Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190737 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 337 AM EDT Thu Oct 19 2017 .SYNOPSIS...
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High pressure will remain across the Mid Atlantic through this weekend. A low pressure system will affect the region early next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Its chilly again this morning, but with higher dew points, its not quite as cold or frosty as the last couple mornings. The higher dew points have led to a little patchy fog, but not much as of this writing. High pressure is centered over the southern Appalachians at present, and will generally remain in control of the weather through the day. We`ll have a few high clouds around, but nothing to prevent temps from rising rapidly after sunrise. With relatively dry air in place and plenty of sun (if filtered a little), we should manage the low 70s in most spots. A very weak cold front will cross the region this evening. This will result in a bit more wind overnight, but little more than that. Because of the wind keeping it stirred up, temps should be a bit higher than the last few nights. In areas where the wind diminishes late, patchy fog could redevelop.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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High pressure will remain over the region through the short term. It will be centered just to our southwest Friday, then slowly migrate northeastward to a position off Cape Cod by Saturday night. WInds may be a little breezy Friday in the wake of the previous night`s cold frontal passage, but should be very light Saturday as the high drifts on by. Temps will remain warm during the day thanks to minimal air mass change, with 70s common both Friday and Saturday, with lows falling back into the 40s each night thanks to good radiational cooling under the high and limited if any cloud cover. Patchy fog will be possible late each night.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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A significant change to the synoptic height pattern is forecast to take place across the Northern Hemisphere this period. A large/deep upper-level low will retrograde out of northern Canada into the Bering Strait/western Alaska over the weekend. This will force a building ridge over western North America, and lowering heights across the eastern CONUS. With a blocking ridge downstream over the North Atlantic, interaction between the northern and southern streams seems likely early next week. The exact evolution is, of course, uncertain at this time range. But the pattern should transition from warm/dry to cool/stormy over the Mid-Atlantic early next week. Latest 00z deterministic runs and their respective ensembles continue to show this overall evolution, with spread in finer scale details which will be ironed out in the coming days.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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Patchy fog possible at MRB/CHO/IAD over the next few mornings, but odds are low and if it does happen, it should generally be MVFR at worst. Otherwise, VFR through Saturday night all terminals with light winds under high pressure. Some low CIGS/VSBYS may develop early Monday morning as moisture returns aroud departing high pressure. Otherwise guidance in agreement with pattern which would favor VFR Sunday into Monday.
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&& .MARINE...
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High pressure will generally keep winds below SCA criteria through Saturday night. The exception will be tonight into Friday morning, when a weak passing cold front will stir the winds up. Soundings show some sustained winds of 20-30 knots just above the surface, and while upstream, near shore areas will probably have a surface inversion, just off shore, especially as one heads further downstream, that inversion should be weaker if present at all given the warm water temps, so expect some of that wind to start mixing down later tonight into Friday morning. As temps warm and the winds just above the surface diminish during the day Friday, gusts should drop below SCA criteria. Southerly channeling to SCA levels possible by Monday as high pressure moves offshore.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 9 PM this evening to noon EDT Friday for ANZ531>534-537-539>541-543.
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&& $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...DFH AVIATION...RCM/DFH MARINE...RCM/DFH

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