Marine Weather Net

Tidal Potomac from Key Bridge to Indian Head MD Marine Forecast




5 - 10


5 - 10



The Marine Weather Forecast In Detail:
ANZ535 Forecast Issued: 735 AM EDT Sun Sep 22 2019

Today...S Winds 5 Kt. Waves Less Than 1 Ft.
Tonight...S Winds 5 To 10 Kt. Waves 1 Ft.
Mon...Sw Winds 5 To 10 Kt. Waves 1 Ft.
Mon Night...Nw Winds 5 Kt. Waves Less Than 1 Ft. A Chance Of Showers.
Tue...Nw Winds 5 To 10 Kt. Waves 1 Ft.
Tue Night...Nw Winds Around 5 Kt. Waves 1 Ft.
Wed...S Winds Around 5 Kt. Waves 1 Ft.
Thu...Nw Winds 5 Kt. Waves Less Than 1 Ft.
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Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
339am EDT Sunday September 22 2019

High pressure will be situated off Cape Hatteras with mostly dry conditions and above normal temperatures expected. The high will drift further off the southeast coast by Monday as a cold front approaches from the Ohio Valley. In the wake of the frontal passage, high pressure will return to the region once again through the middle of the week.

.NEAR TERM Through Tonight
High pressure analyzed just off Cape Hatteras early this morning. Still have some mid-level clouds crossing the area, mostly east of the Blue Ridge, which has prevented fog development thus far. Patchy fog is evident in the Potomac Highlands/northern Shenandoah Valley/Martinsburg-Hagerstown area where skies have cleared and ground is moist from yesterday's rain.

Any fog should erode soon after sunrise. Still have some mid- level energy passing by atop the ridge across the southeastern US today; this will impact Pennsylvania more than Maryland/Virginia, but have increased afternoon cloud cover in diurnal heating/instability. Have backed off previous precipitation forecast, but wouldn't rule out a sprinkle in the Potomac Highlands.

Temperatures at 850 mb should be 1-2 degrees C warmer today vs yesterday (close to 18C). Since temperatures reached 90 degrees at a number of sites yesterday, today should be another 90 degree day. Forecast will be higher than most ensemble/MOS guidance, perhaps most closely resembling ECMWF.

With high pressure in the western Atlantic and southwest flow across the region tonight, the main forecast point should be the temperatures. Since dewpoints will be in the mid 60s, anticipate a more mild night. Lows in the 60s except around 70 along I-95/western shore of the Bay.

Short Term - Monday Through Tuesday Night
A shortwave/trough axis across the Great Lakes Monday morning will transition toward Quebec by Monday night, sending a cold front toward the area. Guidance has slowed the progression of the front, although there is spread in this evolution. While most of the forcing will remain confined north of the area, believe there will be just enough of a baroclinic zone to support at least scattered showers. Probability of Precipitation forecast kept closer to MAV (GFS), which offers some continuity with previous forecast. Instability meager but present. Opted to keep at least a slight chance of thunder too. Best timing will be late afternoon into early evening (west-east), although this won't be a moisture- fed system.

Once again, went above guidance for high temperatures, as 850 mb temps still at 18C. It should be another 90 degree day, especially east of the mountains. Cold advection and dry air should effectively offer some cooling by Monday night. Stuck with MOS suggestion of mid 50s-mid 60s.

By Tuesday, area back to the same pattern we've been in recently...high pressure and dry conditions. Kept temperatures close to guidance, although suspect these may be too cool once again given dry pattern.

Long Term - Wednesday Through Saturday
The second half of the week and into the weekend will continue the theme of above normal temperatures and dry conditions.

Surface high pressure will slide offshore on Wednesday, leading to dry conditions and developing southerly flow. Temperatures will likely top out in the low 80s for much of the region Wednesday afternoon.

On Thursday, a moisture-starved cold front will make its way across the region, with the possibility of a few showers, but the chances of meaningful precipitation are low. Highs will be in the 80s.

By Friday and Saturday, heigheights will rise again as a very large upper ridge builds over the southeastern United States, with 500mb heigheights forecast 594-596dm over the southeast. This will provide for warm to potentially hot weather and dry conditions. Both 22/00z ECMWF (European Centre for Medium-Range Weather Forecasts) and GFS show 850mb temperatures from 18-20C by Saturday which indicate potential for 90F+ readings, although more conservative blended guidance at this point give mid to upper 80s. Will show near 80F on Friday behind the surface front and near 90F Saturday.

Winds light early this morning, and should become onshore this afternoon. As air heats today and flow becomes south, setup will be favorable for channeling winds tonight. Have issued a Small Craft Advisory tonight on the main channel of the Bay below Sandy Point, including Tangier Sound.

Pressure gradient will increase Monday ahead of a cold front Monday night. Will at least have some flow. It's unclear whether there will be additional SCA. The best chance would come Monday night-Tuesday morning in better mixing behind frontal passage.

Largely sub-SCA (Small Craft Advisory) conditions are expected Wednesday and Thursday as high pressure Wednesday gives way to a weakening frontal boundary crossing the waters Thursday.

Tides / Coastal Flooding
Water levels running around a half foot or less above astronomical normals. No issues expected today. South flow should increase on the Bay tonight. That may lead to increased departures. Guidance suggesting that tides at Annapolis will peak near the minor threshold. Parked tide forecast just under the line, but some ensemble members suggest an Advisory may be required.

NOAA Baltimore MD/Washington DC Office: Watches - Warnings - Advisories
DC...None. MD...None. VA...None. WV...None.
Small Craft Advisory from 10pm this evening to 6am EDT Monday for ANZ532>534-543.