AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 745 PM EST Tue Jan 31 2012 SYNOPSIS... AT UPPER LEVELS... DOWNSTREAM from TROUGH from WRN Great Lakes SWWD into CNTRL Plains and Desert SW, the large scale longwave pattern remains fairly zonal and progressive with multiple, short waves embedded within the MEAN FLOW across the Great Lakes and weaker ones across AZ and Gulf Coast. During the next 24 HRS, a WSW split flow regime develops with NRN stream portion of trough tracking from Great Lakes THRU New England and SRN stream component moving from Desert SW to Wrn Gulf before lifting NEWD, deamplifying and phasing with Nrn stream trough across MS/OH Valleys reaching MID-Atlc region early Thurs. Overnight into early Wed, srn stream SHORTWAVE will move from AZ to TX to LA while under increasingly SW steering flow, Gulf shortwave moves NEWD across NE Gulf region. AT LOWER LEVELS... Analysis showed HIGH off Carolina Coast with an east-west oriented RIDGE WWD through Srn GA, and a weak cold FRONT in KS and OK. 24-hour PRESSURE falls over the NW Gulf of Mexico and along the Gulf Coast suggest the beginning of the development a weak LOW pressure system over the western Gulf of Mexico. During the next 24 hrs, low is forecast to move east Wednesday and Thursday ahead of a weak short wave (currently over the southwest U.S.). Advancing UPSTREAM trough will drag weak cold front ESE and (under zonal flow very slowly) aligned from OH Valley thru TN Valley and N TX Wed morning. In response, ridge just N of FL will drift S and E and weaken. Despite the low being so weak, the models forecast ample deep layer MOISTURE and large scale lift to support a large area of RAIN. This reflected in model time heights, i.e. GFS TAE with 0.70 inch PWAT at 00z Wed increasing to 1.51 inch at 00z Thu down under one-inch at 18z Thurs. Expect RAINFALL totals for this event to RANGE from a quarter of an inch over N FL and S Central GA to an inch along the FL Panhandle Coast. There could be ISOLATED amounts of up to 3 inches, mainly Panhandle Coastal areas. Although there may be enough INSTABILITY and lift to support some thunderstorms (mainly near the coast and over the Gulf coastal waters). Rain chances will decrease from NW-SE on Thursday AS a weak frontal system (with slightly drier AIR) moves into the area. As this front stalls Thursday NIGHT and Friday, slight rain chances will return to the region. behind the front, high pressure will build over the area. && .SHORT TERM...(Rest of Tonight through early Wednesday) Increasing mid and high clouds spreading NEWD ahead of Gulf system will be countered by VEERING light low level winds and high DEW points. Expect patchy to areas of FOG to develop especially ERN counties, farthest from clouds and where gradients the weakest. Will add patchy fog to Ern counties. Expect lows from around 50 inland to near 60 coast. && .AVIATION (through 00z Thursday)...Mid and upper level cloudiness continues to spread from west to east across the region and low level clouds will move in overnight with CIGS around 5kft. Periods of MVFR CIGS and VSBYS are also expected before daybreak along with SCATTERED showers mainly at ECP and DHN. After daybreak, patchy light to occasional moderate rain will overspread the area from southwest to northeast throughout the remainder of the TAF period. Winds will be light from the southeast to south. && .MARINE... Winds and SEAS will continue to drop below exercise caution levels. The next CHANCE for near-ADVISORY level conditions will be Thursday night and Friday.