Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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502 FXUS61 KPHI 272005 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 405 PM EDT Mon May 27 2024 .SYNOPSIS... A cold front crosses through our region tonight into Tuesday morning. Weak high pressure builds through the region Tuesday. Low pressure passes through Wednesday and Wednesday night. High pressure returns to close out the week. && .NEAR TERM /THROUGH TUESDAY/... The severe thunderstorm watch has been expanded to include all of the region. The watch continues through 9 PM EDT. That should cover the peak of the severe risk period, but may have storms and showers linger a few hours later than that. Starting to see discrete storm development over central PA and central MD now, which is likely the start of our next round of storms (probably won`t be entering our region until closer to 6 PM) We have seen some brief breaks in the clouds, but it hasn`t lasted long enough yet to make a significant impact on low level lapse rates. Temperatures across our region remain in the lower to mid 70s. Thus, the big question remains how much instability and convective inhibition will be in place once the next round of storms arrives. Models are still depicting surface based cape values near 2000 J/kg by this evening, and even up to 1500 J/kg of Downdraft CAPE. One thing that isn`t lacking is wind shear; 0- 6 km Bulk Shear will generally be around 30 to 40 kt, though in the evening, Bulk Shear values will be 20 to 30 kt in the southern Poconos and northern New Jersey before rising to 30 to 40 kt with the approach of the cold front. It does look like an area of 40 to 50 kt of 0-6 km Bulk Shear will pass south of Delmarva. PWATs will be up around 2 inches. Although heavy rain is a threat throughout the region, given the lower shear values across northern areas, there is a higher potential for bands of heavy rain to develop across areas north and west of the Fall Line. In these areas, the Weather Prediction Center has a Slight Risk (2 out of 4) for Excessive Rainfall. The Storm Prediction Center now has the whole region in a Slight Risk (2 out of 5) for severe weather. The strongest storms will be capable of damaging wind gusts and even large hail. There remains a low tornado threat, especially in the vicinity of any outflow boundaries that may develop, but if the instability is elevated, that should help to limit the tornado threat. The bulk of the activity should be well east of the region before midnight tonight, and then the initial cold front will pass through the region in the predawn hours. A secondary cold front will pass through later in the day on Tuesday. Temperature gradient across either front isn`t significant, so temperatures tomorrow may be close to what we are seeing today. However, the big change will be noticed in the humidity. Surface dew points drop from the upper 60s/low 70s on Monday to the upper 50s/low 60s on Tuesday. We should have mostly dry conditions tomorrow, though isolated storms are possible in the southern Poconos as a lagging mid and upper level short wave trough slides just northwest of the region. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... That upper trough will be over the Northeast/Great Lakes/Ohio Valley/Mid-Atlantic for the mid-week period. A short wave trough will dive into the base of the trough Tuesday night, and surface low pressure develops over the Appalachians. This low will the pass through the region on Wednesday and Wednesday night. Showers will become likely along with scattered thunderstorms for most of the area Wednesday. With highs generally in the mid to upper 70s and dew points mainly in the mid to upper 50s, SB CAPE looks to be minimal, generally up around 500 J/kg and highest 0-6 km Bulk Shear values will be 35-45 kt, mainly over southern New Jersey and Delmarva. So while thunderstorms are possible, there does not look to be a widespread severe weather outbreak at this time. Showers taper off Wednesday night as low pressure departs. Another shortwave trough is expected to cross on Thursday, but by then, moisture will be very limited, so only have a slight chance of showers and storms at this time. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... The Long Term period should mostly be dry as surface high pressure builds over the area. Upper trough departs over the weekend and will be replaced by mid- level ridging. Conditions should remain dry into the weekend with the next system approaching early in the new week. Cooler Friday with below normal temperatures, and then temperatures return to normal levels over the weekend. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas... Through Tonight...Expect periods of MVFR and even IFR during the direct impacts of the storms. The prime period for storms looks to be between 22 and 03Z. Conditions improve to VFR thereafter. S winds around 10 kt, become W after 06Z. Moderate confidence on the overall pattern, but low confidence on details. Tuesday...Mostly VFR. Westerly winds 10 to 15 kt. Moderate confidence. Outlook... Wednesday...Sub-VFR conditions Wednesday in SHRA/scattered TSRA. Thursday through Saturday...VFR. && .MARINE... Small Craft Advisory for the NJ ocean waters for this afternoon and the first half of tonight for as winds will increase to 15 to 20 kt with gusts up to 25 kt. For DE ocean waters and DE Bay, S winds will average 15 to 20 kt. Winds turn W around 10 kt late tonight. Thunderstorms will impact the waters with potentially damaging winds and large hail later today and tonight. Outlook... Tuesday through Saturday...Sub-SCA conditions expected through the week. VSBY restrictions in showers and scattered thunderstorms expected on Wednesday. Rip Currents... S to SE winds will increase to 15 to 20 kt with gusts to 25 kt along the NJ coast. This will result in a MODERATE risk for the development of dangerous and life threatening rip currents for NJ beaches. Since winds will be a bit lighter at DE beaches, the rip current risk there remains LOW. For Tuesday, winds will shift to more of a W to SW flow. There will continue to be a MODERATE risk for dangerous rip currents at NJ beaches and a LOW risk at DE beaches. As always, rip currents can still develop, and often occur in the vicinities of jetties and piers. Utilize any guarded beaches this holiday weekend if venturing out into the water. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 1 AM EDT Tuesday for ANZ450>453. && $$ SYNOPSIS...Johnson/MPS NEAR TERM...Johnson/MPS SHORT TERM...Johnson/MPS LONG TERM...Johnson/MPS AVIATION...Johnson/MPS MARINE...Johnson/MPS