Key MESSAGE 1, Latest surface analysis shows a cold front currently just lee of the Appalachians this afternoon with a prefrontal trough located across the Coastal Plain as a result of differential heating boundaries across ENC. Latest satellite imagery shows some clearing out ahead of the cold front in the Coastal Plain while radar imagery shows some isolated showers tracking from S-N across the coastal waters and along the far eastern zones while broken and scattered line of showers and thunderstorms have developed just off to the west in association with the aforementioned prefrontal trough. This activity just to the west is what we will be monitoring this afternoon for severe potential.
Overall forecast thinking for this afternoon and evening has not changed much as multiple rounds of showers and thunderstorms are expected. The first round of showers and thunderstorms is forecast to be associated with the prefrontal trough. This activity is currently just entering into the western Coastal Plain. Latest RAP analysis shows widespread MLCAPE values of about 500-1000 J/kg with modest mid level lapse rates (less than 6 C/km) and deep layer shear values around 20-30 kts. While normally this would preclude much of a severe threat, given low level lapse rates of 7-8 C/km and 3CAPE values ranging from 100-175 J/kg across the Coastal Plain, this should provide enough of a forcing mechanism for a few storms to organize this afternoon and evening as they enter into ENC. Storm mode will likely be a mix of thunderstorm clusters and linear segments. With Inverted V soundings, low mid level lapse rates and little SRH (on the order of less than 100 m2/s2) think the main threat will be damaging downburst wind gusts. This thunderstorm activity then nears the coast closer to 6-8PM timeframe eventually congealing into linear segments if not a continuous linear segment. This once again would bring a damaging wind threat to the coast as this activity passes through, though with a more stable marine layer, unless a strong cold pool sets up with this activity the severe threat could be limited along the coast this evening. As a result of the above, SPC has our entire CWA under a Marginal Risk (level 1/5) for severe weather.
The second round of thunderstorm activity is then associated with the approaching cold front. The cold front itself doesn't begin entering into ENC until about 8-9PM. While wind shear values will be on the increase with 50+ knots of deep layer shear expected tonight, with much of the area worked over from previous activity this afternoon, instability may be a bit more limited after sunset and therefore think the severe threat will quickly lower after about 7-8 PM, with the cold front it self likely bringing more of a general thunder risk than a severe risk.
This thunderstorm activity will bring some much welcome rainfall to ENC given the area is under a severe drought. Model QPF hasn't changed much with guidance suggesting anywhere from about 0.75-1.5 inches of rainfall for inland areas and 0.25-0.75 inches along the coast. Will note some of the more aggressive guidance and HREF LPMM suggest if thunderstorms can train over each other this afternoon and evening then we could see amounts as high as 1.5-2". This threat corridor mainly looks to be along and west of Hwy 17. Though it is a lower end threat overall. Will note forecast rainfall amounts tend to be overstated in long-term drought conditions like ours, but the forcing and deeper moisture with this system appears strong enough to overcome the antecedent dry conditions.
KEY MESSAGE 2, The front will move offshore early Monday morning and cooler high pressure will build in behind it, resulting in much cooler highs to kick off the new week (mid to upper 60s inland/low 60s beaches). A quick, moisture-starved reinforcing cold front will then move across the area on Tuesday. Although no rain is expected with this FROPA, the post-frontal air mass will bring the coldest high temps of the week on Wednesday (low to mid 60s inland/low 60s beaches). We'll moderate thereafter and be back to low 80s inland/low 70s beaches by next weekend.
18z Sunday through Friday VFR conditions in place across the terminals this afternoon in a warm and humid airmass ahead of an approaching cold front currently moving across western NC this hour. Already seeing some transient shower activity lifting across ENC, but more robust activity is to our west with a brown cluster of thunderstorms developing along the I-95 corridor. Convection is moving in about an hour faster than suggested by most guidance, so timing in TAFs was adjusted accordingly, now favoring 18-19z starting window for PGV/ISO and 19-20z for EWN. Sufficient instability and shear present for thunderstorms to bring the threat of strong wind gusts, and a few gusts exceeding 40 kt are possible in the strongest cells. Shower and storm threat will linger until after sunset when main cold front pushes through the area. A few showers will linger into the early morning hours. Pred VFR conditions expected to return by late tonight with northerly winds gusting to 15 kt at times.
Outlook: Pred VFR expected Monday through Thursday with high pressure over the area, through a dry reinforcing cold front will push through the area Tuesday bringing a period of gusty northerly winds.
Hazardous marine conditions will remain in place across much if not all of our waters through Monday. A tight pressure gradient is noted across the area out ahead of an approaching cold front which has resulted in SW winds of 15-25 kt with gusts to 25-30 kt and seas of 4-7 ft over our area. This has resulted in widespread SCA conditions across all area waters this afternoon. Showers and thunderstorms will occur ahead of and with the front, leaving the door open for convection between early evening and approximately midnight. Within thunderstorms, frequent lightning and strong wind gusts in excess of 40-50 kt will be possible. Otherwise elevated SW winds and seas will continue into this evening with winds potentially easing slightly after about 8PM just ahead of the front before increasing once again back to 15-20 kts but shifting to a N'rly direction behind the front with gusts up around 25-30 kts across most of our area waters. One caveat to this is across the inland rivers where winds will likely be lower tonight due to an inversion, thus capping max potential N'rly wind gusts tonight across these areas at closer to 20 kts. For this reason the SCA's will likely continue everywhere but the inland rivers tonight. After the cold front pushes offshore and moves further out to sea, winds will ease down to 5-10 kts and become NE-E'rly by Mon evening. Though seas will remain elevated into Monday evening with 4-6 ft seas forecast so while, inland water SCA's will end, our central and southern waters will likely see SCA conditions persist into Mon evening before ending.
Outlook: Once SCAs drop tomorrow evening, we should remain headline free until Tuesday evening when the next front is expected to pass. The latest forecast has NE winds at 20-25 kt with gusts to 25-30+ kt and 6-9 ft seas Tuesday night through Wednesday. Behind this front, seas will likely remain elevated through the rest of the week.
Nc, none. Marine, small craft advisory until 7 pm EDT this evening for amz131- 136-137-230-231. Small craft advisory until 11 am EDT Monday for amz135-150. Small craft advisory until 8 pm EDT Monday for amz152-154. Small craft advisory until 2 pm EDT Monday for amz156-158.
