Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/21/21
Area Forecast Discussion
National Weather Service La Crosse WI
1053 PM CDT Tue Jul 20 2021
.SHORT TERM...(Tonight and Wednesday)
Issued at 240 PM CDT Tue Jul 20 2021
Smoke from western and northern wildfires is main weather focus
considering how quiet the pattern is at the moment. Large upper
ridge continues from the southwest US up into the northern Plains.
While there has been some convective activity upstream, it weakens
and dissipates well before it gets close. Unfortunately this pattern
continues to transport smoke or particulates into the area.
While this smoke has mainly been aloft, approaching frontal boundary
from the northeast may concentrate this smoke and lead to more
boundary layer issues /near surface based/ which aligns with air
quality partners who have issued advisories for parts of the area
this afternoon and tonight.
Still been tracking any rain threat too as this front creeps closer.
There was some concern that this boundary could serve as a focus for
some convection, but forcing seems so weak. Little to no shear noted
in this regime either so if anything forms, it should not become
severe. Convective allowing models keep trending drier so have
lowered what was small rain threat.
Same follows for Wednesday where we could not completely rule out a
small rain risk but overall pattern is really not shifting much.
Perhaps a few degrees cooler with slight push of drier air from the
.LONG TERM...(Wednesday night through Tuesday)
Issued at 240 PM CDT Tue Jul 20 2021
While no major weather pattern shift is seen, will have to monitor
the subtle features that might focus any rain threat over the next
Aforementioned boundary may shift a little east or northeast going
into Thursday serving to focus any convective threat that direction
as well. Depending on upstream cloud and rain path, temperatures
Thursday could be much warmer if that boundary shifts far enough
east. Convection threats remain east of the Mississippi and could
even be east of forecast area.
Stronger signal in medium range guidance late Friday into Saturday
morning where passing short wave will flatten upper ridge at least
temporarily. This will pass an associated front and brings a higher
risk for more widespread and stronger convection somewhere in the
region. Initial timing looks less favorable for our immediate area
and still unsure how much shear will be present but does bear
watching as the week evolves. Storm Prediction Center also
mentioning risk for more active weather in this time frame /Day 5/.
Likely a dry stretch after Saturday threat but some differences in
longer range guidance on how strong or broad upper ridge will be.
Idea of summer heat and occasional convective threats still seems
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1050 PM CDT Tue Jul 20 2021
Weak cold front has pushed through the TAF sites accompanied by
patchy near-surface smoke. The smoke/haze has been reducing
visibility to MVFR at some nearby observation points this evening,
but this has been on an isolated basis. As such, did not have
enough confidence to drop visibility at either site the rest of
tonight. If it were to happen, RST would have a slightly better
chance than LSE for a brief vsby reduction per recent HRRR runs.
Bigger concern will be increasing low level moisture advecting
westward from Lake Michigan, which is expected to contribute to
low ceilings toward daybreak. LSE will have a greater likelihood
of MVFR cigs, with RST looking to sit on the edge of the low
clouds. Ceilings should improve toward midday with VFR conditions
then through the rest of the period. With the front stalling west
of the MS River, there is a very small chance of isolated showers
or perhaps a storm in the afternoon/evening, but today`s trends
would favor a dry forecast. HRRR does show another band of near-
surface smoke potentially developing over western WI with a small
chance of impacting LSE near the end of this period.
Winds remain light through the period, shifting from northeast
early in the morning to southeast in the afternoon.
Area Forecast Discussion
National Weather Service State College PA
1128 PM EDT Tue Jul 20 2021
Warmer and more humid conditions are expected today south of a
cold front dropping southward from the eastern Great Lakes. Most
areas will remain dry, but there is a chance of a thunderstorm
or shower north of Interstate 80 this afternoon or evening.
A cold front will sweep through central Pennsylvania on
Wednesday, ushering in cooler temperatures and refreshingly low
humidity for the rest of the work week before rain chances,
heat and humidity make a comeback for the weekend.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As a midlevel shortwave trough and sfc cold front approach the
area this evening, areas of showers and thunderstorms will
continue across mainly the northern half of the CWA. Storms will
generally be on the weakening trend with the loss of daytime
heating / SBCAPE, but there should be sufficient MUCAPE to
maintain scattered thunderstorms through the overnight period.
In areas that do pick up rainfall, patchy fog may develop
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
Heights will be on the rise across the NW half of the area on
Wed as cooler, drier air is advected in from the NW. Showers
and storms will again be possible in eastern zones through Wed
afternoon as the upper trough axis and sfc cold front swing
through in the presence of 1500 J/kg MLCAPE and DCAPE of 800-900
J/kg. There is a MRGL threat for severe thunderstorms across
the east, with wind being the main threat.
High pressure will build in from the Ohio Valley on Thursday,
bringing plenty of sunshine and mild temperatures ranging from
the mid 70s in the north to the mid 80s in southern PA.
Dewpoints in the 50s will feel quite refreshing.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
A warm front will slowly approach from the west beginning on
Fri, bringing with it a slight chance of showers and storms to
the NW. The warm front will advance across the rest of PA on
Saturday, again bringing a chance for isolated showers and
storms, but very dry midlevel air will keep coverage limited.
Moisture will flow back into the area on Sunday, with dewpoints
rising to 65-70F and temperatures returning to the 80-90F range.
Increased moisture and instability along with a weak disturbance
aloft will likely lead to more widespread showers/storms Sun
afternoon and evening.
Warm and humid conditions will continue into early next week
with a chance for additional rounds of showers and storms as
weak upper shortwave troughs pivot around a large ridge of high
pressure set up over the central US.
.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
Smoke from western fires is likely to continuing reducing vsby
to MVFR at most sites overnight. Radar loop at 03Z shows
dwindling showers and a few tstorms across northern Pa in
advance of an approaching cold front. Latest HRRR suggests this
activity will weaken further after midnight, as the atmosphere
Late evening satellite imagery shows valley fog forming across
the northern tier of Pa, where rain fell earlier this evening.
KBFD will be susceptible to IFR vsbys after about 04Z. Model
soundings indicate a likelihood of IFR cigs developing across
the Allegheny Plateau early Wed morning, as cold front pushes
through, followed by a moist, upsloping northwest flow. Current
model soundings and ensemble prob charts indicate onset of IFR
at around 08Z at KBFD and around 10Z at KJST.
Expect improving cigs across the Allegheny Plateau later
Wednesday, as drier air arrives on northwest flow. Model
soundings and ensemble prob charts support widespread VFR
conditions by Wed afternoon. However, can`t rule out a gusty
tstorm forming on exiting cold front across southeast Pa
(KMDT/KLNS) sometime between 16-18Z.
Thu...AM valley fog possible W Mtns.
Fri...No sig wx expected.
Sat...Late day tsra impacts possible, mainly west.
Sun...AM low cigs possible W Mtns. PM tsra impacts possible.
Area Forecast Discussion
National Weather Service Duluth MN
929 PM CDT Tue Jul 20 2021
.DISCUSSION...(This evening through Monday)
Issued at 420 PM CDT Tue Jul 20 2021
Summary: Smoke from the Canadian wildfires is affecting air
quality throughout the region. There are slight chances for
showers and thunderstorms for this evening into tonight in north
central Minnesota. On and off rainfall chances occur throughout
the week, though accumulations are expected to be light. The next
chance for widespread rainfall is Friday.
High particle concentration from the Canadian wildfire smoke has
been transported into the Northland today due to northwesterly
winds. An air quality alert has been issued for the entire area and
continues into tonight. Though air quality is expected to improve,
haze and smoke should linger and could still impact visibilities.
The upper Midwest is currently right between an upper level ridge to
the southwest and an upper level trough to the northeast. A
shortwave within these air masses has brought light precipitation to
the Northland in our western counties. These scattered showers
are expected to continue overnight, with light accumulations. More
shortwaves within the northwestern flow aloft will bring on and
off chances for showers and thunderstorms slowly eastward over
northeastern Minnesota and northwestern Wisconsin through
Thursday. Chances for severe weather in our area is unlikely, as
the greatest instability is off to our west with current model
runs. Accumulations with each round of precipitation will be
Friday will be the next system to bring widespread rain. A strong
trough in northern Canada with a large vorticity maximum reaching
down into the Northern Plains. A resultant cold front will sweep
across the Northland Friday afternoon and evening. Wind shear and
instability should be sufficient with 20-30 kt 0-6km bulk shear and
MUCAPE around 1000 J/kg. A low level jet ahead of the front
should help to sustain convection overnight into Saturday.
As we head into Sunday, flow becomes more zonal before another ridge
sets up to our west, which will bring us dry and seasonal weather
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 649 PM CDT Tue Jul 20 2021
Highlights of the period include reduced visibility in
smoke/haze/fog continuing, lower MVFR ceilings gradually rising,
and there will be a chance for showers and a couple
The Northland was between high pressure to the east and low
pressure off to the west. Shortwaves will be riding the upper
ridge into the region providing some lift for showers and a few
thunderstorms, mainly over western and far northern areas. We
included a mention at KINL and KBRD which would be most likely to
see some rain.
We went with persistence on the visibility early in the period and
relied on the HRRR for smoke/haze trends overnight. It appears
there should be some improvement from east to west tonight but
KBRD may not see much or for a prolonged period of time. We also
expect some fog formation overnight and added that to most TAFs.
The lower ceilings have been persistent as well today and most of
the guidance keeps trying to scour them out. We do think the trend
will be for them to diminish but confidence in just how quick that
will occur is low. We used the RAP as general guidance but went
slower, especially at KDLH. The ceiling at KDLH has risen over
the past hour so that may be a trend that will continue.
Issued at 929 PM CDT Tue Jul 20 2021
Northeast winds will occur for most areas with speeds from 5 to 15
knots. Waves will be 3 feet or less for all areas overnight. A
similar set up will occur Wednesday with high pressure over Lake
Superior and low pressure to the west. East/northeast winds will
occur for most areas from 5 to 15 knots into Thursday, highest
from Two Harbors to the Twin Ports to Port Wing. Some of the
guidance suggest winds could get as high as 15 to 20 knots in the
Twin Ports area Wednesday afternoon so it`s possible a Small
Craft Advisory may be needed there as waves build. There could be
a few thunderstorms Wednesday afternoon into Thursday.
.PRELIMINARY POINT TEMPS/POPS...
DLH 54 73 60 79 / 20 40 50 30
INL 56 74 59 83 / 50 50 50 40
BRD 61 84 66 91 / 30 30 20 10
HYR 52 79 61 86 / 10 30 50 30
ASX 50 78 59 83 / 10 30 60 50
Area Forecast Discussion...UPDATED
National Weather Service Peachtree City GA
1126 PM EDT Tue Jul 20 2021
...Late Evening Update...
The forecast remains on track heading into the overnight hours.
Lingering isolated showers from evening convection are
dissipating, but I am maintaining slight chance PoPs across
portions of the area overnight given the frontal boundary/surface
trough and saturated environment.
.PREV DISCUSSION... /Issued 822 PM EDT Tue Jul 20 2021/
..Updated for 00z Aviation Discussion...
PREV DISCUSSION... /Issued 314 PM EDT Tue Jul 20 2021/
SHORT TERM /Tonight through Wednesday Night/...
Showers and isolated thunderstorms across the area this afternoon
will continue through the late evening hours before diminishing
overnight. Instability is marginal this afternoon and shear values
are almost non existent. The biggest issue are the precipitable
water number values. Seeing 1.75 to 2.06in values through the
short term so while we are not expecting much in the way of severe
storms...any one of these storms could drop a lot of water very
fast. Since we have already seen quite a bit of rain over North GA
over the past 24-36 hours (0.5-2.5 almost 3 inches) any
additional rainfall could cause some flooding across the area.
right now our biggest concern is for N GA and some portions of
west central GA which is why we extended the flood watch earlier
today to include those areas. Expecting another round of showers
and thunderstorms Wed afternoon with the same similar parameters
as today so another flood watch may be needed.
With all the precip occurring daytime high temps will be lower
than normal with highs mainly in the lower to middle 80s. and lows
in the 60s to near 70.
LONG TERM /Thursday through Tuesday/...
Broad/persistent upr trough stretching from the Arklatex to the
central Appalachians will finally begin to break apart by Thursday
leaving the area in a relatively drier NW flow as a weak ridge
attempts to build in from the west. Convection on Thursday/Friday
appears to be confined to the far southern portions of the state
with just an isold storm or two driven by daytime heating expected
across north & central GA. Will have to monitor positioning of
upr ridge to our west as northeast periphery could affect area
with deeper moisture and energy support for better coverage of
convection. POPs will likely continue to favor NBM/Superblend
In response to the upr ridge and expected "drier" conditions,
temps will warm up - approaching seasonal levels for late July by
Early next week, upr ridge appears to strengthen over the Central
Plains/Midwest regions, leaving the area again in a typical "hot"
summer-time pattern with scattered afternoon/evening diurnally-
driven showers and thunderstorms.
There is a slight risk of excessive rainfall for north GA today
and as such, a Flash Flood Watch has been issued for portions of
far NE Georgia. Main reasoning for this watch is given consistent
low-level upslope forcing amid a favorable saturated environment,
evident by HRRR soundings, it should not take much instability to
see an uptick in rainfall rates given the warm rain processes. New
rainfall amounts of 1 to 2" are possible across the watch area,
with locally higher amounts. This area has recently received
between 1 to 2 inches of rain with locally higher amounts of 2.5+
inches. With PWATS approaching 2"+ over much of the CWA and given
the slow moving low and persistent southwesterly low level flow
into the area, there remains the potential for expansion pending
future forecast packages.
Areas of moderate to heavy rain and thunderstorms are underway
this evening across portions of north and central GA. Have VCSH at
all TAF sites until 06z, with TEMPO groups at KATL and metro
sites from 00z-02z for TSRA. Winds will be light and variable
overnight, with cigs dropping to MVFR around 04z-06z and then to
IFR around 06z-08z. Pockets of LIFR will be possible, but
confidence was too low to include in the TAFs. Winds will be W to
SW at 4-7 kts during the daytime hours of Wednesday. Wednesday
afternoon will bring another round of scattered showers and
//ATL Confidence...00Z Update...
Medium confidence on timing of lowering cigs.
High confidence on all other elements.
.PRELIMINARY POINT TEMPS/POPS...
Athens 67 84 70 90 / 60 40 30 40
Atlanta 69 83 71 87 / 60 60 40 50
Blairsville 63 82 63 84 / 40 40 20 30
Cartersville 68 84 69 89 / 60 50 30 40
Columbus 71 85 72 89 / 50 60 30 50
Gainesville 67 83 69 88 / 50 40 30 40
Macon 71 86 71 91 / 60 50 30 50
Rome 69 85 70 90 / 50 50 30 40
Peachtree City 69 83 70 87 / 70 60 40 50
Vidalia 72 86 73 90 / 40 50 30 40
Area Forecast Discussion
National Weather Service Paducah KY
627 PM CDT Tue Jul 20 2021
Issued at 626 PM CDT Tue Jul 20 2021
Updated aviation discussion for the 00Z TAF issuance.
.SHORT TERM...(Tonight through Thursday night)
Issued at 256 PM CDT Tue Jul 20 2021
High pressure over the north central states will continue to
produce a northeast wind flow of rather dry air. Other than
scattered cumulus clouds each afternoon, not much in the way of
cloudiness is expected through the short term.
Temperatures are really not expected to change much until the flow
turns more southerly. The nbm temp guidance continues to try to
warm us up before any change in air mass takes place. Tweaked high
temps down a degree or two from the nbm (national blend of
models). Overnight lows will be in the mid to upper 60s the next
couple nights, warming to around 70 Thurs night.
There is a signal in the 12z href guidance for some showers or
storms Wednesday in a corridor from eastern Iowa to southeast
Illinois. However, the more reliable href members such as the hrrr
are not showing that activity. The 12z gfs does show some activity
coming south, but it dries up under the 850/700 mb layer high
centered over the kstl area. Will keep Wed dry, but with 10
percent pops in the I-64 corridor of southern IL.
The next chance of precip in the forecast will be Thursday, when
isolated afternoon storms will be possible in southern parts of
the region. This activity would be associated with the 850 mb
warm front as it lifts north across the lower Mississippi Valley.
.LONG TERM...(Friday through Tuesday)
Issued at 256 PM CDT Tue Jul 20 2021
On Friday, broad upper level ridging over the western U.S. will
result in northwest flow over the middle Mississippi and lower Ohio
valleys through the weekend. Warm moist air in place combined
with any little ripple in the upper flow will result in some
diurnally driven convection in the afternoon, mainly Friday and
Sunday, with the best potential east of the Mississippi River.
High temperatures Friday will be in the 88-91 range, and in the
lower 90s by Sunday. With dew points in the lower to middle 70s,
heat indices will reach around 100 degrees Saturday afternoon, and
near 105 degrees Sunday afternoon.
By Monday, models show a cold front sinking south toward our region.
This will bring a little better/not dependent on daytime heating
chances of showers and thunderstorms to the PAH forecast starting
Sunday night and especially Monday, with small chances continuing
into Monday night and Tuesday. Since timing is still in question,
pops will be kept in the chance category or lower.
Temperatures Monday and Tuesday will reach the lower 90s. With dew
points in the lower to middle 70s, afternoon heat indices in the 100
to 105 degree range will likely continue. If precipitation chances
trend upward, maybe it could hold these values down a little.
Issued at 626 PM CDT Tue Jul 20 2021
Skies are expected to clear up overnight. With calm winds some fog
could form, more likely over towards KMVN/KCGI where MVFR vsby is
included. Would not be surprising to see KMVN bounce around to
IFR vsbys temporarily. Winds will remain fairly light tomorrow,
4-8 kts out of the N/NE. A few mid-level clouds are likely
tomorrow as well during the day.
Area Forecast Discussion
National Weather Service Las Vegas NV
1246 PM PDT Tue Jul 20 2021
.SYNOPSIS...Moist and unstable air will continue over the region
through the week as a typical summer monsoon set up persists. A
disturbance moving in from Arizona may lead to more extensive
thunderstorm development this weekend.
.SHORT TERM...Today through Thursday.
Yesterday, there was quite a bit of shear over the area that worked
to shear apart a large portion of the convection, resulting in a bit
of an underplay from what we were originally expecting. Today, we`re
observing quite a bit lower effective bulk shear values, and the
PWAT boundary has shifted a little further east as the upper level
area of high pressure shifts over its "sweet spot" over the Four
Corners. PWAT values in southern Nevada, northeastern Arizona, and
eastern San Bernardino County will continue to exceed an inch this
afternoon, with values exceeding an inch and a half along the
Colorado River Valley. Lifting Index values vary from -1 to -4
across the region. This, coupled with little shear will result in
isolated showers and thunderstorms today that have the potential to
train over the same area, with very little movement.
Areas of primary concern will be the Clark County Mountains, higher
elevations of Lincoln County, and across Mohave County. We`re
already seeing some radar returns this afternoon in central Lincoln
County, across the Arizona Strip, and along the northern edges of
the Spring Mountains and Sheep Range with evidence of training.
Isolated flash flooding will be possible, particularly with
stronger, heavy-rain rate storms and storms that continue to
regenerate over the same areas. Otherwise, DCAPE values across
southern Nevada and southeastern California will be in excess of
1200 J/kg this afternoon, indicating the potential for wind gusts 50-
60 mph with stronger storm development.
With all of these factors in mind, scattered thunderstorms can be
expected today, though the latest HRRR does not seem too impressed.
Convective temperature in Las Vegas today is 97F. Current
observation at McCarran reads 99F. Yesterday, the high temperature
struggled to reach convective temp due to the amount of cloud cover.
Convection will be spotty today, as is typical during the monsoon,
so PoPs in the Las Vegas Valley remain low, but non-zero. Regarding
Las Vegas specifically, the HRRR shows storms forming exclusively
over the Spring Mountains and McCullough Range, while the FV3 shows
a couple of light cells passing through the Valley. Will keep an eye
on development and post frequent updates on Twitter as we see them
(@NWSVegas). You do not need a Twitter account to see our
As the area of high pressure persists over the Four Corners through
the week, so do PoPs. Highest chances remain generally south and
east of Interstate 15, with locations north of Interstate 15
focusing along the higher terrain.
.LONG TERM...Friday through Tuesday.
Models continue to agree with a wave of low pressure skirting
westward across the lower 48 through the weekend. This low pressure
will continue to move westward before being pushed up through our
area, around the monsoonal high pressure, and into the upper-level
flow. This wave will tap into deep moisture across southern Arizona
before pushing into the Mojave Desert, bringing aforementioned
moisture with it. Should this come to fruition, widespread
thunderstorm chances will substantially increase this weekend. ECMWF
ensemble runs indicate the potential for PWAT values in excess of an
inch and a half crawling up to Las Vegas. This moisture coupled with
the dynamical instability of the wave could result in moderate-to-
heavy rainfall amounts, frequent lightning, and the potential for
widespread flash flooding. As we get closer, we will further assess
the need for Flash Flood Watches in collaboration with our
neighboring offices. Keep an eye on the forecast, particularly if
you have any outdoor plans next weekend into next week. Monsoon 2021
has arrived, everyone.
.AVIATION...For McCarran...Thunderstorm development on the Spring
Mountains today have the chance of kicking off gusty west winds into
the Las Vegas Valley. Chances are too low to include as a TEMPO
group at the moment, but will update as necessary. Otherwise, winds
will have a diurnal trend with southwesterlies this evening and
northeasterlies Wednesday morning. There remains a chance for a
gusty southeasterly push from Arizona storms this evening around 03Z
with speeds around 12 kts, but low confidence at this time.
For the rest of southern Nevada, northwest Arizona and southeast
California...Isolated thunderstorms expected again today, primarily
over the higher terrain of southeast Nevada and Mohave County.
Locally heavy rain and surface wind gusts up to 50 mph possible with
stronger cells. Drier air and more stable conditions are forecast
for the rest of the area today. Outside of any thunderstorm
influences, light and diurnal winds are expected.
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
For more forecast information...see us on our webpage:
https://weather.gov/lasvegas or follow us on Facebook and Twitter