Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/13/20
Area Forecast Discussion
National Weather Service Boston/Norton MA
1016 PM EDT Sat Sep 12 2020
High pressure provides another night of dry and cool weather.
Likewise not as cool Sunday as the ridge weakens and the airmass
modifies. Morning clouds will slowly break for sunshine Sunday
afternoon. A weakening cold front may bring a few isolated
showers Sunday night, although most locations remain dry. High
pressure builds in on Monday, allowing for blustery conditions
but seasonably cool and dry weather through Tuesday. Moderating
trend to temperatures for Wednesday ahead of another cold front
for either later Thursday or Friday. High surf from Paulette
will likely impact the South Coast early next week especially
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
1015 PM Update...
Dry and quiet weather still expected. Have increased the sky
cover across southern New England toward the latest RAP as the
950 hPa RH is doing well with the strato-cu just offshore of
Long Island. Expect this to spread in from south to north
generally after 2 AM.
Have also decreased low temperatures a few more degrees based on
current observations as we are a tad bit too warm currently.
Should see strong radiational cooling until those clouds move
in. Low temperatures in the mid to upper 40s across the interior
and the 50s across coastal locations.
725 PM Update:
Tranquil conditions continue now just after sundown across
Southern New England under governing high pressure ridge. This
high will continue to shift further offshore as the night
progresses. With it will be a shift in low-level flow to SEly
and allow us to tap some of the lower-level moisture evident in
nighttime microphysics satellite imagery in the waters south of
Nantucket. Should see mainly clear skies with good radiational
cooling thru midnight, but by late in the overnight and into the
pre- dawn Sunday hrs, an increase in stratocu looks probable as
this moisture is drawn landward in the SE flow. RAP-based
BUFKIT soundings indicate this moisture is very shallow and
related cloudiness may be fairly short-lived but will still
linger thru sunrise. Lows still look on track, though
radiational cooling may start to level off given the increased
cloudiness toward daybreak.
A very pleasant fall evening ahead with 1028 mb high pressure along
the Maine coast. Any diurnal cumulus clouds quickly erode yielding
clear skies, diminishing winds and with dew pts in the 40s and 50s
expect temps to fall quickly with sunset. Although as the high
retreats seaward, low level flow (925 mb winds) becomes southeast
and begins to advect low level moisture northward in the form of low
clouds after midnight from south to north. This will level off temps
with lows overnight 45-50, except low to mid 50s in the urban areas
and much of the coastline. Thus did not follow the coldest MOS
guidance. Instead derived min temps from a blend of MOS guidance.
Could have some patchy radiational fog overnight especially in the
CT river valley.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Mostly cloudy to overcast to begin the day with low level moisture
in the form of strato-cu beneath the subsidence inversion. Mid Sep
now so sun angle much lower than just a month or two ago. But with
ridge weakening as the day progresses along with sun going to work,
clouds will lift and break for sunshine in the afternoon. Airmass
slowly modifies with S-SE winds advecting dew pts into the upper 50s
and lower 60s by days end. Thus it won`t feel as cool as today.
Highs should climb to 70-75 throughout the region.
Mid level short wave exiting the Great Lakes into the St Lawrence
River Valley deamplifies with time, thus forcing for ascent is weak
across MA/CT/RI. As a result only expecting a few spot light rain
showers across the region with many locations remaining dry. Mild
prefrontal weather with frontal passage holding off until late
night or even until sunrise for much of RI and eastern MA.
.LONG TERM /MONDAY THROUGH SATURDAY/...
* Blustery but clear skies and dry conditions Monday, with
seasonably cool temperatures. Less breezy but cooler highs on
* Potential for high surf later Monday into Tuesday for ocean
exposed beaches due to long-period swell from Paulette.
* Continued dry but with moderating temperatures with southwest
* Cold front offers next chance for rain later Thursday or Friday.
Monday thru Tuesday Night:
After some Monday early-day showers come to an end on the Cape, cold
front pushes off the coast. The governing feature will be a broad
Canadian anticyclone that ridges into the region Monday mid-morning
through Tuesday. It will bring with it a shot of cooler and drier
air into Southern New England, with clear skies and fairly strong
diurnal temperature ranges (e.g. seasonable days with cooler
nights). Highs in the 70s to near 80 Monday with lows in the 40s to
low 50s. But on Tuesday highs may struggle to reach 70 degrees under
clear skies, with similar lows. Could have some lows in the upper
30s Tuesday night in the typically cooler spots as radiational
cooling conditions project to be better (e.g. less wind than Monday).
Given strong cold advection steepening low-level lapse rates and
boosted by fairly strong 3-hrly pressure rises, expect Mon to be a
fairly breezy to blustery day in the post-frontal air mass as the
PBL deepens. Strongest NW/N wind gusts out across Cape Cod and the
Islands but most areas should see gusts in the 25 to 35 mph range
late Monday afternoon into early Monday night, then subsiding a bit
into early Tues. Occasional breezes on Tues but a decreasing trend
in sustained winds and gusts thru Tues into Tues nite.
Though more of a beach/surf-zone hazard, ocean-exposed beaches
especially southern waters will be seeing long-period 7` seas
associated with sea-swell energy with distant TC Paulette later Mon
into Tues. May not be a great beach day Tues with cooler than
average temperatures, but nonetheless, later shifts will need to
consider a high surf advisory at least for Tues given these
Wednesday thru Wednesday Night:
High pressure area progresses eastward off the waters of Southern
New England. Under full sun, this will lead a period of moderating
temperatures under fairly breezy SW winds (gusts mainly 20-25 mph in
in the interior and more solid 25 mph gusts across Cape Cod/Islands
into the South Coast). 925 mb temps around +16 to +18C and 850 mb
temps around the mid-teens C should bring highs back into the mid/
upper 70s to near 80F in spots, with lows mid 50s to lower 60s.
Dewpoints start to rise more appreciably into Wed nite but should
still fall into the comfortable range (mid-upper 50s commonly).
Thursday into Friday Night:
This period on the whole looks to offer the next chance for rain,
however there`s substantial variation in the 12z NWP on the details
regarding how that shakes out. A cold front moving through the more
active northern stream is a key feature agreed upon by all the
deterministic guidance either later Thursday (GFS/Canadian GEM) or
into Friday (ECMWF). Other than the timing differences, the 12z
ECMWF, which shows more phasing of northern and southern energy
streams, also introduces some question if any of the remnant energy
from what is now Tropical Storm Sally may interact with the front.
That would lead to a much wetter frontal passage than advertised by
the GFS/GEM. So still a lot unresolved but there still remains time
to iron these details out. Official forecast will keep chances for
showers around later Thursday into Friday. Temperatures should turn
near to above normal.
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAF Update:
Tonight (thru 12z Sun): High confidence.
VFR through at least 06z, then start to see borderline VFR/MVFR
ceilings advance landward on SE flow. This may happen as soon as
07z towards the South Coast but better confidence inland after
09-10z. Coverage of these clouds don`t look to be any worse
than BKN with bases 030-040. SE winds 4-7 kt.
Sunday...Moderate confidence...some uncertainty how quickly
ceilings lift from MVFR to VFR.
VFR/MVFR the morning but slowly lifting to VFR in the afternoon.
Light S to SE wind.
Sunday night...high confidence.
MVFR/VFR with a few spot showers possible although most
terminals may remain dry. Light SW wind becoming NW late with
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF.
Outlook /Monday through Thursday/...
Monday: VFR. Windy with areas of gusts up to 35 kt.
Monday Night: VFR. Windy with gusts up to 30 kt.
Tuesday: VFR. Breezy.
Tuesday Night: VFR.
Wednesday through Thursday: VFR. Breezy.
Tonight...high pressure remains over the waters, so quiet boating
weather along with dry weather and good vsby. Low clouds after
midnight may lower vsby some but overall good vsby.
Sunday...high pressure weakens and moves offshore with S-SE winds
developing but remaining light. Dry weather and good vsby prevail.
Sunday night...Cold front approaches from the west with S-SW winds
developing. Increasing low level moisture may yield some patchy fog
but will be short lived with frontal passage toward morning with
wind shift to the NW. Not much if any shower activity with the
Outlook /Monday through Thursday/...
Monday: Low risk for Small Craft Advisory winds with local
gusts up to 30 kt. Seas up to 5 ft.
Monday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft.
Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 10 ft.
Tuesday Night: Winds less than 25 kt. Seas up to 5 ft.
Wednesday: Winds less than 25 kt. Areas of seas approaching
Wednesday Night through Thursday: Winds less than 25 kt. Seas
up to 5 ft.
MARINE...Small Craft Advisory until 2 AM EDT Tuesday for ANZ250-254>256.
Area Forecast Discussion
National Weather Service Houston/Galveston TX
745 PM CDT Sat Sep 12 2020
.SHORT TERM [Tonight through Monday]...
Quick update sent for gusty winds and scattered storms in the
southeastern most areas. These should dissipate quickly between
830-930 pm. A few of the HRRR runs have highlighted some
redevelopment there after after 2 am but for now will follow this
uptick with a lull through 7 am. Still looking like a much more
active day with storms across the southeastern 2/3rds of the
region between noon and 9 pm.
.AVIATION [00Z TAF Issuance]...
Storms waning in the short term and will see some MVFR decks
possibly after 09z advancing in from the northeast and east though
may not reach the TAF sites. Showers should get going around
12-15z near the Galveston/Bolivar/Daisetta area and then expand
inland. Primary impacts should hold off until after 18z Sunday
with passage of bands of showers and thunderstorms with gusty
winds and lowered VISBY.
.PREV DISCUSSION /Issued 308 PM CDT Sat Sep 12 2020/...
.LONG TERM [Monday through Sunday]...
On Monday, an inverted upper trough will be located over Deep South
Texas and a tropical system will be approaching the Mississippi
delta. Moisture on the north side of the upper trough will be
competing with subsidence on the western periphery of TS/Hurr Sally.
At this time, feel Sally will be far enough east to allow moisture
to remain over at least the SE half of the region. PW values in
both the GFS and NAM reach 2.20 inches with convective temperatures
around 90. Subsidence begins to kick in on Tuesday and Wednesday as
Sally slowly meanders across the northern Gulf coast. 850 mb temps
remain warm and with drying noted in area soundings, MaxT values
should still be capable of warming into the lower and possibly mid
90s. By late Wednesday, an upper level trough will develop over West
Texas. Some differences between the Canadian, GFS and ECMWF with
regard to how deep through trough gets and how quickly it will move
across the US. Preferred how the ECMWF initialized and it`s relative
consistency and have leaned toward the ECMWF for the end of the week
into next weekend. Based on the ECMWF, feel the trough will move
slowly across the state and will bring a good chance of showers and
thunderstorms both Thursday and Friday. Rain chances will diminish
Friday night as the upper level trough axis pushes east and a
surface cold front pushes through the area. Upper level ridging will
redevelop over the 4 corners region and expand into Texas next
weekend. A dry northerly upper and low level flow will develop
keeping skies generally clear for next weekend. Drier conditions
expected in the wake of the sfc front with sfc dew pts possibly
falling into the upper 50`s. 43
Offshore flow will become northeasterly tonight as ridge of high
pressure builds to the north. Tropical Storm Sally will track over
the warm waters of the Eastern Gulf next few days...likely
intensifying to a strong tropical storm...then a hurricane before
making landfall somewhere on the coast between SE LA and Wrn FL
Panhandle possibly on Tuesday. WNA wave model period fields suggest
swells from Sally should could arrive on the TX coast as early as
Monday night leading to some increase in surf at that time with
swell continuing for at least 24 to 36 hours coming out from this
slow moving tropical cyclone. The more direct wind and wave impacts
from Sally should remain well to the east of the forecast area as
the storm pushes inland mid week.
Longer term a good deal of uncertainty. ECMWF brings a fairly
impressive cold front from the north with moderate north...then
northeasterly flow behind it next Friday and Saturday. Canadian
actually brings a tropical system up the coast from the Bay of
Campeche at that time. GFS maybe a tad more like the Euro but with a
much weaker front. We are leaning slightly toward the ECMWF solution
here but again note the uncertainty for Days 6 and 7....next Friday
and Saturday. 18
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 72 91 72 91 72 / 0 40 20 30 10
Houston (IAH) 76 95 76 93 76 / 30 60 20 30 20
Galveston (GLS) 81 91 80 91 80 / 40 50 50 30 30
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
924 PM CDT Sat Sep 12 2020
Updated for evening discussion.
There was considerable rain coverage from westward-moving bands
of convection this afternoon in association with a tropical wave
moving across the northwestern Gulf (not to be confused with
Sally). Meanwhile, a stalling front extends from the Midwest into
the southern Plains, with associated convection moving eastward
into the Mid South and Mississippi River Valley this afternoon.
This activity converged over central Mississippi early this
evening, with a corridor of stalled convection now extending
roughly along the Big Black River. Though much of the convection
associated with the tropical wave was more diurnal in nature and
has since fallen apart, persisting low level convergence ahead of
the surface front overnight along with subtle upper diffluence
and forcing will keep scattered showers and a few storms going
mainly north of the Natchez Trace. The inherited forecast had a
decent handle on this, so only minor tweaks were made to adjust to
current trends. /DL/
Prior discussion below:
Tonight and Sunday: Scattered to numerous coverage of showers and
thunderstorms were noted on local radars this afternoon. This
activity will gradually diminish this evening with the loss of
daytime heating but the chance for rain will likely continue tonight
in our west as a quasi-stationary boundary tries to edge into our
CWA. Tropical Storm Sally formed in the eastern Gulf of Mexico
earlier this afternoon and will slowly move our way through Sunday.
Meanwhile, the closed low over the upper Mississippi valley this
afternoon will continue tracking to the northeast across the Great
Lakes region tonight while weakening. This departing shortwave
trough will help the old quasi-stationary frontal boundary just to
our northwest to drift southeast into our CWA later tonight and
Sunday. This boundary will become the focus for convection Sunday
especially during prime heating. Otherwise, warmer than normal
temperatures will continue tonight thanks to our tropical airmass.
High temperatures will continue above normal the southeast half of
our CWA while temperatures are held closer to normal in our
northwest due to the greater rain chances and associated cloud
Sunday night through Friday night: Primary weather concerns in
the longer term forecast are associated with Tropical Storm Sally.
The official NHC forecast strengthens Sally into a hurricane
before making landfall somewhere along the central Gulf Coast
early Tuesday. With guidance generally trending stronger with
Sally and showing a greater chance for intensification as it
approaches land, am a little more concerned for tropical cyclone
impacts extending into the ArkLaMiss region, especially for heavy
rain and wind in the Tues-Wed time frame over the Pine Belt
region. One of the complicating factors will be with motion as
steering currents will likely become very weak and the system
could slow down once near the coast or inland. Given the potential
for a slow-moving tropical system, will go ahead and post a
limited flooding graphic. If trends continue, both rainfall/wind
threats will need to be highlighted more, and we may ultimately
need to issue tropical storm watch/warning for southeast portions
of the area. Going later into the week, an upper level trough in
the westerlies will likely approach and help to send the remnants
of "Sally" out of the area, and this would bring an end to the
heavy rain threat. /EC/
00Z TAF discussion:
Complicated forecast. Dissipating convection over the region will
bring some quick showers and thunder through the next few hours.
Overnight...bringing in MVFR/IFR cigs towards dawn, mainly after
09z, but persistence from the prev night has closer to daybreak
and shortly thereafter and brief. HRRR guidance is spotty with the
IFR cigs... but over a broad area. As a result...blending to the
current trend and more widespread precip/increasing BL humidity.
.PRELIMINARY POINT TEMPS/POPS...
Jackson 73 89 73 89 / 40 55 4 56
Meridian 73 90 73 88 / 18 33 8 63
Vicksburg 74 89 73 91 / 52 65 3 40
Hattiesburg 72 92 73 88 / 22 39 9 68
Natchez 73 89 73 90 / 35 61 5 44
Greenville 73 86 71 88 / 57 66 3 33
Greenwood 72 87 70 90 / 60 69 3 40
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
634 PM CDT Sat Sep 12 2020
.SHORT TERM... (Through Late Sunday Afternoon)
Issued at 237 PM CDT Sat Sep 12 2020
Current surface analysis shows a cold front which is nearly
stationary draped across Missouri and Illinois from KSGF to near
KSTL to KSPI. Short range guidance is in good agreement that this
front will continue to drift southeast tonight with scattered to
numerous showers and a few thunderstorms ahead of it. Some
convection allowing guidance PoPs some fairly hefty storms over
southeast Missouri and southern Illinois a little later this
afternoon, and the RAP does show 1500-1800 J/Kg MLCAPE in those
areas over the next few hours so this is not unreasonable.
Additionally, there is a secondary cold front over southeast
Nebraska that is diving southeast into Missouri which will link up
with the front over our area late tonight and finally push it
through. Short range guidance including the RAP and nearly all of
the CAMs show weak convection developing along this secondary front
as well, so have added in some chance PoPs for this evening over
northeast Missouri into west central Illinois. I do not expect any
thunder in our area with this line of showers, and all guidance has
it dissipating during the late evening.
High pressure will build across the Midwest behind the front on
Sunday. There may be some lingering fog and low clouds over
southeast Missouri and west central Illinois early Sunday morning.
It`s possible there may be some fog over northeast Missouri and west
central Illinois as well if the aforementioned showers along the
secondary front moisten the boundary layer enough. Dense and/or
widespread fog does not seem likely though given persistent dry
advection. With that in mind, Sunday still looks dry and mild with
temperatures peaking out about 3-5 degrees below normal in the mid
70s to around 80.
.LONG TERM... (Sunday Night through Next Saturday)
Issued at 237 PM CDT Sat Sep 12 2020
Sunday night through Tuesday continue to look tranquil with near
normal temperatures as high pressure moves east across the Midwest
into the Great Lakes region. Mass fields on the GFS and ECMWF are in
good agreement into Tuesday night...but by Wednesday morning things
start to fall apart. Over the past few runs, the GFS has been
trending closer to the ECMWF with the pattern of a strong cut off
low over Hudson Bay during the latter half of the week which
develops a long wave trough that digs into the eastern 1/2 of the
U.S. This pushes a cold front through the mid Mississippi Valley.
The primary difference between the GFS and ECMWF is timing. The GFS
is about 24 hours faster than the ECMWF with this process bringing
the front into northern Missouri and central Illinois around 00Z
Thursday while the ECMWF holds the front back until between 18Z
Thursday and 00Z Friday.
This of course leads to a huge difference in sensible weather
between the two models on Wednesday and Thursday. The GFS shows
little if any convergence along the front along and ahead of the
front on Wednesday as the last vestiges of the ridge axis from
earlier in the week keep the flow light and variable. This leads to
a dry FROPA on Wednesday night...and then dry and cool weather
Thursday and Friday as high pressure moves across the Midwest and
Great Lakes. The slower ECMWF is somewhat warmer and more humid on
Wednesday, and then Thursday there is actually some interaction
between the approaching cold front and the tropical system it`s
advertising to be over the lower Mississippi Valley. This leads to a
wet FROPA with convection on Thursday and Thursday night.
Additionally, the trough aloft is positively tilted as it moves into
the Midwest and Great Lakes Region on Thursday, which digs it
further south into the eastern CONUS resulting in a deeper and more
persistent upper level long wave, and allows the cool high pressure
system behind the front to stay anchored over the Great Lakes and
Northeast U.S. longer.
Ensemble guidance members show a pretty wide range of temperatures
for max/mins for Thursday through Saturday as would be expected in
this case. Interestingly, the GEFS temperature spread is very tight
wednesday and Wednesday night, and even Thursday isn`t too bad with
only a 5 degree spread between first and third quartiles and a. few
cold outliers. This lends a degree of confidence in the GFS
solution. However the ECMWF ensemble is also pretty sure of itself
through Wednesday and the same cool outliers into Thursday. I tend
to be more trusting of slower solutions when the pattern includes
tropical systems and cut off lows...so the slower ECMWF is
favored here. Will therefore keep some precip chances and stay
warmer on Thursday then go with a dry and cooler Friday and
.AVIATION... (For the 00z TAFs through 00z Sunday Evening)
Issued at 627 PM CDT Sat Sep 12 2020
A cold front with showers and thunderstorms along it has exited
the area over the past few hours. MVFR stratus has largely
scattered out across the area, with the exception of portions of
south-central Illinois. A secondary front is expected to move
through the region late tonight, but is expected to pass through
dry with winds veering from the west/southwest to the northwest.
There remains some hints at some patchy IFR stratus in northeast
Missouri and west-central Illinois late tonight into early Sunday
morning. Do not have high confidence in the location nor the
coverage of this stratus so left a SCT005 group at KUIN. Fog is
likely tonight across parts of southeast Missouri and southwest
Illinois, but should stay south and east of the terminals.
Therefore, expecting dry/VFR conditions for the terminals with the
possible exception of the aforementioned stratus at Quincy.
SPECIFICS FOR KSTL:
MVFR stratus has scattered out over the past couple of hours and
has exited to the east/southeast. Dry/VFR conditions are forecast
through Sunday evening with a mostly clear sky. A secondary cold
front is forecast to pass through the terminal around 0900 UTC
late tonight, but will pass through dry with a wind shift from the
west/southwest to the northwest.
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
1008 PM EDT Sat Sep 12 2020
High pressure will ridge into the area from the northeast
through Sunday while a trough of low pressure remains off the
coast. A cold front will cross the area Monday followed by high
pressure building in from the northwest through Thursday.
Another cold front could approach the area late in the week.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of 1000 PM Sat...Some drier low level air still trying to
filter into the area with Tds falling into the low 60s in the
northern tier. Adjusted grids accordingly. KMHX radar shows
evidence of a weak low aloft about 50 miles SSE of Cape Lookout
that may try and pull shower activity closer to the coast. In
fact, a few showers have made it to Core Banks but quickly fall
apart as high pressure continues to influence the area. Latest
HRRR suggests this will continue overnight, so no changes needed
Prev disc...High pressure centered over New England will
continue to ridge SW into the Southeast tonight while a coastal
trough remains offshore near the Gulf Stream. KMHX radar showing
just few spotty light showers across southern section early
this afternoon while convection offshore has weakened.
Meanwhile, 18Z KMHX sounding shows the subsidence inversion
around 850 mb has strengthened and the airmass has become more
stable since 12z, MLCAPE down from 750 J/kg to less than 50
J/kg, and doubt any convection will develop across the region
this afternoon. Therefore, have lowered PoPs to 20 percent or
less, highest southern sections.
Continued mostly cloudy and stable tonight with descent moisture
remaining below the subsidence inversion. A weak area of low
pressure may develop along the coastal trough offshore overnight
which could advect a few showers westward toward the coast. The
high across inland areas remains strong and the showers should
dissipate before penetrating too far inland and will limit
mentionable PoPs to the immediate coastal sections. Lows will
range from the mid to upper 60s inland to low to mid 70s along
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
As of 3 PM Saturday...High pressure across the area weakens
Sunday but upper ridging will continue to bring subsidence aloft
serving to limit convection. Still, we could see isolated
showers or storms in the afternoon with more sunshine expected
allowing for greater instability in the afternoon...MLCAPE
peaking around 1000-1500 J/kg. Best chances will be across
southern coastal sections where the sea breeze may develop and
push inland allowing for best convergence with background
northerly flow. High expected in the mid 80s most areas.
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
As of 330 AM Sat...A cold front will cross the area Monday,
with high pressure building in from the north behind it keeping
settled and cooler weather through mid-week as Tropical Cyclone
Paulette passes well offshore. The next cold front will bring
rain chances back to the forecast late in the week into next
Sunday Night...Mainly dry as isolated shower activity will be
confined to the proximity of the coastal trough offshore, with
only slight chance showers in the forecast near the beaches.
Lows will be near 70 away from the beaches, several degrees
Monday and Monday night...Modest height falls aloft occur in
response to troughing developing across the Northeast. At the
surface, a cold front force primarily by strong high pressure
behind it will push through the Mid-Atlantic and toward eastern
NC during the day. Despite the lack of any significant pre-
frontal WAA, lingering low level moisture should be sufficient
to allow for scattered showers and possibly a few storms to
develop Monday afternoon. Most likely frontal timing looks to be
later Monday afternoon through Monday evening, with precip
chances ending with the passage of the front. Temps continue to
be several degrees above normal ahead of the front, with
CAA developing quickly behind the front Monday night.
Tuesday through Thursday...High pres building in from the NW
will lead to dry weather with cooler and noticeably less humid
air spreading in. Highs Tue and Wed will be in the upr 70s to
lower 80s, with low to mid 80s expected Thu. Will see lows drop
to around 60 inland Tue night, than a few degrees warmer Wed
Friday into the weekend...High pressure slides off the Northeast
coast as the next cold front approaches Friday, with deeper
moisture returning. Look for unsettled weather Friday into the
weekend with increasingly warm and humid conditions.
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Short Term /through 00Z Mon/...
As of 730 PM Sat...VFR conditions prevail across the terminals
this evening with a scattered deck of 2-3 kft. Healthy amount of
moisture trapped below a strong frontal inversion will result in
lowering and thickening ceilings overnight. Hi-res guidance in
good agreement over MVFR conditions developing around 06z for
all sites with a corridor of IFR developing around 08-09z,
highest probability closer to the tidewater. Inversion keeps
hold Sunday morning before beginning to slowly break down mid
afternoon as front approaches from the west, and could see some
VFR conditions return by mid to late afternoon. Isolated shower
or storm is possible in areas that can clear out.
Long Term /Sunday night through Wednesday/...
As of 330 AM Sat...Ample low level moisture keep the threat for
nighttime/early morning stratus and patchy fog Monday. Drier
air works in behind front Tue with VFR expected to prevail.
Short Term /through Sunday/...
As of 1005 PM...Winds continue to weaken across the waters this
evening with weakening high pressure. Let the SCA for
Albemarle/Alligator/Roanoke and Croatan expire, and Pamlico and
Neuse/Bay rivers will likely follow suit at the top of the hour.
Prev disc...The front has pushed south of the waters with strong
CAA bringing NE flow around 15-25 kt with gusts up to 30 kt
across the waters and seas around 6-9 ft. The winds will
gradually diminish tonight as the high to the north weakens and
the trough offshore pushes toward the coast with seas subsiding
slightly...to around 4-7 ft. N to NE flow around 10-15 kt
expected Sunday with seas only gradually subsiding to 3-6 ft by
Long Term /Sunday through Wednesday/...
As of 330 AM Sat...Northeast winds remain mainly light and at
times become variable as a coastal trough lingers just offshore
into Monday. Then, a cold front will cross later Monday, with
moderate to breezy northerly flow developing quickly behind it
Monday night. Expect winds to only gradually wane through
midweek, remaining N/NE as what is expected to become Hurricane
Paulette passes well offshore and high pressure ridges inland.
Swell from Paulette begins to arrive Monday, with seas building
in mainly long period swell through Tuesday, when they will
peak around 8-11 ft. The swell will only gradually subside
thorough the rest of the week as Paulette turns north the
northeastward. SCAs will remain in effect for the coastal waters
through duration of the hazardous seas caused by Paulette,
which is currently expected to be through at least Wednesday or
As of 330 AM Sat...Gusty NE winds will develop along the coast
Tuesday as strong high pressure builds in from the north. That,
combined with increasing long period swell from distant
Hurricane Paulette, could result in several threats along the
coast. Some wave guidance indicates 8-10 ft seas every 13-15
seconds. Though still several days out, there is potential for
coastal flooding, ocean overwash, and rough surf along the coast
early to mid next week (especially north of Cape Lookout).
Dangerous rip currents will be likely all of next week. Please
continue to monitor the threat closely over the next several
NC...Beach Hazards Statement through Sunday evening for NCZ195-196-
MARINE...Small Craft Advisory until 11 PM EDT this evening for AMZ135-
Small Craft Advisory until midnight EDT Thursday night for
Small Craft Advisory until midnight EDT Wednesday night for
Area Forecast Discussion
National Weather Service Pocatello ID
130 PM MDT Sat Sep 12 2020
.SHORT TERM...Tonight through Monday night. Satellite imagery shows
a widespread area of smoke extending into southwest Idaho. Expect to
see that smoke drift eastward overnight as ridging aloft slowly
moves to the east. A somewhat stronger southerly flow will return to
the region Sunday night. With smoke still present, temperatures may
be moderated somewhat, but still expected to be in the mid to upper
80s by Monday. Monday should be a bit breezier with a tighter
gradient setting up over the region. Hinsberger
.LONG TERM...Tuesday through next Saturday. Models remain in lock
step through Thursday as the upper low continues to take shape off
NW coast early in the period and the downstream ridge amplifies
across the NRN Great Basin Wednesday. We may yet see locally breezy
conditions across the CNTRL mountains Tuesday afternoon in the wake
of Monday`s ejecting energy from the low off the coast but with the
ridge amplifying Wednesday we should return to a lighter wind
regime. The ridge axis may work east of the region as early as
Thursday if the more progressive operational GFS verifies otherwise
Friday is looking like the most likely time frame as the low off the
NW coast begins to move onshore opening the door for increased SW
flow aloft across the region and a chance of showers and afternoon
thunderstorms Friday and Saturday. Huston
.AVIATION...Visible satellite imagery was showing smoke from the
Oregon wildfires working into SW Idaho with VIS reduced to 5SM at
ONO and 1SM at BKE. For now not anticipating VIS to be reduced any
lower than 6SM with HZ at SUN and BYI. VFR conditions should prevail
through Sunday. Huston
.FIRE WEATHER...Critically low humidity values will be present
tomorrow with poor recovery in the Central Mountains tomorrow night.
Near critical fire weather conditions are anticipated on Monday as
winds increase with gusts approaching 25 mph. Winds should subside
slightly on Wednesday, but humidity will still dip to around 12 to
18 percent across much of the forecast area. A gradual increase in
humidity is in store Thursday through Saturday, with wind speeds
expected to increase as well. Thunderstorm chances increase Friday
night with the approach of a strong upper trough. Hinsberger
.AIR STAGNATION...As high pressure progresses eastward this weekend,
smoke from wildfires to our west will track toward Idaho. HRRR Smoke
is showing reduced visibilities as early as this evening across
Central Idaho and portions of South Idaho. The high continues to
track eastward through Idaho Sunday; allowing for reduced
visibilities across all of Southeast Idaho. A more southwesterly
flow will take over Monday and Tuesday which is likely to bring the
northern and central California wildfire smoke into the region; as
opposed to the Oregon fire smoke. ND
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Charleston WV
1020 PM EDT Sat Sep 12 2020
A cold front moves through Sunday and Sunday night. Dry weather
returns as the cold front exits Monday. Unsettled weather may
return beyond midweek.
.NEAR TERM /THROUGH SUNDAY/...
As of 1016 PM Saturday...
Made a few more adjustments to POPs for NE KY and SE OH,
through midnight. Plenty of rain continues to move northeast
across northeast KY and should graze our western CWA for the
next several hours.
Also made a few tweaks to hourly temps and dewpoints for the
rest of tonight.
As of 807 PM Saturday...
Adjusted POPs for this evening and overnight to align more with
latest radar trends and latest near term guidance. Ongoing
convection across far NE KY is located along the leading nose of
2" PWATS and also on the eastern edge of greater instability.
Latest RAP and HRRR indicate an increase in CINh over the next
couple of hours (due to onset of nocturnal cooling) and this
should translate to a downward trend of overall convective
Later this evening (or more likely during the overnight hours),
nocturnal development of primarily showers should occur as a
quasi-effective warm front stalls along the Ohio River. Most
overnight precip should generally be confined to SE OH and far
NE KY, although an isolated brief shower may occur across WV as
a southerly llvl strengthens just off the surface. Not expecting
a significant flood threat overnight but with a rather deep
moisture profile in place across the western CWA, more
organized showers overnight could be rather efficient. Thus,
isolated high water impacts may occur if heavier rains develop.
Minimal changes were made to precip for Sunday. Mainly adjusted
timing of precip a bit and capped POPs at 80%.
As of 130 PM Saturday...
Moisture has been increasing in advance of a cold front, with
some PWATs forecast to be over 2 inches in western portions of
the forecast area this evening. This will allow for some showers
and thunderstorms this afternoon and evening, more likely in
eastern Kentucky and southeastern Ohio. While storms will be
moving and the ground in relatively dry, will have to watch out
for any training storms that could produce excessive rainfall. The
cold front will slowly push through Sunday and Sunday night.
Expect showers and thunderstorms along and in advance of the
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 240 PM Saturday...
Lingering showers may hang about along the higher terrain Sunday
night as the cold front makes its passage into the start of the
work week. Drier air then filters in from the aid of high
pressure building into the Great Lakes region. This will cause a
slight drop in afternoon high temperatures Monday and Tuesday,
but we`ll see a difference in diurnal range come Tuesday as we
wake up to morning lows in the 50s then rising into the low 80s
across the lowlands by the afternoon. Behind the post-frontal
stratus Monday morning, skies will remain clear and precip-free
through the remainder of the short term.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 245 PM Saturday...
The forecast heading into midweek will be dependent upon
tropical activity currently evolving in the Gulf of Mexico. At
the start of the period, high pressure will still be in place
over the Mid-Atlantic region, eliminating much in the way of
However, upper level trough diving down from Canada will nudge
the high eastward and enforce a return pattern regime to set up
in the Central Appalachia. This will then allow for aforementioned
tropical moisture to glide up into the region and set up
unsettled weather beyond midweek. The outskirts of what will
likely be the remnants of this tropical feature by this time
looks to arrive Wednesday afternoon, mostly confined to the
Ohio River Valley. Model solutions are still up in the air for
the end of the work week, so opted to maintain central guidance
POPs through the remainder of the period. Current WPC depictions
for Day 5 through 7 QPF keeps most of the tropical moisture
south of our forecast area and over the Mississippi Valley.
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
As of 725 PM Saturday...
Ongoing convection across NE KY is currently expected to remain
far enough to the west of KHTS to preclude any impacts there for
early this evening. Elsewhere, VFR should prevail through the
evening (exception being at KBKW where flight rules may
fluctuate b/w VFR and MVFR).
Overnight, shower development is expected to occur across much
of SE OH ahead of the next storm system and may approach the OH
River Sunday morning. Farther east, VFR should generally
prevail, although some fluctuations into MVFR may occur as
patches of CIGs develop. Stronger LLVL wind fields should
generally preclude significant fog development overnight for
Precip activity is then prog to increase and progress from west
to east during the day Sunday as a cold front approaches the
region. Nearly all aerodromes should experience SHRA at some
point on Sunday, but intensity and associated impacts are a
little uncertain. Have carried PROB30 everywhere to account for
possibility of reduced VSBYs/CIGs with precip. Iso TSRA also
possible, but lack of impactful convection has precluded TS
mention at the moment.
Most precip should be exiting the region towards the end of
the valid 00z TAF period with poorer CIGs expected later Sunday
SSErly sfc winds around 5 knots tonight, eventually veering more
SWrly during the day Sunday.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z MONDAY...
FORECAST CONFIDENCE: High tonight. Moderate with Sunday precip.
ALTERNATE SCENARIOS: MVFR CIG coverage could be a little greater
tonight than what TAFs indicate. Fog may be more of an issue at
KEKN overnight. Timing of precip may differ during the day
EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
DATE SUN 09/13/20
UTC 1HRLY 00 01 02 03 04 05 06 07 08 09 10 11
EDT 1HRLY 20 21 22 23 00 01 02 03 04 05 06 07
CRW CONSISTENCY H H H H H H H H H H H H
HTS CONSISTENCY H H H H H H H H H H H H
BKW CONSISTENCY H H H H H H H H M M M M
EKN CONSISTENCY M M M M M L M L M M L L
PKB CONSISTENCY H H H H H H H H M H H L
CKB CONSISTENCY H H H H H H H H H H H H
AFTER 00Z MONDAY...
IFR conditions may occur Sunday night.
Area Forecast Discussion
National Weather Service Seattle WA
812 PM PDT Sat Sep 12 2020
.SYNOPSIS...Smoke from wildfires will remain an issue this weekend
and probably into Monday resulting in air quality issues across
the region. A frontal system will bring some showers Monday night
and Tuesday. An upper low will slowly move onshore later in the
.SHORT TERM /TONIGHT THROUGH TUESDAY/...Smoke continues to plague
the region this evening with widespread visibilities in the 1 to 2
statute mile range. HRRR smoke model output continues to suggest
that there will be some gradual improvement by around Sunday
evening, but conditions are likely to remain rather static over the
next 18 to 24 hours. Low level flow is weaker tonight than yesterday
evening and this may complicate the forecast overnight in terms of
stratus coverage. Nonetheless, fog imagery does show stratus just
offshore with some additional low clouds around the San Juans. With
smoke not having the thermal blanket properties of low clouds, the
short term forecast may need a slight adjustment for overnight low
temperatures. Otherwise, no other forecast adjustments are
anticipated. Temperatures remain on the cool side Sunday as
plentiful smoke and possible morning clouds will cutback on
potential incoming solar radiation significantly. 27
Previous discussion...Smoke and air quality continue to be the main
issues across the region. We`re seeing a mix of low level stratus
and smoke with visibilities generally less than 2 miles across
western WA. Air Quality Index values are mostly Very Unhealthy to
Hazardous. Given the flow pattern, abundance of smoke, poor mixing
and dry air mass, expect little change in the conditions as we move
into Sunday. The smoke is really wreaking havoc on the temperature
forecast. Most areas are seeing temps near 60 degrees this afternoon
which is a good 10 to 20 degrees cooler than guidance. With
persistence in mind, will lower max temps on Sunday.
A frontal system will move inland on Monday (mainly Monday
afternoon or Monday night) bringing much needed rain to the
region. This, along with a stronger air flow pattern and deeper
mixing will help clean things out (at least for areas west of the
Cascades). So improvements are on the way. Tuesday will see more
rain under moist SW flow. 33
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...We`ll see additional
showers in the forecast Wed-Fri as a slow moving upper level low
wobbles inland. The air mass will be slightly unstable over the
Cascades (in south, diffluent flow) for a slight chance of
thunderstorms near the crest. Fortunately, these showers look wet
with wetting rains expected. Temperatures will be close to
average and RHs will be high to keep the overall fire danger low.
This system pushes farther inland over the weekend for drier
.FIRE WEATHER...Varying degrees of onshore flow with marine layer
clouds and high humidity will prevent critical fire weather
conditions from developing in the week ahead. There will be a
chance of rain or periods of shower activity most days next week
and that will allow fuel moisture to recover from the season`s
low mark this past week. Smoke and areas of low marine stratus and
fog will keep visibility low for now - but that will also maintain
the rather stable air mass under the marine inversion. An upper
trough will slowly move over the area next week and the air mass
will become somewhat unstable again.
.AVIATION...Southwest flow aloft expected tonight into Sunday as
upper trough offshore moves closer to the region. Low level flow
will remain weak overnight, but onshore flow will increase Sunday
afternoon. Stratus will increase along the coast tonight, but inland
coverage will be somewhat uncertain in the absence of much onshore
flow. Despite this, light surface gradients will do little to help
the smoke situation with widespread surface visibilities of 1 to 2
statute miles overnight into at least late morning Sunday.
KSEA...Surface visibility in smoke of around a mile or occasionally
less to continue through Sunday morning. A shallow stratus layer
could develop for a few hours around 12Z Sunday morning, but
confidence in this is not high. Surface winds light becoming
southerly 6 knots or less toward daybreak. 27
.MARINE...Continued onshore flow pattern will persist through the
weekend. Smoke will reduce visibility over the waters into Sunday,
with some improvement from west to east later in the day Sunday. A
frontal system will move through the waters Monday into Tuesday with
possible small craft advisory winds over portions of the coastal
waters and the east entrance to the Strait of Juan de Fuca. Low
pressure will develop west of the waters Tuesday and remain through
Wednesday. Seas over the coastal waters generally hold 2-4 feet
through Monday, but build late Monday night through Tuesday to
closer to 5 to 7 feet as the front moves through. Cullen
.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
Area Forecast Discussion
National Weather Service Tucson AZ
148 PM MST Sat Sep 12 2020
.SYNOPSIS...High pressure over Nevada will move east into Utah
allowing for a downward trend in the smoke over the next few days
and a slight upward trend in moisture. The moisture will bring a
slight chance of showers and thunderstorms to mainly eastern mountain
areas Sunday into Tuesday. Also, temperatures will climb to slightly
above normal levels beyond Tuesday.
.DISCUSSION...Dense smoke lingers overhead this afternoon and will
through tonight. Due to heating, a bit of that is mixing down to the
surface and air quality sensors have shown a gradual upward trend
through day. This smoke has stunted our temperature rise and based
on latest satellite trends don`t anticipate much change in that for
the remainder of the day. So we are looking at highs only about 3
degrees warmer than yesterday and a couple of degrees cooler than the
Over the next 24 hours the upper level high over currently Nevada
will shift east into the Utah/Colorado area by Sunday night,
allowing for more northeasterly flow over SE AZ tomorrow into Monday.
This will help to begin thinning the smoke over the area.
For Sunday, we have low level easterly flow advecting a bit of
moisture into the area, while in the mid-levels there is a bit of an
inflection in the ridge over the area with a somewhat unstable
thermal profile. All this to say I decided to raise the pops a bit
over the area for a slight chance (chance over the White Mtns) of
afternoon showers and thunderstorms. The NAM and GFS have been
leaning this way the last couple of days and the shorter range UA and
HRRR CAMS are also showing a bit of convection. Enough to not
ignore, so I didn`t. Should not add up to a stellar day, but there
should be a few storms around, primarily over the mountains.
Much the same on Monday, with a little less smoke and moisture and
with a potentially slightly warmer mid-level temperature profile, a
somewhat lessor threat of convection, but not zero. Temperatures
will again generally remain in the 90s. Tuesday, just a bit more
drying and warming aloft pretty much limiting the storm threat to the
Mogollon Rim country.
Wednesday onward, the ridge is expected to consolidate more over the
area with a trough approaching the west coast, which is good news
for many of the wildfires from Washington through Northern
California. It will help. The difference for us is that it will dry
out the air mass and result in warmer afternoon temperatures, on the
order of 5 degrees above normal. This is where Tucson may add a
day or two to the 100 or greater high temps more total before
temperatures likely settle back a bit next weekend.
.AVIATION...Valid through 14/00Z.
Smoke layer mainly aloft will continue thru the forecast period,
with some lowering of surface visibility due to smoke/haze.
Otherwise, mainly SKC with a FEW-SCT clouds at 8k-12k ft MSL in the
higher terrain east of a KFHU to KSOW line thru 13/04Z. SCT-BKN
clouds at 8k-12k ft MSL will develop aft 13/17Z, with a chance of
-SHRA/-TSRA in the White Mountains NE of KSAD and south/southeast
of KTUS. SFC wind generally less than 12 kts thru the forecast
period, favoring an ELY/SELY direction tonight and Sunday. Aviation
discussion not updated for TAF amendments.
.FIRE WEATHER...High temperatures will warm to near normal Sunday
through Tuesday and then a couple of degrees above normal the second
half of next week. There will be a chance of showers and
thunderstorms in the White Mountains Sunday and Monday, with a slight
chance of showers and thunderstorms to the south/southeast of
Tucson. Drier air moves in Tuesday, with just a slight chance of
showers and thunderstorms in the White Mountains. Dry conditions are
then expected across southeast Arizona Wednesday through Saturday.
20-ft east/southeast winds will develop tonight and continue through
next Friday. Elevated east to southeast winds are expected Monday,
persisting into Tuesday in a few locations.
.CLIMATE...Tucson will make a few attempts at on adding to the
triple digit high total in 2020 later this coming workweek.
Currently standing at 91 days of 100+ highs behind 93 days in 1989
and 99 days in 1994.
Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
Area Forecast Discussion
National Weather Service Las Vegas NV
851 PM PDT Sat Sep 12 2020
.SYNOPSIS...High pressure passing overhead will bring temperatures
back to and above seasonal normals. Midweek, a trough will dip down
from the Pacific Northwest and bring with it cooler temperatures and
breezy winds. As dry conditions persist, this will result in
enhanced fire danger.
.UPDATE...Mostly clear and tranquil conditions continue
across the forecast area tonight. No changes needed to trends
detailed in the previous discussion. -Adair
.DISCUSSION...Today through Friday.
A ridge of high pressure will slowly pass over the Desert Southwest
through the remainder of the weekend and into next week.
Temperatures will continue to climb to at and above seasonal
averages. The caveat will be smoke. Yesterday, smoke limited the
high temperatures quite a bit. Additionally, the smoke cleared out
overnight, so temperatures cooled off more than expected. Manually
brought down a few temperatures tomorrow morning, but otherwise,
blended NBM with CMCnhBC, the local top performer for minimum
temperatures, as well as the previous forecast. Populated HRRR Smoke
in the grids, which is indicating mostly clear conditions for the
short term. California wildfire smoke is wrapping clockwise around
the high pressure, which may allow it to funnel back into southern
Nevada, northwestern Arizona and southeastern California tonight
into tomorrow. As the high pressure moves eastward and directly over
southern Nevada, we will get a brief reprieve of smoke before the
high continues eastward out of our area.
By midweek, a cut off low will drop down from the Pacific Northwest.
It is expected to open up before approaching our region, but
nonetheless will bring with it a strong cold front. This cold front
is not anticipated to drop temperatures near as much as the last,
which dropped us 20-30 degrees over the course of a couple of days.
Rather, this cold front will drop temperatures around than 5
degrees, bringing us back to seasonal normals, and will primarily be
a wind maker. Due to the continued dry conditions, this will result
in an increase in wildfire danger, so outdoor recreation involving
sparks or flames will not be recommended.
.FIRE WEATHER...Dry conditions continue, coupled with very dry
fuels. Afternoon breezes expected to remain below red flag criteria
until about midweek when a cold front will bring with it breezy
southerly winds. Critically low fuels and relative humidities with
weak overnight recoveries will continue, so enhanced fire danger
expected toward the end of next week.
.AVIATION...For McCarran...Low impact weather is expected through
the TAF period with light diurnal winds and dry conditions. Smoke
will drift over the area at times however it should not be as thick
as we have seen the past few days.
For the rest of southern Nevada, northwest Arizona and southeast
California...In general, expecting typical wind patterns across the
region for tonight and Sunday, with winds remaining less than 10kts.
The main aviation concern will be smoke impacts from California
wildfires. Much of the smoke should remain elevated with limited
aviation impacts, except at BIH and down the Owens Valley where
occasional surface visibility restrictions from haze are possible
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
For more forecast information...see us on our webpage:
https://weather.gov/lasvegas or follow us on Facebook and Twitter