textproduct: Baltimore/Washington

SYNOPSIS

A strong cold front will push through the area this morning. High pressure will build in from the west for Saturday. A dry front should move through Sunday afternoon. High pressure will briefly move overhead Monday, but another moisture starved frontal system will likely cross Tuesday into Wednesday.

NEAR TERM /THROUGH TONIGHT/

The warm front has punched northward through most of the area except the northern Shenandoah Valley and Potomac Highlands. A squall line is crossing the Allegheny Mountains ahead of a potent upper level trough in the Ohio Valley. Even though instability is meager, strong wind fields are driving the organization, with some gusts in excess of 45 mph observed to the west. Some warm advection gusts on the ridges were also exceeding 45 mph with the low level jet overhead. Thus moved up the start time of the High Wind Warning to account for the earlier arrival of these winds.

The squall line may break up a bit as it crosses the mountains but should largely remain semi organized as it crosses the area through 10 AM this morning. Besides the higher elevations, the highest chance to see some localized wind damage appears to be closer to the I-95 corridor where the richest low level moisture will be located. One differentiating factor however will be the low level cloud deck in place, indicative of limited mixing depth for downdrafts to accelerate. Some showers could linger briefly behind the line, but overall a drying trend will follow. Southwest winds will be slightly gusty, but the main frontal surge will push eastward during the midday hours to early afternoon, with a quick ramp-up of westerly winds. This is when the Wind Advisory will go into effect for the lower elevations. There may be a second line of showers which accompany this wind shift which could also aid in bringing down gusty winds. High temperatures in the 40s/50s (perhaps even some 60s) occur early in the day with tumbling temperatures in the afternoon.

Over the mountains, post-frontal upslope precipitation will begin, eventually changing to snow. Gusty snow showers and possibly squalls will be possible during the afternoon, with localized dusting possible immediately in the lee as well due to high Froude numbers (indicating unblocked flow). The favored higher elevations are expected to see generally 2 to 4 inches, and a Winter Weather Advisory remains in effect.

Another punch, or perhaps just extension, to the gusty winds occurs during the late afternoon into early evening as the potent trough axis moves overhead. Guidance was consistent with minimal drop off in winds, especially on the hilltops and ridges. Thus extended all wind headlines until 10 PM.

Winds will diminish the second half of the night as high pressure quickly approaches from the west by daybreak. Overnight lows drop back into the 20s, with teens in the mountains.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/

A progressive zonal flow aloft will bring high pressure overhead by Saturday. Some mid and high level clouds are possible in association with a jet streak aloft. Flow becomes southerly by afternoon, and with stronger warm advection from the southwest, the warmest spots (in the 50s) will likely be the Shenandoah Valley and lower elevations of the Potomac Highlands. That flow continues to increase aloft Saturday night as a trough moves through the Great Lakes and Ohio Valley (with surface low pressure well north in Ontario). The exposed peaks above 4000 ft could approach wind advisory criteria, but most of the area will be beneath an inversion. Lows will be milder in the 30s.

The system to the north will push a cold front through on Sunday. With most of the forcing and moisture to the north, only an increase in cloud cover is expected. There will also be gusty westerly postfrontal winds which most likely fall just shy of advisory criteria in the mountains. Daytime temperatures will remain mild in the mid 40s to mid 50s, but temperatures will drop into the 20s Sunday night due to the post frontal cold and dry advection.

LONG TERM /MONDAY THROUGH THURSDAY/

A relatively benign and seasonal weather pattern looks to set up over the region for the week of Christmas. High pressure builds over the region Monday, followed by a couple of fast moving clippers that pass just north of the area during the middle of the week. While these could bring some rain/snow showers to the Alleghenies, conditions look to be mostly dry elsewhere. The best chance to see a few showers will be Tuesday afternoon, and mostly east of the Blue Ridge. Temperatures moderate through the week, with chilly highs in the 30s to low 40s Monday warming to the 50s Wednesday and for Christmas Day.

AVIATION /07Z FRIDAY THROUGH TUESDAY/

A warm front is punching northward early this morning but has yet to reach CHO and MRB as of 08Z. South of the warm front, some gusty southerly winds are reaching the surface, but with 50 kt at 2000 ft and slight veering, some low level wind shear may still be present. MVFR ceilings have spread across the area. The timing and duration of IFR conditions is much more uncertain, except at CHO and MRB where LIFR is occurring. Intermittent light to moderate rain will continue until a potential squall line crosses the area between 10 and 14Z from west to east. This line will bring brief heavy rain and gusty winds, potentially at least 35 kt. Behind the line, there will be a wind shift to the southwest, low clouds should scour out, and lingering showers gradually end. The primary surge of westerly post frontal winds will arrive during the midday to early afternoon hours, with gusts of 30 to 40 kt common, perhaps locally higher. Guidance shows these winds may linger into the early evening as a potent trough swings through.

Winds diminish late this evening before becoming light overnight. Light southerly winds on Saturday morning pick up quickly during the afternoon, but then become light again overnight. This could lead to some LLWS as a 50 kt low level jet moves atop the surface inversion. VFR conditions continue through Sunday, although a dry cold front will shift winds to the west with gusts up to 30 kt possible.

VFR conditions are likely for the start of next week as high pressure moves over the region. A fast moving clipper could bring some showers Tuesday afternoon, though conditions look to remain VFR with low coverage of convection.

MARINE

Winds have been increasing from south to north this morning with the passage of a warm front. Wind gusts likely stay around 20-30 knots, with a signal for occasionally stronger winds over the wider waters. A squall line will cross the waters between 7 and 10 AM this morning which could bring down some brief 35-45 kt gusts. This will be followed by a relative lull, though SW winds may still reach advisory criteria. A surge of winds arrives early this afternoon, which will likely bring gale- force winds to most of the waters. Highest gusts will be in the Chesapeake Bay north of North Beach MD, and over the upper tidal Potomac River. Gusty winds linger into this evening but will quickly diminish overnight into Saturday morning as high pressure builds over the area.

Small Craft Advisories are possible late Saturday afternoon into Saturday night as the high departs and southerly flow increases. A cold front will then cross on Sunday. At least high-end Small Craft Advisory conditions appear likely within northwesterly flow, with low end gales possible. Winds will gradually slack Sunday night but advisories will likely continue for most waters.

Favorable marine conditions are likely for the start of next week as high pressure moves over the local waters. Light northwest winds Monday become south by Tuesday morning. Southerly channeling could produce SCA conditions for most of the waters Tuesday afternoon.

LWX WATCHES/WARNINGS/ADVISORIES

DC...Wind Advisory from noon today to 10 PM EST this evening for DCZ001. MD...Small Craft Advisory until 6 AM EST early this morning for MDZ008. Gale Warning from 6 AM this morning to 1 AM EST Saturday for MDZ008. Wind Advisory from noon today to 10 PM EST this evening for MDZ003>006-008-011-013-014-503>508. High Wind Warning from 6 AM this morning to 10 PM EST this evening for MDZ501-502-509-510. Winter Weather Advisory from 10 AM this morning to 10 PM EST this evening for MDZ509-510. VA...Wind Advisory from noon today to 10 PM EST this evening for VAZ025>031-036>040-053-054-501-505-506-526. High Wind Warning from 6 AM this morning to 10 PM EST this evening for VAZ503-504-507-508. WV...Wind Advisory from noon today to 10 PM EST this evening for WVZ050>053-055. High Wind Warning from 6 AM this morning to 10 PM EST this evening for WVZ501>506. Winter Weather Advisory from 10 AM this morning to 10 PM EST this evening for WVZ501-503-505. MARINE...Small Craft Advisory until 6 AM EST early this morning for ANZ530>533-535>542. Gale Warning from 6 AM this morning to 1 AM EST Saturday for ANZ530>533-535>542. Wind Advisory from noon today to 10 PM EST this evening for ANZ530. Gale Warning until 1 AM EST Saturday for ANZ534-543.