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ANZ530 Chesapeake Bay North Of Pooles Island- 935 Am Est Sun Dec 10 2023
.small craft advisory in effect until 6 pm est this evening...
.gale warning in effect from 6 pm est this evening through Monday afternoon...
Rest of today..S winds 10 to 15 kt with gusts to 20 kt. Waves 1 ft. Rain. A slight chance of tstms. Vsby 1 to 3 nm.
Tonight..NW winds 15 to 20 kt. Gusts up to 25 kt... Increasing to 35 kt after midnight. Waves 2 ft. Rain. Vsby 1 to 3 nm.
Mon..NW winds 15 to 20 kt with gusts to 35 kt. Waves 2 ft. Rain. Vsby 1 to 3 nm.
Mon night..W winds 10 to 15 kt with gusts to 20 kt. Waves 1 to 2 ft.
Tue..SW winds 5 to 10 kt. Waves 1 ft.
Tue night..SW winds 5 to 10 kt. Waves 1 ft.
Wed..NW winds 5 to 10 kt. Waves 1 ft.
Thu..W winds 5 to 10 kt. Waves 1 ft.
winds and waves higher and visibilities lower in and near tstms.

ANZ500 935 Am Est Sun Dec 10 2023
Synopsis for the tidal potomac and md portion of the chesapeake bay..
a strong frontal system will impact the waters today into Monday with on and off gale conditions. High pressure will return Tuesday through Thursday next week. A small craft advisory will likely be needed Monday night into early Tuesday morning.

FXUS61 KCTP 101732 AFDCTP

Area Forecast Discussion National Weather Service State College PA 1232 PM EST Sun Dec 10 2023

SYNOPSIS
An early December storm will bring soaking rainfall of 1 to 2 inches followed by elevation driven wet snow accumulation and 30-40 mph northwest wind gusts over the next 24 hours.
Seasonably colder air and locally heavy snow showers downwind of Lake Erie will impact parts of the western and northern Alleghenies through Monday afternoon before shifting into southwest NY Monday night. The weather pattern from Tuesday through Friday will feature seasonal temperatures and high confidence for mainly dry weather across much of the Commonwealth.

NEAR TERM /THROUGH TONIGHT/
Southern stream trough situated over the lower MS Valley at midday will take on a negative tilt over the mid Atlantic by tomorrow morning as it digs through the central Gulf Coast and zips north/east over the Eastern Seaboard tonight into Monday.
Favorable coupled upper jet dynamics/strong diffluence aloft and 100-150m 500mb height falls will spawn an elongate wave of low pressure along slowing sfc front located just east of State College at 17Z. As the low deepens tracking to the northeast, strong CAA behind the front amid a sufficiently moist column will transition rain to snow from west to east this evening and overnight.

Rainfall totals have continued a lower/downward trend (<2 inches) with higher values shifting slight to the east over the last few model runs. Rate of ptype changeover to snow has also increased with colder air arriving sooner with each successive model run. Flood watch continues only for Schuylkill County at this time.

Colder air will pour into the area behind the front tonight accompanying an increasingly gusty NW wind. This will result in a rain to snow transition from west to east across the entire CWA between 00-12Z Monday. There remains some uncertainty with how the interplay between moisture and colder air materializes.
Recent high-resolution guidance favors little to no snow west of the I-99 corridor and more widespread accumulation to the east.

Elevation will be a significant delineating factor for snow accums. Official expected forecast shows at least few inches (borderline advisory) the from the Laurel Highlands into the Endless mtns/western Poconos. The most consistent signal for advisory level snow has been over Sullivan County, where 4"+ appear possible, esp AOA 1800 ft MSL.

We issued a winter wx advisory late this morning for Sullivan, Columbia, and Schuylkill Counties with 1-2" forecast in the valleys and 3-5" in the surrounding higher elevations AOA 1500ft.

It's possible some of the highest terrain over east-central PA picks up a couple inches with a large spread or gradient between ridgetop and valley locations. Snowfall amounts have trended lower over the NW mtns (with weaker ensemble QPF signal for the synoptic snow), but we raised amounts slightly across the eastern part of the forecast area.

Peak wind gusts late tonight into Monday (especially later Monday morning and Monday afternoon as the colder air dramatically deepens and taps stronger winds aloft) are forecast in the 35 to 40 mph range (just under Wind Advisory Criteria).

SHORT TERM /MONDAY THROUGH MONDAY NIGHT/
As winds become northwesterly behind the exiting system, lake effect snow showers are likely on Monday before fading into Monday night. High-resolution guidance indicates the potential for lake effect streams to reach as far southeast as the I-80/I-99 corridor. Sufficient instability could also lead to an increase risk of snow squalls. The Snow Squall Parameter lights up northwest and Central PA downwind of Lake Erie during the day on Monday. Additional accumulation of a dusting to an inch or two is possible with lake effect snow during the day on Monday.

LONG TERM /TUESDAY THROUGH SATURDAY/
High pressure will provide an extended stretch of dry weather through the end of the work week. There does look to be one shot of reinforcement to the cold air Tues PM which could make some SHSN in the nrn mtns. So, while temps will moderate a few degs on Tuesday to maxes of 35-45F, we'll drop back 3-5F on Wed.
Then, temps crawl back up into the 40s for Fri. The next significant chance for precip is Sunday (Day7). GFS and GEFS mean of solutions brew up a Miller Type-A coastal/storm later in the week over the nrn GOMEX and then roll it across FL and up the East Coast. The temps locally will be 5-10F milder than normal for mid-Dec on Sat. That's not conducive to snow except for the higher elevs. ECMWF is not on board with this idea, keeping development in the GOMEX slower/suppressed to the south and east. That results in only a weak nrn stream/Clipper rolling across NY on Sun. CFS also makes development in the GOMEX farther S than the GFS and very similar to the EC in many respects. National Blend brings some increase in PoPs for Sunday, but does not jump on either bandwagon. Obviously, considerable uncertainty remains regarding the precipitation type and track of the low, but the system bears watching over the next week.

AVIATION /18Z SUNDAY THROUGH FRIDAY/
Low pressure lifting north into Eastern PA will spread rain and IFR cigs over most of Central PA this morning. However, latest model soundings indicate a drier westerly flow will bring improving flying conditions across the NW Mtns, with a return to MVFR likely at KBFD by around 15Z. The first wave of low pressure should lift into New England late today, with a drier/colder northwest flow in its wake potentially bringing modest improvement in cigs during the afternoon and evening.
However, a second area of low pressure lifting up the east coast is likely to result in lingering rain changing to snow tonight across the eastern half of the state. Thus, it is worth preparing for a period of snow with IFR vsbys between 06Z-12Z, mainly from KIPT south through KMDT and KLNS.

Outlook...

Mon...Gusty NW winds. AM snow likely W Mtns and Eastern PA.

Tue-Thu...No sig wx expected.

HYDROLOGY
The Flood Watch was trimmed back overnight with the majority of counties removed with only Schuylkill County remaining at this point.

Given the generally dry soil conditions and near to below average streamflows over east-central Pennsylvania, the 1-2" rainfall will be largely beneficial in nature. Total rainfall continues to trend lower (<2 inches) with higher amounts shifting to the east.

We still can't rule out some isolated minor flooding issues given cold season hydrologic conditions. The threat of flash flooding remains very low given modest rainfall rates less than 1 inch per hour owing to lack of instability. Minor urban, poor drainage, and small stream flooding remain a possibility and would be the most likely outcome.

Within-bank rises of a few to several feet will occur on rivers and streams across east central Pennsylvania. Response time will be quicker on small streams (tonight-Monday) and longer on larger main stem points (Tuesday-Wednesday). The latest MARFC guidance now keeps Swatara Creek at Harper Tavern below action or caution stage. No river flooding is forecast at this time.

CLIMATE
It has been 318 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. 318 days ending 12/09/2023

CTP WATCHES/WARNINGS/ADVISORIES
Winter Weather Advisory from 8 PM this evening to 1 PM EST Monday for PAZ042-053-058.
Flood Watch through Monday afternoon for PAZ058.

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Port Deposit
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Sun -- 04:04 AM EST     0.52 feet Low Tide
Sun -- 04:45 AM EST     Moonrise
Sun -- 07:13 AM EST     Sunrise
Sun -- 07:47 AM EST     1.45 feet High Tide
Sun -- 02:48 PM EST     Moonset
Sun -- 02:56 PM EST     -0.39 feet Low Tide
Sun -- 04:40 PM EST     Sunset
Sun -- 08:57 PM EST     2.57 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Port Deposit, Susquehanna River, Maryland, Tide feet

Havre de Grace
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Sun -- 02:24 AM EST     0.03 feet Low Tide
Sun -- 04:45 AM EST     Moonrise
Sun -- 07:13 AM EST     Sunrise
Sun -- 07:51 AM EST     1.41 feet High Tide
Sun -- 01:36 PM EST     0.06 feet Low Tide
Sun -- 02:48 PM EST     Moonset
Sun -- 04:40 PM EST     Sunset
Sun -- 07:44 PM EST     2.28 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Havre de Grace, Susquehanna River, Maryland, Tide feet

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