textproduct: Wakefield

WHAT HAS CHANGED

Updated discussions. -Marginal SVR Risk for Day3 (Wed 5/27).

KEY MESSAGES

1) Numerous showers and storms into this evening, with at least high chc PoPs continuing overnight. Heavy rainfall is likely in any storm, with localized flash flooding possible in urban and flood prone areas.

2) Additional chances for showers and storms capable of heavy rainfall are expected Tuesday. and Wednesday.

3) Drier weather returns to end the week.

DISCUSSION

As of 340 PM EDT Monday...

KEY MESSAGE 1...Numerous showers and storms into this evening, with at least high chc PoPs continuing overnight. Heavy rainfall is likely in any storm, with localized flash flooding possible in urban and flood prone areas.

Latest analysis indicates the sfc front is now north of the CWA, with a weak sfc trough from the TN Valley to the northern mid-Atlantic, and a WSW flow aloft. Low level winds are from the SW (even on the MD eastern shore). There are some breaks in the clouds, but given a high coverage of showers and tstms, the sky is mostly cloudy on average. Temperatures are as warm as the lower 80s as far north as central VA in areas where it is not currently raining, with readings in the 70s with dew pts around 70F in the rain cooled air. Area 12Z soundings observed PWAT values from ~1.75" to ~1.85", with 19Z SPC mesoanalysis depicting PWATs as high as 2.1" in the SE and 1.9-2.0" elsewhere, indicating that moisture is markedly increased compared to the past few days. ML CAPE values are ~1500 J/KG in the SE and 500-1000 J/KG in the NW, allowing for scattered tstm coverage within the 60-90% coverage of showers.

Heavy rainfall is likely given the deeply- saturated profiles seen in model soundings, and the consensus from the 12Z HREF and REFS places the corridor of highest QPF across the SE through ~22Z, with that region seeing somewhat less QPF after 22Z, as the highest axis of heavy rain shifts to roughly from the I-85 corridor northeastward into the RIC metro and Northern Neck. Instantaneous rainfall rates up to 4-5" per hr are being observed, but there is enough flow aloft to keep the storms moving, and in general, these higher rates are only lasting for 20-30 minutes at a given location. Combined with antecedent rainfall conditions that are not favorable for widespread flash flooding, expect any FFWs to be confined to urban and flood prone areas if 1-2" falls in a short period, along with any repeated training of moderate-heavy showers/storms that occurs. There was additional discussion with WPC on upgrading portions of the region to a slight risk for excessive rainfall. However, given the overall flooding threat is mitigated by the dry antecedent conditions (and with little rainfall Sunday), expect the flash flood risk to be confined to these aforementioned locations, and therefore, the marginal risk has been maintained. The SVR threat is quite limited, but localized wind gusts to 35-45 mph will be possible with a few storms into the evening.

Showers likely persist through the evening and at least the early overnight hours, with a continued threat of heavy rainfall as the front to the north is forecast to sag south and enhance the precip chances beyond the typical early evening timeframe. However, the thunderstorm potential will be much lower given dwindling instability later tonight. Warm and humid with lows mainly from the mid 60s to around 70F.

KEY MESSAGE 2...Additional chances for showers and storms capable of heavy rainfall are expected Tuesday and Wednesday.

The frontal boundary remains near the area Tuesday, with latest guidance suggesting it (mostly) lifts back a bit farther N/NE Tuesday night into early Wednesday, which will focus additional shower/storm development over the local area. The exact position of the front will dictate where the heaviest rainfall falls and also where storms are favored. Surface- based instability (and storms) are likely along and S of the front, with much lower storm chances to the N. Model guidance still varies on the frontal positioning (particularly on Tuesday) with solutions varying from just N of the area to bisecting our CWA. Given these uncertainties, a chance for showers/storms has been maintained for the entire area, highest for southern VA and the Piedmont and lower from the Northern Neck onto the MD Eastern Shore. Anomalously high PWATs again favor a heavy rainfall threat. A stronger storm or two is also possible, but the severe threat is quite low given meager lapse rates and only modest shear. The front's location also has implications on the temperature forecast. At this point, the warmest temps on Tuesday are favored from southern VA into NC, though the gradient will probably be a bit more than currently indicated in the forecast. On Wed, there is more likely to be a mostly dry period in the morning/early aftn, with higher PoPs late in the day. This timing allowing for increased instability, better low level lapse rates, and somewhat drier air aloft has led to the issuance of a Day 3 Marginal SVR threat, with 5% probs for damaging winds as the primary threat. Warmer area- wide Wednesday with highs into the mid- upper 80s for much of the area.

KEY MESSAGE 3...Drier weather returns to end the week.

A cold front will move in from the north Wednesday night, and gradually push south of the area on Thursday as a trough digs out of Eastern Canada into the Northeast CONUS. Will linger some high chc to likely PoPs Wednesday evening (highest SE) in advance of the front, but after that an influx of drier air should shut off precip chances into Thursday. Undercut NBM PoPs a bit on Thursday (still maintaining chc PoPs in the south into the aftn). Otherwise, partly to mostly sunny and less humid but due to a well mixed atmosphere, forecast high temperatures remain well into the 80s Thursday. Friday will be cooler and dry as high pressure settles from the Great Lakes to the local area with highs in the upper 70s to around 80 F inland, and in the mid 70s for coastal areas.

There is increased uncertainty by the weekend as another trough digs out of Canada and potentially interacts with an active southern stream. However, the latest trends are for a stronger northern stream to suppress the moisture south. For now, NBM PoPs are 20% or less across the northern 2/3 of the FA, with 30-40% chances in the south. High temperatures will be below average by about 5-10 degrees, generally in the low-mid 70s.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

As of 750 PM EDT Monday...

Showers with embedded tstms continue from RIC-SBY, while precipitation has diminished some in SE VA/NE NC. High rain rates have been periodically reducing VSBYs to 1/2SM to ~2SM at RIC/SBY. CIGs are MVFR to VFR in SE VA/NE NC, but are periodically dropping to IFR at RIC/SBY. Further degradation to IFR/LIFR is expected again later tonight with continuing shower chances (though rain intensity should continue to gradually decrease overnight). SBY is likely to drop as a weak frontal boundary sags south into the area, but most places (except ECG) have a good chance at dropping to IFR CIGs after 06Z, lasting through 12-15Z Tuesday.

Outlook: Conditions remain unsettled with off and on showers/storms bringing periodic sub-VFR conditions Tuesday aftn and again Wed aftn/evening (Along with early AM CIGs/reduced VSBYs Wed morning). A more significant cold front pushes through late wed night/Thursday, with drier air, N winds and VFR conditions Thursday through Friday.

MARINE

As of 300 PM EDT Monday...

Key Messages:

- A Marine Dense Fog Advisory remains in effect for the coastal waters north of Parramore Island through Tuesday morning.

- Sub-SCA SSW winds prevail through tonight, with a weak cold front leading to light and variable winds Tuesday, then sub- SCA SW winds returning Wednesday. The stationary front that was draped across the area this morning has pushed northwards leaving southerly winds 5-10 kt across the area. Seas are observed 3-4 ft offshore with ~1 ft waves. Showers with locally heavy rainfall are seen on the radar across most of the local waters. There isn't much wind with these showers, although a few storms may gust to 34 kt, which would be handled with a SMW if needed. Reduced visbilities for the coastal waters north of Parramore Island continue this afternoon, albeit slightly improved from this morning. Local coastal cameras and buoy 44009 camera show visbilities at or around 2 NM currently. Visibilities for these northern waters are expected reduce again tonight with light flow and lingering moisture. As a result, the Marine Dense Fog Advisory is in effect through early Tuesday morning.

The front will nudge back south overnight, bisecting the area by mid morning. Winds will remain light, but shift out of the E/NE across the northern tier of the marine area. The front then lifts back to the north Tuesday night into Wednesday with light SW flow developing. Seas in the coastal waters will subside from 3-4ft initially to 2-3ft by Tuesday and Wednesday, with offshore seas subsiding from 4-5ft to 3-4ft. Waves in the Ches. Bay will be ~1ft with light flow, and 1-2ft near the mouth of the Bay.

A stronger cold front moves N-S across the Mid-Atlantic coast Thursday with the wind becoming northerly, but remaining sub-SCA. A stronger cold front potentially crosses the local area next weekend with a N/NE wind developing behind the boundary, which could also result in elevated seas. SCA conditions are possible in the wake of this front.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...Dense Fog Advisory until 7 AM EDT Tuesday for ANZ650-652.