Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/21/20
Area Forecast Discussion
National Weather Service Denver/Boulder CO
813 PM MDT Mon Jul 20 2020
.UPDATE...
Issued at 800 PM MDT Mon Jul 20 2020
Outflow boundaries have been affectng the plains this evening,
however, not much has developed except for a few weak storms over
Douglas county. Meanwhile there are a few stronger storms over
sern WY which are moving southeast. At this time it`s hard to say
whether they will hold together or not as they approach the CO
border by around 10 pm. For now will leave in some low pops thru
midnight in case these storms hold together.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 300 PM MDT Mon Jul 20 2020
A circle of convective initiation is occurring over our area of
responsibility, as the center remains capped under a stable layer
around 730 mb. Northwesterly flow aloft has increased slightly
from a shortwave trough moving over the Northern Great Plains. The
current storms are expected to remain as when the cap is weakened,
the CAPE values are in the 2000-3000 J/kg out east, and 800-1200
J/kg further west. Hail up to ping pong ball size with the
strongest storm and gusts up to 65 mph will be the hazards out
east, further west winds may gust up to 50 mph with small hail. CAMs
continue to show outflow from the storms out east of Lincoln
County to push back west and spark new convection. Some are a bit
more robust, especially back toward the urban corridor where drier
dewpoints are. With ACARS soundings, the cap isn`t that strong,
so wouldn`t discount these models. Storms should remain most
numerous over the northern, southern borders of the area where
terrain is higher or near a pseudo- dryline the rest of this
afternoon. Then storm outflow activity will likely fill it in
later into the evening. Seems as though another MCS will form
tonight and push another outflow after midnight back west into the
area. Will see stratus fill in most of the plains and into the
foothills. Some downsloping off the Palmer will likely keep it
clear there.
With the additional moisture pushed into the area Tuesday, and
shear increasing as well, the threat for severe storms will be
increasing. The morning stratus will limit some heating so
temperatures will be a few degrees cooler. Still, CAPE values of
near 4000 J/kg are forecast over the far northeastern corner. Large
hail and strong damaging outflow winds will be the main hazards,
along with brief heavy rain due to PW values near 1.5 inches out
there. Storms will initiate over the high terrain by the noon
hour, with more concentration along and south of I-70, then begin
to march east.
.LONG TERM...(Tuesday night through Monday)
Issued at 300 PM MDT Mon Jul 20 2020
Strong to severe thunderstorms are expected to become more
organized and spread east across the plains Tuesday evening as
they encounter a weakly capped and CAPE rich airmass. Main threat
will be large hail and heavy rain, as MLCAPEs are expected to
be around 2000 j/kg, and precipitable water (PW) values grow to
1.25-1.5 inch. Meanwhile, the Denver area and Front Range should
clear fairly quickly of any storms during the evening as the
airmass will be mostly worked over from the afternoon/early
evening convection.
For Wednesday, the upper level ridge is expected to amplify over
eastern Colorado. This will occur in advance of an approaching
short wave trough that moves toward the state late in the day.
This will aid convective coverage in the high country, while it
could be a late show or even a no show day for the Front Range
I-25 Corridor if the upper level support arrives too late to
provide some cooling aloft. Temperatures will be returning to
above normal readings given the upper ridging, slight drying, and
lee trough.
On Thursday, there is an opportunity for a couple severe storms
over the northeast corner of the state, but that all depends on
how fast the upper level trough kicks to the northeast. At this
point, think the GFS is a little too fast with the upper trough
and the erosion of low level moisture, so we`ll keep on eye on the
northeastern plains for possible severe storms Thursday. MLCAPE
would be impressive if the moisture can hold - near 2500-3000
J/kg.
For Friday through Sunday, ensembles are pretty stable with regard
to centering the upper level high to our east over Kansas/Missouri.
This would put a good plume of monsoonal moisture over the state,
bringing higher shower and storm coverage especially over the
higher terrain. Lower elevations would see scattered afternoon and
evening storms. At this time, we don`t see much low level forcing
or upslope to support much significant heavy rain threat east of
the mountains.
There is some potential for the ridge to shift slightly westward
as a stronger zonal flow develops over the northern U.S. toward
Sunday or Monday. That could bend the best plume of monsoonal
moisture, and thus shower/storm coverage, just south of our
forecast area at that time. Temperatures should remain at or just
above normal for this period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 800 PM MDT Mon Jul 20 2020
Outflow boundaries have been playing havoc with wind
directions early this evening. For now winds should stay
northeast for the next few hours. By midnight they may
transition to a light north to northwest. For late tonight
there could be some stratus develop by 10z which may linger
thru 14z before breaking up by 15z.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...RPK
SHORT TERM...Kriederman
LONG TERM...Barjenbruch
AVIATION...RPK
Area Forecast Discussion
National Weather Service Houston/Galveston TX
636 PM CDT Mon Jul 20 2020
.AVIATION [00Z Issuance]...
Scattered showers and storms will gradually diminish this evening;
however, another round of this activity is expected later tonight.
The best window for -SHRA and VCTS will be along the coast during
the morning hours, then spreading inland by late morning/early
afternoon. Periods of TSRA will be possible on Tuesday, but opted
not to mention in this set of TAFs due to low confidence in
timing. MVFR ceilings and gusts up to 30 knots are possible with
any storms. Regarding winds, easterly light winds will dominate
most of the sites through late Tuesday morning, then shifting to
the southeast during the afternoon. 05
&&
.PREV DISCUSSION... /ISSUED 355 PM CDT Mon Jul 20 2020/
SHORT TERM [Rest of Today through Tuesday]...
A surface low pressure system located over northwestern Gulf of
Mexico has been producing disorganized showers and thunderstorms
across the Gulf waters since early this morning. Although it is not
a "healthy" looking system at this time, the latest satellite
imagery could be finally hinting at a very small area of circulation
just south of our offshore waters with a boundary line extending
from the northeastern quadrant of the circulation southward. The 2
PM EDT NHC Tropical Weather Outlook placed a 20 percent chance of
formation through 48 hours for this system and is expected to move
inland over TX tonight or Tuesday.
Across SE Texas, a surge of low level moisture filtered into the
region today while the system meandered over the northwestern Gulf
of Mexico. By 9 AM CDT, the GOES 16 TPW was already indicating
values of 1.9-2.4 inches over most of the CWA. Areas of showers and
thunderstorms that have been moving north to northwestward across
the local waters and coastal regions are now gradually expanding a
little further inland. For the rest of this afternoon, the moisture,
diurnal heating and unstable airmass in place will continue to work
together to produce additional showers and thunderstorms for the
rest of today. Some of this activity will produce brief periods of
heavy rainfall, gusty winds and frequent lightning. Although
activity is expected to decrease tonight, it could continue well
through the overnight hours. Chances will increase further by early
Tuesday as the system progresses inland. At this time, no
significant flood threats are forecast but ponding of water along
roadways and areas of poor drainage is likely with the heavy
rainfall. WPC Excessive Rainfall has placed a Marginal Risk
across SE Texas for Tuesday. 24
LONG TERM [Tuesday Night through Monday]...
Periods of showers and thunderstorms will be possible through much of
the long term forecast period. After the active day on Tuesday, expect
to see decreasing coverage in the evening followed by increasing coverage
once again during the overnight through early morning hours on Wednesday
morning, mainly near and along the coast. With a mostly unstable airmass
in place, storms should work their way inland during the day on Wednesday.
Look for a similar pattern Wednesday night and Thursday. As we head
into Thursday night and Friday, expect the arrival of the next tropical
wave/disturbance that is currently located in the Bahamas/Cuba area.
This system is being monitored by the National Hurricane Center for
possible tropical development, and their most recent Tropical Weather
Outlook has a 20% chance of tropical cyclone formation (an Air Force
Reserve Hurricane Hunter aircraft is scheduled to investigate the system
tomorrow, if necessary). Look for increasing shower and thunderstorm
coverage from east to west mainly in a Thursday night through Saturday
time period in association with this system. Models are showing high
precipitable water values (2.0 to 2.5 range) spreading across much of
our area which could lead to periods of locally heavy rainfall. This
forecast could change quite a bit if tropical development does occur,
so stayed tuned to the latest information over the next several
days. 42
MARINE...
Low pressure system over the northwestern Gulf of Mexico will
continue to produce disorganized shower and thunderstorm activity
across the bays and Gulf waters through Tuesday. The latest NHC
Tropical Weather Outlook has a low chance of development (20%)
through the next 48 hours. It is expected to move into TX tonight
or Tuesday. Winds today will continue easterly with onshore flow
returning Tuesday.
Another low pressure system is forecast to move into the local
Gulf waters Thursday night into Friday; NHC is keeping
development chances low (20%) through the next 5 days. Regardless
of development, the system is expected to produce shower and
thunderstorm activity across the local waters and bays. Winds will
also increase to 15-20 KTS and seas will rise up to around 5 feet.
Thus, Caution flags will likely be issued near the end of the work
week. 24
&&
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 95 75 91 76 92 / 40 40 70 20 50
Houston (IAH) 91 77 90 78 91 / 70 60 70 20 50
Galveston (GLS) 88 80 89 82 89 / 70 70 70 40 50
&&
.HGX WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk until 1 AM CDT Tuesday for the following
zones: Brazoria Islands...Galveston Island and Bolivar
Peninsula...Matagorda Islands.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 1 AM CDT Tuesday for
the following zones: Coastal waters from High Island to
Freeport TX out 20 NM...Waters from High Island to Freeport
TX from 20 to 60 NM.
&&
$$
Area Forecast Discussion
National Weather Service Key West FL
1000 PM EDT Mon Jul 20 2020
.DISCUSSION...
The next 24 hours will be thundery and squally across the Keys,
thanks to a westward-moving tropical wave for which NHC carries a
low chance of formation once it gets west of our forecast domain
and well into the Gulf.
Satellite imagery currently shows quite a few deep, tall
convective clusters from central Cuba to the southern Bahamas.
There are hints of a mid-level circulation near Anguilla Cay and
the Cay Sal Bank. Indeed, some mid-level cloud enhancement has
started occurring in the past hour. The 12z ECMWF shows a well-
defined 300 mb divergence bullseye near and east of this feature,
extending into the deeper convection off to the east. This upper-
level support is forecast to move and spread west-northwest
through the Straits overnight and across the Keys on Tue morning.
Models almost unanimously blossom bands of showers and
thunderstorms overnight, spreading across the Keys over the course
of Tue morning. Training of cells within these banded features
will carry the risk of a few inches of rain. The main concern for
flooding would come to fruition if any such bands move slowly
across the more urban-flood prone city of Key West during the mid-
day high tide, which effectively slows drainage of stormwater.
In addition to heavy rain, winds will come up late tonight and
peak on Tuesday as gradients tighten on the northern periphery of
the passing wave. Quite a few models solutions show swaths of at
least 20-knot winds, with some respectable solutions showing 25
knots. GFS-based statistical guidance for Sand Key even shows
sustained winds in excess of 30 knots for a time during the late
morning and mid-day hours. When you superimpose thunderstorm
outflows on top of the strong background breezes, convective gust
potential rises pretty easily into the 40-45 knot range.
Once the wave moves west and away into the Gulf on Tue night, the
Keys will continue to be on the southern periphery of a strong,
deep-layer high pressure ridge extending from near Bermuda
westward across the Southeast States. A long fetch of moderate to
fresh E-SE breezes will continue to impinge on the Keys, along
with the attendant moisture transport and fast-moving showers. So
well above normal rain chances will continue through the rest of
the work week.
&&
.MARINE...
Thundery and squally weather is expected over the waters late
tonight through much of Tuesday, as a tropical wave moves west
across the waters. Small Craft Advisories are already hoisted in
anticipation of the expected freshening of winds overnight and
Tuesday morning. The official forecast currently carries 20 to 25
knots for Tuesday, though some statistical guidance peaks
sustained winds in the 25 to 30+ knot range. When you consider the
bands of thunderstorms within this environment, the convective
wind gust potential will easily pick up into 40-45 kt range for a
time on Tue. Bottom line will be an ugly day for small craft
operators on the waters.
From synopsis...East to southeasterly winds will peak on Tuesday
as strong or possibly near-gale breezes, before decreasing to a
fresh and moderate breeze on Tuesday night. Moderate to fresh
breezes will prevail through Friday as high pressure persists to
our north. Tropical moisture will support periods of thundery
squalls across the Keys through Wednesday morning.
&&
.AVIATION...
The tropical wave is continuing to assist in convective weather
formation and development across the Florida Keys. Waves of broken
lines of fast moving VCSH and occasional embedded VCTS are expected
for both terminals for at least the next couple of days. The
strongest storms will be capable of producing wind gusts up to 30
knots with MVFR ceilings and brief IFR visibility conditions from
moderate to heavy rainfall. Wet runways will affect aircraft
braking, and ponding is possible for taxiways and aircraft
parking areas. Timing and location of these convective events
remain uncertain, but confidence is good enough for at least
steady SHRA Tuesday morning with a PROB30 group for TSRA starting
before noon. Thereafter, uncertainty for evolution of active
weather remains highly uncertain, but still kept VCTS and MVFR
ceilings to indicate persistent unfavorable weather conditions.
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...Small Craft Advisory for GMZ031>035-042>044-052>055-072>075.
&&
$$
Public/Marine/Fire...Haner
Aviation/Nowcasts....Chesser
Data Acquisition.....Williams
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