Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/02/17
Area Forecast Discussion
National Weather Service State College PA
1159 PM EDT Fri Sep 1 2017
The remnants of what was once Hurricane Harvey will track
slowly across the Ohio Valley and cross the region bringing
showers this weekend. High pressure will return for early next
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
High pressure continuing to keep most of the region dry even
though dewpoints have crept up a couple of degrees, while
clouds from what was once Harvey continue to stream into and
thicken over the region.
Best chance for light rain, or more likely just sprinkles into
the early morning hours will continue to be the far SWRN zones.
Radar showing precip splitting over the Appalachians with some
drifting off to the north and the rest tracking nearly eastward,
both avoiding my southern boundary. This is supported by near
term HRRR and NBM forecasts.
Later tonight this begins to change and light precip should fill
in a bit, but PoPs through 12z may still be too high over SW
third of CWA as much of this may fall as drizzle (with scattered
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Saturday looking cloudy, downright chilly and damp. Still a big
question of how much it will rain with an initially very dry
airmass in place. Thinking that much of the day will favor
cloudy and cool conditions with perhaps some periods of light
rain or a misty drizzle. The deeper we get into the day the
better will be the chances for rain.
I did undercut model blended high temps by several degrees. This
looks like a classic warm season cold air damming scenario.
With a strong high off to our north and east and an approaching
low from the SW, the guidance shows a strong low level northerly
component to the ageostrophic flow which will help keep us
anomalously cool for the early days of September. With highs
only in the mid 50s to lower 60s, these temps are 15-20F below
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
*Wet start to holiday weekend followed by improving/rain-free
conditions Sunday into Monday (Labor Day)
*No significant flooding impacts expected from the remnants of
*Moderating/seasonably warmer temperatures Monday-Tuesday will
trend below normal Wednesday-Friday
*Precipitation potential likely maximized between Tuesday-
A northern stream shortwave trough over the western Great Lakes
will merge with the remnants of Harvey and lift northeast through
the Mid Atlantic and New England states on Sunday. Ahead of the
surface system and mid level trough, models still indicate max
PoPs/QPF Saturday night into early Sunday morning as a strong
low level jet transports 1.50 inch PW air into central PA.
Rainfall amounts on the order of 0.25 to 0.75 inches are
expected with hires ARW/NMM/NamNest signaling potential for
north-south training resulting in locally higher amounts up to
1.5 inches. Even the higher amounts should be offset to a
degree by the recent short-term dryness, with 3hr RFC FFG
values well over 2 inches. Therefore, no significant heavy
rain/flooding impacts are expected. Sunday will be a transition
day toward improving weather conditions, followed by a mostly
sunny and pleasant Labor Day.
Models/ensembles continue to agree upon a significant long wave
flow pattern amplification during the second half of the
period, with an anomalous full-latitude trough over the Eastern
U.S. reaching maximum amplitude around the middle of next week.
A well- defined cold front is fcst to sweep eastward from the
Midwest and slow down as it eventually moves off the eastern
Seaboard by Thursday-Friday. The front will be accompanied by
precipitation but the timing/coverage/intensity will be
sensitive to uncertain details aloft impacting the
speed/movement of the boundary. The most likely period for
rain/max PoPs is Tuesday-Wednesday with opportunity for some
enhanced rain associated with one or two frontal waves. For now,
next week should end on a dry note with all eyes likely turning
to Hurricane Irma, forecast by GFS/ECMWF to reach a position
between the northern Bahamas and Bermuda by next Sunday 9/10.
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
VFR will continue into much of the night ahead of the remnants
of Harvey. Cigs will reduce overnight and have included rain in
the TAF for the southern TAF sites, though not expecting
reduced conditions until late tonight or after sunrise Saturday.
IFR is possible for JST after 12Z.
Sat...Lowering conditions spreading slowly northeastward with
occasional light rain/drizzle. Mainly over southern areas.
Sun...MVFR/IFR improving for the afternoon
Tue...An approaching cold front will bring scattered showers and
locally reduced conditions, especially at western terminals by
Wed...Reduced conditions as the cold front pushes through the
August 2017 was marginally cooler than average at Harrisburg
(-1.0F) and Williamsport (-0.1F). Precipitation for the month
was above average with totals of 4.67" (+1.47") at MDT and 5.76"
(+1.90") at IPT.
For the meteorological summer season (June-July-August),
temperatures were slightly above average (around +1.0F) at both
sites. More noteworthy were the 3-month precipitation totals
which ranked in the top-10 wettest summers on record.
Harrisburg recorded 17.76" of precipitation which was +6.35"
above normal and ranked as the 8th wettest summer. Williamsport
recorded 16.91" of precipitation which was +4.79" above normal
and ranked as the 3rd wettest summer season.
The top-10 wettest seasonal rankings are impressive in that
there were no tropical systems that contributed to the
precipitation totals. That said, the wettest summer at both
locations was 1972, helped of course by Hurricane Agnes.
NEAR TERM...La Corte/RXR
SHORT TERM...La Corte/RXR
Area Forecast Discussion
National Weather Service Des Moines IA
642 PM CDT Fri Sep 1 2017
.SHORT TERM.../Tonight through Saturday/
Issued at 147 PM CDT Fri Sep 1 2017
Main forecast challenge through the short term period is the
chance for light showers this evening through Saturday morning.
Satellite and radar imagery through the day has shown a widespread
area of cloud cover and showers over the Dakotas and Nebraska.
This activity will slowly into western Iowa this evening and
overnight. Hi- res models have trended toward the light showers
holding together to about the I-35 corridor early Saturday morning
before dissipating. A shortwave passing near the Canadian border
will send a weak front southward during the morning and afternoon
hours, however models remain dry along the front through 00z
Sunday upper level support passes north of the state.
Also of note, the HRRR vertically integrated smoke product
suggests the potential for more haze and air quality degradation
tomorrow morning as result of significant wildfire activity out
west. Previous HRRR runs did not have a good handle on the degree
of smoke/haze that was observed earlier today. Cloud cover makes
it difficult to discern on satellite the amount of smoke currently
upstream, although the upper level pattern remains in a favorable
orientation to push more Canadian/Montana wildfire smoke into our
area. Confidence is too low at this time to include any mention
in the forecast at this point.
.LONG TERM.../Saturday night through Friday/
Issued at 147 PM CDT Fri Sep 1 2017
No significant weather of note through the long term period.
Isolated storms will be possible Saturday evening along the
aforementioned surface front, but minimal upper level support should
keep the activity isolated and limited to areas near the MO
border. A strong PV anomaly will round the Hudson Bay low and dig
southeast in the eastern conus early next week. Low level response
in advance of this system will advect a much warmer air mass into
the CWA and put highs in the 80s to near 90 for Sunday. A strong
cold front will push through the CWA Monday afternoon and evening.
The timing of the front will have a significant impact on
temperatures Monday. Models have come into fairly good agreement
with respect to the fropa timing, so the blended forecast looks
reasonable which paints highs in the 70s in our north and near
90s in the south. Despite strong baroclinicity and increasing fgen
in low levels, a relative lack of moisture and mid-level cap may
limit precip potential as the front slides through. Slight to low
end chance pops will suffice for now.
Below normal temperatures are likely through the middle and latter
half of the week as a cool air mass settles into the region behind
the front. Not expecting any precip during this time period as
the quasi meridional flow scours out most of our available
.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 642 PM CDT Fri Sep 1 2017
Few real concerns through period...though VFR cigs and few showers
may impact KFOD/KMCW before weakening further aft 08z. Band of
-shra moving into western Iowa encountering drier air. Cigs should
lower to bkn035-bkn080 by 12z then thinning thereafter through
20z. Small risk that MVFR cigs may eclipse KMCW between 12 and
15z Saturday and will evaluate for 06z. Winds also mix out aft
15z Saturday with higher sw gusts at KMCW/KALO/KDSM through 21z
then increasing NW winds aft 21z. /rev
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
837 PM EDT Fri Sep 1 2017
Reasonably high amplitude midlevel ridge and associated high
geopotential heights is currently leading to surface high pressure
and quiet weather over southeastern Michigan. Cool, dry Canadian
airmass will again yield nil potential for boundary layer fog
overnight. The forecast item that requires watching is the remnants
of Harvey as it lifts into the Ohio River Valley on Saturday. Some
fairly high model spread exists with overall likelihood to witness
low-midlevel rich theta e/saturation over the Detroit TAF sites. NAM
completely resides on the wet side while the RAP is significantly
lacking in the amount of column moisture. Given ceiling and rainfall
observation trends down south, will continue to side with the NAM in
aggressive moisture advection, but remain relatively conservative
with MVFR cig heights. Latest time lagged probability metrics suggest
a 30-40 percent 3 hour rainfall probability for DTW after 2 PM
Saturday. Given lack of steep lapse rates, activity will likely be
limited to sprinkles.
For DTW...The easterly flow picks up again after 12z on Saturday as
ceilings develop below 5000 feet.
//DTW THRESHOLD PROBABILITIES...
Issued at 358 PM EDT Fri Sep 1 2017
Another cool night is in store for SE Michigan, especially along and
north of the I-69 corridor. This is where high clouds and surface
wind will be minimal which will allow radiational cooling to send
overnight temperatures well down into the 40s once again. A repeat
of this morning seems reasonable where the usual sheltered locations
made it down to around 40. FNT actually radiated down to 39 which
broke the record of 40 for September 1 set in 1967. Records for
tonight, Sept 2: MBS 38/1946, FNT 39/1994, DTW 44/1885.
The track of Harvey remnants will be the primary concern for
Saturday as it interacts with the northern stream upper level trough
digging from central Canada into the Great Lakes. Rain potential
associated with both of these features will be inhibited initially
by mid level dry air between them associated with resident high
pressure before it is squeezed into eastern Canada during the
afternoon. There should also still be a western edge in the area
where light rain is able to reach the ground with the highest chance
POPs closer to the Canadian border up to near Port Huron. There may
also be a larger chance POP footprint Saturday night with the upper
trough axis before it moves eastward overnight.
The process of squeezing high pressure eastward during Saturday will
also scour out the low level thermal trough tied to our recent
cooler temperatures. Also, the surface pressure trough associated
with the upper wave Saturday night will act more like a warm front
heading into Sunday. Model projections do not show much change in
850 mb temps but there is considerable 1000-850 mb thickness warming
that reflects continued displacement of the cool boundary layer
conditions. The result will be a notable warming trend through the
weekend as high temperatures return to the lower and mid 70s
Saturday and then mid to upper 70s Sunday.
The progression of shortwaves in the northern stream upper level
flow will continue into early next week. The warming trend will
continue Monday as strong southwest flow develops ahead of the next
frontal system. Southwest wind gusting into the 30 mph range will
help boost high temps back into the 80s Monday afternoon ahead of
the associated cold front which remains the subject of shower and
thunderstorm potential into Monday night. The 12Z NWP is
considerably less aggressive on QPF with the passage of the front
which is likely due to the thermal ridge building into the area. NAM
and GFS temperatures are borderline capped in the 850-700 mb layer
which produces a more dramatic negative response compared to the
ECMWF and GEM. Otherwise, global model solutions are in good
agreement on another strong cooling trend post front into the middle
of next week.
A tight pressure gradient will be maintained over the waters of Lake
Erie through much of the night. This onshore flow will build
significant wave heights to 3 to 5 feet with maximum wave heights up
to 7 feet in the Michigan waters. Moderate wind will persist through
the weekend as two systems move through and affect the Great Lakes
region. Easterly winds will become southeast by late Saturday and
then veer to westerly by Sunday. Stronger southwest flow will
develop in advance of a strong cold front on Monday. Very warm air
on Monday will keep winds in the 20 to 30 knot range for Lake Huron,
but expect small craft advisory winds for all of the nearshore
areas. Thunderstorms will be possible Monday and Monday night
followed by developing gusty northwest flow behind the front as
cooler air infiltrates the region.
MI...Lakeshore Flood Advisory until midnight EDT tonight for MIZ076-083.
Beach Hazards Statement until midnight EDT tonight for MIZ083.
Lake St Clair...NONE.
Michigan waters of Lake Erie...Small Craft Advisory until 10 AM EDT Saturday for LEZ444.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Wilmington NC
1006 PM EDT Fri Sep 1 2017
A stalled front to our north will shift northward overnight and
Saturday as another cold front approaches from the west and
moves offshore Saturday night. Showers and thunderstorms are
expected along and ahead of the front as it shifts to the coast
and offshore through Saturday night. High pressure will bring
dry weather to the area Sunday through Tuesday. Another cold
front may bring more thunderstorms Wednesday and Thursday. Swell
from Hurricane Irma will be increasing next week.
.NEAR TERM /THROUGH SATURDAY/...
As of 1000 PM Friday...Tornado Watch has been cancelled and the
risk for severe weather has ended. There have so far been no
reports of severe weather today/this eve. All of the severe reports
today have been further to the north, along a stalled front.
This front is expected to retreat north through Sat.
The last of the showers and a rumble of thunder was moving north
across northern Bladen County and this activity should move
north of Bladen County through midnight.
The HRRR model is showing showers may develop offshore and
skirt portions of the coast overnight and so have trended POPs
accordingly. Will continue to show POPs trending below threshold
for areas well inland. Low level jetting is expected to
mitigate the fog potential, but low stratus may fill in,
Deep moisture will still be in place Sat ahead of a cold front.
Good heating ahead of the front should allow showers and
thunderstorms to develop. The highest risk for thunderstorms
will be shifting to the coast with the front on Sat.
Lows tonight will be in the lower to mid 70s. Highs will be in
the mid 80s.
.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 230 PM Friday...Plume of Gulf moisture will be shifting
off the coast Saturday evening ahead of fropa. A dry slot will
wrap into the forecast area around the mid-level circulation
associated the remnants of Harvey, which by this time will be
opening up ahead of a trough swinging across the Great Lakes.
Shower and thunderstorm activity will taper off from west to
east Saturday evening, trailing off to nil after midnight.
Clouds will scatter out late Saturday night, and should see a
fair amount of sun on Sunday as dry air is ushered in with deep
westerly flow. Weak surface high pressure will build across the
Carolinas Sunday night and push a frontal boundary into the
area. Moisture will be lacking so no PoPs will be introduced
with this feature, but will trend them up towards (but still
below) slight chance across the far southern zones Monday night
to account for some moisture return ahead of the boundary.
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 230 PM Friday...Beautiful start to the week, with high
pressure overhead leading to a dry Labor Day and only a few
stray showers on Tuesday, both days with seasonal temperatures.
Clouds and rain chances increase Tuesday into Wednesday as a
relatively strong cold front descends upon the eastern
Carolinas. The front will be offshore Thursday morning, followed
by cooler and dryer high pressure. The end of the week will
feature dry weather with below normal temperatures.
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 00Z Saturday...KLBT will experience the brunt of
thunderstorm activity through 01z. Otherwise some light showers
will advect northward across the terminals. The HRRR model is
showing some convective redevelopment along the coast overnight,
but this remains a low confidence forecast. Showers and
thunderstorms should redevelop with heating on Sat.
Thunderstorms will continue to have the potential for flight
restrictions to MVFR or lower.
Extended Outlook...VFR conditions are expected Sun into Tue.
Thunderstorms may result in flight restrictions on Wed.
NEAR TERM /THROUGH SATURDAY/...
As of 1000 PM Friday...S to SW winds around 15 kt through Sat.
Seas will be mainly 2 to 3 ft with up to 4 ft across portions of
the outer waters. Showers and thunderstorms are expected to
develop across the waters overnight and will become scattered
to numerous through Sat night with the approach of a cold front
from the W.
SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 230 PM Friday...Southwest flow and shower/thunderstorm
activity will be ongoing Saturday evening ahead of a frontal
boundary, which will push off the coast after midnight. The
surface pressure gradient will wash out quickly behind the
front, so after a period of westerly flow late Saturday night
and Sunday morning, expect some degree of variability as winds
lighten Sunday afternoon. A weak frontal boundary will approach
from the north Sunday night, as high pressure builds across the
Carolinas, and the front may reach the southern waters by
sunrise Monday. Moisture will be limited, so expect no
significant chance of precip with this front, expect perhaps the
waters south of Murrells Inlet Sunday night.
LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 230 PM Friday...High pressure over the western Atlantic
will keep winds from the SW at around 10 kts, with seas ranging
right around 2 ft through the period.
Area Forecast Discussion
National Weather Service Louisville KY
931 PM EDT Fri Sep 1 2017
Issued at 931 PM EDT Fri Sep 1 2017
Remnant circulation of Harvey was located across our far
southeastern counties...just northeast of Liberty KY. The center
continues to move off to the northeast slowly. Radar imagery shows
the bulk of the moderate to occasionally heavy rainfall continuing
to shift to the north. A constant deformation band extends now from
around Shepherdsville (Bullitt County) northeastward to near
Cincinnati (Hamilton County OH). This band should continue into the
overnight hour and shift northeastward with time.
Elsewhere, light to occasionally moderate rainfall continue across
the region. Rainfall rates are generally light with most locations
seeing < 0.25/hr rates. Latest HRRR forecasts continue to show a
little an arcing band of precipitation to continue overnight from
Bowling Green northeast to Cincinnati. However, the overall
rainfall amounts from each successive HRRR run have been tapering
down with each run.
Based on the projected forecasts, we have trimmed up the Flash Flood
Watch for the overnight. We cleared out some of our far western
counties, some of our southern counties, and much of our
southeastern (Lake Cumberland areas). We still expect to see
rainfall in these areas, but the amounts are forecast to be light
and are not expected to aggravated saturated soil conditions in
these areas. It appears that the most at risk ares would be our far
SE IN counties and our far northern KY counties north of I-64 and
west of the I-75 corridor. Though no flooding reports have been
received as of this time, some minor flooding of poor drainage and
low-lying areas will be possible. The remaining section of the
Flash Flood Watch will remain in effect through 06Z (original
With the above changes, a few edits to the forecast were made,
generally to lower PoPs slightly in the west, far south, and far
southeast. Will maintain 100 PoPs across much of north and east
central KY overnight. Overall additional rainfall of 0.25 to 1.25
inches are expected with a diminishing trend in the rain late
Update issued at 712 PM EDT Fri Sep 1 2017
Current forecast remains on track at the moment. Remnants of Harvey
continue to churn across south-central KY this afternoon.
Deformation zone with the heaviest precipitation continues to
stretch from Ohio County northeastward through
Harrison/Clark/Floyd/Jefferson counties in southern Indiana.
Precipitation has been rather heavy at times within the band. Legacy
Doppler and MRMS data suggests 1-1.5 inches of rainfall in this band
with the majority of it falling in Meade and Harrison (IN) counties.
Deformation band is expected to continue to push slowly northward
this evening...likely pushing a little north of the Ohio River
by mid-late evening. The latest HRRR runs suggest a more
southwestward development of the band back down into Butler and
Warren counties later tonight. We can already see the beginnings of
this as a heavier band seems to be developing from Breckinridge
county southward into Butler and western Warren counties.
Elsewhere, precipitation is generally light to occasionally moderate.
This is true south and east of a line from Simpson county
northeastward to Clark (KY) county. Overall, we are not seeing much
in the way of additional development across our southeast this
evening and into the overnight. Current thinking is the heaviest
rainfall would be in an arcing band from Cincinnati-Louisville-
Bowling Green with an additional 1-2 inches of rainfall. Should
current trends continue, it is likely that we`ll trim a bit of the
Flood Watch off in our southeast sections by mid-evening. In the
meantime, we`ll continue to watch for high water within the
deformation band across far northern KY and southern Indiana.
Update issued at 514 PM EDT Fri Sep 1 2017
A couple of real quick updates. First, we have dropped the Wind
Advisory as of 500 PM. Our current thinking is that the wind gusts
of 40-45 MPH are over with. However, we could see some continued
gusts into the 20-25 MPH range for a few more hours as the remnants
of Harvey continue to wind down. Second, we are going through and
contacting counties with regards to flooding conditions. Our plan
is to let the areal flood warnings die off with their respective
expiration times this evening. Digital forecast grids and forecasts
text products have been updated to reflect the dropping of the Wind
In terms of current weather expectations...The latest model
solutions suggests that the heaviest rainfall will continue to move
northward into southern Indiana and far northern Kentucky this
evening. In general, the heaviest rainfall looks to stay mainly
along and north of the I-64 corridor. The 01/18Z NAM and 01/20Z
HRRR runs support this thinking. However, both models are suggest
more development on the back side of Harvey`s circulation as it
treks northeastward across the state.
Generally speaking, a swath of 1-2 inches of additional rainfall may
affect areas west of I-65 this evening, extending from Louisville
back down into the Bowling Green area. Lesser amounts of rainfall
are expected over our far southeastern counties, down in the Lake
Cumberland area. Should these trends hold steady, we may drop the
Flash Flood Watch for our southeast areas in the next few hours. The
severe weather threat associated with Harvey looks to be more
confined to our east over far eastern KY where arcing bands of
convection are moving east of Jackson/Hazard and toward Paintsville
.Short Term...(This evening through Saturday night)
Issued at 255 PM EDT Fri Sep 1 2017
Widespread light to moderate rain, with a few heavier pockets, will
continue tonight as Harvey`s low slowly crosses central Kentucky.
Another general inch of rain is expected, primarily across north
central Kentucky and the northern Blue Grass. Slightly enhanced
amounts will be possible where bands train over a certain spot,
which would be most likely to happen over the Blue Grass. Southern
Kentucky, where the flooding has been the most severe, should see
only light additional amounts.
After talking with JKL and ILN, will keep the FFA in place for now
since there is ongoing flooding and rain is still falling...though
the threat of significant widespread flooding is diminishing and the
watch will likely be dropped, or at least significantly trimmed
back, this evening.
Showers will taper off from west to east Saturday as what was once
Harvey weakens significantly and moves off into Ohio.
Saturday night high pressure will build into the Tennessee Valley. A
weak cold front will approach from the northwest, but the high
should keep us dry.
.Long Term...(Sunday through Friday)
Issued at 230 PM EDT Fri Sep 1 2017
On Sunday, dry northwest flow aloft will take over across the Great
Lakes and Ohio Valley. Expect fair and warmer weather with highs in
the upper 70s to lower 80s. Labor Day Monday also will be dry with
high temperatures in the lower and mid 80s.
By Tuesday, a significant shortwave trough aloft is progged to dig
southeast across the Great Lakes and mid Mississippi Valley before
amplifying across the Ohio Valley mid week. The GFS and ECMWF show a
sharper trough than the GEM as the trough moves into the Ohio
Valley. This would result in scattered to numerous showers and
thunderstorms along and ahead of an accompanying surface cold front
Tuesday and Tuesday night, some with brief heavy rainfall. The GEM,
on the other hand, would bring scattered showers Monday night and
Tuesday morning. The blended forecast favors best chances for rain
Models suggest isolated diurnal showers may occur Wednesday under
cool air aloft. Surface temperatures and humidity levels will be
lower Wednesday and Thursday behind the cold front with afternoon
highs in the upper 60s to mid 70s. By late next week, high pressure
takes control with pleasant dry early September weather.
.Aviation...(00Z TAF Issuance)
Issued at 721 PM EDT Fri Sep 1 2017
The remnants of tropical storm Harvey will continue to track
northeast across the region tonight and off to the northeast through
the day tomorrow. Mainly IFR ceilings are expected through the
night and into the morning hours tomorrow at SDF, LEX, and BWG.
Steady rain and/or rain showers will continue through the night with
generally 2-4 mile visibility through at least 06Z. Thereafter there
could be some occasional improvements. HNB is in the edge of the
system and ceilings are expected to remain higher than sites to the
east. MVFR cigs should prevail through the night.
Ceilings will likely be slow to improve tomorrow. However, all but
LEX should improve to VFR by mid to late afternoon. The ceilings
should improve at LEX towards the end of the TAF period, but will
likely remain MVFR.
The gusts are expected to diminish through the overnight hours. Wind
direction will slowly swing around as the low shifts northeastward.
Updated at 257 PM EDT Fri Sep 1 2017
Light to moderate rain will continue in most locations tonight, but
amounts should be generally less than an inch. Flood Warnings have
been issued for Rochester and Woodbury on the Green River. Rises can
be expected at Alvaton on Drakes Creek, Boston on the Rolling Fork,
and Dundee on the Rough River, but as of this writing those points
are expected to stay below flood stage.
IN...Flash Flood Watch until 2 AM EDT Saturday for INZ079-090>092.
KY...Flash Flood Watch until 2 AM EDT /1 AM CDT/ Saturday for KYZ024-
AREA FORECAST DISCUSSION...UPDATED
NWS LOS ANGELES/OXNARD CA
829 PM PDT Fri Sep 1 2017
Hot weather will continue through Saturday. The remnants of a
tropical system may track close enough to bring some showers and
thunderstorms to portions of the region Sunday afternoon through
Monday, along with some cooling. Temperatures will remain above
normal through late next week.
As expected, another very hot day occurred across the forecast
area. Surprisingly the majority of the Central Coast trended
higher over 20 degrees in several locations. Lompoc was up 27
degrees from yesterday`s hi of 76 degrees to a whopping 103
degrees this afternoon. Both Santa Maria and San Luis Obispo were
over 20 degrees. The big difference was due to the stronger
broad upper level easterly flow that reinforced the offshore
surface gradients. This synoptic pattern is going to continue
through tomorrow with continued offshore flow. The seabreeze will
kick in late tomorrow, but should see a near repeat of high temps
across the Central Coast before some cooling late in the
afternoon. Showers and a few embedded thunderstorms did develop
across the LA/VTU/SBA County Mtns and spilled over into the
valleys late this afternoon. There were a few showers across the
Oxnard Plain as well early this evening. The convective parameters
were not nearly as explosive as yesterday. A few rogue showers
cant be ruled out tonight, especially SBA county where both the
HRR and RAP high resolution models focus best moisture and
lift. In evening update, we will be expanding the slight chance of
showers and tstms to coastal areas of SBA county.
As far as high temps tomorrow, the 00Z NAM WRF continues to show
an eddy spin up across the SoCal Bight overnight. This should
bring some cooling across the coastal areas of LA/VTU and SBA
South Coast. In fact, the marine layer depth could rise to 1000 ft
which should bring a few degrees of cooling to the coastal
valleys as well. At this point, not expecting much in the way of
stratus, but would not be surprised if some low clouds developed
off the Orange County Coast and moved north into LA County.
*** From previous discussion ***
Tomorrow looks somewhat less favorable for convection and best
chances would be in the eastern San Gab mtns.
Forecast gets quite complicated Sunday into Monday as we start to
see the moisture moving in from TS Lidia. What`s left of the the
circulation center is expected to remain well southwest of the
area, however moisture wrapping around it from the southeast
should impact at least the southern half of the forecast area
Sunday and Sunday night and likely reach SLO county. Pwats
increase to over 2" Sunday afternoon and with some instability
with it there`s a decent chance, assuming the forecast track is
reasonably close, that we`ll see some showers and thunderstorms
by Sunday afternoon. And chances are pretty equal everywhere,
though somewhat better towards the south closer to the remnant
The temperature forecast will be very tricky as we`ll still be
dealing with offshore gradients and some better easterly support
aloft with what`s left of Lidia, but then likely plenty of clouds
and potential showers/storms. Even with fairly thick clouds a
scenario like this could still see highs in the 90s for inland
coast/valleys with some lower 100`s possible. But if there`s
widespread precip than temps will definitely be cooler. Obviously
quite a but more humid with the tropical air mass in place so any
cooling would likely be offset but the muggier air.
Going into Monday the moisture will start to exit to the west as
the remnant low shoots out over the Pacific. Still some lingering
shower/storm chances in the morning, especially northern and
western areas, then for the afternoon just some small chances over
the interior. Temperatures still quite warm and muggy, though
decent onshore trends should bring some relief to at least the
After the leftovers of Lidia exit the area Monday we should see a
slow climb in temperatures through the rest of the week as high
pressure strengthens over the Great Basin. The ECMWF wasn`t quite
as far west with the expansion of the high as it had shown in
earlier runs and now looks pretty similar to the GFS, so while
some warming is expected highs aren`t expected to be quite as hot
as they were and certainly not like they`ve been the last couple
days. The other big difference being a fairly persistent onshore
flow which is expected to strengthen as we go through the week so
we should also see a return of some marine lyr clouds to coastal
areas. There`s still a favorable upper level flow pattern to allow
monsoon moisture in from the southeast so will keep the slight
chances of showers and storms over the mountains and Antelope
Valley going each day.
At 2330Z, there was no marine layer at KLAX.
VFR conditions are expected throughout the period. There is a 20%
chance for VLIFR to LIFR conds across the central coast. Also with
an eddy circulation developing overnight. There will be a 30%
chance for IFR to low MVFR cigs developing across LA/VTU county
coast after 10z tonight.
KLAX...VFR conditions are expected throughout the period. There
will be a 40% chance for SE or easterly wind component over 10 kt
between 11z-16z Sat morning. There is a 10 percent chance of
VLIFR to LIFR conditions between 12Z and 15Z.
KBUR...VFR conditions are expected throughout the period. No wind
issues are expected at this time.
Conditions are expected to remain below SCA levels through
Sunday, and possibly through Tuesday. There is a chance of isolated
gusts to 25 knots during the afternoon and evening hours through
the weekend, especially over the San Pedro Channels.
Shower and thunderstorm activity should increase over the weekend
as Tropical Storm Lidia moves north into the offshore coastal
waters. The cyclone, currently over Southern Baja California, or
about 650 miles southeast of Point Conception could bring showers
and thunderstorms to the Coastal Waters. The storms will likely be
capable of producing heavy downpours, gusty erratic winds, and
cloud- to- ocean lightning.
CA...Heat Advisory in effect until 10 PM PDT Saturday for zones
34-35-39-40. (See LAXNPWLOX).
Excessive Heat Warning in effect until 10 PM PDT Saturday for
zones 36>38-41-44>46-51>54-59-88-547. (See LAXNPWLOX).
.HAZARD POTENTIAL OUTLOOK...(MON-FRI)
No significant hazards expected.
Area Forecast Discussion
National Weather Service Miami FL
732 PM EDT Fri Sep 1 2017
.UPDATE...Showers and storms are ongoing over the western half of
South Florida this evening, with prevailing south-southeast winds
focusing the strongest storms just to the north of the lake. RUC
analysis shows cooler temperatures aloft encroaching from the
west as a large area of disturbed weather along a broad trough
slides across the eastern Gulf.
With these features in place, models suggest that the weather will
remain unsettled overnight. Expect overall coverage to decrease
through the evening hours, though showers and a few storms will
linger, mainly over the local waters. Depending on how far east
the Gulf activity gets, coverage may be a little higher.
No significant changes to the ongoing forecast for tonight.
A few thunderstorms and showers will remain in the vicinity of APF
through around 02Z for which a TEMPO remains in place for MVFR
cigs/vis. After 02-03Z VFR is expected to prevail at all terminals
through late Saturday morning. Winds will become light an variable
later tonight. Another round of VCTS is expected Saturday
afternoon as sea breezes push inland. Winds will turn to the SE
at around 10 knots, except APF where westerly onshore flow will
develop with the afternoon seabreeze.
.PREV DISCUSSION... /issued 428 PM EDT Fri Sep 1 2017/
THIS AFTERNOON AND TONIGHT: The Gulf breeze has been more active
as it`s moved into inland Collier/Glades/Hendry with an active
line of showers and storms going up along it. Mesoscale models
suggest that this will kick off an outflow boundary, along with
steering flow becoming more south-southwesterly that will
interact with a diffuse seabreeze over the interior through the
afternoon and early evening hours. Convection wanes through the
late evening hours.
With an approaching disturbance from the Gulf and cooler
temperatures aloft, some storms may linger through the overnight,
especially over the local waters. A few models are a little more
bullish with convective coverage overnight with a faster approach
of the disturbance over the Gulf, and have split the difference,
with storms becoming scattered towards daybreak.
HOLIDAY WEEKEND: Post-Tropical Cyclone Harvey is expected to
continue to move northeast across the OH/TN valleys over the next 24
hours. It then becomes absorbed into the trough swinging through the
Great Lakes, lifting out into New England and the Canadian Maritimes
into Monday. This evolution will erode the western side of the
western Atlantic ridge, allowing a trailing boundary and
associated disturbance over the eastern Gulf into the state over
the next two days. Steering flow will veer more south-
southwesterly, tapping back into an area of tropical moisture to
our southwest. Models show a few impulses moving from SW to NE
within this flow, with temperatures aloft little cooler at -7C to
Shower and storm chances look above normal again on Saturday,
starting earlier in the day as the feature from the Gulf helps get
activity started. Conditons will remain favorable for a few
stronger storms with gusty winds. Coverage is expected to diminish
closer to normal on Sunday as the boundary washes out and a
little stronger easterly flow brings in some drier air, with the
direction focusing activity more towards the interior and Gulf
coast. Stronger easterly flow on Monday should push most storms
towards the Gulf coast, where models hint that the Gulf breeze may
not even develop.
NEXT WEEK: Models continue to show a large upper level trough
digging across the eastern half of the US into mid next week. This
pattern is expected to drive a low level frontal boundary through
OH/TN valley and into the east coast as we enter the latter half of
While both the GFS and ECMWF have the same basic pattern, the
exact impacts to local weather, as always, is in the details.
While the GFS` trough is stronger, the ECMWF shows a more split
pattern with a stronger vort pattern along the southern side of
the trough as it moves east. These differences affect the timing
of the when the trough may move off the east coast and weaken the
western Atlantic ridge, which has implications as to how far east
or west Hurricane Irma may track. Regardless, it looks like an
unsettled weather pattern returns to the region with scattered to
numerous showers and storms each day.
It is important to remember that track errors for tropical systems
are around 200 miles at 5 days, and this is in the day 7 to 9
timeframe with continuing run to run and model differences. While
Irma will remain a system to watch over the next week, it is far to
early to speculate as to if Irma will impact South Florida.
MARINE...Weak boundary moving into the state briefly weakens the
western Atlantic ridge as we move into Saturday, with south-
southeasterly winds continuing around 10 knots. High pressure is
expected to re-strengthen to the west early next week, with winds
becoming east at 10-15kts. Both seabreezes are expected to develop
through the holiday weekend, with winds becoming southwesterly over
the Gulf waters each afternoon. Stronger east flow may hold off Gulf
breeze developing into next week.
A 1-2ft 10-12 sec NE swell is expected to continue across the local
Atlantic waters through the holiday weekend, with seas 3-5ft,
especially off the Palm Beach coast. The swell is expected to slowly
diminish by mid next week.
Scattered to numerous showers and storms can be expected over the
area through the weekend, becoming more scattered into early next
BEACH FORECAST...A 1-2ft long period NE swell as already reached the
local Atlantic waters this afternoon. Local beach patrol has already
reported an increase in rip currents. A moderate risk of rip
currents this afternoon is expected to become high at all
Atlantic beaches through the holiday weekend.
.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach 78 91 77 93 / 20 50 20 10
Fort Lauderdale 79 91 79 92 / 30 40 20 10
Miami 79 90 78 93 / 30 40 20 10
Naples 77 91 76 92 / 20 50 30 30
Area Forecast Discussion
National Weather Service Melbourne FL
933 PM EDT Fri Sep 1 2017
Tonight...Quite active boundary driven convection has lingered into
late evening. There is also some large scale ascent across the area
from a vort max that is lifting northward out ahead of a trough dug
in over the southeast states. The HRRR has been showing the bulk of
this convection lifting out by midnight, but it hints at some
lingering shower chances overnight, as does the local WRF model.
This is already shown in the current forecast, so don`t plan any
Quite a bit of shower/storm activity was lingering this evening and
providing brief IFR-MVFR. After midnight, conditions look like they
will be VFR, but widely scattered showers could produce local MVFR.
The atmosphere will be very moist on Saturday, so slow heating
through considerable debris cloudiness will ignite scattered to
numerous showers and storms from the afternoon into evening.
Tonight-Saturday...High pressure ridge over the Atlantic is shown
providing about a 10 knot southerly wind flow. The latest buoy
observations show seas around 2 feet at the coast and a little over
3 feet offshore. This is a little lower than what our current
forecast was showing so will make slight adjustments. Expect a
chance for lingering showers/storms over the waters early Sat and a
chance for stronger storms moving offshore in the afternoon and
Area Forecast Discussion
National Weather Service Marquette MI
642 PM EDT Fri Sep 1 2017
.SHORT TERM...(This evening through Saturday)
Issued at 359 PM EDT FRI SEP 1 2017
WV imagery and RAP analysis indicated a mid/upper level ridge near
the west coast resulting in wnw flow from BC toward the nrn plains.
A vigorous upstream shortwave trough was located over wrn Manitoba.
At the surface, srly winds were increasing over the upper MS valley
and wrn Great Lakes ahead of a trough extending from ne Manitoba to
the cntrl Dakotas. WAA ahead of the trough supported a band of
showers through wrr MN. Tsra had also developed farther to the north
through se Manitoba with the stronger forcing and higher mid level
lapse rates ahead of the shrtwv.
Tonight, although the dry airmass still lingers over the area, the
combinaton of increasing high clouds and srly winds will keep temps
from falling off nearly as much as the previous couple nights.
Expect lowest inland readings around 40 with lower 50s where
downslope ssw winds prevail. Short range models suggest that the
showers may move into the far west late, mainly aft 09z.
Saturday, showers supported by moderate to strong qvector conv ahead
associated with the shortwave and upper level div with the left exit
of a 120 knot 250-300 mb jet will spread from west to east. Although
the models were in good agreement with the timing, the WAA initial
pcpn may be fairly light and slowed by time to saturate low level
dry air. Similar to what was observed upstream today, MUCAPE
values and tsra chances are expected to lag the initial band with
TS chances mainly in the far west into the west half by midday and
over the rest of the area by mid to late afternoon as the shrtwv
.LONG TERM...(Saturday night through Friday)
Issued at 412 PM EDT FRI SEP 1 2017
Over the last 24hrs, medium range model guidance has slightly
increased the speed of progression of features thru the middle of
next week, but the overall large scale picture remains the same.
Currently, a low amplitude ridge is over the western CONUS with max
positive height anomaly along the Pacific NW coast. Shortwave now
rounding the ridge will track across the Great Lakes region over the
weekend. Early next week, the western ridge will amplify sharply
thru western Canada with 500mb height anomalies peaking around 250mb
above the long term early Sept avg. This will in turn force a
deepening trof downstream over the Great Lakes region Mon thru Thu.
In the 7-10 day time frame, the western ridge is fcst to deamplify
and progress slowly with positive height anomalies gradually
spreading downstream to the Upper Lakes, causing weakening and
progression of the eastern trof. These large scale changes will lead
to temps rising above normal on Sun ahead of a cold front passing
early Mon. Transition day on Mon will be followed by much cooler
conditions for Tue/Wed as 850mb temps bottom out at 1-3C. New change
seen in guidance today is the potential of another shortwave to drop
sse into the Great Lakes region on Thu, helping to maintain deeper
troffing across the area thru Thu and delaying a more sustained
warming trend until next weekend. Farther out, trend toward somewhat
above normal heights into the following week should support normal
to above normal temps into the mid Sept time frame. As for pcpn over
the next 7 days, shortwave/associated sfc trof arriving on Sat will
push a band of shra across Upper MI. Dry weather will follow on Sun.
Shra chc will then return Sun night/Labor Day with next cold front.
Expect unsettled weather for Tue/Wed as amplified trof and chilly
air mass support plenty of cloud cover and at least some diurnally
aided isold/sct shra. There may even be a lake component to shra Tue
night into Wed morning. With the new depiction of a possible
shortwave arriving on Thu, there may be some chc of -shra into Thu
before a period of dry weather likely settles in thru next weekend
as warming trend begins.
Beginning Sat night, lingering shra associated with passing
shortwave/sfc trof will end from w to e. Enough instability is
present to maintain a mention of thunder in the evening.
On Sun, expect a dry day under passing weak sfc high pres ridge. In
fact, it should be a nice late summer/early fall day with mostly
sunny skies and high temps well into the 70s for much of the area. A
few spots may reach 80F.
Sharp ridge amplification over western N America will force next
shortwave to dig into the Upper Mississippi Valley/western Great
Lakes on Labor Day. As previously mentioned, model trend over the
last 24hrs has been to increase the progression of features
slightly. So, it appears now that the cold front associated with the
shortwave may exit the fcst area by mid morning. This would favor a
more optimistic Labor Day fcst with limited risk of more shra
development in the wake of the cold front. However, additional
shortwave energy in the amplifying trof may be sufficient to
generate some isold aftn -shra on Labor Day even though this energy
is dropping more so into the northern Plains rather than the Upper
Lakes. Expect high temps to be mostly in the upper 60s/lwr 70s.
With trof amplifying thru the Great Lakes, much cooler/fall
conditions will follow Tue under n to nw winds/mostly cloudy skies
and isold/sct shra. Wed will be similar to Tue, but with lighter
winds. Timing periods of better shra chc on Tue/Wed will be dictated
by any shortwaves dropping into the trof over the Great Lakes, and
models haven`t shown great consistency on that point. In any event,
would expect some diurnal component to pcpn coverage on both days
with aftn hrs more favorable for isold/sct -shra. Not out of the
question that there could be a lake component to -shra during the
min of the diurnal cycle late Tue night/Wed morning. Max temps
Tue/Wed will likely hold to the 50s across much of the w and n.
Lower 60s expected s central.
Depending on track/strength of a shortwave dropping into the Great
Lakes on Thu, there may be some potential of -shra at that time. Dry
weather and a warming trend will then get underway Fri as trof
shifts e and heights rise.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 642 PM EDT FRI SEP 1 2017
As high pressure slowly shifts to the east, VFR conditions are
expected through tonight with lingering dry air over the region. A
front moving into the area from the west will bring showers into the
west Saturday morning that should be heavy enough to drop cigs into
the MVFR range by mid to late morning at KIWD and KCMX. KCMX will
briefly go IFR Sat afternoon. KSAW will go MVFR by Sat afternoon.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 359 PM EDT FRI SEP 1 2017
Southwest winds will increase to 20 to 30 knots tonight into
Saturday ahead of a front. Behind the front, winds will become
westerly at around or less than 15 knots on Sunday. Another cold
front is expected to move through the region and will increase winds
to 20 to 30 knots Monday through the middle of next week.
Area Forecast Discussion
National Weather Service Pittsburgh PA
908 PM EDT Fri Sep 1 2017
Temperatures will remain cold this weekend with the remnants of
Harvey bringing rain through Sunday. Heavy rainfall totals are
.NEAR TERM /THROUGH SATURDAY/...
Northeasterly flow is continuing to feed dry air down into the
CWA even as the remnants of Harvey trudge northeastward into it.
This was again well reflected in the 00z sounding this evening.
This flow combined with increasing shear over Harvey as well
show Harvey weakening rapidly between now and this time on
Saturday. The ingestion of dry air can already be noticed on
region radar mosaics as higher reflectivity returns have rapidly
diminished in the past several hours. The 18z GFS, latest HRRR
runs, and hi-res NMM/ARW all indicate a continued rapid erosion
of the increasinly ragged rain shield moving northward ahead of
While Harvey transitions from a barotropic structure currently
noted to an open upper/mid-level wave through the day tomorrow
while maintaining a decent low-level center, it does seem that
the precipitation field is set to bifurcate likewise with a
swath following the upper support, which a second area remains
concentrated with the low level warm air advection that will
maximize in Ohio. PoPs were built to favor this which will
likely mean a local minimum in precipitation in western
Pennsylvania. QPF was summarily reduced because of this, not to
mention low level easterly flow is not particularly conducive
to significant QPF over much of western Pennsylvania.
With all this in mind, it is certain that clouds will hold sway
through the day tomorrow, and thus temperatures will be unlikely
to drop much tonight, nor substantially rise tomorrow. This will
mean largely below normal readings will continue. Fries
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Showers will continue Saturday night and linger east of
Pittsburgh early on Sunday before conditions dry out for the
rest of the Labor Day weekend. High temperatures will leap
about 10 degrees on Sunday and rise to seasonable values by
Monday, which should be the warmest day of the upcoming seven
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
A cold front crossing the region Tuesday and Tuesday night will
bring another round of showers to all locations, with showers
lingering into Wednesday and possibly Thursday. Temperatures
will drop below normal again behind the cold front, with cooler
weather continuing for several days. While today`s normal high
temperature is 78, highs will likely remain in the upper 60s and
lower 70s in most locations Wednesday, Thursday, and Friday.
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
Dry low level ENE flow on the northern side of approaching low
pressure should maintain VFR conditions tonight, though mid
level clouds and a few showers are possible. There is some LLWS
wind shear potential overnight with a marginal low lvl jet,
though with sfc winds near 10kt thought LLWS values would remain
Rain and condition deterioration to MVFR, and eventual IFR, is
expected Saturday afternoon as the low advances across the OH
Valley region. Gusty SE winds are expected with a tight pressure
gradient during the day toward the higher terrain ports.
Restrictions are expected through Sunday morning as low
pressure exits. Restriction potential returns with a Tue/Wed
Area Forecast Discussion
National Weather Service Blacksburg VA
906 PM EDT Fri Sep 1 2017
Low pressure that was once Harvey will track into Ohio through
Saturday morning, then into the eastern Great Lakes Saturday
afternoon. A cold front enters the mountains late tonight, and
exits the piedmont early Saturday afternoon. Sunday and Monday
high pressure will cover the region.
.NEAR TERM /THROUGH SATURDAY/...
As of 855 PM EDT Friday...
Deep wedge for early Sept remains in place tonight with
soundings showing quite a stable layer below 850 mb which has
kept more surface based convection just south of the area. This
along with strong east/northeast flow has pushed temps into the
50s with even a few 40s across the far northwest. Otherwise
bands of showers and isolated storms continue to redevelop south
of the region in an area of strong upper diffluence aided by
low level theta-e ridging. Expect this scenario to persist until
around midnight when the tail of the passing speed max aloft
finally exits. Still expect any remaining convection to be quite
elevated above the chilly cool pool with heavy rainfall possibly the
main issue across southeast sections that saw earlier downpours.
Thus have tweaked pops up espcly south to continued likely/categorical
until around midnight with chance or higher pops elsewhere.
Latest HRRR then finally shifts most showers east during the
early morning hours, but still enough residual band potential
around the remnant Harvey low to keep in some low pops into
Saturday morning. Already adjusted lows down to just below
current readings as only expecting another degree or two of
cooling given clouds, and breezy easterly flow which should
also limit fog to the higher ridges overnight.
Previous discussion as of 255 PM EDT Friday...
Early this afternoon, low pressure which was Harvey was located
northeast of Nashville, TN. A frontal boundary extended northeast
into eastern KY, then southeast into far SW VA/NW NC, then east
along I-40 in central NC. This boundary is the zone of concern for
potential severe storms this afternoon. Already seeing warnings for
severe and tornadoes south of our CWA toward Charlotte, NC. High-res
models continue to paint a picture of the wedge front sagging
southward through early evening such that severe potential remains
low over our forecast area. Still given strong upper forcing and
shear, could see isolated damaging wind/tornado threat into early
evening, especially southeast of a line from South Boston to
Yadkinville, but again better threat will be along/south of the
I40/85 corridor in NC.
Another concern will be heavy rain/localized flash flooding as
rainfall rates from this airmass will exceed 2-3 inches at times.
However, we have been relatively dry with high flash flood guidance
values over the southeast CWA where the heavier rain is expected.
Will have to watch for training cells, as movement is fast enough to
keep flooding to a minimum. Also urban areas like Danville/South
Boston/Reidsville could experience some local flooding thru this
evening. Still not enough to warrant a flood watch.
So as we head into the overnight the upper flow becomes more
confluent with the closed low over KY, so rainfall should back off
somewhat while a dry slot pushes into southern WV/far SW VA.
The sfc low weakens Saturday as it shifts to Ohio while a secondary
wave forms over northeast VA into the mid-Atlantic. Should see
drying trend continue east of the Blue Ridge, but upper low opens to
trough and vort tracking over WV will bring another round of showers
in the mountains Saturday. Still cannot completely dry out it in the
east given the strength of the upper trough/vort.
As for temps already starting on the cool side this afternoon with
rain/wedge, so lows tonight with clouds and rain will fall about 4-8
degrees into the 50s, with lower 60s far SW VA into the NC
foothill/piedmont and southside VA.
Saturday wedge breaks and flow turns more southwest ahead of the
trough and cold front. Anticipating more sunshine over the southeast
CWA by afternoon, so highs should be close to 80, while the
mountains warm into the 60s, with 70s in between.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 300 PM EDT Friday...
The remnants of Harvey are expected to weaken and lift northeast
into Saturday night. Refer to the latest statement from WPC on
Harvey. The upper trough axis will rotate east across the region
Saturday night into Sunday. Winds will become northwest and create
downslope subsidence, while in the west upslope pattern continues
with clouds and scattered showers. Low temperatures Saturday night
will range from the lower 50s in the mountains to the lower 60s in
On Sunday, clouds and scattered showers associated with the upslope
flow will decrease in coverage as the day progresses as the 850 mb
flow decreases and backs slightly. High temperatures on Sunday will
vary from the mid 60s in the northwest mountains to the lower 80s in
High pressure to our southwest will build across the region Sunday
night. Low temperatures Sunday night will generally be from the
lower 50s in the west to near 60 degrees in the east.
High pressure will be overhead Monday, then it will slide east
Monday night. High temperatures will be near normal Monday with
readings from the lower 70s in the mountains to the mid 80s in the
Piedmont. A cold front will approach the area from the northwest
Monday night into Tuesday. Low temperatures will feature values from
the mid 50s in the west to the lower 60s in the east.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 300 PM EDT Friday...
Upper trough digs south from the Great Lakes Region into the
Tennessee Valley through Midweek, then it travels eastward into the
weekend. There remains some model differences in extended as too how
far east the trough axis moves, in relation to strength and position
of upper ridge over the western Atlantic.
Ahead of the cold front, Tuesday will be a warm and humid day. The
frontal boundary will reach the mountains by Tuesday evening with
scattered showers and a few thunderstorms along and ahead of it.
The timing of the moisture and the front is faster on the ECMWF
compared to GFS. By Wednesday, most solutions generates scattered
showers and thunderstorms.
Frontal boundary slows down per ridge offshore with waves of low
pressure setting up along it. There will be a good chance for
convection from Midweek into Thursday. High across the Ohio Valley
will build east across our region Thursday night into Friday.
Meanwhile, a shortwave will rotate around the upper trough to our
A cooling trend is expected from Tuesday into the end of the week.
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
As of 650 PM EDT Friday...
Poor flying conditions to persist overnight as a strong wedge of
cool air keeps low cigs in place for the most part with periods
of passing showers/rain through at least late this evening. This
should result in widespread MVFR, with areas of IFR and perhaps
LIFR espcly over the mountains outside of rainfall. Vsbys a bit
more tricky with MVFR at times within rainfall while overall VFR
this evening before perhaps trending MVFR late as perhaps patchy
fog develops along the ridges. Gusty northeast/east wind to also
linger overnight as the gradient between high pressure to the
north and remnants of Harvey to the west continues. Expect may
even see gusts to 20-25 kts espcly along and east of the Blue
Even though showers should become less widespread Saturday,
except across the northwest where will be closer to the passing
remnant low of Harvey, appears the wedge will hold for the most
part. This will allow low cigs to linger with some gradual
improvement to MVFR during the day, although cant totally rule
out periods of VFR in the east by late in the day. With best
chances of showers basically across the northwest, will be
keeping in a VCSH mention excluding KLYH/KDAN at this point
Extended Aviation Discussion...
The remnants of Harvey will track northeast into the Ohio
Valley Saturday night, before becoming absorbed in the northern
stream upper trof.
Sunday into early next week will see improving conditions to
mostly VFR as high pressure moves southeast into the region. The
exception will be late night/early morning patchy dense fog at
the usual locations, KLWB and KBCB.
Shower chances increase again ahead of a front Wednesday, so sub
VFR is possible.
Area Forecast Discussion
National Weather Service Tucson AZ
836 PM MST Fri Sep 1 2017
.SYNOPSIS...Increased moisture from Tropical Storm Lidia will bring
a chance of showers and thunderstorms mainly west to south of Tucson
this weekend. Expect isolated to scattered afternoon and evening
thunderstorms next week.
.DISCUSSION...Yet another quiet afternoon/evening throughout
southeast Arizona. Such is life with dewpoints in the 30`s and a PW
of 0.5". However, change is on the horizon due to TS Lidia. Outer
bands of cirriform clouds associated with the tropical system
continue to expand south to north across the international border.
The latest NHC Advisory #13A showed Lidia currently moving up the
western coastline of Baja California Sur, gradually weakening as it
interacts with mountainous regions and cooler Pacific waters. Good
agreement among the model suite keeps Lidia drifting away toward the
northwest, but moisture in our area will be increasing tonight into
Slight chance of light precip along the southern border in Santa
Cruz County tonight before more organized measurable rainfall
arrives tomorrow morning. The 02/02Z HRRR shows a band of showers
reaching the border around 15Z, slowly expanding toward the north.
This solution holds in line with the earlier guidance and the
forecast appears to be in good shape. No changes are necessary at
this time. Please see previous discussion for further details.
.AVIATION...Valid thru 03/06Z.
Surface winds ely/sely less than 12 kts through tonight. Increasing
clouds mainly above 10k ft AGL from south to north across the area
late tonight into Saturday. Isolated -SHRA mainly near international
border and KOLS Saturday morning. Scattered -TSRA/-SHRA mainly west
of KTUS Saturday afternoon into evening. Winds remain ely/sely
tomorrow with gusts to 20 kts during afternoon. Aviation discussion
not updated for TAF amendments.
.FIRE WEATHER...Isolated showers south of Tucson late tonight into
Saturday morning, then scattered showers and thunderstorms mainly
west of Tucson Saturday afternoon into Sunday. Expect isolated to
scattered afternoon and evening thunderstorms Monday into next
Friday. 20-foot winds will generally be from the east to southeast
at 5-15 mph with occasional gusts to 25 mph through much of the
.PREV DISCUSSION /245 PM MST/...Measurable rainfall is not expected
to occur this evening. Have opted for a slight chance of showers
(with no thunder) mainly near the International border adjacent
Santa Cruz/southern Pima Counties late tonight. Isolated showers
with a slight chance of thunderstorms Saturday morning should be
confined south of an Ajo-Green Valley-Douglas line.
As noted in the morning discussion, the 01/12Z NAM MOS guidance and
especially the 01/12Z GFS MOS guidance suggest markedly reduced
measurable precip chances from Tucson northward/eastward versus
solutions from 24 hours ago. However, precip potential remained
similar versus model solutions from 24 hours ago for locales west to
south of Tucson.
The high resolution models such as the 01/12Z Univ of AZ WRF-NAM and
WRF-GFS suggest that scattered showers/tstms will develop Saturday
afternoon mostly across western/central Pima County. However, the
WRF-GFS remained more robust versus the WRF-NAM by depicting a
potential for showers/tstms to occur Saturday afternoon and evening
further eastward and southeastward to include portions of the Tucson
metro area into Santa Cruz County. The WRF-NAM and WRF-GFS were then
similar with limiting shower/tstm potential to mainly
western/central Pima County Saturday evening.
At any rate, the official forecast continues with scattered showers/
tstms mainly west-to-south of Tucson Saturday afternoon into
Saturday night, and isolated showers/tstms for the Tucson metro
area. Lidia is forecast by the National Hurricane Center to decay to
a remnant low just west of the northern Baja California coast Sunday
morning. The models suggest that dry conditions will occur from
Tucson eastward Sunday, but adequate moisture will justify at least
a slight chance of showers/tstms across western sections.
Thereafter, the 01/12Z GFS/ECMWF/CMC deterministic solutions
continued to depict strong high pressure aloft to remain over the
western CONUS Monday into next Friday. A fairly low grade shower/
tstm potential exists daily Monday through Friday. However, a cold
front moving westward across southern New Mexico and encroaching
upon eastern sections, as well as enhanced northeasterly mid-level
steering flow, may provide increased shower/tstm coverage area-wide
High temperatures this forecast period will mainly be quite close to
seasonal normals. The exception appears to be Monday and Tuesday
when daytime temps may average a few degrees above normal.
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