Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/01/20
Area Forecast Discussion
National Weather Service La Crosse WI
1049 PM CDT Fri Jul 31 2020
.SHORT TERM...(This evening through Saturday)
Issued at 240 PM CDT Fri Jul 31 2020
Main forecast concerns are on valley fog tonight with dense fog
likely.
High pressure moves overhead tonight provide mostly clear skies
and light winds through a very deep layer,from the surface through
nearly 25 kft. This will set the stage for radiational fog
development in river valley locations and the marsh/low lying
areas of central Wisconsin. The fog will likely be locally dense
with the visibility reduced to 1/4 mile or less at times,
especially in river valley locations. The only two slight
negatives for fog development tonight are a 28 degree
temperature/dew point spread this afternoon and the possibility of
a few clouds around, but RAP soundings are starting to dry this
cloud layer out with each model run. So, overall the conditions
look favorable for valley fog tonight.
A frontal boundary edges southeast out of the Norther Plains on
Saturday and edges into the region late Saturday afternoon into
Saturday night. This will bring some late afternoon chances for
showers and a few thunderstorms to portions of northeast Iowa,
southeast Minnesota, and possibly northcentral Wisconsin.
.LONG TERM...(Saturday night through Friday)
Issued at 240 PM CDT Fri Jul 31 2020
Chances for showers last overnight Saturday through Sunday as a cold
front moving in from the northwest slowly continues southeastward
through the region. With little shear and weak instability,
thunderstorm development will be limited, but a few isolated storms
are possible. Cooler conditions are expected Sunday with the showers
and associated cloud cover. Afternoon high temperatures are expected
to range from mid 60s into the upper 70s. Small precipitation
chances may linger into Monday across southern Wisconsin.
An upper-level long-wave trough slowly progresses through the region
behind the surface front. The mid to upper level flow becomes more
meridional and amplified as this trough moves off to the east.
Cooler and dryer conditions persist through the first half of the
work week. Afternoon temperatures from the mid 60s to the mid 70s
are anticipated, with low temperatures dipping into the 40s to upper
50s. The upper-level flow becomes more zonal for the later half of
the week. With a possible slight warmup, a few locations may get
into the low 80s by Friday. Short waves passing through this flow
introduce low precipitation chances near the end of the week.
&&
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1034 PM CDT Fri Jul 31 2020
Fog potential is looking less impactful for the TAF sites late
tonight. Latest guidance is not hitting the fog potential as hard
as it was earlier. Current temperature and dewpoint spread at LSE
is looking too substantial to support LIFR visibility later, but
wouldn`t rule out potential for tempo low end IFR visibility given
the very deep layer of light winds above the surface. Should see
any fog at LSE dissipate between 13-14Z. Removed fog from RST as
this looks to be more of a river valley setup.
VFR conditions then expected through the remainder of the period.
Winds will remain calm or light into Saturday, likely with some
northerly component. A cold front slowly dropping in from the
northwest will introduce shower and storm chances at RST by
evening. Storm coverage looks fairly limited, so have only gone
VCTS at RST for now beginning 00Z Sunday. Rain chances look to
hold off at LSE until after this TAF period.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...Wetenkamp
LONG TERM...Peters
AVIATION...Kurz
Area Forecast Discussion...Updated
National Weather Service Billings MT
736 PM MDT Fri Jul 31 2020
.UPDATE...
Update to add slight chance PoPs to Wheatland County and adjacent
areas. A few thunderstorms formed over the Little Belts and have
moved SE into the NW forecast area. Other storms were dissipating
over the Beartooths/Absarokas. Stronger storms were seen near the
Highline associated with a disturbance in the NW flow. Expect
activity over the forecast area to dissipate before 06Z. E flow
in the low-levels will keep thunderstorms confined to the high
terrain Saturday afternoon. Arthur
&&
.DISCUSSION...
Tonight through Saturday...
Thunderstorms associated with a weak wave moving down the east
side of a building ridge have generally pushed east of the area.
There is still some instability and moisture in eastern Montana.
Still cannot rule out some thunderstorms developing through early
evening, however the HRRR has been trending lower on the activity.
In general, given the higher bases of anything that forms, winds
will be the main hazard, but there could be some hail.
Going into Saturday this will start to dry out as the ridge
dominates the weather over the Northern Rockies. There will be
some moisture under the ridge, so could see some isolated showers
and thunderstorms develop during the afternoon, but this will
mostly be over the high country. High temperatures will be in the
upper 80s to lower 90s again. Reimer
Sunday through Friday...
Mainly dry conditions can be expected over the area through
Monday, with a few showers or thunderstorms possible over the
higher terrain each afternoon/evening. Ridging will be centered
just west of the area, before shifting overhead on Monday.
On Tuesday, a trough sliding east across the US/Canada border
will flatten the ridge, while sending a front across the area.
This will bring chances for showers and thunderstorms, highest
across the far east. Some of the storms could be strong to severe
near the Dakotas border with good instability and moisture in
place. Cyclonic flow over the area on Wednesday will lead to
additional shower and thunderstorm chances, along with cooler
temperatures. Ridging builds back over the area Thursday and
Friday bringing mainly dry conditions and warmer temperatures.
Highs will range from the 80s to 90s Sunday through Monday,
cooling into the 80s most places Tuesday and Wednesday. Mainly 90s
are forecast for Thursday and Friday. STP/RMS
&&
.AVIATION...
VFR will prevail tonight through Saturday. There will be a few
evening thunderstorms that could produce gusty winds, small hail
and MVFR to IFR conditions, as well as localized mountain
obscurations. Additional thunderstorms will occur over the high
terrain Sat. afternoon. Expect gusty E surface winds through the
period. Arthur
&&
.PRELIMINARY POINT TEMP/POPS...
Sat Sun Mon Tue Wed Thu Fri
-----------------------------------------------------------
BIL 064/091 063/092 062/094 064/088 060/086 060/091 061/093
10/U 10/U 01/U 23/T 32/T 11/U 11/U
LVM 057/090 056/093 057/094 056/088 051/087 052/091 054/092
11/U 11/U 13/T 43/T 32/T 11/U 11/U
HDN 062/092 061/092 060/095 063/089 059/087 058/092 060/095
21/U 10/U 01/U 22/T 32/T 11/U 01/U
MLS 062/086 059/086 060/089 063/089 061/086 060/090 061/092
21/U 00/U 00/U 13/T 43/T 21/U 11/U
4BQ 060/086 057/085 058/089 061/091 060/086 060/090 060/092
21/U 10/U 00/U 13/T 43/T 21/U 11/U
BHK 057/081 053/081 053/083 056/086 056/085 057/089 057/090
21/U 00/U 00/U 12/T 53/T 21/U 11/U
SHR 058/090 057/090 058/093 059/090 056/087 056/091 057/093
22/T 22/T 12/T 23/T 43/T 22/T 11/U
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.
&&
$$
weather.gov/billings
Area Forecast Discussion
National Weather Service Corpus Christi TX
604 PM CDT Fri Jul 31 2020
.DISCUSSION...
Updated for 00Z Aviation Discussion.
&&
.AVIATION...
VFR conditions should continue through most of tonight, with MVFR
ceilings building in across the coastal area late tonight. Rain
chances will continue to increase through Saturday, especially
across the Victoria Crossroads where we have a mention of VCTS and
maintain MVFR ceilings. Confidence is low in regards to rain
chances for other sites, so have elected to continue to leave this
out of the TAFs. Brief MVFR ceilings will be possible for all
sites in and around sunrise. Patchy fog could reduce visibility
for ALI as well as VCT as dawn approaches. Conditions should
improve through Saturday afternoon, with MVFR conditions possible
should any showers or thunderstorms occur at any TAF site.
&&
.PREV DISCUSSION... /Issued 402 PM CDT Fri Jul 31 2020/
SHORT TERM (Tonight through Saturday Night)...
Frontal boundary is pushing through central/eastern portions of
Texas this afternoon with showers and thunderstorms developing
along the boundary. Question is when will the activity arrive.
Hi-res models disagree with timing by a few hours, but can
overall, expect activity to move across portions of South Texas,
mainly for areas across the northern Coastal Bend and Victoria
Crossroads. Models wash the frontal boundary out just north of the
region, but some redevelopment of activity along the boundary is
expected later tonight, which is then expected to slowly move
south through early Saturday morning. HRRR keeps most of the
activity just east of the CWA while the Texas Tech WRF enters much
of the eastern zones of the CWA. Decent CAPE values and weak
diffluent flow aloft exist for a few strong storms, but capping
over the region may inhibit strength of storm development.
Lingering moisture and daytime heating will continue at least
slight to low-chance POPs through the rest of Saturday, especially
along any lingering boundary, with activity to diminish in the
evening with the loss of heating.
Otherwise, warm and humid conditions will continue. Another SPS
for heat index values of 105 to 109 will be possible for Saturday.
LONG TERM (Sunday through Friday)...
Not much of a change from the previous extended forecast package.
Slight rain chances will continue to exist on Sunday mainly across
the Victoria Crossroads region due to lingering energy in
association to a long wave trough extending from the Great Lakes
into South Texas. However, by Sunday night/Monday period the
rainfall potential will decrease as the trough slowly transitions
eastward and high pressure builds in from behind over the
southwestern U.S. and northern Mexico. High pressure will then
remain in control aloft through most of the week keeping the rain
out of the forecast with limited moisture available at the lower
levels. Rain chances return to the forecast towards the end of the
week and into next weekend as the high pressure shifts eastward and
deeper moisture slides back in.
Warm/hot conditions will continue into the long-term period with
highs generally in the 90s to lower 100s, and lows is the upper 70s
to lower 80s. High humidity in place will lead to afternoon heat
indices in the 105-109 range daily and likely requiring the issuance
of SPSs.
MARINE...
Surface high pressure east of the area will maintain a mainly
southerly flow through most of the period at light to moderate
levels. Isolated showers and thunderstorms will be possible over the
weekend.
&&
.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi 95 76 94 75 95 / 10 20 30 10 10
Victoria 96 76 94 75 96 / 20 30 40 20 20
Laredo 100 78 99 77 102 / 10 10 20 10 10
Alice 97 75 95 75 98 / 10 20 20 10 10
Rockport 92 79 91 79 92 / 20 20 30 20 10
Cotulla 101 78 100 76 103 / 10 20 30 10 10
Kingsville 96 76 95 75 97 / 10 20 20 10 10
Navy Corpus 93 79 90 79 90 / 10 20 20 10 10
&&
.CRP WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&
$$
LS/77...AVIATION
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
945 PM CDT Fri Jul 31 2020
.UPDATE...
Tonight has turned into storm cluster city driven by outflows of the
various storms. The "front" is still located across the Edwards
Plateau and Hill Country with dewpoints in the 50s to the north of it
and 70s to the south. Most of the storms formed along the front
initially but there driven by the convective outflows. Besides being
prolific lightning producers we have gotten numerous reports of 1 to
2.5 inches of much needed rainfall, a few isolated reports of minor
wind damage that likely was associated with a few downbursts observed
on radar potentially producing 40-55 mph winds, and some pea sized
hail reports. Storms continue at this hour across the Rio Grande
Plains with numerous Significant Weather Advisories and a large Flood
Advisory in place. Remember to both Turn Around, Don`t Drown and
When Thunder Roars, Go Indoors tonight.
It is important to note going forward that models struggled with how
this evening would ultimately play out. The NSSL WRF seems to have
handled it the best, with a few other models also suggesting the
storms would start in Austin but end up along and west of Rocksprings
to Hondo. Based on this struggle the forecast for the rest of the
night and tomorrow remains at low to moderate confidence. That said,
there is a general consensus on the rest of tonight and tomorrow
among the high resolution models so that is encouraging.
The storms will continue to play out across the West tonight into the
early morning hours, shifting more towards Del Rio and south towards
Cotulla. Models do show a decent signal that as the front tries to
sag southward there may be additional development by Saturday morning
in the Bastrop/Lee/Fayette/Lavaca County areas. Have kept PoPs in the
20 to 30 percent range to cover this. For tomorrow proper models are
mostly dry in the morning with isolated activity being sparked off by
the front in the afternoon and evening. Coverage appears to be a lot
less than today, but with the moist atmosphere and warm temperatures
still to the south of the front a bit skeptical about the lack of
convection. Also the progress of the front will play a huge role in
where any precipitation falls on Saturday. If it hangs up tonight
across the north then rain chances could include the Austin area on
Saturday, if it moves further south this will limit the extent of
precipitation. For now think mainly along and south of I-10 will be
the focus for Saturday.
Have left the forecast beyond 6pm Saturday unchanged.
&&
.PREV DISCUSSION... /ISSUED 633 PM CDT Fri Jul 31 2020/
AVIATION...
Line of storms have cleared AUS, there still is the possibility of
redevelopment close to AUS over the next hour or so, kept VCTS in for
this reason. Line of storms and gust front is getting ready to move
through the San Antonio sites with wind speeds near 20 knots and
possible gusts up to 40 knots. VCTS in for SAT and SSF through
midnight with the possibility of this boundary washing out close to
I-10 and US 90 and keeping cold pool dominated activity persisting
late tonight. DRT also has VCTS in for the next couple of hours with
convection expected to push south of the terminal by 03Z. A bit of
uncertainty regarding redevelopment tomorrow, having to do with
where residual convective boundaries are left tonight.
PREV DISCUSSION... /ISSUED 425 PM CDT Fri Jul 31 2020/
UPDATE...
Did a quick update to up PoPs over our southwestern zones. Seeing
some moisture convergence along a line from Eagle Pass to Devine,
this coupled with daytime heating has led to some development over
the last hour or so. Overall storm motion with this activity is
fairly slow but rainfall rates have been generally 1-2 inches per
hour. Also retrended temps given the rain and cloud cover now
covering the northern portion on the CWA. This line of storms is
expected to slowly make it`s way southward this evening.
PREV DISCUSSION... /ISSUED 258 PM CDT Fri Jul 31 2020/
SHORT TERM (Tonight through Saturday Night)...
A tricky short term forecast for today and tomorrow. An upper level
trough axis extending from the Midwest into South Central Texas has
generated a weak late July front that is expected to make it`s way
across the region tonight. The placement of the front is difficult
to differentiate from the residual convective boundary left over
from yesterday`s thunderstorm activity that occurred well north of
the CWA. Current thinking is the initial boundary that will move
through is the convective boundary from yesterday and a second push
will pass through late tonight being the actual front. This residual
convective boundary is currently infringing upon our northern tier
of counties and has generated a line of cells over Williamson County
as of 2:00pm.
Given sufficient heating this afternoon, moderate instability is in
place with 2000-2500 J/kg CAPE and steep low level lapse rates of
about 7 c/km. Surface dewpoints will be in the low 70s across much
of the region. So while there is sufficient instability and
moisture, the limiting factor will be a forcing mechanism. Namely,
enough surface convergence along the boundary as it pushes through.
Convective allowing models have a number of solutions on handling
convection over the next 24 hours but there seems to be two general
solutions. The first being, enough storms can get going this
afternoon and evening to become cold-pool dominated and sustain
themselves further into the overnight period. WRF, ARW, and NMM all
depict something similar to this solution. While the NAM Nest and
HRRR have isolated to scattered storms this afternoon into this
evening but dwindling with the loss of daytime heating.
Interestingly enough, the NAM Nest does have storms re-firing early
tomorrow morning, perhaps along the second push of the actual front.
SPC does have much of South Central Texas under a marginal risk for
severe storms with the main threats being strong winds and hail. A
weak late July front with a convective boundary ahead of it along
with NW flow aloft will make the next 24 hours a bit tricky to
forecast. Convective allowing models should converge on a solution
once storms, and to what extent, get going this afternoon and
evening.
What takes place tomorrow will heavily depend on how things go this
evening. Any residual boundary left over from tonights activity
could be a focus for initiation tomorrow with daytime heating. Highs
for Saturday afternoon will be in the mid to upper 90s for most
locations with areas along the Rio Grande approaching or exceeding
100 degrees.
LONG TERM (Sunday through Friday)...
A similar type of upper level pattern will still be around on Sunday
into early next week with upper ridging out west and troughing to
the NE. This will continue to give us good NW flow aloft. The
question is how much moisture will still be around and will any
smaller disturbances or remnant boundaries help to trigger
convection. Some models are pointing toward more development on
Sunday afternoon and have thus kept mention of chance pops during
that time. The wind will be fairly light Sunday and Monday which will
enhance the hot and humid weather. Monday will still see some
lingering pop mainly over the Hill Country, but any sort of
significant QPF will be absent. Looks like a pattern that will set up
some isolated to widely scattered convection for a few lucky folks.
By mid and late week, the upper ridge shifts east and puts a better
hold on Texas and should keep most convection at bay. That far out,
can`t rule out some isolated storms especially seabreeze related
over the far SE, but confidence is not high enough right now for any
pop of significance. Temps will remain very warm...near 100 degrees
most days as he head into the beginning of August...historically our
warmest time of the year for South Central Texas.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 75 97 75 99 75 / 20 10 - 20 -
Austin Bergstrom Intl Airport 74 96 74 98 74 / 30 10 - 20 -
New Braunfels Muni Airport 75 97 74 98 74 / 30 20 - 20 -
Burnet Muni Airport 73 96 72 98 73 / 10 - - 10 -
Del Rio Intl Airport 79 101 77 104 79 / 40 20 10 20 -
Georgetown Muni Airport 74 96 73 100 74 / 10 - - 10 -
Hondo Muni Airport 76 98 75 102 75 / 50 20 10 20 -
San Marcos Muni Airport 75 96 74 98 74 / 30 10 - 20 -
La Grange - Fayette Regional 77 95 76 99 76 / 30 20 10 20 -
San Antonio Intl Airport 76 97 77 100 76 / 30 20 10 30 10
Stinson Muni Airport 77 97 77 99 76 / 30 20 10 20 -
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Short-Term/Aviation...Treadway
Long-Term...17
Warnings...04
Area Forecast Discussion
National Weather Service Lake Charles LA
929 PM CDT Fri Jul 31 2020
.DISCUSSION...
Wx map shows cool front moving through North Texas across the
ArkLaTex. Ahead of the front was a line of strong TSRA, with a
couple of severe thunderstorms across Central Louisiana, mainly
for radar indicated winds above 50 kts. What`s left of the outflow
boundary is across lower Acadiana. Radar showing additional
showers and thunderstorms developing across Southeast Texas.
For the forecast, updated evening temperature/dewpoint grids to
reflect the cool pool of air behind the thunderstorms, likely to
moderate a couple of degrees upward to the mid 70s just before
daybreak. Latest HRRR keeps at least scattered showers and
thunderstorms over the area as the front continues to approach
couples with available moisture and upper level lift. Thus, will
keep the chances in overnight.
DML
&&
.PREV DISCUSSION... /issued 642 PM CDT Fri Jul 31 2020/
AVIATION...A line of storms is currently working southeast across
the area with lower vis and gusty winds. While these storms should
exit the area later this evening, additional showers can be
expected through most of the period. This will cause spotty lower
flight categories. Winds outside of the storms will be southwest
and become west to northwest tonight then back more southerly
tomorrow.
PREV DISCUSSION... /issued 351 PM CDT Fri Jul 31 2020/
DISCUSSION...
A short wave is moving out of the Plains and int the Mid-
Mississippi Valley with the trough axis trailing down into central
Texas. This system will continue to move off to the east, and
bring a surface trough, basically a weak "cool" front/dryline
feature into the forecast area this evening, then stalling near
the coast on Saturday.
Already seeing a good deal of showers and thunderstorms north of
the forecast area with this feature, and the activity will
gradually work its way to the southeast during the evening and
overnight.
A few strong thunderstorms will be possible for the remainder of
the afternoon into early evening while instability is still
adequate, with the main hazards being occasional cloud to ground
lightning and strong gusty winds. Shower activity should continue
through the night, however intensity should decrease.
The trough axis at the surface will stall out on Saturday, keeping
decent chances of showers and thunderstorms in the forecast,
before the surface feature begins to wash-out by Sunday.
Some lower pops can be expected on Sunday into early next week as
the forecast area is on the west side of the trough, with a dry
northwest flow in the mid levels. Some of this dry air may mix
down during the daytime, allowing for slightly lower dewpoints and
a little less humid conditions.
Surface moisture begins to increase by the middle part of the
week, along with the forecast area still being in a little bit of
weakness as the upper level ridge will be center over the
southwest US. So expect pops to increase to seasonal norms during
that time frame.
Rua
MARINE...
A modest southwest flow will continue tonight ahead of a surface
trough that will near the coastal waters, with winds becoming more
westerly over the weekend, as the trough stalls and dissipates
north of the coast. This trough will briefly increase showers and
thunderstorms for late tonight into Saturday.
Early next week, weak high pressure will be situated over the
northern Gulf with mainly light and variable winds and low seas.
Rua
&&
.PRELIMINARY POINT TEMPS/POPS...
AEX 72 90 71 93 / 50 20 10 20
LCH 76 89 75 91 / 50 30 10 30
LFT 76 89 74 91 / 40 40 10 30
BPT 76 90 76 92 / 50 30 10 30
&&
.LCH WATCHES/WARNINGS/ADVISORIES...
LA...None.
TX...None.
GM...None.
&&
$$
PUBLIC...08
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
627 PM CDT Fri Jul 31 2020
.SHORT TERM...
308 PM CDT
Through Saturday night...
The forecast messages in the short term are 1.) a continued risk
of rip currents into early-mid evening, especially Chicago and
points south and east, 2.) the chance for a few spotty showers
through early evening in mainly north central Illinois and
through tonight south of the Kankakee River Valley, and 3.) a
chance for showers Saturday especially into Saturday night over
northwest Indiana.
Satellite imagery throughout today has shown the upper low over
Missouri being extremely sluggish to move. This has helped provide
a canopy of higher clouds with filtered sun as well as low-level
northeasterly flow. There has been a dry wedge between the high
clouds and the low-level cumulus. Upper level diffluence aloft
has resulted in just enough moisture creeping into the far
southwestern CWA for a couple showers. Further north, there is a
low-level convergent axis in the winds from southern Kane County
southwestward through northwest LaSalle County. There have been a
couple very small footprint showers, which have not been
noteworthy for rain (almost non-existent) and more so their brief
funnels near Sublette and Mendota. This axis has 50-100 J/kg of
low-level CAPE along it and wind streamlines indicate the
boundary is oriented with some surface vorticity along it. This
should not result in anything more than sporadic funnels through
early afternoon and have issued a graphical NOWcast for this.
The low-level northeast winds are not what they were last night
but with continued swell on Lake Michigan as seen in wave period
observations, the wave heights will remain around 4 ft into early
this evening. That`s the threshold with a direction perpendicular
to the shoreline to support rip currents. With the wind direction
bending a little more northerly the highest waves will especially
be seen in Cook County and into northwest Indiana.
As the Missouri upper low shifts to near St. Louis by Saturday
morning and then to southern Indiana by Saturday evening, it will
result in slight height falls over the area as the wave itself
becomes somewhat stretched (although more neutrally tilted from
positive). As this occurs, the aforementioned dry mid-level wedge
over the forecast area today will narrow especially in the
southern and eastern forecast area (along and east of I-55).
Models vary considerably on just how far north and west this dry
wedge is eroded, with the ECMWF being consistently less impinging
with moisture and rain compared to the RAP and more so GFS. The
NAM seems to be a reasonable compromise, in line with several
convection allowing models. Have rain shower chances creeping up
to the northwest to near I-55 through the mid to late afternoon
and more so the evening as the system strengthens some and PVA
spreads over mainly northwest Indiana. Feel that PoPs could end up
needing to be higher for the far southeast CWA (Benton & Jasper
County area) where even locally heavy rainfall in excess of one
inch is quite possible if a northwestern-most solution pans out.
Otherwise during the day Saturday clouds should prevail enough
in the southern forecast area to keep temperatures cooler with
highs potentially only staying in the mid 70s. Also further
northwest across mainly north central Illinois, it should be
noted there is a non-zero chance for isolated showers, There could
even result a convergent axis in the form of a subtle inverted
trough that extends from the low north-northwest into the
southern CWA toward I-39. This could provide another convergent
axis and possibly similar behavior to this afternoon with a few
funnels. It`s always difficult to get much predictability with
such a setup, however.
MTF
&&
.LONG TERM...
340 PM CDT
Sunday through Friday...
Sunday will be the transition day from a near seasonable into a
decidedly cooler than average pattern, certainly the coolest
weather we`ve had since mid June. Main concerns/items of note
include: potential for showers and a few isolated thunderstorms
Sunday afternoon through Monday afternoon; a long duration of
brisk northerly winds late Sunday night through Tuesday night that
will cause dangerous conditions on the lake and possibly minor
lakeshore flooding; and temperature trends Monday-Wednesday.
On Sunday morning, focus for any precip. would appear to be any
lingering light rain/showers east of I-57 from a mid-level short-
wave trough and the vigorous surface low over the eastern Great
Lakes. Confidence remains lower than average on the exact
evolution Sunday afternoon and evening. There should be some
subsidence on the backside of the Sunday morning wave. A weak
inverted surface trough extending back west over our area will
very gradually slide south as a cold front advances south.
Meanwhile, lead short-wave from long-wave trough axis extending
from upper level low pressure over northeastern Canada will be
swinging east across the MS River. With the gap in forcing until
toward evening, shower coverage well could be mostly isolated
until later, with best focus over northwest/north central
Illinois. Weak mid-level lapse rates and meager instability
continue to suggest that any thunderstorms will be widely
isolated.
As the front gradually pushes south Sunday evening and night and
the lead short-wave continues to dumbbell east, we could see an
increase in low and mid-level convergence and possibly some at
least transient frontogenesis. Thus, shower coverage may be on the
increase (possibly higher than in official PoPs) despite
diurnally unfavorable timing due to large scale and mesoscale
support. Additional short-waves wrapping around the long wave
trough axis could keep this general showery regime going into
Monday, so Monday is starting to appear it could be a rather
inclement day, especially along/south of I-90, as dry air
impinging from the north could yield a sharp cut-off in precip
during the afternoon. Somewhere between Chicago shore and the
Kankakee River Valley could have healthy rainfall totals owing to
the convergence and f-gen contribution, again despite lacking
instability likely yielding at most isolated embedded t-storms.
Warm-rain processes may allow for periods of efficient rainfall
and pockets of rain totals greater than an inch.
With the clouds and showery weather and gradual cool advection on
Monday, high temps may struggle to reach the mid 70s. Behind the
cold front on Monday and Tuesday, breezy northeast to northerly
winds are expected which will set the stage for another round of
dangerous swimming conditions along the entire Illinois and
northern Indiana Lake Michigan shoreline. With ECMWF ensemble mean
wind speeds over southern Lake Michigan from Monday PM into early
Tuesday around 20-25 mph and gusts >30 mph, wave heights of 5 to
8 feet are a decent bet with potential for even larger peak
heights. Parks and trails along the lakeshore may also experience
minor flooding as well, considering baseline Lake Michigan water
levels remain at a historic high.
With 850 mb temperatures dropping into the +7-9 C range behind
the front, high temperatures Tuesday should top out in the lower
to mid 70s with lows Tuesday and Wednesday morning outside of
Chicago likely dropping into the low to mid 50s, with even a few
upper 40s possible in sheltered cool spots Tuesday night. Even
while accounting for upwelling to cool Lake Michgian surface
temperatures, 850mb to lake surface delta Ts may become favorable
for pockets of lake effect cloud cover and even a few sprinkles
from time to time, especially on Tuesday. Medium-long range
guidance consensus supports a trend toward more seasonable and
drier conditions midweek and onward as the upper-level trough
moves eastward. May have to watch for a quicker breakdown of the
pattern to close out the work week, though GFS may be a fast
outlier.
Castro/Borchardt
&&
.AVIATION...
For the 00Z TAFs...
Aviation forecast concerns:
* Gradually decreasing northeast winds (may shift NNW overnight
with weak land breeze).
* Chance of a shower Saturday afternoon/evening, though better
potential south/southeast of terminals.
Surface low pressure remains in the vicinity of the lower Ohio
Valley early this evening, in response to a series of mid-level
disturbances drifting across the region. With weak high pressure
farther north, this continues to produce northeast winds across
the terminals, though with a gradual decrease in winds as the
gradient slowly weakens. ORD/MDW may see winds shift slightly NNW
later tonight as a weak land breeze develops as the flow weakens.
Winds should turn northeast again after sunrise Saturday morning,
as the low slowly lifts northeast through the Ohio Valley. Winds
will likely back more north-northwest later Saturday evening as
the low pulls away.
In the near term, low levels are fairly dry with more substantial
cloud cover mainly limited to high levels tonight. As upper trough
traverses the area Saturday, VFR mid-level ceilings are likely,
with showers spreading from central IL into northern IN. Model
guidance varies on how far the north/northwest edge of this
precipitation will get in relation to our Chicago TAF sites,
though it may be close. Have added a VCSH mention for KGYY for
Saturday afternoon, as Gary will be more at risk than locations
farther north and northwest. Will have to monitor further model
trends for the possible need to expand shra mention into the
ORD/MDW areas Saturday afternoon/evening.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement...ILZ006-ILZ103-ILZ104 until 7 PM Friday.
IN...Beach Hazards Statement...INZ001-INZ002 until 10 PM Friday.
LM...None.
&&
$$
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Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
944 PM CDT Fri Jul 31 2020
.UPDATE...
Issued at 755 PM CDT Fri Jul 31 2020
The surface and upper-level patterns continue to emulate those of
a March pattern rather than late July. A broad mid-level trough
continues to progress slowly eastward, with two main vorticity
maxima pivoting around the low. The more southern disturbance has
better access to moisture, and will stir more showers through
tonight across southeastern Missouri and southern Illinois. The
Flash Flood Watch remains in effect through midnight in this area
given the potential for localized heavy rainfall. While the
bullseye of higher PWATs is following the surface low out of the
CWA, considerable moisture still exists around the STL
metropolitan area. Weak frontogenetic bands in the lower levels
will continue to interact with this moisture tonight, keeping
pesky showers in east-central Missouri.
The second vorticity lobe over north-central Missouri appears
primed to interact with the low-level moisture on its way around
the mid-level low overnight. Given the efficient rainfall rates
from this system so far, locally heavy rainfall is still a concern
along and east of the Mississippi River. Instability and CAPE
values continue to be unimpressive, which should keep thunderstorm
activity nearly non-existent. Through the day tomorrow, rain will
taper off from west to east. Though there is some uncertainty as
to the speed of the system, by the early evening most of the area
should be dry.
MRB
&&
.SHORT TERM... (Through Late Saturday Night)
Issued at 306 PM CDT Fri Jul 31 2020
The upper level low currently centered over Missouri will move
slowly eastward tonight. There seems to be two lobes of vorticity
within the low based on satellite pics, that are pivoting around
each other. The interaction of these two vortmaxes is producing two
distinct areas of heavy rain, one over east central Missouri and
another over south central and southeast Missouri. The latest WV
satellite pics are hinting that the northern vortmax which is
between Moberly and Mexico Missouri might be moving back to the
northwest slightly which could lead to a weakening trend in the rain
headed into the St. Louis Metro Area. At any rate, short range
guidance has not handled this situation very well. The RAP has been
doing the best, so have followed its precip trends closely. To that
end, the RAP continues to show moderate to strong low level moisture
convergence over the area through the evening, mainly over east
central and southeast Missouri into southwest Illinois. Have
therefore extended the flash flood watch both in area and in time to
cover the STL Metro area and points south until midnight.
The focus for precip eventually shifts southeast overnight as the
flow turns to the north behind the 850mb low, pulling drier air into
the area. Scattered showers continue to be possible across parts of
southeast Missouri and south central Illinois though as the upper
level trof axis shifts east. Clouds and showers will keep
temperatures suppressed in the 70s across most of the area. Another
short wave will be diving into the trough on Saturday night which
could bring more showers to parts of central and northeast Missouri
late Saturday night.
Carney
.LONG TERM... (Sunday through Next Friday)
Issued at 306 PM CDT Fri Jul 31 2020
Little change in the forecast for Sunday through next Friday. The
upper level pattern becomes highly amplified as the low over
Missouri phases with another strong short wave trough moving through
central Canada. This carves out a long wave trough that extends all
the way from northern Quebec through through the Mississippi Valley
into eastern Texas. Medium range models have been showing this for
several days with good agreement ensemble model from the GEFS, EPS,
and NAEFS. Blocking ridges to the west and east of the trough will
ensure that this pattern will be slow to shift east. This trough
through the middle of the country will keep considerable cloudiness,
occasional showers, and cool temperatures in the forecast until at
least Wednesday when the trough begins to weaken a bit and slide
eastward allowing a large surface high to slide into the Great Lakes
and Midwest. The below normal temperatures will likely linger
through Thursday even with the trough moving out since northwest
flow will persist. GFS and ECMWF are hinting that there could be a
warm up back to around seasonal normals on Friday ahead of a fast-
moving short wave that shifts the low level flow over the lower
Missouri and mid Mississippi Valley back to the south and southwest.
However, that`s a long way off and there are timing/strength
differences between the ECMWF and GFS that far out.
Carney
&&
.AVIATION... (For the 00z TAFs through 00z Saturday Evening)
Issued at 624 PM CDT Fri Jul 31 2020
A broad area of low pressure is moving ever-so-slowly through
southeastern MO and southern IL. Lower CIGs north of the system
will keep the STL metropolitan terminals in MVFR for a majority of
the period. Scattered showers continue to impact those sites,
with slightly reduced visibility in these pockets of rain. Any
visibility restrictions will not be long-lived. By Saturday
afternoon, CIGs should improve to low-end VFR as the system exits
the area. COU and UIN are too far removed from the system and
should remain VFR through the period.
MRB
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flash Flood Watch until midnight CDT tonight for Crawford MO-
Franklin MO-Iron MO-Jefferson MO-Lincoln MO-Madison MO-
Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis
City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO-
Washington MO.
IL...Flash Flood Watch until midnight CDT tonight for Calhoun IL-
Jersey IL-Madison IL-Monroe IL-Randolph IL-Saint Clair IL.
&&
$$
WFO LSX
Area Forecast Discussion
National Weather Service Pueblo CO
808 PM MDT Fri Jul 31 2020
.UPDATE...
Issued at 808 PM MDT Fri Jul 31 2020
Updated pops across the plains based on radar trends.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 307 PM MDT Fri Jul 31 2020
Afternoon convection a little slow to develop over the mountains
today, though storms have started to become slightly more numerous
as of 21z. Main question is how far east will activity spread this
evening, as steering flow remains fairly N-S. Meso-analysis suggests
fairly deep instability across Pueblo County and the east slopes of
the Wet Mts this afternoon, with diffuse surface boundary roughly
along the Arkansas River. Many CAMs, including several runs of the
HRRR point to this area as having an enhanced potential for storms
this evening, as mt convection interacts with deeper instability.
Will nudge up pops accordingly, and wouldn`t be surprised to see a
strong storm or two moving quickly south, similar to last night.
Lower risk for storms in the Colorado Springs area, as low level
winds have shifted to nly behind the boundary, which will limit
surface convergence. Over the mts/valleys, sct storms continue into
the evening, before activity ends almost all areas after sunset.
On Saturday, strong N-S steering flow again in place over the
region, with CAPE around 1000 j/kg along the I-25 corridor and 0-6km
shear of 35-40 kts by late afternoon. Expect another round of
afternoon convection over the mountains/valleys, with potential for
some stronger storms eastern mts/I-25 corridor where instability is
greatest. Farther east, chances for convection on the plains look
low, as storms generated over the mts will tend to move nearly due
south. SWODY1 has much of the eastern half of the area in a marginal
risk, which looks ok for the mts/I-25, but may be overdone farther
east on the plains. Max temps will begin to creep upward slightly as
swrn upper ridge begins to expand slowly northward.
.LONG TERM...(Saturday night through Friday)
Issued at 307 PM MDT Fri Jul 31 2020
Saturday night through Monday...An upper ridge of high pressure will
be located over the desert sw and Great Basin through Monday, with
the ridge axis roughly along the UT and CO state line. A cold front
is forecast to drop south into eastern CO Sat evening, increasing
llvl moisture across the eastern plains through the night and
persisting through Sun and even Mon. SPC has covered all of the
eastern plains with a Marginal risk for severe storms on Sat and
again on Sun, since there will be abundant storm fuel and shear.
Once storms do develop Sat along and behind the cold front, strong
to severe storms will be possible which could linger into the late
evening. The lower atmosphere will be primed for another round Sun
aftn and eve, and considering the overall pattern, mon aftn and eve
may be a repeat before the upper pattern shifts. Expect overnight
low temps to be rather mild, with readings in the mid 40s to mid 50s
for the high valleys, and around 60F for the plains. Max temps for
Sun and Mon are expected to climb into the 80s for most areas.
Tuesday through Friday...A couple of upper low pressure systems are
forecast to track across the Pacific NW and West Coast through the
remainder of the work week, flattening the ridge overhead and
shunting it to the east. This repositioning of the ridge will push
the dryline a bit further east into Kansas, it will open the Four
Corners tap once again for moisture to push in from the southwest,
and the flow aloft will become more westerly which means slightly
warmer aftn high temps. There will be a daily chance of aftn and eve
thunderstorms, mainly tied to the higher terrain with some spill
over across the I-25 corridor. However, storm coverage will likely
not be as enhanced as it will be on Sun and Mon, with just isolated
to scattered POPs forecast. As for temps, look for highs in the
upper 70s to mid 80s for the high valleys, and mid 80s to lower 90s
for the plains. Moore
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 307 PM MDT Fri Jul 31 2020
VFR at all taf sites the next 24 hrs, with scattered thunderstorms
late this afternoon and evening, and again Saturday
afternoon/evening. Best chance for vcts into this evening will be at
KALS, where gusty/erratic outflow winds are likely from 21z-01z.
Vcts also possible around KPUB this evening, with a pool of fairly
unstable air developing near/just east of the Wet Mts, and will
include a mention until 03z-05z. Lowest chance of a vcts at KCOS,
and won`t include at this point, as most storms stay to the south of
the airport. Convective activity wanes 03z-05z, with weak diurnal
downslope/downvalley winds all sites by early Saturday morning.
Repeat performance of convection Saturday afternoon, with storms
moving south through the San Luis Valley and I-25 corridor late in
the day.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...MW
SHORT TERM...PETERSEN
LONG TERM...MOORE
AVIATION...PETERSEN
Area Forecast Discussion
National Weather Service Blacksburg VA
727 PM EDT Fri Jul 31 2020
.SYNOPSIS...
A weak frontal boundary will remain stalled across southern
Virginia tonight then push north through the Mid Atlantic region
on Saturday. Hurricane Isaias is projected to track north near
the east coast from Florida to the Mid-Atlantic through the
weekend and into early next week. The weather across our region
will remain warm and humid with scattered to numerous showers
and thunderstorms into early next week.
&&
.NEAR TERM /THROUGH SATURDAY/...
As of 720 PM EDT Friday...
Keeping showers/few storms across the piedmont and mountains
this evening. Namely looking at more organized convection
associated with better upper support across eastern KY/TN moving
along the TN Valley, and should reach our Mountain Empire of SW
Virginia into the NC mountains and southern WV between 8-9pm.
Some weakening is expected, but expect some heavier downpours
and frequent lightning. Overall should see activity weaken into
the late evening.
Previous discussion from early this afternoon...
Water vapor loops show short wave over central and eastern Kentucky
late this morning. Expect this feature to combine with the low level
convergence along the surface boundary to trigger scattered to
numerous thunderstorms this afternoon and evening. RAP Near Storm
Analysis showed best instability and shear southeast of a Buckingham
to Wilkesboro line.
500MB trough over the Ohio Valley and ridging over the western
Atlantic will amplify tonight and Saturday, leaving the region in SW
flow and pushing the surface boundary to the north. So area will be
well into the warm sector, heat, humidity and instability on
Saturday.
Models bring 850MB temperatures back into the +18 to +20 range on
Saturday. Barring any substantial morning clouds and outside of
afternoon thunderstorms, heading for another day of afternoon highs
in the lower 80s to lower 90s, which is near normal. Due to the very
high surface dew points, overnight lows will remain mild, roughly 5
to 10 degrees above normal.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 115 PM EDT Friday...
The main item of focus during this portion of the forecast period
will be what, if any, impacts Hurricane Isaias will have on our
region of the country.
Two weather features may interact during this part of the forecast.
First, a broad upper trough is expected to extend south from Ontario
Canada into the Lower Mississippi River Valley. Within this broader
flow, a shortwave trough is expected to be heading east through the
Great Lakes Region. Hurricane Isaias is expected to be heading north
along the East Coast of the U.S. Please review the latest official
forecast from the National Hurricane Center for details. Confidence
is increasing that northward advecting deep moisture associated with
this tropical system may interact with the advancing shortwave
trough as a Predecessor Rain Event (PRE) over at least some portion
of the forecast area. Specific location and timing vary from model
to model, but the potential pattern of a PRE appears on the latest
operational runs of the GFS, European, Canadian, and NAM guidance.
If this comes to fruition, a swath of very heavy rain, potentially a
fairly narrow one, thus the challenges of timing and location, may
manifest itself over a part of the region as early as Sunday
afternoon, and linger until around sometime Monday afternoon, night
or the day Tuesday. Again, we see the challenge of the timing of
this feature.
Once the stalling influence of Isaias has ended with its departure
northeast, this will allow the broad and shortwave trough to our
west to start working their way eastward. This process will help
maintain precipitation in the forecast, but without the effects of
any PRE that develops in advance of it.
Temperatures during this portion of the forecast will average near
normal for high temperatures and about five degrees above normal for
low temperatures.
Confidence in the above weather scenario is moderate. The biggest
question is whether or not the PRE will develop - if yes, then when
and where.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 100 PM EDT Friday...
Our typical late summertime pattern continues with tropical
ingredients sprinkled on in. Ample tropical moisture, a deep upper
level trough, an incoming front, and a tropical system slowly
working along the coast mean more unsettled conditions through most
of the extended period.
A strengthening Bermuda high will continue to hold steady off the
southeast Atlantic coast keeping healthy southerly flow firmly
entrenched across the area for daily afternoon and evening storm
chances to continue. This high will act as a steering mechanism with
to where Hurricane Isaias will go. As of now the track is
through eastern North Carolina and the Outer Banks Monday into
Tuesday with a departure through the Delmarva and Jersey Shore
Tuesday afternoon. It is still way too early though to pin down
an exact location or time on the system, and the impacts for our
local area, especially with the acting features mentioned
above. For more information on Isaias you can go to the National
Hurricane Center`s website at hurricanes.gov.
What we do know is that we are likely to see widespread moderate to
heavy rain chances through at least Wednesday when our expected
front looks to pull on through. The front on most models looks to
arrive Wednesday into Thursday. The GFS holds the front in place
longer which means higher chances for showers and storms continuing
through Friday despite high pressure over the mid Great Lakes. The
European model though is a bit more optimistic in pulling the front
through with a steady decline in rain chances from Thursday into
Friday as high pressure builds in. The Canadian is also on a similar
approach here with a far less significant tropical system and a front
that pulls the ample moisture out of here late Wednesday into
Thursday as high pressure builds. Best coverage for storms
Thursday and Friday would be over the higher terrain while
everyone else sees a drier result.
Temperatures remain at or slightly below average through the
period. Most locations east of the Blue Ridge and out over the
piedmont will continue to see high temperatures in the mid to
upper 80s and low 90s with overnight lows in the upper 60s and
low to mid 70s. The mountains of southern West Virginia and
North Carolina though will be slightly cooler with highs in the
upper 70s and low 80s and overnight lows back into the low to
mid 60s. Locations such as the New River Valley, Grayson
Highlands, and Mountain Empire could see similar temperatures
during the period especially with orographic and diurnally
driven afternoon convection.
Those Dog Days of Summer continue to roll on!!!
Confidence in precipitation and temperatures remain moderate to high
through the period.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 724 PM EDT Friday...
Will likely see some showers/possible tsra near DAN/BLF this
evening, possible LWB/BCB and LYH. Appears showers/storms will
fade after midnight, though some models hanging on to some til
4am across a TNB-DAN line, though confidence is low for now.
Similar to the past several nights, river valleys west of the
Blue Ridge will have fog overnight with LIFR conditions at KLWB
and KBCB, barring any limitation by cloud cover. Locations that
have rain this evening will also have MVFR fog in the early
morning.
Expecting all fog to dissipate by 14Z/10AM Saturday, then
another afternoon and evening of scattered to numerous
thunderstorms.
Average confidence in ceilings, visibility and wind, as well as
the timing and location of thunderstorms.
Extended Aviation Discussion...
Expecting daily rounds of afternoon and evening thunderstorms
and abundant MVFR to LIFR fog, and even some rain showers at
night. Hurricane Isaias tracking along the east coast late in
the weekend into early next week and has the potential to bring
widespread rain and MVFR conditions to the region Monday-
Tuesday.
A front comes through the area around Wednesday which will bring
more thunderstorms, but guidance differs on how far south the
boundary advances.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
$$
SYNOPSIS...AMS
NEAR TERM...AMS/WP
SHORT TERM...DS
LONG TERM...ET
AVIATION...AMS/RAB/WP