Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/02/20
Area Forecast Discussion
National Weather Service Lincoln IL
856 PM CDT Tue Sep 1 2020
.SYNOPSIS...
Issued at 255 PM CDT Tue Sep 1 2020
A slow moving front will bring showers and thunderstorms to
portions of the area through Thursday. The best chance will be
confined to areas south of I-72 Wednesday and then south of I-70
on Thursday. Dry weather and lower temperatures are expected
Friday into Saturday.
&&
.UPDATE...
Issued at 856 PM CDT Tue Sep 1 2020
Rich moisture across the region with current dewpoints from the
upper 60s west of I-55 to the lower 70s to the east should result
in fog development across the area overnight as higher level
clouds clear out. Widespread rain that fell today should help
supply moisture, especially west of I-55 where many areas
received over an inch. Otherwise, have trimmed PoPs east of I-55 late
this evening and overnight based on recent trends, but also added
slight chance PoPs in the northwest due to approaching showers
associated with approaching surface cold front. Lows should reach
as low as 63 in Galesburg, but otherwise range up to as warm as 70
in Lawrenceville.
&&
.SHORT TERM...(This evening through Wednesday)
ISSUED AT 255 PM CDT Tue Sep 1 2020
A nearly stationary frontal boundary is draped from near Kansas
City across the Peoria area and into NW Indiana this afternoon.
Dew points in the upper 60s to lower 70s are in place south of the
front and quickly drop through the 60s into the 50s north.
Meanwhile, outflow boundary from earlier storms has moved across
the I-57 corridor and has helped kick off new line of
thunderstorms early this afternoon from roughly Shelbyville to
Danville. Latest RAP shows fairly modest instability in place
across east central Illinois with MLCAPE around 500-700 J/kg.
Given expansive cloud cover and weak flow, do not anticipate any
significant further destabilization this afternoon. Still, deep
layer shear values of 30-40 kt mean storms will bear some watching
this afternoon. Any low end severe threat should be fairly short
lived over the next couple hours only as what little instability
that is present is overturned by ongoing convection.
On Wednesday, effective front is expected to push south of the
I-72 corridor and will serve as the focus for additional
isolated to widely scattered storm development. Further north,
lower dew points do start to creep back into portions of central
Illinois north of I-72, with values into the lower to mid 60s.
Temperatures will warm into the lower to mid 80s area wide
Wednesday afternoon.
.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 255 PM CDT Tue Sep 1 2020
Upper pattern will be characterized by a broad and flat longwave
trough spanning much of the country with a compact shortwave
moving along the international border across the northern Great
Plains into Great Lakes Thursday. Attendant surface low will stay
over Canada, but a trailing cold front will sweep across the
Midwest, crossing central Illinois Thursday night. At this time,
no precip is expected with the front, but 850mb temps fall from
around 15-16C ahead of the front to 9-10C behind the front.
Meanwhile broad surface high will spread from the Great Plains
across the Midwest Friday and Saturday. This should amount to
temps falling back to near or slightly below seasonal norms with
otherwise fair weather to close the week and start the weekend.
Upper pattern begins to amplify over the weekend with a strong
ridge building across the west coast and trough deepening
downstream centered over the Midwest. Another shortwave trough
will dig across the Upper Midwest Saturday night into Sunday. Warm
advection ahead of the wave will moderate temps Sunday with temps
back into the lower to mid 80s, but this will be short lived as
yet another cold front pushes across the region later Sunday.
There remains large differences in how far south this front pushes
and placement of later storm tracks, thus extended forecast has
broad brushed chance PoPs given the uncertainty but well below
normal temperatures appear possible if the more southerly
solutions verify.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 653 PM CDT Tue Sep 1 2020
Expect diminishing showers affecting the central IL terminals this
evening as scattered showers and isolated thunderstorm potential
move eastward. Mention of SHRA/VCSH confined to KDEC and KCMI
until 03Z-04Z. Primarily VFR conditions initially, then cigs and
vsbys likely to reduce to IFR or MVFR with locally worse
conditions overnight as fog and low clouds develop. Improvement in
conditions should develop rapidly from 14Z-18Z as diurnal heating
dissipates morning fog. Winds S 6-9 kts initially, becoming light
and variable overnight, then increasing out of the west after 14Z
after a front moves eastward through the area.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...37
SYNOPSIS...Deubelbeiss
SHORT TERM...Deubelbeiss
LONG TERM...Deubelbeiss
AVIATION...37
Area Forecast Discussion...UPDATED
National Weather Service Shreveport LA
1013 PM CDT Tue Sep 1 2020
.UPDATE...
Convection continues to slowly advance eastward across North
Central Texas, and the first band is finally beginning to enter
East and Northeast Texas. Two more distinct areas of intense
thunderstorms trail south of Interstate 20 back to the west of the
first band. The intensity has decreased with the loss of daytime
heating and as the storms encounter more stable air near the
ArkLaTex. However, the development of a low-level jet tonight
should help to sustain the convection during the overnight hours.
There is a quite a bit of uncertainty regarding the southeastward
extent of this activity. Some of the models suggest a more
northeastward track, basically in line with the Flash Flood Watch.
Other models, notably the HRRR suggest a more southeastward track,
followed by a turn to the south after daybreak. The HRRR may be on
to something as radar and satellite loops do show some south and
southeast propagation. However, confidence is still low, so will
maintain the highest pops generally northeast of a line from Tyler
TX to Prescott AR.
PoPs were removed from the far eastern zones over North Central
Louisiana.
CN
&&
.PREV DISCUSSION... /issued 703 PM CDT Tue Sep 1 2020/
UPDATE...
See below for 02/00z Aviation Discussion.
Heat Advisory will be allowed to expire at 00z this evening. There
is quite a bit of uncertainty regarding the eventual track of the
convection ongoing across North Central Texas as it moves into
East Texas later tonight, and this will have implications in where
an advisory might be needed for Wednesday. Some of the model
guidance turns this complex more to the southeast, while others
keep which matches very well to our Flash Flood Watch from Mineola
TX to Hope AR. Therefore, a re- issuance of the Heat Advisory
will be left to the midnight shift.
CN
AVIATION...
For the 02/00z TAFs, a temporary lull in the convection will occur
early in the period before another complex of strong thunderstorms
moves into East Texas, Southwest Arkansas, and Southeast Oklahoma
beginning around 02/05z. There may be yet another brief break for
some locations around sunrise before another round of showers and
thunderstorms develop in the same areas before noon Wednesday.
KTXK, KTYR, and KGGG will likely be the TAF sites most affected by
thunderstorms during the period.
MVFR ceilings are expected to develop areawide during the
overnight hours. Flight conditions will gradually improve except
at sites where thunderstorms are ongoing.
CN
PREV DISCUSSION... /issued 215 PM CDT Tue Sep 1 2020/
SHORT TERM.../Tonight through Wednesday Night/
Finally beginning to see some widespread convection moving into our
northwest zones, roughly north and west of the I-30 Corridor this
afternoon and it has taken a strong southeastward moving outflow
boundary to direct this precipitation into our region. Rainfall
amounts have not been too excessive as of yet, nothing like our
neighboring counties in Southeast Oklahoma and Southwest Arkansas
have had to deal with earlier this morning with high water rescues,
widespread flooding and several inches of rainfall. This evening
into the overnight hours, several CAM suites are picking up on the
outflow boundary to our northwest and rather intense convection
developing later this evening into the overnight hours with the
development of a southwest to northeast oriented 30-35kt low level
jet max oriented parallel to the surface outflow boundary. This
coupled with continued deep southwesterly flow aloft with ripples
in this flow moving north and east towards the Middle Red River
Valley overnight through Wednesday, providing the necessary upward
forcing for scattered to numerous showers and thunderstorms with
an increasing flood threat. For this reason, have added some
counties south and west into Northeast Texas to the existing Flash
Flood Watch which remains in effect through 00z Thu. The latest
run of the 12z NAM is hinting at an axis of 8+ inches from just
northwest of Smith County to just northwest of Texarkana beginning
this evening and continuing through the day Wednesday. While this
appears to be a worse case scenario, cannot ignore the potential
given the players mentioned above.
The upper trough will move out of the Four Corners Region of the
Country overnight tonight and will attempt to become cutoff from the
westerlies as it meanders across the Upper Red River/Tx Hill Country
during the day Wednesday before slowly ejecting eastward Wednesday
Night. Current FFA will likely need to be extended in time beyond
00z Thu but will let future shift make the call on just where it
needs to be extended depending on rainfall over the next 24 hours.
The same goes for the current Heat Advisory which remains in effect
through 7 pm this evening. Uncertain on counties/parishes along the
I-20 Corridor needing an extension to the Advisory into Wednesday
but I could easily see our southern and eastern third needing the
extension. Will allow future shifts to make this determination based
on how much debris cloud cover we are dealing with on Wednesday from
nocturnal convection overnight.
13
LONG TERM.../Thursday through Monday Night/
An upper-level trough from the Red River Valley of north Texas into
Oklahoma and Missouri to linger through the weekend while slowly
drifting south east. Instability associated with the upper-trough to
maintain periods of convection through the weekend with a continued
flash flood threat persisting each day. A frontal boundary will move
through the region on Friday evening introducing a reinforcement of
slightly cooler air across the region. Temperatures late in the week
into the weekend to range from highs in the 80s to lows in the upper
60s to around 70.
Rain chances to diminish through the weekend as the upper-trough
shifts east and weak ridging builds in its wake.
/05/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 79 88 75 89 / 30 50 40 40
MLU 77 95 75 93 / 10 20 20 20
DEQ 72 80 70 84 / 80 90 60 60
TXK 74 82 72 83 / 70 80 60 50
ELD 76 85 72 88 / 30 50 40 40
TYR 75 85 74 88 / 70 70 60 50
GGG 75 86 74 89 / 50 60 50 40
LFK 78 94 76 94 / 30 30 20 40
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...Flash Flood Watch through Wednesday evening for ARZ050-051-
059>061-070.
LA...None.
OK...Flash Flood Watch through Wednesday evening for OKZ077.
TX...Flash Flood Watch through Wednesday evening for TXZ096-097-
108>112-124-125.
&&
$$
09/33
Area Forecast Discussion...UPDATED
National Weather Service San Angelo TX
659 PM CDT Tue Sep 1 2020
.AVIATION...
/00Z TAFS/
Scattered to numerous thunderstorms are moving east-northeast
across the eastern Big Country, and across Coleman and Brown
Counties this evening. Additional development of showers and
thunderstorms is anticipated through late evening and tonight,
mainly to the south across parts of the eastern half of West
Central Texas. Localized strong, gusty winds are possible
in and near the storms. Brief reductions in ceilings and
visibilities are expected in the locally heavy rain
accompanying the convection. Currently carrying a mention of
thunderstorms in the KABI and KSJT TAFs, with VCTS at our
other terminals. Will monitor radar trends and update TAFs
as needed. Outside of convective activity, VFR conditions are
expected, and winds will be primarily from the south tonight.
On Wednesday morning, winds will become north at KABI and
KSJT, but should remain generally from the south at our
southern terminals.
19
&&
.PREV DISCUSSION... /issued 257 PM CDT Tue Sep 1 2020/
SHORT TERM...
(Tonight and Wednesday)
Current water vapor imagery shows an upper level low digging into
southern Colorado and northern New Mexico...with southwesterly
flow aloft in place across West Central Texas. At the surface, an
outflow boundary from morning convection extended from the D/FW
Metroplex westward across the northern Big Country. Isolated to
scattered showers and thunderstorms are developing across the Big
Country back down into the Heartland. High res model guidance and
CAMs continue to develop numerous showers and thunderstorms
through the remainder of the afternoon and into the overnight
hours...as a shortwave trough in the southwest flow approaches
from the west. In addition, current RAP analysis shows MLCAPE
values of 2500+ J/KG along with 25- 35 knots of bulk shear across
the northern half of our area. Thus, strong to severe storms are
possible this afternoon and tonight with large hail and damaging
winds the main hazards. SPC does have roughly the northern half of
our CWA in a slight risk for severe storms. Also, heavy rainfall
leading to localized flash flooding will also be possible given PW
values of 1.9-2.1 inches across the Big Country and Heartland.
The upper level trough axis will linger across the area on
Wednesday leading to scattered showers and storms in the
afternoon, with the highest rain chances across the eastern half
of the CWA. Temperatures on Wednesday will only be in the 80s and
lower 90s with the cloud cover and rain in the area.
42
LONG TERM...
(Wednesday Night through next Tuesday)
By Wednesday evening, models depict the axis of the upper level
trough that will move into the area tonight along our eastern
border or just east of our area. So, expect the scattered showers
and thunderstorms if they develop tomorrow afternoon to be largely
across the eastern half of the CWA, but could still have a few
lingering showers and storms farther west. The upper low continues
to slowly move east on Thursday, making it into eastern Texas.
This would normally end rain chances, but with as much moisture as
we will still have available, and the center of the upper ridge
well west of our area, we could see a few showers/storms Thursday,
so will keep a Slight Chance to Chance going on Thursday as well.
The low then weakens, and is expected to slowly drift back to the
southwest, grazing our southeastern counties. Because of that,
will have to continue some PoPs through Saturday, but will show
mainly Slight Chance PoPs through Friday and Saturday. The
forecast then dries out for Sunday and Monday. Temperatures are
expected to be fairly typical for this time of year through this
weekend with highs in the upper 80s to mid 90s, with lows from the
upper 60s to lower 70s.
20
&&
.PRELIMINARY POINT TEMPS/POPS...
Abilene 71 86 68 90 / 60 70 40 30
San Angelo 72 89 70 93 / 50 50 30 20
Junction 75 91 71 93 / 60 50 50 30
Brownwood 71 87 69 90 / 70 80 60 50
Sweetwater 70 86 69 92 / 50 50 20 20
Ozona 72 91 71 93 / 40 30 30 20
&&
.SJT WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
...Update to aviation forecast discussion...
.SHORT TERM...(This evening through Wednesday)
Issued at 340 PM CDT Tue Sep 1 2020
Showers depart this evening with fog possible tonight and
seasonable weather for Wednesday.
Upper level lift associated with a departing northern stream wave
was slowly decreasing over the forecast area, and with it the low
clouds from west to east. To the west, an upstream PV lobe has
dived southward towards the Four Corners region, detaching from
the more vigorous polar jet and becoming embedded in a much
slower sub- tropical jet. This feature meanders eastward over the
next few days, gradually filling and being swept up with the next
northern stream wave on Thursday.
The resultant southwest flow and weak undulations in the mid-
level flow ejecting from this western trough interacting with a
complex, quasi-stationary lower tropospheric baroclinic zone have
been responsible for periods of light showers over the eastern
half of the forecast area today. Convection thus far has been
shallow and short-lived, likely owing to a +10 C H700 warm nose.
Some RAP forecast soundings depict a risk for deeper updrafts by
late this afternoon at peak heating, but weak mid-level flow
should result in poorly organized storm structures that would pose
little more than a lightning risk.
The threat for rain shifts south of the I-35 corridor tonight,
with skies gradually clearing from west to east. While not the
most ideal setup, the combination of light winds and recently
wetted soils may result in overnight fog across much of the area.
High clouds streaming northward from convection in OK/TX also may
dampen fog prospects in the eastern forecast area; therefore,
focused the highest fog potential between Clay Center and Topeka.
Areas southeast of this region may see fog early in the evening,
but there is considerable uncertainty with how the fog will behave
towards sunrise as the clouds thicken. Will need to watch trends
closely overnight.
The ill-defined H925-H850 boundary meanders southward towards
southeastern Kansas tonight into Wednesday as weak H300 ridging
and an attendant surface high slide through the region. Forcing
for ascent along the boundary lessens with the weakening of the
sub-tropical jet and synoptic ridging building across the
Northern Plains. Therefore, have kept the forecast dry for the day
on Wednesday. Increasing sunshine and a downslope-modified H850
airmass should result in highs reaching the mid to upper 80s.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 340 PM CDT Tue Sep 1 2020
The longer term forecast looks dry through the weekend with
seasonal temperatures giving way to much cooler weather.
The first in a series of strong Canadian cold fronts dives
southeastward during the day on Thursday, but the parent upper
trough rapidly progresses out ahead of the front, resulting in a
dry frontal passage. With an amplified and progressive pattern in
place, the trailing surface high passes east of the area by Friday
morning, with return flow and WAA ensuing by the afternoon. Highs
look to reach the upper 80s to low 90s for the first two days of
the Labor Day weekend with southerly flow well-established. The
medium range ensemble guidance diverges significantly on the
timing of the next cold front late in the holiday weekend, with a
24+ hour spread amongst the various GEFS/EC members. Thus,
confidence in the temperature and precipitation forecast for Labor
Day is quite low.
A fall-like change in temperatures awaits behind this front with
polar air possibly lingering for much of the next week. Raw
temperature guidance has some locations only reaching the 50s and
60s for highs and lows falling into the 40s. We may be flirting
with record low max and min temperature values, which are around
the mid-50s to low 60s for max temps and the upper 30s to low 40s
for min temps.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 625 PM CDT Tue Sep 1 2020
Main concern for the forecast is with visibilities due to mist and
fog, especially after 09Z. Forecast soundings show shallow
saturation with nearly calm winds so have gone with mvfr to ifr
vsbys at this time from 10Z-13Z. High clouds may inhibit vsbys
falling to ifr or lifr, so will continue to monitor this evening.
VFR conditions are expected after 14Z Wednesday.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Skow
LONG TERM...Skow
AVIATION...53