textproduct: Charleston

WHAT HAS CHANGED

There are no significant changes with this package, as the zeitgeist of the forecast remains on track.

KEY MESSAGES

- 1) Unsettled weather is still expected for much of the week with multiple chances of rain. The best chance of widespread rain will be Thursday into Friday, when thunderstorms are also possible.

- 2) It will remain springlike the balance of the work week.

- 3) A pattern shift to colder weather will arrive over the weekend, with light snow showers possible Sunday into Monday as lake-effect moisture flows into the mid Ohio Valley and Appalachians, and a mid/upper-level low crosses.

DISCUSSION

KEY MESSAGE 1...

The weather pattern becomes increasingly active for the balance of the work week, starting today. While a mid/upper-level short wave trough and surface cold front bring a few rain showers, mainly north, and breezy to windy conditions, with gusts to around 30 mph today, a stronger system will bring more widespread showers, and possible thunderstorms, Thursday through Thursday night.

The Storm Prediction Center has maintained their Marginal Risk for Severe Thunderstorms along our western flank, our northeast KY and southeast OH counties, in their latest Day 2 Convective Outlook, SWODY2. All three severe weather hazards, damaging wind, large hail and tornadoes, are indicated at 5, 5 and 2 percent, respectively, to go along with categorical Marginal Risk, which is on the eastern flank of a Slight Risk area over the lower Ohio and mid Mississippi valleys with 15, 15 and 5 percent risks for most of it, where earlier warm frontal passage will allow better instability to develop Thursday afternoon.

The culprit is a mid/upper-level short wave trough which crossed the west coast overnight. It becomes negatively tilted as it crosses the western states today and tonight, and then may close off as it crosses the plains Thursday and the midwest Thursday night. Its associated surface low pressure center slowly intensifies as it takes a similar and slight farther south track Thursday and Thursday night, possibly getting below 990 MB by Friday morning.

The warm front associated with the system is likely to spread rain showers across the area from southwest to northeast Thursday, starting early in the morning, before crossing the area late Thursday and Thursday night. As such, instability will be limited late Thursday and Thursday evening. However, any convective instability that can be realized given surface dew points climbing well into the 50s will have high shear to work with, to go with a strong upper level jet, modest mid-level forcing and low level warm advection veering with height. Elevated convection associated with warm fronts is generally maximized during the overnight and early morning hours, but surface/near surface-based convection along the warm front itself could support all three severe weather hazards more independently of the time of day. It is also plausible upscale growth upstream makes inroads into the forecast area in the evening with a wind threat, before weakening Thursday night.

Meanwhile, the cold front associated with the system whizzes across the area first thing Thursday morning, also unfavorable timing for thunderstorms diurnally, but additional showers will occur with it overnight into Friday morning.

The overall QPF with the system ranges from about one half inch to one inch, not a significant hydrologic concern. However, locally higher terrain-enhance amounts over the higher terrain, combined with residual snow and ice melt, could give rise to localized minor issues.

Drier air with transient ridging surface and aloft promotes drier weather later Friday into Saturday.

KEY MESSAGE 2...

Mid/upper-level ridging along the Gulf and southeast coasts, coupled with a return low-level southwest flow of warmer air ahead of a weak cold front, will maintain well-above normal temperatures the balance of the work week, with lowlands highs in the 60s and overnight lows above freezing even in the mountains, and well above freezing, in the 40s and even 50s, over the lowlands.

The weak cold front crossing today has a barely discernible wind shift, and returns as a warm front Thursday into Thursday night. While a cold front crosses Friday morning, significant cooling awaits a secondary, mainly dry front later in the day, and some guidance indicates highs of 70 or better for portions of the lowlands on Friday.

There should be little if any snow and ice in our environment by the time this week is out.

KEY MESSAGE 3...

The mid/upper-level trough that brings a cold front across the area Friday morning is followed by another right behind it, which finally eradicates the Gulf ridge giving rise to the springlike weather this week, as it closes off into a modestly deep mid/upper-level low over the broader northeast U.S by Sunday.

Depending upon the timing and evolution of this low, surface low pressure forming in response to it will either track up the east coast, or farther offshore. The chance for rain increases Saturday as the system unfolds, but as precipitation transitions to snow in response to the colder air Sunday, the track of the surface low could make the difference between a widespread snow from a closer coastal low pressure system, versus just snow showers from low level upslope flow and the mid/upper-level low, Sunday into Monday.

The latest deterministic solutions trended toward the more offshore solution overnight, although coastal impacts could still be significant, as mentioned in the latest Extended Forecast Discussion, PMDEPD. However, for the central Appalachians, and especially the middle Ohio Valley, the ensemble-infused NBM PoPs this weekend may be too high until Sunday afternoon or evening, when the mid/upper-level low, cold air and upslope flow start becoming established.

Nonetheless, temperatures trend sharply downward Saturday through Monday, in the wake of the cold frontal passage on Friday, and then the deep mid/upper-level low crossing Sunday into Monday amid long-wave troughing along the east coast. Temperatures will be back below normal by the second half of the weekend, and the nadir of the cold wave appears to be most likely during the early portion of the following work week, with highs in the 30s lowlands and 20s mountains Monday and Tuesday, and lows Monday night in the 10s across much of the area.

However, the pattern appears to remain progressive, with the east coast long wave trough shifting offshore heading into the middle of next week. Temperatures recover to, if not even above, normal amid mid/upper-level ridging ahead of the next cold front next Wednesday.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

A mid/upper-level short wave trough and surface cold front whisking through the area today may bring MVFR visibility in rain showers for up to a couple of hours midday into this afternoon, when ceilings also lower to MVFR. However, once ceilings lower to MVFR, they will remain that way throughout the balance of the TAF period, although they will scatter out for a time tonight. MVFR mist may settle in overnight tonight as ceilings reform and lower to low MVFR, especially in and near the mountains. Ceilings and visibility may lower to IFR at BKW overnight tonight.

Light and variable to south to southeast surface flow early this morning will quickly increase and become gusty southwest this morning, with gusts to around 25 kts at times through this afternoon, before diminishing to light southwest tonight, as the weak front does not even bring a discernible wind shift. Surface flow may go calm to light and variable overnight tonight. Moderate to strong southwest flow aloft early this morning will become moderate west as the cold front aloft crosses this afternoon, and then light southwest overnight tonight. Allowed for low level wind shear for an hour or two this morning until some of the higher momentum aloft mixes down to the surface in the form of gusts.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z THURSDAY... FORECAST CONFIDENCE: Medium to high.

ALTERNATE SCENARIOS: Timing and minimum height of MVFR or lower ceilings may vary from the forecast through tonight, as may timing and degree of visibility restrictions in rain showers today. Gusty winds will fluctuate today. Mist/fog formation overnight tonight is uncertain.

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 11 12 13 14 15 16 17 18 19 20 21 22 EST 1HRLY 06 07 08 09 10 11 12 13 14 15 16 17 CRW CONSISTENCY H H H H H H H H H H M M HTS CONSISTENCY H H H H M H H H H H H H BKW CONSISTENCY H H H H H H M H H H M M EKN CONSISTENCY H H H H H M H H H H H H PKB CONSISTENCY H H H M H H H H M M M M CKB CONSISTENCY H H H H H H H H H M M M

AFTER 12Z THURSDAY... IFR conditions possible in rain showers at times, and even a thunderstorm or two, Thursday and Thursday night. IFR possible in snow Sunday.

RLX WATCHES/WARNINGS/ADVISORIES

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