Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/28/21
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
902 PM CDT Tue Jul 27 2021
.UPDATE...
Issued at 901 PM CDT Tue Jul 27 2021
Temperatures have fallen in the last hour, so allowed the heat
advisory to expire.
UPDATE Issued at 630 PM CDT Tue Jul 27 2021
Given the current temperatures and heat indices which show
multiple sites remaining above 100 degrees, decided to extend the
heat advisory until closer to sunset when temperatures will fall
more quickly. Otherwise, the forecast remains on track this
evening with no further changes needed.
&&
.SHORT TERM...(This Evening through Wednesday Night)
Issued at 231 PM CDT Tue Jul 27 2021
Upper high centered over the Western High Plains will continue to
build over the forecast area through Wednesday. Meanwhile, a sfc
front stretching across northern South Dakota is expected to
gradually push back north tonight as the LLJ returns to the region.
The LLJ impinging upon this frontal boundary may be enough to get
convection to develop later this evening and overnight across NE SD,
and WC MN. The activity would then move southeast across parts of
eastern SD and western MN. Any convection that forms would be on the
southern edge of the westerlies (good shear), and would have plenty
of moisture/instability to work with, so a severe storm or two isn`t
out of the realm of possibilities. Again tonight, wind and hail are
the main threats given the abundance of CAPE. At the same time you
have a pretty healthy EML developing across the region, with H7
temps climbing to 15C or greater across the western CWA tonight and
Wednesday. This should effectively cap off most convection chances
west of the James valley. A sfc front will move southeast across the
CWA on Wednesday, and as the winds turn more southwest/west,
temperatures are likely to go up even further vs today. Hundred
degree readings may well be common in the afternoon. As for any
chance of rain, it appears that it`ll be capped with little if any
chance for measurable pcpn as front migrates to the south. Behind
that front, a much drier airmass will advect into the area for
Thursday, along with cooler temperatures. Will also maintain
elevated smoke mention through Wednesday given the output from the
HRRR smoke model. Last item, heat indices. Again on Wednesday the
heat index should reach into the 100s and thus will maintain the
advisory for Wednesday afternoon across the forecast area.
.LONG TERM...(Thursday through Tuesday)
Issued at 231 PM CDT Tue Jul 27 2021
The period opens Thursday with the upper ridge west/upper trough
east pattern intact over the CONUS. That leaves the CWA under
northwest flow aloft. With only minor variations expected in
amplitude and position of this upper level pattern, northwest flow
early on in the period eventually becomes north-northwest flow late
in the period. Deterministic and ensemble-based model solutions all
generally support a cooler/closer-to-normal low level thermal/mixing
pattern from Thursday through Tuesday. Typical of northwest flow
pattern sequences, most of the period is dry and when models do
generate qpf over the CWA it is more isolated in nature vs.
widespread, and they generally lack agreement on timing/placement of
areas of qpf. From the probabilistic perspective, other than the far
southwestern zones from late Thursday night through Friday evening,
the chances of seeing just 0.01 to 0.10 inch of qpf over the CWA are
fairly low. Not saying there couldn`t be a handful of forecast
periods with a couple of storms to deal with. However, trying to
resolve that kind of detail this far out in time within this kind of
weather pattern holds very little skill/confidence.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 630 PM CDT Tue Jul 27 2021
Terminals KABR,KATY,KPIR,KMBG
VFR conditions are expected through the next 24 hours.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from noon CDT /11 AM MDT/ to 7 PM CDT /6 PM MDT/
Wednesday for SDZ003>011-015>023-033>037-045-048-051.
MN...Heat Advisory from noon to 7 PM CDT Wednesday for MNZ039-046.
&&
$$
UPDATE...Wise
SHORT TERM...TDK
LONG TERM...Dorn
AVIATION...Wise
AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
1059 PM EDT Tue Jul 27 2021
.SYNOPSIS...
A frontal boundary will wash out across the region today as
weak high pressure builds in from the north. A stronger cold
front crosses the region Friday with high pressure building in
from the north on Saturday.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
As of 1055 PM EDT Tuesday...
Latest sfc analysis reveals a rather diffuse sfc boundary
in place across area this evening. Localized/isolated
convection earlier this evening produced some locally heavy
rainfall in Richmond and just south into northern Chesterfield
county, with additional locally heavy showers and embedded TSRA
over eastern Chesapeake/inland Va Beach and the MD eastern shore
south of KSBY. Rainfall amounts of 2-3 inches with locally
heavier amounts occurred across Chesapeake/VB, with lesser
amounts of up to 1.5 over RIC metro and the lower MD eastern
shore.
Convective coverage has, as expected, quickly waned with loss
of heating, owing to minimal effective shear. Expect mainly
quiet wx for the balance of the evening and the overnight,
though we have maintained a slight chc PoP over NC counties, as
ongoing iso convection across the foothills/ (VA/NC piedmont)
potentially making it across to our western tier of counties and
NE NC coastal plain zones now through 06Z (new 00z NAM and past
few runs of HRRR have shown this potentially occurring). Otherwise,
seasonably warm/humid overnight under a partly cloudy sky...with
some patchy fog late tonight. Early morning lows in the upper
60s/low 70s most areas (locally mid 70s along the coast in SE
VA/NE NC.
On Wed, the flow aloft shifts more to the NW (compared to WNW)
as the next shortwave pivots around the base of the deep upper
trough across eastern Canada. This may bring a slightly better
chance for aftn/early evening tstms. The low level flow remains
fairly weak so once again expect some sea-breeze influence to
get the storms going in the aftn. Will still only have PoPs
20-30% across the area, but the storms may be a little stronger
and longer lived than on Tue. Partly sunny on avg with highs
low- mid 90s inland except upr 80s/around 90F at the immediate
coast.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 335 AM EDT Tuesday...
Partly cloudy other than a few early evening showers/tstms with
lows Wed night upper 60s- lwr 70s.
For Thu, partly to mostly sunny ahead of an approaching cold
front. Models show sct convection developing late aftn/eve
across the nrn third of the fa but will spread at least 20% PoPs
into southern VA late. The front pushes S Thu night with the
potential for some redevelopment of showers/tstms mainly over
the S on Fri. Highs in the 90-95F range for Thu (upper 80s NE),
with lows in the upper 60s to lower 70s. Highs Fri mainly in the
upper 80s to lower 90s. Then cooler Fri night with lows mostly
into the 60s except lower 70s far SE.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 355 PM EDT Tuesday...
Flow aloft shifts more to the W this weekend with the upper
level ridge centered from the western Gulf of Mexico to the
northern Rockies and the upper trough sharpening over eastern
Canada and pivoting S into the NE CONUS. This should push the
cold front S of the area Fri night with weak high pressure
settling in from the N for Sat. Mainly dry/cooler conditions
Sat with highs in the mid 80s. The models then show another push
of a rather strong shortwave across the eastern Great Lakes into
New England later Sun into Mon. This would potentially drive
another cold front through the area Sun into Mon. Will have low
chc PoPs during this period then mainly dry for Mon with highs
in the 80s. By later Mon into Tue, the models are in decent
agreement that the upper ridge amplifies into western Canada
with a trough diving S nearly to the Gulf of Mexico. The flow
aloft shifts to the SW and increasing moisture is expected Mon
night into Tue as a sfc trough develops across the SE CONUS.
Will have PoPs above climo for Tue with highs only in the lower
80s.
&&
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
As of 755 PM EDT Tuesday...
Isolated showers and t-storms have quickly diminished in areal
coverage to begin the 00z TAF period. Mainly VFR conditions
are expected for much of tonight, though some late night mist
possible in the piedmont, mainly W-SW of KRIC and around KSBY
after 06z. Mainly VFR again for Wed morning, before additional
showers and storms Wed aftn and evening. SCT-BKN CU deck 5-8 kft
AGL expected after 16z, with potentially a bit higher coverage
of aftn/evening tstms compared to earlier today.
Outlook...A higher chance for convection once again later Thu
aftn/Thu night across the N, then shifting S on Fri with the
next cold frontal passage. Mainly dry/VFR for Sat.
&&
.MARINE...
As of 330 PM EDT Tuesday...
Winds are expected to remain sub-SCA for the next week outside of
convection. A few isolated storms will be possible late this
afternoon into early this evening, particularly over SE VA/NE NC and
may push over the local waters. Otherwise, isolated storms will be
possible each afternoon/evening this week.
A weak stationary front NW of the local waters will continue to
weaken later this afternoon into this evening. Winds this afternoon
are SE/S 5-10 kt but will shift to W/WNW late tonight as the weak
stationary front pushes SE again before washing out. Another diurnal
wind shift is expected Wed as winds shift from W in the morning to
S/SE onshore flow in the afternoon. S/SSE winds 5-10 kt continue
through Thurs over the Ches Bay/rivers with 10-15 kt winds by the
afternoon over the coastal waters. Winds become SW 10-15 kt Thurs
evening into early Thurs night as a cold front begins to push south
over the local waters. By late Thurs night, winds become W 10 kt,
eventually becoming NW 5-10 kt by late Fri morning before turning to
N Fri afternoon. The strongest CAA surge behind the cold front is
expected to lag until Fri night through Sat morning with N winds 10-
15 kt.
Seas of 2-3 ft and waves of 1-2 ft continue through late week. By
late Thurs night, seas of 3-4 ft and waves of 2-3 ft will be briefly
possible.
&&
.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...None.
&&
$$
SYNOPSIS...LKB/MAM
NEAR TERM...LKB/MAM
SHORT TERM...LKB
LONG TERM...LKB/MPR
AVIATION...LKB/MAM
MARINE...RMM/TMG
Area Forecast Discussion
National Weather Service Gaylord MI
1142 PM EDT Tue Jul 27 2021
.UPDATE...
Issued at 932 PM EDT Tue Jul 27 2021
With the loss of the heat of the day, we should be losing the
chances for showers and thunderstorms. The satellite and radar
trends would support this as well as the models. So the focus now
shifts to the possibility of fog. currently the grids have patchy
fog in them, with areas of fog possible toward 12z, with some
locations. If you use the UPS method for fog, with the fact that
the winds will be calm and the skies clear, we should have fog
around the region. Winds look like they stay light enough to
continue into the morning (past 12z) limiting the mixing until the
sun can break through.
&&
.NEAR TERM...(Through Tonight)
Issued at 312 PM EDT Tue Jul 27 2021
...Convection possible in spots thru this evening...
High Impact Weather Potential...a few strong t-storms possible
into early evening.
An old outflow boundary has settled just south of the forecast
area, while a more traditional w-e synoptic front has drifted down
to M-32. A fair bit of cu away from Lake MI, but the most
widespread lower clouds over ne lower MI (near APN) has a capped
look on sat imagery. Things are more bubbly further south, toward
and south of OSC, and radar is showing a few blips down that way.
Onshore lake breezes are seen at OSC and Tawas, and with light
westerly synoptic breezes inland, convergence is maximized along
that lake breeze boundary.
Do still expect some convection to fire in se sections this
afternoon and evening. MlCape values have risen above 500j/kg, and
Cin is reduced below 25j/kg. HRRR and Rap runs both ignite precip
in this area. These will have a minimal time to evolve before
they move over the somewhat more stable air behind the lake breeze
front. A few stronger storms with gusty winds will be possible,
but svr might be a stretch.
Congested cu are also over Canada, north thru east of the Sault.
Given expanding outflow boundaries, there is a small chance for a
shower to clip parts of the St Marys River. Further west, cu
continue to develop in the zone between the slowly converging lake
breezes in central/western Chip/Mack Cos. This is also an area
where showers and perhaps a t-storm may still form into this
evening.
And also, like yesterday, convection could also fire late this
afternoon and early this evening in the MNM area. MlCape values
are near 1k j/kg here. Se-ward movement of these cells could try
to bring activity into the MBL area again this evening.
Clearing skies and light winds overnight will contribute to some
fog, probably more so than we`ve seen over the past few nights.
Min temps will range from the mid 50s north to around 60f south.
&&
.SHORT TERM...(Wednesday through Friday)
Issued at 312 PM EDT Tue Jul 27 2021
...Shower/Storm Chances then Cooler...
High impact weather: Strong to severe storms possible Wednesday
night.
Low pressure moving across central Canada will swing a cold front
across the region Wednesday night into early Thursday. This system
will likely bring scattered showers and perhaps a few thunderstorms
across northern Michigan mainly Wednesday night (but perhaps
lingering into Thursday morning as well). The next question is the
potential for severe storms as winds aloft are respectable (0-6 km
bulk shear 40 to 45 knots). In addition, will have to monitor a
possible ongoing MCS which most likely tracks across eastern
Minnesota and central Wisconsin. A majority of guidance keeps much
of the instability to our south so am not too enthused about the
severe weather potential across northern Michigan at this point but
will have to keep an eye on latest guidance trends. Heavy downpours
are possible with precipitable water values increasing to between an
inch and 1.5 inches. Humidity levels will increase once again during
the day Wednesday into Wednesday night then begin to drop Thursday
with lower humidity expected Friday. Highs in the low and mid 80s
Wednesday, the mid 70s to low 80s Thursday and the mid and upper 70s
Friday. Lows in the muggy low and mid 60s Wednesday night then the
cooler low and mid 50s Thursday night.
.LONG TERM...(Friday night through Tuesday)
Issued at 312 PM EDT Tue Jul 27 2021
...Cooler and Less Humid...
High impact weather potential: Low.
Classic ridge west, trough east pattern across the lower 48 is
expected to lead to cooler temperatures and relatively low humidity
levels through the period. An upper level disturbance moving through
the flow will bring shower chances (possibly a thunderstorm?)
Saturday. There could be additional disturbances moving through the
flow during the period but pinning down exactly when is up in the
air so will leave out pops for Sun-Tue for now (but don`t be
surprised if we end up adding some later). Highs are only expected
to range from the upper 60s to mid 70s with lows in the upper 40s to
mid 50s.
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1140 PM EDT Tue Jul 27 2021
Fog looks like it will be an issue early Wednesday morning as low
temperatures will fall to around 4 to 6 degrees below the
dewpoints during the warmest part of the day, with calm winds, and
relatively clear skies over most of N Lower and E Upper, will
expect that patchy fog, that would be MVFR VSBY will start, and
then progressively have areas of fog, that would drop into IFR
VSBYs, and maybe with LIFR CIGs. Will, of course watch and
evaluate this over the next few hours, and amend accordingly. MBL
is the most likely TAF site to run into this problem, and TVC the
least, with APN and PLN likely to run into issues similar to MBL
during the morning hours on Wednesday. With the high over the
region, winds don`t look like they pick up much during the day, so
with the lack of mixing, MVFR VSBYs are possible through the day.
&&
.MARINE...
Issued at 312 PM EDT Tue Jul 27 2021
Light winds and minimal wave action expected, as a broad and
diffuse frontal zone is hung up across northern MI. There will be
an increasing southerly breeze late Wednesday, before a system
finally moves thru. Winds will veer w and nw by late Wed night and
Thu, and again will be a bit gusty.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&
$$
UPDATE...JL
NEAR TERM...JZ
SHORT TERM...AS
LONG TERM...AS
AVIATION...JL
MARINE...JZ
Area Forecast Discussion
National Weather Service La Crosse WI
628 PM CDT Tue Jul 27 2021
.SHORT TERM...(This evening through Wednesday)
Issued at 302 PM CDT Tue Jul 27 2021
At 2 PM, scattered storms continue to develop along the Mississippi
River. This is due to the low level convergence and little capping
aloft in this area. With favorable 0-6 km shear, there may be even
a few supercell thunderstorms. The main threat will be large hail.
Temperatures ranged from 76F at Medford to 88F in Charles City IA.
For late this afternoon and evening, a shortwave trough, currently
located over eastern South Dakota, will move southeast through the
area. There several different model solutions on how this convection
may develop. The NAM 4 km NEST and ARW suggest that this convection
will develop along a west-east boundary in between Interstates 94
and 90. The FV3 keeps the area dry. Finally, the HRRR suggests that
storms will develop near the Mississippi River. At this time, I am
leaning more toward the HRRR solution. How widespread the convection
becomes will depend on how much recovery we can occur during the
remainder of the afternoon. Due to this uncertainty, kept rain
chances in the 20 to 30 percent range. With 0-6 km effective shear
in the excess of 40 knots, there will be a large hail and
potentially a damaging wind threat.
Another weak wave will move through the area late tonight and
Wednesday morning. At this time, it continues to look like the
convection will be scattered. With weak shear, not expecting any
severe weather with this system.
Behind this wave, there will be a surge east by the ridge west of
the Mississippi River. 700 mb temperatures will climb into the 12 to
14C range. This strong capping will likely inhibit convection in
this area, and it will allow 0-1 km ML CAPES to climb into the 2500
to 4000 J/kg range. Moderate to strong moisture transport into
Wisconsin ahead of another much strong shortwave trough will bring
some of this instability into western Wisconsin. With 0-6 km shear
over 40 knots in Wisconsin, expect any initial convection to be
supercells and favor large to very large hail. As the cold pools
congeal, expect a squall line to race southeast and south across
Wisconsin. This would likely develop during the late
afternoon/evening.
Besides the severe weather threat, heat indices south of Interstate
94 will climb into the 100 to 105 degree range. As a result, there
will be a need for a Heat Advisory. There were even a few places
in northeast Iowa where the heat indices may even get into the 105
to 110 range. Probably too small of an area for an Excessive Heat
Warning.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 302 PM CDT Tue Jul 27 2021
Wednesday night looks to be the main period of interest in the long
term period with a severe weather threat contingent on whether
storms initiate. Still a strong thermal ridge over the nation`s mid-
section with our area in the northern periphery with northwest flow.
A front will still be hanging out somewhere in the area Wednesday
evening, most likely between the Mississippi River and the I-94
corridor. By evening, it looks like a surface low will drop from the
Twin Cities metro into west-central Wisconsin, accompanied by some
loosely organized mid-level energy rippling through aloft. Also a
developing low level jet nosing into central Wisconsin with strong
moisture transport. Overall forcing looks to be greatest along and
east of the Mississippi River. As these features drop into the area,
they will encounter a formidable cap in place with 850mb temps up
to 25C. However, an elevated mixed layer will yield favorable mid-
level lapse rates in excess of 8C/km. A rich supply of instability,
mostly elevated, will be available for storms to tap into IF forcing
ends up being adequate to overcome the capping. HREF suggests a high
likelihood of 2000-4000 J/kg MUCAPE persisting into the evening
given the abundance of moisture and hot daytime temperatures. CAMs
indicate convection initiating along the Minnesota/Canada border
around midday Wednesday, then bring the MCS southeastward into
northern Wisconsin by early evening. As the activity continues to
roll southeastward, CAMs keep bulk of it focused along and east of
the MS River in tandem with placement of strongest forcing and
weakest capping. In fact, most solutions suggest dry conditions
along and west of US 63. A lot could still change between now and
then depending on how any earlier rounds of convection affect
location of the boundary. But there is definitely potential for
severe weather if storm complex manages to initiate as models
suggest. Bulk shear from 0-6km ranges from 45 to 65 knots east of
the MS River, suggesting potential for some supercells at least
initially before activity transitions into a forward-propagating
MCS. Main threats look to be large hail and damaging winds. Perhaps
a small tornado risk given favorable helicity and the boundary
somewhere in vicinity, but degree of stability in the low-levels
casts some doubt. Certainly a torrential rainfall threat given
anomalous PWATs and a deep warm cloud layer, but flooding threat
should be tempered somewhat by fairly progressive MCS motion.
We then trend towards somewhat cooler, less humid, and drier
conditions Thursday and beyond as strong Central Plains ridge is
suppressed further south by deepening Hudson Bay trough. Highs
generally look to range from the mid 70s to mid 80s with daytime
dewpoints largely in the 50s and 60s. Not looking like much for rain
potential aside from an incoming shortwave/front on Saturday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 628 PM CDT Tue Jul 27 2021
As of early evening, all the convective activity has ended across
the area leaving behind just some high level clouds and VFR
conditions. A small chance that some activity could develop this
evening as a weak short wave trough moves across the area. A
couple of the hi-res meso-scale models do show some development,
but confidence not high enough to include for now, but will
quickly update if activity does develop. More activity may
develop late tonight over western Minnesota and then roll
southeast across the region in a weakening state. Other than the
HRRR, the hi-res models show not much more than sprinkles from
this activity or it misses the airports. Again, confidence not
high enough to include at this time. More convection is expected
to develop late Wednesday afternoon, but at this time, this looks
to be east of both airports.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Heat Advisory from 10 AM to 9 PM CDT Wednesday for WIZ032>034-
041-042-053>055-061.
MN...Heat Advisory from 10 AM to 9 PM CDT Wednesday for MNZ079-
086>088-094>096.
IA...Heat Advisory from 10 AM to 9 PM CDT Wednesday for IAZ008>011-
018-019-029-030.
&&
$$
SHORT TERM...Boyne
LONG TERM...Kurz
AVIATION...04
Area Forecast Discussion
National Weather Service Quad Cities IA IL
813 PM CDT Tue Jul 27 2021
.UPDATE...
Issued at 804 PM CDT Tue Jul 27 2021
Convection is starting to fire in southeast MN this hour, in line
with the 23Z HRRR which develops a small cluster of storms up
there which follows the CAPE gradient and drops into northeast
IA. Weak pressure falls and weak surface convergence are
supporting development now, and expect low-level jet support to
develop soon too.
Thus SPC watch issuance which includes our Highway 20 counties
looks reasonable, especially given the very large hail that
environment produced earlier today. Fortunately as storms dive
further south out of the watch area, they should weaken quickly as
they encounter the drier air to the south of the watch area over
east-central Iowa.
&&
.SYNOPSIS...
Issued at 248 PM CDT Tue Jul 27 2021
Weather was mixed across eastern Iowa, northwest Illinois and
northeast Missouri early this afternoon. Areas generally east of a
Cedar Rapids IA toe Galesburg IL line were under mostly cloudy
skies, which we the remains of morning convection that occurred over
northeast Iowa and southwest WI (storms that produced baseball hail
near LaCrosse!). To the west, skies were void of any clouds with
south to southwest winds ushering increasing moisture levels into
the area. Temperatures were in the upper 80s to low 90s with
dewpoints in the mid to upper 70s. This air mass will continue to
advance eastward, and will be in place across the area for the
entirety of the short term period.
&&
.SHORT TERM...(This Evening through Wednesday Night)
ISSUED AT 248 PM CDT Tue Jul 27 2021
[Key Messages]
*Hot and humid Wednesday with PM heat index values of 100-105;
locally higher values possible
*Threat for showers/storms during the morning and and late afternoon
& evening; slight risk for severe storms in northwest Illinois
[Discussion]
Main concerns for the short term period will be the heat and
humidity, and chances for showers & storms Wednesday.
Very broad surface high pressure centered over Illinois and Indiana
has kept our weather quiet over the past few days. Through the short
term, this high is forecast to slowly sag south into the Ohio River
Valley and mid-Mississippi River Valley, allowing a train of
disturbances and surface cold front to move into the area.
Thanks to the surface high and the presence of a strong cap aloft,
much of the area will see dry conditions for the short term,
especially southeast Iowa, west central Illinois and far northeast
Missouri. Things get tricky to the north where the cap is weaker and
shortwaves/impulse aloft are more prevalent.
There are several chances of showers/storms across the area
Wednesday. The first comes mid-morning Wednesday as CAMs show a
complex of showers and storms from south central Minnesota riding
the instability gradient into the area. There are disagreements on
whether that complex will survive the trip south, and like today may
be tied to the LLJ. If this holds true, then the 12z HRRR is likely
the most favored solution of what will happen, which shows a
gradually decay with showers and storms as they move towards the Hwy
20 corridor. More aggressive solutions like the RAP advertise more
widespread showers and storms, but this has a history of overdoing
lift and moisture in these sceneries.
Once the complex decays, clouds will stick around before gradually
dissipating by the afternoon. Once this happens, temperatures will
soar into the low to mid 90s, with dewpoints climbing into the mid
to upper 70s as moisture pools ahead of a southward advancing cold
front. This will push PM heat index values in the 100-105 range,
with potential for locally higher values where maturing crop
concentration is higher. I have collaborated to expand the heat
advisory CWA wide as confidence has increased with this package of
meeting criteria across northwest Illinois. In addition, the heat
advisory has been extended for counties along and south of I-80
through Wednesday night into Thursday, with heat indices expected in
the 100 to 105 range again Thursday afternoon.
The next chance for showers and storms arrives Wednesday evening and
overnight ahead of the cold front and a more potent shortwave moving
into the northern Great Lakes. A large complex of showers and storms
will develop in central Minnesota and western Wisconsin, with the
track progged in northern Illinois into the night. Areas in our
northwest and north central Illinois counties will have the highest
chance of precip and potential for severe storms. As of this
writing, the Storm Prediction Center has a Level 2 (slight risk) for
severe storms in this area, with a Level 1 (marginal) risk extending
further west into far eastern Iowa and northwest Illinois. The main
concern will be damaging winds, as discrete cells initially
consolidate via cold pools into a line of storms as they move south.
The threat of large hail and tornadoes is lower, and is greater into
Wisconsin with more discrete activity.
.LONG TERM...(Thursday through Tuesday)
ISSUED AT 248 PM CDT Tue Jul 27 2021
[Key Messages]
*Hot and humid for areas along and south of I-80 Thursday with
heat index values of 100-105
*Threat for showers/storms continues into the weekend; low threat
for severe storms in southeast Iowa, west central Illinois and far
northeast Missouri Thursday.
*Reprieve from the heat with daily highs in the 70s/80s and lows
in the 50s/60s beginning Friday and lasting through next week
[Discussion]
Heat and humidity will stick around for one more day before a more
pleasant summer air mass moves into the area in time for the
weekend. Northwest flow will increase after a cold front passes
through the area Thursday afternoon and evening, ushering in 925-850
temperatures near to below 20 celcius through early next week. This
will translate to daily highs in upper 70s/mid 80s, and overnight
lows in the 50s/60s this weekend into early next week. Dewpoints
dropping into the 50s/60s will mean a nice break from the humidity
as well!
We will have a few chances of showers and storms as the front will
stall briefly near the Iowa/Missouri border Thursday and Friday.
With the strong heating and forcing along the front, storms should
have no trouble firing over our far south. The Storm Prediction
Center has a Level 1 (marginal) risk of severe storms over far
northeast Missouri and west central Illinois Thursday, but
confidence on this is low and directly tied to where the front
stalls. If storms develop over our area, the main concerns will be
damaging winds and large hail. Chances for precipitation decrease
after Sunday, with high pressure providing dry condtions through mid-
next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
ISSUED AT 641 PM CDT Tue Jul 27 2021
VFR conditions with light winds will prevail through the forecast
period. There is a low chance of thunderstorms near the Dubuque
terminal tonight and again tomorrow, but chances are too low to
include in the forecast at this time.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory from 11 AM to 10 PM CDT Wednesday for Benton-
Buchanan-Clinton-Delaware-Dubuque-Jackson-Jones-Linn.
Heat Advisory from 11 AM Wednesday to 8 PM CDT Thursday for
Cedar-Des Moines-Henry IA-Iowa-Jefferson-Johnson-Keokuk-Lee-
Louisa-Muscatine-Scott-Van Buren-Washington.
IL...Heat Advisory from 11 AM to 10 PM CDT Wednesday for Bureau-
Carroll-Jo Daviess-Putnam-Stephenson-Whiteside.
Heat Advisory from 11 AM Wednesday to 8 PM CDT Thursday for
Hancock-Henderson-Henry IL-McDonough-Mercer-Rock Island-
Warren.
MO...Heat Advisory from 11 AM Wednesday to 8 PM CDT Thursday for
Clark-Scotland.
&&
$$
UPDATE...Wolf
SYNOPSIS...Speck
SHORT TERM...Speck
LONG TERM...Speck
AVIATION...Wolf
Area Forecast Discussion
National Weather Service Grand Forks ND
908 PM CDT Tue Jul 27 2021
.UPDATE...
Issued at 908 PM CDT Tue Jul 27 2021
Still playing the waiting game. The SPC meso page shows the area
with the most MLCAPE/no CIN across southern Minnesota, where a
large storm east of Rochester is tracking southeast. A weak 20 to
25 knot low level jet is currently across western South Dakota,
focused into the ND/SD border region south of Bismarck. The
regional radar loop shows nothing in this region yet. The latest
HRRR shows a few showers/storms developing over southeast ND in
the 2-4 am time frame, but no model run has been very consistent
with the timing or placement of any convective activity overnight.
UPDATE Issued at 654 PM CDT Tue Jul 27 2021
Lots of smoke and high level clouds are drifting across the FA
early this evening. At the moment, the most clouds are west of the
Red River Valley. The regional radar display is also picking up
on fairly widespread returns, but surface observations are showing
no clouds below 12,000 feet and nothing is reaching the ground.
700mb temperatures are quite warm where these clouds and radar
echoes are, or +12 to +14C. So it is likely going to take until
later this evening, when the low level jet starts to increase,
before some shower and storm activity might get underway. The
latest model data shows that by midnight, the low level jet focus
may be into the Bismarck area. By 4 am, this starts to turn more
southwesterly, and begins to focus into southeast North Dakota. So
at this point, it is looking like an overnight event, although
uncertainty remains high. And for this FA, the best potential
looks to be over southeast North Dakota into adjacent portions of
west central Minnesota. This is not going to be widespread rain
event, with any higher amounts tied to any thunderstorm tracks.
&&
.SHORT TERM...(This evening through Wednesday night)
Issued at 302 PM CDT Tue Jul 27 2021
Focus within the short term will be thunderstorm chances tonight
into Wednesday, some of which may produce hail to the size of golf
balls and gusty winds up to 60 mph.
This afternoon, a wedge of surface high pressure centered over ON
will keep the area dry (with help from elevated smoke). This wedge
of high pressure will slide east tonight allowing return low level
south-southwesterly flow into the region this evening. This will help
push a stationary front northward into the southern CWA as a warm
front. This comes ahead of an incoming shortwave trough within
broader northwest flow aloft. The shortwave will promote the
development of a LLJ over the warm front into southeast ND and RRV
tonight. South of the warm front is a pool of elevated, unstable
air. With elevated weak to moderate instability and forcing from
LLJ/warm front combo, thunderstorms are expected to develop
overnight tonight. Additionally, strong shear will be in place
composed of a veering and increasing wind profile, maximized near the
LLJ. This wind shear will bring the chance for robust updrafts. With
the anticipation of elevated convection tonight due to warm low
level temps, hail would be main concern. Given the magnitude of
shear, it wouldn`t be surprising to see elevated supercellular
structures capable of producing hail to the size of golf balls.
Currently favored location for severe convection resides near the SD
border, although confidence is not as high.
Expectation is for storms to continue into Wednesday morning before
moving east deeper into Minnesota. There is still a chance for
additional thunderstorm development in the afternoon behind morning
convection within Minnesota as a cold front/surface low moves
through, although will depend on timing of cold fropa and amount of
daytime heating behind morning storms/clouds to overcome capping.
Will similar thermodynamic and kinematic environment in place ahead
of the front, afternoon storms may be severe,large hail and high
winds being main threats.
Otherwise tomorrow will be the last hot day with heat indices in the
mid to upper 90s, especially near the tri-state area.
.LONG TERM...(Thursday through Tuesday)
Issued at 302 PM CDT Tue Jul 27 2021
The extended time frame features more of the same with respect to
dry conditions with ensemble guidance suggesting temps to cool
closer to normal for the end of July and beginning of August. As
for the precip, the next chance in the forecast will be associated
with a short wave traversing the northern plains either late
Friday or Saturday. Again not a widespread rain maker but some
showers and storms will be possible as the wave interacts with
some moderate instability. Then chances dry up as western conus
ridging and eastern conus troughing amplifies into the next week
with SFC ridge axis persisting under the nearly northerly and
diffluent flow aloft across the northern plains. As a result of
the pattern shift our 500mb thicknesses do decrease some and shunt
the warmer air to the west allowing a more seasonable temp regime
with highs in the 80s valley west and 70s in the MN trees and
lakes country with lows in the 50s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 654 PM CDT Tue Jul 27 2021
Any storm activity over the next 24 hours is highly uncertain, so
elected not to mention any at any of the TAF sites. If something
indicates more certainty for a TAF site, will update then.
Otherwise, the main story will be shifting wind speeds and
directions over the next 24 hours. The most impactful period will
be behind the north wind switch by Wednesday afternoon. Winds will
get pretty gusty during the afternoon period, especially along
and west of the Red River Valley.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$
UPDATE...Godon
SHORT TERM...CJ
LONG TERM...JK
AVIATION...Godon
Area Forecast Discussion
National Weather Service Indianapolis IN
1147 PM EDT Tue Jul 27 2021
...Updated Aviation Discussion...
.Forecast Update...
Issued at 1011 PM EDT Tue Jul 27 2021
Mostly clear skies expected for much of the night based on satellite
loop, with some mid and high cloud debris arriving late
overnight/near daybreak from convection to the north. Going low
forecast in the upper 60s to around 70 look on track. May see some
patchy fog in low lying areas with dew points right now in the mid
60s to lower 70s and likely to stay near there. However, boundary
layer dew point depressions are still staying up in the 4 to 7+
degree range, indicating there is still some mixing and dry air in
the boundary layer if not at the surface, so think any fog should
remain pretty isolated (ie patchy fog in a few low lying areas) and
thus will continue to leave out of the grids. No significant changes
to the going forecast.
&&
.Short Term...(This Evening through Wednesday Night)
Issued at 258 PM EDT Tue Jul 27 2021
Another toasty afternoon for the region with a noticeable increase
in the haze over Monday as more smoke aloft has drifted into the
region. 1830Z temperatures were in the mid and upper 80s but
humidity levels were again manageable today and keeping heat indices
from peaking much higher than the lower 90s.
Much of the next roughly 36-40 hours is setting the table for what
is likely to be a rather active Thursday on multiple fronts. That
will be focused on in much greater detail in the long range
discussion below. Through Wednesday night...the upper level pattern
will shift slightly as the core of the broad ridge focused over the
central Plains gradually shifts south and east. While central
Indiana will remain on the periphery of the ridge through Wednesday
night...mid level heights will rise due to the shift of the ridge
core. This will result in potentially hotter temperatures for much
of the region Wednesday. At the surface...high pressure will remain
a dominant influence across the Ohio Valley through late Wednesday.
For tonight...may see sporadic mid and high level clouds drift
through the region from convective cluster remnants over the upper
midwest. In general...skies will be mostly clear with haze levels
falling back as the higher smoke concentration shifts south of the
region this evening. The HRRR vertically integrated smoke parameters
look to increase again on Wednesday as another surge of greater
concentrated smoke extends into the region...although the highest
levels of smoke should largely remain to the northwest. Expect
another day with plenty of sunshine. Model soundings do show a
greater potential for diurnal cu as low level moisture advection
begins. While much of Wednesday should see tolerable humidity levels
again...a transition to southwesterly low level flow by late day
will enable much higher dewpoints in the 70s to spread back into the
forecast area by late day and into Wednesday night. This will set up
the potential for an oppressively muggy airmass for Thursday ahead
of the cold front and expected robust convective development.
The final issue for the short term and the one that is likely to
have the greatest impact on just exactly how Thursday plays out
focuses on the expectation of a mesoscale convective complex to
organize across the upper Midwest Wednesday evening in tandem with a
strong upper level wave. Trajectories support a southeast moving
cluster that will likely produce severe weather Wednesday night
aided by an impressive near 50kt 850mb jet. The general movement on
the system would bring it into N/NE Indiana during the predawn hours
Thursday with at least some potential that the tail end of the
cluster works south into part of the northern forecast area.
Considering the possibility that this system will mature enough to
develop a cold pool...am almost anticipating that the convection
will develop further back on its southwest flank into parts of
central Indiana near daybreak Thursday.
The questions that remain are...how far S/SW into the forecast area
the storms can make it Thursday morning and what intensity will they
have when they arrive? The nocturnal jet will weaken by 12Z Thursday
and largely remain to the north of central Indiana. That would
suggest that if the convective complex becomes cold pool
dominant...at some point the storms will outrun their low level fuel
source...weaken and eventually diminish. At this point...that will
likely take place somewhere across the northern half of the forecast
area Thursday morning. Still a lot of details to work out...but
there is some merit that this could serve as the initial salvo in a
1-2 convective punch for the region by leaving a leftover boundary
for new storms to fire on later on Thursday. It also presents some
uncertainty with how much convective cloud debris departs Thursday
morning and how that might impact available instability for new
storms later in the day. Much more on this in the long term section
below.
Temps...low level thermals are a touch warmer on Wednesday with
solid potential for temperatures to peak in the low to possibly mid
90s. Lows will fall into the upper 60s and lower 70s tonight with
low to mid 70s and noticeably more humidity for Wednesday night in
advance of what is shaping up to be a hot and very humid Thursday
ahead of the storms.
&&
.Long Term...(Thursday through Tuesday)
Issued at 258 PM EDT Tue Jul 27 2021
Thursday...
Early in the long term, the focus will be on the advancement of a
positively tilted mid level trough of which should initiate a MCS
over the Upper Great Lakes region Wednesday. The remnants of this
potent MCS is expected to pass over northern and eastern portions of
central Indiana early Thursday morning, but with a nearly stable
surface layer, thunderstorms should remain isolated with scattered
light showers more predominant. Eventually the bulk of the mid level
moisture should diminish as the trough nears, leaving relatively dry
mid levels over a capped surface layer. This should produce a brief
lull in rain chances late Thursday morning into the early afternoon
hours. Cloud cover midday Thursday will begin to diminish in
response to the dry air entrainment creating partly to mostly sunny
conditions at times.
Temperatures are expected to rapidly increase over this time period
with a combination of diurnal warming and warm air advection aided
through enhanced SW flow out ahead of the trough. Temperatures
should top off in the low 90s, with highest values located in
western portions of central Indiana, where prolonged clear skies are
more likely. The advection within SW flow will also push dew point
temperatures into the mid 70s, creating potentially hazardous heat
indices in the low 100s. Some uncertainty still lies within timing
of afternoon convection. Initiation is expected to be slightly
delayed over western central Indiana, where excessive heat is of
most concern.
As mentioned previously, thunderstorms are expected to develop over
central Indiana Thursday afternoon. The cold pool created by the MCS
over the upper Great Lakes is expected to stall overnight Wednesday
somewhere over north to north central Indiana, resulting in a quasi-
stationary boundary. This feature will be the main source of lift
for convective initiation. Thermodynamic profiles depict plenty of
buoyant energy in the mixed layer, supported my 3-6km lapse rates
above 7 C/km. This should allow for initiation to begin shortly
after surface temperatures/dew points are high enough to break a
weak WAA cap (50-100 J/kg CIN). Current expectations are for this to
occur during within the early afternoon hours from east to west
along the boundary.
A surface environment of around 91/75 (T/Td), in conjunction with
steep mid level lapse rates will produce MLCAPE values near or even
above 3000 J/kg, plenty enough for deep, robust updrafts to develop.
This along with Effective Bulk Shear values of around 30kts
should support organized convection, especially along the
aforementioned boundary. DCAPE values around 1000 J/kg, and
theta(e) index (TEI) values well above 10 support the idea of
possible damaging winds within organized convective structures and
will be the primary severe threat with this event. Some
bows/surges will be possible within convective lines given SFC-3km
shear near 30kts, and with this creates the possibility for
isolated tornadoes. There is still plenty of uncertainty with the
timing and location of initiation with this event, as upstream
convection on Wednesday will play a major factor.
Thursday Night through Monday....
Much cooler air will push into the Ohio Valley following the passage
of a cold front and associated thunderstorms. Overnight temperatures
should fall into the mid to low 60s. CAA will continue to lower low
level temperatures heading into Friday. Even with high pressure
induced clear skies, temperatures shold top[ off in the low 80s,
with much more pleasant dew points in the low 60s. High pressure is
expected to stick around for Saturday, keeping similar, dry
conditions.
Weak short waves within NW flow could bring slight chances for
showers and thunderstorms on Sunday and Monday, but some dry air
entrainment from the high to the SE could limit shower development.
Without any significant advection present, overall temperatures
should remain similar with highs in the low 80s.
&&
.Aviation...(06Z TAF Issuance)
Issued at 1146 PM EDT Tue Jul 27 2021
IMPACTS:
- mainly VFR conditions through the period
- outside chance for patchy ground fog at outlying sites
- winds less than 4 kts through the overnight
DISCUSSION: High pressure will continue across central Indiana
through the rest of the night and much of Wednesday. Leftover mid
and high level clouds from convective complexes over the upper
Midwest may occasionally drift across the sites into Wednesday. With
ample low level moisture could see some patchy ground fog, but don`t
expect it to be prevailing and too low of confidence in
location/timing to include. Should see few to scattered cu develop
Wednesday afternoon AOA 4kft. Winds will largely be light and
variable through the overnight hours, but could have a westerly
component. Winds should be less than 10 kts out of 270 to 290 from
midmorning Wednesday through Wednesday evening. Could see some
convection move in from the northwest late Wednesday night, but low
enough confidence to leave out at this time.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...CP
Short Term...Ryan
Long Term...Updike
Aviation...CP
Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
926 PM EDT Tue Jul 27 2021
.SYNOPSIS...
A weak frontal zone will remain draped near or over the Middle
Atlantic through Wednesday, reinforced by disturbances aloft. A
stronger cold front will cross the region Thursday into Friday.
High pressure will follow for the first half of the weekend
before another frontal boundary approaches by early next week.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
An isolated shower has developed over Augusta County this
evening. Hoping that this is short-lived as there is an
abundance of dry air per 00Z IAD RAOB. A thicker layer of smoke
was also seen right around sunset over southern PA and western
MD progressing southeast. Mainly clear, but hazy skies are
expected overnight with lows ranging from the mid 60s in the
mtns to the mid 70s along the bay.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
A shortwave trough currently over Saskatchewan in Canada is
expected to cross the region Wednesday afternoon. This should
enhance the pre-existing frontal zone/lee trough (possibly
merging with another weak front/surface reflection). Lift from
these features will act on the instability present to result in
scattered afternoon and evening showers and thunderstorms. Modest
flow aloft may lead to some loose organization, perhaps
resulting in a focused cluster/corridor or two of gusty to
damaging winds, but certainty in specifics is low a day in
advance given the overall marginal environment for organization.
Notably, the 12z HRRR mixes dew points to around 50 during the
afternoon, whereas as the NAMNest holds dew points in the mid
60s (as does most other guidance). This plays a big role in
available CAPE and subsequent depth of convection. Regardless,
very steep lapse rates in the lower levels and ample DCAPE
should result in an environment favorable for strong
downdrafts/bursts in the stronger cells.
A much more potent (convectively augmented) shortwave trough and
accompanying mid-level speed max are expected to pivot across
the area Thursday afternoon. There are uncertainties in the
extent of upstream convection and clouds which may temper
instability, though the 12z guidance overall has trended higher
with projected instability/CAPE. The seasonably strong trough
and wind field with moderate to strong CAPE may result in one or
more clusters of organized thunderstorms (perhaps initiating as
more discrete cells for a time) capable of damaging wind and
hail, heavy rain/flooding given high humidity, and even a
tornado threat. The extent of severe weather will be highly
dependent on the evolution of upstream convection over the next
48 hours as well as the magnitude of instability locally.
Overall, the threat is marginal at this time due to low
confidence, but with a high ceiling; a worst case scenario would
be one where widespread gusty to damaging winds are observed
due to the favorable background environment.
Temperatures should run a little above normal Wednesday through
Thursday before heat and humidity take a tumble behind the front
by the end of the week.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
A few isolated showers are possible across our southern zones
and bay waters both Friday afternoon and again Saturday evening
with a weak boundary nearby. Otherwise, the weekend looks
slightly cooler by a couple of degrees compared to previous
days with highs in the middle to upper 80s. The warmer day
appears to be Friday.
Later Sunday into Monday would be the next better chance of showers
and thunderstorms as a cold front pushes in from the northwest and
nearly stalls to the south by later in the day Monday. High
temperatures will approach 90 ahead of the front but could be
held in the middle to upper 80s in any cloud cover and convection.
&&
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Mainly VFR conditions are forecast through the end of the week,
with a few potential exceptions:
(1) Patchy fog may encroach on the CHO/MRB terminals 8-12z Wed
(2) TSRA potential both Wed PM and Thu PM w/ gusty wind possible
Otherwise, flow will be somewhat erratic in direction with
multiple weak frontal boundaries nearby, and river/bay breeze
influences for DCA/BWI/MTN during the afternoon and evening.
Any shower activity could pose an MVFR threat near CHO and possibly
DCA Friday and Saturday. Otherwise, VFR conditions. Winds generally
northwest 10 to 15 knots gusts up to 20 knots Friday, becoming
northwest around 5 knots Friday night. Winds northwest 5 to 10 knots
Saturday, becoming southwest then south around 5 knots Saturday
night.
&&
.MARINE...
Through early Thursday, wind outside of convection should stay
under SCA levels. There is some increase in southwesterly winds
expected on Thursday which may require a SCA for portions of
the waters. A better chance for thunderstorms exists on
Wednesday and Thursday, with Special Marine Warnings possible.
A Small Craft Advisory is possible Friday. Winds northwest 10 to 20
knots w/ higher gusts Friday. Winds diminishing northwest 5 to
10 knots Friday night and Saturday, becoming south 5 to 10 knots
Saturday night.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.
&&
$$
SYNOPSIS...DHOF
NEAR TERM...LFR
SHORT TERM...DHOF
LONG TERM...KLW
AVIATION...LFR/KLW
MARINE...LFR/KLW
Area Forecast Discussion
National Weather Service Pendleton OR
854 PM PDT Tue Jul 27 2021
.UPDATE...The latest radar was showing a plume of moisture from
central Oregon that stretched into south central Washington. This
area of mostly rain showers had been slow to move eastward. The
rap and hrrr models have these rain showers drifting east tonight
while slowly dissipating. Meanwhile some isolated showers were
developing even more ahead of this area over Grant county.
Portions of the pcpn should slowly migrate into the eastern
sections of our area overnight. Due to the extensive cloud over
today thunderstorm activity had been limited and the forecast was
updated to reflect this overnight. Also the pops were adjusted
along with the location of the pcpn to better reflect the current
and projected movement overnight. Minor changes were done to
low temps that are forecast mostly in the 60s with 50s in the
mountains and now the present short term forecast appears on
track.
&&
.PREV DISCUSSION... /issued 458 PM PDT Tue Jul 27 2021/
SHORT TERM...Tonight through Thursday...Band of showers continues
to impact areas of central OR northeast into the WA Columbia Basin
this afternoon, with very little lightning being produced in
these showers. Showers across these areas will persist into the
evening as the band moves east across the Blues and into Wallowa
county. Areas that see lingering cloud cover tonight will likely
see warmer morning lows tomorrow, with possible muggy conditions
where surface moisture lingers.
Tomorrow, upper ridge will begin to amplify over the region with a
noted warm-up into this weekend. Overnight lingering showers will
diminish tomorrow morning across the forecast area as dry air
aloft swings around upper high pressure. That said, monsoonal
moisture across southern and into portions of central OR will
allow for the development of isolated storms in these areas in the
afternoon. Thursday, upper ridging centered over the northern
Rockies will continue to amplify, allowing for warm air advection
into the PacNW. By Thursday afternoon, many locations will see
afternoon temps in the upper 90s to 104. That said, cloud cover
from potential thunderstorms across southern and central OR on
Thursday could act to limit some of the daytime heating.
Otherwise, overnight lows by Thursday night will not offer much
relief, as by sunrise, temperatures will have just cooled to the
mid 60s to lower 70s. With this in mind, an Excessive Heat Watch
has been issued starting Thursday for elevated heat risk across
the lowland areas. As mentioned earlier, the thunderstorm threat
will return Thursday afternoon as a weak moisture surge into
southern and south central OR is supported by an impulse moving
north from CA/NV. Instability associated with this system will be
enough for abundant lightning with any storm developing. With the
potential for elevated fire weather concerns, a Fire Weather Watch
has been issued for a portion of central OR. Otherwise, winds the
next couple of days will continue to be locally breezy, especially
through the Cascade Gaps. Lawhorn/82
LONG TERM...Friday through Tuesday...A deep upper level ridge is
expected to start the extended period over the Central US,
stretching across the Rockies and into the PNW. This ridging will
reach its peak across our region Saturday; however, moisture and
cloud cover should help prevent even higher temperatures from
being possible compared to Friday. Triple digit temperatures are
expected for the Columbia Basin both days.
The aforementioned moisture and an embedded feature in the pattern
will then bring much needed rainfall and possible thunderstorms
to Central through Eastern OR and Southeastern WA. High
PW values could spell periods of heavy precipitation and training
activity, which could bring a risk of localized very heavy
rainfall.
Ensemble models have a good handle on this pattern still with
solid agreement moving into the weekend. The ridge should then
shift eastward across the Rockies with the center of the upper
high retreating into the Four Corners as the trough off California
and deep low near Canada push into the coastline of North America.
This pattern will help us drop 5-15 degrees across the entirety of
the forecast area to begin August, with temperatures seeing a
slight increase then on Monday and Tuesday.
Ensembles diverge early next week on the strength of both the
offshore trough and ridge declining into the Desert SW. The GEFS
would allow for a deeper area of ridging and a tighter pressure
gradient for our region, while the ECMWF Ensembles have the ridge
further south, allowing for more influence from the offshore
trough and allow us to remain cooled off longer. Analysis reveals
better agreement for the ECMWF deterministic and its ensemble,
making it the favored outcome at this time.
AVIATION...Isolated showers may effect each taf site
overnight except for kykm while some of the heavier showers may
lower ceilings to sct-bkn050 especially at kbdn. Also an isolated
thunderstorm could approach taf sites krdm and kbdn until 04z.
Otherwise mainly vfr conditions should persist for the next 24 hours.
FIRE WEATHER...Band of showers observed from central OR up into the
Basin will continue through the evening into the early morning hours
of Wednesday, with strongest activity expected around central OR.
LALs of 2 to 3 with this system, however monsoon moisture will make
any storms that develop very wet, partially offsetting lightning
ignition chances. Wednesday afternoon onward, storm chances become
limited to mostly central OR. Models indicate plenty of instability
over the area Thursday, with PW amounts still relatively high,
however have elected to issue a Fire Weather Watch for OR611 in
light of abundant lightning threat. Moisture over the area today
through early Thursday may help wet fuels, however amount of
instability forecasted over the area suggests enough lightning to
potentially trigger critical fire risks. 74
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 67 92 64 100 / 30 10 10 10
ALW 71 94 69 102 / 30 10 0 10
PSC 71 98 68 102 / 30 0 0 10
YKM 65 97 66 101 / 10 0 0 10
HRI 70 97 67 103 / 30 0 0 10
ELN 64 94 62 98 / 10 0 0 10
RDM 60 93 57 97 / 30 20 20 20
LGD 65 91 62 97 / 20 10 10 10
GCD 64 94 62 98 / 30 10 10 20
DLS 68 98 69 103 / 20 0 0 10
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Watch from Thursday morning through Saturday
evening for ORZ041-044-507-510-511.
Fire Weather Watch from Thursday afternoon through Thursday
evening for ORZ611.
WA...Excessive Heat Watch from Thursday morning through Saturday
evening for WAZ024-026>029-521.
&&
$$
SHORT TERM...97
LONG TERM....99
AVIATION...97
Area Forecast Discussion
National Weather Service Shreveport LA
1013 PM CDT Tue Jul 27 2021
.UPDATE...
Reduced pops and lowered a few overnight low temperatures.
&&
.SHORT TERM...
Well the radar is quiet for our area with the last brief
thunderstorms seen in southern DeSoto during this update.
Elsewhere, a few remaining anvils or raining out with some light
rain still in Lufkin. There is still a cluster of activity in the
delta about to cross the MS River. This may help touch off some
noctural showers for areas well south of I-20 overnight. The HRRR
shows little in that way now, but did have some output in
previous updates.
Our sounding showed a NE direction for all winds aloft. A weak
cold front is pulling up stationary over southern Arkansas with
it`s air mass core at 1017mb over the boot heel of MO. The models
show it to sink just a little farther south so we may see a few
sites showing NE wind early, but more like calm or light and
variable for most of the area. As such, we still have a mention of
patchy fog for the daybreak timeframe. /24/
&&
.PREV DISCUSSION... /issued 731 PM CDT Tue Jul 27 2021/
UPDATE...
Changes to evening pops for E TX primarily with active outflows.
SHORT TERM...
Weak cold front on approach is plugging into our Easterlies
pattern with NE winds aloft now for much of the area and the
prevailing direction of movement for convection. Active outflows
continue with the remaining surface based cape of 3500-5000J/Kg
over E TX. Two areas just north of I-20 and back into NW LA with
multiple boundaries. Also the Sabine Parish to Sabine County hand-
off across the lake. One last cluster of activity out of
Arkadelphia AR, but lots of worked over air lying ahead of that
one. We will take a look at overnight lows and fog areas again
later this evening. For now needed to update to remove HX headline
for today and focus on tomorrow`s. /24/
PREV DISCUSSION... /issued 700 PM CDT Tue Jul 27 2021/
AVIATION...
For the ArkLaTex terminals, decent push of convection into the
area today with approaching cool front. TX terminals will see the
most of any action 01-03Z with an active outflow sagging toward
KGGG/KTYR and also a cluster crossing Toledo Bend which could
affect KLFK. Toward daybreak we may see some VCSH down that way
w/ LIFR FG briefly. A few sites may see IFR/MVFR BR as well with
calm. Light and Var. winds will occasionally be ENE5-10KT tmrw.
Right now our winds aloft are already NE all the way up. /24/
PREV DISCUSSION... /issued 233 PM CDT Tue Jul 27 2021/
SHORT TERM.../Tonight through Wednesday Night/
For the rest of Tuesday...Latest radar imagery is starting to
light up early this afternoon with showers and thunderstorms.
Expecting this activity to continue through the afternoon before
generally diminishing after sunset. There is a chance that a few
thunderstorms could produce a few strong downbursts that will
bring gusty winds at times and perhaps some small hail. Surface
observations are showing high temperatures ranging from the 80s to
upper 90s across the region with heat indices in the lower to mid
100s. The convection and cloud cover could really impact how much
warmer we get this afternoon, so while some forecasted highs will
be achieved, others may not make it.
As mentioned earlier, any showers and thunderstorms that do
develop this afternoon will begin to diminish shortly after
sunset, with only a few lingering showers possible. PoPs will then
begin to increase once again early Wednesday morning across
portions of deep east Texas, spreading to adjacent areas in
Louisiana through the day. The best chances for showers and
thunderstorms on Wednesday will generally be along and south of
I-20. Perhaps a few showers will be possible north of I-20, but no
farther than the I-30 corridor. Once again, showers and
thunderstorms during the day Wednesday will quickly diminish
shortly after sunset.
As for temperatures, overnight lows will generally be around the
mid 70s across the region tonight with a similar rinse and repeat
set-up for Wednesday night. High temperatures on Wednesday will
once again hover around the mid 90 degree mark across the region.
However, couple that with our high dewpoints and once again we
will reach afternoon heat indices ranging from 105 to 109 degrees.
As such, have maintained our daily Heat Advisory which will go
into effect at 17z Wednesday and continue through 00z. /33/
LONG TERM.../Thursday through Tuesday/
Upper ridging centered over the Central Plains will continue to
expand southeastward across the region into the Lower MS Valley and
across portions of the SE CONUS. This should result in slightly
warmer temps and mostly dry conditions for the end of the work week
into the first half of next weekend. Some weakness aloft along the
Srn periphery of the ridge axis could allow for some seabreeze and
isolated afternoon convection during this timeframe, with the best
chances along and south of the US HWY 84 corridor of Deep East Texas
and adjacent Central Louisiana. Afternoon highs will likely top out
in the upper 90s during this period, with some guidance suggesting
lower 100s across a large portion of the region. Decided to go
conservative a bit and keep highs just shy of that, but some
isolated triple digit marks are very possible. It appears that Heat
Advisories will be needed as these temps combined with upper 60s to
lower 70 dewpoints will keep heat indices near or above 105
degrees.
By Sunday, the upper level pattern across the region will start to
change. The upper ridge will start to retrograde westward into the
Rockies, as a longwave trough begins to dig southward out of the
Midwest into the SE CONUS and Lower Mississippi Valley, bringing a
weak cool front into Central OK/AR Sunday. This boundary will
continue to slowly drop southward into the northern sections of the
CWA by Monday and eventually through the entire CWA on Tuesday.
Convection is expected to increase along the frontal boundary Sunday,
eventually moving into our northern zones by late Sunday afternoon
into Sunday evening. This convection will likely continue into
Monday and Tuesday, as the boundary slowly moves through the region.
There could be some compressional warming ahead of the boundary,
which could factor into max temps Monday for areas near the I-20
corridor. But at this time, decided to stay with NBM and keep highs
in the low to mid 90s, as cloud cover could offset the compressional
heating. Overall, rain and cloud cover should give us lower max
temps for the first half of next week, bringing some relief from the
heat. /20/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 76 96 77 98 / 30 30 10 20
MLU 75 95 77 97 / 40 30 10 20
DEQ 74 96 75 98 / 20 10 0 10
TXK 77 96 77 98 / 20 10 0 10
ELD 72 95 74 98 / 30 20 0 10
TYR 77 95 77 96 / 30 30 10 20
GGG 75 94 76 96 / 40 30 10 20
LFK 72 95 76 96 / 30 50 10 30
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...Heat Advisory from noon to 7 PM CDT Wednesday for ARZ050-051-
059>061-070>073.
LA...Heat Advisory from noon to 7 PM CDT Wednesday for LAZ001>006-
010>014-017>022.
OK...Heat Advisory from noon to 7 PM CDT Wednesday for OKZ077.
TX...Heat Advisory from noon to 7 PM CDT Wednesday for TXZ096-097-
108>112-124>126-136>138-149>153-165>167.
&&
$$
24/33/20