• HVYRAIN: Excessive Rainfa

    From Dumas Walker@21:1/175 to All on Sat Feb 8 09:04:00 2025
    FOUS30 KWBC 080733
    QPFERD

    Excessive Rainfall Discussion
    NWS Weather Prediction Center College Park MD
    233 AM EST Sat Feb 8 2025

    Day 1
    Valid 12Z Sat Feb 08 2025 - 12Z Sun Feb 09 2025

    ...West Virginia...

    Strong N-S quasi-zonal mid and upper level flow will be perturbed
    a bit during Day 1 (12Z Sat-12Z Sun) as a 150+ kt upper level jet
    streak traverses the Upper Midwest and Ohio Valley, while a flat
    500 mb vort lobe pushes across the Lower Great Lakes. Broad-scale
    exit region forcing associated with the upper jet axis will surge
    southwesterly low-level inflow ahead of the surface frontal wave,
    with 850 mb moisture flux anomalies peaking between 4-5 standard
    deviations above normal later this afternoon into Sat night, while
    TPW values peak around 1". Robust synoptic-scale support and low-
    level moisture transport will be offset somewhat by the weak
    elevated instability, with MUCAPEs generally less than 500 J/Kg.
    Nevertheless, even though not advertised on the latest (00Z Sat)
    HREF, the aforementioned dynamic and thermodynamic ingredients will
    be sufficient for spotty hourly rain rates of 0.5"+ and 3-hourly
    rates of 1.0"+, with localized event totals between 1.5-2.0"+.

    Current 3-hr flash flood guidance values remain quite low (1" or
    less) across the outlook area, which includes much of WV. Despite
    the lack of instability, the low FFG values could be exceeded over
    isolated areas with 2 consecutive hours of 0.5"+/hr rainfall rates.
    Since the soils in these areas are saturated, and the terrain is
    rugged, we have maintained the Marginal Risk area for much of WV
    (outside of its northern or eastern Panhandles).

    Hurley/Roth


    Day 2 Valid 12Z Sun Feb 09 2025 - 12Z Mon Feb 10 2025

    The probability of rainfall exceeding flash flood guidance is less
    than 5 percent.

    Hurley


    Day 3
    Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

    The probability of rainfall exceeding flash flood guidance is less
    than 5 percent.

    Hurley

    $$
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  • From Dumas Walker@21:1/175 to All on Sun Feb 9 08:58:00 2025
    FOUS30 KWBC 090808
    QPFERD

    Excessive Rainfall Discussion
    NWS Weather Prediction Center College Park MD
    308 AM EST Sun Feb 9 2025

    Day 1
    Valid 12Z Sun Feb 09 2025 - 12Z Mon Feb 10 2025

    The probability of rainfall exceeding flash flood guidance is less
    than 5 percent.

    Hurley


    Day 2
    Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

    The probability of rainfall exceeding flash flood guidance is less
    than 5 percent.

    Hurley


    Day 3
    Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

    ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
    THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

    ...ArkLaTex-ArkLaMis into the Mid-South and Tennessee Valley...
    Strong NW-SE upper level jet streak will dive southeast into CA
    late on Day 3 (Tue night) -- on the western periphery of the
    longwave trough towards the base. As this occurs, the broad western
    U.S. trough will amplify, thereby enhancing the deep-layer ascent
    and southwesterly flow/moisture transport within a maturing Warm
    Conveyor Belt (WCB) downstream across the Mid South-Lower MS Valley
    and TN Valley. 850-700 mb moisture flux anomalies increase to 2-3
    standard deviations above normal Tue-Tue night, while TPW values
    climb to 1.5-1.75" (around +2 standard deviation above normal). The strengthening dynamical and thermodynamical support will make for
    efficient rainfall rates despite the lack of deep-layer
    instability. Much of the guidance, non-CAM at this point being a
    Day 3 forecast, depicts a widespread swath of 1.5-2.5" of rain
    within the outlook areas, with more stripes of >3" within the
    Slight Risk area. Storm motions nearly parallel to the WSW-ENE
    oriented surface boundary will boost the potential for training,
    and even though currently the non-CAM guidance is advertising
    meager deep-layer elevated instability (MUCAPEs generally 250-500
    J/Kg), believe these values will be amplified somewhat as the event
    gets within the high-res CAM windows, again given the dynamic and
    thermodynamic response to the broad-scale upper trough amplification.

    2.00"+/3hr rainfall rates are anticipated where the cells do
    train, again most likely within the Slight Risk area, which could
    lead to localized-scattered instances of flash flooding.

    Hurley

    $$
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  • From Dumas Walker@21:1/175 to All on Mon Feb 10 09:13:00 2025
    FOUS30 KWBC 100829
    QPFERD

    Excessive Rainfall Discussion
    NWS Weather Prediction Center College Park MD
    329 AM EST Mon Feb 10 2025

    Day 1
    Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

    The probability of rainfall exceeding flash flood guidance is less
    than 5 percent.

    Beginning Monday afternoon, an increase of convergence on the nose
    of 850mb flow extending from Texas into Tennessee will support an
    increase in light to moderate rain and a few rumbles of thunder
    from eastern Oklahoma through Kentucky/Tennessee. Rain rates are
    expected to be modest (around 0.25-0.5 inch/3-hour period),
    although some of this rainfall will eventually reach areas of
    southeastern Kentucky where soils are moist and sensitive from
    antecedent rainfall. The relatively short duration of light to
    moderate rainfall in this area precludes an introduction of
    Marginal/5% risk probabilities, although one may be needed in later
    outlook updates if a longer duration of rainfall (greater than 3-6
    hours) becomes apparent across southeastern Kentucky.

    Cook


    Day 2
    Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

    ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
    THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

    ...ArkLaTex-ArkLaMis into the Mid-South and Tennessee Valley...
    Increasing coverage of showers and thunderstorms along and ahead of
    a well defined cold front trailing a developing area of low
    pressure taking shape over the Tennessee Valley will lead to an
    increasing threat of excessive rainfall Wednesday into early
    Thursday from easter Texas and parts of Arkansas and Louisiana
    into the west aspect of the Appalachians of Tennessee and southeast
    Kentucky. At the synoptic scale, a broad trough over the western
    U.S. will amplify, thereby enhancing the deep-layer ascent and
    southwesterly flow/moisture transport over this part of the country
    due to a increasing low level flow. 850-700 mb moisture flux
    anomalies still look to increase to 2-3 standard deviations above
    normal Tuesday/Tuesday night while Precipitable Water values climb
    to 1.5-1.75" (around +2 standard deviation above normal). The
    strengthening dynamical and thermodynamical support will make for
    efficient rainfall rates despite the lack of deep- layer
    instability and the exit region of a 125 to 150 kt upper level jet
    should aid deep layer vertical ascent. Much of the guidance
    generally depicts a widespread swath of 1.5-3" of rain within the
    outlook areas, with the most aggressive model being the ECMWF with
    maximum values exceeding 4 inches. Storm motions nearly parallel
    to the WSW-ENE oriented surface boundary will boost the potential
    for training despite meager deep- layer elevated instability
    (MUCAPEs generally 250-500 J/Kg). With 2.00"+/3hr rainfall rates
    still being anticipated where the cells do train, again most
    likely within the Slight Risk area, which could lead to localized-
    scattered instances of flash flooding.

    Bann


    Day 3
    Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

    ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
    TENNESSEE VALLEY INTO THE MID-SOUTH,,,

    ...Tennessee Valley into the Mid-South...
    The threat of excessive rainfall will continue on Wednesday and
    early Thursday ahead of the same system which brought the
    excessive rainfall potential on Tuesday into early Wednesday as a
    cold front makes its way eastward. Broad scale ascent will continue
    to aided by the southern entrance region of a 135 to 155 kt upper
    level jet...while moisture convergence is maximized along a well
    defined surface cold front which intercepts a plume of moisture
    being pulled northward by a 40 to 50 knot low level jet. There is
    still spread in the guidance about placement of where the heaviest
    rainfall will occur but amounts generally in the 1 to 3 inch
    range...with locally higher amount where any enhanced rainfall
    rates set up due to banding/training. Given antecedent
    conditions...feel that a Slight risk should suffice.

    ...California Coast...
    The plume of moisture from the Pacific Ocean towards the end of Day
    2 will start to bring rain to the coastal areas during the Day 3 period...beginning in northern and central portions of California
    on Wednesday that propagates southward during Wednesday night and
    Thursday. Present indications are that the heaviest amounts remain
    off shore...but a general uptick in amounts was noted over the past
    24 hours in this area.

    Bann

    $$
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  • From Dumas Walker@21:1/175 to All on Tue Feb 11 09:53:00 2025
    FOUS30 KWBC 110836
    QPFERD

    Excessive Rainfall Discussion
    NWS Weather Prediction Center College Park MD
    336 AM EST Tue Feb 11 2025

    Day 1
    Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

    ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
    THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

    Few changes needed to the old Day 2 ERO as it propagates into the
    Day1 period. Main focus for heavy rainfall and the potential for
    excessive rainfall will be along and ahead of a cold front
    associated with a developing synoptic scale low pressure system
    within a broad/fairly flat flow pattern. Inclusion of more CAM
    guidance supports the idea of higher intensity rainfall extending
    as far west as eastern Texas...a tendency we often see convection
    get organized farther southwest than expected in events like this,
    and there is growing QPF signal in the 12z ECMWF, UKMET and Gem Reg
    over this area. The Slight risk area extended northeastward where
    there is a bit of instability that develops later in the period but
    looks to be lacking initially. At expect the flash flood risk to
    pick up more over this area as we head into day 2.

    Bann


    Day 2
    Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

    ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
    TENNESSEE VALLEY INTO THE MID-SOUTH...

    ...Tennessee Valley into the Mid-South...

    The prolonged heavy rainfall event will continue om Wednesday into
    Wednesday night over the Southeast. The extended duration of this
    event will lead to storm total rainfall into the 3-5" range, with
    locally higher totals possible. As stronger forcing ejects eastward
    on Wednesday, an increase in the low level jet should aid in both
    increasing moisture convergence and advecting instability
    northward. The best overlap of ingredients that has the potential
    for excessive rainfall looks to be over parts of AL/GA into far
    southwest Tennessee. This is approximately the same area as the
    previous Day 3 outlook...and given no major shifts in the synoptic
    pattern saw little reason to make too many changes.

    ...California Coast...
    The plume of moisture from the Pacific Ocean towards the end of Day
    2 will start to bring rain to the coastal areas during the Day 3 period...beginning in northern and central portions of California
    on Wednesday that propagates southward on Wednesday night and
    early Thursday. Present indications are that the axis of the
    Atmospheric River and the associated heaviest amounts remain off
    shore or right along the coastal terrain...but a general uptick in
    amounts was noted over the past 24 hours in this area.

    Bann


    Day 3
    Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

    ..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL PARTS OF THE
    SOUTHERN CALIFORNIA COAST...

    There is a Moderate Risk of excessive rainfall over portions of the
    Southern California coast embedded within a broader Slight risk of
    excessive rainfall covering much of the central and southern
    California coast. An atmospheric river is expected to skirt the
    coast as it makes its way south and east. The primary concern is
    for damaging flooding and debris flow from the numerous fresh burn
    scars in the region given the 24-hour QPF in the 1.5 to 3.5 inch
    range...with potentially localized higher amounts. In
    addition...the area is highly urbanized and an environment in which
    much of the rainfall will turn immediately to runoff. Farther
    north...the Slight risk was extended into portions of the
    Sacramento Valley and San Joaquin Valley...where QPF is not
    expected to be as great but the conditions have been wetter and
    soils are more saturated than soils farther south.

    Bann

    $$
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  • From Dumas Walker@21:1/175 to All on Wed Feb 12 08:36:00 2025
    FOUS30 KWBC 120741
    QPFERD

    Excessive Rainfall Discussion
    NWS Weather Prediction Center College Park MD
    241 AM EST Wed Feb 12 2025

    Day 1
    Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

    ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE
    DEEP SOUTH AND COASTAL AREAS OF CALIFORNIA...

    Large Marginal and Slight Risk areas extend from Louisiana to the
    central Appalachians and portions of Virginia. The Marginal and
    Slight Risk areas cover multiple regimes for excessive rainfall potential:

    1) Long-duration, moderate to heavy rainfall along an axis
    extending from east Texas (beginning at 12Z) east-northeastward
    into northern Georgia and the southern Appalachians. Much of this
    axis has experienced appreciable antecedent rainfall amounts (in
    the 2-3 inch range on February 11) and models are consistent in
    depicting at least one more round of heavy rain across that same
    axis as a thunderstorm complex organizes and moves east-
    northeastward from in Texas later this morning. Another 1-3 inches
    of is expected (heaviest from western in to central Mississippi).
    Given the wet soils from prior rainfall, several instances of
    flash flooding are expected from central Louisiana through the
    southern Appalachians and northern Georgia.

    2) Somewhat lighter rainfall should occur across portions of
    Virginia and West Virginia through the day. Not only are soils
    water-logged and streamflows above average across these areas, but
    recent snow/ice could melt under persistent warm advection and
    temperatures slowly rising above freezing through the forecast
    period. Light to moderate rainfall could enhance excessive
    runoff/ponding especially in sensitive areas and low spots.

    3) CAMs are in very loose agreement in depiction of east-west
    oriented outflow boundary left behind by convective complex(es)
    across portions of southern MS/AL through early afternoon. Strong south-southwesterly 850mb flow and abundant moisture should result
    in reignition of deep convection focused along boundaries for much
    of the afternoon and early evening. The orientation of these
    boundaries should focus convective development and may allow for
    training and intense rainfall rates at times. This is supported in
    particular by the 00Z HRRR, which depicts 5-9 inch rain amounts
    across southern Alabama through 12Z Thursday. Uncertainty in the
    specific placement of boundaries/heavy rainfall corridors and dry
    antecedent conditions are factors that preclude a higher risk,
    although some higher-end flash flood potential exists in this
    scenario - especially if complexes can materialize over more
    populated areas of LA/MS/AL/GA.

    Cook


    Day 2
    Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

    ..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL PARTS OF THE
    SOUTHERN CALIFORNIA COAST...

    ...California...
    The peak of the atmospheric river is expected during this period
    with the initial focus on coastal central California at the start
    of the period, then the best IVT shifts southward through the
    period, reaching southern California by the end of the period
    Thursday night. IVT values from the GFS peak at around 600-700
    kg/m/s initially along the central coast then settle around 400-500
    kg/m/s as the AR reaches SoCal. The greatest QPF amounts will be
    confined to the coastal terrain areas as well as for the Sierra.
    Total amounts for the 24-hour period look to be between 1-3" with
    the favored terrain areas and peaks topping out between 4- 6"+.

    The primary concern is the potential for damaging and potentially life-threatening burn scar flash flooding and debris flows,
    particularly for southern California where the Moderate Risk (Level
    3/4) is in place. Even outside the burn scar regions, the intense
    rain rates and rainfall totals over the highly urbanized area could
    bring scattered to numerous instances of flash flooding. Elsewhere,
    a broad Slight Risk (Level 2/4) exists for much of the coastal
    ranges as well as the Central Valley and lower elevations of the Sierra Nevada.

    A Moderate Risk of excessive rainfall continues from yesterday's Day
    3 ERO across portions of the Southern California coast, and for the
    new Day 2 ERO was expanded slightly on the northwest side to
    encompass the Lake Burn Scar (2024), while also eastward to include
    the southwest San Bernardino Mountains, including the Line Burn Scar
    (also 2024). Again, the primary concern is for damaging flooding and
    debris flow from the numerous fresh burn scars in the region given
    the 24-hour QPF in the 1.5 to 3.5 inch range (with localized higher
    amounts). In addition, the area is highly urbanized and an
    environment in which much of the rainfall will turn immediately to runoff.

    Farther inland, given the QPF trends and snow levels, the Slight
    Risk was extended into eastern portions of the San Joaquin Valley
    and southern Sierra/adjacent foothills. This expansion includes the
    Borel burn scar (2024).

    ...Florida Panhandle and Southern Georgia...
    Lingering heavy rainfall will continue Thursday across portions of
    the Florida Panhandle and southern Georgia, ahead of the approaching
    cold front. Rainfall amounts look to be generally in the 1-3"
    range, with some potential for localized rain rates sufficiently
    high enough to cause some urban/localized flooding concerns.

    Hurley/Taylor


    Day 3
    Valid 12Z Fri Feb 14 2025 - 12Z Sat Feb 15 2025

    ...Southern California...
    IVT plume weakens while pushing southward across SoCal to begin
    the Day 3 Period. While the bulk of the event (Slight-Moderate
    excessive rainfall risk) is expected on Day 2 or through Thursday
    night, will maintain a Marginal Risk into the early part of Day 3
    (Friday morning), especially if the southward AR progression slows down a bit.

    ...Mid South...
    Amplifying longwave trough across the Southwest-4 Corners Region
    Fri-Fri night will lead to backing mid/upper layer flow and
    deepening WAA/moistening downstream within a maturing Warm Conveyor
    Belt (WCB). Thermodynamic profiles will respond appreciably as a
    result, especially late in the period (Fri night) as the low- level
    flow backs SSW and increases (to 50+ kts at 850 mb). This leads to
    robust low-level moisture transport late Friday night into early
    Saturday morning, with 850-700 mb moisture flux anomalies ramping
    up to 4-5 standard deviations above normal per the ensembles. There
    will also be a corresponding uptick in elevated instability as
    well, to the tune of 500-1000 J/Kg towards 12Z Sat. While the main
    event will be on Saturday (see Day 4 ERO), will maintain the
    Marginal Risk inherited from yesterday's Day 4 ERO given the
    anticipation of the ingredients ramping up fairly quickly Friday
    night, which given the probabilistic QPF along with the latest CSU UFVS-verified ERO first-guess fields, could lead to localized
    runoff issues across portions of the Mid South. by the pre-dawn hours Saturday.

    Hurley
    $$
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  • From Dumas Walker@21:1/175 to All on Thu Feb 13 08:45:00 2025
    FOUS30 KWBC 130812
    QPFERD

    Excessive Rainfall Discussion
    NWS Weather Prediction Center College Park MD
    312 AM EST Thu Feb 13 2025

    Day 1
    Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

    ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
    OF SOUTHERN CALIFORNIA...

    ...California...
    Overall, not much change to the previous forecast, with the
    unfolding atmospheric river expected to peak near the start of the
    period. A long warm front currently extending along the coast is
    expected to press inland this morning, with IVTs climbing to around
    700-800 kg/m/s near the upstream cold front as it approaches the
    coast later this morning. The strongest moisture flux is expected
    to center near SF Bay at the start of the period, before steadily
    shifting south along the coast today. Models continue to show IVTs
    decreasing as the axis moves south, dropping to around 400-500
    kg/m/s as the AR reaches Southern California later this afternoon
    into the evening. Guidance has remained fairly consistent,
    indicating precipitation amounts of 4-6 inches along the central to
    southern coastal ranges and the Sierra Nevada, falling mostly as
    rain below 6000 ft.

    A Moderate Risk (level 3/4) remains in place across portions
    Southern California, from Santa Barbara County southeastward into
    the San Gabriel and San Bernadino mountains, where damaging and
    potentially life-threatening burn scar flash flooding and debris
    flows remain a primary concern. Even outside of the burn scar areas,
    intense rain rates over complex terrain and urban areas may produce
    scattered to numerous instances of flash flooding. Elsewhere, a
    broad Slight Risk (Level 2/4) exists for much of the remaining
    coastal ranges as well as parts of the Central Valley and the lower
    elevations of the Sierra Nevada.

    ...Florida Panhandle and Southern Georgia...

    Lingering heavy rainfall will continue this morning across
    portions of the Florida Panhandle and southern Georgia ahead of an
    approaching cold front. HREF neighborhood probabilities indicate
    that additional rainfall amounts of 1-2 inches are likely within
    the highlighted area, with some potential for localized rain rates
    high enough to cause some urban/localized flooding concerns.

    Pereira


    Day 2
    Valid 12Z Fri Feb 14 2025 - 12Z Sat Feb 15 2025

    ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
    THE MID-SOUTH...

    ...Mid-South...

    Although most of the convective activity, and thus heavy rainfall
    threat, in the region should be concentrated in the Day 3 period
    (after 12Z Saturday), model guidance does indicate that convection
    is likely to begin blossoming late Friday Night. Conditions will
    become increasingly favorable after 06Z Saturday with a strong 55-65
    knot low-level jet expanding east from the Plains, and significant
    northward moisture transport leading to rapid moistening of the
    boundary layer. MUCAPE values of around 500-1000 j/kg should support
    organized convection with the potential for rainfall rates in excess
    of 1 inch per hour at times. Although there is a lack of a
    significant front or boundary to help organize a band of convection,
    the strength of the LLJ may support backbuilding within a broad zone
    of developing convective clusters. This may be enough for some brief
    training and a ramp-up in flash flood potential prior to 12Z
    Saturday. The 00Z runs of the NAM Nest and FV3 show more widespread
    convection than other models; if this trend persists as additional
    hi-res guidance becomes available, an expansion of the Marginal Risk
    and/or the addition of a Slight Risk area may become warranted with time.

    ...Southern California...

    The Marginal Risk was removed for southern California given a more
    limited QPF signal on the latest guidance, and hi-res models in
    excellent agreement on a lack of organized convection. The bulk of
    the threat should be in the Day 1 period.

    Lamers


    Day 3
    Valid 12Z Sat Feb 15 2025 - 12Z Sun Feb 16 2025

    ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
    THE TENNESSEE AND OHIO VALLEYS AND THE CENTRAL APPALACHIANS...

    ...Ohio and Tennessee Valleys...

    Confidence remains high in significant rainfall-related impacts on
    Saturday and Saturday Night with model guidance in excellent
    agreement depicting a swath of 3-6 inches of rainfall in the 24-hour
    period across the region. Although models vary slightly with the
    placement, they almost unanimously depict a corridor of heavy rain
    about 750mi long centered somewhere in TN/KY. This same region has
    generally seen above average precipitation in recent weeks, with the
    14-day precip in much of KY, N TN, WV, and W VA at least double the
    normal values. The confluence of these factors should make the
    region especially vulnerable to flooding from the predicted
    rainfall. For additional context on the current hydrologic picture
    across the region, refer to the National Hydrologic Discussion from
    the National Water Center at water.noaa.gov.

    Convection may be ongoing at the beginning of the forecast period
    and should become increasingly focused along a developing warm front
    to the east of a surface low that will be emerging out of the Plains
    on Saturday. The front will be positioned on the nose of very strong
    SW, or even WSW, inflow, which should favor backbuilding and
    training and a corridor of very heavy rainfall. The environment will
    be atypical of mid-February with PWATs reaching around 1.5 inches
    and MUCAPE of 500-1000 j/kg. For example, the Nashville sounding
    archive exists back to 1948 and they've only ever reached 1000 j/kg
    MUCAPE once in February, and 1.5 inch PWATs a few times. The
    environment will support rainfall rates in excess of 1 inch per
    hour, and given the potential for training and backbuilding, these
    rates may be sustained for several hours in some locations. These
    would be the areas of greatest concern for flash flooding -- not
    only in terms of likelihood but severity -- particularly if the
    higher rain rates are sustained over urban areas or vulnerable
    terrain for extended periods of time.

    The inherited Moderate Risk was mostly maintained as-is with a
    slight expansion to the southwest in the vicinity of Memphis, TN;
    and a more significant expansion eastward into S WV and W VA. The WV-
    VA border region just received some significant snowfall, and model
    guidance indicates a fairly high probability of warm, moist air (dew
    points in excess of 45 degrees) accompanying the rainfall into this
    area, which may lead to a combination of runoff from rain and snow melt.

    It's worth noting a couple additional things. First, the amount of
    rain forecast from E KY into S WV and W VA in particular is quite
    unusual for the heart of the winter season. Calendar day precip
    records across that area for January and February are generally in
    the 2-3 inch range, and NBM probabilities indicate it is likely (60+
    percent chance) we will see these types of 24-hour rainfall totals
    in those areas. Second, this relatively rare winter rain event would
    be delivered to an area that has been quite wet recently, and in
    some areas has snow on the ground. And third, the high-end scenarios
    in much of the Moderate Risk area would be significant by historical
    standards. The NBM 90th percentile from N TN into S/E KY and S WV is
    on par with the top several wettest days (for any season!) in the
    station records in the area. This corridor is where the greatest
    concern for severe impacts exists, and it's possible an upgrade to
    High Risk may be needed for portions of the area in subsequent updates.

    Lamers
    $$
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