Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/21/24
Area Forecast Discussion
National Weather Service La Crosse WI
1030 PM CDT Mon May 20 2024
.KEY MESSAGES...
- Storms begin to move in late evening/overnight and into the morning
tomorrow bringing heavy rainfall and an isolated threat for
damaging wind gusts and large hail.
- A significant severe weather event with an enhanced risk
(Threat level 3 of 5) for severe storms locally for Tuesday.
Multiple rounds of storms continue from the morning into
evening on Tuesday. The highest severe threat appears to begin
late afternoon and into the evening with damaging wind gusts
and tornadoes being the primary threats, large hail is a
secondary threat. With multiple rounds of storms expected,
flood prone areas should be on alert for possible river rises.
- Quieter conditions expected to return beginning on Wednesday
with some shower/storm chances into the weekend.
&&
.DISCUSSION...
Issued at 305 PM CDT Mon May 20 2024
This Evening - Tuesday Morning: Storms With Isolated Severe Threat
Storms will begin to initiate across portions of southern MN as a
piece of shortwave energy passes through late this evening. As
storms develop they will have minimal 0-6 km shear (20-30 kts) but
fairly robust MLCAPE (1000-1500 J/kg) shown in the 20.15z RAP late
this evening. With steeper low-level lapse rates across southeast MN
later this evening, some severe hail will possible. Furthermore,
one thing of note is much of the 0-6 km shear is suspended
aloft with winds closer to the surface remaining fairly light at
model soundings for KRST this evening. As a result, storms may
have some trouble maintaining themselves with unorganized cold
pools.
Overnight, a surface low begins to approach associated with
increasingly negatively tilted upper-level low. This surface low
will feature a warm front that will progress into the region during
the day Tuesday. As it progresses, instability will begin to be
advected into our region during into the morning hours which
with the forcing from the warm front help develop an mesoscale
convective system from some of the aforementioned convection
across our forecast area. Initially the 20.15z RAP effective
bulk shear (20-30 kts) and MLCAPE values (500-1000 J/kg) are
fairly minimal during the morning hours with the warm front
hanging out to our south. However, one signal some of the CAMs
have been showing is hints at some gravity wave convection north
of the front with elevated instability profiles somewhat more
favorable (MUCAPE of 1000-2000 J/kg). As a result, some of this
morning convection could pose some damaging wind threat into
early afternoon even if much of the severe parameters are on the
marginal side initially, however this would be fairly isolated
in nature with the 20.12z HRRR Machine learning probabilities
having some potential (15-30% probabilities) with the morning
and early afternoon convection for damaging wind gusts of 58 mph
or greater south of I-90.
Tuesday Afternoon - Evening: Impactful Severe Weather Event
As we continue throughout the day, the warm front will slowly push
its way into the region as the parent surface low progresses,
convection will continue to develop along and north of the front
which will provide continuous thunderstorm activity across the
region throughout the day. With the persistent convection over the
region, flash flooding will be a consideration. Generally, the
20.12z HREF shows mean QPF across the region of 1 to 2 inches with
75th percentile values eclipsing 3 to 4 inches in areas.
Precipitable waters really surge quickly during the afternoon with
values in the 20.12z NAM/GFS/CAMs of over 1.5" which is around the
climatological maximum at KDVN. While storm motions will be fairly
progressive, the greater concern would be more the persistent
training of storms over a given area. Consequently, the WPC has our
region in a slight risk (level 2 of 4) for excessive rainfall when
considering that 3-hr flash flood guidance is around 2 inches across
much of the forecast area. Therefore, would expect some flooding
is possible, primarily in areas that are prone to river rises.
The severe threat then really begins to ramp up by later
afternoon and into the evening, which by this time the surface
low begins to lift northwest of the local area. As this occurs,
850mb moisture transport sharply increases allowing for
instability to quickly be advected into our region. MLCAPE
values will increase to around 2000-2500 J/kg with the most
robust instability profiles presenting mainly south of I-90. Our
region becomes subjected to more favorable synoptic winds
Tuesday evening allowing bulk shear profiles to become more
optimal as 0-6km shear values in the 20.15z RAP increase to 40-
60 kts. Ahead of the cold front, storm mode may be fairly messy
with multi-cells, linear segments and isolated supercells
(mainly southern portions of our forecast area) ahead of an
incoming cold front throughout the day with some clearing
possible during the afternoon as some of the CAMs try to show.
Eventually during the evening, the cold front approaches and
more robust ascent accompanied with a strong 850mb low-level jet
to 60-70 kts will allow for an organized QLCS (Quasi-Linear
Convective System) along the cold pool. The passage of the cold
front will usher in a more stable airmass ending convective
concerns with it from west to east during the late evening hours.
Damaging wind gusts will be the most widespread severe threat during
this period with the aforementioned low-level jet and DCAPE values of
1000-1300 J/kg along the cold front shown in the 20.15z RAP.
Consequently, expecting more widespread gusts to 60-70 mph with
the QLCS as reflected in the 20.12z HRRR Machine Learning
Probabilities with high values (60-80% chance). Cannot rule out
higher gusts to 80 mph in any localized bows/surges. As a
result, SPC has an enhanced risk (Threat level 3 of 5) for most
of our area. Increasing low-level shear and 0-1km storm relative
helicity into the evening shows an environment where a few QLCS
tornadoes may occur, especially along and south of I-90 where
low-level curvature in model hodographs is most apparent. Some
uncertainty remains in how far north the QLCS tornado threat
will extend due to waning instability gradient as you head
north. Large hail appears to be more a secondary threat for our
region, much of the CAPE appears to be south of our local area that
would be more favorable for severe hail, cannot rule out some severe
hail across northeast Iowa and southwestern Wisconsin with MUCAPE
values of up to 3000 J/kg and steeper mid-level lapse rates.
Some sources of uncertainty still remain as there appears to be
questions remaining as to where exactly the surface low is
positioned which may have implications for how far north the
favorable instability is able to be advected into our region. This
uncertainty can be best seen between the 20.06z and 20.12z runs of
the HRRR which has different ideas of where the surface low is
situated. Additionally, with the warm front positioned south of the
region initially, widespread convection throughout the day may limit
the amount of instability that can build in across the region.
Consequently, it will be very important to continue to monitor
the forecast over the next 24-36 hours for changes.
In any case, Tuesday has the potential to be a very impactful severe
weather day for our forecast area with multiple rounds of storms
throughout the day, all of which pose some level of severe
potential. Be sure to have multiple ways of receiving warnings as
power outages are possible with the increased damaging wind and
tornado threat. Remember, this environment is fairly favorable
for QLCS tornadoes which can spin up very quickly and are
difficult to see so it is important to get to your safe location
promptly when a warning is issued.
Wednesday & Beyond: Quieter Conditions
Conditions certainly begin to calm down by Wednesday as the
aforementioned trough swings north of the Great Lakes region
allowing for some upper-level ridging to work its way in later
Wednesday into Thursday allowing for some drier conditions. There is
some signal later Friday and into the weekend for some shortwaves
pass to our north which will increase our shower/storm chances
during this period but any severe threat is unknown at this
time.
&&
.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1030 PM CDT Mon May 20 2024
CIGS: bkn VFR into the overnight. Short term trends then favor a
drop into MVFR with extensive shra/ts moving toward 10-12z Mon
morning. Confidence in how long the low cigs hang around isn`t high,
but some consensus to hold them into the afternoon. Some improvement
for a few hours into low VFR possible next convective complex
moves in late afternoon, but then back into MVFR for Tue night.
WX/vsby: scattered shra/ts could impact KRST for the first few hours
into the overnight before a more organized mass of shra/ts is
progged by the CAMS models to spread across the area toward 10-12z.
Tue morning looks wet before another break and then a larger complex
of shra/ts move in for the late afternoon. Some strong/severe storms
are expected Tue aft/early evening with enhanced wind gusts.
WINDS: generally lighter southeast tonight...increasing with
stronger wind gusts Tue, swinging west/northwest Tue night but
staying strong. Strong/severe winds possible with storms Tue
afternoon/evening.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
DISCUSSION...Naylor
AVIATION.....Rieck
Area Forecast Discussion
National Weather Service Binghamton NY
959 PM EDT Mon May 20 2024
.SYNOPSIS...
A warm, early summer weather pattern will be over the region
through Wednesday. Chances for scattered showers and
thunderstorms gradually increase, especially by late Wednesday
and Thursday. The weather looks to turn mainly dry and
seasonably warm for Friday into the upcoming Memorial Day
Weekend, although a scattered shower can`t be ruled out.
&&
.NEAR TERM /THROUGH TUESDAY NIGHT/...
955 PM Update:
A small cluster of showers and thunderstorms developed across
Steuben County, which was on par with previous expectations.
However, while on a weakening trend, these showers/thunderstorms
have been able to hold together further east than previously
expected. Therefore, made some adjustments to PoPs for the next
couple of hours. Otherwise, the rest of the area is dry and will
remain that way through tonight.
645 PM Update:
The forecast remains on track and no changes were necessary. Any
pop-up showers or thunderstorms across the Finger Lakes Region
will dissipate over the next few hours, leading to a dry night
with patchy fog in the valleys.
230 PM Update
Some cumulus clouds are developing this afternoon, with MLCAPE
reaching 600-1200 J/Kg over the forecast area and LIs down
around -3. An inhibiting factor is the weak mid level lapse
rates around 6C/km and low level dry air, with sfc Tds only in
the mid-50s to lower 60s. CAMs such as the 12z 3km NAM and HRRR
continue to show an isolated storm or two popping up over the
western Finger Lakes and/or Central southern tier region heading
into the early evening hours. With light winds through the
column and basically no deep layer shear, any storms that do pop
up will be pulse type and shouldn`t last very long or become
organized. The weather turns quiet overnight, with some patchy
fog possible...mainly in the valleys. Mild with lows in the
upper 50s to 60s.
Tuesday starts off quiet in the morning, with mostly sunny
skies. A weak wave rides over the top of the ridge in the
afternoon, which could spark off a few showers and t`storms. The
main timing for these looks to be about 2 PM to 9 PM. Mixed
Layer instability will reach 800-1200 J/Kg with deep layer shear
increasing a bit...upwards of 20-30 kts. SPC is carrying a
marginal risk for severe hail and wind just to the north of our
CWA for the afternoon and evening hours...so we will need to
keep a close eye on any storms that do form over Central NY and
the Mohawk Valley region. Otherwise, outside of the convective
activity it will be partly to mostly sunny and hot, with highs
in the mid-80s to low 90s over the region.Leaned toward the
bias corrected guidance and NBM25-50th percentile, which was a
bit higher than the Operational NBM...as that seemed too low
based recent trends. Dew points are in the upper 50s to low 60s,
so it won`t feel overly humid.
After any lingering evening convection, Tuesday night is quiet
and warm once again, under partly cloudy skies. Temperatures
hold in the 60s areawide.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
3 PM update...
A cold front in Michigan Wednesday morning will move southeast
through CNY Wednesday night, then stalls in PA Thursday. The front
will have warm humid air to work with ahead of the front. With the
front getting here late in the day with increasing clouds,
temperatures will peak in the mid and upper 80s and around 90 in
Syracuse. Dewpoint temperatures will be in the low and mid 60s.
CAPE is still forecasted to be 1k or a little higher. The CAPE
is tall and skinny but better than Tuesday. Mid level lapse
rates are good. Shear is weak at 20 to 25 kts. Low level winds
remain light but the upper level jet approaches northern NY. SPC
has the NW half of CNY in a marginal chance of severe
thunderstorms. Wind is the most likely threat. Late Wednesday
into Wednesday night the convection moves through. Low
temperatures will be in the 60s.
Thursday the front stalls in northern PA as a weak surface low
moves east. Most of the showers and thunderstorms move southeast
out of the area late Thursday. Some of the thunderstorms could
be strong again. CAPE is lower but shear is higher. Highs range
mostly in the 70s but around 80 in the Wyoming Valley. Thursday
night with cold air advection and clearing skies lows will be in
the 50s.
&&
.LONG TERM /FRIDAY THROUGH MONDAY/...
3 PM update...
Friday into Saturday now looks dry as the front sags south. A
ridge of high pressure builds in from the northwest. Models are
trending drier for the weekend. Low chance pops for NEPA and
Sullivan County NY Saturday afternoon and night. A front moving
east from the upper Midwest looks slower and may wait until
Monday to bring widespread showers and thunderstorms here. This
front is ahead of an upper level trough.
Highs mostly in the 70s Friday and Saturday will fall into the
upper 60s to mid 70s Sunday and Monday. Lows Friday night will
be from the mid 40s to the lower 50. Lows rise into the 50s
Saturday night and Sunday night.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
VFR conditions are expected through the next 24 hours. There is
a small chance for fog briefly at ELM Tuesday morning. However,
at this time it does not appear ELM will reach crossover
temperature, so left fog out of the forecast for now.
Outlook...
Tuesday night through Thursday...Mainly VFR. Patchy early
morning valley fog possible. Also isolated to scattered
afternoon and evening thunderstorms around.
Friday and Saturday...VFR expected. Moderate to high confidence.
&&
.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...None.
&&
$$
SYNOPSIS...MJM
NEAR TERM...AJG/BJG/MJM
SHORT TERM...TAC
LONG TERM...TAC
AVIATION...MPK
Area Forecast Discussion
National Weather Service Cheyenne WY
218 PM MDT Mon May 20 2024
.KEY MESSAGES...
- The potential for strong to severe thunderstorms exists from
4PM and 11PM in far southeast WY and southwest NE. Large hail
up to two inches in diameter, strong winds up to 60mph, and an
isolated tornado can not be ruled out. The strongest storms
will likely develop after 6pm.
- Much cooler temperatures with more widespread to numerous
showers and thunderstorms on Tuesday. Accumulating snow likely
above 8000 feet, with a rain and snow mix possible down to
6000 feet late Tuesday night into early Wednesday morning.
- Daily shower and thunderstorm chances continue through the
long term. Could see some elevated winds in the wind prone
regions throughout the week and weekend.
&&
.UPDATE...
Issued at 1142 AM MDT Mon May 20 2024
Noontime visible satellite imagery reveals a thick band of cloud
cover over much of southeast Wyoming as well as the far
northwest Nebraska panhandle. Pockets of lower-level clouds were
observed streaming northward and eastward, providing some visual
clues to an increase in lower level moisture in upslope flow.
Surface observations across the southwest Nebraska panhandle
and southeast Wyoming have shown a steady change in wind
direction over the past 2-3 hours as northerly post-frontal flow
shifts to easterly. However, of note is the rather paltry
moisture in that surface easterly upslope flow. Td values in
the Pine Bluff area remain in the low to mid-30s as of the
noontime hour with obs farther east in the SNY vicinity showing
Td values in the low 40s. A few pockets of elevated instability
over the mountains of southeast WY and far northwest NE have
resulted in some isolated weak thunderstorm activity, primarily
tied to the differential heating boundary between the cloud
shield to the west and clearer skies to the east.
Over the next several hours, continued easterly upslope flow
will slowly transport higher surface moisture values in from the
east. This pool of deeper moisture is evident as a band of
thicker near-surface stratus over northwest Kansas and the MCK
area of Nebraska. Given the rather high T/Td spreads, initial
thunderstorm development in southeast Wyoming will be high-based
with a marginal hail and wind threat through around 22z. After
around 23z or so, CAM guidance does remain consistent supporting
the development of some deeper convection over far southeast
Wyoming and moving into the NE panhandle. While deeper surface
moisture and better low-level directional shear will likely
remain south of the Colorado state line, RAP guidance does
indicate long, straight hodographs over the NE Panhandle which
would support an early supercell storm mode. With a deeply mixed
boundary layer and plenty of cold air aloft, storms will likely
tend to be outflow dominant and may quickly transition to
bowing line segments with primarily a high wind threat. This is
particularly evident in the past few runs of the HRRR over
southwest Nebraska in the Scotts Bluff, Banner, and Morrill
county corridor from around 6-9pm this evening. Areas along I-80
may ultimately remain shielded from stronger convection as any
dominant supercells in northeast Colorado may block deeper
moisture return. Regardless, it is looking like the 6-9pm
timeframe will be the time window to watch today for storms,
especially from the Wyoming state line eastward in the SW NE
panhandle.
&&
.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 206 PM MDT Mon May 20 2024
Lingering rain showers are possible early Tuesday morning
across much of the NE panhandle after Monday night`s convective
activity with the initial leading shortwave continuing off
towards the upper midwest. Additionally, ongoing precipitation
will continue over east-central WY associated with the slow
moving vort max over western WY. This feature will continue to
drop 700/500mb temps across the area on Tuesday supporting of
high elevation snowfall, mainly above 8000 feet elevation. This
will lead to near advisory snow accumulations in the higher
terrain of the Snowy and Sierra Madres throughout the day
Tuesday.
Cooler temperatures will continue into Tuesday night as skies begin
to clear, especially after midnight, leading to much of south-
central WY dropping near the freezing mark. East of I-25, lows will
drop into the mid-30s with a few localized areas dropping near the
freezing mark. Latest NBM probability of dropping to/below 32F
degrees is 30-50%, especially extending eastwards off the Cheyenne
and Pine Ridges. However, with the average date of the last spring
freeze being in mid-to-late May across most areas east of I-25,
no frost/freeze headlines are expected at this time.
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 400 AM MDT Mon May 20 2024
Models continue to trend towards an active long term forecast for
southeast Wyoming and western Nebraska. Several upper-level
disturbances are progged to traverse across the region. Wednesday
morning, an upper-level trough will move off to the east as another
builds the coast of Washington and Oregon. Forecast soundings from
the GFS for Wednesday morning no longer suggest a potential for snow
across the region. Dry low-levels will likely not allow much
precipitation to fall to the surface Wednesday morning. Therefore,
removed the mention of snow from the Wednesday forecast. With the
lack of snow expected now, temperatures should increase as 700mb
increase to the 4-6C range. Surface temperatures should warm back
into the low-60s to low-70s across the region. Could see some
isolated showers throughout the day as residual energy remains
overhead behind the departing trough, but widespread precipitation
is not anticipated at this time.
The second of many upper-level troughs digs through the region
Thursday, with long range models in good agreement on the evolution.
This trough is progged to quickly swing across the area with decent
precipitation chances in the afternoon hours. At 700mb, a low is
expected to develop across western Montana and move overhead
throughout the day. A weak cold front will move through with the
passage of this low, though the coldest air is expected to remain
off to the north in eastern Montana. However, the cold front will
act as a catalyst for more showers and potentially thunderstorms to
develop in the afternoon hours before dropping temperatures for
Friday. Thursday`s highs look to be in the low-60s to upper-70s
again, with highs on Friday in the upper-50s to low-70s across the
area. The trough will move out the region Friday with brief riding
developing for Saturday before a third trough pushes towards the
area. Behind the cold front, winds will pick up significantly and be
further amplified by the 700mb low passing to the north. Height
gradients will tighten throughout the day, favoring strong winds
across the wind prone regions and likely spilling out into the
adjacent plains.
On Saturday, brief ridging is progged to develop aloft, allowing
700mb temperatures to increase back into the 4-6C range once more.
Residual energy from the departing trough, as well as some energy
ejecting out ahead of the incoming trough will be enough to spark
some showers and thunderstorms during the afternoon hours.
Temperatures will warm into the mid-60s to mid-70s, with isolated to
scattered precipitation possible. With the passage of a 700mb low to
the north of the CWA, height gradients will tighten across the
region once more. Could see some elevated winds in the wind prone
regions of southeast Wyoming and likely see some winds spill out
into the adjacent plains. Daily shower and thunderstorm chances
continue through the weekend, with the incoming upper-level trough.
Some disagreement appears between long range models for Sunday
evening, as the GFS has a closed upper-level low and the ECMWf has
an open wave across the northern CONUS. However, both models still
suggest precipitation chances so kept PoPs in the 20-30% range for
the remaining long term forecast.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1142 AM MDT Mon May 20 2024
Main aviation concern remains the thunderstorms currently near KRWL
and soon KLAR, then KCYS, KBFF, KCDR, KAIA, and KSNY later this
evening and overnight. Gusty and erratic strong winds, large hail,
and lightning will be the primary hazards in these thunderstorms.
CIGS and VIS will drop to low MVFR to IFR in these thunderstorms.
The thunderstorms will transition to more of a stratiform rain early
tomorrow morning with low IFR CIGS persisting and gusty north to
northwesterly winds.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
UPDATE...MAC
SHORT TERM...MB
LONG TERM...AM
AVIATION...LEG
Area Forecast Discussion
National Weather Service Des Moines IA
825 PM CDT Mon May 20 2024
.KEY MESSAGES...
- Storms will develop this evening and continue overnight into
Tuesday morning. Severe storms are possible with wind as the
main hazard. Flash flooding is also a concern with the
overnight and Tuesday morning storms.
- Strongest storms are forecast Tuesday afternoon into evening.
Tornadoes, damaging wind, and large hail are all concerns
with a Moderate Risk (level 4 of 5). Localized heavy rain may
enhance any flood concerns lingering from Tuesday morning.
&&
.UPDATE...
Issued at 825 PM CDT Mon May 20 2024
Some uncertainty regarding the southernmost location of possible
heavy rainfall overnight into early Tuesday. Subjective H850
analysis shows remnant upper level boundary sitting over central
Iowa with strong H850 front across northern Kansas and southern
Nebraska. Storms are congealing into an eventual MCS over
southeast Nebraska and are anticipated to drift east northeast
overnight. Any cold pool development may keep the area farther
south; as shown by a few HRRR runs today. In that event, higher
rainfall totals would arch from southwest Iowa northeast across
Central to northeast sections by 17z. A lot to digest and much
of tomorrows storm evolution will depend on how quickly the
synoptic forcing overcomes the overnight mesoscale forcing. With
all that, have expanded the FFA for portions of southwest to
south central given Sunday nights higher rainfall there already.
&&
.DISCUSSION...
Issued at 301 PM CDT Mon May 20 2024
All is quiet across Iowa early this afternoon as the thermal ridge
has sent temperatures into the upper 70s and mid 80s. Off to the
west the leading shortwave is sweeping across the central plains,
quickly noted in GOES imagery across South Dakota. By this evening,
after 7 pm, storms will develop across Iowa with this wave.
With the later onset, storms are expected to be elevated in nature
with wind as the primary severe threat. ML CAPE exceeds 2000 J.kg
through the late evening and overnight, along with 0-6 km shear
over 30 kts. The low level jet increases across the area
overnight which will help to fuel storms through the overnight
and lasting into Tuesday morning.
As we move into Tuesday morning the severe threat will diminish with
increase hydrologic concerns. Training storms overnight may
develop, which would result in multiple rounds of rain over the
same areas. Additionally, storms are expected to be efficient
rain producers with deep warm cloud layers and good deep
moisture transport into the area. PWATs exceed 1.5-2" through
the period. Antecedent conditions include near normal soil
moisture and river levels (rather than exception dry conditions
which have plagued the area previously). With heavy rain
overnight and into Tuesday morning flash flood problems are
possible for areas that see training storms, especially in urban
areas. A quick check for flash flood warnings before the
morning commute would be worthwhile. Additional details on the
possible hydrologic response is available in the Hydro
discussion below.
Expect to see a bit of a break in convection late morning to midday
before the next round of convection swings across the area from
west to east in early afternoon to early evening. The
environmental parameter space is primed for robust convection,
which led to the upgrade to a Moderate (level 4 of 5) Risk
issued by SPC for tomorrow. CAPE exceeds 3000 J/kg with deep
layer shear over 50 kts, supporting initial discrete supercell
development. With LCLs around 600m in the soundings and the sig
tornado parameter at 2-4 tornadoes are a risk, especially with
initial convection. Perhaps working against the tornado set up
is the relatively straight hodographs. If anything it would
squash longer duration tornadic storms and worth monitoring. As
the storms grow upscale into a line expect robust storms with
wind and hail worthy of elevated tags. Models also indicate a
strongly wrapped up system which may set up a wake low scenario.
What could mitigate convection tomorrow? The morning convection
may work over the atmosphere with less time for recovery. And
perhaps the morning storms will push the boundary south, and
shift the more robust axis out of the area. While both scenarios
are possible, the risk for severe storms is substantial
tomorrow. The mesoscale environment will be monitored closely
tomorrow for impact to storm development and mode. Worth noting,
additional thunderstorms on Tuesday afternoon could exacerbate
any flooding that does occur on Tuesday morning.
Wednesday and Thursday should be quieter before another system moves
into the area by Friday.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 645 PM CDT Mon May 20 2024
Active with higher end storms next 24 hours. Scattered -TSRA may
impact FOD/MCW through 06z, then more widespread area of TSRA
with moderate rain through 13-14z FOD/MCW/ALO/DSM. Potential for
bow echo MCS to track into central/eastern Iowa aft 12z. Will
need to be ready. HIRES models having difficulty on placement,
but I80 north to US20 corridor the most likely. Aft 18z, some
additional tornado threat with PM storms through 00z. /rev
&&
.HYDROLOGY...
Issued at 301 PM CDT Mon May 20 2024
Just as our last high water and flood event has wound down recently
it looks as if we will enter another one in short order.
Before proceeding it should be stressed that the hydrologic response
will depend heavily on the amount, location and timing of the
rainfall forecast over the next few days. Having said that, the
hydrologic response described below is based on the best information
we have at the present time.
Heavy rainfall last night led to elevated soil moisture values
across southeastern 1/2 to 2/3rds of the CWA and especially from the
Osceola to Grinnell/Montezuma area. SAC-SMA soil moisture saturation
values in that area are as high as 40-60%. Flash flood potential
typically increases markedly once values approach or exceed 50% so
we will have to keep an eye on those areas tonight. That being said,
heavy rain across the CWA tonight may lead to flash flooding
concerns elsewhere due to the potential rainfall rates as well as
the sheer amounts of potential rainfall. Flash flooding will remain
a concern into Tuesday and Tuesday night due to the expected
continuing rainfall.
Concern then turns to rises on area rivers. Our latest official
river forecasts as of this morning incorporate QPF through 12Z
Tuesday. With additional rainfall expected beyond that time frame,
the rivers may indeed rise beyond what is presently shown in our
official river forecasts. Latest QPF ensemble hydrographs (which
incorporate up to 72 hrs of probabilistic QPF) are suggesting
significant rises will occur on area rivers especially in the Des
Moines (mainly above Saylorville Lake), Raccoon and Cedar/Iowa river
basins including their tributaries. The most likely scenario at this
time would be rises to within a few feet of flood stage with a
couple locations possibly exceeding flood stage with the crests
occurring within the two to seven days depending on location.
Additional rain is possible beyond the next few days and our longer-
range hydrologic tools are suggesting additional rises further out
are possible.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 1 AM CDT Tuesday through Tuesday evening for
IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>083-092.
&&
$$
UPDATE...REV
DISCUSSION...Hagenhoff
AVIATION...REV
HYDROLOGY...Zogg
Area Forecast Discussion
National Weather Service Hastings NE
840 PM CDT Mon May 20 2024
...Hydrology Update...
.KEY MESSAGES...
- BY FAR the main issue is the likelihood for at least a few (if
not several?) severe storms this evening and overnight,
followed by one final round of strong to potentially severe
storms mainly during the first half of Tuesday daytime
(particularly 9 AM-1 PM time frame). Large hail, damaging wind
the main hazards, but a tornado or two is not out of the
question especially if any isolated supercells can get
established near/after sunset.
- Although not as big of a concern overall compared to severe
storm hazards noted above, there is at least "some" concern
for rainfall being abundant enough/heavy enough in narrow
corridors to promote localized flooding/flash flooding tonight
into Tues daytime, and a Flash Flood Watch has been issued
for most of our Nebraska coverage area (CWA). Please see
separate HYDROLOGY section below for more details.
- Once any strong/possible severe storms vacate our CWA to the
east late Tues AM-early afternoon, we`ll have a fairly quiet
and mostly dry 48+ hours (especially Wed) with little to no
severe storm threat.
- From especially Thursday night onward, our forecast is again
"littered" with various/intermittent chances for
rain/thunderstorms, as a very active upper air pattern
continues. At least for now, there are no "obvious" severe
storm threats during this time (and we are not outlooked by
SPC), but early signs do point to at least a marginal severe
environment returning already Thurs evening and/or overnight.
- Temp-wise: Nothing unusual at all for late-May, with highs on
most days between the upper 60s to around 80, and lows on most
nights mainly 40s-50s.
&&
.UPDATE...
Issued at 822 PM CDT Mon May 20 2024
Please see updated HYDROLOGY section below regarding an areal-
expansion of the previously-issued Flood Watch.
&&
.DISCUSSION...
Issued at 507 PM CDT Mon May 20 2024
-- 7-DAY FORECAST OVERVIEW/HIGHLIGHTS (heavily focused on these
first 24 hours):
- CURRENT/RECENT WEATHER SCENE AS OF 430 PM:
As expected, the vast majority of our CWA (save for some limited
shower activity mainly over Webster County this morning) has
remained dry and storm-free today thus far. Under what has
become partly to mostly cloudy skies, high temps have or soon
will top out in the 74-82 range most areas (coolest north/west
and warmest south/east. In the mid-upper levels, the main
player(s) tonight will be a series of subtle waves embedded in
west-southwesterly flow aloft, downstream from the main wave
still out over the Desert Southwest that will track directly
overhead the first half of the day Tuesday and take any severe
storm/flooding out with it. At the surface, nearly our entire
CWA currently resides just north of a developing/somewhat
diffuse warm front stretched across northern KS, with breezes
most areas currently out of the east-northeast 5-15 MPH. Surface
dewpoints are seasonably-moist...mainly low-mid 60s.
- THIS EVENING-OVERNIGHT:
Most of our CWA should remain storm-free until around 7 PM.
However, after that, and especially after 9-10 PM, all bets are
off as scattered to numerous/widespread thunderstorms are
expected to blossom over mainly our Nebraska CWA (along and
north of the warm front) as weak upper forcing arrives from the
southwest, and the low level jet (evident at 850 millibars)
begins to ramp up. Closely leaning on higher-res models such as
HRRR, a series of individual storms (possibly supercellular)
along with clusters and perhaps broken, mainly west east
oriented lines of convection will traverse our area overnight,
with a sharp south edge likely somewhere between Highway 6 and
the KS border (very little activity expected in KS). The later
storms form, there is some question as to how truly surface-
based they might be, but at the very least the environment is
primed for a large hail and/or damaging wind threat, given
mixed-layer CAPE at least 1500-2500 J/kg and deep layer shear
40-50 KT. This is a somewhat concerning environment as it is,
and if any storms are able to remain at least semi-
discrete/supercellular and tap into increasing low-level shear
mainly near/after sunset, then at least a brief/transient
tornado threat could be on the table as well, not to mention
some hydro concerns (see separate section below).
- TUESDAY DAYTIME:
Following what could be a relative lull in activity around
sunrise, the main upper wave and associated surface cold front
will cross overhead by late-morning/early afternoon. As this
occurs, one final round of more north-south oriented strong to
severe storms is expected to cross much of our mainly Nebraska
CWA from west to east between 9 AM-1 PM, perhaps offering up
more potential for large hail/damaging winds and localized
flooding. Once this activity clears, our severe storm and
flooding threat should end, as the severe threat focuses farther
east of our CWA through the afternoon and evening. Behind the
front, it will be very breezy/somewhat windy on Tuesday, with
northwest winds sustained 15-25 MPH/gusts 25-35 MPH. High temps
will depend on "exact" frontal timing, cloud cover etc. but we
are calling for roughly a 15-degree gradient from mid 60s far
north/west to upper 70s far southeast.
- TUESDAY EVENING-OVERNIGHT:
Most areas will likely remain dry, but isolated to scattered
showers and maybe a few WEAK storms could affect some counties
mainly south of I-80 into KS through the night. Winds will die
down, and this will be one of the cooler nights coming up with
lows mainly 44-51 most places.
- WED DAYTIME-THURS DAYTIME:
This is mainly a DRY/storm-free period in between upper
disturbances. High temps low-mid 70s Wed and upper 70s-low 80s
Thurs as south winds increase.
- THURS NIGHT-SATURDAY:
Intermittent shower/thunderstorm chances return as various upper
waves move through again. We`ll have to watch Thursday
evening/overnight for MAYBE our next, at least limited severe
storm chance.
-SUNDAY-MONDAY (Memorial Day):
The parade of low-confidence rain chances/PoPs continue as both
the ECMWF/GFS bring another disturbance somewhere across the
Northern/Central Plains. Although still several days out, at
least an early glance suggests instability levels fairly muted
by late-May standards and thus a lower severe threat.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 724 PM CDT Mon May 20 2024
- General overview for KGRI/KEAR:
This is a very complex period, with at least a few (if not
several?) rounds of thunderstorms possible through the first 18
hours (some of which could be severe), along with the likelihood
for several hours of MVFR/IFR ceilings (mainly after 04-06Z),
and finally an increase in northwest winds with breezy to
moderately-windy conditions prevailing much of Tuesday daytime.
- Ceiling/visibility/precipitation details:
Right out of the gate, scattered thunderstorms are in the
general area, and off-and-on thunderstorm activity could easily
continue through the majority of these first 18 hours, with the
best chance for any possible, multiple-hour break most likely
focused between 09-15Z. Some of the storms during the period
could be severe, which IF they were to directly impact KGRI/KEAR
could be capable of producing hail of at least quarter
size/wind gusts to 50+KT. By roughly 18Z, all convection should
be vacated east of the area.
As for ceiling/visibility trends, obviously visibility be
reduced at times during periods of heavier rain. As for ceiling,
the most pronounced period of MVFR/IFR is expected to focus
04-06Z through 18Z, with MVFR perhaps hanging on until very
late in the period closer to 22-23Z.
- Winds:
Aside from any direct thunderstorm-related influences (which are
actually fairly likely at times and could greatly increase
speeds and/or result in erratic directions), the basic
expectation is for: 1) winds generally around 8-13KT from the
east-northeast this evening...2) gradually switching to more
northerly at similar speeds late tonight-early Tues AM...3)
picking up out of the northwest Tuesday daytime commonly
sustained 16-22KT/gusts 25-32KT.
&&
.HYDROLOGY...
Issued at 839 PM CDT Mon May 20 2024
-- Latest comments regarding the Flood Watch valid through 1 PM
Tuesday that was recently included to include 6 more counties
in our Nebraska CWA:
- Within the last hour, the Flood Watch was expanded to include
6 more counties along and south of the Highway 6
corridor...mainly in response to last few HRRR runs shifting
axis of overall-heaviest rain south a bit from runs of 6 to
especially 12 hours ago.
- Still believe the MAJORITY of our Nebraska counties sees
widespread amounts no more than 1-3" (and with little to no
flooding issues given that most areas should be able to take
on at least 1-2" given lack of very recent heavy rainfall).
However, with potential for at least a narrow swath of perhaps
3-5" still in play, felt the continuation/expansion of the
Watch was warranted.
- There is still uncertainty in the EXACT placement of potential
amounts of 3+", but given that it could be almost anywhere
OTHER THAN probably Webster/Nuckolls/Thayer counties (least
favored of all to see higher-end rainfall), wanted to be more
generous with the Watch area.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Flood Watch through Tuesday afternoon for NEZ039>041-046>049-
060>064-072>077-082>084.
KS...None.
&&
$$
UPDATE...Pfannkuch
DISCUSSION...Pfannkuch
AVIATION...Pfannkuch/Thies
HYDROLOGY...Pfannkuch
Area Forecast Discussion
National Weather Service Goodland KS
626 PM MDT Mon May 20 2024
.KEY MESSAGES...
- A Tornado Watch is in effect until 11 PM MDT this evening for
Yuma County in Colorado, Dundy County in Nebraska and Cheyenne
County in Kansas. East of the watch area, along the Kansas and
Nebraska border, severe thunderstorms capable of producing
very large hail, damaging winds and torrential rainfall are
possible late this evening into tonight.
- A Flood Watch remains in effect until sunrise Tuesday morning
for Dundy, Hitchcock and Red Willow counties in southwest
Nebraska (where 1 to 3 inches of rain fell over the weekend).
- Potential for patchy frost in northeast Colorado early
Wednesday morning. Very low confidence.
&&
.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 250 PM MDT Mon May 20 2024
Across the region this afternoon, with a low/front sitting over west
central Kansas, skies are mixed with sunny conditions west, and
partly sunny east due to a persistent veil of low cloud associated
with the vicinity of the low/front. Winds have shifted easterly from
the mornings northerly fetch, and temperatures as of 200 PM MDT are
ranging mainly in the 70s with some 60s due to extensive clouds.
Looking aloft, the latest RAP40 500mb analysis is showing broad SW
flow over the region, with a elongated trough pushing through the
north central Rockies. It will be this trough, via current guidance,
that swings off the Rockies and east-northeast into the north
central Plains this evening. This will be followed by a weaker
system on Tuesday with a more easterly track along the northern
fringe of the cwa.
For the short term period, the latest wx concerns continue to focus
on the threat for severe wx this afternoon/evening, flooding chances
later tonight into Tuesday morning. There are also chances
Tuesday/Tuesday night for another round of rain/thunder.
Currently, with a frontal boundary extending west from the central
Kansas area into central Colorado, this will be the focus for storm
initiation as the upper trough moves off the Rockies. Current
CAMs(HRRR, RAP and NamNest) show development around 00z Tuesday,
moving east through northeast Colorado, before shifting into SW
Nebraska this evening. Some differences as to the placement/movement
of the convection as it moves out of Colorado, but the overall trend
does impact SW Nebraska at the minimum. Threats do diminish as your
push southward through the cwa. Best chances look to occur along and
north of highway 36. SPC does continue to carry an Enhanced Risk for
Nebraska, tapering to a Slight Risk for severe for areas south of
this to Interstate 70, then Marginal concerns thereafter.
Model soundings show decent instability from 00z-06z Tuesday across
the Enhanced Risk area as SBCape/MUCape all reach into the 2000-
3000j/kg range. Hodographs do support tornado potential, but large
hail up to baseballs and winds up to 70-80 mph are possible,
especially north of the Interstate. Things do taper sharply the
further south you go away from the shortwave vicinity.
Other concerns through tonight will be the threat for flooding due
to heavy rainfall as the storms pass. We do have the Enhanced Risk
area under a Marginal for excessive rainfall. This will all depend
on storm speed through the area tonight. PW values do approach the 1-
1.3 inch range this evening as east-southeast flow persists. Have
continued the Flood Watch with the addition of Dundy county through
12z Tuesday.
Another round of rain is expected on Tuesday/Tuesday evening, with
the passage of another shortwave. Surface low south of the cwa will
help funnel moisture into the area, with the focus along and north
of the Interstate. Currently instability is low so not expecting
severe storms at this time, but another round rain could impact
already prone areas. Another Flood Watch could be needed but will be
highly dependent on what is received tonight in certain areas.
The final issue in the short term will be the threat for patchy
frost Tuesday night. Guidance continues to show cloud cover
meandering over the expected impacted areas in Colorado. With the
uncertainty, have left out mention as temps into the upper 30s at
worst.
For temps, with a cold front moving through the region on Tuesday, a
wide range in daytime highs is expected with mid 60s to mid 70s
forecasted. Warmest locales will be along/south of Highway 40.
Overnight lows tonight expected to range widely with mid 40s to
lower 50s west, into the mid 50 through 60F east. A bit colder
Tuesday night, especially west of Highway 27, with a range from the
upper 30s west into the upper 40s east. The lows for tonight are
highly dependent on cloud cover from remnant storms through tonight.
Tuesday night, cloud cover will impact temps, especially for
northeast Colorado. Current guidance keeps frost chances low at this
time, but could encompass much of Kit Carson, Cheyenne and Yuma
counties if cloud cover clears out.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 156 PM MDT Mon May 20 2024
From the latest GFS/ECMWF, west-southwest aloft at 500mb will
persist during the long term period, supplemented by the passage of
a few weak shortwaves through Friday with both models carrying a few
stronger system over the region for the upcoming weekend. The timing
of each system looks to occur during the evening hours at this time,
but can`t rule out some late afternoon development, especially this
weekend.
At the surface, inverted trough Wednesday evening will give way to a
stronger lee-side trough Thursday. while the placement west of this
system during the day will give the region decent above normal
warmth, this will sink south and east of the CWA Thursday night
into Friday. A low on the south side of the trough on Friday
remains over the OK Panhandle region for Saturday, followed by
another lee-side trough for the end of the upcoming weekend.
Looking for low chances(30-40%) for rw/trw in the Wed-Fri timeframe,
but it will be the weekend/early next week systems which will give a
better potential for areal coverage of qpf. Of course these will be
highly dependent on storm track timing through the CWA. With all the
rain expected before the midweek timeframe, additional qpf could put
more locales into flood prone status and will have to be monitored.
For temps, daytime highs on Wednesday will range in the lower to mid
70s. Warmest day in the extended will occur on Thursday with lower
to mid 80s expected. Thereafter, Friday will have another cooler day
with mainly 70s, increasing to a range from the upper 70s to mid 80s
by next Monday. Overnight lows will mainly range from the mid 40s
west into the lower and mid 50s east. Warmest locales will be
along/east of Highway 83.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 600 PM MDT Mon May 20 2024
GLD: Expect conditions to deteriorate in assoc/w the
development of low ceilings this evening and overnight.. with
IFR-LIFR conditions possible after midnight (~06Z). While
convection cannot be ruled out late this evening (mainly
~03-07Z).. guidance continues to suggest that activity will
remain ~30-50 miles north of the GLD terminal. Ceilings are
anticipated to gradually lift/improve to VFR late Tue morning
and early Tue afternoon. 15-25 knot ESE winds are anticipated to
become variable late this evening and overnight.. as a
developing lee cyclone progresses eastward from CO into western
KS. Winds will abruptly shift to the NNW-NW and strengthen to
20-30 knots an hour or two on either side of sunrise Tue
morning.. as the aforementioned cyclone progresses eastward into
central KS-NE.
MCK: Expect conditions to deteriorate in assoc/w thunderstorms
(this evening) and the development of low ceilings (overnight).
Guidance suggests that the MCK terminal may be directly impacted
by severe thunderstorms capable of producing very large hail
and damaging winds in the 03-07Z time frame. Ceilings are
anticipated to gradually lift/improve to VFR by early afternoon,
though.. episodic showers and storms are possible throughout
the day on Tuesday. 10-15 knot E to ESE winds may become
variable late this evening and overnight.. as a developing lee
cyclone progresses eastward from CO into western KS. Winds will
shift to the NNW-NW and increase to 15-25 knots a few hours
after sunrise (by ~15Z).. as the aforementioned cyclone
progresses eastward into central KS-NE.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...None.
CO...None.
NE...Flood Watch through late tonight for NEZ079>081.
&&
$$
SHORT TERM...JN
LONG TERM...JN
AVIATION...Vincent
Area Forecast Discussion
National Weather Service North Platte NE
930 PM CDT Mon May 20 2024
.KEY MESSAGES...
- An all hazards severe weather situation including flooding
appears likely tonight.
- Tornado potential appears to be focused south of Interstate 80.
- Very strong winds aloft and dry air moving in from Colorado will
support the potential for very large hail and wind gusts 75 mph
or stronger. This is most likely along and south of Interstate
80.
- The flood potential appears to be focused along and south of
Interstate 80 including Custer county.
&&
.MESOSCALE...
Issued at 929 PM CDT Mon May 20 2024
A cold front has sagged south into the central Sandhills this
evening and as of 9 PM CT, this feature was oriented from south
of Alliance, to south of Thedford, to near Ord Nebraska. Low
level easterly winds were present south of the front from the
I-80 corridor into northern Kansas. Currently two areas of
potential severe modes are anticipated across the far southern
Sandhills and southwestern Nebraska. First: A tandem of
supercell thunderstorms is currently just west of Yuma County
Colorado. This activity may touch Chase, Hayes and Frontier
counties over the next 2 to 5 hours. Tornado potential is
highest in these areas. Second: The tornado threat will
diminish further north toward Interstate 80. However, the threat
for very large hail and intense wind gusts up to 80 MPH remain
possible. The latest WoFS initiates convection just west of Lake
McConaughy in the next hour and translates this east along I-80
over the next 2 to 4 hours. Composite reflectivity indicates
some bowing segments traversing along and south of I-80.
Ensemble probabilities for hail > 1" in diameter are near 100%
from Perkins and Chase counties, east to southern Lincoln, Hayes
and Frontier counties. SW Nebraska needs to monitor the weather
situation closely into the early overnight hours!
&&
.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 342 PM CDT Mon May 20 2024
All eyes are on the progress of a sfc low across the Colo Rockies
this afternoon. The sfc low should move on to the plains early
this evening setting up return moisture into Nebraska. An upper
level plume of subtropical moisture across the srn Rockies this
afternoon will move over Nebraska tonight raising the specter of
heavy rain as storms repeat across swrn Nebraska. The HRRR has
been predicting storm development near Denver 21-22z this
afternoon. This lead storm will move east along a predicted
stationary front across swrn Nebraska with more storms
developing across the cntl high Plains to move through swrn
Nebraska overnight. Arrival time in swrn Nebraska for the lead
storm is 02-03z this evening and all hazards are possible with
this storm.
A disturbance across srn ID this afternoon will move east and set
off a second area of thunderstorms across the Panhandle this
evening. These storms will generally be elevated or post-frontal
mainly posing a large or very large hail threat.
Jet stream winds will be very strong, 50-70kts at h300mb, with deep
layer shear well above 50kts. The MLCAPE will be confined to srn
Nebraska and the BRN south of Interstate 80 is generally less than
25 tonight. This would seem to suggest isolated sfc based severe
storm coverage but repeat storms shown by the CAMs increases
coverage to scattered along and south of I-80.
Storms over swrn Nebraska will be ingesting subtropical moisture
aloft and a mix of very dry air from the southwest and moist air
from the southeast. This is the basis for the SPC 75 mph+
significant wind gust threat. The very strong deep layer shear
supports the 2+ inch hail threat.
The risk of upscale storm growth leading to an organized "high end"
wind event across swrn Nebraska is uncertain; the CAMs don`t show
it. The CAMs do show the cap weakening and storms developing across
cntl Nebraska late this evening. One or both of the storm
complexes across wrn Nebraska are expected to merge over cntl
Nebraska forming large complex of thunderstorms lasting
overnight.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 342 PM CDT Mon May 20 2024
Two more storm systems are in the forecast Thursday and Sunday.
Chance-likely POPs for thunderstorms are in place Thursday
night. High-end chance POPs are in place for the system Sunday.
The models are in very good agreement tracking a system across nrn
British Columbia through the nrn Plains Thursday night into Friday.
The focus for storms Thursday evening is a cold front moving through
wrn Nebraska. The GFS and ECM show the front lighting up along and
east of highway 83 near or after 00z Thursday evening.
Another system across the Bering Sea this afternoon could track
through the nrn Plains Sunday setting off thunderstorms across wrn
and ncntl Nebraska.
Both systems will be operating in a strongly sheared environment
featuring h500mb winds around 50kts and instability appears to be
limiting storm coverage. A check on the GFS in CONRAD in Bufkit
shows potential for severe weather Thursday nonetheless. The
situation next Sunday is beyond the reach of Bufkit and the ECM is
fairly quiet in terms of QPF.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 623 PM CDT Mon May 20 2024
Multiple aviation weather concerns exist through the forecast
period, including thunderstorms, low ceilings, and gusty winds.
Storm coverage will rapidly increase this evening and continue
into the night, with some becoming severe with large hail and/or
50 kt wind gusts. Torrential rain will also significantly limit
visibility. Ceilings will likely drop into IFR category
overnight, then gradually lift tomorrow midday. Meanwhile, east
winds transition to northeast and eventually northwest and gust
20+ kts outside any thunder.
&&
.HYDROLOGY...
Issued at 1116 AM CDT Mon May 20 2024
The HRRR suggests repeating storms across swrn and scntl
Nebraska tonight which will likely be supercellular. This could
lead to 3 inches of rainfall. A single storm putting down 1.5
inches in less than an hour isn`t a big problem but the second
storm of the same caliber a few hours later would probably cause
flooding.
The RAP model viz Bufkit suggests deep moisture extending to
300 mb will be in place supporting heavy rainfall and it is
worth noting satellite shows an expansive plume of subtropical
moisture feeding in through the srn Rockies and Mexico. Some of
this moisture will be drawn into a developing upper low across
Nebraska tonight.
The h850-700mb moisture transport in the RAP model is perhaps modest
but the theta-e advection looks strong. Winds at h850mb are very
modest at just 10-20kts so this doesn`t appear to be a blockbuster
heavy rain event. Moisture availability and repeating storms are the
basis for a Flood Watch across swrn and scntl Nebraska tonight. The
watch outline generally follows the 100 percent probability of 1
inch of rain in 12hr shown by the HREF.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Tuesday morning for NEZ038-057>059-069>071.
&&
$$
MESOSCALE...Buttler
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Snively
HYDROLOGY...CDC
Area Forecast Discussion
National Weather Service Louisville KY
855 PM EDT Mon May 20 2024
.KEY MESSAGES...
* Dry weather and above normal temperatures continue on Tuesday.
* Unsettled weather returns Wednesday, with on and off chances for
showers and storms through the weekend.
* Strong to severe storms possible Wednesday afternoon into
Wednesday night, with an increased risk for localized flooding
Thursday through Saturday.
&&
.UPDATE...
Issued at 854 PM EDT Mon May 20 2024
Another warm, dry evening with temperatures ranging from the mid 70s
to lower 80s at this hour. Skies are partly to mostly cloudy, with
an area of cirrus associated with an upper level shortwave trough
sliding east. These clouds will move off to the east later tonight,
leaving mainly clear skies for the early morning hours of Tuesday.
No significant weather expected overnight with a very light
southerly wind.
&&
.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 327 PM EDT Mon May 20 2024
This afternoon, the surface high pressure axis is moving east of the
Appalachian Mountains, allowing weak anticyclonic S/SW flow to
emerge across central KY and southern IN. Another warm day is
underway, as temperatures have already risen into the mid 80s in
most locations, with highs expected to range from the mid 80s to
around 90 later this afternoon. Reasonable amounts of low-level
moisture have supported the development of scattered cumulus clouds,
with development generally being suppressed by warm air around 700
mb. Localized convergence, possibly driven by terrain effects, has
allowed for a few taller cu to develop into small showers over
middle and eastern TN. While a very isolated shower cannot be ruled
out across in the Lake Cumberland area this afternoon, most if not
all should remain dry, and we`ll continue with a dry forecast for
now.
Another dry night is expected tonight across the region, with the
diurnal cumulus field expected to dissipate during the hours around
sunset. While additional mid-level clouds are expected to move
across southern IN during the evening and early overnight hours,
there should still be enough clearing for reasonably good
radiational cooling tonight. It is worth noting that some high
resolution guidance (e.g., the 12Z HRRR and RRFS) do show a couple
light showers developing late tonight on the leading edge of a 925
mb theta-E surge; however, would expect this to be overdone given
how well-mixed the sfc-850 mb layer will be this afternoon and
evening. Lows should be a few degrees warmer Tuesday morning
compared to today, with almost all falling into the 60s.
Tomorrow`s setup looks pretty similar to today with another mid-
level shortwave ejecting into the central Plains as ridging
amplifies from the lower Mississippi Valley into the Tennessee and
lower Ohio Valleys. Falling heights to the north and west of the
region will increase wind speeds tomorrow, with 10-15 mph S/SW winds
expected during the late morning and afternoon hours as the sfc
pressure gradient strengthens. Once again, hi-res guidance tries to
develop a diurnal cu field into a few showers and storms across the
Bluegrass region during the afternoon hours; however, convection
would be expected to struggle given poor mid-level lapse rates. At
this time, will advertise a 10% chance for a shower or storm
tomorrow afternoon, though almost all should remain dry.
Late Tuesday night, ongoing convection across the mid-Mississippi
Valley will begin to approach northwestern portions of the area as
the mid- and upper-level shortwave and associated sfc cold front
moves closer to the region. Convection will outrun the best
instability and shear by sunrise Wednesday morning, with storms
generally weakening as they approach southern IN. For most
locations, Tuesday night will remain dry, with temperatures
remaining mild in the presence of increasing clouds and
southwesterly winds.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 327 PM EDT Mon May 20 2024
Wednesday through Wednesday Night...
A deep, nearly vertically stacked low pressure system will rotate
from northern MN into southern ON Wednesday, with a trailing cold
front sagging southeast into the Ohio Valley. A warm, moist airmass
will be in place to the south of this boundary in southern IN and
central KY, characterized by sfc dewpoints in the mid/upper 60s and
PW values near 1.5 inches. HREF members indicate we could have
weakening showers and perhaps a few storms ongoing at the start of
the period Wednesday morning, but this activity would most likely
continue to dissipate.
A (relatively) much greater chance for renewed convection exists
Wednesday afternoon into the overnight hours. Moderate
destabilization appears likely by the afternoon with SBCAPE
exceeding ~1000-1500 J/kg. 3-6 km lapse rates will approach 7 C/km
over southern IN and northern KY. And with a moist environment and
steep low-level lapse rates during peak heating, there is at least
some risk for isolated damaging winds/wet microbursts. The strongest
updrafts may produce small to marginally severe hail, but the hail
potential will be kept in check by the moist profile and marginal
(30-35 kt) deep-layer shear.
Rain and thunderstorm chances will gradually ramp up Wednesday
afternoon into the overnight hours. Exact timing/evolution remains
somewhat unclear, but unsettled weather is expected along with warm,
humid conditions. Highs will be in the 80s with lows in the
mid/upper 60s.
Thursday through Sunday...
Unfortunately, it still looks like Wednesday`s frontal boundary is
likely to stall in the vicinity of the Lower Ohio Valley on Thursday
as it parallels the W/SW flow aloft. Multiple mid-level shortwave
disturbances, some convectively-enhanced, rippling through broad SW
flow will keep a chance of showers and storms in the forecast
Thursday into the weekend.
Some stronger storms will be possible at times, but it is impossible
to try to time individual waves of convection at this point.
Mesoscale evolution each day will be dependent on the prior day`s
and night`s activity. Moderate destabilization of a warm, moist
airmass does look possible each day, but in general, deep-layer
shear weakens late in the week. Depending on day-to-day evolution,
think there will be an increasing risk for flooding Thursday into
the weekend. Slower-moving storms and any cell training will boost
the flash flood potential. Each day will not be a total washout, but
there will be an increased risk for localized flooding.
&&
.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 751 PM EDT Mon May 20 2024
VFR conditions are expected to continue through the current forecast
period. SCT-BKN cirrus will spread east at the start of the TAF
period, with mainly clear skies by the early morning hours of
Tuesday. Very light southerly to calm winds expected overnight.
A strengthening low pressure system is forecast to lift northeast
from Kansas to Minnesota on Tuesday, which will tighten the pressure
gradient and increase SSW winds to ~10 kts with gusts up to 15-20
kts from late morning through the afternoon hours. Expect another
healthy cu field Tuesday afternoon. There is a 5-10% chance for an
isolated shower in the Bluegrass Region Tue afternoon, but of course
will not mention precip in the TAF given the low probability.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...EBW
SHORT TERM...CSG
LONG TERM...EBW
AVIATION...EBW