J E Taylor Lake, VA Hourly Weather Updates

Key Messages

• 1) Severe thunderstorms and some instances of flash flooding are possible on Sunday.
• 2) Seasonably warm conditions and daily shower and thunderstorm chances are expected through Monday, before another round of storms are possible on Thursday.

Discussion

... KEY MESSAGE 1...Severe thunderstorms and some instances of flash flooding are possible on Sunday.

Some residual convective activity may be ongoing on Sunday morning. This remains to be seen and will be guided by the degree of overnight instability and boundary placement. How the atmosphere recovers through the day should ultimately dictate the degree of severe thunderstorm threat during the core diurnal heating hours. The ingredients are certainly present for a more impactful event if meteorological parameters all come together.

Looking a bit more closely at this event, a broad mid/upper ridge persist across the Four Corners eastward to the southwestern Atlantic. Amplified flow north of this expansive anticyclone will continue to be a conduit to active convection, many in the form of mesoscale convective systems (MCS). As mentioned above, a remnant MCS might still be ongoing early Sunday across the region. While above average heights persist, expect some non-zero height falls to cross the area in response to an approaching shortwave. Within this northwesterly flow aloft, vertical shear is ample for the time of year, generally around 30 to 35 knots. Depending on model choice, mixed-layer CAPE values approach 1,500 to 2,500 J/kg. The combination of these two will easily support a risk of severe weather. While damaging wind gusts are the most likely threat, other severe types loom if storms can remain discrete in nature.

Additionally, a Slight Risk for excessive rainfall continues along much of the Alleghenies eastward along/north of I-66/U.S. 50. Precipitable water values rise markedly, possibly into the 2 to 2.25 inch range. While a single thunderstorm will be capable of torrential downpours, the bigger threat would be for repeat and/or training convection. The latter potential exists which supports the flash flood risk. Although drought continues over much of the region, many areas have seen a one category improvement over the past week. Convection will likely be ongoing into Sunday night with the cold front not passing through until early Monday.

KEY MESSAGE 2...Seasonably warm conditions and daily shower and thunderstorm chances are expected through Monday, before another round of storms are possible on Thursday.

High pressure building across southern Quebec down into New England will favor a mostly quiet day for the area on Saturday. An onshore component to the winds should favor a mix of clouds and sun through the day. Highs will rise into the mid/upper 80s with any shower/thunderstorm chances confined to the Potomac Highlands across the central Shenandoah Valley toward I-64. Recent high-resolution models are showing an MCS racing across the Ohio Valley late Saturday. Some of this could leak across the Alleghenies, but confidence is low given a fairly mixed model signal.

As Sunday`s cold front tracks offshore, upper-level zonal flow bringing drier air from the Great Lakes persists over the Mid- Atlantic through midweek, creating a break in the rain and thunderstorms. While temperatures & dewpoints drop a few degrees by Tuesday in the wake of the front, temperatures should gradually increase again in the latter half of the week as high pressure builds overhead.

Meanwhile, an upper-level trough will begin to form over the Northern Plains and then track across the Great Lakes late in the week, with a strong cold front potentially moving through the Mid- Atlantic between Thursday and Friday. Medium-range algorithms are already highlighting a potential for severe thunderstorms with this system. However, severe probabilities currently vary widely across models, with CSU ML probabilities highlighting only a marginal 5%- 15% probability as of the 12Z model runs while the WxNext2 Mean AI outlook is already showing a 30%-45% probability. Deterministically, the GFS/ECMWF also have not quite aligned on the timing and placement of the trough 7 days out. Should this setup materialize, storms capable of heavy downpours and damaging winds would be possible. As drought conditions continue to improve area-wide, localized flooding becomes more of a concern with any thunderstorms that form in the region. For now, this will be a feature to continue to monitor as the synoptic setup becomes more defined.

Aviation

/01Z SATURDAY THROUGH WEDNESDAY/... VFR conditions are expected for Saturday as high pressure builds over New England into southern Quebec. Any shower chances are likely confined to those west of the Blue Ridge and south of I-66. A decaying MCS could move through late Saturday night, but there is plenty of uncertainty at this point. Sunday presents itself as a much more active weather day which would include some convective-driven restrictions. Ahead of the approaching cold front, southerly winds pick up in strength with afternoon gusts to around 15 to 20 knots. Convection could loom into Sunday night and Monday morning which would support additional sub-VFR conditions. Conditions turn drier for later in the day as the cold front moves off toward the southeast.

Prevailing VFR conditions are anticipated at terminals Tuesday through Wednesday. Light northwest winds shift southerly on Wednesday.

Watches / Warnings / Advisories

/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None.