textproduct: Wakefield

WHAT HAS CHANGED

Small Craft Advisories have been issued for the Bay for this afternoon into tonight.

KEY MESSAGES

1) A typical summertime pattern prevails Sunday through the middle of next week, with near average temperatures, increasingly humid conditions, and daily chances of showers and thunderstorms.

DISCUSSION

As of 300 PM EDT Saturday...

KEY MESSAGE 1...A typical summertime pattern prevails Sunday through the middle of next week, with near average temperatures, increasingly humid conditions, and daily chances of showers and thunderstorms.

GOES water vapor channels depict a slow moving upper low over the mid-Mississippi Valley with moist southerly flow ahead of the upper low over the Mid-Atlantic. Surface high pressure is now centered well offshore of the Southeast coast. There is a lee-side trough over the Piedmont and low-level SSE flow has allowed moisture to pool along that boundary. Given this, some isolated showers/tstms have developed in an environment featuring SBCAPE ~1500 J/kg and low- level lapse rates of 7.0-7.5 C/km. Mid-level lapse rates are rather poor, so these showers/tstms are not particularly tall. Temperatures are in the mid/upper 80s, and slightly more humid than the past few days with dewpoints in the mid 60s to lower 70s. Warm and more humid tonight with low temperatures of 70-75F. Mainly dry, with a slight chc of showers over the Piedmont and coastal SE VA/NE NC toward morning.

The pattern becomes more unsettled by Sunday, and this will continue into early next week as the slow moving upper-level trough approaches from the west. At the same time, a weak cold front approaches from the north, but will remain north of the local area through Monday (and likely wash out by Tuesday). With the approaching trough and Bermuda high pressure well offshore, deep- layered S to SW flow will prevail. This will allow rich Gulf moisture to overspread the area on Sunday and remain over us early next week. PWs surge to 2.2-2.4" by later Sunday/Sunday night. Scattered to potentially numerous showers/tstms are expected Sunday. The highest precip chances will initially be across south-central VA during the afternoon (as the deep moisture arrives here first). Showers and tstms should gradually spread NE through the evening (though it may very well remain dry near the immediate coast and on the Eastern Shore).

Showers/tstms are likely across the entire area on Monday as a lead shortwave potentially tracks over the area. Monday appears to be the day with the highest convective coverage during the period. The trough dampens a bit from Tuesday/Wednesday, but scattered showers and tstms are still expected during the aftn/evening on both days as weak SW flow aloft continues and deep moisture remains nearby. Given the environment, and relatively weak unidirectional flow aloft and tall/skinny CAPE, there will be a threat of localized flash flooding each day, but the severe threat should remain relatively low with these tstms. Days 2-4 (Sunday through Tuesday) are in a 'Marginal' ERO as the overall flash flood risk is more isolated given a lack of a larger scale focusing mechanism, as the aforementioned front remains north of the local area. High temperatures dip down slightly below average during the early week period thanks to the cloud cover and multiple rounds of showers/tstms. Though not quite as unsettled as the first half of the week, the latter half of the week will see isolated to scattered afternoon showers and tstms. With the decreased convective coverage forecast, temperatures will return to near to slightly above normal with highs in the upper 80s to lower 90s.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

As of 200 PM EDT Saturday...

High pressure was centered well off the Southeast coast as of 18z, with a subtle trough over the Piedmont. VFR with a few showers/tstms in vicinity of the trough, but this activity should remain N/NW of RIC. The wind was S 8-12kt. Primarily VFR the remainder of the aftn through tonight, with a slight chc of showers near the coast late tonight/early Sunday morning. Patchy MVFR cigs are possible Sunday morning, with some IFR W of RIC. Otherwise, showers/tstms are likely Sunday aftn, which have the potential to produce brief IFR vsby in heavy rain. The wind will mainly be S/SSE 5-10kt tonight, and then S/SSW 8-12kt Sunday.

Outlook: Shower/tstm chances continue Sunday night and Monday as a slow moving upper trough approaches the area, and linger into Tuesday through Thursday. Periodic sub-VFR conditions are possible during this time, mainly from early morning stratus, and brief vsby restrictions in heavy rain.

MARINE

As of 140 PM EDT Saturday...

Key Messages:

- Small Craft Advisories have been issued for the Chesapeake Bay from this afternoon into the early overnight hours.

- Another period of SCA conditions is likely Sunday afternoon into Monday ahead of a weakening cold front.

High pressure is now offshore as of this afternoon. Meanwhile, a sfc low has become nearly vertically stacked with the upper low over the lower midwest. Latest obs show southerly winds around 10kt with gusts to 15kt. Seas are around 2ft and waves in the bay/rivers are around 1ft.

The stacked low will slowly move east over the next couple of days. Guidance suggests that the gradient between this low and high pressure offshore will tighten sufficiently to result in 15-20 kt SE winds over the Ches Bay later this afternoon through the evening hours. SCAs are in effect for the bay from 4pm to 1am to cover this. Winds in the tidal rivers, Currituck Sound, and offshore zones are expected to stay below SCA thresholds. Winds are expected to relax back into the 10-15 kt range after midnight. Waves and seas briefly build to 2-3 ft during the enhanced SE flow tonight. The surface low and its associated cold front will translate slowly eastward on Sunday, allowing the pressure gradient to steepen again. Additional SCA headlines are likely Sunday night into Monday for the majority of the local waters. Given a longer duration SW flow event, seas will have more time to build into the 3-6 ft range (0-20nm range, highest N). Farther offshore, seas increase to 5-7 ft for a period late Sunday into Monday. The front is forecast to wash out over inland areas late Monday into Tuesday.

Afternoon and evening shower and storm chances return Sunday and linger well into next week with locally higher winds/waves/seas likely to accompany the stronger convection.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 1 AM EDT Sunday for ANZ630>632-634.