098 FXUS63 KEAX 181537 AFDEAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO 1037 AM CDT FRI SEP 18 2015 .UPDATE... Issued at 1037 AM CDT FRI SEP 18 2015 After much deliberation...have elected to hoist a flash flood watch for the entire forecast area...with headline running from 10 AM today through 7 AM Saturday. A few things has led us to this decision...which we/ll try to elaborate on in this update AFD. First thing of notice is the very high precipitable water content air that remains in place this morning. Quick look at the SPC Meso page reveals values of approximately 1.9" inches...directly over the EAX CWA. These values are further confirmed on the 12z TOP RAOB which too showed a PWAT value of 1.8". Secondly...layered precipitable water satellite imagery continued to highlight converging subtropical and northern stream moisture plumes over the Lwr Missouri Vly this morning. Subtropical moisture feed is very well-established...and see no interruption until main front goes through later tonight. And thirdly...mid-morning mosaic radar imagery shows additional rounds of thunderstorms inbound from the south Central Plains this morning...as strong warm air advection remains in place ahead of the main cold front. All told...cannot rule out repeated rounds of heavy rain over any one particular area and considering the amount of atmospheric moisture in place...felt best to hoist the watch. In addition...we/re still concerned for developing severe convection later this morning/afternoon. Shear values will increase throughout the day as mid-level speed max approaches the area. Main caveat right now appears to be the degree of destabilization that can be achieved later today thinks in part to this morning/s convection. Regardless...early morning ROABs from TOP/OAX show plenty of instability aloft which will certainly help maintain ongoing convection across the area. Will continue to monitor and update as necessary. && .DISCUSSION... Issued at 421 AM CDT FRI SEP 18 2015 Today/tonight: A complex forecast exists over the next 18 hours as several surface and upper air features will provide the potential for multiple rounds of convection in varying locations. The forecast reflects a blend of operational models, convective-resolving models, and current conditions and trends. As of early this morning, pockets of deep convection were redeveloping over west central Missouri into south central Kansas. Satellite imagery showed a region of ACCAS in the area of ongoing convection southwestward into northern Oklahoma. Water vapor showed a strong wave over Wyoming with strong diffluence ahead of the disturbance. At the surface, a cold front was nearly stationary over the northwest quarter of the forecast area in northwest Missouri. This front has and will initially make little progress southward in response to pressure falls upstream from a developing surface low currently located over southwest Kansas. Much uncertainty lies with the potential for morning convection and the effects from said activity to later convective potential/severity. Most high-res models suggest additional convection to develop over south and east central Kansas during the next 3-6 hours, partially in response to the surface low progressing northeastward up the frontal boundary and increasing large scale ascent. Based on the current convection in KS, which is several hours earlier than models depicted, and ACCAS observations, confidence is moderate some degree of convection will continue developing/evolve over eastern Kansas within the warm sector and move into the forecast area during the mid/late-morning hours. Some of these storms may be strong, but widespread severe weather is currently not expected as a diurnal minimum of instability will be present downstream of convective activity, with ~1000 J/KG of MUCAPE. A second area of convection is expected to develop around sunrise north of the cold front over northwest Missouri, generally NW STJ. These post-frontal storms will be partially tied to the increasing large-scale ascent with the approach of the upper wave. These storms will expand in coverage, spread to portions of far northern Missouri, before mainly lifting into Iowa by early afternoon. To what degree the warm sector convective coverage becomes this morning is challenging to ascertain at this time, but the potential exists for these storms to partially reduce strong insolation over much of the CWA, likewise limiting the overall severe weather threat this afternoon. Areas of the far southeastern CWA may have the best potential to destabilize by this afternoon, with moderate CAPE-shear combo to support robust severe convection. With the uncertainty in other areas, the simplistic approach is areas that are south of the front and see the sun for an extended period of time this morning/early afternoon will see a risk for severe weather during the afternoon and early evening. A mixed storm mode is expected with an eventual evolution into a line along whatever serves as the effective cold front. Large hail and damaging winds will be the primary severe weather concerns. A tornado cannot be ruled out with supercellular-like storms along an existing boundary and immediately ahead of the surface low where low-level winds can back, but the threat is not particularly high based on the overall pattern at hand. That said, if the surface low is slower and deeper as one model suggests, a slightly increased risk could develop, once again assuming moderate instability can materialize. Localized flash flooding will also be possible in areas with repeated strong convection as PW values near 2 inches, which is relatively high for this time of year. With the progressive nature, do not expect to see widespread flash flooding, and should be confined to repeat areas. Convection is expected to exit the CWA between 02-06Z Sat. Temperatures today will be strongly tied to morning convection and remnant cloud debris, as well as the position of the cold front. Highs in the 70s are expected in far NW MO, with 80s elsewhere. Weekend and beyond: A dry and fall-like weekend is expected, with highs in the upper 60s to middle 70s. No notable weather is expected next week with gradually moderating temperatures with highs back in the upper 70s to lower 80s. && .AVIATION...(For the 12Z TAFS through 12Z Saturday Morning) Issued at 612 AM CDT FRI SEP 18 2015 VFR conditions will generally prevail at TAF sites, although cannot rule out brief periods of MVFR if robust portion of storms moves overhead. Most precipitation will be VFR in nature with relatively high ceilings and visibility. Two rounds of thunderstorms are anticipated, the first between 12-16Z and the next between 20-03Z. Precipitation will end thereafter, but MVFR stratus is expected to move into sites overnight. && .EAX WATCHES/WARNINGS/ADVISORIES... KS...FLASH FLOOD WATCH through Saturday morning for KSZ025-057-060- 102>105. MO...FLASH FLOOD WATCH through Saturday morning for MOZ001>008- 011>017-020>025-028>033-037>040-043>046-053-054. && $$ UPDATE...32 DISCUSSION...Blair AVIATION...Blair