Marine Weather and Tide Forecast for Indian Head, MD

KEY MESSAGES
- 1) Confidence remains low in regards to the track of an area of low pressure and precipitation type Sunday into early next week.

- 2) Upslope wintry precipitation is expected along the Alleghenies in the wake of a cold front through Thursday, with relatively milder weather elsewhere through Saturday.

DISCUSSION
KEY MESSAGE 1...Confidence remains low in regards to the track of an area of low pressure and precipitation type Sunday into early next week.

Plenty of uncertainty remains amongst the deterministic/ensemble guidance given the placement and strength (or even existence) of high pressure to the north/east, as well as a southern stream low pressure likely to pass in the vicinity of or just south of the region. The placement of the high will determine how much cold air remains trapped along and east of the mountains. For instance, the 12Z UKMET/GDPS have a moderately strong high pressure over the NY/VT border, while the GFS/ICON/ECMWF have a weaker high over eastern Quebec. Meanwhile, each of these solutions have low pressure over the Mid-South Sunday pushing east into the central and southern Appalachians Sunday afternoon/evening (but with residual timing and track differences). The GDPS still remains the outlier with cutting the low toward the Delmarva coast Sunday night into Monday while the GFS, UKMET, ICON, and ECMWF take the low off the VA/NC coast. These varying differences in low pressure track and placement of the high to the north will ultimately dictate the difference between accumulating snowfall or flooding rainfall (or only light precipitation).

Moderate to large uncertainty is noted in ensemble spread due to two main factors: (1) the ultimate track, strength, and timing of the southern stream low, and (2) the track, strength, and speed of a TPV/cold upper low near New England and whether or not it leaves a cold high pressure favorably placed in its wake.

Based upon the model discussion above, the trend amongst the guidance appears to be wet over wintry given marginal temperatures at the surface/aloft and track of low pressure just to the south.
The GDPS still remains the outlier, especially in favored climo zones west of the Blue Ridge, but has been notably the most consistent single model over the last few days; it also has some ensemble support to some degree from the EPS/AIFS and even the GEFS (in addition to its own ensemble/GEPS). The probabilities for 2" of snow remain between 15 to 25 percent generally for higher elevations near/west of the Blue Ridge into northern MD, with similar probs for 0.01" of ice. The probabilities of 1" of liquid QPF per the latest NBM remain between 25 to 30 percent along the MD/PA border to 35 to 45 percent across the central VA Piedmont/southern MD.

6z/12z guidance is relatively solid on timing with a focus on the Sunday into Sunday night timeframe for any potential impacts. There still remains a non-zero threat for winter weather mainly west of the Blue Ridge. Areas further east will likely see rain for most of the day Sunday with some snow maybe mixing in Sunday night into Monday as colder air rushes in. The uncertainty remains in what impact this will cause given significant thermodynamic struggles with a retreating marginally cold airmass. High temperatures Sunday will range from the mid 30s to low 40s across the area with overnight lows at or just above freezing, though as expected spread in forecast temperatures is large during this time period. Highs Monday should warm back into the upper 30s and mid 40s as the system pulls away.

Pending the outcome of the track of the low pressure system, intensity, and overall QPF amounts, flooding could be an issue.
This is largely due to residual snow/sleet pack, especially along and north of I-66/US-50. In addition to this, ice jams in area rivers, streams, and creeks combined with excess runoff from melting snowfall and any weekend rain could exacerbate the flood concern. Keep checking the discussion in the coming days to see how things evolve with this forecast.

KEY MESSAGE 2...Upslope wintry precipitation is expected along the Alleghenies in the wake of a cold front through Thursday, with relatively milder weather elsewhere through Saturday.

In the wake of a cold front exiting the region, surface high pressure builds over the region through the end of the week.
While this yields mild and dry conditions for most of the area, gusty northwest winds will bring upslope wintry precipitation to the Alleghenies.

Periods of snow showers are likely through Thursday near and west of the Allegheny Front through Thursday. The source region (Lake Erie) is mostly frozen over, so moisture may be a bit limited. Also, although amounts around 3 or even 4 inches are possible, this will likely be limited and localized to ridges above 2500 feet and spread over a 24 to 36 hour period. Have issued a Special Weather Statement in lieu of a Winter Weather Advisory for this reason. Also, some downslope enhancement to the wind is possible (along with a bit of spillover) into the foothills through this evening with gusts around 45 mph possible at times.

Temperatures cool through Thursday with high temperatures in the 30s and 40s (20s mtns). As high pressure builds overhead through Friday, winds diminish later in the week and temperatures begin to moderate.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/
VFR conditions continue across the terminals through Saturday.
Surface high pressure will build over the area through Thursday before sliding north and east Saturday. Expect gusty winds through Thursday as a cold front departs east and pressures rise with the building surface high. Northwesterly winds will gust 20 to 30 kts into this evening with 15 to 25 kts gusts likely overnight into Thursday. Winds will slowly diminish Thursday night into Friday with gusts around 15 to 20 kts at times.

Sub-VFR conditions look to return to the area late Saturday into Sunday as an area of low pressure passes south of the region. This storm system will bring increased cloud cover and precipitation chances to the region. Rain and some wintry precipitation is possible mainly north and west of the metro corridor terminals Sunday into Monday morning. Confidence remains low for substantial wintry precipitation (i.e. 2+ inches of snow) with 15 to 25 percent probs focused toward HGR/MRB compared to IAD.
Once again, this is subject to change based upon the availability of cold air and track of low pressure. The storm system pulls out of the area Monday with conditions briefly improving Tuesday before another system by the middle of next week.

MARINE
Small Craft Advisories will continue over the waters through Thursday due to gusty northwest winds in the wake of a departing cold front. SCAs may need to be extended for portions of the waters into Thursday night. Winds will gradually diminish Friday into early Saturday. Additional Small Craft Advisories may be needed this weekend into early next week as low pressure passes to the south. Winds will turn westerly Saturday before switching to the east and northeast Sunday into Monday.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 4 PM EST Thursday for ANZ530>543.