Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221359 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 959 AM EDT Mon May 22 2017 .SYNOPSIS... A warm front will cross the region this morning. A cold front will move through the area later today. High pressure will briefly return Monday night before low pressure develops over eastern Carolina Tuesday and moves northeast off the DelMarVa Tuesday night. Upper-level low pressure will linger over the area Wednesday through Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Warm front remains difficult to pick out this morning, although other surface features and observations indicate we are still entrenched within the wedged airmass. A small surface low is located over Caswell County, NC, with the warm front likely bending back and intersecting the cold front which is entering the western Appalachians. Moderate rainfall is beginning to pull eastward. Rainfall amounts have been up to two-thirds of an inch, with possibly a higher stripe near an inch in St. Marys County...but well less than anything that would produce flooding. Trends this afternoon are more optimistic. The break in the rain seen over the Shenandoah Valley should work eastward. Slow moving cold front will be inching eastward this afternoon, though it may not reach the I-95 corridor until this evening. Instability will be limited at best due early precip and clouds. However, in daytime heating behind the first round of precip, 500-800 J/kg of CAPE will be possible along and east of I-81, and have entertained a chance of thunder in this area, with any scattered showers that form along the front. Think shear/instability will be weak enough to preclude stronger storms, but trends will need to be monitored. Will be ending precip chances along with the dry air infiltrating behind the front. Temperatures will still have the opportunity to rise into the 70s this afternoon, but how far will depend on the clouds.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... High pressure will briefly build across the region tonight. However, the frontal zone won`t be all that far offshore, and clearing unlikely for point east of the Blue Ridge. Guidance has, for a couple of cycles now, been inducing cyclogenesis across the southeastern United States late tonight near a 500mb shortwave and the right rear quad of the upper jet. The track of this low will bring rain back to central Virginia and southern Maryland by late tonight. The focus will remain across southern/eastern areas, with a good dose of associated precipitation though Tuesday. One difference this cycle though is the compact nature of the low (tight precip gradient on the northwestern edge) and progressive speed. That means that precip will be exiting by Tuesday evening. Have backed off on Tuesday night precip substantially. Am hesitant to drop PoPs entirely as current guidance suggests, but am at a lower confidence "chance". A closed upper low will be moving south into the Mid-west Wednesday while a sfc low and associated cold front moves eastward across the Ohio Valley. A brief period of subsidence is expected across the Mid- Atlantic Wednesday leading to mostly dry conditions for most of the day however instability will increase across the Allegheny Front and creep northward into central VA Wed afternoon. This may cause a few showers and thunderstorms to form however confidence is low through the afternoon. Mostly dry conditions will come to an end Wed evening as rain progresses from south to north across the Mid-Atlantic region into Thu morning. Elevated instability is expected and thunderstorms are possible Wed night. && .LONG TERM /THURSDAY THROUGH SUNDAY/... A cold front will be in vicinity of the Mid-Atlantic region Thursday. Showers and a few thunderstorms should be ongoing Thu morning as low pressure rides along the cold front. Depending on the speed of the front showers and thunderstorms may continue through the day Thursday. Shear profiles show weak shear and therefore thunderstorms are expected to be sub-severe. The caveat is that heavy rain is possible in thunderstorms. Will need to monitor the threat if training storms occur. An upper level trough will move over head Thu-Thu night. The cold front should be east of the Mid-Atlantic region by Fri morning and northwest flow is expected. Disturbances may move across the region under the influence of the upper level trough Friday and a chance for showers exists. High pressure will build into the Mid-Atlantic region Friday- Saturday. Dry weather is expected through Saturday. Low pressure will move into the Ohio Valley Sat night and Sun and showers and thunderstorms are possible during this time. && .AVIATION /14Z MONDAY THROUGH FRIDAY/...
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Conditions have dropped to IFR in low clouds this morning, and occasionally vsby in more moderate pockets of rain. This rain is beginning to pull to the east. After this initial round of showers, ceilings should gradually lift. The afternoon will be at least above IFR. By evening, VFR should prevail. The precise timing of category crossings still a little bit nebulous. Also, there could be a few more showers in the afternoon ahead of a cold front, and maybe even a thunderstorm. Spatial and temporal uncertainties preclude a TAF mention. VFR for the rest of the TAF period. However, more rain, with reduced flight categories will return for the morning push Tuesday. Once again, IFR a good possibility for much of the day, with improvement in the evening. SHRA/TSRA possible Wed night-Thu night as a cold front moves across the terminals. Sub-vfr conditions possible during this time.
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&& .MARINE...
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Winds have dropped to less than 10 kt. Mixing should be rather poor today in vicinity of showers. Southerly flow will become west/northwest this evening with a cold frontal passage. Will have to monitor the potential of thunderstorms reaching the waters this evening. At the moment wind fields look light and storms weak, but localized stronger gusts can`t be ruled out should activity develop. The pressure gradient will tighten Tuesday as low pressure moves up the coast. Have raised a Small Craft Advisory for the mid Bay and lower Potomac, where the gradient will be the best. As the situation unfolds, the Advisory may need to be expanded or extended. A cold front will cross the waters Thu-Thu night. Showers and a few thunderstorms are possible Wed night through Thu night. Winds become W-NW Friday.
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&& .TIDES/COASTAL FLOODING...
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Anomalies have continued to fall to 3/4 foot or less. In addition, the next tide cycle will be lower astronomically across all waters. A cold front tonight will bring northwest winds. Therefore there are no indications that any additional flooding is imminent. However, a coastal low Tuesday provides some uncertainty. Guidance ensembles then diverge substantially through midweek.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 2 PM to 6 PM EDT Tuesday for ANZ533- 534-537-543. && $$ SYNOPSIS...HTS NEAR TERM...ADS/HTS SHORT TERM...HSK/HTS LONG TERM...HSK AVIATION...ADS/HSK/HTS MARINE...ADS/HSK/HTS TIDES/COASTAL FLOODING...ADS/HTS

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