Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 202045 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 345 PM EST Tue Feb 20 2018 .SYNOPSIS... After another mild night, a cold front crosses the Middle Ohio Valley Wednesday. The front stalls or wavers through the end of the week, with significant rainfall possible into the weekend. && .NEAR TERM /THROUGH WEDNESDAY/... As of 135 PM Tuesday... Bermuda high will continue the unseasonably warm and dry weather through tonight, and into Wednesday. A flat short wave trough in the upper level southwest flow will drive a surface cold front through the middle Ohio Valley Wednesday. This will reverse temperatures there, as well as introduce the chance for showers either side of the front. There is also the chance for thunder given some surface based instability, along with more than ample shear. With upper heights almost as high Wednesday afternoon as this afternoon, the front will be undercutting these high heights quite a bit, and afternoon precipitation coverage does not quite warrant categorical PoPs. After record high temperatures this afternoon, some records already broken -see climate section, and even some monthly records falling, another mild night is on tap tonight, but with some ridge / valley differences again. The low MAV is somewhat reflected in the forecast for the valleys, otherwise much closer to the higher MET. Temperatures for Wednesday are an hourly blend of MOS, near term blend and even raw NAM, reflecting the front cutting off the diurnal heating in its tracks in its wake, and, in fact, reversing temperatures over the middle Ohio Valley Wednesday afternoon. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... As of 245 PM Monday... The aforementioned front sags southward and stalls Wednesday night along the eastern mountains with continued shower activity through Thursday night. Being on the cool side of the front, Thursday will be cooler especially toward the North with high temperatures near 50 in SE Ohio and warmer conditions in the 60`s in southern WV and SW VA. The heaviest bout of rainfall will move through the Mid-Ohio valley and northern WV Thursday morning, coincident with an area of healthy synoptic lift in the right entrance region of a strong jet. PWAT nearing 1.4" and strong equivalent potential temperature convergence indicates this enhancement would generate moderate rainfall rates with this wave. Total precipitation through this period will near an inch at the highest in the Tristate area of WV/KY/OH waning to less than 0.5" in SE WV and SW VA. Friday, the front lifts back northward increasing afternoon temperatures back into the 70`s in the lowlands. Destabilization will occur with afternoon heating with SFC based CAPE reaching up around 500 J/kg, so have opted to include the possibility for thunder with any warm front/warm sector shower activity. In spite of strong winds aloft lending decent sheer, lack of instability and a water-logged profile aloft doesn`t leave much in the way of strong updraft development. So, there is low severe potential. rain showers continue through Friday night with the same frontal boundary draped across the northern tier of zones. Given uncertainty in the location of the axis of heaviest precipitation, have opted to leave flood threat in the HWO for now. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 315 PM Monday... Multiple waves not unlike the prior (Thu AM) move across the the frontal boundary through the weekend - specifically, Saturday evening and Sunday morning, meaning this time frame will have to be refined and paid special attention to for possible flooding concerns. High moisture availability remains while strong eastern Canadian jets continue to generate large scale ascent and induce surface waves along the front. Highest precipitation amounts will again fall in the northwestern half of the CWA across SE Ohio and northern West Virginia near the frontal boundary. Quite aggressive models like the GFS peg as much 4+" of rain from Friday through Sunday, however the conservative blended approach yields an axis of 2-3" or so up through the Ohio Valley and northern WV. This seems realistic for widespread amounts across this heaviest axis but storm training will bear watching as we approach the event itself armed with higher resolution forecast information. By the weekend, soils will already be saturated, so hydrological systems will be quite prone to flooding. Although there is not the confidence in flooding on specific small-scale basins given location uncertainty, heavy rain in the Mid to Upper Ohio River basin as a whole could lead to another flood of the Ohio River. While not forecast at this time, probabilistic forecasts like those found at weather.gov/erh/mmefs indicate a strong possibility given recent model trends. A break in the pattern shows late Sunday as an upper-level trough rotates through the Great Lakes region, pushing the front past the mountains and out to the East Coast. High pressure quickly builds in behind to dry out the region. A small handful of models quickly brings another trough/front pair through Monday night/Tuesday, so have kept PoPs from the blend of models for this period to indicate this chance. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... As of 135 PM Tuesday... The area will be in an unseasonably mild southwest flow of warm air, between a strong Bermuda high, and a cold front approaching from the northwest. This will keep aviation conditions mainly VFR. However, as the cold front moves into the middle Ohio valley Wednesday, MVFR stratocu is likely to show up behind it, reaching PKB late Wednesday morning, or about 16Z. Also, MVFR to IFR stratocu may show up along the eastern slopes early Wednesday morning, which may creep into BKW for a time. Showers associated with the front may show up Wednesday, but PoPs through 18Z were a bit low to explicitly include in the TAFs at this point, However, thunder is also possible. Strong and gusty southwest surface flow will back to south and become light tonight, except on the ridges, and then return to gusty southwest on Wednesday, but not quite as. Moderate to strong southwest flow aloft will continue through the period, with a low level jet somewhat strengthening overnight and early Wednesday morning. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z WEDNESDAY... FORECAST CONFIDENCE: High. ALTERNATE SCENARIOS: MVFR may show up for a time at BKW early Wednesday morning. MVFR stratocu may become more prevalent over the middle Ohio Valley by noon or so Wednesday, toward the end of the TAF period /18Z Wednesday/, and showers, even a thunderstorm, may directly impact TAF sites with flight category changes. 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 EST 1HRLY 13 14 15 16 17 18 19 20 21 22 23 00 CRW CONSISTENCY H H H H H H H H H H H M HTS CONSISTENCY H H H H H H H H H H H M BKW CONSISTENCY H H H H H H H H H H H M EKN CONSISTENCY H H H H H H H H H H H M PKB CONSISTENCY H H H H H H H H H H H M CKB CONSISTENCY H H H H H H H H H H H M AFTER 18Z WEDNESDAY... IFR possible in showers late Wednesday or Wednesday night into Thursday. && .CLIMATE... Below are the temperatures so far, as of 1 pm this afternoon, forecast highs today, record high temperatures for this date and record highs for the month of February as a whole, at the official climate sites, along with the most recent dates that the record temperature was recorded. All daily record highs for today have been blown through, and all sites mentioned here are 1-2F degrees away from tying overall all-time record highs for the month of February. -------------- Temperatures --- Record ---- Record for -------------- As of 1 PM/Fcst Today ----- February Beckley ------ 73F/73F -------- 69F/1916 -- 75F - 2/17/1927 Charleston --- 78F/81F -------- 77F/1939 -- 80F - 2/24/2017 Elkins-------- 76F/76F -------- 68F/1955 -- 77F - 2/24/2017 Huntington --- 78F/81F -------- 74F/1955 -- 80F - 2/24/2017 Parkersburg -- 77F/80F -------- 71F/2016 -- 79F - 2/24/2017 && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...TRM/MZ/MC NEAR TERM...TRM SHORT TERM...MC LONG TERM...MC AVIATION...TRM CLIMATE...

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