Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/26/18
Area Forecast Discussion
National Weather Service Columbia SC
946 PM EDT Fri May 25 2018
The region will remain moist and unstable the next few days
between a ridge offshore and weak low pressure to the west.
Scattered to numerous showers and thunderstorms, mainly during
the afternoon and evening, are expected. Periods of heavy rain
are possible Sunday and Monday as a plume of tropical moisture
from Subtropical Storm Alberto is directed into the area.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
The deep moist southerly flow will continue through tonight
associated with high pressure at the surface and aloft off the
coast and low pressure to our west. Precipitable water values
will remain 1.8 to 2.0 inches with weak instability. Shower and
thunderstorm coverage has been greatest in the Central Savannah
River Area associated with a surface trough and mid-level
shortwave trough. Expect continued diminishing coverage tonight
because of nocturnal cooling. The HRRR displays little shower
coverage overnight. The high moisture will help hold up
temperatures. As with the previous 2 nights expect lows in the
upper 60s to lower 70s.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Saturday, the moist air mass will remain over the FA through
the afternoon allowing mainly diurnal showers and thunderstorms
to develop. With the upper-level ridge axis shifting east of
the FA there may be some weak upper-level support for
thunderstorms late in the day. However 850 mb high pressure
ridging into the area will help keep coverage limited. Overall
the chance for rain will be lower than the past few days with a
low threat of severe weather. Although we cannot rule out the
possibility of a severe storm with slightly drier mid-level air
in place and possible weak upper-level support.
Saturday night should provide a brief break in the wet pattern.
Mid-level drier air moves into the region and precipitable
water values drop to below 1.5 inches.
Highs will generally be in the mid to upper 80s with lows overnight
in the mid to upper 60s.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
A surge of tropical moisture will move northward into the forecast
area Sunday afternoon or Sunday night. Strong moisture transport and
weak potential instability should yield widespread showers and some
thunderstorms along with a heavy rain threat through Monday. Flash
flooding may be possible, particularly in flood-prone areas and
where heavy rainfall in the past several days have saturated soils.
The CSRA and areas along and south of I-20 have received 2 to 5
inches of rain in the last seven days and may be more prone to flash
flooding. A flash flood watch may be needed.
The unsettled weather pattern is expected to continue through much
of the extended forecast period. Moderate to heavy rainfall may be
possible through the remainder of the long term, although confidence
is not high enough to include heavy rain in the forecast after
Tuesday mainly because of the possible track and intensity of
Subtropical Storm Alberto. Nevertheless, there is high
confidence in an abundantly moist air mass with precipitable
water values around or above 2 inches throughout the period with
persistent southerly flow off the Gulf of Mexico. There is at
least a high chance of showers and thunderstorms through Thursday.
High temperatures during this period will be near normal, in the mid
to upper 80s, and above normal for lows, in the upper 60s to lower
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Shower and thunderstorm coverage should continue to diminish
because of nocturnal cooling. Most of the guidance indicates
IFR ceilings again developing overnight given abundant low-
level moisture combined with nocturnal cooling. Fog development
may be limited given a 15-knot low-level jet and weak
instability. Should see improving conditions by 26/15Z because
of heating and mixing. We leaned toward the GFS LAMP for the
timing of IFR conditions. Showers and thunderstorms are not
expected to be as widespread Saturday afternoon with a little
more pronounced ridging. The thunderstorm chance was too low to
include in the terminal forecasts at this time.
EXTENDED AVIATION OUTLOOK...Restrictions in late night and
early morning fog and stratus should develop Saturday night into
early Sunday morning. Tropical moisture associated with
Subtropical Storm Alberto will increase by the late Sunday into
Monday, increasing the frequency and intensity of showers and
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
838 PM CDT Fri May 25 2018
Isolated severe storm moving into San Saba county mid evening. The
storm is on track to clip Llano county and has necessitated an update
to the PoP/WX forecast for this evening. The storm is shown by the
HRRR to gradually weaken with loss of daytime heating/increasing
convective inhibition as it clips the far northern CWA and should
eventually dissipates around 11 PM.
.PREV DISCUSSION... /ISSUED 656 PM CDT Fri May 25 2018/
See below for the 00z aviation discussion...
Currently VFR at all sites under mostly clear skies and light
southeasterly winds. Convection across portions of northern central
Texas is moving south, but should dissipate before reaching the
Austin area. VFR conditions are expected to persist at all sites
through the evening hours and into early Saturday morning. SAT may
see ceilings lower to MVFR intermittently between 10z and 15z
Saturday morning due to a stratus deck developing. Also included a
scattered cloud deck at around 2500 feet at AUS and SSF during this
same time period to indicate the possibility of a brief moment or
two where ceilings may lower to MVFR. Any lowered ceilings to MVFR
should end by 15z Saturday morning with mostly clear skies persisting
for the remainder of Saturday. DRT is expected to remain VFR for the
entire forecast period. Winds at all sites will remain light and out
of the south.
PREV DISCUSSION... /ISSUED 229 PM CDT Fri May 25 2018/
SHORT TERM (Tonight through Saturday Night)...
All is fairly quiet across South-Central Texas at the present hour
with just some fair weather cumulus clouds around the region. Showers
and isolated storms have remained well east of the CWA and think the
bulk or if not all of the activity will remain out of the CWA this
afternoon. Have left the mention of isolated thunder with a 10 PoP
through the afternoon hours for the eastern counties. The focus then
shifts to a complex of storms northeast of Dallas that continues to
slide to the southeast. This main complex will remain well to our
northeast and am not expecting any direct impacts from it. However,
the past few runs of the HRRR develops some storms along the western
end of the outflow boundary west of Fort Worth around 4 PM. The
northwest flow aloft pattern we are in would eventually bring any
storms in this area south to near Williamson County this evening.
Have kept PoPs below 15 percent for now, but did include a mention of
isolated thunderstorms for Williamson County in the 00z-03z time
frame. Latest visible satellite imagery does show from agitated cu
in the area the HRRR develops convection and this increased
confidence slightly to warrant a mention of the iso thunder. The
forecast will likely be updated closer to 00z to either increase or
decrease PoPs depending on how the potential storms evolve. If a
storm does develop and make it to the CWA, it could be strong.
Otherwise, tonight will be warm with lows in the 70s for much of the
CWA with upper 60s possible for the Hill Country. Have a rain-free
forecast for the remainder of the short-term forecast as the upper
ridge continues to amplify and move closer to our area from the west.
Highs tomorrow will be quite warm, especially for the western CWA
where highs above 100 are expected. Middle to upper 90s can be
expected for the eastern counties. Lows tomorrow night will be very
similar to tonight.
LONG TERM (Sunday through Friday)...
The long-term forecast will remain dominated by the upper level
ridge. Hot and dry weather can be expected with highs in the upper
90s to 104 degree range each day with the higher values in the
southwestern CWA. The GFS has come more into an agreement with the
ECMWF for our area as south/southeast winds in the lower levels of
the atmosphere keep temperatures from getting too out of hand.
Otherwise, no rain is expected in the long-term under the ridge, Welcome
to Summer 2018.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 73 96 73 96 74 / 10 10 - 0 0
Austin Bergstrom Intl Airport 72 95 72 95 73 / 10 10 - 0 0
New Braunfels Muni Airport 72 95 71 96 73 / 10 - 0 0 0
Burnet Muni Airport 71 95 71 96 72 / 10 10 - 0 0
Del Rio Intl Airport 74 104 74 103 75 / 0 0 0 0 0
Georgetown Muni Airport 72 95 72 95 73 / 10 10 - 0 0
Hondo Muni Airport 71 98 70 99 73 / 0 0 0 0 0
San Marcos Muni Airport 72 96 71 97 73 / 10 - 0 0 0
La Grange - Fayette Regional 73 94 72 94 73 / 10 10 - 0 0
San Antonio Intl Airport 72 97 72 98 74 / 10 - 0 0 0
Stinson Muni Airport 73 97 73 98 74 / 0 - 0 0 0
Area Forecast Discussion
National Weather Service Grand Forks ND
657 PM CDT Fri May 25 2018
Issued at 655 PM CDT Fri May 25 2018
Nicely defined vort max moving toward Winnipeg at 23z. This vort
responsible for enough lift to get sct t-storms going over parts
of the RRV/NW MN. As for max moves east and the sun sets the
threat for convection will diminsh in NW MN. On southwest side of
vort we have had good mixing with drier air aloft mixing down and
this has caused wind gusts into the 30-40 mph range in NE ND the
last few hours.
.SHORT TERM...(This afternoon through Saturday)
Issued at 321 PM CDT Fri May 25 2018
Organized forcing is mainly north of our CWA with shortwave troughs
over southern Canada. Despite disorganized forcing locally,
instability, mid level moisture, and several weak surface
troughs/convergence zones have helped kick of isolated
showers/thunderstorms over parts of our CWA. Most CAMs show isolated
activity over much of our CWA, but HRRR does indicate maybe an
increase in coverage over NW MN. ML CAPE is still 500-1000 J/KG
limiting severe concern somewhat, but surface based parcels would
still feed into a very unstable air mass, so isolated/stronger cells
still can`t be ruled out. Moisture profiles (inverted-V) and DCAPE
over 1000 J/KG raises concern for microburst/downdraft potential
with activity, but without more organization threat should be very
localized/isolated. With marginal to unfavorable mid level lapse
rates and middling forcing activity should be highly diurnally
driven and wind down quickly after sunset.
Upper troughs are even further east on Friday, so other than Lake of
the Woods region, most locations should see dry conditions. Near
record or record highs are expected once again Friday with many
locations around 90F or warmer (a little "cooler" in the northern
RRV). As has been the case winds may also be underdone in guidance
based on mixing heights, so I trended winds up a bit from standard
blend towards MOS blend which has tended to be closer on wind
speeds (still a little low). Winds should be low enough and RH
high enough to keep us below RFW criteria, but it is worth
monitoring like today (could be "near" critical again).
.LONG TERM...(Saturday night through Friday)
Issued at 321 PM CDT Fri May 25 2018
Hot, possible record heat for Memorial Day Weekend. Cooler but still
above normal temperatures Tuesday through the rest of the next work
week. Chance for showers and thunderstorms in the Northern Plains
throughout the next week.
Upper level ridge with an upper low over the Nevada/Utah area
defines the upper level pattern at the start of the period. Some
embedded short waves will move over the area to help increase the
chances of showers and thunderstorms. Saturday night into Sunday
morning the east chance for shower and storms will be in eastern
North Dakota associated with a surface low to the southwest. Sunday
night the shower and rain threat increases as another surface low
moves in from the west. MU CAPE late Sunday could approach 1500 to
2000 J/kg. On Monday MU CAPE could be higher with values over 3000
J/kg in the NAM and GFS. Bulk shear over 40 knots also present in
the Northern Plains so there is severe potential with these storms.
One of the major limiting factors here will be the amount of CIN as
it is forecast to be high as well over this period.
Tuesday into Wednesday high precipitable water values in the NAM and
GFS are above the 90th percentile for nearby sounding climatologies
(BIS, ABR, and INL). This is supported by the previous upper low
becoming dislodged and the trough moving towards the Northern
Plains. Dryer weather expected Thursday before another chance for
rain late next week.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 655 PM CDT Fri May 25 2018
Gusty west winds to 30 kts in NE ND and isold tsra in NW MN will
occur thru sunset. Winds will calm down under 10 kts after dark
and the convection will diminish. Quite overnight into Saturday
with VFR conditions. Daily CU Sat aftn likely...esp N/E.
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1107 PM EDT Fri May 25 2018
Issued at 1102 PM EDT FRI MAY 25 2018
Pops have been updated based on recent radar, satellite, and
convective allowing model trends. This led to a bit higher pops in
parts of Pike County and McCreary County over the next hour or so
with a lull for a few hours overnight. However, several of the
convective allowing models including the HRRR have showers and
possibly a thunderstorm moving north into the TN and VA border
counties prior to dawn as the upper level trough approaches. Some
slight chance pops were added during that time frame in the south.
Also, coverage of fog was adjusted to add more fog in Pike County
down into Letcher County where heavier rain fell.
UPDATE Issued at 840 PM EDT FRI MAY 25 2018
A few showers and even a thunderstorm near the TN and KY border
linger as sunset approaches. This convection is largely diurnally
driven and should wane over the next 1 to 2 hours. The overnight
hours should generally be dry. With the upper trough working in,
some of the convective allowing models indicate the potential for
an isolated shower toward dawn in the southwest part of the area.
We will continue to monitor trends on this. Otherwise, outside of
showers, clouds will decrease and locations that picked up
heavier rainfall from showers and thunderstorms today are expected
to experience more widespread fog and it may become dense. Some
of these locations include Whitley County near the I 75 corridor
and portions of the Big Sandy region and portions of Letcher
county. More widespread coverage of fog has been added overnight
in these areas. Otherwise, fog development is anticipated in the
.SHORT TERM...(This evening through Saturday night)
Issued at 405 PM EDT FRI MAY 25 2018
The afternoon surface analysis shows a weak boundary across the
the Tennessee Valley and a surface high pressure off the North
Carolina Coast. This high pressure is continuing pump more
moisture into the region this afternoon, with dewpoints climbing
into the mid 60s this afternoon. The latest radar data shows some
showers and perhaps a isolated thunderstorm developing across the
region. Interestingly, the lack of steering flow is leading to
arcing outflow boundaries this afternoon and this could make
convection more difficult to nail down through the early evening.
Given this will keep thunder in isolated to scattered wording
this afternoon and early evening. The CAMs have the mess of
convective outflows and thunderstorm complexes across western
Kentucky weakening this evening. Given this and the waning
convection through the evening, and did lower POPs overall given
the lack of steering flow from the west and loss of daytime
heating. There could be some fog tonight in the river valleys or
perhaps more so where rain has fallen this afternoon. This will
have to be more fine tuned this evening. Temperature splits remain
possible tonight, but they should be less overall given a little
more cloud cover to contend with.
An upper level trough across the Midwest will slowly spill weak
height falls into the Ohio Valley Saturday. This in combination
with strong low level lapse rates, modest mid level lapse rates,
increased moisture and MUCAPE around 2000 J/kg should yield more
numerous coverage in convection mainly in the afternoon on
Saturday. Given the lack of larger scale forcing or surface
features to work with this will be harder to nail down exact
locations. The main threats will be heavy rain and frequent
lightning given the lack of shear. By later in the afternoon,
this maybe driven by convective outflows to a extent, but that
will have to be evaluated as we get closer to that time. This
convection may linger into the evening and perhaps some showers
linger into the overnight. Did add some fog again for Saturday
night, but again this is hard to nail down given the uncertainty
on exactly where rain will fall. The temperatures splits will
likely be more limited Saturday night as well given the additional
.LONG TERM...(Sunday through Friday)
Issued at 405 PM EDT FRI MAY 25 2018
A large but weak upper trough axis will extend from the Great Lakes
to the Gulf of Mexico at the start of the period, with a
strengthening tropical system (Alberto) over the northern Gulf. The
northern extent of the trough will be progressive, while the flow
around the tropical system becomes more closed as it deepens. This
would shear the deep moisture regime originally over our area at
start the period, shunting it southeastward, and allowing drier air
aloft to advance southeastward over eastern KY. This would tend to
keep precip more sparse, especially over the northwest part of the
area. Meanwhile, the developing col in the geopotential heights over
our area would lead to weak flow and rather featureless mid/upper
levels, resulting in the movement and coverage of any precip
becoming more limited from Sunday into Monday.
As Alberto moves inland and weakens beginning Tuesday, we will come
more under its influence and deep moisture should make a comeback.
Along with this would come an increase in precip coverage. Aside
from this generality, there is still a lot of uncertainty. The mid
week forecast depends largely on the development and demise of
Alberto, and models do not agree on the timing and track of the
system in its waning stages. It`s still possible for it to track
north, south, or over our area. Whatever the case, it should be to
our east by Friday. However, without any real change in air mass,
there still could be diurnal convection which pops up on Friday.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 835 PM EDT FRI MAY 25 2018
Much of the first 6 hours of the period should feature VFR,
outside of the few locations experiencing some initial showers
and or an isolated thunderstorm with brief MVFR or IFR
reductions. Otherwise, valley fog with mainly MVFR reductions and
spotty IFR is expected to develop by 6Z to 8Z and generally not
affect the TAF sites with the exception of SJS that received rain
this evening. Reductions to at least MVFR by 3Z are anticipated
there and some IFR fog is anticipated from about 6Z to 12Z.
Convection is expected on Saturday, possibly before 15Z with
chances lingering through the end of the period. Confidence in
timing of onset and thunder on station at any one location was to
low for more than prevailing VCTS during the second half of the
period. Winds will average light and variable outside of any
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
834 PM CDT Fri May 25 2018
834 PM CDT
Pattern far more reminiscent of mid-summer than May with weak
synoptic forcing convection largely being driven by MCVs. One
weakening MCV from last night`s convection is supporting a small
cluster of showers a couple t-storms across east central IL,
including our far southern CWA. This activity is likely to weaken
over the next couple hours, likely dissipating by midnight as it
encounters drier and more stable air mass.
Upstream over NE IA and SW WI another area of convection has begun
to show some signs of mesoscale organization, with a QLCS bowing
toward SE. The evening sounding from DVN sampled a modestly
unstable environment with CAPE around 1000 j/kg, however boundary
layer is currently cooling and atmosphere is beginning to
stabilize. Could see another MCV develop in the bookend of this
developing bow, which could augment the weak ambient shear
environment and help this activity sustain itself as it pushes
into NW IL mid-late this evening. Would generally expect a
weakening trend, particularly with the eastern extent of this line
as it encounters a more stable and worked over air mass. GOES-16
1-min IR imagery has shown a tendency for warming cloud tops and
weakening of the convection over SW WI and some cooling cloud tops
(intensification) over IA where instability is greater. Will
likely be a bit of battle of opposing forces the next several
hours as instability axis over eastern IA would tend to support
more of a southward propagation of this convection, while current
storm motion and the development of a MCV would tend to favor more
of a SE motion toward our CWA.
At this point, planning to increase pops far western CWA late this
evening to account for this activity potentially spreading in.
However, given the weaker instability in our area, suspect the
threat of more robust storms should remain west of our CWA, though
certainly lightning and heavy downpours look quite possible.
253 PM CDT
Scattered shower and thunderstorm trends are the main forecast
concerns through this evening, with continuation of very warm
summer-like weather persisting into the holiday weekend.
Early afternoon surface analysis depicts weak low pressure over
western IL, along a pseudo-warm front extending from along the
Mississippi River into far southern IL. This weak low, and an area
of thunderstorms over western IL, were associated with a mid-
level short wave trough propagating across the region. The primary
low level focus for storms appears to be the warm frontal trough,
further enhanced by differential heating due to cloud cover, and
convective outflow. These storms should continue to move slowly to
the east-northeast across the forecast area through the remainder
of the afternoon and early evening hours, though instability
gradually decreases farther east. This, combined with weak mid-
level lapse rates and weak deep-layer shear, should allow for a
general decrease in intensity and coverage with eastward extent
into early evening as diurnal instability diminishes with sunset.
While SPC has stretched the day 1 marginal severe risk east to the
IL/IN border, overall lack of deep shear and warm thermal
profiles should preclude much of a severe threat, with the main
concern being the potential for isolated wind gusts. Locally heavy
rainfall is likely a greater threat, given slow cell movements
and p-wats approaching 1.80".
High-res CAM guidance continues to indicate some potential for
storms currently developing over southeastern MN to develop
southeastward into parts of northwest/north central IL after
midnight tonight. Forecast soundings, especially from the NAM,
suggest substantial elevated CAPE may be present over northwest IL
during the early overnight hours, though veering of the H8 winds
and overall lack of deep shear suggests that storms may struggle
to push too far south. 3km WRF, HRRR and ARW runs all weaken these
storms as they spread into IL during the pre-dawn hours, and have
generally limited mention to low chance pops for these.
Primary mid-level trough passes across the region early Saturday,
with weak height rises developing during the day. While low level
wind fields turn light westerly behind the trough, air mass
remains very warm and moist. While no significant forcing is
noted, an isolated shower or thunderstorm can`t be ruled out
during the peak heating hours of the afternoon where weak low
level convergence of subtle mid-level vort may interact, however
most areas will likely remain dry. With at least partly sunny
conditions, temps should again reach the upper 80`s/around 90
degrees, with a weak lake breeze likely keeping areas along the
immediate Lake Michigan shore a little cooler.
231 PM CDT
Saturday night through Friday...
Surface high pressure will be across the area Saturday night
while upper ridging to the west slides into the area into Sunday
night. Overnight lows will remain warm with mid and upper 60s
while the heart of the Chicago metro see lows around 70, if not
warmer. With the upper ridge pushing in Sunday low and mid level
warming peaks with 850 mb temps around 20C. This supports low 90s
with a few mid 90s possible given that sunshine should be
abundant. Limiting factor from reaching mid 90s may be weak low
level winds. This weak flow will also allow a lake breeze to
develop which should provide some relief from the hottest temps
near the lake. Main question will be how high temps peak before
some modest cooling into the mid/upper 80s in the afternoon. Peak
heat index values should be around 95 away from the lake. The
upper ridge broadens for Monday with surface high pressure still
in place so may not see much change from Sunday and may need to
bump high temps up a couple degrees similar to the forecast for
Sunday. Expect either a weak easterly flow on the west side of the
high or a lake breeze to develop keeping lakeshore areas cooler.
The upper ridge starts shifting east Tuesday and an upper trough
will move east across the northern plains. The current sub
tropical low is expected to move into the Gulf coast states by
Wednesday will have an impact on pattern evolution and may phase
the northern plains trough. Quiet a few things need to occur
before mid week so confidence in details is low but the area may
get into some precip chances as early as Tuesday and could
continue through mid week. Am fairly confident that a warm
pattern, though not as warm as the next few days, will continue
with highs generally in the 80s. The pattern may favor an easterly
flow or lake breeze development so lakeshore areas look to be
cooler through much of the week.
For the 00Z TAFs...
VFR conditions expected through the forecast period. S/SW winds
will remain generally under 10kts at all sites. A weak lake breeze
should pass ORD/MDW late Saturday afternoon into the early
evening. At RFD, a cluster of TSRA currently over far southeast MN
is expected to remain just west of the terminal, but a few showers
may brush the terminal between 03-07Z.
231 PM CDT
South to southwest winds will prevail across the open waters
through the weekend with the strongest winds occurring into this
evening. A weaker flow pattern will allow winds to ease Saturday
and Sunday and will also favor the development of onshore flow
across the Illinois and Indiana nearshore waters each day. A weak
front drops down the lake later Monday bringing at least a
temporary shift to northeasterly flow. After that the pattern
becomes less certain with the sub tropical system currently off
the Yucatan Peninsula moving into the Gulf coast states early next
week. This may interact with a trough moving across the northern
Plains but this is not certain. Do not foresee any major wind
producing systems affecting the lake but wind speed and direction
details from Tuesday onward may change.
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This extended forecast discussion will be focused on two weather
items. The first will be the strength of a southwest to northeast
oriented, vertically stacked, high pressure ridge to suppress
convective activity on Monday (Memorial Day), and secondly, the
impacts of the subtropical named circulation Alberto on parts of the
WFO PAH forecast area between Tuesday and Thursday of next week.
For Monday and Monday night(Memorial Day), subsidence associated
with the ridge should suppress any convection (showers and
thunderstorms during the morning and evening hours. A few storms
may develop during the heating of the day in the afternoon, so a
small chance of storms was added during this time period.
Heat index values will likely reaching into the 90 to 95 degree
range during the afternoon outside of any rain areas. The 12z
ECMWF is a little more robust about developing afternoon
convection over the WFO PAH forecast area on Monday, but kept the
WFO PAH forecast area dry to reflect the collaborative input from
surrounding offices and to keep within the regional model guidance
For Tuesday through Friday, given the range of forecast
possibilities associated with the current subtropical storm
Alberto, plan to keep the local forecast close aligned to the
Tropical Prediction Center/National Hurricane Center (TPC/NHC) and
the Weather Prediction Center (WPC) forecasts. Those with specific
interests associated with this circulation should refer to these
NOAA/NWS websites for more information.
A this time, the TPC/NHC forecast most closely aligns with the 00z
ECMWF guidance with the position and general intensity of the
expected remnants of Alberto, as it is forecast to move through
eastern Mississippi, western Tennessee, and near the Pennyrile
region of West Kentucky. The latest 12z Friday model run of the
ECMWF places the center of the circulation near the Todd/Muhlenberg
County KY by 7 pm Wednesday. At this point, frictional effects of
the circulation over land, the diurnal expansion and contraction of
the dynamic precipitation core with the circulation, and the
interaction with the surrounding ridge may play havoc with the
timing, location, and intensity of the circulation and attendant
From a QPF (rainfall amount) perspective, a majority of the rainfall
associated with the circulation is expected to fall during the
afternoon/evening hours on Tuesday, Wednesday, and Thursday. With
this forecast package (subject to many changes the next several
days), rainfall amounts are forecast to range from 0.6" to 1.00"
across the Pennyrile region of West Kentucky and into southwest
Indiana. WPC`s seven day forecast of QPF, suggests 1.5" to 2.00"
over the same area, but this includes any and all forecast rain from
today (Friday) through next Friday, June 1st. This would suggest
that at least half of the rainfall next week may likely be
associated with the remnants of Alberto, assuming it maintains a
similar track. Again, there will be some uncertainty as to the
eventual track and impact of Alberto for our area.
Temperatures next week will remain coolest (lower 80s) in the
vicinity of the greatest rainfall and cloud cover expected with
subtropical storm Alberto. However, after the passage of this
system, temperatures will be on the rise with subsidence behind the
circulation. This will likely generate heat index values in the
upper 90s on May 31st, with some locations see heat index values
around 100 during the afternoon on June 1st.
Issued at 622 PM CDT Fri May 25 2018
With the loss of daytime heating, convective intensity will dwindle
through the evening hours. However, the atmosphere is very moist, and
there is a disturbance in the upper levels of the atmosphere. These
factors will likely keep some isolated showers going overnight. Where
heavy rain fell today, some fog is likely during the overnight hours.
The fog could become rather dense if skies cleared out totally, but
mid level clouds are forecast to be rather persistent.
On Saturday, quite a bit of sun in the morning will give way to lots of
cumulus clouds and more scattered storms in the afternoon. Any storms
will again have the potential for heavy rain.
Area Forecast Discussion
National Weather Service Blacksburg VA
833 PM EDT Fri May 25 2018
High pressure offshore will maintain a moist southerly flow of
air across the region into the weekend. Subtropical Storm
Alberto moving into the Gulf of Mexico this weekend will move
ashore and wobble over the lower Mississippi Valley early next
week. Tropical moisture will stream northward into the region
with a return of showers and storms especially during the
afternoons and evenings over the next few days.
.NEAR TERM /THROUGH SATURDAY/...
As of 800 PM EDT Friday...
A quick update to reduce pops, cloud cover, and bring
temperatures into line with current readings. No major changes
though. Convective activity, just showers so far, with outer
fringes of tropical moisture very widely scattered so far and
confined to areas west of the Blue Ridge. HIRES HRRR and NAMNest
suggest this activity will dissipate quickly after sunset, but
showers may drift back into the area later in the night. Cloud
cover is also quite scattered at this point, so reduced the
percentages about 20% across the board at this time.
As of 230 PM EDT Friday...
Seeing small clusters of convection develop within southeast flow along
the southern Blue Ridge and foothills as well as across the far western
ridges where an axis of higher instability off to the west prevails.
Latest short term guidance continues to focus most convergence across
the far western/southwest counties through sunset with added
clusters/bands of at least shallow convection espcly along the I-77
corridor. Otherwise expect only isolated coverage at best elsewhere
over the southern/western tier and just some leftover cumulus across
the northeast where residual ridging lingers.
Appears will see most coverage fade with loss of heating this evening
given lack of support with the boundary well to the south, so trimmed
back pops to isolated or low chance mainly west which may be generous
into the overnight. However combination of increasing southwest flow
and deeper moisture may lead to added showers espcly south before
daybreak where forecast soundings show a rather saturated column late.
Should also see some fog around in the valleys and where earlier rain
occurred but likely limited via cloud cover so keeping coverage patchy
at this point. Lows again mainly in the 60s with some cooler 50s
Upper heights continue to slowly decrease on Saturday as the surface
high slides farther offshore. This in conjunction with increasing
southwest flow and a surge in moisture, per PWATs rising to above 1.5
inches, should allow for more widespread convective coverage by
afternoon. Appears initial coverage along the southern Blue Ridge and
points west by midday per forecast 85h theta-e axis/southwest flow,
with showers/storms spilling east into better forecast instability east
of the ridges in the afternoon as weak mid level wave also tracks east.
This along with slow movement given forecast steering of around 10
knots or less likely to result in a heavy rain concern with even some
stronger pulse storms possible within bands. Therefore expecting a
quick diurnal increase in convection from chance pops west early to
likelys most locations in the afternoon with even categorical in spots
along the eastern slopes of the Blue Ridge. Otherwise still warm and
quite muggy with highs low/mid 80s east and mostly 70s mountains.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 300 PM EDT Friday...
Northern stream trof will move east through New England this holiday
weekend as Subtropical Storm Alberto slowly moves up the eastern
Gulf and into the Southeast. Please refer to the latest advisory or
statements from the NHC on Alberto.
Unsettled weather is expected during the period with a flow of deep
moisture into the Appalachians. A series of weak shortwaves will
rotate up from the south and spark good coverage of diurnally
showers and thunderstorms for the weekend. It will not be raining
the whole time, and most should be able to work in a holiday picnic.
Potential tropical system will remain near the Gulf Coast
Monday through Wednesday between upper ridge over the southwest
then central United States and the off the southeast coast.
Thursday the low opens and fills and moves northeast. Models
have come into better agreement taking this feature into the
Tennessee Valley by Thursday morning. ECMWF has the deeper
moisture over Virginia and North Carolina again Wednesday and
SPC keep our forecast area in general thunderstorms on the
convective outlook. However, the instability looks healthy but deep
shear is lacking. The combination of recent rains and high PWATs
will support heavy rainfall and set up the possibility of flooding
with training convection, along with some degree of severe threat
with the most vigorous storms.
Saturday evening convection will taper off to isolated to scattered
showers Saturday night. Low temperatures Saturday night will range
from the upper 50s in the mountains to the mid 60s in the piedmont.
The best chances of thunderstorms on Sunday will be along and west
of the Blue Ridge mountains. High temperatures will vary from the
lower 70s in the mountains to the mid 80s in the piedmont.
On Sunday night, Alberto lifts northward along the Gulf coast as the
upper trof over the northeast pulls out. This may stretch dynamic
forcing out and may keep the highest precipitation in the south.
Low temperatures Sunday night will generally be from the lower 60s
in the west to the upper 60s in the east. Unfortunately, there a
good to likely chance of showers and thunderstorms for Monday. Highs
will vary from the lower 70s in the mountains to around 80 degrees
in the piedmont. Kept scattered showers and isolated thunderstorms
in for Monday night with low temperatures from the lower 60s to the
Will continue to highlight the region for potential hydro issues in
the HWO and wait for a more specific region to declare itself in
time before considering any watches.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 300 PM EDT Friday
There is the potential for periods of heavy rain during the medium
range with Alberto and its track. Please refer to the latest
advisory from the NHC on Alberto. By mid to late week, remnants of
the tropical system could bring tropical moisture and heavy rains to
our region. Flooding potential will depend on the track of the
system and how much rainfall is accumulated from the showers and
thunderstorms earlier in the week.
The latest NHC track places Alberto in southern Mississippi by
Tuesday morning, then its lifts northward into the Tennessee valley
on Wednesday. The timing of the ECMWF was quicker and further north
and west (Ohio Valley) compared to the GFS which was slower and more
compacted (along the Appalachians. By Thursday and Friday, the low
will open up and weaken as it moves northeast. There is a continued
threat for showers and thunderstorms into the end of the week. Urban
and small stream flooding risk will be highest early in the week
with river flooding possibly by the end of the week depending on
actual rainfall totals.
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
As of 800 PM EDT Friday...
Generally VFR conditions in place across the CWA and at all TAF
sites at this hour. Would expect this to continue through the
next several hours as the atmosphere above 850mb remains quite
dry. Outer fringes of tropical moisture from Alberto beginning
to encroach on the area and isolated light to moderate showers
developed along the Blue Ridge this evening. The immediate
activity will likely dissipate, but with tropical moisture
increasing through the period, additional showers are possible
along and west of the Blue Ridge overnight. Main thing of note
is increasing layers of clouds as tropical moisture spreads
north from the Gulf of Mexico through the period. Would expect a
trend to MVFR ceilings by morning west of the Blue Ridge, but
most likely remaining VFR to the east. Fog potential is limited,
given expected cloud cover, but MVFR BR seems plausible at BCB
and LWB during the early morning hours.
Winds will be SSE to SSW through most of the period at speeds of
5-8 mph, slightly higher during the daytime Saturday with low
end gusts possible east of the Blue Ridge.
As of 1250 PM EDT Friday...
MVFR conditions across southern/western sections will continue
to slowly improve to VFR as cigs scatter out and lift this
afternoon. However sub-VFR cigs likely to remain along the Blue
Ridge southwest of KROA where a few showers appear likely along
the KHLX-KMWK-KUKF corridor. A few storms will also be close
enough to KBLF, mainly along and west of the Interstate 77
corridor this afternoon to warrant a VCTS or TEMPO group, while
keeping out mention elsewhere except for perhaps a VCSH at KBCB
Still looks like showers possible mainly southwest of a BLF-
BCB line this evening, with broken deck of mainly high end MVFR
to low end VFR cigs. Potential for fog is there, but only
putting in where its typical and where it may rain. Cloud cover
will limit the fog coverage outside of where rainfall occurred.
Any fog or low cigs will slowly improve on Saturday but likely
to see at least periods of MVFR cigs persist with deeper
moisture in place. This should also lead to more in the way of
showers/storms espcly over the mountains by midday, and across
much of the region during the afternoon. This supports a VCSH
mention at most locations outside of KLYH.
.Extended Aviation Discussion...
Wet pattern with periods of at least diurnally driven sub-VFR
conditions in convection will take place into the middle of
next week. Fog at night is possible if we clear enough due to
wet ground conditions and rain. Worse conditions heading south
to the Gulf Coast states, as a tropical system moves into the
that area Monday or Tuesday.
Area Forecast Discussion
National Weather Service Shreveport LA
919 PM CDT Fri May 25 2018
For the 26/00Z terminals forecast will prevail with mostly VFR
with lingering showers and thunderstorms associated with several
outflow boundaries reducing flight categories briefly to MVFR.
Could see visibility restrictions in rain and possibly mist/BR
through 26/04Z. Later overnight after 26/09Z-26/12Z MVFR flight
categories will be returning with patchy mist/BR. Will enter
mention of convection earlier in the day Saturday with the
position of the upper trough of low pressure across the Central
and Eastern sections of the Four State Region. Surface winds will
be light and variable less than 7 knots through most of the
forecast period with a period of Southwest to West speeds near
7 knots early on Saturday from mid morning to mid afternoon. /06/
.PREV DISCUSSION... /issued 253 PM CDT Fri May 25 2018/
SHORT TERM.../Tonight through Saturday Night/
A line of showers and thunderstorms that developed along an outflow
boundary from a southeastward moving MCS across southeast OK earlier
this morning, has slightly loss its perfectly linear look late this
aftn. Though scattered showers and thunderstorms continued to affect
portions of southeast OK, northeast TX and southwest AR, with
isolated showers and thunderstorms elsewhere. Earlier this aftn,
portions of the line of storms across McCurtain County did reach
strong levels as it interacted with rather moist low levels
/dewpoints in the upper 60s to lower 70s/ with hail, wind gusts and
brief moderate rainfall being the main results, but have since
become sub-severe. Can not rule out the occasional wind gusts
that could warrant a Significant Weather Advisory or even a
Warning but a widespread severe weather threat is low.
As we continue to approach sunset, high-res solutions such as the
HRRR exhibited a waning trend though with lingering precip as we
head into the overnight hours. Thereafter, northwest flow aloft
persists and another embedded impulse could once again ignite an MCS
across southern OK, hence the mean-flow will propagate it to
across the northwest zones aoa sunrise. Will once again have to
look out for an outflow boundary that could aid in the generation
of additional isolated showers and thunderstorms that model
solutions sometimes struggle to pick up on. Elsewhere, daytime
destabilization and plentiful moisture will yield isolated showers
and thunderstorms. Just like what is expected tonight, the
convection will gradually dissipate several hours after sunset
MOS guidance overnight temps is over-doing it a bit as persistence
over the last several nights have been a few degrees cooler than
what guidance have depicted. Furthermore, guidance is also a few
degrees cooler during the day than what actually occurs. Will
therefore continue to manually tweak both the overnight and daytime
temps accordingly /overnight lows in the upper 60s to lower 70s and
daytime highs mainly in the lower 90s/.
Side Note: We continue to monitor the newly upgraded Subtropical
Storm Alberto as it continues to become better defined just east of
the Yucatan Peninsula. The National Hurricane Center still has a
track that shows Alberto making landfall somewhere between southeast
LA and the FL Panhandle Monday/Tuesday. The Weather Prediction
Center still has the heaviest rainfall /4-7 inches/ across extreme
southeast LA and eastward to the remaining Gulf coast States. /29/
LONG TERM.../Sunday through Thursday/
Alberto will be approaching the northern Gulf Coast while the
ArkLaTex will still be under the influence of surface high
pressure coupled with an upper level ridge. Our region will be on
the west side of Alberto through about Wednesday before Alberto
begins to pull out of the southeast US to the northeast. With this
current forecast track, only far eastern portions of the area
will see showers and thunderstorms from Alberto.
Being on the west side of Alberto and under the influence of the
ridge aloft will allow for the area to experience compressional
heating from subsidence. The extended timeframe will see some 10 to
15 degree high temperature readings well above normal. Some
locations will be experiencing near record high temperatures towards
the latter part of the extended, if not flirting with triple digit
readings. Long range guidance keeps the area dry throughout the
.PRELIMINARY POINT TEMPS/POPS...
SHV 70 92 69 93 / 30 30 20 20
MLU 69 91 70 90 / 30 40 20 40
DEQ 69 91 67 92 / 30 30 10 10
TXK 69 90 68 91 / 30 30 20 20
ELD 69 89 68 91 / 30 40 20 30
TYR 72 92 72 93 / 30 20 10 10
GGG 71 92 71 92 / 20 30 10 20
LFK 71 93 72 93 / 10 20 10 20