Area forecast discussion National Weather Service Baltimore Maryland/Washington District of Columbia 821 PM EDT Tuesday may 21 2013 Synopsis... offshore high pressure will continue to bring warm moist southerly air into the region through Thursday. Afternoon and evening thunderstorms are possible each day. A cold front will pass through the region Thursday night into Friday. Cooler conditions are expected over the weekend. && Near term /tonight/... Line of thunderstorms prntly entering western west.V. Will likely weaken b4 getting to the eastern part of the state. Light fog possible aftr mdngt...most prevalent right b4 sunrise and then quickly burning off. Lows in the 60s xcpt l70s in the cities. && Short term /Wednesday through Thursday/... County warning forecast area will be warm sector through period...as surface high well off eastern Seaboard aids southerly flow/moisture advection. Thus air mass will remain unstable...W/ probability of precipitation gnly increasing in response to dropping middle level heights. Will still have a diurnal trend to storms. Thursday looks to be the better day in terms of thunderstorms and rain development as cold front/upper low drops through Great Lakes. Have raised probability of precipitation both days and introduced lklys on Thursday. Storm Prediction Center has western Maryland/Highlands outlooked in slt risk Thursday ahead of the cold fnt. && Long term /Thursday night through Tuesday/... cold front passage Thursday night. Aftr that the next several days looking good as Canadian high pressure builds in with temperatures 5-10 degrees below normal. Shortwave over the Tennessee Valley on Sunday should remain west of the lwx County Warning Area...will have to monitor for increased probability of precipitation. As of now expect some high clouds Sunday with a warming trend starting that continues into middle next week. && Aviation /00z Wednesday through Sunday/... VFR conds at all terminals. Expect areas of low clouds/fog to develop lt tonight...continuing into the Wednesday morning push but dissipating aftr sunrise. This time have leaned more toward fog development inland since skies will be prtly clear supporting radl cooling down to moist dewpoints. However low clouds will be lurking just east of dca/BWI. Diurnal thunderstorm activity Wednesday/Thursday with IFR conds possible in the heaviest ones. Southerly flow until a cold frontal passage Thursday night. Northwesterly flow with clear conds Saturday. Just some high clouds on Sunday. && Marine... the pressure gradient will strengthen over the region Wednesday afternoon and night as lopres moves through the Great Lakes and hipres remains parked over the western Atlantic. Southerly return flow will increase accordingly between both systems. A Small Craft Advisory GOES in effect Wednesday afternoon for the waters that are most prone to southerly channeling in the middle chesepeake Bay and Lower/Middle tidal Potomac River. Small Craft Advisory expands Wednesday night to include all of the Maryland chesepeake Bay as a southerly nocturnal jet develops. Southerly flow with high pressure offshore ahead of a cold front that comes through Thursday night. Southerly channeling to 20 knots possible Wednesday evening...and Thursday. Northwesterly flow to 20 knots possible Friday. Light and variable flow this weekend. && Tides/coastal flooding... expect positive tidal anomalies to develop during the midweek as southerly flow strengthens. Cbofs guidance...which has verified fairly well of late...forecast water levels to stay below minor coastal flooding thresholds through at least Thursday morning. Cold front moves through early Friday morning. Westerly winds behind the front should erase any positive tidal anomalies. && Lwx watches/warnings/advisories... District of Columbia...none. Maryland...none. Virginia...none. WV...none. Marine...Small Craft Advisory from 9 PM Wednesday to 6 am EDT Thursday for anz530-531-539. Small Craft Advisory from 2 PM Wednesday to 6 am EDT Thursday for anz532>534-536-537-540>543. && $$ Update...Woody!