Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/19/21
Area Forecast Discussion
National Weather Service Cheyenne WY
522 PM MDT Tue May 18 2021
.SHORT TERM...(This evening through Wednesday)
Issued at 155 PM MDT Tue May 18 2021
The upper level trough that has been dominate in the region is
expected to get absorbed into the main flow ahead of a Pacific
Northwest trough digging towards the southeast early tomorrow
morning. This feature is expected to bring a swath of moisture into
the region on Wednesday. Most of the stronger moisture conveyor
stays a bit further to the west. However, could still see some
increased precipitation over the Mullen Burn Scar, with models
indicated more upper level diffluence across the Snowys and Sierra
Madres.
Active pattern remains in place as we transition to the later
portion of the week. Current model guidance has an omega blocking
pattern setting up over the central CONUS with an upper level closed
low developing over the Pacific Northwest. This blocking pattern is
expected to limit the movement of the upper level low, as it digs
slightly to the southeast, before becoming nearly stationary
Thursday night. Guidance from the SREF convective probabilities
indicate a 50 percent chance for MLCAPEs values to exceed 1000 J/kg
across the Nebraska Panhandle. Combined with some moisture and
moderate shear could lead to some stronger thunderstorms
development. Models typically put these systems a bit on the drier
side for this region. As a result, went ahead and started bumping up
the POPs. Will need to monitor this event to determine the
likelihood of severe potentials. Nevertheless, the interactions
between the upper level high to the east and upper level low to the
west is likely to increase the wind speeds Thursday evening into
early Friday morning, increasing the impacts along I-80 near our
wind prone areas.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 155 PM MDT Tue May 18 2021
The omega block pattern will continue into Thursday afternoon into
early next week affecting our precipitation, temperatures, and
winds. Short batches of precipitation will push through our region
starting Thursday into next Monday therefore PoPs have increased.
Instability, moisture and moderate shear could lead to severe
thunderstorm development starting on the I-25 line into the western
Nebraska Panhandle. With the assistance of a small amount of
helicity in the Nebraska Panhandle, severe thunderstorms could
produce moderate hail. This event is still a few days out and will
continue to monitor as we move closer this week. The interaction of
of an upper level low and a high pressure to our east will cause
gradients to tighten which will bring strong wind gusts across our
region starting Thursday afternoon into Saturday morning.
Additionally, there is another chance of scattered severe
thunderstorms Friday into early next week but if the GFS hold true,
the low pressure system may move majority of the moisture to our
east while the omega pattern finally dissipates. A short ridge
pattern is possible mid next week which will clear our skies and
increase our temperatures for a small teaser of summer.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 521 PM MDT Tue May 18 2021
Wyoming TAFS...VFR. Wind gusts to 23 knots at Laramie and Cheyenne
after 18Z Wednesday.
Nebraska TAFS...VFR. Wind gusts to 30 knots until 03Z, and to
25 knots at Sidney after 15Z Wednesday.
&&
.FIRE WEATHER...
Issued at 155 PM MDT Tue May 18 2021
Showers and thunderstorms over the course of the week keeps the
minimum RH values on the north side of 25 percent east of the
Laramie Range tomorrow through Thursday. Main concern exists where
some drying out is expected west of the Laramie Range and humidites
could drop to the 15 to 25 range. Some breezy conditions are
expected Thursday, which may increase critical fire weather
conditions. However, the majority of those fuels are still green.
Increased change of showers persist through the remainder of the
week, decreasing fire weather concerns.
&&
.HYDROLOGY...
Issued at 155 PM MDT Tue May 18 2021
Chance for a couple of showers and thunderstorms to develop over
parts of the burn scar later today, with the HRRR indicating some
popcorn convection possible. These showers may produce brief
downpours, but rainfall amounts are still estimated to be less than
an tenth of an inch. The more enhanced threat for showers and
thunderstorms over the burn scar is still set for Wednesday as the
Pacific Northwest trough develops and brings more moisture into the
region.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
SHORT TERM...MD
LONG TERM...TJT/AW
AVIATION...RUBIN
FIRE WEATHER...MD
HYDROLOGY...MD
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
742 PM CDT Tue May 18 2021
.UPDATE...
The tornado watch has been allowed to be dropped for the I-35
corridor from Williamson to Bexar County as the convective complex
producing severe weather, heavy rainfall and flash flooding has
advanced eastward into the coastal plains. Tornado watch remains in
effect for these areas through at least 9 pm cdt. Additionally, have
made grid edits, including PoPs, temperatures, dew points, over the
next 6 hours given the latest observational trends and convective
short term allowing model guidance.
&&
.PREV DISCUSSION... /ISSUED 659 PM CDT Tue May 18 2021/
AVIATION...
/00Z TAFS/
Radar trends and latest model guidance show convective activity
staying to the south and east of the AUS and SAT airports for the
rest of this evening. KDRT should be clear of any convection as well
for this evening as storms over Mexico die this evening and new
redevelopment overnight stay well south of the airport. The HRRR
and Texas Tech solutions bring new showers and storms around 12Z
Wednesday while keeping convective activity through the afternoon
hours. As of this writing (23:50Z Wed), all airports are observing
VFR conditions. However, cigs are forecast to become MVFR overnight
through the morning hours with IFR vsbys as storms move over the
terminals. The forecast late afternoon/early evening is a bit tricky
as the new round of convection slowly departs the I-35 corridor.
PREV DISCUSSION... /ISSUED 307 PM CDT Tue May 18 2021/
SHORT TERM (Tonight through Wednesday Night)...
Convection is growing stronger as an outflow boundary moves into our
CWA. We expect showers and thunderstorms to become more widespread
this afternoon and we have issued a Tornado Watch for most of the
eastern half of South Central Texas. There may be sufficient low
level shear to produce a few tornadoes this afternoon and evening.
The upper level low we`ve been watching for the past few days will
move into West Texas tonight and then northeastward to the central
Plains. The low levels remain warm and very moist. Rain chances
remain high through the short term period. Beyond the Tornado Watch
we will continue to have a chance for some storms to be strong to
severe with ample instability and deep layer shear. PW values will
also be high and locally heavy rainfall will be possible. Models are
especially bullish for strong storms and heavy rain Wednesday. The
most likely area for heavy rain will be the eastern half of the
forecast area. Rainfall totals through Wednesday night will be two to
four inches with isolated totals to six inches possible. The highest
totals will be east of I-35/I-37. The Flash Flood Watch continues.
LONG TERM (Thursday through Tuesday)...
As the first upper trough moves away from Texas, another will move
onto the West Coast. This will keep rain chances high Thursday over
the eastern half of the CWA. An additional 1/2 to one inch of rain is
possible during the day. The rain chances will decrease Thursday
night, but not end. The heavy rain threat will end as the deep
moisture moves farther to the east. The second upper trough will drop
down through the west and keep Texas under southwesterly flow.
Shortwave troughs moving through this pattern will generate showers
and thunderstorms at times through the weekend. The high moisture
plume with PW values around 2.0 inches will move back over our CWA
and we could see another round of locally heavy rain over the
weekend. For the start of next week an upper ridge will push in from
the east and force any rain chances to the western part of our CWA.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 67 77 66 80 69 / 50 90 70 60 40
Austin Bergstrom Intl Airport 67 78 65 80 68 / 60 90 70 60 40
New Braunfels Muni Airport 67 78 66 82 69 / 60 90 60 50 30
Burnet Muni Airport 65 75 64 79 66 / 40 80 50 40 30
Del Rio Intl Airport 70 83 67 87 70 / 30 50 10 - 10
Georgetown Muni Airport 66 75 65 79 68 / 60 90 70 60 40
Hondo Muni Airport 69 79 64 83 68 / 50 90 40 30 20
San Marcos Muni Airport 68 78 65 81 68 / 60 90 60 50 30
La Grange - Fayette Regional 70 80 68 81 71 / 80 100 80 70 40
San Antonio Intl Airport 69 77 66 81 69 / 50 90 50 40 30
Stinson Muni Airport 70 79 67 82 69 / 50 90 50 40 30
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Thursday afternoon for Atascosa-Bandera-
Bastrop-Bexar-Blanco-Burnet-Caldwell-Comal-De Witt-Fayette-Frio-
Gillespie-Gonzales-Guadalupe-Hays-Karnes-Kendall-Kerr-Lavaca-Lee-
Llano-Medina-Travis-Williamson-Wilson.
&&
$$
Update...Brady
Area Forecast Discussion
National Weather Service Grand Junction CO
545 PM MDT Tue May 18 2021
.SHORT TERM...(Tonight through Wednesday night)
Issued at 141 PM MDT Tue May 18 2021
The midlevel circulation is over the CO/NM state line as evident on
satellite. Wrap around moisture and frontogenesis on the NW side of
the low is supporting a band of showers over portions the central
and southern mountains. Despite all of the moisture it may be
hindering the instability due to a lack of steep lapse rates. Also,
it would appear that there is some midlevel capping that is keeping
convection from developing. Persistent heating and lift on the NW
edge of this band is the best location for storms later this
afternoon. The models are still struggling with how far west this
convection will extend. In fact, the HRRR is consistent with showing
not much removed from the band itself. The northeastern side of the
San Juans and southern Sawatch will see the most precipitation due
to the frontogenesis band, upslope and possible convection through
the late evening. A few showers and or storms may move over the
Grizzly Creek burn scar, but as of now the potential for heavy
rainfall is low. Only small concern would be training as shown by
some high-res models. Luckily those rainfall amounts are generally
below trigger amounts. The precipitation diminishes after midnight
as the band weakens and the atmosphere stabilizes.
Tomorrow residual moisture will support terrain driven convection
over most of the ranges, but focused along the Divide. A subtle
wave may also track over the area in the evening, and possibly
support additional convection that develops over the higher
terrain in eastern Utah before moving eastward. Most of the lower
valleys in this region will stay dry, but have the potential for
virga showers and strong wind gusts. Temperatures will climb above
normal tomorrow as a weak ridge builds over the forecast area.
.LONG TERM...(Thursday through Tuesday)
Issued at 141 PM MDT Tue May 18 2021
The pressure gradient will tighten as a large low pressure trough
dives into the northern Great Basin from the Pacific Northwest by
Thursday afternoon. Drier air will advect in from the Desert
Southwest ahead of this low with H7 winds in the 30 to 40 kt range
out of the southwest. This will lead to the potential for critical
fire weather conditions across much of the area, dependent on the
fuels status. Either way, it looks to be dry and windy on Thursday
with a return to warm, above normal temperatures as highs jump to
about 10 degrees above normal. A 100 kt jet streak will rotate
around the base of this low into eastern Utah by Thursday night,
allowing decent moisture to advect into the Four Corners region
heading into the day on Friday. Specific humidities are forecasted
to jump upwards of 5 to 6 g/kg with precipitable water values up to
0.7 inches in some areas. Friday appears to be the best chance for
more widespread precipitation. Extensive cloud cover coming in
Thursday night may limit convective potential for the day on Friday,
but still wetting rains will be welcome. The best QPF at this time
appears to favor the San Juans. Cooler temperatures will also follow
for Friday due to increased clouds and showers.
Conditions dry out again by the weekend as the upper low gets closer
and moves into Nevada with a 125 kt jet moving overhead. This will
again advect drier air by Saturday and Sunday with increasing winds,
leading to potential fire weather concerns once again dependent on
fuels status and how much wetting rain is received Friday. Daytime
heating and instability under the trough will still result in some
afternoon convection over the higher terrain both Saturday and
Sunday with most lower elevations remaining dry as this trough lifts
northeast over the northern Rockies. Our CWA will remain under the
influence of the upper level jet at the base of the trough during
this time, leaving us on the drier side of things. Monday appears to
be a transition day with calmer conditions before the next trough
moves into the Pacific Northwest Tuesday. Conditions remain dry
Monday and Tuesday with occasional daytime breezes. Temperatures
will return to near to above normal levels over the weekend through
early next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 545 PM MDT Tue May 18 2021
Scattered showers and storms continue this evening, mainly east
of a line from KEGE to KMTJ to KTEX to KDRO, including KASE and
KGUC. Any shower or storm will be capable of brief reductions in
ceilings to ILS breakpoints and visibility to MVFR. Storms can
also produce erratic wind gusts upwards of 40kt. Shower and storm
activity will wane shortly after sunset with quiet weather to
follow overnight. Wednesday will be a drier day for most, but the
risk for a pop-up shower or storm will return after 18-20Z,
primarily for the eastern mountain terminals.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&
$$
SHORT TERM...KJS
LONG TERM...MDA
AVIATION...MDM
Area Forecast Discussion
National Weather Service Lake Charles LA
1010 PM CDT Tue May 18 2021
.UPDATE...Another round of storms is inbound. The line is
currently passing through the Houston metro. It will advance to
the TX/LA line by around 2 AM and to roughly along I-49 by 6 AM.
The line is moving, however a quick 1 to 3 inches will be
possible. Strong gusty winds may also occur in stronger storms.
&&
.PREV DISCUSSION... /issued 716 PM CDT Tue May 18 2021/
DISCUSSION...
For 00z TAF issuance.
AVIATION...
Satellite imagery/sfc obs show generally clear skies across the
area at this time which should continue next few hours. Forecast
soundings/time-height sections indicate low clouds returning later
this evening in advance of the next MCS getting cranked up over
cntl TX. Latest runs of the HRRR have this feature well sited and
have followed its guidance as far as precip goes...with the squall
line moving into KBPT after midnight, then KLCH/KAEX an hour or so
later, and finally the Acadiana terminals just before sunrise.
IFR/MVFR ceilings should prevail most of the remainder of the
period. Various CAM guidance shows another round of showers/storms
moving in for tomorrow afternoon.
25
PREV DISCUSSION... /issued 352 PM CDT Tue May 18 2021/
DISCUSSION...
Wx map shows tight pressure gradient continuing between high
pressure over the East Coast and low pressure over NM/W TX/OK this
afternoon. Had a localized wake low behind the TSRA complex
across South Louisiana into the coastal waters. This increased
the winds and tides along the coastal parishes, as winds/seas
across the coastal waters. The ongoing Small Craft Advisory
handled the coastal waters. However, the increase in winds this
afternoon, as well as a continued moderate to strong southeast
flow, prompted the need for a wind advisory for the coastal
parishes and counties through Wednesday evening. The increase in
east to southeast winds this afternoon along the coast increased
tidal levels to around 1.0 to 1.5 feet above predicted levels,
which is at high tide now through this evening. Thus, have a
Coastal Flood Advisory for Jefferson, Cameron, Vermilion through
10 PM.
Now for the precipitation/rainfall forecast. Radar showing the
numerous coverage over Lower Acadiana into the coastal waters,
otherwise, no precipitation is occurring for Southeast Texas and
only patchy light rain over Central and Southwest Louisiana. This
will change later this evening and especially overnight as the
next upper level impulse has already ignited the next wave of
thunderstorms over Northeast Texas and another batch over Central
Texas. This will continue to move east to southeastward this
evening and overnight, increasing chances of thunderstorms
significantly around late evening/early morning hours over
Southeast Texas, and the remainder of the area overnight into
Wednesday morning. Will have intermittent breaks by Wednesday
afternoon and evening, but appears to be yet another significant
impulse to bring widespread thunderstorms with heavy rainfall
Thursday. Very challenging to attempt rainfall numbers for now
through Thursday afternoon, but latest coordinated QPF numbers
will continue the 5 to 10 inches of additional rainfall with
locally higher amounts possible. This is stated in the Flash Flood
Watch that continues through Thursday evening.
For the remainder of Thursday night into Friday, continues to look
fairly wet with showers and thunderstorms likely. Will have to
address this later this week if the Flash Flood Watch may have to
be extended. By the weekend, high pressure at the surface and
aloft over the Southeast U.S. likely to build westward over the
Central Gulf States, bringing drier air aloft and an end to this
prolonged rainfall event.
DML
MARINE...
A moderate to strong onshore flow will continue this week due to
the strong pressure gradient between a surface high pressure area
over the southeast United States and a surface low pressure area
east of the Rockies. The Small Craft Advisory has been extended
through Thursday morning. A series of upper level disturbances
will move across the region producing additional daytime and
overnight showers and thunderstorms over the coastal waters. Some
thunderstorms will be capable of producing strong gusty winds,
higher seas.
&&
.PRELIMINARY POINT TEMPS/POPS...
AEX 69 81 67 80 / 70 80 50 80
LCH 72 82 70 81 / 80 90 80 90
LFT 70 82 70 81 / 60 80 60 90
BPT 71 82 70 81 / 80 70 80 90
&&
.LCH WATCHES/WARNINGS/ADVISORIES...
LA...Flash Flood Watch through Thursday evening for LAZ027>033-
041>045-052>055-073-074.
Wind Advisory until 7 PM CDT Wednesday for LAZ052>055-073-074.
TX...Flash Flood Watch through Thursday evening for TXZ180-201-215-
216-259>262.
Wind Advisory until 7 PM CDT Wednesday for TXZ215.
GM...Small Craft Advisory until 7 AM CDT Thursday for GMZ435-450-452-
455-470-472-475.
Small Craft Exercise Caution through Thursday morning for GMZ430-
432.
&&
$$
Area Forecast Discussion
National Weather Service Medford OR
248 PM PDT Tue May 18 2021
.DISCUSSION...The weather pattern will shift from a long period of warm
and dry to a period of cool and cloudy with some shower chances.
Breezy to windy and cooler conditions are expected this afternoon.
Temperatures this afternoon will be about 10 degrees lower than
yesterday. A broad upper trough is responsible for this change in
weather, and an upper low will slowly push south and east over the
forecast area through Thursday, lingering just to the east of the
forecast area through the weekend.
Some of the weather with this low will be impactful, including
cold overnight low temperatures, high terrain snowfall, and
thunderstorms. First, Wednesday night/Thursday morning low
temperatures will be 5 to 10 degrees below morning. This means
that some freezing conditions (32F and lower) are possible in
Siskiyou County, and generally frost conditions (33-36F) will be
possible in some of the colder valleys west of the Cascades. If
there were no clouds, temperatures would likely be colder
Wednesday night, but some clouds are expected and should keep
temperatures from reaching their coldest potential readings.
Growing/agricultural interests should stay tuned and take
necessary precautions.
As the upper low moves overhead Wednesday night, some models
(particularly HRRR and GFS) suggest significant late season snowfall
in portions of Lake and Modoc Counties. Significant is subjective
this late in the season, but we`re highlighting areas where 1-4
inches of snow will be possible, including Highway 299 at Cedar Pass
and Highway 140 at Warner Mountain Pass. The Warner Mountains should
be the focus for most of the snowfall because of the high elevation
and the upslope/enhanced precipitation under northwest flow. Some
snowmelt is likely on lower elevation roadways, but visibilities
will be low in snowfall.
Another effect from the low will be thunderstorm chances. First,
some instability in Douglas County Wednesday afternoon brings a
slight chance of thunderstorms there. The cold pool of air aloft
that could generate storms in Douglas County will move southeast to
a location over Modoc and Southern Lake County Thursday afternoon,
and there is a slight chance of storms there. Because the low
lingers through the weekend, there will be continued chances for
thunderstorms east of the Cascades Friday and Saturday afternoons.
Precipitation with this low, as can happen during the springtime,
will be focused along and east of the Cascades. Data from the
National Blend of Models suggests there`s about a 40 percent chance
for many areas east of the Cascades to get a tenth of an inch of
precipitation in 24 hours on Wednesday, Thursday, and Friday. In
contrast, the chances for 0.1 inches of daily rainfall west of the
Cascades are much less on these days. So while temperatures will be
cool, and there will be some clouds west of the Cascades, we`re not
expecting much in the way of rainfall for these areas.
As the influence from the upper low wanes late in the weekend into
next week, temperatures will moderate with values returning to near
or above normal. Of note, there have been previous model
run/ensemble indications that upper troughing will return/continue
over the forecast area and keep things cool, but the morning suite
of model data did not favor this solution.
&&
.AVIATION...For the 18/18Z TAF Cycle...Overall, conditions are VFR
this morning west of the Cascades, but higher terrain will likely
remain obscured into the afternoon with scattered cumulus clouds in
the area. VFR will prevail east of the Cascades and winds will
become gusty across the region this afternoon and evening. -Miles
&&
.MARINE...Updated 200 PM PDT Tuesday, 18 May 2021...A change to a
more spring-like pattern is expected this week as upper level
troughing settles over the Pacific Northwest. This will bring
periods of gusty north to northwest winds as well as light
precipitation at times. Northwest swell will be increased compared
to last week, but is only expected to peak in the 5 to 7 foot range.
However, this swell combined with choppy wind seas will result in
conditions hazardous to small craft beginning Wednesday afternoon
and likely continuing into Friday. At first, conditions hazardous to
small craft will be limited to areas south of Gold Beach on
Wednesday. Then, as north winds increase across all areas Wednesday
night, hazardous conditions are likely to spread across all the
waters Thursday into Friday. Conditions improve over the weekend as
northerly winds diminish and swell subsides.
&&
.FIRE WEATHER...Updated 230 PM PDT Tuesday 18 May 2021...Winds will
remain breezy this afternoon as an upper level low begins to move
onshore. Once that low moves onshore, we`ll see temperatures trend
lower and humidities continue to trend slightly higher compared to
today, Tuesday. There is a 20% chance for some cloud to ground
lightning around Douglas County Wednesday afternoon once the low
moves onshore. Otherwise, We`ll see breezy winds continue on the
afternoons of Wednesday through Friday.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 11 PM Wednesday to 11 AM PDT
Thursday for ORZ031.
CA...Winter Weather Advisory from 11 PM Wednesday to 11 AM PDT
Thursday for CAZ085.
Pacific Coastal Waters...Small Craft Advisory from 2 PM Wednesday to 5 PM PDT Thursday
for PZZ356-376.
Small Craft Advisory from 5 AM to 5 PM PDT Thursday for
PZZ350-370.
$$
AREA FORECAST DISCUSSION
National Weather Service Morristown TN
1009 PM EDT Tue May 18 2021
.UPDATE...
EVENING UPDATE.
&&
.DISCUSSION...
Still a few light returns on radar mainly to our southwest that
have been diminishing as they edge into our area, but a few
sprinkles/light showers may make it to the surface over the next
few hours so will bump PoPs up to slight chance for our southwest
corner. Otherwise, forecast generally looks to be on track so just
a few tweaks mainly to temps and dew points.
&&
.AVIATION...
00Z TAF DISCUSSION.
There will be varying amounts of mainly high/mid clouds around,
along with some scattered cu mainly afternoon/evening hours. Main
aviation weather concern looks to be the possibility of fog
developing later tonight mainly at TRI. Right now confidence in
any fog development is low so will just include a tempo group of
fog with MVFR level vsby at TRI for a few hours late tonight.
Otherwise, VFR conditions expected for the period all sites.
LW
&&
.PREV DISCUSSION...
/ISSUED 328 PM EDT Tue May 18 2021/
SHORT TERM...(Tonight and Wednesday)
Key Messages:
1. Light showers and isolated thunderstorms dissipate this evening.
2. Heat builds Wed with just isolated thunderstorms mainly over
higher terrain areas of the eastern mountains, SW VA, and Plateau.
Discussion:
Late Afternoon/Evening...
Light showers associated with WAA/weak isentropic ascent and lift
near the right entrance of a 40-50 kt upper jet streak on the NE
side of the building ridge across the Carolinas continue this
afternoon. Most of this activity has been confined to the S Plateau
and S Valley and has struggled to reach the ground due to low-level
dry air, and recent radar loops suggest a diminishing trend. Cloud
cover and weak mid-level lapse rates around 5 C/Km per RAP soundings
have limited MLCAPE to generally less than 250 J/Kg this afternoon,
so convection is unlikely. However, given the aforementioned jet
support and weak ascent, kept isolated thunder in the forecast from
the N Plateau through NE TN and SW VA through mid evening before
dissipating.
Tonight and Wednesday...
The mid/upper ridge will continue to build across the eastern CONUS
through the period as deep mid/upper troughing digs into the Pacific
NW, with anomalous H5 height values nearing 590 DAM across the
Carolinas and Mid Atlantic by late Wed. These dramatically
increasing height and thickness values combined with strong WAA on
the west side of a 1030 mb surface high offshore of the Carolinas
will allow highs to reach the low/mid 80`s Wed after a mild morning
start with lows tonight only in the upper 50`s/low 60`s. The
sharpening mid/upper ridge axis poking into the Great Lakes will
also shunt the greatest moisture plume westward toward the MS
Valley. The best moisture plume shifting W, relatively dry low-
levels with Td`s only in the 50`s, and strengthening mid-level
capping will greatly limit the coverage of diurnal convection.
Despite this, stayed with slight chance PoPs for higher terrain
areas of the E TN mountains, SW VA, and the N Plateau in the
afternoon since southeasterly low-level flow will produce upsloping
that could ignite isolated cells in the terrain. HREF guidance hints
at this possibility as well with a few cells depicted forming over
western NC/Blue Ridge and drifting west/northwestward. Any
thunderstorm will be short lived.
Garuckas
LONG TERM...(Wednesday Night through Tuesday)
Key Messages:
1. Anomalously strong ridging will bring much above normal
temperatures from Friday through early next week.
2. Strong upper ridge will keep us dry through the period.
Discussion:
Surface ridging will be centered across the Southern Appalachians
through the Mid Atlantic on Thursday with upper ridging rapidly
strengthening across the Southeast CONUS and Midwest. This 591 to
593 dam 500mb ridge will be centered across the Tennessee Valley and
Mississippi River Valley on Friday through the weekend. NAEFS
forecast data shows that these upper heights are at the maximum of
climatological record for this time of year. In addition, low-level
heights at 850mb are forecast to be at record high values for this
time of year. This will result in strong subsidence across the
forecast area with anomalous warmth. Temperatures are forecast to be
at least 10 to 15 degrees above normal, and max temperatures may
approach record highs in this weekend through early next week.
With the strong ridging and subsidence, precip is unlikely through
the extended. Due to differential heating along the higher
elevations, isolated light convection will be possible late this
weekend and early next week; however, it is expected to be too
isolated and minor to even mention in the forecast at this time. In
addition, guidance is beginning to shift the ridge axis westward
late weekend and early next week which would place parts of our area
within NW flow aloft along the eastern periphery of the ridge. In
this scenario, the short-term forecast would need to be closely
monitored early next week for any minor shortwaves or MCVs within
the NW flow which could produce more widespread convection across
portions of the forecast area.
JB
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 63 84 62 86 60 / 20 10 0 0 0
Knoxville McGhee Tyson Airport, TN 61 83 59 85 57 / 10 10 0 0 0
Oak Ridge, TN 60 83 58 86 57 / 10 10 0 0 0
Tri Cities Airport, TN 55 80 54 83 53 / 10 10 0 0 0
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
Area Forecast Discussion
National Weather Service Topeka KS
557 PM CDT Tue May 18 2021
...AVIATION UPDATE...
.DISCUSSION...
Issued at 325 PM CDT Tue May 18 2021
Latest water vapor satellite and profilers show a mid level vort
lobe moving northeast out of Oklahoma at 19Z. An area of convection
has been moving across south central Kansas and into parts of
southeast Kansas. CAMS and HREF members have shown various scenarios
through the day with them being split. Now that convection has
developed expect it to continue to move northward through the rest
of the afternoon and through the evening hours. With PWs remaining
high across eastern Kansas and moisture flux continuing through the
night, isolated locally heavy rainfall will again be possible which
may cause some additional flooding concerns across the CWA. Low end
to marginal shear and instability may lead to an isolated strong to
severe storm with hail the main hazard tonight.
Scattered storms may be ongoing in the morning on Wednesday morning
with additional redevelopment in the afternoon and overnight hours
as additional lobes move northward into central and eastern
Kansas. Again little will change with regards to moisture flux in
to eastern Kansas with low level southerly flow off the Gulf into
the central Plains. Isolated locally heavy rainfall will again be
possible. The trough over the Rockies today will gradually move
out across the southern and central Plains through Thursday
keeping chances for showers and storms in the forecast. Highs
remain in the 70s Wednesday and Thursday with 80s on Friday where
chances of precipitation wane.
Low end chances for precipitation continue from late weekend into
early next week. A frontal boundary may move back into the area
which will be a focus for convection once again.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday)
Issued at 557 PM CDT Tue May 18 2021
Timing TS will be the bigger challenge this evening. A very humid
airmass is setting the stage for heavy rain, so when TS impact the
terminals brief IFR conditions with restricted VSBY are expected.
Will use the consensus of the CAMs to get an initial timing for
storms at the terminals. The other concern is low clouds once
again. CONSShort is slower to bring MVFR CIGS into the terminals
while the RAP is much more aggressive. Given the past several
days, am inclined to follow the RAP. But confidence is marginal so
will stick with the blend and watch for signs conditions are
lowing quicker.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...53
AVIATION...Wolters