textproduct: Wakefield

WHAT HAS CHANGED

Updated full discussion.

KEY MESSAGES

1) Widespread showers and thunderstorms are expected this afternoon and evening with better potential for severe weather. The main threat is damaging wind gusts with large hail and a couple of tornadoes also possible.

2) 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 245 AM EDT Tuesday...

KEY MESSAGE 1...Widespread showers and thunderstorms are expected this afternoon and evening with better potential for severe weather. The main threat is damaging wind gusts with large hail and a couple of tornadoes also possible.

An anomalously strong upper trough and sfc low are progged to deepen over the Northeast CONUS today while we remain under NW flow aloft. The deepening has already started, with decent height falls being observed from the Great Lakes to Northeast over the past few hours. At the surface, low pressure is developing along a cold front over the eastern Great Lakes. Convection has developed over western and central Ohio and is organizing into an MCS. Will need to watch this convection later this morning, but it appears that it will pass by just far enough to our W/SW as to not inhibit sfc heating (and thus instability) in a meaningful way for at least the eastern 2/3 of the area. There is a low chc of late AM/midday showers in the Piedmont from this feature. The surface low will continue to deepen over the Northeast today, and in fact, could deepen to 995mb 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 35-45 kt 500mb winds on the SW side of the trough that is progged move over the local area during the afternoon. The above mentioned cold front will move toward the area later today and will cross the area tonight. Since the upstream MCS activity should pass far enough to our W/SW, temperatures will be able to climb into the upper 80s in most areas by the afternoon with lower-mid 70s dew pts. This, coupled with solid 700-500mb lapse rates around 7.0 degrees C, should allow MLCAPE to rise to 2000-2500 J/kg across much of the area.

While there are slight differences in the CAMs with respect to exact timing, convective mode, and convective evolution...the general consensus is for numerous tstms to initially develop just to our north during the early-mid aftn before moving through the area from NW-SE during the late aftn-evening. The most likely timing for storms is from 3-7 PM N/NW, 5-8 PM from south central VA to Richmond to the MD eastern Shore, and from 6-11 PM in SE VA/NE NC. Whether the storms consolidate into a line or remain more discrete is not known. The main threat appears to be damaging wind gusts, which would be fairly robust whether storms remain more discrete or consolidate into a line/line segments. There is also a large hail threat, mainly across the NW 2/3 of the area where storms are more likely to be discrete. Lastly, a couple of brief tornadoes cannot be ruled out, 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, with 30% wind probs and a 5% tornado risk for much of the area. The main bust potential will be that the developing MCS over OH becomes stronger and tracks farther NE than expected. If this happens, it could potentially contaminate our environment and lead to a lower than anticipated severe threat later today. 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 2...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, but guidance has trended down on this. Have maintained slight chance PoPs across the northern portion of the forecast area for consistency. Thursday through Friday looks mostly dry, with near to slightly below average temperatures, as LLVL flow will continue to be out of the NW. Tstm chances may return by late this weekend.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

As of 130 PM EDT Tuesday...

VFR conditions prevailed as of 18z with high pressure well offshore and an upper trough and cold front approaching from the NNW. The wind was SSW 8-12kt with occasional gusts to ~20kt. The main aviation concern through the period is the potential for numerous tstms late this aftn/evening. Convection has initiated over PA and WV and should shift toward the Blue Ridge and northern VA by ~20z, then track NW-SE across the local area from about 21-04z. The main threat with any tstms will be strong to severe wind gusts, along with brief IFR/LIFR vsby restrictions in heavy rain. TEMPO groups for tstms will be maintained as confidence in timing is not high enough to include as a prevailing group. Patchy MVFR CIGs are possible later tonight after the convection exits, mainly at SBY. Additionally, some patchy shallow ground fog is possible if the wind becomes calm late tonight/early Wednesday prior to the cold frontal passage. Otherwise, drier air arrives behind the cold front Wednesday morning, with VFR conditions expected and a NW wind of 8-12kt (locally 10-15kt gusting to ~20kt at SBY). An isolated shower/tstm is possible near the coast, but the probability is quite low.

Outlook: Drier conditions return by late week and likely linger into much of next weekend.

MARINE

As of 200 PM EDT Tuesday...

Key Messages:

- Small Craft Advisories remain in effect for the Chesapeake Bay, Lower James River, and northern coastal waters.

- Scattered showers and thunderstorms are expected late this afternoon through this evening with the potential for strong winds, heavy rain and frequent lightning.

A cold front will move across the local waters tonight. Ahead of the front, S winds increase to 10-15 kt with gusts up to 25 kt late this afternoon across the local waters and will continue at similar speeds through late this evening. Additionally, a round of showers and thunderstorms will proceed the cold fropa and any storms will contain strong winds, heavy rain and frequent lightning through late evening. Winds become W 10-15 kt overnight behind the cold front, and then NW late tonight into Wed morning. Winds diminish to 5-10 kt by Wed afternoon as high pressure begins to build into the area. After that, a period of benign marine conditions is expected to last into the coming weekend.

Waves and seas build to 2-3 ft and 3-4 ft respectively by this evening before subsiding Wed. A period of 4-5 ft seas is possible across the northern coastal waters tonight.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 1 AM EDT Wednesday for ANZ630>632- 634-639-650-652-654.