Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/24/20
Area Forecast Discussion
National Weather Service Bismarck ND
950 PM CDT Thu Jul 23 2020
Issued at 948 PM CDT Thu Jul 23 2020
We will cancel Severe Thunderstorms Watch 397. Scattered
thunderstorms are still forecast by several CAM models across teh
northwest and north central later tonight. At this time we feel
there is an isolated threat late tonight northwest and north
UPDATE Issued at 808 PM CDT Thu Jul 23 2020
With this update we will drop the southern counties from Severe
Thunderstorm Watch 397, Bowman, Slope, Adams, Hettinger and Stark.
UPDATE Issued at 644 PM CDT Thu Jul 23 2020
Scattered thunderstorms hugging the western border this evening.
RAP soundings still show a weak EML across portions western North
Dakota, which may be hindering some of the initiations.
We slowed the eastward progression of the system slightly this
evening. otherwise current forecast looks ok.
UPDATE Issued at 328 PM CDT Thu Jul 23 2020
This update for severe thunderstorms watch 397 for western North
Dakota until 10 pm CDT.
.SHORT TERM...(Today through Tonight)
Issued at 118 PM CDT Thu Jul 23 2020
Forecast highlights in the short term period will be strong to
severe thunderstorm chances later today through this evening west
into north central.
Currently, upper level ridge axis over the central Dakotas early
this afternoon, with a potent S/WV upper trough lifting into
southeastern Montana. Associated sfc trough stretched from south
to north across northeastern Wyoming and far eastern Montana.
Strong southerly flow ahead of the sfc trough has resulting in
warm and humid conditions across western and central North Dakota,
with heat index values well into the 90s many areas.
The aforementioned S/WV will continue to lift north/northeast
across eastern Montana this afternoon, then crosses into
northwestern North Dakota early this evening. Not much has
changed from earlier thinking regarding thunderstorm development,
coverage, and severity. Convection still expected to fire off
along the sfc trough axis/frontal boundary over far eastern
MT or far western North Dakota during peak heating as forcing
aloft increases, then proceed north and northeast over western and
north central areas of the state through the evening.
Plenty of instability for strong to severe storms with 2500-3500
J/kg of CAPE, though bulk shear is still lacking at roughly 20-30
Kts. Capping inversion will also likely limit storm coverage, and
as mentioned in earlier discussions may suppress convection
entirely especially farther south. Regardless, will keep the
mention of severe in all products for the west and north central
given the instability and forcing. Shear/deep layer mean wind
vectors oriented mainly parallel to the surface trough, though
maybe more orthogonal south though this area may remain capped
but can`t rule out a discrete storm or two here. To the north
where the stronger forcing will be, a multicell mode with linear
clusters would be more favored meaning damaging winds the primary
Severe storm risk should end by 09Z at the latest as the S/WV
lifts north into Canada.
.LONG TERM...(Friday through Thursday)
Issued at 118 PM CDT Thu Jul 23 2020
Warm and humid conditions continue both Friday and Saturday,
especially over my southeast where models depict mid 70s dewpoint
temperatures both days. Excessive heat watch in effect for the
southern James River Valley for Friday afternoon/eve, and will
leave this as is with this product issuance to allow the mid shift
tonight to get the latest data to make headline decisions.
Introduced some low POPs Friday morning 12-18Z across my south.
Upper level jet streak will be lifting northeast into the Dakotas
along with elevated instability for a few showers/storms. A few of
the CAMs have this as well, or did, so this was added.
Chance for strong to severe convection for Friday aft/eve remains
along to east of the frontal boundary, across far south central
and eastern North Dakota. Best bulk shear lags a bit to the west
though, but maybe a bit better linkage right along the front. Shear
vectors are also parallel to the boundary favoring messy multicell
convection. One thing the previous forecast picked up was the
heavy rain potential Fri aft/eve. Strong low level moisture
transport and high precipitable water will increase the threat for
heavy rainfall, especially if we see any storms moving over the
For Saturday, sfc boundary reestablishes over western North Dakota
in the morning, then shifts east during the day as a vigorous
northern stream S/WV approaches and moves into northeast Montana
by late Sat afternoon, which is faster than previous models had
depicted. Still better 0-6km bulk shear and instability linkage
along the front on Saturday, though shear vectors a mix of
orthogonal and parallel to the eastward moving boundary,
resulting in a mix of storm modes possible given latest model
Sunday will be quiet, cooler, and less humid with sfc high
pressure building across the Dakotas, with dry conditions lasting
into Monday as well. Upper level ridge moves into our area
Tuesday, then to our east Wednesday when we see a return of
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 644 PM CDT Thu Jul 23 2020
At 6 pm CDT, VFR conditions prevail. A wind shift/surface trough
in eastern Montana will be the focus for thunderstorms this
evening across western North Dakota. Hazards to aviation will be
the scattered thunderstorms KXWA-KDIK between 00-03z, and a
scattered thunderstorms after 03z KBIS-KMOT.
Excessive Heat Watch from Friday afternoon through Friday
evening for NDZ048-051.
Area Forecast Discussion
National Weather Service Birmingham AL
703 PM CDT Thu Jul 23 2020
Evening Update and 00Z Aviation.
/Updated at 0642 PM CDT Thu Jul 23 2020/
The latest RAP analysis has the precipitable water axis shifting
northward and into Central Alabama. This gradient area was also
the highest SBCAPE zone and highest low level lapse rates. There
are at least two distinct outflow boundaries moving through
Central Alabama at this time. One was more east/west moving north
while another was more north/south and moving north northwest. The
flow through the atmospheric layer is also becoming much more
cyclonic due to the presence of Tropical Depression 8 in the
northern Gulf. Upward vertical motion decrease combined with loss
of daytime heating should allow a slow decrease of the convective
activity the next few hours. Did increase pops up to near TCL-BHM
and areas south.
Previous short-term discussion:
/Updated at 0112 PM CDT Thu Jul 23 2020/
The Bermuda High remains branched across the Southeast, especially
strong in the lower levels while a shortwave trough is moving
through the Ohio Valley. Convection and expansive cloud cover,
associated with the trough, is currently located over a large area
from Tennessee to the New England states. For Central AL, less
activity has been noted so far due to a pocket of dry air and
subsidence over the area, especially in the north. This dry air
should reduce rain chances north of I-20 this afternoon as the
majority of synoptic lift remains north of Alabama while highs rise
into the low to mid 90s.
However, abundant, tropical moisture is present over the Florida
Panhandle (PWATs ~2-2.1 inches per RAP mesoanalysis) which is
surging northwestward as Tropical Depression Eight continues to
track towards the Texas coast. On radar, scattered showers and
thunderstorms are focused primarily along the Florida Panhandle
and southern Georgia with a northwestward motion. Expect the
highest coverage of scattered to possibly numerous
showers/thunderstorms to move into our southern half this
afternoon, especially along and south of the US 80/I-85 corridor,
diminishing gradually through the evening.
Tomorrow, the setup is quite similar. 40-50% PoPs will be focused in
our far southwest as Tropical Depression Eight moves into the
western Gulf with similar chances expected in our northeast as the
aforementioned shortwave trough flattens over the eastern coastline,
unable to overcome the persistent subtropical ridge in the western
/Updated at 0151 PM CDT Thu Jul 23 2020/
The long-term forecast trends remain mostly on track this
afternoon with the continuing trend of a more unsettled pattern
shaping up next week with tropical moisture dominating over the
region. Long-range guidance is still picking up on the mid to
upper level features developing to our southwest near the
Louisiana coastline by Monday morning which is more pronounced on
the GFS as opposed to the ECMWF. Scattered to numerous showers and
storms can be expected to develop each afternoon from Monday
through Wednesday in response to the synoptic lift from the mid to
upper level disturbances along with tropical moisture and
diurnally driven convective activity. Likely rain chances will be
maintained during this time, along with temperatures a degree or
two lower due to increased clouds and rain chances.
Previous long-term discussion:
/Updated at 0315 AM CDT Thu Jul 23 2020/
Saturday and Sunday.
Broad deep-layer ridging is forecast to amplify and strengthen
across the Central CONUS by the weekend. Low to mid-level sub-
tropical ridging will continue to remain in place across the
Southeast Coast and offshore, with weak southeasterly low-level flow
across Central AL. Ample heat & humidity is expected to persist
across the area, with a scattering of afternoon showers and
thunderstorms again Saturday and Sunday. PoPs continue to be a
tricky forecast, though I`ve favored areas where better moisture and
forcing is expected. This appears to be in the northeast/east on Sat
and Sun in association with a remnant/weak upper-level perturbation
(this is the tail end of a more prominent trough ejecting across the
Northeast). Highs are forecast in the low to mid 90s, with perhaps
an upper 90 value in places. This continues to promote heat indices
in the 100-105 range which will remain mentioned in the HWO.
Monday through Wednesday.
Weak flow is progged to remain across the Deep South as we remain
wedged between tropical easterlies to the south, and prevailing
westerlies to the north. In between the two, guidance continues to
suggest weak upper-level features which could meander about our
area. These could have an impact on day-to-day rain chances, but
it`s hard to say how this far out. Nonetheless, afternoon heating
and sufficient moisture continue to promote diurnally-driven
convective rain chances into next week. With less prominent ridging
finally working into the region, as well as mean PW values possibly
in the 1.9-2.1" range after Mon, I did show a trend of decreasing
temperatures and leaned more toward the upper 80s to low 90s by
Tue/Wed. By then, a distinct Rossby Wave is progged to move across
the Great Lakes region with a trough axis and associated surface
front farther south and into the Deep South Wed afternoon. Against
my better judgment I included likely PoPs Wed in anticipation of
additional forcing amidst an already moist/unstable tropical warm
sector. Outside of these considerations, any tropical disturbances
in the Caribbean and Gulf of Mexico will be watched.
00Z TAF Discussion.
It appears that there is more saturation potential in the lowest
levels of the column overnight, therefore added mention of MVFR
ceilings at a few locations and will monitor for lower ceilings.
Additionally, added mention of SHRA/TSRA the next few hours at
several sites due to ongoing convection. Similar conditions
anticipated on Friday.
One outflow oriented east/west and another north/south were moving
over Central Alabama at this time. The loss of daytime heat and
decrease in vertical motions should allow the activity to slowly
decrease the next several hours. However, there is enough coverage
to mention prevailing or tempo at a few spots. The strongest
storms will produce some wind gusts into the 25-35kt range.
Deep southeast flow will keep plenty of moisture overhead and it
appears there is a better chance tonight to experience low
ceilings. Started off with MVFR mention in a few locations and
will have to monitor closely for ceilings the 025 mentioned. More
of the same on Friday as thunder develops in the afternoon.
Afternoon minimum RH values should remain near or above 40
percent today and above 45 percent Friday through Monday.
Isolated to scattered showers and thunderstorms will remain in the
forecast through the period with best chances during the
afternoon and into the early evening hours. Some localized areas
of patchy fog may develop overnight in areas that receive heavy
rain earlier that day. Surface and transport winds are expected to
remain fairly light but generally out of the southeast through
this weekend. Afternoon heat indices are expected to peak in the
100-105 range through this weekend. Moisture values and rain
chances remain somewhat elevated into next week.
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 71 92 71 92 71 / 20 50 20 50 20
Anniston 71 92 71 93 71 / 20 50 20 50 20
Birmingham 73 93 74 94 74 / 30 30 20 50 20
Tuscaloosa 73 93 74 94 73 / 50 20 20 40 20
Calera 71 91 71 92 72 / 60 20 20 50 20
Auburn 71 90 73 91 72 / 40 20 20 50 20
Montgomery 73 93 74 94 73 / 40 30 20 50 20
Troy 72 92 72 94 72 / 30 30 20 50 20
Area Forecast Discussion
National Weather Service Grand Forks ND
1038 PM CDT Thu Jul 23 2020
Issued at 1033 PM CDT Thu Jul 23 2020
Storms to the west have weakened and stayed mostly along the MT
state line. Guidance continues to show a cluster move across north
central MN around midnight as the main wave moves north. Will
maintain low POPs in the west but hi-res models are a tad further
west than previous runs, so thinking they will likely remain west
of Devils Lake.
UPDATE Issued at 627 PM CDT Thu Jul 23 2020
The main concern for this evening`s updates will relate to how
things evolved out west, as a cluster of storms moves from far
northwest SD into southwest ND. There is decent model agreement
with a cluster of storms moving from current location into the
Turtle Mountain area later tonight, and just clipping our
northwest zones. However, the latest NAM guidance continues to
bring a cluster from central South Dakota into southeastern North
Dakota. This has been an outlier although the HRRR does bring
storms into west central MN closer to daybreak, so will be
something to watch as things continue to develop in the western
half of the state. No changes planned now for the ongoing
.SHORT TERM...(This evening through Friday night)
Issued at 314 PM CDT Thu Jul 23 2020
Convective chances and strength along with heat will be the main
issues for the period.
Storms that have been riding over the ridge and into the northern
Red River Valley are finally starting to dissipate. SPC meso page
has the mixed layer CAPE still pretty capped, so think we should
have a bit of a break in convection until the main shortwave
currently over southeastern MT lifts northeastward. The main upper
forcing will be staying mostly northwest of our counties, and deep
layer bulk shear is not too impressive at 25 to 30 kts. However,
MU CAPE values late tonight are very high at over 3000 J/kg, and
there will be a low level jet feeding into eastern ND. Some storms
pulsing up to produce 1 inch hail or brief downbursts are not out
of the question.
Many of the CAMs and even global models are showing some lingering
of the convection across western MN into Friday morning. The
surface trough axis will have stalled to the west of us and
southerly winds bringing humid air will continue. Depending on how
much clearing and heating behind the morning convection, temps
will rise into the 90s and there could be heat index values in
the 100 to 105 F range by tomorrow afternoon. However, still
uncertain with cloud cover and how convection plays out tomorrow,
so will keep our area in the watch phase for now.
The heat and moisture will provide plenty of CAPE to work with
tomorrow as the next weak shortwave comes through the
southwesterly flow aloft. Deep layer bulk shear is not overly
impressive at least early on, but improves later in the evening.
At this point it seems likely that storms will fire to our west
closer to the surface trough and then coming into our CWA as a
messy complex with the potential for wind. Heavy rain will also be
a threat with PWATs around 1.8.
.LONG TERM...(Saturday through Thursday)
Issued at 314 PM CDT Thu Jul 23 2020
Chances for impactful weather will come mostly at the beginning of
the period Sat, with much lower chances from Sun into next week.
This will be in the form of strong to svr tstms and excessive
Severe Wx - A moist airmass with dewpoints in the 70s, steep low
level lapse rates, and CAPE values trending toward 5000 J/Kg will
combine to create opportunities for severe wx overnight Fri into the
first part of Sat. The degree of shear concurrent with the other
ingredients will determine the magnitude of the event; the lack
thereof would lead to more pulse-type convection. Later Sat into Sat
night, the shear may really drop off, leading to more unorganized,
isolated to scattered activity.
Excessive Rainfall - PWATS in the 99th percentile to MAX (near 2
inches south and east of RRV) are still depicted by the NAEFS/GEFS
ensembles; quite reasonable owing to the upper ridge moving to the
east as more hot and humid SW flow heads over our region once again.
As mentioned earlier, except for the Lake of the Woods region, most
areas have received an abundance of rainfall recently, so flooding
concerns could once again surface over the weekend.
Quieter weather will return from Sun into early next week as an
upper trough heads back over the Northern Plains before shifting
east, establishing a "cooler" and drier regime of northwest flow.
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1033 PM CDT Thu Jul 23 2020
CAVOK. Main concern will be convection for remainder of tonight,
and a much higher probability of convection during the last six
hours of this set of TAFs. For tonight, decreasing confidence KDVL
will see TSRA but not out of the question. Latest guidance brings
activity no further east than Leeds ND. Still a chance for
development in SD to move into w cntrl MN near daybreak, but not
enough confidence in this scenario to mention in TAFs. More
widepsread storms expected late in the TAF period tomorrow.
ND...Excessive Heat Watch from Friday afternoon through Friday
evening for NDZ016-027-029-030-038-039-049-052-053.
MN...Excessive Heat Watch from Friday afternoon through Friday
evening for MNZ001>003-007-029-030-040.
Area Forecast Discussion
National Weather Service Houston/Galveston TX
549 PM CDT Thu Jul 23 2020
A few showers will be possible this evening as a weak disturbance
rotates into the area but probabilities look too small to mention
in the TAFs but latest HRRR suggests that some showers could
affect KHOU and KGLS after 06z. Better rain chances will develop
on Friday as PW values increase to 2.40 inches as TD 8 approaches.
Could be some brief MVFR ceilings between 11-15z with BKN VFR cigs
in the afternoon. Transitioned from AM showers to PM storms.
Winds will be E-NE and increase with gusts possible in the
.PREV DISCUSSION... /ISSUED 422 PM CDT Thu Jul 23 2020/
SHORT TERM...(Tonight through Friday Night)
CHANGES: Dropped the TS Watch for southern Liberty County and
added a TS Warning for inland Jackson and Matagorda Counties.
A Tropical Storm Warning is in effect from San Luis Pass southward
along the Texas coast and a Tropical Storm Watch remains in
effect from High Island to San Luis Pass. TD 8 continues to churn
in the west central Gulf of Mexico and satellite imagery is
looking more impressive with the storm.
A few showers and thunderstorms developed along the coast but most
of the area has been hot and dry this afternoon. A weak disturbance
rotating around the broad circulation of TD 8 could bring additional
showers into the coastal sections of SE TX tonight. PW values
increase overnight and reach 2.20 inches by morning. With the
increase in moisture, showers near the coast will begin to
increase in coverage toward sunrise. As TD 8 moves closer to the
coast, moisture levels will increase further reaching 2.60 inches
by tomorrow afternoon. Fcst soundings look saturated between
18-00z and will carry chance PoPs over the NW zones, likely PoPs
over the central zones and numerous at the coast. Rain chances
will continue Friday night as TD 8 nears the middle Texas Texas
Coast. With PW values at or above 2.50 inches, feel there is some
threat for locally heavy rainfall totals. Will hold off on a Flash
Flood Watch for now but the southern part of the region may
require a Watch with later updates. 43
LONG TERM...(Saturday through Thursday)
The circulation of TD 8 will move inland early Saturday but a
weak trough will develop from the circulation and extend east
northeast across the NW gulf. The trough will remain nearly
stationary through Monday and serve as focus for scattered to
numerous showers and thunderstorms. PW values remain near 2.50
inches on Saturday and will mention locally heavy rain for
for the southern half of the region. PW values decrease a bit
Sunday and Monday but will remain close to 2.25 inches both days.
Probably still some risk for locally heavy rains both days with
the high PW air and the stationary trough. Clouds and precip
should keep high temperatures a bit below climo. Moisture levels
will drop a bit more on Tuesday and Wednesday but it still looks
sufficient for mainly diurnally driven showers and thunderstorms.
MaxT on both days will show a gradual warming trend as convection
will become more scattered. 500 mb heights will begin to increase
on Thursday as upper level ridging over the Rockies begins to
expand. Moisture levels will decrease further and temperatures
will begin to warm with high temperatures probably making a return
into the mid/upper 90s by the end of next week. 43
Will maintain the Tropical Storm Warning over the Gulf waters and
adjacent bays as TD 8 slowly strengthens. Sustained winds could
reach 50 knots as TD 8 approaches the middle Texas coast. Water
levels will increase as well and could reach 3.4 feet at high tide
on Friday. If winds reach 50 knots, there will be a healthy bump
up in seas with some potential for seas to reach or exceed 10
feet over the southern waters. Once TD 8 makes landfall, moderate
SE winds will persist through Tuesday with a decrease in seas.
Winds will veer to the south on Wednesday and persist through
Friday. Mariners should keep up with the latest forecasts and stay
alert for changes. 43
Periods of heavy rain will be possible through the weekend in
association with TD 8. The best potential for heavy rain will be
along the coast and over the SW zones. If heavy rain develops,
watersheds mostly likely to be impacted will include the Lavaca-
Navidad system and possibly the lower end of the San Bernard
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 77 94 77 90 75 / 10 30 30 70 30
Houston (IAH) 78 91 78 88 77 / 20 70 60 80 50
Galveston (GLS) 81 89 81 89 80 / 50 80 80 90 70
TX...Tropical Storm Warning for the following zones: Brazoria
Islands...Coastal Brazoria...Coastal Jackson...Coastal
Matagorda...Inland Jackson...Inland Matagorda...Matagorda
Tropical Storm Watch for the following zones: Chambers...Coastal
Galveston...Coastal Harris...Galveston Island and Bolivar
Peninsula...Inland Brazoria...Inland Galveston...Wharton.
GM...Tropical Storm Warning for the following zones: Coastal waters
from Freeport to Matagorda Ship Channel TX out 20 NM...
Matagorda Bay...Waters from Freeport to Matagorda Ship
Channel TX from 20 to 60 NM.
Tropical Storm Watch for the following zones: Coastal waters
from High Island to Freeport TX out 20 NM...Galveston Bay...
Waters from High Island to Freeport TX from 20 to 60 NM.
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
903 PM EDT Thu Jul 23 2020
A cold front will drop south across our region late Friday.
High pressure will then dominate over the weekend before a warm
front advances back northward across the region on Monday.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Main shortwave trough remains near the upper Ohio Valley, while
a weaker perturbation may be near the local area. Earlier, a
broken line of convection slowly moved east from the mountains
while other storms developed over southeast Virginia. The
outflows from these areas of convection are currently colliding
across the Washington DC metro. Mesoanalysis shows 2000+ J/kg of
MUCAPE, precipitable water greater than 2 inches, deep warm
cloud layers, and weak flow (augmented by variable winds from
the outflows). Since it became evident this would occur across
the metro area, where flash flood guidance is 1-1.5 inches
across most of the area, though those values could easily be
exceeded, leading to at least localized flash flooding.
Therefore hoisted a small short-fused Flash Flood Watch. The
only uncertainty is what happens to the storms after they
develop and where they move (or collapse). However,
radar/satellite trends over the past 30 minutes are seeming to
verify there will at least be a short term flooding threat.
There could still be a brief severe threat with any stronger
updrafts with locally damaging winds.
Elsewhere, convection is generally trending downward. However,
many models show a persisting threat of showers (and perhaps a
few thunderstorms) lasting into the night. Since a lot of the
area has seen showers or storms this evening, and instability is
expected to generally decrease, don`t think convection will be
strong... although HRRR simulated reflectivity has been showing
the potential for stronger cells.
Patchy fog may form where it has rained and if there is
sufficient clearing. Overnight lows will range from the mid 60s
to mid 70s.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
A cold front will push across the region on Friday. Until then,
additional showers and thunderstorms will develop late Friday
morning and Friday afternoon. Severe threat is substantially
lower as well, but non-zero, particularly over southern MD.
Marginal risk out from SPC for this area, with damaging winds
the primary threat.
Showers and thunderstorms should move to our south Friday
evening. High pressure will build in Friday night.
High temperatures on Friday will be in the upper 80s/low 90s,
and perhaps slightly less humid as well. As a result, don`t see
any need for any heat headlines on Friday at this point.
Dry weather is expected for most of the area. Lows will be
slightly cooler than Thursday nights lows, with readings in the
mid 60s to low 70s.
High pressure will be building in from the west Saturday.
However, there may be a bit of surface troughing remaining, and
some guidance shows some isolated convection developing, mainly
along the terrain. Temperatures will generally be seasonable,
with highs in the low 90s. Humidity will be slightly lower too
in the wake of the cold front, so again not expecting heat
headlines on Saturday. Dry conditions continue into Saturday
night with lows in the same range as Friday night.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Drier conditions should prevail during the later part of the weekend
on Sunday with a strong upper level ridge building in from the Great
Plains and Midwest. Hot and humid conditions will return in the
early part of next week bringing in a consecutive round of chances
for showers and storms through Wednesday with any type of shortwave
energy that finds its way into our CWA. Most model guidance favors a
fairly dry Monday leading to a wet pattern starting up Tuesday
afternoon and evening with a cold front linked to an upper level
trough north of the Canadian border. This will progress into early
Wednesday with the afternoon and evening hours drying out with high
pressure starting to build back in.
Hot and humid conditions will build back in on Sunday allowing for
temperatures to reach the low to mid 90s with heat index values
potentially reaching triple digits through Tuesday with a very warm
air mass overhead. Heat advisories will be possible Sunday through
Tuesday. Cold front passage Tuesday night into Wednesday will bring
the temperatures down to seasonal averages with lower humidity added
in, trends are working more in favor for this later in the week but
still early in the forecast.
.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
Heavy thunderstorms near KDCA this evening. A little bit
uncertain as to what transpires moving forward with
counteracting forces between an approaching disturbance and
areas which have already been "worked over" by thunderstorms.
Have kept some mention of precip in the TAFs through 04-06Z,
though there could certainly be some showers and maybe an
isolated storm the second half of the night. Kept a mention of
MVFR BR at MRB and CHO, though relatively overcast skies most of
the night may prevent much fog from forming.
Guidance hints some MVFR ceilings may develop Friday morning for
a few hours near MRB/IAD/BWI/MTN. Scattered storms will be
possible again Friday as a front drops through, though coverage
and intensity should be less. Patchy fog is possible again
Saturday should be a drier day overall, though there could still
be an isolated shower or storm.
No significant impacts expected for terminals Sunday through Monday.
Isolated sub-VFR conditions possible early Tuesday with any storms
that initialize in the area.
Light winds continue through Saturday, except near any
thunderstorms. A threat of storms will linger through tonight
and into Friday, though coverage may be a bit less by Friday
afternoon than in recent days. Drier weather is more likely
Conditions are not expected to reach SCA criteria at this time
Sunday and Monday with a weak disturbance bringing a few showers and
storms to the area. Could see an isolated marine hazard be issued
for any adjacent storms along the bay.
Aside from the one day last week that broke the streak of
consecutive 90+ F days at Ronald Reagan Washington National
Airport (KDCA), every day this month has had a high of at least
As of Thursday afternoon, that total (for July) was up to 22
days. The most 90+ F days ever in any month in the immediate
Washington, DC, area is 25 days (set in July 2011). Looking at
the pattern over the next 7 days, as well as probabilities for
above normal temperatures from our colleagues at the Climate
Prediction Center (CPC) out to 14 days, it seems it will be very
difficult to NOT break that record.
For the Baltimore, Maryland, and Dulles, Virginia long-term
climate records, the record most 90+ F days in a month is 24
days (also set in July 2011). As of Wednesday afternoon,
Baltimore site had hit 90 F 18 times so far this month, and the
Dulles site had hit 90 F 16 days.
Temperature records have been kept at what is now KDCA since
1941. The official temperature records for the immediate
Washington, DC, area consist of data from KDCA starting in 1945,
and observations taken in downtown Washington, DC, extend the
region`s period of record back to 1872.
Temperature records for the Baltimore, Maryland, area have been
kept at what is now Baltimore-Washington International Thurgood
Marshall Airport (KBWI) since 1950. Additional temperature
records observed in downtown Baltimore extend the period of
record back to 1872.
Temperature records for the Sterling-Dulles, Virginia, area
have been kept at what is now Washington Dulles International
Airport (KIAD) since 1960.
All climate data are considered preliminary until reviewed by
the National Centers for Environmental Information (NCEI).
DC...Flash Flood Watch until 2 AM EDT Friday for DCZ001.
MD...Flash Flood Watch until 2 AM EDT Friday for MDZ013-504.
VA...Flash Flood Watch until 2 AM EDT Friday for VAZ052>054.
Area Forecast Discussion
National Weather Service Memphis TN
812 PM CDT Thu Jul 23 2020
A moist, unstable airmass remains in place across the Mid-South
this evening. Convection has been well behaved this evening with
most of today`s diurnal activity already dissipated. We continue
to watch a band of showers and thunderstorms across central MS/AL
that is lifting to the northwest. Most of the CAM guidance doesn`t
seem to handle this well, though the past several runs of the
HRRRv4 have picked up on it. The latest operational HRRR is on
board as well, maintaining at least isolated convection toward
Tupelo between 03-05z. PoPs were removed for most of the area
tonight, but left in the forecast from Tupelo south.
After this convection dissipates, we anticipate mainly dry weather
overnight but some patchy fog is possible late, mainly in portions
of west Tennessee. Additional changes to the forecast were
.PREV DISCUSSION... /issued 234 PM CDT Thu Jul 23 2020/
Rinse and repeat for the next couple of days expect widespread
highs in the low 90s with overnight lows in the low to middle
70s. Afternoon heat indices will likely exceed 100 degrees. We may
see slightly less coverage of thunderstorms Saturday, but any
location could see a storm resulting in locally heavy rainfall,
lightning and gusty wind. However, it will provide a bit of relief
from the heat.
Showers and thunderstorms can be expected daily through the
weekend. Temperatures during this time will remain in the upper
80`s and low 90`s with heat indices close to, if not exceeding
100F during the daylight hours. Nighttime temperatures will remain
in the low to mid 70`s.
The pattern changes as we head into the new work week. A trough
digs in over The Great Lakes region. The ridge we are under
shifts westward over the Rockies on Sunday. A weak cold front as a
result should pass through the Mid-South by Tuesday morning. This
will bring a new round of showers and thunderstorms. Behind the
front the temperatures will drop slightly, as will the humidity
levels, giving us all some relief come midweek.
VFR conditions will continue through most of the TAF period.
However, diurnally driven thunderstorms will develop tomorrow
afternoon which may bring in lower ceilings temporarily. Coverage
will be isolate, so I`ve have kept the VCTS wording in for now
unless confidence increases on where exactly thunderstorm
development will occur. Winds will be light from the east-
Area Forecast Discussion
National Weather Service Reno NV
209 PM PDT Thu Jul 23 2020
We are seeing thunderstorms once again this afternoon, but the
coverage and intensity will be much less than yesterday.
Thunderstorm chances decrease Friday and Saturday with renewed
chances Sunday into Monday. Drier conditions along with typical
afternoon winds and summer heat is expected Tuesday onward next
Thunderstorms are developing once again today, but the coverage and
strength of the storms will not be as intense as what we saw
yesterday. The main focus of the storms is over the Sierra as well
as north central Nevada. Latest HRRR guidance is showing chances
along the Sierra Front, including the Reno-Carson-Minden corridor.
The HREF is showing lower end probabilities around 15% through these
areas. Based on the latest satellite/radar trends we are likely to
see a few isolated cells through the population centers this
afternoon into early evening. Storms today could produce gusty and
erratic outflow winds of 35-40 mph, small hail, and brief heavy
rainfall. While the rain cores appear to be rather small on the
cells so far today and updrafts not nearly as vigorous as what we
saw yesterday, we`ll continue to monitor burn scars carefully for
any flash flood concerns.
Smoke and haze remain in the area today, but should be more confined
to ongoing fires. The worst conditions are likely to be in the
vicinity of the Hog and Gold Fires in Lassen County, but will
dependent on wildfire activity. We also are seeing lingering haze
into the central Nevada Basin and Range, a combination of smoke and
lofted dust from storms yesterday. This should improve as we
continue to mix this afternoon.
A few storms will remain possible in favored areas of the eastern
Sierra, such as northern Mono and Alpine counties Friday and
Saturday, with lesser coverage anticipated.
One new concern is a negatively tilted shortwave that lifts through
the region Sunday into Monday. This could easily be another trigger
for increased thunderstorm coverage, especially through northeast
California and northern Nevada. Nocturnal storms are also possible
Sunday night with increased diffluence aloft over northeast
California. Negatively tilted waves tend to be a concern for new
ignitions from lightning, so we`ll continue to monitor this.
Drier and more stable southwest flow returns for Tuesday onward with
typically afternoon breezes and temps near normal. -Dawn
Main concern today is once again thunderstorms, with the focus in
the Sierra and north central Nevada. A few stray cells may work
their way north along the Sierra Front with a 15% chance for a storm
at KRNO/KCXP and a 20% chance for KMEV. Best chances for terminal
sites will be at KMMH with a 25% chance. Other Sierra sites, KTVL
and KTRK have about a 20% chance as well. Storms may produce erratic
outflow winds up to 35 kts along with brief heavy rainfall
leading to visibility reductions and terrain obscuration.
Otherwise, smoke and haze continue to be a concern around ongoing
wildfires. The worst conditions are present in Lassen County due to
the Hog and Gold fires. Slantwise visibility may also be a concern
into the west central Nevada Basin and Range due to a combination of
wildfire smoke and dust lofted from storms yesterday. The extent of
smoke and haze into Friday will be dependent on wildfire activity.
* Isolated to scattered thunderstorms are expected again for today,
although with little to no steering flow will make these storms
rather wet. The threat for dry lightning is much reduced when
storm motions are stationary. Thunderstorms over the area today
will create gusty outflow winds up to 40 mph, localized heavy
rainfall, and small hail. Any ongoing fires could be affected by
gusty outflow winds late this afternoon and into the evening, so
we will headline the thunderstorms in the forecast.
* A few thunderstorms are expected each afternoon and evening
through the weekend, mainly over the Southern Sierra Front and
Eastern Sierra, with localized effects of heavy rainfall and gusty
* Low pressure moving up from Southern CA will help to bring a
favorable diffluent area over northeast California and
northwestern Nevada Sunday into Monday. This negatively tilted
trough will help to kick off some increased thunderstorms over the
region and even some potential nocturnal thunderstorms Sunday
night into early Monday morning. We will not issue a Fire Weather
Watch for this event at this time, but as we get closer to the
event we may need to consider a watch for dry lightning and gusty
outflow winds mainly for areas north of Interstate 80. -Hoon
For more information from the National Weather Service visit...
Area Forecast Discussion
National Weather Service Sacramento CA
225 PM PDT Thu Jul 23 2020
Slightly below normal temperatures continue, trending a little
above normal by Sunday. A few late day thunderstorms are possible
over the Sierra Crest south of I-80. Southwest breezes continue
near the Delta with periods of breezy conditions spreading into
Mostly sunny conditions dominate the skies across much of central
and northern California this afternoon. Visible satellite imagery
is starting to show some convective cumulus bubbling along the
crest of the Sierra Nevada between Yosemite National Park and Lake
Tahoe. High resolution models such as the HRRR and 3 km NAM have
been suggesting that this would be the favored area for
afternoon/evening showers and thunderstorms as an upper level low
passes over the Golden State. As always, backpackers, climbers,
campers, and other outdoor enthusiasts are encouraged to keep an
eye on the skies and take action if/when inclement weather
Temperatures this early afternoon are largely within several
degrees of what they were this time yesterday. By the time the
afternoon wraps up, highs will range in the 80s in the vicinity of
the Delta, low 90s in the southern Sacramento Valley and northern
San Joaquin Valley, and middle to upper 90s for the northern
Sacramento Valley. These values are generally at or a few degrees
below late July normals. A deep marine layer off the California
coast along with decent onshore surface pressure gradients will
bring locally breezy conditions to the Delta region again this
afternoon and evening.
Upper level ridge will begin to build off the Oregon Coast over
the weekend with a weak upper low just off the central California
coast. If anything, this low would mainly bring a renewed
opportunity for showers and thunderstorms to the mountains during
the afternoon/evening hours. Despite this trough, temperatures are
forecast to generally nudge upward with widespread triple digits
returning to communities such as Redding and Red Bluff over the
weekend and into early next week. // Rowe
.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
After short wave energy moves through Wrn Canada on Sat re-
establishment/re-orientation of the weak slightly negative trof over
the area could trigger isolated convection over the Nrn Mtns/Srn
Cascades on Mon. This may be somewhat of a continuation of Sun`s
convection over the Sierra south of Tahoe which the GFS model
suggests will continue Nwd up the Sierra Sun nite and then into
the Nrn mtns/Srn Cascades on Mon; albeit elevated instability and
low modified TTs make the nocturnal convection very problematic.
At least some of the mid level moisture and ACCAS/Floccus may
continue overnight and into Mon morning given the swath of one
inch PWs forecast over Norcal from Sun evening into Mon afternoon.
This is something for later shifts to monitor in the coming days.
However, all of this will be followed by drier, more stable flow
over Norcal on Tue ahead of a longer wave trof that is forecast to
develop over the Ern Pac/along the Wrn Coast of NOAM by the middle
of next week.
Temperatures are forecast to trend a few degrees above normal next
week which will mean a return to triple digit temps up north and mid
to upper 90s in the Srn Sac/Nrn San Joaquin Valley and lower
foothills. Onshore flow will have an ameliorating influence on temps
in the marine/Delta influenced areas. As the trof approaches the W
Coast by late in the EFP, temps are expected to trend toward normal
on Wed, then a couple of degrees below normal on Thu. (Looks as if
max temps at RDD will finally fall below 100 deg on Thu). Overnight
lows in the inland areas (away from the marine/Delta influence) will
be in the 60s, with 70s in the warmer thermal belt areas of the
foothills, where humidity recovery will trend lower by the middle of
next week. However, cooler mins are expected to prevail in the
thermal belts by Thu. JHM
VFR conditions expected through 00z Sat, except for chance of
marine stratus and local MVFR conditions developing in the
Carquinez Strait area and possibly into the Srn Sac Vly early Sat
morning. Otherwise, scattered thunderstorms over the high Sierra
mainly south of Tahoe will continue through about 03z Fri. SWly
surface wind gusting to 30-35kt through the Carquinez Strait/Delta
overnight and into Fri morning, but elsewhere winds generally
around 12 knots with local gusts up to 20 knots in the afternoon.
Stratus Calculator indicates Patchy Stratus Possible early Fri
morning with a swath of stratus forming through the Carquinez
Strait into Srn Sac Vly with bases around 010 and tops 025 given
forecast conditions. However, HREF probability of MVFR conditions
shows very small chance, less than 10 percent.