Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/10/19
Area Forecast Discussion
National Weather Service Jacksonville FL
1048 PM EDT Thu May 9 2019
...HURRICANE HUNTER AIRCRAFT WILL BE AVAILABLE FOR PUBLIC TOURS
AT BRUNSWICK GOLDEN ISLES AIRPORT ON FRIDAY AFTERNOON...
.Update...
Late evening surface analysis depicts strong high pressure (1029
millibars) centered just east of Cape Cod and wedging down the
U.S. eastern seaboard. Meanwhile, a cold front extends from the
eastern Great Lakes region southwestward through Deep South Texas.
Aloft...ridging centered over the Yucatan peninsula is flattening
but has deflected a potent shortwave trough northeastward through
the upper Midwest, while weak shortwave troughs are embedded
within deep southwesterly flow that extends from the western Gulf
of Mexico across the southeastern states. The easternmost
shortwave in this deep southwesterly flow pattern is progressing
across southwestern Georgia and has developed persistent
convection just west of our region, with a line of showers and a
few embedded thunderstorms making very slow eastward progress
towards the Ocmulgee River. Otherwise, slow moving shallow
convection that developed over southwestern Marion County has
dissipated. Nighttime infrared satellite imagery indicates that
mid-level cloudiness downstream of this convective complex are
migrating towards coastal northeast and north central Florida,
while anvils are moving over inland southeast Georgia and the
western Suwannee Valley. Temperatures as of 02Z were mostly in the
mid to upper 70s, with dewpoints in the mid and upper 60s.
Latest LAPS analysis depicts a slow increase in instability over
our western counties, with SB-CAPE values now in the 250-500 j/kg
range in place now that the Atlantic sea breeze boundary has
moved westward through our region. Short-term, high resolution
models continue to bring weakening convection towards the I-75
corridor shortly after midnight before activity completely
dissipates before the predawn hours for locations west of a line
from Waycross to Live Oak. We will not raise POPs appreciably due
to the trends in the evening model guidance and the very slow
movement of the convection to our west thus far. Otherwise,
convergent onshore winds may develop a few brief showers over the
near shore waters and area beaches towards sunrise. Debris
cloudiness will increase from west to east overnight, which should
negate significant fog development overnight. Lows will only fall
to the upper 60s inland and the lower 70s at the coast. Shortwave
energy migrating through the southeastern states will likely
develop widely scattered convection over inland southeast Georgia
and the western Suwannee Valley on Friday afternoon and early
evening. Onshore winds will keep coastal highs in the low to mid
80s, while inland highs soar to near 90.
&&
.Aviation...
Periods of MVFR ceilings around 1000-1500 feet are possible after
06Z through around 14Z at the regional terminals. Otherwise, VFR
ceilings of 6000-9000 feet will prevail through around 06Z.
Southeasterly surface winds will remain sustained around 10 knots
through 06Z at the coastal terminals before decreasing during the
predawn hours. A few showers will be possible at the coastal and
Duval County terminals after sunrise through around 16Z, with
widely scattered afternoon thunderstorms possible at GNV and VQQ,
where VCTS was placed in the evening TAFs due to uncertainty in
timing and intensity on Friday afternoon. Light southeasterly
surface winds will develop after sunrise and will shift to east or
east-southeasterly after 18Z, with speeds increasing to 10-15
knots at the coastal terminals.
&&
.Marine...
Strong high pressure centered off of coastal New England will
slowly weaken as it slides southeastward towards Bermuda by early
Saturday. A long period northeasterly ocean swell is combining
with a long fetch of southeasterly winds to create Caution
conditions on the offshore waters, where sustained winds overnight
will be in the 15-20 knot range with seas of 4-6 feet. Sustained
winds near shore tonight will be around 15 knots with 3-5 foot
seas. Caution level seas will continue through Friday offshore as
the long period swell only gradually subsides. Meanwhile, low
pressure will develop over southeast Texas on Friday night and
will strengthen as it accelerates northeastward, reaching the
Tennessee and Ohio Valleys by Saturday night. Winds will veer to
south-southeasterly by early Saturday and then south-
southwesterly by late Saturday night, with the evening wind surge
on Saturday bringing speeds up towards Caution levels offshore.
This system`s cold front will move into the southeastern states
on Sunday, with southwesterly winds strengthening and showers and
thunderstorms gradually increasing in coverage by Sunday evening.
Winds should reach Caution levels offshore Sunday night, and
showers and thunderstorms should continue to increase in coverage
on Monday as the front slowly moves southeastward across our
region. Outside of thunderstorm activity, westerly winds should
remain at Caution levels offshore on Monday, with seas of 2-4 feet
forecast. Weak high pressure will then push into our region from
the northwest on Monday night and Tuesday, with winds shifting to
west-northwesterly by Monday evening and speeds falling below
Caution levels. Light onshore winds are expected by Tuesday
afternoon as a weak pressure gradient prevails over our area.
Rip Currents: A persistent long period northeasterly ocean swell
will combine with onshore winds to create another high risk of rip
currents on Friday at the northeast Florida beaches, with a
moderate risk expected at the southeast Georgia beaches.
&&
.PRELIMINARY POINT TEMPS/POPS...
AMG 66 89 67 91 / 10 40 30 40
SSI 72 83 71 84 / 10 20 10 10
JAX 69 87 68 89 / 10 20 10 20
SGJ 71 85 71 85 / 10 20 10 20
GNV 67 89 67 90 / 20 20 10 10
OCF 69 90 68 91 / 20 20 10 10
&&
.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.
&&
$$
Nelson/McGinnis
Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
505 PM MST Thu May 9 2019
.UPDATE...Updated aviation discussion.
&&
.SYNOPSIS...
Unsettled weather will continue across the Desert Southwest as a
cutoff low develops off the coast of southern California and
slowly pushes across the Desert Southwest this weekend. This will
continue to support cooler than normal temperatures with increased
rain chances beginning on Friday through the weekend. The best
chances for widespread showers and isolated thunderstorms will be
on Saturday and Sunday afternoon as the storm system moves east
across the region. Rain chances will into Monday for locations
north and east of Phoenix before warmer and drier weather finally
returns to the region during the middle of next week.
&&
.DISCUSSION...
Showers and thunderstorms have developed across northern Arizona
this afternoon in response to a shortwave trough that is currently
deepening over the Great Basin into southern California. This has
caused an increase in south-southwest flow aloft over the southern
half of the state with westerly flow over the northern half of the
state to prevent these storms from pushing south into the lower
deserts. Very isolated convective showers are attempting to
develop over the higher terrain of northern La Paz County where
PWAT values remain above 0.8 inches and some modest instability is
in place as moisture and warm air advection surges northward over
the Colorado River Valley. However, aircraft soundings in the
region show some midlevel stability supported by modest 6.5 deg
C/km midlevel lapse rates on SPC Mesoanalysis that should prevent
deeper development. This modest warm air advection at low levels
has helped most lower desert locations to warm up into the upper
80s and lower 90s despite high clouds aloft.
Surface moisture/dewpoints will steadily increase throughout the
evening and overnight hours as a second shortwave trough quickly
moves southwestward through the Great Basin. This will reinforce
the shortwave trough over southern California before it becomes
cutoff just of the Pacific coast by tomorrow evening. Hi-res
models are showing scattered to widespread light shower activity
over Gila County overnight in response to isentropic ascent and
diffluent flow ahead associated with a shortwave rotating around
the main low center. A few hi-res models also show some isolated
convective showers and possibly a thunderstorm over Yuma and La
Paz Counties along with higher terrain locations in Riverside
County including Joshua Tree NP tomorrow afternoon, but modest
lapse rates should generally prevent thunderstorm development.
Most lower desert locations will be dry due under mostly cloudy
to cloudy skies that should keep temperatures down in the lower to
mid 80s across the lower deserts.
The upper level low is forecast to deepen Friday night as it sits
just off the southern California coast while a west to east upper
level jet max in the base of the trough also strengthens. This
will keep difluent flow aloft over the southern half of Arizona
with the upper level cold core situated near southeast California.
High clouds will also thin on Saturday resulting in better
daytime heating and steeper lapse rates. These factors point
toward better shower and thunderstorm chances beginning Saturday
afternoon, likely lasting through Sunday as the upper level low
center tracks eastward along the Arizona/Mexico border. Model PoPs
vary quite a bit this weekend, but generally show best chances
across southeast California on Saturday, transitioning eastward
into Arizona late Saturday night into Sunday. The best chance of
thunderstorms over the Phoenix metro continues to be on Sunday
afternoon as the cold core upper low passes through southern
Arizona or northern Sonora. PWATs will remain in the 0.8-1.0 inch
range through the entire weekend into possibly Monday to support
some heavy downpours. In addition, CAPE values around 100-500 J/kg
will support isolated thunderstorms and a fairly dry sub-cloud
layer indicating some gusty outflow wind potential. Rainfall
amounts will mostly be light, but any organized areas of showers
or thunderstorms may bring over a half an inch of rain.
The upper level low is forecast to push into New Mexico on Monday,
but residual moisture and modest lapse rates should bring at least
a few showers or thunderstorms to the eastern Arizona high terrain
Monday afternoon into Tuesday. In the wake of the exiting low,
temperatures will start an upward climb Monday, eventually
reaching near normals during the middle part of next week with
temperatures approaching the upper 90s by Thursday. Yet another
relatively deep Pacific trough is forecast to move into California
by Friday to likely stop this warming trend and keep 100 degree
temperatures at bay through next weekend.
&&
.AVIATION...Updated at 0005 UTC.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The greater Phoenix area will see a short break with respect to
potential showers or storms as very weak transitory high pressure
aloft moves overhead. Still, we will see a fair amount of clouds
over the terminals. Cirrus CIGs this afternoon will continue, with
BKN mid decks developing later this evening as a weak impulse moves
into southern Gila County ahead of the next main developing upper
low. After 06z, TAFs have CIGs around 10k which will remain into the
morning hours Friday. There will also be low level moisture feed
into the central deserts Friday leading to FEW-SCT cumulus decks
around 5-7k feet. Don`t really expect CIGs at this level but cannot
rule it out at least for a portion of the afternoon on Friday.
Winds have been rather problematic this afternoon and were having
problems turning from the southeast to the southwest. For now, most
signals indicate we should see SSW or SW winds at the TAF sites
after 5-6pm, continuing through the evening before becoming light
variable and eventually southeast again. Most speeds should be less
than 12kt. Again on Friday morning the southeast winds will become
more southerly and remain so through much or most of the afternoon
on Friday.
Southeast California/Southwest Arizona including KIPL and KBLH:
Conditions should be rather quiet across the western deserts tonight
as weak high pressure aloft is in place ahead of the next Pacific
low that will bring showers later tomorrow and into Saturday. Look
for variable amounts of mainly high clouds tonight; after 12z Friday
a thick low level moist feed spreads in from the west leading to SCT-
BKN decks in the 5-6k foot range. It is possible that virga or even
a few showers could form if the moisture becomes thick enough but
confidence is too low for now to mention a shower threat in the
TAFs. Could see adding at least VCSH in the later TAF packages.
Otherwise, winds should be relatively light next 24s hours. At KIPL
they will favor the west except for a few hours early this evening
when lingering southeast wind may continue at the terminal. Also,
cannot rule out a few westerly gusts to around 20kt during the mid
evening hours. Winds at KBLH to favor the south next 24 hours
typically between 8 and 15kt.
Aviation Discussion not updated for amended TAFs.
&&
.FIRE WEATHER...
Sunday through Thursday:
A slow-moving cutoff low pressure system moving across the region
will result in cooler than normal temperatures, elevated humidity
values, and increased chances for light showers and thunderstorms
over most districts on Sunday and Monday. Showers and at least
isolated thunderstorms capable of producing pockets of wetting
rains are likely over higher elevations and possibly the lower
deserts, with the best chance of thunderstorms on Sunday and
Monday afternoon. Minimum humidity levels will be quite moist for
May standards only falling into a 25-35 percent range through
Monday. Occasional breezy afternoon winds will exist with the
approach of these weather systems, but winds may become light and
variable over the weekend into Monday as clouds and showers settle
over the area. Drier and warmer conditions should begin to filter
into the region by the middle of next week with rain chances
confined to Gila County on Tuesday and all spots dry on Wednesday
as minimum relative humidity values drop into the teens.
&&
.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected for the next 7 days.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Hopper/Kuhlman
AVIATION...CB
FIRE WEATHER...Hopper/MO