456 FXUS63 KLSX 172347 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 647 PM CDT Fri Mar 17 2017 .SHORT TERM... (Through Late Saturday Afternoon) Issued at 353 PM CDT Fri Mar 17 2017 A short wave is fcst to track from near DLH this evng to NW PA by Sat evng. A cold front assoc with the short wave currently extends from N cntrl IL to the STL metro area to SW MO. Low clouds continue to clear from NW to SE with the back edge roughly along I44 in MO and I70 in IL. This is just in advance of the bndry which should clear the sthrn zones this evng. Most guidance indicates FROPA will be dry this aftn/evng but can't rule out a couple light SHRAs across the ern Ozarks...but the bulk of the activity should remain S of the CWA overnight. 1030mb SFC ridge builds into the region tonight and should keep conditions quiet thru Sat. CAA thru the day Sat will keep temps in check. After some areas that cleared out by early aftn today reached into the lower 70s...most locations will remain in the 50s tomorrow. The exceptions are portions of cntrl and SE MO which could rebound into the lower 60s after a chilly start in the mid 30s to near 40. BM .LONG TERM... (Saturday Night through Next Friday) Issued at 353 PM CDT Fri Mar 17 2017 Saturday night will be relatively cold across west central and southwest IL near the surface ridge axis where the best radiational cooling will occur. Rain may move into central MO as early as Sunday morning as low-mid level warm air advection increases over the area and low level moisture moves into the western portion of the forecast area, although it appears that the GFS model may be a little overdone on its pops and qpf Sunday and Sunday night. Highs on Sunday will be warmer as surface winds veer around to a southerly direction on the backside of the surface ridge. Elevated convection is expected across northeast MO and west central IL late Sunday night as 850 mb theta-e advection and moisture convergence increases over this area on the nose of a west-southwesterly low level jet. This convection will likely weaken Monday morning as it shifts southeastward, but then redevelop across southeast MO and southwest IL Monday afternoon along a southeastward moving cold front. Despite cloud cover and at least scattered showers and a few storms, the highs on Monday will be unseasonably warm, around 15 degrees above normal. The GFS model is now keeping the chance of post frontal rain going Monday night through Tuesday evening, especially across southeast MO and southwest IL with low-mid level warm air advection over the cold front and weak northwest flow shortwaves moving through the area. The precipitation should finally shift south of the entire forecast area by late Tuesday night as a surface ridge over the northern Plains continues to build southward into the region. Will see a gradual cooling trend from Monday night through Wednesday, although temperatures will never get much below normal. Will likely see a break in the precipitation threat late Tuesday night through Wednesday evening as an upper level ridge builds over the region ahead of a developing storm system in the lee of the Rockies. Will also see the start of a warming trend beginning Wednesday night and Thursday. Convection will return to the area late Wednesday night and Thursday as a warm front lifts north- northeastward through the area. GKS && .AVIATION... (For the 00z TAFs through 00z Saturday Evening) Issued at 647 PM CDT Fri Mar 17 2017 VFR conditions and dry wx will prevail at the TAF sites for much of the valid period. The only item of concern is area of MVFR CIGs to the north across northeastern IA and WI. The NAM has the best handle on the current extent and tracks it southeastward overnight and into early Saturday morning before retreating to the east. The models have some disagreement on where this southwestern backedge sets up, but using the NAM as the main source of guidance, it has a decent probability of some of these MVFR cloud bases to reach UIN and edge into the STL metro sites. Have handled in TAFs with a CIG for a few hours at UIN and introduced a SCT layer at the STL metro sites and will adjust as we track it southward tonight. Otherwise, surface winds will become NW and persist for much of the valid period, only veering NE and becoming light around sundown Saturday night. SPECIFICS FOR KSTL: VFR conditions and dry wx to prevail. Will need to watch region of MVFR CIGs to the north as they drop southward overnight and into early Saturday morning. Have placed a SCT layer between 14-18z and may need to upgrade to a CIG later this evening. Otherwise surface winds becoming NW this evening and pesisting until Saturday night when they become light and variable as a RIDGE of high pressure builds in. TES && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX