725 FXUS63 KLSX 060503 AFDLSX AREA FORECAST DISCUSSION...UPDATED AVIATION NATIONAL WEATHER SERVICE ST LOUIS MO 1203 AM CDT Fri Jun 6 2014 .UPDATE: Issued at 910 PM CDT Thu Jun 5 2014 Making some changes to the forecast for the rest of tonight. Primarily to PoPs. Looks like focus for convection will be down across southern Missouri and that the storms up in Iowa which might have threatened parts of northeast Missouri/west central Illinois have pretty much died out. With the shortwave moving rapidly east through the Upper Mississippi Valley, I think regeneration is unlikely. Latest RAP and HRRR still indicate that some of the southern convection could clip the far southern portions of our CWFA overnight, but it looks like the vast majority of our area should stay dry. Carney && .SHORT TERM: (Through Late Tonight) Issued at 256 PM CDT Thu Jun 5 2014 Unsettled weather is expected to continue over the next several days due to multiple shortwaves interacting with a quasistationary front as it sloshes back and forth across the region. Tonight...There are two areas where precipitation is possible this evening and overnight. The first area is across the northern CWA within a zone of ascent ahead of an elongated mid/upper trough moving through the northern plains. Afternoon SHRA/TSRA have already developed along an upstream surface trough/front in NE/KS aided by ascent from this trough, and the precip could move eastward into northeast MO/west central IL if it persists. However, the H5 trough axis is forecast to move quickly eastward, and upstream SHRA/TSRA may not persist long enough to reach the LSX CWA in the absence of upper level support. The second area is across the far southern CWA where a developing LLJ should interact with a quasistationary front across southern MO, leading to another MCS tonight. The position of the synoptic scale quasistationary boundary has been pushed farther south by a mesoscale outflow boundary from the large MCS which moved across southwestern MO earlier today. Initial thoughts are that today's MCS will have pushed the effective boundary far enough south that the main precip threat from an MCS during the overnight hours should be south of the CWA, although there is uncertainty about the location of scattered WAA pcpn. This fits reasonably well with forecasts from the local WRF, GFS, and ECMWF regarding placement of MUCAPE and H7-H85 moisture convergence. The areal coverage of likely PoPs has been reduced accordingly, although it may still be too high depending on where the MCS forms. Kanofsky .LONG TERM: (Friday through Next Thursday) Issued at 256 PM CDT Thu Jun 5 2014 Friday through Sunday...There may be a brief break in the precipitation on Friday due to shortwave ridging aloft across most of the area. Scattered SHRA/TSRA remain possible across the southern CWA due to the presence of a boundary and weak shortwaves. High pressure moving out of Canada will push a cold front into the northern and central plains on Fri night and Sat, but this boundary appears to remain distinct from the quasistationary front/developing warm front located farther south, at least initially. In any event, precipitation should spread across the area on Sat/Sat night due to a combination of factors associated with an approaching shortwave, starting with a developing H85 LLJ on Fri night which will interact with the quasistationary boundary across MO/KS, leading to increasing precipitation chances by daybreak as the shortwave progresses eastward. Isentropic ascent also increases along the 305-315 K surfaces during the day on Sat as the boundary starts to lift north as a warm front. Models have been consistently showing that this shortwave also induces a surface low along the western part of the stalled boundary (which may have been reinforced by the cold front dropping south out of the northern plains) which then tracks northeastward through MO into IL. Forecast PW values of 1.8-2" on Sat are at +2 SD for June across this part of the country, suggesting that locally heavy rainfall is possible. The precipitation should taper off on late Sat night with the passage of the shortwave. Another shortwave may or may not approach the area on Sunday, but it is difficult to discern whether this feature is a shortwave or the result of convective feedback. Monday through Wednesday...Compared to the 04/12z runs and the 05/00z runs, the 05/12z model runs have come into astounding agreement regarding the large scale pattern during Mon-Wed. ECMWF/GFS/GEM all show a closed low developing over the central CONUS after two vort maxes become phased over MO/AR/IL. Despite the remarkable agreement between models, I am hesitant to buy into this solution right away because it seems unlikely that all of the models are accurately capturing the timing and placement of weak, unsampled, and occasionally ill-defined shortwaves this far in advance and in the presence of convective feedback issues. Due to low confidence, this forecast package generally followed the recommended CR initialization for Mon-Wed. Kanofsky && .AVIATION: (For the 06z TAFs through 06z Friday Night) Issued at 1155 PM CDT Thu Jun 5 2014 Latest surface analysis shows convective generated outflow boundary continues to extend from north-central Oklahoma through far northwest Arkansas then southeast into northern Alabama. This front will begin to move northeast late Friday evening and early Saturday morning. Specifics for KSTL: Clear skies will give way to lower visibilities in light fog after 0900 UTC Scattered to borken layer of stratus around 010 kft may form after 0900 UTC. Stratus clouds will give way to scattered clouds above 030 kft after 1400 UTC. Winds will be light and variable. RP && .LSX WATCHES/WARNINGS/ADVISORIES: MO...NONE. IL...NONE. && $$ WFO LSX