Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/04/17
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1147 PM EDT Thu Aug 3 2017
.AVIATION...
The next round of thunderstorms is lifting into SW Lower Mi in
advance of a mid level cold pool associated with an upper low across
the western Great Lakes. These storms are expected to undergo at
least some slight weakening as they rotate into Se Mi (06Z to 09Z
time frame) where the available instability will be less. There is
some question as to how much this region of convection will fill in
farther north, raising some doubt as to whether or not FNT and MBS
will see any convection. An associated cold front will push through
around 12Z. Increasing low level moisture will support some MVFR
based strato cu. Increasing post frontal mixing depths will result
in gusty SSW winds by late Fri morning, persisting through the
afternoon.
For DTW...The cluster of storms across far Sw Lower Mi and NW
Indiana should track across metro Detroit during the first couple
hours of the TAF period. Although some weakening is expected, the
current radar suggests they will hold together into metro Detroit,
arriving around or shortly after TAF issuance.
//DTW THRESHOLD PROBABILITIES...
* Low in ceilings at or below 5000 ft tonight. Moderate on Friday.
* Moderate in thunderstorms early this morning.
&&
.PREV DISCUSSION...
Issued at 913 PM EDT Thu Aug 3 2017
UPDATE...
A region of mid level subsidence/anticyclonic flow has emerged in
the wake of the earlier convection. This will suppress additional
convection through the next several hours over most of the forecast
area. Additional thunderstorms are located across far ern Wisconsin
and Lake Michigan along the lead edge of the mid level cold pool.
This convection is expected to track across Se Mi overnight as the
upper low rotates across nrn Wisconsin. The latest CAMs continue to
suggest this convection will weaken as it head into Se Mi, with some
solutions actually suggesting it falling apart completely. This
remains very much in line with the thoughts in the earlier forecast
discussion. A forecast update was already issued simply to lower the
chances of convection through the remainder of the evening.
PREV DISCUSSION...
Issued at 400 PM EDT Thu Aug 3 2017
DISCUSSION...
Hefty convective potential and severe weather remains a concern for
the late afternoon through evening. The early to mid afternoon
convection has struggled to make the most of surface based CAPE
around 2500 J/kg and 100 mb MLCAPE in the 1500-2000 J/kg range
mainly due to the lack of a good wind shear profile. Upstream
convection over SW lower MI, northern IN, and points west is
expected to develop eastward through the warm sector and along the
warm front that will be making a stronger northward move as low
pressure approaches Lake Michigan. The upper wave and associated
stronger wind field aloft will also be moving closer which will
provide a modest increase in the wind profile. The RAP component in
the hourly mesoanalysis indicates 0-6 km shear near 30 knots will be
reachable. Combine that with sfc-3 km helicity in the 100-150 m2/s2
and the CAPE values mentioned above for convection to possibly
organize supercell modes through the peak heating cycle. Storms with
large hail and damaging wind remain possible over all of SE MI while
the I-69 corridor northward will be the primary area affected by the
northward moving warm front and supercell/tornado possibilities.
Storms developing over the MS valley at press time represent round 2
of storms expected to move through lower MI overnight, along and
ahead of the cold front. The 3 km NAM has the most aggressive
solution and maintains a broken line of storms through SW lower MI
while CAPE remains surface based around 1500 J/kg. It then depicts a
weakening trend and some reduction in areal coverage overnight as
the band moves through SE MI during the diurnal minimum. Considering
the moderate forcing associated with the front/low pressure system
and the potential for lingering elevated instability, expect numerous
coverage of showers and scattered thunderstorms with not much severe
potential.
Forecast concerns Friday are limited to gusty southwest wind post
front, especially in the dry slot of the system as low level cold
advection combines with daytime heating to build the mixed layer.
The result will be wind gusts around 30 mph into early evening. This
will be followed by the trowal/deformation band of showers projected
to rotate through lower MI Friday night with greater coverage toward
the Tri Cities and northern Thumb. The system remains progressive
enough to exit eastward by Saturday in favor of weak high pressure
that will salvage one day of the weekend.
The region will remain in longwave troughing to finish the weekend
and start off next week as an associated surface low also treks
across the Ohio Valley. This will continue to bring chances for
unsettled weather as highs remain in the 70 degree range. By Tuesday,
conditions will dry out as weak ridging and surface high pressure
move in behind the departing low. Temperatures moderate back into the
80s to round of the extended forecast period.
MARINE...
A warm front will be lifting north over southern Lake Huron this
afternoon and evening. Winds vary relative to the front, with modest
northeasterly winds on the north side and southerly winds on the
south. Unstable airmass with the front will support thunderstorm
chances through the evening hours. Low pressure lifting northeast
through the western Great Lakes tonight will pull a strong cold
front through the eastern Lakes on Friday. Another round of
thunderstorms may accompany the front. In addition, winds will
increase behind the front while becoming southwesterly with gusts
approaching 30 knots. This may necessitate small craft advisories
for all nearshore zones. A period of higher west to northwest winds
may also accompany the passage of the strong low pressure Friday
night and early Saturday. Gusts may reach gale force over much of
the Lake Huron Basin during this period.
HYDROLOGY...
Scattered thunderstorms will continue to develop through the
afternoon and evening hours as a warm front lifts north through the
area. A second round of storms will then be possible late tonight
into Friday morning as a cold front sweeps through the area.
Rainfall totals will vary greatly across the region given the
scattered nature of any development. Higher amounts in excess of 2
inches will be possible on a localized basis within any heavier
thunderstorms in part due to storms moving very slowly. This could
result in significant runoff and some flooding, particularly within
urbanized and poor drainage areas. The passage of the cold front on
Friday will bring an end to the showers and storms.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Watch from late Friday night through Saturday evening for
LHZ361>363-462>464.
Small Craft Advisory from noon Friday to 6 PM EDT Saturday for
LHZ421-422-441>443.
Lake St Clair...Small Craft Advisory from noon Friday to midnight EDT Friday night
for LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory from noon Friday to midnight EDT Friday night
for LEZ444.
&&
$$
AVIATION.....SC
UPDATE.......SC
DISCUSSION...BT/SP
MARINE.......DRK
HYDROLOGY....DRK
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1042 PM EDT Thu Aug 3 2017
.SYNOPSIS...
A cold front will move in from the northwest Friday night and become
stationary west to east across our region this weekend. Low
pressure will move northeast from Texas late Sunday and pull the
front northward as a warm front into Monday. As this low pressure
moves off the New England coast, the trailing cold front will become
stationary again across the region into mid week. The next low
pressure system and associated front moves closer to our region
later in the week.
&&
.NEAR TERM /THROUGH FRIDAY/...
As of 1040 PM EDT: As expected, radars to the southwest are showing
diminishing late evening returns on the upstream precipitation over
central GA as the activity moves into less unstable air over NE GA.
Still cannot rule out a stray shower over the piedmont overnight,
but the better moisture through daybreak Friday should pass mainly
southeast of our piedmont zones. The current temperature forecast
appears on track, with high clouds slowly thinning from the west,
but with mid clouds returning from the south late tonight.
Otherwise, the upper trough will sharpen during the period, as
strong short wave energy progresses across the Great Lakes. This
will send a weak front into our area from the west by the end of the
day tomorrow. With moist SW flow becoming established east of the
frontal boundary through tomorrow afternoon, and the cirrus shield
finally shifting east of the area, the models develop some
respectable instability across the forecast area Friday afternoon.
We should see scattered afternoon convection develop across the
usual high terrain spots, while additional convection could fire
along cloudy/clear differential heating boundaries near our southern
and eastern zones. Additional pre-frontal scattered convection, or
even clusters of convection may also move into the area from East TN
by the end of the day. Pops will be advertised in the 30-50% range
across much of the area, with some high terrain locations near the
TN border seeing likely by late afternoon. Forecast max temps fall
just short of climo.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 215 PM EDT Thursday: A sfc cold front should push into the NC
Mountains Friday evening, and may stall along the Blue Ridge until
after daybreak Saturday. From there, the operational models seem to
be trending toward pushing the front a little further south into the
Midlands by Saturday AFTN, before stalling. convection along/ahead
of the front should gradually wane, but PoPs don`t completely cut
off, due to the front in the area Friday night. With the front a
little to the south, Saturday may be largely dry for most of the
area, except for the southern Upstate and Upper Savannah Valley.
However, I only blended in the new guidance, so the fcst still
features slight CHC to CHC PoP everywhere in the CWFA. A small
severe threat may linger Friday evening, as convection may be
quasi-organized along the front. But otherwise, there doesn`t look
to be enough overlap of bulk shear and high CAPE for severe weather
thru Saturday evening. Temps will be near normal Friday night, and
slightly below normal Saturday.
For Saturday night thru Sunday, upper level flow becomes quasi-zonal
with an impulse streaming thru the Central Plains to the mid-MS
Valley. This wave will back the lower and mid-level flow atop the
CWFA, and bring moisture and instability back into the area. I don`t
know if I`d call it a warm front, but in any case, the stalled
frontal zone will lift back north slightly by Sunday morning. Models
are in good agreement on better instability and more widespread
convection across the area. Shear will remain weak, so severe threat
should be low. Temps will continue to show less diurnal range than
climo due to the unsettled weather.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 155 PM EDT Thursday: The medium range period begins Sunday
evening with our west to east oriented stationary front beginning to
move north as a warm front. This is in response to low pressure
moving northeast from Texas pulling the front north and with a
trailing cold front which will approach our region from the
northwest late Monday. This scenario will enhance our POPs for late
Monday and could result in a few severe storms, especially if some
period of solar heating ahead of the approaching cold front occurs.
The coverage of strong to severe storms will have much to do with
the timing of the front. Models show good moisture advection along
and ahead of the frontal zone with Precipitable Water values on the
GFS around 2 inches and even above south of I-85. The current ECMWF
has the front arriving in time for late Monday solar heating while
the GFS has the front arriving early Tuesday. As the low pressure
moves to the New England coast Monday night or Tuesday, the front
eventually lays out across our area becoming stationary into
Wednesday. PWat values remain high and peaking again above 2 inches
south of I-85 late Wednesday and Thursday as the next northern wave
in the 500mb flow passes just north of the Great Lakes. The high
PWats and potential training of convection along the stationary
front will present hydro concerns in the upcoming week. Surface dew
points across the foothills and piedmont late Monday and again late
Wednesday and Thursday will be 70 or above.
Max temperatures 2 to 5 degrees below normal and Min Temperatures 2
to 3 degrees above normal due to the extensive cloud cover.
On the GFS beyond the current forecast shows a hurricane Sunday
morning August 13 between the Bahamas and Bermuda. The trough over
the Eastern part of the nation would steer it to go between Bermuda
and the Carolinas then away from Eastern Seaboard.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Another round of fog/low stratus in the mtn
valleys around KAVL Fri morning appears possible, although signals
are mixed with the RAP rather bullish while the MOS sources much
less so. Will feature a fairly solid window of IFR fog and stratus
at KAVL given recent history at the site. Otherwise, any showers
encroaching from the south overnight should pass mainly by to the
southeast of the terminal forecast area. Some models also hint at
low stratus for southern and eastern piedmont sections, and will
feature SCT010 at KCLT in a nod in that direction, but confidence is
too low for restrictions at present. Lower to mid clouds will
thicken up through the day on Friday ahead of the approaching front,
and convective chances will ramp up from the west during the
afternoon hours. PROB30 throughout appears warranted mainly after
17Z west and 18Z east. Winds should generally be southerly, with
some low end gusts across the SC sites during the afternoon hours.
Outlook: Showers and thunderstorms may continue across the region
into Friday night as a cold front moves in from the northwest before
stalling over the lower piedmont. Moisture returning over the front
may permit convection to return through the late weekend and then
conditions will become quite unsettled through the middle of next
week. Restrictions will be possible with any showers or
thunderstorms and fog and low clouds will be possible each morning
around daybreak, mainly in the mtn valleys, but also in areas that
receive heavy rainfall the day before.
Confidence Table...
02-08Z 08-14Z 14-20Z 20-00Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% Low 29% High 81% High 100%
KHKY High 100% High 100% High 100% High 100%
KGMU High 100% High 100% High 100% High 100%
KAND High 100% High 98% High 80% High 100%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
www.weather.gov/gsp/aviation
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...DEO
NEAR TERM...HG/JDL
SHORT TERM...ARK
LONG TERM...DEO
AVIATION...HG/JDL
Area Forecast Discussion
National Weather Service Wilmington OH
1019 PM EDT Thu Aug 3 2017
.SYNOPSIS...
A cold front will approach the region tonight and move through
on Friday. Dry conditions and high pressure will then move into
the region for Friday night into Saturday.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Surface cold front is currently located across central Illinois
this evening and has made good progress over the last couple of
hours. Evening showers and thunderstorms triggered by daytime
heating have slowly decreased in coverage with this trend
forecast to continue. There are some pockets of PV racing
northeast ahead of a cutoff low approaching Wisconsin. High res
models have been inconsistent with this very early morning
precipitation so for the most part have left the area dry.
Friday morning between 4 and 6 AM the prefrontal trough will be
approaching the area from the west. The upper level support
looks promising but with the passage at daybreak the instability
is paltry. Even with PWATs around 1.55" high res models only
show a thin line Friday morning. The prefrontal trough axis will
then push east towards Wilmington between 9 and 11am. The
prefrontal then looks to clear the CWA early Friday afternoon.
The surface cold front will then push through right behind the
trough axis. The latest runs of the HRRR try to reignite
convection along the front. The ARW and NMM aren`t this
aggressive. Most likely convection will get going across our
far eastern CWA border and then continue to push east. Behind
the cold front PWATs will plunge to ~0.65" (1 to 2 standardized
anomalies below normal for this time of year). Winds will also
be breezy with gusts up to 20kts possible (GFS forecast
soundings slightly more aggressive with wind gusts than NAM
forecast soundings). Temperatures will hold steady and then
slowly fall behind the front with clouds being slow to clear.
Prev Discussion->
Isolated to scattered showers and thunderstorms will be in
place this afternoon and into the early evening hours due to
daytime heating and instability. An isolated damaging wind gust
cannot be ruled out, however not expecting more than an isolated
severe potential.
Activity will briefly taper off later this evening, however
additional shower and thunderstorm activity will begin to move
into the region late in the overnight hours in advance of a cold
front.
Temperatures will only drop into the middle to upper 60s
overnight with some cloud cover through the overnight hours.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
A cold front will move through the forecast area on Friday.
Expect the greatest coverage of thunderstorm activity across
eastern portions of the area where there will be more daytime
heating. This will also be the area that has a higher potential
for damaging wind gusts with the storms. Will continue to have
severe mention in the hazardous weather outlook. After this
feature moves through expect cooler and drier conditions for
Friday night.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Surface high pressure will build in across the area through the day
on Saturday. This will be accompanied by a cooler and drier airmass
with daytime highs five degrees or so below normal, generally in the
mid to upper 70s.
The surface high will shift off to the east through the day on
Sunday and with progressive zonal flow aloft, some embedded mid
level energy will push east across the region. There are still some
timing differences between the models with these features with the
12Z ECMWF still the fastest bringing pcpn into our area. Will
therefore go ahead and allow for chance pops to spread in from the
west through the day on Sunday. Instability is pretty marginal so
would expect mainly showers with perhaps some embedded thunder.
Temperatures on Sunday will be dependent on how fast the clouds and
any pcpn moves in but for now will keep highs in the 75 to 80 degree
range.
A stronger short wave will approach from the west Sunday night into
Monday with an associated surface wave riding up through the Ohio
Valley. This will lead to increasing chances of pcpn for Sunday
night and continuing into Monday. Instability remains fairly
negligible Sunday night but is forecast to increase some through the
day on Monday. Expect highs on Monday again in the 75 to 80 degree
range.
We will then remain in a fairly progressive westerly upper level
flow pattern through the mid to late part of next week. There are
some model differences through mid week with the GFS trying to bring
a surface wave up across the Appalachians. This could eventually
lead to a chance of showers toward mid week but will trend toward
the drier ECMWF at this point. Highs will trend back up into the
upper 70s to lower 80s through the end of the period.
&&
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Isolated convection has formed thanks to daytime heating this
afternoon, but the main show for convection has remained in
Indiana towards the better upper level diffluence and
divergence. Activity will diminish later this evening as daytime
heating is lost. Overnight into Friday morning a potent upper
level low will push east towards Michigan. As this happens high
res models are trying to show some midlevel energy pulling
northeast out in front. Not surprisingly high res models try and
develop some light showers after midnight Friday morning and
quickly pull them northeast. For now have left the mention of
precipitation out of the TAFs until the prefrontal trough
arrives later Friday morning given low confidence on location/
occurrence.
Friday morning between 5 and 7 AM the prefrontal trough will
push towards the OH/ IN state line. Most likely a weak band of
showers will be present with this trough axis. Latest runs of
the HRRR and RAP are not impressive to say the least. Thunder
will be possible as elevated instability remains, but think the
chance is low at this time. Friday morning (or before noon) the
RAP and HRRR actually have the prefrontal trough approaching
KCMH/ KLCK. Behind the prefrontal trough winds will veer to the
SSW and the chance of thunder will begin to greatly diminish.
The cold front will be right behind the trough axis and usher in
much drier air (PWATs falling from ~1.5" to 0.75") and breezy
conditions. GFS forecast soundings are indicating wind gusts up
to 20kts possible while the NAM is slightly lower (via momentum
transfer). The other concern will be MVFR cigs as the upper
level low pushes east across Michigan (moisture being trapped
underneath the inversion). Overall thinking is that most TAF
sites will remain VFR with the exception being the northern TAF
sites. Even at the northern TAF sites confidence is only
moderate.
Friday evening surface high pressure will slowly build in from
the west with winds being slower than normal to decouple (due to
the pressure gradient). Clouds will also slowly decrease in
coverage.
OUTLOOK...Showers and isolated thunderstorms are possible
Sunday night into Monday.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...Haines/Novak
NEAR TERM...Haines/Novak
SHORT TERM...Novak
LONG TERM...JGL
AVIATION...Haines
Area Forecast Discussion
National Weather Service Lincoln IL
839 PM CDT Thu Aug 3 2017
.UPDATE...
Issued at 839 PM CDT Thu Aug 3 2017
Cold front progressing across central IL this evening is currently
aligned from near Jacksonville to Pontiac, moving steadily
eastward. Ahead of the front, MLCAPE values up to around 2000
J/KG, and these are steadily diminishing from a peak of 2500-3000
J/KG late this afternoon. As a result, thunderstorm activity is
diminishing as well, with severe weather likelihood diminishing.
Behind the front, precipitation and thunderstorms ending, with a
period of clearing skies moving in. Expect the front to pass I-57
by midnight, and move into Indiana a few hours later. Only minimal
updates needed for clearing behind the front this evening. Much
cooler and drier air behind the front should result in lows
dropping into the mid and upper 50s across central IL, with low
60s south of I-70.
&&
.SHORT TERM...(This evening through Friday)
ISSUED AT 259 PM CDT Thu Aug 3 2017
Pre-frontal convection has been tracking across central Illinois
this afternoon, aided by surface based CAPE`s reaching 3500 J/kg.
The storms are still ahead of the better shear though, and have
mainly been responsible for heavy rain and some winds to around 40
mph or so. Main cold front is still back across eastern Iowa into
west central Missouri, with a sizable gap in convection along it.
In terms of any threat of strong storms, what`s going on now may
actually be the main show, as the higher resolution models suggest
more of a disorganized line ahead of the front this evening. The
NAM and ARW suggest the rain should be done as early as midnight
in our CWA, while the HRRR, GFS and RAP linger it a bit longer in
the far southeast. In the forecast, rain will be gone from the
Illinois River valley by about 10 pm, and will limit any post-
midnight rain to areas along and east of I-57.
Strong upper low currently over north central Minnesota will swing
eastward toward eastern Lake Superior by Friday afternoon.
Associated stratocumulus deck is expected to linger across areas
northeast of I-74 into the afternoon hours, which should help keep
high temperatures down, close to 70 degrees. Some afternoon
sunshine further west and a warming air mass behind the main
trough will allow for some warmer conditions, but still only in
the mid 70s.
.LONG TERM...(Friday night through Thursday)
ISSUED AT 259 PM CDT Thu Aug 3 2017
Main focus in this period will be with timing of rain trends
Saturday night into Monday night, as a strong west-east upper
trough near the Canadian border swings southeast toward the mid-
Mississippi Valley. The ECMWF and NAM models develop an MCS west
of the Mississippi Saturday afternoon and roll it into much of the
CWA as early as Saturday evening, associated with a leading
shortwave, while the GFS is weaker and keeps us dry most of the
night. Didn`t go quite as fast with the rain, but have brought in
healthy chance PoP`s in most areas by midnight, with likely PoP`s
in the far southwest after midnight Saturday night. As this MCS
tracks toward southern Illinois, the northwest CWA will see
temperatures kept down a fair amount with a northeast flow, mainly
lower 70s for Sunday. Areas further south will see periods of rain
and a few storms as the system passes, largely out of the area by
late Sunday evening as the cold front exits the area. Beyond that,
while the ECMWF would suggest dry conditions with high pressure
building eastward, the arrival of the earlier mentioned trough
axis would support at least chance PoP`s on Monday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 659 PM CDT Thu Aug 3 2017
A cold front just west of the Illinois River at 00Z will push
eastward across central IL through the evening, reaching Indiana
shortly after 06Z. A broken line of thunderstorms will accompany
the frontal passage as well as some isolated thunderstorms well
ahead of the front. Most thunderstorm activity is expected to pass
through the central IL terminals by 04Z. A region of low cloud
cover will pass over the area Friday morning, promoting a period
of MVFR cigs from KPIA-KDEC northeastward starting around 12Z.
Conditions expected to return to VFR after 18-20Z. Winds S 6-12
kts this evening, shifting to W-NW behind the cold front this
evening, and increasing to around 15 kts with gusts to 25 kts by
18Z.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...37
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...37
Area Forecast Discussion
National Weather Service Northern Indiana
1026 PM EDT Thu Aug 3 2017
.SYNOPSIS...
Issued at 345 PM EDT Thu Aug 3 2017
Thunderstorms will continue across the area through early tonight
ahead of a strong cold front and associated vigorous upper level
system. Much cooler weather will arrive Friday with highs only in
the 60s over northwest Indiana and the lower 70s over most of
northwest Ohio. The cool air will continue over the area through
Tuesday with highs in the 70s.
&&
.UPDATE...
Issued at 1020 PM EDT Thu Aug 3 2017
Round 1 of storms departing to the east with next batch already on
our doorstep with scattered storms in far NW parts of the area,
extending back to the southwest. Few strong to locally severe
storms were noted earlier back over Illinois but storms have
generally congealed and are tracking ENE. Unsure how much more
coverage will change in the coming hours with HRRR suggesting more
expansion and some intensification possible. Still some bowing
segments noted from time to time but one of the better looking
ones that passed through Kankakee, IL did little more than around
35 mph winds. Will hold with 50 pops as the storms move through
and go with sct wording for the time being with the bulk of the
convection moving through in the span of an hour or 2 tops.
Other change to grids was to increase winds into tomorrow over
land and lake and move up start of small craft advisory and beach
hazards a few hours based on faster arrival of winds.
&&
.SHORT TERM...(This Evening through Friday)
Issued at 342 PM EDT Thu Aug 3 2017
Storms were continuing to develop upstream over Illinois ahead of an
upper level TROF and an associated cold front. Mid afternoon surface
based CAPEs had risen above 4000 J/Kg per SPC meso analysis over
Central Illinois where storms were becoming better organized. Mid
level lapse rates were still quite stable and should limit overall
storm development. Expect marginally severe storms with hail to near
1 inch and wind gusts approaching 58 mph mainly west of highway 31
before 10 pm EDT, with activity diminishing overnight. Otherwise,
the cold front will move across the area tonight and bring much
cooler weather for Friday. Kept highs in the 60s over northwest
areas. Will continue the Beach Hazard Statement for Friday given a
fall type strong pressure gradient behind the front.
&&
.LONG TERM...(Friday Night through Thursday)
Issued at 342 PM EDT Thu Aug 3 2017
Cooler air will continue over the area through early next week with
highs in the 70s as northwest flow aloft persists. Occasional upper
level disturbances moving through an amplifying upper level TROF
will provide chances for showers and storms Sunday and Monday, and
possibly again Thursday. High temperatures should recover a few
degrees by Wednesday and possibly top 80 degrees.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 725 PM EDT Thu Aug 3 2017
A lull in showers and thunderstorms occurs early before the cold
front comes in perhaps with one more chance of showers and
storms. Behind the cold front, expect cooling and subsidence and,
with the entrance of a low level jet, a hint at the possibility of
stratus clouds enters the mind rather than fog. Models have CIGs
dropping to MVFR levels and will go with that thinking for now.
Also, with the low level jet nearby, we`ll have to keep an eye on
if any LL Shear forms overnight, but will keep it out at this
time.
Low level jet will remain nearby the region on Friday allowing for
gusty winds during the time of diurnal heating.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Beach Hazards Statement from 5 AM CDT Friday through Saturday
morning for INZ003.
MI...Beach Hazards Statement from 6 AM EDT Friday through Saturday
morning for MIZ077.
OH...NONE.
LM...Small Craft Advisory from 6 AM Friday to 11 AM EDT Saturday for
LMZ043-046.
&&
$$
UPDATE...Fisher
SYNOPSIS...Skipper/Roller
SHORT TERM...Skipper
LONG TERM...Skipper
AVIATION...Roller
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Area Forecast Discussion
National Weather Service San Francisco Bay Area
440 PM PDT Thu Aug 3 2017
.SYNOPSIS...Monsoonal moisture overhead will bring a slight
chance for showers and thunderstorms going into tomorrow.
Gradual cooling is expected from Friday through the weekend.
A weak disturbance will bring another opportunity for showers
and thunderstorms over the North Bay Saturday night into Sunday.
&&
.DISCUSSION...As of 12:40 PM PDT Thursday... Monsoonal moisture
continues to stream into the southern two thirds of California in
a band at 700 to 500MB, bringing a dynamic cloudscape across the
region. KMUX radar has picked up on some light radar returns
within the primarily weak convective development, but most
precipitation occurring will fall as virga due to the relatively
drier air mass below the cloud bases/closer to the surface. Most
convective development has been limited in vertical development (a
proxy of storm cell strength) due to the limited PWAT values and
limited instability aloft. PWATs across our forecast area area
gradually ticking upward and are around 0.8-1.0", however, more
deeper convection does not appear to be occurring until PWATs push
above 1.5" to 2.0" (such as the case in SoCal). That said,
forecast models indicate there is still enough moisture and
instability aloft to include a slight chance of thunderstorms
across the area. Both the NAM12 and HRRR short term forecast
models are suggesting that the most likely time frame for any
thunderstorms will be late this evening through tomorrow morning,
focusing around the 3-6am time frame. The latest few HRRR runs
focus the bulk of convective development from the Golden Gate
southward towards Big Sur during this time frame, however,
elevated convection is notoriously difficult to resolve spatially
and temporally. Any thunderstorms that do develop will generate only
a few lightning strikes before weakening as the convective
parameters are still marginal at best. Models show convection
potential waning by midday tomorrow.
A second opportunity for convection will occur as a small
retrograding cut off low reverses course and makes landfall over
the North Bay/Northern California coast. This will bring the best
chance of the week for thunderstorms, primarily to the
aforementioned regions, late Saturday through Sunday morning.
Otherwise, temperatures today are running a fair bit cooler
farther inland and at higher terrain, while coastal locations are
actually a degree or two warmer, primarily due to the higher dew
points and overnight minimums from the monsoonal airmass saturating
the lower levels. The heat advisory for elevations at or above 750
ft will continue through the remainder of the day and expire this
evening as the ridge subsides.
The next few days will play out similar to today, with warm but
gradual cooling temperatures inland, slightly below normal
temperatures along the coast, an increased onshore presence and
marginally deepening marine layer, and a continuation of the partly
to mostly cloudy skies in the mid to upper level layers with a
slight risk of isolated thunderstorms. For those interested, the
next few sunsets and sunrises will be extremely photogenic as the
low level stratus contrasts with the mid to upper level fractured
cumulus.
&&
.AVIATION...as of 4:40 PM PDT Thursday for 00Z Friday TAFs. VFR
conditions are expected to prevail at all sites as high clouds
associated with monsoonal moisture continue to pass over the
region. There remains a slight chance that an isolated shower or
even a thunderstorm could develop this evening and overnight, but
the odds of it impacting a single site remain slim. Therefore,
will continue to withhold from TAFs.
Vicinity of KSFO...VFR conditions expected to prevail through the
period.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR conditions expected at both KSNS and
KMRY. Similar to yesterday, think the chances of seeing any low
clouds remain low as the high clouds blanket the region. Will
continue to monitor and amend if necessary.
&&
.MARINE...as of 04:25 PM PDT Thursday...Light winds are expected
to continue across the coastal waters through the week. There`s a
slight chance of thunderstorms for the waters tonight and into
tomorrow morning as mid and high level monsoonal moisture
continues to sweep over the region.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Heat Advisory...CAZ507-511-512-517-518
SCA...SF Bay until 11 PM
&&
$$
PUBLIC FORECAST: DRP
AVIATION: Rowe
MARINE: AS
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Area Forecast Discussion
National Weather Service Pueblo CO
319 PM MDT Thu Aug 3 2017
.SHORT TERM...(This evening through Friday)
Issued at 256 PM MDT Thu Aug 3 2017
Initial upper wave and associated precip dropping south into NM as
of 21z, while next weak feature was already forcing an area of tsra
along the Front Range from Pikes Peak northward. LAPS and SPC
mesoanalysis suggest narrow ribbon of instability is still present
along and west of I-25 at mid-afternoon, with CAPES above 1000 J/KG
from west of Colorado Springs south to Trinidad. Expect at least
weak convection to move southward over the eastern mountains and
adjacent plains into the evening, with HRRR suggesting a few
stronger storms over the Wets and srn I-25 corridor in the 22z-02z
time frame. Main concern the next few hours will be heavy rain on
the Junkins/Hayden Pass burn scars, though rather brisk storm
motions of 20-30 mph may help limit rainfall amounts somewhat.
Plains east of the interstate look fairly stable, and will keep
convective chances in the isolated range here. Convection shifts
southward and weakens after sunset, with some lingering -shra over
the srn mts and along the NM border after 06z.
On Friday, warmer and somewhat drier conditions spread across the
region as low level southerly flow strengthens by midday, especially
across the eastern plains. With best low level moisture suppressed
south and west, expect greatest coverage of afternoon convection to
sink sw into the San Juans/La Garitas, while remaining higher
terrain locations and interior valleys see mainly isolated storms.
Interstate 25 corridor will see some isolated spill-over storms late
in the afternoon, as higher terrain convection drifts se. Tsra
chances over the far sern plains look rather low, though one or two
storms could fire along the lee trough just east of I-25 by early
evening. Max temps will climb several degf from Thursday`s cool
readings, especially over the eastern plains, though most locations
will still end up at or slightly below seasonal averages.
.LONG TERM...(Friday night through Thursday)
Issued at 256 PM MDT Thu Aug 3 2017
Northwest flow will remain over the area resulting in a relatively
cool and unsettled extended forecast period. Friday evening most
of the thunderstorm activity will be over the mountain areas
though a few my drift off into the adjacent plains and may fire
along the surface trof axis. Saturday looks like a relatively
quiet day across the plains...but moisture and another disturbance
will trigger scattered to numerous showers and thunderstorms
across the mountains during the afternoon and evening. Saturday
night a cold front drops through the plains increasing surface dew
points and CAPE values for Sunday afternoon. This could be
another potential severe day across the plains as deep layer
shears are running around 35-40 kts. Thunderstorms could carry
over into Sunday night as an MCS forms north of the frontal
boundary. It appears we enter another wet period for much of the
following week...as upslope flow keeps low level moisture across
the plains, and west to northwest flow aloft sends a series of
disturbances across the region. Monday may be pretty stable on the
plains given the previous nights convection...but after that CAPE
values climb back up to 1000 j/kg or better each afternoon (depending
on the day) across the plains. -KT
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 256 PM MDT Thu Aug 3 2017
Scattered -shra/-tsra will impact all taf sites late this afternoon
and evening, with brief periods of MVFR cigs/vis under any heavier
convection. Precip ends late this evening, then MVFR or brief IFR
cigs/vis in stratus/fog become possible at KCOS and KPUB after 10z
as low level winds SE winds continue. On Friday, afternoon
convection will again develop over the mountains after 18z, with at
least a low chance of -tsra at all terminals after 20z.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...PETERSEN
LONG TERM...KT
AVIATION...PETERSEN
Area Forecast Discussion
National Weather Service Las Vegas NV
702 PM PDT Thu Aug 3 2017
.SYNOPSIS...Much of the Mojave Desert and southern Great Basin will
have a chance thunderstorms through this evening. Heavy rain and
flash flooding will be possible with storms across the Mojave
Desert. Thunderstorm coverage will trend more isolated and shift
eastward Friday into the weekend with thunderstorm activity becoming
more limited to the higher terrain by Sunday. Temperatures will be
a little below normal through the weekend.
&&
.UPDATE...I`ve trimmed the watch back, eliminating the Morongo
Valley, the Colorado River Valley south of Bullhead City, and
Southern Mohave County this evening. In addition, I extended the
remaining areas of the watch through 10z since storms are likely to
arrive around the previous expiration time. The rest of the details
from the previous update still stand. Will continue to monitor and
update as needed. -Wolcott-
&&
.PREV UPDATE...440 PM PDT Thu Aug 3 2017
Convection has struggled somewhat to get going this afternoon across
much of the forecast area. Conditions are becoming more favorable
for scattered storms (likely developing into broken line segments)
to push south/southwest late this afternoon/early this evening
across Esmeralda, Nye, Lincoln, northeastern Clark, and northern
Mohave Counties. This is due to a combination of ample
destabilization from daytime heating as well as a developing cold
pool that should help create lift. Current short range guidance and
mesoanalysis suggests that the cold pool with push south to around
the Clark/Lincoln county line or perhaps to near the Sheep Range
north of Las Vegas before dissipating and shearing off the the west.
This means that Las Vegas and areas south may not see much activity
through the evening.
To the south, cloud cover and trailing subsidence behind the
vorticity max across San Bernardino County has limited afternoon
convection. The Flash Flood Watch has been cancelled for those
areas. For the moment I left the Morongo Valley, Lower Colorado River
Valley, and southern Mohave Counties in place with a few storms
nearing those areas. However, depending on the evolution over the
next 2-3 hours, I may cancel those areas early as well.
The aforementioned vort lobe will continue to ever so slowly weaken
and drift north through tonight, becoming elongated in an east/west
fashion in the process. As a result, precipitation is most likely to
dissipate from both the north and south, possibly lingering across
the central portions of the forecast area through sunrise. The
forecast has been updated to account for the details mentioned
above. Will continue to monitor and make changes as needed.
-Wolcott-
&&
.PREV DISCUSSION...
200 PM PDT Thu Aug 3 2017
.SHORT TERM...Through Friday night.
Vort max well defined on satellite over eastern San Bernardino
County early this afternoon will continue to move north through this
evening while stretching apart or elongated with an east-west
orientation. Although weakening, it should still provide some
generally lift into the evening hours while the air mass remains
quite moist and fairly unstable. Thunderstorm chances will continue
in most areas at least through this evening with some overnight
showers possible. Indications from most of today`s HRRR runs are t
hat the strongest storms will likely be over Mohave County moving
westward this afternoon with storms later this afternoon over
Lincoln and central Nye Counties moving southward into this evening.
How far west and south this activity maintains it`s strength is a
big question and most of these model runs are tending to weaken the
activity significantly during the evening with any overnight
activity pretty weak. It looks like the focus for convection will
shift to areas mainly north and east of Las Vegas Friday as the
weakening vort max shifts northeast. Somewhat drier and more stable
air will start to push into San Bernardino County and maybe southern
Inyo County. There will still be enough moisture and instability for
a slight chance of thunderstorms in the Las Vegas Valley and along
the Colorado River.
.LONG TERM...Saturday through Thursday.
Models have been consistent past two days in showing a weak
disturbance over southern Nevada and northwest Arizona Saturday.
Associated dynamics along with plenty of moisture and instability
will lead to isolated to scattered thunderstorms across Inyo
County, southern Nevada and northwest Arizona. Sunday-Thursday
period models still advertising a gradual drying trend with the
coverage of thunderstorms becoming less each day, especially Tuesday-
Thursday. Temperatures will probably hover at or just below normal
over the weekend. As the airmass drys would expect temperatures to
rise a few degrees above normal mid-week.
&&
.FIRE WEATHER...Scattered to numerous thunderstorms expected
again today, with gradually drying commencing Friday. Over the
weekend, storm activity will begin favoring the higher terrain of
mainly southern Nevada and Northwest Arizona. Even drier
conditions are expected to push in next week, with only isolated
thunderstorms expected across the southern Great Basin and higher
elevations of Mohave county. Temperatures will be near normal
through the period.
&&
.AVIATION...For McCarran...Prevailing south to southeasterly flow
will be present for much of the afternoon with best chances for
showers and storms in the Las Vegas Valley between 21z-22z and again
between 01z-05z. A southerly push after 00z with winds of 10-15
knots and brief gusts near 20-25 knots will be possible through 04z.
After this point winds come down to around 8 knots or less remaining
out of the south to southwest through Friday afternoon when winds
are expected to increase to around 10-15 knots. Development of
showers and storms Friday afternoon will be focused across the
higher elevations with an isolated storm in the valley not out of
the question.
For the rest of southern Nevada, northwest Arizona and southeast
California...Prevailing south to southwesterly flow between 10-15
knots is expected today. Areas of showers with embedded storms
across southeast California, southern Clark, and Mohave counties
will continue to slowly drift northward through the afternoon with
heavy rain and brief, erratic wind gusts possible. Storms this
evening will be focused across the southern Great Basin as they
slowly drift southward through around midnight. Otherwise, diurnal
wind pattern expected late tonight into early tomorrow with showers
and storms focused further north on Friday afternoon.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&
$$
SHORT TERM...Harrison
AVIATION...Guillet
LONG TERM....Pierce
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