• MESO: Heavy Rain/Flooding

    From Mike Powell@618:250/1 to All on Tue Apr 16 09:25:00 2024
    AWUS01 KWNH 161421
    FFGMPD
    MOZ000-MNZ000-IAZ000-KSZ000-NEZ000-SDZ000-161800-

    Mesoscale Precipitation Discussion 0158
    NWS Weather Prediction Center College Park MD
    1021 AM EDT Tue Apr 16 2024

    Areas affected...eastern Nebraska, southeastern South Dakota,
    northeastern Kansas, northwestern Missouri, and western into
    central Iowa

    Concerning...Heavy rainfall...Flash flooding possible

    Valid 161420Z - 161800Z

    Summary...Bands of convection are resulting in prolonged rain
    rates (including 2+ inch/hr rates at times) across the discussion
    area. Areas/spots of flash flooding are possible through 18Z this
    morning.

    Discussion...Over the last hour or so, a couple of dominant
    convective bands have taken on a favorable orientation for
    training despite relatively fast steering flow and storm motions.
    One of these bands extended from near Yankton, SD to near
    Columbus, NE, with rightward-moving structured embedded and
    assisting in both 1 inch/hr rain rates and 2-2.5 inch/3-hr rain
    rates beneath the band. This area was continuing to ingest
    surface-based parcels due to southeasterly low-level flow and near
    60F dewpoints beneath very cold air aloft (-20C at 500mb),
    contributing to relatively efficient rain rates. Local FFGs in
    the 1.5 inch/hr range were being approached on a localized basis,
    suggesting a continued flash flood risk as long as convection
    remains rooted near the surface. Some cells were moving northward
    toward cooler surface air, however, which may weaken storms and
    lower rain rates as they drift into southeastern South Dakota.

    Southeast of this area, a second band of more robust convection
    extended from near Clarinda in southwest Iowa through Topeka, KS.
    These cells are also training and fostering areas of nearly 2
    inch/hr rain rates due to favorable orientation to south-southwest
    steering flow aloft. Stronger buoyancy in this area was also
    contributing to slightly stronger/deeper updrafts per satellite
    imagery. These storms were also lifting northward toward a
    low-level boundary and stable air across central Iowa, although
    ascent/forcing aloft may sustain training cells toward the Des
    Moines, IA area after 16Z or so.

    Models suggest that warm advection/destabilization will develop
    northward into areas of central/northwestern Iowa over time,
    resulting in a broader spatial opportunity for deep, training
    updrafts and heavy rain rates. Areas of 1-2 inch/hr rain rates
    are expected to approach FFG thresholds over the discussion area
    on at least a spotty basis through 18Z or so. The threat could
    persist beyond 18Z, although model trends seem to indicate a
    faster forward progression of convection (and less training)
    through the afternoon hours. This scenario will be re-evaluated
    for another potential MPD after 18Z.

    Cook

    ATTN...WFO...DMX...EAX...FSD...ICT...MPX...OAX...SGF...TOP...

    ATTN...RFC...ABRFC...MBRFC...NCRFC...NWC...

    LAT...LON 44399753 44339634 43329360 41849265 39539264
    38389370 38069443 38039543 39329568 40479675
    42379784 43669793

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  • From Mike Powell@618:250/1 to All on Thu Apr 25 18:44:00 2024
    AWUS01 KWNH 252235
    FFGMPD
    KSZ000-NEZ000-COZ000-260345-

    Mesoscale Precipitation Discussion 0172
    NWS Weather Prediction Center College Park MD
    634 PM EDT Thu Apr 25 2024

    Areas affected...Northwest Kansas...Southwest Nebraska...Northeast
    Colorado...

    Concerning...Heavy rainfall...Flash flooding possible

    Valid 252235Z - 260345Z

    SUMMARY...Increasing moisture flux convergence into convective
    clusters within potentially favorable flow regime for
    back-building and training rotating cells pose possible localize
    flash flooding concerns particularly after 00z this evening.

    DISCUSSION...22z surface analysis depicts rapidly deepening
    surface low in east-central CO with well defined dry line and warm
    fronts extending from a triple point near the Colorado/Kansas
    border at the Cheyenne/Sherman county line. The dry line is wavy
    extending southward along the state line though appears to be
    short-term retreating into southeast Colorado which may provide a
    pivotal development region for later training/repeating as they
    move northward toward the triple point. The effective warm sector
    is represented by low to mid 80s Temps over lower 60s Tds.
    Strong/steep lapse rates via a strong EML above the boundary layer
    suggest higher than normal evaporatimve effects especially in the
    early stages of development. However, the very moist low levels
    are strongly convergent while also being reinforced along the
    north side of the warm front by cooler but still mid to upper 50s
    Tds that may entrain into elevated updrafts that meander north of
    the frontal zone. Compound this with strong rotating updrafts
    will support localized isallobaric inflow/moisture flux loading
    the lower updraft profile with ample moisture to develop heavy
    rainfall accompanying hail generation.

    GOES-E WV suite also depicts favorable left exit jet ascent for
    cell evacuation and potential for cells to grow upscale into
    clusters and perhaps a small complex. Cell motions within the
    cluster are expected to have a northeast motion at 30-40kts but
    stronger rotation, should slow to 20kts per RAP Bunker propagation
    vectors. Additionally, with the approach of shortwave ridging,
    backing cell motions toward a more northerly component will
    support the potential for repeating/training profiles particularly
    after 00z as mid-level drying reduces from earlier evaporation
    into the environment. As such, cells producing 1-1.5"/hr rates
    may start to encroach into the 1.5-2"/hr rates. This presents the
    increasing possibility of pockets/scattered clusters of 2-3"
    totals in 2-3 hour period. While the grounds have been dry,
    natural FFG values would be in reach of being exceeded in
    localized spots given 1hr values of 1.5-2" and 2-2.5/3hrs. So
    while severe threat is currently the primary hazard, the
    hydrological risk will be steady increasing through 00z and even a
    very strong slow moving high influx super-cell may induce
    localized flash flooding in the short-term.

    Gallina

    ATTN...WFO...BOU...DDC...GID...GLD...LBF...

    ATTN...RFC...ABRFC...MBRFC...NWC...

    LAT...LON 41159979 40979916 40289894 38930043 38480142
    39010188 39510237 39990323 40730306 41020220
    41080090

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  • From Mike Powell@618:250/1 to All on Fri Apr 26 08:04:00 2024
    AWUS01 KWNH 261023
    FFGMPD
    MOZ000-ARZ000-TXZ000-OKZ000-KSZ000-261530-

    Mesoscale Precipitation Discussion 0175
    NWS Weather Prediction Center College Park MD
    622 AM EDT Fri Apr 26 2024

    Areas affected...Portions of Far Northern TX...South-Central to
    Northeast OK...Far Southeast KS...Far Northwest AR...Southwest MO

    Concerning...Heavy rainfall...Flash flooding possible

    Valid 261020Z - 261530Z

    SUMMARY...Heavy showers and thunderstorms with some instances of
    cell-training may result in areas of flash flooding this morning.

    DISCUSSION...Radar and satellite imagery shows a broken QLCS
    advancing generally east-northeast across portions of the Red
    River Valley, with somewhat more disorganized activity noted
    farther up to the northeast across northeast OK and southeast KS.

    A shortwave trough continues to cross the region while interacting
    with a moderately unstable airmass characterized by MUCAPE values
    of 2000 to 2500+ J/kg, and with a persistently moist
    south-southwest low-level jet of 40 to 50 kts. Given the level of
    forcing and instability that is in place, the convective activity
    should persist through the morning hours and may even locally
    expand in coverage.

    Some cell-training will be possible as the convection evolves
    close to the Red River Valley and up through eastern OK over the
    next few hours. Rainfall rates are expected to reach as high as
    1.5 to 2 inches/hour given the level of moisture transport and
    instability focusing across the region. The latest HRRR guidance
    has been trending wetter and strongly supports the idea of the
    convection becoming oriented more parallel to the deeper layer
    southwest steering flow. The HRRR does favor some potential for
    localized 3 to 5 inch rainfall totals across eastern OK going
    through late this morning given the cell-training concerns. This
    may result in some instances of flash flooding as a result across
    this region.

    The other concern this morning is also farther northeast up across
    far southeast KS and into southwest MO where heavy rainfall over
    the last 24 hours has led to notably moist soil conditions and
    elevated streamflows at least locally. Some additional broken
    clusters of convection are expected here with the arrival of the
    aforementioned shortwave energy, with an additional 2 to 3 inches
    of rain possible by late morning. Some instances of flash flooding
    will be possible here as a result.

    Orrison

    ATTN...WFO...EAX...FWD...ICT...LZK...OUN...SGF...SHV...TSA...

    ATTN...RFC...ABRFC...LMRFC...MBRFC...WGRFC...NWC...

    LAT...LON 38479407 38079297 36629322 35049410 33859524
    33159699 33219861 33599872 34259776 35109704
    35949631 36519582 37299536 38119463

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  • From Mike Powell@618:250/1 to All on Sun May 5 08:35:00 2024
    AWUS01 KWNH 051226
    FFGMPD
    MOZ000-ARZ000-OKZ000-KSZ000-051800-

    Mesoscale Precipitation Discussion 0227...Corrected
    NWS Weather Prediction Center College Park MD
    825 AM EDT Sun May 05 2024

    Corrected for Corrected Discussion

    Areas affected...Northeast Oklahoma through Central Arkansas

    Concerning...Heavy rainfall...Flash flooding likely

    Valid 051156Z - 051800Z

    SUMMARY...Flash flooding likely as storms developing out ahead of
    an advancing MCS moving across eastern Oklahoma and southern
    Arkansas move into the hydrologically sensitive Ozarks.

    DISCUSSION...Storms that have developed across Oklahoma and
    eastern Arkansas have been producing localized rainfall rates of
    up to 2 inches per hour. Instability is between 500 and 1,000 J/kg
    of MUCAPE based on SPC Mesoanalysis, and PWATs are around 1.75
    inches. The abundant moisture and decent instability will support
    additional thunderstorm development through midday across
    northeast Oklahoma and much of Arkansas.

    The leading edge of the MCS, as well as any pre-MCS convection
    will lift northward with time. The MCS is wrapping around a center
    point near southeast Oklahoma in response to a northward moving
    shortwave in the upper levels. This will keep convection ongoing
    and slow-moving to nearly stationary across northeast Oklahoma and
    northwest Arkansas. Meanwhile, storms developing on the south and
    east side of the line will move faster to the north, which would
    decrease flash flooding potential...except those storms will have
    a greater tap of moisture and instability, which will allow them
    to grow stronger than the convection to their west.

    Soils across much of the area are nearly saturated. Heavier
    convection will have the potential to produce rates to 2.5 inches
    per hour, however even in areas that don't see the heavier
    convection, steady rainfall through the morning falling on nearly
    saturated soils will result in most of the rainfall converting to
    runoff. This will result in widely scattered instances of flash
    flooding, with the potential in both hydrologically sensitive
    areas of terrain and urban areas for isolated instances of significant/considerable flash flooding.

    Wegman

    ATTN...WFO...ICT...LZK...SGF...SHV...TSA...

    ATTN...RFC...ABRFC...LMRFC...NWC...

    LAT...LON 37169592 37049493 36819374 36549306 36399223
    35939152 34919135 34319178 33839227 33229275
    33229322 33639393 34949495 36109606 36559633


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  • From Mike Powell@618:250/1 to All on Mon May 6 13:22:00 2024
    AWUS01 KWNH 061800
    FFGMPD
    MTZ000-WYZ000-062300-

    Mesoscale Precipitation Discussion 0230...Corrected
    NWS Weather Prediction Center College Park MD
    159 PM EDT Mon May 06 2024

    Areas affected...Portions of Eastern Montana and Northeastern
    Wyoming

    Concerning...Heavy rainfall...Flash flooding possible

    Valid 061659Z - 062300Z

    SUMMARY... The comma-head region of a deepening cyclone will
    feature steady rainfall with embedded thunderstorms capable of
    producing flash flooding.

    DISCUSSION...Low-level moisture inflow into portions of the upper
    High Plains is advecting an air mass with dew points into the 50s
    into this typically dry part of the country. This is being driven
    by a developing strong low-pressure system threatening to break
    monthly low pressure records in the western Dakotas. The moisture
    feed into the storm originates in the Gulf, and is advecting into
    the area on up to 50 kt winds in the lower levels. Meanwhile, as
    is typical with mature storms, dry air aloft making up the comma
    is ending the precipitation further east into the western Dakotas.
    The dry air aloft is enhancing potential instability, which has
    allowed for a few thunderstorms to develop on the
    dry-slot/comma-head interface. These storms have caused greater
    than an inch per hour rainfall rates, which have already caused
    some localized flash flooding.

    CAMs guidance suggests additional thunderstorm development is
    likely, as noted by the line extending north of the Black Hills.
    The storms are most likely to form along the eastern edge of the
    precipitation shield, or as the current line shows, extending as a
    band of storms into the dry slot. Should the storms move over
    flood sensitive areas, additional flash flooding is possible.

    Wegman

    ATTN...WFO...BYZ...GGW...RIW...UNR...

    ATTN...RFC...MBRFC...NWC...

    LAT...LON 48340694 48170640 48050624 47650605 46740561
    45920545 44590520 44280563 44190675 44250714
    44730778 45910816 46410823 46950826 47430803
    48110748

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  • From Mike Powell@618:250/1 to All on Mon May 6 17:51:00 2024
    AWUS01 KWNH 062122
    FFGMPD
    VAZ000-NCZ000-TNZ000-KYZ000-070300-

    Mesoscale Precipitation Discussion 0232...Corrected
    NWS Weather Prediction Center College Park MD
    522 PM EDT Mon May 06 2024

    Corrected for typo in last paragraph

    Areas affected...central/eastern KY/TN into the Appalachians

    Concerning...Heavy rainfall...Flash flooding possible

    Valid 062117Z - 070300Z

    SUMMARY...Periods of training could allow for a quick 2-3 inches
    of rain across portions of southern KY into TN and the adjacent
    Appalachians through ~03Z. Localized flash flooding may result
    with 1-2 in/hr rates.

    DISCUSSION...Visible imagery at 2045Z showed the presence of an
    low level low (centered 925-850 mb) along the eastern IN/KY
    border, tracking toward the east. A smaller mesoscale circulation
    was noted to the south, over south-central KY. South of the
    925-850 mb low were active thunderstorms, most of which were along
    an elevated convergence axis noted on visible imagery, extending
    west to east through central TN before curving toward the
    northeast into south-central KY. The environment over southern KY
    into TN was represented by 1000 to 2500 J/kg MLCAPE and near 1.5
    inches via the 20Z SPC mesoanalysis.

    Average cell motions were toward the east at 20-25 kt over TN, but
    concern has increased for the potential for cells to repeat or
    train from west to east through the evening. As the 925-850 mb low
    tracks toward the east into the early overnight hours, ongoing
    storms along the convergence axis are expected to generally track
    into eastern KY/TN and the Appalachians, posing a localized threat
    for flash flooding due to repeating west to east motions. A
    continued influx of moist and unstable air from the south may
    support additional convective development along the rain-cooled
    outflow with similar potential for west to east repeating and
    training later this evening...which could support 1-2 in/hr
    rainfall rates and localized 2-3 inch totals in ~2 hours or less
    time. Area flash flood guidance is generally 1.5 to 2.5 inches in
    3 hours for the region, some exceedance and localized flash
    flooding may result through roughly 03Z .

    Otto

    ATTN...WFO...GSP...HUN...JKL...LMK...MEG...MRX...OHX...

    ATTN...RFC...LMRFC...OHRFC...SERFC...NWC...

    LAT...LON 36978440 36958300 36888241 36798197 36578189
    36178209 35968238 35708279 35508311 35258385
    35048520 35158791 36128806 36678694 36938528


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