Key MESSAGE 1, A cold front will approach the Carolinas tomorrow and cross ENC late tomorrow night into Monday morning. Ahead of the front, Gulf moisture advection will continue to increase as Tds climb into the mid 60s by mid-afternoon. Combined with temps in the low to mid 80s, this will fuel weak instability of around 500 J/kg MLCAPE (but in a worst case scenario, up to 750 J/kg). Combined with modest pre-frontal shear of 20-25 kt, tomorrow's environment will be marginally favorable for stronger storms, with stronger winds being the primary threat. Lapse rates appear too low to support severe hail, and hodographs do not favor a mentionable tornado risk. Spc. Spc has our area in a Marginal (Level 1/5) risk for tomorrow.
With PWATs increasing to around 1.5" tomorrow, potential has increased for some meaningful rainfall from this frontal passage. Nbm precipitation probabilities have trended upwards from yesterday:
> 0.5": 70-80% > 1.0": 25-35%
Higher amounts are likely in thunderstorms, potentially in excess of 2" in a worst case scenario. 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, Once the front is offshore, cooler high pressure will build back in behind it. A quick moving reinforcing cold front will race across the region on Tuesday into Wednesday, although it will be moisture starved and unlikely to bring any rain with it. Low level thickness values and N-NE flow behind the front will lead to below normal temps with highs mostly in the 60s before warming back into the 70s by late week.
18z Saturday through Thursday A SCT cumulus cloud layer, with occasional periods of BKN CIGs, will continue for several more hours this afternoon. Skies are expected to clear out for several hours this evening. Overnight into early Sunday morning, guidance suggests the potential for an area of low stratus to develop within an area of increasing low-level moisture advection. Synoptically, the pattern is favorable for this, but guidance is mixed on whether or not it will occur. For now, I've added a FEW/SCT layer at 2500ft to highlight this potential. See below for the probability of MVFR conditions late tonight into Sunday morning:
ewn: 20-40% pgv: 30-50% oaj: 20-40% iso: 30-50%
As the seabreeze moves inland this afternoon, a period of gusty south winds is expected to develop for a short time. Winds may be occasionally gusty tonight, but a more solid period of frequent wind gusts of 20-25kt is then expected to develop fairly early Sunday morning. This will occur ahead of a cold front that will be approaching the area from the west. This front is expected to carry a risk of SHRA and TSRA, but with the primary window coming after 18z. Of note, though, some guidance suggests the TSRA risk may develop as early as 16-18z for KISO and KPGV.
Outlook: A cold front will move through the area Sunday afternoon and evening with an increased risk of TSRA and sub-VFR conditions. Areas of enhanced wind gusts to 45kt will be possible with any TSRA. Improving aviation conditions are then anticipated as we move into the start of the work week.
Regional observations depict south to southwesterly winds this afternoon 5-10 kt with a few gusts up to 20 kt and seas around 3-4 feet. Expect a gradual uptick in winds through tonight and into tomorrow as a cold front approaches area waters from the west, peaking out of the southwest tomorrow afternoon and evening with gusts to 25-30 kt and seas rising up to 4-6 feet. Showers and thunderstorms will accompany the front with a risk of strong wind gusts in excess of 40-50 kt at times.
The cold front will cross the waters overnight Sunday and veer the winds to the north. The northerly surge behind the front will be short- lived with gusts dropping below 25 kt by early Monday afternoon. Elevated seas, however, may linger a bit longer across the outer central waters.
SCA have been expanded to all area waters for tomorrow. Inland rivers and sounds are only in effect for tomorrow during the day time hours when mixing will be at its strongest.
Outlook: Once SCAs drop on Monday, we should remain headline free until late Tuesday 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 for much of the week.
Nc, none. Marine, small craft advisory from 10 am to 6 pm EDT Sunday for amz131- 136-137-230-231. Small craft advisory from 10 am Sunday to 11 am EDT Monday for amz135. Small craft advisory from 11 am Sunday to 11 am EDT Monday for amz150. Small craft advisory from 2 am Sunday to 5 pm EDT Monday for amz152-154. Small craft advisory from 2 am Sunday to 2 pm EDT Monday for amz156. Small craft advisory from 11 am Sunday to 2 pm EDT Monday for amz158.
