006 FXUS61 KLWX 081933 AFDLWXArea Forecast Discussion National Weather Service Baltimore MD/Washington DC 333 PM EDT Mon Sep 8 2025
.SYNOPSIS... Canadian high pressure will build in from the west today before settling north of the area by the middle of the week. Meanwhile, a wave of low pressure passes offshore around mid- week. A dry cold front will cross the region Thursday, reinforcing below normal temperatures and a continued dry stretch. Canadian high pressure will return for the end of the week into this weekend.
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.NEAR TERM /THROUGH TONIGHT/... Expansive Canadian high pressure at the surface has parked over the Great Lakes into the northeastern U.S. At the same time, a stalled frontal zone stretches from near the Gulf Stream down through northern Florida into the Gulf of America. Combining these synoptic features has allowed for prevailing dry northerly winds over the Mid-Atlantic region.
The lack of moisture is evident in multiple water vapor channels as well as surface observations. After seeing a daily record for lowest precipitable water on the 12Z IAD sounding, very little has changed since then. Early afternoon dew points have fallen into the upper 30s to mid 40s, coupled by temperatures in the upper 60s to low 70s. Given continued late summer surface heating, expect temperatures to rise another few degrees underneath mainly sunny skies. Any cloud cover is restricted to shallow cumulus fields mainly south of U.S. 50.
High pressure maintains its influence on the local weather with a chilly and dry night ahead. A lack of clouds and wind should afford a decent radiational cooling night. Tonight`s low temperatures are forecast to drop into the mid 40s to low 50s, locally in the mid 50s across the urban centers and near the Chesapeake Bay. For portions of the Alleghenies and low-lying areas across the Shenandoah Valley, some low 40s are looking possible as well. Any frost development should be very localized given the marginal temperatures.
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.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... A few changes begin to unfold on Tuesday into Wednesday. A broad elongated upper trough will push eastward from the Mississippi River Valley. Along the southern extension of this trough will be a more defined shortwave that tracks along the mentioned stalled frontal zone. As showers break out near this boundary, southwesterly flow aloft will begin to increase high clouds over areas along and east of I-95. Clouds might be a tad more concentrated over southern Maryland given closer proximity to any such showers. Also expect an uptick in northeasterly winds given the increase in large-scale pressure gradients. Gusts up to 15 to 20 mph are possible during the day, especially closer to the Chesapeake Bay. High temperatures are forecast to push into the low/mid 70s, with mainly 60s over the higher terrain.
As the wave of low pressure traverses the frontal zone, the 12Z high-resolution model suite shows some activity pivoting back toward southern Maryland Tuesday evening into Wednesday morning. The one issue working against showers reaching the ground is the extensive dry air in place. A few models show hints of saturation occurring in the surface to 900-mb layer, but aloft it is very dry (mid-level RH values of 15 to 25 percent).
Overall, expect a milder night given the further increase in high clouds along with prevailing northeasterly onshore flow. For areas east of the Blue Ridge where clouds should be more commonplace, forecast lows will be in the 50s to low 60s. Off to the west, widespread mid/upper 40s are more likely.
Sparse shower chances persist into Wednesday morning along the Chesapeake Bay shores. However, it is more likely that these showers remain over the Eastern Shore and points eastward. Cloud cover remains over areas east of the Blue Ridge, but these will edge eastward in time. Some late day sunshine is possible across the I-95 corridor. High temperatures are forecast to remain in the low/mid 70s (60s in the mountains). Overnight lows drop into the 50s, with some mid/upper 40s possible over the central Shenandoah Valley back into the Potomac Highlands.
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.LONG TERM /THURSDAY THROUGH MONDAY/... High pressure will dominate the weather Thursday through Sunday. Dry conditions and below average temperatures each day and night with highs in the lower 80s and lows in the middle 50s. Winds will be generally north to northeast 5 to 10 mph gusts to 15 mph in the afternoon. There could be a brief shift to easterly winds as low pressure offshore interacts with reinforcing high pressure to the north during the middle of weekend.
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.AVIATION /19Z MONDAY THROUGH SATURDAY/... Canadian high pressure settling over the northeastern U.S. will maintain VFR conditions across all sites. Any patchy fog development is likely to remain west of the terminals. Initial winds should generally stay out of the north before shifting to northeasterly on Tuesday. Gusts up to 10 to 15 knots are possible as gradients tighten, especially during the afternoon hours. Winds return to northerly on Wednesday as the coastal front shifts offshore.
VFR conditions Thursday through Friday night. Winds north to northeast 5 to 10 knots through the period.
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.MARINE... The combination of Canadian high pressure to the north and a stalled frontal zone will aid in enhanced north to northeasterly winds through mid-week. Expect gusts up to around 20 to 25 knots, particularly over the more open waters of the Chesapeake Bay. Small Craft Advisories will remain effect through early Wednesday across vast portions of the Chesapeake Bay into the lower tidal Potomac. This may even persist a bit longer depending on how quickly the synoptic configuration holds. For now, the upper/middle tidal Potomac should see winds just short of advisory criteria.
No marine hazards Thursday through Friday night. Winds north to northeast 5 to 10 knots gusts to 15 knots.
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.TIDES/COASTAL FLOODING... Due to the combination of winds not quite aligned to push water south and out of the Bay, and the recent full moon, tides will be somewhat elevated in the coming days. NE winds during the middle of the week may assist in locking in higher water levels and pushing the water toward the western shore. Annapolis is most likely to reach minor flood stage, but some other locations may be close. The first opportunity for flooding will be Tuesday evening, and then could occasionally be an issue through the end of the week with no real pattern change in sight.
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.LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ532>534-537- 541>543.
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SYNOPSIS...BRO NEAR TERM...BRO SHORT TERM...BRO LONG TERM...KLW AVIATION...BRO/KLW MARINE...BRO/KLW TIDES/COASTAL FLOODING...ADS
NWS lwx Office Area Forecast Discussion