Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/17/17
See below for an aviation forecast discussion for the 00Z TAFs.
&&
.SHORT TERM...(This Evening through Thursday Afternoon)
Issued at 341 PM CDT Wed Aug 16 2017
An area of rain associated with an upper level shortwave trough
overhead and a surface low pushing up from the south will continue
to affect mainly the southern and eastern portions of the CWA late
this afternoon, then just the eastern CWA this evening into the
overnight hours. Areas along and east of Interstate 29 may see
rainfall amounts in excess of half an inch into the evening hours.
This system will push east of the area on Thursday, with high
pressure dropping in and bringing a return to dry and warmer
conditions, along with mostly sunny skies.
Low temperatures tonight will range from the mid 50s to the lower
60s. High temperatures on Thursday will range from the upper 70s to
the mid 80s.
.LONG TERM...(Thursday Evening through Wednesday)
Issued at 341 PM CDT Wed Aug 16 2017
Short wave trough and surface cool front still on track to affect
the region Thursday night into Friday as they slide in from the
northwest. Models continue to agree well and have been consistent
with this system bringing scattered showers and thunderstorms.
Otherwise, surface high pressure ridging will build in behind
Friday afternoon and night, and then to the southeast on
Saturday. The models continue to show an upper level low pressure
area moving across central Canada forcing a surface cold front
slowly southeast and across much of the Dakotas Saturday through
Sunday. The upper level flow will be westerly aloft allowing for
this boundary to slow down or stall out. At this time, this
boundary does not look to be active with showers/storms from
Friday night through Sunday until a short wave trough moves in
from the west. Thus, have it dry from Friday night through Sunday
with chances of showers/storms coming back for Sunday night. As
this boundary slows down/stalls chances of showers/storms remain
across the southern CWA Monday. The upper level flow then becomes
northwest from Monday night into Tuesday with Canadian surface
high pressure pushing in from the northwest bringing dry and
cooler conditions for Tuesday and Wednesday.
Temperatures will be warming up from Friday into Saturday as winds
become south behind the exiting high pressure area. Above normal
temperatures in the mid 80s to the lower 90s are expected on
Saturday in advance of the surface front. Would not be surprised
with some mid 90s out west on Saturday afternoon. Cooler air will
bring temperatures back to near to slightly below normal for Sunday
through Wednesday dominated by surface high pressure.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 640 PM CDT Wed Aug 16 2017
Expect rain to persist across northeast South Dakota into west
central MN for several more hours on north-northwest winds. Rain
should be tapering off at KABR by 03Z this evening, and at KATY by
07Z tonight. But, sub-VFR conditions are expected to persist at
KABR/KATY tonight into Thursday morning before conditions begin
to improve at those two terminals. KPIR/KMBG should remain VFR
over the next 24 hours.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
UPDATE...Dorn
SHORT TERM...Parkin
LONG TERM...Mohr
AVIATION...Dorn
Area Forecast Discussion
National Weather Service Duluth MN
910 PM CDT Wed Aug 16 2017
.UPDATE...
Issued at 910 PM CDT Wed Aug 16 2017
Adjusted pops to account for the current radar trends. Still
expecting a slight chance of thunder later tonight. Not
anticipating any flooding as soil moisture is fairly dry yet
according to the CREST and SAC-SMA soil moisture. Made some other
minor tweaks.
UPDATE Issued at 636 PM CDT Wed Aug 16 2017
Have bumped up pops and brought them in a bit earlier than
previous forecast across northwest Wisconsin to better time in the
activity moving in from southeast Minnesota. Rest of the forecast
is on track.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 310 PM CDT Wed Aug 16 2017
The focus remains on the widespread moderate to heavy rainfall
forecast across the Northland through Thursday in association with
an area low pressure lifting through the Upper Midwest. The latest
trend in the models has been to shift the axis of heaviest rain a
bit farther east, resulting less rainfall forecast across
northwest Wisconsin and more across parts of northeast Minnesota.
The RAP seems to have a good handle on the situation, especially
in its earlier depiction of a dry slot moving for the middle of
today. Used extra weighting towards the RAP on timing and
rainfall through tonight.
A deepening area of low pressure over northwest Iowa, as of during
the middle of this afternoon, is expected to lift across southern
Minnesota through tonight and into central/northern Wisconsin
Thursday. It will become somewhat vertically stacked tonight as it
deepens. This low will bring a period of deep moisture and
moderate large-scale forcing for ascent across the Northland.
Precipitable water values will increase to 1.5 to 1.75 inches. The
forcing will producing widespread moderate to heavy rain across
the Northland, primarily tonight through early Thursday afternoon,
as the low lifts across the region. The heaviest rains, about
1.5" to perhaps as much as 2.5", are now expected to fall in a
wide band from central Minnesota through northeast Minnesota in
association with the deformation zone on the northern and western
periphery of this system.
There could be some thunder here and there through Thursday,
mainly across the southern forecast area due to the potential for
elevated- based instability and forcing from embedded shortwaves
or from the main upper-level low. The instability will likely be
fairly weak, so the storms should only result in occasional
lighting, heavier rainfall rates, and breezy winds.
The rain will gradually pull out of the Northland Thursday
afternoon, with drier air filtering into the western forecast area
as the low departs. Considering the rain and high moisture, even
once the deeper cloud cover exits the western forecast area in the
afternoon, broken/overcast cumulus cloud cover should quickly
develop, meaning not much sunshine until maybe close to sunset.
Expect a cooler and humid day, with highs from the low 60s in the
Arrowhead to the middle and upper 60s elsewhere.
.LONG TERM...(Thursday night through Wednesday)
Issued at 310 PM CDT Wed Aug 16 2017
An upper ridge will be over the Pacific northwest into
Alberta/British Columbia Thursday night with a trough from Hudson
Bay through the central CONUS. The flow will become zonal over the
region through the weekend into early next week then another
trough will move over the region early next week.
The strong low pressure system will be moving away from the
Northland Thursday night with lingering showers ending overnight
for most areas. Additional rainfall will be light Thursday night.
Brief weak ridging will develop overnight behind the departing low
but another shortwave in northwest flow will be moving in during
the day Friday. There will be a chance for showers and a few
thunderstorms roughly from near Walker to Siren and points west
and south during the afternoon and evening.
Dry conditions will occur Saturday as the low level flow becomes
south to southwest. Highs will range from the upper seventies to
lower eighties. Another shortwave and front will move through the
Northland Saturday night into Sunday bringing another chance for
showers/storms to parts of the area. Highs Sunday will again be in
the upper seventies to lower eighties.
A stronger shortwave will bring a better chance for
showers/storms to the region later Sunday night into Monday night.
A dry period is then expected Tuesday into Wednesday. High
temperatures Monday through Wednesday will be in the seventies.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 636 PM CDT Wed Aug 16 2017
Mainly MVFR/IFR across the terminals through the forecast with
rain and some BR. The exception is HYR starting the forecast with
VFR. Expect the MVFR ceilings to reach HYR by 06Z along with a few
thunderstorms nearby. Have a VCTS mention due to timing issues
with storms. Rain will end gradually from west to east as the
system responsible for this activity departs. Some improvement to
VFR is also expected toward the end of the forecast.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 58 63 55 75 / 90 90 20 10
INL 58 64 51 77 / 100 100 10 10
BRD 60 69 55 77 / 100 100 0 30
HYR 63 68 55 74 / 90 60 40 10
ASX 61 70 57 76 / 70 60 50 10
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 4 PM CDT Thursday for LSZ141>147.
Small Craft Advisory until 4 PM CDT Thursday for LSZ140.
&&
$$
UPDATE...GSF
SHORT TERM...Grochocinski
LONG TERM...Melde
AVIATION...GSF
Area Forecast Discussion
National Weather Service Des Moines IA
706 PM CDT Wed Aug 16 2017
...Updated for Near Term Trends and 00z Aviation Discussion...
.UPDATE...
Issued at 706 PM CDT Wed Aug 16 2017
Biggest changes were to the PoPs, wind, and wind gusts for tonight
through tomorrow. Subjective analysis at 6:30pm shows low
pressure is over southwestern Minnesota near Worthington with a
cold front extending southward nearing Estherville, Fort Dodge,
Des Moines, and Osceola. 23z objective SPC mesoanalysis shows
MLCAPE ahead of the front is between 1000 and 1500 J/kg with
effective bulk shear generally 25 to 35 knots. Overall, the best
shear has stayed ahead of the best instability and forcing.
GOES-16 low level water vapor imagery shows plenty of dry air over
the cold front, though moisture is streaming northward into south
central Iowa from convection that is crossing from Kansas into
Missouri.
Looking at current radar and satellite trends, HRRR and ESRL HRRR
seem to have the best handling of the situation with dry slot
pushing into the western part of the state. Post-editing from the
HRRRs accounted for showers that have been trying to develop
along the front and may move into northern Iowa this evening. PoPs
were greatly lowered over the southwest forecast area through the
metro this evening. Still have some PoPs in the east and south,
especially southeast, where showers and storms may come out of
Missouri and clip the southeast forecast area.
Sustained winds and corresponding wind gusts were increased
slightly overnight as low pressure deepens a bit as it moves
eastward over Minnesota. Winds were also increased moreso tomorrow
as low pressure moves into the Great Lakes and with cold
advection prevailing for a good part of the day. Wind gusts over
will average between 20 and 30 mph with the highest gusts over
northern Iowa.
&&
.SHORT TERM.../Tonight through Thursday/
Issued at 243 PM CDT Wed Aug 16 2017
Surface low pressure was located across northwest Iowa at 19Z with a
cold front extending southward into southwest Iowa. Convection thus
far today has been relatively light. Although instability exists,
lack of coherent forcing has limited the convection.
Expect the cold front to help provide some coherent forcing for
convection this evening and tonight as it slides eastward across
Iowa. CAMs keep most of the convection to the south in Missouri and
southward, however cannot rule out an isolated severe storm across
southern Iowa. Damaging wind and large hail would be the primary
threats.
Wrap-around moisture and instability behind the system on Thursday
will keep chances of showers and possibly thunderstorms mainly
across the northeastern CWA.
.LONG TERM.../Thursday night through Wednesday/
Issued at 243 PM CDT Wed Aug 16 2017
Thursday Night through Sunday Night:
Confidence: Medium
Main concern will be next upstream short-wave/frontal boundary that
is expected to arrive Friday into Friday night. Quiet weather will
continue into the night with lows in the 50s to lower 60s. Bulk
shear will be increasing through the morning/afternoon hours...so
potentially a few storms may be strong to severe and we continue
outlooked for marginal. Highs will be similar to the past few days
with upper 70s to mid 80s in the south. There are some minor
differences between the GFS/Euro as for timing and best forcing. The
Euro is a bit farther north with the better forcing Friday into
Friday evening. After a quick exit warm air advection will return
for late Saturday into Sunday as another system begins to move into
the Great Plains. Both the GFS/Euro are hinting at increased warm
air advection into the northwest Sunday...which may lead to late day
thunder/storms over the far northwest. As a warm front lifts
northeast into Minnesota Sunday night convection will be favored
over the north/west during the nighttime hours.
Monday through Wednesday
Confidence: Low to Medium
Though the pattern is active through the period...timing differences
based on model choice and consensus continue to lead to low
confidence. Models diverging Monday with the GFS farther south
with the main forcing compared to the European model. The GFS
develops an MCS over eastern Nebraska by 06z Monday and slowly
decays the activity through 18z...taking the complex over western
Iowa/northwest Missouri through 18z. Previous model packages were
in better agreement with timing/placement of features. Given the
interest in the forecast for Monday...too early to have a
definitive answer regarding cloud cover/rain chances given the
current information. H850 temperatures continue to be warm both
Sunday into Monday and if sunshine is present...should allow highs
to reach well into the 80s both days...especially across the
south. Models continue to focus more of the thunderstorms through
the overnight hours Monday night into Tuesday with some lingering
storms in the south later in the afternoon. There remain some
timing difference later Tuesday night into Wednesday.
&&
.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 706 PM CDT Wed Aug 16 2017
A cold front will continue to move through central Iowa this
evening and overnight bringing a shift of winds from the south to
more of a westerly direction. Showers have been widely scattered
and have only mentioned VCSH at KMCW and KALO early this evening.
Otherwise, fairly high confidence of wrap around clouds with MVFR
ceiling restrictions over the northern terminals arriving tonight.
Highest confidence of these restrictions is at KMCW where there
is also a period of IFR restrictions mentioned. Slightly lower
confidence at KFOD and KALO preceded mention of IFR ceilings at
this time. For the southern terminals, showers and storms may come
close to KOTM, but did not include due to lower confidence.
Overall for KDSM and KOTM, have VFR conditions prevailing through
the TAF period. Will monitor trends and send amendments if needed.
Otherwise for the terminals, winds will become gusty from the
northwest through the daylight hours Thursday.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Ansorge
SHORT TERM...Zogg
LONG TERM...REV
AVIATION...Ansorge
Area Forecast Discussion
National Weather Service Quad Cities IA IL
710 PM CDT Wed Aug 16 2017
...AVIATION UPDATE...
.SYNOPSIS...
Issued at 330 PM CDT Wed Aug 16 2017
18Z surface data has a warm front just north of I-80 with low
pressure in western Iowa. Across Missouri a squall line was moving
toward the east. Dew points from the Great Lakes into the upper
Midwest were in the 60s. Near and south of the warm front, dew
points were in the 70s.
&&
.SHORT TERM...(This Evening through Thursday)
ISSUED AT 330 PM CDT Wed Aug 16 2017
Through late afternoon convection will continue to develop and
increase in areal coverage north of highway 30 as forcing associated
with the warm front moves into Wisconsin. South of highway 30
isolated showers and storms are expected.
The question is what happens from roughly 6 PM to midnight.
Satellite trends show little in the way of cloud development from
central Iowa back into northwest Missouri. Satellite does show a
nice push of dry air aloft moving into western Iowa from eastern
Kansas. However, the better instability and forcing will be from
Kansas into Missouri.
What may happen is that another organized line of strong convection
will move east across Missouri that slowly develops northeast into
eastern Iowa. Recent trends with the RAP suggests this scenario. If
this scenario occurs, the overall severe risk would be low as storms
across Missouri take advantage of the stronger forcing and greater
instability.
After midnight, the cold front will sweep through the area. Rain
behind the front decrease in coverage with time through sunrise
Thursday.
On Thursday, wrap around clouds will be over much of the area during
the morning and slowly exit the area during the afternoon. Any
lingering rain will become more spotty during the morning hours with
only isolated showers expected over the northeast third of the area
during the afternoon.
Temperatures Thursday will be highly dependent upon cloud cover.
Areas north of highway 30 may spend much of the day in the 60s
before popping into the mid 70s late in the afternoon with clearing
skies. ..08..
.LONG TERM...(Thursday Night through next Wednesday)
ISSUED AT 330 PM CDT Wed Aug 16 2017
Thursday night and Friday...Wrap around stratocu to clear off to the
east Thu evening, with incoming sfc ridge lobe and seasonably cool
night in store. Lows in the low 60s and more coverage in the 50s. As
for Friday, most of the 12z model runs have continued to be more
progressive with vigorous digging short wave in northwest upper
flow, with the potential for sctrd showers and a few storms spilling
into the western/northwestern CWA by late Fri afternoon. The prime
lift window with this passing upper wave now appears will be from
00z-06z Sat, wiht the chance most any precip this feature kicks up
will be east out of the local area by early Sat morning. Thus sctrd
showers and some storms moving acrs portions of the area Friday
evening and into the overnight. Interaction with lift from this
system and a more pronounced moisture convergence/THTA-E feed will
look to occur on this systems southwestern flank to generate more
significant storm clusters or even a MCS type feature, from the
MO RVR Valley southward into KS and western/central MO Fri
evening.
Saturday and Sunday...In the wake of the Fri night system, latest
suite of medium range model runs generally suggest a fair weather and
warming period for most of the upcoming weekend. High temps by
Sunday with adequate return flow, may warm well up in the 80s, with
a few guidance solutions even suggesting some 90 degree readings
possible along and south of I80. Now looking at the Sunday night MCS
generation area potentail, the 12z ECMWF has the southerly warm
moist conveyor converging upon a boundary acrs the Dakotas, with
resultant storm cluster or MCS propagating eastward acrs MN into
early Mon morning. The 12z GFS maintains a further south mode with
initiation acrs Neb and the MO RVR Valley, but keeps it festering
out to the west through 12z Monday. Just low chance POPs warranted
for now in the western CWA for late Sunday night, with a bias that
maybe the further south MCS spawning grounds of the GFS may be more
in line.
Monday through next Wednesday...Latest GFS and ECMWF runs suggest
the eclipse day Monday may be hot and humid in the upper 80s to
lower 90s acrs much of the area. Latest MCS generation and
propagation paths out of Sunday night may not be as impactful acrs
the local area with respect to debris clouds...but still way too
early to determine those kind of details for that far out at this
point. Could see where either an MCV or outflow boundary from
earlier upstream convective complex activity becomes the focus for
renewed thunderstorm development in or close to the local area later
Monday or Monday evening. Long range progs then suggest another
digging upper trof acrs the northern plains and upper MS RVR Valley
to interact with a warm moist feed up off the Gulf, and possible
southwesterly tentacle of monsoonal influence, to fuel strong
thunderstorms complexes acrs portions of the upper Midwest(including
the local area), Monday night into Tue. Then, for a secondary day in
a row, decent longer range agreement of the various medium range
models in shunting the active storm track to the south of the region
to the southern plains and OH RVR Valley by mid next week. Canadian
high pressure will then look to take grip of the region with cooler,
drier, and less humid weather for the mid to late next week
period. ..12..
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 705 PM CDT Wed Aug 16 2017
A cool front will pass this evening with a chance of showers and thunderstorms
which may briefly produce MVFR conditions. Winds will shift from the
south to the west by midnight with skies clearing over the region until
near sunrise. After 17/10Z...low clouds will overspread locations along
and north of I-80 corridor including the MLI terminal by 10/14Z with
MVFR to higher end IFR conditions lasting until mid to late PM when
skies will clear. The BRL terminal will remain fair. Winds will be
westerly at 10 to 20 mph through the day on Thursday.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
SYNOPSIS...08
SHORT TERM...08
LONG TERM...12
AVIATION...Nichols
Area Forecast Discussion
National Weather Service Grand Rapids MI
1022 PM EDT Wed Aug 16 2017
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 334 PM EDT Wed Aug 16 2017
Showers and storms will arrive overnight and continue into Thursday.
Some storms could be strong to severe Thursday afternoon, perhaps
lingering into Thursday evening. After a muggy highs in the upper
70s to lower 80s on Thursday, we will cool down to the low and mid
70s Friday and become less humid. A few showers may continue into
Friday morning, north of I-96.
The weekend looks mainly dry, then another chance of showers and
storms should move back in Monday night through Tuesday night. Daily
highs for the weekend into next week should remain in the upper 70s
to mid 80s.
&&
.UPDATE...
Issued at 1022 PM EDT Wed Aug 16 2017
Based on the radar trends, and trends in the HRRR and ESRL HRRR I
have increased the pop to near 100% over the western CWA after
midnight.
The instability is not all that great (most unstable cape near 600
j/kg, but what is really happening is the deep moisture is coming
into our area. Precipitable water values rise from under 1.5" at
8 pm to over 2.0", which is within a tenth of an inches of the
all time record for the 17th of August. The 1000/850 moisture
transport increases dramatically between now and midnight over our
western CWA and more so our NW CWA. Both the HRRR and RAP models
show two low level jets tonight, one around midnight that is
mostly focused on NW lower Michigan then a second one, currently
helping the convection in MO, heads into our Southern CWA toward
Sunrise. So I see two periods of showers / isolated thunderstorms,
one around midnight then next around sunrise. Given the amounts
of water in the air, we will likely get some brief heavy down
pours, I can see isolated locations getting well over an inch
tonight then again around sunrise with the next band of
convection. Most areas through will likely see less than a quarter
inch between now and noon.
As for thunderstorms tomorrow afternoon, the primary low level jet
is aimed near SE MI. We do get another one that is aimed toward NW
Lower Michigan in the evening, that needs to be watched for late
day convection with the cold front.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 255 PM EDT Wed Aug 16 2017
Showers and storms will move in overnight and continue Thursday.
Severe storms are possible Thursday afternoon/early evening,
depending on the timing of several ingredients.
A quiet evening will become increasingly wet overnight as the upper
ridging that was overhead moves east, and a strong upper wave moves
into the Western Great Lakes by daybreak. A warm advection surge of
moisture and lift will be over the heart of the CWA by 12Z. Showers
and a few storms will be on the increase from 06Z, and covering much
of the CWA by 12Z. No severe weather is expected with this wave of
pcpn.
However severe storms will be possible into Thursday. But it will
depend on all factors coming together. With the morning showers and
storms exiting we will need to destabilize again into the afternoon.
The models do indicate some clearing behind the morning wave,
allowing for instability to build into the afternoon. The most
likely region where this occurs should be for areas east of U.S.
131. Bulk shear values are most favorable into the afternoon for
organized storms with hail, around 35 knots, then it tails off to
around 25 knots by early evening. However a large portion of this
shear is in the lowest 1km into the evening. A warm front will be
crossing the CWA, passably supplying more shear locally, and with
low LCLs we may see the risk of an isolated tornado. Damaging winds
will also be possible with bowing line segments.
Precipitable water values spike to over two inches by Thursday
morning. So we will also have to watch the heavy rain potential,
with very heavy localized rains likely with the WAA rains. Additional
heavy rains will be possible into the afternoon, but this will be
very more localized with the diurnal convection.
A breezy Friday with some warp around showers possible in the
morning. Temps will be about 5 degrees cooler, along with falling
dew points. More isolated showers and storms possible late Friday
night with another upper wave coming through.
.LONG TERM...(Saturday through Wednesday)
Issued at 255 PM EDT Wed Aug 16 2017
Two main periods of rain look possible in the long term, one on
Saturday, and then another centered around the Tuesday timeframe. We
are looking for temperatures to warm up quite a bit by Monday of
next week, before a pronounced cool down comes in for mid-week next
week.
A decent short wave will dive in quickly on Saturday, in the wake of
the upper system supporting the system for tomorrow into Friday.
There is decent agreement that this looks to affect mainly the srn
portion of the CWFA. We would not be surprised if this system digs a
little further south, and moves south of the area. We will roll with
chcs of showers/storms for Sat for the time being.
Dry and increasingly warmer weather is expected for Sunday and
Monday. We will see a flat upper ridge migrate over the area. Even
though the ridge will not be very strong, we will see a solid SW
flow bring in very warm air aloft from the Plains states. The
atmosphere will likely be capped through Monday. This is favorable
for eclipse viewing in the area Mon, aside from some small cumulus
development or high clouds that might approach the area.
The threat for rain will increase beginning Mon night and will
likely max out on Tue. The flat ridge will slip east, and we will
see an amplifying trough taking shape to our west. The stronger
nature of the wave combined with some Gulf moisture advecting in
looks to bring a good shot of showers/storms to the area. This
should move out by Wed, leaving a much cooler and drier air mass in
its wake.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 751 PM EDT Wed Aug 16 2017
There is some concern for convection to move through the TAF sites
overnight and during the day Thursday. As is typical for here,
seems most of the convection will struggle to reach our TAF sites.
The large area of convection ahead of the warm front lifts north
over Wisconsin this evening and we will mostly see virga from mid
clouds at least till around 06z. There is some chance a few
showers or Thunderstorms will come through the TAF sites at two
times. The first window (based on the HRRR and ESLR HRRR) is
between 05z and 09z (west to east) and from 09z to 14z (west to
east). The trend through is for the more widespread convection to
stay north of MKG so I only put VCTS at any of the TAF sites.
As the warm front comes through around sunrise I am expecting a
period of MVFR CIG but not much rainfall. As the cold front pushes
through the area Thursday afternoon, again it is not out of the
question there would be thunderstorms after all there is
instability and low level convergence ahead of the cold front.
However most of the models show a lot of mid-level subsidence and
the Low Level jet on the NAM is aimed at TVC in the 21z to 00z
time frame. More than likely any convection would be toward the
Detroit area in the evening.
However we will be watching just in case the storms do become
better organized for our TAF sites.
&&
.MARINE...
Issued at 255 PM EDT Wed Aug 16 2017
Will issue a small craft advisory for Thursday afternoon north of
Holland and extend it through Friday. Southerly winds will pick up
Thursday, then become westerly by late Thursday night. Most likely
we will need to add the areas south of Holland into Thursday night
as this wind shift occurs.
&&
.HYDROLOGY...
Issued at 330 PM EDT Wed Aug 16 2017
Multiple rounds of thunderstorms are possible Thursday. This may
lead to localized heavy rainfall where storms more frequently
occur. Early to mid morning showers and storms are expected along
a warm front and afternoon/evening showers and storms are possible
especially east of US 131. PWAT values will be quite high,
approaching 2.0 inches, along with surface dew points above 70.
There is some potential for a few training thunderstorms with MBE
velocities occasionally dropping below 10 kts. However, this does
not look like a classic flood setup outside of localized ponding
of roads. We will continue to monitor trends.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from Thursday afternoon through Friday
evening for MIZ037-043-050-056.
LM...Small Craft Advisory from noon Thursday to 9 PM EDT Friday for
LMZ846>849.
&&
$$
UPDATE...WDM
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...NJJ
AVIATION...WDM
HYDROLOGY...Hoving
MARINE...JK
Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
143 PM PDT Wed Aug 16 2017
.SYNOPSIS...Near to slightly above normal temperatures through the
forecast with the possibility of thunderstorms over the Sierra
Nevada each afternoon and evening through next week.
&&
.DISCUSSION...An upper trough continues to impact California this
afternoon...providing enough instability over the Sierra Nevada to
generate showers. Showers were beginning to develop over the
Sierra Crest this afternoon mainly in Fresno County...but this
activity is expected to expand in coverage into the evening hours.
The high res ARW...NMM...and the HRRR all indicate that activity
will generally be concentrated from Sequoia National Park
northward.
Something of note...snow levels look to be right around 13,500 to
14,000 feet...so if showers form over the very high
Sierra...expect snow flurries. Snow in August is not
uncommon...but can catch hikers off guard.
With regards to the unseasonably cool temperatures we have been
experiencing this week...today looks to be the last day of below
normal temperatures. Upper level high pressure over the Eastern
Pacific will begin to build slowly east over
California...resulting in a warming trend across the area.
Temperatures are forecast to remain near normal through the
weekend with little change in the upper level pattern. Showers
and thunderstorms will be possible each afternoon and evening over
the Sierra Nevada through the weekend.
On Sunday an upper low will form off the central California
coast bringing a subtle cooling trend. In addition to
cooling...there will likely be an increase in shower and
thunderstorm coverage over the Sierra Nevada...possibly as far
south as the Kern mountains and even the desert. We will continue
to watch this closely as there are still subtle differences with
the location and movement of the upper low.
We heard there is a big event on Monday...the eclipse! As of
now... it looks like much of the area will see mostly sunny
skies...so viewing looks good at the moment. We will continue to
monitor the cloud cover forecast closely and update accordingly.
&&
.AVIATION...
VFR conditions will prevail across the central CA interior during
the next 24 hours.
&&
.AIR QUALITY ISSUES...
None.
&&
.CERTAINTY...
The level of certainty for days 1 and 2 is medium.
The level of certainty for days 3 through 7 is medium.
Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.
&&
.HNX Watches/Warnings/Advisories...
NONE.
&&
$$
public...Riley
avn/fw...Meadows
synopsis...Riley
weather.gov/hanford
Area Forecast Discussion
National Weather Service Jackson MS
932 PM CDT Wed Aug 16 2017
.UPDATE...
Updated for evening discussion.
&&
.DISCUSSION...
The POPs have been shaped up for this evening update, mainly
focused a few showers to the east--near I-20 AL/MS border. Within
an hour everyone should be drying out across ARKLAMS region.
The latest run of the HRRR and the CONSShort is throwing in some
patchy fog down near Hwy 84 and Hwy 98. With clearing skies down
near the coast as dry air starts to seep in, low level moisture
from afternoon rain showers, & light winds, I expect a few
isolated areas to get a bit foggy. /12/
Prior discussion below:
Quick update for early evening...convection has been progressive
and has evolved in a manner where the main storm activity is
across east-central MS here to start the Tonight period. The
remainder of the forecast area is seeing lingering light rain due
to convective debris fallout from prev storms. The PoP forecast
was updated to show these trends here for early evening then have
values lower for the remainder of the night. Thunder wording was
drastically lower as well and only focused for a short period
across east-central. Temps were also lower to match the rain
cooled trends. Overnight lows were not changed. Graphics were
removed as late afternoon threats for heat/flooding have
diminished. /CME/
Prev discussion Thursday:
As that upper & surface ridge build east Thursday over the Florida
Panhandle & north-eastern Gulf of Mexico. As an upper jet
strengthens over the central Plains & ejects into the mid-northern
Mississippi Valley & into the Great Lakes by Thursday afternoon, a
surface low & attendant cold front will be diving through the
central Plains & towards the area. In addition as the upper low over
the western Gulf of Mexico today propagates eastward, flow aloft
will be be slightly different with less diffluent flow. Moisture
will lessen, with closer to one and three quarters to two inch PWs,
& 850mb Theta E only near 340K. Low level moisture will continue to
linger & not mix too much. With thermal profiles gradually warming,
especially with any compressional heating, expect highs to be
slightly warmer potentially around the 92-94 degree range. With
dewpoints hovering in the mid-upper 70s, we should be able to
maintain some high heat indices near & above 105 degrees across most
areas. Heat stress can be expected tomorrow, especially along & west
of the I-55 corridor. Updated the HWO/graphics to include an
elevated risk for heat while wrapping the limited risk down into the
Golden Triangle as well. Issued a heat advisory from 9AM through 7PM
Thursday.
Due to the changing jet dynamics & less moisture, PoPs will be lower
tomorrow, but some 2 inch PWs pooling in the Delta will help more
convection to be sparked in the ArkLaMiss Delta & Highway 82
corridor. Global models & CAM guidance (including ARW) indicate this
idea. Surface winds & low-mid level flow will be stronger due to an
increased gradient & there could be some potential for some stronger
storms due to 15-20kts of 0-2 & 0-3km bulk shear. Lapse rates are
meager but if we warm enough & dewpoints hold, we should be able to
get some better vertical total, which the GFS shows in Delta. Did
not introduce anything in the HWO/graphics for now but expect
scattered convection across the Delta & Highway 82 corridor with
more isolated convection elsewhere. Locally heavy downpours are
possible but storms should be moving enough to preclude mentioning
anything in the HWO/graphics. /DC/
Thursday night through next Wednesday:
The upper low over the Great Lakes will sink a weak frontal boundary
down through our region on Friday. Rain chances over the southern
half of the CWA will be a bit higher than previous days due to extra
lift along the boundary. However, still expect precip to be in the
form of scattered afternoon showers and storms, but not widespread.
This rainfall will help mitigate the heat stress just a bit. Still
expect heat indices on Friday to be near 100 though.
Over the weekend, the trough pushes to the east and low level
ridging builds in behind it. PWs will remain high, especially in the
southern half of the area, 2" and higher, thus this will be where
the best rain chances over the weekend will exist. Temps will creep
upwards just a bit through the weekend and heat stress will
therefore increase as well. Heat indices could approach 105 degrees
by Sunday again. Heights will continue to increase going into next
week as the upper ridge builds back over the Southeast. Expect the
typical diurnal showers and storms with average seasonal temps as
well. /10/
&&
.AVIATION...
00Z TAF discussion:
Afternoon convection is dissipating across most of the forecast
area with the exception being MEI where a solid TSRA is occurring.
Look for a brief period of IFR restrictions at MEI due to the
storm with improving conditions by 0020z or 0030z to VFR. The
remainder of the area will see the lingering -RA convective debris
but remain in VFR conditions. Much of the overnight period will be
VFR. However, low level flow and moist conditions will support
stratus developing by 10-11z across the NW and N half. A few of
the central/southern sites may see that as well, but it may start
later and occur in the 12-14z window. Overall, Thursday looks less
active for precip/storms with the NW sites having the better
chances during the afternoon. Surface winds may also be a tad
breezy across the north half as well. /CME/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 73 93 75 91 / 36 20 25 48
Meridian 73 93 75 90 / 60 18 14 49
Vicksburg 73 92 75 91 / 22 25 31 50
Hattiesburg 71 93 75 92 / 33 18 7 54
Natchez 72 91 75 90 / 23 24 16 48
Greenville 74 91 75 91 / 19 35 28 31
Greenwood 74 91 74 90 / 31 33 30 28
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Heat Advisory from 9 AM to 7 PM CDT Thursday for MSZ018-019-025-
027-034>036-040>043-047>049-053>055-059>062.
LA...Heat Advisory from 9 AM to 7 PM CDT Thursday for LAZ007>009-015-
016-023>026.
AR...Heat Advisory from 9 AM to 7 PM CDT Thursday for ARZ074-075.
&&
$$
12
Area Forecast Discussion
National Weather Service North Platte NE
552 PM CDT Wed Aug 16 2017
.SHORT TERM...(This evening through Thursday)
Issued at 321 PM CDT Wed Aug 16 2017
The blend of the HRRR models and the RAP appear to be lifting the
upper level cold pool and resultant showers/isolated thunderstorms
northeast too quickly by 2 or 3 hours. With the loss of heating and
collapse of the boundary layer at sunset, the showers should
dissipate.
Weak high pressure will build in tonight produce clear skies. Drier
air and lower precipitable water should stabilize the atmosphere.
The NAM will develop thunderstorms off the Cheyenne divide and Black
Hills Thursday afternoon. Very modest h850mb return flow develops
during the afternoon and sfc winds will be very light. The northwest
flow aloft near 35kt would support a multicell environment. SPC gave
Wrn Nebraska a 5 percent severe weather chance and the primary
hazard is strong wind gusts.
blended guidance plus bias correction produced lows in the 50s and
highs in the 80s.
.LONG TERM...(Thursday night through Wednesday)
Issued at 321 PM CDT Wed Aug 16 2017
The storm activity Thursday afternoon could grow upscale and the
model consensus suggested a chance to likely POP Thursday night
across Ncntl Neb. The best storm coverage and heavier rainfall might
remain north across SD or slip southeast into the eastern edge of
Ncntl Neb.
Better return moisture and forcing develops late Saturday and both
the NAM and GFS show some pretty good rain centers developing across
either Swrn or Ncntl Neb. Precipitable water increases to around
1.25 inches. Chance POPs are in place, mainly Saturday night.
500mb Winds aloft become zonal and decrease to around 25 kt, perhaps
lessening the chance of severe storm development.
The moisture remains in place Sunday and yet another upper air
disturbance is progged to set off showers and thunderstorms Sunday
evening.
The cloud forecast Monday continues to evaluate the potential for
high cloudiness which could partially obscure the eclipse.
The ECM and GFS shows subtropical moisture aloft moving across the
Rockies which could produce scattered or broken high cloudiness
around noon Monday. The GFS also indicates substantial low level
moisture and stratus across Wrn/Ncntl Neb leftover from heavy
thunderstorms across Ern Neb Sunday night. The ECM produces the
thunderstorms across SD but shows the same moisture in place like
the GFS. Thus, it is possible significant cloudiness will occur
Monday.
As a result, the sky forecast for noon Monday has been increased
from 35-40 percent yesterday, to 40 to 60 percent with the forecast
today.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 549 PM CDT Wed Aug 16 2017
Skies will become mostly clear tonight behind a departing system
currently moving toward the western Great Lakes region. Only
few250 expected at KLBF and KVTN the next 24 hours with light
winds below 10 kts.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Roberg
Area Forecast Discussion
National Weather Service Nashville TN
858 PM CDT Wed Aug 16 2017
.UPDATE...
FOR EVENING DISCUSSION.
&&
.DISCUSSION...
Widely scattered showers are lingering well into the evening
across Middle Tennessee. A very humid air mass is now in place,
with dew points still running in the mid 70`s most locations. The
00Z sounding from OHX shows considerable instability, now that
the surface ridge has shifted to our east and allowing for some
return southerly flow. The HRRR does suggest the existing activity
will further diminish with very little activity overnight. So
will leave in isolated showers only after 06Z. Hourly grids seem
to be doing well, so no forecast changes are planned at this time.
&&
.AVIATION...
00Z TAF DISCUSSION.
Scattered showers with a few thunderstorms mixed in have developed
in the last couple of hours. Have prevailed some activity at
KCKV/KBNA/KMQY through 01Z, though I don`t think flight categories
should get any worse than MVFR. This activity should wane this
later this evening as we lose the heat of the day.
Winds will be relatively light this evening, calm overnight and
pick up out of the southwest on Thursday with a few gusts of 15-20
kts.
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION......08
AVIATION........Unger
Area Forecast Discussion
National Weather Service Pueblo CO
330 PM MDT Wed Aug 16 2017
.SHORT TERM...(This evening through Thursday)
Issued at 310 PM MDT Wed Aug 16 2017
Limited CAPE (ML CAPE around 500 J/kg or less) and less forcing has
resulted in lower storm coverage and strength across the forecast
area today. Best coverage will be across the Pikes Peak region
through this evening where high res models have been consistent in
spreading showers and thunderstorms eastward off the mountains. Most
showers and thunderstorms will diminish during the evening with the
loss of heating...however several HRRR runs have been generating
another round of showers across northern portions of the southeast
plains towards morning. Will maintain some isolated pops across the
area to account. Otherwise...most areas will be dry and low
temperatures will be on the cool side.
Tomorrow will be a more active day for thunderstorms as de-amplifying
upper trof moves across the area in the afternoon. Return southerly
flow will advect upper 50 dew points back northward into the far
southeast plains while passing trof helps mix out low level moisture
again and sharpens up a dry line across the far southeast plains.
Shear will be stronger...around 30-40 kts...and ingredients come
together best across the far southeast corner of the state including
Las Animas, Baca, Prowers, and Bent counties. One or two severe
storms will be possible in this area with large hail and damaging
winds the primary threats. Temperatures will return to closer to
normal. -KT
.LONG TERM...(Thursday night through Wednesday)
Issued at 310 PM MDT Wed Aug 16 2017
Storms that will have developed along the shortwave trough axis
earlier in the day Thursday will continue to propagate easterly, and
once the storms move over the Colorado - Kansas border, the
environment will be favorable for rotating supercells. Forecast
BUFKIT sounding over Lamar, CO indicate CAPE values exceeding 2000
J/Kg and 6 km bulk shear values near 40 knots. The main threat from
the storms that strengthen over eastern Colorado will be strong
thunderstorm winds and large hail. The low level shear is not all
that impressive, so the tornado threat is small, but still possible.
SPC is in agreement with our severe weather forecast, they upgraded
the day 2 outlook over extreme southeastern Colorado to a slight
risk this morning, whereas the rest of the southeastern plains are
under a marginal risk. The complex of thunderstorms should exit
Colorado by midnight, Friday.
Moving onto Friday now, the shortwave trough will have passed and
lower dew point values fill the region. The GFS20 has storms
developing later in the day over the Upper Arkansas River Valley and
over Pikes Peak, in response to weak easterly upslope flow, whereas
the NAM12 does not have thunderstorms developing, suggesting that
there will be westerly flow at the surface. Some uncertainty does
exist for Friday, but for the time being, a chance of thunderstorms
is included in our forecast grids over the mountains, Palmer Divide,
and Raton Mesa.
The synoptics over the weekend and into next week include an upper-
level low developing over southern California and a broad upper-
level ridge building over the southern contiguous United States. The
response from the previously mentioned synoptic set-up will be a
monsoonal surge of moisture impacting southeastern Colorado. The
common daily theme will be thunderstorms initiating over the
mountains, followed by the upper-level steering flow propagating the
storms over the plains. The intensity of the thunderstorms and showers
will be dependent on how much moisture exists and how strong the
upslope component of the wind is. According to the GFS20, the
precipitable water amounts trend higher as the next week
progresses. On Tuesday, models suggest that a cold front will
pass, which may spark some showers over the plains in the early
morning hours and will lead to moist upslope flow for Wednesday
afternoon.
-Skelly
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 310 PM MDT Wed Aug 16 2017
TAF sites will predominantly see VFR conditions with
KCOS seeing the best chance for a stray thunderstorm in the vicinity
of the TAF site. Gusty winds up to 40 kts and brief VFR cigs will
be the primary impacts. Thunderstorms will diminish during the
evening with light winds expected overnight. Thursday will see
another round of thunderstorms develop over the mountains and move
off into the adjacent plains. These should remain pretty isolated
for the TAF sites with VCTS most likely for KCOS. -KT
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...KT
LONG TERM...SKELLY
AVIATION...KT
Area Forecast Discussion...UPDATED
National Weather Service Reno NV
831 PM PDT Wed Aug 16 2017
.UPDATE...
Thunderstorms around the Tahoe Basin have ended with only few
showers/sprinkles lingering near the crest and south of Hwy 50.
Thunderstorms put down some decent rain on the west side of the
Tahoe Basin with a couple of gauge reports including 0.75 inches
around Tahoe City and 0.47 inches near Homewood. We will be
updating to remove chances for showers/thunderstorms for the
remainder of the night as a more stable northerly flow prevails.
Hohmann
&&
.PREVIOUS DISCUSSION... /Issued 235 PM PDT Wed Aug 16 2017/
SYNOPSIS...
Mainly light winds with temperatures near or slightly above
average is expected into next week. A few afternoon and evening
thunderstorms will be possible near the Sierra south of Highway 50
through Thursday. Thunderstorm coverage will expand across the
rest of the Sierra Friday, and into northeast California and
western Nevada for the weekend into early next week.
SHORT TERM...
Minimal change to the forecast through Saturday.
Easterly flow aloft has kept thunderstorms confined to just west
of the Sierra crest so far today, with a few outlier showers over
eastern Mono County and far eastern Pershing/Churchill Counties.
Most deep convection (thunderstorms) should remain near or west
of the crest today; however, very isolated storms cannot be ruled
out (due to small-scale forcing/convergence) as far east as
Highways 395 and 89 in the Sierra through around sunset.
Thursday should feature isolated showers and thunderstorms once
again. Flow aloft will remain northeast to east, so any storms
should remain west of Highway 395 and south of Highway 50 in
eastern California. However, by Friday flow aloft becomes very
light so a few storms could eek a bit farther north and east by
evening, possibly to near the California-Nevada border and up into
Sierra and Plumas Counties. Thunderstorms will not have any
large-scale help (shear or strong instability) to increase
intensity on Friday so they will rely on small-scale, unpredictable
forcing for their intensity. Therefore, most storms should remain
modest with outflow winds to around 35 kts, brief heavy rain, and
a few lightning strikes.
Saturday, GFS/NAM simulations show an increase in westerly flow
aloft, especially from Tahoe north, as a weak trough moves over
Oregon and far northwest California. This is shown by those models
to nudge convection off the crest north of Highway 50. As this was
already indicated in the forecast, POP was largely left alone for
Saturday. Snyder
LONG TERM...Sunday through Wednesday...
Sunday into Monday, low pressure is simulated to drop along the
California coast. Monday through at least Tuesday, the low is
expected to hang out near the central and southern CA coast,
putting eastern CA and western NV in divergent flow aloft. This
will favor continued rounds of isolated to scattered thunderstorms,
mainly during the afternoon and evening but possibly continuing
overnight depending on any minor waves moving around the upper
low. At this time, storm motions appear slow so the threat for
localized flash flooding (especially downhill from burn scars and
in steep terrain) will increase over the weekend into early next
week.
As far as the partial eclipse Monday morning, there is a
low to moderate chance that partly cloudy skies will prevail by
Monday with residual convective clouds and general divergence
aloft favoring at least some clouds. That`s all we can tell you
for now so stay tuned if you plan on watching the eclipse.
Temperatures should be moderated by clouds and convection early
next week so near or even slightly below average temperatures are
expected. Snyder
AVIATION...
Afternoon and evening thunderstorms are expected to remain near
or west of the Sierra crest and south of Highway 50 through
Thursday, with a 5-10% chance for a storm at KTVL and 15-20% at
KMMH. Storms look relatively weak with outflow winds to 35 kts, a
lightning strike or two, and brief light rain possible.
Valley/terminal winds should remain generally less than 10 kts
from a northwest to northeast direction through Thursday.
Friday, isolated thunderstorms are forecast to creep farther north
and may drift to near the California-Nevada border by evening.
This will bring an increase (but still low) in storm chances for
KTVL/KTRK, with a storm or two within sight of KCXP/KRNO possible
(over Carson Range).
As far as significant reductions in visibility (both horizontal
and slantwise) due to wildfire smoke, the flow pattern and HRRR
smoke forecasts suggest that smoke/haze will be kept along and
west of the Sierra crest through Friday. Snyder
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno
Area Forecast Discussion
National Weather Service Blacksburg VA
1146 PM EDT Wed Aug 16 2017
.SYNOPSIS...
Though the majority of the forecast area is dry tonight, a weak
upper-level disturbance should spark scattered showers and embedded
thunderstorms mainly south and west of Interstate 77. An even more
humid air mass settles in for Thursday, with a better chance for
showers and thunderstorms during the afternoon. A cold front
moving into the region on Friday sparks another round of showers
and storms followed by clearing along with drier conditions
for the weekend.
&&
.NEAR TERM /THROUGH THURSDAY NIGHT/...
As of 1140 PM EDT Wednesday...
Just a minor update to bring T/Td readings in line with current
trends and adjust pops according to latest trends. Since HRRR
has a fairly good handle on the trend of showers moving into
southwest VA at this hour, will follow its trend through the
night. Activity in Smyth and Grayson counties should work its
way through the CWA near the I-81 corridor over the next few
hours, then gradually dissipate across the Piedmont by 10Z. New
activity will likely begin developing/moving into western areas
toward daybreak.
Thursday looks like an active day in terms of convection as a
short wave interacts with a very warm and humid air mass. A good
theta-e ridge evident through the heart of the CWA Thursday
afternoon. Would expect fairly widespread convection Thu.
Instability and shear values are not overly impressive, but an
isolated strong storm certainly could not be ruled out. Heavy
rainfall will likely be the more significant problem.
As of 825 PM EDT Wednesday...
Isolated showers still feeding off lingering surfaced based
instability early this evening across the Mountain Empire of VA
through the piedmont of NC. Expect generally dry conditions
overnight but some isolated activity may be wafting around
mainly east of the Blue Ridge.
Previous discussion...
HRRR and 3-km NAM solutions display good consistency in showing
ongoing shower activity trudging slowly to the east. This
general area roughly bounded along and southwest of a line from
Bluefield to Hillsville VA to Danbury NC. Otherwise, the rest
of the forecast area stays dry through the evening. Some
question if showers can linger after midnight in weak
convergence field in the NC Piedmont and Southside as modeled by
the GFS and the 3-km NAM. I am dubious as mid- level feature
should have advanced far enough east by that point to allow for
weak subsidence. After midnight, it appears that we see a
considerable increase in moisture levels and clouds amid light
southwesterly low to mid- level flow. GFS LAMP guidance
dewpoints at MOS forecast points all trend upward overnight, so
if you thought today was on the humid side, more is on the way.
I`ve indicated some patchy fog in for the overnight hours in the
Greenbrier and New River Valley, but less cooling due to clouds
cast doubt much will develop. It`s currently doubtful we see
as much fog as experienced this morning. A mild and rather humid
evening with lows from the mid upper 60s to the lower to mid
70s, mildest further southeast.
For Thursday/Thursday Night: Looking at quite a muggy air mass
areawide. Outside of the higher elevations along the Blue Ridge,
upper 60s to mid 70s dewpoints should be rather common Thursday.
This moisture extends at depth as well, reflected in PWAT values
progged from 1.9-2.2". Though we should likely have a good amount of
cloudiness, BUFKIT soundings show an air mass that is weakly capped.
So it won`t take much heating to generate enough instability to
spark at least scattered showers and thunderstorms. While 500 mb
height tendencies are neutral early in the day, they start to fall
by the afternoon and should be enough lift, augmented by a pre-
frontal or lee trough. Indicated high chance to lower Likely PoPs
for showers and thunderstorms. I wouldn`t necessarily discount a
couple of SPSable type storms tomorrow, but the deeper layer shear
and tall, skinny CAPE profiles summing to values 1000-1500 J/kg
should keep severe threat mitigated. With Corfidi vector speeds
ranging from 5 to 15 kts indicating slow cell motion and potential
for nearby cell growth on old outflow, along with the aforementioned
high PWAT air could have some potentially heavy downpours. Showed
rainfall amounts from a quarter inch up to localized 0.50-0.70"
amounts along the lee of the Blue Ridge south of Roanoke. Confidence
wasn`t high enough to address in the HWO or to add heavy rain
wording, though WPC`s overnight Day-2 outlook does have our Blue
Ridge counties in a Marginal Risk for excessive rain. A general
decrease in coverage and intensity of showers and storms should be
expected with sunset and generally ending near midnight, though may
have a good deal of cloudiness ahead of the primary cold front. Kept
highs in the mid to upper 80s with at least partly/mostly cloudy
skies, with lows still on the muggy side in the upper 60s to mid
70s.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 230 PM EDT Wednesday...
Weak shortwave trough should lift by to the north on Friday allowing
a surface cold front to slowly pivot east toward the region by late
in the day. Expect some degree of residual showers preceding the
boundary across the west early in the day that could jump into the
eastern lee trough during the afternoon where deeper convection
still appears possible. Most guidance still not overly impressive
with lift ahead of the front, given most upper support shearing out
to the north with the passing weak 500 mb trough. This while seeing
the boundary layer flow turn more westerly espcly mountains behind
the pre-frontal axis early on. However progged instability still
quite strong east of the mountains where models suggest a narrow
band of shortwave energy crossing into the piedmont late. Late day
timing could allow for better convergence from the Blue Ridge east
espcly if the low level flow backs southwest, and progged very high
850 mb theta ridging materializes. Therefore keeping chance pops
with highest out east. Highs again mostly 80-85 mountains to lower
90s east given downslope but also convection dependent.
Surface cold front should cross the region Friday night into early
Saturday, booted along by a stronger upstream shortwave trough that
will pass just north Saturday night. Model consensus shows some
lingering convection along the front mainly southeast early Friday
night before deeper moisture gets shunted to the east early
Saturday. However just how far southeast dry advection can get
Saturday remains iffy espcly ahead of the strong upstream shortwave.
Latest trends suggest perhaps just enough low level moisture with
heating to still spark an isolated shower/storm mainly southeast
sections later Saturday so left in a mention. Otherwise should be a
bit drier Saturday afternoon with dewpoints dropping off espcly west,
and only slight evening pops far south Saturday night for now. Still
quite warm Saturday with highs low/mid 80s to near 90 southeast with
somewhat cooler lows in the 60s overnight behind the front.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 130 PM EDT Wednesday...
Exiting upper trough by late in the weekend will evolve into strong
ridging across the region for early next week as Bermuda high
pressure links with building heights over the southeast states.
Appears this in combination with weak surface high pressure ridging
in from the north and lack of upper support, will act to keep a lid
on most organized convection for Sunday into Monday. However given
close proximity of at least low level moisture near the residual
front over far southern sections, will need to leave in an isolated
diurnal convective mention espcly southern Blue Ridge for now.
Otherwise will be leaving things mostly dry with more clouds
far south and less northern half into Monday.
Ridging will begin to flatten Tuesday in advance of the next digging
500 mb trough that looks to push another cold front toward the
region by midweek. Return moisture ahead of the boundary and less
cap should support a scattering of showers/storms Tuesday afternoon
especially mountains. Expect a bit more organized convection ahead
of the front and under cooling aloft Wednesday when will have medium
to high chance pops. Better ridging and warming 850 mb temps to
around +22C suggests a rather warm/hot period with highs mostly 80s,
except around 90 or warmer piedmont, before cooling slightly on Day7
per more showers around.
&&
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
As of 810 PM EDT Wednesday...
Upper short wave is pulling off to the east but surface frontal
boundary continues to linger over the region with some isolated
showers/rumble of thunder. Believe there will be some isolated
showers stewing around through the overnight and expect low/mid
clouds to be on the decrease, but there is a good amount of
uncertainty in how much cloud cover will remain overnight. While
this will limit radiational cooling, ample moisture in the
boundary layer will allow for some fog formation late. Expect
LIFR cig/vsby to set in at KLWB where cloud coverage is already
scant, and a tempo to MVFR conditions elsewhere with KROA
expected to remain VFR. However, confidence in fog/stratus
formation is medium at best as it is tied to extent of higher
cloud cover. More upper clouds will result in less fog.
Better forcing and increasing moisture along the frontal
boundary tomorrow will yield greater coverage of
showers/thunderstorms by Thursday afternoon.
Winds will generally be light through the period.
Extended Aviation Discussion...
Expect a continued increase in shower/thunderstorm coverage
and strength, lasting until 03z Friday. Outside of
thunderstorms look for VFR conditions. Overnight fog is a
possibility in the river valleys and in areas that do see rain,
though cloud cover/convective debris may limit its spatial
extent.
Another round of scattered afternoon showers and thunderstorms
Friday associated with the primary cold front, though VFR
prevails outside of showers or storms. Dry advection and light
to moderate west to northwest winds behind the front Friday
night could keep overnight fog coverage limited, but a potential
sub-VFR ceiling is possible at Lewisburg and Bluefield.
Mainly VFR conditions for the weekend under weak high pressure.
&&
.EQUIPMENT...
As of 755 PM EDT Saturday Aug 12th...
KFCX doppler radar will continue to be down for the rest of the
month due to a failing bull gear. It will only be operational
during this time frame for brief periods if an imminent
significant widespread severe weather and/or hydrologic event
occurs. Operating the system for any amount of time until the
bull gear is replaced risks a catastrophic failure that would
further extend system downtime. From the 17th through the 27th
the radar will most likely be down completely as the repairs
are expected to be made during this period.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
$$
SYNOPSIS...AL
NEAR TERM...AL/MBS/RAB
SHORT TERM...JH
LONG TERM...JH
AVIATION...AL/MBS
EQUIPMENT...RAB/WERT
Area Forecast Discussion
National Weather Service Shreveport LA
949 PM CDT Wed Aug 16 2017
.UPDATE...
Isolated evening convection has ended for the time being but now
we begin to look upstream across Oklahoma where a line of
convection currently exists along a southwest to northeast
oriented cold front. This convection is probably best progd by the
HRRR which is quicker bringing the convection down into the I-30
Corridor than the slower 00z NAM output which has initialized too
slow. For this reason, have beefed up late night pops...mainly
along and northwest of the I-30 Corridor and beefed up pops across
mainly our northern zones Thu morning and across our eastern half
by Thu aftn.
Concerning the update, cirrus has really thinned across our
southeast most zones and thus have gone with partly cloudy sky
grids through all but the predawn hours when we should begin to
see the effects of the convection to the northwest add some sky
cover to at least this portion of our region. Hourly fcst temps
are in the ballpark to current temps as are fcst overnight min
temps so no other changes were necessary attm.
Updated zone package out shortly...13.
&&
.PREV DISCUSSION... /issued 728 PM CDT Wed Aug 16 2017/
AVIATION...
VFR conditions to prevail through the evening and much of the
overnight hours, with MVFR/patchy IFR stratus to move in to most
sites around sunrise. In addition, a cold front will dip swd into
our area early Thursday, bringing shwrs/tstms to several of our
sites through the day. Have opted to only use VCTS attm, but will
consider prevailing groups for some sites with a later TAF
package.
/12/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 78 93 76 94 / 10 40 20 40
MLU 76 92 75 92 / 10 40 20 40
DEQ 76 87 73 91 / 60 50 20 40
TXK 77 88 74 92 / 30 50 20 40
ELD 77 90 74 92 / 10 50 20 40
TYR 79 92 77 94 / 10 40 20 20
GGG 79 92 77 94 / 10 40 20 30
LFK 78 96 77 95 / 10 30 10 20
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...Heat Advisory from noon to 7 PM CDT Thursday for LAZ010>014-
017>022.
OK...None.
TX...Heat Advisory from noon to 7 PM CDT Thursday for TXZ149>153-
165>167.
&&
$$
12/13