textproduct: Wakefield

WHAT HAS CHANGED

Updated discussion. Pushed best rain chances a bit later tomorrow late day into tomorrow night. A Climate Section was added for reference to show tomorrow's record high temperatures.

KEY MESSAGES

1) Heating up tomorrow, with highs back in the mid to upper 90s inland and heat index values around 100.

2) Strong to Severe storms are possible Thursday night, though confidence in convective initiation remains low. Lingering showers are possible Friday morning. Gradual clearing late Friday and Friday night looks to give way to a mainly dry, pleasant weekend.

3) In light of the breezy and hot conditions, a late-season Increased Fire Danger Statement has been added for most of our NC counties for tomorrow.

DISCUSSION

As of 240 PM EDT Wednesday...

KEY MESSAGE 1...Heating up tomorrow, with highs back in the mid to upper 90s inland and heat index values around 100.

As low pressure crosses the upper Great Lakes through Thursday, warm W-SW winds will pump a hot airmass back into the region tomorrow. Thickness tools match multi-model consensus regarding temperatures. Furthermore, 18-20C 850mb temps, combined with ongoing drought conditions and dry downslope flow, should yield highs in the mid-to-upper 90s away from the immediate coast. This dry flow aloft will help mix out afternoon dewpoints, keeping heat index values partially in check but still peaking in the 100 to 105F range. Given the potential for increasing afternoon clouds, as well as the marginal, short-lived nature of this heat, will not issue any heat headlines for now and will allow for later shifts to re-evaluate.

KEY MESSAGE 2...Strong to severe storms are possible Thursday night, though confidence in convective initiation remains low. Lingering showers are possible Friday morning. Gradual clearing late Friday and Friday night looks to give way to a mainly dry, pleasant weekend.

Model trends continue to lean slower with the frontal passage Thursday night into Friday, with the attendant surface low lifting into Ontario/Quebec and slowly dropping the cold front across the area late Thu night into Friday. The slower timing and persistent pre-frontal downslope flow continues to cast some doubt regarding the timing and overall coverage of showers and storms late tomorrow afternoon into the early evening. While SPC has maintained a Day 2 Slight Risk (Level 2 of 5) for counties north of the VA/NC line, the severe threat remains highly conditional on when forcing can overcome the dry boundary layer.

The well-mixed, hot, and dry airmass will allow for plenty of surface-based instability, with MLCAPE of 1000-1500 J/kg likely to develop by early to mid-afternoon. However, a weak capping inversion is also forecast to develop tomorrow afternoon. While this cap is relatively weak, it will take time to break, narrowing the already small convective window a bit more. While the potential for strong to severe storms exists, the window will be relatively narrow (~ 6 to 11 PM/22-03z), since local storms will be conditional upon convective development. Specifically, we will need upstream convective outflows and cold pool propagation to do much of the heavy lifting. The considerable difference in simulated convective footprint amongst CAM guidance reflects this uncertainty well. Storms firing earlier in the afternoon to our N/NW where forcing is stronger, as modeled by the NSSL WRF and a majority of the RRFS runs, would efficiently utilize the high-DCAPE environment to organize convection. On the other hand, the past few HRRR runs remain far less bullish on convective chances, keeping most of the area dry through sunset Thursday. Given the noted challenges, a drier solution is well within the range of outcomes.

In terms of kinematics and storm mode, a reasonably steep N-S gradient in deep-layer bulk shear remains forecast across the region tomorrow afternoon and evening. Across our far northern tier N of a RIC-SBY line, 30-40 kt of shear is forecast and would be able to support more organized multicell convection and perhaps some bowing segments. Farther south into central portions of the area, 25-30 kt of shear would portend a more messy, or loosely-organized multicell mode. Meanwhile, across the southern third of the area where bulk shear drops to 20 kt or less, single-cell to pulse-type, disorganized convection remains the primary expected storm mode. Unidirectional soundings and stark inverted-V look to soundings indicate a high-DCAPE environment exceeding 1000 J/kg. This environment, combined with the enhanced kinematics across the north, suggests that any storms managing to develop across the north or into our northern tier will be capable of better organization. The primary hazard remains damaging straight-line winds from intense downbursts or accelerated gust fronts. The highest probabilities for this conditional severe threat remain focused from the VA Piedmont north of US-360 into the RIC metro and Northern Neck/Lower Eastern Shore for late Thursday evening.

The front likely becomes hung up across the southern portions of the area late Thursday night. Another northern stream shortwave, attendant to a potent upper low over central Canada, will ultimately push the slow-moving cold front through the region Friday morning. Regarding QPF potential, the ECMWF, and to a lesser extent the CMC, have been most aggressive in pushing more of tropical moisture up into our area, while the GFS and its member ensembles are far less aggressive in bringing this additional QPF our way. Unfortunately, given the flat, quasi- zonal flow, this setup is still unlikely to yield the widespread, drought-busting rains the region needs. While some welcome measurable rainfall looks likely during this period, as gulf moisture overspreads the crossing front, this synoptic setup typically limits the window for appreciable totals, as rapid clearing takes place Friday afternoon and night as the front sweeps south. Trends continue to favor a dry weekend with seasonable temperatures and lower humidity. Rain chances then ramp up early next week ahead of our next frontal passage later Monday into Monday night.

KEY MESSAGE 3...In light of the breezy and hot conditions, a late-season Increased Fire Danger Statement has been added for most of our NC counties for tomorrow.

A tightening pressure gradient and downslope W-SW flow will result in dry, breezy conditions on Thursday. After collaboration with neighboring offices and NCFS fire officials, concern for 20-30 mph gusts and hot temperatures, despite marginal RH values (~35-40%), justifies the IFD statement. This is especially true given the ongoing drought conditions and very dry fine fuels across the area.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

As of 145 PM EDT Wednesday...

VFR conditions across area terminals to begin the 18z/17 TAF period look to prevail through early Thursday afternoon. Mainly clear/SKC, with only some scattered mid to high clouds north of KRIC to KSBY. S-SW back to the S-SE ~7-10kt this evening, then become SSW late tonight and Thursday. Gusts to 20-25 kt are likely across terminals tomorrow, with occasional gusts to ~30 kt through tomorrow afternoon.

Outlook: Showers/storms possible as early as late Thu afternoon, but are more likely Thu evening into early Fri. Lingering showers and embedded storms then continue into Fri afternoon, with best chances at PHF/ORF/ECG. Drier conditions/VFR conditions return late Fri through the upcoming weekend.

MARINE

As of 255 PM EDT Wednesday...

Key Message:

- A period of elevated SW winds is likely tonight into Thursday night with Small Craft Advisories going into effect by late tonight/early Thursday.

- The Gale Watch for the 20-60nm zone south of the VA/NC border has been upgraded to a Gale Warning for Thursday afternoon/evening.

A rather diffuse pressure pattern is in place this afternoon across the region. Winds are mainly SE 5-10 kt with sea breeze influence/enhancement noted across the southern Ches Bay/VA Beach. Waves and seas are 1-2 ft and 2-3 ft, respectively.

SE winds will likely peak around 15 kt with gusts to 20 kt in the early evening before becoming S 10-15 kt tonight. Low pressure over the Midwest today will deepen and translate into the Great Lakes by sunrise Thursday. The gradient between this low and high pressure anchored off the Southeast coast will steepen tonight and especially Thursday. Forecast soundings also show very deep mixing across the region tomorrow from late morning into the afternoon. Sustained winds will average 15-25 kt with gusts 25-30 kt. The highest gusts will likely occur near shore, including the lower James River and southern Ches Bay. In coordination with the Morehead City office, have upgraded the Gale Watch for the far offshore waters south of the VA/NC border. Local wind probabilities continue to show a ~60% chance for 35 kt gusts. Still thinking the highest gusts will be confined to the SE third of the zone. Waves in the bay increase to 2-3 ft on Thursday with seas 4-6 ft nearshore and 5-8 ft well offshore. Will need to watch the potential for strong to severe storms, mainly Thursday evening into the overnight hours. Locally gusty winds along with increased waves/seas can be expected in the vicinity of any thunderstorms. The surface front finally drops southward during the day on Friday with winds becoming N and NW 5-10 kt behind the boundary. Much improved marine conditions are expected this weekend as high pressure moves into the area. The next system approaches the region early next week with increasing SW winds.

CLIMATE

As of 145 PM EDT Wednesday...

Record Highs for tomorrow 6/18

Record High/Year Location 6/18 -------- ---- Richmond 100 (1970) Norfolk 99 (1944) Salisbury 98 (2014) Eliz. City 100 (2011)

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...INCREASED FIRE DANGER from Thursday morning through Thursday evening for NCZ012>017-030>032. VA...None. MARINE...Small Craft Advisory from 1 AM Thursday to 1 AM EDT Friday for ANZ630-631. Small Craft Advisory from 1 AM Thursday to 7 AM EDT Friday for ANZ632-634. Small Craft Advisory from 7 AM Thursday to 7 AM EDT Friday for ANZ633-650-652-654-656-658. Small Craft Advisory from 7 AM to 7 PM EDT Thursday for ANZ635>637. Small Craft Advisory from 4 AM Thursday to 7 AM EDT Friday for ANZ639. Gale Warning from 4 PM Thursday to 1 AM EDT Friday for ANZ688.