Marine Weather and Tide Forecast for Frederick, MD

KEY MESSAGES
1) Showers and thunderstorms will accompany a strong frontal system through this evening.

2) Below normal temperatures are expected Thursday through Sunday night, with frost and/or freezing temperatures possible especially west of the Blue Ridge Mountains.

3) Showers remain possible at times early next week as temperatures gradually climb.

DISCUSSION
KEY MESSAGE 1...Showers and thunderstorms will accompany a strong frontal system through this evening.

The current surface analysis differs very little from what was observed 6 hours ago, with a warm front lingering across eaastern WV and down along eastern VA into eastern NC. With very little eastward progression today, showers have very gradually moved across the region as a result. This will continue to hinder our ability to destabilize ahead of the approaching strong cold front. Off to our west, over central/eastern WV, there are a few breaks in the cloudcover, so a little more instability is developing there, with some convection occurring as a result. However, none has grown severe yet.

Looking towards southwestern WV, there are some more breaks in the clouds, with better instability. Maybe this works its way into our western areas later this afternoon/evening. If this does occur, perhaps convection could start to grow stronger than we are seeing currently as the powerful cold front approaches from the west. If we can get into this area of subtle clearing ahead of the frontal passage, perhaps a discrete cell or two could form. The magnitude of deep-layer shear (40 to 50 knots) could make up for lower CAPE, but there still needs to be at least some destabilization compared to what we are seeing now. If we do achieve that, an isolated tornado cannot be ruled out. However, still have this as a very low likelihood scenario, as I am just not condient in the environment being able to rebound before peak heating ends.

On the rainfall side of the equation, a broad axis of 0.50 to 0.75 inches of rain is expected. This should prove to be more beneficial in nature given the longstanding rainfall deficit.

Showers finally exit into the Eastern Shore overnight. Drier conditions ensue along with a shift to northwesterly winds. Low temperatures tonight should fall into the 40s to low 50s, with spotty upper 30s along the Allegheny Front.

KEY MESSAGE 2: Below normal temperatures are expected Thursday through Sunday night, with frost and/or freezing temperatures possible especially west of the Blue Ridge Mountains.

A closed upper low will persist to our north from Thursday into next week. It will gradually retreat northward with time, but some reinforcing troughs will sweep across the eastern US at times. The net effect will be below normal temperatures and occasional shower chances. Unfortunately for the drought, a widespread soaking is not anticipated.

The main hazard through this period will be the potential for frost/freeze conditions, with the greatest threat west of the Blue Ridge Mountains. Thursday night into Friday morning will offer the first opportunity as gusty northwest winds subside after sunset.
While still chilly, clouds may mitigate the threat somewhat Friday night. While Saturday night is forecast to be the coldest of the stretch, elevated northwest winds may limit the frost threat.
However, the higher elevations in particular will likely drop below freezing. The airmass will start to moderate Sunday night into Monday morning. However, residual sub-freezing dew points west of the Blue Ridge could lead to at least a localized frost threat.

Subtle perturbations in the cyclonic flow will result in mainly daytime shower chances Thursday and Friday. This threat may be relegated to the Alleghenies Thursday, with greater coverage expected on Friday. The deepest trough will approach on Saturday, likely leading to an area of low pressure developing along the Carolina coast. Some rain could spread into southeastern portions of the forecast area, but the northwest edge of precipitation shield remains uncertain. At a minimum, clouds will be more prevalent.
Overall precipitation type should be rain, especially considering the highest chances are during the daytime periods. However, can't totally rule out some snow flakes or graupel pellets on the higher ridges on days with convective showers. Surface high pressure will cross the area Sunday with the upper level pattern flattening, leading to the driest day of the forecast.

KEY MESSAGE 3: Showers remain possible at times early next week as temperatures gradually climb.

Shortwave troughs will continue to drive relatively weak frontal systems toward the area next week. Depending on the timing of these systems, there will be shower chances each day. However, these chances may eventually consolidate as timing agreement increases. A few thunderstorms could also be in the mix, although severe weather probabilities appear low. With the main upper level gyre well to the north and surface high pressure setting up off the east coast, there will be a gradual warming trend in temperatures through mid week, reaching near to above normal values.



AVIATION /18Z WEDNESDAY THROUGH MONDAY/
Abundent showers are now being observed for most of the terminals along the warm front. This is resulting in VSBY restrictions intermittently. This is paired with MVFR CIGs that have been around all day, which won't be going away until after the frontal passage later this evening. Could see some gusty winds in showers/storms along the front when it comes through this evening. However, most terminals may be east of the warm front and remain stable enough to mitigate this threat. May have to do some nowcasting later on as the line moves through to truly assess the thunder threat, as well as stronger wind gusts.

Any convective threat winds down by late this evening while winds shift to northwesterly overnight behind the cold front.
VFR conditions return into the night.

For Thursday and Friday, expect mainly VFR conditions. Breezy northwesterlies are likely to start off with afternoon gusts to around 20 to 25 knots. Any shower chances are likely relegated to the Allegheny Front. An upper low to the north will bring a better shot of isolated/scattered showers on Friday. These could support a few brief restrictions and some locally gusty downdraft winds. Otherwise, the overall winds will remain out of the west.

VFR conditions are expected at the terminals this weekend. Winds are forecast to be out of the northwest on Saturday, and then west on Sunday.

MARINE
Small Craft Advisories remain in effect for all waters until early Thursday morning as winds shift to northwesterly behind tonight's cold front. Additionally, this front will pose a risk of some stronger storms which may require some evening Special Marine Warnings. However, that threat is uncertain, as it may be too stable to get stronger winds down to the surface. Such storms push into the Eastern Shore by after midnight. There may be a brief overnight "lull" in winds, falling below SCA criteria for a few hours, but expect those to increase Thursday morning yet again.

Breezy northwesterly winds are expected on Thursday with Small Craft Advisories likely needed through much of the day. Winds begin to decrease into Thursday night as well as Friday with a shift to westerlies. An upper low will aid in some shower development on Friday, many of which will be high based. Some of these could produce locally gusty winds so Marine Weather Statements may be needed at times.

Sub-SCA level northwesterly winds are expected over the waters on Saturday. Westerly gusts may reach low-end SCA levels on Sunday.

TIDES/COASTAL FLOODING
Southeasterly flow continues to keep anomalies elevated at most of the tidal sites. Many locations will reach Action Stage during high tide through tonight, with Minor tidal flooding expected at Annapolis. While it will come close this afternoon as well, it being the lower of the high tide cycles should keep it just below minor flood stage. A few other tidal sites like Alexandria, Dahlgren, and Havre de Grace could get close during the higher of the two astronomical high tides this evening as well. There are no advisories out yet, as there is still at least some uncertainty with the frontal passage maybe coming through just before high tide. Once we are more confident on exact timing of the wind shift, a final decision can be made.

Water levels begin to drop off tonight into Thursday as winds shift to northwesterly.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 7 PM EDT Thursday for ANZ530>543.