textproduct: Wakefield

WHAT HAS CHANGED

Flood Watch issued for most of central and eastern VA today

Marginal severe risk introduced for Tuesday

KEY MESSAGES

1) A Flood Watch is now in effect for central and eastern VA and interior NE NC today. Widespread slow-moving showers and storms may lead to flash flooding, particularly in urban, poor drainage, and flood prone areas. Storms could also approach severe levels with damaging winds the primary threat. Additional storms capable of flash flooding and damaging winds are possible Tuesday.

2) Near-normal temperatures are expected for most of this week, with additional chances for afternoon/evening thunderstorms.

DISCUSSION

As of 315 AM EDT Monday...

KEY MESSAGE 1...A Flood Watch is now in effect for central and eastern VA and interior NE NC today. Widespread slow-moving showers and storms may lead to flash flooding, particularly in urban, poor drainage, and flood prone areas. Storms could also approach severe levels with damaging winds the primary threat. Additional storms capable of flash flooding and damaging winds are possible Tuesday.

Earlier convective activity has generally diminished over the local area. However, a remnant outflow boundary on the lower MD Eastern Shore has sparked some showers and embedded storms. This activity should remain confined to this area and gradually diminishes over the next hour or so.

The main story today will be the potential for heavy rain and localized flash flooding. A very moist air mass will be in place, characterized by PWATs over 2.0" and saturated atmospheric profiles. While forcing is rather weak, moderate-strong instability, diffluent flow aloft, a weak low at the surface, and any remnant convective boundaries will support the development of rather widespread showers and storms by later this afternoon and evening. CAMs also suggest storms could initiate as early as the late morning/early afternoon on the MD Eastern Shore. As with previous days, the exact details remain unclear and there are quite varied solutions among the CAMs. The low convective coverage on the latest HRRR runs appears to be an outlier compared to the rest of guidance; this could potentially be related to its over- mixing bias (it shows dew points in the low-mid 60s inland this afternoon, which appears very unlikely). Otherwise, temperatures will again be on the hot side today. Heat indices could approach 105 F in the urban corridor of SE VA into NE NC. However, the duration and spatial extent appears too limited for additional Heat Advisories. Furthermore, afternoon convection and cloud cover introduces some uncertainty in the temperature forecast.

Regarding today's heavy rainfall threat, the aforementioned moist air mass appears very supportive for high and efficient rain rates. Storm motions will also tend to be slow and erratic. There remains an impressive signal in both the HREF and REFS for localized significant rainfall totals. Neighborhood probabilities for >4" in the 12z Monday-12z Tuesday 24 hr period are 20-40% with locally higher probs. Ensemble max totals also approach 6-8" in this period, reflective of localized worst case scenarios where prolonged training and backbuilding could occur. Additionally, probs for high rain amounts in a short period are also elevated, with 30-50% probs for 3"/3hr this afternoon and evening for most locations W of the Chesapeake Bay. These rainfall amounts could quickly lead to flash flooding, particularly in urban and poor- drainage areas, despite antecedent conditions being mostly dry. However, should note that some spots have seen higher rainfall totals over the past few days and these locations could be at higher risks for flooding today. Taking all of this into account, think there is sufficient justification for a Flash Flood Watch for a large portion of our CWA. Uncertainty is higher on the Eastern Shore so will hold off on a watch for these areas. Storms will also be capable producing sporadic wind damage given ample instability and (initially) steep low-level lapse rates. SPC has a Marginal Risk (level 1/5) for damaging wind gusts, but there is mention of a potential upgrade if models and convective trends suggest corridors of higher wind potential. The severe threat should generally diminish after sunset, with an increasing focus on the heavy rain threat after that time.

Additional storms are likely Tuesday with a similar setup in place. A flash flooding risk may again materialize, in addition to continued risks for sporadic wind damage in storms (SPC has a marginal risk generally S of I-64).

KEY MESSAGE 2...Near-normal temperatures are expected for most of this week, with additional chances for afternoon/evening thunderstorms.

A weak flow pattern very typical for the middle of summer with daily chances for showers and storms continues into the midweek period. Chance PoPs are in place Wednesday and Thursday, with lower PoPs Friday. Temperatures will be near seasonal norms for most of next week, ranging from the upper 80s to lower 90s. A weak front will cross the area Wednesday, resulting in the coolest day this week with high temps in the mid 80s. Another front may cross the area Saturday with higher PoPs returning.

AVIATION /12Z MONDAY THROUGH FRIDAY/

As of 645 AM EDT Monday... Primarily VFR is expected through the early-mid afternoon. Any lingering MVFR should stay confined just N of SBY this morning. Another round of storms are expected later this afternoon and evening with higher confidence that the coastal terminals see storms today. Locally higher winds, heavy rain, frequent lightning, and reduced VSBY are likely within storms. Storms may linger into early tonight before diminishing/weakening after 06z Tuesday. Winds today will generally be out of the S-SW, but the overall flow field is quite weak and variable directions are likely in and around storms. MVFR-IFR CIGs are possible tonight but this depends on the evolution of the precip overnight.

Outlook: Additional thunderstorms are likely Tuesday and Wednesday. Localized flight restrictions would be expected in storms, but prevailing VFR is expected outside of storms.

MARINE

As of 315 AM EDT Monday...

Key Messages:

- Sub-SCA marine conditions are expected to prevail early to mid- week, with mainly south-southwesterly winds today gradually becoming east-northeast by mid-week.

- Elevated wind gusts from strong thunderstorms are possible during afternoon and evening hours today and Tuesday.

High pressure continues to extend from the Southeast US to off the Mid-Atlantic coast early this morning with a weak front extending W- E from NE MD across the northern Delmarva. The wind is mainly S 5- 10kt. Seas are ~2ft with ~1ft waves in the Ches. Bay. High pressure remains in vicinity of the Southeast coast today into tonight. The wind will generally be S-SW 5-10kt through early aftn, and then become SSE 8-12kt later this aftn/early evening, before becoming SW 5-10kt tonight. Scattered showers/tstms are expected to develop this aftn and linger through early evening. Tstms will be capable of producing locally strong wind gusts. The boundary to the N this morning gradually settles into the region by Tuesday. The wind will be light, and primarily NE to the N of the boundary, and SSW to the S of the boundary. Scattered showers/tstms are expected again Tuesday aftn/evening, with tstms potentially producing locally strong wind gusts. The latest guidance has the boundary dropping S of the region Wednesday as a weak cold front. The wind becomes ENE 8- 12kt. The front lifts back to the N Thursday, with sub-SCA S/SE flow Thursday becoming SW Friday and remaining sub-SCA. Seas will be ~2ft Monday/Tuesday, with 1ft to occasionally 1-2ft waves in the Ches. Bay. Seas build to 2-3ft by Wednesday, and potentially ~3ft coastal waters/3-4ft offshore waters given onshore flow, with 2-3ft waves in the mouth of the Ches. Bay, and 1-2ft waves elsewhere. Seas subside back to 2-3ft later in the week with 1-2ft waves in the Ches. Bay.

EQUIPMENT

KAKQ radar is down due to mechanical issues without an estimated time of return.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...Flood Watch from 2 PM EDT this afternoon through this evening for NCZ012>014. VA...Flood Watch from 2 PM EDT this afternoon through this evening for VAZ048-060>062-064>069-075>090-092-097-098-509>525- 528>531. MARINE...None.