Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/19/17
Area Forecast Discussion
National Weather Service Albany NY
815 PM EDT Fri Aug 18 2017
.SYNOPSIS...
Scattered showers and muggy conditions will continue into tonight
ahead of a cold front. Behind this front, most of Saturday
looks fair and breezy before a second cold front crosses the
area Saturday night with a chance for showers and thunderstorms.
Fair weather and seasonable temperatures are forecast for
Sunday.
&&
.NEAR TERM /UNTIL 7 AM SATURDAY MORNING/...
At 7 PM...after coordination with surrounding offices, have
decided to cancel severe thunderstorm watch.
Previous...
Strongest storms are now over Dutchess and Litchfield Counties.
They appear to be sub-severe, but likely producing high
rainfall rates. A second line of storms has developed in clear
area over central New York and extends from near watertown to
Syracuse southwest towards Elmira. A couple of cells in this
line have lightning. This line of storms will likely reach
Herkimer County between 730 and 8 PM. HRRR shows the line of
storms reaching the Hudson Valley between 11PM and midnight and
then weakening.
Lingering showers and thunderstorms this evening will exit east
but since the primary cold front lags behind, there will be a
threat for clouds and isolated to scattered showers into the
late night tonight. Patchy fog also expected in areas that see
clearing and have moist ground from today`s rainfall.
&&
.SHORT TERM /7 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
After some early morning fog and stratus burns off, Clearing is
progged by models to be over the Albany Forecast Area on
Saturday until late in the day or early evening when next cold
front approaches.
Trailing strong upper energy tracks through the region Saturday
night the boundary layer thermal gradient associated with the
low level cold front also tracks though. The upper jet is
fairly strong for this time of year also. Surface based
instability is expected to be limited but midlevel lapse rates
are forecasted to steepen considerably. West low level flow does
not suggest much convergence but the low level temperature and
dew point boundary could provide enough forcing to support some
isolated to scattered shower and thunderstorm activity during
the evening and overnight. Lows Saturday in the 50s and 60s. Highs
Saturday in the 80s but mid to upper 70s higher terrain.
Dry weather returns Sunday but even with cooler boundary layer
temperatures west to northwest boundary layer flow and
considerable sunshine, highs Sunday should be in the 80s again
with mid 70s higher terrain. Sunday night is expected to be
mainly clear with lows in the 50s to around 60.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
The long term portion of the forecast starts out with fair weather
and summer-like warmth, as a ridge of high pressure moves across the
region and off the mid Atlantic coast. Relatively high mid level
heights and subsidence should allow daytime highs to reach the mid
80s in valleys Monday, with upper 70s/lower 80s across higher
terrain, followed by 85-90 for valleys, and 80-85 across higher
elevations Tuesday. Last time Albany hit 90 was on June 13
(KGFL, June 12 and KPOU, July 21), and we have a shot to do it
again on Tuesday. An approaching cold front could spark some
showers/thunderstorms late Tuesday afternoon, mainly across the
western Adirondacks. Overnight lows Monday night should mainly
be in the lower/mid 60s, except for some 50s across higher
terrain.
For Tuesday night-Wednesday, a cold front is expected to approach
from the northwest. The uncertainty at this time is how quickly
and how much the low strengthens. This also impacts frontal
timing across the region, with the general consensus of a late
night/early morning frontal passage. This would tend to decrease
the overall threat for severe weather on Wednesday. However, a
slower frontal passage for sometime later Wednesday would
increase this potential, as mid tropospheric winds would be
quite strong, combined with better instability for the afternoon
hours. For now, have sided with consensus with best chances for
showers/thunderstorms late Tuesday night into Wed morning. It
should be warm/humid Tue night ahead of the front, with lows
mainly in the 60s, then highs Wednesday mainly in the 70s to
around 80 for valleys, and 60s to lower 70s across higher
terrain.
Wednesday night-Thursday, assuming the aforementioned cold front
does not slow down, high pressure is expected to build in from
southern Canada and the Great Lakes region with cooler and less
humid conditions. There could be a few showers across mainly higher
elevations of the southern Adirondacks/southern VT due to lingering
cold air aloft and some mid/upper level cyclonic flow. Expect lows
Wed night mainly in the 50s, with some 40s expected in sheltered
upland valleys; highs Thursday mainly in the 70s for lower
elevations, and 60s across higher terrain.
Cold advection continues on Friday with generally fair weather,
but cool, fall- like conditions expected. Lows in the 40s and
50s and highs in the 60s and 70s.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
A cold front will move across the region this evening into the
early morning hours. A secondary front and short wave trough will
sweep across the Saturday night leaving the local area between
the features for Saturday.
Convection is occurring just ahead of the cold front and will
move across the area this evening. Have addressed storms in TAFs
with TEMPO group for KGFL, KALB and KPSF. No more storms are
expected at KPOU.
The air mass across the area is very humid and will remain so
through the overnight. Clouds cover will break up after the
passage of the front. With light winds and wet ground across
much of the area expect fog and stratus to form overnight with
MVFR-IFR conditions. Conditions will improve Saturday morning
after sunrise as flow picks up and the atmosphere mixes with VFR
conditions by mid-morning. VFR conditions are then expected for
the TAF period.
Southerly winds will shift to the west with the passage of the
front then quickly diminish with light to calm winds overnight.
Westerly flow develops Saturday morning with gusty conditions
during the afternoon with gusts into the teens.
Outlook...
Saturday Night: Low Operational Impact. Slight Chance of SHRA...TSRA.
Sunday: No Operational Impact. NO SIG WX.
Sunday Night: No Operational Impact. NO SIG WX.
Monday: No Operational Impact. NO SIG WX.
Monday Night: No Operational Impact. NO SIG WX.
Tuesday: Low Operational Impact. Slight Chance of SHRA...TSRA.
Tuesday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Wednesday: High Operational Impact. Likely SHRA...TSRA.
&&
.FIRE WEATHER...
Scattered showers and muggy conditions will continue into tonight
ahead of a cold front. Behind this front, most of Saturday
looks fair and breezy before a second cold front crosses the
area Saturday night with a chance for showers and thunderstorms.
Fair weather and seasonable temperatures are forecast for
Sunday.
RH values will be near 100 percent at night. RH values will be
50 to 65 percent Saturday and Sunday afternoon.
Winds will be south at 15 mph or less through tonight when winds
shift to west. Winds will be west at 15 mph or less Saturday,
and northwest at 15 MPH or less on Sunday.
&&
.HYDROLOGY...
A frontal system will bring showers and thunderstorms to the
region through late tonight. Locally heavy downpours are
possible. Heavy downpours may lead to minor flooding of poor
drainage, urban and low lying areas. Main stem rivers may see
some minor rises, but no river flooding is expected with this
rainfall.
Total rainfall amounts through tonight will be variable
depending on exactly where showers/thunderstorms track. While
most areas should see at least a half inch of rain, its possible
that some point locations may see an inch or two of rain.
Other isolated to scattered thunderstorms are possible Saturday
night along a reinforcing cold front. Less humid air will start
to work its way into the region after the cold front tracks
through. Drier weather is expected Sunday into Monday.
For details on specific area rivers and lakes, including
observed and forecast river stages and lake elevations, please
visit the Advanced Hydrologic Prediction Service /AHPS/ graphs
on our website.
&&
.EQUIPMENT...
While repairing the azimuthal gear box, radar technicians have
determined that the bull gear on KENX radar needs to be
replaced. This will require the radar to be out of service until
at least next Friday, August 25th.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.
&&
$$
SYNOPSIS...SND
NEAR TERM...SND
SHORT TERM...SND
LONG TERM...SND
AVIATION...IAA/Thompson
FIRE WEATHER...SND
HYDROLOGY...SND
EQUIPMENT...
Area Forecast Discussion
National Weather Service Taunton MA
959 PM EDT Fri Aug 18 2017
.SYNOPSIS...
Widespread rain with embedded heavier showers and thunderstorms
overnight. Main threat of localized flooding. Drying out into
Saturday ahead of a cold front which moves offshore Saturday
night. High pressure returns with fair seasonable weather Sunday
through Tuesday. Another cold front sweeps through New England
Wednesday, followed by more dry weather Thursday into Friday.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
10 pm update...
Upstream convection, predominantly across the mid Atlantic
earlier this evening usurped a lot of the available
moisture/unstable air within the warm sector, as warm front
continues to slowly pivot offshore. Still with high
PWATs/K-indices, enough moisture still left to work with LLJ
which is increasing mainly across SE MA. This is likely to be
the focus for the remainder of the night except some pop-up
SHRA/TSRA along the advancing cold front which is moving into
the Hudson valley at the time of this update. This will be slow,
and likely not even offshore by 12Z, hence the continued risk
for SHRA/TSRA through the overnight hours. However, the
dwindling instability with its typical diurnal trend, combined
with the core LLJ shifting E should allow this risk to wane
through the morning. POP update reflects this. Otherwise, very
humid tonight, as temps/dwpts will remain in the upper 60s and
low 70s.
Previous discussion follows...
*/ Overview (4p update)...
Ahead of a deep low center over the N Great Lakes Region, tropical
moisture is surging N, converging and over-running along a warm
frontal boundary presently hung up along the E-waters immediately
offshore of New England as discerned via H925-85 SPC mesoanalysis.
Meanwhile the atmosphere has destabilized ahead of a pre-frontal
trough where partial clearing has occurred in an area of higher
surface dewpoints, deeper tropical moisture, and modest shear. All
of this activity is forecast to converge over S/E New England and
adjacent waters this evening and overnight out ahead of a surface
cold front and attendant H5-7 mid-level dry punch. The H925-85 low
level jet intensifying per isallobaric response out ahead of the mid-
upper level ridge over the NW Atlantic, maintaining convection and
heavy rain threats N/E through Saturday morning prior to cold frontal
passage. Drying out NW to SE as winds turn westerly. Any dense fog
that develops during the overnight period as it is expected with
the very humid, muggy, moist airmass, eroding. Lows around the low
70s.
*/ Discussion (4p update)...
Straight-forward, continued forecast of widespread rain with embedded
heavier downpours and thunderstorms. Two things of continued concern:
1.) localized flooding, and 2.) strong to severe storms.
Near-term high-res guidance such as the HRRR is preferred. However,
18.12z NAM and WRF models are only partially considered given poor
initialization.
Localized flooding...
While all of S New England remains under threat, higher confidence
of potential impacts is across S/E MA and CT and all of RI. Expect
thunderstorms over SW PA into NJ to advect N/E with the mean wind,
maintained and fueled by an inflow of low-level H925-85 tropical
moisture. A measure of instability running up against the warm
front still lingering along the immediate E waters as discerned
via H925-85 SPC mesoanalysis, and out ahead of a sweeping cold
front and mid-level dry punch, a convergence of moisture leading
to heavy rain is progged. This along with high freezing level
heights and H85 dewpoints well in excess of +12C (up to +17C),
efficient warm-rain processes signaled .As we have seen already
with prior heavy showers / storms, rainfall rates of around 1-2
inches per hours are easily possible. Quick dousing amounts up
to 3 inches within 2 hours is not out of the question. The
propensity of flash flooding is there but thinking isolated,
localized rather than widespread. Will forego any headlines at
this point and focus on short-fused products.
Strong to severe storms...
Watching closely as to whether we need to coordinate with SPC on
a SEVERE THUNDERSTORM WATCH for portions of S New England. Per
SPC mesoanalysis, instability has manifested across S/W MA and
CT. However marginal, the better environment still resides well
S/W where partial clearing has allowed for better low-level lapse
rates and subsequent destabilization which has resulted in present,
ongoing convection. Still convinced that ongoing activity presently
is going to rob the environment to the N. However, not ignoring the
low LCLs, high shear, and measure of instability across the region.
While the greater threat is S/W, still need to maintain a watch for
portions of our area. Somewhat banking on the convection over SE
PA and NJ as it advects N/E across SE areas of New England to have
some strong, possibly severe elements. Heavy rain and frequent
lightning the main threats, but gusty winds also possible.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Not a washout. Widespread rain with embedded heavier showers,
possibly a thunderstorms, lingers over SE MA during the morning
period, eroding with the influx of mid-level H5-7 drier air
despite the cold front lagged. This is easily evident within the
K-indices, contrary to other convective parameters such as CAPE.
Should see gradual clearing across the region for a brief period
before comma-wrap moisture sweeps through the region behind the
low filling back in the dry punch. Some scattered cumulus through
the day, however the cyclonic flow and some favorable mid level
lapse rates with a weak cold pool aloft, could see some shower
activity over the N/W MA and CT overnight by which point the
surface cold front will have pushed offshore, winds becoming W
and turning light as high pressure builds into the region of the
OH River Valley behind the low.
Lower surface dewpoints during the day but still out ahead of
the cold front, should turn a bit more comfortable with highs
into the mid to upper 80s. Clouds
lingering overnight with the
comma-low, may hamper what might be a favorable night of
radiational cooling given light winds. Lows back down into the
60s.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Much of this period will feature a mid level ridge across the
southern USA. For our neck of the woods, nearly zonal flow should
prevail through early next week. Expecting a potent mid level trough
to get close to our region towards late next week.
Latest guidance suite is in reasonable agreement with the overall
pattern, with the typical detail differences. Favoring a consensus
blend to smooth over the less predictable details.
Thinking heat and humidity slowly builds from Sunday on, peaking
Wednesday before a cold front moves through our region. Temperatures
during this period should be near to above normal. Once this cold
front passes Wednesday night, expecting near to below normal
temperatures which much more comfortable humidity levels.
Increasing risk for showers and possible thunderstorms Tuesday night
into Wednesday, otherwise mainly dry much of next week.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Saturday Night/...
Through tonight...Moderate confidence.
Conditions lowering IFR-LIFR over much of the region as the
threat of RA/+RA with becomes more widespread. TEMPO VSBY
impacts with RA/+RA and expected dense fog, more likely over S/E
coastal terminals. Clearing out towards morning. Blustery S/SW
winds with a few gusts up to 30 kts, strongest over the S/SE
coastal terminals. Despite, LLWS impacts possible especially
over far SE MA with 40 kts SW at 2 kft AGL. Gradual improvement
NW to SE across the interior towards Saturday morning.
Saturday into Saturday night...Moderate confidence.
Gradual improvement for S/E terminals, lowest IFR-LIFR conditions
with -RA/RA lingering for SE coastal terminals. SW winds prevailing
turning W towards evening. SCT 4-5 kft low-end VFR CIGs during
the day, becoming BKN-OVC N/W overnight with the low risk of -RA.
KBOS Terminal...Moderate confidence.
MVFR-IFR mix through morning. Feel there is a threat of RA/+RA
this evening around 0-6z. TEMPO IFR VSBY impacts possible. Low
risk of TSRA, feel that may stay S of the terminal, so will
continue VCTS mention.
KBDL Terminal...Moderate confidence.
MVFR-IFR through the overnight period with the threat of RA/+RA
along with TSRA roughly 21-03z. Should see improvement after
midnight into the Saturday morning hours with CIGs lifting.
Outlook /Sunday through Wednesday/...
Sunday through Tuesday...High confidence.
VFR. Areas of IFR in early morning fog/low clouds, then improving
to VFR by mid morning each day.
Tuesday night and Wednesday...Moderate confidence.
Mainly VFR. Scattered MVFR is SHRA/TSRA, especially Wednesday.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Saturday Night/...Moderate confidence.
S winds will be on the increase, gusting up to 30 kts across
the S/SE waters. Small Craft Advisory remain as winds will
result in heightened seas up around 5 feet.
Heavy rain with embedded thunderstorms sweeping SW to NE across
the waters tonight. Will likely be some visibility restrictions.
Conditions improving Saturday into Saturday night as a cold
front sweeps the waters late in the period with winds turning W.
Outlook /Sunday through Wednesday/...
Sunday through Tuesday...High confidence.
High pressure builds over the waters. Winds remain 20 knots or less,
and seas 4 feet or less.
Tuesday night and Wednesday...Moderate confidence. Increasing
southwest winds ahead of a cold front should lead to rough seas
across the outer coastal waters, especially on the southern coastal
waters. There may be a few gusts to 25 kt on Wednesday, too.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 9 AM EDT Saturday for ANZ231>234.
Small Craft Advisory until 2 AM EDT Saturday for ANZ236.
Small Craft Advisory until 11 AM EDT Saturday for ANZ235-237.
Small Craft Advisory until 5 PM EDT Saturday for ANZ250-254.
Small Craft Advisory until 8 PM EDT Saturday for ANZ255-256.
&&
$$
SYNOPSIS...Belk/Sipprell
NEAR TERM...Doody/Sipprell
SHORT TERM...Sipprell
LONG TERM...Belk
AVIATION...Belk/Sipprell
MARINE...Belk/Sipprell
Area Forecast Discussion
National Weather Service Cleveland OH
925 PM EDT Fri Aug 18 2017
.SYNOPSIS...
Weak high pressure will slide across the Ohio Valley this
this evening and early tonight. Towards morning, weak low
pressure associated with a disturbance aloft will drop across
the lower Great Lakes and Ohio Valley on Saturday. High pressure
will build across the Great Lakes Sunday, then move east of the
area on Monday.
&&
.NEAR TERM /THROUGH SATURDAY NIGHT/...
As expected most of the diurnal clouds have dissipated. Some
clouds continue to impact the immediate lakeshore areas east of
CLE. These too should lift to the north leaving a period of
mostly clear to partly cloudy skies. Mid level clouds will begin
to arrive from the west later tonight. Much of the new guidance
coming in including the latest HRRR and SREF suggest that our
precip forecast may be overdone for Saturday. Have gone ahead
and lowered pops into the chance category and have removed all
likely wording. This seems reasonable as coverage should be no
more than scattered in coverage with chances at any given
location limited to just a few hours. Best chances remain at the
southeast end of the area during the afternoon. No changes to
temps as dewpoints at the surface continue to slowly come down.
Previous...Satellite shows clouds thinning across northern Ohio
and nwrn PA as weak high pressure and drier air move in and the
low north of the area continues to pull northeast. Expecting
this trend to continue into the evening with clearing for late
evening and the early overnight. Towards morning however models
show another weak low moving in from the west supported by a
developing upper level trough. Models differ graphically on
cloud cover and associated moisture but both the NAM and GFS do
print out likely pops for the event which seems reasonable given
the upper support. Will not however be an all day rain...
Believe the best chance for the western half of the area is from
dawn through 16z or so shifting east in the afternoon as drier
air again moves into the west. Saturday night should be dry
outside of a possible lingering shower for an hour or so in the
evening. Will have only a 20 pop for that possibility. Night
temps near normal. Saturday temps near to a couple degrees below
normal.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
High pressure will be over the area providing dry wx Sun thru
Mon before moving off to the east for Tue to allow a cold front
to drop SE into the area by Tue evening. Moisture is limited
with this front so will keep pops in chc category. Near normal
temps on Sun will warm above normal for Mon and Tue.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
Broad troughiness will move east across the eastern half of Canada
by mid week causing a fairly strong area of low pressure to move
east northeast across the central and eastern Canada as well. A
strong cold front will push east across the area Tuesday night
ushering in some colder air to the local area from the north. The
front will bring showers and thunderstorms to the area Tuesday night
and push east of the area Wednesday morning. There the is the
possibility for some lake effect rain showers following the frontal
passage Wednesday into Thursday. Strong cold air advection will
likely cause waterspouts to develop provided winds are not too
strong to shear them apart. Strong high pressure at the surface
will build east across the Great Lakes region through the latter
half of the week even though upper level troughiness will persist
through this period. Cold air advection will begin to wane by the
end of the forecast period as the high pressure begins to move east
of the area.
&&
.AVIATION /00Z Saturday THROUGH Wednesday/...
Things remain quiet with lot`s of diurnal looking cumulus
floating about. These clouds should go away for a few hours
before mid level clouds begin to spread back east across the
local area overnight. Precip chances will hold off till around
12z in the west and till late in the morning or even early
afternoon across the eastern end of the area. The new guidance
coming in is backing off on precip coverage from earlier models
runs. So will back off on thunder chances in the new TAFs. Most
locations will have a 3 or 4 hour of window for precip during
the period with it dry otherwise. Winds have started to come
down and the gustiness should end after sunset. The flow will be
mainly west or southwest under 10 knots.
OUTLOOK...Non-VFR possible in scattered showers/tstms on
Tuesday.
&&
.MARINE...
High pressure ridging moving into the lake will cause the winds to
diminish some tonight and allow the SCA conditions to end. A trough
will push east across the lake Sat into early Sat night causing the
winds to waver from SW to West. High pressure moves over the lake
for Sun thru Mon to produce light mostly south to southwest winds.
A cold front is expected to push SE across the lake Tue night
causing SW winds to increase to 10 to 20 knots on Tue ahead of the
front, veering to NW by the end of the night and continuing Wed.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...Beach Hazards Statement until 4 AM EDT Saturday for OHZ011-012-
089.
PA...Beach Hazards Statement until 4 AM EDT Saturday for PAZ001.
MARINE...Small Craft Advisory until 4 AM EDT Saturday for LEZ146>149.
&&
$$
SYNOPSIS...TK
NEAR TERM...TK/Kubina
SHORT TERM...Adams
LONG TERM...Adams/Oudeman
AVIATION...Kubina
MARINE...Adams
Area Forecast Discussion
National Weather Service State College PA
1147 PM EDT Fri Aug 18 2017
.SYNOPSIS...
A cold front will pass east of the area tonight. An upper
trough will move across the region Saturday afternoon and
evening. Temperatures will stay above normal but rise even
higher each day through Tuesday as a ridge builds aloft. Another
cold front should trigger showers around mid-week and the week
should end on a cooler note.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Satellite loop at 01Z still showing a line of cumulus along
trailing cold front running from near KIPT south to near KHGR.
Will maintain the chance of a shower/storm along and east of
this boundary through the late evening hours. Latest radar
trends and HRRR support POPs of only around 20 pct across this
area through around midnight, then patchy fog will become the
issue. Latest SREF and downscaled NAM suggest the weakest
gradient and best chance of fog will be across the Susq Valley,
but patchy valley fog is also likely further west.
A push of drier air behind the cold front, along with light wind
and mostly clear skies, should allow temps to fall to near 60F
over the northwest counties and to the upper 60s in the
southeast part of the forecast area.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
After a mostly sunny Saturday morning, a sharp upper trough
will swing eastward from the Ohio Valley, generating afternoon
showers and tstorms. Will maintain the highest POPs across the
northwest counties, where passage of trough will coincide with
time of max heating during early to mid afternoon. SPC continues
to highlight the northwest half of the forecast area in a MRGL
risk. Model data showing decent mid level winds and deep layer
shear, but limiting factor will be only modest instability.
Expect convection to diminish in intensity/coverage as it pushes
into eastern Pa during the cooling hours of Saturday evening.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
The mid range models are all in good agreement on the timing and
strength of the passing shortwave Saturday night. Once that
passes, the heights will rise and become quasi-zonal. This will
bring fair weather to the region Sunday through Tuesday. Dry
westerly flow will also bring warm summertime temperatures with
Tuesday continually trending warmer. A new shortwave moving
through SRN Canada will an bring an increasing chance for rain,
possibly as early as Tuesday afternoon over western sections of
the forecast area.
There are differences in timing of the rain with the ECMWF
suggesting it holds off until Tuesday night. Blended MOS POPs
show a small chance of showers moving into western sections
Tuesday afternoon, but the highest POPs are reserved for the
overnight.
Cyclonic flow aloft will then dominate the flow pattern through
Thursday. The cool air aloft will help trigger a few mainly
diurnal showers Wednesday and Thursday. The showers will tend to
favor northern and western higher elevations. Temperatures will
be significantly cooler for the second half of the week.
&&
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Mainly clear skies over the region this evening. Fog is
expected for most of the area tonight, with MVFR to IFR
restrictions. Lowest restrictions expected in the southeast,
where most significant rain fell this evening.
An upper level trough and rather strong forcing passing
directly overhead in the cooler air aloft could make scattered
SHRA/TSRA across the northern third/half of Pennsylvania on
Saturday afternoon.
Much drier air will make for a mainly-VFR Sun-Mon with only
valley fog in the AM a potential issue.
.OUTLOOK...
Sat...Mainly VFR, but with sct SHRA/TSRA northern 1/3.
Sun-Mon...Mainly VFR, but restrictions in morning fog.
Tue-Wed...SHRA/TSRA poss.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Dangelo/Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...La Corte/Ceru
AVIATION...Jung
Area Forecast Discussion
National Weather Service Dodge City KS
608 PM CDT Fri Aug 18 2017
...Updated aviation discussion...
.SHORT TERM...(This afternoon through Saturday)
Issued at 1238 PM CDT Fri Aug 18 2017
Virtually full sunshine across SW KS as of midday, with convective
debris clouds now SE of the CWA. Overnight thunderstorm activity
has pretty much wiped instability out of SW KS, with only
marginal CAPE trying to hold on near the KS/OK border.
Mesoanalysis also reveals a strong mesohigh situated across the
eastern TX panhandle and western Oklahoma, which will continue to
prevent moisture return and recovery through today. Removed all
remaining pops for the SE zones through this evening (pops < 15%).
12z NAM and HRRR solutions are both dry. Highs this afternoon in
the low to mid 90s. It`s still summer.
Tonight...Clear. Light and variable (mostly E/SE) winds of 5 mph
or less. Lows in the 60s (except lower 70s from Coldwater to
Kiowa).
Saturday...Breezy and hot. Lee trough strengthens across eastern
Colorado into NW Kansas during the afternoon, with south winds
increasing in response. South winds will average 10-20 mph with
some gusts near 30 mph at times. Temperature trends at 850 mb show
a net increase of +2C compared to Friday, so highs in the mid 90s
will be common. Did hold back from the hotter MOS guidance a few
degrees with recent rainfall and moist soils, and lack of better
downslope. NAM forecasts decent convergence and modest CAPE along
the lee trough axis near the NW zones by late afternoon. With this
in mind, included a slight chance of thunderstorms for the NW
zones Saturday 5-7 pm.
.LONG TERM...(Saturday night through Friday)
Issued at 205 PM CDT Fri Aug 18 2017
Sunday...Still plenty hot, with an isolated late day thunderstorm
possible. With sprawling Bermuda High to the east, and weak
cutoff low near Los Angeles, gentle SW flow aloft will allow
monsoonal moisture to seep into SW KS, at least at the mid and
upper levels of the atmosphere. Despite the moisture and hot
temperatures, forcing and instability appear weak. Kept pops very
low. Afternoon temperatures in the mid 90s.
Monday...Isolated afternoon/evening thunderstorms remain possible.
A few degrees cooler, mainly in the lower 90s. Broad 500 mb trough
will progress through the northern plains during the day, with
attendant lee trough persisting over SW KS. Isolated convection
expected along this boundary during the afternoon, with some
strong storms possible. Expect thunderstorm coverage to increase,
particularly across the northern zones, Monday evening as strong
cold front approaches. This front looks rather robust for August,
and will need to monitor for severe weather potential (mainly
NE counties) Monday evening/night. ECMWF strongly suggests an MCS
over north central Kansas.
Tuesday...North winds and cooler. 12z ECMWF drops 850 mb
temperatures to near 18C NE to near 20C at Dodge City. Heights
aloft will still be substantial (592 dm), so the cooldown will be
modest, mainly upper 80s.
Wednesday and Thursday...Mainly dry, with highs in the 80s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 608 PM CDT Fri Aug 18 2017
VFR conditions are expected through this forecast period. A weak
frontal boundary pushing south across western Kansas will bring
north to northeast winds to all the terminals early in the period.
This front will wash out with winds becoming southerly on Saturday.
The Garden City and Liberal terminals could become gusty to 10-20
knots by Saturday afternoon.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 67 96 70 95 / 10 10 10 20
GCK 65 96 68 93 / 0 10 20 20
EHA 63 95 64 90 / 10 20 20 20
LBL 66 96 69 94 / 10 20 10 20
HYS 65 97 70 96 / 0 0 30 10
P28 71 97 73 96 / 10 0 10 10
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Turner
LONG TERM...Turner
AVIATION...Gerard
AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
620 PM CDT Fri Aug 18 2017
.Discussion...
Issued at 250 PM CDT FRI AUG 18 2017
GOES-16 visible imagery showing a fair amount of clearing this
afternoon across western Missouri following this morning`s weak
shwr activity. Further north, agitated CU is noted just north of
the Iowa border, with this activity occurring directly in advance
of a cold front that is forecast to track south across our region
later this evening. As a result, forecast concerns this afternoon
remain fixed on possible severe storm development as the boundary
tracks south over the region later tonight. Latest SPC meso page
still shows some weak inhibition across our area, however this
will soon be eroded in response to an increase in solar heating.
Aloft, water vapor shows a positively-tilted trough axis tracking
across southern Minnesota and northern Iowa this afternoon, and
near term model guidance supports the idea that deep-layer shear
will continue increasing with time as secondary shortwave energy
dives southeast into eastern Iowa and northeast Missouri through
06z. Biggest caveat to the current forecast is just how far west
developing convection will extend and whether the Metro will be
impacted. For several hours the HRRR suggested the bulk of
activity would remain east, however the latest run has now shifted
west which is in better alignment with the NAMNest and RAP.
Isolated storms initially will be capable of large hail, but
models show activity congealing into a forward propagating MCS
before tracking south into central Missouri by 06z. As this
occurs, the main threats will likely transition more to a straight
line wind concern with gusts in excess of 50 mph possible,
especially east of the KC Metro.
Storm activity to quickly come to an end after midnight with clear
sky development expected during the predawn hours as high
pressure starts building into the area. There may be some fog
development during the predawn hours but the best potential for
such development may be east of the Metro where better rain
chances exist this evening. Despite the passage of a cold front,
southerly flow will return fast enough by Saturday afternoon to
allow temps to warm into the upper 80s to lower 90s across much of
the area. Another MCS is expected Saturday night early Sunday as
a shortwave in developing zonal flow tracks east from the Central
Plains. For now, chance pops appear reasonable until trends become
better established with later model guidance.
Beyond this, fcst guidance remains all over the place as we head
into early next week as several weak disturbances are expected to
impact the lwr Missouri Vly in the aforementioned zonal flow. How
this impacts/impairs viewing the solar eclipse remains up in the
air right now as model solutions remain all over the place (see
eclipse discussion below). What does seem certain is that MCS
activity will be possible across the region Monday morning with
additional convection possible Monday afternoon. Unsettled weather
to continue right through Tuesday with hints that conditions will
start improving by Wednesday following the passage of yet another
cold front. In fact the latter half of next week may be a tad
cool for mid/late August standards as strong high pressure extends
south from the upper Miss Rvr Vly.
&&
.Specifics for the Total Solar Eclipse on August 21st...
Issued at 250 PM CDT FRI AUG 18 2017
Uncertainty still remains with respect to Monday`s cloud cover
fcst as models continue to highlight overnight and early morning
convective activity across the Lwr Missouri Vly. As a result,
the prevailing idea that convective debris cloud cover will
remain in the area Monday morning appears likely once again this
afternoon, with additional concern also seen in the form of a
possible northward extending cirrostratus shield from the Southern
Plains into the upper Miss Rvr Vly. Unfortunately there remains
too many variables at play right now to really increase
confidence on where the best viewing potential will be, but
hopefully these questions will start being answered with
additional model runs in the coming days.
&&
.Aviation...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 619 PM CDT FRI AUG 18 2017
Storms currently moving through the KC area will be short-lived
and should only be impacting the terminals for another hour to two
hours as they move to the southeast. Once the storms pass, VFR
conditions are likely through the forecast with light winds. Will
monitor for potential for light fog late tonight to around sunrise
Saturday. But for now will keep things VFR.
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...NONE.
&&
$$
Discussion...32
Aviation...CDB
Eclipse...32
Area Forecast Discussion
National Weather Service Flagstaff AZ
314 PM MST Fri Aug 18 2017
.SYNOPSIS...Dry conditions will continue across most of northern
Arizona through much of Saturday. There will be a slight chance
of thunderstorms over eastern Arizona on Saturday afternoon.
Higher chances of showers and thunderstorms then move back north
and west and affect much of the area by Sunday and into next week.
&&
.DISCUSSION...Cumulus clouds persist over high elevation locations
in northern Arizona this afternoon, most robust over areas near
the Utah state line. The latest runs of the HRRR indicate that we
may yet see a little rainfall from a few of the convective clouds
over the Kaibab Plateau and Black Mesa late this afternoon, so we
will continue with the minimal precip/thunder chances up there.
Situated between a ridge over the southern Plains and a trough off
the California coast, we expect moisture to begin to return to
northern Arizona on Saturday, and return in earnest on Sunday. A
A few thunderstorms are forecast over eastern Arizona on Saturday.
With NAEFS mean precipitable water values approaching 1 inch near
the Mogollon Rim by Sunday afternoon, storms on Sunday are
expected to maintain higher rain rates and be capable of producing
flash flooding.
The southerly flow pattern mentioned above is forecast to persist
through at least Wednesday, maintaining moisture and afternoon
showers/thunderstorms. Ensemble models indicate nocturnal
thunderstorm/precipitation activity on Sunday evening, and the
latest GFS forecasts a short wave trough moving northward from
Sonora affecting northern Arizona from late Tuesday night through
Wednesday night. As stated in this morning`s discussion, evening/overnight
thunderstorm activity is a distinct possibility in this pattern
and will have to be watched for.
Southwesterly flow is forecast to develop over Arizona from about
Thursday into next weekend as the trough off the California coast
begins to move eastward. The GFS ensemble mean is more aggressive
with this drying than the ECMWF mean. At any rate, we should
expect a decreasing trend in thunderstorm activity late next week.
&&
.AVIATION...For the 00Z package...VFR conditions are forecast to
persist at all TAF sites throughout the next twenty-four hours. A
few thunderstorms are possible over eastern Arizona after 18-19Z
Saturday which could produce localized MVFR visibility and cloud-
to- ground lightning strikes. Aviation discussion not updated for
TAF amendments.
&&
.FIRE WEATHER...Most areas of northern Arizona will remain dry on
Saturday, with a few thunderstorms possible over eastern Arizona.
Moisture returns to all of northern Arizona on Sunday, and with
it chances of mainly afternoon and evening showers and
thunderstorms.
Monday through Wednesday...Thunderstorm chances persist through
the period. Light southwesterly afternoon breezes are expected.
High temperatures are forecast to be slightly below average.
&&
.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
PUBLIC...AT
AVIATION...AT
FIRE WEATHER...AT
For Northern Arizona weather information visit
weather.gov/flagstaff
Area Forecast Discussion
National Weather Service Wilmington NC
702 PM EDT Fri Aug 18 2017
.SYNOPSIS...
High heat and humidity will continue into Saturday with
scattered showers and thunderstorms ahead of a cold front. This
front will stall in close proximity to the coast during the
weekend before dissipating Monday. High pressure will build
across the area Tuesday and Wednesday. Another cold front will
approach from the northwest Thursday.
&&
.NEAR TERM /THROUGH SATURDAY/...
As of 7 PM Friday...Forecast area is convection-free this
evening and high-res guidance indicates this will be true
through the overnight period. Have allowed the Heat Advisory to
expire on time at 6 PM as heat index values have dropped below
criteria except in a few isolated locations. Forecast requires
no major adjustments. Previous discussion follows:
The HRRR continues to show almost no convection over the
forecast area. When the HRRR does not want to produce convection
you know it will be hard for it to develop. A few showers and
thunderstorms are still possible along the coast mainly north of
Little River. The heat continues to be a factor for this
afternoon with heat indices in the 105 to 108 range.
Models continue to show a cold front moving into the eastern
Carolinas on Saturday and stalling along the I95 corridor. Models
have backed off on the rain percentages slightly and will go with a
30 to 50% chance of showers and thunderstorms. The coverage is
expected during Saturday afternoon. High temperatures are expected
to be a few degrees cooler and the heat indices overall will range
just below heat advisory criteria.
With the new moon on Monday the tides are becoming a little higher
and there is a threat of minor coastal flooding downtown tonight
between 7 and 9 PM.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 300 PM Friday...A cold front makes a run for the coast
but comes against the sea breeze and should keep a few lingering
showers into Sat evening close to the coast. The steering flow
is W-SW up to 15 kts or so and therefore any storms will move
off to the E-NE through the evening, basically off shore.
Expect diurnal heating to cut off and any convection to
dissipate into Sat night.
The dynamics associated with mid to upper trough helping to
give the front a push will lift off to the northeast through the
latter half of the weekend. Ridging tries to build in aloft with
enough subsidence and dry air to keep pcp mainly along the
coast or offshore on Sun. Looks like best moisture will be off
the coast with pcp water values dropping from 2 inches in
isolated spots along the coast in late day convection on
Saturday, down to 1.5 inches or less Sat night into Sun. The NAM
is a little more bullish bringing moisture back on shore as
Bermuda High builds westward. Overall looks like iso to sct
convection is possible along sea breeze as it pushes inland on
Sunday. Will keep lower end PoPs for Sunday then dissipating
into the evening and increasing again toward Mon morning as
boundary and moisture get a nudge back on shore.
Heat indices will be much lower on Sunday inland and probably
will only reach near 100 along the coast with dewpoint temps
down near or below 70 west of I-95 and closer to 75 Sun aftn.
It will still be very warm on Sunday with plenty of sunshine
especially inland with temps reaching into the 90s. Lows will
be in the 70s Sun night, but about 5 degrees lower than
previous nights.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 300 PM Friday...A flat mid-level ridge will extend from the
Atlantic across the Carolinas Monday-Tuesday, then get suppressed
south as a trough carves out across the Eastern seaboard for the
latter half of the week. With no real airmass change evident in
guidance until perhaps Thursday, precipitable water values will
hover around 2 inches until then. Scattered pulse showers and
thunderstorms are expected each afternoon and evening Monday through
Wednesday, with the highest chances Wednesday night through Thursday
when convection becomes organized along and ahead of a frontal
boundary. As usual in the extended period, and especially in August,
there is a great deal of uncertainty with timing the front and
determining how far south it will push. Will hang on to higher PoPs
across the southern CWA on Friday to account for that.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 00Z...Good confidence VFR all terminals through the
overnight period. Limited convection in evidence this afternoon
has faded for the evening. Possibility that scattered
showers/thunderstorms will re-develop by late morning along the
sea breeze front on Saturday, affecting our coastal terminals.
Extended Outlook...Scattered TSTMs Sun through
Wed. Flight restrictions will be possible in early morning
stratus/fog Sun-Wed.
&&
.MARINE...
NEAR TERM /THROUGH SATURDAY/...
As of 7 PM Friday...Latest obs show SW winds in the 15 kt range
with seas of around 3 ft. Forecast good to go with no changes
needed. Previous discussion follows:
At this time there are south winds along the beaches due to a
mature sea breeze circulations. Farther off the coast outside
the circulation, winds will be from the southwest. Currently,
wind speeds are running between 15 and 18 knots and seas on
average are around 3 feet. With a cold front approaching and
stalling inland, winds speeds over the waters will be 14 to 18
knots overnight and will slowly weaken on Saturday with the
front stalling. Seas are expected to run 3 to 4 feet tonight and
fall off to 3 feet late Saturday afternoon.
SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 300 PM Friday...A front will make a run for the waters but
should stall upstream of the waters Sat and then slowly begin
to dissipate late in the weekend. Winds will diminish Sat night
down to 10 kts or so by Sun morning. Expect lighter more
westerly winds on Sunday as front remains nearby. Looks like
convection could be focused moreso off the coast then inland.
Seas will subside down to 3 ft Sun, diminishing further, to
around 2 ft or less by Mon morning. Higher winds and seas will
be possible in and near thunderstorms.
LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 300 PM Friday...A benign pressure field across the waters will
keep winds 10 knots or less Monday and Tuesday, as a weak Bermuda
high pressure remains in place off the coast. Winds will begin to
pick up out of the southwest by Tuesday afternoon as a surface
trough takes shape across the Carolina piedmont. Shower and
thunderstorm activity is expected to remain isolated to widely
scattered over the waters in a general southerly flow through the
period.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...Coastal Flood Advisory until 9 PM EDT this evening for NCZ107.
MARINE...None.
&&
$$
SYNOPSIS...99
NEAR TERM...REK/DRH
SHORT TERM...RGZ
LONG TERM...CRM
AVIATION...REK
MARINE...REK/RGZ/DRH/CRM
Area Forecast Discussion
National Weather Service Lincoln IL
702 PM CDT Fri Aug 18 2017
.SHORT TERM...(This evening through Saturday)
ISSUED AT 309 PM CDT Fri Aug 18 2017
Vigorous short-wave trough noted on 19z/2pm water vapor imagery
over western Wisconsin will track eastward into the Great Lakes
tonight. Synoptic lift associated with this feature will help
trigger scattered convection across Iowa over the next couple of
hours...with this activity pushing into central Illinois this
evening. Current satellite imagery is beginning to show a few
cells developing just south of a weak surface low near Des Moines,
Iowa. These storms will become more widespread later this
afternoon as they track E/SE and spill into the Illinois River
Valley early this evening. HRRR has been quite consistent
today...showing a few storms arriving across the far NW KILX CWA
around Galesburg by 00z/7pm. With daytime instability gradually
waning after dark and strongest upper dynamics remaining further
north in conjunction with the short-wave, think areal coverage of
convection across central Illinois will remain limited. As a
result, have opted to go with scattered wording in the forecast
for tonight. Most of the activity will push eastward into Indiana
and diminish toward dawn. With partial clearing expected late
tonight and plenty of boundary layer moisture in place from
rainfall during the evening, think patchy fog will develop.
Overnight lows will drop into the lower to middle 60s. A mostly
sunny and dry day is anticipated on Saturday, with afternoon highs
topping out in the lower to middle 80s.
.LONG TERM...(Saturday night through Friday)
ISSUED AT 309 PM CDT Fri Aug 18 2017
Once the short-wave tracks toward the East Coast, a zonal flow
pattern will develop across the CONUS early next week. Rising
upper heights will allow temperatures to climb into the upper 80s
and lower 90s by Sunday and Monday, with heat index readings
reaching the middle to upper 90s Monday afternoon. While the bulk
of any significant convection will remain focused further west
across the Plains, a few models are suggesting scattered storms
could potentially reach west-central Illinois by Monday afternoon.
The GEM is particularly bullish with its eastward push of precip,
while the ECMWF is keeping all the convection well to the W/NW.
Since the flow remains flat through the period and the next major
short-wave is still off to the northwest, prefer the ECMWF
solution here. As a result, will confine PoPs to the far W/NW CWA
on Monday and keep them in the slight to low chance category.
All models agree that a vigorous wave will drop southeastward out
of Canada and dig a significant upper trough over the Great Lakes
by the middle and end of next week. With the corresponding cold
front progged to pass through central Illinois on Tuesday, will
continue to focus likely PoPs at that time. Once the front passes,
cooler and drier weather will arrive late in the period...with
highs dropping into the middle to upper 70s by next Thursday and
Friday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 658 PM CDT Fri Aug 18 2017
Scattered thunderstorms will move across central Illinois tonight,
mainly this evening. Coverage will not be great and a VCTS mention
should suffice at most local terminals. However, did include a
couple hour Tempo group at KSPI & KPIA. VFR condtions should
prevail away from thunderstorms, with the possible exception of a
few hours of MVFR fog later tonight. Winds will generally be
light.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Bak
Area Forecast Discussion
National Weather Service Jacksonville FL
910 PM EDT Fri Aug 18 2017
.UPDATE...Strong instability and abundant moisture (PWAT 2.34
inches on JAX 00Z sounding) led to scattered to numerous showers and
storms in the mid to late afternoon today but has gradually faded
with loss of heating and low level forcing. Some isolated residual
weak convection continues over parts of inland southeast GA and
inland northeast FL as overall mean layer CAPEs are less than 1500
J/kg, which continues to decrease. Having said that, abundant
moisture and weak troughing across southern GA and northern FL may
spark additional isolated showers later tonight. Thus, have left in
some low POPs near 15-20% through late tonight. Min temps in the mid
70s expected with some temps upper 70s to near 80 at the coast. Mid
to high clouds will tend to thin overnight.
&&
.AVIATION...Prevailing VFR through tonight, and there is a chance of
showers and storms again on Saturday. Some indications per short
range guidance, including HRRR and NAM soundings, of some patches of
low stratus and fog over parts of northeast FL but not too confident
for going any lower than MVFR for GNV. VCTS and PROB30 groups put in
for Saturday afternoon as convection gets an early start around the
15z-17z time frame with highest chances from 17z-21z.
&&
.MARINE...No significant changes to the CWF. Winds south to
southwest around 10-15 kt and seas generally 2-4 ft.
&&
.PRELIMINARY POINT TEMPS/POPS...
AMG 75 94 74 94 / 20 40 20 40
SSI 79 92 79 89 / 10 30 20 40
JAX 75 93 76 92 / 10 40 40 30
SGJ 77 93 78 89 / 20 30 20 20
GNV 75 93 75 92 / 30 60 40 50
OCF 74 93 75 91 / 40 60 40 50
&&
.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.
&&
$$
Shashy/Shuler/Corless
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
837 PM CDT Fri Aug 18 2017
.UPDATE...
837 PM CDT
No big changes planned to going forecast. GOES-16 imagery this
evening shows a pair of shortwave troughs pivoting around the
backside of the larger scale long wave trough over the region. The
shortwave most noteworthy for our area is moving across
southeastern IA this evening. Small cluster of showers and
isolated thunderstorms developed in response to this wave and is
moving across central IL. Evening sounding from KILX measured
SBCAPE/MUCAPE around 1800 j/Kg, however that was being driven
largely by a very shallow near surface layer of moisture, once
atmosphere decouples this evening, instability should be much
weaker. Lifting 950mb parcel yields around 500 j/Kg of CAPE,
which is still sufficient to maintain some convection as this
shortwave track across mainly southern portion of the CWA.
Short range convective allowing models had been fairly bullish
with coverage/intensity of this activity. Thus far, guidance has
been too aggressive when compared with what`s materialized. Latest
HRRR has begun to trend a little skimpier with the convection and
given recent satellite and radar trends, this seems reasonable.
Going grids handle timing and areal extent of the precip well,
focusing pops over southern CWA, especially far south.
Will freshen up the derived text products (ZFP, LFP) shortly.
- Izzi
&&
.SHORT TERM...
209 PM CDT
Main concerns for the near term forecast is with the coverage and
timing of showers and thunderstorms tonight.
Surface low pressure continues to pull away to the northeast of
the Great Lakes region this afternoon. While weak surface high
pressure ridging was developing east across the forecast area this
afternoon, attention turns to an area of surface low pressure
over southern IA, and an associated upper trough across the
eastern Dakotas, MN and IA. This upper trough is progged to
amplify across the forecast area through early Saturday morning,
as fairly strong vort north of the FSD/SUX area digs southeast
into IL. In response, the weak surface low over IA will develop
eastward along a modest low-level baroclinic axis, and is expected
to support the development of showers and a few thunderstorms
this evening into the overnight hours. Most of the high-res
convective allowing model guidance is in good agreement in
developing convection across southeast IA and into western IL
through early this evening, then spreading it east across portions
of northern/central IL generally along/south of the I-80/88
corridors. Guidance generally downplays showers farther north,
with lighter more scattered precip expected across far northern
IL.
Short wave continues to dig into the southern Lakes and Ohio
Valley early Saturday, with mid-level drying noted in forecast
soundings across the forecast area during the early morning hours.
Nearly all guidance has precip out of the forecast area by
sunrise. Fairly strong subsidence then develops in the wake of
this wave during the day, with H5 rises of 70+ meters by
afternoon. Broad area of weak high pressure reflects this at the
surface, setting up light winds and decreasing cloud cover (save
for some flat cu) by midday. Light winds and high pre-dawn RH
could produce some shallow patchy fog in a few spots prior to
sunrise. Low level thermal progs from models support highs in the
low-mid 80`s in most spots, with a weak lake breeze keeping
readings a bit cooler along the Lake Michigan shore.
Ratzer
&&
.LONG TERM...
209 PM CDT
Saturday night through Friday...
Hot, humid, and at times active weather expected Sunday though
midweek with cooler and drier conditions in place to close out the
upcoming work week as pattern transitions from zonal early in the
period to highly meridional late.
Sunday and Monday, broad area of low pressure will be in place
across the central Great Plains while 850mb thermal ridge is in
place out ahead of the low across portions of the mid to upper
Mississippi Valley. This will allow for continued hot and humid
conditions Sunday and Monday with afternoon highs well into the 80s
and dew points creeping towards or into the 70s. Forecast soundings
show decent capping in place Sunday and there is no notable
source of forcing, so expect primarily dry conditions through the
day Sunday.
Nocturnal convection appears favored Sunday night as low level jet
intensifies well to our west, and now the 12Z GFS tries to bring a
convective complex across the local area Monday morning. NAM and
ECMWF paint a similar picture which raises concerns for PoPs and
cloud cover through the day Monday, including around the time of
the eclipse. Confidence in the details remains low at this
distance given the lack of any strong synoptic scale ascent and
models struggling with convective feedback generating low
amplitude waves over the area. Remnant showers and storms
somewhere in the region if not here locally seems plausible though
so have increased cloud cover and PoPs some through the day
Monday.
A strong upper wave is expected to begin digging into the Upper
Midwest Tuesday and continue to carve out a deep trough across the
Great Lakes through the day Wednesday. Showers and thunderstorms are
more favored on Tuesday in response to this wave and attendant
surface cold front that will push across the region later in the
day Tuesday. An expansive area of high pressure will build south
from the Canadian Prairies Thursday and Friday resulting in drier
weather to close out the week, but also cooler with afternoon
highs only in the low to mid 70s Thursday and Friday.
Deubelbeiss
&&
.AVIATION...
For the 00Z TAFs...
642 pm...An upper wave will move across the area tonight bringing
showers and few thunderstorms...mainly south of the terminals.
There remains quite a bit of uncertainty regarding precip coverage
across the terminals with perhaps some showers developing over
the terminals late this evening into early Saturday morning. Given
the low confidence...maintained previous vicinity shower mention
and trends will need to be monitored this evening.
West/northwest winds will turn more northerly this evening with
speeds under 10kts. Winds will remain light northwesterly into
Saturday morning and a lake breeze is expected to develop Saturday
afternoon and move inland toward ord/mdw by mid/late afternoon.
Confidence that the lake breeze will reach ord/mdw is medium. cms
&&
.MARINE...
209 PM CDT
Low pressure over the northern Great Lakes will lift north away
from the region while high pressure builds in from the west
tonight and tomorrow. Moderate winds in place this afternoon will
diminish overnight as the high builds over the region. Modest
west to southwest flow will persist across the northern half of
Lake Michigan Saturday peaking around 20 kt at times, while
lighter flow across the south end will allow for afternoon lake
breezes and variable/onshore flow. South to southwest flow will
increase again Sunday as another low advances east across the
Canadian Prairies. A trailing cold front is expected to push south
across the Lake through the day Tuesday turning winds northerly
in its wake.
BMD
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Little Rock AR
628 PM CDT Fri Aug 18 2017
.AVIATION...
Scattered TSRA across extreme NW Arkansas will move ESE and
likely affect KHRO and KBPK between 00Z and 03Z. Brief heavy rain
will like reduce visibilities along with gusty winds that could
exceed 40kts. As the storms track further SE, KLIT, KPBF, could
see storms in the vicinity around midnight. Otherwise, VFR
conditions and nearly calm winds will be the rule through the
remainder of the forecast period.
&&
.PREV DISCUSSION...(ISSUED 252 PM CDT Fri Aug 18 2017)
SHORT TERM...Tonight Through Sunday
With quite a bit of sunshine today and only some afternoon CU
across the state, temperatures have been steadily climbing
throughout the day. But, for mid to late August we are still at or
a bit below normal with temps generally in the upper 80s to lower
90s. Dewpoints have made temps a bit more uncomfortable, with
values ranging from the mid 60s to upper 70s.
Not many changes were made to the ongoing forecast during the short
term period. The one exception to that is rain chances for the late
afternoon and evening hours, mainly across the north. Previously
advertised shortwave is progressing eastward across northwest
Arkansas as of 1930z and seems to have provided enough lift to get
some rain and thunderstorms to develop this afternoon. This activity
has been confined to northeast OK and southwest MO and given the
latest HRRR guidance will translate east and impact areas mainly
north of Little Rock.
Looking ahead, can`t rule out some isolated to scattered showers and
thunderstorms through Sunday but activity shouldn`t be too
widespread. The heat gets turned up a bit on Saturday as surface
high pressure becomes more centered over the area and mid level
ridging builds over and just south of the state. Heat indices
will likely make it to 100 in most areas, with the exception being
across the north. Some locations will flirt with heat advisory
criteria across southern/southeastern areas but current forecast
remains just below criteria attm.
LONG TERM...Sunday Night Through Friday
A flat ridge will be in place across the region at the beginning of
the long term, while a moist southerly flow remains at the surface.
Monday is of heightened interest to most people because of the solar
eclipse, and although only a partial eclipse will be visible from
Arkansas, interest is still quite high in the midday weather
conditions.
This could certainly change, but at the moment it looks like much of
the area will probably be partly to mostly cloudy, which could
certainly present a challenge to viewing the eclipse. The least
cloud cover will probably be in the northeast and perhaps in the
southeast as well. The very warm temperatures and humid airmass will
also result in 20-30 percent rain chances during the time of the
eclipse.
By the Tuesday-Wednesday time frame, the upper level ridge will give
way to an upper level trof dropping down into the area. This will be
accompanied by a surface front, which should result in increased
rain chances on those two days. Cooler and drier air will move in
behind the front once again, and will allow max temperatures to drop
down below climatological normals in the Wed-Fri time frame,
particularly on Thu-Fri. In fact, there may not be any 90 degree
readings on either of those days.
&&
.LZK Watches/Warnings/Advisories...NONE.
&&
$$
Short Term...32 / Long Term...61
Aviation...32
Area Forecast Discussion
National Weather Service Miami FL
950 PM EDT Fri Aug 18 2017
.UPDATE...
Updated PoPs for tonight and tomorrow with most recent model data.
This caused PoPs and chances of thunderstorms to drop over much of
the area into the chance category, and pushed the better chances
into the afternoon, with generally only slight chances for the
morning hours. Otherwise, only tweaked forecast to be in line
with current observations.
&&
.PREV DISCUSSION... /issued 755 PM EDT Fri Aug 18 2017/
AVIATION...
Convection in the western interior should diminish over the next
couple of hours. Afterwards, should be a quiet night across South
Florida. By mid morning, chances of showers and storms increase
quickly. Have added PROB30 for TSRA at all east coast TAF sites
after 17z. APF may see some activity later in the afternoon.
PREV DISCUSSION... /issued 728 PM EDT Fri Aug 18 2017/
UPDATE...
Convection is still ongoing over portion of the interior and w
this afternoon producing some very heavy rainfall and frequent
lightning. Although the activity observed is not severe, an
isolated stronger storm can not be ruled out before sunset. With
the loss of daytime heating, expect most of the convection to
diminish across South Florida with light and variable winds
overnight. As the tropical wave approaches the peninsula tonight
into Saturday, the chance of rain will gradually increase over
the Atlantic waters tonight and east coast into Sat morning. The
forecast remains on track.
PREV DISCUSSION... /issued 428 PM EDT Fri Aug 18 2017/
DISCUSSION...
Heavy rain possible Saturday into Sunday for South Florida...
FRIDAY AFTERNOON THROUGH SUNDAY
A large, well-defined upper-level low is currently centered over the
region. Scattered thunderstorms are developing over the interior
this afternoon. Expect this activity to continue over the
interior and west coast through early evening. Several
thermodynamic ingredients from the 12Z adjusted sounding and RAP
model soundings indicate that some of the thunderstorms this
afternoon will be strong over the interior and west coast areas.
Cannot rule out one or two severe storms. Hail and gusty winds are
the main threats. Expect thunderstorm activity to diminish after
sunset.
On Saturday, a tropical wave will approach South Florida, bringing
rainier than normal conditions from Saturday afternoon through
Sunday morning, and possibly lasting through Sunday afternoon. Most
guidance indicate PWATs in the 2.0-2.4" range during much of the
period. There will be a risk of localized street flooding. There
is a chance for sunshine Saturday morning prior to the arrival of
the tropical wave, so can`t completely rule out some strong storms
on Saturday afternoon. Again, the primary threat on
Saturday/Sunday is for heavy rain and localized flooding.
SUNDAY NIGHT THROUGH FRIDAY
Sunday night and Monday, there will be an influence of mid-upper
ridging from the Bermuda high, which will serve as a short-lived
break from the higher than normal rain chances. A strong
mid/upper-level high pressure area will move westward and anchor
itself over the southeastern United States by Tuesday. At the same
time, the tropical disturbance currently located about 600 miles
east-northeast of the northern Leeward Islands (Invest 92L), is
likely to be approaching the region. NHC indicates a 60% chance of
development as their 2 PM Tropical Weather Outlook. Regardless of
development, this system is likely to bring a chance for enhanced
rainfall to South Florida early Tuesday through Wednesday. All
residents and visitors of South Florida need to continue to
monitor this tropical disturbance through the weekend.
Even though the threat from 92L should be gone by late next week,
the GFS and other models hint that we could remain in a rainy
pattern associated with a left-over trail of moisture from 92L
combined with a frontal boundary to our north. Low-mid level
southerly winds will advect deep tropical moisture over South
Florida toward the boundary, resulting in a continued rainy
pattern that lasts through the week.
MARINE...
Mostly good boating conditions are expected for South
Florida waters off both coasts through the first part of the weekend
with seas 2 feet or less. By Saturday night, winds increase to 15
kt and seas build to around 3 feet for the Atlantic waters.
Expect these 3 foot seas to continue through Sunday, with 2-3
foot seas for the Gulf waters. By Sunday night, seas build to 4
feet with a few areas of 5 feet possible for the Atlantic waters.
Seas averaging around 4 feet can be expected to last through early
next week for the Atlantic waters.
Small craft exercise caution conditions may be possible by late
Saturday night or Sunday morning for Atlantic waters due to winds
in the 15-20 knot range.
&&
.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach 81 94 80 91 / 10 50 60 70
Fort Lauderdale 82 92 80 91 / 20 50 50 60
Miami 81 93 80 91 / 20 50 50 60
Naples 73 94 78 91 / 30 30 40 60
&&
.MFL WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...None.
GM...None.
&&
UPDATE...13
DISCUSSION...98/ABH
MARINE...98/ABH
AVIATION...13
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1052 PM CDT Fri Aug 18 2017
.SHORT TERM...(This evening through Saturday)
Issued at 413 PM CDT Fri Aug 18 2017
Wave that brought rain to southern MN much of the day is now over
southeast MN, but the cool cloud tops associated with it are all up
by Lake Superior, well north of where the precip is around southeast
MN, so this area of precip is expected to continue it`s diminishing
trend the rest of the afternoon. Right on the heels of this wave is
a much more compact, but stronger wave over northeast South Dakota.
This SD wave will be the source of strong to severe storms this
afternoon/evening in southwest MN. Expect these storms to more or
less follow the CAPE gradient (where sbCAPE maxes out around 2000
j/kg) southeast toward northwest IA, more or less paralleling the
Buffalo Ridge. Farther east, subsidence on the backside of the first
wave, along with more stable air in its cloud cover will limit
storms from the SD wave from making it much farther east of a
Willmar to Mankato line. Not only will the first wave limit eastward
coverage of storms from SD, but it will also keep storms in northern
MN, which went up just north of the cloud shield, from making much
progress into central MN. In the end, followed a blend of the CAMs
pretty close for PoP/QPF grids through this evening, which has the
best chances running from west central into southwest MN, with
pretty small chances outside of that area.
This activity will move south of the area pretty quick this evening,
with high pressure expected to slide over Iowa tonight. This will
leave us with our biggest issue for tonight, the potential for dense
fog. Given where the high is going and where the rain has fallen
today, it is looking increasingly likely that we will see dense fog
across at least southern MN, with the HRRR developing dense fog
pretty much everywhere west if I-35. Beefed up the fog mention in
the grids, and based the fog description (patchy, areas, widespread)
off of the visibility forecast from a blend of the short term models.
For Saturday, once the fog is gone, there will be no issues, with
mainly clear skies and highs in the low 80s expected. The only area
where we could see things play out a bit different is in west
central MN, where highs could get a bit warmer if the thermal ridge
coming across the Dakotas gets here faster than currently
forecast.
.LONG TERM...(Saturday night through Friday)
Issued at 413 PM CDT Fri Aug 18 2017
The main focus in the extended will be a slow moving front that
will stall over the area Sunday night into Monday night, providing
multiple chances of showers and thunderstorms.
High pressure over the Mississippi Valley will be sliding
southeast into the Ohio Valley Saturday night. Meanwhile, a
boundary will approach from the northwest as the next trough
advances eastward across Canada. A few showers and thunderstorms
are possible along it over western MN late Saturday night, but the
coverage should be limited due to deeper low moisture not
arriving until Sunday afternoon and a strong cap in place with the
EML overhead. The front will be orphaned from the Canadian trough
while another system developing over the western High Plains
transitions it into a quasi-stationary boundary Sunday. Deeper
moisture with pwats rising above 1.5 inches and continued steep
mid level lapse rates will make it easier to break the cap and
shear is strong enough to organize storms into line segments,
possibly into an upscale growing MCS by Sunday night.
Beyond Sunday night, it`s difficult to determine where the front
will be given convective activity from the preceding 24 hours
which lends to a higher level of uncertainty with subsequent
development. But, it does appear the front won`t be surging too
far south and even deeper moisture will pool along and south of it
with pwats around 2 inches Monday. The MCS Sunday night may
progress enough eastward for some breaks in the cloud cover here
in time for the eclipse around 1 pm, before more development
occurs later in the afternoon. Continued steep lapse rates and
very high moisture content in the lower atmosphere will allow the
pattern to repeat Monday. The system will shift east Monday night.
Cooler and drier air following next week will solidify a below
average month for temperatures region wide with a deep trough
developing across the northeastern half of the CONUS.
&&
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1047 PM CDT Fri Aug 18 2017
Main concern is for fog overnight. Still thinking widespread fog
is a good bet, but the HRRR has backed off considerably. But, the
setup remains unchanged with cool overnight lows under clear
skies, and a moisture reach shallow layer under the inversion.
Hydrolapses increase with height as well, further indicating that
potential. As of this writing, a few sires around the region are
already reporting reduced visibilities. NAM/ARW/NMM still indicate
dense fog potential overnight, which I especially think is valid
across RWF and MKT where even more rain was received earlier
today. Once the fog burns off around 13-14Z, a VFR period ahead
with mostly clear skies. Winds will pick up above 7 knots in
western MN tomorrow afternoon, from the southwest and becoming
southerly.
KMSP...Still thinking fog is possible overnight. Otherwise no
changes from the main discussion.
/OUTLOOK FOR KMSP/
Sun...VFR. Chance MVFR/TSRA overnight. Wind SW 5 kts.
Mon...Chc MVFR/-TSRA. Wind SE 5 kts.
TUE...Chc MVFR/-TSRA early, bcmg VFR. Wind N 5-10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&
$$
SHORT TERM...MPG
LONG TERM...BORGHOFF
AVIATION...SPD
Area Forecast Discussion
National Weather Service Pueblo CO
310 PM MDT Fri Aug 18 2017
.SHORT TERM...(This evening through Saturday)
Issued at 310 PM MDT Fri Aug 18 2017
With drier air over the area today, little in the way of pcpn is
expected this afternoon and evening. The models continue to show
the potential for some isolated showers/tstms over the mtns,
although the HRRR also shows a few drifting out over the lower
elevations of El Paso and Pueblo counties this evening.
With the upper level ridge being over the area on Sat, the chances
for pcpn still look quite limited. The forecast models show isolated
pcpn over the mtns in the afternoon. However, a weak disturbance
in the flow aloft, is expected to move across southern CO in the
afternoon and the NAM and GFS show it kicking off some pcpn across
mainly the far southeast plains. Temps on Sat are expected to be
a little above average acrs the southeast plains, with highs close
to average in the San Luis and Upper Arkansas River Valleys.
.LONG TERM...(Saturday night through Friday)
Issued at 310 PM MDT Fri Aug 18 2017
Saturday night-Monday...Generally weak westerly flow aloft expected
across the region into early next week, as upper level high pressure
persists across the southern High Plains through the Desert
Southwest. Models continue to suggest a slow increase in available
moisture across the area, first moving into southwestern Colorado
Sunday and into eastern Colorado on Monday. With that said, should
see a slow increase in afternoon and evening showers and
thunderstorms into the early next week, with storms generally
diminishing and ending with the loss of solar heating. The best
coverage of storms will be over and near the higher terrain,
especially the southwestern mountains on Sunday, and all of the
southern mountains on Monday.
Some model differences for Sunday night and Monday, as the EC has a
minor wave undercutting the ridge across the southern Rockies,
possibly aiding in keeping showers and storms ongoing across the
southern Rockies, and spreading mid and high level clouds across
eastern Colorado through the day on Monday. The GFS spreads the
moisture further east through early Monday morning, where as the NAM
is somewhere in between. Time will tell. Temperatures through this
period to be generally at to slightly above late summer levels.
Tuesday-Friday...There looks to be a continued increasing in showers
and storms through the rest of next week, as upper high builds
across the Rockies. This will allow for monsoonal moisture to
increase across the area within weak south to southwesterly flow
aloft, leading to better coverage of afternoon and evening showers
and storms. With the increased moisture and weak steering flow
aloft, storms will be capable of producing locally heavy rainfall,
owning to an increase in flash flooding potential as well. With the
increase in convection, temperatures are expected cool to slightly
below seasonal levels through the period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 310 PM MDT Fri Aug 18 2017
VFR conditions are expected through the next 24 hrs at KCOS, KPUB
and KALS. There is a small chance for showers/tstms at KCOS this
evening. Saturday afternoon some isolated showers/tstms could
impact the vicinity of the terminal forecast sites, however chances
are too low at this time to include in the forecast.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...28
LONG TERM...MW
AVIATION...28