textproduct: Wakefield

WHAT HAS CHANGED

Potential for significant severe weather continues ahead of a strong cold front Monday. The Storm Prediction Center has maintained a Moderate Risk (level 4/5) and probabilities of 60% for wind and 15% for tornadoes across much of the area.

Gale Warnings are now in effect for most local waters on Monday ahead of and just behind the strong cold frontal passage.

A Wind Advisory is in effect for all of the Eastern Shore.

KEY MESSAGES

1) Showers and storms prevail Monday, following increasing moisture and shower chances this evening into tonight as a warm front lifts north. The greatest threat for severe storms will be from mid to late morning through the early evening hours. SPC has introduced a Moderate Risk(level 4/5) for western and central portions of the area with an Enhanced Risk (level 3/5) in place for the rest of the area (except eastern portions of the Eastern Shore with a Slight Risk).

2) Cold and breezy Tuesday, with a hard freeze likely for most of the area Tuesday night/early Wed morning. It remains dry, with seasonable temperatures returning late in the week.

DISCUSSION

As of 330 PM EDT Sunday...

KEY MESSAGE 1...Showers and storms prevail Monday, following increasing moisture and shower chances this evening into tonight as a warm front lifts north. The greatest threat for severe storms will be from mid to late morning through the early evening hours. SPC has introduced a Moderate Risk(level 4/5) for western and central portions of the area with an Enhanced Risk (level 3/5) in place for the rest of the area (except eastern portions of the Eastern Shore with a Slight Risk).

High pressure has shifted off the Northeast coast this afternoon, with the gradient tightening across the region. Aloft, an amplifying upper trough is digging into the Plains with a strong jet streak poised to round the base of the trough. This jet streak will serve to further amplify the trough and deepen the surface low as it tracks northeastward through tomorrow. Winds have remained from the SE today and gradually increased. A warm front is currently draped across the Carolinas and will make its way across our area overnight, with winds becoming southerly in its wake. Shower chances increase significantly in the evening as the deeper moisture lifts north as the warm front lifts through the area. Forecast soundings continue to minimal sfc-based instability until after ~09Z/5AM Monday which will be confined to the S. Instability aloft does increase earlier, and MUCAPE of 200-400 J/Kg spreads north after midnight, which could lead to a few rumbles of thunder within overnight convection. SPC has maintained a Marginal Risk for strong storms, mainly for the early morning hours tomorrow behind the warm frontal passage. Wind fields aloft will be increasing during this time and some stronger cells are possible despite the unfavorable diurnal timing. Temperatures will be quite mild tonight with lows only falling into the 50s to low 60s across the area, and probably rising overnight in many areas as the southerly low level flow increases.

The setup on Monday continues to look extremely favorable for severe thunderstorms, with all severe threats possible (wind, hail, tornadoes). 12z guidance continues to be in excellent agreement showing the extremely robust mid and upper level trough amplifying well to our west this evening into tonight, while taking on a negative tilt, and eventually becoming nearly cutoff over the western Great Lakes tomorrow. At the sfc, intense low pressure is forecast to lift NE through the Ohio River Valley into the western Great Lakes late tonight/early Mon, with all of the forecast models depicting this feature deepening to ~980mb or lower and then occluding as the surface and upper level features stack vertically.

A prefrontal surface trough will sharpen to our west tomorrow morning into the early afternoon. Ahead of the trough/cold front, robust moisture transport will bring 60s dew points northward into the entire region. Very strong winds aloft (on the order 120-150 kts) will overspread the region in tandem with a 60-70 kt low level jet. Deep layer shear will likely be in excess of 50 kts which is more than sufficient for strong to severe thunderstorms, and potential supercells. The deepening sfc trough will enhance what will already be impressive shear, and potentially allow the sfc to 1 km winds to back to the SSE ahead of the cold front. Forecast soundings/hodographs show very favorable curvature in the low levels with 0-1km SRH generally on the order of 200-400 m2/s2, and 0-3km SRH even higher still.

The local area will be in the right entrance region of the mid and upper level jet on Monday which will provide forcing for ascent even well ahead of the surface cold front. The latest hi-res guidance shows a batch of mid to late morning convection across portions of the area. These storms could be strong to severe with the potential for discrete or semi-discrete supercellular convection. All severe hazards are possible (including wind, large hail, and tornadoes) with this pre-frontal convection, especially if these storms can maintain some separation from each other. Some of the hi-res guidance continues to show the potential for a lull in convective coverage behind these morning/early afternoon storms with some possible breaks in the clouds, allowing surface based instability to potentially rise into the 1000-1500 J/Kg range ahead of the main squall line. If this scenario were to materialize, the potential for widespread damaging winds and strong tornadoes would increase above and beyond the already very robust potential we are expecting. Though this increased instability would propel the intensity of these storms, even if there is no break, these storms have all they need to still become very dangerous in this high-shear low-CAPE environment. The timing of the front is a little uncertain as some hi-res has it trending quicker, while others have slowed it down some. Have tried to capture a more broad timeframe with our forecast as to not get too specific with exact timing for now. The best timeframe for tornadoes is roughly between 1-7 pm, but a few tornadoes may still occur outside of these times. For winds, the most likely timeframe extends from 12 pm-9 pm (though strong to severe wind gusts cannot be ruled out earlier/later), with the earlier threat being with the first round of storms being with the first round that is expected mainly east of I-95. Wind gusts of 70- 75 mph+ are possible with the squall expected in the evening, with embedded tornadoes along the line. SPC has maintained a Moderate Risk (level 4/5) for most of the area. This is a fairly rare occurrence (especially for the Mid-Atlantic) and highlights the potential for a very significant and widespread severe weather episode across the region. Severe wind probs are now as high as 60% for the NW 2/3 of the area with tornado probs up to 15% for the western half of the area. While the probabilities drop off a bit for the eastern and southeastern portions of the area, damaging winds and tornadoes are still quite possible before the front finally moves offshore in the evening. This is a very potent severe weather setup and users are encouraged to have multiple ways to receive warnings and have a plan in place on Monday.

In addition to the severe threat, decent pressure falls ahead of the front will allow for strong southerly flow to develop during the day. Outside of convection, winds could gust to 30-40 mph, with the Eastern Shore potentially seeing gusts as high as 40-45 mph. A Wind Advisory has been issued for all of our Eastern Shore counties starting early tomorrow afternoon through late tomorrow evening. This advisory may need to be expanded in the case that a good mixed environment can bring down some of those strong winds aloft across portions of our forecast area, and this will be looked at again with the next forecast update.

KEY MESSAGE 2...Cold and breezy Tuesday, with a hard freeze likely for most of the area Tuesday night/early Wed morning. It remains dry, with seasonable temperatures returning late in the week.

Solid pressure rises are expected behind the front, which will keep breezy conditions through Tuesday afternoon with gusts of 20-25 mph possible. A very cold airmass will move in behind the front, bringing temperatures down below normal on Tuesday and Wednesday, with highs only reaching the 40s. Most of the area can expect a hard freeze on Tuesday night/Wednesday morning as high pressure builds in overhead and winds trend downwards. Lows will drop into the upper 20s to lower 30s, with the exception being the NC OBX, where temperatures will be a little more modified by the surrounding bodies of water. Temperatures will start to trend warmer by late week, with generally dry conditions currently forecast through the weekend.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

As of 157 PM EDT Sunday...

VFR conditions will continue over the next few hours become CIGS start to drop across the area. After 00z, the first round of convection is expected to move across the terminals, and a TEMPO has been included at all sites for possible gusty winds and thunder. There will likely be some breaks in the convection overnight, however, timing those breaks is tricky, so have included either SHRA or VCSH to cover those bases. Confidence increases for tomorrow's secondary round of convection that will move through mid-morning into the afternoon, so have included PROB30 to highlight the timeframe and aviation hazards. There is still some uncertainty in exact timing of the convection, so amendments will likely be necessary as thunderstorms start to develop late this evening/overnight. LLWS will become an issue overnight into tomorrow, with very strong winds expected just above the surface. Most, if not all, terminals will see LLWS out of the south at 40- 50kt. At the surface, winds will start to ramp up Monday morning, with gusts of between 25-30 kt expected through a majority of the day outside of convection.

Outlook: A strong cold front will bring the potential for additional flight restrictions and strong to severe TSRA Monday evening. Dry/VFR Tue with breezy WNW winds, remaining dry Wed- Thu with less wind.

MARINE

As of 355 AM EDT Sunday...

Key Messages:

- A strong cold front approaches from the west Monday and crosses the coast Monday night. Small Craft Advisory conditions persisting in advance of the front followed by gale conditions Monday afternoon and evening, primarily for the coastal waters and Chesapeake Bay.

- There is a Moderate risk (level 4 out of 5) for severe thunderstorms Monday inland with an Enhanced Risk (level 3 out or 5) over the Bay and coastal waters. The main threat is strong to damaging wind gusts along with the potential for a few waterspouts as the cold front moves through.

Southeast flow increased today as high pressure drifts off the New England coast and strong low pressure deepens well to the W. SCAs remain in effect for the lower James, Bay and coastal waters this afternoon and evening. SCAs go into effect for all the rivers and Currituck Sound 7 pm this evening.

Deepening low pressure lifts NE through the Great Lakes Monday with a strong cold front approaching from the W, which then crosses the Mid-Atlantic coast Monday night. High-end SCA conditions are likely Monday morning followed by a period of gale conditions Monday aftn/evening. Gale conditions will occur in southerly flow ahead of the front, and also briefly in WNW flow immediately behind the front during the late evening/ early overnight hours. Modestly strong pressure falls Monday afternoon, a tight pressure gradient, and a 60-75kt LLJ favor a 3-6hr period of southerly gales. The gust factor could be rather high Monday depending on mixing and scattered storms late morning to early afternoon could also produce high winds. The only limiting factor will be stable low- level lapse rates with a mild and moist airmass overspreading cold ocean water. Local wind probs depict the greatest probability of 34kt gusts over the coastal waters N of the VA/NC border. However gale probabilities have increased for the Bay this afternoon with best timing from 2pm Monday to 1 am Tuesday.

Gale Warnings are now in effect for the coastal waters and Bay from late Monday morning through late Monday evening. Gale warnings may be needed for the Currituck Sound, but as of now winds of 34 kt or greater there look limited to just a few hours late Monday afternoon into the evening ahead of the front. Same is true for the lower James River. SCAs are in effect for the rivers and begin Monday morning though they may need to be backed up to start later tonight. Additionally, there is a risk for strong tstm wind gusts or 50 kt and waterspouts possible in tstms ahead of the front Monday afternoon and early evening. Seas build to 5-8ft S to 9-12ft N Monday into Monday night, with 3- 5ft waves in the Ches. Bay and locally higher at the mouth of the Bay.

Remaining breezy Tuesday, with a secondary surge possible for the Ches. Bay and coastal waters Tuesday night. This may allow for SCA conditions to continue for portions of the marine area. Otherwise, m ore benign marine conditions are expected by the middle of next week as high pressure settles across the region.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...Wind Advisory from 1 PM Monday to 1 AM EDT Tuesday for MDZ021>025. NC...None. VA...Wind Advisory from 1 PM Monday to 1 AM EDT Tuesday for VAZ099- 100. MARINE...Small Craft Advisory until 1 PM EDT Monday for ANZ630>632-634- 656-658. Gale Warning from 1 PM Monday to 1 AM EDT Tuesday for ANZ630>632-634-656-658. Small Craft Advisory from 7 PM this evening to 6 AM EDT Tuesday for ANZ633. Small Craft Advisory from 7 AM Monday to 6 AM EDT Tuesday for ANZ635>637. Small Craft Advisory until 6 AM EDT Tuesday for ANZ638. Small Craft Advisory until 10 AM EDT Monday for ANZ650-652-654. Gale Warning from 10 AM Monday to 1 AM EDT Tuesday for ANZ650- 652-654.