textproduct: Baltimore/Washington

SYNOPSIS

A front will sag across the region overnight and stall for several days and into the weekend. Disturbances will move along the front and bring a threat for more showers and thunderstorms each day and into the evening hours.

NEAR TERM /THROUGH WEDNESDAY/

Numerous showers and embedded thunderstorms are moving east across eastern Virginia, the Lower Potomac, southern Maryland, and central Chesapeake Bay. These are the zones that still have 2000 to 3000 J/kg MLCAPE. Over the next few hours, the convection will wane as it moves our over the Delmarva. Otherwise, patchy fog could form across the western half of our region overnight, while some low stratus clouds develop in the east as the convection fades. Low temperatures will drop into the upper 60s over the mountains and into the middle 70s along and east of I-81.

Through the day on Wednesday, a stronger mid-level trough of low pressure will move across the region. Stronger convergence will provide more widespread convection through the middle and latter part of the afternoon and continuing into the evening. Most of the prolonged and heavier activity will be focused along and east of the Blue Ridge. Hence, with this in mind, a Flood Watch for the potential for Flash Flooding has been re-issued. It goes into effect from 2pm Wednesday through Midnight Thursday. Showers and strong to severe thunderstorms that develop from mid-afternoon on will have the potential to produce torrential downpours, damaging winds, lightning, and hail. A tornado can't be ruled out either given the strong mid-level trough, a jet streak moving by to the north, rich humidity, and strong convergence. Rainfall rates could reach 2 inches per hour in areas where the Flood Watch is in effect. Winds could gust over 60 mph too.

SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/

While there is expected to be some strong to severe thunderstorms through mid-evening in the central and eastern zones on Wednesday, much of the convection will once again wane later in the evening and overnight. Highs will be near or slightly above average in the upper 80s to lower 90s.

This scenario of strong convection in the afternoon and early evening, then waning, is expected to repeat itself on Thursday into Thursday evening. The stationary front doesn't appear to have a shove in any one direction out of our region. Highs should reach the upper 80s for the most part on Thursday.

LONG TERM /FRIDAY THROUGH TUESDAY/

Not much change in the extended pattern as there is no real progressive storm system to clean us out of this warm, muggy, and stormy pattern. Temperatures will trend slightly cooler for the end of the workweek and into the weekend given added cloud cover with the stalled front nearby. Pieces of shortwave energy will continue to ride along the stalled boundary as it bisects the area. Current 12z synoptic guidance shows the front stalling somewhere in the vicinity of southwest PA, central MD, and northern VA during the Saturday and Sunday timeframe. With the front nearby expect continued chances for showers and thunderstorms during the afternoon and evening hours. As for severe weather, uncertainty remains given the placement of the front and timing of shortwave energy as it pivots across. Current CSU learning machine guidance, CIPS pattern recognitions, and long range NSSL probs are leaning toward the Saturday and Sunday timeframe as the next potential period for organized convection. Either way thunderstorms will have the potential of producing locally damaging winds and instances of flash flooding each afternoon. This is due largely in part to the stagnant warm and moist airmass hanging tough over the region. Temperatures Friday through the weekend will range from the mid to upper 80s and low 90s. Heat indices will make it feel more like the mid to upper 90s.

Beyond Sunday, uncertainty continues in regards to a potential frontal passage. 12Z synoptic/ensemble guidance show a cold front ejecting out of the Midwest and Ohio River Valley some time Monday into Tuesday next week. This front does not appear to arrive until mid next week leading to a continuation of daily shower and thunderstorm chances until it passes through. Temperatures and precipitation will continue to remain above average within the back half of the long term period.

AVIATION /01Z WEDNESDAY THROUGH SUNDAY/

A shower or two could move across MTN, BWI or CHO over the next 2 hours or so, but terminals look dry for the most part throughout the night. VFR conditions most likely. Should some mist or patchy fog develop overnight, CHO would be more likely to encounter with a minor drop in visibility.

As for the day Wednesday into Wednesday evening, another round of showers and strong thunderstorms are expected to develop along a stalled front with a moderately strong mid-level trough moving along it. The rapid development and movement of strong to possibly severe thunderstorms across the terminals could drop visibility and ceilings into the MVFR category briefly, before VFR conditions return later in the evening and overnight. The development and intensity of such convection could lead to flooding near or at the terminal as well. Otherwise, damaging winds and hail may occur as well. Through the latter half of Wednesday night, patchy fog could form at the terminals.

MARINE

Additional showers and thunderstorms are possible Wednesday afternoon and evening that could prompt more Special Marine Warnings.

Sub-SCA level winds are expected Thursday through the upcoming weekend despite a stalled front nearby. Gradients will remain fairly weak with variable wind directions dictated by the placement of the front. Once again SMWs will be needed at times during the afternoon and evening hours on Thursday given daily convective development.

LWX WATCHES/WARNINGS/ADVISORIES

DC...Flood Watch from Wednesday afternoon through Wednesday evening for DCZ001. MD...Flood Watch from Wednesday afternoon through Wednesday evening for MDZ004>006-008-011-013-014-016>018-503>508. VA...Flood Watch from Wednesday afternoon through Wednesday evening for VAZ036>040-050-051-053>057-501-502-505-506-526-527. WV...None. MARINE...Flood Watch from Wednesday afternoon through Wednesday evening for ANZ530.