Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/25/17
Area Forecast Discussion
National Weather Service Bismarck ND
841 PM CDT Mon Jul 24 2017
Issued at 835 PM CDT Mon Jul 24 2017
Scattered showers and thunderstorms continue along the cold front
as it moves though west central North Dakota. Thunderstorms are
moving into a region of CIN and this may start to weaken and elevate
them. Trends continue to show diminishing updrafts so expect the
storms to diminish rapidly after sunset. Did have to increase the
area of POPs across south central North Dakota where thunderstorms
have persisted longer than earlier thought.
UPDATE Issued at 601 PM CDT Mon Jul 24 2017
Showers and isolated thunderstorms are forming along the advancing
cold front in western North Dakota at this time. Current forecast
has the location pretty well defined but will add some 20-30 POPs
to account for what may become a line of showers and scattered
thunderstorms in west central North Dakota. Otherwise current
forecast looks good.
.SHORT TERM...(This evening through Tuesday)
Issued at 237 PM CDT Mon Jul 24 2017
A compact upper level shortwave trough was noted on water vapor
imagery over south central North Dakota, sparking some showers and
isolated thunderstorms near the South Dakota border over the
south central and James River Valley. As this circulation moves
east, clouds will begin to dissipate with rapidly warming
temperatures in it`s wake. Additionally, a closed upper low
located near the central Alberta Saskatchewan border will push
another shortwave towards North Dakota late this afternoon and
At the surface, a cold front was moving through northwestern North
Dakota, extending from a surface low over central Saskatchewan.
This cold front will be the focus for isolated to scattered
showers and thunderstorms later this afternoon and evening, some
of which may become severe. The main question with regards to
thunderstorms will be coverage. Strong capping was noted on the
12z Bismarck sounding with an 850mb temperature near 21 degrees
Celsius. Early morning cloud cover may also limit high temperature
potential in the south and we may struggle to reach our
convective temperature of 95 degrees Fahrenheit here in Bismarck.
The better chance for thunderstorms appears to be over the north,
initiating in the 21 to 23z time frame from just west of Minot to
the international border. It should be noted that there is
disagreement in the high resolution models. The operational HRRR
has kept any convection relegated to the very northern tier of
our counties for numerous runs, while the 12z NAM nest and
experimental HRRR initiate storms much further south. At this
time, the best guess is somewhere in between and have tried to
reflect that in the precipitation chances. The 18z RAP shows a
narrow corridor of MLCAPE approaching 2000+ J/kg along and ahead
of the front co-located with 35 to 40 knots of 0-6km shear.
Therefore, if any thunderstorms can break the cap, there will be
a chance for some high based supercells. Large hail and damaging
winds would be the greatest threats.
The cold front continues to sweep southeast overnight. Tuesday
will see cooler high temperatures for most of the forecast area,
with another chance for a strong to severe storm across our far
southeast in the afternoon along the front.
.LONG TERM...(Tuesday night through Monday)
Issued at 237 PM CDT Mon Jul 24 2017
Precipitation chances will fade by Tuesday night and Wednesday and
Thursday should remain dry as upper level ridging once again
builds to the west placing North Dakota in northwest flow aloft.
As the ridge moves east, return flow sets back in as does a slight
chance of showers and thunderstorms on Thursday. Over the
weekend, ridging builds once again, increasing temperatures with
only slight chances of periodic hit and miss thunderstorms.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 601 PM CDT Mon Jul 24 2017
At 6 PM CDT a cold front extended across northwest into west
central North Dakota. The front will move east and will be the
focus for showers and scattered thunderstorms tonight which will
be the main hazard to aviation. VFR is forecast for all TAF
sites. Low confidence in timing and location of thunderstorms so
have used VCTS at KDIK only this evening.
Area Forecast Discussion...Updated
National Weather Service Billings MT
859 PM MDT Mon Jul 24 2017
A few showers and thundestorms developed this evening, but had a
difficult time staying organized. Some gusty winds with the
stronger activity, but mostly shortly lived cells. Have trimmed
back some of the PoPs for the remainder of the evening. High
resolution models were pointing toward the cells north of Billings
holding on until around midnight and then weakening out. GFS
wants to keep the cells going over eastern Montana through the
night. Went with a combination of the two for this update. TWH
.SHORT TERM...valid for Tue and Wed...
Broad range of temperatures across the region this afternoon with
areas north of the Musselshell river under cloud cover in the 70s
and near 100 degrees over portions of southeast Montana. Higher
dewpoints have moved into the area from the north so humidity is
not quite as low as previous days. Upper level low over
Saskatchewan moving east with strong westerly flow aloft over the
region. A series of cold fronts have moved through most of the
area already and one more push of reinforcing cooler air expected
after midnight. Ahead of this front a weak impulse moving in from
southwest Montana tapped into a piece of monsoonal moisture is
projected to bring a round of isolated thunderstorms across the
area. Convective allowing models trended weaker with this activity
and have it pretty fast moving so expect mainly dry thunderstorms
with out much precipitation. Outlier is the GFS which looks wetter
but GEFS plumes and HRRR accumulations look much lighter so have
trended drier overnight. Maybe a strong wind gusts from the storms
but with higher dewpoints downburst potential is lesser.
Coolest day so far in July on tap for Tuesday as the amplitude of
the upper level ridge is weakened by the Canadian low and
northerly pressure gradients create weak upslope winds. Models
hint at moisture pooling a bit over southern Montana so
thunderstorm activity expected later in the afternoon and evening
as a ripple moves through southern Montana. Deepest moisture
appears to remain to the south of Montana with monsoon stronger
over Wyoming and ECMWF is drier solution so have gone with
thunderstorms without a shower mention. Winds will be lighter and
humidity not as critically low so Tuesday will be a very welcome
day for firefighters aside for some lightning triggering new
Warmer weather on tap for Wednesday as heights build but thermal
trough to the west of the area pulls southeasterly winds across
the forecast area which cuts of some of the mixing. This
southeasterly flow does try to deepen moisture over the area and
this may be the best chance to pick up significant moisture but
with lack of much forcing it looks to be diurnally terrain driven
so best chance for picking up rain will be over the mountains. As
the ridge axis strengthens Wednesday night it tries to pull this
moisture northward into the plains but again the GFS is much
wetter than the ECMWF and have leaned towards the drier solution.
.LONG TERM...valid for Thu...Fri...Sat...Sun...Mon...
Semi-zonal southwesterly/westerly upper flow pattern should
persist through the extended period. This pattern generally means
periods of isolated to scattered showers and thunderstorms over
the area mainly during the afternoon and evening hours. Best
chance of showers/storms looks to be on Thursday as a better-
defined shortwave trough crosses Montana. These showers/storms
should be high-based so main threats would be gusty winds and
lightning but little rainfall.
High temperatures will be in the upper 80s to lower 90s on
Thursday, lower to middle 90s Friday and Saturday, then lower to
upper 90s Sunday and Monday as upper ridge builds northward into
our area. Highest readings should generally be east of Billings.
Isolated showers and thunderstorms will continue to move east
across the area tonight. Expect the activity to be over around
KLVM and KBIL by 06Z, and over around KSHR by 09Z. The chance of
precipitation will persist until around 12Z Tuesday in KMLS. Brief
MVFR conditions are possible with the precipitation, as well as
gusty winds in the evening. There will be areas of obscuration
over the Absaroka and Beartooth mountains with localized
obscurations over the NE Bighorns. VFR will prevail on Tuesday,
with areas of obscuration over the Absaroka/Beartooth and NE
Bighorn mountains in the afternoon. Expect a surface wind shift to
the NNE over most of the area Tue. morning. Arthur
.PRELIMINARY POINT TEMP/POPS...
Tue Wed Thu Fri Sat Sun Mon
BIL 064/083 061/088 063/090 064/093 064/094 064/097 065/095
21/B 22/T 23/T 32/T 22/T 22/T 12/T
LVM 056/081 053/086 057/087 054/090 054/091 054/093 055/091
32/T 22/T 34/T 22/T 22/T 22/T 12/T
HDN 062/086 060/090 063/092 061/095 062/095 062/098 062/098
22/T 22/T 23/T 32/T 22/T 22/T 12/T
MLS 065/088 063/091 067/093 066/095 065/097 067/098 067/099
31/B 11/B 12/T 32/T 22/T 21/U 11/U
4BQ 065/088 061/088 065/090 063/093 063/095 064/096 064/096
22/T 31/B 23/T 32/T 22/T 21/U 12/T
BHK 062/087 058/088 062/089 061/092 061/094 061/094 062/094
21/B 11/U 11/B 31/B 01/U 11/U 11/U
SHR 059/084 056/085 058/088 057/090 057/092 057/092 057/093
23/T 44/T 43/T 32/T 22/T 22/T 22/T
Area Forecast Discussion
National Weather Service Goodland KS
537 PM MDT Mon Jul 24 2017
.SHORT TERM...(This evening through Tuesday)
Issued at 257 PM MDT Mon Jul 24 2017
Mid-afternoon visible satellite imagery shows a line of scattered
convection forming along a surface wind shift/convergence zone
stretching from Merriman Nebraska to just west of Sidney to Fort
Morgan Colorado. Guidance suggests activity will remain isolated
this evening with most if not all activity remaining northwest of
the forecast area. Only the HRRR is persistent with recent runs
bringing convection into Yuma county before dissipation this
evening. SPC mesoscale analysis still shows capping in the mixed
layer instability field there. That, coupled with a weak steering
flow from the southwest and forecast little movement of the
convergence line suggests convection may ultimately stay just
northwest of the forecast area which is reflected in current
Tuesday looks hot and dry but heat indices will remain below
advisory levels. High temperatures will range from 95 to 100
degrees. The upper ridge over the central High Plains will weaken
and flatten out a bit Tuesday into Wednesday as a short wave trough
in mid levels moves out of the Rockies and into the Plains. This
feature will initiate convection along a surface lee trough/dryline
in Colorado Tuesday afternoon which will continue Tuesday night.
.LONG TERM...(Tuesday night through Monday)
Issued at 257 PM MDT Mon Jul 24 2017
Tuesday night: Near zonal upper flow will bring through a shortwave
with a decent vorticity lobe across the Central High Plains Tuesday
evening. Combined with leeside troughing and a surface low, this
will help to bring the area chances of storms and showers through
the overnight. While bulk shear values look modest at best, decent
MUCAPE values and high PWATs will give the CWA a chance of seeing
strong to severe storms and very heavy rainfall. Main threats will
be damaging winds and the potential for flash flooding. Main threat
area looks to be Yuma County in CO and our Nebraska counties where
SPC has highlighted a Marginal Risk.
Wednesday-Thursday: Cold front should push through the area
Wednesday/Wednesday night. Will have a chance for showers and
thunderstorms areawide through early Thursday morning as the front
pushes southward. Could possibly see a strong/severe storm mid-
afternoon on Wednesday where GFS is advertising MUCAPE around 2500
J/kg and 0-6km effective shear near 25kt. Thursday afternoon and
overnight looks dry and cooler with highs mainly in the low to mid
80s and lows in the lower 60s areawide.
Friday-Monday: Upper level ridge amplifies over the Rockies placing
us in strong NW flow aloft. Monsoonal moisture plume builds back
into the area, especially at 700mb level. Will have chance of
showers and thunderstorms each afternoon and evening. Temperatures
will be near normal for the period.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 531 PM MDT Mon Jul 24 2017
Vfr conditions are expected through the period. For Kgld, south
winds of near 18 knots with gusts to around 25 knots will decrease
to near 12 knots without gusts in a couple of hours. These winds
will stay steady until late tomorrow morning when they will
increase to near 18 knots with gusts to around 26 knots.
Thunderstorms are expected tomorrow but they will affect the site
until after this period.
For Kmck, south winds near 18 knots with gust to around 24 knots
will decrease to around 10 knots in a couple of hours. Those winds
will continue late tomorrow morning. From 07z tonight 13z tomorrow
morning llws will affect the site. Late in the morning the south
winds will once again increase to near 16 knots to around 24
knots. As with kgld, thunderstorms will affect the site after this
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1118 PM EDT Mon Jul 24 2017
Low pressure tracking through the Gulf of Maine tonight will
keep rain in the forecast through the evening with lingering
showers tapering off Tuesday morning. High pressure builds in
from the west on Tuesday and shifts offshore on Wednesday. Some
warmer air moves in on Wednesday, bringing temperatures back up
to near normal. But a cold front pushes toward the area on
Thursday, with low pressure possibly forming along the front
bringing another chance of rain and cooler temperatures.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
1117 PM Update...
Minor changes to account for current observational trends.
Rain has transitioned to heavy drizzle along the coast with any
bona fide showers relegated to the mountains and foothills.
Shower activity may pick up again as upper level support arrives
959 PM Update...
Shower activity still ongoing across the region as both the 700
and 500 mb lows have yet to cross New England. Expect weak
showery activity overnight as this occurs. Euro and GFS20 are
more bullish with precip overnight with the HRRR and RAP models
much more spotty. The latter models have a better handle on the
situation attm and have kept only slight chance or chance PoPs
in where warranted.
Regardless plenty of low level moisture is still lingering and
stratus will continue to be an issue as well as patchy fog and
drizzle over southern sections. Temperatures are not going to
change much through daybreak with overnight lows just a few
degrees lower than they are now. Adjusted the forecast for these
605 PM Update...
PoPs were adjusted as well as stratiform vs. shower wording as
rain shield moves to the east and is slowly replaced by lighter
and more showery activity. This will also be the case overnight.
Also added drizzle over southern portions of NH and SW Maine
near the coast where ceilings are around 200-800 ft and not
expected to lift for a while.
The large area of steady, moderate rains will continue to exit
to the east this evening. This will leave the region with
pockets of mainly light rainfall and patchy fog. The latest HRRR
continues to show most of the precipitation exiting eastern
areas during the 03Z to 06Z range.
With the cloud cover and a northeasterly gradient, temperatures
will not move all that much from their current readings.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
Much of the precipitation will be east of the region on Tuesday.
Low level winds will back to the north during the day, allowing
for limited drying. However, the upper level low pressure system
will remain overhead during this period. Scattered showers will
develop as lapse rates increase and surface temperatures reach
milder conditions than today, about 70 degrees for many
locations. This precipitation will be mainly away from the
The scattered showers will diminish around sunset on Tuesday
evening as high pressure builds over northern New England. This
will leave the remainder of Tuesday night rainfree. However,
plenty of low level moisture will linger over the region,
allowing patchy fog to form once again.
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
High pressure crosses the area Tuesday night, bringing decent
radiational cooling conditions with a dry air mass in place.
Temperatures will fall into the 40s and 50s overnight, rather
cool for this time of year.
High pressure shifts offshore on Wednesday with a return
southerly flow developing. This will bring warmer and more humid
conditions back into the area, though we will still see
temperatures near normal for late July.
Models diverge a bit on the handling of the next trough. The GFS
sends most of the energy with this trough eastward in
progressive fashion to our north, sliding a cold front through
our area on Thursday. This would bring a chance of showers and
thunderstorms as the front moves through, with less humid but
still seasonable temperatures behind the front for Friday. The
ECMWF and CMC models, however, are in agreement that the better
energy will linger near the base of the upper trough, spinning
up a rather strong surface low which tracks across southern New
England on Friday. This would send a good chunk of rain headed
our way, with temperatures staying quite cool on Friday. Given
the newly upgraded GFS is the outlier, it would seem that the
ECMWF/CMC might be on to something here. Have tilted the
forecast in favor of this scenario for Friday, though
High pressure builds in behind the departed front/low for the
weekend, bringing fair weather and temperatures near seasonal
normals but with only moderate humidity.
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Short Term...Pockets of light rain and fog will continue
overnight, bringing some areas of IFR and LIFR conditions.
Ceilings will be lowest along the coast. A gradual lifting of
the clouds will occur on Tuesday, but there will still be
Long Term...There will be a chance of thunderstorms on Thursday
and a chance of more widespread IFR to LIFR conditions in rain
Short Term...Prolonged northeasterly flow over the waters will
allow waves to build into the 4 to 7 foot range. Increased
gradient will allow for wind gusts to 25 to 30 knots along the
outer waters. Seas will be slow to subside on Tuesday.
Long Term...Winds and seas remain fairly calm over the waters
for the next several days as high pressure crosses the Gulf of
Maine. A return southerly flow begins on Thursday, with a cold
front or low pressure passing through on Friday. Depending on
the track of this low, it is possible that advisory level
conditions could occur.
The astronomical high tide in Portland Harbor is 11.5 feet
tonight. Northeasterly winds will allow for a half foot or more
storm surge overnight, bringing the storm tide to between 12 and
12.5 feet. Flood stage is 12 feet. Minor flooding is expected
along the wharfs and wharf side streets in Portland, Granite
Point Road in Biddeford and the Backbay area of Hampton.
Nearshore waves building to 4 to 7 feet may allow for some
splash-over in Saco tonight.
ME...Coastal Flood Advisory until 3 AM EDT Tuesday for MEZ023-024.
NH...Coastal Flood Advisory until 3 AM EDT Tuesday for NHZ014.
MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ150-152-154.
Area Forecast Discussion
National Weather Service Jackson MS
938 PM CDT Mon Jul 24 2017
Updated for evening discussion.
As of 215z, latest RAP analysis indicates a mid/upper-level cold
core low centered over east central Louisiana with a ridge
centered over the western CONUS and a trough swinging through the
Great Lakes and into the Northeast. A deep moisture axis,
characteristic of 2-2.3 inch PWATs, is centered across central
Mississippi keeping a soupy airmass locked in across the CWA. The
main headline today was torrential rainfall and areas of flash
flooding, especially along the Hwy 84 corridor where 340-345 K
ThetaE air combined with the aforementioned PWAT axis and
convergent flow to produce an area of training storms with some
locally higher rainfall totals before activity spread further
north into the Hwy 82 corridor where sufficient daytime heating
allowed for robust convection and more heavy rain. Any remaining
convection has been quickly dissipating over the last few hours
with only a few showers left on area radars. Expect a lull in the
activity during most of the overnight before precip chances ramp
back up Tuesday morning. Some patchy fog cannot be ruled out
either with the main focus being in the Hwy 82 corridor.
By tomorrow morning, the upper-low that has been plaguing the area
will finally get picked up by the departing trough over New
England and lifted through the area. Latest guidance is in
agreement showing a similar setup to what we saw today across the
southern portion of the area. 2.25+ inch PWATs in concert with an
axis of deep moisture convergence and ThetaE advection, and
forcing from the vort max associated with the low will lead to an
early start to shower and storm activity Tuesday morning along and
south of I-20. This activity is expected to spread east during the
morning hours before tapering off during the early to mid
afternoon as the better moisture and forcing pull northeast out of
the area. Given the axis of heavy rain totals observed today from
Claiborne to Franklin counties and points east opted to go ahead
and introduce a limited risk for flash flooding in this area as
it won`t take much rain to lead to another round of flooding
issues. This setup will have to be closely monitored as a flash
flood watch could possibly be needed given the already saturated
soils from Monday`s heavy rain. /TW/
Prior discussion below:
Tonight and Tuesday:
An upper level disturbance swinging east through the region,
coupled with a very moist airmass, and westerly low level flow
along a theta-e axis, continues to cause showers and storms to
develop and train over the same areas while producing heavy
rainfall across South Central and Southeast Mississippi this
afternoon. This prompted a Flash Flood Watch, that remains in
effect for South Central and Southeast Mississippi until 7 PM,
along with several Flash Flood Warnings and reports of flash
flooding over the area today. My current thinking is, and latest
high-res models agree, that this activity will subside and shift
east southeast out of the area through the afternoon and evening
as low level flow becomes more northwesterly and this better area
of convergence responsible for the redevelopment and training of
convection shifts out of the CWA. As a result, I`m currently not
anticipating having to extend the current Flash Flood Watch. In
addition, simply with the loss of daytime heating, convection as a
whole is expected to wane over the CWA during the evening hours.
However, some isolated activity looks to remain possible across
the southern half of the CWA overnight.
On Tuesday, strong high pressure aloft will begin to build east and
back into the forecast area. This will cause the better rain
chances to shift more to the eastern half of the CWA. Still, with
the warm moist and unstable airmass over the CWA during the
afternoon, showers and storms are expected to develop across the
forecast area during the heat of the afternoon. Highs in the low to
mid 90s across locales west of the Mississippi River, primarily
across the Delta, combined with dew points in the middle 70s will
cause heat indices to peak around 100F during the afternoon. Again,
any convection that develops during the afternoon, will begin to
wane around sunset. /19/
Tuesday night through next Monday morning:
The period will begin with convection slowly winding down through
mid- week & heat stress will be on the increase by mid-late week
before a cold front brings in increasing rain & storm chances &
relief to the recent heat stress issues.
At the start of the period, a strong deep upper ridge will be
centered over the western Plains into the Texas panhandle while
strong zonal flow/disturbance on the top of the mid-upper level
ridge will be moving through the northern Plains/Great Lakes &
through southern Canada while the troughing will be departing the
eastern seaboard. At the surface, a strong surface high will be
situated over the northeast with a lingering frontal boundary
extending southwest well into the Appalachians. Any disturbance
in the Gulf or any perturbations will be slowly on the decrease as
we approach mid-week. As the surface low and cold front shift well
off into the Atlantic Ocean, expect the stalled frontal boundary
to gradually shift east. This will help convection to slowly pull
east by Wednesday & into Thursday. PWs will slowly fall from
around 2+ inches currently on Monday to nearly 1.5-1.75 inches by
late Wednesday & into Thursday. This will help convection to
become more scattered and diurnal. Lapse rates/low-mid level flow
are weak so not expecting much in the way of strong storms.
Heat looks to be the main story as the strong ridging becomes more
amplified & pivots the ridge axis and increasing heights building
from west to east by Thursday & into Friday. This and increasing
boundary layer temperatures at 850mb, 20-21+ deg C each evening,
(some 90-97th+ percentile) will support warming back into the mid
90s or so. We should be able under full sun to reach up to around
95+ degrees, especially around Thursday and with the best warming
near 95-97 degrees in the Delta. With dewpoints peaking in the
low-mid 70s, heat stress will be on the increase. Expanded the
area in the graphic closer to I-55 but kept the HWO the same.
Couldn`t rule out some areas being expanded even more or a heat
advisory being possible as we get closer. The hottest and
muggiest day is expected on Thursday. Heat stress & heat related
illnesses will be possible. Make sure to drink plenty of water &
The pattern will change by late week & into the weekend as a cold
front moves into the area. The upper ridge axis will slowly
weaken its grip on our area and begin to build back to the west
over the western Plains & into the Rockies. In addition, a strong
deep trough will amplify over the eastern half of the nation,
east of the Rockies and into the Plains, as a strong surface low &
associated cold front traverse into the northeast CONUS. This
will help drive a more significant cold front with anomalous
moisture, near 2+ inch PWs & 345+K 850mb Theta E, in by around
Friday & especially Saturday. This will help more convection moving
in by Friday afternoon, with the bulk of the rain & storm chances
moving in by the weekend. This will help temper down our heat
stress issues. Lapse rates/flow look meager, but due to high
moisture, there could be some locally heavy downpours with this
cold front. Temperatures will slowly cool down into the mid-upper
80s due to increasing convection Saturday. As a strong high
pressure filters in the wake of the cold front, much drier air,
potentially near 1 inch or so, could move in by Sunday & into
Monday. This will bring temperatures a few degrees below average
and much drier conditions at least through the end of the period.
00Z TAF discussion:
Scattered to numerous showers and thunderstorms will continue
through 25/03Z which could quickly lower ceilings and visibilities
at affected TAF sites. Otherwise, MVFR conditions will develop
after midnight and linger until 25/14Z with improving conditions
thereafter. Scattered showers and thunderstorms will develop once
again by 25/16Z and continue through the end of the period./26/
.PRELIMINARY POINT TEMPS/POPS...
Jackson 74 89 74 94 / 55 47 15 22
Meridian 74 88 73 93 / 36 56 20 32
Vicksburg 73 91 73 95 / 32 46 12 11
Hattiesburg 73 88 73 92 / 50 60 20 35
Natchez 72 90 73 92 / 50 60 10 11
Greenville 74 92 75 96 / 38 30 12 11
Greenwood 75 91 74 94 / 55 43 15 16
Area Forecast Discussion
National Weather Service Jacksonville FL
849 PM EDT Mon Jul 24 2017
.UPDATE...Convection now gradually decreasing over se Ga but still
lingering as storms continue ahead of an mid/upper level trough.
Expect showers to persist til around midnight and then end as
models indicate...with the HRRR continuing the rain the longest.
Shower activity will get off to an early start Tuesday morning
with numerous showers/storms expected across se Georgia as the
trough pushes even closer to the area. Locally heavy rainfall will
be possible as PWATs remain near 2.25".
.AVIATION...VFR conditions will prevail tonight as shower activity
has ended across ne Fl and gradually decreasing over se Ga. Expect
showers and thunderstorms to affect ne Fl TAFs by early Tuesday
afternoon...and possibly by late morning at SSI.
.MARINE...SCEC offshore tonight as sw winds will reach the 15 to
20 knot range. Winds will be 10 to 15 knot range near shore. Seas
will be 3 to 5 feet. Showers and isolated thunderstorms possible
over mainly the Ga waters tonight.
Rip Currents: Low risk.
.PRELIMINARY POINT TEMPS/POPS...
AMG 75 90 74 89 / 40 70 40 70
SSI 77 90 77 87 / 60 70 50 60
JAX 76 92 75 90 / 20 50 40 60
SGJ 76 91 76 88 / 10 30 40 50
GNV 74 93 73 91 / 10 30 20 50
OCF 75 93 73 91 / 10 20 20 50
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
930 PM EDT Mon Jul 24 2017
A cold front will pass through the area tonight. High pressure
will build into the Mid Atlantic Tuesday before moving offshore
Wednesday. Another cold front will approach the area Thursday
before passing through Friday into Friday night. High pressure
is expected to return for the weekend.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Storms that developed in PA have outrun the cold front, which
looks to be pushing across the Alleghenies at 9 PM. The southern
extent of this line is currently moving across north central
MD. The 00Z IAD sounding shows 3000 J/kg of SBCAPE and about 40
kt of 0-6km shear, so the attendant severe threat (localized
damaging wind) is not a surprise. However, a mid level stable
layer is likely otherwise inhibiting storm development. Thus
it`s uncertain if any storms will develop along the outflow to
the south (affecting DC and areas to the southeast). While the
HRRR has been suggesting it`s possible, the 00Z run backed off.
Will have to watch radar, and have maintained chance POPs in the
forecast through 1 AM. After that time, the cold front will
likely have pushed through most of the CWA except perhaps
Afterwards some pretty nice weather for late July - the
climatologically hottest part of the year. Dewpoints will drop
into the lower to mid 60s by sunrise. Skies will be mostly clear
by morning. Lows west of I-95 will be in the mid to upper 60s,
lower 70s east.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
This will lead into a Tuesday with plenty of sunshine, dewpoints
in the lower 60s, and air temperatures reaching the lower to mid
Pleasant weather continues Tuesday night with lows in the mid
60s. Wednesday will see moisture begin to creep back into the
Mid Atlantic as high pressure moves offshore. Highs will reach
the lower to mid 80s. And with the return moisture lows will not
be as cool, falling to the upper 60s/lower 70s.
.LONG TERM /THURSDAY THROUGH MONDAY/...
Warm front lifts back north through the area early Thursday, which
will bring a return to the heat and humidity...as highs climb back
near 90F and dewpoints rise back into the 70s. Increasing chances
for showers and thunderstorms late Thursday into Friday as cold
front and its associated upper-level trough approach and then cross
High pressure builds into the area behind the front for the weekend
into early next week. Though, low pressure developing along the
front to our south could bring some precipitation back into SE
portions of the area Sunday. However, that is not the favored
solution at this point. Otherwise, remaining dry with highs in the
M80s and dewpoints in the 60s.
.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
The thunderstorm threat will be exiting the Baltimore area
between 10 and 11 PM. While no storms are currently targeting
DCA, will leave VCTS mention in case a storm fires along the
outflow. Cold front should then cross within a few hours of
midnight with a wind shift to the northwest.
High pressure will affect the area Tuesday and Wednesday. Will
have to watch for low cloud potential with onshore flow early
Showers and thunderstorms with brief flight restrictions are
possible ahead of a cold front mainly late Thursday into Friday.
Improving conditions into the weekend as high pressure builds into
Strong storms will affect northern portions of the Bay through
late evening. Cold front will then push through after midnight.
Some guidance hints at SCA potential in NW flow through Tuesday
morning. Will evaluate that threat over the next couple of
hours. Otherwise lighter winds through Wednesday with high
A cold front will approach the waters Thursday into Thursday night
before passing through Friday. Showers and thunderstorms are
possible ahead of the front...especially late Thursday into Friday.
A Small Craft Advisory may be needed for portions of the waters
Thursday and Friday. Improving conditions into the weekend as high
pressure builds into the area.
Straits Point may approach minor flood levels for the overnight
high tide cycle if water levels do not drop.
Area Forecast Discussion...UPDATED
National Weather Service Little Rock AR
614 PM CDT Mon Jul 24 2017
Updated to include the 00Z aviation discussion below...
Some isolated SHRA/TSRA will be seen over the next few hrs...but
should see any activity dissipate by later this evening. Some
patchy fog could be seen overnight...especially near sunrise.
However...not expecting any widespread dense fog at this time.
Some isolated SHRA/TSRA will again be possible on Tue...but will
only mention VCTS at this time.
.PREV DISCUSSION...(ISSUED 248 PM CDT Mon Jul 24 2017)
Short Term...Tonight thru Wednesday...
Convection has been a bit late to fire up across the area this
afternoon and latest HRRR runs show convection being more spotty
tonight. With that in mind I backed off on POPs just a bit for
As far as the general weather is concerned, the upper level ridge
will be building back over us during the short term, which will make
the issue of excessive heat a greater concern again. With dewpoints
remaining on the high side, many areas will be topping 105 degree
heat index values tomorrow, and again on Wednesday.
That said, I am issuing a heat advisory for tomorrow and Wednesday,
which will include the AR River Valley and the northeastern delta
areas. This meshes up with adjacent advisories being issued by Tulsa
and Memphis. While this advisory will remain in effect through
Wednesday...I should point out that it`s likely that the area will
have to be expanded to include a greater area on Wednesday.
Extended Term...Wednesday night through Monday...
A couple more hot days are expected at the start of the long term
across the state, but changes will slowly begin to take place by the
end of the work week. At the start of the period, significant
ridging aloft will continue just to the west of the state. At the
surface, high pressure will be centered to our south along the Gulf
Coast. This will provide abundant moisture and likely another day of
heat indices at or above 105 for many areas across the forecast
To the northwest of the state a cold front will be positioned and
will slowly move through the area from late Thursday into the day
Saturday. During this timeframe, rain chances will increase bringing
possible rainfall totals between one half to one inch across
northeastern areas, with less than one half inch elsewhere. As the
front moves through, the mid/upper level pattern changes
significantly (especially for this time of year) with significantly
elongated ridging setting up across the western US and deep
troughing across the east.
So, Arkansas will find itself between the two and under northwest
flow aloft this weekend, with northerly to even northeast flow by
early next week. What does this mean for us locally? In combination
with surface high pressure to the north, much drier and cooler air
will make its way into the state. Expect both daytime and nighttime
temps nearly 10 degrees below normal at times late this weekend into
the early part of next week. Some parts of northern Arkansas could
be looking at overnight lows in the 50s Sunday and Monday morning.
Heat Advisory from noon Tuesday to 8 PM CDT Wednesday FOR Conway-
Area Forecast Discussion
National Weather Service Medford OR
904 PM PDT Mon Jul 24 2017
.SHORT TERM...An upper low off the coast of northern California is
sending moisture into the area. This combined with instablity and
impulses moving into the area from the south is bringing isolated
to scattered thunderstorms inland areas this evening into
Storms developed from the Cascades eastward today with
isolated strong storms. Strong gusty winds and hail have occurred
with stronger storms. Also isolated heavy downpours are possible,
mainly in stronger and slower moving storms. Otherwise, rainfall
with storms have been light due to the dry subcloud layer.
Frequent lightning has occurred with these thunderstorms as well.
For late this evening into tonight, the high resolution model,
HRRR, shows thunderstorms and showers continuing especially from
the Cascades east, diminishing in coverage and intensity after
midnight. Showers and isolated thunderstorms are possible west of
the Cascades tonight as well, mainly over the Siskiyous and
Cascade foothills, but possible as well in western valleys in
Josephine, Jackson and Siskiyou county.
On Tuesday, thunderstorm activity is expected to be more
widespread across the area. Scattered storms are expected to
develop across Northern California and from the Cascades east. A
mix of isolated to scattered storms are possible in areas west of
the Cascades in Southern Oregon. Strong storms are again possible
on Tuesday with strong gusty winds and hail.
This active pattern continues into Wednesday as the upper low
moves inland as an open trough. This will bring a continued risk
for thunderstorms across the area with best chances from the
western foothills of the Cascades eastward, the Siskiyous and
across Siskiyou and Modoc county in Northern California.
.AVIATION...25/00Z TAF CYCLE...Along the coast and over the
coastal waters. Areas of MVFR/IFR cigs over the waters will spread
back onshore this evening and become widespread tonight and
persist through Tuesday morning. Low clouds are expected to
gradually lift and clear along the coast in the early afternoon.
Inland...areas of MVFR/IFR cigs will spread into the lower Umpqua
Basin late tonight...then burn back to the coast by late Tuesday
morning. KOTH will be affected by the lower cigs but at this time
it looks like KRBG will not be affected. Over the remainder of the
area...VFR conditions will prevail through Tuesday...but so will
isolated to scattered thunderstorm activity...especially east of
the Cascades. Strong gusty and erratic winds and local obscuration
of higher terrain will be likely near thunderstorms. Hail is also
possible with stronger storms. /CC
.MARINE...Updated 800 PM PDT Monday 24 July 2017...A thermal trough
will continue to produce gusty north winds and steep to very steep
seas through Tuesday, with gales south of Cape Blanco persisting
into Tuesday morning. The thermal trough will weaken mid week, and
winds will diminish slightly, but seas will remain elevated as
residual wind seas and fresh swell remain. At least small craft
conditions will remain in the area through Thursday. With weaker
thermal troughing then continuing through the weekend, somewhat
marginal winds and seas are expected into early next week, but small
craft conditions will be possible at any time. -BPN/CC
.PREV DISCUSSION... /Issued 238 PM PDT Mon Jul 24 2017/
DISCUSSION...An upper low will continue to spin off the California
Coast for the next couple of days bringing increasing moisture,
instability, and multiple shortwaves resulting in isolated to
scattered thunderstorms. The upper low will slowly move inland on
Wednesday with a continued chance of thunderstorms. The most active
days will be this afternoon, Tuesday and Wednesday before dry
weather returns Thursday.
The latest water vapor image shows the upper low spinning off the
California Coast near Point Area. Ahead of the low there is
plenty of instability and multiple shortwaves which are allowing
storms to light up. Right now, storms are mostly confined to Modoc
County, but storms are already starting to develop in portions of
Lake and eastern Kalamth Counties. The latest short range high
res HRRR run has been consistent showing storm development in
these areas during the afternoon and evening. Storms will to
continue develop and migrate north to northeast later this
afternoon into this evening with south winds between 10-15 kts
mainly affecting Lake and Klamath County. However, could not rule
out storms developing along the Cascades and portions of the
Siskiyous late this afternoon with the latest mesoscale analysis
showing surface based capes between 1500 and 2000 J/kg.
Additionally, some of the models show lots of instability even
here in the Rogue Valley (>1000 J/KG). While we can`t completely
rule out an isolated storm on the west side, model soundings also
show significant CIN (convective inhibition) and this will be the
main limiting factor to any convection west of the Cascades.
Storms today should be a bit wetter with PW values everywhere in
the 0.75-1.00" range late this afternoon, increasing to 1.00-1.25"
by this evening. Showers and isolated thunderstorms could linger
through the nighttime hours, but most should dwindle again with
the loss of instability.
Another active day is in the cards on Tuesday and could be the most
active days in terms of thunderstorm coverage and chances. The upper
low will remain just off the California coast, but it will tap into
more moisture. Instability is still greatest along and east of the
Cascades, but there is some evidence portions of the westside,
including the Rogue and Illinois Valleys could see more frequent
storms. Once again CIN is expected to be high, so we could miss out
again. Also there is a better chance for wetting rains as PWATS are
expected to increase with a swath of 1+ inches along and east of the
Cascades and portions of Northern California Tuesday afternoon. Also
winds at 700mb will be lighter, therefore storms could be slow
movers which means there is the potential for some of these storms
to produce moderate to heavy rain.
Nocturnal storms again are possible along with lingering overnight
showers and some remaining cloud cover Tuesday night as the upper
low slowly moves onshore and multiple shortwaves rotate ahead of it.
Right now it`s unclear how the area of storms shapes up, but we
could see a fair amount of activity.
Wednesday will be another active days as the upper low slowly moves
inland and opens up. All of the ingredients for thunderstorms will
be present again. However as the low/upper trough shifts east
Wednesday afternoon, we expect most of the action to also shift east
of the Cascades. However, keep in mind the models have been trending
slower with the inland progression of the upper low/trough,
therefore the details on this could change.
Dry weather will return Thursday and could last through next
weekend. A southwest flow will remain over our area with the ridge
centered near the four corners, but 500mb heights will gradually
increase and we could see temperatures get close to triple digits
for inland west side locations and low to mid 90s east of th e
Cascades. The models show the ridge retrograding west towards our
area next Sunday weekend into early next week with continued hot
temperatures for inland locations. -Petrucelli
FIRE WEATHER...Updated 230 PM Monday 23 July 2017...Currently
thunderstorms are limited to Modoc and Lake counties. There is more
moisture to work with today so lightning frequency should increase
as well. In addition, models are pointing to an area from eastern
Modoc north into Strawberry/Coffeepot RAWS then east into Harney
County where storms could produce wetting rain. This area is covered
by an LAL of 4. Southeast flow aloft continues and storms that form
in Siskiyou County could drift into southern Jackson County tonight.
Ashland may be affected but Medford is much less likely to see any
activity. Models also bring these storms into the Cascades around
this evening. SE flow could bring these storms into the west slope
of the Cascades this evening and tonight. Confidence is higher today
that the eastern Umpqua NF and High Cascade Fire Zone could see
thunderstorms tonight. Thunderstorm activity will continue through
Tuesday and spread farther west...affecting just about everywhere
except the coast.
Thunderstorm potential covers a much larger area than described in
the Fire Weather Warning/Watch. The area reflects forecasted LALs of
3 or more. The thunderstorm threat will diminish Wednesday afternoon
and evening as the upper low moves out to the east of the area and
westerly flow develops over the area. This however will likely lead
to breezy west winds during the second half the week.
OR...Red Flag Warning until 11 PM PDT Tuesday for ORZ617-622>625.
Fire Weather Watch from Wednesday morning through Wednesday
evening for ORZ617-623>625.
Red Flag Warning from 11 AM to 11 PM PDT Tuesday for ORZ620-621.
CA...Red Flag Warning until 11 PM PDT Tuesday for CAZ284-285.
Fire Weather Watch from Wednesday morning through Wednesday
evening for CAZ280-281-284-285.
Red Flag Warning from 11 AM to 11 PM PDT Tuesday for CAZ280.
Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Wednesday for
Gale Warning until 8 AM PDT Tuesday for PZZ356-376.
Hazardous Seas Warning until 5 AM PDT Wednesday for PZZ356-376.
Small Craft Advisory for hazardous seas from 8 AM Tuesday to 5
AM PDT Wednesday for PZZ350-370.
Hazardous Seas Warning until 8 AM PDT Tuesday for PZZ370.
Area Forecast Discussion
National Weather Service Mobile AL
847 PM CDT Mon Jul 24 2017
.DISCUSSION...See updated information for land areas below.
.UPDATE...Updated grids and forecast products a little earlier
this evening to reflect rapidly dissipating convection. Removed
Flash Flood Watch headline from southeast MS zones, as the FFA was
allowed to expire at 7pm. Also lowered PoPs from likely to chance
category for overnight hours. Otherwise, no changes required for
overnight forecast period. 12/DS
.PREV DISCUSSION... /issued 703 PM CDT Mon Jul 24 2017/
DISCUSSION...Updated for latest aviation discussion below.
25/00Z issuance...Convection has ended (for the time being) across
most of the forecast area, with only a few lingering showers
noted. Primarily mid-upper level clouds with no restrictions to
vsby expected at terminals through much of the evening and into
the early predawn hours Tuesday. Will likely see convective
redevelopment late tonight however, especially near the coast,
where ocnl IFR conditions return in and near showers and
thunderstorms. Scattered convection expected across much of the
area, especially over land areas Tuesday. Light southwesterly
surface winds (3-6 knots) expected through tonight into early
Tuesday, increasing slightly during the afternoon Tuesday (8-12
knots) before subsiding again after sunset Tuesday evening (3-6
PREV DISCUSSION... /issued 551 PM CDT Mon Jul 24 2017/
DISCUSSION...Updated for latest aviation discussion below.
24/18z Issuance Update...Made a few adjustments to TAFs as most of
the convection has ended (for the time being), especially along
the coast and at the air-terminal forecast locations. Primarily
mid-upper level clouds with no restrictions to vsby expected
through much of the evening. Will likely see convective
redevelopment late tonight, especially near the coast, when ocnl
IFR conditions return in and near showers and thunderstorms. Light
southwesterly surface winds expected through tonight into early
PREV DISCUSSION... /issued 420 PM CDT Mon Jul 24 2017/
NEAR TERM /Now through Tuesday/...An upper level trough axis
continues to extend southwest from the Eastern Seaboard through
central and southwest AL, southeast MS, and back into LA this
afternoon. Weak impulses embedded within this larger scale feature
moving across the region, along with convergence along an axis of
deep moisture (precipitable water values locally enhanced between
2.2" and 2.4") has resulted in a training complex of showers and
thunderstorms across portions of southeast MS today, particularly
Stone county, where multiple rounds of heavy rain resulted in
rainfall amounts of 4" to 8" across much of the county and isolated
amounts approaching 12" in the far northwestern part of the county.
Farther east, convection has been more limited today given a bit
more subsidence east and south of the convection over MS. It is
interesting to note that a mesoscale convective vortex (MCV) is also
noted across Washington/Clarke counties on visible satellite and
radar imagery as of 340 PM - and lift ahead of this feature was
resulting in some scattered convective development in the far
northern and northeastern part of the area.
A challenging forecast continues across our local area through the
next 24 hours. Latest mesoscale model trends have been consistent
with gradually diminishing convection over southeast MS into the
early evening hours. Still some opportunity for lingering showers
into late afternoon/early evening and have kept POPs fairly high
over southeast MS for through early evening, and more scattered
coverage farther east over the rest of the area. The upper trough
axis will hold overhead through the rest of tonight and again into
the day Tuesday. We have maintained at least a chance of
showers/storms into the local area through the night given the
presence of this feature and continued moist environment. We have
decided not to extend the Flash Flood Watch for southeast MS past 7
PM for now as convection should be diminishing in coverage. However,
will need to watch trends overnight/early Tuesday morning carefully,
as if additional convection re-develops near Stone county, it won`t
take much rain to exacerbate flooding problems. The past couple of
runs of HRRR and a look at the WRF-ARW are not as robust with
convective development tonight. Later shifts will monitor trends
Expect additional scattered to numerous showers and storms to re-
develop inland over the area through the day Tuesday. Given the
quality of moisture over the region, a few storms could once again
be capable of producing very heavy rainfall and perhaps localized
flooding. Lows tonight range in the lower to mid 70s inland, and mid
to upper 70s along the beaches. Highs Tuesday should range in the
mid 80s to around 90 degrees. /21
SHORT TERM /Tuesday night through Thursday night/...Guidance has
come into better agreement with the handling of an upper trough
over the Lower Mississippi River Valley. Guidance is advertising
the upper trough stretching as it shifts southeast towards the
northeastern Gulf Coast, then the northeastern Gulf. This will
allow an upper high over the Southern Plains to build east over
the Lower Mississippi River Valley. A surface ridge that has built
west over the northern Gulf of Mexico gets split, leaving a
surface high centered over the western Gulf and a surface ridge
stretching west from the Florida Peninsula.
With the upper trough overhead into Wednesday, the chance of rain
remains above normal, though is decreasing. Wednesday on, with the
splitting surface ridge, northwesterly flow brings in a drier
airmass as compared to the current tropical soup over the forecast
area. Through the short term, with the Southern Plains upper
ridge building east, increased subsidence will work with the
decreased moisture levels along with weakening upper support to
decrease the chances of rain into mid week, along with increasing
temps. Overnight lows around seasonal expected (low to mid 70s,
upper 70s along the coast) with daytime highs well above seasonal
( mid 90s expected with around 90 close to the coast). With the
increasing highs, a return of high Heat Indices returns, with
Wednesday seeing Heat Indices topping out in the 102 to 107 degree
range over most of the area.
LONG TERM /Friday Through Monday/...Guidance is advertising
shortwave energy digging an upper trough over the East Coast. The
first round of shortwave energy moves south across the forecast
area late Friday into Saturday. A return of a bit below seasonal
temps for Sunday is expected with above seasonal chances of rain.
A second round moving southeast across the eastern Conus is not so
consistently handled by the guidance Sunday on. The ECMWF keeps
it well north of the area, whilst the GFS digs it farther south,
hot on the heels of the first round of shortwave energy. Both
ultimately organize the energy into a closed low Monday, with the
GFS advertising it over the Southeast, the ECMWF over the
Tennessee River Valley. The quicker GFS solution also brings in a
drier airmass behind the first round, resulting in a significantly
drier forecast in the Sunday through Monday time frame. The ECMWF
solution brings a decrease, enough of a decrease in moisture to
advertise a decrease in PoPs, but still advertise scattered
daytime/evening shra/tsra. consensus leans towards the ECMWF
solutions, with temps and PoPs around to a bit below seasonal.
MARINE...A ridge of high pressure will gradually build across the
central Gulf of Mexico this week. A light to moderate westerly wind
component generally prevails. Winds, waves and seas will be locally
higher with the passage of storms. Frequent lightning activity
likely in and near any of the stronger marine storms. A few
waterspouts remain possible, mainly with overnight and early
morning storms. /21
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Area Forecast Discussion
National Weather Service Portland OR
245 PM PDT Mon Jul 24 2017
.SYNOPSIS...Expect a mix of morning clouds along the coast and lower
Columbia River valley, plenty of afternoon sunshine and high
temperatures near to slightly above average for much of the next
.SHORT TERM...Today through Thursday...Overall expect few noticeable
changes to our weather over the next few days. Southwesterly to
westerly flow aloft and low level northwesterly flow will continue to
produce some morning clouds along the coast and lower Columbia River
valley with plenty of sunshine elsewhere. High temperatures will cool
closer to seasonal averages towards Thursday.
The primary issue in the short term is a small thunderstorm threat
across primarily the Lane and Linn County Cascades through Tuesday.
This is in response to moisture and instability sneaking its way
northward into the region due to an upper level low pressure
currently spinning off the California coast. This low pressure is
forecast to slowly shift eastward over northern California over the
next couple of days, which should produce few changes between today
and Tuesday across Lane and Linn Counties. Even though the GFS model
produces QPF bullseyes over eastern Lane County both afternoons,
model soundings do not appear conducive for surface based convection
given a sizeable cap. The HRRR and NCAR ensemble do suggest that
storms over eastern Douglas and northern Lake and Klamath Counties
could sneak their way towards Willamette Pass later this evening and
overnight as outflows intersect so kept a slight chance mention for
this period near the immediate Cascade crest.
As the aforementioned upper level low pressure shifts inland,
southwesterly to westerly flow aloft should increase just enough
Wednesday and Thursday that any thunderstorm development should
remain east of the Cascade crest. This will also help to produce
more marine clouds along the coast and lower Columbia River valley
Wednesday and Thursday, which should help to cool temperatures
closer to seasonal averages. Both the GFS and EC suggest some light
showers could impact the northern coastal zones Wednesday morning.
Given the instability appears quite shallow in model soundings, kept
PoPs below mentionable criteria for now. /Neuman
.LONG TERM...Thursday night through Monday...Onshore flow from a
series of weak shortwave troughs will continue through next week.
This will maintain near normal temperatures with low clouds at the
coast most mornings. No chance of precipitation or thunder during
this time. -Bishop
.AVIATION...VFR across the area as of 20Z, except for a narrow
ribbon of IFR stratus/fog from near Tillamook Bay south to
Florence. Expect the current IFR stratus/fog area to extend
inland to the coastal valleys by around 04Z and possibly reach
the west slopes of the Central Oregon Coast Range by 07Z. IFR
returns to the North Oregon coastal strip around 04Z and up the
Columbia River to near KKLS overnight. Elsewhere, VFR to prevail
through Tue afternoon.
Cannot rule out some TCU or CB developing in the Cascades E-SE of
KEUG this late this afternoon into the evening. Thunder is not
expected for any of our terminals, but is a possibility in the
Lane County Cascades, although the likelihood appears less
probable based on latest model guidance.
KPDX AND APPROACHES...VFR through Tue afternoon. Surface wind
gusts to around 20 kt late this afternoon through the evening.
.MARINE...Strong north wind continues over the waters today.
Several models indicating 20-25 kt boundary layer wind speeds
with gusts to 30 kt through late evening. A few gusts to 35 kt
can be expected over PZZ255 and PZZ275. Latest model runs suggest
wind speeds ease just a bit Tue, but will extend the Small Craft
Advisory for all waters through late Tue night. The pressure
gradient and associated surface and boundary layer wind speeds
ease even more Wed through late week.
Very steep and choppy sea conditions to persist for the next
couple of days. This is nearly a uni-wave pattern with spectral
guidance showing a wind wave component up to 8 ft at buoy 050
this afternoon through Tue, with a minimal background swell.
Combined seas could briefly reach 10 ft at times this afternoon
through the evening. However, the combination of at least 7 ft
seas with 6-8 seconds periods constitutes hazardous sea
conditions. Slightly less fetch and gradually decreasing wind
over the next couple of days will result in less wind wave
component. However, expect choppy conditions to continue through
at least mid-week. Overall, seas subside to 4 ft or less Wed
and hold through late week. Weishaar
PZ...Small Craft Advisory until midnight PDT Tuesday night for
Coastal Waters from Cape Shoalwater WA to Cascade Head OR
out 60 nm.
Small Craft Advisory until 2 AM PDT Wednesday for Coastal
Waters from Cascade Head OR to Florence OR out 60 nm.
Small Craft Advisory for Rough Columbia River Bar from 4 PM
this afternoon to 8 PM PDT this evening.
Small Craft Advisory for Rough Columbia River Bar from 3 AM to
7 AM PDT Tuesday.
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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.
Area Forecast Discussion
National Weather Service Phoenix AZ
845 PM MST Mon Jul 24 2017
After a very active period over the past few days, drier
southwesterly flow aloft is expected to bring warmer temperatures
along with fewer storms across the region Tuesday through Thursday.
More active monsoon conditions return by next weekend.
After a very active period (especially across South-Central AZ) from
yesterday afternoon into today, due to a weak shortwave rotating
northward across the region interacting with a very moist airmass,
it has turned out to be a much quieter evening across he region. The
reduction in convective activity is likely due to a heavy worked-
over airmass, anticyclonic flow behind the shortwave, and the
beginnings of some mid-level drying (as seen on the latest KPSR
balloon sounding). The only convective activity that is occurring in
our cwa at this time is over SW AZ and Se CA, mainly at locations
that have seen much less convective activity over the last 24 hours.
As far as the forecast for the rest of tonight and early Tuesday is
concerned, recent HRRR high-res model runs are showing the
afomentioned activity over SE CA/SW AZ decreasing through the rest
of tonight, with little or no additional convective activity
expected through the early/mid morning hours on Tuesday, as
drier/more stable air moves into the region from the south and east.
Thus, have reduced POPS in the gridded forecasts during this period.
Tuesday still looks like it will be a rather quiet day (compared to
the last 2 weeks), as mid-level drying continues.
Short-term satellite and radar trends show drier air aloft has
quickly spread northward, effectively ending chances for rainfall
temporarily across the Phoenix area. Rainfall has persisted across
west-central Arizona within a band of richer moisture, and
flooding concerns remain elevated there through the mid-afternoon.
Otherwise, isolated thunderstorms have developed from northern
Pima County east-northeastward into southern Gila County, where
stronger heating has occurred this morning and early afternoon.
Rainfall appears to have stabilized the air mass sufficiently to
prevent any sustained convection from moving north of I-8 towards
Phoenix. With a couple more hours of heating, it`s possible the
air mass could recover enough to support isolated thunderstorms
into the Phoenix area this evening, but confidence is low.
Another area of short-term concern will be across southwest
Arizona and southeast California, where the air mass is relatively
unperturbed but very moist. There is certainly potential for
strong thunderstorms with heavy rain across these areas, but
forcing for ascent remains more nebulous.
Still anticipating a trend towards warmer/drier conditions through
the middle of the week as the primary anticyclone aloft redevelops
westward out of the Southern Plains towards the Four Corners.
However, this should remain short-lived as the anticyclone
eventually shifts northward, and the eastern Pacific becomes more
active, which could supply moisture to the Southwest this weekend
into early next week. No changes have been made to the extended
forecast given the short-term concerns.
Tuesday through Sunday...
With a lot less moisture available, look for quiet a downtrend in
PoPs (limited to south-central AZ - mainly higher terrain). Temps
climb as well but not out of hand. Late in the week and over the
weekend, a more favorable flow pattern sets up. Plus it appears
there will be a tropical storm of some sort passing south and west
of Baja which helps advect moisture back into the region. Thus a
gradual return of PoPs from east to west. Temps nudge down as
South-Central Arizona including KPHX, KIWA, and KSDL:
A rather quiet period appears to be in store through Tuesday as
drier/more stable air moves into the region with winds becoming
light easterly at all of the terminals by late this evening, under
mid-high level sct-bkn cigs. Storm development on Tuesday will
likely remain well to the north and east of the taf sites, with
winds becoming westerly by late afternoon.
Southeast California/Southwest Arizona including KIPL and KBLH:
A rather quiet period across SE CA as well, with sct-bkn mid/high
level cigs prevailing across this region as well. Winds to remain
mainly out of a southeasterly direction at KIPL and a southerly
direction at KBLH through the taf period.
Aviation discussion not updated for amended TAFs.
Thursday through Monday:
Humidities and storm chances begin to increase Thursday with
chances reaching southeast California by Saturday. Temperatures
will be near normal Wednesday and Thursday (a bit above normal
near and west of the Lower Colorado River Valley) before beginning
to decrease late this week. Apart from thunderstorms, winds will
follow familiar warm season patterns.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
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Area Forecast Discussion
National Weather Service Blacksburg VA
934 PM EDT Mon Jul 24 2017
A weak cold front will slide southeast through the area tonight
before stalling over the Carolinas Tuesday into Wednesday. High
pressure builds north of the region behind the front bringing a
return to more seasonal temperatures later tonight through mid
or late week. Another cold front approaches from the northwest
on Friday and works slowly through the area by the weekend.
.NEAR TERM /THROUGH TUESDAY/...
As of 930 PM EDT Monday...
Lingering showers Mountain Empire/NRV will be dissipating
shortly as approaching weak frontal boundary starts moving into
the region from the northwest. Clouds will then gradually
decrease overnight and it will feel a bit more comfortable with
lows overnight in the low/mid 60s west of the Blue Ridge, upper
60s/around 70 to the east.
This front should finally slide southeast and across the region
later this evening as the upper trough to the north swings by
to the northeast. Should see clearing take shape overnight as
the front sags to the south allowing for a bit more comfortable
air to advect into the mountains where expect lows well into the
60s. Moisture may linger across the south/east so kept lows
mainly upper 60s to lower 70s there. Also despite good drying
today, appears some fog/stratus development possible espcly
valleys given heavy rain from last night and better radiational
cooling west tonight.
High pressure builds in from the north on Tuesday with weak
northerly flow resulting in enough dry advection to limit most
convection to across far southern sections at best. This seen
via model lowering of PWATS from north to south and axis of
deeper moisture well to the south closer to the residual surface
front. Therefore reduced pops to slight chance mainly across
northwest NC where perhaps enough low level moisture/instability
may linger to pop a shower or two but iffy. Otherwise enough
subsidence for overall mostly sunny skies and not quite as
hot/humid with highs low/mid 80s mountains to 87-92 east of the
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 1245 PM EDT Monday...
Little change in the weather pattern and no synoptic scale forcing
Wednesday and Thursday. Will keep minimal probability of
precipitation, mainly in southern Virginia and northern North
Carolina each afternoon and evening. Persistence combined with bias
corrected MET/MAV guidance will be reasonable for daily highs and
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 1245 PM EDT Monday...
Upper pattern amplifies starting on Friday with the upper ridge over
the western United States slightly retrograding and a trof digging
in the east. An upper low may eventually close off somewhere over
the Tennessee Valley or Mid Atlantic region by Sunday or Monday.
This closed low solution was not supported by a majority of the
extended guidance. Probability of showers and thunderstorms will
increase on Friday and Saturday with some vorticity advection and
lowering heights. Air mass ahead of the trough stays in the +16 to
+20 range for temperatures at 850MB and will be a little cooler on
Sunday and Monday.
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
As of 745 PM EDT Monday...
Line of showers and isolated thunderstorms stretches from DCA to
JFZ, very close to the I-81 corridor at this hour. Activity
associated with final short wave tracking through the base of
the northeastern U.S. upper trough. Latest HRRR has this
activity persisting for another couple of hours, especially in
the far southwest VA/northwest NC area, then dissipating quickly
toward 03Z. Have indicated this trend in the grids and TAFs,
with the only TAF to include VCTS at this time BLF due to a
nearby TSRA in Tazewell county. Have included VCSH at BCB and
LYH because of nearby activity that could affect these sites
before they dissipate in the next couple of hours. Ceilings
associated with these showers are mostly in the 040-050 range.
Concerns overnight mainly focus around fog development and
possible low cloud development along the Alleghany front. Will
discuss the later first as that possibility seems limited due to
decreasing upslope W-NW flow becoming near calm or light and
variable, possibly even light northeast. Will include for now as
it remains a possibility per model soundings. Fog development at
LWB and BCB especially seems a better possibility due to recent
rainfall, hence moist ground in the area, clearing skies, and near
calm winds. Have continued earlier thinking on this and
continued potential for IFR-LIFR FG at BCB and LWB in the 08Z-
12Z time frame. Will hold off on fog elsewhere, although MVFR BR
conditions at LYH and DAN do not seem out of the question, just
not enough confidence to include at this time.
Winds will be light WSW-WNW 4-6kts this evening, becoming calm
overnight at most sites. Winds will be light and variable
Tuesday, but good potential for light northeast winds east of
the Blue Ridge.
Medium confidence in ceilings through 13Z, then high confidence
in VFR ceilings.
Medium to high confidence in visibilities through 13Z, then
high confidence in VFR visibilities.
Medium to high confidence in wind speed and direction through
the TAF valid period.
Aviation Extended Discussion...
A frontal boundary will remain stalled to our south through Wed,
with high pressure wedging southward on Wed from the northeast
U.S. Overall VFR, but with flow turning more east, this could
bring some MVFR/IFR ceilings, which should quickly dissipate by
Thursday. Any convection also likely to remain isolated and
south of the TAF sites again later Wednesday. Next best threat
for showers and storms arrives late Thursday as a new front
approaches from the north with more widespread activity in the
area Friday as the front drifts slowly southeast through the