textproduct: Baltimore/Washington

SYNOPSIS

High pressure over northern New England will persist through the first part of the upcoming weekend. A cool air wedge will remain entrenched southward along the East Coast into the Mid- Atlantic. An active weather pattern will evolve over the weekend into the middle of next week as multiple areas of strong low pressure and their associated fronts track from the middle Mississippi River Valley to the Northeast.

NEAR TERM /THROUGH TONIGHT/

Unlike last night, there are more breaks in cloud cover across the region. However, multi-hour satellite and observational trends show some uptick in low stratus east of the Blue Ridge into central Virginia and southern Maryland. The most notable change over the past 12 to 24 hour has been a weakening of the elevated subsidence inversion. On the other hand, light winds resulting from high pressure over the Eastern Seaboard has supported decent radiational cooling effects. This has favored the development of radiation inversions, especially over the Shenandoah Valley. Surface observations over this area has seen visibility drop to around 4 to 6 statute miles at times as moisture gets trapped underneath the inversion. Given it is late December, any such radiation inversion will likely not mix out until the mid-morning hours. Thus, some areas of reduced visibility is possible during this mentioned period.

After starting off the day in the upper 20s to mid 30s, temperatures are expected to rebound through the day. Although heights will further build aloft as the mean ridge settles over the eastern U.S., net gains at the surface should be stunted by the residual cloud cover. The forecast currently calls for mostly cloudy skies with high temperatures mainly in the upper 30s to mid 40s. Such readings are fairly close to typical climatological values. Like previous days, winds should stay light given weak gradients around the persistent surface high. Heading into tonight, broad high pressure remains over southern Quebec while extending down the Eastern Seaboard. Models favor some clearing for those east of U.S. 15. As such, a few spots in this zone could drop into the mid 20s, while most stay in the upper 20s to near freezing.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/

Friday will offer a sort of transition as the pattern shifts to being more active in nature. As broad upper ridging slowly pulls toward the western Atlantic, a series of upstream perturbations approach from the west. Within the southwesterly flow, such impulses in the jet will help increase clouds through the day. These should also be an impetus toward some light rain pushing in from the south by near sundown on Friday. Ahead of these rain bands, expect a mix of clouds and sun during the afternoon hours. This comes with forecast highs topping out in the mid/upper 40s, with upper 30s to low 40s across mountain locales.

A soaking rain overspreads the area during the nighttime hours. Forecast lows are mainly in the mid/upper 30s, with a few spots possibly closer to the freezing mark. Thus, there may be some pockets of mixed wintry precipitation at the onset. However, these should be rather localized and brief in nature. Besides the increasing rain chances, some gusty winds overspread the Potomac and Allegheny Highlands as a 925-mb jet pushes through. The latest guidance shows this southerly jet ushering in 30 to 40 knot winds to these higher elevation locations. However, the stable nature of forecast soundings suggests some limitation in turbulent mixing processes.

There is quite a bit of uncertainty in the temperature forecast as noted by the ensemble box-and-whisker plots. Have favored the cooler side of the guidance given the cold air damming (CAD) signature in place. Such a phenomena often hinders daytime warming, particularly in light of the strength of the high to the north. Consequently, forecast highs on Saturday stay in the upper 40s to low 50s, locally pushing into the mid 50s across the Shenandoah Valley and Allegheny mountain valleys. This all comes with passing bands of light rain. Expect an uptick in rainfall intensity by late Saturday as a stronger shortwave approaches from the Tennessee Valley. An increasingly diffluent flow aloft coupled with enhanced moisture transport will support periods of moderate rain overnight. Thick clouds combined with the rain favors rather low diurnal temperature ranges. Forecast lows on Saturday night are in the 40s which is around 10 to 20 degrees above climatology.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

A powerful upper shortwave will swing out of the Mississippi River Valley and into the Ohio Valley on Sunday, taking on a negative tilt. The surface low associated with this system will push into the Great Lakes during this time, with the warm front having lifted well to our north. High temperatures will jump well into the 60s as a result ahead of the approaching cold front attached to this low. Model guidance continues to hone in on an intense line of showers traversing the region as the cold front pushes through. There is even some consensus that there may be enough instability (albeit elevated) to get some thunder as well. Deep-layer shear will be in the neighborhood of 40 to 50 knots, which could raise at least some concern for some gusty winds with the main line of convection. Do think our surface-based instability will be lacking, with most guidance struggling to produce much at all. This could be one of those days where we could see some interesting elevated signatures on radar, but may struggle to get anything to the surface. Will monitor trends in the coming days, especially as we get into the range of the CAMs, to see if there is any trend towards more instability. For now though, thinking this will just be a beneficial rainfall to the region, which has struggle to get consistent precipitation as of late.

Showers may linger into early Monday morning, but conditions should dry out for much of the day as high pressure returns and we take on zonal mid-level flow briefly. Monday likely remains pretty warm, as the cold front that pushed through doesn't bring a significant air mass change into the region.

A train of weak upper-level systems then sets up through the middle of next week, which will bring more unsettled conditions to the region. Temperatures remain in the 50s for most during this time (40s in the mountains).

AVIATION /09Z THURSDAY THROUGH MONDAY/

Mainly VFR conditions are expected today, although there is some hint the lower visibility in central Virginia could sneak into KCHO. Have maintained a period of MVFR visibility at this location until the mid-morning. Otherwise, mostly cloudy skies will fill out the skies, with ceilings around 3,000 to 5,000 feet. Winds remain light under the influence of stout high pressure extending down from southern Quebec.

VFR conditions likely persist into much of Friday before this area of high pressure slowly departs into the western Atlantic. Warm advection rain enters the picture late Friday, while continuing into Saturday. Expect some periods of restrictions, especially on Saturday as a bulk of the rain moves through. Winds shift to southerly as a frontal system approaches from the west. 925-mb winds increase in earnest, but this should be confined to the higher terrain and away from the area terminals.

A more potent line of showers looks to push through on Sunday as a more powerful system impacts the region. Sub-VFR conditions are likely Sunday afternoon/evening as a result. These could linger into early Monday with lingering showers. During this time also, winds will be around 15 to 20 knots out of the S/SSW.

VFR conditions then return for the rest of Monday and Monday night with winds turning out of the WNW.

MARINE

High pressure continues from southern Quebec down along the Eastern Seaboard. Weak gradients with this feature will maintain the extended period of lighter winds for the wintertime months. Southerly warm advection ensues on Saturday which comes with local enhancement owing to channeling effects. Small Craft Advisories may be needed Saturday evening into the night as gusts push to around 20 knots or so.

By Sunday, winds will pick up more substantially out of the south ahead of an approaching cold front. Winds ahead of the front could near SCA criteria, especially over the open waters of the Chesapeake Bay where southerly channeling will occur. Additionally, gusty winds may get enhanced by a line of heavier showers moving through during the afternoon/evening hours which may need to be monitored for an SMW threat.

Winds turn out of the WNW on Monday in the wake of this front, gusting to around 10 to 15 knots. SCAs may be needed, but don't seem particularly likely at this time.

TIDES/COASTAL FLOODING

A potent storm system will move into the Great Lakes region on Sunday, eventually pushing a cold front through the region later Sunday into Monday morning. Gusty southerly winds ahead of this front will lead to a gradual increase in tidal anomalies Saturday into Sunday. Some of the more sensitive areas (primarily Annapolis) could come close to minor flood stage during this time.

Once the front pushes through, tidal anomalies will quickly drop again as winds shift back out of the west-northwest.

LWX WATCHES/WARNINGS/ADVISORIES

DC...None. MD...None. VA...None. WV...None. MARINE...None.