Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
406 FXUS61 KLWX 100723 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 323 AM EDT Wed Jul 10 2024 .SYNOPSIS... High heat and humidity look to continue through at least Thursday with brief relief later this week. Meanwhile, the remnants of Beryl will pass to the northwest of region with a cold front set to cross the Mid-Atlantic late tonight before stalling along the coast Thursday and Friday. Increased shower and thunderstorm chances can be expected as a result along with locally heavy rainfall. The front slowly washes out for the weekend as weak high pressure builds into the region. && .NEAR TERM /THROUGH TONIGHT/... Excessive heat and humidity continue today along with increased chances for showers and thunderstorms. Convection will be a bit more widespread today given added moisture from Beryl passing to our northwest across PA/NY and an increased southerly flow ahead of an approaching cold front from the Ohio River Valley. The combination of the front, remnants of Beryl to the north, and excessive heat/humidity put us in a favorable setup for widespread thunderstorm development. Current 00z CAM guidance shows mixed layer CAPE values on the order of 1500-2200 j/kg this afternoon and evening. Meanwhile, 0-6 km shear values will sit between 30-35 kts with 0-1 and 0-3 km shear values sitting between 25-30 kts. The slightly higher vertical shear in the lower levels indicates some curvature in the hodographs given the warm front nearby (over western/central PA). With that said, the Storm Prediction Center keeps most of western and central MD as well as northern and central VA in a Marginal (Level 1 out of 5 risk ) for severe weather. The primary threat for thunderstorms today looks to be damaging winds and locally heavy rainfall. An isolated tornado cannot be ruled out especially across western and central MD (near the PA line) although models continue to push this threat further north into northern PA and western NY where the warm front/remnants of Beryl look to reside. As for thunderstorm timing, expect convection to begin to bubble over areas just east of Alleghenies (ahead of the dry slot) early to mid-afternoon before advancing toward the I-81 corridor and Blue Ridge around 20-23z/4-7pm. Beyond this point convection continues east toward the metros between 22-2z/6-9pm. Convection gradually wanes before midnight with any severe threat wrapping up after sunset. Convection looks to be fairly progressive with most of the guidance either forming a line or a combination of multicellular clusters. Even with that said, any thunderstorms that due form will be efficient rain producers given PWAT values upwards of 2.2 inches. Thunderstorms will fuel off of highs in the mid to 90s east of the Alleghenies and heat index values of 100-108 degrees. Heat Advisories have been issued for areas east of Allegheny Front until 8pm this evening. Highest heat indices will be observed east of the Blue Ridge and in particularly across the Baltimore/Washington DC metro area. Current 00z guidance suggest Excessive Heat Warning criteria being met in some of these locations with heat index values as high as 110 degrees. Given the duration of excessive heat and humidity, continue to practice heat safety techniques and find ways to stay cool and hydrated. Limited relief is expected overnight as the front is slow to cross. Lows will range from the low to mid 60s over the Alleghenies where the drier air arrives first to mid and upper 70s east of the Blue Ridge. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... A cold front across the Delmarva early Thursday morning will become a stationary front and possibly retrograde westward into the metro areas of Baltimore and Washington DC late Thursday morning through Thursday afternoon and into early Thursday evening. Strengthening high pressure offshore of the East Coast will enable an onshore flow to help push this front westward. The stationary front could take on a zig-zag appearance across the heart of our CWA during the day Thursday. Shower and thunderstorm chances could increase in coverage and intensity from east to west with respect to this retrograding stationary front. The best chances for showers and thunderstorms will be along and east of I-95 and mainly late in the day Thursday into Thursday night. Although temperatures are still anticipated to be above average and hit 90 degrees or higher over 60% of our CWA, temperatures will be 3 to 5 degrees lower than what they are expected to be on Wednesday. Any thickening in cloud cover and/or shower and thunderstorm coverage could knock our high temperatures lower on Thursday. During the day on Friday into Friday night, additional showers and thunderstorms could develop along the same stationary front. Again, the better chances for this activity will be near and along and east of the I-95 corridor. Additional activity could develop farther west to the Blue Ridge, but may be short-lived or limited. High temperatures should be cooler with highs reaching the middle 80s in most places on Friday. High pressure to the northwest will eventually try to push this front to the east as a weak low pressure system develops along it later Friday night into early Saturday. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Excessive heat and humidity make a return this weekend into early next week. Slightly drier conditions are expected Saturday and Sunday with daily shower and thunderstorm chances early next week. Weak high pressure over the eastern Great Lakes will gradually build south into the Mid-Atlantic Saturday into Sunday. This will nudge our stalled frontal boundary back closer to the coast while decreasing shower and thunderstorm chances across the region. Low end Pops will remain mainly east of I-95 where the washed out front resides and over the terrain due to orographic lift during the peak heating period. Thunderstorm chances continue to drop on Sunday under light west to southwest flow. Forcing will also be less along with low level moisture with weak high pressure remaining nearby. High temperatures Saturday will sit in the upper 80s and low 90s east of the Alleghenies. By Sunday, expect high temperatures back in the mid to upper 90s east of the Blue Ridge. Heat indices will head back over the 100 degree mark during this time as well. Much of the same can be expected Monday into Tuesday as weak high pressure slides offshore and southwest flow builds moisture back into the region. This will renew diurnally driven shower and thunderstorm chances especially across the terrain. The coverage of storms will remain isolated to scattered with the greatest uptick coming Tuesday and Wednesday as an upper level trough/front swing into the region. High temperatures will remain in the mid to upper 90s east of the Alleghenies each afternoon with heat indices around 100 degrees. && .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... A cold front approaches the area from the west later this afternoon and into the late evening hours. Southerly gusts increase during the late morning through the daylight hours, potentially gusting 20-25 kt at times. The main opportunity for thunderstorms will come during the late afternoon into the evening, with current guidance suggesting a timing window of 2-6 pm for storm initiation west of KMRB/KSHD and 6pm until midnight or 1 AM in the metro areas (KIAD, KDCA,and KBWI). Storms may be weakening by that time, but could still take the form of a line or broken line. This system eventually stalls off to the east before retrograding back to the Chesapeake Bay late Thursday. Prevailing winds on Thursday should be out of the west before becoming more variable with return of the front. MVFR conditions possible Thursday night and again during the day Friday into Friday evening due to showers and thunderstorms along a stationary boundary. The MTN, BWI and DCA terminals appear to have the better opportunity of encountering MVFR conditions. Prevailing VFR conditions are expected this weekend into early next week as weak high pressure builds back into the region. Winds will turn toward the west Saturday before switching back to the southwest Sunday into early next week. A few thunderstorms cannot be ruled out at terminals along and west of the Blue rIdge although coverage should be fairly sparse. High probabilities for thunderstorm activity return to the forecast early to mid next week. && .MARINE... Small Craft Advisories remain in effect for later this afternoon and early evening due to continued southerly channeling. All waters are included in this advisory for gusts up to 30 kts. These advisories may need to be extended into late tonight given the progression of a front across the region. Showers and thunderstorms will accompany the front prompting the potential need for Special Marine Warnings later this afternoon and evening. The front will stall toward the coastal Delmarva Thursday as winds shift toward more of a westerly direction. Conditions will remain dry with an outside chance of an isolated shower or thunderstorm. A brief period of SCA level winds can be expected late in the evening and overnight hours Thursday as the front wavers back across the area. Additional showers and thunderstorms look to accompany this front as moisture increases once again Friday. Cannot completely rule out an SMW if any strong thunderstorms approaching the marine zones. Thunderstorm chances drop off this weekend as weak high pressure builds into the region. Sub-SCA level winds expected during this time. && .TIDES/COASTAL FLOODING... Tides at Annapolis could reach Minor Flood later this evening into the overnight. Elsewhere, Havre de Grace and Baltimore area tides will see Action Stage and will be monitored for any possible push to Minor Stage. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory from noon today to 8 PM EDT this evening for DCZ001. MD...Small Craft Advisory from 10 AM this morning to 6 PM EDT this evening for MDZ008. Heat Advisory from noon today to 8 PM EDT this evening for MDZ003>006-008-011-013-014-016>018-502>508. VA...Heat Advisory from noon today to 8 PM EDT this evening for VAZ026>031-037>040-050-051-053>057-501-502-505-506-526- 527. WV...Heat Advisory from noon today to 8 PM EDT this evening for WVZ050>053-055-502-504. MARINE...Small Craft Advisory from 10 AM this morning to 6 PM EDT this evening for ANZ530-535-536-538. Heat Advisory from noon today to 8 PM EDT this evening for ANZ530. Small Craft Advisory until 6 PM EDT this evening for ANZ531>534-537-539>543. && $$ SYNOPSIS...EST NEAR TERM...EST SHORT TERM...KLW LONG TERM...EST AVIATION...KLW/EST/ADS MARINE...KLW/EST TIDES/COASTAL FLOODING...KLW