Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/13/18
Area Forecast Discussion...corrected AVIATION
National Weather Service La Crosse WI
600 PM CDT Thu Jul 12 2018
.SHORT TERM...(This evening through Friday)
Issued at 301 PM CDT Thu Jul 12 2018
Latest 18z surface analysis shows cold front extending from over
Lake Superior into southeast South Dakota. Weak moisture convergence
in the 925-850mb layer continues to allow scattered showers/storms
to linger/develop across central Minnesota this afternoon...per
latest mosaic radar.
Main forecast concerns are severe possibilities/showers and storms
over forecast area this evening into tonight. The deterministic
12.12z GFS/NAM/ECMWF are in good agreement in moving surface cold
front slowly southward into southern Minnesota and central Wisconsin
by 12z Friday. Latest hi-resolution and 12.12z deterministic models
show a slower progression of the surface front into the forecast
area than previous runs. This will impact timing of shower/storm
activity to move into the forecast area. At this time...timing of
convection looks to be in the 01-03z into northern parts of the
forecast area. As the front moves slowly south...convection will
overspread southeast Minnesota and western Wisconsin during the
overnight hours tonight. Some of the storms could be strong to
severe mainly north of Interstate 90 this evening and into the
early morning hours Friday...as the latest 12.17z RAP shows 0-3km
of 20 knots and 0-6km most unstable CAPE of 2500-3500 j/kg over
the forecast area. Damaging winds would be a main threat. The
12.12z deterministic models suggest precipitable water values of
1.5 inches to 2 inches over the forecast area.
Shower/thunderstorms will have the potential for sufficient
rainfall amounts and a locally heavy rain threat.
Surface front remains nearly stationary across forecast area during
the day Friday. The 12.12z deterministic models show moisture
transport/convergence at 925-850mb layer and weak lift along front
and this will linger scattered showers and thunderstorms across
forecast area. The latest hi-resolution models indicate scattered
showers/thunderstorms across the forecast area and will continue
this trend in the forecast. At this time...storms should remain
below severe limits...however a few could be strong...as models
suggest 0-6km most unstable CAPE of 3000-3500 j/kg.
Depending on how far south surface front moves and if skies will
be mostly sunny Friday...temperatures will climb to around 90
degrees over the southern forecast area with heat indices of 95
to around 100.
.LONG TERM...(Friday night through Thursday)
Issued at 301 PM CDT Thu Jul 12 2018
The front that is across Minnesota, South Dakota and Nebraska today
will still be in the area at the start of this period. Just where
the front will be is not clear and this is where the uncertainty
resides in the forecast. The variation in the models is from near
the Iowa/Minnesota border from the 12.00Z ECMWF to across northern
Missouri from the 12.12Z GFS with the 12.12Z NAM in between but
closer in position to the GFS.
The upper level ridge will still be in place across much of the
country with the local area still expected to be on the northern
periphery of the ridge and on the southern edge of the westerlies.
The positive tilt short wave trough working across the northern
Rockies today is expected to be moving across the area Friday night
and Saturday. By the time the wave gets to the Upper Midwest it
looks to have lost much of its amplitude and thus should come
through with just some very weak pv advection in the 500-300 mb
layer. While not that strong, there will be increase in the low
level moisture transport ahead of this wave and into the front
Friday night. This forcing should be enough to generate another
round of convection along the front that would primarily be over the
southern sections of the forecast area. With a lack of shear, any
threat for damaging winds and large hail looks very low, but
certainly some potential for heavy rain. Precipitable waters will
still be around 2 inches ahead of the front and warm cloud depths
Friday night will be in the 4 to 4.5 km range. As of now, the area
can take some rain without any concerns for flooding, but if this
round of convection would happen to fall over areas that receive
rain tonight and Friday, it may be necessary with later forecasts to
consider a flash flood watch.
This front should then get pushed far enough south of the area for
relative minimum in the rain chances for Saturday night. The rain
chances will then start to ramp back up Sunday as the next front
gets pushed into the area. An upper level low will be moving across
central Canada with the southern tip of the associated trough
getting drug across the Upper Midwest. The GFS shows more short wave
energy in the southern extent of the long wave trough than the ECMWF
does. With these differences, the GFS has much more convection along
the front than the ECMWF does which for now, will result in just
some general 30 to 40 percent chances Sunday and Sunday night with
the passage of this front. Some lingering chances into Monday across
the southeast until the front is well away from the area and then it
looks like high pressure will build in at the surface for a period
of dry weather from Monday night through Tuesday night. Some rain
chances will then be reintroduced starting Wednesday with the
potential for another system to be running along the northern edge
of the upper level ridge. Significant timing differences between the
models having the upper level ridge becoming centered over the West
Coast and how fast this will happen to allow this next system to
come into the area.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 600 PM CDT Thu Jul 12 2018
Cold front will bring a bkn line of showers/storms across the area
this evening, a few strong to severe. The pcpn will continue
overnight into Fri morning. The front is progged to slip south of
the TAF sites by early afternoon, with more convective potential
later in the day, but also moving south with the front.
Cigs: still looking at mainly VFR through the period, although a
drop into mvfr with any storm remains possible.
WX/vsby: some indications in the meso models that the bulk of the
shra/ts could stay just north of I-90. Will hold with -shra vcts
mention for now, updating for greater impacts from storms as/if
needed. Heavy rain will restrict vsbys at least mvfr, but probably
ifr for a short period also.
Winds: look for a shift from south to more northwest with passage of
gust front/front later this evening. Should hold mostly northwest to
variable for the overnight, trending more west northwest later in
the day Friday.
WI...Heat Advisory until 8 PM CDT this evening for WIZ032>034-041-
MN...Heat Advisory until 8 PM CDT this evening for MNZ079-086>088-
IA...Heat Advisory until 8 PM CDT this evening for IAZ008>011-018-
Area Forecast Discussion
National Weather Service Billings MT
817 PM MDT Thu Jul 12 2018
Water vapor imagery shows a weak shortwave moving from eastern MT
into the Dakotas. There remains a few showers and weak
thunderstorms east of Miles City and Broadus, but nothing to the
west as we move past peak heating and with increasing subsidence.
Have adjusted pops to account for current activity. Expect
convection in our east to be done by midnight if not sooner. It
will be a quiet night of weather thereafter, with mostly clear
skies, light winds and lows in the 50s to mid 60s. JKL
.SHORT TERM...valid for Fri and Sat...
Extensive cumulus field was seen on visible satellite imagery over
the central and eastern forecast area this afternoon. A wave over
W WY could be seen on satellite as well. This wave will propagate
eastward into NE WY by 00Z tonight. For the evening PoPs, used
HREF reflectivities and RAP soundings. Expect convection over the
southern mountains spreading E through the southern tier of the
area this evening. Best lift, CAPE and shear was noted from K4BQ
to KBHK E until about 04Z. Expect heavy rain with any
thunderstorms that develop in this area due to precipitable waters
well above 1 inch. Given the above, cannot rule out hail and
gusty winds with stronger storms as well. Some energy lingers near
the NE Bighorns overnight for a slight chance of thunderstorms.
Forecast for Friday has changed a little, as weak energy and
monsoonal moisture trapped under the ridge, will bring a slight
chance of thunderstorms to the southern mountains and nearby KSHR
and parts of SE MT in the afternoon. The focus for storms will
shift further E into SE MT during the evening. Decent CAPE with
low shear and continued high PWAT`s will continue the threat of
heavy rainfall with storms. The temperature forecast came in a bit
lower with highs in the upper 80s E and NW, and low to mid 90s
elsewhere. The energy under the ridge dissipates for late Fri.
night through Saturday morning for a dry forecast. Energy under
the ridge increases again for Sat. afternoon. At the same time, an
upper low pushes E into N. Saskatchewan, driving a cold front S
through the area. The energy will combine with some frontogenesis
and increasing moisture to bring a chance of thunderstorms to the
mountains and portions of SE MT and Sheridan County. Some storms
could be strong due to decent CAPES and some shear. Highs will
reach the low to mid 90s ahead of the front. Low-level flow
becomes more easterly behind the front Sat. night. The upslope
flow will combine with lift from the mid-level front to produce
scattered showers and thunderstorms Sat. night across the area.
.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...
Little in the way of changes today, as models remain fairly
consistent with periodic isolated shower and thunder potential.
Timing of individual waves of precip continue to be uncertain.
Precip associated with Saturday cold front appears to linger of
southern tier as ridging slowly builds over Idaho. A weak
disturbance trapped beneath the developing low will tap some
monsoonal moisture to additional isolated shower and thunder
potential across mountains and southern zones on Tuesday. Models
diverge significantly art this point, with different takes on
where Ridge builds back into the region. Have continued to carry
more widespread pops through much of the extended period, with nod
toward consistently more active pattern that has required very
little to initiate isolated convection.
As for temperatures. Expected highs in the 70s to around 80 across
the region on Sunday. Highs will trend upward through the next
couple of days as shallow ridging crosses the region, with highs
around 90 for Tuesday. Temps are expected to cool slightly, but
remain in the mid to upper 80s through the remainder of the
VFR conditions will prevail through the period. Isolated
thunderstorms are possible over southeastern Montana and northern
Wyoming, including KSHR and KMLS through about 06z. STP
.PRELIMINARY POINT TEMP/POPS...
Fri Sat Sun Mon Tue Wed Thu
BIL 062/093 065/091 059/078 059/088 061/090 062/085 060/084
00/U 00/U 43/T 21/U 10/U 23/T 21/U
LVM 053/090 055/087 053/078 051/086 053/087 052/083 051/083
01/U 00/U 43/T 11/U 20/U 22/T 11/U
HDN 061/093 063/093 060/079 058/089 060/091 061/087 059/086
00/U 01/U 43/T 21/U 11/U 23/T 22/T
MLS 064/092 067/093 060/077 057/087 062/090 062/085 061/084
10/U 00/U 43/T 11/U 10/U 13/T 31/B
4BQ 062/091 066/096 062/077 057/086 061/089 061/086 060/085
41/U 22/T 54/T 11/U 11/B 23/T 32/T
BHK 061/087 065/093 058/074 054/082 058/086 059/083 057/082
20/U 10/U 44/T 11/U 10/U 23/T 31/B
SHR 057/090 059/092 057/077 054/086 056/088 057/085 055/084
12/T 11/U 44/T 32/T 23/T 23/T 23/T
Area Forecast Discussion
National Weather Service San Francisco Bay Area
900 PM PDT Thu Jul 12 2018
.SYNOPSIS...A weak upper level disturbance and associated
monsoonal moisture will move through from the southeast tonight
into Friday morning, resulting in a slight chance of showers or
thunderstorms from around the Santa Clara Valley northward.
Otherwise, typical July weather conditions are expected to prevail
through the forecast period, with coastal stratus moving inland
around the bays night and morning hours and mostly clear skies
.DISCUSSION...As of 9:00 PM PDT Thursday...Today was a typical
summer day with low clouds clearing to the coast by midday, warm
temperatures inland, and afternoon highs within a few degrees of
The situation developing this evening is not typical, although
an influx of monsoon moisture into our area during the summer
months is not exactly unusual. The incoming monsoon moisture had
increased precipitable water values on the 00Z Oakland sounding to
1.32 inches and PW values will probably increase further overnight
as southeast flow aloft continues to advect mid and upper level
moisture across our area. The most uncertain part of the forecast
is whether a weak mid-level disturbance embedded in the southeast
flow aloft will trigger development of precipitation over our
area later tonight and into Friday morning. Radar data shows high-
based returns currently moving towards the WNW across the San
Joaquin Valley and tracking towards the East Bay. This is
consistent with the 12Z local WRF model which shows light
precipitation developing in the East Bay later this evening and
then tracking to the NW and into the North Bay by around midnight.
The HRRR has the same general idea, but develops precipitation
somewhat later tonight and initially farther to the south over the
South Bay. Current forecast includes shower chances tonight and
Friday morning from Santa Clara County northward and this looks
The primary concern in the short term is whether thunderstorms may
develop overnight and into early Friday. Thus far, all
thunderstorms have been confined to the southern Sierra Nevada
with lightning activity dissipating as the storms move westward
over the Central Valley. However, models indicate there could be
enough mid level instability to trigger isolated thunderstorms
over our area later tonight and into Friday morning and so will
maintain slight thunderstorm chances across the SF Bay Area. 00Z
OAK sounding shows a dry layer below about 8000 feet which may
evaporate much of any precipitation that develops over our area
before it reaches the surface. So there is a potential for dry
lightning, although relatively high PW values may help lower that
potential to some extent.
Shower/thunderstorm chances will primarily be focused over the
North Bay by tomorrow morning as the upper level disturbance
continues to lift to the north. Shower/thunderstorm chances will
then end in all areas by midday as the flow aloft over our area
veers from southeast to southwest, bringing in a drier airmass.
For the remainder of the forecast period, the models forecast an
upper ridge to be centered over or near California, which will
mean continued seasonably warm and dry conditions inland. Onshore
flow is forecast to persist, maintaining a marine layer and
relatively cool conditions in coastal areas. Both the GFS and
ECMWF hint at another influx of monsoonal moisture by late next
.AVIATION...As of 4:30 PM PDT Thursday...Satellite image shows
stratus along the coast with mid and high clouds moving through
the area from SE to NW. While low clouds are expected to spread
onto the coast and possibly into STS...the SE flow is expected to
keep stratus out of SFO and the approach tonight. A few sprinkles
are possible anywhere tonight and Friday and there is an outside
chance of a thunderstorm over the northern SFO Bay Area and North
Vicinity of KSFO...VFR. A few sprinkles possible with a very
remote chance of a thunderstorm.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Southerly winds off MRY Bay will allow
stratus to move in early tonight. IFR after 02Z at SNS and 03Z at
.MARINE...As of 8:57 PM PDT Thursday...A weak low off the central
California coast will keep light southerly winds through Friday.
Winds will become northwest later Friday into the weekend as high
pressure rebuilds over the eastern Pacific. Monsoonal moisture
from the Desert Southwest will bring a slight chance of
thunderstorms tonight and early Friday mainly from the Golden Gate
and points north. A mixed swell is expected to develop over the
PUBLIC FORECAST: Dykema
AVIATION: W Pi
MARINE: W Pi
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Area Forecast Discussion
National Weather Service Blacksburg VA
1126 PM EDT Thu Jul 12 2018
High pressure will build across the region from the north
overnight and remain in place through much of the upcoming
weekend. This should allow for drier weather under seasonable
temperatures the next few days. Increasing heat and humidity
should return along with better chances of showers and storms
ahead of the next cold front for early next week.
.NEAR TERM /THROUGH FRIDAY/...
As of 1123 PM EDT Thursday...
Forecast challenge overnight will be whether we get low clouds
forming in this wedge as winds in the low levels turn more
southeast. The latest high-res models and NAM depict more cloud
cover forming over much of the forecast areas east of the WV/VA
border down into the NC mountains. Will up the sky cover to
trend this way. Showers if any will be mainly isolated and
confined to the Blue Ridge south of Floyd VA overnight with best
threat south of Boone NC. Patchy fog where it rained and in
areas with less cloud cover.
Previous discussion from early this evening...
No major change needed to going forecast. Still looking at
isolated to widely scattered showers with perhaps a rumble of
thunder in the mountains of NW NC, with individual cells
drifting southward. These showers/embedded thunderstorms forming
due to east flow on northern end of 850 mb stalled frontal zone
over central NC, aided by a weak 500 mb vort max pivoting out
of east-central KY. Most recent 18z NAM and past couple HRRR
cycles suggest a continuation of at least showers from Grayson
County VA into the mountains of NW, NC even after sunset and in
spite of cloudy/rain- cooled air as easterly flow continues.
Later tonight and into the overnight, majority of guidance
advects axis of of 925-850 mb RH westward against the Blue Ridge
on the northern extent of the stalled front. This should lead
to an increase in cloud cover especially near and within a few
miles either side of the Blue Ridge/mountains of NW NC. It`s
less certain how far north/east the extent of clouds will be,
which could be low-based. May see intervals of mist at times in
the western mountains but likelihood of at least partly to
mostly cloudy skies limits how low visbys may get in any
fog/mist. Temps look to be on track with lows in the 60s, though
will tend into the lower 60s further north and west into the
Alleghany Highlands/Greenbrier Valley.
Previous discussion follows...
Convection remains limited across the region this afternoon
with the latest SPC mesoscale analysis showing only weak
instability across far southern and eastern sections. This in
locations where higher dewpoints and subsequent low level
moisture persist near the stalled 850 mb front aloft. Latest CAM
model solutions including the HRRR still show isolated showers
mainly NC ridges late afternoon/early evening with much of this
after sunset once mixing relaxes. Also seeing a weak shortwave
remnant within the upper trough pushing through the far
southwest overnight. This may tend to keep some convection going
until midnight if not longer per latest Nam so keeping in low
pops mainly NC mountains overnight. Also guidance indicates a
bit stronger boundary layer easterly trajectory developing
behind the exiting wave late, possibly resulting in more low
clouds near the Blue Ridge by daybreak so boosted clouds some
late given consensus. Otherwise clear north to partly/mostly
cloudy south as current cumulus fields likely transition to
trapped strato-cu in spots with loss of heating. Lows mostly
low/mid 60s with a few 50s northwest/valleys.
Better push of drier air will occur on Friday with any residual deeper
moisture over the southwest sliding to the south Friday morning as the
earlier shortwave exits. Guidance then suggests a pretty dry column by
afternoon as the surface high to the north continues to build in.
However still perhaps enough low level moisture along with weak upslope
southeast flow to pop isolated showers across the NC ridges, but
chances less than today given lack of instability and soundings showing
very limited moisture beneath the inversion around TNB. Otherwise
expect any low clouds/fog to quickly mix out Friday morning with
sunshine increasing under rather deep easterly flow during the
afternoon. High temperatures appear similar to Thursday despite more
sunshine with highs mainly low/mid 80s per only slight warming aloft.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 325 PM EDT Thursday...
Ridge of high pressure initially extending from Halifax to the mid-
Atlantic coast will maintain near normal temperatures along with dry
conditions for most of the Blacksburg forecast area through Saturday
Exception will continue to be from the NW NC mountains north toward
the Grayson Highlands of SW VA, where combination of upsloping
easterly flow on the periphery of the high pressure system and a
slightly moister and marginally unstable airmass will persist
supporting the development of mid-afternoon into evening isolated
showers or thunderstorms.
Situation expected to change slightly Sunday into Sunday night as
surface ridge drifts offshore allowing lower tropospheric flow to
veer into more of a south to southwesterly component. Weak warm
moist advection on backside of departing surface ridge and approach
of subtle weak short wave trofs embedded in nearly zonal flow aloft
will support an expansion of the threat for widely scattered to
scattered showers/thunderstorms to most of the forecast area,
especially in the afternoon and evening - maximized across the
western flanks of the Appalachians.
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 325 PM EDT Thursday...
Longer range models continue to reflect a series of weak, but
randomly spaced and difficult to time short waves embedded in
westerly flow aloft - each of which will support redevelopment of
diurnally-driven widely scattered to scattered showers/storms - with
the threat again maximized across the mountains due to upsloping
flow across the western flanks of the Appalachians coupled with
better differential heating due to local topographical influences.
The highest threat for precipitation during the long-term period now
looks to be in the Tuesday into Tuesday night timeframe. The ECMWF
has now come more in line with what was the more progressive GFS in
maintaining the integrity of a cool front pushing southeast
into/through the Blacksburg forecast area during this period. A
higher degree of confidence now exists for this more aggressive
scenario; however, as is typical for this time of year for weakening
fronts pushing this far south, boundary expected to slow/stall just
south of the area before washing out or beginning a drift back
northward toward the mid-Atlantic region on Thursday.
Uncertainty of frontal position warrants maintaining at least a low
threat of precipitation on Wednesday into Wednesday night, although
it may very well end up being a dry period if front indeed remains
progressive. Regardless, by Thursday, especially by later in the day
across southern portions of the forecast area, threat should again
be on the increase as lower level winds begin to veer into the south
in advance of an even stronger cool front that is expected to arrive
on Friday or Saturday.
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
As of 731 PM EDT Thursday...
VFR conditions should prevail through the rest of the afternoon
until late this evening. Isolated to scattered showers with embedded
thunder still possible through 01z along the mountains of NW NC,
with isolated showers in this general area through the rest of
the overnight. After around 05z, should see a period of
restricted conditions develop as low clouds begin to develop
across at least the southern Blue Ridge into Floyd/Montgomery
Counties. 15z SREF probabilities of MVFR ceilings are quite
high (around 70-90% within a few miles of the Blue Ridge). Have
currently shown MVFR ceilings in this area (mainly affecting
Blacksburg and later Bluefield TAFs), though some level of
uncertainty on northern extent of this MVFR deck from Roanoke
north. May see some mist in the western mountains but coverage
limited to the river valleys and visbys no worse than IFR. Winds
tonight from the east between 3-6 kts.
Should be able to scatter out any MVFR low clouds by around
mid- morning Friday revealing SCT Cu/SC and VFR conditions.
Winds mainly east 3-5 kts except southeast at Bluefield on the
western end of the wedge.
High pressure will dominate with VFR conditions into Saturday
before moisture increases ahead of the next upstream cold front
for early next week. This may allow for isolated convection
Sunday, including localized restrictions to ceilings and
visibilities, to become more widespread especially mountains by
Monday afternoon and across the region on Tuesday. However
confidence is too low to pinpoint where the showers and
thunderstorms may occur.
As of 1205 PM EDT Thursday...
The NOAA weather radio transmitter in Hinton, West Virginia, WXM72
on a frequency of 162.425 MHz, is back on the air. We thank our
listeners for their patience during this extended outage.