textproduct: Charleston

WHAT HAS CHANGED

18Z aviation discussion has been issued.

340 AM Update... Wildfire smoke brings haze today. Increasing confidence in severe weather with all three hazards occurring Tuesday afternoon into Tuesday night.

KEY MESSAGES

1) Mostly dry and hazy today after a foggy start this morning.

2) Increasing confidence in severe storms and heavy downpours occurring Tuesday into Tuesday night.

3) Quieter weather for the end of the work week.

DISCUSSION

KEY MESSAGE 1...

A front loitering near the Virginia/North Carolina border could prompt a few showers or thunderstorms in southwest Virginia or far southeast West Virginia this afternoon. Showers and thunderstorms are also possible in and near the mountains tonight into Tuesday, as a mid/upper-level short wave crosses, further encouraged by upslope southeast flow on the southeast side of the mountains tonight, in a moisture-rich modestly unstable environment. This system is not to be confused with that associated with a severe thunderstorms and heavy rainfall threat for Tuesday afternoon into Tuesday night, Key Message number 2. Otherwise, high pressure will provide dry conditions to the majority of the area today into Tuesday morning.

Smoke from distant Canadian wildfires should gradually diminish today, as a residual layer of low-level east to northeast flow this morning becomes south to southwest this afternoon, cutting off the Canadian sources.

Temperatures and dew points will continue a little above normal for mid Summer.

KEY MESSAGE 2...

Long wave trough in the east/ridge in the west pattern amplification via an embedded short-wave trough crossing the forecast and county warning area on Tuesday will drive a surface cold front toward the area Tuesday afternoon and evening, and then on through the area overnight Tuesday night into Wednesday.

The trick of the tale to this forecast is the well defined embedded short wave ahead of the surface cold front on Tuesday, encouraging instability amid the midday heating in the moisture rich, high shear environment. The associated 0-6 band 0-8 km shear of 40 to 60 kts will encourage an area of organized convection that crosses Tuesday midday into the afternoon that will carry a damaging wind threat, as well as hail and a tornado threat with more discrete cells or supercells.

The round of convection Tuesday midday into Tuesday afternoon will leave behind a cool pool suppressing surface based instability for a time Tuesday afternoon. Driven by a more subtle embedded short wave driving the surface cold front toward the area Tuesday evening, the strength of showers and thunderstorms ahead of the cold front Tuesday evening will depend upon how much the atmosphere can recover, but the high shear environment will encourage organization of convection into a line or line segments, giving rise to a second damaging wind threat Tuesday evening.

Furthermore, impressive low level flow for mid to late July, 40 to 50 kts at h85 and 30 to 40 kts at h925, contribute to 0-3 km shear of 30 to 40 kts Tuesday afternoon and evening. With the help of low LCLs, this elevates the Significant Tornado Parameter above, even well above, 2 Tuesday evening, thus elevating the Tornado threat.

The strong flow through the column, veering in the low to mid levels and at times in the mid to upper levels, gives rise to curved hodographs throughout much of the Tuesday/Tuesday night period, with all three severe weather hazards, damaging wind, tornado and hail, at play to at least some degree during both rounds of convection.

The Storm Prediction Center has expanded the enhanced risk for severe thunderstorms southeastward, to now include nearly all of the forecast and county warning area, with all three severe weather hazards at play Tuesday into Tuesday night.

In addition, the rich moisture, with surface dew points in the mid 70s F, h85 theta e values up to around 350 K and PW values up to around two inches, contributes to significant instability as will as high rainfall rates. With multiple rounds of high coverage convection, flash flooding is likely to become an issue wherever heavy rainfall is most persistent or repetitive.

The Weather Prediction Center has a slight risk for excessive rainfall throughout the forecast and county warning area for Tuesday and Tuesday night.

KEY MESSAGE 3...

Wednesday is likely to begin with fog and stratus, as the cold front contributing to the severe weather threat on Tuesday pushes out of the area to the southeast in the morning. Also, showers and thunderstorms are still possible in and near the mountains before the front pushes all the way through.

While a mid/upper-level trough lingers amid a trough in the east/ridge in the west pattern, high pressure at the surface brings quieter weather for the conclusion of the work week.

An embedded mid/upper-level short wave trough will encourage the front southeast of the area to buckle back toward the area as well as an inverted trough in or just west of the mountains. Similar to the pattern this afternoon and tonight, this may encourage showers and afternoon thunderstorms there Friday afternoon through the weekend.

Models are coming into better agreement on another cold front bringing the chance for showers and thunderstorms to the area next Monday afternoon into Monday night.

Wednesday through Friday will be a bit cooler than normal for mid summer, with lows in the 50s to around 60, and highs in the 70s to around 80, along with comfortably low humidity. Temperatures and dew points will return to more typical mid Summer values by the end of next weekend.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Some brief reductions to VSBY from smoke and haze may occur at a few of the terminals through sunset, but VSBYs are forecast to remain at or above 6SM. Isolated -SHRA/-TSRA will be possible INVOF KBKW and possibly KEKN this afternoon, but the mention of TSTMs has been withheld from KEKN due to lower confidence. MVFR CIGs/VSBYs are then forecast to return to KCRW, KBKW, KEKN, and KPKB tonight, with -SHRA also possible at those terminals during the predawn hours. IFR conditions are forecast at KEKN tonight. Valley fog that develops during the predawn hours Tuesday will dissipate after sunrise, with a return to VFR overcast and a southwesterly breeze increasing to around 10 kt at all terminals.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z TUESDAY... FORECAST CONFIDENCE: High through this evening, then medium for fog and ceiling potential Tuesday morning.

ALTERNATE SCENARIOS: Impacts due to haze and smoke this afternoon and evening could be worse than forecast. MVFR CIGs Tuesday morning may affect more terminals than forecast.

EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.

UTC 1HRLY 18 19 20 21 22 23 00 01 02 03 04 05 EDT 1HRLY 14 15 16 17 18 19 20 21 22 23 00 01 CRW CONSISTENCY H H H H H H H H H H H H HTS CONSISTENCY H H H H H H H H H H H H BKW CONSISTENCY H H H H H H H H H H H H EKN CONSISTENCY H H H H H H H H H H H H PKB CONSISTENCY H H H H H H H H H H H H CKB CONSISTENCY H H H H H H H H H H H H

AFTER 18Z TUESDAY... IFR/LIFR is likely in heavy showers and thunderstorms Tuesday afternoon, some of which may be severe.

IFR or lower is forecast Wednesday morning due to valley fog, with similar conditions each morning through Friday.

RLX WATCHES/WARNINGS/ADVISORIES

WV...None. OH...None. KY...None. VA...None.