Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/28/21
Area Forecast Discussion
National Weather Service Amarillo TX
536 PM CDT Tue Apr 27 2021
VFR conditions expected in the first 18 hours or so of the TAF
period. Winds have been strong and gusty especially for KDHT and
KGUY but should diminish within the hour or two into 00Z TAF
period. There is a slight chance for KAMA to see a shower or
thunderstorm in the first 12 hours of the period. However,
confidence is low and have left out of the TAF for now. Some
amendments may be needed if things change. There will be a
wind shift to the NNW behind a cold front towards 12Z today.
There will be increase chances for thunderstorms later in the
period mainly after 20Z for all three terminals.
.PREV DISCUSSION... /Issued 258 PM CDT Tue Apr 27 2021/
SHORT TERM (Today/Tonight)...
A somewhat busy 24 hours is on tap across the Panhandles
depending on which side of the dryline you are on.
* Severe thunderstorms across the southeast TX Panhandle
* Wind Advisory across the northwest Panhandles
* Critical fire weather conditions across the western Panhandles
Current (~19z) mid-level water vapor imagery indicates an area of
low pressure over southern Nevada with a stream of subtropical
moisture just south and east of the Panhandles. At the surface,
there is a low over eastern Nebraska with a dryline sagging south
through Kansas and Oklahoma into the southeast TX Panhandle. Lee
cyclogenesis has led to another surface low developing over
southeast Colorado. The latter surface low is also helping produce
strong wind speeds in the northwest, and will help usher in a
Pacific cold front tonight. The surface low eventually slides
southeast/east overnight putting a northerly wind in place across
700 mb theta-e indicates the moisture axis is better east of the
Panhandles, and forecast to be better east through the overnight
period. The location of the H5 low is forecast to produce large
scale ascent over the Southern Plains with several smaller
perturbation expected to pass over as well. There is also a strong
upper level jet streak that will help our forcing through
ageostrophic circulations as a 300mb jet noses into the
Panhandles. Wind shear today/tonight is high with effective shear
around 40-60 knots in the southeastern TX Panhandle. Low level
wind shear is also moderate as 0-1 km helicity values indicate
100-200 m2/s2 and 0-3 km around 200-300 m2/s2. Instability is the
biggest question today as models differ the most on this
variable. Anywhere from 500-1500 J/kg of MLCAPE. The RAP actually
has an area of nearly 3000 J/kg of MLCAPE in the southeastern
corner of the TX Panhandle. Besides CAPE, nearly every other
variable is consistent with the models, and the better chance for
convection should remain south and east of the Panhandles.
Boundary location, moisture axis, shear, CAPE, and forcing are all
better south and east of the forecast area. However, if a storm
can get going over the Panhandles, there is a good chance it will
become severe in the far southeast TX Panhandle.
Behind the dryline conditions will be favorable for critical fire
weather conditions this afternoon/early evening. RH values will be
around 10-15 percent across the western half of the Panhandles.
Wind speeds are also forecast to be 20-35 mph. Strongest speeds
are expected in the far northwest close to the surface low where
gusts could occasionally be as high as 50-60 mph.
RFTI values will be around 3-4 across the western half of the
forecast area with some isolated 5 in western OK Panhandle. These
are primarily driven by the wind. ERC values this afternoon are
around the 70th to 89th percentile. A combination of ERC and RFTI
values will lead to critical fire weather conditions this
LONG TERM...Wednesday through Monday...
Wednesday morning starts off with a cold front coming through the
area. By 7 AM the front looks to be about midway through from Vega
to Slapout and by 10 AM it looks to be either all the way through
or just about there with possibly needing to push through
Collingsworth County. The front can be seen currently in obs from
Omaha, NE draped down to Scott City, KS, back up through
northeastern CO towards Cheyenne, WY. The mid level clouds seen on
satellite are expected to hang around through tomorrow morning.
What happens for the afternoon is a bit more unsure. Short range
models aren`t in the best of agreement with how to handle the
moisture profile across the area behind the front. Some models
indicate we will dry out, while others insist that there may be
showers and plenty of cloud cover. For now have stuck with more of
a blend of the short range models and kept in some precip chances.
The chances for shower activity looks to lower after midnight, but
prior to that, there could be some elevated instability bringing
rumbles of thunder to the area. Some soundings indicate the
southeast could see enough breaks in clouds even behind the front
to have enough instability for some severe storms, but the CAPE
profiles are fairly small. Thus, not expecting very large hail.
With all the cloud cover and breezy north winds, the northwestern
Panhandles will struggle to reach the 60s. By evening, forecast
soundings continue to struggle with the moisture profile. Some
suggest it isn`t going to be deep enough for rain, but that we
may have fog or at most drizzle. For now have left the fog
potential out of the forecast to see if more of the models will
trend one way or another.
After the fog/rain potential for Thursday morning, the dry air
looks to win out in all the models and clear skies return. The
northerly air will keep the area highs topping out around 70
degrees. By Friday, high pressure settles in at the surface and we
finally see southerly flow. A lee side low looks to develop for
the weekend through early next week, which will help us warm up
again into the 80s to low 90s. The upper level pattern has just as
much disagreement between models for the weekend as the middle
part of the week. The GFS wants to be progressive and open the
mid level closed low that is currently sitting over southeast
AZ/southwest NM and open it to a wave that moves through the
southern Plains. The Canadian and EC hold it back as a closed low
in western TX/northwestern Mexico. Depending on which way the
upper pattern plays out, if the low remain in the west, there may
be chances for precip just to the east of the Panhandles. Will
have to watch to see if the low remains further west that
forecast, bringing precip chances to the eastern Panhandles.
FIRE WEATHER...Wednesday through Monday...
Wednesday looks to be free of fire weather concerns due to RH
being 30 percent or better. By Thursday though, RH comes back down
to around 20 percent. Northerly winds on Thursday may be breezy at
20-30 mph, creating RFTI values of 1 to 3 with some 4 in the
northwest. Depending on how the ERC values play out from the
possible precip chances tonight through Wednesday, there may be
elevated to critical fire weather conditions around the
Panhandles. If the ERCs drop low enough, we may not have fire
Friday, the winds will remain below 15 mph so no fire weather
concerns that day. Elevated to critical fire weather concerns come
back for the weekend with possible RFTI values of 1 to 4. RH will
dip into the teens on Saturday and single digits on Sunday. Winds
will be around 15-25 mph. ERCs will start to creep up again over
the weekend with the warm temps and sunny skies.
TX...Red Flag Warning until 9 PM CDT this evening for the following
zones: Dallam...Deaf Smith...Hartley...Moore...Oldham...
Wind Advisory until 7 PM CDT this evening for the following
OK...Red Flag Warning until 9 PM CDT this evening for the following
Wind Advisory until 7 PM CDT this evening for the following
Area Forecast Discussion
National Weather Service Cheyenne WY
942 PM MDT Tue Apr 27 2021
Issued at 938 PM MDT Tue Apr 27 2021
One last update for this evening. Extended the Winter Weather
Advisory for the southern Laramie Range foothills just west of
Cheyenne for slushy and partially snow covered roadways.
Visibility has been reduced to one half mile at times with
snowfall expected to continue through midnight. Only expecting a
few inches of snow accumulation, but travel impacts have been
confirmed on webcams in the area. Thought about adding the
northern Snowy Range foothills, including Elk Mountain and
Arlington, to the Advisory, but snowfall rates have come down
considerably in the last hour with the HRRR showing the precip
shield moving east for the rest of tonight. It is snowing in
Cheyenne now, but snow will have trouble sticking to the roadways
at 35 degrees. Will continue to monitor but do not expect to
extend the Advisory into central Laramie County at this time.
Updates have been sent.
.SHORT TERM...(This evening through Wednesday Night)
Issued at 245 PM MDT Tue Apr 27 2021
Forecast challenges deal with snow amounts/locations as well as
severe thunderstorm potential.
Currently...Frontal boundary lays from southeastern Colorado to
near Leadville Colorado to just east of Rawlins this afternoon.
Radar imagery showing storms wakening as they cross the Colorado
state line into Wyoming...but we are still getting some lightning
and reports of hail. Had a report of half inch hail and pea sized
hail in Laramie this afternoon from a cell that moved through a
little while ago. Precip area filling in on radar across our
southern zones. IR imagery showing cooling cloud tops across
Laramie and Kimball Counties...most likely the anvil from the
storms down in Colorado. So far...only place seeing snow is over
the Summit...where webcams are showing the ground turning white up
there. Latest road temperatures still quite warm...with mid to
upper 40s still being reported from Wyoming RWIS sites.
Current SPC Mesoanalysis parameters showing current CAPE around
500J/KG CAPE across Laramie County and southern Panhandle. Still
thinking sub severe thunderstorms. With expanding precip
area...would think the CAPE is going to begin coming down as well
as we are seeing temperatures only in the low 40s across Laramie
County and low 50s at Kimball and Sidney.
Pretty good rain event still on track for the southern panhandle
and I-80 Corridor in southeast Wyoming from Pine Bluffs to
Laramie. These areas still looking at a half to three quarters of
an inch of QPF through Wednesday morning.
Evening shift will need to watch current conditions tonight as
road temperatures cool. Contemplated a winter headline for
Arlington and the eastern foothills...but am not getting the snow
amounts. Would not be surprised if we do need a short fused
advisory for these locations later this afternoon and early
.LONG TERM...(Thursday through Monday)
Issued at 315 AM MDT Tue Apr 27 2021
Broad upper level ridging is expected to dominate the western portion
of the CONUS, bringing much milder conditions expected Thursday through
early morning Saturday. Daytime highs associated with this pattern
start in the mid to high 60s Thursday and climbing to the high 70s
into Saturday. High temperatures in the 50s to lower 60s above 9000
feet will result in snow melt runoff and small rises along nearby
creeks and streams below. Sunday and Monday shows vastly different
model outcomes for the precipitation, and has lead to the widespread
precipitation event being much more scattered afternoon and evening
showers, with some isolated thunderstorms. The current GFS guidance
has most of the precipitation to the north across southeastern Wyoming
for Sunday, which shifts eastward into the Panhandle for Monday. At
this time, the precipitation coverage for Sunday through Tuesday morning
is likely overdone. As a result, started backing the POP totals downwards.
Will need to monitor the latest model runs for this event as there
is a fair amount of uncertainty. Cooler temperatures expected beginning
in the early part of next week as a cold front associated with a deeper
shortwave passes over the region. Daytime highs will be in the mid
50s to low 60s, and nighttime lows almost reaching freezing by Tuesday.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 523 PM MDT Tue Apr 27 2021
Wyoming TAFS...MVFR at Rawlins until 05Z, then VFR.
Occasional MVFR at Laramie until 03Z, then IFR until 15Z, then
Occasional IFR at Cheyenne until 06Z, then IFR until 15Z, then
Nebraska TAFS...MVFR until 04Z at Chadron, with occasional IFR
until 02Z, then IFR until 14Z, then VFR. Wind gusts to 22 knots
MVFR at Alliance until 08Z, then IFR until 14Z, then VFR. Wind
gusts to 30 knots until 02Z.
MVFR at Scottsbluff until 03Z, then IFR until 09Z, then MVFR until
15Z, then VFR. Wind gusts to 25 knots until 03Z.
MVFR at Sidney until 03Z, then IFR until 15Z, then MVFR until 18Z,
then VFR. wind gusts to 25 knots until 03Z.
Issued at 315 AM MDT Tue Apr 27 2021
A cold front over along the Wyoming/Colorado/Nebraska border will slowly
push south into northeast Colorado today. A low pressure system will
track east across the central Rockies through this evening, bringing
a variety of precipitation including lower elevation rain showers, high
elevation snow showers, and widely scattered thunderstorms. Precipitation
will diminish from west to east late tonight and Wednesday morning.
Higher humidities and much cooler temperatures will preclude fire weather
concerns. Warmer, breezy and drier conditions are expected Thursday
WY...Winter Storm Warning until 6 AM MDT Wednesday for WYZ114.
Winter Weather Advisory until 6 AM MDT Wednesday for WYZ112-116-
AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
708 PM CDT Tue Apr 27 2021
Issued at 250 PM CDT TUE APR 27 2021
-Breezy southwest winds are expected to gradually decrease this
-Thunderstorm chances increase tonight after 10 PM, and become
likely towards sunrise Wednesday morning as a series of disturbances
move through the area. Can`t rule out a strong storm or two.
-Drier conditions expected Thursday into the weekend with a warming
Stout southwest winds drawing moisture into the region with surface
dew points climbing into the lower 60s. Fairly strong capping
inversion in place, but as moisture ~850 mb increases, cap weakens
to the point where convection is possible. Not much in the way of
mass convergence with low level jet tonight, but do get some
added lift from the left exit region of the upper level jet. CAMs
have offered a variety of solutions throughout the day, with the
HRRR suggesting convection developing along the cold pool of
convection originating in Oklahoma to clusters of storms advecting
in from Oklahoma. NAM Nest is less aggressive with convective
initiation, holding off the storm potential till Wednesday
morning. Tend to believe the NAM Nest more than HRRR/RAP, but have
some low chance pops after 03Z to cover the instance that the
moisture return is enough and cap is able to break. 1-6 km bulk
shear values are generally in the 15-25 knot range. CAPE values
are generally expected to be 800-1200 J/kg. If we can get a storm
to develop, a few strong-marginally severe storms are possible
late tonight into Wednesday morning.
More widespread convection is expected on Wednesday as shortwaves
lift northeast from upper trough across the dessert southwest. This
upper trough is expected to slowly sag south into Mexico, and remain
there through the weekend. Track of the leading shortwaves within
southwest to northeast flow appears to be across southern Missouri.
Marginal severe risk across the central Missouri looks reasonable
with 500-1000 J/kg of CAPE along with 30-40 knots of 0-6 km bulk
shear. Instability tapers off to the north, and with stalled front
across northern Missouri, may be difficult to get much in the way of
appreciable precipitation along and north of the boundary. Slight
risk of excessive rainfall across central and southern Missouri
tomorrow, though 12Z model suite has been trending ever so slightly
south with rainfall focusing more on the Ozarks region.
Precipitation trends decrease on Thursday as stalled boundary works
south leading to cooler more stable conditions. Warming trend is
expected Friday into the weekend. Thereafter, models are suggesting
upper trough across Mexico may try to eject into the plains, but
precise trajectory of the wave remains uncertain at this time.
.Aviation...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 707 PM CDT TUE APR 27 2021
Gusty winds southwesterly winds continue through sunset as a
front approaches the region. This front is ushering in an area of
precipitation into E KS; however, capped, stable air has been
weakening showers as they approach the state line. This is
expected to continue this evening. A stray showers is possible as
the front approaches (~03Z-06Z). Winds become VRB as the front
stalls near STJ Weds morning. Showers and thunderstorms stick
around throughout the day Wednesday primarily south and east of
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
828 PM CDT Tue Apr 27 2021
Only a small band of light rain or sprinkles continues across the
central portions of the CWA at the present time. Most hi-res models
continue to show development of robust thunderstorms out west around
midnight as the low-level jet strengthens. However, the special 21z
sounding from DRT showed a sizable CAP with only a small reduction
in the CAP noted on the 00z sounding. The 00z HRRR now shows no
strong to severe thunderstorm development out west with only some
scattered showers and maybe an isolated storm. Will have to continue
to watch and assess the CAP strength for any possible signs of
initiation through the next several hours. If an updraft were to
break through the cap, very steep lapse rates from 850-600 mb would
lead to very large hail production. Made some minor adjustments to
the PoP grids, but no substantial chances were made to the ongoing
.PREV DISCUSSION... /ISSUED 621 PM CDT Tue Apr 27 2021/
Scattered light rain or sprinkles continue to move overhead around
the I35 sites. However, much of this is not reaching the ground as
dry air remains in the mid-levels of the atmosphere. Will cover this
with VCSH for the next few hours. The attention then turns to near
DRT later this evening as more robust convection may develop around
midnight with possible showers and perhaps a thunderstorm affecting
the I35 sites before daybreak. Any activity should be east of the
area by the mid-morning hours. Another round of convection is likely
to develop near DRT tomorrow afternoon then move near the I35 sites
in the late evening or overnight hours. In addition to the
precipitation chances, MVFR ceilings will eventually lower to IFR
overnight before slow improvements can be expected tomorrow.
PREV DISCUSSION... /ISSUED 245 PM CDT Tue Apr 27 2021/
SHORT TERM (Tonight through Wednesday Night)...
A rather busy, active 24-36 hours are ahead of us as several rounds
of thunderstorms appear likely, with all modes of severe weather
possible. Latest SPC RAP mesoanalysis has an H5 trough centered over
the Great Basin, and slowly pushing eastward. Out ahead of this upper
trough, a series of impulses/shortwaves will ripple through the
flow, sparking two rounds of severe thunderstorms, one late tonight,
and another round expect Wednesday afternoon and evening.
At the surface, rich, Gulf moisture continues to stream northward
into the CWA, as low level flow accelerates out of the southeast out
ahead of a developing sfc low over the Texas Panhandle. This feature
will progress eastward over the next 24-48 hours, with a sloshing
dryline feature out ahead of both this evening and tomorrow
afternoon/evening. First, let`s talk about this evening`s storm
chances. On and off scattered showers and isolated thunderstorms
will continue through this evening over the Hill Country and western
zones. This activity is unlikely to be severe, with some thunder
possible due to elevated CAPE and instability. SBCAPE is on the
order of 1000-2000 J/kg, but SBCIN is quite high, given the
considerable cloud cover, and the lack of any sort of forcing
mechanism to aid in parcel bouyancy through the evening hours. Out
west, over the Rio Grande Plains and Southern Edwards Plateau, SPC
has a Slight risk in place, with the threat for all modes of severe
weather. The primary concern will be hail and even an isolated
tornado. The reason being? The LLJ really gets cranking after 00Z,
with very impressive low level veering on model forecast soundings
and humped hodographs. If any storms can become rooted in the
boundary layer quickly, there is a short window of opportunity for
supercells capable of large hail to 2"+ and an isolated tornado
threat. Once storms move off the Rio Grande Plains, the tornado
threat lessens as SRH values decrease quickly. However, with good
elevated CAPE, hail threat will continue through early morning
hours, possibly stretching into the San Antonio metro.
Turning attention to the next severe threat: Wednesday. This second
round looks to be the main event for this week, as a rather strong
shortwave moves through South-Central Texas tomorrow afternoon and
early evening. All modes of severe weather are possible, with an
isolated tornado possible, especially west of a Kerrville to San
Antonio to Pearsall line Wednesday afternoon/evening. Latest CAMs
indicate a very favorable supercell environment, especially between
18Z-00Z, with discrete storms possible over the Rio Grande, then
pushing east-northeastward through the late afternoon/early evening.
Storms should grow upscale and congeal into a line, but some
training of cells looks more likely with each passing run. Add to
that the fact the PWATs are practically off the charts for this time
of year, and localized flash flooding could become a concern with
any storms that move over the same region for several hours.
Residence time will be key, especially for portions of Caldwell,
Bastrop, and Lee counties, which picked up substantial rainfall last
Friday. With regard to the parameters in place, they are rather
impressive, with the TT WRF and SPC HREF CAMs indicating 0-3km SRH
in the 200-400 m2/s2 range, 0-6km bulk shear of 55-65 kts, MUCAPE of
1500-2500 J/kg, and modest mid-level lapse rates of 6.5-7.0 C/km.
Combine all these factors, and the expectation is that the region
will experience a rather active day on Wednesday and stretching into
LONG TERM (Thursday through Tuesday)...
The cold front should be over our eastern counties by daybreak
Thursday with most of the severe threat winding down as the upper low
shears and leans strongly positive tilted to the NE. Lingering
convection along the front is expected to keep the front moving SE.
The more progressive GFS remains the preferred model in keeping the
front moving while the ECM/CMC solutions continue to stubbornly hold
back most of the upper low energy upstream. Between these two
opposing choices is the NAM and some NAM influence has this
afternoon`s forecast for Friday into Saturday not looking quite as
warm and stable as the early morning forecast package, but favoring
the stable options moreso than the redundantly unstable ECM/CMC
patterns. By Sunday, the deterministic models somehow come back into
alignment with all taking the remant upper low east and warming up
the forecast area nicely.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 71 88 67 78 60 / 40 30 80 50 20
Austin Bergstrom Intl Airport 70 88 66 79 60 / 40 20 70 50 20
New Braunfels Muni Airport 72 89 68 82 61 / 40 20 70 40 20
Burnet Muni Airport 70 85 63 76 57 / 40 40 80 40 20
Del Rio Intl Airport 74 90 66 86 61 / 40 30 50 10 10
Georgetown Muni Airport 70 87 66 77 59 / 30 30 80 50 20
Hondo Muni Airport 71 89 65 84 60 / 40 30 80 20 10
San Marcos Muni Airport 70 88 66 81 60 / 40 20 70 50 20
La Grange - Fayette Regional 73 88 70 82 62 / 30 10 50 60 20
San Antonio Intl Airport 72 88 68 81 61 / 40 30 80 40 20
Stinson Muni Airport 73 90 69 83 62 / 40 30 70 30 20
Area Forecast Discussion
National Weather Service Grand Rapids MI
1022 PM EDT Tue Apr 27 2021
Issued at 306 PM EDT Tue Apr 27 2021
- Risk for strong/svr storms tonight/early Wed
- Additional rounds of showers/storms next week
Issued at 1022 PM EDT Tue Apr 27 2021
A few showers and isolated thunderstorms have formed,just north of
I-96. That is just north of the surface front. The showers and
isolated thunderstorms as an area of moisture ahead of the main
system move into the area. It would seem this area of showers
should be done by 1-2 am. The second area of showers and a few
thunderstorms is still expected after 4-5 am. The latest (9 pm )
run of the RAP and HRRR models show equilibrium levels below
20000 ft through 8 am Wednesday morning. I do not expect these
will be anything more then generic showers and isolated
UPDATE Issued at 833 PM EDT Tue Apr 27 2021
I have coordinated with SPC and we both agree the severe weather
threat for Southwest Lower Michigan between now and sunrise is
very low. They agreed to cut back on the size of the marginal risk
on their next update so only a small part of Southwest Lower
Michigan remains in the threat.
The effective buck shear is below 30 knots all night
(SPC SREF) and increases to 30 - 40 knots south if I-94 after
sunrise. There is no hail cape (cape between -10c and -30c) on
either the RAP, NAM or NAMNEST models over Michigan tonight. That
does show up after sunrise near and south of I-94. Model sounding
are very dry between 700 mb and 500 mb most of the night and there
is a significant amount of CIN to overcome. Beyond that here is a
significant surface inversion that would have to be overcome to
get severe winds to the ground.
On a lager scale we have a shortwave tracking over the top of the
upper ridge (which is directly over the state of Michigan most of
the night). That shortwave created the storms north of HTL late
this afternoon. Those storms have now moved east of Michigan. We
also have a digging northern stream shortwave over BC and Alberta
rotating toward the base of the upper low, which is centered over
Hudson Bay. While that is happening we have an ejecting shortwave
coming out of the upper low over the Southwest CONUS. The
combination of those to features pushes the frontal boundary south
of I-94 in the 4 am to 10 am time frame. It is that southern
stream wave that brings up the deeper moisture and instability
from the south into Ohio and Indiana and extreme southern Lower
Michigan Wednesday morning.
My spin on this is the convection over N WI stay north of our CWA
most of the night since that is where the thermal boundary stays
anchored until the upstream wave moves into the area after 4 am.
At that point we will get an area of showers and isolated
thunderstorms that will trail more south to southwest into
Illinois. That area of showers and a few thunderstorms will reach
our norther CWA after 5 am. It will cross into the MKG/BIV/GRR
area around sunrise. That band of showers will reach the Detroit
area before noon. Finally the southern stream wave will act on the
frontal boundary, which by then will be south of Michigan and
develop a decent area of thunderstorms south of I-94.
The bottom line it is hard for me to envision much in the way of
severe storms over Southwest Michigan until the sun comes up
Wednesday morning and has a chance to heat the air some. By then
the convective threat will be near and south of I-94.
.DISCUSSION...(This evening through next Tuesday)
Issued at 306 PM EDT Tue Apr 27 2021
- Risk for strong/svr storms tonight/early Wed
The axis of elevated instability moves in from the west tonight
into Wednesday morning. Guidance also shows a low level jet nosing
in around 08z from the southwest which pushes east through the CWA
by about 15z. The combination of stronger wind fields and
instability with steeper mid level lapse rates around supports an
increased risk for severe weather. Large hail and a risk for
high winds looks possible. SPC has the day 1 outlook featuring a
marginal risk for severe weather for much of the CWA.
- Additional rounds of showers/storms next week
A lot of uncertainty exists with how next weeks pattern will
unfold. The main reason for this is that mid level low over the
Western U.S. cuts off and remains that way for 24 to 48 hrs.
Eventually it does get pushed out Sunday into Monday. Some models
keep it down along the Gulf while others lift it up into the Great
Lakes region. Either way the system will be an efficient rain
producer as it will have abundant moisture to work with. We will
keep the pattern unsettled for now.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 833 PM EDT Tue Apr 27 2021
I see a largely quite night over Southwest Lower Michigan. The
threat for thunderstorms should largely stay north of our CWA
until nearly sunrise Wednesday morning. At that point I could see
a broken area of showers and possibly and isolated thunderstorm
moving through the TAF sites in the 10z to 16z time frame. I did
not put the threat of thunderstorms in the I-94 TAF sites for the
16z to 21z time frame to limit the length of the VCTS in the TAFs.
As for MVFR and IFR conditions, we will need the cold front to get
through first. The latest run of the RAP model suggests through
15z, the low clouds will stay north of I-96, meaning only MKG has
a risk of MVFR or IFR cigs. After 15z, it seems the RAP model
wants to mix that layer out so for the most part, MKG will be most
impacted. GRR is possible for a few hours, as well as LAN (in the
12z to 18z time frame). It would seem AZO, BTL and JXN should
largely stay VFR expect if a storm were to get to one of those
sites. Then we would have 15 minutes of MVFR while the storm moved
through. So,I did not include that since timing this point would
Issued at 504 PM EDT Tue Apr 27 2021
I have canceled the Small Craft Advisory early since all of our
near shore sites have winds 15 knots and most are under 10 knots.
With the front coming into the area winds will only decrease. Also
I looked a several web cams and seems waves are under 3 feet.
Area Forecast Discussion
National Weather Service Louisville KY
1024 PM EDT Tue Apr 27 2021
Issued at 1020 PM EDT Tue Apr 27 2021
Current satellite shows high cloud filling in from the west as
regional observations show a decrease in winds across the area. Not
many changes with the near term forecast this evening. Updated wind
and sky grids with latest guidance that best initializes. Otherwise
just refreshed near term grids to better match regional
Looking forward to the rain event beginning tomorrow through
Thursday evening, latest guidance continues to paint the highest QPF
over southern Indiana and roughly along the OH River. 28/00Z HRRR
did pick up the convective activity Wednesday afternoon compared to
the 27/18Z run. Best timing for storms right now appears to be
between 28/16Z through 29/00Z, which the current forecast has well
covered. No changes made to the Flash Flood Watch valid from 28/18Z
through 30/00Z, but will reissue with extended product valid time.
Updated products will be sent shortly.
.Short Term...(This evening through Wednesday)
Issued at 309 PM EDT Tue Apr 27 2021
Warm and dry conditions are persisting across the region as high
pressure hangs on a bit longer. Seeing temperatures in the upper 70s
and low 80s at this hour, with another couple/few degrees expected
before peak heating. In addition, gusty SSW winds in the 25 to 30
mph range will continue until around sunset.
Expect a mild overnight as steady SSW winds will continue, but upper
sky cover will also filter into the region ahead of the next system.
As a result, expect lows only bottoming out in the mid to upper 60s.
A few light rain showers could arrive by dawn under a warm
advection/isentropic lift setup.
...SHOWERS & THUNDERSTORMS LIKELY WEDNESDAY - THURSDAY, SLIGHT RISK
FOR EXCESSIVE RAINFALL/FLASH FLOODING...
The upper ridge breaks down off the SE CONUS on Wednesday, with an
elongated baroclinic zone stretching from the Rio Grande, up through
the mid Mississippi/Wabash/Ohio River Valleys, and into New England.
Deep SW flow over our area will be in place between two western
trough features, and that upper ridge breaking down off the SE
CONUS. This will set up a nearly stationary surface boundary to our
NW with deep/moist flow nearly parallel to that feature for a
prolonged period getting going on Wednesday and lasting through late
Thursday. Given the potential for some modest instability, PWATs up
above 1.8" through the column, some training potential, and a
tall/skinny CAPE profile widespread rainfall with pockets of heavy
rainfall are expected for areas along and north of the Ohio River.
WPC has expanded the slight risk of excessive rainfall, and QPF
amounts have also come up in agreement. As a result, will lift a
Flash Flood Watch beginning Wednesday afternoon and lasting through
Thursday evening. Widespread 2 to 4 inch amounts of rain, with
locally high amounts are possible in the watch area.
The other issue for Wednesday afternoon, is the threat for severe
weather. This threat will be conditional upon destabilizing, but
given the chance for better destabilization south of the heavy rain
axis, and better 0-6 km bulk shear values in the 35 to 40 knot
moving in by afternoon a few organized updrafts seem possible. The
main threats would be damaging wind along with brief torrential
rainfall, and perhaps some marginally severe hail with the strongest
storms. One limiting factor tied into the instability concerns will
be lack of steeper lapse rates.
.Long Term...(Wednesday night through Tuesday)
Issued at 235 PM EDT Tue Apr 27 2021
...Potential for Training Showers/Storms Wed/Thu...
Southwesterly flow over the region now just starting to tap into
some deeper moisture currently over TX/LA. At the start of this
period, expect showers and storms to be ongoing just ahead of a slow-
moving frontal boundary...which at that point still will be well
northwest of the region. Strong moisture transport will bring our
precipitable water values up to near record levels for this time of
year...which typically means heavy rainers whenever you are able to
tap some kind of convective element within the environment.
12Z high-resolution short-term models all show it won`t take much
for new rounds of showers and storms to develop and potentially
train Wed. night and Thursday. By Thursday daytime, we may also have
some kinematic forcing, as the favorable quadrant of an upper jet
resides over parts of the region. Agree with previous forecasts that
the best chance for some of the responding lower level wind fields
to bring in some stronger storms likely will be more across southern
and eastern KY...away from where previous rains would have helped
stabilize the surface boundary layer.
All told we are looking at rainfall totals through Thursday night of
3 to 4 inches in our southern IN and some northern KY
counties...with lesser amounts to the south. There could be some
localized flooding where those swaths of training storms form. Given
the potential for these training cells...decided to go ahead and
push out a flash flood watch for our southern IN and some north
central KY counties.
The tap shuts off as the cold front clears the region by Friday and
high pressure builds in for the weekend. That high center over us
Saturday morning could bring some temperatures in our cold spots
down into the 30s...again have to watch for patchy frost potential
Sunday night through Tuesday`s forecast is muddied some by how the
various models are handling a slow moving upper low crossing the
Deep South/Appalachians and/or another wave/cold front coming down
from the northwest. Despite this uncertainty...the trend in model
data is for temperatures to remain above normal in this period.
.Aviation...(00Z TAF Issuance)
Issued at 742 PM EDT Tue Apr 27 2021
- Winds gusts diminishing this evening.
- Lower ceilings (MVFR), showers, and a few storms possible Wednesday
DISCUSSION: Current satellite shows high cloud spilling in over the
region as latest surface analysis places an elongated NE-SW oriented
stationary frontal boundary roughly from KORD-KDSM-KRSL with high
pressure retreating across the OH Valley. Overnight, a low level
nocturnal jet will see increased winds around FL020 from 30-40kt
mainly affecting HNB, SDF, and LEX, but surface winds remain high
enough that LLWS criteria were not met so have left mention out of
TAFs. Expect CIGs to lower to MVFR Wednesday morning with isolated
light showers. By afternoon, expect chances of TS with SW winds
gusting to 15-20kt. By Wednesday evening more moderate rainfall is
expected with VIS and CIG deteriorating to IFR overnight.
CONFIDENCE: Medium on timing of TS. High on all other forecast
IN...Flash Flood Watch from Wednesday afternoon through Thursday
evening for INZ076>079-083-084-089>092.
KY...Flash Flood Watch from Wednesday afternoon through Thursday
evening for KYZ023>025-030>034.
Area Forecast Discussion
National Weather Service Phoenix AZ
514 PM MST Tue Apr 27 2021
.UPDATE...Updated 00Z Aviation Discussion.
A weather system affecting the region will bring well below
normal temperatures today. Lingering showers and potentially a
few thunderstorms will remain a possibility across Gila County on
Wednesday, while the lower deserts will see clearing skies and
warmer conditions. A strong high pressure system will then take
over late week resulting in much warmer temperatures and highs
likely topping 100 degrees as early as Friday and lasting through
Rainfall gauges from around central Arizona indicate that in
general, a few hundredths of an inch of rain fell overnight. Up to
a tenth of an inch of rain was observed across the higher terrain
east of Phoenix, such as in Fountain Hills. Latest MRMS indicates
shower activity across Pinal and Gila Counties has generally
decreased in coverage over the past few hours. Meanwhile, water
vapor imagery reveals a well-defined vort max diving southward
through central California, which is invigorating a broad area of
low pressure near Las Vegas. With well below normal heights across
the Desert Southwest, temperatures have struggled to reach the
lower 70s, making this the coolest day in a month.
Residual low-level moisture in the wake of last nights light
rain is contributing to modest 100-500 J/kg SBCAPE across portions
of Gila County and even locations as far west as Joshua Tree
National Park. Latest HREF suggests isolated showers will persist
into the evening as the aforementioned vort max drops southward
and begins to pivot. Further eastward, central Arizona remains in
somewhat of a col region, where ascent, moisture and instability
are less than ideal. Consequently, PoPs have been lowered to the
single digits to the rest of today.
Latest guidance is in good agreement a closed low will
consolidate across southern Arizona tonight. This will promote a
cyclonic flow across Arizona Wednesday along with a continued
threat of showers and thunderstorms, particularly across Gila
County and portions of southeastern Arizona, per the latest HREF.
Latest runs of the HRRR even suggest wrap-around convection could
reach as far westward as the East Valley, and PoPs were nudged
upwards in the these areas.
By Thursday, focus will shift to the potential for well above
normal temperatures as an anomalously strong ridge builds eastward
across the Desert Southwest. Latest GEFS members are in good
agreement, but this could also just be a symptom of an
underdispersive ensemble. ECMWF ensemble normalized standard
deviation suggests the closed low to our east could slow or even
become cut off through the end of the week. This is also evident
in the NCEP cluster analysis, where this scenario accounts for
one-quarter of the total members. If this comes to fruition, high
temperatures Friday and Saturday wont be quite as warm as
earlier advertised. Nevertheless, the most likely solution still
indicates a 50% chance of tying or reaching record values
Saturday. It is worth mentioning the NBM mean has trended a bit
cooler, likely in response to the uncertainty in the ECMWF
By Sunday, the trough to our north should suppress heights aloft
enough over our region to provide some slight cooling as highs
drop back to between 98-100 degrees. Models mostly agree this next
dry trough will move into the Great Basin on Sunday and then
stick around the Southwestern U.S. through early next week
providing some gradual cooling. Although temperatures are likely
to remain above normal through early next week, highs should drop
back down into the 90-95 degree range by Monday.
.AVIATION...Updated at 0014Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
In the shorter term, the main forecast uncertainty is whether
winds will shift easterly at KPHX tonight. There is a slight
indication they may stay west or just become variable, but for
now will still show an easterly shift around 13Z. Diurnal shifts
are expected at the other terminals. An early west shift is then
expected Wednesday, by 17-18Z. Wind speeds will be light overnight
and then become breezy Wednesday afternoon with gusts to around 20
Uncertainty increases late Wednesday afternoon as showers and
storms are likely to develop to the north and east of Phoenix with
a 10-20% chance of moving into the metro area between 23-2Z. While
the activity could dissipate before reaching terminals, outflow
boundaries with up to 25-30 kt gusts have a better chance of
reaching terminals and creating an abrupt change in wind
direction. Cloud bases will mostly be FEW to SCT around 9-10 kft.
Southeast California/Southwest Arizona including KIPL and KBLH:
An isolated shower cannot be ruled out at either terminal through
about 3-4Z this evening. Following that, skies will gradually
clear. Winds will remain out of the northwest to west at KIPL
through the period with elevated speeds this evening and again
Wednesday afternoon. Light west to northwest winds, and at times
variable, is expected at KBLH. Increased northerlies are
anticipated at KBLH by 14-15Z. Gusts up to 20-25 kts will be
possible at both terminals late morning through the afternoon
Friday through Tuesday:
Strong high pressure will work into the region early in the period
with near record heat likely for Friday into the weekend. High
temperatures will climb each day through Saturday with 100-105
degrees possible Friday and Saturday before cooling slightly
starting Sunday. Seasonably dry conditions are expected through
the period with min RH values mostly in the upper single digits.
Winds will follow diurnal trends with fairly breezy conditions
expected for Saturday and Sunday.
...Daily Record Highs...
Phoenix Yuma El Centro
.......... .......... .........
Fri 4/30 102 (1943) 103 (1943) 104 (1965)
Sat 5/1 103 (1985) 106 (1947) 106 (1947)
Sun 5/2 107 (1947) 111 (1947) 113 (1947)
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
Area Forecast Discussion
National Weather Service Blacksburg VA
819 PM EDT Tue Apr 27 2021
High pressure off the South Carolina coast brings a Summer tease
through Wednesday. A front will begin to approach the area late
Wednesday into Thursday with a few showers and storms over
central and southern West Virginia. Better chances for rain and
storms arrive Thursday night into Friday as the front passes
through. High pressure and seasonable temps for the weekend
.NEAR TERM /THROUGH WEDNESDAY/...
As of 280045 PM EDT Tuesday...
...Our early Summer preview continues with above average
temperatures through Wednesday afternoon...
Hope everyone enjoyed the warm sunshine and was able to get
outdoors and take advantage of the nice weather. Temperatures
topped out well above the seasonal norm...80s for most.
Dewpoints are gradually coming up, with 50s beginning to show up
in the piedmont. Southwest winds will continue to draw this
moisture northward such that the humidity minimums will not be
as extreme Wednesday. Clouds will also be on the increase too.
Synoptically an abnormally strong upper level ridge remains
firmly intact across the eastern 2/3rd of country along with a
strong high pressure off the coastal of North/South Carolina.
Good south to southwesterly flow continues to flood into the
region as a result with afternoon 850 mb temperatures on the
order of +16 to +18 degrees C through Wednesday. Beyond this
point our next front approaches first as a warm front north
followed by a cold front later in the week.
For Wednesday, the stickiness factor looks to climb as the
surface high drifts further off the Carolina coast increasing
broad west to southwest flow. Moisture also increase as a result
of our cold frontal boundary getting closer to the region. As a
result we can expect more of a milky appearance to the sun and
a chance at a few showers/storm creeping down into southern WV
and the Alleghany Highlands. The HRRR and NAMnest illustrate
this well with subtle difference in regards to timing/placement
with activity as it funnels in from eastern Ohio and central
West Virginia. Most of the models including the ensembles bring
the activity as far east as the BLue Ridge Parkway with a few
dropping isolated showers/storm toward Lynchburg. For now, have
opted to keep chance pops along and west of the Blue Ridge with
highest confidence over the Greenbrier Valley and southern West
Temperature wise we fall back into the low to mid 50s with a few of
the urbanized areas hanging close to 60 degrees tonight. It`s
another warm one for Wednesday with just a few more high clouds
around as the front gets closer to the region. Highs will top back
out in the upper 70s and low 80s in the west with mid to upper 80s
.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 250 AM EDT Tuesday...
Unseasonable mild weather continues into Thursday.
High pressure will remain off the Southeast Coast into Thursday. A
cold front will approach us from the Ohio valley. A southwest flow
will push warm air into our region. An isolated shower or
thunderstorm may be possible in the northwest portion of the
forecast area closer to the frontal boundary Wednesday afternoon
into Wednesday night. The GFS and NAM hint at development of more
showers along the higher terrain. However, believe the dry air in
place and subsidence from the high will limit any convection
Wednesday. High temperatures Wednesday will range from the upper
60s in the northwest mountains to the mid 80s in the piedmont. Low
temperatures Wednesday night will vary from the lower 50s in the
west to the lower 60s in the east.
For Thursday into Thursday night, a upper level low/trough will head
eastward across the Great Lakes region and push the cold front
southeastward towards our region. This will result in increasing
moisture in advance of the cold front. Scattered showers and
isolated thunderstorms will move east across region. The best chance
of rain will be in the west. High temperatures Thursday will
moderate to the mid 70s in the mountains to the mid 80s in the
piedmont. Low temperatures Thursday night will range from around 50
degrees to the mid 60s in the piedmont under plenty of clouds
Confidence in the short term forecast is moderate to high.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 250 AM EDT Tuesday...
Cold front will move through Friday followed by gusty winds, then
drier air for the weekend into early next week...
The cold front travels through the region on Friday. The model
guidance differs on precipitation associated with the front as it
crosses our area. The GFS is the wettest with a solid line of
showers. While the European and Canadian solutions keep the bulk of
the associated energy and precipitation split to the north or south
of our area. Will play the highest pops in the west Friday into
Friday night. The timing of the front looking like in the morning.
This will hinder deeper convection development with limited
instability. In coordination with AKQ and RAH will allow for an
isolated thunderstorm in the east.
Winds increase behind the frontal boundary with the GFS the
strongest, from 40 kts to 50 kts 850mb winds possible Friday across
parts of the region. ECMWF and Canadian have more conservative
around 35 kts 850mb wind across the area. In any case,it will be
gusty Friday into Friday night, but not gusts enough to warrant any
headlines at this time.
Saturday into early next week, upper level ridging is expect for the
East. This will result in a warming trend across our area with
isolated precipitation chances.
Temperatures will be the coolest on Friday, generally below normal
with clouds and rain, then temperatures will moderate each day to
Confidence in the Long Term Forecast is moderate.
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 815 PM EDT Tuesday...
VFR conditions are expected tonight and into the first half of
Wednesday. Surface high pressure remains in control as it slowly
drifts from the Carolina coast. As broad low level westerly to
southwesterly flow increase so does the moisture for pockets of
scattered to broken high cirrus over KLWB/KROA/KBLF/KBCB/KTNB
heading into Wednesday morning. VFR conditions will continue
through this period with an increase in pockets of sub-VFR from
KLWB/KBLF to KTNB by Wednesday afternoon as our incoming front
encroaches upon the region. HRRR and NAMnest guidance/soundings
are in good agreement with this as a few showers and even a
couple of isolated thunderstorms try to sneak there way in from
KCRW and KHTS by late Wednesday afternoon. For now, have left
out the mention of VCSH and VCTS since confidence remains low to
moderate at this time.
As for the wind, nocturnal inversion should promote diminishing
winds overnight. Once the inversion lifts between 0900-1000 EDT
Wednesday expect a return to gusty conditions from the west to
southwest. Winds will remain sustained out of the west/southwest
5-15 knots with gusts upwards of 15 to 20 knots Wednesday
Above average confidence for cloud bases, visibility, and winds
through the TAF period. Low-Moderate confidence in regards to
precipitation chances in the WV mountains from KLWB to KBLF.
Extended Aviation Discussion...
A late week cold front brings a return to sub-VFR conditions
Thursday into Friday. By late Thursday afternoon and most of Friday
will see the ceiling and visibility deteriorate to MVFR/IFR as a
cold front brings showers and higher winds to the entire area. There
are some differences in timing with the frontal passage in the
models, but at this time the best probability of precipitation will
be Thursday night and Friday morning.
Conditions improve over the weekend as another dome of high pressure
enters the region.
...Update to aviation forecast discussion...
Issued at 345 PM CDT Tue Apr 27 2021
High clouds continue to stream in overhead, with broad isentropic
ascent in place ahead of the deep trough over the Southwest CONUS.
Surface analysis depicts a surface low over Iowa this afternoon,
with another low in the lee of the Rockies over southeast Colorado.
Between the two, a cold front lies across northwest Kansas, with a
dryline stretching from north-central Kansas into western Texas.
Despite the high clouds, temperatures have warmed into the mid to
upper 70s, while gusty southwest winds have brought dewpoints
into the 60s east of the dryline.
The severe weather setup for tonight is on the complicated side,
with no well-defined forcing for storm development and little
consistency in short-term model guidance. Thunderstorms will
continue to develop this afternoon and evening across northwest TX
and western OK. This is the key area to focus on. The main
uncertainty is if a left- moving cluster can develop out of these
storms and move northeast into east- central Kansas this evening.
The HRRR and a few other convective allowing models did depict
this scenario earlier today, but have somewhat backed off over the
past few runs. However if storms are able to move into the area,
the environment would be supportive for a few strong to severe
storms. Low level shear is weak/messy, but effective shear of
50-60 kts, MUCAPE around 2500 J/kg, and mid- level lapse rates
around 7-8 C/km would support large hail up to around golf ball
size with any storms that can move into the area. Damaging winds
would be a secondary hazard, given somewhat surface based storms
and a drier layer below 700 mb.
By late tonight and early tomorrow morning, a second round of
scattered showers and thunderstorms is more likely, as a vort max
approaches within the southwest flow aloft. Instability will likely
be weaker by this time, as lapse rates will be negatively impacted
by earlier convection to the south. As a result, while there still
could be a few stronger storms with this round, the overall severe
threat will be lower. Additional showers and storms will continue
into the day tomorrow, particularly across portions of southeast
Kansas. Some uncertainty with exactly how this will play out, with
overnight convection the main complicating factor. However, as
instability will likely continue to weaken, the better chance for
additional strong to severe storms will likely remain south of the
area. The heavy rain threat will likely also remain to the south,
with east-central KS likely seeing 0.5-1.0" of rain. Lesser amounts
should occur across most of northeast and north-central KS, though
isolated higher amounts can`t be ruled out with any heavier
Conditions should turn drier for the end of the week and into the
weekend, as the upper trough gets cut off over northern Mexico and
ridging builds in over the Central Plains. Temperatures should
remain near average Thursday and Friday behind the cold front, with
highs in the low 70s. As the ridge builds in for the weekend, highs
should warm back above average, into the upper 70s to mid 80s.
The next trough approaches late Sunday into Monday. Moisture
return ahead of this system won`t be great, given the cutoff low
to the south, but still may be sufficient enough for a few
showers and storms to develop. Details on this are naturally a bit
hazy this far out, but the overall pattern does not appear to
support any significant hazards at this time.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 635 PM CDT Tue Apr 27 2021
For the 00Z TAF update, removed mention of storms in the short
term as confidence in timing at TAF sites is low. Radar trends
will be monitored closely and amendments will be made if
necessary. Confidence is higher after 12Z with precip chances, so
have included mention at that time. CIGS are expected to drop to
MVFR with Wednesday morning rain, and a period of IFR is also
looking likely by mid-morning. Wind shifts will occur through
this period as a boundary lingers in the area. Speeds should
generally be less than 10 kts.