textproduct: Wakefield

WHAT HAS CHANGED

Updated full discussion. Increasing confidence for severe storms Tuesday afternoon and evening.

KEY MESSAGES

1) Typical summer weather through this evening with scattered thunderstorms near the coast, then becoming mostly dry overnight.

2) Widespread showers and thunderstorms expected Tuesday afternoon and evening with better potential for severe weather. The main threat is damaging wind gusts with large hail also possible.

3) Isolated showers and storms are possible on Wednesday, with mainly dry weather to end the week. Temperatures drop to slightly below average late this week.

DISCUSSION

As of 320 PM EDT Monday...

KEY MESSAGE 1...Typical summer weather through this evening with scattered thunderstorms near the coast, then becoming mostly dry overnight.

Isolated to scattered thunderstorms have developed across SE VA, NE NC, and the Eastern Shore. The initial line that developed along a weak surface boundary across NE NC appeared to be moving, however, the motion of storms has since become very slow to nearly stationary. The more stationary storms have likely developed along a sea-breeze boundary, with no storms developing inland thus far. This has lead to some flash-flooding across the VA Beach area, as well as areas near Melfa, VA on the Eastern Shore (radar estimated rainfall has reached nearly 4" of rain over the past hour or so in this area). Additionally, some of these storms have been able to develop impressive cores that has led to the issuance of a few Severe Thunderstorm Warnings. Current environmental analysis shows decent bulk shear values ranging between 30-40 kt, ML CAPE values of 1,000- 2,000J/kg, and strong ridging over the central/southern CONUS and troughing over New England and offshore keeping our area within a NW mid/upper low regime. With this kind of environment, additional severe storms and localized flash flooding are possible along the coast. Hi-res guidance is not excited about additional convection developing farther inland this evening, and rain chances remain very low west of I-95. As the afternoon convection wanes, rain chances will dwindle to 10% or less through tomorrow morning. With light winds forecast tonight, areas that saw rain may see some patchy fog.

KEY MESSAGE 2...Widespread showers and thunderstorms expected Tuesday afternoon and evening with better potential for severe weather. The main threat is damaging wind gusts with large hail also possible.

An anomalously strong upper trough and sfc low are progged to deepen over the Northeast CONUS. In fact, the low could deepen to 993mb with -2 to -3 sigma height anomalies over the northern Mid- Atlantic/Northeast. The synoptic features are impressive especially considering it is late July. There will be a belt of 40-50 kt 500mb winds on the SW side of the trough that may move over the local area during the afternoon. At the same time, the low will drag a cold front toward the area. Ahead of any developing convection, temperatures will be able to climb into the upper 80s in most area and help increase the instability across the area. Forecast soundings currently show solid mid level lapse rates of 6.5-7.0 degrees, and MLCAPE values of 2000-3000J/kg. With very good convective parameters, combined with the NW flow aloft, there could be a robust damaging wind and hail threat for tomorrow. Isolated brief tornadoes cannot be ruled out tomorrow, especially closer to the coast where the winds will be more backed. SPC has maintained a Slight Risk (level 2/5) for the entire area, but has expanded the 30% wind contour all the way to the coast and upped the tornado threat slightly to account for the better environment near the coast. The main bust potential will be any upstream MCS activity overnight into tomorrow morning that could potentially contaminate our environment and lead to a lower than anticipated severe threat tomorrow. Storms will be moving quickly, which will act to limit flooding, but cannot rule out localized flash-flooding, mainly in urban/flood prone areas.

KEY MESSAGE 3...Isolated showers and storms are possible on Wednesday, with mainly dry weather to end the week. Temperatures drop to slightly below average late this week.

There is some uncertainty in regards to rain chances in the wake of the cold front on Wednesday. With the closer proximity of the upper low, there cold be some showers on Wednesday. Blended guidance still has low PoPs, but have decided to include slight chance PoPs across the northern portion of the forecast area. This may need to be expanded pending the location of the upper low. Thursday through Friday looks mostly dry, with near to slightly below average temperatures, as LLVL flow will continue to be out of the NW.

AVIATION /19Z MONDAY THROUGH SATURDAY/

As of 142 PM EDT Monday...

There is a smattering of convection across SE VA, NE NC, and the MD Eastern Shore. The main terminal being impacted is ECG, though satellite imagery shows some growing cumulus clouds near PHF and ORF which may indicate that storms are attempting to develop in that area. Additionally, SBY could see some impacts from the storms to the west if they continue to build towards the terminal. Winds are generally light and variable across the area this afternoon and will remain that way through tomorrow morning. Winds will then shift to south by tomorrow morning. While there is higher confidence that most terminals will see flight restrictions due to thunderstorms tomorrow, the exact timing of these storms remains somewhat uncertain. Most storms will likely move in the afternoon, so tempos will likely be necessary. Some of the storms will likely produce strong to severe winds.

Outlook: Storms will continue into Tuesday night, with continuing flight restrictions likely. Isolated showers/tstms are possible Wednesday, but PoPs are much lower than on Tuesday. Drier conditions return by late week.

MARINE

As of 320 PM EDT Monday...

- Sub-advisory conditions prevail with southerly winds through tonight.

- A cold front approaches on Tuesday, which could bring a brief period of low-end SCAs with S-SW winds along with strong to severe thunderstorms.

Weak surface high pressure is centered offshore this aftn, with a trough immediately inland. The wind is generally S 5-10kt and occasionally up to 10-15kt. A few stronger gusts are possible with any tstms near the coastlines. Seas are primarily 2-3ft, with 1-2ft waves in the Ches. Bay. The pressure gradient gradually tightens tonight as the trough washes out with the wind becoming SSW 10-15kt by later tonight. Further tightening of the pressure gradient is expected Tuesday as strong low pressure pushes E across NY/PA with a trailing cold front through the central Appalachians. Local wind probs show about a 50-70% chc of sustained 18kt N of Windmill Point noon to 6PM Tuesday. However, strong to severe tstms are possible by mid-late aftn, which will likely disrupt the synoptic flow. Have opted not to issue any SCAs for the Ches. Bay at this time given marginal conditions, which could be impacted by convection. SCAs on the ocean are even more uncertain as local probs for 25 kt gusts are below 50%. Also, this is a WAA regime, so seas may struggle to get to 5 ft, especially if the flow becomes more SW than S. Regardless, the main weather concern Tuesday is strong to severe tstms over all of the waters during the afternoon and evening with gusty winds the primary threat, although there is a risk for waterspouts as well. In the wake of the front, winds will decrease to 5-15 kt and shift to the NW. NW winds may increase with low-end SCAs possible Wed night into Thursday but a lot of uncertainty remains at this range.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...None.