Marine Weather and Tide Forecast for Groveton, VA

KEY MESSAGES
- (1) A weak frontal boundary will linger across the region through Sunday delivering waves of showers and thunderstorms.

- (2) Significant heat risk next week heading into the Independence Day holiday.

DISCUSSION
KEY MESSAGE 1...A weak frontal boundary will linger across the region through Sunday delivering waves of showers and thunderstorms.

A front has stalled in the vicinity of the Potomac River, essentially bisecting Washington DC as of 18Z/2PM EDT.
Subsidence in the wake of an early morning vort along with widespread cloud cover has kept a lid on most things for the moment. However, some filtered sun as well as increasing theta-e along the front later this afternoon into early evening is expected to result in scattered to numerous showers and thunderstorms. PWs increasing to near or over 2 inches coupled with slow storm motions (less than 20 mph) roughly parallel to the front could result in training and localized heavier rainfall amounts of 1 to 3 inches. Should this occur in an hour or two over an urban area, there could be a few flooding issues.
Outside of urban areas, ongoing drought should keep the flood risk very low. Went ahead and issued a small/brief Flood Watch for potential flash flooding in urban areas. It is possible that persistent cloud cover keeps instability just low enough to keep things from coming together, but with potential for a few inches of rain in a short time felt it prudent to have a watch out.

Coverage of any storms should decrease through the evening, but a few showers may linger through the overnight hours. In addition to low clouds, patchy fog may be possible later tonight. Overnight low temperatures will be in the mid 60s to around 70.

Upper ridging will start to build to our west over the Mississippi Valley and Great Lakes on Sunday. This will cause flow to turn northwesterly aloft. A weak shortwave disturbance is expected to dive southeastward from the Great Lakes and approach the area from the northwest. Showers and thunderstorms are forecast to develop once again ahead of this disturbance Sunday afternoon. Coverage of showers and storms should be much higher than Saturday with stronger daytime heating and large scale ascent ahead of the approaching shortwave. Model soundings show largely saturated profiles once again, with PWATs still near 2 inches. However, instability is much greater, at around 1000-2000 J/kg of MLCAPE. With ample instability, high PWATS, and deep warm cloud layers extending up to around 15kft, storms should be capable of producing heavy rainfall. The most recent runs of the HRRR and RRFS show localized maxima of 2-4" scattered about the forecast area. As a result, there could be a threat for flash flooding in urban areas. Outside of the urban areas, the background drought conditions should help to limit the threat for flooding. While flooding looks to be the greater threat, there could also be a low-end threat for damaging winds, with DCAPE values around 600-800 J/kg.

Upper ridging will continue to build in from the west on Monday.
Coverage of storms is expected to be lower on Monday, with most of the activity likely remaining confined to the higher terrain to the west of the Blue Ridge.

KEY MESSAGE 2...Significant heat risk next week heading into the Independence Day holiday.

Increased confidence for a prolonged period of extreme heat and humidity starting Tuesday, June 30th and lasting through the Independence Day July 4th holiday weekend. Synoptically, subtropical high pressure and a building upper-level ridge will allow temperatures and humidity values to climb toward record levels over a multi-day period mid to late next week. Temperatures start to climb Tuesday as the upper-level ridge expands eastward from the Ohio River Valley. Look for highs in the 90s with heat indices running between 95-100 degrees. Wednesday through Sunday will be the peak of the dangerous heat with highs for most in the upper 90s and lower 100s. Heat indices each afternoon will run between 102-108 degrees with a few readings around 110 along the immediate I-95 metro corridor, western shore of the bay/southern MD, and down across the VA Piedmont region. Minimal relief is expected across the mountains with highs in the mid 80s and low 90s and heat indices in the mid to upper 90s as the heat peaks mid to late week. No relief at night either with widespread lows in the upper 60s to mid 70s (upper 70s-80 urban areas) Wednesday through Saturday. With that said, looking at major to extreme heat risk across the region during this period. Heat headlines will likely be needed and evaluated as the event gets closer. More at weather.gov/lwx/heat.

Model guidance (00z, 06z, and 12z) has come into better alignment in regards to temperatures next week with only a few degrees of spread.
On the other side of the spectrum, some uncertainty remains in regards to storm chances given the placement of boundaries and any waves of low pressure that may clear away the heat. The ridge looks to sit just west of the region if not overhead Tuesday before shunting eastward late week into the weekend. This would keep storm chances suppressed across most of the region outside of the mountains Tuesday through Thursday given the lack of any real forcing mechanisms outside the terrain or perhaps bay/river breezes. This changes Thursday through the weekend where storm chances may be amplified given a few pieces of energy pivoting over the top of the upper-level ridge in west to northwest flow.

With excessive heat and humidity there will be plenty of instability to work with. You combine this with any potential ripples of low pressure moving around the ridge or a bay/river breeze to get convective development. This is illustrated by CSU/CIPS/NSSL (15-40 percent probabilities) outlooks along with Google WxNext AI model which suggest the risk for severe weather during the Thursday July 2nd to Saturday July 4th timeframe. Something we'll continue to monitor in subsequent forecast shifts given all the ongoing outdoor activities across the region.

Historically, near record summer heat often ends with widespread strong thunderstorm activity, and latest guidance starts to break down the heat next weekend (July 4) into early next week.

AVIATION /20Z SATURDAY THROUGH THURSDAY/
Mainly VFR outside of TS (chances peak 20Z-00Z). A front bisects DC so winds at the Baltimore terminals and MRB are NE while they remain S at IAD/DCA/CHO. Expect only slow southward progress of this front into the evening, with heavy rain/low VSBY possible in stronger storms.

Patchy fog appears possible overnight, and ceilings could briefly approach IFR near daybreak. Gradual improvement back to VFR ceilings is expected through the day Sunday. Additional showers and thunderstorms may develop Sunday afternoon. Patchy fog and lower ceilings may be possible once again Sunday night.
Winds will be light out of the southwest today, and then light out of the east to northeast on Sunday.

Prevailing VFR conditions are likely Tuesday through Saturday next week. Light southerly winds Tuesday will become southwesterly mid to late week. Spotty thunderstorms may pop up west of MRB Tuesday through Thursday with t-storm development working into the corridor Thursday into the weekend pending the placement of a piece of energy/boundaries pushing through.

MARINE
Winds turn light out of the east to northeast through Sunday.
Showers and thunderstorms are expected on and off over the course of the weekend, with Special Marine Warnings possible especially during the late afternoon and evening hours. Light winds persist Monday with minimal rain/storm chances.

Winds will become more southerly Tuesday before turning southwesterly mid to late week. SCA conditions will be tied to channeling mainly over the Chesapeake Bay Tuesday afternoon and evening and again Wednesday afternoon and evening. This is especially true over the middle and open waters where brief SCA conditions are possible during this time. Sub-SCA conditions return Thursday into the weekend although shower and thunderstorm activity may pick up in the diurnal heating periods due to excessive heat and humidity.

CLIMATE
There is a significant heat risk next week. The numbers below aren't a forecast, but rather a reference for historical context for comparison. Latest forecast: weather.gov/lwx.

================================================================== *** ALL-TIME RECORD HIGHS *** ================================================================== Baltimore 107 (set on Jul 10, 1936)
Washington 106 (set on Jul 20, 1930 + Aug 06, 1918)
Sterling-Dulles Airport 105 (set on Jul 22, 2011)
Baltimore Downtown 108 (set on Jul 07, 2012 + Jul 22, 2011)
Annapolis 106 (set on Aug 06, 1918)
Hagerstown 105 (set on Jul 14, 1954)
Martinsburg 112 (set on Jul 11, 1936)
Charlottesville 107 (set on Sep 07, 1954 + 3 other times)

================================================================== *** ALL-TIME RECORD WARM LOWS *** ================================================================== Baltimore 83 (set on Aug 05, 1930 + 2 other times)
Washington 84 (set on Jul 24, 2011 + 2 other times)
Sterling-Dulles Airport 79 (set on Aug 08, 2007)
Baltimore Downtown 88 (set on Jul 02, 2011 and Jul 10, 1993)
Annapolis 92 (set on Jul 07, 1994)
Hagerstown 86 (set on Jun 15, 1899)
Martinsburg 86 (set on Jul 21, 1930)
Charlottesville 85 (set on Aug 07, 1918)

================================================================== *** JULY MONTHLY RECORD HIGHS *** ================================================================== Baltimore 107 (set on Jul 10, 1936)
Washington 106 (set on Jul 20, 1930)
Sterling-Dulles Airport 105 (set on Jul 22, 2011)
Baltimore Downtown 108 (set on Jul 07, 2012 + Jul 22, 2011)
Annapolis 105 (set on Jul 21, 1930 + Jul 02, 1901)
Hagerstown 105 (set on Jul 14, 1954)
Martinsburg 112 (set on Jul 11, 1936)
Charlottesville 107 (set on Jul 10, 1936 + Jul 20, 1930)

================================================================== *** JULY MONTHLY RECORD WARM LOWS *** ================================================================== Baltimore 83 (set on Jul 21, 1930)
Washington 84 (set on Jul 24, 2011 + 2 other times)
Sterling-Dulles Airport 78 (set on Jul 24, 2010 + Jul 08, 2010)
Baltimore Downtown 88 (set on Jul 22, 2011 + Jul 10, 1993)
Annapolis 92 (set on Jul 07, 1994)
Hagerstown 83 (set on Jul 24, 2010)
Martinsburg 86 (set on Jul 21, 1930)
Charlottesville 84 (set on Jul 22, 1930)

================================================================== *** DAILY RECORD HIGHS | WARM LOWS *** VALID: Jul 01 ================================================================== Baltimore 103 (1901) | 80 (1933 + 1901)
Washington 102 (1901) | 79 (1977)
Sterling-Dulles Airport 96 (2012) | 72 (2017 + 3)
Baltimore Downtown 101 (2012) | 82 (2012)
Annapolis 103 (1901) | 79 (1945 + 1901)
Hagerstown 100 (1901) | 74 (2017 + 1977)
Martinsburg 102 (1933) | 74 (1933)
Charlottesville 101 (2012 + 1945) | 78 (1901)

================================================================== *** DAILY RECORD HIGHS | WARM LOWS *** VALID: Jul 02 ================================================================== Baltimore 103 (1901) | 80 (1901)
Washington 101 (1898) | 79 (2012 + 1872)
Sterling-Dulles Airport 98 (1966) | 75 (2022)
Baltimore Downtown 102 (1966) | 84 (2002)
Annapolis 105 (1901) | 80 (1901)
Hagerstown 100 (1966) | 74 (2018 + 1901)
Martinsburg 102 (1933 + 1931) | 75 (1933 + 1901)
Charlottesville 100 (1954) | 76 (1910)

================================================================== *** DAILY RECORD HIGHS | WARM LOWS *** VALID: Jul 03 ================================================================== Baltimore 104 (1898) | 80 (1898)
Washington 101 (1966 + 2) | 80 (2018)
Sterling-Dulles Airport 103 (1966) | 73 (2018 + 2)
Baltimore Downtown 102 (1997) | 82 (2018 + 1983)
Annapolis 100 (1901) | 84 (1896)
Hagerstown 102 (1966) | 76 (2002)
Martinsburg 102 (1941 + 1911) | 74 (1980)
Charlottesville 100 (1966 + 1954) | 79 (1911)

Period of Record (POR) context...
Area (obs site) Records since ------------------------------------------------------------------ Baltimore (BWI) Jan 1872 Washington (DCA) Jul 1872 Sterling-Dulles Airport (IAD) Jan 1960 Baltimore Downtown (DMH) Jul 1950 Annapolis (NAK) Jan 1894 Hagerstown (HGR) Jan 1899 Martinsburg (MRB) Jan 1891 Charlottesville (CHO) Jan 1893

LWX WATCHES/WARNINGS/ADVISORIES
DC...Flood Watch until 10 PM EDT this evening for DCZ001.
MD...Flood Watch until 10 PM EDT this evening for MDZ013-014-504.
VA...Flood Watch until 10 PM EDT this evening for VAZ053-054.
WV...None.
MARINE...None.