Marine Weather and Tide Forecast for Harrisburg, PA

KEY MESSAGES
1) Summerlike warmth visits the region this week with near-record daily maxes and daily mins on tap for Wednesday and Thursday.

2) Several periods of showers and thunderstorms expected during the upcoming week, with the greatest amount of rainfall likely occurring across northern and western PA. Some storms may be severe, particularly on Wednesday.

DISCUSSION
KEY MESSAGE 1: Summerlike warmth visits the region this week with near-record daily maxes and daily mins on tap for Wednesday and Thursday.

Ensemble prediction systems are in good agreement showing a mean upper-level trough across the western CONUS, with downstream upper ridging taking hold from the Gulf states up the eastern seaboard. This will bring a notable warming trend, with daily highs ranging from the 70s-mid 80s across central PA from today onward.

The latest forecast brings near-record temperatures across the region Wednesday morning through Friday morning, with lows both Wednesday and Thursday morning forecast to be warmer than our average highs this time of year (25 to 30 deg F above normal).

Highs in the 70s and 80s will accompany lows in the 50s and 60s. Dewpoints will start to approach the 60F mark, so it will feel a bit humid but not overly uncomfortable.

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KEY MESSAGE 2: Several periods of showers and thunderstorms expected during the upcoming week, with the greatest amount of rainfall likely occurring across northern and western PA. Some storms may be severe, particularly on Wednesday.

In general for the workweek ahead, the storm track will run from SW to NE across the Great Lakes, with several waves of low pressure drifting into Ontario, CA. A frontal boundary will set up generally west to east across New York and keep unsettled weather in place across northwest PA in particular.

This afternoon and evening, a few clusters of thunderstorms could tap into 500-1000 J/kg of MLCAPE to produce isolated pockets of damaging wind gusts. A lack of upper level forcing over Central PA means we will be dependent on surface-based organization associated with a potential MCS to produce a significant/sustained wind threat. The SPC issued an MCD around 2PM for a developing MCS over northeast Ohio. That complex will make its way into Central PA between 5 and 8PM, which is the most likely window for severe weather.

The severe weather outlook climbs to Slight Risk for Wednesday, fueled in part by increasing low level heat and humidity as dewpoints rise to near 60F. Cool temps aloft will result in steep lapse rates with SBCAPE progged above 1000J/kg across much of central PA. With about 30 kts of 0-6 km bulk shear, discrete cells and clusters/linear segments will be possible.

Over the course of the workweek, the probability for showers/storms will be highest in northwest PA. Locations that have been wet lately will continue to see more rain with 1-2 inches expected by Friday, while drought-stricken locations across the southeast part of our CWA will see less rainfall.

AVIATION /18Z TUESDAY THROUGH SUNDAY/
Showers and thunderstorms earlier have diminished; however, increasing chances for showers and thunderstorms across the area in the near term (mainly through 03-04Z Wednesday) with the remnants of an MCS approaching from the west. Airfields under the gun for thunderstorms at this time mainly look to be BFD/JST and potentially AOO/UNV/IPT; however, highest odds for the airfields closest to NW PA. Timing has been been brought in to encompass tighter timing windows compared to previous TAF packages; however, there does remain some uncertainty with respect to coverage/timing. A secondary wave of showers and thunderstorms will be expected overnight (~08-13Z Wed); however, coverage on this looks more limited so have kept mentions to BFD/JST based on recent RAP/HRRR/NBM model guidance. Slightly lower confidence in any lingering elevated instability so have no mentions of TSRA, but not totally out of the question some TSRA at BFD/JST for this secondary timeframe.

Lowest ceilings look to be just above MVFR thresholds across all airfields outside of BFD, where more low-level moisture in recent RAP soundings outline the potential for MVFR-to-IFE ceilings overnight. Previous forecast also had these mentions and main changes came with respect to timing of low-level deck onset. After sunrise, all model guidance points towards VFR conditions area wide with a scattered low-to-mid level deck across the region. Scattered showers and thunderstorms will be on the docket for tomorrow as well; however, most mentions will not be coming until after 18Z Wed so no mentions towards the end of this TAF package at this juncture.

Outlook...

Thu...VFR most of the time, but brief restrictions possible in hit and miss showers and thunderstorms, mainly across the north and west.

Fri...Restrictions possible early, then improving to VFR in the afternoon.

Sat-Sun...Restrictions in SHRA possible.

CLIMATE
Record high daily maxes and mins are possible this week as summerlike warmth visits the region. Here's a look at the records as they stand right now, with a * indicating that the forecast is equal to or greater than the record.

Record High Daily Max / Daily Min...

For Harrisburg: April 15: 87* (1941) / 61* (2023)
April 16: 89 (2002) / 63* (1941)
April 17: 91 (2002) / 60* (2002)

For Williamsport: April 15: 86 (1994) / 57* (2023)
April 16: 90 (2002) / 55* (2023)
April 17: 91 (2002) / 58* (1896)

CTP WATCHES/WARNINGS/ADVISORIES
None.