Scientific Forecaster Discussion
000 FXUS64 KLCH 180313 AFDLCH Area Forecast Discussion National Weather Service Lake Charles LA 913 PM CST Sat Feb 17 2018 .UPDATE... As of 9 PM, radar and surface observations indicate the shallow cold front has continued to progress southward and extends roughly along Interstate 10. Reflectivity of the showers along the front has decreased over the past several hours and short-term guidance indicated further weakening of showers can be expected over the next few hours. Therefore, PoPs have been decreased through the rest of this evening. Behind the cold front, temperatures have already dropped into the upper 50s/low 60s. The inherited forecast indicated a slower southward progression of the surface cold front and current temperatures were already at or near forecast lows for the evening. Radiational cooling and cold air advection should yield additional cooling through the overnight hours and temperatures have been decreased accordingly. The rest of the inherited forecast remains on track with no adjustments needed at this time. && .PREV DISCUSSION... /issued 540 PM CST Sat Feb 17 2018/ AVIATION... A front that has stalled over southeast Texas and southern La this afternoon is producing sctd showers. Showers are moving to the northeast. It appears that this boundary is again on the move to the east. Ceilings are beginning to drop over srn La attm w/ ceilings and vsby better over se Tx. But se Tx and srn La will see the same outcome w/ both ceilings and vsby becmg IFR/LIFR twrds midnight hr. This will cont thru sr before a slowly improving. PREV DISCUSSION... /issued 401 PM CST Sat Feb 17 2018/ DISCUSSION... A shallow cold front extends from near Natchitoches southwest to near Lufkin where temperatures are in the mid 50s compared with Alexandria which reported 74 degrees last hour. The front is producing enough lift to spark scattered showers across the area this afternoon. Expect these showers to sink further south through the evening before the front stalls somewhere over the area. Exactly where the front comes to rest may potentially wreak havoc on overnight lows which are presently based on relatively little CAA. Should the front advance to near the coast, this may need to be revised. The front will lift back to the north Sunday as a warm front which will be enough to sustain at least low end POPs early Sunday before precipitation comes to an end Sunday afternoon. Marine fog is once again expected to begin moving inland after sunset this evening although the northward extent should be limited to near the coast due to the boundary. Thus, opted to forgo any inland dense fog advisories at this time. That said, areas along the immediate coastline will likely see visibilities drop to a mile or less. Fog should abate from land areas by mid morning. Guidance remains very consistent in bringing drier mid and upper level air across the region Monday into early Tuesday which might be enough to give the area a break from the mostly cloudy skies that have been the hallmark of the last couple of weeks. Another slow moving frontal boundary is progged to approach the area late Tuesday. The GFS is the only reliable guidance actually that actually pushes the front through the area while the remaining guidance stalls the front over east Texas setting up a prolonged period of potentially heavy rain. Following the majority rule approach, I am inclined to lean the forecast towards the stalling solution which will result in widespread showers and thunderstorms beginning late Tuesday through Thursday. QPF values were based on WPC's forecast and show widespread totals of two to two and a half inches Tuesday through Thursday. Forecast soundings also show more instability than we've seen recently indicative of potentially stronger thunderstorms. However, given the considerable model uncertainty, that is subject to change. Jones MARINE... Widespread dense marine fog is expected to develop across the nearshore coastal waters and coastal lakes and bays beginning shortly after sunset this evening. Visibilities of less than a mile area expected. Patchy dense fog will also be possible across the outer coastal waters. The fog is expected to begin to dissipate late Sunday as drier air works its way into the region. && .PRELIMINARY POINT TEMPS/POPS... AEX 52 71 60 77 / 30 20 10 10 LCH 58 73 62 75 / 30 10 10 10 LFT 60 75 64 78 / 30 10 10 10 BPT 60 73 62 76 / 30 10 10 10 && .LCH WATCHES/WARNINGS/ADVISORIES... LA...None. TX...None. GM...Dense Fog Advisory until noon CST Sunday for GMZ430-432-435-450- 452-455.