (supported also by latest HRRR runs), decided to add slight
chance POPs across the far west to handle this possibility starting
around 07Z. The bulk of the heavier rain associated with the potent
short-wave is still on pace to arrive in our western zones near
~12Z. Clouds will continue to thicken overnight supportive of warm
lows in the upper 60s to lower 70s.
&&
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 310 PM Wednesday...
A vigorous upper-level trough will dig across the Appalachians and
then across the Carolinas Thursday before exiting off the coast
Thursday evening. Additionally, a surface low moving by to the north
and associated cold front pushing east across the region Thursday
will support another period of showers and thunderstorms on
Thursday. Conditions will become unstable as the upper trough
approaches the region, and with large low-level and 0-6km shear
values, the threat of severe weather looks more certain. The only
change to the SPC convective outlook for Thursday has been an
expansion of the Slight Risk, which the previous issuance only left
a small area of Sampson county in a Marginal Risk.
The details have come better together in the 12Z runs of the high-
res models, and confidence has increased that a broken line of
showers and potentially severe thunderstorms will move west to east
across the area. The broken line could first arrive near the Triad
around the morning commute, then move across the Triangle late
morning, and off the Coastal Plain by early afternoon. Scattered
showers/storms may develop ahead of the broken line, and then there
may be a lull in activity after. The surface front may then generate
another area of strong storms, with the greatest instability and
coverage of showers and storms along the NC/VA border in the
afternoon. Details are still coming together for the second chance
of severe weather, and confidence remains lower with the location
and timing of the second round.
Damaging wind gusts are the main threat with the initial broken
line, along with the chance of an isolated tornado with the strong
lower-level shear. By the afternoon, increasing instability could
lead to an additional hail threat where the strongest storms
develop. Heavy could lead to urban flooding, however widespread
flash flooding is not expected as precipitable water is only
slightly above seasonal normals.
Highs will range from the mid-80s across the NW to the low 90s SE,
and lows will dip into the upper 60s to low 70s.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 400 PM Wednesday...
Frontal boundary will shift east of the region early Friday.
Although, a slight chance of showers in the SW region will be
possible in the morning Friday before expanding north by the
afternoon as the next weak disturbance moves into the region from
the SW. As the low pressure becomes a weak unorganized disturbance,
it will move across the region late Friday early Saturday with dry
air behind. Saturday and Sunday is expected to be hot and dry other
than an isolated shower areas in the SE closer to the coast due to a
sea breeze thunderstorm developing in the late afternoon, coverage
at this time is expected to be very limited. The heat however will
be more widespread across the region with highs on Saturday in the
low to mid 90s, heat indices will be up to 106 in areas of the
Triangle south. On Sunday H5 heights and lower level temperatures
will increase even more on Sunday as ridging builds in from the
west. Temperatures Sunday are to be in the mid to upper 90s across
the region with dangerous heat indices ranging from 105 in the areas
of the Northeast Piedmont to 110 across the Sandhills and southern
Coastal Plain, thus a Heat Advisory may be necessary Sunday.
Early next week a mid/upper level trough will move across the OH and
TN valley and by mid week into the Mid-Atlantic region. By the time
the deepening trough gets to the Mid-Atlantic region, models show an
organized cold front at the surface moving through the area. For the
timing of the passage, it is still low confidence but is expected to
cross the region between late Monday afternoon into the overnight
hours. With deep shear values of up to 45kts Monday afternoon and
early evening some there would be some potential for organized
severe storms as the fronts move over the area. Will keep a close
eye on Monday/ Tuesday time frame for severe potential.
For the rest of the long term period, the aforementioned front will
move across the region with high pressure building in across the Mid-
Atlantic region through mid week. Highs Tuesday and Wednesday will
be in the mid upper 80s with some areas in the south reaching 90
degrees. Afternoon isolated showers will be possible each day mainly
in the SE region closer to the coast.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 800 PM Wednesday...
24-hour TAF period: VFR conditions will prevail through tonight,
with increasing mid and high level clouds from west to east as an
upper disturbance approaches the area. Scattered showers can`t be
ruled out overnight, first around INT/GSO after about 06z and around
RDU/FAY/RWI after about 09z. Then a heavier and more widespread line
of showers and thunderstorms with MVFR ceilings is expected to move
in from the west, affecting INT/GSO early to mid morning (roughly 12-
15z) and the eastern terminals late morning to early afternoon
(roughly 14-17z). Some of the storms could be severe, and they could
be accompanied by a period of gusty winds and IFR
ceilings/visibilities, so added a TEMPO group everywhere to show
this potential. Skies are expected to clear somewhat with mainly VFR
conditions returning in the afternoon. Additional showers and storms
will be possible in the afternoon and early evening, but coverage
looks like it will be more isolated. Light winds tonight will
increase out of the southwest tomorrow morning and continue into the
afternoon, gusting up to 20-25 kts even outside of any convection.
Outlook: Isolated to widely scattered showers and storms are
expected through Sunday, although coverage should be minimal on
Saturday. More widespread convection is possible on Monday as a cold
front approaches.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...GIH
NEAR TERM...Luchetti
SHORT TERM...JJT
LONG TERM...CA
AVIATION...Danco/Green
...Update to aviation forecast discussion...
.DISCUSSION...
Issued at 256 PM CDT Wed Aug 9 2023
Key Points:
- Quiet and dry through Thursday, then chances for thunderstorms
Friday and again Sunday
- Heating up again late this week, then a brief cool-down Monday
before warming back up
Early this afternoon, water vapor imagery depicts the main upper
trough axis extending from Ontario southward through the Upper
Midwest and into KS. The system responsible for this morning`s rain
is mostly east of the area, although there is a smaller mid-level
circulation that has moved out of southwestern NE into the state.
This appears to be merging into the main trough, and the
precipitation associated with that circulation has shown a weakening
trend likely due to subsidence winning out on the back side of the
departing system. The surface trough has pushed well south and high
pressure is expected to slowly move across the area tonight through
Thursday. Can`t rule out some patchy fog around sunrise, especially
in low-lying areas and river valleys given the recent rainfall.
Otherwise, we should see quiet conditions with partly cloudy skies
leading to highs in the 80s area-wide Thursday.
Late Thursday night into Friday morning, there are some weak
perturbations within northwest flow just north of the area, which
could bring some isolated weak thunderstorms near the KS/NE border.
While the best forcing looks to be north of our area, the 12Z HRRR
shows the possibility of a few storms clipping our northern areas
overnight. Storm chances increase during the day as a weak frontal
boundary approaches, and instability and shear would be sufficient
for severe storms by the afternoon. However, convergence along the
boundary may not be strong enough to develop storms in the first
place, so PoPs remain on the lower side. WAA also looks to increase
as we go into Friday with temperatures back into the 90s and dew
points in the mid 70s. This could bring heat indices back into the
triple digits, but will need to get a better handle on the
convective trends to get a better idea on if advisory criteria will
be met.
A more robust system looks to eject out of the northern Plains and
develop into a cut-off low over the Upper Midwest early next week.
This would bring a more meaningful cold front across the area on
Sunday, which brings our best chance for thunderstorms in the next 7
days. There is some variability in how much it deepens and exactly
how quickly it progresses east. Current indications favor
precipitation moving out of the area by Monday with a brief cool-
down as temperatures fall back into the low to mid 80s. Upper
ridging would then bring a return to average or above average
temperatures in the middle of next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 623 PM CDT Wed Aug 9 2023
Light/variable winds and mostly clear skies are expected overnight
as surface high pressure stays nearby. Still can`t rule out some fog
towards sunrise, but think this looks more likely to the east of
KTOP/KFOE. Winds become southerly tomorrow but still light, with
just some VFR cumulus during the afternoon.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Picha
AVIATION...Reese