AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 320 AM EST Wed Feb 8 2012 .SYNOPSIS... 07Z water vapor and H4 RUC analysis continues to show a rather complex upper level pattern across the CONUS this morning. REX block configuration from 24 hours ago over the western portion of the continent has broken down, with the closed upper LOW over Colorado now having opened up and become progressive. This TROUGH and any significant associated forcing will pass north of our region today. We continue to see an ACTIVE southern stream FLOW with abundant MID/upper level energy in the form of HIGH level CIRRUS streaming northward over the Gulf of Mexico. At the surface, forecast area resides in a region of weak GRADIENT between 1035mb high PRESSURE over the central Plains, and a surface trough in place across the southern FL Peninsula/FL Straits. Weak/subtle cold FRONT is analyzed slowly approaching our area across AL. This front is better defined above the surface, but should at least result in a somewhat drier low level airmass in its WAKE over the next couple of days. Regional radars do show a FEW showers up into central AL/Northern GA in closer proximity to the passing synoptic forcing. However AS mentioned above, this sufficient forcing will remain to our north and keep SHOWER chances out of our forecast. && .SHORT TERM (TODAY THROUGH FRIDAY)... Today, Mid/Upper level SHORTWAVE passes from the TN valley this morning to the mid-Atlantic coast this evening. Atmospheric momentum associated with this energy will be enough to pass a weak cold frontal boundary through the forecast area by mid/late afternoon. This will be an uneventful frontal passage with only some clouds and a slight WIND shift to mark its arrival. Overall, will be a pleasant February day with filtered sunshine and high temperatures ranging from the upper 60s north to the lower 70s south. Tonight, Dry and somewhat cooler NIGHT upcoming to what has been experienced lately. The drier airmass will allow temperatures to FALL into the upper 30s to lower 40s for much of the area. The high CENTER will still be well to our NW keeping the gradient fairly tight. With this in mind, don`t anticipate much CHANCE of any normally sheltered areas de-coupling and getting much colder than is currently forecast. Therefore, temperatures and dewpoint depressions should stay above the level of a FROST threat. Thursday/Thursday night, Little change in the forecast with any significant northern stream energy remaining well to our north. High level clouds will LIKELY be on the increase once again by the end of the day as southern stream JET energy re-develops along the northern Gulf Coast. Plenty of dry AIR in the lower levels will keep RAIN out of our forecast with high TEMPS reaching up into the 60s. Surface ridging will SET up just to our north Thursday night which will bring the potential for some mid 30s temps inland, and a resulting frost potential. However, some uncertainly remains regarding the amount of mid/high level clouds that will be overspreading the area. Impressive southern stream jet energy suggest we will see the cirrus. Even high level cloudiness can sometimes disrupt the radiative process and help keep temps warmer than expected. This portion of the forecast will need to be monitored closely for those with sensitive outdoor vegetation. Friday, Uncertainly is beginning to increase by the end of Friday with regards to energy propagating across the southern Plains and northern Gulf coast. GFS is showing a scenario in which much of this energy is absorbed by a large cut-off low near the California Baja region. ECMWF/Canadian are much more aggressive, and allow the majority of this shortwave energy to bypass the upper low into the southern Plains. These models offer solutions that are potentially wetter for our western zones by Friday evening, and for all of our zones Friday night. Tough call on this one, but out of respect for the ECMWF will add slight chance POPS to the GRIDS beginning Friday afternoon in the far west, and for all zones Friday night. Should the ECMWF/Canadian solution be the correct trend, then these rain chances would need to be adjusted upward in future forecast packages. && .LONG TERM (SATURDAY THROUGH NEXT WEDNESDAY)... The complex and generally messy large scale pattern is expected to remain so during the forecast period, while undergoing some RETROGRESSION, with axis of the MEAN RIDGE over the western U.S. shifting westward into the eastern Pacific, and the large polar VORTEX over eastern Canada also evolving westward. The main effect will be to broaden the mean trough westward across the CONUS, resulting in a positive tilted trough axis across the Intermountain West, and a nearly zonal flow eastward across the eastern half of the country. The southern portion of the stream will remain quite strong. A series of short waves will drop southward into the mean trough axis over the Intermountain West, then weaken as they HEAD rapidly east or northeast across the eastern U.S. As always, the devil is in the details when it comes to the forecast for he Tri-State Area. The GFS and Euro continue to diverge predictably towards the end of the period, in how they handle the short waves dropping into the mean trough position. The Canadian and EURO are in better agreement, showing more short wave energy in the southern stream, which gives me some confidence, and a blend of the two solutions seems the way to go. Friday night and Saturday short wave energy will be moving eastward across the eastern U.S. pushing a cold front well to the south across the southern Florida peninsula, bringing at least a slight chance of rain, and a SURGE of colder drier air behind it across the southeast U.S. Temperatures may drop to near or a little below freezing in some areas on Monday morning. Then expect a fairly rapid rebound in temperatures by mid week, along with an increasing chance of rain, as the next short wave rounds the bottom of the trough and heads northeast. Temperatures will start out near NORMAL on Saturday, then drop below normal Sunday and Monday, then trend back to above normal by Wednesday. && .MARINE A weak cold front will cross the forecast area today. The gradient behind this front will increase and result in near ADVISORY level northerly winds tonight through Thursday morning. A surface ridge will slowly build down from the north later Thursday into Friday which will act to drop winds and SEAS back down below headline criteria. Another period of cautionary to advisory level northerly flow looks to develop during the upcoming weekend. && .AVIATION (THROUGH 06Z THURSDAY)... VFR conditions will continue across the Tri-State Area through the forecast period and beyond, with patches of cirrus occasionally streaming across the area. Although a drier airmass has spread into the region, good nighttime cooling will result in temperatures dropping to near the DEW point temperatures in some areas, allowing for the formation of some MIST before daybreak. The mist, in combination with some lingering SMOKE, will produce patches of MVFR visibilities primarily across south central Georgia before SUNRISE. && .FIRE WEATHER... Drier air is spreading across the Tri-State Area, and relative humidities across inland portions of Florida will drop to at or below 35 percent for several hours this afternoon, along with relatively high dispersions. However, dispersions are not expected to be quite high enough to warrant a Red Flag WATCH or WARNING, and ERC values will continue relatively low. Thursday will remain dry, with longer periods of critical relative HUMIDITY values, while dispersions are expected to be a little lower. However, ERC values are currently expected to remain below critical levels, so while conditions for Thursday afternoon should be closely monitored, there are no fire weather concerns at this time.