Area Forecast Discussion
Issued by NWS Sterling, VA

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412 FXUS61 KLWX 301901 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 301 PM EDT Thu Mar 30 2017 .SYNOPSIS... High pressure will move offshore tonight. Low pressure will pass through the area Friday. High pressure will gradually return Saturday and Sunday before another low pressure impacts the area Monday and Tuesday. && .NEAR TERM /THROUGH TONIGHT/... Latest surface analysis shows high pressure near the Jersey shore, wedging southward along the east side of the Appalachians. A warm front snakes its way northwest from near Savannah, Georgia to a low pressure centered near St. Louis, Missouri, with a cold front extending southward to Lousiana and the western Gulf of Mexico. Another center of high pressure is located over the southern Rockies. Aloft, a ridge is located directly over our area, with a closed low is centered over western Missouri, and another ridge over the southern Rockies. Tonight, the surface high will slide east off the coast and the surface low will also move east, reaching Indiana by dawn. The warm front to our southwest will slowly push northward, reaching southwestern Virginia and North Carolina by dawn. Our area will remain stable through the night, but elevated convection may move overhead, resulting in some showers during the evening. A stray thunderstorm can`t be ruled out. Steadier rain will develop overnight as warm advection/isentropic lift increases. Temperatures will drop into the 40s in most of the region with a southeasterly upslope flow. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Surface low pressure in the midwest will slide into western Pennsylvania during the day Friday, with a secondary low developing over western North Carolina and heading northeast across our area. The two surface lows will consolidate near New Jersey Friday evening. Aloft, the shortwave to the south of the approaching closed low will develop a negative tilt as it slides eastward towards us Friday, with the closed low itself then crossing over the region overnight Friday. Both the surface and upper level systems will move eastward away from the region during the day Saturday. The negatively tilted shortwave will promote signifcant rainfall and perhaps a little embedded convection Friday morning. At the very least, some periods of moderate to occasionally heavy rain look likely given the ample moisture flow from the south and good forcing, and soundings also suggest some instability above the inversion. While the area has been dry, soils are significantly more moist than they were a month ago. Thus I am a little concerned about potential for isolated flooding, or at least significant ponding of water on roadways. Given that right now threat seems isolated, will not yet introduce any enhanced wording for it just yet. Steadier rain looks likely to taper to a more showery pattern by afternoon as the warm front tries to lift northwest into the DC metro ahead of the approaching secondary low. Some modest instability looks likely to develop just ahead of the cold front which will be trailing from the secondary low, and with some decent wind aloft, some gusty if not severe storms are certainly possible. SPC marginal risk area looks reasonable for areas near and south of the metro. Highs will be dependent on just how far north the warm front gets, with 60s likely south of the front and perhaps even 70s in the warmest spots south of the front, while 50s will hold north of it. Showers will diminish Friday night with the surface low passing east, but may linger as the upper low crosses the area overnight. Temperatures will fall back into the 40s on the northwesterly flow. The system will head off the coast and leave a gusty but drying northwest wind for Saturday. Winds may gust to 25-30 mph, but temperatures should be able to rebound to the 50s and low 60s. Some upslope showers will linger along the Allgheny Front, but east of the mountains it should be dry. All areas turn out dry for Saturday night as high pressure pushes in from the west and the upslope flow weakens. Temps may try to drop into the 30s in the cooler spots but the northwest flow should stay up and prevent strong radiational cooling. && .LONG TERM /SUNDAY THROUGH THURSDAY/... High pressure will settle into the region Sunday through early Monday. Dry and seasonable temperatures expected throughout the period. The next storm system will move into the region midday Monday through Tuesday, bringing more rain showers to the region once again. Brief high pressure will build into the region Wednesday and Wednesday night before the next storm system approaches Thursday. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... Conditions will deteriorate through tonight as low pressure approaches from the west. Showers will become more common with steady rain, reduced cigs and vis expected late tonight. IFR likely all terminals Friday morning before conditions relax a bit in the afternoon as rain diminishes to showers, though a thunderstorm will be possible through the day, with best odds in the afternoon. Strong winds just off the deck may also result in some wind shear on Friday. Conditions improve slowly back to VFR Friday night into Saturday, though a gusty NW wind will remain. Winds will diminish Saturday night. Vfr conditions expected Sunday through early Monday. Winds light and variable Sunday through early Monday. Mvfr to ifr conditions midday Monday and Monday night. Winds southeast 5 to 10 knots midday Monday and Monday afternoon becoming northeast 5 to 10 knots Monday night. && .MARINE... Approaching low pressure will bring southerly winds across the waters, with gusts increasing to SCA (20-30 knots) as we head through tonight and Friday. A gusty thunderstorm may cross the waters on Friday, most likely later in the day. Showers diminish and winds shift NW behind the front Friday night, with SCA gusts remaining possible behind the system Saturday. No marine hazards expected Sunday through Monday night. Winds northwest 5 to 10 knots Sunday through Monday. Winds becoming northeast 5 to 10 knots Monday night. && .TIDES/COASTAL FLOODING... An onshore flow will increase tonight into Friday as high pressure continues to move offshore. Low pressure will pass through the area Friday night. The onshore may increase ahead of this system. Elevated water levels are expected tonight through Friday night and minor tidal flooding is likely near times of high tide. Coastal flood advisories are likely. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM this evening to midnight EDT Friday night for ANZ531>534-537-539>541-543. Small Craft Advisory from noon to 6 PM EDT Friday for ANZ536- 538. Small Craft Advisory from 6 AM Friday to midnight EDT Friday night for ANZ530-542. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...KLW AVIATION...RCM/KLW MARINE...RCM/KLW TIDES/COASTAL FLOODING...LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.