Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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944 FXUS61 KPHI 222142 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 442 PM EST Mon Jan 22 2018 .SYNOPSIS... Low pressure located in Iowa this afternoon will progress to the northeast and it should reach the Saint Lawrence River Valley and northern New England late on Tuesday. The low is forecast to pull a cold front through eastern Pennsylvania, northeastern Maryland, Delaware and New Jersey on Tuesday afternoon. High pressure is expected to build into our region from the west during the balance of the work week. The high is anticipated to move out to sea on Saturday with a cold front following in its wake on Sunday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 345 PM...Low pressure currently situated near Iowa with a warm front extending east across the area. As a result, quite a spread in temperatures with temps currently in the 60s over much of the Delmarva but only around 40 across the southern Poconos where there are currently a few showers north of the front. Heading into tonight, the aformentioned low heads north and east toward the Great Lakes with mild temps persisting as the area will be in the warm sector. Any showers across the north lift out of the area this evening but areas of mist and fog will be possible across the Poconos tonight in association with the warm front. Elsewhere, breaks in the cloud cover persist farther south through this evening with dry conditions. However overnight, clouds thicken up as showers in association with the low approach from the west and also expect coastal fog to develop due to the warm, moist air flowing north over the relatively colder ocean waters. Expect these showers to arrive west to east beginning in the predawn hours with even a few rumbles of thunder possible as there will be elevated instability. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Low pressure will track well to our north and west through the day Tuesday moving from Michigan across Ontario into Quebec by late day. This will drag a cold front with associated showers across the area. To begin the day, the low will be around Michigan with showers ahead of the system`s cold front quickly overspreading the area by 12z. These showers persist through the morning and concern is that forecast models, especially the NAM, are depicting several hundred J/KG of elevated CAPE so at least a few thunderstorms look like a good bet. Also, worth noting, mid level lapse rates will be fairly steep (near 7 C/km) with a very strong LLJ ahead of the cold front...around 60 knots at 925 mb. For these reasons, we have concerns that any thunderstorms or heavier showers could mix locally damaging winds down to the surface...especially over SE PA, southern NJ, and the Delmarva where the instability will be the greatest. In fact the Storm Prediction Center has placed these areas in a marginal risk for severe storms. The limiting factor will be that the low levels will be fairly stable so confidence of severe weather is not high. The most likely window for this occur looks to be mid morning through early afternoon after which time the cold front will clear the area with showers ending. Also, worth noting, PWATs will be 1.0 to 1.25 inches so heavy rain and local poor drainage flooding may also be a concern. Highs Tuesday range from near 50 across the southern Poconos to the upper 50s to mid 60s across SE PA, southern NJ, and the Delmarva. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... Surface low pressure is forecast to be located in Maine on Tuesday evening. The system is expected to strengthen as it moves across Atlantic Canada on Tuesday night and Wednesday. The gradient between the departing low and high pressure building into our region from the west should result in brisk conditions developing for Wednesday. A west northwest wind around 10 to 20 MPH is anticipated at that time. Surface high pressure should move from the south central states on Wednesday to the Carolinas and Virginia late on Thursday. The center of the high is anticipated to slide over the western North Atlantic on Friday and Saturday. The air mass is forecast to bring dry weather conditions for the period from Wednesday into Saturday. Temperatures are expected to be seasonable on Wednesday and Thursday with a warming trend as we head toward and into the weekend. Low pressure and a cold front are forecast to approach from the west over the weekend. There is a spread in the guidance solutions regarding the timing of the arrival of the cold front in our region. We will carry a chance of showers for Sunday and Monday. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Conditions will deteriorate during this period on multiple fronts. Low-level (southwesterly) wind shear is a concern after 00Z as a strong low-level jet develops. CIGs will lower through the evening hours, becoming MVFR at most terminals between 09Z and 10Z and IFR shortly thereafter. VSBYs may also become sub- VFR with fog development possible, at least locally. Finally, showers will move in from the west after 06Z, likely affecting the Philly terminals around/after 09Z. Lightning cannot be completely ruled out, though confidence in this is too low for TAF mention at this point. Overall confidence is average. Tuesday...IFR or lower in rain and isolated TSRA. Locally heavy rain possible. Strong, gusty winds possible in heavier showers and isolated TSRA. Showers taper off from west to east Tuesday afternoon as cold front moves through the region. South winds 15-20 KT with gusts up to 25 KT Tuesday morning become W-NW in the afternoon. VFR conditions likely in the afternoon. LLWS will be an issue to start the day but diminishes by afternoon. Outlook... Tuesday night through Saturday...Mainly VFR. && .MARINE... For tonight, south winds should begin to increase, especially after midnight, with speeds reaching small-craft advisory criteria a couple of hours before daybreak. Also, areas of fog likely to develop over the waters overnight with showers arriving west to east near morning. Tuesday...Strong Small Craft Advisory conditions over the waters with a few gusts to Gale force possible around midday...especially in any heavier showers. Since this looks to be brief, we opted for SCA, not Gale Warning. Marine Weather Statements and possibly a Special Marine Warning may be needed for these locally stronger winds. SCA conditions expected for DE Bay Tuesday. South winds in the morning shift to the west in the afternoon behind the passage of a cold front. Outlook... Tuesday night...A Small Craft Advisory is in effect on our ocean waters for westerly wind gusts around 25 knots. Wednesday through Thursday...A west northwest wind could gust around 25 knots and the Small Craft Advisory may be extended in time. Thursday night through Saturday...No marine headlines are anticipated. && .CLIMATE... One temperature record was set today (Jan 22): GED- The high was 68 degrees (occurred at 153 PM EST) which ties the previous daily high temperature record from 1959. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 4 AM Tuesday to 6 AM EST Wednesday for ANZ450>455. Small Craft Advisory from 4 AM to 6 PM EST Tuesday for ANZ430- 431. && $$ Synopsis...Iovino Near Term...Fitzsimmons Short Term...Fitzsimmons Long Term...Iovino Aviation...Fitzsimmons/Iovino Marine...Fitzsimmons/Iovino Climate...Klein

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