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Weatherdemon

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    MO/KS/AR/OK 2019-2020 Winter Wonderland Discussion

    in Central/Western States

    Posted

    Tulsa NWS

    Benton-Carroll-Washington AR-Madison-Crawford-Franklin-Osage-
    Washington OK-Nowata-Craig-Ottawa-Pawnee-Tulsa-Rogers-Mayes-
    Delaware-Creek-Okfuskee-Okmulgee-Wagoner-Cherokee-Adair-Muskogee-
    McIntosh-Sequoyah-
    Including the cities of Rogers, Bentonville, Berryville, 
    Eureka Springs, Fayetteville, Springdale, Huntsville, Van Buren, 
    Ozark, Charleston, Pawhuska, Bartlesville, Nowata, Vinita, Miami,
    Pawnee, Tulsa, Claremore, Pryor, Grove, Jay, Sapulpa, Okemah, 
    Okmulgee, Wagoner, Tahlequah, Stilwell, Muskogee, Checotah, 
    and Sallisaw
    429 AM CST Thu Dec 6 2018

    ...WINTER STORM WATCH IN EFFECT FROM LATE FRIDAY NIGHT THROUGH
    SATURDAY EVENING...

    * WHAT...Heavy mixed precipitation possible. Total snow and sleet
    accumulations of 1 to 3 inches, with localized amounts up to 6
    inches, and ice accumulations of up to two tenths of an inch are
    possible. The most likely area for the locally heavier snow
    amounts will be over the higher terrain of northwest Arkansas.

    * WHERE...Portions of east central, northeast and southeast 
    Oklahoma and northwest and west central Arkansas.

    * WHEN...From late Friday night through Saturday evening.

    * ADDITIONAL DETAILS...Plan on difficult travel conditions. 
    Significant reductions in visibility are possible

    MO/KS/AR/OK 2019-2020 Winter Wonderland Discussion

    in Central/Western States

    Posted

    Tulsa NWS needing more data before issuing watch. 

    Area Forecast Discussion
National Weather Service Tulsa OK
933 PM CST Wed Dec 5 2018

...UPDATE...

.DISCUSSION...
A rather wide range of temperatures was observed this evening,
with low dewpoints/light winds allowing a few spots to quickly
fall below forecast lows already. Have generally lowered temps
across most of the area the remainder of the night, although
increasing clouds should keep lows from completely bottoming out.

Quick look at the 00Z NAM doesn't clear up the winter weather
potential, as it maintains a band of significant snow/sleet northwest
of I-44 with a secondary max across parts of northwest AR. NAM has
been consistent with previous runs but also a significant outlier
as far as amounts go. A winter storm watch will likely be needed,
but don't have the confidence yet to put one out without seeing
more 00Z data/model runs

    MO/KS/AR/OK 2019-2020 Winter Wonderland Discussion

    in Central/Western States

    Posted

    OUN Discussion:

     

    Area Forecast Discussion
    National Weather Service Norman OK
    405 PM CST Wed Dec 5 2018

    .DISCUSSION...
    We have high confidence in impactful winter weather across the 
    forecast area. The main changes were 1) to confined to precipitation 
    chances to southern portions of the area through early Friday 
    morning, and limited probabilities across northern Oklahoma until 
    late Friday/Friday night, 2) to make minor adjustments to ice 
    accumulations and amounts, 3) increase snow amounts across portions 
    of western and northern Oklahoma, 4) increase precipitation 
    probabilities, and 5) significantly lowered post-event temperatures 
    Sunday into Monday given expected snow cover. 

    Low level saturation near/behind the cold front tomorrow doesn't 
    appear to be sufficient for drizzle or freezing drizzle but we'll 
    need to watch the trends in the observations. Further south, deeper 
    moisture and a more pronounced near-surface saturated layer below 
    capping warm/dry layer may yield some drizzle. Temperatures there 
    will be warm enough for no freezing concerns. For post-frontal 
    temperatures through Friday we went with the low end of model 
    guidance (NAM, WRF-ARW) which seems most reasonable given the 
    pattern and character of upstream cold/dry cP air mass. 

    Models are in fairly good agreement with synoptic scale features. A 
    closed mid-upper low will move across the Southwest tomorrow night 
    and Friday and through the southern Plains Saturday. Large scale 
    ascent and deepening moisture will eventually lead to light 
    precipitation across the area, but it's onset, amounts, and 
    resultant impacts from icing are probably the most uncertain part 
    of the forecast at this point. There will be a west-southwest to 
    east- northeast corridor of potentially impactful icing, including
    the possibility of tree and powerline damage as well as travel 
    problems. This would be commensurate with icing amounts that 
    approach or exceed 0.25 inches Friday and Friday night, and 
    appears to be most likely across southwest Oklahoma extending up 
    near and south of the I-44 corridor. We may need to adjust the 
    highest chance of freezing rain further south from current 
    graphics based on the latest model forecast soundings which show a
    deeper cold layer across the northern half of the area supporting
    just light freezing drizzle, and eventually sleet once dendrite 
    probabilities increase through saturation <-12C. It's also worth 
    noting that our cold NAM/ARW hourly temperatures may not be cold 
    enough and at least low-end icing event may evolve further south 
    than earlier thought, to around the Red River and into western 
    north Texas. 

    Where freezing rain does occur, accretion should be tempered by 
    latent heat release where temperatures are at or just below 
    freezing. But, 10-15 knot northeasterly winds may help offset that 
    some. So fairly optimal ice-to-liquid ratio according to the FRAM 
    model could develop. Again, potential rainfall amounts will need to 
    be monitored closely. Fortunately, this is not expected to be the 
    most optimal scenario for significant icing which would occur with 
    colder temperatures and higher QPF amounts. 

    We trended more aggressive with sleet potential given strengthening 
    warm nose aloft and it's possible that sleet could at least briefly 
    be the dominate precipitation type in a band from southwest/west-
    central Oklahoma eastward along and either side of the I-40 
    corridor, especially Friday evening and overnight. Saturday morning, 
    as the closed low passes to our south cooling aloft will support all 
    snow. There are some model differences by then with regards to the 
    degree at which the low becomes closed. However, ECMWF matches well 
    with its ensemble mean counterpart, and the spread in GEFS members 
    is minimal for this time range as well. Deterministic GFS matches 
    this reasonably well, and the GFS-FV3 is slightly more closed 
    off/anomalous. All this is to say that although some slowing or 
    slight variations in track could alter ptype placement and amounts, 
    overall confidence is fairly high given that the peak of the event
    is about 3 days out. 

    The aforementioned described synoptic setup is favorable for
    development of a pronounced TROWAL and deformation snow event as
    the deep low passes south and southeast of the area. One potential
    limiting factor for more robust snowfall amounts could be mixing
    of sleet given currently depicted thermal profiles, but current
    thinking is that models could be too aggressive with this and a
    longer duration of moderate to heavy snow could form across
    portions of the area. 2-4 inch snowfall amounts should be common
    across much of the area (especially the northwest half), and there
    could be a band of 6+ inches given impressive QPF amounts that
    have been consistent in models. 

    We lowered temperatures after the system departs given likely snow
    cover. 

    BRB/PW

    • Like 1

    MO/KS/AR/OK 2019-2020 Winter Wonderland Discussion

    in Central/Western States

    Posted

    1 minute ago, Wx 24/7 said:

    There is more than enough in that graphic to prompt TSA to issue a Winter Storm Watch. Wonder if they are waiting to analyze the 00z data first?

    Their discussion below. No mention yet but I would bet you're right.

    A

    rea Forecast Discussion
    National Weather Service Tulsa OK
    322 PM CST Wed Dec 5 2018

    .DISCUSSION...
    The big story continues to be the potential for wintry 
    weather Friday into Saturday. Winter weather headlines 
    will likely be needed as impactful weather is expected 
    across portions of eastern Oklahoma and western Arkansas. 

    A cold front is slated to move through eastern Oklahoma 
    and western Arkansas on Thursday with the potential for 
    rain in the vicinity of the boundary as it moves through 
    the area. Temperatures will be noticeably cooler on Thursday
    behind the cold front. 

    The precipitation shield will begin to return to the north 
    on Friday as isentropic lift increases north of the frontal 
    boundary as it continues to sag south toward the northern 
    Gulf of Mexico. Some of the precipitation along the north edge of 
    the precipitation shield may fall as a wintry mix of freezing 
    drizzle and light snow Friday. 

    The potential for wintry weather really ramps up later Friday 
    night into Saturday as an upper level moves out of the Southwest
    United States and across the Southern Plains. With this forecast 
    Package went with slightly colder surface temperatures than the 
    blended model guidance provided and an even blend of the GFS,NAM12
    and ECMWF thermal profiles. Stayed fairly close to the WPC QPF 
    with a small increase Saturday Night as a nod to the slower moving 
    ECMWF. A wintry mix will transition to mostly all snow across the 
    majority of the area by Saturday Evening as the cold air deepens 
    before ending Sunday Morning.

    Of course, it is still early to give any real specific amounts of 
    snow and ice. However, it is looking more likely that there will be 
    impactful amounts of snow and ice across much of northeast Oklahoma 
    and northwest Arkansas Friday Night into Saturday. It all depends on 
    the ultimate track and strength of the upper level as it moves across 
    the Southern Plains.  

    As we move into next week high pressure will build at the surface 
    and aloft resulting in a slow warming trend across the region.

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