Marine Weather and Tide Forecast for Lancaster, PA

NEAR TERM /THROUGH TONIGHT/
Aside from some cirrus streaming in across northwest PA, nighttime microphysics imagery depicts clear skies across all of the northeast US. With high pressure now in control, valleys have decoupled into the low 30s across the north and upper 30s across the southeast, with 40s in the more urbanized spots of the Lower Susq Valley. Frost concerns remain limited mainly to the Allegheny Plateau, where the growing season has yet to begin, therefore no Frost/Freeze products were issued for this morning.

Upper level ridging building into PA and the surface high passing off of the East Coast will support fair and warmer weather today. Model RH profiles point to sunny skies and GEFS 2m temp anomalies of +5-8F support highs ranging from the upper 60s over the high terrain of the Alleghenies, to the low 70s most other locations. Fire concerns today will be mitigated somewhat by lighter winds today compared to yesterday along with recent rainfall and green-up across southeastern Pennsylvania. As a result, we've opted for no fire weather headlines this afternoon.

Dry conditions with clear to partly cloudy skies continue into tonight. A freshening southerly breeze will keep temperatures +10 to +20F warmer by daybreak Tuesday compared to this morning.
Cloud cover begins to increase early Tuesday morning ahead of an approaching upper- level trough tracking north of the area, but the entire region should stay rain-free into Tuesday morning.

SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/
An upper-level trough will push through the Great Lakes Tuesday afternoon and bring a warm front/cold front progression through the Commonwealth on Tuesday afternoon. This warm front is expected to lift north of central Pennsylvania Tuesday morning, allowing for much of the area to have some residence time in the warm sector. This is expected to allow for warmer temperatures, especially across western Pennsylvania where there is higher confidence on the warm sector pushing north/east of the region.
Despite these warmer temperatures, cloud cover is expected to limit instability across the western half of the forecast area; however, increasingly diffluent upper level westerly flow and ample shear/veering wind with height, beneath the right entrance region of a mid/upper-level jet will lead to a notable potential for severe weather with a high shear-low to moderate CAPE environment during the afternoon and evening hours Tuesday.

Current storm mode favors multicell with some supercells likely as hodographs take on a broad loop across the NW half of the CWA by late Tuesday afternoon with 0-1KM EHI values from 2-3.5 M2/S2 across the Central and NW Mtns between 20Z Tue-00Z Wed. Main threats at this time for severe weather will be damaging winds in mini bow echoes within short line segments considering strong, westerly 0-3 KM bulk shear of 40-45 KTS, and large hail, especially across northwest PA. Given the potential for some "right movers" creating significantly better storm relative inflow and lowered pressure/LCLs beneath the strong updrafts, there is risk for a few isolated tornadoes across the NW 1/3 or so of Pennsylvania, especially from 22Z-00Z when LCL heights will be lowering and storms interact with llvl outflow boundaries from the initial convection. SPC continues the Enhanced Risk (Level 3 out of 5), which happens about 6 times per year on average across Pennsylvania. Have multiple ways to receive warnings and stay weather aware Tuesday afternoon and evening.

Storms will continue moving eastward late Tuesday afternoon/evening; however, less instability will be in place and shear becomes less favorable, thus severe threat becomes more limited across the Lower Susquehanna Valley. Precipitation exits quickly and becomes more upslope/lake- enhanced rain showers in the wake of the cold front Tuesday night into early Wednesday morning. Storm total rainfall amounts will be generally less than 0.25" southeast of the I-99/I-81 corridor and perhaps exceeding 1" in parts of northwest PA that receive multiple rounds of storms.

LONG TERM /WEDNESDAY THROUGH SUNDAY/
Latest medium range guidance supports warm and dry weather Wednesday, as the cold front stalls out south of the Mason-Dixon Line and high pressure noses into PA from the Grt Lks. However, the boundary will remain close enough to justify low POPs across the southwest part of the forecast area.

Latest EPS and GEFS both track a surface low north of PA Thursday night, with the trailing cold front coming through Friday. Latest ensemble plumes suggest the best chance of showers/tsra will come Thu PM, as the low level jet and plume of highest pwats overrun the arriving warm front. Most likely rainfall Thursday PM into Friday AM based on EPS plumes ranges from near 0.5 inches over the NW Mtns, to 0.10 inches over the Lower Susq Valley. However, locally heavier amounts are likely in the path of any stronger tsra.

Scattered convection is likely to accompany the trailing cold front on Friday, then there is broad model consensus in drier and cooler conditions Friday night into next weekend, as surface high pressure builds in from the Grt Lks. However, diurnal heating combined with passage of the upper trough supports a slight chance of an afternoon shower Saturday.

AVIATION /11Z MONDAY THROUGH FRIDAY/
High pressure across the region will (100% confidence) provide light and variable winds and clear skies through 29/12Z. Winds will be light and variable throughout the entire TAF period, potentially taking on more of a southerly component by the afternoon. High-level clouds will begin to move into western Pennsylvania ahead of showers/thunderstorms Tuesday afternoon; however, ceilings will remain above 25,000ft AGL.

Tue...PM showers and possibly a few thunderstorms with restrictions possible. Brief gusty winds across W PA.

Wed...A few lingering showers across primarily SW PA.

Thu...Showers/t-storms return areawide, restrictions possible.

Fri...Showers with restrictions possible.

CTP WATCHES/WARNINGS/ADVISORIES
None.