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ANZ530 Chesapeake Bay North Of Pooles Island- 933 Pm Est Fri Dec 8 2023
.gale watch in effect from Sunday evening through Monday afternoon...
Rest of tonight..SE winds 5 kt. Waves less than 1 ft. Patchy fog with vsby 1 to 3 nm.
Sat..S winds around 5 kt. Waves 1 ft. Patchy fog. Vsby 1 to 3 nm.
Sat night..S winds 5 to 10 kt. Waves 1 ft. A chance of showers.
Sun..S winds 15 to 20 kt. Gusts up to 20 kt... Increasing to 30 kt in the afternoon. Waves 1 to 2 ft. Rain.
Sun night..SW winds 20 to 25 kt...becoming nw after midnight. Gusts up to 35 kt. Waves 2 to 3 ft. Rain.
Mon..NW winds 20 to 25 kt with gusts to 35 kt. Waves 2 ft.
Mon night..NW winds 10 to 15 kt with gusts to 25 kt. Waves 1 to 2 ft.
Tue..SW winds 5 to 10 kt. Waves 1 ft.
Wed..W winds 5 to 10 kt. Waves 1 ft.

ANZ500 933 Pm Est Fri Dec 8 2023
Synopsis for the tidal potomac and md portion of the chesapeake bay..
broad high pressure will build across the southeast states through Saturday. A strong frontal system will impact the region Sunday into Sunday night. High pressure will return early next week. Small craft advisories may be needed starting Saturday night into Sunday afternoon, and again Monday night. Gale conditions are likely across all waters Sunday evening into Monday afternoon.

FXUS61 KCTP 090400 AFDCTP

Area Forecast Discussion National Weather Service State College PA 1100 PM EST Fri Dec 8 2023

SYNOPSIS
A surge of warmth into the weekend will precede a strong frontal system that will bring heavy rain, snow and strong wind gusts to central PA. A noticeable change in temperatures is expected by Monday with the return of seasonably colder air and snow showers downwind of Lake Erie. After Monday, the pattern signal for the rest of next week favors seasonal temperatures and little to no precipitation.

NEAR TERM /THROUGH SATURDAY/
Mainly clear skies and a nearly calm wind tonight will set the stage (boundary layer decoupling) for fog/stratus development which could become locally dense in the central and eastern valleys. HRRR signal is quite bullish on this scenario. With fcst low temps dropping to around the freezing mark, will need to watch for icy spots especially bridges and overpasses.
Meanwhile, an active southerly wind over the western mtns will help min temps stay around 40F or +15-20F above normal.

Intervals of clouds and sun to start the second weekend of December 2023. The shallow/colder airmass and llvl inversion that will initially be entrenched to the east of the Alleghenies Saturday morning will be slow to mix out with light east- southeast flow helping to hold high temps in the 40s (still +5-10F above normal). The warmest temps with highs in the mid to upper 50s are expected over the western counties (+15-20F above normal).

SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
*Flood watch issued for east-central PA from Sunday afternoon through Monday afternoon

Precip probs tick higher Saturday afternoon into Saturday evening over the western Alleghenies as strong cold front reaches the Upper Ohio Valley by 00Z Sun. There is good agreement in the front moving slowly across CPA on Sunday as the associated longwave mid/upper trough becomes negatively tilted.

There is increasing confidence in the potential for heavy rain ahead and along the cold front given strong upper jet and GOMEX moisture feed surging pwats to 1+ inches or +2SD above the mean.
Despite the lack of instability, forcing and available moisture should be enough to generate some heavier rainfall rates of ~0.5"/hr and 1"+ per 3 hours, with good model agreement for event total rainfall of 1.00-2.50" across the area.

The heaviest rain (2+ inches) is expected over the eastern portion of the CWA where isolated minor (urban/poor drainage and river) flooding is most likely. We plan to issue a flood watch adjacent to BGM/PHI to highlight the flood risk heading into the weekend.

Colder air will pour into the area behind the front Sunday night behind increasingly gusty NW flow. This will result in a rain to snow transition from west to east across the Alleghenies between 00-12Z Monday. There is still some uncertainty in how this baroclinic zone translates to snowfall amounts as quick cooling catches up to backside of the precip axis. Marginal sfc to BL temps also adds to low confidence especially from the central ridges to the eastern/Susquehanna Valley. Elevation will be a factor with latest forecast showing at least few inches of snow accum across the highest terrain from the Laurel Highlands into the north central mtns and adjacent Endless mtns/western Poconos. Min temps in the 35-40F range will significantly reduce the probability of accumulating snow in the lower to middle Susq Valley.

Peak wind gusts Sunday night into Monday are forecast in the 35 to 45 mph range. As temperatures drop below freezing, there could be a freeze-up risk of water/slush with icy spots possible Monday morning.

Pattern eventually transitions full-send to seasonably cold NW flow with snow showers likely on Monday before fading into Monday night.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
After the deepening surface low lifts northeastward Monday night, high pressure centered over the southeastern US will bring tranquil weather to the Commonwealth for the rest of the week. Prevailing westerly winds will oscillate some through the week as a boundary stalls just north of the area. When the wind exhibits a more northerly component, a few light rain/snow showers could affect the far northern tier of PA. Outside of that very low chance of precipitation, the rest of the area should stay dry with plenty of sunshine.

The sunshine will be a bit deceiving, though. Temperatures will be near average with highs in the middle 30s in the north to middle 40s across the southeast and overnight lows generally be in the 20s. That being said, a breezy westerly wind each day will shave 5 to 10 degrees off of the temperature making it feel more like 10 to 20 degrees in the morning and 25 to 35 degrees in the afternoon.

AVIATION /04Z SATURDAY THROUGH WEDNESDAY/
The primary aviation hazard during the TAF period will likely be the development of fog and low cigs across the eastern airfields, including IPT and especially MDT and LNS. East to southeast flow will advect Atlantic moisture in at the sfc, while a thermal inversion develops in the lowest 1000 ft due to strong warm advection. Between 06Z and 10Z Saturday, fog is expected to develop within the Susquehanna Valley and piedmont region. IFR/LIFR restrictions are very likely (>80%) at MDT and LNS with a slightly lower chance (near 60%) at IPT.

Farther to the west, low cigs are moving into the northern Alleghenies. Latest guidance shows the cigs hovering between 3000 and 3500 ft at BFD, so confidence in MVFR conditions is only moderate through the overnight hours.

The forecast over the eastern airfields is uncertain for the morning on Saturday. If the near sfc saturated layer is deep enough, the early morning fog will lift a bit but moisture trapped beneath the robust inversion would suggest the potential for IFR cigs persisting through about 15-18z before breaking up and/or pushing east out of the area. Given the weak December insolation (and limited mixing), it isn't out of the question that cig restrictions persist through much of the afternoon as well. The HRRR and SREF suggest an 80% chance of IFR cigs at MDT and LNS at 15z Saturday, then dropping to 50% after 18z.

Warm advection will continue into Saturday night. Low level wind shear is possible at all airfields as SW flow at 2000 ft increases to 40+ kts after 00z Sunday. Vsby and cig restrictions are possible once again across the east as Atlantic moisture resides beneath the stout inversion. Rain and lower cigs will then overspread the entire area, mainly after 06z Sunday.

Outlook...

Sun...CFROPA. Widespread reductions in rain/snow. Windy.

Mon...Rain/snow showers poss N/W. Breezy west wind.

Tue-Wed...Mainly dry with VFR conditions.

CLIMATE
It has been 316 days since the last measurable snowfall (>=0.1") at Harrisburg. This ranks as the 3rd longest run on record.

1. 330 days ending 12/13/2020 2. 328 days ending 01/21/2007 3. 316 days ending 12/07/2023

CTP WATCHES/WARNINGS/ADVISORIES
Flood Watch from Sunday afternoon through Monday afternoon for PAZ042-051>053-057>059-065-066.

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Port Deposit
Click for Map
Fri -- 01:53 AM EST     0.61 feet Low Tide
Fri -- 02:35 AM EST     Moonrise
Fri -- 06:18 AM EST     1.76 feet High Tide
Fri -- 07:12 AM EST     Sunrise
Fri -- 01:48 PM EST     -0.13 feet Low Tide
Fri -- 01:55 PM EST     Moonset
Fri -- 04:40 PM EST     Sunset
Fri -- 07:30 PM EST     2.12 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Port Deposit, Susquehanna River, Maryland, Tide feet

Havre de Grace
Click for Map
Fri -- 12:29 AM EST     0.29 feet Low Tide
Fri -- 02:35 AM EST     Moonrise
Fri -- 06:02 AM EST     1.47 feet High Tide
Fri -- 07:12 AM EST     Sunrise
Fri -- 12:05 PM EST     0.12 feet Low Tide
Fri -- 01:55 PM EST     Moonset
Fri -- 04:40 PM EST     Sunset
Fri -- 06:25 PM EST     2.03 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Havre de Grace, Susquehanna River, Maryland, Tide feet

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