Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/30/18
Area Forecast Discussion...UPDATED
National Weather Service Corpus Christi TX
934 PM CDT Sat Sep 29 2018
.DISCUSSION...Water vapor imagery shows the upper trough axis from
southwest Texas into northern Coahuila. Shower activity has
lingered this evening over the Brush Country in weakly divergent
flow aloft over this area. But showers have shown a diminishing
trend over the last hour. Will keep low chance PoPs for the rest
of the evening for western Brush Country. Also, along the coast
where low level convergence is slowly increasing and moisture
remains high in this region. Lowered PoPs to slight chance across
the northern counties for rest of this evening. Latest HRRR and
12Z HREF show convection should increase in low level convergence
zone along the coast overnight, similar to last night. Weak
divergence aloft ahead of the slow moving upper trough will aid
in development also. No changes to the PoP forecast for overnight.
Wind speeds have lowered along the coast to below SCEC but still
in that range over the Gulf waters.
.PREVIOUS DISCUSSION... /Issued 649 PM CDT Sat Sep 29 2018/
DISCUSSION...See Marine section for update wind speeds to SCEC
range for this evening for most of the coastal waters. See
Aviation section for 00Z TAFs.
AVIATION...Isolated convection will continue for a couple of
hours from northwest of Beeville to near Laredo. High resolution
models again depict activity will diminish for the latter part of
the evening hours. VFR conditions will exist except for MVFR
ceilings/vsbys near convection this evening. MVFR ceilings are
expected to develop over the coastal plains from 06-08Z and over
the Brush Country toward daybreak. Expect convection will again
develop near coastal convergence zone during the overnight hours
with MVFR vsbys expected with convection. IFR vsbys will be
possible in heavy rain with thunderstorms. The activity will move
inland during the morning hours and become more scattered by the
afternoon with activity reaching LRD area by 16Z Sunday.
MARINE...Onshore flow has been elevated after convection over
the coastal waters has diminished. Wind speeds will be in the SCEC
range for most of the evening for the coastal waters except for
the northern bays.
.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi 73 85 75 87 75 / 50 60 40 40 20
Victoria 72 84 71 87 73 / 40 60 40 50 20
Laredo 72 84 73 89 74 / 30 50 30 30 20
Alice 72 85 73 88 74 / 30 60 20 40 20
Rockport 74 83 75 86 77 / 60 70 50 50 20
Cotulla 71 85 71 88 73 / 20 50 20 30 10
Kingsville 73 85 73 88 75 / 40 60 30 40 20
Navy Corpus 75 85 77 86 77 / 60 70 50 40 20
Area Forecast Discussion
National Weather Service Duluth MN
634 PM CDT Sat Sep 29 2018
.SHORT TERM...(This evening through Sunday)
Issued at 328 PM CDT Sat Sep 29 2018
The FGEN generated area of precipitation has been diminishing
some in strength this afternoon per area radars and the latest
version of the RAP shows weaker FGEN into the evening compared
with earlier model runs. We still expect some precipitation across
the southern third of the CWA this evening, some of which could
be a rain and snow mix. However, since the precipitation rate may
be weaker than earlier, more may fall as rain versus snow as
observed earlier. A trough and shortwave will also move through
the area tonight providing more lift for light precipitation and
we have the highest POPs over far northeast Minnesota. Lows
tonight will be in the lower to middle thirties for most areas.
As the trough departs on Sunday, high pressure will build in
briefly and bring an end to any lingering light precipitation.
Highs will be in the mid forties to around fifty.
.LONG TERM...(Sunday night through Saturday)
Issued at 328 PM CDT Sat Sep 29 2018
Sporadic precipitation chances through the extended with a warm up
mid week followed by a return to cooler than normal temperatures
late in the week heading into the weekend.
A weak high will build over northern Minnesota and northwest
Wisconsin Sunday evening into Monday morning. The high will quickly
slide into Ontario while a trough lifts from the Northern Plains
into the Upper Mississippi River Valley on Monday. Despite the high,
skies will remain partly to mostly cloudy with increasing cloud
cover heading into Monday morning. Most areas will see rain become
likely Monday morning. Initially precipitation will start out as all
snow along the International Border down to the Eveleth area. By mid
morning precipitation will change over to all rain. The low
associated with the trough will quickly exit the region and
precipitation should come to an end by Monday evening. Sunday night
lows range from the upper 20s to the upper 30s. Highs on Monday will
be in the 40s.
High pressure will nudge itself into the region through Tuesday from
Quebec. Flow aloft will gradually become southwesterly which will
advect warm 850 hPa air into the region. By 00Z Wednesday 850 hPa
temperatures will range from +3 degrees Celsius to +15 degrees
Celsius. Skies will remain mostly cloudy across the region. Tuesday
highs range from the upper 40s to the upper 50s.
A more substantial trough will dig into the Northern Plains from
British Columbia Tuesday evening into Wednesday morning. At the
surface this will develop a broad low over the Northern Plains and
northern Central Plains. The warm front associated with the system
will lift through late Tuesday night through Wednesday afternoon.
This will bring us the warmest readings of the extended with highs
ranging from the mid 50s along the International Border to the low
70s across southern portions of northwest Wisconsin. The latest
ECMWF and GFS guidance show a few hundred to nearly 1000 J/kg of
CAPE over eastern portions of Minnesota and northwest Wisconsin.
Decided to introduce thunderstorm chances, but somewhat skeptical
this much instability develops with as much cloud cover in the
forecast. The low will exit the region Wednesday evening into
Thursday morning as the trough lifts into Ontario.
High pressure will briefly build in on Thursday before another round
of precipitation moves in on Friday. Flow aloft will become
northwesterly which will advect cold air into the region and bring
the cooler temperatures back to the Northland. Highs on Friday range
from the low 40s to the low 50s.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 631 PM CDT Sat Sep 29 2018
VFR with light winds and isolated light precip - mainly in the
form of rain. Expect MVFR to become more prevalent overnight as
low level moisture advects into the region. No IFR in TAFs but it
may be possible especially in areas where precip has been
occurring today. A return to VFR Sunday.
.PRELIMINARY POINT TEMPS/POPS...
DLH 35 49 38 44 / 40 10 10 60
INL 35 45 30 47 / 50 0 0 20
BRD 36 50 38 47 / 20 10 20 60
HYR 36 51 39 48 / 40 10 10 60
ASX 37 51 39 47 / 50 20 10 60
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1032 PM EDT Sat Sep 29 2018
Forecast will be dominated by high pressure with some chance for
isolated showers at times over the mountains. Winds will be light,
and temperatures will remain above normal and humidity will remain
.NEAR TERM /THROUGH SUNDAY/...
As of 1015 PM EDT Saturday: Updated pops again to increase along the
Blue Ridge. Showers have anchored on the terrain and while the
gauges we have up there are reporting only about 1" in the last 3
hours, some radar estimates are indicating upwards of 2" and so
certainly isolated locations have received more. With the anchoring
on terrain, issued an SPS earlier but opted to do a Flood Advisory
and will continue to watch rates. HRRR not doing a great job with
this convection and so not sure if its diminishing trends are to be
Otherwise, lower clouds should be able to reconsolidate and become
widespread again with areas of fog as well. Sunday morning minimum
temperatures will be warm for late September, on the order of 10 deg
F above normal.
Morning clouds will give way to mixed sun and developing shallow
convective clouds as Sunday wears on. The llvl flow will remain weak
from the east to southeast as ridging aloft builds atop the SE CONUS.
At this point, there remains the possibility of isolated diurnally
fired tstms limited to mainly within the axis of high blyr dwpts
acrs the sw cwfa and into the mtns. Maximum temperatures should be
similar to today, slightly above normal.
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 2pm EDT Saturday: Short term forecast is dominated by a flat
ridge over the South that changes little Monday and Tuesday. This
will lead to continued above normal temperatures and low chances for
precipitation. Surface ridge is also fairly stable through Monday
and Tuesday, running northeast to southwest well east of the
Appalachians. Surface ridge is far enough eastward to limit cold-
air-damming effects, but easterly surface flow is expected Sunday
evening, becoming more southeasterly Monday night as ridge moves a
little farther eastward. Winds should be fairly light in any case,
at 5 to 10 kts. Easterly to southeasterly flow will keep some
Atlantic moisture in the area, supporting dewpoints, and giving low
temperatures 10 degrees above normal. Highs will run 5 to 10 above
Forecast soundings show that, despite decent boundary layer
moisture, mid to upper levels are warm, and the atmosphere is well-
capped, leading to practically no chance of convective activity.
Only chances for significant precipitation Monday and Tuesday are
isolated showers in the mountains, where upslope low-level flow may
be sufficient for some isolate, though weak, showers.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 2pm EDT Saturday: Upper ridge over the South remains the
dominant feature Wednesday through Friday. A weak disturbance that
crosses the top of the ridge (and has the strongest dynamics well
north of the area) may enhance changes for precipitation over the
mountains Wednesday evening, but soundings are otherwise forecast to
remain capped and convectively stable. Once this disturbance passes,
the ridge recovers on Thursday what little strength it lost, and
even strengthens late in the week. Surface ridge will remain well
east of the mountains, giving continued fairly light winds, and
continued southerly to southeasterly flow that will keep dewpoints
elevated. The result will be continued low chances for
precipitation with unseasonably humid and warm conditions, with
highs 10 degrees above normal and lows 15 degrees above normal.
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Still not much in the way of convection
near any of the TAFs but KCLT, so will keep VCSH there through 02z.
The moist easterly flow will continue overnight and expect another
round of MVFR cigs developing in the next few hours, dropping to IFR
in most places overnight (KCLT may remain MVFR). Vsby at KAVL likely
to drop to LIFR, and cannot rule out at least brief LIFR cigs at all
but KCLT. Slow improvement after daybreak Sunday, and though
isolated convection is possible again Sunday afternoon, not enough
to include in any TAFs at this point.
Outlook: Drier conditions are expected from Monday thru at least
midweek, as high pressure dominates over the Southeast.
02-08Z 08-14Z 14-20Z 20-00Z
KCLT High 100% High 83% High 83% High 100%
KGSP High 97% Low 49% Med 69% High 100%
KAVL High 82% Med 76% High 88% High 89%
KHKY High 95% Low 59% High 80% High 100%
KGMU High 97% Med 63% Med 70% High 100%
KAND High 98% Med 67% High 93% High 100%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
Area Forecast Discussion
National Weather Service Jacksonville FL
743 PM EDT Sat Sep 29 2018
.UPDATE...Radar imagery shows a primary convective cluster
nearing our northwestern counties, with no convection ending
everywhere else. HRRR shows cluster continuing a few hours over
our northwestern counties, then fall apart. Have adjusted
hourly POP/Weather grids to reflect this. Otherwise clear to
partly cloudy skies with low temperatures in the lower 70s
well inland, mid 70s I-95 corridor, upper 90s coast.
.AVIATION...VFR conditions next 24 hours. Latest guidance
is not showing much in the way of potential for fog or low
clouds...though patchy shallow fog possible around dawn near
some TAF sites.
.MARINE...Onshore flow and long period swell will continue to
build Sunday into Monday time frame. East winds 10-15 knots and
seas 3-6 ft into early Sunday with Small Craft Exercise Caution
(SCEC) headlines tonight. E-NE winds increase to 15-20 knots by
Sunday Night into Monday with combined seas into the 4-8 ft range
and expect will eventually need Small Craft Advisory (SCA) flags
for the offshore waters and SCEC headlines for the nearshore
waters that will continue well into next week as high pressure
builds north of the waters.
Rip Currents: Long period swells will continue to build and expect
High Risk of Rip currents for all beaches on Sunday into early
next week. Surf/Breakers will build into the 3-5 ft range by late
Sunday into Monday.
.PRELIMINARY POINT TEMPS/POPS...
AMG 72 88 70 87 / 40 60 10 40
SSI 77 85 75 84 / 20 50 60 70
JAX 73 88 74 85 / 10 30 40 70
SGJ 77 87 76 85 / 10 20 50 70
GNV 72 91 72 89 / 10 20 10 50
OCF 71 92 72 90 / 10 10 0 60
Area Forecast Discussion
National Weather Service Medford OR
719 PM PDT Sat Sep 29 2018
.DISCUSSION...After a long, hot, dry, fiery, and smoky summer, rainfall
has reached the Rogue Valley! The last measurable rainfall was a
meager 0.01 inches on July 15, and amounts this evening in the
Rogue Valley have ranged from a few hundredths of an inch to 0.29
inches of rain. This came from one of a handful of thunderstorms
in the forecast area...developing over Southern Jackson County and
moving northward towards Butte Falls. Cloud to ground lightning
has been minimal so far, as expected, with about 28 strikes so
far, mostly in Douglas County.
Other areas west of the Cascades have received generally less than a
tenth of an inch of rain from isolated to scattered showers. Models
show more rainfall through the evening, mainly from
Jackson/Siskiyou/Eastern Douglas County and eastward. Many areas
will see a quarter inch or more of rainfall through Sunday morning
as the upper low opens up and pushes eastward.
We`ve increased precipitation chances tonight, but amounts still
look good. Please see the previous discussion below for more details
on the next chance of rain.
.AVIATION...For the 30/00Z TAFs...Along the coast and over the
coastal waters...VFR with areas of MVFR cigs in showers with
isolated thunderstorms will prevail into this evening, then the MVFR
cigs will spread with local IFR cigs/vsbys near the coast. Any
thunderstorms will end this evening. Showers will end Sunday morning
and conditions will improve to VFR by Sunday afternoon. Over the
remainder of the area...VFR conditions in showers and isolated
thunderstorms with areas of higher terrain obscured will prevail
into this evening. The thunderstorms will end this evening but
showers will continue into Sunday morning with isolated MVFR cigs
developing. The showers will end Sunday morning, and conditions
will improve to VFR by Sunday afternoon.
.MARINE...Updated 700 PM PDT Saturday 29 September 2018...Showers
and even an isolated thunderstorm are possible through this evening
as an upper level low moves through the area. South winds will
persist through Monday, strongest Sunday afternoon and evening.
Winds will approach small craft advisory strength, but should remain
below criteria. Seas will remain below criteria as well, but could
be a bit chaotic due to a southerly wind wave combined with an 8
second northwest swell.
Winds will return to northerly by early Tuesday, but will remain
below small craft conditions. Seas will also remain below criteria
through mid-week, then begin building as northwest swell moves into
the waters Wednesday into Thursday. /BR-y
.FIRE WEATHER...Updated 200 PM PDT Friday, 28 September 2018...The
upper low that is expected to bring our first wetting rain in quite
some time is knocking on our doorstep. Showers are already moving up
along the California coast with Arcata already reporting 0.09 of an
inch of precipitation in the past 3 hours. This area of showers
should hold together enough as it moves north and affect western
Siskiyou County later this afternoon. At the same time gusty winds
are already occurring in the Shasta Valley with the strongest winds
near Weed. Winds are also increasing over the ridges west of the
Cascades and portions of the eastside. The good news is relative
humidity is higher compared to yesterday at this time. Gusty winds
will continue into this evening, but the combination of winds and
relative humidity will remain below Red Flag Criteria. Despite this,
we`ll continue to headline the winds and low relative humidity in
the fire weather forecast.
There`s good agreement showers will start to increase in coverage
between 4-6 pm pdt with scattered to numerous showers and isolated
thunderstorms starting between 6-8 pm pdt mainly west of the
Cascades. There may be enough instability for scattered
thunderstorms from about Crater Lake north, but this will be
accompanied by moderate to occasionally heavy rainfall at times.
Given the convective nature of precipitation, rainfall amounts could
vary greatly depending on where your at. The best chance for 0.25"
or more rainfall is expected along and near the Cascades,
Siskiyous, and Marble Mountains. Wetting rainfall (>0.10") is also
likely across much of southern and western Siskiyou County,
southeastern Josephine County, Jackson County, eastern Douglas
County, and portions of western and northern Klamath County. Note
the rainfall amounts mentioned are expected from this evening until
around midnight. Showers will continue into the overnight period as
the upper low moves overhead. However the focus for heavier
precipitation will shift east, primarily from the cascades east.
Altogether, we expect lightning coverage to be isolated, except from
around Crater Lake NP northward including portions of FWZs 623, 617,
624, and 611, where scattered coverage is expected. Due to the
expectation of temperatures 15-25 degrees cooler than yesterday and
RHs 20-50% higher, and because any thunderstorms that do occur will
produce significant wetting rainfall, this does not appear to be a
RFW lightning event. While isolated thunderstorms are possible
anywhere from the Cascades west to the Coast Range, the greatest
chance of them is in a swath from western Siskiyou County north-
northeastward into northern Klamath County.
The upper low will weaken as it moves overhead tonight, then will
shift east of the area late Sunday morning and afternoon. Could not
rule out showers Sunday morning, but most should be confined to the
Cascades east. Sunday afternoon looks dry as upper ridging builds
into the area with temperatures similar to today.
There`s fairly good agreement among the models showing another upper
low phasing in with a northern branch upper trough on Monday.
Several impulses are expected to move from southwest to northeast
into our area on Monday over northern California and possibly
southern Oregon so we could pick up a bit more rain on Monday.
The upper low will continue to move south just west of the Bay area
in California Tuesday. Ahead of the low the models show
precipitation moving from south to north in northern California and
this combined with upslope flow could enhance precipitation rates in
the favorable upslope areas near Mount Shasta. However this is not
completely clear due to differences in the details depicted by the
models. Oregon should stay mainly dry Tuesday, but isolated showers
could slip though near the Siskiyous.
Beyond Tuesday, the operational models show the the upper ridge
portioned near 150w with a northwest flow along with upper level
disturbances moving southeast in the northwest flow over our area.
it`s not a pattern that is conducive to significant rain. In fact
depending on exactly where the upper ridge to the west sets up, we
could actually stay mainly dry with not much more than hit and miss
light showers. Of note, the GFS ensemble means show a general
troughiness over our area with the upper ridge centered around 150W
and another upper ridge in the southeastern U.S. One thing we can
say with confidence is no significant warm up is expected for most
of next week. Precipitation chances will have to be monitored and
confidence on the specifics should increase as we get into next
.PREV DISCUSSION... /Issued 303 PM PDT Sat Sep 29 2018/
DISCUSSION...Winds have gusted to around 40 mph in the southern
end of the Shasta Valley, and over high terrain east of the
Cascades, including Summer Lake. Showers are on tap for later
today and tonight. While at the time of this writing there have
been no rainfall observation in the Medford CWA yet, much of
Humboldt County has received around 0.10" today and radar shows a
steady band of showers approaching western Siskiyou County, so
it`s only a matter of time. The main upper low driving this
weather change looks to be centered near 40.5N/125.5W and will
continue trekking northeastward over the next 12 hours.
Expect showers to develop from southwest to northeast, first in
western Siskiyou, then coverage should spread into the southern
Josephine and Jackson Counties, then up to the Umpqua Divide and
the Cascades. Higher terrain will receive more precipitation than
lower lying areas due to the convective nature of this system, but
the duration and fact that the bulk of precipitation over the
west side is expected at night (thus with higher RH at lower
levels) should set the Rogue and Illinois Valleys to accumulate
around 0.10" to 0.20"... while ridges in the Cascades and
Siskiyous could see closer to a half inch. HiRes models continue
to indicate potential for a quarter inch of precipitation in parts
of the Upper Klamath Basin, so decided to maintain that part of
the forecast, with some reservations. Most GEFS members are well
below, but the HRRR has been depicting the track of the low better
than the GEFS, so opted to lean more towards the HRRR.
Precipitation will probably start within the next few hours in
the southwestern portion of the forecast area (western Siskiyou
County) and over the highest peaks of the Cascades, then expect
the bulk of precipitation before midnight for the Cascades and
westward roughly before midnight, then later heavier precipitation
will be more focused east of the Cascades. It`s possible that
some of the showers will produce lightning strikes. The main
threat for lighting will be in the Cascades and west of the
Cascades, though it can`t be ruled out east of the Cascades. While
thunderstorms can produce erratic winds, showers should mostly
mitigate the threat of fire starts from lightning strikes.
Of note, since this will be the biggest rainfall in months, safe
driving practices will be important. Oil buildup from the past
several months will cause slippery roads when rain begins to fall,
and likely increased accident rates. Take it slow on the roads today
and tomorrow, especially when traveling around corners and going
Sunday will be a bit of a transition day, with light showers tapering
off by the afternoon and brief ridging. Clouds will largely clear
up by the afternoon and high temperatures will be near normal.
Monday into Tuesday, another low will approach the central California
coast, bringing potential rain to northern California. There`s
uncertainty as to how far north precipitation will propagate, so
stuck with chance and slight chance pops for the time being, but
if nothing else expect substantial cloud cover Monday into
Tuesday. Cloud cover should suppress Monday highs a few degrees,
and keep overnight lows Monday night into Tuesday morning a few
degrees warmer than the previous Monday morning.
The forecast becomes more uncertain Wednesday into Thursday... the
latest few runs of the EC and GFS show the low continuing eastward
Wednesday with possible wrap-around showers over northeastern
California. Then the low will fill as it heads into the Great
Basin and a dirty ridge will build from the north, bringing a
slight warm up towards the end of the week. -McAuley
Pacific Coastal Waters...None.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
904 PM PDT Sat Sep 29 2018
.SYNOPSIS...Scattered showers will continue across the far North
Bay overnight through Sunday morning. Otherwise expect dry and
seasonable weather for the Bay Area to finish out the weekend. The
next front will slowly approach on Monday with increasing clouds
and southerly winds. Rain showers will develop Monday night into
Tuesday for most areas and possibly linger into Wednesday for the
South Bay and Central Coast. Dry weather should return late in the
week and into next weekend.
.DISCUSSION...as of 9:04 PM PDT Saturday...Upper low now over far
northern California brought some rain to the North Bay today into
this evening. For the most part rain appears to have ended but
lots of left over clouds remain along with lingering spotty
showers possible overnight. Was considering removing the morning
shower chances in the North Bay with the 00z nam fairly dry.
However the rap and hrrr mesoscale models indicate shower chances
will continue across Marin/Sonoma on Sunday morning in cyclonic
onshore flow. However the rest of the Bay Area should enjoy partly
cloudy skies with highs mid 60s to mid 70s to wind out the
Attention will quickly turn to next incoming trough. Monday should
be mostly dry as the front slowly approaches from the west with
increasing southerly winds and thickening clouds. However a nice
day overall with highs in the 70s and some downslope southeast
flow possible across the region with no marine layer.
Will let mid shift peruse over all the 00z guidance but may need
to cut back on the Monday pops given the incoming and slower west
trajectory of the upper low. Light rain should develop most
coastal areas late Monday night and biggest impacts would be for
a wet Tuesday morning commute. The 00z nam then shows the trough
dropping south along the Central Coast and tapping into some deep
moisture with a possible 1 inch tpw plume setting up over the
Central Coast Tuesday night into early Weds. Will await the full
gfs and ecmwf before fine tuning those details.
18z gfs suggests drying beyond that but the 12z euro did keep the
trough axis too close for comfort. The new 00z euro will be
arriving shortly and will update the long range overnight based on
.DISCUSSION as of 2:00 PM PDT Saturday... Rain has returned to
the forecast area due to the arrival of a cool, moist and somewhat
modest 559dm 500mb upper level low. This upper low is currently
centered less than 50 miles northwest of Cape Mendocino and is set
to move ashore north of the Cape over the next few hours. Earlier
in the week, this upper low was conjoined with a high pressure
circulation several hundred miles offshore in a Rex block, a
feature which acts as a barrier in the mean westerly atmospheric
flow. Over the last few days, the Rex block broke up, allowing for
this low pressure system to advance towards the California
coastline. This storm system was forecast to mainly impact the
North Bay, and so far it has done so. It is fair to say that
previous forecast precipitation amounts underestimated this
system, given that Stewarts Point 0.21" (nearly all between 11am
and noon), 0.18" at both Point Reyes seashore and Sea Ranch, 0.17"
at Cazadero, and 0.15" at Mt Tamalpais. Locations east of the
Sonoma coastal range in the North Bay have picked up lesser
amounts -- to the range of a few to several hundredths. Additional
lighter rain showers accumulations are possible over the next 24
hours as this upper low transitions through Northern California.
Otherwise for today, the positioning of this upper level low has
mixed out the marine inversion due to cooler air aloft. The Fort
Ord and Bodega Bay profilers showed the the marine layer pushing
well beyond 3500 ft in depth earlier today, generally a sign the
marine inversion is no longer present to cap the cooler, moister
air in the marine layer. Temperatures are running a bit higher
than forecast and versus 24 hours ago given slightly weaker cold
air advection and less cloud coverage than previously anticipated.
Temperatures should level off sooner this afternoon than
yesterday, however, as the upper low moves closer to the area. For
tomorrow, the upper low will exit the area, allowing for slight
warming by the afternoon.
More widespread rainfall is forecast to arrive early in the work
week as a cooler, wetter, more organized low pressure system
advancing towards the region. Short and medium term forecast
models are in good agreement that widespread rainfall is possible
for the area, however, they continue to show a moderate amount of
disagreement regarding the amount. Broadly, first expect to see
lighter warm sector rain showers to precede the heavier rainfall.
These lighter showers will move ashore as early as Monday morning
through early Monday afternoon, bringing light accumulations. So
far, the highest skill/resolution models show the heavier rain
band beginning to move ashore over the North Bay overnight Monday
before spreading southward into Tuesday morning. Models show some
disagreement regarding the orientation of the main frontal rain
band, with some models suggesting a more west to east aligned
while others show the more typical northwest to southeast line. As
for amounts, the afternoon forecast package will continue to
feature a slightly wetter forecast -- with local amounts in the
higher terrain ranging from 0.75" to around an inch, 0.25 - 0.66"
for most urban locations (with lesser amounts in rain shadowed
locations and more on wet side of terrain/closer to the coast),
and less than 0.20" for the drier remote locations inland areas.
One potential snag to watch for is how much the trajectory of the
upper low changes as a secondary vorticity maxima enters and
rounds the base of the trough -- which could cause the trough to
dig farther southward while offshore instead of pushing inland.
This storm is expected to be in the beneficial range as far as
impacts go -- mainly serving to moisten up the extremely dry fuels
(dead trees, grasses, ground detritus, etc) that often spark late
fire season concerns.
The new water year begins October 1st, which may coincide with the
first rainfall of the season. The 2017-2018 water year came in
below seasonal normal, with most climatological stations in the
region reporting somewhere between 66-80% of normal rain
accumulations. Last year, San Francisco picked up its first
measurable rainfall on October 19th, at 0.29". The current
forecast calls for closer to 0.50" for San Francisco over the
first two days of the upcoming water year. This forecast value
will likely continue to change as the storm system comes into
better focus over the next couple of days.
.AVIATION...as of 5:57 PM PDT Saturday...Light rain, low ceilings,
IFR carrying over into this evening and overnight over the North
Bay. Visibilities quite likely lowering to LIFR-VLIFR in the North
Bay due to fog, mixed with occasional light rain, tonight and early
Sunday morning. VFR-MVFR elsewhere tonight and Sunday.
Vicinity of KSFO...VFR. Wind near 10 knots from the south and
southwest. Runways likely to remain dry.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR. South to southwest winds becoming
light southeast tonight. Onshore wind resumes by Sunday afternoon.
.MARINE...as of 08:45 PM PDT Saturday...Chances of showers will
continue across the waters due to an upper low that will be making
its way into the Pacific Northwest tomorrow. Southerly winds will
persist through Tuesday as a second upper low moves through the
waters and exits to the south. Once the upper low passes, winds
will shift back out of the northwest. More widespread showers are
forecast Monday night and Tuesday that will be associated with
that second upper low. Expect southerly swell generated by
Hurricane Rosa to increase through Monday.
PUBLIC FORECAST: RWW
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Area Forecast Discussion
National Weather Service Pittsburgh PA
936 PM EDT Sat Sep 29 2018
Clouds will diminish as evening approaches. Dry and warmer
weather is expected for Sunday and the start of the new week.
.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
Mid clouds are pushing eastward across Ohio in zonal flow aloft.
These clouds continue to erode somewhat as they move east. 00Z
KPBZ sounding supports this, with dry air above 850 mb. Think
that clouds will eventually increase more over the northern CWA
as opposed to the south, which is suggested by HRRR soundings
and satellite trends. Have tailored the sky grids to show a
north-to-south gradient. Left in patchy valley fog for now,
although this could become iffier, especially north of
Pittsburgh, depending on eventual cloud coverage. Areas that
remain clear will remain susceptible due to cooler air over the
relatively warmer rivers. Temperatures will end up near
climatology for the most part.
.SHORT TERM /SUNDAY THROUGH MONDAY/...
Due to an expanding ridge Sunday into Monday, precipitation
chances in our area will remain low; rainfall will be mainly
focused to the north of Lake Erie. However, above climatological
temperature averages near the order of 10 degrees is expected
Monday with that building upper level ridge.
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Expect that warming trend to continue through the week as the
southern upper ridge expands. Precip chances will be shortwave
dependent, with the best chance expected Tuesday through
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Clear sky at the start of the TAF period. Clouds will move in
overnight, especially across southeast Ohio and areas north of
PIT. The timing and extent of the clouds will determine the
extent of valley fog somewhat. Think FKL/ZZV will be spared the
thickest fog due to arrival of clouds before fog can become too
dense. Kept a period of IFR/LIFR at HLG/AGC/DUJ/MGW as cloud
coverage there remains more uncertain. Confidence is moderate at
best, and some adjustments are likely with the 06Z forecast.
Any fog that does develop should lift by 13-14Z. VFR conditions
will then prevail thereafter, as remaining clouds should remain
above 3500-4000 feet. Light southeast wind will veer towards the
SSW with time on Sunday.
Restrictions are likely for Monday night and Tuesday as another
shortwave trough approaches, and crosses the region.
Area Forecast Discussion
National Weather Service Springfield MO
555 PM CDT Sat Sep 29 2018
.SHORT TERM...(This evening through Sunday)
Issued at 228 PM CDT Sat Sep 29 2018
A warm front was moving north through the area today with partly
cloudy skies and increasing southerly winds. At 2pm, the warm
front was roughly along the US Highway 54 corridor in Central
Missouri. A definite increase in moisture was occuring with
dewpoints ranging from the lower 60s at JLN to around 50 at VIH.
Air temps were responding nicely into the lower and middle 70s.
Much like the last few nights, areas of fog are expected to form
mainly south and east of Springfield where winds will be lighter
and less cloud cover will occur. Generally used a blend of the RAP
and other high res models which shows good potential for
visibilities to drop below 1 mile, perhaps less than 1/2 mile by
morning. Later shifts will need to monitor for a potential fog
advisory if confidence increases in dense fog production.
The NAM shows some signal of light drizzle overnight west of SGF
however inspection of soundings and isentropic forecast shows the
best chances of this will be further west into Kansas closer to
the 850mb low level jet, however it is something to watch. Any
fog/low cloud cover will likely burn off shortly after sunrise.
Increasing mid level heights and thicknesses will lead to
temperatures in the low to middle 80s for most locations on
.LONG TERM...(Sunday Night through Saturday)
Issued at 228 PM CDT Sat Sep 29 2018
Next week is looking very warm with summer time high pressure
anchored over the southeast US. A subtle piece of energy looks to
move along the western periphery of the high on Monday and may
create a few showers across the southeast half of the area however
it will likely not amount to much.
The strong mid level high is forecast to retrograde slightly west,
closer to the area from Tuesday through Thursday, this will allow
for a strong fetch of southerly winds to continue with 850mb temps
reach 16-18C. Using these temps with 850mb climatology for this
time of year would correlate to high temps easily reaching the
middle to upper 80s. High temperatures may need to be adjusted
upwards in later forecasts. Dry weather is expected during the mid
week timeframe under this pattern.
From Thursday on into next weekend, several strong disturbances
look to move out of the southwest US and move close to or just
north of the area. A front will also interact with these
disturbances to produce showers and thunderstorms. There is
disagreement with the timing and placement of the waves that come
out of the southwest, however with time, unsettled weather will
return to the area given an increasing southwest flow aloft. CIPS
extended analogs for the days 6-12 timeframe favor high
percentages for above average temperatures and above average
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 551 PM CDT Sat Sep 29 2018
VFR conditions for now across the area. Surface ridge was well to
the northeast and have seen winds veer to the south today behind a
warm front. The increase in moisture and light wind over the
eastern Ozarks could lead to some fog development towards morning
which some of the models are hinting at. Have dropped Branson down
into MVFR towards 10-12z, but have kept fog out of SGF/JLN for now
and will monitor visibility trends during the evening.
Area Forecast Discussion
National Weather Service Shreveport LA
1018 PM CDT Sat Sep 29 2018
.SHORT TERM.../Tonight through Sunday/
The evening sfc analysis indicates a weak sfc bndry (pseudo warm
front) extending from near the Red River of N TX SE across E TX in
VC of the I-20/I-30 corridors, to along the I-20 corridor of N LA.
To the N of this bndry, the cirrus shield has been notably
thinner, with patchy FG developing across portions of SE
OK/adjacent sections of SW AR, where temp/dewpoint depressions are
very small. However, within the breaks of the cirrus, areas of
stratocu have redeveloped across portions of E TX, with additional
development expected overnight across much of E TX/SE OK, and
well as portions of SW AR/Wrn LA. Meanwhile, a weak shear axis
extending from SE and Deep E TX NE into Ncntrl LA will continue to
slowly lift N overnight, as a well defined shortwave trough over
SW TX continues to shift E into S TX. Areas of -SHRA over S LA
within a high PW environment characteristic with PW`s of 2.0-2.2
inches over S LA, is also progged to slowly spread N into Cntrl LA
overnight as well, with the HRRR and 00Z NAM both suggesting that
isolated -SHRA may eventually spill N into the Srn sections of N
LA as well as adjacent areas of the Lower Toledo Bend Country
prior to daybreak.
Have added slight chance pops late tonight for the aforementioned
areas, and also beefed up pops a bit for Lower E TX/Ncntrl LA as
sct convection should quickly increase by mid to late morning over
these areas as the shortwave trough to our W enhances large scale
forcing across Deep E TX/N LA. The high chance pops for the
afternoon generally along-S of I-20 still looks good, with this
convection gradually diminishing late in the day as it enters Srn
AR. Have also toned down the FG wording tonight for just SW AR/SE
OK given the very low temp/dewpoint depressions and thin cirrus,
with some minor tweaks to the forecast min temps as well.
Zone update already out...grids will be available shortly.
.PREV DISCUSSION... /issued 652 PM CDT Sat Sep 29 2018/
MVFR cigs ranging between 2.0-3.0kft will persist this evening
over much of E TX/Wrn LA, with cigs expected to lower to IFR after
08Z over E TX, with even some LIFR cigs and vsby reductions
possible across the TYR/GGG/LFK terminals. MVFR cigs should linger
overnight across Wrn LA, and eventually develop/spread NNE into
portions of SW AR, affecting TXK after 06Z, and possibly ELD
after 12Z. These cigs will begin to slowly improve by late morning
Sunday, although MVFR cigs will likely persist through the
afternoon across E TX/Wrn LA, as sct convection is expected to
develop by mid and late morning across Deep E and SE TX/Cntrl LA,
and spread N across much of E TX/N LA through the afternoon. Have
inserted VCSH mention at 16Z for LFK, before prevailing SHRA at
18Z with some vsbys restrictions possible. Have also carried VCSH
mention for the TYR/GGG/SHV terminals after 18Z, with this
convection expected to gradually diminish during the evening.
Can`t rule out isolated thunder, but low confidence precludes
mention attm. VFR cigs should return to SW AR by afternoon, and
remain VFR at MLU through the end of the TAF period. Lt/Vrb winds
tonight will become ESE 4-7kts after 16Z Sunday. /15/
.PRELIMINARY POINT TEMPS/POPS...
SHV 69 83 70 88 / 10 50 20 30
MLU 66 84 69 90 / 10 40 20 40
DEQ 64 83 68 85 / 10 20 10 20
TXK 64 82 68 84 / 10 30 20 30
ELD 63 83 68 87 / 10 30 20 30
TYR 70 80 69 84 / 10 50 20 30
GGG 69 80 69 86 / 10 50 20 30
LFK 70 79 70 87 / 10 50 20 40
Area Forecast Discussion
National Weather Service Tucson AZ
400 PM MST Sat Sep 29 2018
.SYNOPSIS...Isolated to scattered showers and thunderstorms mainly
south to west of Tucson Sunday, then widespread showers and
occasional thunderstorms Sunday night through Tuesday. Expect heavy
rainfall at times, especially west of Tucson. Lingering moisture
will provide isolated to scattered showers and thunderstorms
Wednesday into Friday. Cooler than normal temperatures will
occur during the upcoming work week.
.DISCUSSION...Mostly sunny skies across southeast Arizona this
afternoon with a few to scattered vertically-challenged cumuloform
clouds across the area. However, isolated to scattered showers and
thunderstorms extended from northern Sonora Mexico into west central
Sonora Mexico. Several HRRR solutions have hinted at the possibility
of an isolated shower/tstm early this evening as far north as
southern sections of this forecast area. However, have maintained
single digit PoPs for tonight with the expectation that any
measurable rainfall will remain south of this forecast area.
The National Hurricane Center 2 pm MST advisory regarding Hurricane
Rosa stated the center was located near 21.4N/118.7W, and was moving
toward the north near 12 mph, and this motion is expected to
continue tonight. A turn toward the north-northeast with increased
forward speed is expected Sunday. On the forecast track, the center
of Rosa will approach central and northern Baja California peninsula
Based on various 29/12Z numerical weather prediction model solutions
and per coordination with neighboring WFO`s, there were no
significant changes to the inherited forecast regarding rainfall
potential associated with increased moisture across southeast
Arizona ahead of tropical system Rosa. Based on the latest NHC
forecast track, Rosa`s path as a decaying tropical system is still
projected to generally remain west of this forecast area into
Tuesday morning, with the system becoming a remnant depression late
Tuesday morning over west central Arizona.
At any rate, the official forecast continues with isolated to
scattered showers/tstms developing Sunday especially south to west
of Tucson, then widespread showers with occasional thunderstorms
Sunday night into Tuesday. The models suggest that a vort max ahead
of Rosa will initiate showers/tstms Sunday, and another leading vort
max will continue showers/tstms Sunday night into Monday. The
"remnants" of Rosa and associated rainfall appears to move
northeastward across the area Monday night into Tuesday.
Based on the various 29/12Z models and neighboring WFO`s, only very
minor changes were made to expected rainfall totals through Tuesday.
The heaviest rainfall amounts are still forecast to occur west to
northwest of Tucson. As such, the Flash Flood Watch with respect to
timing and area coverage remains unchanged from the previous
midnight shift. Please see AWIPS product PHXFFATWC / WMO HEADER
WGUS65 KTWC / for detail.
A break in any significant rainfall appears to occur Tuesday night
and perhaps into Wednesday as subsidence occurs behind the departing
remnants. However, additional showers/tstms should yet occur
Wednesday into Friday as an upper trough moves eastward across the
Great Basin and eventually into the Four Corners region. The
operational GFS was more amplified with this upper trough versus the
deterministic ECMWF which accounted for a generally wetter GFS
scenario for later in the week versus the ECMWF. The upshot for
Wednesday through Friday is for a continuation of isolated to
scattered showers/tstms. A slight chance of showers/tstms also
continues into next Saturday, especially northeast of Tucson.
High temps Sunday will remain at least a few degrees above normal,
the cooler temps will occur Monday. High temps Tuesday into next
Saturday reflect only very minor daily changes, and will be below
normal through that period.
.AVIATION...Valid through 01/00Z.
Isolated -SHRA developing Sunday morning south to southwest of KTUS,
then isolated to scattered -TSRA/-SHRA across southeast Arizona
Sunday afternoon. The bulk of this activity should occur south to
west of KTUS followed by more widespread coverage after the valid
period; or, Sunday evening into Monday. Otherwise, scattered clouds
mostly 10k-15k ft AGL into Sunday morning, then cloud decks
generally 6k-12k ft AGL Sunday afternoon. Surface wind variable in
direction mainly less than 12 kts. Aviation discussion not updated
for TAF amendments.
.FIRE WEATHER...Expect isolated to scattered showers and
thunderstorms mainly south to west of Tucson Sunday, then widespread
showers with isolated to scattered thunderstorms Sunday night into
Tuesday. The heaviest rainfall will favor locales west to northwest
of Tucson. Thereafter, isolated to scattered showers and
thunderstorms mainly east of Tucson Wednesday into Friday. A slight
chance of showers and thunderstorms continues next Saturday mainly
northeast of Tucson. Gusty south to southwest winds should occur
Tuesday into Tuesday evening. 20-foot winds will be terrain driven
mainly less than 15 mph at other times.
Flash Flood Watch from Monday morning through late Tuesday night
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