Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/26/17
Area Forecast Discussion
National Weather Service Charleston SC
1029 PM EDT Tue Jul 25 2017
Broad low pressure will remain across the Carolinas and Georgia
through tonight. A weak cold front will then stall over or near
southeast South Carolina through Thursday. Another cold front
will move into the area this weekend and stall into early next
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As of 1020 PM: IR detected rapidly warming cloud tops and radar
indicated largely stratiform rainfall across SE GA. It appears
that the remaining rainfall will generally dissipate before
midnight. I will update the forecast to increase sky cover and
decrease PoPs. Latest runs of the HRRR have indicated that the
rest of the night will remain quiet. However, near range
guidance shows that the core of the mid level low will reach the
Altamaha River by day break. As the low approaches, convection
is expected to develop near the coast and drift inland. Based on
the guidance, I will maintain CHC PoPs beginning around dawn.
Otherwise, temperatures across most of the forecast area is
expected to remain steady at the latest readings in the mid to upper
As of 725 pm: At the top of the hour, an automated raingauge at
Midville, GA indicated that 3.11 inches of rain fall in one
hour. At this time, a multi-cell thunderstorm over McIntosh was
producing torrential rainfall rates that ranged close to what
was observed at Midville. In addition, a line of thunderstorms
should drift north across the Altamaha River Valley, likely
raining out and becoming stratiform rain by 10 pm. Elsewhere,
light stratiform rain should continue or areas that are dry will
remain dry overnight. However, there is a chance that
convection may approach Berkeley County form the north. I will
update the forecast to reflect the latest radar trends and
To start, ahead of an upper low advancing east across southern
GA, thunderstorm coverage will range from numerous/widespread
across SE GA to isolated/scattered across SE SC into early
evening. Primary concerns focus on the threat for locally
excessive rainfall within an environment featuring PWATs
exceeding 2 inches and weak steering flow, especially where
coverage is maximized across SE GA. MLCapes exceeding 2000 j/kg
could translate to an isolated/brief pulse severe event with
damaging wind gusts, but the probability for severe weather will
Thunderstorms should undergo diurnal weakening/dissipation later
this evening. Then, as the upper low continues to roll toward
the region, isolated/scattered showers/thunderstorms could
redevelop later tonight. Locally heavy rain could again occur,
especially along the coast.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Troughing will linger through the period, although it will be
strongest through Thursday. The deepest moisture is also likely
through Thursday so through this time is when we expect the highest
rain chances, especially Wednesday. Although cannot rule out isolated
severe storms, the bigger risk will be heavy rainfall/flooding given
weak wind fields and very deep moisture. This wetter than normal
pattern will lead to lower than normal high temperatures and
generally above normal low temperatures. By Friday temperatures
could reach above normal in the mid 90s with heat index values
peaking in the lower 100s.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Deep moisture will advect to the Southeast United States ahead of a
cold front that is expected to move into the area Saturday. PWATs
between 2.25 to 2.5 inches and forcing associated with the front
support numerous showers and thunderstorms Saturday into Sunday
while the front slowly progresses south and eventually stalls over
or near southern areas of Southeast Georgia. A few thunderstorms
could become more organized than previous days given greater wind
fields aloft, but the overall threat of stronger thunderstorms could
be limited due to the timing of fropa during earlier hours on
Saturday. At least chances of showers and thunderstorms could linger
into early next week while moisture continues to lift over or near
the stationary front.
Temps will generally be a few degrees below normal this weekend and
early next week given extensive cloud cover and precip activity. In
general, temps should peak in the mid/upper 80s. Overnight lows will
range in the low/mid 70s.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Thunderstorms are expected this afternoon at both terminals,
with most significant impacts at KSAV. Then, VFR conditions are
forecast at both terminals through the 18Z TAF cycle. However,
low-level moisture could support MVFR/IFR ceilings later
tonight. Then, as an upper level low advances east and deep-
layered moisture spreads north across the region, showers could
redevelop late tonight, and thunderstorms could develop before
the end of the 18Z TAF period. Any showers/ thunderstorms could
produce flight restrictions.
Extended Aviation Outlook: Brief flight restrictions are possible
with showers and thunderstorms, especially Wednesday into Thursday
as weak low pressure approaches the region. VFR conditions should
prevail late Thursday and Friday before flight restrictions return
with showers and thunderstorms along/near another cold front
Seas of 2-3 feet will persist through tonight. The sea breeze
and synoptic winds will combine to produce S/SW winds 10-15
knots into early evening, then synoptic SW winds mainly 15 kt
or less will prevail for the remainder of tonight.
Thunderstorms could produce locally hazardous conditions over GA
waters this afternoon/evening and anywhere across the coastal
waters later tonight.
Wednesday through Sunday: A cold front looks to stall near the SC
waters through Thursday before dissipating before another cold front
moves into the area this weekend. Conditions are expected to remain
below Small Craft Advisory levels through the period. However, a
southwest/south flow could gust around 20 knots Friday night into
early Saturday until cold fropa occurs. Seas will gradually build
from 2-3 ft up to 4 ft at times later this week as the pressure
gradient tightens a bit ahead of the front.
Area Forecast Discussion
National Weather Service State College PA
1200 AM EDT Wed Jul 26 2017
A large area of high pressure will slide southeast from the
Great Lakes to blanket most of the Middle Atlantic Region
with an airmass consisting of slightly below normal
temperatures, comfortably low humidity, and abundant sunshine
for most places on Wednesday. Low pressure and an attendant cold
front will approach from the Ohio Valley for later Thursday
into Friday bringing a few periods of showers and scattered
thunderstorms. Another refreshingly drier and cooler airmass
will overspread the commonwealth this coming weekend.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
00Z observed soundings support trapping thin layer of
moisture below the inversion. Clouds are breaking up, but
slow to do so. Also some mid and high clds from central
Lake Erie to western PA.
Will adjust grids some more for this.
Earlier discussion below.
Some sunshine at times, but still a lot of clds. Even a hint
of perhaps some drizzle across the far northeast.
Adjusted cloud grids some.
Low level thermal trough was situated from northcentral PA into
the New England states, while warmer air was advecting into the
region in the mid levels. This increasingly stable vertical
thermal profile will help to maintain plenty of mainly shallow
strato cu with sprinkles scattered across the central and nrn
mtns. A few brief showers could drop a quick 0.01 or 0.02 of an
inch, but that will be about the extent of it in the QPF dept
until Thursday afternoon or night.
The clouds should slowly break from west to east (but
temporarily in some places) late this afternoon. High pressure
will gradually build in from the Great Lakes Region late today
and tonight, as the coolest air aloft shifts east of the CWA
with llvl downsloping helping to dry out the boundary layer SE
of the I-99/RT 220 corridor.
Across the east, an inverted sfc trough/marine layer boundary
will be located mainly to the east of the Susq Valley through
early tonight, bringing with it a slight enhancement to llvl
theta-e convergence and the chc for a brief/light shower in some
Skies should become mostly clear across the western mtns for
most or all of the overnight, and clear out temporarily across
the Central Mtns through around midnight. Afterward, the HRRR
looks quite realistic is pushing a layer of 1-2kft agl
stratus/stratocu wwd across the Susq Valley between 05-08Z Wed
and reaching a KELZ to KUNV and KMRB line around or shortly
Prior to the arrival of the low clouds, a 20-25F air/stream
delta T will lead to patchy valley fog (mainly across nrn PA)
where min temps will dip into the 50-55F range. Elsewhere, mins
early Wednesday will upper 50s to lower 60s.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
High pressure will build over the region Wednesday, bringing
clear to partly cloudy skies and dry conditions across the
NW mtns and Laurel Highlands. There is some concern that
whatever lower clouds spread wwd into the Susq Valley and
Central Mtns may have a difficult time eroding through the
morning hours under very light NE to SE breeze, and a stable
llvl profile with subsidence aloft placing a lid on any
appreciable vertical mixing. Something to watch closely, but
not to jump into with both feet just yet.
For now, we`ll play the middle road and have the morning clouds
across the east transition into a mix of sun and sct-bkn flat
strato cu for the afternoon across the Susq Valley and points
Highs Wednesday will be slightly below normal across the eastern
half of the CWA, and near normal across the Western Mtns.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Increasing dual to multi-layer clouds advect east into the
state later Wednesday night through Thursday morning with little
more than some scattered and brief showers moving East to NE.
Deep layer warm advection and a return to a notable higher PWAT
airmass will occur in advance of a cold front and another upper
trough headed our way from the Great Lakes region. Anomalous PWATs
on a SW to NE axis will top out between 1.5-1.75 inches over
the state Thursday afternoon and night before likely settling
just south of the state on Friday. It appears that a highly
anomalous North-Northeast flow in the sfc-850 mb layer may be
sufficiently strong to push much of the precip (forming beneath
the left exit region of a potent upper level speed max) to the
southern half of PA. Precip chcs and QPF display a distinct
north-south gradient for Friday from under 40 percent just NW of
KBFD to over 70s percent in the far SE near or just north of
the path of a 1002-1005 mb sfc low.
Some 12Z model solutions linger the precip accompanying this
wave of low pressure into the first part of Saturday as weak
high pressure building over Lake Michigan (and the surge of
drier air) may be too far west to nudge the baroclinic zone to
Conditions eventually dry out later Saturday and Saturday night
as high pressure builds in. Sunday and Monday appear dry at this
.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
Lower clouds beginning to develop over norther tier airfields
(KBFD and KIPT).
As high pressure builds in from the west, shallow marine layer
under lowering inversion will try and sneak lower stratus deck
back to the west overnight. This lower stratus deck will likely bring
MVFR to IFR conditions overnight into early Wednesday morning.
Secondly, in central areas, scattered to clear skies exist at
04z...but radiational cooling, combined with light winds, will
promote valley fog formation, with it`s own associated
restrictions in visibility and low ceilings.
Overall, certainty is increasing that low clouds and fog will
manifest themselves overnight. Have bolstered low clouds and
fog in the TAFs with this 04z issuance. Models rather insistent
in these conditions developing as well.
Morning clouds and fog will erode Wednesday morning, with VFR
conditions expected by mid day Wednesday across the region.
Numerous showers and scattered thunderstorms return for
Thursday afternoon and night with the approach of another cold
Thu...VFR, but with restrictions developing in SHRA/TSRA.
Fri...Scattered SHRA north with more numerous and heavier
SHRA/TSRA across the south.
Sat-Sun...No sig wx.
Area Forecast Discussion
National Weather Service Cheyenne WY
848 PM MDT Tue Jul 25 2017
Issued at 848 PM MDT Tue Jul 25 2017
Evening GOES-R water vapor animation showed the center of the
upper ridge over the south-central CONUS and upper low near the
northern CA coast. Abundant mid/upper level subtropical moisture
was streaming north-northeast across WY/CO/NE. A cold front was
located from south-central WY to northwest NE and eastern SD.
Regional radars indicated mostly light to moderate showers with
isolated t-storms. Convection allowing models maintain this
precipitation trend through most of the nighttime period. Also,
moistening low level upslope flow north of the front will promote
patchy fog and low ceilings later tonight into Wednesday morning,
especially along and east of the Laramie Range. Zones were updated
earlier this evening to lower t-storm coverage to isolated and
.SHORT TERM...(This evening through Wednesday)
Issued at 147 PM MDT Tue Jul 25 2017
Thunderstorms will likely become more numerous across southeast WY
and the western NE Panhandle over the next few hours w/the passage
of a strong mid-level short wave tracking across southwest WY late
this afternoon. GOES-16 Water Vapor satellite imagery shows plenty
of monsoonal moisture spreading northeast from Utah and western CO
on the back side of upper-level ridging anchored over the southern
high plains. The GFS and NAM have been somewhat meager w/ coverage
of storms this evening, but the HRRR has shown very strong run-to-
run consistency with widespread showers/thunderstorms mainly after
21z. We lean toward the HRRR given the amount of available mid and
high level moisture and dynamic support. Main hazards through this
evening will be locally heavy rain w/ tall and skinny CAPEs, but a
risk for strong/gusty winds is also there with stronger flow aloft
and an inverted-V signature on forecast soundings. It appears that
the overall threat for severe weather is low, but will need to pay
close attention to the northern Panhandle w/ a surface low lifting
northeast early this evening. This will likely enhance directional
shear and lead to a ribbon of stronger instability with CAPES over
1500 J/kg courtesy of dew points in the mid 60s. If LCLs were just
a bit lower, this would be a concern for a tornadic threat but the
main concern appears to be hail if a discrete storm can form. Mode
of storms will likely be too messy and disorganized to support any
kind of substantial severe threat. Widespread precipitation in the
next few hours will contribute to enhanced boundary layer moisture
early Wednesday morning, so anticipate low stratus over the plains
along with the possibility of some fog. Forecast soundings suggest
this burning off by mid morning. For Wednesday, expect to see less
storm coverage outside of the mountains with the upper-level ridge
axis building into the CWA through the day.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 230 PM MDT Tue Jul 25 2017
We maintain a fairly active pattern for afternoon and evening
showers and thunderstorms Thursday and Friday as we remain under
southwesterly monsoonal flow aloft. Friday would appear the most
active for sheer coverage of storms east of the Laramie Range as
a shortwave moves across the region. By Saturday, it would appear
that upper ridging will be extending northward and pushes the
deeper moisture to our southeast, so we will advertise a little
less coverage of showers and thunderstorms over the weekend into
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 520 PM MDT Tue Jul 25 2017
Area of mostly showers should move northeast across much of the area
this evening with some MVFR cigs and vsbys possible in the heavier
ones. Surface front will move across the area this evening with a
more moist upslope flow behind it likely producing widespread
MVFR/IFR cigs and some fog east of the mtns late tonight into Weds
morning before lifting.
Issued at 147 PM MDT Tue Jul 25 2017
No fire weather concerns with widespread showers and thunderstorms
likely this evening and overnight. Thunderstorms may produce gusty
and erratic surface winds. Afternoon RH values should remain above
30 percent for most areas over the next several days.
Area Forecast Discussion
National Weather Service Goodland KS
926 PM MDT Tue Jul 25 2017
Issued at 922 PM MDT Tue Jul 25 2017
Just completed an update. Raised mins in the east. Guidance has
been consistent in having the lows in those locations a few
degrees warmer than currently forecast. Also adjusted winds to
match the recent trend of a gust front moving across the area in
advance of the incoming cold front. Hrrr caught this nicely and
Thunderstorm coverage and intensity has been decreasing. Model
guidance has been poor and inconsistent with this, even the high
resolution and rapidly updating output is not doing well. So will
leave alone for now, and continue to watch trends. Still may trend
UPDATE Issued at 632 PM MDT Tue Jul 25 2017
Just completed an update to adjust pops. All scale of model output
having difficulty as to where to pinpoint locations of
thunderstorms. Majority of output emphasizes the west and
especially northwest portion of the area. Current activity does
support that. However, where the models are lacking and where the
update had to be made through the rest of the night was for the
convection over the south and west central portion and activity
approaching from the southwest.
The model catching the details the best right now, especially over
and near our southern areas is the Nam. Using it and latest trends
expanded pops further east faster and also farther east. Based on
that also adjusted the qpf.
.SHORT TERM...(This afternoon through Wednesday)
Issued at 1126 AM MDT Tue Jul 25 2017
17Z Water vapor imagery indicated large anticyclonic circulation
centered over south central Colorado. Morning soundings indicated
a large change in airmass qualities between KDDC and KDEN. KDEN
sounding was primarily dry with steep (greater than 8 C/km) lapse
rates off of the surface. KDDC was much more humid with PW values
of 1.29 inch and a fairly deep moist layer, but with overall poor
lapse rates between H7 and H5. At the surface, trough axis was
draped across eastern Colorado with dewpoints in the mid and upper
60s to its east and dewpoints in the 50s to the west.
Thunderstorm chances will be primary forecast concerns tonight and
tomorrow, followed by magnitude of cool down behind cold front
Various short range models show a lot of variance with respect to
how afternoon and evening thunderstorms develop. Solutions vary
from storms remaining near sfc trough to forming into large
cluster and advancing across whole CWA. Starting to see cumulus
development along trough which may shed some light on how storms
will evolve. As cold front advances south tonight and short wave
trough flattens ridge somewhat, expect storms to advance to the
east and south with best coverage mainly along and north of
Interstate 70 where large scale forcing and available instability
most in line.
Expect storms to diminish in the morning hours with the bulk of
the morning and afternoon being dry across the area. Thunderstorm
development will be heavily influenced by how much clearing and
heating can occur. Should a low stratus deck maintain itself this
will greatly diminish potential for any post frontal storms.
Overall confidence high that temps will be around 15 degrees
cooler than today in northwestern CWA, but confidence in frontal
position lower to the south so not ready to dial down temps a lot
in this area.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 141 PM MDT Tue Jul 25 2017
Wednesday night-Thursday: As front pushes through the area, there
will continue to be a a chance of storms and showers across our
southern CWA. Model soundings are not that impressive on shear and
CAPE, therefore, widespread severe weather is not expected at this
time. Thursday should be dry with ridging aloft. Temps will be
below normal Thursday with highs in the low to mid 80s and
overnight lows in the upper 50s and low 60s.
Friday-Tuesday: Upper level ridge amplifies over the Rockies placing
us in strong NW flow aloft. Monsoonal moisture plume builds back
into the area. A series of shortwaves should traverse the periphery
of the ridging through the period. Will have chance of showers and
thunderstorms each afternoon and evening. Saturday night into Sunday
looks to have the best chance of precipitation. Models also hinting
at a good amount of fog Sunday morning, but chose to leave out of
the forecast at this time, since it was in the Day 5/6 period.
Temperatures will be near normal for the time frame.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 544 PM MDT Tue Jul 25 2017
For Kgld, vfr conditions and south southeast winds are expected
through mid evening. From 04z to 07z thunderstorms are expected to
be near or affect the site. At this time chose to just have vcts
because high resolution models are showing a variety of scenarios.
There are currently storms to the west and north of the area. Will
amend if storms become move certain. However, mvfr conditions
will be possible with the stronger storms. Because of surface
boundaries and outflow from storms the winds will be variable in
direction from mid evening until mid morning tomorrow. A cold
front will start moving through the area around 15z with sustained
winds near 18 knots with gusts to near 26 knots. This and mvfr
ceilings are expected until 20z. At that time vfr conditions and
north winds near 15 knots are expected.
For Kmck, at this time vfr conditions are expected through the
entire period. south southeast winds near 15 knots with gusts to
near 22 knots will decrease to 12 knots near sunset and will
continue until the middle of the night. At this time it looks like
thunderstorms will be near or affect the site from 05z until 08z.
As with Kgld uncertainty is above average due to model
differences so will have vcts during this time. This will also be
the time period where mvfr conditions could occur and high
variable winds due to outflow. Around 15z a cold front will also
move through this site as north winds increase to near 15 knots
with gusts to near 22 knots. This will continue until the end of
Area Forecast Discussion
National Weather Service Elko NV
238 PM PDT Tue Jul 25 2017
.SYNOPSIS...The weather will remain active through the evening
tonight. Some storms may be strong and could produce brief
moderate to heavy rain. Drier air will start to move in tomorrow,
bringing with it lessening storm chances.
.SHORT TERM...Tonight through Friday. Convective activity is
getting a slow start this afternoon as high temperatures are
cooler today than what they were yesterday. Many readings were
about 7-10 degrees cooler and thus have delayed the convection.
Storms are not moving too fast with 700-500mb speeds progged at
around 5 knots or so. The showers and storms will continue to form
through the afternoon and evening hours per the latest HRRR runs.
In addition, we have seen some training storms in northern Nye
county, and the possibility does exist further north. Still
concerned about heavy rain on recently created burn scars. Based
on these factors, will keep the flash flood watch going at this
time. Overnight lows will be in the 50s for the most part.
All model solutions are showing the closed upper level trough off
the California coast slowly shifting to the northeast. There will
continue to be a jet max over the northern parts of the forecast
area. It looks like another active day across the region. Storm
motions will be a little quicker at 10-15 knots. But precipitable
water values are expected to be down slightly, with many locales
coming in around 0.75 inches or so. The highest readings will be
in the eastern spots along the border with Utah. High temperatures
will be in the low to mid 90s. Winds will be light.
Wednesday night into Thursday. The upper trough energy will shift
east. Southwest flow will bring some drier air into the area, with
precipitable water values decreasing to 0.66 to 0.75 inches. Will
need to see how much drier air will be over the area. Have kept
isolated showers and thunderstorms in the forecast as model
solutions typically are too quick with removing the moisture.
Highs will be in the low to mid 90s with light winds.
Thursday night into Friday. Drier air continues to move into the
area. Have limited thunderstorm coverage to isolated only.
Afternoon highs will be in the low to mid 90s again.
.LONG TERM...Friday night through next Tuesday.
Upper ridge will gradually rebuild over the Great Basin this
weekend into early next week. Lingering moisture and weak
instability under this feature will result in a chance of isolated
thunderstorms across portions of central and eastern NV each day.
ECMWF is more aggressive and quicker to build a closed upper high
right on top of Nevada by early next week which would lead to an
overall hotter and drier solution. GFS has slowly rising heights
through the weekend while bringing some monsoonal moisture back
into southern and central parts of the state later Sunday into
Monday. Eventually, the GFS does build a closed high back over
southern California during the later half of next week while
keeping some moisture in place over Nevada. Overall, will lean
toward the GFS solution with above normal temperatures likely for
the balance of next week.
.AVIATION...Scattered showers and thunderstorms will redevelop
this afternoon around and en route of all TAF sites given
available monsoonal moisture and instability. Scattered storms
will persist through mid-evening before diminishing to pockets of
light rain later this evening/overnight. Outflow winds over 30
knots, locally heavy heavy downpours and small hail along with
reduced visibilities to at least MVFR are likely in the vicinity
of stronger convective cells this afternoon and early evening.
Cannot rule out the possibility of an isolated severe gust/wet
microburst to 50 knots associated with a more intense descending
AMD NOT SKED will continue for KWMC until further notice due to
comms line issue.
.FIRE WEATHER...Scattered to numerous showers and thunderstorms
will continue this evening across all zones. Some of these storms
can produce brief heavy rain and strong gusty outflow winds.
Localized flash flooding and strong to severe storms are still
possible and remain the main threats. Additionally, awareness of
recent burn scars for the potential of flash flooding and/or
debris flows in and around recent burn scars is critical and will
be monitored closely. This active pattern will diminish towards
the end of the week.
Flash Flood Watch until 11 PM PDT this evening for Humboldt
County-Northeastern Nye County-Northern Elko County-Northern
Lander County and Northern Eureka County-Northwestern Nye County-
Ruby Mountains/East Humboldt Range-South Central Elko County-
Southeastern Elko County-Southern Lander County and Southern
Eureka County-Southwestern Elko County-White Pine County.
Area Forecast Discussion...UPDATED
National Weather Service Reno NV
820 PM PDT Tue Jul 25 2017
Storm coverage has diminished considerably as drier air aloft
works into the Sierra and western NV. Storms were becoming lower
topped with more rain than hail being reported. Thus some minor
flooding is still possible with stronger isolated cells. We will
be allowing the flash flood watch to expire on time as the threat
for flash flooding is diminishing. Coverage is expected to remain
isolated overnight across western NV and northeast CA with a new
round firing Wednesday afternoon as afternoon heating gets going.
The best chances will be across the Basin and Range and from
northeast CA into northwest NV. Hohmann
Drier air will intrude Wednesday resulting in reduced coverage of
thunderstorms, with dry weather expected Thursday through
Saturday. Near average high temperatures rise to above average
late in the week.
.PREVIOUS DISCUSSION... /Issued 115 PM PDT Tue Jul 25 2017/
Thunderstorms have formed again today for northeast California
and western Nevada. Stronger storms could bring strong winds, as
well as heavy rain with localized flash flooding. Drier air
intrudes Wednesday resulting in reduced coverage of thunderstorms,
with dry weather expected Thursday through Saturday. Near average
high temperatures rise to above average late in the week.
Another day of thunderstorms is on tap with the greatest coverage
this afternoon and evening expected to be from a Mono Lake-Pyramid
Lake eastward and north of I-80 toward the Oregon border. Isolated
coverage is possible in the eastern Sierra and western Nevada Sierra
Front, but this is expected to move eastward through the afternoon.
The greatest risks from storms today will once again be localized
heavy rainfall and plentiful small hail, with strong outflow winds
looking more likely than they did yesterday due to some drier air
moving in aloft. With decent shear aloft, storms are likely to be
organized which lends itself to stronger storm development. Heavy
rainfall may cause flash flooding and debris flows, especially over
recent burn scars and steeper terrain and a Flash Flood Watch
remains in effect for portions of western Nevada. Despite the
localized heavy rain, new fire starts due to lightning are always a
possibility and the gusty/erratic outflow winds could cause rapid
Nocturnal convection is looking probable overnight, and coverage has
been expanded in the forecast to include areas mainly east of a
Susanville-Reno-White Mtn line. Instability remains elevated aloft
and there is a passing upper wave to help add some forcing to the
equation. The HRRR and NCAR ensembles are hinting at this scenario
as well. PWATs remain high, which lessens the risk of a dry
lightning outbreak (as is common with nocturnal events), however
once again new fire starts could occur.
The upper level low sitting off the California coast moves inland
Wednesday into Thursday, bringing a drier airmass with it. This will
lessen thunderstorm coverage, but isolated storms are still likely
for Wednesday, with lessening chances heading into Thursday. -Dawn
LONG TERM...Friday through Tuesday...
High pressure begins to strengthen across the region going into the
weekend bringing warming temperatures, with triple digit highs
expected for valleys of western Nevada and upper 80s-low 90s for
Sierra valleys. A few weak shortwaves approach the California coast
Saturday and Sunday, with latest forecast models indicating one
possibly strengthening by the end of the weekend. Typically this
would bring drier southwest flow across the Sierra and extreme
western Nevada while southerly flow across central and eastern
Nevada advects modified monsoonal moisture northward. This would
lead to greater thunderstorm chances from approximately Highway
395/Interstate 580 eastward for the weekend.
Additional thunderstorms remain possible going into next week with
temperatures continuing to be near to slightly above normal. -Dawn
Concerns today include thunderstorms across the region in addition
to smoke and haze from wildfires creating pockets of reduced
visibility and terrain obscuration.
The greatest thunderstorm coverage this afternoon and evening is
expected to be from a Mono Lake-Pyramid Lake eastward and north of I-
80 toward the Oregon border. Isolated coverage is possible in the
eastern Sierra and western Nevada Sierra Front, but this is expected
to move eastward through the afternoon. Storms will bring localized
heavy rainfall, creating short-lived periods of IFR CIGS/VIS and
obscuring terrain. Abundant lightning, small hail, gusty and erratic
winds, blowing dust, and turbulence are also concerns.
Chances for a storm to affect a terminal site:
KRNO/KCXP/KMMH: 20 percent
KTRK/KTVL: 10 percent
KNFL/KLOL/KSPZ/N58: 40 percent
As far as the smoke and haze...the majority of it is from the
Preacher Fire just east of Gardnerville, NV and the Detwiler fire in
Mariposa County, CA. Smoke may be blown in erratic directions
through the evening due to thunderstorm activity. -Dawn
For more information from the National Weather Service visit...
Area Forecast Discussion
National Weather Service Blacksburg VA
703 PM EDT Tue Jul 25 2017
A weak front across northern North Carolina will shift south of
the area tonight into Wednesday before dissipating. High
pressure north of the region should continue to ridge south
across the area through Wednesday night keeping overall dry
weather in place. Another cold front approaches from the
northwest Thursday into Friday exiting to our southeast by
.NEAR TERM /THROUGH WEDNESDAY/...
As of 702 PM EDT Tuesday...No major changes needed to the going
forecast. Did make a few minor adjustments though. First was to
remove isolated/slight chance PoPs for northern NC tonight as
it appears that in surface METARs that the inverted trough axis
has shifted southward. Visible satellite imagery trends imply
that deeper cumulus development has been few and far between in
this area where residual instability is the greatest (though is
not significant). Also increased sky cover some for the after-
midnight period east of the Blue Ridge into the foothills in
VA/NC. Recent RAP and 18Z NAM/GFS guidance continue to show
increased low-level RH/stratus as 2-m AGL to 850 mb flow becomes
light easterly with passage of backdoor front to our northeast.
Coverage may be somewhat greater in the southern Blue Ridge
versus along the southern Shenandoah Valley. Outside of that
though, forecast appears to be in good shape with counties west
of the Blue Ridge likely to see sharply falling temps with
sunset and areas of patchy fog in the New, Holston and
Greenbrier River Valleys. Lows in the upper 50s to middle 60s
appear on track, though if stratus comes in sooner than
presently anticipated, possible that lows may need to be
adjusted up some in late-evening update.
Previous near-term discussion issued at 215 PM follows...
Surface front has drifted farther south this afternoon with dry
advection having pushed into northern North Carolina per latest
dewpoints. This has basically shifted instability to the south of
the CWA with only the far southwest currently holding onto a bit
more of a cumulus field. Appears best chance at seeing any isolated
showers will be across the North Carolina mountains where a weak
inverted trough lingers and expect a little more convergence as
winds start to turn more easterly by early evening. However not more
than a 20 pop at best with clear skies elsewhere this evening.
High pressure to the north shifts east overnight allowing a
little deeper easterly trajectory to develop by morning. Some
guidance again trying to bring low level moisture back into the
Blue Ridge espcly far south where dewpoints should be a little
higher. Think too dry elsewhere as models remain too moist, so
running with mostly clear to partly cloudy overnight with patchy
fog/stratus around. Should be quite comfortable overnight with
low dewpoints and better radiational cooling under the high
allowing temps to fall well into the 60s most spots, with even
some 50s possible in the valleys.
Will start to see low level moisture start to slowly rebound on
Wednesday as the high to the north shifts farther east resulting in
a gradual veering of the flow to a more southerly component later in
the afternoon. This seen via model jump in dewpoints and northward
shift in progged PWATs from south to north during the day. However
instability remains lacking as well as upper forcing with any
convection likely due to weak southeasterly flow convergence and
orographics. This again mainly over the southwest with ridging
holding across the north and east so trimmed pops back to only
isolated/low chances mainly southern Blue Ridge. Otherwise expect
any low clouds to mix out to more sunshine by afternoon with highs
cooler, mostly upper 70s to mid 80s, within a lingering east-
southeast flow until late.
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 205 PM EDT Tuesday...
Surface high pressure will weaken Wednesday night into Thursday as a
cold front approaches from the west. This front is stuck in zone
flow and will slowly move from the upper Midwest Wednesday night to
the Ohio Valley Thursday. This front will pick up speed, moving over
the mountains early Friday morning, then east of the Blue Ridge
Friday afternoon as an upper level low tracks across the Great Lakes.
Diurnal heating and orographical lift should generate isolated to
scattered showers and thunderstorms across the mountains early
Thursday afternoon. These storms may slowly drift over the foothills
towards evening. As the front approaches the mountains early Friday
morning, the chance for wide spread showers will increase. Despite
these showers coming in during non-diurnal heating, linger
instabilities and a 30-40 knot low level jet could allow some strong
storms to pass over the area overnight. The chances for showers and
thunderstorms will move east of the Blue Ridge Friday morning,
exiting the piedmont by sunset. The best dynamics with this front
will remain north over Pennsylvania and Maryland Thursday night then
along the New England coast Friday. For the forecast area, the
severe weather outlook for Friday is marginal with scattered strong
storms to possibly a few severe cells across the foothills and
piedmont counties. If the front is slower by 6 or more hours, the
severe threat could increase to slight as this would place the
frontal passage during peaking heating Friday afternoon. Even if the
timing is slower, the best dynamics will remain to the north.
Temperatures will be slightly warmer than normal Thursday with low
to mid 80s west of the Blue Ridge and upper 80s to lower 90s east.
Friday will be a lot cooler across the mountains with morning
showers and a frontal passage. High temperatures will range from the
mid 70s to near 80F across the mountains. Temperatures will warm to
near normal east of the Blue Ridge with afternoon temperatures in
the mid 80s.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 240 PM EDT Tuesday...
An upper level low will track from the Great Lakes Friday, then
south over Virginia Saturday. Heating under this cold pool will
bring scattered showers to the region Saturday afternoon.
Temperatures will actually be cooler than normal for the first time
since late June.
Surface high pressure will build over the region starting Sunday.
This ridge of high pressure will keep the area cool and dry into
early next week.
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 702 PM EDT Tuesday...
VFR through at least 06z Wednesday. Thereafter, potential for
some degraded flight categories in two general areas:
(1) In developing easterly stratus along and east of the Blue
Ridge, affecting Lynchburg and the southern Blue Ridge after 06z.
(2) MVFR to LIFR patchy river valley fog in the New and
Greenbrier Valleys, affecting Lewisburg and Blacksburg between
Confidence is moderate at best on stratus ceilings; expect at
least BKN/OVC VFR which at times may drop to MVFR category.
Indicated potential for lower ceilings as a SCT025 group.
Confidence is higher on fog development and end time. If
stratus ceilings develop as anticipated, they may linger until
mid-morning. Light north winds become northeast 3-6 kts in the
Piedmont and foothills, though become light and variable west
of the Blue Ridge.
For Wednesday, again some question on timing stratus scattering
out but by 15z most areas should be VFR. Should see renewed VFR fair
weather cumulus for the afternoon; recent guidance continues to
show spotty showers later in the TAF period but feel these are
overdone with large mid-level dry air in place. Thus will not
mention in the TAF at this point. Winds mainly light east to
southeast through Wednesday.
Aviation Extended Discussion...
Should start to see a front approaching with better threat of
showers/thunderstorms Thursday into Friday. Outside of storms
expect VFR conditions, with possible late night fog by Friday
Saturday looks drier with northwest flow, but could see
lingering low end VFR/high end MVFR ceilings in SE WV along with
a few added shra/tsra mainly southern sections Saturday
afternoon. Expect widespread VFR to return Sunday under high
pressure following the front.