Marine Weather and Tide Forecast for North Chevy Chase, MD

KEY MESSAGES
- (1) Above average temperatures continue today before a cold front crosses overnight into Sunday morning.

- (2) Notably cooler Monday with widespread frost/freeze concerns Monday night.

DISCUSSION
KEY MESSAGE 1...Above average temperatures continue today before a cold front crosses overnight into Sunday morning.

UL trof and corresponding sfc cldfrnt will approach during daylight hrs before crossing over Mid-Atl tonight into Sun morn. Not the best overlapping synoptic setup with sfc cldfrnt being displaced from UL trof. There is a decent signal for intermittent SHRA Sat aft (west of I-81) to as late as Sun aft (east of I-95). Cannot rule out a few t-storms this aft into eve west of I-81. SPC does have a MRGL (west of I-81 generally)
or even SLIGHT risk (far wrn MD). Main concern is gusty winds given steep LLLR. Areas further east are more stable given onshore flow and cooler waters, lowering thunder chances.
Guidance continues to show some elevated instability early Sun morn resulting in localized pockets of RA. Still favoring a gusty line of SHRA with the front itself late Sat night into Sun morn with notable wind shift from S/SE to W/NW.

Once precip moves out, NW CAA will bring breezy conditions Sunday aft/eve. High temps on Sun may be reached early in the day, and are expected to be 15 to 25 degrees cooler than Sat - a stark contrast to the recent spell of record heat.

Depending on how much rain falls and how quickly humidity drops, a fire wx threat could develop mainly west of the Blue Ridge and Catoctin Mountains by late Sun aft. See the Fire Wx section below.

KEY MESSAGE 2...Notably cooler Monday with widespread frost/freeze concerns Monday night.

Sfc high pressure will build over the Mid-Atl early next week with dry conditions expected. A pressure gradient between sfc high overhead and a departing cldfrnt front and associated waves of low pressure will lead to gusty NW winds blowing 10 to 15 mph with gusts between 20 and 30 mph expected Mon. Despite some rainfall expected over the weekend, persistent moderate to severe drought, gusty winds, and dry conditions (lower RH) will allow for fuels to dry out early next week. Confidence is highest across central VA.

Highs on Mon in the 50s to low 60s (40s mtns). Frost/freeze concerns return Mon night as low temps drop into the 20s and 30s.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
Brief low-end MVFR to perhaps very brief high-end IFR CIGs near KMTN should lift thru 14-15Z.

VFR conditions prevail through this aft. Probs for rain increase after 00Z Sun near KMRB, 03Z near KCHO, and by 06Z for the metro TAF sites. Thunder probs are highest west of the metros Sat evening. Some LLWS is also possible Sat eve, mainly near the metros.

FROPA will likely be accompanied by an abrupt wind shift and wind gusts of 25-35 kts 06Z-12Z Sun. SHRA likely lingers into Sun aft. VFR conditions are expected Mon-Tue as high pressure builds over the area leading to dry conditions across the terminals. NW winds gust 15 to 20 kts Mon aft before diminishing overnight. Wind shift to southerly on Tue, blowing 5 to 10 kts with gusts up to 15 kts expected.

MARINE
An increase in S/SE flow is likely today, especially this aft, so have issued SCAs that go through Sun eve for the waters. The central and northern Potomac and Bay drop out tonight when the winds are expected to be lower. This aft/eve is due to favorable channeling and an increasing background gradient/wind field.
After a brief lull over most of the waters (except near southern MD) late Sat night, winds will shift to the NW and quickly become gusty as a strong cold front crosses early Sun morning.
Gale-force gusts are quite possible with 30-40 kts in the mixed- layer amid cold advection and strong pressure rises. However, the most favorable window for gusts may be brief (less than 3 hours, i.e. in the SMW vs. GLW realm). Therefore, have the SCA going through Sun eve with anticipation of SMW along FROPA.

It will be breezy nonetheless Sun into Sun night, likely right on into early next week. SCAs are likely on Mon as NW winds gust up to 20 knots in the wake of the cold front. Winds shift to S and diminish to below SCA criteria overnight through Tue morn.

Winds may briefly reach low-end SCA levels within channeled S'ly flow Tue night. Sub-SCA level W'ly winds are forecast for Wed.

FIRE WEATHER
Elevated fire weather conditions may persist through today due to above normal temps, low RHs and no wetting rain. However, RH will be more marginal with minRH values in the 30s generally limited in area to the Shenandoah Valley into VA piedmont through this afternoon.

Sunday...While some rain is expected late this evening into Sunday morning, amounts of a tenth to two tenths will not be sufficient to wet fuels significantly. It should be noted some hi-res guidance does have localized amounts near a half an inch, but pinpointing those amounts this far out is very difficult. Furthermore, strong gusty winds of 35 mph with potential for gusts as high as 45 mph will create renewed fire weather concerns despite marginal humidities and the overall light rainfall. Given the short duration of precipitation, the 100-hour fuel moisture values aren't likely to rise much at all, if anything; while the 10-hour fuel moisture likely rises considerably, but drops quickly through the day due to the drying effects of strong winds and rapidly lowering humidity.

Rest of next week...Much cooler temperatures are expected Monday and Tuesday with a moderating trend in temperatures expected during the middle and second half of the week.
Strongest winds look to be on Monday out of the northwest with gusts to 25 mph (30 mph over ridges). For the rest of the week, winds will be on light side thanks to high pressure overhead, but humidities will be marginally low to near critical levels. A dry pattern seems likely to continue with little to no rainfall.

TIDES/COASTAL FLOODING
SE flow will cause tides to rise to around or a little over one foot above normal later today into tonight ahead of a cldfrnt.
Minor tidal flooding is possible at many sites especially for the waters around central to southern MD, with near moderate flooding possible in a high-end scenario at Annapolis, though a wind shift to the northwest right around high tide should prevent that.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Coastal Flood Advisory from 3 AM to 10 AM EDT Sunday for MDZ014.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 2 PM this afternoon to 8 PM EDT this evening for ANZ530>533-535-536-538>542.
Small Craft Advisory from 6 AM to 6 PM EDT Sunday for ANZ530>533-535-536-538>542.
Small Craft Advisory from 2 PM this afternoon to 6 PM EDT Sunday for ANZ534-537-543.